New multihydride complexes of rhenium containing diphosphine ligands: low-temperature protonation of [ReH7(Ph2PCHCHPPh2-PP′)]

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Abstract
Treatment of oxochloro complexes of the type [ReOCl3(L–L)](L–L = diphosphine) with sodium tetrahydroborate gave complexes of the type [ReH7(L–L)]. Treatment of [ReH7(dppen-PP′)]1a[dppen =cis-1,2-bis(diphenylphosphino)ethylene =cis-Ph2PCHCHPPh2] with triphenylphosphine gave a mixture of the pentahydride [ReH5(dppen-PP′)(PPh3)] and the trihydride [ReH3(dppen-PP′)(PPh3)2]. However, treatment of 1a with dppm [bis(diphenylphosphino)methane, Ph2PCH2PPh2] in refluxing toluene, followed by slow crystallisation, gave [ReH5(dppen-PP′)(dppm-P)] which was isolated and characterised by variable-temperature NMR spectroscopy. Prolonged heating of 1a with dppm gave the trihydride [ReH3(dppen-PP′)(dppm-PP′)], the fluxionality of which was studied by NMR spectroscopy between +90 and –70 °C. Protonation of 1a with HBF4·Et2O, at –80 °C, gave a complex formulated as [ReH6(η2-H2)(dppen-PP′)]+ which, on warming to ambient temperature, was cleanly converted to a dirhenium multihydride species tentatively formulated as [(dppen-PP′)H3Re(µ-H)2ReH3(dppen-PP′)] on the basis of IR and NMR evidence.