Prototypical Transition-Metal Carbenes, (CO)5Cr═CH2, (CO)4Fe═CH2, (CO)3Ni═CH2, (CO)5Mo═CH2, (CO)4Ru═CH2, (CO)3Pd═CH2, (CO)5W═CH2, (CO)4Os═CH2, and (CO)3Pt═CH2: Challenge to Experiment.

Abstract

Transition-metal carbenes are useful in organometallic chemistry due to their demonstrated use as catalysts in carbon-carbon bond-forming reactions. Yet the prototypical transition-metal carbenes, consisting of a single metal center doubly bonded to a methylene ligand and surrounded by carbonyls, have been elusive to experimental synthesis. This theoretical work examines the structures and properties of nine prototypical transition-metal carbenes. Optimized values for M═CH2 bond lengths, dissociation energies, and vibrational frequencies are reported. The M═CH2 bond distances range from 1.81 (Ni) to 2.05 Å (Pd). The M═CH2 dissociation energies fall in the range of 16.4 (Pd) to 92.3 kcal mol-1 (Os). The spectroscopic observation of several of these molecules should be possible.