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