Complexation between MOTf (M = Li and Na) and N-Phosphine Oxide-substituted Imidazolylidenes via Coordination of the N-Phosphoryl Groups

A reaction between an N-phosphine oxide-substituted imidazolylidene (PoxIm) and MOTf (M = Li or Na) in THF afforded the complexes [(PoxIm)(x)(MOTf)(y)(THF)(z)] through the coordination of the N-phosphoryl group to Na+ or Li+, which was unambiguously confirmed by C-13 and (PNMR)-P-31 spectroscopy and single-crystal X-ray diffraction analyses. These measurements confirmed that the carbene moieties in these complexes remain intact. In solution, PoxIm and MOTf might form the complexes in a 3:2 ratio (i.e., x = 3, y = 2), while ratios of 1:1 (M = Li; x = 1, y = 1) and 2:1 (M = Na; x = 2, y = 1) were observed in the solid state.