A Flexible Synthetic Strategy for the Preparation of Heteroleptic Metallacycles of Porphyrins.

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl2(CO)(2)}(2)(4'cisDPyP)(3'cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4'cisDPyP [i.e., 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin] and 3'cisDPyP [i.e., 5,10-bis(3'-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90 degrees-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl2(CO)(2)(dmso-O)}(2)(4'cisDPyP)] (3) with 1 equiv of 3'cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl2(CO)(2)(dmso-O)}(2)(3'cisDPyP)] (4) with 1 equiv of 4'cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments.