Reactions of rhenium cyclopentadienyl and indenyl dichloromethane complexes of the formula [(.eta.5-CxHy)Re(NO)(PPh3)(ClCH2Cl)]+BF4- with ketones: substitution rates and mechanism Academic Article uri icon

abstract

  • Rates of reaction of the coordinatively saturated cyclopentadienyl and indenyl dichloromethane complexes [formula omitted] and cyclohexanone to give [formula omitted] are measured by 31P{1H} NMR under pseudo-first-order conditions (CH2C12, −70 to −30 °C, 10–60-fold excesses of cyclohexanone). These substitutions are first-order in both 1/2 and cyclohexanone, even at cyclohexanone concentrations of 1.0–3.4 M. Eyring plots of the second-order rate constants give ΔH* of 15 ± 1 kcal/mol and ΔS* of −5 ± 4–5 eu. There is only a modest kinetic indenyl ligand effect (factor of 6 at −60 to −50 °C). Thus, CxHy ring slippage is viewed as unlikely during substitution. Faster reactions of 1 with tropone (ΔH* 12 ± 2 kcal/mol, AS* −17 ± 11 eu) and methyl ethyl sulfide give similar rate data. These results and competition experiments with ethyl chloride exclude pathways involving initial dichloromethane dissociation. An associative mechanism that features a square pyramidal intermediate with a bent nitrosyl ligand is considered. Testable aspects of this model and stereochemical implications are discussed. © 1993, American Chemical Society. All rights reserved.

author list (cited authors)

  • Dewey, M. A., Zhou, Y., Liu, Y., & Gladysz, J. A.

citation count

  • 15

publication date

  • October 1993