Sequential C−H and C−Ru Bond Formation and Cleavage during the Thermally Induced Rearrangement of Aryl Ruthenium(II) Complexes with [C6H3(CH2NMe2)2-2,6]-as a Bidentate η2-C,NCoordinated Ligand. The Crystal Structures of the Isomeric Pairs [RuCl{η6-C10H14}{η2-C,N-C6H3(CH2NMe2)2-2,n}] (n= 4 or 6) and [Ru(η5-C5H5){η2-C,N-C6H3(CH2NMe2)2-2,n}(PPh3)] (n= 4 or 6)

Abstract

New air-stable ruthenium(II) complexes that contain the aryldiamine ligand [C6H3(CH2NMe2)2-2,6]- (NCN) are described. These complexes are [RuCl{η2-C,N-C6H3(CH2NMe2)2-2,6}(η6-C10H14)] (2; C10H14 = p-cymene = C6H4Me-iPr-4), [Ru{η2-C,N-C6H3(CH2NMe2)2-2,6}(η5-C5H5)(PPh3)] (5), and their isomeric forms [RuCl{η2-C,N-C6H3(CH2NMe2)2-2,4}(η6-C10H14)] (3) and [Ru{η2-C,N-C6H3(CH2NMe2)2-2,4}(η5-C5H5)(PPh3)] (6), respectively. Complex 2 has been prepared from the reaction of [Li(NCN)]2 with [RuCl2(η6-C10H14)]2, whereas complex 5 has been prepared by the treatment of [RuCl{η3-N,C,N-C6H3(CH2NMe2)2-2,6}(PPh3)] (4) with [Na(C5H5)]n. Both 2 and 5 are formally 18-electron ruthenium(II) complexes in which the monoanionic potentially tridentate coordinating ligand NCN is η2-C,N-bonded. In solution (halocarbon solvent at room temperature or in aromatic solvents at elevated temperature), the intramolecular rearrangements of 2 and 5 afford complexes 3 and 6, respectively. This is a result of a shift of the metal−Caryl bond from position-1 to position-3 on the aromatic ring of the NCN ligand. The mechanism of the isomerization is proposed to involve a sequence of intramolecular oxidative addition and reductive elimination reactions of both aromatic and aliphatic C−H bonds. This is based on results from deuterium labeling, spectroscopic studies, and some kinetic experiments. The mechanism is proposed to contain fully reversible steps in the case of 5, but a nonreversible step involving oxidative addition of a methyl NCH2−H bond in the case of 2. The solid-state structures of complexes 2, 3, 5, and 6 have been determined by single-crystal X-ray diffraction. A new dinuclear 1,4-phenylene-bridged bisruthenium(II) complex, [1,4-{RuCl(η6-C10H14)}2{C6(CH2NMe2)4-2,3,5,6-C,N,C‘,N‘}] (9) has also been prepared from the dianionic ligand [C6(CH2NMe2)4-2,3,5,6]2- (C2N4). The C2N4 ligand is in an η2-C,N-η2-C‘,N‘-bis(bidentate) bonding mode. Compound 9 does not isomerize in solution (halocarbon solvent), presumably because of the absence of an accessible Caryl−H bond. Complex 9 could not be isolated in an analytically pure form, probably because of its high sensitivity to air and very low solubility, which precludes recrystallization.