We developed ruthenium-catalyzed cycloisomerization of alkynylanilides that gave 3-substituted indoles in high yields. The reaction proceeded via the disubstituted vinylidene ruthenium complex that was formed by the 1,2-carbon migration.

The first tellurocarbonyl complex with a half-sandwich structure [CpRuCl(CTe)(H2IMes)] was synthesized by a ligand substitution reaction. The practically complete series of the CpCE complexes [CpRuCl(CE)(H2IMes)] (E = O, S, Se, Te) were systematically explored. The tellurium atom in the CTe complex could be smoothly replaced with lighter chalcogen atoms.

Although molecular thioamide complexes of late-transition metals have been prepared since 1979, the chemistry of primary thioamide complexes remains relatively unexplored. To shed light on this area, we have investigated synthesis, structures, and reactivities of simple rhodium organometallic complexes with a primary arenecarbothioamide ligand [Cp*RhCl2{S═C(Ar)NH2-κ1S}] (Cp* = η5-C5Me5). Intra- and intermolecular hydrogen bonding in the thioamide complexes is discussed on the basis of 1H NMR spectroscopy and X-ray analysis. When these rhodium complexes were treated with a large excess amount of Et3N, desulfurization of the thioamide ligand took place to give arenecarbonitriles (ArCN) in high GC yield and the cubane-type cluster [(Cp*Rh)4(μ3-S)4] (3) in good yield as the organometallic product. Use of a smaller amount (2.4 equiv) of Et3N followed by treatment with NaBArF4 (ArF = 3,5-(CF3)2C6H3) led to the isolation of the cationic clusters [(Cp*Rh)4(μ3-S)4](BArF4) or [(Cp*Rh)4(μ3-S)4](BArF4)2 in low yield. Reaction mechanisms of the desulfurization of the coordinated thioamides and the formation and one- or two-electron oxidation of 3 during the desulfurization are discussed.

Reaction of the indenylruthenium complex [(η5-C9H7)RuCl(dppe)] with internal alkynes (MeC≡CR, R = Et, Ph) in the presence of NaBArF4 gives rise to two types of C–C bond activation, i.e., alkyne insertion/β-carbon elimination and internal alkyne/disubstituted vinylidene rearrangement, as reversible processes. At 70 °C, regioisomeric complexes [Ru{C(Me)═C(R)–(η6-C9H7)}(dppe)][BArF4] (2) and [Ru{C(R)═C(Me)–(η6-C9H7)}(dppe)][BArF4] (2′) are formed through insertion of the alkyne into the Ru–indenyl bond followed by haptotropic rearrangement. Complexes 2′ isomerize completely to 2 at this temperature after longer reaction time. At 130 °C, 2 are further converted into the disubstituted vinylidene complexes [(η5-C9H7)Ru{═C═C(R)Me}(dppe)][BArF4] (3) through alkyne–vinylidene rearrangement of the η2-alkyne intermediate. This provides a rare example of direct observation of the β-carbon elimination from an unstrained transition metal alkenyl complex.

The reaction of diphenylacetylene at a cationic ruthenium complex with a dppm (Ph2PCH2PPh2) ligand, [CpRu(dppm)]+, has been studied to reveal essentially for the first time the existence of an equilibrium between an η2-internal alkyne and η1-disubstituted vinylidene at a transition metal center. The reaction mixture at 70 °C for 69 h unexpectedly afforded a coupling product of diphenylacetylene and the dppm ligand, an (alkenylphosphonio)phenyl complex [CpRu{Ph2PCH2P(C6H4)Ph(η2-C(Ph)═CHPh)}]+ with the extremely rare coordination mode of κ1P,η1C,η2C,C′. The (alkenylphosphonio)phenyl complex further undergoes inversion of the coordination face of the alkene moiety at p-xylene reflux temperature. Both isomers of (alkenylphosphonio)phenyl complexes as well as the intermediary η2-internal alkyne and η1-disubstituted vinylidene complexes were fully characterized spectroscopically and crystallographically. By considering the structure of the (alkenylphosphonio)phenyl complexes obtained, the coupling reaction has been proposed to involve the attack of a phosphorus atom on the coordinated diphenylacetylene, which is in equilibrium with an η1-diphenylvinylidene ligand, and the C–H bond activation of a phenyl group on the cationic phosphorus atom leading to the products. Theoretical calculations support the proposed mechanism.

The first tellurocarbonyl complex with a half-sandwich structure [CpRuCl(CTe)(H2IMes)] was synthesized by a ligand substitution reaction. The practically complete series of the CpCE complexes [CpRuCl(CE)(H2IMes)] (E = O, S, Se, Te) were systematically explored. The tellurium atom in the CTe complex could be smoothly replaced with lighter chalcogen atoms.