Theoretical Study of Primary and Secondary Deuterium Equilibrium Isotope Effects for H2 and CH4 Addition to trans-Ir(PR3)2(CO)X

Faraj Abu-Hasanayn, Karsten Krogh-Jespersen, Alan S. Goldman

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Deuterium equilibrium isotope effects (EIE) for H2 and H-CH3 addition to Vaska-type complexes, trans-Ir(PM3)2(CO)X(XM), have been determined using vibrational frequencies obtained from ab initio calculations on XM and on cis,trans-H2Ir(PH3)2(CO)X (XMH2). Inverse primary EIE values for H2/D2 addition to XM are computed to be 0.46 (X=Cl), 0.57 (X=CH3), and 0.33 (X=H;0.66 after statistical normalization) at 300 K. The EIE values and the computed enthalpy and entropy terms are consistent with several experimental studies. Secondary thermodynamic deuterium isotope effects for H2 addition to XM are computed for X = H/D (α-EIE = 0.44; 0.88 after statistical normalization) and for X = CH3/CD3 (β-EIE = 0.86). Computations on the addition of CH4/CH3D or CH4/CD4 to HM reveal EIEs of 7.77 (1.94 per bond) and 3.64, respectively. These results are analyzed and discussed using equilibrium statistical mechanics.

Original languageEnglish
Pages (from-to)8019-8023
Number of pages5
JournalJournal of the American Chemical Society
Issue number18
Publication statusPublished - Sep 1 1993

ASJC Scopus subject areas

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

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