Trans influence of oxo and dithiolene coordination in oxidized models of molybdenum oxidoreductase: Synthesis, structures, and properties of Q(2)[MoVIO2(1,2-benzenedithiolato)(2)] (Q=NEt(4), PPh(4)) and related complexes

Three cis-dioxomolybdenum(VI) complexes with dithiolene-like benzenedithiolate ligands, Q(2)[(MoO2)-O-VI(1,2-benzenedithiolato)(2)] (Q = NEt(4) (1a), PPh(4) (1b)), [(MoO2)-O-VI(3-triphenylsilyl-1,2-benzenedithiolato)(2)](2-) (2), and [(MoO2)-O-VI(4-methyl-1,2-benzenedithiolato)(2)](2-) (3), were synthesized as models of oxidized sulfite oxidase and compared with the structure of (PPh(4))(2)[(MoO2)-O-VI(S2C2(CN)(2))(2)]. 2MeOH (4). The crystal data for 1b, chemical formula C60H48O2P2S4Mo, are a 13.938(6) Angstrom, b = 16.65(1) Angstrom, c = 22.645(5) Angstrom, beta = 103.81(2)degrees, V = 5104(5) Angstrom(3), Z = 4, and space group P2(1)/c and the data for 4 . 2MeOH, chemical formula C58H48O2P2S4Mo, are a = 20.273(3) Angstrom, b = 15.632(5) Angstrom, c = 17.685(4) Angstrom, V = 5604(3) Angstrom(3), Z = 4, and space group Pbcn. 1b and 4 have a slightly distorted octahedral structure with two long Mo-S bonds (2.588(3) Angstrom, and 2.608(3) Angstrom for 1b and 2.635(2) Angstrom for 4) trans to each of the Mo=O groups and with two short Mo-S bonds (2.417(3) Angstrom and 2.434(3) Angstrom for 1b and 2.440(2) for 4) cis to them. The short S-C bond distances of the thiolate trans to the Mo=O groups in 4 suggest the presence of partial double bonding at the S-C (thioketone-like) bond, which contributes to the stabilization of the dioxomolybdenum(VI) species by weakening pi-bonding in the Mo-S bonds trans to the Mo=O groups. The electron-donating or -withdrawing substituents, e.g. 4-CH3 or 3-SiPh(3), on the 1,2-benzenedithiolate Mo(VI) complexes accelerate or retard its ore-transfer reaction, respectively. The formation of any binuclear Mo(V) complex does not occur in the reaction between [(MoO2)-O-VI(1,2-benzenedithiolato)(2)](2-) and [(MoO)-O-IV(1,2-benzenedithiolato)(2)](2-) when the cis-dioxomolybdenum(VI) complex is reduced by triphenylphosphine or benzoin.