A sugar-derived ligand for room temperature aerial oxidation or non-aqueous Markovnikov hydration of styrenes using a preformed or generated Co complex

• Published in: Catalysis science & technology 2024-08, Vol.14 (16), p.4487-4495
• Main Authors: Pandey, Sachchida Nand, Sengupta, Arunava, Bera, Rajib, Ali, Sohel, Yadav, Somnath
• Format: Article
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d4cy00522h

The oxidation of styrenes to acetophenones is an industrially relevant transformation that has been traditionally conducted with the Wacker-type reaction using pure oxygen at high temperature and pressure using Pd-Cu catalysts. Herein, we report a Co( ii ) complex of a salen appended l -diaminoribose-derived ligand that is catalytically active for the room temperature, selective aerial oxidation of styrenes to acetophenones. Further, the in situ generated Co( ii ) complex (from a mixture of the salen appended l -diaminoribose-derived ligand and a Co( ii ) salt) is also found to enable the catalysis. The oxidation is efficiently conducted in the presence of Et 3 SiH as a hydrogen atom transfer (HAT) agent and provides very high isolated yields (71-95%) of the acetophenones. Further, the HAT mediated transformation with NaBH 4 also enables the non-aqueous, Markovnikov hydration of styrenes, providing the corresponding benzylic alcohols, exclusively as a single product in over 72-97% isolated yields via an oxidation-reduction mechanism. The methodologies provided very high exclusive yields of the products and were compatible with various substitutions on the aryl ring of the styrene. Detailed experimental and computational studies revealed a structural feature of the ligand that enabled the facile formation and stabilization of a pseudo -octahedral Co( iii ) intermediate that facilitated the oxidation reaction. A novel diaminosugar-salen derived Co( ii ) square-planar complex catalyzes the room temperature, aerial oxidation and non-aqueous hydration of styrenes. DFT studies reveal mechanistic details and key ligand features that enable its catalytic ability.