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

Abstract

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 · xH 2O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ 2- 2) 2Ru(μ-Cl) 2Ru(κ 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-μ-bromo bridged derivative [(κ 2- 2) 2Ru(μ-Br) 2Ru(κ 2- 2) 2] 2+ [ 3b] 2+ was obtained from RuCl 3 · xH 2O 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(κ 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 · H 2O are reported.