Preparation and Characterization of N,N′‐Dialkyl‐1,3‐propanedialdiminium Chlorides, N,N′‐Dialkyl‐1,3‐propanedialdimines, and Lithium N,N′‐Dialkyl‐1,3‐propanedialdiminates

Abstract

AbstractWe describe convenient preparations of N,N′‐dialkyl‐1,3‐propanedialdiminium chlorides, N,N′‐dialkyl‐1,3‐propanedialdimines, and lithium N,N′‐dialkyl‐1,3‐propanedialdiminates in which the alkyl groups are methyl, ethyl, isopropyl, or tert‐butyl. For the dialdiminium salts, the N2C3 backbone is always in the trans‐s‐trans configuration. Three isomers are present in solution except for the tert‐butyl compound, for which only two isomers are present; increasing the steric bulk of the N‐alkyl substituents shifts the equilibrium away from the (Z,Z) isomer in favor of the (E,Z), and (E,E) isomers. For the neutral dialdimines, crystal structures show that the methyl and isopropyl compounds adopt the (E,Z) form, whereas the tert‐butyl compound is in the (E,E) form. In aprotic solvents all four dialdimines (as well as the lithium dialdiminate salts) adopt cis‐s‐cis conformations in which there presumably is either an intramolecular hydrogen bond (or a lithium cation) between the two nitrogen atoms.