Trends in the reactivity of the C pMn(CO) 2(η 2-arene) bond [arene = benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene]: an experimental and theoretical investigation

Abstract

The displacement of η 2-coordinated arenes [arenes = benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene] from the photolytically generated C pMn(CO) 2(η 2-arene) complex by pyridine was studied. The substitution reaction proceeds by a dissociative mechanism, and the relative rates of displacement provide information about the interplay between electronic and steric factors in determining the overall stability of the Mn-(η 2-arene) bond. The regioselectivity of metal binding to the arene ligand was determined by examining the observed trends in the relative displacement rates for the xylenes. Theoretical modeling of the Mn-(η 2-arene) complexes lends support for the experimental analysis. Interestingly, unlike the other arenes, DFT (density functional theory) calculations suggest that mesitylene is bound to the Mn center by an arene C-H bond rather than by a C=C edge of the aromatic system. © 2009 American Chemical Society.