Arene Exchange in the Ruthenium-Naphthalene Complex [CpRu(C10H8)]+

Substitution of the naphthalene ligand in [CpRu(C10H8)]+ (1; Cp = cyclopentadienyl ligand) by other arenes occurs upon heating or visible-light irradiation and gives complexes [CpRu(arene)]+ [arene = C6HnMe6–n, C6H5OH, C6H5OMe, C6H4(OMe)2, indene, 2,2-paracyclophane] in 70–90 % yield. The reaction rate increases with coordinating ability of the solvent, CH2Cl2 < THF/CH2Cl2 < Me2CO, and counterion, [B(3,5-(CF3)2C6H3)4]– < PF6– < BF4– < CF3SO3–. Acceptor or bulky substituents in the incoming arene slow down the exchange. Complexes with acceptor arenes C6H5COMe, C6H5COOH, and C6H4(COOH)2 were obtained by the exchange reaction in water. Complexes [CpRu(η6-cycloheptatriene)]+ and [CpRu(η6-cyclooctatetraene)]+ were obtained by irradiation of 1 with the corresponding cyclic polyenes. A similar reaction with α-phellandrene is accompanied by dehydrogenation to give [CpRu(cymene)]+. Cation 1 reacts with 2-naphthoic acid anion to give the zwitterionic complexes [CpRu]+[C10H7COO]– in which the [CpRu]+ fragment coordinates either at the substituted or unsubstituted ring. Upon protonation and subsequent irradiation, both isomers convert into [CpRu(C10H7COOH)]+ in which the metal atom coordinates only to the unsubstituted ring. The structures of [CpRu(p-xylene)][PF6], [CpRu(2,2-paracyclophane)][PF6], [CpRu(C6H5COOH)][BF4], and [CpRu(cymene)][BPh4] were determined by X-ray diffraction.