Electronically tuneable orthometalated RuII–NHC complexes as efficient catalysts for C–C and C–N bond formations via borrowing hydrogen strategy. Issue 1 (29th November 2021)

• Record Type: Journal Article
• Authors: Illam, Praseetha Mathoor; Rit, Arnab
• Is Part Of: Catalysis science & technology. Volume 12:Issue 1(2022)
• Page Start: 67
• Page End: 74
• Publication Date: 2021-11-29
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d1cy01767e
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : A series of simple and electronically tuneable cyclometalated Ru II –NHC complexes have been explored as efficient catalysts for various C–C/N bond forming reactions via a BH methodology. Abstract : The catalytic activities of a series of simple and electronically tuneable cyclometalated Ru II –NHC complexes (2a–d ) were explored in various C–C/N bond formations following the borrowing hydrogen process. Slight modifications in the ligand backbone were noted to tune the activities of these complexes. Among them, the complex 2d featuring a 1, 2, 4-triazolylidene donor with a 4-NO2 –phenyl substituent displayed the highest activity for the coupling of diverse secondary and primary alcohols with a low catalyst loading of 0.01 mol% and a sub-stoichiometric amount of inexpensive KOH base. The efficacy of this simple system was further showcased in the challenging one-pot unsymmetrical double alkylation of secondary alcohols using different primary alcohols. Moreover, the complex 2d also effectively catalyses the selective mono- N -methylation of various aromatic and aliphatic primary amines using methanol to deliver a range of N -methyl amines. Mechanistically, the β-alkylation reaction follows a borrowing hydrogen pathway which was established by the deuterium labelling experiment in combination with various control experiments. Intriguingly, in situ 1 H NMR and ESI-MS analyses evidently suggested the involvement of a Ru–H species in the catalytic cycle and further, the kinetic studies revealed a first order dependence of the reaction rate on the catalyst as well as the alcohol concentrations.