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

Abstract

Ru(II) bimetallic [(p‐cymene)2(RuCl)2L1]2X (X = BF4 (Cat2); X = PF6 (Cat3)) and monometallic [(p‐cymene)(RuCl)L2]BF4 (Cat4) (where L1 = N,N'‐(3,3',5,5'‐tetraisopropyl‐[1,1'‐biphenyl]‐4,4'‐diyl)bis(1‐(pyridin‐2‐yl)methanimine); L2 = N‐(2,6‐diisopropyl‐phenyl)‐1‐(pyridin‐2‐yl)‐methanimine) catalyse selective synthesis of saturated ketones using β‐alkylation of secondary alcohol or α‐alkylation of ketones with primary alcohol. Notably, a single catalyst facilitates the oxidation of both secondary and primary alcohols followed by condensation and hydrogenation yielding α‐alkylated saturated ketones. Remarkably, this system allows catalyst loading as low as 0.01 mol% for β‐alkylation of secondary alcohols and 0.005 mol% for the α‐alkylation of ketone, delivering access to a wide array of α‐alkylated ketones derivatives with yields of ~ 97%. Complex Cat2, in particular, orchestrates one‐pot alkylation reactions with a high turnover frequency (TOF) of 5.6  105 h‐1 using as low as low catalyst loading of 0.0001 mol%. A comparative study between bimetallic and monometallic complexes reveals that complex Cat2 exhibits better selectivity for the formation of saturated ketones presumably owing to a cooperative effect between the metal centres. The scale‐up synthesis highlights the practical applicability of the catalytic approach. To delve into the plausible mechanisms, we conducted initial investigations through meticulously controlled experiments and spectroscopic analysis.