Imidazolidene Carboxylate Bound MBPh4 Complexes (M = Li, Na) and Their Relevance in Transcarboxylation Reactions

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• 作者：Bret R. Van Ausdall ; Nils F. Poth ; Virginia A. Kincaid ; Atta M. Arif ; Janis Louie
• 刊名：Journal of Organic Chemistry
• 出版年：2011
• 出版时间：October 21, 2011
• 年：2011
• 卷：76
• 期：20
• 页码：8413-8420
• 全文大小：954K
• 年卷期：v.76,no.20(October 21, 2011)
• ISSN：1520-6904

文摘

Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO₂) with the Lewis acids MBPh₄, where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh₄ yielded a dimeric species, yet coordination of IPrCO₂ with LiBPh₄ yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO₂) with LiBPh₄ also afforded a dimeric species that was similar in global structure to that of the IPrCO₂+NaBPh₄ dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC路CO₂ (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO₂ to acetophenone with NaBPh₄ to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO₂ and acetophenone, whereas zero -order dependence was observed for NaBPh₄. Direct dicarboxylation was observed when I^tBuCO₂ was added to MeCN in the absence of added MBPh₄.