Coordinatively Unsaturated Ruthenium Complexes As Efficient Alkyne–Azide Cycloaddition Catalysts

The performance of 16-electron ruthenium complexes with the general formula Cp*Ru(L)X (in which L = phosphine or N-heterocyclic carbene ligand; X = Cl or OCH2CF3) was explored in azide-alkyne cycloaddition reactions that afford the 1,2,3-triazole products. The scope of the Cp*Ru((PPr3)-Pr-i)Cl precatalyst was investigated for terminal alkynes leading to new 1,5-disubstituted 1,2,3-triazoles in high yields. Mechanistic studies were conducted and revealed a number of proposed intermediates. Cp*Ru((PPr3)-Pr-i)(eta(2)-HCCPh)Cl was observed and characterized by H-1, C-13, and P-31 NMR at temperatures between 273 and 213 K. A rare example of N,N-kappa(2)-phosphazide complex, Cp*Ru(kappa(2)-(Pr3PN3Bn)-Pr-i)Cl, was fully characterized, and a single-crystal X-ray diffraction structure was obtained. DFT calculations describe a complete map of the catalytic reactivity with phenylacetylene and/or benzylazide,