AMINO-SUBSTITUTED 2-AZONIAALLENYLIDENE CO MPLEXES OF CHROMIUM AND TUNGSTEN

The successive reaction of chromium and tungsten hexacarbonyl, (CO)6M (M = Cr, W), with [N=C(Ph)R]- and [Et3O]BF4 yields the alkylideneamino (ethoxy)carbene complexes (CO)5M[C(OEt)N=C(Ph)R] (M = Cr (1), W (2); R = NMe2 (a), (t)Bu (b)). Ethoxide abstraction from 1 and 2 affords 2-a zoniaallenylidene complexes, {(CO)5M[CNC(Ph)R]} + BF4- (3/4). The comp lexes 3 and 4 are best described as resonance hybrids of several limit ing structures. On the basis of the spectroscopic data of the complexe s 3a and 4a the limiting structure of an iminium-substituted isocyanid e complex dominates.