Metal-Olefin Bond Energies in M(CO)_5(C_2H_(4-n)Cl_n) M = Cr, Mo, W; n = 0-4: Electron-Withdrawing Olefins Do Not Increase the Bond Strength

摘要

Metal-olefin bond dissociation enthalpies have been calculated for the series of complexes M(CO)_5(C_2H_(4-n)Cl_n), M = Cr, Mo, W; n = 0-4 using density functional theory. Experimental values of the bond enthalpies have been measured for M(CO)_5(C_2H_(4-n)Cl_n) M = Cr, Mo, W; n = 2 (vinyl chloride), 3, and 4 using laser photoacoustic calorimetry in n-hexane solution. Experimental and calculated values indicate that the trend in metal-olefin bond energies is opposite to the electron-withdrawing ability of the olefin, which is counter to expectations based on the Dewar_Chatt_Duncanson model for metal_olefin bonding. An in-depth analysis of the metal_olefin interaction using a bond energy decomposition scheme implies that the observed and calculated decreasing trend is influenced by the increase in steric interactions and olefin reorganizational energy which is concomitant to the increase of the number of electron-withdrawing halogen atoms.