Synthesis of Ruthenium Half‐Sandwich Complexes by Naphthalene Replacement in [CpRu(C₁₀H₈)]⁺

Abstract

Abstract 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 , t BuNC; 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 X‐ray diffraction. Reaction of 1 with Br – and 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 cationic complexes [CpRuL 3 ] + [L = CO, P(OMe) 3 , P(OEt) 3 , t BuNC] in 80–90 % yields. Complex 1 (2 mol‐%) catalyzed cyclotrimerization of dipropargyl Meldrum's acid with various alkynes RC≡CH [R = H, Bu, Hex, Ph, SiMe 3 , (CH 2 ) 4 C≡CH, (CH 2 ) 3 OH, (CH 2 ) 2 Br, CH 2 OMe, CH 2 OAc, CH 2 NMeBoc] producing benzene derivatives in 50–85 % yields. According to DFT calculations, the attack of the first ligand (Cl – or L) is a rate‐determining step in the naphthalene replacement in 1 . The activation barrier for attack of the Cl – anion 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 )] + .