Phenoxy-Linked Mesoionic Triazol-5-ylidenes as Platforms for Multinuclear Transition Metal Complexes

Abstract

The preparation and full characterization of a variety of mono-([L1-H]), di-([L2-H 2 ], [L2A-H2]), and tri-([L3-H 3 ]) 1,2,3-triazolium salts constructed form "clicked" hydroxybenzene derivatives are reported. Deprotonation with potassium hexamethyldisilazide, followed by in situ metalation, allowed for the synthesis of a series of mono-(L1•[M]), di-(L2•[M] 2 , L2•[M] 2 ), and trinuclear (L3•[M] 3 ) group 9−11 (M = [Rh(CO) 2 Cl], [Pd(allyl)Cl], and [AuCl]) triazol-5-ylidene metal complexes. In solution, all metal complexes feature symmetrical patterns displaying C 2 and C 3 fold axes when supported by di-and tritriazol-5-ylidene ligands. The vibration frequencies of Ln•[Rh(CO) 2 Cl] n (n = 1−3) complexes indicate that the electron-donor properties of the new ligands are comparable to those for previously reported MIC complexes and superior to classical NHCs. Prompting coordination of the vicinal phenoxy group to the metal centers proved unsuccessful after treatment of the Ln•[Rh(CO) 2 Cl] n and Ln•[Pd(allyl)Cl] n (n = 1−3) precursors with AgBF 4 ; the expected chelated cationic complexes were highly unstable, indicating a weak or no coordination availability through the oxygen atom. Crystal structures of the complexes L1•[AuI] and L2A•[Pd(allyl)I] 2 illustrated the metal center geometrical environment and confirmed the lack of coordination through the phenoxy moiety of the ligand. Preliminary catalytic trials established the enhanced performance of di-and trimetallic palladium complexes in cross-coupling reactions and the intramolecular cyclization of enynes catalyzed by gold complexes.

Synthesis and Catalytic Applications of Palladium(II) Complexes Supported by Hydroxyl‐Functionalized Triazolylidenes

“…Initial reaction conditions included loading of 5 mol‐% of the appropriate precatalyst, NaO t Bu as the base, tetrahydrofuran, and 12 h of reaction at 100 °C. [10a] As observed in Table , the cinnamyl palladium complexes 4 and 5 are the most active of the series with yields over 99 %. Complex 6 led to moderate cross coupling reaction yields (< 72 %) and interestingly, the allyl‐substituted complexes 1 – 3 show the lowest conversions (< 53 %).…”

“…The synthesis of the 1,2,3‐triazolium salt precursors A – C was performed according to the literature procedure by means of a copper catalyzed cycloaddition (CuAAC) of mesityl azide with the appropriate propargyl alcohol, followed by N‐quaternarization with methyl iodide. [10b] The preparation of the palladium complexes relied in the one pot reaction of the triazolium precursors A – C with a slight excess of potassium hexamethyl disilazane and half equivalent of appropriate the palladium dimer in tetrahydrofuran. This procedure provides the respective palladium complexes 1 – 6 in a single step without the need of free MIC species isolation.…”

“…In order to investigate the effect of the hydroxyl pendant arm featured in complexes 4 and 5 , their catalytic efficiencies in the coupling of chloroanisole with phenylboronic acid were compared with a phenoxy‐functionalized complex containing an allyl group ( 7 ),[10a] and a non‐oxygen functionalized version with a cinnamyl moiety ( 8 ) (Figure ).…”

“…Triazolium salts A – C were synthesized as reported in the literature. [10b] Synthesis of all metal complexes was performed under an atmosphere of dry nitrogen using standard Schlenk techniques. Solvents were dried by standard methods and distilled under nitrogen.…”

Synthesis of the First Resorcin[4]arene-Functionalized Triazolium Salts and Their Use in Suzuki–Miyaura Cross-Coupling Reactions

“…Their precursors, namely 1,2,3-triazoles, are easily accessible through copper-catalyzed Huisgen [3 + 2] click-type cycloaddition of azides and alkynes (CuAAC) [6,7], followed by N3-quaternarization. The resulting 1,2,3-triazolium salts can then be converted to transition metal complexes that, i.a., are suitable for Suzuki-Miyaura [8][9][10][11][12][13][14][15][16][17][18], Mizoroki-Heck [19,20], and Sonogashira coupling reactions [19,21], as well as for various reduction or oxidation reactions [22][23][24][25][26][27], and C-heteroatom bond forming reactions [28][29][30][31][32].…”