Activation of the C-H Bonds of Benzene by Reaction with platinum(0), Generated by the Thermolysis of cis-hydridoneopentylplatinum(II)

Article abstract of DOI:10.1021/ja00213a015

Reductive elimination of neopentane from cis-hydridoneopentylplatinum(II) (1) generates the reactive intermediate platinum(0) (2), which forms cis-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(excit.)(69 deg C) = 25.7 (0.7) kcal/mol, ΔH(excit.)(69 deg C) = 27.3 (0.3) kcal/mol, and ΔS(excit.)(69 deg 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 dipenylacetylene and bis(dicyclohexylphosphino)ethane as (diphenylacetylene)platinum(0) (4) and bisplatinum(0) (5), respectively.The X-ray crystal structure of 1 is reported.The compound crystallizes in space group C⁵_2h-P2₁/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) Angstroem, and β = 90.32 (3) deg.The structure has been refined to an agreement index R(F₀²) of 0.069 for 311 variables and 10182 observations.The Pt center has its expected pseudo-square-planar coordination with a Pt-H distance of 1.56 (5) Angstroem.