Aggregation tendency and reactivity toward AgX of cationic half-sandwich ruthenium(II) complexes bearing neutral N,O-ligands

The aggregation tendency of complexes [Ru(eta(6)-cymene)(N,O)Cl]X[N,O = 2-benzoylpyridine (2-bzpy), 1, and 2-acetylpyridine (2-acpy), 2, X- = BPh4- or PF6-] has been studied by means of PGSE NMR experiments. It was found that complexes with PF6- as counterion are mainly present in CD2Cl2 as ion pairs at low concentration, as a mixture of ion triples and free anions at medium concentration and as ion quadruples at elevated concentration. F-19, H-1-HOESY NMR experiments revealed that in ion triples and ion quadruples two cationic Ru-units pair up. Consistently, in the solid-state structure of 1PF(6), determined through X-ray single-crystal investigation, two cationic Ru-units are held together by an intermolecular pi-pi stacking interaction between the pyridyl rings. Complexes having BPh4- as counterion are only present in solution as even aggregates, namely ion pairs at low concentration and ion quadruples at elevated concentration. In such a case a counteranion bridges two cationic Ru-units as observed in the solid-state structure of 1BPh(4). The reactivity of complexes 1 - 2 toward AgX salts has been investigated in different solvents. Bicationic [Ru(eta(6)-cymene)(N,O)(MeCN)]X-2 (N, O = 2-bzpy, 3, and 2-acpy, 4) and [Ru(MeCN)(4)(N, O)]X-2 (N, O = 2-bzpy, 5, and 2-acpy, 6) complexes were obtained by the reaction of 1 and 2 with AgX in the presence of three equivalents of acetonitrile or in acetonitrile, respectively. The reaction of 1 with AgPF6 in acetone afforded complex [Ru(eta(6)-cymene)(N, O, O)]PF6 (7, where N, O, O = 4-alcoxide-4-phenyl-4-(pyridin-2-yl) butan-2-one) from the C - C coupling of a deprotonated methyl group of the coordinated acetone and the C=O moiety of 2-bzpyn ligand.