Transition Metal Complexes with Sulfur Ligands. 136. Enforced Trans Coordination of Thiolate Donors in Electron Rich Iron, Ruthenium, and Nickel [M(L)(pyN₂H₂S₂)] and [M(L)(pyS₄)] Complexes (L = CO, PPh₃, DMSO) (pyN₂H₂S₂^2- = 2,6-Bis(2-mercaptophenylamino)dimethylpyridine(2−); pyS₄^2- = 2,6-Bis(2-mercaptophenylthio)dimethylpyridine(2−))

In the course of a systematic study of transition metal complexes exhibiting three properties, electron rich metal centers, core structures with trans thiolate donors, and the capability to bind nitrogenase related small molecules, the pentadentate ligands pyN2H2S2-H2 (=2,6-bis(2-mercaptophenylamino)dimethylpyridine) and pyS4-H2 (=2,6-bis(2-mercaptophenylthio)dimethylpyridine) have been synthesized. Alkylation of 2(3H)-benzothiazolone by 2,6-bis[(tosyloxy)methyl]pyridine and subsequent alkaline hydrolysis yielded pyN2H2S2-H2 (3). Template alkylation of [Ni(S2C6H4)2]2- (6) by 2,6-bis[(tosyloxy)methyl]pyridine gave [Ni(pyS4)]2 (7) whose acidic hydrolysis yielded pyS4-H2·HCl (9). The reaction of Fe(II) salts with pyN2H2S22- gave [Fe(pyN2H2S2)] (10). Five-coordinate 10 is paramagnetic (μeff (293 K) = 5.34 μB), has a trigonal bipyramidal structure, and coordinates CO to give diamagnetic [Fe(CO)(pyN2H2S2)] (11). Although the ν(CO) of 11 (1928 cm-1 (KBr)) indicates electron rich Fe centers and strong Fe−CO bonds, 11 readily dissociated CO in solution. Reactions of pyN2H2S22- with ruthenium precursor complexes yielded diamagnetic [Ru(L)(pyN2H2S2)], (L = DMSO (12), PPh3 (13), or CO (14)) which have practically substitution inert Ru−L bonds. Only 12 could be converted into 14 under drastic conditions (140 bar CO, 120 °C, 12 h, THF). Methylation of the thiolate donors to give [Ru(L)(pyN2H2S2-Me2)]I2 (L = DMSO (15) and PPh3 (16)) did not labilize the Ru−L bonds. The reaction of Fe(II) salts with pyS42- in the presence of CO yielded [Fe(CO)(pyS4)] (17). Complex 17 has a higher ν(CO) (1955 cm-1 in KBr) than 11 but is stable toward Fe−CO dissociation. The spectroscopic data of all synthesized complexes and X-ray structure analyses of 7, 10, 13, 15, 16, and 17 showed that all six-coordinate [M(L)(pyN2H2S2)] and [M(L)(pyS4)] complexes uniformly have C2 symmetrical core structures and trans thiolate donors, thus differing from analogous complexes of pentadentate NxHxSy2- ligands (x + y = 5) whose [MNxSy] cores exhibit either CS or C1 symmetry and cis or trans thiolate donors. The ν(CO) frequencies in homologous [Fe(CO)(NxHxSy)] complexes (x + y = 5) showed that exchange of aromatic thioether S for amine NH donors considerably increases the electron density at the iron centers. A minor influence was observed for the exchange of aliphatic thioether S for NH donors or changes of the [FeNxSy] core structures.