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

Abstract

A panel of six new arene Ru (II)-NHC complexes 2a-f, (NHC = 1,6dimethyl)benzimidazolin-2-ylidene 1a, 1,3-dicyclohexylmethyl-(5,6-dimethyl) benzimidazolin-2-ylidene 1b and 1,3-dibenzyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1c) were synthesized from the transmetallation reaction of Ag-NHC with [(η 6 -arene)RuCl 2 ] 2 and characterized. The ruthenium (II)-NHC complexes 2a-f were developed as effective catalysts for α-alkylation of ketones and synthesis of bioactive quinoline using primary/amino alcohols as coupling partners respectively. The reactions were performed with 0.5 mol% catalyst load in 8 h under aerobic condition and the maximum yield was up to 96%. Besides, the different alkyl wingtips on NHC and arene moieties were studied to differentiate the catalytic robustness of the complexes in the transformations.

Efficient Organoruthenium Catalysts for α‐Alkylation of Ketones and Amide with Alcohols: Synthesis of Quinolines via Hydrogen Borrowing Strategy and their Mechanistic Studies

“…1‐(4‐bromophenyl)‐3‐phenylpropan‐1‐one (3 ae) Yield 260.2 mg 90 % (Catalyst Ru1 ), 274.7 mg 95 % (Catalyst Ru2 ); 1 H NMR (400 MHz, CDCl 3 ) δ 7.80 (d, J =8.7 Hz, 2H), 7.58 (d, J =8.6 Hz, 2H), 7.31–7.26 (m, 2H), 7.21 (d, J =8.6 Hz, 2H), 3.25 (t, J =7.8 Hz, 2H), 3.04(t, J =7.8 Hz, 2H). 13 C‐NMR (101 MHz, CDCl 3 ) δ 200.19, 135.63, 132.00, 129.65, 128.65, 128.48, 126.31, 125.08, 40.50, 30.11.…”

“…2‐(naphthalen‐1‐yl)quinoline (5 j) Yield 234.9 mg 92 % (Catalyst Ru2 ), 229.8 mg 90 % (Catalyst Ru3 ); 1 H NMR (500 MHz, CDCl 3 ) δ 8.60 (s, 1H), 8.36 (d, J =8.5 Hz, 1H), 8.25 (d, J =8.6 Hz, 1H), 8.21 (d, J =8.5 Hz, 1H), 8.03–7.98 (m, 3H), 7.89–7.87 (m, 2H), 7.74 (t, J =7.6 Hz, 1H), 7.53 (t, J =7.4 Hz, 3H). 13 C NMR (126 MHz, CDCl 3 ) δ 157.20 (s), 148.40, 136.98, 136.83, 133.88, 133.52, 129.75, 128.85, 128.60, 127.74, 127.52, 127.21, 126.73, 126.35, 125.09, 119.19.…”

“…1,2,3,4‐tetrahydroacridine (5 n) Yield 164.9 mg 90 % (Catalyst Ru2 ), 170.4 mg 93 % (Catalyst Ru3 ); 1 H NMR (400 MHz, CDCl 3 ) δ 7.95 (d, J =8.4 Hz, 1H), 7.72 (s, 1H), 7.63 (d, J =9.2 Hz, 1H), 7.57 (d, J =6.9 Hz, 1H), 7.39 (d, J =8.0 Hz, 1H), 3.09 (t, J =6.6 Hz, 2H), 2.91 (t, J =6.3 Hz, 2H), 1.97–1.92 (m, 2H), 1.86–1.80 (m, 2H). 13 C NMR (101 MHz, CDCl 3 ) δ 159.34, 146.66, 135.06, 131.02, 128.52, 128.30, 127.26., 126.95, 125.56, 33.62, 29.30, 23.29.…”

Ruthenium(II) Complexes of Heteroditopic N-Heterocyclic Carbene Ligands: Efficient Catalysts for C–N Bond Formation via a Hydrogen-Borrowing Strategy under Solvent-Free Conditions

“…Electrospray ionization mass spectrometry (ESI-MS) spectra of the complexes that exhibit only peaks corresponding to the [M – BF 4 ] + ion, with isotopic patterns in perfect agreement with the calculated patterns, further foster complex formation, which is validated by a single-crystal X-ray diffraction study of a crystal of 3d (obtained by the slow diffusion of pentane into a saturated solution of the complex in dichloromethane). The complex possesses a typical piano-stool structure, and the pseudooctahedral geometry around the metal center is occupied by a p -cymene ligand and one chloride ligand and the other two sites are occupied by two carbene donors from the chelating ligand …”

Nickel(II)–NΛNΛO Pincer Type Complex-Catalyzed N-alkylation of Amines with Alcohols via the Hydrogen Autotransfer Reaction

“…In continuation to our previous reports on the catalytic activity of metal complexes for various coupling reactions, herein we report the Ni­(II)-N Λ N Λ O pincer type complexes as homogeneous catalysts for alcohol amination reactions (Scheme b). The feature of the present approach merits attention as it is eco-friendly due to the use of readily available less toxic alcohols and elimination of water as the only byproduct.…”