Trinuclear ruthenium dendrons based on bridging PHEHAT and TPAC ligands

Abstract

Novel polynuclear compounds, the trinuclear precursor complex cis-{[(phen)₂Ru(PHEHAT)]₂Ru(CH₃CN)₂}⁶⁺4 and the trinuclear TPAC (tetrapyrido[3,2-a:2′,3′-c:3′′,2′-h:2′′′,3′′′-j]acridine) complex {[(phen)₂Ru(PHEHAT)]₂Ru(TPAC)}⁶⁺5 have been prepared. Their electrochemistry and photophysics indicate that the ³MLCT (metal to ligand charge transfer) emissions involve the external {Ru(PHEHAT)} moieties for both complexes and there is no spectro-electrochemical correlation. The trinuclear dendron with the TPAC ligand represents a key compound for future constructions of much larger species thanks to the TPAC that could bridge another polynuclear precursor. For decreasing the length of preparation of these compounds, microwave assisted syntheses have been tested and used not only for the targeted complexes but also for the precursors ((phen)₂RuCl₂, {(phen)₂Ru(phendione)}²⁺, {(phen)₂Ru(PHEHAT)}²⁺ (PHEHAT = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene), (DMSO)₄RuCl₂), and for the bridging TPAC ligand itself. The microwave method allows a drastic decrease of the preparation times, especially in the case of the TPAC, from 8 days to 60 min.