Synthese und reaktivität ternärer cluster: thermisch ausgelöste addition von alkinen an (ν₃-RP)Fe₃(CO)₁₀

The ν₃-RP-bridged clusters (ν₃-RP)Fe₃(CO)₁₀ (1) react with terminal alkynes R′CCH to give the adducts (RPCHCR′)Fe₃(CO)₁₀ (2). The adducts 2 contain the C₂ entity of the alkyne inserted into a PFe edge of the starting cluster 1. The dependence of the relative reaction rates upon the nature of R and R′ groups, is investigated in detail. A mechanism for the formation of 2 from 1 is proposed, involving the opening of 1 at an iron edge as an essential step. The structure of the adducts 2 has been determined for two examples, by X-ray diffraction anaysis. It indicates the existence of a bent cyclopentadiene-like five-membered cycle RPCHCR′Fe(CO)₃Fe(CO)₄, which is coordinated "side-on"to an Fe(CO)₃ group via its heterobutadiene fragment PCCFe.