Local Density Functional Calculations on Metathesis Reaction Precursors
Calculations were carried out to assess the role of Local Density Functional (LDF) programs in following the course of metathesis reactions in large molecular systems. This study was designed to provide preliminary information on: (1) the nature of weakly bound ligands in cocatalyst structures, (2) the influence of phenyl ring substitution on catalytic activity, (3) the role of AlCl3 as a cocatalyst, and (4) the influence of macroenvironment on the basic electronic structure of the reactive site. For this purpose, calculations were carried out on an MoCl4O/tetrahydrofuran (THF) complex, ring substituted derivatives of MoCl5O-phenyl, the basic metallacyclobutane ring prototype, Mo(CH2)3CH3ClO/AlCl3, and a large fluorinated molybdenum complex.
The data indicate that atomic charges and Mayer bond orders (based on the second order density matrix) show considerable promise for making quantitative correlations (QSAR) between structure and catalytic activity. The results for the THF complex and the metallacyclobutane prototype suggest that increased catalytic activity may be associated with lowered bond orders at the active metal site. It was found that the orbital populations were 80–90% d in all cases. This is in contrast to the strong bonding associated with sp3d2 hybridization. There is evidently a certain amount of delocalization, which promotes the facile bonding changes necessary for low barrier catalysis.
KeywordsBond Order Transition Metal Complex Density Functional Method Rotational Barrier Metathesis Reaction
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