Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N'-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N'-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl(3) center dot xH(2)O to give a racemic mixture of dinuclear di-mu-chloro bridged ruthenium complexes [(kappa(2)-2)(2)Ru(mu-Cl)(2)Ru(kappa(2)-2)(2)](2+) [3a](2+). The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-mu-bromo bridged derivative [(kappa(2)-2)(2)Ru(mu-Br)(2)Ru(kappa(2)-2)(2)](2+) [3b](2+) was obtained from RuCl(3) center dot xH(2)O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a](2+) reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4](+). Reaction of [3a](2+) with the sodium salt of L-proline resulted in a diastereomeric mixture of complexes [5](+). The free N-heterocyclic carbene 2 reacts with [FeCl(2)(PPh(3))(2)] to give after anion exchange with NaBPh(4) cis/cis/trans coordinated [Fe(kappa(2)-2)(2)(MeCN)(2)](BPh(4))(2) [6](BPh(4))(2). The molecular structures of [3b](PF(6))(2), [4]PF(6) and [6](BPh(4))(2) center dot H(2)O are reported. (C) 2008 Elsevier B.V. All rights reserved.