Functional group transformations at the group 4 metallocene framework have been demonstrated, which have provided relatively straightforward access to otherwise synthetically challenging derivatives. The pendant nitrile group in Ti and Zr metallocene complexes of the type [(η5-C5Me5)(η5-C5H4CMe2CH2CN)MCl2] was converted into an intramolecularly bound ketimido moiety by alkylation, which took place not only at the nitrile, but also at the metal centre. The choice of an alkylating reagent (alkyl/aryl lithium, Grignard reagent) was crucial: e.g., 2 equiv. of MeMgBr effected the alkylation only at the metal, yielding selectively complexes [(η5-C5Me5)(η5-C5H4CMe2CH2CN)MMe2], while the use of PhMgBr, PhLi, or MeLi instead gave selectively the ketimido complexes. Organyl lithium reagents were, however, not compatible with the titanocene derivatives. The metal-bound ketimides were subsequently cleaved off by the reaction with HCl, which afforded metallocene dichlorides with a pendant imino group. These compounds were easily protonated again at the nitrogen atom to produce a cationic iminium moiety. Aqueous hydrolysis of the imine or its respective hydrochloride proved to be viable in the case of Zr and it finally afforded a pendant ketone group attached to the zirconocene framework.
在4族
金属
烯框架上,功能团转化的示范已经提供了相对简单的途径来获取在合成上具有挑战性的衍
生物。类型为[(η5-C5Me5)(η5-C5H4CMe2CH2CN)
MCl2]的
钛和
锆金属
烯复合物中的悬挂腈基通过烷基化转化为分子内结合的
酮亚胺基团,这一过程不仅发生在腈基上,还发生在
金属中心上。烷基化试剂(烷基/芳基
锂、格里格纳试剂)的选择至关重要:例如,2当量的MeMgBr仅在
金属上进行烷基化,选择性地生成复合物[(η5-C5Me5)(η5-C5H4CMe2CH2CN)
MMe2],而使用PhMgBr、PhLi或MeLi则选择性地产生
酮亚胺复合物。然而,芳基
锂试剂与
钛烯衍
生物相容性差。
金属结合的
酮亚胺随后通过与HCl反应被裂解,生成具有悬挂亚
氨基的
金属
烯二
氯化物。这些化合物可以在
氮原子上轻易地被质子化,生成阳离子亚
氨基团。在
锆的情况下,对
亚胺或其相应
氯化氢的
水解被证明是可行的,最终产生一个附着在
锆烯框架上的悬挂
酮基。