Deuterium equilibrium isotope effects (EIE) for H2 and H-CH3 addition to Vaska-type complexes, transIr(PH3)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.
|Number of pages||5|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - Sep 8 1993|
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