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High variety of coordination modes of π-conjugated phospholes in dinuclear rhenium carbonyls. Fluxional behavior of σ,π-complexes

Abstract:

A variety of dirhenium carbonyl complexes containing π-conjugated phosphole derivatives were obtained from reaction of [Re2(CO)8(CH3CN)2] with each of the following phospholes: 2,5-bis(2-thienyl)-1-phenylphosphole (btpp), 2,5-bis(2-pyridyl)-1-phenylphosphole (bpypp) and 1,2,5-triphenylphosphole (tpp). The π-conjugated phospholes were found to behave as two-, four- or six-electron donor ligands via σ or σ-π interactions with the metal centers, presenting bridging or chelating coordination modes as determined by spectroscopic methods and single crystal X-ray diffraction analysis. Metal-metal bond cleavage was evidenced when btpp was used, leading to a mono-substituted mononuclear complex. Variable-temperature 1H NMR studies for σ,π-complexes showed a fluxional behavior due to the restricted rotation around the P–C and C–C bonds of the 1,2,5-trisubstituted phosphole ring.