Selective Alkane Hydroxylation in a Fluorous Solvent System Catalyzed by a Fluorocarbon-Soluble Transition-Metal
Yuma Morimoto1, Yuki Shimaoka1, Kosuke Fukui1
1Department of Molecular Chemistry, Division of Advanced Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Abstract:
Hydroxylation of aliphatic hydrocarbons requires highly reactive oxidants, but their strength can lead to undesired oxidation of the initially formed alcohols and solvents, undermining the product selectivity. To address these problems, we developed a novel catalytic system using fluorocarbon solvents. A cobalt complex supported by the fluorinated ligand, N,N,N',N',N″-pentakis-[CF3(CF2)7(CH2)3]-diethylenetriamine (Rf-deta), acts as an efficient catalyst [turnover number (TON) = 1203, turnover frequency = 51 ± 1 min-1] for cyclohexane hydroxylation with the m-chloroperbenzoic acid oxidant, achieving high alcohol selectivity (96%). Overoxidation to form cyclohexanone is minimized due to the separation of cyclohexanol from the reaction phase, comprising perfluoromethylcyclohexane and α,α,α-trifluorotoluene. The catalyst hydroxylates primary carbons (5 examples) and exhibits significant reactivity toward the terminal C-H bond of normal hexane (TON = 13). This system extends to the hydroxylation of the gaseous substrate butane, yielding the corresponding alcohols.
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