Ruthenium Complexes Bearing α-Diimine Ligands and Their Catalytic Applications in N-Alkylation of Amines, α-Alkylation of Ketones, and β-Alkylation of Secondary Alcohols

Abstract

New Ru(II) complexes encompassing α-diimine ligands were synthesized by reacting ruthenium precursors with α-diimine hydrazones. The new ligands and Ru(II) complexes were analyzed by analytical and various spectroscopic methods. The molecular structures of L 1 and complexes 1 , 3 , and 4 were determined by single-crystal XRD studies. The results reveal a distorted octahedral geometry around the Ru(II) ion for all complexes. Moreover, the new ruthenium complexes show efficient catalytic activity toward the C–N and C–C coupling reaction involving alcohols. Particularly, complex 3 demonstrates effective conversion in N-alkylation of aromatic amines, α-alkylation of ketones, and β-alkylation of alcohols.

Recent advances in cross-coupling of alcohols via borrowing hydrogen catalysis

“…34 As observed, the Ru-6 complex having a pendant thiazolyl group, Scheme 6 Ruthenium-catalysed cross b-alkylation of secondary and primary alcohols (ref. [30][31][32][33][34][35][36][37][38][39][40].…”

“…However, Ru-8 proved to be the best catalyst for balkylation of secondary alcohols. 36 N-heterocyclic carbenes are promising ligands due to their s-donation properties and have been employed for the crossalkylation of secondary alcohols with primary alcohols. Rit and co-workers, in 2022, utilized this concept and designed a chelating ligand with an NHC donor.…”

Bimetallic Ru(II) Complex Catalysed β‐Alkylation of Secondary Alcohols and α‐Alkylation of Ketones: Selective Formation of Saturated Ketones

“…[24] Recent studies have explored the use of various transition metal catalysts, including Ru, Rh, Ir, Pd, and other first-row transition metals for β-alkylation of secondary alcohols using the BH strategy (Scheme 1). [25][26][27][28][29][30][31] Despite the numerous catalysts employed, the primary challenge remains in achieving the desired selectivity. In many of these reports, the reaction tends to predominantly yield saturated alcohols instead of ketones.…”

β‐Alkylation through Dehydrogenative Coupling of Primary Alcohols and Secondary Alcohols Catalyzed by Thioether‐Functionalized N‐Heterocyclic Carbene Ruthenium Complexes

“…Different families of mainly pincer ligands (PCP, [13e] NNN, [15g,16] NPN, [8b] NNP [17] and NNC, [17] ) or tridentate Tp ligands [15d] have been successfully developed for this transformation. Bidentate ligands have been also investigated trough α‐diimine [18] or bipyridine motif [10b,17] . Well‐established N‐heterocyclic carbene (NHC) ligands have also been investigated due to their high versatility and their strong σ‐donation to the metal.…”