Pyridylporphyrin metallacycles with a slipped cofacial geometry: spectroscopic, X-ray and photophysical characterization.

Treatment of the octahedral Ru(II) complex [ trans,cis,cis -RuCl 2 (DMSO-O) 2 (CO) 2 ] with an equimolar amount of 5,10- bis(3′-pyridyl)-15,20-diphenylporphyrin (3′- cis -DPyP) yielded, upon selective replacement of the DMSO ligands, the neutral 2 + 2 metallacycle 2. NMR spectroscopy provided unambiguous evidence that only one highly symmetrical species, in which the two chromophores are held in a slipped cofacial arrangement by the external Ru(II) metal fragments, exists in solution. The unprecedented geometry of 2, and of the fully zincated analogue 2a, were confirmed in the solid state by X-ray structural investigations.