Coordinatively Unsaturated Ruthenium Complexes As Efficient Alkyne–Azide Cycloaddition Catalysts

Abstract

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 OCH 2 CF 3 ) was explored in azide–alkyne cycloaddition reactions that afford the 1,2,3-triazole products. The scope of the Cp*Ru(P i Pr 3 )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(P i Pr 3 )(η 2 -HCCPh)Cl was observed and characterized by 1 H, 13 C, and 31 P NMR at temperatures between 273 and 213 K. A rare example of N, N -κ 2 -phosphazide complex, Cp*Ru(κ 2 - i Pr 3 PN 3 Bn)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.