<i>Trans</i> Influence of Oxo and Dithiolene Coordination in Oxidized Models of Molybdenum Oxidoreductase: Synthesis, Structures, and Properties of Q₂[Mo^VIO₂(1,2-benzenedithiolato)₂] (Q = NEt₄, PPh₄) and Related Complexes

Abstract

Three cis-dioxomolybdenum(VI) complexes with dithiolene-like benzenedithiolate ligands, Q2[MoVIO2(1,2-benzenedithiolato)2] (Q = NEt4 (1a), PPh4 (1b)), [MoVIO2(3-triphenylsilyl-1,2-benzenedithiolato)2]2- (2), and [MoVIO2(4-methyl-1,2-benzenedithiolato)2]2- (3), were synthesized as models of oxidized sulfite oxidase and compared with the structure of (PPh4)2[MoVIO2(S2C2(CN)2)2]·2MeOH (4). The crystal data for 1b, chemical formula C60H48O2P2S4Mo, are a = 13.938(6) Å, b = 16.65(1) Å, c = 22.645(5) Å, β = 103.81(2)°, V = 5104(5) Å3, Z = 4, and space group P21/c and the data for 4·2MeOH, chemical formula C58H48O2P2S4Mo, are a = 20.273(3) Å, b = 15.632(5) Å, c = 17.685(4) Å, V = 5604(3) Å3, Z = 4, and space group Pbcn. 1b and 4 have a slightly distorted octahedral structure with two long MoS bonds (2.588(3) Å and 2.608(3) Å for 1b and 2.635(2) Å for 4) trans to each of the MoO groups and with two short MoS bonds (2.417(3) Å and 2.434(3) Å for 1b and 2.440(2) for 4) cis to them. The short SC bond distances of the thiolate trans to the MoO groups in 4 suggest the presence of partial double bonding at the SC (thioketone-like) bond, which contributes to the stabilization of the dioxomolybdenum(VI) species by weakening π-bonding in the MoS bonds trans to the MoO groups. The electron-donating or -withdrawing substituents, e.g. 4-CH3 or 3-SiPh3, on the 1,2-benzenedithiolate Mo(VI) complexes accelerate or retard its oxo-transfer reaction, respectively. The formation of any binuclear Mo(V) complex does not occur in the reaction between [MoVIO2(1,2-benzenedithiolato)2]2- and [MoIVO(1,2-benzenedithiolato)2]2- when the cis-dioxomolybdenum(VI) complex is reduced by triphenylphosphine or benzoin.