Gas-phase S-alkylation of benzenethiol with aliphatic alcohols, ethers, esters, alkyl halides and olefins over halide cluster catalysts of Groups 5 and 6 transition metals

Benzenethiol was reacted with methanol under a hydrogen stream over [(Nb6Cl12)Cl2(H2O)4]·6H2O supported on silica gel. Catalytic activity of the cluster commenced above 250 °C, yielding methyl phenyl sulfide. The selectivity was 98% at 400 °C. Molybdenum, tantalum and tungsten halide clusters with the same octahedral metal framework also catalyzed the reaction. Primary alcohols with shorter alkyl chains were effective reagents for the S-alkylation. Aliphatic ethers, dialkyl carbonates, orthoesters and alkyl halides were effective reagents for the S-alkylation. When 1-hexene was applied to the reaction, spontaneous and catalytic S-alkylation proceeded simultaneously above 200 °C, yielding n-hexyl phenyl sulfide. When alkyl acetates were subjected to this reaction, the niobium cluster afforded S-phenyl thioacetate, and the other clusters afforded alkyl phenyl sulfides selectively. A Brønsted acid site attributable to a hydroxo ligand, which is formed on the cluster complex by thermal activation, is proposed as the active site of the catalysts.

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► Halide clusters are versatile catalysts for the S-alkylation of benzenethiol.
► The gas-phase catalysis proceeds above 200 °C without any solvents or additives.
► Alcohols, ethers and esters are preferable for the cases of shorter alkyl chains.
► Olefins and alkyl halides are preferable for the cases of longer alkyl chains.