Synthesis, characterization and coordination chemistry of indigo diimines

Date

2008-12-17T22:42:08Z

Authors

Oakley, Simon R.

Journal Title

Journal ISSN

Volume Title

Publisher

Abstract

This work presents the synthesis and characterization of a new family of bridging ligands, indigo diimines (Nindigos). Nindigos are bis(bidentate) N-donor type ligands derived from the dye indigo. These Nindigos have been synthesized via reaction of indigo with primary amines, using TiCl4 as a catalyst, in bromobenzene. A family of Nindigo ligands was prepared with p-tolyl, p-methoxyphenyl, p-chlorophenyl, mesityl, and tBu functional groups. The UV-Vis properties of the Nindigos were investigated. The λmax for these ligands occurs in the range of 580-640nm, with extinction coefficients in the order of 1x104 M-1 cm-1. These absorptions are similar to that of indigo itself, which also shows a λmax close to 600nm. The reactions of selected Nindigo derivatives with Pd(hfac)2 formed bimetallic complexes. Upon complexation with palladium, the major absorption of the Nindigo complexes was found to red-shift to ~ 910nm, while the extinction coefficient increased to approximately 2x104 M-1 cm-1. This demonstrates that both the Nindigos and their complexes are functional molecular dyes. The electrochemistry of the p-tolyl, p-methoxyphenyl, and mesityl complexes show two reversible oxidations, with E1/2 at approximately + 0.0V and + 0.50V. There is also a quasi-reverisble reduction at approximately -1.4V. The alkyl derivatized complex, tBu Nindigo showed only one reversible oxidation at +0.32 V and one irreversible reduction at ~ -1.7 V. The Nindigo complexes now represent a new class of redox active bridging ligands, and thanks to the facile derivatization, they have more options for electronic and steric control around the metal center, which ultimately means greater control over redox activity.

Description

Keywords

Citation