Reaction chemistry of tri-substituted mesitylene derivatives and the synthesis of sterically buttressed 1,3,5-triaminocyclohexyl ligands
作者:David Parker、Kanthi Senanayake、Jouko Vepsailainen、Stefania Williams、Andrei S. Batsanov、Judith A. K. Howard
DOI:10.1039/a701364g
日期:——
The sterically buttressed triamine
cis,cis-2,4,6-trimethyl-1,3,5-triaminocyclohexane is
weakly basic in aqueous solution (pKa: 7.83, 6.73,
5.15; 298 K) because of steric inhibition to solvation. As a result of
intramolecular hydrogen-bonding and stabilising
σC–H–σ*C–N
interactions, the free amine and its monoprotonated salt adopt a
conformation in which the three amino groups are axially disposed. It
possesses a reduced reactivity in SN2 reactions and may be
converted via selective alkylation or condensation to
polydentate ligands incorporating carboxylate, hydroxyphenyl or
phosphinate groups. An intramolecular hydride transfer mechanism
accounts for the formation of a stable bicyclic amidine formed during
acidic hydrolysis of a tricyclic bis-aminal derived from the parent
triamine by a phosphinoxymethylation. The crystal structures of two of
the mesitylene derivatives have been determined.
由于对溶解的立体抑制作用,三氨基顺式,顺式-2,4,6-三甲基-1,3,5-三氨基环己烷在水溶液中呈弱碱性(pKa:7.83、6.73、5.15;298 K)。由于分子内氢键和稳定的 σC-H-σ*C-N 相互作用,游离胺及其单质子盐采用了三个氨基轴向排列的构象。它在 SN2 反应中的反应活性较低,可通过选择性烷基化或缩合转化为含有羧酸基、羟苯基或膦酸基的多齿配体。分子内氢化物转移机制解释了一种稳定的双环脒的形成过程,这种脒是在酸性水解三环双脒的过程中通过膦氧甲基化作用从母体三胺中衍生出来的。目前已经确定了其中两种甲脒衍生物的晶体结构。