Synthesis of Triazolylidene Nickel Complexes and Their Catalytic Application in Selective Aldehyde Hydrosilylation

Abstract

A set of nickel­(II) Cp complexes with triazolylidenes containing various different wingtip groups (aryl, alkyl, pyridyl, CH2OH) have been synthesized by direct metalation of the corresponding triazolium salt with nickelocene. Distinct effects of the substituents on electronic and steric properties of the formed complexes are demonstrated by NMR spectroscopy and single-crystal structural analysis, as well as by the catalytic activity of the complexes in the hydrosilylation of aldehydes. While all complexes display appreciable catalytic performance, the cyclometalated pyridyl-functionalized triazolylidene nickel complex 2e is highly active and reaches turnover frequencies of >20 000 h–1 with good catalyst stability (full conversion at 0.05 mol % catalyst, maximum turnovers of ∼6000). A variety of functional groups on the benzaldehyde are tolerated. Ketones are not converted, which identifies complex 2e as a highly selective precatalyst for the hydrosilylation of aldehydes in the presence of ketones.

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

“…A trinuclear nickel complex, 106 , containing additional cyclopentadienyl (Cp) ligands was also recently reported. [96a] The most recent report on nickel complexes, 107 and 108 , deals with the use of bidentate ligands of type L19a/L20a . These complexes were synthesized by the direct reaction of triazolium salts with NiCp 2 , with one of the Cp ligands acting as a base for the deprotonation of the triazolium salts.…”

“…These complexes were synthesized by the direct reaction of triazolium salts with NiCp 2 , with one of the Cp ligands acting as a base for the deprotonation of the triazolium salts. Inclusion of an additional pyridyl donor seems to impart additional stability to the nickel complexes, 107 + and 108 + . These nickel complexes were used as pre‐catalysts for the reduction of aldehydes to alcohols through hydrosilylation.…”

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].…”

“…], as well as for various reduction or oxidation reactions [22][23][24][25][26][27], and C-heteroatom b ng reactions [28][29][30][31][32].…”

Palladium(II), Rhodium(I), and Iridium(I) Complexes Containing O‐Functionalized 1,2,3‐Triazol‐5‐ylidene Ligands

“…In contrast to imidazole‐derived NHCs, triazolylidenes can be functionalized on the β‐position relative to the carbene. We have therefore become interested in probing the synthesis and catalytic applications of O ‐functionalized wingtips adjacent to the carbene , . Here we report on the synthesis and metalation of a range of triazolylidene ligand precursors containing O‐ functionalized wingtip groups including esters, ethers, and alcohols.…”