Selective synthesis of cyclic alcohols from cycloalkanes using nickel() complexes of tetradentate amidate ligands

• Published in: RSC advances 2024-09, Vol.14 (41), p.344-3451
• Main Authors: Rajeev, Anjana, Muthuramalingam, Sethuraman, Sankaralingam, Muniyandi
• Format: Article
• Language: English
• Subjects: Alcohols; Catalysts; Catalytic activity; Chemical bonds; Chemical synthesis; Chemistry; Coordination compounds; Cycle ratio; Cycloalkanes; Cyclohexane; Ligands; Methylcyclohexane; Nickel; Oxidation; Oxidizing agents; Substrates; Transition metal compounds
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d4ra05222f

Selective functionalisation of hydrocarbons using transition metal complexes has evoked significant research interest in industrial chemistry. However, selective oxidation of unactivated aliphatic C-H bonds is challenging because of the high bond dissociation energies. Herein, we report the synthesis, characterisation and catalytic activity of nickel( ii ) complexes ([Ni( L1-L3 )(OH 2 ) 2 ](ClO 4 ) 2 ( 1-3 )) of monoamidate tetradentate ligands [ L1 : 2-(bis(pyridin-2-ylmethyl)amino)- N -phenylacetamide, L2 : 2-(bis(2-pyridin-2-ylmethyl)amino)- N -(naphthalen-1-yl)acetamide, L3 : N -benzyl-2-(bis(pyridin-2-ylmethyl)amino)acetamide] in selective oxidation of cycloalkanes using m -CPBA as the oxidant. In cyclohexane oxidation, catalysts showed activity (TON) in the order 1 (654) > 2 (589) > 3 (359) with a high A/(K + L) ratio up to 23.6. Using catalyst 1 , the substrate scope of the reaction was broadened by including other cycloalkanes such as cyclopentane, cycloheptane, cyclooctane, adamantane and methylcyclohexane. Further, the Fenton-type reaction in the catalytic cycle was discarded based on the relatively high 3°/2° ratio of 8.6 in adamantane oxidation. Although the formation of chlorinated products during the reactions confirmed the contribution of the 3-chlorobenzoyloxy radical mechanism, the high alcohol selectivity obtained for the reactions indicated the participation of nickel-based oxidants in the oxidation process. Selective synthesis of cyclic alcohols catalysed by nickel( ii ) complexes of tetradentate amidate ligands.