Chemistry of the metal carbonyls. Part 78. Synthesis and X-ray crystal structures of [NiOs3(µ-H)2(µ-CO)2(CO)8(PPh3)2] and [Os3Rh(µ-H)2(acac)(CO)10](acac = acetylacetonate)

Abstract

The zerovalent nickel compound [Ni(C₂H₄)(PPh₃)₂] reacts with [Os₃(µ-H)₂(CO)₁₀] to give the 60 valence electron cluster complex [NiOs₃(µ-H₂)(CO)₁₀(PPh₃)₂], the structure of which has been established by a single-crystal X-ray diffraction study. It crystallises in the monoclinic space group P2₁/n with four molecules in a cell of dimensions a= 15.579(6), b= 17.205(4), c= 18.976(5)Å, and β= 99.97(3)°. The structure has been determined from 8 595 unique reflections (2.9 ⩽ 2θ⩽ 55°, Mo-K_αX-radiation) collected at 190 K, and refined to R 0.038 (R′ 0.042). The metal atoms form a slightly distorted tetrahedron with two Ni–Os edges each bridged by a carbonyl group, and with the third Ni-Os edge and an Os–Os bond bridged by hydrido-ligands. Although the latter were not located by the diffraction study their assigned positions are argued on a variety of other evidence. The nickel atom carries one PPh₃ ligand, while the second PPh₃ group is bound to an osmium atom. The unsaturated triosmium compound [Os₃(µ-H)₂(CO)₁₀] also reacts with [Rh(acac)(C₂H₄)₂](acac = acetylacetonate) affording in high yield the cluster complex [Os₃Rh(µ-H)₂(acac)(CO)₁₀]. An X-ray diffraction study on a single crystal revealed that it was triclinic, space group P(no. 2), Z= 2, in a unit cell of dimensions a= 8.759(3), b= 9.463(2), c= 13.680(4)Å, α= 100.59(2), β= 93.86(2), and γ= 107.84(2)°. The structure has been refined to R 0.052 (R′ 0.059) for 4 240 independent reflections (2.9 ⩽ 2θ⩽ 60°, Mo-K_αX-radiation) collected at 200 K. The four metal atoms adopt a ‘butterfly’ configuration. The pentane-2,4-dionato-ligand is chelated to the rhodium atom at one extremity but one of its oxygen atoms also bridges to an Os atom forming the other wing-tip of the ‘butterfly’, so that this Os–Rh separation is 3.292(2)Å. The pentane-2,4-dionato-group thus functions as a five-electron donor, hence the cluster has 60 valence electrons. The rhodium atom also carries a carbonyl ligand, and this, and the remaining nine carbonyls on the osmium atoms, are all terminally bound. On the basis of ¹H n.m.r. studies, osmium–osmium distances, and other evidence the two hydrido-ligands bridge two of the Os–Os bonds. The compound is chemically unsaturated forming an adduct with triphenylphosphine; n.m.r. studies (¹H and ³¹P) show that the PPh₃ group becomes attached to the rhodium atom of the cluster.