Rhodium(I)–iron(0) carbonyl complexes containing one bridging Ph2PCH2PPh2 ligand, including the formation of a tetranuclear cluster from a heterobimetallic precursor: crystal structures of [(OC)4Fe(µ-Ph2PCH2PPh2)RhCl(CO)] and [Fe2Rh2(µ-Ph2PCH2PPh2)2(CO)8]

Abstract

Treatment of [Fe(CO)₄(dppm-P)](dppm = Ph₂PCH₂PPh₂) with [Rh₂Cl₂(CO)₄] in benzene gave [(OC)₄Fe(µ-dppm)RhCl(CO)](1) in 90% yield. The structure of (1) has been established by a single-crystal X-ray diffraction study; the crystals are monoclinic, space group P2₁/n, with a= 1 246.5(2), b= 1 849.0(3), c= 1 612.3(2) pm, β= 110.34(1)°, and Z= 4; final R factor 0.0481 for 4 053 observed reflections. The structure shows that there is a metal–metal bond [Fe–Rh 269.9(4) pm], formulated as a donor → acceptor bond, viz. Fe → Rh. None of the carbonyl ligands shows any bridging interactions. Treatment of (1) with lithium acetate in dichloromethane–methanol converted the binuclear complex into the tetranuclear cluster [Fe₂Rh₂(µ-dppm)₂(CO)₈](3) in 69% yield, also characterised by an X-ray diffraction study. Crystals of (3) are monoclinic, space group P2₁/n, with a= 2 074.6(5), b= 1 385.1(3), c= 2 271.6(5) pm, β= 117.48(2)°, and Z= 4; final R factor 0.0578 for 6 212 observed reflections. The structure is that of an unsupported Fe₂Rh₂ butterfly, the Rh–Rh distance of 405.4 pm indicating no interaction between the wing-tip atoms. Similar complexes are described for Ph₂P(CCH₂)PPh₂.