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.