Title

Thermochemistry of Silane Substitution of CO in Metal Carbonyl Complexes. Interaction of Silanes with Metal Centers

Abstract

By using photoacoustic calorimetry, the enthalpy of CO substitution by triethylsilane for M(CO)6 (M = Cr, Mo, W), (η6-C6H6)Cr(CO)3, and η5-CpMn(CO)3 (Cp = cyclopentadienyl) in neat triethylsilane was found to be 16, 19, 18, 17, and 31 kcal/mol, respectively. The enthalpy of CO substitution by alkane solvent for (η6-C6H6)Cr(CO)3 (in heptane) and η5-CpMn(CO)3 (in cyclohexane) was found to be 33 and 45 kcal/mol, respectively. By using these data and metal-CO bond energies, the enthalpies of the metal-silane and metal-alkane binding in the adducts were estimated to be in the range of 21-28 and 9-13 kcal/mol, respectively. Thus, the variation in the binding energies is 7 and 4 kcal/mol, respectively, while the variation for the corresponding metal-CO bonds is 18 kcal/mol. These results suggest the metal-silane interactions are more like the corresponding metal-alkane interactions than metal-CO bonds. It is concluded that for the cases studied the silane undergoes an incomplete oxidative addition to the metal, and the metal-silane interaction is a three-center two-electron bond. Silane adducts from Cr(CO)6 and W(CO)6 have been detected by UV-vis and IR spectroscopy. The results suggest the M(CO)5(HSiEt3) may be more stable than previously presumed. © 1990, American Chemical Society. All rights reserved.

Publication Title

Journal of the American Chemical Society

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