Bimetallic systems. Part 19. Chromium(0)–, molybdenum(0)–, or tungsten(0)–iron(0) carbonyl complexes containing one or two bridging Ph2PCH2PPh2 ligands: crystal structure of [(OC)3Mo(µ-Ph2PCH2PPh2)2Fe(CO)3]

Abstract

Treatment of mer-[M(CO)₃(dppm-PP′)(dppm-P)](M = Cr, Mo, or W)(dppm = Ph₂PCH₂PPh₂) or fac-[M(CO)₃(dppm-PP′)(dppm-P′)](M = Mo or W) with [Fe₂(CO)₉] or [Fe₃(CO)₁₂] gave the bimetallics [(OC)₃M(µ-dppm)₂Fe(CO)₃](M = Cr, Mo, or W) in moderate (2–52%) yields. The bimetallics were protonated with HBF₄·Et₂O to give the hydrides [(OC)₃HM(µ-dppm)_2^–Fe(CO)₃]⁺BF₄^–. Proton n.m.r. studies indicated that the hydride ligand was located terminally on the Group 6 metal. In addition, complexes tentatively formulated as mer-[(dppm-PP′)(OC)₃M-(µ-dppm)Fe(CO)₄](M = Cr, Mo, or W) and fac-[(dppm-PP′)(OC)₃W(µ-dppm)Fe(CO)₄] are also formed in the above reactions and have been characterised by ³¹P-{¹H} n.m.r. spectroscopy. These complexes appear not to be the simple precursors to the bimetallics containing two bridging dppm ligands. Crystals of [(OC)₃Mo(µ-dppm)Fe(CO)₃] are triclinic, space group P, with a= 1 219.1 (3), b= 1 225.2(2), c= 2 142.4(4) pm, α= 92.97(2), β= 95.42(2), γ= 100.58(2)°, and Z= 4; final R factor 0.0791 for 6 771 observed reflections. The structure shows that there is a metal–metal bond [304.7(5) pm], probably best considered as a weak donor → acceptor bond, viz. Fe → Mo. Both metal centres show distortions from idealised geometries.