Quadruply bonded dimolybdenum complexes containing pairs of bridging diphosphine and acetate ligands; synthesis and structural characterization of trans-Mo2Cl2(OAc)2(μ-dppa)2 and its transformation to Mo2Cl4(μ-dppa)2, where dppa is N,N-bis(diphenylphosphino)amine

Abstract

By reaction of Mo2 (OAc)4 with (CH3)3SiCl and dppa (dppa=Ph2PN(H)PPh2) in THF, two complexes can be prepared. The red complex trans-Mo2Cl2(OAc)2(μ-dppa)2 (1) was obtained in 42% yield while the green complex Mo2Cl4(μ-dppa)2 (2) was prepared in 31% yield. Complex 2 can also be derived by reacting K4Mo2Cl8 or Mo2Cl4(PPh3)2(CH3OH)2 with dppa in methanol and acetone, respectively. Reaction of 1 with (CH3)3SiCl leads to the formation of 2. Their UV-Vis and 31P{1H} NMR spectra have been recorded and the structures of both 1 and 2 have been determined. Crystal data for 1: space group Pbca, a = 16.699(1), b = 16.784(1), c = 19.728(2) Å, V = 5529.3(7) Å3, Z = 4, with final residuals R = 0.0606 and Rw = 0.0620. The diphosphine ligands are bridged to the metal centers with an eclipsed configuration around the metal-metal bond. The chloride atoms are forced to coordinate to the Mo atoms in the axial positions. Crystal data for 2: space group Ibca, a = 16.165(2), b = 16.576(2) Å, c = 37.024(3) Å, V = 9921(2) Å3, Z = 8, with final residuals R = 0.0933 and Rw = 0.0990. The two dppa ligands are bridged to the metal centers. The interconversions between 1 and 2 are discussed.