Simultaneous Cation/Anion Coordination by Bifunctional 1,2-Diimine/1,2-Diamine Type Ligands: Synthesis, Structures, and Properties of Tight Ion Pair Complexes of Ruthenium and Iron

The reaction between [(η6-p-cymene)RuCl2]2 and tetra-p-tolyloxalic amidine (oxam1) results in a coupled cation/anion coordination forming the ion-paired complex [(η6-p-cymene)RuCl(oxam1)Cl] (1a). According to an X-ray single crystal diffraction analysis the Ru moiety is coordinated at the 1,2-diimine part yielding a five-membered chelate ring. Furthermore, the 1,2-diamine group on the opposite side binds to a chloride anion via two N−H groups. Exchange of the chloride anion by trifluoractetate yields [(η6-p-cymene)RuCl(oxam1)CF3CO2] (1c) in which the C=O group is bonded to the diamine part. Similarly, bis(mesityl)bis(pyridylmethyl)oxalic amidine (oxam2) reacts with FeX2 to yield the ion-paired complexes 3a (X: Cl), and 3b (X: Br). X-ray diffraction studies of both compounds reveal that the oxalic amidine ligand acts as a four-dentate chelating ligand. One halide is fixed in the same way as in 1a. The complex 1a reacts with Pd(acac)2 (acac: acetylacetonate) to give the tetranuclear heterobimetallic complex [(η6-p-cymene)RuCl(oxam1)PdCl]2 (2). The related complexes [(tbbpy)2Ru(bbimH2)(OOC−CF3)](PF6) (4), [(tbbpy)2Ru(bbimH2){OOC(CF2)7CF3})][OOC(CF2)7CF3] (5), [{(tbbpy)2Ru(bbimH2)}2(OOC−C6F4−COO)](PF6)2 (6), and [{(tbbpy)2Ru(bbimH2)}2(OOC−C6F4−COO)] (7), (bbimH2: bibenzimidazole; tbbpy: 4,4′-di-tert-butyl-2,2′-bipyridine) also form ion-paired compounds. According to the X-ray diffraction analyses of 4−6 both oxygen atoms of the carboxylate ions are coordinated to the two N−H functions via strong N−H···O bonds. Although 5 contains a dication, the compound is soluble in solvents of low polarity, even in supercritical carbon dioxide. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)