Experimental and Theoretical Evidence of an SN2-Type Mechanism for Dissociation of B-N Coordination Bonds in 2,6-Bis((dimethylamino)methyl)phenylborane Derivatives

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• 作者：Shinji Toyota ; Tadahiro Futawaka ; Mitsuhiro Asakura ; Hiroshi Ikeda ; and Michinori <img src="http ; //pubs.acs.org/images/entities/Omacr.gif" border="0">ki
• 刊名：Organometallics
• 出版年：1998
• 出版时间：September 14, 1998
• 年：1998
• 卷：17
• 期：19
• 页码：4155 - 4163
• 全文大小：207K
• 年卷期：v.17,no.19(September 14, 1998)
• ISSN：1520-6041

文摘

To distinguish between dissociation of a B-N coordination bond by S_N1- and S_N2-typemechanisms, two series of 1,3,2-dioxaborolanes (boronates) and BEt₂ (borane) complexescarrying a 2,6-bis((dimethylamino)methyl)phenyl group as a third substituent were synthesized by the reaction of the corresponding organolithium compound with an appropriateboron reagent. In the solid state, the boronate complex exhibits a structure in which onlyone NMe₂ group is coordinated to a tetracoordinated boron atom according to the X-rayanalysis and the solid-state NMR. In solution there is a rapid exchange between thecoordinated and uncoordinated amine ligands. The barriers to B-N dissociation in theboronate and borane complexes are lower by >3.4 and 6.6 kcal/mol than in the correspondingmonoamino complexes, respectively, which is due to electronic assistance in an S_N2-typemechanism. This observation is supported by ab initio calculations for the system of NH₃and BH₃. The dynamic process observed in the boronate complex with 4,4-diphenylsubstituents is also discussed.