Stereoselective recognition of vicinal diamines with a Zn(II) complex

摘要

Zn(II) complex of L (N, N'-bis(2-pyridylmethyl)-N,N'-di-methyl-trans- 1,2-diaminocyclohexane) binds chiral vicinal diamines (1,2-diphenylethylenediamine (dpen) and 1,2-diaminocyclohexane (dach)) stereoselectively. Crystallographic studies reveal that the ternary complex has the C-2 symmetric cis-alpha topology. H-1 NMR shows that the R, R form of the tetradentate zinc complex binds rapidly and reversibly to the R, R form of the diamine over the S, S form with a streoselectivity of about 5:1. Although the diamine exchange rate is rapid it is slower than the NMR time scale, and distinct signals for the diastereomeric complexes are observed when racemic mixtures of the host and guest molecules are mixed. Origin of stereoselectivity is discussed in terms of steric effects.