Investigating the reactivity of the (eta(6)-C6H5R)Cr(CO)(2)-(eta(2)-C6H5R) [R = H, CH3,CF3] bond: A laser flash photolysis study with infrared detection
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abstract
The ( 6-C 6H 5R)Cr(CO) 2-( 2-C 6H 5R) complexes (R = H, CH 3, CF 3) are generated upon photolysis of ( 6-C 6H 5R)Cr(CO) 3 in the appropriate arene. The energetics and mechanism of the displacement of the 2-coordinated arene from the metal center by piperidine are studied using the technique of laser flash photolysis. The substitution reaction is tentatively assigned as proceeding through an Id mechanism, and the activation enthalpy of 11.5 0.9 kcal/mol provides a lower limit for the strength of the ( 6-C 6H 6)Cr(CO) 2-( 2-C 6H 6) bond. The substitution rate decreases as the metal center becomes more electron poor or the arene electron rich, suggesting that LM donation is the primary bonding interaction between the ( 6-C 6H 5R)Cr(CO) 2 fragment and the arene ligand. This reactivity is different from that of the Cr - ( 2-alkene) bond, where it was found that increasing the electron density on the metal center decreased the rate of substitution of cyclooctene from the ( 6-C 6H 5R)Cr(CO) 2-( 2-cyclooctene) complex by pyridine. 2005 American Chemical Society.
