Time-Resolved IR Study of Gas-Phase Reaction of Benzene with Group VIB Metal Pentacarbonyls and Tetracarbonyls

Article abstract of DOI:10.1021/j100148a013

The gas-phase reactions of benzene and deuterated benzene (benzene-d6) with group VIB metal pentacarbonyls M(CO)5 (M=Cr and W) and tetracarbonyl W(CO)4 were probed with time-resolved infrared spectroscopy.Benzene reacts with M(CO)5 forming presumably (η²-benzene)M(CO)5 in which benzene coordinates to the metal via an isolated double bond.The rate constants for reactions of C6H6 and C6D6 with Cr(CO)5 were found to be (3.0 +/- 0.7) and (3.3 +/- 0.2) x 10¹³ cm³ mol^-1 s^-1, respectively.The corresponding values with W(CO)5 are (2.8 +/- 0.4) and (3.5 +/- 0.6) x 10¹³ cm³ mol^-1 s^-1.From the temperature dependence of the rate of dissociative loss of benzene from (η²-benzene)Cr(CO)5, a bond dissociation energy of 9.2 +/- 0.8 kcal mol^-1 was determined for (η²-benzene)Cr(CO)5.The lower limit for bond dissociation energy for loss of the benzene ligand from (η²-benzene)W(CO)5 was estimated to be 11.7 kcal mol^-1.Benzene reacts with W(CO)4 producing a species, presumably (η²-benzene)W(CO)4, which is stable in the milisecond time scale.The rate constants for reactions of C6H6 and C6D6 with W(CO)4 were determined to be (3.5 +/- 0.2) and (4.1 +/- 0.4) x 10¹³ cm³ mol^-1 s^-1, respectively.Secondary addition of CO to (η²-benzene)W(CO)4 forms (η²-benzene)W(CO)5, and the rate constants are (9.4 +/- 0.9) and (8.7 +/- 1.0) x 10¹¹ cm³ mol^-1 s^-1, respectively, for additions of CO to (η²-C6H6)W(CO)4 and (η²-C6D6)W(CO)4.