NOVEL BEHAVIOR AND REACTIVITY IN 1,1'-BIS(DIPHENYLPHOSPHINO)FERROCENEAND 1,1'-BIS(DIPHENYLPHOSPHINO)COBALTOCENE CLUSTER DERIVATIVES

The clusters [Ru6C(CO)(16){Fe(C5H4P(Ph)(2))(2)}] 2 and [Ru6C(CO)(15){m u-Fe(C5H4P(Ph)(2))(2)}] 3 have been synthesised from the reaction of t he parent cluster [Ru6C(CO)(17)] 1 with 1,1'-bis(diphenylphosphino)fer rocene (dppf) in THF. The related compound [Ru5C(CO)(13){mu-Fe(C5H4P(P h)(2))(2)}] 4 is produced from 2 and 3 in more forcing conditions. Bot h clusters 3 and 4 have been structurally characterised by single crys tal 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 adjacen t basal atoms of a square-base pyramid. The P-31-NMR spectra of 3 and 4 in CD2Cl2 at various temperatures show a high degree of stereochemic ally non-rigid behaviour. Magnetic susceptibility measurements across a range of temperatures indicate that 3 is paramagnetic at all tempera tures. An electrochemical study of 1, 3, 4 and the related [Ru6C(CO)(1 5){mu-dppm}] 5 has demonstrated a significant degree of communication between the redox-active sites in 3 and 4. The cluster [Ru5C(CO)(13){m u-Co(C5H4P(Ph)(2))(2)}] 7 has also been synthesised from the direct re action of the parent cluster [Ru5C(CO)(15)] 6 with 1,1'-bis(diphenylph osphino)cobaltocene (dppc). Synthesis of the dppc analogue of 3 was at tempted 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 stereochemica lly 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. (C) 1998 Elsevier Scienc e S.A. All rights reserved.