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 RuCl3 · xH2O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ2-2)2Ru(μ-Cl)2Ru(κ2-2)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 [(κ2-2)2Ru(μ-Br)2Ru(κ2-2)2]2+ [3b]2+ was obtained from RuCl3 · xH2O 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 [FeCl2(PPh3)2] to give after anion exchange with NaBPh4cis/cis/trans coordinated [Fe(κ2-2)2(MeCN)2](BPh4)2 [6](BPh4)2. The molecular structures of [3b](PF6)2, [4]PF6 and [6](BPh4)2 · H2O are reported.

The unsymmetrically substituted donor-functionalized imidazolium salts 1a and 1b react with RuCl3 · xH2O to give the dinuclear ruthenium(II) complexes [3a](PF6)2 or [3b](PF6)2. Reaction of [3a](PF6)2 with silver pyridylcarboxylate or sodium l-prolinate produces the mononuclear complex [4]PF6 and diastereometric complexes [5]PF6, respectively.Figure optionsDownload as PowerPoint slide