The reductive activation of [M5C(CO)15](M = Ru or Os) and subsequent reactions of the dianion [Os5C(CO)14]2–, carbonylation of [M5C(CO)15](M = Ru or Os), and the crystal structures of [Os5C(CO)16], [N(PPh3)2]2[Os5C(CO)14], and [Os5C(CO)14{Au(PPh3)}2]

Abstract

High pressure infrared (h.p.i.r.) studies indicate that the cluster [Ru₅C(CO)₁₅](1) adds carbon monoxide under relatively mild conditions (20 °C, 80 atm) to give [Ru₅C(CO)₁₆](2), while under more forcing conditions (90 °C, 80 atm) the cluster (2) reverts back to (1). The osmium analogue, [Os₅C(CO)₁₅](3), gives [Os₅C(CO)₁₆](4) at 70 °C and 50 atm but may be obtained in quantitative yield from an autoclave reaction in the absence of solvent. Complex (4) crystallises in space group P with a= 10.017(3), b= 15.823(5), c= 16.507(8)Å, α= 96.78(3), β= 103.20(3), γ= 93.41(2)°, and Z= 4. The structure was solved by a combination of direct methods and Fourier-difference techniques and refined by blocked full-matrix least squares to R= 0.073 for 6 120 reflections. The five Os atoms define a ‘bridged-butterfly’ configuration with a carbide at the centre. There are four terminal carbonyl groups bound to the bridging metal atom and three to each of the other four metal atoms. A h.p.i.r. study of the reaction of (4) with H₂ has shown that at a pressure of 75 atm and at temperatures around 90 °C the cluster [Os₅H₂(C)(CO)₁₅](5) is produced. The electrochemical or chemical reduction of [M₅C(CO)₁₅][M = Ru (1) or Os (3)] produces the corresponding dianion [M₅C(CO)₁₄]^2–[M = Ru (6) or Os (7)]. An X-ray analysis of the [N(PPh₃)₂]⁺ salt of (7) shows that the squarepyramidal Os₅C core geometry of (3) is retained. One of the Os–Os bonds in the basal plane is symmetrically bridged by a carbonyl group. The remaining 13 carbonyl ligands are co-ordinated terminally, two each to the carbonyl-bridged metal atoms, and three each to the other three metal atoms. The salt crystallises in space group P with a= 13.244(6), b= 14.648(9), c= 21.963(14)Å, α= 86.78(5), β= 85.54(5), γ= 81.22(5)°, and Z= 2. The structure was solved using the same techniques as for (4) and refined by blocked-cascade least squares to R= 0.065 for 5 780 observed diffractometer data. The dianion (7) reacts with two equivalents of [Au(PPh₃)Cl] to give the neutral complex [Os₅C(CO)₁₄{Au(PPh₃)}₂](10) which has also been characterised crystallographically. In (10) the Os₅C core shows significant distortions from square-pyramidal geometry. Two opposite Os(basal)–Os(apical) bonds are bridged by the Au atoms of the Au(PPh₃) ligands and these two bonds are significantly longer than the other two unbridged Os(basal)–Os(apical) bonds. Two carbonyl groups are bonded terminally to the apical Os atom, and three each to the four basal Os atoms. This complex crystallises in space group P2₁/c with a= 20.307(4), b= 9.843(2), c= 27.980(6)Å, β= 100.53(2)°, and Z= 4. The structure was solved and refined as for (7) to R= 0.060 for 7 013 observed diffractometer data.