LASER-PULSE PHOTOLYSIS AND TRANSIENT INFRARED INVESTIGATION INTO THE EFFECT OF SOLVENT OR SUBSTITUENTS (X) ON THE REACTIVITY OF PHOTOGENERATED (ETA-6-C6H6-YXY)CR(CO)2 INTERMEDIATES

Time-resolved infrared spectroscopy identified the first observable species following nanosecond laser photolysis of (benzene)Cr(CO)3 in alkane solution as (benzene)Cr(CO)2(alkane). UV/vis-monitored laser flash photolysis was used to observe the reaction of this species with CO. The reactivity toward CO of the primary photoproducts derived from related arene complexes (arene = C6H5Cl, C5H6Me, p-ClC6H4Me, C6H5Et, C6H5But, o- and P-C6H4Me2, C6H3Me3, C6Me6, C6Et6) were also determined by this technique. The rate of reaction with CO was found to depend on the alkane solvent and on the nature and degree of substitution of the arene ligand. The enthalpies of activation for all reactions were constant (24 +/- 2 kJ mol-1), while the entropy of activation increased upon methyl substitution of the arene and upon a change in the solvent from cyclohexane to a linear alkane.