Synthesis of triphyrin(2.1.1)-triphyrin(2.1.1) homo dimers and bis-Re(i) triphyrin dimer complex

Abstract

First examples of covalently linked triphyrin(2.1.1)-triphyrin(2.1.1) homo dimers connected via flexible alkoxy linkers at β-pyrrole positions were synthesized in 28–30% yields by reacting 2-bromo triphyrin(2.1.1) with three different alkane diols such as 1,2-ethanediol, 1,4-butanediol and 1,6-hexanediol in toluene under Pd₂(dba)₃/DPEphos catalyzed conditions by refluxing for 12–20 h. One of the free base triphyrin–triphyrin homo dimers was metallated by treating the homo dimer with Re(CO)₅Cl in toluene under reflux and afforded bis-Re(I) homo dimer complex in 53% yield. Three free base homo dimers and one bis-Re(I) homo dimer complex were thoroughly characterized and studied using HR-MS, 1D and 2D NMR, absorption spectroscopy, cyclic voltammetry and DFT calculations. Our attempts to obtain the X-ray structure of homo dimers were not successful. However, DFT studies revealed that homo dimers prefer to exist in anti-conformation rather than syn-conformation and both triphyrin macrocycles in homo dimers were similar in terms of the deviation of pyrrole rings from the mean plane defined by the four meso carbons of the respective triphyrin unit. Absorption spectra of homo dimers showed similar absorption features such as in triphyrin(2.1.1) with slight changes in their absorption peak maxima. Electrochemical studies revealed that the homo dimers were electron rich, whereas the bis-Re(I) complex was electron deficient in nature.