Pulsed laser flash photolysis of M(CO)6 (M = Cr, W) in cyclohexane with a small amount of benzene results in three sequential reactions. The first is the photodissociation of the parent to yield a M(CO)5:C6H12 complex, which takes place faster than the time resolution of our experiments. The second reaction is the replacement of the cyclohexane ligand with benzene to form a M(CO)5:C6H6 complex, in which benzene is coordinated to the metal via one side of the ring. This complex then falls apart in solution as M(CO)5 coordinates with a trace impurity in the solution that is likely water. Kinetic studies over a range of temperatures result in the following activation energies: 39 kJ/mol for the dissociation of W(CO)5:C6H6; 30 kJ/mol for conversion of Cr(CO)5:C6H12 to Cr(CO)5:C6H6; 33 kJ/mol for the dissociation of Cr(CO)5:C6H6. DFT calculations of binding energies for each complex suggest that all reactions proceed through a combination of an associative and dissociative mechanism. Further calculations of carbonyl vibrational frequencies for 13 weak metal–solvent complexes using three different density functionals: B3LYP, M06, and M06-L allowed us to calculate scale factors for predicting experimental vibrational frequencies. The scale factors are: 0.952 for B3LYP, 0.943 for M06, and 0.957 for M06-L. Using these scale factors leads to average errors in predicted experimental vibrational frequencies of less than 1% for each functional.
College and Department
Physical and Mathematical Sciences; Chemistry and Biochemistry
BYU ScholarsArchive Citation
Sheffield, Carolyn Evans, "Time-Resolved Infrared Spectroscopy and Density Functional Theory Study of Weak Interactions of Metal Carbonyls and Organic Solvents" (2010). Theses and Dissertations. 2096.
Transition metal, IR spectroscopy, carbonyl, density functional theory, W(CO)6, Cr(CO)6