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

Marifaith Hackett, George M. Whitesides, James A. Ibers*

*Corresponding author for this work

Research output: Contribution to journalArticle

122 Scopus citations

Abstract

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: Ea= 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 C52H-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) 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.

Original languageEnglish (US)
Pages (from-to)1436-1448
Number of pages13
JournalJournal of the American Chemical Society
Volume110
Issue number5
DOIs
StatePublished - Mar 1 1988

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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