Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 46. Synthesis of heteronuclear trimetal compounds from the dimetallic compounds [ReM(CC6H4Me-4)(CO)9](M = Cr, Mo, or W) and [CoW(CC6H4Me-4)(CO)8]; X-ray structure of [CrReFe(µ3-CC6H4Me-4)(µ-CO)(CO)11]

Abstract

The compounds [ReCr(CC₆H₄Me-4)(CO)₉] and [Fe₂(CO)₉] in diethyl ether at room temperature afford the trimetal complex [CrReFe(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₁₁]. An X-ray diffraction study established that there are two independent molecules in the asymmetric unit and that the molecular structure consists of a µ₃-CCrReFe core with the chromium and the rhenium atoms ligated by four carbonyl groups and the iron atom by three such groups. A carbonyl ligand bridges the Cr–Re vector, however, the chromium and rhenium sites are disordered (60 : 40) and since the molecules have pseudo-mirror planes relating the metal tetracarbonyl fragments the bridging CO group may not be symmetrically disposed. Reactions between the compounds [ReM(CC₆H₄Me-4)(CO)₉](M = Mo or W) and [Fe₂(CO)₉] afford the related cluster compounds [MReFe(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₁₁], but these species were shown to be formed via the intermediary of the complexes [MReFe(µ-CC₆H₄Me-4)(CO)₁₃]. The compounds [CoW(CC₆H₄Me-4)(CO)₈] and [Fe₂(CO)₉] react to give the cluster complex [CoFe₂(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₉], and reactions of the latter with PPh₃ and with Ph₂PCH₂PPh₂ are described. Spectroscopic data for the new complexes are reported and discussed. Analysis of the ¹³C-{¹H} n.m.r. data for [CoFe₂(µ₃-CC₆H₄Me-4)(µ-CO)(CO)₉] has shown that the aromatic ring of the tolylmethylidyne group is locked into a fixed position at –80 °C. However, in the closely related cluster [Co₃(µ₃-CC₆H₄Me-4)(CO)₉] the group is free to rotate about the µ₃-C–C¹ axis at this temperature. These results have been interpreted in the light of extended Hückel molecular orbital calculations on the bonding of these molecules.