Substantial progress in ruthenium-catalyzed cycloadditions of organic azides and alkynes are reported. A series of ruthenium(II) complexes have been evaluated as the catalytic precursors for cycloaddition reactions of azides with alkynes. The catalytic activity of the ruthenium complexes and regioselectivity of the catalytic reactions were found to be dependent on the ligand environment around ruthenium. The Cp*RuCl complexes such as Cp*RuCl(PPh₃)₂, Cp*RuCl(COD) and Cp*RuCl(NBD) are effective at promoting the [3+2] cycloaddition. Under the influence of Cp*RuCl(PPh₃)₂ and Cp*RuCl(COD), alkylazides readily react with terminal alkynes to give selectively 1,5-disubstituted triazoles. The catalytic reactions proceed easily at room temperature. The present Cp*RuCl system can also catalyze the...[ Read more ]

Substantial progress in ruthenium-catalyzed cycloadditions of organic azides and alkynes are reported. A series of ruthenium(II) complexes have been evaluated as the catalytic precursors for cycloaddition reactions of azides with alkynes. The catalytic activity of the ruthenium complexes and regioselectivity of the catalytic reactions were found to be dependent on the ligand environment around ruthenium. The Cp*RuCl complexes such as Cp*RuCl(PPh₃)₂, Cp*RuCl(COD) and Cp*RuCl(NBD) are effective at promoting the [3+2] cycloaddition. Under the influence of Cp*RuCl(PPh₃)₂ and Cp*RuCl(COD), alkylazides readily react with terminal alkynes to give selectively 1,5-disubstituted triazoles. The catalytic reactions proceed easily at room temperature. The present Cp*RuCl system can also catalyze the reactions of alkylazides with internal alkynes to provide 1,4,5-trisubstituted triazoles. However, the catalytic activity could be deactivated due to the formation of catalytically inactive tetrazene complexes.

DFT calculations suggest that the Cp*Ru(II)-catalyzed cycloaddition reactions of azides with alkynes involves oxidative coupling of azides and alkynes to give metallacycles, followed by a rate-determining reductive elimination. The proposed mechanism is approved by the isolation of the complexes Cp*RuCl{η³-NH(R²)NNCH=C(OR)(R¹)}(R = Me or Et; R¹ = Bu, Ph or –C₁₀H₇; R² = -C₆H₄Me or -CH₂Ph).

In the second part of this thesis, we studied the cyclometallation of 2-vinylpyridine with MCl₂(PPh₃)₃ and MHCl(PPh₃)₃ (M = Ru, Os). Treatment of RuCl₂(PPh₃)₃ in benzene at room temperature with 2-vinylpyridine produces the vinylpyridine complex RuCl₂(2-CH₂=CHC₅H₃N)(PPh₃)₂. In the presence of Cs₂CO₃, RuCl₂(PPh₃)₃ reacts with 2-vinylpyridine at room temperature to give the cyclometallated complex RuCl(CH=CHC₅H₄N)(CH₂=CHC₅H₄N)(PPh₃), which is also produced from the reaction of RuHCl(PPh₃)₃ with 2-vinylpyridine. OsCl₂(PPh₃)₃ reacts with 2-vinylpyridine/Cs₂CO₃ at room temperature to give the analogous cyclometallated complex OsCl(CH=CHC₅H₄N)(CH₂=CHC₅H₄N)(PPh₃). In the presence of NaBF₄, the reaction produces [Os(CH=CHC₅H₄N)(CH₂=CHC₅H₄N)(PPh₃)₂]BF₄. The dihydrogen complex Os(H₂)Cl(CH=CHC₅H₄N)(PPh₃)₂ is produced from the reaction of OsHCl(PPh₃)₃ with 2-vinylpyridine.