Synthesis, ~1H/~(13)C NMR spectroscopic and structural studies of sterically induced internal dynamics in novel mono- and di-ruthenium (II) 2, 2':6', 2'-terpyridine complexes of 2, 3-bis(2, 2'-bipyridin-6-yl) pyrazine

摘要

The mono- and di-metallic N_6-ruthenium (II) complexes [Ru(terpy)L][PF_6]_2 1 and [{Ru(terpy)}_2L][PF_6]_4 2, where L is 2, 3-bis(2, 2'-bipyridin-6-yl) pyrazine and terpy is 2, 2':6', 2"-terpyridine, have been prepared. Extensive and careful ~1H and ~(13)C NMR spectroscopic studies at ambient temperature showed that complexation induces steric strain in the scaffolding of L and thereby fluxional behaviour in both complexes. In 1, rotation of the free 2, 2'-bipyridyl (bpy) group of L relieves these interactions and results in two enantiomerically related conformations. In 2, a mutual twisting of both complexes bpy fragments results in helicene-like, P- and M-configured enantiomeric complexes. Dynamic low-temperature NMR studies of 1 and 2 in acetone-d_6 solutions have provided activation energy data for both processes. The behaviour of 2 is paralleled by its crystal structure, which indicated a strong twisting of the bpy groups of L. Cyclic voltammetric and UV-spectroscopic studies conducted on both indicated a mild electrochemical and electronic coupling of the metal centres in 2.