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Step Dance on a Pentagon: Copper(I) and Copper(I)-Tungsten(0) Triphospholyl Triphenylphosphane Complexes

[(3,5-di-teri-butyl-1,2,4-triphospholyl)Cu(PPh3)] (8) is, in contrast to the related dinieric complex [(3,5-di-teri-butyl-1,2,4- triphospholyl)Cu(PMe3)2]2, monomeric and thighly fluxional in solution. 3 is synthesized from the corresponding trimethylstannyl 1,2,4-triphosphole la and [ClCu(PPh3)]4. Evidence for a three-sided rearrangement process between different molecular structures in solution could be obtained from dynamic 31P NMR spectroscopy. An η5-π coordination mode (3a) of the copper ion is preferred at room temperature. The equilibrium shifts to the two spectroscopically distinguishable, but almost isoenergetic, σ complexes 3b and 3c at low temperature, which interconvert with the activation barrier ΔG? = 37 kJ/mol. The σ-donor orbitals of the triphospholyl ligand are believed to be an sp3 hybrid P orbital in the case of 3b and an sp2 P lone pair for 3c. The reaction of 3 with [(THF)W(CO)5] leads to the binuclear CuW complex 4 and the trinuclear W2Cu complex 5 with σ-phosphorus-coordinated W(CO)5 moieties. 5 bears an additional η5-π coordinated W(CO) 3 unit and a unique W-Cu-P bridge, as established by X-ray crystallography. Both complexes are fluxional in solution, and the activation barriers of their rearrangement processes have been established.