Circular dichroism in copper(II) complexes of some bis(glycyl)ethylenediamine analogs

Circular Dichroism of the Copper(II) N,N′-Bis(alanyl)stilbenediamine Complexes

“…Accordingly, we present here the circular dichroism (c.d.) spectra for copper(I1) complexes of some dissymmetric diamides of known absolute configurations, comparable to those previously described (8,12).…”

“…A h chirality here relates to S substitution, that is, the substituent becomes axial. This effect is seen in N,N1-bis(S-alanyl)ethanediamine, in 1, in RS-N,N'-bis(S-alanyl)cyclohexanediamine, and in N,N1-bis(S-alany1)butanediamine (8,12).…”

“…2. If these spectra are compared to those previously described (8,12), it seems evident that there are the expected three contributory bands beneath the total absorption envelope. The central band at about 500 nm has a negative c.d.…”

“…at 450 nm and negative at 550 nm is associated with S substitution and the magnitude of the effect varies according to the bulk of the substituent. This is seen in 2 and 3, in S-N,N1-bisglycylpropanediamine, in SS-N,N'-bisglycylbutanediamine (8,12) and in SS-N,N1-bis(S-alany1)butanediamine and RR-N,N1-bis-(S-alany1)butanediamine (14). In these cases, i.e., in other than fused ring systems, there appears to be no significant preference transmitted to the terminal rings (e.g., terminal h for R bridge substitution), as judged by the absence of any marked optical activity in the 500 nm region.…”

“…A 6 chirality is then transmitted to the terminal rings via the planar C-N-CO system (I). This effect is observed in RR-N,N1-bisglycylcyclohexanediamine, in RR-N,N1-bis(S-alanyl)cyclohexanediamine and in SS-N,N'-bis(S-alany1)cyclohexanediamine (8,12). Secondly, the terminal rings will tend to be non-planar in order to minimize any carbonyl-methyl interaction (13).…”