Formation of Bridging Acylium and Nitrilium Complexes by Reaction of CO and CNC(CH3)3with a Bridging Diiron Methylidyne Complex. Evidence for Strong Electron Donation from the Fe2C Core onto the μ-CHC≡O and μ-CHC≡NR Ligands

Charles P. Casey, Mark Crocker, Gerald P. Niccolai, Paul J. Fagan, Mark S. Konings

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29 Scopus citations

Abstract

The reaction of the μ-miethylidyne complex [C5H5(CO)Fe]2(μ-CO)(μ-CH)+PF6-(1) with CO gave the cationic 1:1 adduct (C5H5(CO)Fe]2μ-CO)(μ-CHCO)+PF6-(2) in 90% yield. The structure, spectra, and chemical properties of 2 suggest that the bonding of the μ-CHCO ligand in 2 should be regarded as analogous to that in organic acylium cations, with a contributing formulation as a two-electron three-center bound-bridging ketene. 2 reacted with nucleophiles at the acylium carbon; reaction with Et4N+HFe(CO)4-gave the aldehyde [C5H5(CO)Fe]2(μ-CO)(μ-CHCHO) (3), water gave the carboxylic acid [C5H5(CO)Fe]2(M-CO)(M-CHCO2H) (4), and ammonia gave the amide [C5H5(CO)Fe]2(μ-CO)(μ-CHCONH2) (5). 1 also reacted with CNC(CH3)3to give the 1:1 adduct [C5H5(CO)Fe]2(μ-CO)[μ-CHCNC(CH3)3]+PF6-(6), the structure of which was determined by X-ray crystallography: 6 crystallizes in the monoclinic space group P21/c, with unit cell constants a = 10.771 (2) Å, b = 11.420 (2) Å, c =18.092 (3) Å, β = 106.09 (1)°, and Z = 4. The μ-ethylidyne complex [C5H5-(CO)Fe]2(μ-CO)(μ-CCH3)+BF4-(7) underwent a similar reaction with CNC(CH3)3to afford the adduct [C5H5(CO)Fe]2-(μ-co)[μ-c(ch3)CNC(CH3)3]+BF4-(8), which was isolated as a mixture of two cis and one trans Cp isomers. The structure of 6, together with the spectroscopic properties of 6 and 8, suggests an analogous bonding mode to that in 2. Fenske-Hall molecular orbital calculations performed on 2 and 6 provide further support for the importance of a ketene-like formulation that contributes to the overall structure of these complexes.

Original languageEnglish
Pages (from-to)6070-6076
Number of pages7
JournalJournal of the American Chemical Society
Volume110
Issue number18
DOIs
StatePublished - Aug 1988

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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