Direct Aerobic Strategy for Synthesis of Imines via Alcohols and Amines Promoted by Ruthenium(II) (η⁶‐p‐cymene) Complexes

Abstract

Neutral ruthenium(II) p‐cymene complexes were synthesised by complexation of [Ru(η6‐p‐cymene)(μ‐Cl)Cl]2 with substituted methyl‐2‐pyrrolyl ketone benzhydrazone ligands in good yields. The characterization of the synthesised complexes was accomplished by analytical and spectroscopic techniques (FT‐IR, UV‐Vis, NMR, and ESI‐MS). Crystal structures of two of the complexes exhibited that the hydrazone ligand was bonded to ruthenium ion in a bidentate fashion via imine nitrogen and imidolate oxygen and witnessed ruthenium centered pseudo‐octahedral geometry. The catalytic feasibility of these Ru(II) complexes was explored for the direct aerobic synthesis of imine from the coupling of alcohols and amines in toluene medium with Cs2CO3 as a base without molecular sieves or any additives. The scope and versatility of the present catalytic system were performed with the diverse range of alcohols and amines such as primary/secondary aromatic, aliphatic, heteroaromatic, cyclic as well as chiral substrates under open atmospheric condition. Further, the tolerance of steric and electronic effects on substrates was evaluated. Besides, the effect of promoters on the reaction including solvents, bases, temperatures and catalyst loading was carried out as well.

New ruthenium(ii) catalysts enable the synthesis of 2-amino-4H-chromenes using primary alcohols via acceptorless dehydrogenative coupling

“…The Ru-Cl has a bond length of 2.4093(16) Å and a Ru-centroid distance of 1.677 Å which is comparable with other reported p-cymene ruthenium(II) complexes. 24 Therefore, the single crystal XRD studies corroborated the binding of the hydrazone ligand with the Ru(II) ion through the ylidene nitrogen and imidolate oxygen to form a five-membered metallacycle. The residual sites of the octahedron have been occupied by p-cymene and chloride ligands resulting in the formation of a piano-stool geometry.…”

NNO Pincer Ligand-Supported Palladium(II) Complexes: Direct Synthesis of Quinazolines via Acceptorless Double Dehydrogenative Coupling of Alcohols

“…The condensation reaction of methyl-2-pyrroleketone with substituted benzhydrazides in equimolar ratios yielded benzhydrazone ligand derivatives as reported in the literature. 22 The obtained ligand derivatives were reacted with an equimolar ratio of the Pd(II) precursor, [PdCl 2 (PPh 3 ) 2 ], in the presence of Et 3 N as a base. The above reaction yielded 85− 89% of complexes with general formula [Pd(L)(PPh 3 )] (Scheme 2).…”

Ru(II)–NNO pincer‐type complexes catalysed E‐olefination of alkyl‐substituted quinolines/pyrazines utilizing primary alcohols

“…The simple NNO pincer‐type ligands (L1–L3) were easily prepared from condensation methyl‐2‐pyrrole and 4‐substituted benzohydrazides in methanol. [ 18 ] The synthesis of Ru(II)–NNO pincer‐type complexes was accomplished in good yield from the reaction of [RuHClCO(AsPh 3 ) 3 ] with the prepared ligands in 1:1 molar ratio in benzene medium using Et 3 N as a base (Scheme 2). The synthesized Ru(II)–NNO pincer‐type complexes are stable in air and can be dissolved in most organic solvents.…”