Reaction of azole heterocycles with tris(dimethylamino)borane, a new method for the construction of tripodal borate-centred ligands

Chemistry : a European Journal
Philip J BaileyAlejandro Sanchez Perucha

Abstract

Reaction of 2-mercapto-1-methylimidazole (methimazole) with tris(dimethylamino)borane, B(NMe2)3, provides the tetrahedral dimethylamine adduct of tris(methimazolyl)borane, [(Me2HN)B(methimazolyl)3]. By contrast, imidazole, 2-methylimidazole, 2-chloroimidazole and benzimidazole provide the homoleptic tetra-azolyl systems H[B(azolyl)4], and the same product is obtained even when a substoichiometric quantity of the heterocyle is employed. The change in reaction outcome is correlated with the variation of basic pKa for the heterocycles. A simple acid-base reaction with elimination of HNMe2 is proposed for the reaction with the weakly basic, but more strongly acidic, methimazole. However, for the more strongly basic imidazoles, initial coordination of the heterocycle imine nitrogen to the weakly Lewis acidic boron centre in B(NMe2)3 to form the tetrahedral adduct [(azole)B(NMe2)3] is proposed. The greater availability of the NMe2 lone pairs in this species results in increased basicity and a rapid reaction with further heterocycle to provide the observed H[B(azolyl)4] products. For 2-nitroimidazole, the low basicity (and increased N-H acidity) results in the formation of [(HNMe2)B(2-nitroimidazolyl)3] on reaction with B(NMe2)3, anal...Continue Reading

Citations

Jul 12, 2017·Dalton Transactions : an International Journal of Inorganic Chemistry·Kyounghoon LeeScott R Daly
Dec 17, 2008·Dalton Transactions : an International Journal of Inorganic Chemistry·Istemi KuzuFrank Breher
Jan 29, 2010·Chemistry : a European Journal·Philip J BaileyFraser J White
Feb 17, 2010·Magnetic Resonance in Chemistry : MRC·Günter Paulus Schiemenz
Oct 5, 2019·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Bin QianIvan S Cole
Jul 3, 2013·Dalton Transactions : an International Journal of Inorganic Chemistry·Philip J BaileyGary S Nichol

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