Carbon monoxide formation from trimethylamine-boranecarboxylate: DFT studies of SNi and chelotropic mechanisms.

Trimethylamine-boranecarboxylic acid (CH3)3N-BH2COOH and other amine carboxyboranes have been observed to undergo slow decarbonylation in neutral aqueous solution. This reaction, when it occurs in vivo, may have a therapeutic effect by delivering low concentrations of carbon monoxide over an extended period. In order to identify a possible mechanistic pathway for decarbonylation, the smallest tertiary amine derivative and its corresponding carboxylate ion were studied using CCSD(T)/PCM/6-311++G(2d,p)//M06-2X/PCM/6-311++G(2d,p) model chemistry. The proposed mechanistic pathway begins with a trimethylamine boranecarboxylate ion, which first undergoes an internal substitution reaction (SNi) to give free amine and the carboxyborane anion BH2COO-. The latter cyclic ion then releases CO via a rapid chelotropic fragmentation. The role of water solvent in these reactions was explored by structural and energetic analysis of hydrogen-bonded complexes. It was found that complexation with water inhibits dissociation of trimethylamine by stabilizing the trimethylamine carboxyborane anion, whereas water accelerates CO loss by stabilizing the polar chelotropic transition state.

Crystal structure of memantine-carb-oxy-borane.

The synthesis and crystal structure of the title compound, C13H24BNO2 [systematic name: 3,5-di-methyl-adamantanyl-amine-borane-carb-oxy-lic acid or N-(carb-oxy-boranyl-idene)-3,5-di-methyl-adamantan-1-amine], derived from the anti-Alzheimer's disease drug memantine is reported. The C-N-B-CO2 unit is almost planar (r.m.s. deviation = 0.095 Å). The extended structure shows typical carb-oxy-lic acid inversion dimers linked by pairwise O-H⋯O hydrogen bonds [O⋯O = 2.662 (3) Å]. The amino group forms a weak N-H⋯O hydrogen bond [N⋯O = 3.011 (3) Å], linking the dimers into [001] chains in the crystal. Highly disordered solvent mol-ecules were treated using the SQUEEZE routine of PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18], which treats the electron density as a diffuse contribution without assignment of specific atom locations. A scattering contribution of 255 electrons was removed. The crystal studied was refined as a two-component twin.