Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of ( Z )-1- R -2-(4',4'-Dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates.

The coordination chemistry of the title ligands with Mo metal centers was investigated. Thus, the synthesis and characterization (NMR, X-ray diffraction) of four mononuclear formally Mo(6+) complexes of ( Z )-1- R -2-(4',4'-dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates (L: R = -Ph, -Ph- p -NO 2 , -Ph- p -OMe and - t -Bu), derived from the part enols (LH), is described. The resulting air-stable MoO 2 L 2 complexes ( 1 - 4 ) exist, as shown by single-crystal X-ray diffraction experiments, in the cis -dioxido- trans(N) -κ 2 - N , O -L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes 1 - 4 represent the first Mo complexes of this ligand class and, indeed, of Group 6 metals in general. Structural and spectroscopic comparisons were made between these and related Mo(6+) compounds. Complex 1 (R = -Ph) was studied for its ability to selectively catalyze the production of poly -norbornene from the monomer in the presence of MAO. This, unfortunately, only resulted in the synthesis of insoluble, presumably highly cross-linked, polymeric and/or oligomeric materials. However, complexes 1 - 4 were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the O -transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.