Bridged metallocenes of Group IVb metals provide improved results when the bridge comprises a neutral electron-donor substituent of general formula R'" Z R"".sub.j wherein R'" is a rigid unsaturated hydrocarbon radical between Z and the bridge, such that Z is separated from the bridge by 2 to 5 carbon atoms Z is nitrogen, phosphorus, oxygen or sulphur, R"" is H or an alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl having a maximum of 15 carbon atoms, each R"" being the same or different, j is 1 when Z=O or S and 2 when Z=N or P.
当桥接部分包含一个一般公式为R'" Z R"".sub.j的中性电子给体取代基时,IVb族
金属的桥接茂
金属提供了改进的结果,其中R'"是在Z和桥之间的刚性不饱和碳氢基团,使Z与桥之间相隔2至5个碳原子,Z是氮、
磷、氧或
硫,R""是H或最多具有15个碳原子的烷基、环烷基、芳基、烷基芳基或芳基烷基,每个R""相同或不同,当Z=O或S时,j为1,当Z=N或P时,j为2。