Abstract
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°-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.
Highlights
Nature uses sophisticated arrays of tetrapyrrolic macrocycles to perform precise energy and electron transfer processes
For each porphyrin in 2, (i) the two pyridyl rings are in a syn conformation and (ii) the plane of the heterocycle is almost orthogonal to the equatorial coordination plane (N, N, C, and C) of each Ru linker
We aimed to develop a new flexible synthetic strategy that might be used for the construction of ruthenium-mediated heteroleptic systems of meso-pyridylporphyrins containing PyPs that differ in the number of peripheral pyridyl rings and/or in the position of the pyridyl N atom (3′ or 4′)
Summary
Nature uses sophisticated arrays of tetrapyrrolic macrocycles (e.g., chlorophyll, cytochromes, etc.) to perform precise energy and electron transfer processes. The metal-mediated self-assembly approach, which exploits the formation of coordination bonds between peripheral basic site(s) on the porphyrins and suitable metal centers, has afforded a variety of discrete two-dimensional (2D) and threedimensional (3D) arrays of porphyrins of the type Mx(porp)y, including several 2+2 and 4+4 metallacycles (M can be a naked ion or bear ancillary ligands).[1−15] In this context, mesopyridylporphyrins, PyPs,[16] which feature one to four pyridyl moieties in meso positions, have been largely exploited.[1,17−24]. 15,20-diphenylporphyrin (i.e., 3′cisDPyP), are connected through 1);[25,26] two 90°-angular {t,c,c-RuCl2(CO)2} fragments For each porphyrin in 2, (i) the two pyridyl rings are in a syn conformation and (ii) the plane of the heterocycle is almost orthogonal to the equatorial coordination plane (N, N, C, and C) of each Ru linker
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