Syntheses, 95Mo NMR Spectroscopy and Structures of Distorted Cubic Mo4(μ3-O)4(μ2-O2P(CH2C6H5)2)4O4 and the Open Mixed-Valent Cluster, Mo4(μ3-O)2 (μ2-O2P(CH2C6H5)2)6O6

The reaction of MoO2(acac)(2) and dibenzylphosphinic acid in ethanol leads to a red distorted cubic tetrameric cluster, Mo-4(mu(3)-O)(4)(mu(2)-O2P(CH2C6H5)(2))(4)O-4, and a pink open mixed-valent cluster, Mo-4(mu(3)-O)(2)(mu(2)-O2P(CH2C6H5)(2))(6)O-6, when the reduction is carried out at 120 and 75 degrees C, respectively. Mo-95 NMR spectroscopy revealed a singlet for Mo-4(mu(3)-O)(4)(mu(2)-O2P(CH2C6H5)(2))(4)O-4 (1) at 584.9 ppm (Delta(v1/2) = 4500 Hz) and two resonances for Mo-4(mu(3)-O)(2)(mu(2)-O2P(CH2C6H5)(2))(6)O-6 (2) at 238.8 ppm (Delta(v1/2) = 1250 Hz) and 6.4 ppm (Delta(v1/2) = 5999 Hz), which were assigned to the Mo(V) and Mo(VI) sites, respectively. DFT geometries and Mo-95 DFT-GIAO chemical shifts for Mo-4(mu(3)-O)(4)(mu(2)-O2P(CH3)(2))(4)O-4 (3) and Mo-4(mu(3)-O)(2)(mu 2-O2P(CH3)(2))(6)O-6 (4) are consistent with X-ray crystallography and Mo-95 NMR of 1 and 2. The open complex, Mo-4(mu(3)-O)(2)(mu(2)-O2P(CH2C6H5)(2))(6)O-6 center dot 2(CH2Cl2), exhibits a central Mo(V)-Mo(V) single bond at 2.6217(5) angstrom with each Mo(V) atom bonded to one oxo (trans-disposed) terminal ligand.