Cross-Coupling versus Homo-Coupling at a Pt(IV) Center: Computational and Experimental Approaches

C–C cross-coupling versus homo-coupling from the Pt(IV) complex [Pt(pbt)Br(CH2Ph)(Me)2], 2a (pbt = 2-(2-pyridyl)benzothiazole), was studied experimentally and through density functional theory calculations. The calculations show that from the three competitive C–C reductive eliminations, (A) Me–Me homo-coupling, (B) benzyl–Me cross-coupling (Me trans to Npy), and (C) benzyl–Me cross-coupling (Me trans to Nbz), the Me–Me homo-coupling reaction is preferred over the other two due to the lower energy barrier of the Me–Me vs the benzyl–Me bond formation. The reaction is initiated by a dissociation of the Br– ligand followed by Me–Me homo-coupling from the resulting five-coordinate intermediate. Experimentally, complex 2a undergoes reductive elimination in toluene at 70 °C producing ethane and the Pt(II) complex [Pt(pbt)Br(CH2Ph)] 3a in over 99% yield, fully in line with the calculations. 1H195Pt HMBC experiments allowed studying even sub-% products in this study.