Magnesium catalysis of imine hydroboration

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Abstract

The β-diketiminato magnesium alkyl complex [LMgnBu] (L=CH{CMe(NDipp)}, Dipp=diisopropylphenyl) is shown to be a highly effective precatalyst for the hydroboration of alkyl and aryl substituted aldimines and ketimines with pinacol borane (HBpin). Catalysis is proposed to occur through a sequence of Mg-N/B-H metathesis and rate-determining Mg-H/N=C insertion steps, a proposal strongly supported by stoichiometric studies and kinetic analysis. The reactions are observed to proceed through the intermediacy of well-defined magnesium amides, two examples of which have been isolated and structurally characterized. Mechanistic investigations suggest that the catalytic rate-determining process occurs at an isolated magnesium center and requires the presence of two molecules of the imine substrate for effective turnover. This latter observation is rationalized as a requirement for the secondary substrate molecule to displace HBpin from the coordination sphere of the catalytic magnesium center.
Original languageEnglish
Pages (from-to)2776-2783
Number of pages8
JournalChemistry - A European Journal
Volume19
Issue number8
Early online date10 Jan 2013
DOIs
Publication statusPublished - 18 Feb 2013

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Imines
Magnesium
Catalysis
Boranes
Molecules
Substrates
Amides
Kinetics

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Magnesium catalysis of imine hydroboration. / Arrowsmith, M.; Hill, M.S.; Kociok-Kohn, Gabriele.

In: Chemistry - A European Journal, Vol. 19, No. 8, 18.02.2013, p. 2776-2783.

Research output: Contribution to journalArticle

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N2 - The β-diketiminato magnesium alkyl complex [LMgnBu] (L=CH{CMe(NDipp)}, Dipp=diisopropylphenyl) is shown to be a highly effective precatalyst for the hydroboration of alkyl and aryl substituted aldimines and ketimines with pinacol borane (HBpin). Catalysis is proposed to occur through a sequence of Mg-N/B-H metathesis and rate-determining Mg-H/N=C insertion steps, a proposal strongly supported by stoichiometric studies and kinetic analysis. The reactions are observed to proceed through the intermediacy of well-defined magnesium amides, two examples of which have been isolated and structurally characterized. Mechanistic investigations suggest that the catalytic rate-determining process occurs at an isolated magnesium center and requires the presence of two molecules of the imine substrate for effective turnover. This latter observation is rationalized as a requirement for the secondary substrate molecule to displace HBpin from the coordination sphere of the catalytic magnesium center.

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