The carbonyl compounds, TpRMo(NO)(Ld)(CO) where TpR = tris(pyrazolyl)borate (Tp) and tris(3,5-dimethylpyrazolyl)borate (Tp*), and Ld = 1-methylimidazole (1-MeIm), 4-dimethylaminopyridine (DMAP), PMe3, pyridine, 3-chloropyridine, 3-fluoropyridine, P(p-tolyl)3, PPh3, and P(OMe)3 have been prepared from the dicarbonyl complex TpRMo(NO)(CO)2 by thermal displacement of CO. An N-heterocyclic carbene complex has also been prepared where Ld = 1,3-dimethylimidazol-2-ylidene (NHC) using 1,3-dimethylimidazolium-2-carboxylate as the carbene precursor. The analogous tungsten complexes cannot be prepared via this method due to the reticence of TpRW(NO)(CO)2 to release CO upon heating. Oxidation of TpRMo(NO)(Ld)(CO) complexes by cumene hydroperoxide, t-butyl hydroperoxide, or O2 gives η2-carbon dioxide complexes, TpRMo(NO)(Ld)(η2-CO2), for Ld = 1-MeIm, DMAP, PMe3, NHC, pyridine, 3-chloropyridine and 3-fluoropyridine. Complexes featuring νCO &gt; 1893 cm-1 and νNO &gt; 1607 cm-1 did not result in isolated η2-CO2 complexes upon oxidation. However, all isolated TpRMo(NO)(Ld)(CO) complexes featuring νCO and νNO lower than these have led to isolable η2-CO2 complexes upon oxidation. These η2-CO2 complexes have been characterized by X-ray crystallography, IR and NMR spectroscopy. The η2-CO2 complexes are air stable and are thermally stable at room temperature in solution. Reduction of TpRMo(NO)(Ld)(η2-CO2) back to TpRMo(NO)(Ld)(CO) can be accomplished using chemical reductants.

Synthesis of molybdenum carbon dioxide complexes via oxidation of a carbonyl ligand

251st National Meeting (2016)

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