用ADF模拟[O,N]CpTiMeCl与MAO作用的一般机理

利用分子模拟技术探讨了钛配合物O,N]CpTiMeCl（其中O,N]为2－甲基－喹啉－8－氧基C10H8NO])在助催化剂甲基铝氧烷（MAO）作用下催化烯烃聚合过程中形成活性中心的一般反应历程，量子力学计算表明，MAO大阴离子对负电荷的分散作用使形成金属阳离子的过程更加容易；乙烯单体与金属阳离子中心的配位反应是放热反应（－2.76kcal/mol），即乙烯能够稳金属阳离子，促进分离离子对的形成；AlMe3更易与MAO中氧原子作用形成加合物，而不是形成二甲基桥加合物；金属阳离子与MAO形成的氯桥加合物比形成与氧原子配位的加合物要稳定，计算结果表明，MAO中含一定量的AlMe3可以保护助催化酸性位，并对金属阳离子与MAO的加合物起着稳定化作用。

Mechanistic Simulation of Reaction of [O, N] CpTiMeCl with MAO by ADF

Molecule Simulation was performed to investigate the formation mechanism of active species in the initiation step of ethy-lene polymerization catalyzed by the titanium complex O, N] CpTiMeCl with MAO activation, where 0, N] is 8-oxyl-quino-line ( C10H8NO]) . ADF quantum-mechanical calculations suggest that negative charge dispersion in MAO macroanions makes the formation of free cationic species more easy. The reaction of ethylene coordination to the titanium cation is exothermic ( -2.76kcal/mol) , and the stabilization of cationic species promotes the ion-pair separation. Free AlMe3 tends to be coordinated to MAO through oxygen atoms as well as by methyl bridges to form adducts. The chlorine-bridged adduct formed by the complex with MAO is more stable than the oxygen-coordinated adduct. The presence of AlMe3 in MAO not only protects the acidic cocatalytic sites, but also plays an important role in stabilization of the complex/MAO adducts.