Palladium(II), Ruthenium(II), and Ruthenium(III) Complexes of 23-Thiaazuliporphyrin: The Case of Coordination-Induced Contraction.

Abstract

5,10,15,20-Tetraaryl-23-thiaazuliporphyrin (SAz) was synthesized starting from nonfunctionalized azulene using a "1 + 3" method to be applied as a monoanionic macrocyclic ligand that provides a peculiar [CNSN] coordination cavity. An insertion of palladium(II) afforded the cationic [Pd(II)(SAz)](+), which readily undergoes the seven-membered ring contraction to form palladium(II) 23-thiabenzocarbaporphyrin [Pd(SBzC)] providing the first example of metal azuliporphyrinoid contraction. A reaction of SAz and a ruthenium source ([RuCl2(CO)3]2, [RuCl2(p-cymene)]2, or [RuCl2(cod)]) yielded ruthenium(II) 23-thiaazuliporphyrin [Ru(II)(SAz)Cl(CO)]. As shown by X-ray crystallography the thiophene ring in [Ru(SAz)Cl(CO)] is sharply tilted out of the plane of the two pyrrole nitrogen and carbon atoms being bound to the ruthenium through the pyramidal sulfur in the η(1) fashion. In solution, as demonstrated by variable-temperature (1)H NMR investigations, [Ru(SAz)Cl(CO)] exists as an equilibrium mixture of two isomers that are differentiated by the direction of thiophene folding (toward or outward of the axial chloride ligand). Apart of [Ru(II)(SAz)Cl(CO)], ruthenium(III) 23-thiaazuliporphyrin [Ru(III)(SAz)Cl2] was obtained when [RuCl2(p-cymene)]2 or [RuCl2(cod)]n were used for insertion. The most characteristic (1)H NMR features of paramagnetic [Ru(SAz)Cl2] are negative isotropic shifts of resonances assigned to meso-aryl, azulene, and pyrrolic hydrogen atoms. The analysis of contact shifts and the parallel density functional theory calculations of spin density distribution documented that in [Ru(SAz)Cl2] the metal ion acquires the d(xy)(2)(d(xz)d(yz))(3) ground electronic state. This C(s) symmetry complex has singly occupied d(xz) or d(yz) orbitals that are symmetrically unequivalent. The resulting two different spin density distributions, when merged, reflect the spectroscopic image with the very specific π-spin delocalization, also including the azulene moiety.