Remote ligand substituent effects on the properties of oxo-Mo(V) centers with a single ene-1,2-dithiolate ligand

The oxomolybdenum mono-ene-1,2-dithiolate complex (Tp*)MoO(bdtCl2) (3) has been synthesized and characterized (Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdtCl2 is 3,6-dichloro-1,2-benzenedithiolate). The X-ray structural data show that 3 crystallizes in the monoclinic space group, P21/c, where a=7.963 (3), b=26.272 (11), c=14.016 (6) Å, β=105.352 (7). The (Tp*)MoO(bdtCl2) molecule exhibits a distorted pseudo-octahedral coordination geometry, with the Mo atom ligated by a terminal oxo atom, two sulfur donor atoms of the bdtCl2 ligand and three nitrogen atoms of the tridentate facially coordinated Tp* ligand. The coordination environment about the Mo atom is similar to that of (Tp*)MoO(bdt) (1) (bdt is 1,2-benzenedithiolate), but the fold angle between the MoS2 plane and S2C2 plane of the bdtCl2 ligand (θ=6.9°) is substantially smaller than the feature in 1 (θ=21.3°). The similar IR, EPR, and electronic absorption spectroscopic results for 1 and 3 indicate that the electron withdrawing nature of the chlorine substituents of 3 does not significantly perturb the electronic structure of the Mo(V) center. However, the solution redox potentials and the gas-phase ionization energies are sensitive to remote substituent effects.