New multihydride complexes of rhenium containing diphosphine ligands: low-temperature protonation of [ReH7(Ph2PCHCHPPh2-PP′)]

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.