Synthesis, crystal structure and reaction of differentially ring-substituted titanocene dichlorides
SummaryA new class of differentially ring-substituted titanocene dichlorides of the type Cp′Cp″TiCl2 has been prepared by reacting Cp″M (M=Li, K; Cp″=RC5H4) with Cp′TiCl3 (Cp′=MeOCH2CH2C5H4). The crystal structure of Cp′(PhCEt2C5H4)TiCl2, the first example, has been determined by x-ray diffraction and refined to a final R factor of 0.0532 for 2304 reflections. The crystal belongs to the monoclinic space group C2h5−P21/c with unit cell parameters:a 10.205(6),b 13.003(5),c 17.591(9) Å, β 101.91(4)°, V=2284 Å3, Z=4 and Dc=1.32 g/cm−3. Replacement of one neomenthyl in bis(neomenthyl-cyclopentadienyl)titanium dichloride by one MeOCH2CH2 — raises the e.e. value from 5.8% to 11.2% in the catalytic asymmetric hydrogenation of 2-phenyl-1-butene.
Addition of crotyltitanocenes to aldehydes: influence of cyclopentadienyl substituents on the diastereoselective formation of homoallylic alcohols
The addition of (η 3 -crotyl)titanocenes (2, R=H, Me, i-Pr) to primary, secondary, and tertiary aldehydes has been investigated. The products of this reaction, homoallylic alcohols, are formed with good to excellent selectivity favoring the anti diastereomer in all cases. The degree of diastereoselectivity correlates with the size of the substituent on the cyclopentadienyl ring and that on the aldehyde. For aliphatic and aromatic aldehydes an increase in diastereoselectivity with increasing steric hindrance at the metal center was observed
Zur polymerisation und copolymerisation von α‐methoxystyrol
α-Methyoxystyrol last sich weder anionisch oder kationisch noch radikalisch homopolymerisieren. Bei der kationischen Copolymerisation erweist sich dieses Monomere reaktionsfahiger als Vinylather. Seine Unfahigkeit, dabei langere Sequenzen zu bilden, weist auf das Vorliegen einer tiefen Ceilingtemperatur hin. 
 
 
 
Bei der radikalischen Copolymerisation mit Styrol, Acrylnitril, Methylacrylat und Methylmethacrylat (MMA) wird fur das α-Methoxystyrol stets ein Parameter r2 = 0 gefunden. Aus den Parametern der ersten drei Comonomeren last sich Q = 0,65 und e = −1,20 abschatzen. Der relativ niedere Q-Wert und die sehr geringe Reaktivitat gegenuber dem Poly-MMA-Radikal zeigen, das erhebliche sterische Hinderungen bei Polymerisationen mit diesem Monomeren auftreten. 
 
 
 
α-Methoxysyrene cannot be homopolymerised, neither by an anionic nor by a cationic or free radical mecanism. This monomer is more reactive in the cationic copolymerisation than vinyl ethyl ether. Its incapability to form longer sequences indicates a low ceiling temperature. 
 
 
 
In the free radical copolymerisation with styrene, acrylonitrile, methacrylate and methyl methacrylate (MMA) the parameter for α-methoxystyrene is always found to be zero. From the parameters of the first three comonomers the Q-and e-values are estimated to Q = 0.65 and e = -1.20. The relatively low Q-value and very low reactivity towards poly (MMA radicals) demonstrate the occurance of considerable steric hindrance during polymerisations with α-methoxystyrene.