Reactivity of the binuclear hydride [Fe2(CO)4(µ-H)(µ-CO)(µ-PPh2)(µ-Ph2PCH2PPh2)] to generate phosphido and hydroxide moieties at the diiron centre

Abstract

Thermolysis of [Fe₂(CO)₄(µ-H)(µ-CO)(µ-PPh₂)(µ-dppm)]1(dppm = Ph₂PCH₂PPh₂) results in benzene loss via phosphorus–carbon bond cleavage yielding [Fe₂(CO)₅(µ-PPh₂)(µ-PhPCH₂PPh₂)]2. In a number of other reactions of 1, carbon monoxide and the hydride are replaced by three-electron donor ligands. Chromatography on alumina afforded the bridging hydroxide complex [Fe₂(CO)₄(µ-OH)(µ-PPh₂)(µ-dppm)]3, while thermolysis in the presence of secondary phosphines gave the bis(phosphido) complexes [Fe₂(CO)₄(µ-PPh₂)(µ-PR₂)(µ-dppm)](R = Ph 4 or C₆H₁₁5). Complexes 2–4 have been characterised crystallographically. All show a diiron centre bridged by two cis three-electron donor ligands. Both 4 and 5 are fluxional on the NMR time-scale, the observed changes being ascribed to a ‘rocking’ of the phosphido-bridges and ‘twisting’ of the diphosphine respectively.