Novel behaviour and reactivity in 1,1′-bis(diphenylphosphino)ferrocene and 1,1′-bis(diphenylphosphino)cobaltocene cluster derivatives

Abstract

The clusters [Ru 6C(CO) 16{Fe(C 5H 4P(Ph) 2) 2}] 2 and [Ru 6C(CO) 15{ μ-Fe(C 5H 4P(Ph) 2) 2}] 3 have been synthesised from the reaction of the parent cluster [Ru 6C(CO) 17] 1 with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in THF. The related compound [Ru 5C(CO) 13{ μ-Fe(C 5H 4P(Ph) 2) 2}] 4 is produced from 2 and 3 in more forcing conditions. Both clusters 3 and 4 have been structurally characterised by single crystal X-ray analysis. In 3 the dppf ligand is coordinated in the vicinal form and the cluster core is a highly distorted octahedron. In 4 the vicinal mode is retained but the dppf ligand is coordinated to adjacent basal atoms of a square-base pyramid. The 31P-NMR spectra of 3 and 4 in CD 2Cl 2 at various temperatures show a high degree of stereochemically non-rigid behaviour. Magnetic susceptibility measurements across a range of temperatures indicate that 3 is paramagnetic at all temperatures. An electrochemical study of 1, 3, 4 and the related [Ru 6C(CO) 15{ μ-dppm}] 5 has demonstrated a significant degree of communication between the redox-active sites in 3 and 4. The cluster [Ru 5C(CO) 13{ μ-Co(C 5H 4P(Ph) 2) 2}] 7 has also been synthesised from the direct reaction of the parent cluster [Ru 5C(CO) 15] 6 with 1,1′-bis(diphenylphosphino)cobaltocene (dppc). Synthesis of the dppc analogue of 3 was attempted but was thwarted by unfavourable redox chemistry. EPR spectra have been obtained for both dppc and 7. The oxidation product of 7 has also been produced ( 7 +) and displays a high degree of stereochemically non-rigid behaviour in a fashion similar to 3 and 4. The magnetic suceptibility of 7 has also been measured, showing an extraordinarily large magnetic moment at ambient temperature.