The interaction between H2 and M(CO)n(PH3)5-n (M = Cr, Mo, W; n = 0, 3, 5) metal fragments has been studied by means of CCSD(T)//B3LYP calculations. Three steps in the dihydrogen addition path that starting from the ML5 and H2 separated fragments leads to a stable dihydride have been considered: (i) dihydrogen coordination; (ii) cleavage of the H-H bond in a dihydrogen-like structure, leading to a PB1 cis-dihydride; (iii) reorganization of the pentagonal bipyramidal cis-dihydride formed to a more stable PB2 dihydride structure. From the thermodynamic results and the energy profiles for the oxidative addition the nine complexes under study can be classified in three groups: (i) only dihydrogen observable; M(CO)5H2 (M = Cr, Mo, W); and M(CO)3(PH3)2H2 (M = Cr, Mo); (ii) equilibrium between dihydrogen and PB2 dihydride: W(CO)3(PH3)2H2 and M(PH3)5H2 (M = Cr, Mo); (iii) only dihydride observable; W(PH3)5H2. The different behavior for dihydrogen addition is related to the energetics of the M-H2 and M-H bonds and to the singlet-triplet separation in the ML5 fragment. © 1998 American Chemical Society.
|Publication status||Published - 1 Dec 1998|