THEORETICAL-STUDY OF PRIMARY AND SECONDARY DEUTERIUM EQUILIBRIUM ISOTOPE EFFECTS FOR H-2 AND CH4 ADDITION TO TRANS-IR(PR3)2(CO)X

Deuterium equilibrium isotope effects (EIE) for H-2 and H-CH3 addition to Vaska-type complexes, trans-Ir(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 H-2/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 H-2 addition to XM are computed for X = H/D (alpha-EIE = 0.44; 0.88 after statistical normalization) and for X = CH3/CD3 (beta-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.