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

Synthesis and Structures of Stable PtII and PtIV Alkylidenes: Evidence for π-Bonding and Relativistic Stabilization

Isolable cationic Pt^II and Pt^IV alkylidenes, proposed intermediates in catalytic organic transformations, are reported. The bonding in these species was probed by experimental, structural, spectroscopic, electrochemical and computational methods, providing direct evidence for π-bonding, the often-theorized relativistic stabilization of these species, and the influence of oxidation state.