Preparation and characterization of chloro- and polyhydride complexes of rhenium: Variable-temperature NMR spectroscopy and protonation studies

The rhenium complex fac-[ReOCl3L] [1; L = 1,3-bis(diphenylphosphanyloxy)propane] was prepared by reacting L with [ReOCl3(AsPh3)2]. Refluxing complex 1 in ethanol gave [ReOCl2(OEt)L] (2), which X-ray crystallography showed to have an octahedral rhenium environment and an Re–O–Et fragment of unusual linearity. The paramagnetic chlorocomplexes mer-[ReCl3LL′] [3; L′ = P(OEt)3 in 3a, PPh(OEt)2 in 3b, PPh2(OEt) in 3c] were obtained by treating compound 1 with L′. Reaction of complexes 1 and 3a–c with excess NaBH4 gave the polyhydrides [ReH7L] (4) and [ReH5LL′] (5a–c), respectively, all of which were characterized by variable-temperature (VT) NMR spectroscopy as highly fluxional classical hydrides. Complete protonation of these polyhydrides with HBF4 · OMe2 required 3 equiv. of acid, and the cationic polyhydride complexes so obtained were characterized as non-classical species by VT NMR spectroscopy and T1 measurements.