Activation of the C-H Bonds of Benzene by Reaction with [Bis(dicyclohexylphosphino)ethane]platinum(0), Generated by the Thermolysis of cis-[Bis(dicyclohexylphosphino)ethane]hydridoneopentyl-platinum(II)¹

Reductive elimination of neopentane from cis-[bis(dicyclohexylphosphino)ethane]hydridoneopentylplatinum(II) (1) generates the reactive intermediate [bis(dicyclohexylphosphino)ethane]platinum(0) (2), which forms cis-[bis(dicyclohexylphosphino)ethane]hydridophenylplatinum(II) (3) upon reaction with benzene. The rate-determining step is reductive elimination of neopentane: E_a= 28.0 (0.4) kcal/mol, log A = 14.3 (0.2), ΔG*(69 °C) = 25.7 (0.7) kcal/mol, ΔH*(69 °C) = 27.3 (0.3) kcal/mol, and ΔS*(69 °C) = 5 (1) eu. Kinetic and spectroscopic studies rule out coordination of benzene to the platinum center before or during the transition state. Variable-temperature NMR studies establish that the bis(phosphine) ligand remains chelated to the platinum atom during reductive elimination. The presumed intermediate, 2, can be trapped by diphenylacetylene and bis(dicyclohexylphosphino)ethane as [bis(dicyclohexylphosphino)ethane](diphenylacetylene)platinum(0) (4) and bis[bis(dicyclohexylphosphino)ethane]platinum(0) (5), respectively. The X-ray crystal structure of 1 is reported. The compound crystallizes in space group C⁵_2H-P2_1/n of the monoclinic system with 4 molecules in a cell of dimensions a = 11.517 (8), b = 15.730 (11), c = 17.364 (13) Å, and β = 90.32 (3)°. The structure has been refined to an agreement index R(F₀²) of 0.069 for 311 variables and 10 182 observations. The Pt center has its expected pseudo-square-planar coordination with a Pt-H distance of 1.56 (5) Å.