The interaction of [Ru(eta(6)-C(10)H(8))(Cp)](+) (Cp=C(5)H(5)) with aromatic amino acids (L-phenylalanine, L-tyrosine, L-tryptophane, D-phenylglycine, and L-threo-3-phenylserine) under visible-light irradiation gives the corresponding [Ru(eta(6)-amino acid)(Cp)](+) complexes in near-quantitative yield. The reaction proceeds in air at room temperature in water and tolerates the presence of non-aromatic amino acids (except those which are sulfur containing), monosaccharides, and nucleotides. The complex [Ru(eta(6)-C(10)H(8))(Cp)](+) was also used for selective labeling of Tyr and Phe residues of small peptides, namely, angiotensin I and II derivatives.

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.

Naphthalene in the [CpRu(η 6 C 10 H 8 )] + complex (1) is substituted for other arenes under reflux in 1,2 dichloroethane to form the [CpRu(η 6 arene)] + cations (arene = C 6 H 6 , 1,2 C 6 H 4 Me 2 , 1,2,4,5 C 6 H 2 Me 4 , or C 6 Me 6 ) in 70-80% yields. The reaction is accelerated in the presence of a catalytic amount of acetonitrile. The structure of [1]PF 6 was established by X ray diffraction.

Replacement of the naphthalene ligand in ruthenium complex [CpRu(C 10 H 8 )] + (1) by halide anions readily proceeds at room temperature to give insoluble oligomeric species [CpRuX] n (X = Cl, Br, I). Similar reactions in the presence of mono-or bidentate ligands afford complexes [CpRuL 2 X] where L = CO, P(OMe) 3 , tBuNC; L 2 = dppm, dppe, dppp, bipy, phen, cod, nbd, or 1,4-diphenylbutadiene. Useful catalysts [CpRu(cod)X] were obtained by this method in 70-90 % yields. The structure of [CpRu(cod)I] was determined by Xray diffraction. Reaction of 1 with Brand allyl bromide afforded Ru IV complex [CpRu(η 3 -C 3 H 5 )]Br 2 . Cation 1 also was found to react with azide anion in the presence of bidentate phosphanes to afford [CpRuL 2 N 3 ] (L 2 = dppm, dppe). Reaction of 1 with neutral ligands in the absence of nucleophilic anions proceeded under visible-light irradiation to give cat-[a] A. N. Nesmeyanov Institute of Organoelement Compounds, 481 ionic complexes [CpRuL 3 ] + [L = CO, P(OMe) 3 , P(OEt) 3 , tBuNC] in 80-90 % yields. Complex 1 (2 mol-%) catalyzed cyclotrimerization of dipropargyl Meldrum's acid with various alkynes RCϵCH [R = H, Bu, Hex, Ph, SiMe 3 , (CH 2 ) 4 -CϵCH, (CH 2 ) 3 OH, (CH 2 ) 2 Br, CH 2 OMe, CH 2 OAc, CH 2 NMe-Boc] producing benzene derivatives in 50-85 % yields. According to DFT calculations, the attack of the first ligand (Clor L) is a rate-determining step in the naphthalene replacement in 1. The activation barrier for attack of the Clanion is ca. 10 kcal mol -1 lower in energy than that of the neutral ligands L = CO, MeNC, MeCN, thus providing a rationale for the faster reaction in the presence of halide anions. The barriers for naphthalene replacement in 1 were also found to be ca. 10-15 kcal mol -1 lower in energy than those for the benzene replacement in [CpRu(C 6 H 6 )] + . Scheme 1. Reactions of 1 with neutral 2-electron ligands.

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