Preparation, Characterization, and Reactivity of Azido Complex Containing a Tp(tBuNC)(PPh3)Ru Fragment and Ruthenium-Catalyzed Cycloaddition of Organic Azides with Alkynes in Organic and Aqueous Media

Treatment of the TpRu complex (PPh3)­[Ru]-Cl (1, [Ru] = Tp­(tBuNC)­Ru) with an excess of sodium azide affords the yellow ruthenium azido complex (PPh3)­[Ru]-N3 (2). The triazolato complexes (PPh3)­[Ru]-N3C2(R)2 (3a, R = Me; 3b, R = Et) are synthesized via [3+2] cycloadditions of 2 with RO2CCCCO2R. Complete characterization of these triazolato complexes elucidates the structures and establishes the N(2)-bonding type of the addition products. Alkylation of 3a with organic bromides causes cleavage of the Ru–N bond and affords 1,4,5-trisubstituted triazoles. Moreover, addition of CS2 to 2 produces thermally unstable thiothiatriazolate (PPh3)­[Ru]-N3CS­(S) (5), which converts to the isothiocyanate complexes (PPh3)­[Ru]-NCS (6) and (tBuNC)­[Ru]-NCS (7). Other reagents also react with 2, but the products do not result from [3+2] cycloadditions. Terminal alkynes undergo ligand substitution reactions rather than a [3+2] cycloaddition with 2 in the presence of H2O to produce the carbonyl complexes (CO)­[Ru]-CH2R (8a, R = Ph; 8b, R = 4-CH3Ph) through ruthenium vinylidene intermediates. Reaction of 2 with H-CC-CMe2OH in MeOH gives the cationic Fischer carbene complex {(PPh3)­[Ru]C­(OMe)-HCC­(Me)2}+ (10). In contrast, reaction of H-CC-CH2CH2OH gives rise to the five-membered cyclic oxycarbene complex {(PPh3)­[Ru]C4H6O}+ (11). Several cationic imine complexes {(tBuNC)­[Ru]-(NHCHR′)}+ (12a, R′ = H; 12b, R′ = CH3; 12c, R′ = Ph) are formed by the reaction of RCH2X with 2. If the reaction of 2 with CH3I is carried out at 35 °C for 24 h, (tBuNC)­[Ru]-I (13) could be isolated. Preliminary results on the catalytic activity of 2 are also presented. Complex 2 catalyzes cycloaddition of alkynes and benzyl azide to give the triazoles in organic and aqueous medium. The structures of 1, 2, 3a, 7, 8a, 10, 11, 12b, 12c, and 13 have been determined by X-ray diffraction analysis.