Synthesis, photochemistry, and electrochemistry of ruthenium(II) polypyridyl complexes anchored by dicobalt carbonyl units

A novel hybrid complex system of ruthenium polypyridyl complexes anchored by dicobalt carbonyl units, [Ru(bpy)2{phen–C{Co2(CO)4(dppm)}C–tolyl}](PF6)2 (1) and [Ru(bpy)2{tolyl–C{Co2(CO)4(dppm)}C–phen–C{Co2(CO)4(dppm)}C–tolyl}](PF6)2 (2), has been prepared from the dicobalt carbonyl complex Co2(CO)6(dppm) (dppm = bis(diphenylphosphino)methane) and the ruthenium complex [Ru(bpy)2(phen–triple bond; length of mdash–tolyl)](PF6)2 (3) or [Ru(bpy)2(tolyl–triple bond; length of mdash–phen–triple bond; length of mdash–tolyl)](PF6)2 (4). The present Ru–Co2 hybrid complexes 1 and 2 are nonluminescent at room temperature, although precursor ruthenium polypyridyl complexes, such as 3 and 4, clearly show phosphorescence from the 3MLCT excited state. The emission quenching of these hybrid complexes indicates the intramolecular energy transfer from the ruthenium polypyridyl unit to the dicobalt carbonyl unit(s) and then to the ground state by a radiationless deactivation process accompanied by a vibrational relaxation of the dicobalt carbonyl unit(s). This interpretation is supported by spectral change measurements along with constant potential electrolysis and electrochemical data.