J. Heyrovský Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic.
Dalton Trans. 2013 May 21;42(19):7101-10. doi: 10.1039/c3dt50209k.
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 [(η(5)-C5Me5)(η(5)-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 [(η(5)-C5Me5)(η(5)-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.
已证明四价茂金属骨架上的功能团转化，这为原本具有挑战性的合成衍生物提供了相对直接的途径。[(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MCl2]型钛和锆茂金属配合物中，侧链上的腈基通过烷基化反应转化为分子内结合的酮亚胺基，该反应不仅发生在腈基上，还发生在金属中心上。烷基化试剂（烷基/芳基锂、格氏试剂）的选择至关重要：例如，2 当量的 MeMgBr 仅在金属上进行烷基化，选择性地得到[(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MMe2]配合物，而使用 PhMgBr、PhLi 或 MeLi 则选择性地得到酮亚胺配合物。然而，有机锂试剂与钛茂衍生物不兼容。金属结合的酮亚胺随后通过与 HCl 的反应而脱除，得到带有侧挂亚氨基的茂金属二氯化物。这些化合物很容易在氮原子上再次质子化，生成阳离子亚胺基部分。在锆的情况下，亚胺或其相应盐酸盐的水解除了可行外，最终还在锆茂骨架上生成了一个侧挂的酮基。
