Preparing α,β-unsaturated Fischer-type carbene complexes via an unforeseen route

Four 4-(NH-amino)-1-metalla-1,3-diene carbene complexes, two of which contain novel 4-membered heterometallacycles, formed regioselectively from the reaction of a mixture of [(CH3)(2)(CH3S)S][BF4], the acetonitrilium electrophile, CH3CNCH3+, and the deprotonated alkoxycarbene complexes, (CO)(5)M=C(OCH3)CH2Li (M = Cr, W). The preferred Z-configurations of the alkoxy and amino groups are determined by strong H-bonding in the products. The metal-carbene bonds in the chelates are shorter by 0.08 angstrom than those in the acyclic compounds.