Mechanism of Oxidatively Induced Migratory Insertion of Carbon Monoxide: Evidence for a 19-Electron Intermediate

Published

Journal Article

The mechanism of oxidatively induced CO insertion for CpFe(CO)(PPh3)CH3has been probed by transient electrochemical techniques. the data presented herein suggest that the alkyl-to-acyl migration at 17-electron CpFe(CO)-(PPh3)CH3+proceeds by a mechanism consisting of two chemical steps. the first step is a second-order process, first order in both the metal radical and entering pyridine nucleophile (Nu), that produced a 19-electron species CpFe(CO)(PPh3)(Nu)CH3+. This complex can be observed directly at low temperature in cyclic voltammetry measurements and in the EPR and IR spectra. the rate of nucleophilic attack at CpFe(CO)(PPh3)CH3+depends on the a-basicity of the nitrogen Lewis base as seen from second-order constants, kl, that vary over 5000-fold from 200 (3,4-dimethylpyridine) to 0.04 (3-cyanopyridine) M-1s“-lat 20 °C. Hammett analysis of the rate data shows that log klcorrelates well with the σ-meta and σ-para values for eight 3-and 4-substituted pyridines. the second chemical step that occurs is a nucleophile concentration independent first order process that converts the intermediate CpFe(CO)(PPh3)(Nu)CH3+to the acyl product, 17-electron CpFe(PPh3)(Nu)(COCH3)+. We rule out a mechanism for the oxidatively induced migratory insertion that proceeds via a 15-electron intermediate, where insertion occurs before nucleophile coordination at CpFe(CO)(PPh3)CH3+. © 1987, American Chemical Society. All rights reserved.

Full Text

Duke Authors

Cited Authors

  • Therien, MJ; Trogler, WC

Published Date

  • August 1, 1987

Published In

Volume / Issue

  • 109 / 17

Start / End Page

  • 5127 - 5133

Electronic International Standard Serial Number (EISSN)

  • 1520-5126

International Standard Serial Number (ISSN)

  • 0002-7863

Digital Object Identifier (DOI)

  • 10.1021/ja00251a014

Citation Source

  • Scopus