since its discovery in the mid-1960s , the development of stable , 
 well - defined , and functional - group - tolerant olefin metathesis catalysts 
 has greatly influenced the fields of organic synthesis and polymer 
 and materials science . although alkene metathesis has 
 found a wide range of applications , alkyne metathesis has only recently 
 become the focus of attention . moreover , living ring - opening olefin metathesis polymerization ( romp ) 
 has had a great impact in the areas of biomimetic synthetic polymers , 
 self - assembled nanomaterials , and monolithic supports . despite recent synthetic advances toward highly functionalized 
 ring - strained alkynes , the application of ring - opening alkyne metathesis 
 polymerization ( roamp ) to the field of polymer synthesis has remained 
 limited due to the lack of commercially available well - behaved catalysts . presently , poly(arylene ethynylene)s , used in applications 
 ranging 
 from molecular photonics , electronics , to sensing , can be accessed 
 through acyclic diyne metathesis ( adimet ) polymerization of diynes 
 using highly active molybdenum and tungsten catalysts . however , this step - growth process provides only very limited control 
 over the polydispersity , length , and modality of the polymer product . previous attempts at synthesizing polymers using ring - opening of strained 
 alkynes showed polydispersities ranging from 1.1 to 7.0 . while polymers with polydispersities 
 as low as 1.1 have been obtained , the active catalyst species is poorly 
 defined , and the reaction requires low temperatures and rigorous air - free 
 conditions . polymers resulting from these 
 catalysts tend to have higher molecular weights than predicted on 
 the basis of the monomer to catalyst loading . h nmr experiments 
 show that only a fraction of the catalyst is activated and contributes 
 to the linear chain growth , indicating that the rate of propagation 
 is larger than the rate of initiation ( kp / ki > 1 ) . the poor selectivity of 
 alkyne 
 metathesis catalysts for strained over unstrained alkynes in the growing 
 polymer chain leads to significant broadening of the polydispersity 
 index ( pdi ) through chain - transfer processes and  backbiting  
 to form cyclic structures . in this study , we report the synthesis 
 and the detailed mechanistic 
 investigation of the first molecularly defined living 
 ring - opening alkyne metathesis catalyst [ tolcmo(ono)(or)]kor ( r = cch3(cf3)2 , ono = 6,6-(pyridine-2,6-diyl)bis(2,4-di - tert - butylphenolate ) ) 1 ( figure 1 ) . in solution , a rapid equilibrium between the -ate complex 1 and the pentacoordinate 14-electron complex 2 is observed ( electron count does not include potential -donation 
 of electron density from alkoxide lone pairs ) . while the reversible 
 association of a free alkoxide prevents undesired side reactions , 
 the dissociation of 1 does not represent a rate - limiting 
 step during the propagation . kinetic studies reveal that the growing 
 polymer chain efficiently limits the rate of propagation with respect 
 to the rate of initiation ( kp / ki  10 ) . we herein 
 demonstrate the outstanding control over molecular weight and polydispersity 
 achieved in living roamp with 1 and the first synthesis 
 of block copolymers through alkyne metathesis . catalyst 1 was synthesized through ligand exchange 
 from the trisalkoxy molybdenum benzylidyne complex [ tolcmo(or)3(dme ) ] 3 . while structurally 
 related 12-electron molybdenum and tungsten complexes have been reported 
 as catalysts for alkyne cross - metathesis and ring - closing metathesis , 
 these highly active complexes are unsuitable for controlled roamp . extensive chain transfer reactions lead to undesired broad weight 
 distributions ( pdi > 2 ) . in an effort to increase the selectivity of our catalyst for the 
 activation of strained monomers over unstrained alkynes in the growing 
 polymer chain , we incorporated a permanent electron donating , sterically 
 demanding ono pincer ligand 4 . this tridentate ligand stabilizes the high oxidation state of the 
 molybdenum benzylidyne complex , prevents its dimerization in solution , and irreversibly blocks one of the catalyst s 
 active sites . deprotonation of the ono pincer 
 ligand 4 with potassium benzyl followed by addition to 
 [ tolcmo(or)3(dme ) ] in toluene 
 quantitatively converted 3 to the desired 
 product 1 , by h and f nmr spectroscopy . color coding : c ( gray ) , o 
 ( red ) , n ( blue ) , f ( green ) , mo ( turquoise ) . dark brown crystals of 1 were isolated 
 in 36% yield 
 after recrystallization from diisopropyl ether at 35 c . x - ray crystallography 
 of 1 ( figure 1 ) confirms the presence 
 of a c(1)mo(1 ) triple bond with bond length of 1.760(2 )  
 and c(2)c(1)mo(1 ) angle of 176.91(19). the tridentate 
 ono pincer ligand adopts a skewed conformation featuring typical mo(1)o(1 ) 
 and mo(1)o(3 ) distances of 1.9876(16 ) and 2.0010(16 )  , 
 respectively . the mo(1)n(1 ) distance of 2.2227(19 )  
 corresponds to a neutral l - type n mo bond , indicating the presence 
 of an interaction between the lone pair of the pyridine ring and the 
 metal center . the presence of two alkoxides and one potassium cation 
 in the crystal structure of 1 confirms that only one 
 alkoxide in 3 has been displaced by the ono pincer ligand . 
 the mo  o distances are 2.0038(16 ) and 2.2475(16 )  for 
 the hexafluoro - tert - butoxide cis , mo(1)o(2 ) , and trans , mo(1)o(4 ) , 
 to the carbyne , respectively . the elongated mo(1)o(4 ) bond 
 for the alkoxide trans to the carbyne suggests a 
 weak interaction with an oxygen lone pair . crystals of 1 are stable in air for hours and can 
 be stored for indefinite time under an atmosphere of nitrogen . in 
 the absence of moisture and air , a solution of 1 in toluene - d8 shows less than 5% decomposition after one 
 month at 24 c . in toluene - d8 , the 
 pseudo - octahedral -ate complex 1 is in dynamic equilibrium 
 with the dissociated pentacoordinate complex [ tolcmo(ono)(or ) ] 
 ( r = cch3(cf3)2 ) 2 ( supporting information figure s1 ) . in thf - d8 the alkoxide trans to the 
 carbyne is replaced by the solvent , and only a single species , corresponding 
 to a thf bound hexacoordinate complex , is observed by h and f nmr . we studied the roamp of 3,8-dihexyloxy-5,6-dihydro-11,12-didehydrodibenzo[a , e]annulene ( 5a ) ( scheme 1 ) , a readily accessible highly solubilized ring - strained 
 alkyne , with 1 . addition of 1 to a solution 
 of 5a in toluene ( [ 5a]/ 
 = 10 ) at 24 c does not lead to the formation of polymeric species 
 within 24 h. h and f nmr indicate that the 
 roamp catalyst 1 quantitatively initiates with a half - life 
 of t1/2 < 5 min with 1 equiv of 5a to form the initiated complex 6 ( n = 1 ) ( scheme 1 ) . at 90 c , however , 
 the initiation reaction is instantaneous , and the living roamp of 
 monomer 5a ( 10 equiv ) in toluene is completed in less 
 than 2 h , as determined by h nmr spectroscopy . in the 
 absence of monomer , the molybdenum catalyst attached to the propagating 
 polymer chain remains active and continues to incorporate equivalents 
 of monomer added sequentially to the reaction mixture ( supporting information figure s2 ) . precipitation 
 of the resulting polymers in meoh affords poly-5a in greater than 90% isolated yield . gpc analysis for various 
 monomer / catalyst loadings at 90 c in toluene shows a pdi of 
 1.02 , the lowest value ever reported for roamp ( figure 2 , table 1 ) . extended reaction 
 times the molecular weights 
 of poly-5a determined by gpc , calibrated 
 to polystyrene standards , scale linearly with the conversion of monomer 
 ( supporting information figure s2 ) , are 
 proportional to the initial [ 5a]/ loading , 
 and show a unimodal distribution ( figure 2 ) . no evidence for branching or the formation of cyclic polymers could 
 be observed by h nmr analysis and mass spectrometry ( supporting information figure s3 ) . h nmr end - group analysis of the tolyl group reveals that gpc overestimates 
 the mn of poly-5a . a correction factor 0.71.0 correlates well with the degree of polymerization determined by nmr analysis 
 and the expected molecular weight based on the [ 5a]/ loading . gpc traces for poly-5a produced through 
 roamp of 5a with catalyst 1 at variable 
 loadings of [ 5a]/ = 100 ( red ) , 50 ( blue ) , 
 20 ( green ) , 10 ( black ) ( t = 90 ) , calibrated 
 to polystyrene standards . the proposed kinetic scheme for the polymerization of a ring - strained 
 monomer 5a with catalyst 1 is depicted in 
 scheme 2 . in a fast initiation reaction , 1 
 equiv of 5a reacts with 2 to form the initiated 
 complex 7 ( n = 1 ) . binding of kor to 7 stabilizes the initiated complex and reversibly blocks the 
 active site . dissociation of kor from 6 regenerates the 
 active propagating species that undergoes linear chain - growth polymerization 
 with further equivalents of 5a to form extended living 
 polymer chains . calibrated to narrow polydispersity 
 polystyrene standards . degree 
 of polymerization determined 
 by h nmr end - group analysis . to meet the stringent criteria 
 for a living polymerization the 
 initiation of the catalyst must be fast and quantitative ( ki > kp ) , the 
 concentration 
 of propagating species has to remain constant throughout the reaction , 
 all propagating chains have to grow at the same rate , and irreversible 
 termination and chain - transfer processes should be absent . the rate laws for both the initiation and the propagation reaction 
 are derived employing the following assumptions : ( i ) the release of 
 ring - strain stored in the cyclic monomer 5a makes the 
 initiation and the propagation irreversible . ( ii ) the rate of propagation kp is comparable for all propagating species 
 irrespective of the degree of polymerization . ( iii ) the dissociation 
 equilibria are faster than the rate of initiation / propagation . it is thus reasonable 
 to assume that , during the polymerization , the concentration of 7 reaches steady state . the resulting rate law for the polymerization 
 is1where [ m ] is the concentration 
 of monomer 5a , [ c]0 is the starting concentration 
 of 1 , and kdiss , p is the 
 dissociation 
 constant of 6 . since the rate of initiation of complex 2 is very fast at the temperatures used throughout the polymerization , 
 we herein rely on an approximation based on initial rates of reaction2where [ ci ] is 
 the concentration 
 of all initiated species 6/7 , and kdiss is the dissociation constant of 1 . plots 
 of ln([m]/[m]0 ) over time ( figure 3 ) are linear throughout the entire polymerization and fit a rate 
 law first order in monomer . the concentration of propagating species 
 is constant throughout the reaction , and irreversible termination 
 processes are absent . the observed rate of propagation shows a linear 
 dependence on the catalyst loading ( supporting 
 information figure s4 ) . a plot of 1/([kor]/kdiss , p+1 ) versus kp , obs at 
 90 c shows a linear correlation between the rate of propagation 
 and the inverse of the concentration of kor ( supporting 
 information figure s5 ) . similarly , the rate of initiation shows 
 a linear dependence on the concentration of monomer [ m ] and catalyst 
 [ c]0 . the observed rate constants ki , obs and kp , obs at various 
 temperatures are summarized in table 2 . the 
 standard activation enthalpy for the initiation ( h = 20.7  1.2 kcal mol ) and for the propagation reaction ( h = 23.0  1.2 kcal mol ) can 
 be derived from eyring analysis ( supporting information figures s6s7 ) . kinetic studies of the rate of polymerization 
 of 5a and 5b by 1 at various 
 temperatures . from eyring analysis we conclude that , for the polymerization of 5a with catalyst 1 at 90 c , the rate of 
 initiation is 10 times faster than the rate of 
 propagation . quantitative initiation of catalyst 1 is 
 practically instantaneous upon addition to a solution of the monomer . all propagating species incorporate monomer 5a at comparable 
 rates ( kp ) to give polymers with exceptionally 
 narrow weight distributions . the rate of initiation at t > 
 40 c is too fast to be monitored by f nmr . we studied the role of the weakly 
 coordinating alkoxide ligand 
 during the initiation and the polymerization reaction . at elevated 
 temperatures ( t > 60 c ) a rapid equilibrium 
 is established between the -ate complexes 1 and 6 , and the dissociated complexes 2 and 7 , respectively ( supporting information figure s1 ) . the dissociation constants of 1 ( kdiss ) and 6 ( kdiss , p ) at selected temperatures are summarized in table 3 . vant hoff analysis reveals that the changes 
 in standard free enthalpy ( h = 7.1  
 0.2 kcal mol ) and entropy ( s = 13.8  0.6 eu ) associated with the dissociation of 
 kor from 6 are smaller than the respective changes observed 
 for the dissociation of 1 ( h 
 = 9.5  0.5 kcal mol , s = 16.8  2.1 eu ) ( supporting information figures s8s9 ) . the rates of dissociation ( k1 and k2 ) at various temperatures 
 were measured by selective inversion recovery ( sir ) f 
 nmr experiments ( table 3 , supporting information figures s10s12 ) . the standard activation enthalpies for the dissociation of 1 ( h = 10.4  
 0.6 kcal mol ) and 6 ( h = 12.8  0.4 kcal mol ) were derived from eyring plots ( supporting 
 information figures s13s14 ) . to highlight the importance 
 of the kor dissociation equilibrium for the performance of roamp catalyst 1 , we polymerized 5a in the presence of varying 
 amounts of a lewis acid . addition of 2 equiv of bph3 to 
 a solution of 1 in toluene efficiently shifts the dissociation 
 equilibrium toward the pentacoordiante complex 2 ( 2 equiv 
 of a lewis acid are required to trap the labile hexafluoro - tert - butoxide and the isopropyl ether found in the crystal 
 unit cell of 1 ) . polymers formed in the absence of free 
 hexafluoro - tert - butoxide feature broad weight distributions 
 ( pdi > 1.3 ) and mn values that do not 
 reflect the initial [ 5a]/ loading ( supporting information figure s15 ) . the resonance signals 
 in the f nmr are broadened and could not be inverted 
 for sir experiments . figure 4 summarizes the experimentally determined 
 kinetic and thermodynamic parameters for the initiation and the propagation 
 reaction at standard conditions . the association of kor is a fast 
 pre - equilibrium to the rate - determining step . the rate of initiation 
 is faster than the rate of propagation even though the equilibrium 
 concentration of 2 is lower than the concentration of 
 the propagating species 7 . the rate - determining transition 
 state for the propagation is 3.6 kcal mol higher 
 than the transition state for the initiation reaction . the observed 
 difference in metathesis activity between 2 and 7 can be rationalized by a combination of electronic and steric 
 effects imposed by the growing polymer chain . the steric bulk associated 
 with the ortho - substituted polymer backbone increases 
 the barrier for the incorporation of the next ring - strained monomer . 
 the initiated catalyst 7 features an electron donating 
 hexyloxy substituent on the benzylidyne that further stabilizes the 
 mo(vi ) complex as compared to the ch3 group in 2 ( scheme 1 ) . reaction coordinate diagram for the initiation 
 ( black ) and the 
 propagation reaction ( red ) at 25 c . to expand the substrate scope of roamp with catalyst 1 we synthesized ring - strained monomer 5b ( scheme 1 ) featuring solubilizing triethylene glylcol chains . 
 even though the ether oxygen atoms in the side chains compete with 
 the free alkoxide and the ring strained monomer for binding to the 
 propagating molybdenum species 7 , the mn and the pdis for polymers obtained from the ring opening 
 of 5b are comparable to 5a and the observed rate constant for 
 the roamp of 5b at 90 c is slower ( kp , obs = 0.144 m s ) than for 5a resulting in a t1/2  38 min ( figure 3 ) . sample taken from the reaction mixture 
 after t = 30 min . with two chemically distinct monomers at hand we studied 
 the performance 
 of roamp catalyst 1 in the synthesis of amphiphilic block 
 copolymers . at 90 c , 10 ( 20 ) prior to the addition of 10 ( 20 ) equiv 
 of 5b , an aliquot was removed from the reaction mixture 
 and analyzed by gpc . after the consumption of all monomers , as judged 
 by h nmr spectroscopy , the reaction was quenched with 
 meoh . unlike poly-5a , low molecular 
 weight ( mn = 8000 ) poly-5a - block - poly-5b is soluble in meoh and only precipitates from concentrated 
 solutions as a pale orange solid in > 90% yield . gpc analysis reveals 
 an increase in mn upon addition of 5b to the living chains of poly-5a ( supporting information figure s16 ) . the pdi of poly-5a - block - poly-5b is exceptionally low ( 1.08 ) 
 and matches the catalyst performance achieved for the respective homopolymers . end - group analysis reveals that the ratio of monomers in poly-5a - block - poly-5b scales linearly with the monomer loading . in summary , we have described the synthesis of the first molecularly 
 well - defined 16-electron roamp catalyst based on a molybdenum benzylidyne 
 ono pincer complex [ tolcmo(ono)(or)]kor ( r = cch3(cf3)2 ) 1 . the incorporation 
 of a permanent electron donating tridentate ligand irreversibly blocks 
 one of the catalyst s active sites , prevents undesired alkyne 
 polymerization reactions , and significantly increases its stability 
 toward air and moisture . the catalyst is capable of selectively ring - opening 
 strained alkynes in a controlled polymerization to yield high molecular 
 weight polymers with exceptionally low pdis ( 1.02 ) . mechanistic studies 
 reveal that the roamp catalyst 1 meets all the criteria 
 for a controlled living polymerization : the initiation reaction is 
 quantitative and 10 times faster than the propagation 
 ( ki > kp ) , 
 the concentration of catalytically active complex is constant throughout 
 the reaction , and all propagating chains grow at the same rate . the 
 reversible coordination of kor to the propagating catalyst prevents 
 undesired chain termination and bimolecular decomposition of the catalyst . we demonstrate for the first time the synthesis of structurally well - defined 
 block copolymers through a controlled living roamp . the catalyst developed 
 herein provides an unprecedented control and access to functionalized 
 homo- and block copolymers derived from ring - strained alkynes with 
 potential applications in advanced thin - film electronics / photonics , 
 molecular sensing , and nanopatterning . unless otherwise stated , 
 all manipulations of air and/or moisture sensitive compounds were 
 performed in oven - dried glassware , under an atmosphere of ar or n2 . solvents were dried by passing through a column of alumina 
 and were degassed by vigorous bubbling of n2 or ar through 
 the solvent for 20 min . all h , { h}c , and f nmr spectra were recorded on bruker av-600 , 
 drx-500 , av-500 , and av-900 mhz spectrometers , and are referenced 
 to residual solvent peaks ( cdcl3h nmr  
 = 7.26 ppm , c nmr  = 77.16 ppm ; c6d6h nmr  = 7.16 ppm , c nmr 
  = 128.06 ppm ; tol - d8h nmr  = 2.08 ppm ; thf - d8h nmr  = 1.78 ppm , c nmr  = 67.21 
 ppm ) or trifluorotoluene ( f nmr  = 63.72 
 ppm ) . the concentrations of 1 , 2 , 6 , 7 , and kocch3(cf3)2 were determined by f nmr using the eretic method 
 against an external standard of 13.6 mm trifluorotoluene in tol - d8 . the concentration 
 of monomer 5a , b was verified by h nmr applying the eretic method against an external standard of 
 19.4 mm of hexamethyldisiloxane in tol - d8 . selective inversion recovery ( sir ) 
 experiments were performed using topspin for data acquisition , and 
 fitted with cifit . the temperature in all vt nmr 
 experiments is calibrated to ethylene glycol or meoh standards . esi 
 mass spectrometry was performed on a finnigan ltqft ( thermo ) spectrometer 
 in positive ionization mode . maldi mass spectrometry was performed 
 on a voyager - de pro ( applied biosystems voyager system 6322 ) in positive 
 mode using a matrix of dithranol . elemental analysis ( chn ) was performed 
 on a perkinelmer 2400 series ii combustion analyzer ( values are given 
 in % ) . gel permeation chromatography ( gpc ) was carried out on a lc / ms 
 agilent 1260 infinity set up with a guard and two agilent polypore 
 300 mm  7.5 mm columns at 35 c and calibrated to narrow 
 polydispersity polystyrene standards ranging from mw = 100 to 4  068  981 . x - ray crystallography 
 was performed on apex ii quazar , using a microfocus sealed source 
 ( incoatec is ; mo k radiation ) , kappa geometry with dx 
 ( bruker - axs build ) goniostat , a bruker apex ii detector , quazar multilayer 
 mirrors as the radiation monochromator , and oxford cryostream 700 
 for 1 . crystallographic data were refined with shelxl-97 , 
 solved with sir-2007 , visualized with ortep-32 , and finalized with 
 wingx . 4 , and kbn were synthesized following literature procedures . a 25 ml vial was charged with 4 ( 88 
 mg , 0.18 mmol , 1.0 equiv ) in dry toluene ( 3 ml ) . a suspension of kbn 
 ( 48 mg , 0.37 mmol 2.05 equiv ) in dry toluene ( 8 ml ) was added dropwise 
 and the reaction mixture stirred for 15 min at 24 c . the resulting 
 suspension was added dropwise to a solution of 3 ( 164 
 mg , 0.2 mmol , 1.1 equiv ) in toluene ( 7 ml ) . an immediate color change 
 to dark brown was observed , and the reaction mixture was stirred for 
 30 h at 24 c . the suspension was filtered , and the solvent was 
 removed under dynamic vacuum . the precipitate was dissolved in cold 
 ch2cl2/pentane ( 3:2 , 4 ml ) and filtered through 
 a precooled frit . pr2o ( 1 
 ml ) was added to the solution , and the solvent was removed under vacuum . the residue was recrystallized from pr2o ( 2 ml ) ( 35 c ) , to yield pure 1 ( 78 mg , 36% ) as a dark brown crystalline solid . crystals for x - ray 
 analysis were grown from saturated pr2o solutions at 35 c . in toluene , 1 is in equilibrium with the dissociated pentacoordinate complex 2 and free koc(cf3)2ch3 . h nmr ( 500 mhz , tol - d8 , 22 c ) 
  = 7.70 ( 2 ) , 7.63 ( s , 2h , ar - h ) , 7.42 ( s , 2h , ar - h ) , 7.27 ( 2 ) , 7.20 
 ( d , j = 8.0 hz , 2h , 3,5-nc5h2h ) , 6.91 ( t , j = 8.0 hz , 1h , 4-nc5h2h ) , 6.58 ( d , j = 7.6 hz , 2h , c6h2h2ch3 ) , 6.44 ( 2 ) , 6.30 ( d , j = 7.6 hz , 2h , c6h2h2ch3 ) , 6.26 ( 2 ) , 2.01 ( s , 3h , c6h4ch3 ) , 1.93 ( s , 3h , 
 oc(cf3)2ch3 ) , 1.71 
 ( 2 ) , 1.64 ( s , 18h , bu - h ) , 1.46 ( s , 18h , bu - h ) , 1.37 ( 2 ) , 1.00 ( s , 3h , k - oc(cf3)2ch3 ) ppm . f 
 nmr ( 470 mhz , tol - d8 , 22 c )  
 = 76.79 ( 2 ) , 77.80 , 78.26 , 81.18 
 ( dissociated koc(cf3)2ch3 ) ppm . in thf , only the dissociated species 2thf is observed , resulting in the presence of free koc(cf3)2ch3 . h nmr ( 500 mhz , thf - d8 , 22 c )  = 7.92 ( t , j = 8.0 hz , 1h , 4-nc5h2h ) , 
 7.70 ( d , j = 8.0 hz , 2h , 3,5-nc5h2h ) , 7.52 ( d , j = 2.3 hz , 2h , 
 ar - h ) , 7.46 ( d , j = 2.3 hz , 2h , 
 ar - h ) , 6.74 ( d , j = 7.9 hz , 2h , 
 c6h2h2ch3 ) , 6.12 ( d , j = 7.9 hz , 2h , c6h2h2ch3 ) , 2.20 ( s , 3h , 
 c6h4ch3 ) , 1.78 ( s , 
 3h , oc(cf3)2ch3 ) , 
 1.52 ( s , 18h , bu - h ) , 
 1.39 ( s , 18h , bu - h ) 
 ppm . { h}c nmr ( 126 mhz , thf - d8 , 22 c )  = 307.5 , 166.2 , 155.6 , 141.5 , 140.5 , 
 139.1 , 138.8 , 137.5 , 136.8 , 130.3 , 127.6 , 126.0 , 125.4 , 124.9 , 123.1 , 
 84.2 , 36.0 , 34.8 , 32.4 , 30.8 , 23.5 , 21.6 ppm . f nmr ( 470 
 mhz , thf - d8 , 22 c )  = 76.92 
 ppm . ftms ( esi - tof ) ( m / z ) : [ [ tolcmo(ono)(occh3(cf3)2 ) ] + h ] calcd [ c45h54f6mono3 ] , 868.3056 ; 
 found 868.3076 . calcd for [ [ tolcmo(ono)(occh3(cf3)2)2]kopr2]2pr2o : c , 56.21 ; h , 6.26 ; n , 1.13 . found : c , 56.04 ; h , 
 6.40 ; n , 1.38 . crystal data : ccdc no . , 998197 ; formula , c60.5h83f12kmono6.25 ; fw , 1297.32 
 g mol ; temp , 100(2 ) k ; cryst syst , monoclinic ; 
 space group , p21/n ; color , 
 black ; a , 12.751(5 )  ; b , 29.140(5 ) 
  ; c , 17.008(5 )  ;  , 90.000(5) ; 
  , 93.406(5) ;  , 90.000(5) ; v , 6308(3 )  ; z , 4 ; r1 , 0.0367 ; 
 wr2 , 0.0818 ; gof , 1.051 . a 10 ml resealable schlenk tube was charged with 
 a stock solution of 5a ( 220 mm ) in toluene . if required , 
 the solution was diluted with additional dry toluene to reach a total 
 of 0.5 ml . a stock solution of 1 ( 11 mm , 100 l ) 
 in toluene was added , and the reaction mixture was heated in a bath 
 at 90 c for 2 h. the reaction mixture was cooled , and polymers 
 were precipitated with meoh ( 2 ml ) . the precipitate was filtered , 
 washed with meoh ( 2 ml ) , and dried in vacuum to yield poly-5a ( 92% isolated yield ) as a pale brown solid . h nmr ( 600 mhz , cdcl3 , 22 c )  = 7.40 
 ( d , j = 8.4 hz , 2h , ar - h ) , 6.776.52 
 ( m , 4h , ar - h ) , 3.67 ( t , j = 6.5 
 hz , 4h , och2 ) , 3.19 ( s , 4h , ch2 ) , 1.691.58 ( m , 4h , o(ch2)5ch3 ) , 1.411.19 ( m , 12h , o(ch2)5ch3 ) , 0.87 ( t , j = 7.0 hz , 6h , ch3 ) ppm . nmr ( 151 mhz , cdcl3 , 22 c ) 
  = 159.2 , 145.3 , 133.5 , 115.3 , 114.6 , 113.0 , 90.5 , 67.9 , 36.6 , 
 31.8 , 29.4 , 25.9 , 22.8 , 14.2 ppm . a 10 ml resealable schlenk tube was charged with 
 a stock solution of 5b ( 220 mm ) in toluene . if required , 
 the solution was diluted with additional dry toluene to reach a total 
 of 0.5 ml . a stock solution of 1 ( 11 mm , 100 l ) 
 in toluene was added , and the reaction mixture was heated in a bath 
 at 90 c for 7 h. the reaction mixture was concentrated and the 
 solid residue suspended in cold meoh ( 2 ml ) . the precipitate was filtered , 
 washed with cold meoh ( 2 ml ) , and dried in vacuum to yield poly-5b ( 53% isolated yield ) as a pale orange 
 solid . h nmr ( 900 mhz , cdcl3 , 22 c )  
 = 7.38 ( s , 2h , ar h ) , 3.913.24 
 ( m , 30h ) , 3.17 ( s , 4h , ch2 ) ppm . nmr ( 226 mhz , cdcl3 , 22 c ) 
  = 158.8 , 145.1 , 133.6 , 115.7 , 114.8 , 113.1 , 90.6 , 72.0 , 70.9 , 
 70.7 ( 2c ) , 69.7 , 67.4 , 59.2 , 36.2 ppm . a 10 ml resealable schlenk 
 tube was charged with a stock solution of 5a ( 230 mm , 
 200 l ) in toluene . a stock solution of 1 ( 7.7 
 mm , 300 l ) in toluene was added , and the reaction mixture was 
 heated at 90 c for 30 min . an aliquot ( 150 l ) was quickly 
 removed and precipitated with meoh ( 2 ml ) . a stock solution of 5b ( 46 mm , 700 l ) in toluene was added , and the reaction 
 was heated for an additional 7 h. the reaction mixture was cooled , 
 and polymers were precipitated with meoh ( 2 ml ) . the precipitate was 
 filtered , washed with meoh ( 2 ml ) , and dried in vacuum to yield poly-5a - block - poly-5b ( 94% isolated yield ) as a pale orange solid . h nmr ( 500 
 mhz , cdcl3 , 22 c )  = 7.40 ( d , j = 8.4 hz , 4h , ar - h ) , 6.796.42 ( m , 8h , ar - h ) , 4.193.42 ( m , 34h ) , 3.18 ( s , 8h , ch2 ) , 1.791.49 ( m , 4h , o(ch2)5ch3 ) , 1.401.16 ( m , 12h , o(ch2)5ch3 ) , 0.86 ( t , j = 6.9 hz , 6h , ch3 ) ppm . { h}c nmr ( 126 mhz , cdcl3 , 22 c ) 
  = 159.2 , 145.2 , 133.4 , 115.2 , 114.5 , 113.0 , 90.4 , 72.0 , 70.9 , 
 70.7 ( 2c ) , 69.7 ( 2c ) , 67.9 , 59.2 , 36.6 , 31.8 , 29.4 , 25.9 , 22.8 , 14.2 
 ppm .