Ethylene dichloromethane, structure

Waters and Mortimer [235] with catalysts (Tr-CjHs )2TiRCl/AlR Cl2 found polymerization rates to be unaffected by the structure of the alkyl groups, for ethyl and higher homologues. The rate in toluene was lower (by a factor of 4 at Al/Ti = 1.0) than in dichloromethane, which was attributed to involvement of the aromatic solvent in the polymerization, presumably in the monomer coordination step. Rates increased with ethylene pressure and with Al/Ti ratio, and, as the latter was increased, the time before which a decay in rate occurred decreased maximum rates with 0.01 mole 1 of titanium complex, 760 torr ethylene pressure and 0°C, increased from 8 to 120 x 10 mole 1 sec with increase in Al/Ti ratio from 1.0 to 4.0. Assuming ethylene solubility of approximately 0.15 mole r these would correspond to apparent rate coefficients of 0.5 to 7 1 mole sec , not greatly different from other quoted values (Table 10). 

The cycloaddition reaction proceeded smoothly, even at -78 °C, when a mixture of methacrolein 106 and cyclopentadiene 107 in dichloromethane was added to a slurry of the freshly prepared catalyst (Scheme 18). The performance of the catalyst was found to be strongly dependent on its cross-Hnked structure, due to the specific microenvironment created by the ethylene glycol chains. Fligh exojendo se-lectivities (up to 96 4) were achieved, with enantiomeric excesses (ee) of up to 95 % (Scheme 18) [72]. This is comparable to the selectivity obtained with the unsupported catalyst in solution (up to 86 % ee) [73]. The catalyst was recovered and could be used several times without a loss of activity, an observation that triggered investigations into continuous-flow processes. Passing a mixture of methacrolein 106 and cyclopentadiene 107 in dichloromethane through a catalyst-filled column at -30 °C allowed the isolation of the (P)-product 108 with 71 % ee on a scale of up to 138 mmol [72]. 

Theopold [26] has reported a cationic chromium (III) complex with structural similarities to the chromocene/sillca catalyst that polymerizes ethylene as a homogeneous catalyst in dichloromethane (CH cy. This complex, [Cp Cr(THF)2CH3] [BPhJ (where Cp is pentamethylcyclopen-tadienyl) is shown in Figme 3.26 undergoing an ethylene polymerization reaction [51]. 

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