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Title: Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes

Abstract

A series of complexes of vanadocene or molybdenocene with unsymmetrical ketenes were prepared, either by reaction of the various ketenes with vanadocene itself or by reaction with the molybdenocene phosphine complex (C/sub 5/H/sub 5/)/sub 2/Mo(PEt/sub 3/). All of the complexes exhibited the expected ketene C=O bonding mode, and all reactions were very specific in their formation of the facial isomer with metallocene fragment located on the side of the smaller ketene substituent. Kinetic studies were used to assess the sensitivity of the incoming vanadocene to steric and electronic effects, with the latter found to dominate. Kinetic studies and activation parameters for reaction of Cp/sub 2/Mo(PEt/sub 3/) with EtPhC=C=O indicated a second-order associative mechanism, proposed to involve a nucleophilic attack of the metal center on the ketene central carbon in the rate-limiting step. Lastly, reactions of the bound ketenes with nucleophiles (alkyllithiums or Grignard reagents) proceeded readily to either ketone or aldehyde enolates (the latter via transfer of a ..beta..-hydride from the alkyl); the clean production of only Z enolates from the unsymmetrical ketenes is indicate of a metal-mediated internal attack of nucleophile on the bound ketene.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Wesleyan Univ., Middletown, CT (USA)
OSTI Identifier:
7148654
Resource Type:
Journal Article
Journal Name:
Organometallics; (United States)
Additional Journal Information:
Journal Volume: 7:5
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 01 COAL, LIGNITE, AND PEAT; KETENES; CHEMICAL PREPARATION; CHEMICAL REACTION KINETICS; MOLYBDENUM COMPLEXES; ORGANOMETALLIC COMPOUNDS; VANADIUM COMPLEXES; ABSORPTION SPECTROSCOPY; EXPERIMENTAL DATA; GAS CHROMATOGRAPHY; MAGNETIC SUSCEPTIBILITY; NUCLEAR MAGNETIC RESONANCE; CHROMATOGRAPHY; COMPLEXES; DATA; INFORMATION; KINETICS; MAGNETIC PROPERTIES; MAGNETIC RESONANCE; NUMERICAL DATA; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; REACTION KINETICS; RESONANCE; SEPARATION PROCESSES; SPECTROSCOPY; SYNTHESIS; TRANSITION ELEMENT COMPLEXES; 400201* - Chemical & Physicochemical Properties; 010408 - Coal, Lignite, & Peat- C1 Processes- (1987-)

Citation Formats

Galante, J M, Bruno, J W, Hazin, P N, Folting, K, and Huffman, J C. Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes. United States: N. p., 1988. Web. doi:10.1021/om00095a009.
Galante, J M, Bruno, J W, Hazin, P N, Folting, K, & Huffman, J C. Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes. United States. https://doi.org/10.1021/om00095a009
Galante, J M, Bruno, J W, Hazin, P N, Folting, K, and Huffman, J C. 1988. "Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes". United States. https://doi.org/10.1021/om00095a009.
@article{osti_7148654,
title = {Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes},
author = {Galante, J M and Bruno, J W and Hazin, P N and Folting, K and Huffman, J C},
abstractNote = {A series of complexes of vanadocene or molybdenocene with unsymmetrical ketenes were prepared, either by reaction of the various ketenes with vanadocene itself or by reaction with the molybdenocene phosphine complex (C/sub 5/H/sub 5/)/sub 2/Mo(PEt/sub 3/). All of the complexes exhibited the expected ketene C=O bonding mode, and all reactions were very specific in their formation of the facial isomer with metallocene fragment located on the side of the smaller ketene substituent. Kinetic studies were used to assess the sensitivity of the incoming vanadocene to steric and electronic effects, with the latter found to dominate. Kinetic studies and activation parameters for reaction of Cp/sub 2/Mo(PEt/sub 3/) with EtPhC=C=O indicated a second-order associative mechanism, proposed to involve a nucleophilic attack of the metal center on the ketene central carbon in the rate-limiting step. Lastly, reactions of the bound ketenes with nucleophiles (alkyllithiums or Grignard reagents) proceeded readily to either ketone or aldehyde enolates (the latter via transfer of a ..beta..-hydride from the alkyl); the clean production of only Z enolates from the unsymmetrical ketenes is indicate of a metal-mediated internal attack of nucleophile on the bound ketene.},
doi = {10.1021/om00095a009},
url = {https://www.osti.gov/biblio/7148654}, journal = {Organometallics; (United States)},
number = ,
volume = 7:5,
place = {United States},
year = {Sun May 01 00:00:00 EDT 1988},
month = {Sun May 01 00:00:00 EDT 1988}
}