Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of ()-1--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 ()-1--2-(4',4'-dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates (L: R = -Ph, -Ph--NO, -Ph--OMe and --Bu), derived from the part enols (LH), is described. The resulting air-stable MoOL complexes (-) exist, as shown by single-crystal X-ray diffraction experiments, in the -dioxido--κ-,-L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes - 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 (R = -Ph) was studied for its ability to selectively catalyze the production of -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 - were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the -transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.