Electrochemical synthesis and structural characterization of bis(triphenylphosphine)copper(I) fluoroacetates

Abstract

Bis(triphenylphosphine)copper(I) fluoroacetate complexes have been prepared by the electrochemical oxidation of copper metal in acetonitrile solutions of triphenylphosphine and mono-, di- and tri-fluoro-acetic acid respectively. Recrystallization from toluene yields unsolvated mononuclear complexes [Cu(PPh₃)₂(O₂CCH_3–nF_n)], n= 1–3, which have been characterized by single-crystal X-ray crystallographic determinations. Crystals of the three complexes are isomorphous with the acetate complex (n= 0), crystallizing in the monoclinic space group P2₁/a with cell dimensions a≈ 18.0, b≈ 11.0 and c≈ 19.3 Å and β≈ 120°. Residuals for the complexes with n= 1,2 and 3 were R= 0.077, 0.045 and 0.048 for 3677, 2789 and 3527 ‘observed’[I > 3σ(I)] reflections respectively. The bond distances Cu–P are 2.232(3), 2.222(3); 2.234(2), 2.219(2); and 2.235(2), 2.228(2)Å with the corresponding P–Cu–P angles increasing from 135.0(1) to 135.8(1) to 136.7(1)°, this latter value being the largest recorded for [Cu(PPh₃)₂]⁺. The asymmetry of the co-ordination of the carboxylate group increases along the series with Cu–O distances of 2.144(6) and 2.363(7); 2.118(4), 2.465(6); and 2.113(4), 2.545(5)Å for n= 1, 2 and 3 respectively. Crystallization of the difluoro- and trifluoro-acetate complexes from ethanol results in isomorphous orthorhombic Pb2₁a crystals (a≈ 22.2, b≈ 18.5, c≈ 9.0 Å) with monodentate carboxylate and co-ordinated ethanol; the monofluoroacetate is unsolvated. For [Cu(PPh₃)₂(O₂CCHF₂)(EtOH)]R was 0.052 for 2090 ‘observed’ reflections with Cu–P 2.248(3), 2.236(3)Å and P–Cu–P 120.5(1)°; Cu–O (carboxylate) is 2.074(8)Å and Cu–O (ethanol) is 2.169(8)Å. For [Cu(PPh₃)₂(O₂CCF₃)(EtOH)]R was 0.043 for 2350 ‘observed’ reflections, Cu–P being 2.248(2), 2.240(2)Å and P–Cu–P 120.8(1)°; Cu–O (carboxylate) is 2.104(6)Å and Cu–O(ethanol) is 2.160(6)Å.