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

Abstract

Treatment of the TpRu complex (PPh 3 )[Ru]-Cl (1, [Ru] = Tp( t BuNC)Ru) with an excess of sodium azide affords the yellow ruthenium azido complex (PPh 3 )[Ru]-N 3 (2). The triazolato complexes (PPh 3 )[Ru]-N 3 C 2 (R) 2 (3a, R = Me; 3b, R = Et) are synthesized via [3+2] cycloadditions of 2 with RO 2 CCCCO 2 R. 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 CS 2 to 2 produces thermally unstable thiothiatriazolate (PPh 3 )[Ru]-N 3 CS(S) (5), which converts to the isothiocyanate complexes (PPh 3 )[Ru]-NCS (6) and ( t BuNC)[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 H 2 O to produce the carbonyl complexes (CO)[Ru]-CH 2 R (8a, R = Ph; 8b, R = 4-CH 3 Ph) through ruthenium vinylidene intermediates. Reaction of 2 with H-CC-CMe 2 OH in MeOH gives the cationic Fischer carbene complex {(PPh 3 )[Ru] C(OMe)-HCC(Me) 2 } + (10). In contrast, reaction of H-CC-CH 2 CH 2 OH gives rise to the five-membered cyclic oxycarbene complex {(PPh 3 )[Ru]C 4 H 6 O} + (11). Several cationic imine complexes {( t BuNC)[Ru]-(NHCHR′)} + (12a, R′ = H; 12b, R′ = CH 3 ; 12c, R′ = Ph) are formed by the reaction of RCH 2 X with 2. If the reaction of 2 with CH 3

Metal-catalyzed azide-alkyne “click” reactions: Mechanistic overview and recent trends

“…This is in line with Boz and Tüzün's theoretical work (see above) that indicated the importance of the electronic and steric effects for the regioselectivity, both thermodynamic and kinetic parameters playing a crucial role in the reactions [41]. Lo's group presented the first case of ruthenium azido complexes catalyzing the cycloaddition reaction of terminal alkynes with alkyl azides [90,91]. The new ruthenium azido complexes were synthesized from the mother TpRu complex [Ru(Cl)(Tp)(PPh 3 ) 2 ], Tp = HB(pz) 3 , pz = pyrazolyl), yielding first [Ru(N 3 )(PPh 3 )[Tp( t BuNC)] [90], then the amine-substituted ruthenium azido complex [Ru(N 3 )(Tp(PPh 3 )(EtNH 2 )] [91].…”

“…Lo's group presented the first case of ruthenium azido complexes catalyzing the cycloaddition reaction of terminal alkynes with alkyl azides [90,91]. The new ruthenium azido complexes were synthesized from the mother TpRu complex [Ru(Cl)(Tp)(PPh 3 ) 2 ], Tp = HB(pz) 3 , pz = pyrazolyl), yielding first [Ru(N 3 )(PPh 3 )[Tp( t BuNC)] [90], then the amine-substituted ruthenium azido complex [Ru(N 3 )(Tp(PPh 3 )(EtNH 2 )] [91]. Although the detailed mechanism could not be established, the authors speculated a similar mechanism to previous proposed by Fokin et al [28].…”

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications

“…10), was an efficient catalyst for the RuAAC reaction between benzyl azide and various terminal acetylenes. 98,99 Interestingly, the catalyst gave similar results in toluene and in water. A practical approach to RuAAC was reported by Astruc and co-workers, who prepared ruthenium complex 42 ( Fig.…”

Strain‐Promoted Azide–Alkyne Cycloaddition with Ruthenium(II)–Azido Complexes

“…Although, numerous publications have appeared on the conversion of metal-coordinated azido ligands into metal-coordinated triazolato ligands, the majority of these studies relied on alkynes as dipolarophiles that are activated by conjugation with electron-withdrawing groups, such as carboxylic esters and nitriles. [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] However, due to their high electrophilicity and susceptibility to conjugate addition, such activated dipolarophiles are incompatible with biological systems. [69][70][71][72][73] In contrast, reports on 1,3dipolar cycloadditions between metal-coordinated azido ligands and non-activated alkynes are rare.…”