COMPARISON OF ISOLOBAL FRAGMENTS - PHOTOELECTRON-SPECTRA AND MOLECULAR-ORBITAL CALCULATIONS OF (ARENE)TRICARBONYLCHROMIUM, (ARENE)TRICARBONYLMOLYBDENUM, AND (ARENE)TRICARBONYLTUNGSTEN COMPLEXES
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Gas-phase ultraviolet photoelectron spectra (PES) and parameter-free Fenske-Hall molecular orbital (MO) calculations are reported for the following complexes: (12 3 4 5 6 78-C6H6)M(CO)3, (i76-l,3,5-CeH3(CH3)3)M(CO)3, and (t7 6-C6(CH3)6)M(CO)3, where M = Cr, Mo, or W. The two most important bonding interactions between the arene ring and metal fragment give rise to two e-type MO's of the (7r-arene)M(CO)3complex. The calculations and PES show that the most stable e MO increases in stability relative to the free ligand on progressive methylation of the benzene ring and on substituting the metal atom in the order Mo < Cr W. The calculations and PES also show that the second e MO decreases in stability on progressive methylation of the benzene ring and on substituting the metal atom, but now the order is W < Cr < Mo. An analysis of the spin-orbit splitting of the first band in the PES of the tungsten complexes indicates that the metal axMO is above the metal e MO in the benzene complex but below it in the hexamethylbenzene complex. The experimental results show that substitution of the metal atom is a much more important effect in causing the arene ring distortion observed in the low-temperature X-ray crystal structures of these species. 1987, American Chemical Society. All rights reserved.
