Introduction {#sec1}
============

(Frustrated) Lewis pair ((F)LP)--alkyne cycloaddition reactions have been intensively explored in recent years, which can be considered as method for synthesizing a novel class of multiple heteroatom-containing cycles of zwitterionic nature.^[@ref1]^ (F)LPs that have Lewis acid and base groups intramolecularly linked by an organic group are necessary for building the cycle compounds. Such Lewis acid and base groups undergo asynchronous but cooperative electrophilic and nucleophilic reactions toward the C≡C bond of the alkyne.^[@ref1],[@ref2]^ When compared with the Huisgen--Sharpless azide--alkyne 1,3-dipolar cycloaddition, which is usually effected by catalysis of the transition metals,^[@ref3]^ the (F)LP--alkyne cycloaddition is free from catalysis.^[@ref1],[@ref2],[@ref4]^ However, it has been reported that P/Sn(II) LPs Ph~2~PCHPhSn-2,6-Trip~2~C~6~H~3~ and Ph~2~PC~6~H~4~-*o*-Sn-2,6-Trip~2~C~6~H~3~ did react with the terminal alkyne, but this was not the case for a similar LP, Ph~2~PC~12~H~8~-*o*-Sn-2,6-Trip~2~C~6~H~3~ (Trip = 2,4,6-*i*Pr~3~C~6~H~2~).^[@ref5],[@ref6]^ The Te/B FLP Ph(CH~2~)~2~TeC(Ph)=C(C~6~F~5~)B(C~6~F~5~)~2~ was tested to be reactive toward the terminal alkyne but nonreactive toward the internal alkyne.^[@ref7]^ Therefore, (F)LP--alkyne cycloaddition relies on the reactivity of not only the Lewis acid and base groups of the (F)LPs but also the alkyne substrate. A number of (F)LPs have been investigated, which exhibit electronic and/or steric reaction characteristics of the Lewis acid and base groups.^[@ref1],[@ref2],[@ref4]^ The reactivity of the alkynes depends on the C≡C bond nature and where the C≡C bond reactivity is usually influenced by its substituents. Currently, only a handful of (F)LP--alkyne cycloadditions to zwitterionic heterocycloalkenes of A,^[@ref7],[@ref8]^ B,^[@ref9]^ C,^[@ref10]^ D,^[@ref11]^ and E^[@ref5],[@ref6]^ types have been documented ([Scheme [1](#sch1){ref-type="scheme"}](#sch1){ref-type="scheme"}).

![Reported Zwitterionic Heterocycloalkenes Formed by (F)LP--alkyne Cycloadditions](ao-2017-00236q_0008){#sch1}

More recently, we have prepared amino group-bridged N-geminal P/Si, P/Ge, and P/Sn FLPs, whose reactivity is unquenched.^[@ref12]^ The P/Si and P/Ge FLPs reacted readily with dimethyl acetylenedicarboxylate or methyl propiolate to produce zwitterionic heterocyclopentenes \[Ph~2~PN(Ar)MR~3~\]\[C(CO~2~Me)=CR′\] (MR~3~ = SiCl~3~, SiCl~2~Me, SiClMe~2~, Ar = 2,4,6-Me~3~C~6~H~2~, 2,6-*i*Pr~2~C~6~H~3~, R′ = CO~2~Me; MR~3~ = GeCl~3~, Ar = 2,4,6-Me~3~C~6~H~2~, 2,6-*i*Pr~2~C~6~H~3~, C~6~H~11~, R′ = CO~2~Me; MR~3~ = SiCl~3~, GeCl~3~, Ar = 2,4,6-Me~3~C~6~H~2~, R′ = H).^[@ref12]^ However, these FLPs did not react with other alkynes (R^1^C≡CR^2^: R^1^, R^2^ = Me, Me; Ph, Ph; Ph, Et; Ph, CO~2~Et; Ph, SiMe~3~; Ph, PPh~2~; H, SiMe~3~; and EtO, H). These results suggest the weak Lewis acid reactivity of the SiR~3~ and GeCl~3~ groups. This prompted an amelioration of this type of FLPs, and in this regard, alternation of the SiR~3~ (or GeCl~3~) group with an aluminum-containing group was considered. (Aluminoamino)phosphines, Ph~2~PN(R)AlR′~2~ (R, R′ = *i*Pr, Me; *i*Pr, Et; *t*Bu, Et; *t*Bu, Ph; and Ph, Me), have been synthesized, which showed amphoteric reactivity toward (η^5^-C~5~H~5~)Fe(CO)~2~Me and other metal carbonyls.^[@ref13]^ Hydrocarbon group-linked P/Al LPs, (R^1^~2~PCH~2~AlR^2^~2~)~2~ (R^1^, R^2^ = Me, Me; Me, Cl; Ph, Me; and *t*Bu, Me),^[@ref14]^ and FLPs, Mes~2~PC(=CHR)AlR′~2~ (R, R′ = Ph, *t*Bu and *t*Bu, CH~2~*t*Bu),^[@ref11]^ have also been reported, which exhibited remarkable reactivities with a variety of small molecules, such as alkynes, CO~2~, aldehydes, benzoyl chloride, benzamide, and isocyanates.^[@ref15]^ Herein, we prepared an amino group-bridged N-geminal P/Al LP, \[Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]~2~ (**1**). The reaction of **1** with RC≡CR yielded \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CR=^⌝^CR) (R = Me (**2**), Ph (**3**)) and with the other molecules generated \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CR^1^=^⌝^CR^2^) (R^1^, R^2^ = CO~2~Et, Ph (**5**), SiMe~3~, Ph (**6**), PPh~2~, Ph (**7**), SiMe~3~, H (**8**), and H, EtO (**9**)). However, reaction with PhC≡CEt produced two isomers, \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CPh=^⌝^CEt) (**4a**) and \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CEt=^⌝^CPh) (**4b**). These results inspire a discussion on the regioselective cycloaddition of **1** with alkynes. Investigations using **1** with alkene, nitrile, and carbodiimide molecules were also carried out.

Results and Discussion {#sec2}
======================

Synthesis and Characterization of Amino Group-bridged N-Geminal P/Al LP {#sec2.1}
-----------------------------------------------------------------------

Starting from primary amine 2,6-*i*Pr~2~C~6~H~3~NH~2~, compound \[Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]~2~ (**1**) was prepared through consecutive one-pot synthesis reactions ([Scheme [2](#sch2){ref-type="scheme"}](#sch2){ref-type="scheme"}). Ph~2~PNH-2,6-*i*Pr~2~C~6~H~3~ was prepared from the reaction of 2,6-*i*Pr~2~C~6~H~3~NH~2~ with *n*BuLi and then PPh~2~Cl, which was not isolated but used for further reaction with *n*BuLi and then AlClEt~2~. Compound **1** was isolated as an off-white solid in 78% yield. A similar method has proven to be useful for synthesizing the N-geminal P/M (M = Si, Ge, Sn) FLPs reported by our group.^[@ref12]^ Using Ph~2~PNH-2,6-*i*Pr~2~C~6~H~3~^[@ref16]^ as the precursor, compound **1** was produced in a similar yield (80%).

![Synthesis of N-Geminal P/Al LP](ao-2017-00236q_0009){#sch2}

Compound **1** has been characterized by ^1^H, ^13^C, and ^31^P NMR spectroscopy and CHN elemental analysis. The ^31^P NMR spectrum exhibits a resonance at δ 35.76 ppm, which is close to that for complexes Ph~2~PN(R)AlR′~2~ (δ 25.0--33.2 ppm).^[@cit13b]^ The ^1^H NMR spectrum shows one broad resonance at δ 0.76 ppm and one triplet resonance at δ 0.95 ppm, assignable to the respective methylene and methyl protons of the ethyl groups at the Al atom. Furthermore, compound **1** was subjected to X-ray single-crystal diffraction study, which confirmed its composition and dimeric structure ([Figure [1](#fig1){ref-type="fig"}](#fig1){ref-type="fig"}). In the structure of **1**, an Al~2~N~2~P~2~ heterocycle is formed, having P → Al donor--acceptor bonds. The P--Al bond lengths are 2.545(1) and 2.563(1) Å, which are longer than those found in methylene-bridged P/Al LPs (R~2~PCH~2~AlMe~2~)~2~ (R = Me, *t*Bu) and \[ClAl(CH~2~PMe~2~)~2~\]~2~ (2.425(1)--2.5001(5) Å)^[@ref14]^ and also in dialkylaluminum phosphides \[R~2~AlP(SiMe~3~)~2~\]~2~ (R = Me, Et, *i*Bu; 2.457(2)--2.476(2) Å).^[@ref17]^ This suggests a weaker P → Al bonding in **1**, which is probably caused by adaption of a bulky arylamino bridge.^[@ref18]^ The Al~2~N~2~P~2~ heterocycle exhibits a twisted boatlike conformation, and this conformation differs from the chairlike one for the Al~2~C~2~P~2~ heterocycle found in methylene-bridged P/Al LPs.^[@ref14]^ The N atom of the arylamino group bonds to the P and Al atoms within a rigid plane (the least square planes Δ~PAlNC(aryl)~ = 0.0094 and 0.0174 Å).

![X-ray crystal structure of **1**. The carbon atoms of the aryl groups at both the P and N atoms are drawn with thermal ellipsoids at a 10% probability level for clarity and the other atoms, at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)--P(1), 1.674(2); P(1)--Al(2), 2.545(1); Al(2)--N(2), 1.903(2); N(2)--P(2), 1.670(2); P(2)--Al(1), 2.563(1); Al(1)--N(1), 1.893(2); P(1)--N(1)--Al(1), 122.87(11); P(2)--N(2)--Al(2), 122.09(11); N(1)--Al(1)--P(2), 106.19(7); N(2)--Al(2)--P(1), 106.47(7).](ao-2017-00236q_0014){#fig1}

At room temperature, one set of either ^1^H or ^31^P NMR data was obtained, and at a low temperature (−50 °C), this data set did not change. However, the addition of excess tetrahydrofuran (THF) into a C~6~D~6~ solution of **1** led to the formation of a THF coordination compound, Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~(THF) (δ~P~ 49.9 ppm, [Figure S1](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf) in the Supporting Information (SI)), and that of an equivalent amount of *N*-heterocyclic carbene produced a similar compound, Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\[C(N*i*PrCMe)~2~\] (δ~P~ 53.0 ppm; [Figure S2](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). Uhl et al. suggested the formation of a THF donor coordination compound, *t*Bu~2~PCH~2~AlMe~2~(THF), as well.^[@cit14b]^ Therefore, when compared with N-geminal P/M (M = Si, Ge, Sn) FLPs that have a monomeric nature,^[@ref12]^ compound **1** exhibits increasing Lewis acidic reactivity through the AlEt~2~ group.

Reactions of **1** with Alkynes {#sec2.2}
-------------------------------

We first carried out reactions of **1** with internal alkynes. Thus, monitored by ^31^P NMR spectroscopy, the reaction with MeC≡CMe was indicated to occur at 60 °C, giving C~2~PNAl-heterocyclopentene **2** (δ~P~ 31.22 ppm). The reaction with PhC≡CPh occurred at 80 °C, producing a similar compound, **3** (δ~P~ 24.18 ppm) ([Scheme [3](#sch3){ref-type="scheme"}](#sch3){ref-type="scheme"}). Through scaled-up reactions, these two compounds were obtained with respective isolated yields of 76 and 74%. On using PhC≡CEt instead, the reaction completed at 60 °C, and to our surprise, a mixture of **4a** (δ~P~ 31.47 ppm) and **4b** (δ~P~ 23.93 ppm) was obtained, with an approximate molar ratio of 1:1.5 (see [Figures S3a,b](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). This result differs from that for the reaction of the S/B FLP with PhC≡C*n*C~4~H~9~ to give only \[PhSCH~2~B(C~6~F~5~)~2~\](CPh=C*n*C~4~H~9~).^[@ref8]^ We repeated this reaction on an NMR scale or a larger scale and obtained these two compounds again, with almost no change in their molar ratio. By fractional crystallization, it was possible to isolate compounds **4a** (30%) and **4b** (45%) separately.

![Dipolar Cycloaddition Reactions of **1** with Internal Alkynes to Zwitterionic C~2~PNAl-Heterocyclopentenes **2**--**7**](ao-2017-00236q_0010){#sch3}

We further chose alkynes PhC≡CCO~2~Et, PhC≡CSiMe~3~, and PhC≡CPPh~2~ for the reaction with **1**. The former two reactions proceeded smoothly at room temperature, whereas the third reaction involved heat treatment at 60 °C. In all cases, a single product was produced (δ~P~ 25.30 ppm for **5**, 18.28 ppm for **6**, and δ~P~ 19.90 ppm for **7** (the resonance at δ~P~ 4.2 ppm is assigned to the exocyclic PPh~2~ group)) with a good isolated yield (77% for **5**, 72% for **6**, and 76% for **7**).

The formation of **2--7** reveals dipolar cycloaddition of the AlEt~2~ and PPh~2~ groups of **1** to the C≡C bond of the alkynes. The generation of **5**--**7**, each as a single product, is considered to be a result of regioselective cycloaddition. However, that of isomeric **4a** and **4b** indicates during the cycloaddition an undergoing of different C≡C bond orientation reactions of the alkyne towards **1**. Essentially, an electronic matching interaction between **1** and the C≡C bond is crucial for generating these products. We carried out natural bond orbital (NBO) analysis of the charge separation of the C≡C bond of the alkynes involved. The NBO values of α-C and β-C were calculated to be 0.008 and −0.451 for PhC≡CSiMe~3~, 0.135 and −0.359 for PhC≡CPPh~2~, 0.040 and −0.107 for PhC≡CCO~2~Et, and −0.074 and 0.012 for PhC≡CEt, respectively ([Table S3](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). Large separations of 0.459 and 0.494 are estimated for the former two alkynes, which suggest strong electronic matching interactions, giving regioselective **6** and **7**. A separation of 0.147 is observed for the third alkyne, and a similar interaction is favored for the formation of **5**. A prior donor--acceptor interaction between the Al site and CO~2~Et carbonyl O atom facilitating Al--C(CO~2~Et) bond formation would enhance this result. A similar reaction mode has been observed for a P/B FLP with MeC≡CC(O)Ph to \[Mes~2~PCH~2~CH~2~B(C~6~F~5~)~2~\]\[CC(O)Ph=CMe\].^[@ref8]^ The separation of 0.086 is for PhC≡CEt, which appears small. This could not allow regioselective cycloaddition, and then, a mixture of **4a** and **4b** was indeed produced.

We then chose two terminal alkynes, Me~3~SiC≡CH and EtOC≡CH, for investigation. Still monitored by ^31^P NMR spectroscopy, the reaction of **1** with Me~3~SiC≡CH proceeded from a low temperature (−50 °C) to room temperature, giving **8** (δ~P~ 17.24 ppm), which was isolated as an off-white solid (70%). The reaction of **1** with EtOC≡CH completed in the temperature range from −50 to 10 °C to afford **9** (δ~P~ 20.37 ppm), which was isolated as colorless crystals (73%) ([Scheme [4](#sch4){ref-type="scheme"}](#sch4){ref-type="scheme"}). Both **8** and **9** are single products. The NBO calculations gave α-C and β-C charge values of −0.487 and −0.187 for Me~3~SiC≡CH and 0.327 and −0.383 for EtOC≡CH ([Table S3](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). The significant C≡C bond charge separations (0.300 for the former and 0.710 for the latter) allow regioselective formation of **8** and **9** under electronic matching interactions as well.

![Dipolar Cycloaddition Reactions of **1** with Terminal Alkynes To Form Zwitterionic C~2~PNAl-Heterocyclopentenes **8** and **9**](ao-2017-00236q_0011){#sch4}

Characterization of the Cycloaddition Products {#sec2.3}
----------------------------------------------

Compounds **2**--**9** were characterized by NMR spectroscopy and CHN elemental analysis, among which **2**, **4a**, **6**, and **8** were further authenticated by X-ray crystallography. The structures of **2**, **4a**, **6**, and **8** are shown in [Figures [2](#fig2){ref-type="fig"}](#fig2){ref-type="fig"}--[5](#fig5){ref-type="fig"}, with selected bond lengths and angles. All four of these compounds feature the C~2~PNAl-heterocyclopentene structure (least square plane Δ: 0.0233 Å for **2**, 0.0692 Å for **4a**, 0.0678 Å for **6**, and 0.0604 \[0.0653\] Å for **8**; C--C bond length: 1.345(3) Å for **2**, 1.349(2) Å for **4a**, 1.350(3) Å for **6**, and 1.348(3) \[1.343(3)\] Å for **8** (the value in brackets is for another independent molecule)). In each structure, both the P and Al atoms are tetracoordinated, adopting a tetrahedral geometry, and both the P--C~C2PNAl~ and Al--C~C2PNAl~ bonds within each central cycle have a single-bond character. Thus, these heterocyclopentenes are zwitterionic, with the P atom at the formal positive charge center and the Al atom at the negative charge center.

![X-ray crystal structure of **2** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): P(1)--N(1), 1.626(2); N(1)--Al(1), 1.956(2); Al(1)--C(2), 2.007(2); C(2)--C(3), 1.345(3); C(3)--P(1), 1.786(2); Al(1)--N(1)--P(1), 112.23(8); N(1)--P(1)--C(3), 106.28(8); P(1)--C(3)--C(2), 114.16(14); C(3)--C(2)--Al(1), 116.61(14); C(2)--Al(1)--N(1), 90.46(7).](ao-2017-00236q_0001){#fig2}

![X-ray crystal structure of **4a** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)--P(1), 1.623(1); P(1)--C(2), 1.788(2); C(2)--C(1), 1.349(2); C(1)--Al(1), 2.024(2); Al(1)--N(1), 1.960(1); Al(1)--N(1)--P(1), 111.69(7); N(1)--P(1)--C(2), 106.23(7); P(1)--C(2)--C(1), 113.64(12); C(2)--C(1)--Al(1), 116.38(12); C(1)--Al(1)--N(1), 89.85(6).](ao-2017-00236q_0002){#fig3}

![X-ray crystal structure of **6** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)--P(1), 1.623(2); P(1)--C(2), 1.819(2); C(2)--C(1), 1.350(3); C(1)--Al(1), 2.017(2); N(1)--Al(1), 1.952(2); Al(1)--N(1)--P(1), 112.48(8); N(1)--P(1)--C(2), 104.59(8); P(1)--C(2)--C(1), 114.67(13); C(2)--C(1)--Al(1), 115.31(13); C(1)--Al(1)--N(1), 90.78(7).](ao-2017-00236q_0003){#fig4}

![X-ray crystal structure of **8** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°) (the value in brackets is for another independent molecule): N(1)--P(1), 1.619(2) \[1.622(2)\]; P(1)--C(1), 1.783(2) \[1.781(2)\]; C(1)--C(2), 1.348(3) \[1.343(3)\]; C(2)--Al(1), 2.018(2) \[2.019(3)\]; Al(1)--N(1), 1.959(2) \[1.966(2)\]; P(1)--N(1)--Al(1), 112.54(10) \[112.02(10)\]; N(1)--P(1)--C(1), 104.03(10) \[104.23(10)\]; C(2)--C(1)--P(1), 117.47(18) \[117.60(18)\]; C(1)--C(2)--Al(1), 113.25(16) \[113.36(16)\]; N(1)--Al(1)--C(2), 90.94(9) \[90.85(9)\].](ao-2017-00236q_0004){#fig5}

Combining ^1^H, ^13^C, ^1^H-^13^C HMBC and ^1^H-^13^C HSQC NMR spectral analysis, the P*C*= and Al*C*= carbon resonances inside the C~2~PNAl-heterocycles of **2** and **3** and **5** and **6** were assigned. As seen in [Table [1](#tbl1){ref-type="other"}](#tbl1){ref-type="other"}, the former carbon resonances range from δ 121.4 to 146.1 ppm, with a ^1^*J*~PC~ of 87.2--118.8 Hz. Correspondingly, the latter resonances are found to range from δ 187.0 to 204.4 ppm, having a ^2^*J*~PC~ of 24.4--34.2 Hz. Compounds **4a** and **4b** are isomeric, but different P*C*= and Al*C*= resonances are displayed (δ 131.0 (^1^*J*~PC~ = 110.9 Hz) and δ 195.7 (^2^*J*~PC~ = 35.4 Hz) ppm for **4a** and δ 131.3 (^1^*J*~PC~ = 118.8 Hz) and δ 200.7 (^2^*J*~PC~ = 29.6 Hz) ppm for **4b**). In compound **7**, because of bonding of another PPh~2~ group outside the C~2~PNAl cycle at the AlC= carbon atom, both the P*C*= and Al*C*= carbons exhibit the dd signal, with resonances at δ 138.0 (^1^*J*~P(inside)C~ = 108.6 and ^2^*J*~P(outside)C~ = 16.1 Hz) and δ 198.6 (^2^*J*~P(inside)C~ = 30.9 and ^1^*J*~P(outside)C~ = 51.7 Hz) ppm, respectively. In addition, in the ^13^C NMR spectrum of **5**, the resonance at δ 173.2 (d, ^3^*J*~PC~ = 33.5 Hz, *C*O) ppm is due to the CO~2~Et group. In the ^29^Si NMR spectrum of **6**, the *Si*Me~3~ resonates at δ −9.10 (d, ^3^*J*~PSi~ = 39.7 Hz) ppm.

###### Selected ^13^C and ^31^P NMR Data for the C~2~PNAl-Cycle of **2**--**10** and CPN~2~Al-Cycle of **11** and **12** and ^31^P NMR Data for **1** (ppm)

  comp.    *P*Ph~2~   P*C*= (*J*~PC~, Hz)   Al*C*= (^2^*J*~PC~, Hz)
  -------- ---------- --------------------- -------------------------
  **1**    35.76                             
  **2**    31.22      123.6 (118.5)         192.2 (38.0)
  **3**    24.18      131.7 (118.6)         196.6 (27.3)
  **4a**   31.47      131.0 (110.9)         195.7 (35.4)
  **4b**   23.93      131.3 (118.8)         200.7 (29.6)
  **5**    25.30      126.7 (87.2)          187.0 (32.6)
  **6**    18.28      146.1 (96.9)          204.4 (24.4)
  **7**    19.90      138.9 (108.6)         198.6 (30.9)
  **8**    17.24      131.4 (103.3)         209.1 (15.8)
  **9**    20.37      149.8 (161.6)         129.7 (45.6)
  **10**   34.78      45.6 (75.5)           13.6 (2.6)
  **11**   42.54      147.7 (4.5)            
  **12**   10.85      145.5 (77.2)           

Similarly, in **8** the P*C*(H)= and Al*C*(SiMe~3~)= carbon resonances are at δ 131.4 (^1^*J*~PC~ = 103.3 Hz) and δ 209.1 (^2^*J*~PC~ = 15.8 Hz) ppm, respectively. The ^29^Si NMR spectrum shows a resonance at δ = −5.76 (d, ^3^*J*~PSi~ = 43.0 Hz) ppm for the SiMe~3~ group, and the ^1^H NMR spectrum displays a resonance at δ 7.55 (d, ^2^*J*~PH~ = 63.6 Hz) ppm, assignable to the PC(*H*)= proton. In **9**, Al*C*(H)= and P*C*(OEt)= resonate at δ 129.7 (d, ^1^*J*~PC~ = 45.6 Hz) and δ 149.8 (d, ^1^*J*~PC~ = 161.6 Hz) ppm, respectively. The ^1^H NMR spectrum indicates that the AlC*H*= proton resonates at δ 6.67 (d, ^3^*J*~PH~ = 44.2 Hz) ppm and the PC(O*Et*)= proton resonates at δ 0.75 (t, ^3^*J*~HH~ = 6.6 Hz, C*H*~3~) and δ 3.61 (q, ^3^*J*~HH~ = 6.6 Hz, C*H*~2~) ppm.

Reaction of **1** with Other Unsaturated Organic Molecules {#sec2.4}
----------------------------------------------------------

We further explored the reactions of **1** with alkene, nitrile, and carbodiimide molecules. The reaction of **1** with α-olefin 4-BrC~6~H~4~CH=CH~2~ proceeded in toluene from −50 °C to room temperature, giving compound **10** as a colorless crystalline solid, which was isolated in 70% yield ([Scheme [5](#sch5){ref-type="scheme"}](#sch5){ref-type="scheme"}). Cycloaddition reactions of the (F)LPs with alkenes were reported rarely.^[@ref5],[@ref9]^ The highly selective attack of the Lewis acidic Al atom at the terminal olefinic carbon atom is in accord with the charge separation of the C=C bond calculated from the NBO analysis (α-C, −0.200 and β-C, −0.350; [Table S3](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). The reactions of **1** with 4-BrC~6~H~4~C≡N and *i*PrN=C=N*i*Pr each progressed in toluene at room temperature, and compounds **11** and **12** were readily produced ([Scheme [5](#sch5){ref-type="scheme"}](#sch5){ref-type="scheme"}). Compound **11** was isolated as a light-yellow solid in 78% yield, and **12**, as an off-white solid in 72% yield. Owing to the well-polarized C≡N and C=N bond character, regioselective formation of **11** and **12** is expected.

![Dipolar Cycloaddition Reactions of **1** with an Alkene, Nitrile, and Carbodiimide To Form Zwitteric Heterocycles **10**--**12**](ao-2017-00236q_0012){#sch5}

X-ray crystallographic study confirms the formation of **10**, a C~2~PNAl-heterocyclopentane ([Figure [6](#fig6){ref-type="fig"}](#fig6){ref-type="fig"}). This cycle deviates from planarity (Δ = 0.1756 Å), mostly due to formation of the C--C single bond (1.551(3) Å) inside. The other bond lengths inside this cycle are comparable to those of C~2~PNAl-heterocyclopentenes **2**, **4a**, **6**, and **8** (see [Table S1](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)). Compounds **11** and **12** both feature a CPN~2~Al-heterocycle that is planar or closely planar (Δ = 0.0506 Å for **11** and 0.0638 Å for **12**; [Figures [7](#fig7){ref-type="fig"}](#fig7){ref-type="fig"} and [8](#fig8){ref-type="fig"}). Within the cycle of **11**, the C--N bond converts into a double bond (1.244(4) Å). In the cycle of **12**, the C(1)--N(1) bond is seen to have a length of 1.369(2) Å, which is intermediate between that of exocyclic N--C~2,6-*i*Pr2C6H3~ (1.459(2) Å) and N--C~*i*Pr~ (1.459(2) and 1.489(3) Å) single bonds and that of the C(1)--N(2) double bond (1.279(3) Å). Furthermore, this C(1)--N(2) bond appears to be a little longer than the C--N double bond in the CPN~2~Al-cycle of **11**. These data indicate remaining electron conjugation over the N=C--N part after cycloaddition. Compounds **10**--**12** have also been characterized by ^1^H, ^13^C, ^31^P, ^1^H-^13^C HMBC and ^1^H-^13^C HSQC NMR spectroscopy, which affirmed their structures to be in line with those determined by X-ray crystallography. It was noted that compound **10** was formed as a mixture of racemic enantiomers ([Scheme [5](#sch5){ref-type="scheme"}](#sch5){ref-type="scheme"}). This can be indicated by the observance of two sets of ^1^H and ^13^C NMR data ([Figures S4--10a](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf) and [S4--10b](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf)).

![X-ray crystal structure of **10** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): P(1)--N(1), 1.624(2); P(1)--C(2), 1.834(2); C(2)--C(1), 1.551(3); C(1)--Al(1), 2.019(2); Al(1)--N(1), 1.972(2); Al(1)--N(1)--P(1), 112.61(9); N(1)--P(1)--C(2), 103.97(8); P(1)--C(2)--C(1), 106.19(13); C(2)--C(1)--Al(1), 108.25(12); C(1)--Al(1)--N(1), 91.86(7).](ao-2017-00236q_0005){#fig6}

![X-ray crystal structure of **11** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(2)--P(1), 1.625(2); P(1)--C(1), 1.891(3); C(1)--N(1), 1.244(4); N(1)--Al(1), 1.905(2); Al(1)--N(2), 1.944(2); Al(1)--N(2)--P(1), 113.19(12); N(2)--P(1)--C(1), 100.04(11); P(1)--C(1)--N(1), 115.0(2); C(1)--N(1)--Al(1), 119.62(18); N(1)--Al(1)--N(2), 91.04(9).](ao-2017-00236q_0006){#fig7}

![X-ray crystal structure of **12** with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(3)--P(1), 1.623(2); P(1)--C(1), 1.862(2); C(1)--N(1), 1.369(2); N(1)--Al(1), 1.895(2); Al(1)--N(3), 1.941(2); C(1)--N(2), 1.279(3); Al(1)--N(3)--P(1), 112.65(9); N(3)--P(1)--C(1), 104.30(8); P(1)--C(1)--N(1), 108.99(14); C(1)--N(1)--Al(1), 121.54(12); N(1)--Al(1)--N(3), 90.65(7).](ao-2017-00236q_0007){#fig8}

Conclusions {#sec3}
===========

In summary, we have prepared an N-geminal P/Al LP, \[Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]~2~ (**1**). Compound **1** exists as a dimer in the solid state, which can easily form a THF or *N*-heterocyclic carbene coordination compound (at Al atom). Reactions of **1** with a series of alkynes yielded zwitterionic C~2~PNAl-heterocyclopentenes \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CR=^⌝^CR′) (R, R′ = Me, Me (**2**); Ph, Ph (**3**); Ph, Et (**4a**); Et, Ph (**4b**); CO~2~Et, Ph (**5**); SiMe~3~, Ph (**6**); PPh~2~, Ph (**7**); SiMe~3~, H (**8**); H, EtO (**9**)), and reactions of **1** with alkene, nitrile, and carbodiimide molecules produced zwitteronic C~2~PNAl-heterocyclopentane (**10**) and CPN~2~Al-heterocycles (**11** and **12**). When compared with the N-geminal P/M (M = Si, Ge, Sn) FLPs reported by us,^[@ref12]^ an alternation by the AlEt~2~ group increases the Lewis acidic reactivity and allows expansion of the reactions of **1** with other alkynes as well as alkene, nitrile, and carbodiimide molecules. Further study on the reaction of **1** with other molecules with multiple bonds is in progress.

Experimental Section {#sec4}
====================

Materials and Methods {#sec4.1}
---------------------

All manipulations were carried out under a dry argon or nitrogen atmosphere using Schlenk line and glovebox techniques. Solvents toluene, *n*-hexane, and tetrahedron were dried by refluxing with sodium--potassium alloy in the presence of benzophenone under N~2~ prior to use. NMR (^1^H, ^13^C, ^31^P, ^29^Si) spectra were recorded on a Bruker Avance II 400 MHz spectrometer. The melting point of the compound was measured in a sealed glass tube using the Büchi-540 instrument. Elemental analysis was performed on a Thermo Quest Italia SPA EA 1110 instrument. Commercially available reagents were purchased from Aldrich, Acros, or Alfa-Aesar Chemical Co. and used as received. Compounds Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~)^[@ref16]^ and PhC≡CPPh~2~^[@ref19]^ were prepared according to the literature.

Synthesis of \[Ph~2~PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]~2~ (**1**) {#sec4.2}
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Method A (starting from 2,6-*i*Pr~2~C~6~H~3~NH~2~): At −78 °C, *n*BuLi (4.2 mL of a 2.4 M *n*-hexane solution, 10 mmol) was added dropwise to a solution of 2,6-*i*Pr~2~C~6~H~3~NH~2~ (1.77 g, 10 mmol) in diethyl ether (60 mL). The mixture was left to warm to room temperature with continuous stirring, during which the lithium salt 2,6-*i*Pr~2~C~6~H~3~NHLi was formed. This solution was cooled again to −78 °C, and to it, neat Ph~2~PCl (1.80 mL, 10 mmol) was added. The mixture was left to warm to room temperature and stirred for 12 h, giving Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~). Compound Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~) was not isolated but was used for further reaction. Thus, the Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~)-containing mixture was cooled again to −78 °C, and to it, *n*BuLi (4.2 mL of a 2.4 M *n*-hexane solution, 10 mmol) was added dropwise. The mixture was left to warm to room temperature, giving lithium salt 2,6-*i*Pr~2~C~6~H~3~N(PPh~2~)Li. Then, the mixture was cooled again to −78 °C, followed by the addition of neat AlClEt~2~ (5 mL of a 2 M *n*-hexane solution, 10 mmol); the mixture was warmed to room temperature and stirred for a further 12 h. All of the insoluble LiCl was filtered off, and the filtrate was dried under reduced pressure to give a solid residue. The *n*-hexane (10 mL) extract of this residue was kept at −20 °C for 1 day, giving an off-white solid of **1**, which was collected by filtration. Yield: 3.48 g, 78%. Method B (starting from Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~)): At −78 °C, *n*BuLi (2.5 mL of a 2.4 M *n*-hexane solution, 6 mmol) was added dropwise to a solution of Ph~2~PNH(2,6-*i*Pr~2~C~6~H~3~) (2.17 g, 6 mmol) in toluene (40 mL). The mixture was left to warm to room temperature with continuous stirring, giving lithium salt 2,6-*i*Pr~2~C~6~H~3~N(PPh~2~)Li. The mixture was cooled again to −78 °C, and to it, AlClEt~2~ (3 mL of a 2 M *n*-hexane solution, 6 mmol) was added. The mixture was left to warm to room temperature and stirred for a further 12 h. The insoluble LiCl was filtered off. The filtrate was evaporated to dryness to give an off-white solid of **1**, which was collected and washed with cooled *n*-hexane (−20 °C, 2 mL). Yield: 2.14 g, 80%; mp: 134 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.29 (d, ^3^*J*~HH~ = 5.6 Hz, 12H, CH*Me*~2~), 0.76 (br, 8H, AlC*H*~2~CH~3~), 0.95 (t, ^3^*J*~HH~ = 7.8 Hz, 12H, AlCH~2~C*H*~3~), 1.42 (d, ^3^*J*~HH~ = 5.6 Hz, 12H, CH*Me*~2~), 3.81 (sept, ^3^*J*~HH~ = 5.6 Hz, 4H, C*H*Me~2~), 6.98--7.05 (m), 7.10--7.16 (m), 7.61 (br) (26H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 6.7 (Al*C*H~2~CH~3~), 9.8 (AlCH~2~*C*H~3~), 24.0 (CH*Me*~2~), 27.0 (CH*Me*~2~), 28.3 (*C*HMe~2~), 124.9, 125.3, 125.6, 128.5 (d, *J*~PC~ = 77.1 Hz), 130.3, 135.4 (d, *J*~PC~ = 11.0 Hz), 141.7 (d, *J*~PC~ = 17.2 Hz), 147.6 (*C*~6~H~5~ and *C*~6~H~3~). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 35.76 (*P*Ph~2~). Anal. calcd (%) for C~56~H~74~Al~2~N~2~P~2~ (*M*~r~ = 891.12): C, 75.48; H, 8.37; N, 3.14. Found: C, 75.13; H, 8.28; N, 3.08. X-ray quality single crystals of **1** were grown through slow evaporation of its CHCl~3~ solution under an argon atmosphere at room temperature for 1 day.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CMe=^⌝^CMe) (**2**) {#sec4.3}
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A mixture of **1** (0.160 g, 0.18 mmol) and MeC≡CMe (0.020 g, 0.36 mmol) in toluene (10 mL) was slowly heated to 60 °C, and a clear solution was formed. After 5 min, the solution was cooled to room temperature. The toluene solvent was removed, giving an off-white solid of **2**, which was collected and washed with cooled *n*-hexane (−20 °C, 2 mL). Yield: 0.136 g, 76%; mp: 194 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.13 (d, ^3^*J*~HH~ = 6.4 Hz, 6H, CH*Me*~2~), 0.60 (m, 4H, AlC*H*~2~CH~3~), 1.23 (d, ^3^*J*~HH~ = 6.4 Hz, 6H, CH*Me*~2~), 1.44 (d, *J*~PH~ = 13.6 Hz, 3H, =C(P)*Me*), 1.65 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 2.42 (d, *J*~PH~ = 3.2 Hz, 3H, =C(Al)*Me*), 3.39 (sept, ^3^*J*~HH~ = 6.4 Hz, 2H, C*H*Me~2~), 6.87--6.91 (m), 6.96--6.98 (m), 7.04--7.08 (m), 7.30--7.34 (m) (13H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 1.9 (Al*C*H~2~CH~3~), 10.9 (AlCH~2~*C*H~3~), 13.1 (d, *J*~PC~ = 25.9 Hz, =C(P)*Me*), 20.9 (d, *J*~PC~ = 26.5 Hz, =C(Al)*Me*), 22.6 (CH*Me*~2~), 27.0 (CH*Me*~2~), 28.0 (*C*HMe~2~), 123.6 (d, *J*~PC~ = 118.5 Hz, P*C*=), 124.3 (d, *J*~PC~ = 2.8 Hz), 125.1 (d, *J*~PC~ = 3.1 Hz), 126.7, 128.4 (d, *J*~PC~ = 11.1 Hz), 131.6, 133.6 (d, *J*~PC~ = 8.9 Hz), 136.6 (d, *J*~PC~ = 6.2 Hz), 147.8 (d, *J*~PC~ = 5.0 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 192.2 (d, *J*~PC~ = 38.0 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 31.22 (*P*Ph~2~). Anal. calcd (%) for C~32~H~43~AlNP (*M*~r~ = 499.65): C, 76.92; H, 8.67; N, 2.80. Found: C, 76.81; H, 8.75; N, 2.68. After collection of the NMR data in C~6~D~6~, the solution was left at room temperature for 2 days, giving X-ray quality single crystals of **2**.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CPh=^⌝^CPh) (**3**) {#sec4.4}
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A mixture of **1** (0.107 g, 0.12 mmol) and PhC≡CPh (0.043 g, 0.24 mmol) in C~6~D~6~ (0.8 mL) was slowly heated to 60 °C, and a clear solution was formed. ^1^H and ^31^P NMR spectral analyses indicated no reaction at all. The solution was then heated to 80 °C for 10 min, and the related NMR spectral measurements showed completion of this reaction. After cooling to room temperature, the C~6~D~6~ solvent was removed, giving an off-white solid of **3**, which was collected and washed with cooled *n*-hexane (−20 °C, 1 mL). Yield: 0.110 g, 74%; mp: 188 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.19 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 0.74 (q, ^3^*J*~HH~ = 8.0 Hz, 4H, AlC*H*~2~CH~3~), 1.31 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 1.43 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~*3*~), 3.55 (sept, ^3^*J*~HH~ = 6.8 Hz, 2H, C*H*Me~2~), 6.62--6.71 (m), 6.84--7.16 (m), 7.36--7.54 (m) (23H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 2.2 (Al*C*H~2~CH~3~), 10.5 (AlCH~2~*C*H~3~), 22.9, 26.6 (CH*Me*~2~), 28.3 (*C*HMe~2~), 124.5 (d, *J*~PC~ = 2.6 Hz), 125.3, 125.4 (d, *J*~PC~ = 2.9 Hz), 126.6, 127.0, 128.1 (d, *J*~PC~ = 13.7 Hz), 128.3 (d, *J*~PC~ = 15.8 Hz), 128.4 (d, *J*~PC~ = 11.3 Hz), 129.5 (d, *J*~PC~ = 4.9 Hz), 131.6 (*C*~6~H~5~ and *C*~6~H~3~), 131.7 (d, *J*~PC~ = 118.6 Hz, P*C*=), 131.9 (d, *J*~PC~ = 2.4 Hz), 134.1 (d, *J*~PC~ = 8.6 Hz), 136.6 (d, *J*~PC~ = 5.9 Hz), 138.5 (d, *J*~PC~ = 23.2 Hz), 145.8 (d, *J*~PC~ = 26.3 Hz), 147.7 (d, *J*~PC~ = 5.0 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 196.6 (d, *J*~PC~ = 27.3 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 24.18 (*P*Ph~2~). Anal. calcd (%) for C~42~H~47~AlNP (*M*~r~ = 623.78): C, 80.87; H, 7.59; N, 2.25. Found: C, 80.72; H, 7.73; N, 2.21.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CPh=^⌝^CEt) (**4a**) and \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CEt=^⌝^CPh) (**4b**) {#sec4.5}
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A mixture of **1** (0.258 g, 0.29 mmol) and PhC≡CEt (0.076 g, 0.58 mmol) in toluene (10 mL) was slowly heated to 60 °C, and a clear solution was formed. After 20 min the solution was cooled to room temperature. The toluene solvent was removed, and the residue was extracted with *n*-hexane (4 mL). The extract was kept at −20 °C for 3 days, affording a crystalline solid of **4a**, which was collected by filtration. After collection of **4a**, the mother filtrate was again kept at −20 °C. Two days later, a crystalline solid of **4b** was formed, which was collected by filtration. Data for **4a**: Yield: 0.100 g, 30%; mp: 146 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.17 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~2~), 0.29 (t, ^3^*J*~HH~ = 7.4 Hz, 3H, CCH~2~C*H*~3~), 0.66 (q, ^3^*J*~HH~ = 8.0 Hz, 4H, AlC*H*~2~CH~3~), 1.26 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~*2*~), 1.50 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 2.14 (dq, ^4^*J*~PH~ = 14.8 Hz, ^3^*J*~HH~ = 7.3 Hz, 2H, CC*H*~2~CH~3~), 3.50 (sept, ^3^*J*~HH~ = 6.6 Hz, 2H, C*H*Me~2~), 6.92--7.00 (m), 7.02--7.09 (m), 7.30--7.34 (m), 7.47--7.52 (m) (18H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 2.1 (Al*C*H~2~CH~3~), 10.8 (AlCH~2~*C*H~3~), 13.3 (CCH~2~*C*H~3~), 22.9 (CH*Me*~2~), 23.0 (d, *J*~PC~ = 24.1 Hz, C*C*H~2~CH~3~), 26.9 (CH*Me*~2~), 28.1 (*C*HMe~2~), 124.4 (d, *J*~PC~ = 3.3 Hz), 124.7, 125.3 (d, *J*~PC~ = 2.9 Hz), 128.3, 128.4 (*C*~6~H~5~ and *C*~6~H~3~), 131.0 (d, *J*~PC~ = 110.9 Hz, P*C*=), 131.9 (d, *J*~PC~ = 2.5 Hz), 133.9 (d, *J*~PC~ = 8.9 Hz), 147.4 (d, *J*~PC~ = 29.3 Hz), 147.8 (d, *J*~PC~ = 5.0 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 195.7 (d, *J*~PC~ = 35.4 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 31.47 (*P*Ph~2~). Data for **4b**: Yield: 0.150 g, 45%; mp: 143 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.19 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~2~), 0.69 (m, 4H, AlC*H*~2~CH~3~), 1.32 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~2~), 1.40 (t, ^3^*J*~HH~ = 7.6 Hz, 3H, CCH~2~C*H*~3~), 1.61 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 2.77 (m, 2H, CC*H*~2~CH~3~), 3.53 (sept, ^3^*J*~HH~ = 6.6 Hz, 2H, C*H*Me~2~), 6.58 (m), 6.83--7.09 (m), 7.41--7.46 (m) (18H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 2.5 (Al*C*H~2~CH~3~), 10.9 (AlCH~2~*C*H~3~), 14.5 (CCH~2~*C*H~3~), 23.1, 26.5 (CH*Me*~2~), 28.1 (*C*HMe~2~), 29.5 (d, *J*~PC~ = 23.3 Hz, C*C*H~2~CH~3~), 124.5 (d, *J*~PC~ = 2.5 Hz), 125.2 (d, *J*~PC~ = 2.9 Hz), 126.7, 128.1 (d, *J*~PC~ = 5.0 Hz), 128.2, 129.5 (d, *J*~PC~ = 4.5 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 131.3 (d, *J*~PC~ = 118.8 Hz, P*C*=), 131.7 (d, *J*~PC~ = 2.5 Hz), 133.9 (d, *J*~PC~ = 8.6 Hz), 137.1 (d, *J*~PC~ = 5.9 Hz), 138.2 (d, *J*~PC~ = 25.0 Hz), 147.7 (d, *J*~PC~ = 4.8 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 200.7 (d, *J*~PC~ = 29.6 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 23.93 (*P*Ph~2~). Anal. calcd (%) for C~38~H~47~AlNP (*M*~r~ = 575.74): C, 79.27; H, 8.23; N, 2.43. Found: C, 79.10; H, 8.12; N, 2.41. After collection of the NMR data of **4a** in C~6~D~6~, the solution was left at room temperature for 7 days, giving X-ray quality single crystals.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]\[C(CO~2~Et)=^⌝^CPh\] (**5**) {#sec4.6}
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At room temperature, PhC≡CCO~2~Et (0.110 g, 0.63 mmol) was added to a suspension of **1** (0.280 g, 0.315 mmol) in toluene (10 mL) with stirring. Within 5 min a clear solution was formed. After stirring for a further 5 min, the toluene solvent was removed and the residue was extracted with *n*-hexane (5 mL). The extract was kept at −20 °C for 1 day, giving a light-brown crystalline solid of **5**, which was collected by filtration. Yield: 0.30 g, 77%; mp: 178 °C (dec.). ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.12 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~2~), 0.78 (m, 4H, AlC*H*~2~CH~3~), 0.93 (t, ^3^*J*~HH~ = 7.6 Hz, 3H, OCH~2~C*H*~3~), 1.21 (d, ^3^*J*~HH~ = 6.6 Hz, 6H, CH*Me*~2~), 1.71 (t, ^3^*J*~HH~ = 7.8 Hz, 6H, AlCH~2~C*H*~3~), 3.44 (sept, ^3^*J*~HH~ = 6.6 Hz, 2H, C*H*Me~2~), 4.08 (q, ^3^*J*~HH~ = 7.6 Hz, 2H, OC*H*~2~CH~3~), 6.77--6.81 (m), 6.85--6.96 (m), 7.00--7.13 (m), 7.43--7.48 (m) (18H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 2.0 (Al*C*H~2~CH~3~), 10.3 (AlCH~2~*C*H~3~), 14.2 (OCH~2~*C*H~3~), 23.7, 26.8 (CH*Me*~2~), 28.3 (*C*HMe~2~), 59.4 (O*C*H~2~CH~3~), 124.6 (d, *J*~PC~ = 2.7 Hz), 125.3, 125.6 (d, *J*~PC~ = 2.9 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 126.7 (d, *J*~PC~ = 87.2 Hz, P*C*=), 128.1 (d, *J*~PC~ = 6.5 Hz), 128.2, 128.6 (d, *J*~PC~ = 11.5 Hz), 128.9, 132.2 (d, *J*~PC~ = 2.6 Hz), 133.9 (d, *J*~PC~ = 8.9 Hz), 135.2, 135.6 (d, *J*~PC~ = 5.6 Hz), 138.5 (d, *J*~PC~ = 22.4 Hz), 147.9 (d, *J*~PC~ = 5.0 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 173.2 (d, *J*~PC~ = 33.5 Hz, *C*O), 187.0 (d, *J*~PC~ = 32.6 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 25.30 (*P*Ph~2~). Anal. calcd (%) for C~39~H~47~AlNO~2~P (*M*~r~ = 619.75): C, 75.58; H, 7.64; N, 2.26. Found: C, 75.77; H, 7.81; N, 2.17.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]\[C(SiMe~3~)=^⌝^CPh\] (**6**) {#sec4.7}
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At room temperature, PhC≡CSiMe~3~ (0.085 g, 0.49 mmol) was added to a suspension of **1** (0. 218 g, 0.245 mmol) in toluene (10 mL) under stirring. Within 3 min a clear solution was formed. After stirring for a further 5 min, the toluene solvent was removed and the residue was extracted with *n*-hexane (5 mL). The extract was kept at −20 °C for 1 day, giving a crystalline solid of **6**, which was collected by filtration. Yield: 0.218 g, 72%; mp: 141 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.22 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 0.25 (s, 9H, Si*Me*~3~), 0.68 (m, 4H, AlC*H*~2~CH~3~), 1.34 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 1.59 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 3.52 (sept, ^3^*J*~HH~ = 6.8 Hz, 2H, C*H*Me~2~), 6.64--6.66 (m), 6.81--6.92 (m), 6.99--7.09 (m), 7.38--7.43 (m) (18H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 1.2 (Si*Me*~3~), 2.7 (Al*C*H~2~CH~3~), 11.2 (AlCH~2~*C*H~3~), 23.4, 26.2 (CH*Me*~2~), 28.1 (*C*HMe~2~), 124.5 (d, *J*~PC~ = 1.9 Hz), 125.2 (d, *J*~PC~ = 2.6 Hz), 127.2 (d, *J*~PC~ = 1.2 Hz), 127.8, 128.2 (d, *J*~PC~ = 11.0 Hz), 129.4 (d, *J*~PC~ = 3.5 Hz), 131.7 (d, *J*~PC~ = 2.3 Hz), 133.9 (d, *J*~PC~ = 8.5 Hz), 137.5 (d, *J*~PC~ = 5.5 Hz), 142.8 (d, *J*~PC~ = 33.8 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 146.1 (d, *J*~PC~ = 96.9 Hz, P*C*=), 204.4 (d, *J*~PC~ = 24.4 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 18.28 (*P*Ph~2~). ^29^Si NMR (79 MHz, C~6~D~6~, 298 K, ppm): δ = −9.10 (d, *J*~PSi~ = 39.7 Hz, *Si*Me~3~). Anal. calcd (%) for C~39~H~51~AlNPSi (*M*~r~ = 619.87): C, 75.57; H, 8.29; N, 2.26. Found: C, 75.36; H, 8.33; N, 2.16. After collection of the NMR data in C~6~D~6~, the solution was left at room temperature for 7 days, giving X-ray-quality single crystals of **6**.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]\[C(PPh~2~)=^⌝^CPh\] (**7**) {#sec4.8}
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A mixture of **1** (0.098 g, 0.11 mmol) and PhC≡CPPh~2~ (0.063 g, 0.22 mmol) in C~6~D~6~ (0.8 mL) was slowly heated to 60 °C, and a yellow solution was formed. After 20 min, the solution was cooled to room temperature. The toluene solvent was removed to give a light-yellow solid of **7**, which was collected and washed with cooled *n*-hexane (−20 °C, 1 mL). Yield: 0.122 g, 76%; mp: 211 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.24 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 0.37 (m, 2H), 0.45 (m, 2H) (AlC*H*~2~CH~3~), 1.24 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 1.38 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 3.62 (sept, ^3^*J*~HH~ = 6.8 Hz, 2H, C*H*Me~2~), 6.64 (s), 6.81--7.10 (m), 7.44--7.49 (m), 7.72--7.76 (m) (28H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 3.1 (Al*C*H~2~CH~3~), 10.6 (AlCH~2~*C*H~3~), 23.5, 26.2 (CH*Me*~2~), 28.3 (*C*HMe~2~), 124.5 (d, *J*~PC~ = 2.5 Hz), 125.3 (d, *J*~PC~ = 2.7 Hz), 126.7 (d, *J*~PC~ = 0.9 Hz), 128.1 (d, *J*~PC~ = 6.6 Hz), 128.2 (d, *J*~PC~ = 6.1 Hz), 128.7 (d, *J*~PC~ = 2.0 Hz), 128.9 (m), 131.8 (d, *J*~PC~ = 2.3 Hz), 134.1 (d, *J*~PC~ = 8.6 Hz), 134.9 (d, *J*~PC~ = 20.8 Hz), 137.6 (d, *J*~PC~ = 6.0 Hz), 138.7 (d, *J*~PC~ = 9.5 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 138.9 (dd, *J*~PC~ = 108.6 and 16.1 Hz, P*C*=), 140.1 (d, *J*~PC~ = 8.6 Hz), 147.5 (d, *J*~PC~ = 4.8 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 198.6 (dd, *J*~PC~ = 51.7 and 30.9 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 4.16 (d, *J*~PP~ = 33.2 Hz, C*P*Ph~2~), 19.90 (d, *J*~PP~ = 33.3 Hz, N*P*Ph~2~). Anal. calcd (%) for C~48~H~52~AlNP~2~ (*M*~r~ = 731.86): C, 78.77; H, 7.16; N, 1.91. Found: C, 78.64; H, 7.07; N, 1.86.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]\[C(SiMe~3~)=^⌝^CH\] (**8**) {#sec4.9}
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A suspension of **1** (0. 257 g, 0.29 mmol) in toluene (10 mL) under stirring was cooled to −50 °C, and to it, HC≡CSiMe~3~ (0.057 g, 0.58 mmol) was added. The mixture was left to warm to room temperature, and a clear solution was formed. The toluene solvent was removed to give an oil residue. Addition of *n*-hexane (4 mL) precipitated **8** as an off-white solid, which was collected by filtration. The *n*-hexane filtrate was left at room temperature for 2 days, affording pieces of X-ray quality single crystals of **8**. Yield: 0.221 g, 70%; mp: 155 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.19 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 0.41 (s, 9H, Si*Me*~3~), 0.61 (m, 4H, AlC*H*~2~CH~3~), 1.27 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 1.57 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 3.37 (sept, ^3^*J*~HH~ = 6.8 Hz, 2H, C*H*Me~2~), 6.85--6.95 (m), 6.99--7.08 (m), 7.34--7.39 (m) (13H, C~6~*H*~5~ and C~6~*H*~3~), 7.47 (d, ^3^*J*~PH~ = 63.6 Hz, =C*H*). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = −0.9 (Si*Me*~3~), 2.4 (Al*C*H~2~CH~3~), 10.8 (AlCH~2~*C*H~3~), 23.0, 26.5 (CH*Me*~2~), 28.0 (*C*HMe~2~), 124.4 (d, *J*~PC~ = 2.6 Hz), 125.2 (d, *J*~PC~ = 2.8 Hz), 128.4 (d, *J*~PC~ = 11.1 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 131.4 (d, *J*~PC~ = 103.3 Hz, P*C*=), 131.9 (d, *J*~PC~ = 2.7 Hz), 133.0 (d, *J*~PC~ = 8.7 Hz), 136.9 (d, *J*~PC~ = 5.7 Hz), 147.6 (d, *J*~PC~ = 4.8 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 209.1 (d, *J*~PC~ = 15.8 Hz, Al*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 17.24 (*P*Ph~2~). ^29^Si NMR (79 MHz, C~6~D~6~, 298 K, ppm): δ = −5.76 (d, *J*~PSi~ = 43.0 Hz, *Si*Me~3~). Anal. calcd (%) for C~33~H~47~AlNPSi (*M*~r~ = 543.77): C, 72.89; H, 8.71; N, 2.58. Found: C, 72.75; H, 8.81; N, 2.53.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CH=^⌝^COEt) (**9**) {#sec4.10}
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A suspension of **1** (0.40 g, 0.45 mmol) in toluene (10 mL) was cooled to −50 °C under stirring, and to it, HC≡COEt (0.14 g, 45% w/w in *n*-hexane, 0.90 mmol) was added. The mixture was left to warm to ca. 10 °C, and a clear solution was formed. A pickup of an aliquot for the ^31^P NMR spectral analysis indicated completion of this reaction. After warming to room temperature, the toluene solvent was removed and the residue was extracted with *n*-hexane (5 mL). The extract was kept at −20 °C for 1 day, giving colorless crystals of **9**, which were collected by filtration. Yield: 0.348 g, 75%; mp: 104 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.20 (d, ^3^*J*~HH~ = 6.4 Hz, 6H, CH*Me*~2~), 0.63 (m, 4H, AlC*H*~2~CH~3~), 0.75 (t, ^3^*J*~HH~ = 6.6 Hz, 3H, OCH~2~C*H*~3~), 1.24 (d, ^3^*J*~HH~ = 6.4 Hz, 6H, CH*Me*~2~), 1.65 (t, ^3^*J*~HH~ = 7.8 Hz, 6H, AlCH~2~C*H*~3~), 3.49 (sept, ^3^*J*~HH~ = 6.4 Hz, 2H, C*H*Me~2~), 3.61 (q, ^3^*J*~HH~ = 6.6 Hz, 2H, OC*H*~2~CH~3~), 6.67 (d, ^3^*J*~PH~ = 44.2 Hz, 1H, =C*H*), 6.92--7.08 (m), 7.53--7.57 (m) (13H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 2.3 (Al*C*H~2~CH~3~), 10.8 (AlCH~2~*C*H~3~), 13.7 (OCH~2~*C*H~3~), 22.8, 26.7 (CH*Me*~2~), 28.1 (*C*HMe~2~), 62.8 (O*C*H~2~CH~3~), 124.3 (d, *J*~PC~ = 2.8 Hz), 125.3 (d, *J*~PC~ = 3.0 Hz), 126.4, 128.3 (d, *J*~PC~ = 11.8 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 129.7 (d, *J*~PC~ = 45.6 Hz, Al*C*=), 131.9 (d, *J*~PC~ = 2.5 Hz), 133.5 (d, *J*~PC~ = 9.5 Hz), 136.4 (d, *J*~PC~ = 5.9 Hz), 147.7 (d, *J*~PC~ = 5.1 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 149.8 (d, *J*~PC~ = 161.6 Hz, P*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 20.37 (*P*Ph~2~). Anal. calcd (%) for C~32~H~43~AlNOP (*M*~r~ = 515.65): C, 74.54; H, 8.41; N, 2.72. Found: C, 74.37; H, 8.38; N, 2.59.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](CH~2~^⌝^CH-4-BrC~6~H~4~) (**10**) {#sec4.11}
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A suspension of **1** (0.680 g, 0.765 mmol) in toluene (20 mL) was cooled to −50 °C under stirring, and to it, 4-BrC~6~H~4~CH=CH~2~ (0.280 g, 1.53 mmol) was added. The mixture was left to warm to room temperature, and a clear solution was formed. After stirring for a further 4 h, the toluene solvent was removed and the residue was extracted with *n*-hexane (5 mL). The extract was kept at −20 °C for 1 day, giving a crystalline solid of **10**, which was collected by filtration. Yield: 0.687 g, 70%; mp: 121 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.11 (d, ^3^*J*~HH~ = 6.8 Hz, 3H, CH*Me*~2~), 0.49 (d, ^3^*J*~HH~ = 6.8 Hz, 3H, CH*Me*~2~), 0.52 (m, 2H, AlC*H*~2~CH~3~), 0.77 (m, 2H, AlC*H*~2~CH~3~), 0.89 (m, 1H, AlC*H*~2~CH), 1.36 (d, ^3^*J*~HH~ = 6.8 Hz, 3H, CH*Me*~2~), 1.38 (d, ^3^*J*~HH~ = 6.8 Hz, 3H, CH*Me*~2~), 1.50 (q, ^3^*J*~HH~ = 6.8 Hz, 1H, AlC*H*~2~CH), 1.60 (t, ^3^*J*~HH~ = 8.0 Hz, 3H, AlCH~2~C*H*~3~), 1.70 (t, ^3^*J*~HH~ = 8.0 Hz, 3H, AlCH~2~C*H*~3~), 3.30 (sept, ^3^*J*~HH~ = 6.8 Hz, 1H, C*H*Me~2~), 4.04 (sept, ^3^*J*~HH~ = 6.8 Hz, 1H, C*H*Me~2~), 4.24 (ddd, ^3^*J*~HH~ = 7.1 Hz, ^3^*J*~HH~ = 12.0 Hz, ^2^*J*~PH~ = 20.0 Hz, 1H, PC*H*CH~2~), 6.10 (d, ^2^*J*~HH~ = 7.4 Hz, 2H), 6.92 (d, ^2^*J*~HH~ = 7.4 Hz, 2H) (C~6~*H*~4~), 6.69--6.73 (m), 7.00--7.02 (m), 7.06--7.13 (m), 7.49--7.53 (m) (13H, C~6~*H*~5~, C~6~*H*~4~, and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 1.6, 2.1 (Al*C*H~2~CH~3~), 10.7, 10.8 (AlCH~2~*C*H~3~), 13.6 (*J*~PC~ = 2.6 Hz, Al*C*H~2~CH), 23.3, 24.5, 25.3, 26.9 (CH*Me*~2~), 27.8, 28.0 (*C*HMe~2~), 45.6 (d, *J*~PC~ = 75.5 Hz, P*C*HCH~2~), 123.9 (d, *J*~PC~ = 82.9 Hz), 124.4 (d, *J*~PC~ = 2.6 Hz), 124.6 (d, *J*~PC~ = 2.6 Hz), 125.3 (d, *J*~PC~ = 2.8 Hz), 128.3 (d, *J*~PC~ = 10.8 Hz), 130.3 (d, *J*~PC~ = 7.0 Hz), 131.1, 132.3 (d, *J*~PC~ = 4.4 Hz), 133.1 (d, *J*~PC~ = 7.2 Hz), 134.1 (d, *J*~PC~ = 9.0 Hz), 141.2 (d, *J*~PC~ = 3.3 Hz), 147.2 (d, *J*~PC~ = 4.7 Hz), 147.4 (d, *J*~PC~ = 5.6 Hz) (*C*~6~H~5~, *C*~6~H~4~, and *C*~6~H~3~). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 34.78 (*P*Ph~2~). Anal. calcd (%) for C~37~H~45~AlBrNP (*M*~r~ = 641.62): C, 69.26; H, 7.07; N, 2.18. Found: C, 69.16; H, 6.99; N, 2.16. A saturated toluene solution of **10** was prepared, and then, *n*-hexane was top-layered onto it. The mixture was kept at −20 °C for 4 days, giving X-ray quality single crystals.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\](N=^⌝^C-4-BrC~6~H~4~) (**11**) {#sec4.12}
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A mixture of **1** (0.276 g, 0.31 mmol) and 4-BrC~6~H~4~C≡N (0.113 g, 0.62 mmol) in toluene (10 mL) was stirred at room temperature. One hour later, a yellow solution was formed. The toluene solvent was removed to give a light-yellow solid of **11**, which was collected and washed with cooled *n*-hexane (−20 °C, 2 mL). Yield: 0.303 g, 78%; mp: 113 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.39 (br, 6H, CH*Me*~2~), 0.63 (m, 4H, AlC*H*~2~CH~3~), 1.22 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~*2*~), 1.66 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 3.49 (sept, 2H, ^3^*J*~HH~ = 6.8 Hz, C*H*Me~2~), 6.89--6.96 (m), 7.00--7.02 (m), 7.06--7.13 (m), 7.49--7.53 (m) (17H, C~6~*H*~5~, C~6~*H*~4~, and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 1.8 (Al*C*H~2~CH~3~), 10.5 (AlCH~2~*C*H~3~), 23.2, 26.3 (CH*Me*~2~), 28.2 (*C*HMe~2~), 124.3, 125.0, 128.6 (d, *J*~PC~ = 9.6 Hz), 128.9, 130.9 (d, *J*~PC~ = 10.3 Hz), 131.4 (d, *J*~PC~ = 20.6 Hz), 131.7, 133.7 (d, *J*~PC~ = 11.8 Hz) (*C*~6~H~5~, *C*~6~H~4~, and *C*~6~H~3~), 147.7 (d, *J*~PC~ = 4.5 Hz, P*C*=). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 42.54 (*P*Ph~2~). Anal. calcd (%) for C~35~H~41~AlBrN~2~P (*M*~r~ = 627.57): C, 66.98; H, 6.58; N, 4.46. Found: C, 66.72; H, 6.67; N, 4.34. After collection of the NMR data of **11** in C~6~D~6~, the solution was left at room temperature for 7 days, giving X-ray quality single crystals.

Synthesis of \[Ph~2~^⌜^PN(2,6-*i*Pr~2~C~6~H~3~)AlEt~2~\]\[N(*i*Pr)^⌝^C=N*i*Pr\] (**12**) {#sec4.13}
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A mixture of **1** (0.516 g, 0.58 mmol) and *i*PrN=C=N*i*Pr (0.146 g, 1.16 mmol) in toluene (15 mL) was stirred at room temperature. After 0.5 h, a clear solution was formed. The toluene solvent was removed to give an off-white solid of **12**, which was collected and washed with cooled *n*-hexane (−20 °C, 2 mL). Yield: 0.478 g, 72%; mp: 190 °C. ^1^H NMR (400 MHz, C~6~D~6~, 298 K, ppm): δ = 0.05 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 0.60 (d, ^3^*J*~HH~ = 6.0 Hz, 6H, NCH*Me*~2~), 0.63 (m, 4H, AlC*H*~2~CH~3~), 1.27 (d, ^3^*J*~HH~ = 6.8 Hz, 6H, CH*Me*~2~), 1.51 (t, ^3^*J*~HH~ = 8.0 Hz, 6H, AlCH~2~C*H*~3~), 1.75 (d, ^3^*J*~HH~ = 6.0 Hz, 6H, NCH*Me*~2~), 3.13 (sept, ^3^*J*~HH~ = 6.0 Hz, 1H, NC*H*Me~2~), 3.31 (sept, ^3^*J*~HH~ = 6.8 Hz, 2H, C*H*Me~2~), 4.84 (sept, ^3^*J*~HH~ = 6.0 Hz, 1H, NC*H*Me~2~), 6.90--7.05 (m), 7.51--7.75 (m) (13H, C~6~*H*~5~ and C~6~*H*~3~). ^13^C{^1^H} NMR (100 MHz, C~6~D~6~, 298 K, ppm): δ = 3.3 (Al*C*H~2~CH~3~), 10.5 (AlCH~2~*C*H~3~), 22.3 (NCH*Me*~2~), 22.8 (CH*Me*~2~), 23.9 (NCH*Me*~2~), 26.7 (CH*Me*~2~), 28.2 (*C*HMe~2~), 47.3 (d, *J*~PC~ = 8.9 Hz, N*C*HMe~2~), 50.8 (d, *J*~PC~ = 17.9 Hz, N*C*HMe~2~), 124.5 (d, *J*~PC~ = 2.6 Hz), 125.6 (d, *J*~PC~ = 2.7 Hz), 126.4 (d, *J*~PC~ = 80.9 Hz), 128.6 (d, *J*~PC~ = 11.6 Hz), 132.4 (d, *J*~PC~ = 2.1 Hz), 133.7 (d, *J*~PC~ = 9.8 Hz), 133.7 (d, *J*~PC~ = 9.8 Hz), 134.9 (d, *J*~PC~ = 10.5 Hz), 147.6 (d, *J*~PC~ = 5.0 Hz) (*C*~6~H~5~ and *C*~6~H~3~), 145.5 (d, *J*~PC~ = 77.2 Hz, *C*N). ^31^P{^1^H} NMR (162 MHz, C~6~D~6~, 298 K, ppm): δ = 10.85 (*P*Ph~2~). Anal. calcd (%) for C~35~H~51~AlN~3~P (*M*~r~ = 571.75): C, 73.52; H, 8.99; N, 7.35. Found: C, 73.48; H, 9.03; N, 7.19. After collection of the NMR data in C~6~D~6~, the solution was left at room temperature for 7 days, giving X-ray quality single crystals of **12**.

X-ray Crystallographic Analysis {#sec4.14}
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Crystallographic data for **1**, **2**, **4a**·C~6~D~6~, **6**·1.5C~6~D~6~, **8**, **10**·toluene, **11**, and **12**·C~6~D~6~ were collected on an Oxford Gemini S Ultra system. During measurements, graphite monochromatic Mo Kα radiation (λ = 0.71073 Å) was used for **1**, **2**, **4a**·C~6~D~6~, **6**·1.5C~6~D~6~, **8**, and **12**·C~6~D~6~, whereas Cu Kα radiation (λ = 1.54178 Å) was used for **10**·toluene and **11**. Absorption corrections were applied using the spherical harmonics program (multiscan type). All structures were solved by direct methods (SHELXS-96)^[@ref20]^ and refined against *F*^2^ using SHELXL-97.^[@ref21]^ In general, the nonhydrogen atoms were located by difference Fourier synthesis and refined anisotropically and the hydrogen atoms were included using a riding model, with *U*~iso~ tied to the *U*~iso~ of the parent atoms. In **2**, one Et group at the Al atom was disordered and treated by the PART splitting mode method. The final refinement gave 51.9% occupation of the C(5)- and C(6)-containing groups, whereas 48.1% occupation of the C(5A)- and C(6A)-containing groups was obtained. Because of this disorder, the ADP max/min ratio of 4.6 appears a little larger, giving a B-level alert. In **6**·1.5C~6~D~6~, two Et groups at the Al atom were disordered and treated by the PART method (C(12)C(13) 50.4% and C(12A)C(13A) 49.6% and C(14)C(15) 33.0% and C(14A)C(15A) 67.0%). One C~6~D~6~ molecule was also observed to be disordered, which was treated by the PART method (C(41)C(42)C(43)C(44)C(45)C(46) 45.2% and C(41A)C(42A)C(43A)C(44A)C(45A)C(46A) 54.8%). In **8**, two independent molecules were disclosed. In one molecule, two Et groups at the Al atom were disordered and treated by the PART method (C(6)C(7) 36.6% and C(6A)C(7A) 63.4% and C(8)C(9) 7.5% and C(8A)C(9A) 92.5%). In this case, one Et group of another independent molecule showed a B-level alert by a Hirshfeld test difference of 7.3 for C(36)···C(37). However, the C(36)--C(37) bond length of 1.520(2) Å is suitable. Therefore, this alert should be ignored. In **12**·C~6~D~6~, one Et group at the Al atom was disordered and treated by the PART method (C(8)C(9) 60.2% and C(8A)C(9A) 39.8%). One C~6~D~6~ molecule was found to be disordered as well, which was treated by the PART method (C(31)C(32)C(33)C(34)C(35)C(36) 54.1% and C(31A)C(32A)C(33A)C(34A)C(35A)C(36A) 45.9%). In compounds **10** and **11**, the calculated sin θ~max~/wavelength of 0.5735 is minutely less than 0.575, and these B-level alerts can be ignored. A summary of cell parameters, data collection, and structure solution and refinements is given in [Table S1](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf).

The Supporting Information is available free of charge on the [ACS Publications website](http://pubs.acs.org) at DOI: [10.1021/acsomega.7b00236](http://pubs.acs.org/doi/abs/10.1021/acsomega.7b00236).Table of crystal data and refinements; table of important bond lengths; NMR spectra of the reactions; NBO analysis; and collected ^1^H, ^13^C, ^31^P, and ^29^Si NMR spectra ([PDF](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_001.pdf))Crystallographic data for **1**, **2**, **4a**·C~6~D~6~, **6**·1.5C~6~D~6~, **8**, **10**·toluene, **11**, and **12**·C~6~D~6~ ([CIF](http://pubs.acs.org/doi/suppl/10.1021/acsomega.7b00236/suppl_file/ao7b00236_si_002.cif))

Supplementary Material
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ao7b00236_si_001.pdf

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ao7b00236_si_002.cif

The authors declare no competing financial interest.

This work is supported by the National Nature Science Foundation of China (21473142 and 21673191) and the Program for Innovative Research Team in Chinese Universities (2013B019 and IRT_14R31).
