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 sp ecies following nanosecond laser photolysis of (benzene)Cr(CO)3 in alk ane 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 rel ated arene complexes (arene = C6H5Cl, C5H6Me, p-ClC6H4Me, C6H5Et, C6H5 But, o- and P-C6H4Me2, C6H3Me3, C6Me6, C6Et6) were also determined by this technique. The rate of reaction with CO was found to depend on th e alkane solvent and on the nature and degree of substitution of the a rene ligand. The enthalpies of activation for all reactions were const ant (24 +/- 2 kJ mol-1), while the entropy of activation increased upo n methyl substitution of the arene and upon a change in the solvent fr om cyclohexane to a linear alkane.