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Proton walk in the aqueous platinum complex tpptmeco via a sticky sigma-methane ligand

Academic Article
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Overview

authors

  • Lo, H. C.
  • Iron, M. A.
  • Martin, J. M. L.
  • Keinan, Ehud

publication date

  • 2007

journal

  • Chemistry-a European Journal  Journal

abstract

  • Both experimental and theoretical evidence suggest that the proton exchange between water and the methyl group in [TpPt(CO)CH(3)] (1, Tp=hydridotripyrazolylborate) involves the formation and deprotonation of a "sticky" sigma-methane ligand. The efficiency of this nontrivial process has been attributed to the spatial orientation of functional groups that operate in concert to activate a water molecule and then achieve a multistep proton walk from water to an uncoordinated pyrazolyl nitrogen atom, to the methyl ligand, and then back to the nitrogen atom and water. The overall proton-exchange process has been proposed to involve an initial attack of water at the CO ligand in 1 with concerted deprotonation by the uncoordinated pyrazolyl nitrogen atom. The pyrazolium proton is then transferred to the Pt--CH(3) bond, leading to a sigma-methane intermediate. Subsequent rotation and deprotonation of the sigma-methane ligand, followed by reformation of 1 and water, result in scrambling of the methyl protons with the hydrogen atoms of water. An alternative two-step process that involves oxidative addition and reductive elimination has also been considered. The two competing mechanistic routes from 1 into [D(3)]-1, as well as the conversion of 1 into [TpPt(CH(3))H(2)] (2), have been examined by density functional theory (DFT) using a variety of exchange-correlation methods, primarily PW6B95, which was recently shown to be highly accurate for evaluating reactions of late-transition-metal complexes. The key role played by the free pyrazolyl nitrogen atom, acting as a proton carrier that abstracts a proton from water and transfers the proton to the Pt--CH(3) bond, is reminiscent of the dual functionality of histidine in the catalytic triad of natural serine proteases.

subject areas

  • Borates
  • Ligands
  • Magnetic Resonance Spectroscopy
  • Methane
  • Models, Chemical
  • Nitrogen
  • Organometallic Compounds
  • Platinum
  • Protons
  • Pyrroles
  • Spectrometry, Mass, Electrospray Ionization
  • Thermodynamics
  • Water
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Research

keywords

  • alkanes
  • hydrogen transfer
  • methane complexes
  • platinum
  • proton exchange
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Identity

International Standard Serial Number (ISSN)

  • 0947-6539

Digital Object Identifier (DOI)

  • 10.1002/chem.200600709

PubMed ID

  • 17236226
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Additional Document Info

start page

  • 2812

end page

  • 2823

volume

  • 13

issue

  • 10

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