| Summary: | 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 (<i>Z</i>)-1-<i>R</i>-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates (L: R = –Ph, –Ph-<i>p</i>-NO<sub>2</sub>, –Ph-<i>p</i>-OMe and –<i>t</i>-Bu), derived from the part enols (LH), is described. The resulting air-stable MoO<sub>2</sub>L<sub>2</sub> complexes (<b>1</b>–<b>4</b>) exist, as shown by single-crystal X-ray diffraction experiments, in the <i>cis</i>-dioxido-<i>trans(N)</i>-κ<sup>2</sup>-<i>N</i>,<i>O</i>-L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes <b>1</b>–<b>4</b> 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 <b>1</b> (R = –Ph) was studied for its ability to selectively catalyze the production of <i>poly</i>-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 <b>1</b>–<b>4</b> were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the <i>O</i>-transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.
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