Dimolybdenum Complexes Containing Pairs of Bridging Diphosphine and Carboxylate Ligands. Synthesis and Structures of trans-Mo2(O2CCH3)2(μ-dppa)2(BF4)2 and trans-Mo2X2(O2C(CH2)nCH3)2(μ-dppa)2 (n = 2, 10 or 12; X = Cl or Br; dppa = N,N-Bis(diphenylphosphino

Abstract

The red complex trans-Mo2(O2CCH3)2(μ-dppa)2(BF4)2, 1, was prepared by reaction of [Mo2(O2CCH3)2(CH3CN)6][BF4]2 with dppa (dppa = Ph2PN(H)PPh2) in THF. The reactions of Mo2(O2C(CH2)nCH3)4 with dppa and (CH3)3SiX (X = Cl or Br) afforded the complexes trans-Mo2X2(O2C(CH2)nCH3)2(μ-dppa)2 (X = Cl, n = 2, 2; X = Br, n = 2, 3; X = Cl, n = 10, 4; X = Cl, n = 12, 5). Their UV-vis, IR and 31P{1H}-NMR spectra have been recorded and the structures of 1, 2 and 3 have been determined. Crystal data for 1: space group P21/n, a = 12.243(1) Å, b = 17.222(1) Å, c = 13.266(1) Å, β = 95.529(1)°, V = 2784.1(6) Å3, Z = 2, with final residuals R = 0.0509 and Rw = 0.0582. Crystal data for 24CH3Cl2: space group P21/n, a = 13.438(1) Å, b = 19.276(1) Å, c = 14.182(1) Å, β = 111.464(1)°, V = 3418.9(6) Å3, Z = 2, with final residuals R = 0.0492 and Rw = 0.0695. Crystal data for 3·4CH2Cl2: space group P21/n, a= 13.579(1) Å, b = 19.425(1) Å, c = 14.199(1) Å, β = 111.881(2)°, V = 3475.6(7) Å3, Z = 2, with final residuals R = 0.0703 and Rw = 0.0851. Comparison of the structural data shows that the effect of the axial ligand on weakening the Mo-Mo bond strength is X− > CH3CN > BF4−. The Tm values are 121.7 °C for 2, 111.1 °C for 3 and 91.5 °C for 5, respectively.