Robin G. Hicks , University of Victoria
The coordination chemistry of the Nindigo ligand has been explored. Our first forays focused on Pd(II) substrates. We were able to prepare binuclear Pd complexes with the Nindigo ligand adopting the anticipated bis-bidentate binding mode – most of the time; when the aniline substituents are relatively large, reactions with Pd(hfac)2 led to ligand isomerization and isolation of mononuclear Nindigo-Pd species in which the Nindigo core has switched from a trans to a cis alkene. The physicochemical properties of the complexes turn out to be extremely interesting. The pi-pi* absorption of the ligand persists in the metal complexes but is shifted into the near infrared region; aborsption intensities remain extremely high (~10E4 M-1 cm-1). Even more interesting is the discovery of several reversible oxidation/reduction processes (monitored by cyclic voltammetry) which are attributable to the coordinated Nindigo ligand. As such, the Nindigo structure represents a brand new type of bridging ligand which (a) can be readily tuned (in terms of steric and electronic properties) by simple choice of the aniline reagent, (b) holds two metal centres in very close proximity, which bodes well for strong metal-metal interactions mediated by the bridging ligand, and (c) exhibits a range of functionalities such as near infrared absorption and redox activity.
Overall this project has worked out more successfully than I had imagined it could in a relatively short period of time; our recent discoveries have opened up a huge range of opportunities and ‘new directions’ which I am now enthusiastically pursuing. This project would not have been possible without funding support from PRF and I am immensely grateful for the opportunity provided by this grant.