Aminosubstituierte 2-azoniaallenyliden-komplexe des chroms und wolframs

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)₅MC(OEt)N=C(Ph)R] (M = Cr (1), W (2); R = NMe₂ (a), ^tBu (b)). Ethoxide abstraction from 1 and 2 affords 2-azoniaallenylidene complexes, {(CO)₅MCNC(Ph)R]}⁺BF₄⁻ (3/4). The complexes 3 and 4 are best described as resonance hybrids of several limiting structures. On the basis of the spectroscopic data of the complexes 3a and 4a the limiting structure of an iminium-substituted isocyanide complex dominates.