Synthesis, structure and properties of new iron–molybdenum and –tungsten fulvalene-bridged heterobimetallic complexes

Abstract

Reaction of Li[C₅H₄Fe(C₅H₅)] with 2,3,4,5-tetramethylcyclopent-2-enone followed by acid work-up afforded the ferrocenyl-substituted cyclopentadiene [Fe(C₅H₅)(C₅H₄C₅Me₄H)]1. Lithiation of 1 with LiBuⁿ in hexane gave Li[C₅Me₄C₅H₄Fe(C₅H₅)]. Reactions of this salt or the previously described lithium 3,4-dimethylcyclopentadienide or indenide homologues, Li[C₅H₂Me₂C₅H₄Fe(C₅H₅)] or Li[C₉H₆C₅H₄Fe(C₅H₅)], with the allyl complexes [MoBr(MeCN)₂(CO)₂(η-C₃H₅)] or [WCl(MeCN)₂(CO)₂-(η-C₃H₅)] led to the corresponding fulvalene (and related)-bridged, Fe–Mo or Fe–W heterobimetallic derivatives [(C₅H₅)Fe(C₅H₄C₅Me₄)Mo(CO)₂(η-C₃H₅)]2, [(C₅H₅)Fe(C₅H₄C₅H₂Me₂)M(CO)₂(η-C₃H₅)](M = Mo 3 or W 4) and [(C₅H₅)Fe(C₅H₄C₉H₆)M(CO)₂(η-C₃H₅)](M = Mo 5 or W 6). The crystal structure of 5 has been determined. Reaction of the cinnamyl complex [MoBr(MeCN)₂(CO)₂(η-C₃H₄Ph)] with Li[C₅H₂Me₂-C₅H₄Fe(C₅H₅)] or Li[C₉H₆C₅H₄Fe(C₅H₅)] yielded [(C₅H₅)Fe(C₅H₄C₅H₂Me₂)Mo(CO)₂(η-C₃H₄Ph)]7 or [(C₅H₅)Fe(C₅H₄C₉H₆)Mo(CO)₂(η-C₃H₄Ph)]8 respectively, both of which exist as a mixture of isomers. Treatment of 7 with [Cr(CO)₆] in Buⁿ₂O–tetrahydrofuran gave the Fe–Mo–Cr heterotrimetallic complex [(C₅H₅)Fe(CH₄C₅H₂Me₂)(OC)₂Mo(µ-η³:η⁶-C₃H₄Ph)Cr(CO)₃]9. The new monometallic analogue [Mo(CO)₂-(η-C₃H₅)(η-CMe₅)]10 has also been prepared. Cyclic voltammetric studies of some of the new heterobi-metallic complexes and of 10, [Mo(CO)₂(η-C₃H₅)(η-C₅H₅)] and [Mo(CO)₂(η-C₃H₅)(η-C₉H₇)] are described.