Synthesis, characterization, and solution lability of N-heterocyclic carbene adducts of the heavier group 2 bis(trimethylsilyl)amides

Anthony G.M. Barrett, Mark R. Crimmin, Michael S. Hill, Gabriele Kociok-Köhn, Dugald J. MacDougall, Mary F. Mahon, Panayiotis A. Procopiou

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54 Citations (Scopus)

Abstract

A series of N-heterocyclic carbene (NHC) adducts of the heavier group 2 bis(trimethylsilyl)amides, of the general formulas [(L1)M{N(SiMe 3)2}2], [(L2)Ca{N(SiMe 3)2}2], and [(L1)Ca{N(SiMe 3)2}Cl] (L1 = 1,3-bis(2,4,6-trimethylphenyl) imidazol-2-ylidene and L2 = 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene, M = Ca, Sr, and Ba), have been synthesized by either the addition of the group 2 amide to the appropriate imidazolium salt or direct addition of the carbene to the solvent-free, homoleptic, metal amide. X-ray diffraction studies of the reaction products revealed the formation of monomelic three-coordinate alkaline earth metal species in which the NHC binds via conventional σ-donation of the lone pair to the electrophilic metal center. Although 1H, 13C, and NOESY NMR experiments suggest this coordination is retained in solution, reactions with protic substrates such as 2-methoxyethylamine, diphenylamine, and di-p-tolylphosphine demonstrate the lability of the NHC under catalytically-relevant conditions. Furthermore, a series of reactions of [L1Ca{N(SiMe3)2} 2] with Lewis bases suggest that the strength of the interaction between the metal and neutral ligand decreases across the series Ph 3P=O > NHC ∼ THF > PPh3. In the case of triphenylphosphine oxide the structure of the reaction product, [(Ph 3P=O)2CaJ N(SiMe3)2}2], was confirmed by independent synthesis from addition of Ph3P=O to [Ca{N(SiMe3)2}2].

Original languageEnglish
Pages (from-to)3939-3946
Number of pages8
JournalOrganometallics
Volume27
Issue number15
DOIs
Publication statusPublished - 11 Aug 2008

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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