Ruthenium(II) Picolyl-NHC Complexes: Synthesis, Characterization, and Catalytic Activity in Amine N-alkylation and Transfer Hydrogenation Reactions

Abstract

Ruthenium(II) p-cymene complexes with picolylfunctionalized N-heterocyclic carbenes [(η 6 -p- (1g)) have been synthesized and characterized. Compounds 1a−g were recrystallized, and X-ray crystal structures are reported for 1a,f. Furthermore, compounds 1a−f show catalytic activity in transfer hydrogenation of ketones and N-alkylation of amines. Notably, complexes 1a,c,f were found to be very efficient and versatile catalysts toward transfer hydrogenation of a wide range of ketones and imines in addition to N-alkylation of several amines.

Synthesis and Structures of Arene Ruthenium (II)–NHC Complexes: Efficient Catalytic α‐alkylation of ketones via Hydrogen Auto Transfer Reaction

“…At this juncture, we also studied the effect of wingtip group of the complexes 2a‐f in the α‐alkylation reaction. From these experimental observations, the complex 2a showed an excellent catalytic performance with 92% yield and outperformed other complexes in the formation of alkylated product (Table ; entries 13–18), indeed the complexes having smaller wingtip in NHC22a, b along with lability of arene moiety22c probably influence the hydrogen borrowing process in α‐alkylation reactions when compared to bulky wingtips. Also, the catalytic activity of 2c and 2f (Table ; entries 15 and 18) showed a sluggishness in the formation of appreciable yield, this behavior represents the possible π‐coordination22d of benzyl wingtip to the ruthenium atom on removal of arene moieties or other ligands under the catalytic conditions, thus hindering the coordination and further activation of substrates and intermediates.…”

N-Propylphthalimide-Substituted Silver(I) N-Heterocyclic Carbene Complexes and Ruthenium(II) N-Heterocyclic Carbene Complexes: Synthesis and Transfer Hydrogenation of Ketones

“…Typical results are summarized in Table 1. When compared with similar studies, particularly in terms of reaction time [39][40][41][42][43], all complexes 3a-f seem to be reasonably active in transfer hydrogenation reactions. Generally, all complexes 3a-f are seen to be reasonably active in hydrogen transfer reactions.…”

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

“…At catalyst loadings of 0.01 mol %, TOF of 1 – 3 are 3000, 3233, and 3200 h −1 for transfer hydrogenation of acetophenone which are nearly identical to that of [Ru( Me CC meth ) 2 (CH 3 CN) 2 ](BF 4 ) 2 ( Me CC meth = 1,1'-dimethyl-3,3'-methylene-diimidazol-2,2'-diylidene) [40]. Ruthenium picolyl–NHC complex [( η 5 -C 5 Me 5 )-Ru(L)(CH 3 CN)][PF 6 ] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene) is so far one of the most efficient catalyst for transfer hydrogenation of acetophenone which gave 1-phenylethanol in a conversion of 93% with a catalyst loading of 0.1 mol % [20,41]. When the same amount of complexes 1 – 3 was used, the reaction gave 1-phenylethanol in 89%, 99% and 99% yields, respectively.…”