NEW MULTIHYDRIDE COMPLEXES OF RHENIUM CONTAINING DIPHOSPHINE LIGANDS - LOW-TEMPERATURE PROTONATION OF [REH7(PH2PCH=CHPPH2-PP')]

Treatment of oxochloro complexes of tge type (ReOCl3(L-L)] (L-L = diph osphine) with sodium tetrahydroborate gave complexes of the type [ReH7 (L-L)]. Treatment of [ReH7(dppen-PP)] la [dppen = cis-1,2-bis(diphenyl phosphino)ethylene = cis-Ph2PCH=CHPPh2] with triphenylphosphine gave a mixture of the pentahydride [ReH5(dppen-PP)(PPh3)] and the trihydride (ReH3(dppen-PP')(PPh3)2]. However, treatment of la with dppm [bis(dip henylphosphino)methane, Ph2PCH2PPh2] in refluxing toluene, followed by slow crystallisation, gave [ReH5(dppen-PP)(dppm-P)] which was isolate d and characterised by variable-temperature NMR spectroscopy. Prolonge d heating of la with dppm gave the trihydride [ReH3(dppen-PP)(dppm-PP) ], the fluxionality of which was studied by NMR spectroscopy between 90 and -70-degrees-C. Protonation of la with HBF4.Et2O, at -80-degrees -C, gave a complex formulated as [ReH6(eta2-H-2)(dppen-PP)]+ which, on warming to ambient temperature, was cleanly converted to a dirhenium multihydride species tentatively formulated as [(dppen-PP')H3Re(mu-H)2 -ReH3(dppen-PP')] on the basis of IR and NMR evidence.