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Protonolysis of Platinum(II) and Palladium(II) Methyl Complexes: A Combined Experimental and Theoretical Investigation.

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Title: Protonolysis of Platinum(II) and Palladium(II) Methyl Complexes: A Combined Experimental and Theoretical Investigation.
Authors: John E. Bercaw1, George S. Chen1, Jay A. Labinger1, Bo-Lin Lin1
Source: Organometallics. Oct2010, Vol. 29 Issue 19, p4354-4359. 6p.
Subjects: Organoplatinum compounds, Organopalladium compounds, Complex compounds, Density functionals, Temperature effect, Quantum tunneling, Electron donor-acceptor complexes, Ligands (Chemistry)
Abstract: The protonolysis of platinum(II) and palladium(II) methyl complexes has been investigated by both experiment and computation. Previously the protonolysis of (COD)PtII(CH3)2by CF3COOY or (dppe)PdII(CH3)2by CF3CY2OY (Y = H, D) was found to be accompanied by abnormally large and highly temperature-dependent kinetic isotope effects (KIEs), suggesting the involvement of tunneling. Here we find normal KIEs and no evidence of tunneling for protonolysis of (tmeda)PtII(CH3)Cl by CF3COOY (Y = H, D). Density functional theory (DFT) calculations indicate that protonation at the metal center followed by reductive coupling to the methane σ adduct (stepwise pathway) is favored for Pt complexes with good electron donor ligands, whereas direct protonation of the M−CH3bond to generate the methane σ adduct (concerted pathway) is favored for Pt with electron-withdrawing ligands as well as for Pd. We suggest that KIE behavior consistent with tunneling may be an experimental indicator of the concerted pathway. [ABSTRACT FROM AUTHOR]
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Abstract:The protonolysis of platinum(II) and palladium(II) methyl complexes has been investigated by both experiment and computation. Previously the protonolysis of (COD)PtII(CH3)2by CF3COOY or (dppe)PdII(CH3)2by CF3CY2OY (Y = H, D) was found to be accompanied by abnormally large and highly temperature-dependent kinetic isotope effects (KIEs), suggesting the involvement of tunneling. Here we find normal KIEs and no evidence of tunneling for protonolysis of (tmeda)PtII(CH3)Cl by CF3COOY (Y = H, D). Density functional theory (DFT) calculations indicate that protonation at the metal center followed by reductive coupling to the methane σ adduct (stepwise pathway) is favored for Pt complexes with good electron donor ligands, whereas direct protonation of the M−CH3bond to generate the methane σ adduct (concerted pathway) is favored for Pt with electron-withdrawing ligands as well as for Pd. We suggest that KIE behavior consistent with tunneling may be an experimental indicator of the concerted pathway. [ABSTRACT FROM AUTHOR]
ISSN:02767333
DOI:10.1021/om100655w