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)A, and β= 99.97(3)°. The structure has been determined from 8 595 unique reflections (2.9 ⩽ 2θ⩽ 55°, Mo-KαX-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)A, 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-KαX-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)A. 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.