Divergent Reactivity of Agostic B-CH3 → PtIV Complexes: A Computational Study on the Role of Axial Ligand Trans-Influence on Methyl Migration Versus Methane Elimination

Abstract

The anionic di(2-pyridyl)dimethylborate-supported dimethyl PtII complex was previously reported to undergo three distinct reactions: aerobic oxidation in ethanol, protonolysis in methanol, and sequential reaction with methyl iodide and methanol. These reactions respectively result in B-to-PtIV methyl group migration (Path I), methane evolution via C–H reductive coupling (Path II), or B-to-PtIV methyl group migration followed by methane evolution via PtIV–CH3 methanolysis (Path III). DFT calculations performed here reveal that these seemingly divergent outcomes originate from intermediates featuring agostic B-CH3 → PtIV interactions, differing primarily in the axial X ligand installed at PtIV. For the weakly trans-influencing X = OOH, B-to-PtIV methyl migration through Path I is facile. In contrast, the strongly trans-influencing X = H redirects reactivity toward Path II in preference to Path I. For the strongly trans-influencing X = CH3, the absence of a PtIV–H intermediate required for Path II permits B-to-PtIV methyl group migration, forming a tetramethyl-PtIV intermediate that undergoes facile methanolysis of a PtIV–CH3 via Path III. This final step is assisted by a combination of destabilization of mutually trans CH3 ligands and B-coordination-enhanced acidity of methanol. These results mechanistically unify the aerobic, anaerobic, and methylation-induced reactivity previously observed for this class of Pt complexes.