Bis-Triazolylidenes of Manganese and Rhenium and Their Catalytic Application in N-Alkylation of Amines with Alcohols

Abstract

A new family of air-stable Mn and Re complexes bearing bidentate bis(1,2,3-triazol-5-ylidene) ligands with the general formula [M(bis-triazolylidene)(CO)3X] (M = Mn or Re; X = Cl or Br), containing a methylene linker or a direct link between the two triazolylidene ligands, is presented. All complexes have been applied as catalysts for the N-alkylation of anilines with benzylic alcohols. The Mn complex bearing a bis-triazolylidene with a methylene bridge between the two triazolylidene fragments was shown to be a highly efficient catalyst, affording the corresponding amine in 92% yield in the presence of a low base loading (t-BuOK, 0.1 equiv). Comparison between Mn complexes bearing imidazolium- and triazolium-derived N-heterocyclic carbene ligands showed that Mn triazolylidenes displayed higher catalytic activity when a low base loading was used.

Application of first-row transition metal complexes bearing 1,2,3-triazolylidene ligands in catalysis and beyond

“…This method is also suitable for metalation of ligand precursor L3 (R = Et) with a methylene group between the two carbene units to form manganese complex Mn3 ( Scheme 7b ). 79 These complexes showcase a combination of strategies A and B ( cf. Fig.…”

“…In addition, complexes Mn1b and Mn3 are active in the catalytic N -alkylation of amines with alcohols ( Scheme 9b ). 79 Thus, aniline alkylation with benzyl alcohol at 50 °C in the presence of KO t Bu and 1.5 mol% catalyst loading affords 42% N -benzylaniline within 24 h when complex Mn3 is used, yet only 15% yield are obtained with complex Mn1b. Increasing the temperature to 100 °C increases the yields to 99% and 45%, respectively.…”

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

“…In 2023, Royo and co-workers conveyed the N-alkylation of amines with alcohols using the bis-triazolylidene manganese complexes [ 49 ]. Complex Mn10 showed superior activity with low catalyst loading (1.5 mol %) and base (50 mol % of t -BuOK) at 100 °C for 2 h to afford the N-alkylated products ( Scheme 22 ).…”

Revealing the Mechanism of Alcohol Dehydroxylation and C–C Bond Formation through Concerted Catalysis by Ir/Cu Bimetallic Complexes

“…The Barton–McCombie reaction , marked the inception of alkyl radicals deoxygenation from alcohols. Subsequently, various methods for activating the C–O bond in alcohols have been further developed including catalysis by transition metals, − electrocatalysis, photocatalysis, and other approaches.…”