Seeking a Mechanistic Analogue of the Water–Gas Shift Reaction: Carboxamido Ligand Formation and Isocyanate Elimination from Complexes Containing the Tp′PtMe Fragment

A series of stable, isolable Tp′Pt­(IV) carboxamido complexes of the type Tp′PtMe2(C­(O)­NHR) (R = Et, nPr, iPr, tBu, Bn, Ph) has been synthesized by addition of amide nucleophiles to the carbonyl ligand in Tp′Pt­(Me)­(CO) followed by trapping of the Pt­(II) intermediate with methyl iodide as the methylating reagent. These compounds mimic elusive intermediates resulting from hydroxide addition to platinum-bound CO in the Water–Gas Shift Reaction (WGSR). Seeking parallels to WGSR chemistry, we find that deprotonation of the carboxamido NH initiates elimination and the isocyanate-derived products form; the resulting platinum fragment can be protonated to reoxidize the metal center and generate Tp′PtMe2H, the synthetic precursor to Tp′Pt­(Me)­(CO). Mechanistic studies on the formation of and elimination from Tp′PtMe2(C­(O)­NHR) suggest a stepwise process with deprotonation from a Pt­(IV) species as the key step prompting elimination.