Exploration of solvent free and/or microwave assisted syntheses of bismuth(iii) thiolates

Abstract

A variety of synthetic approaches to the formation of bismuth(III) thiolates has been explored and compared. BiPh3 was treated with a series of thiols of varying pKa and functionality (2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptopyrimidine, 2-mercapto-1-methylimidazole and thiosalicylic acid) in a 1:3 ratio under a variety of reaction conditions: with toluene or mesitylene under standard reflux conditions and under microwave irradiation, and solvent free with conventional and microwave heating. All reactions, except those with 2-mercapto-1-methylimidazole and thiosalicylic acid, yielded the tris-substitution product in good yield and high purity. Thiosalicylic acid gave the complex Bi2L3 in all reactions carried out in solvent and PhBiL when solvent free, both complexes containing the doubly deprotonated dianion (L = O2CC6H4-2-S). Reactions carried out in the microwave reactor generally gave comparable yields to the conventional methods but in significantly shorter times. However, the solvent free microwave reactions of 2-mercaptobenzoxazole and 2-mercaptopyrimidine caused partial decomposition to give microcrystalline Bi2S3. The solvent free reactions conducted with conventional heating methods were highly effective in the formation of the bismuth thiolates. Reactions with 2-mercapto-1-methylimidazole were problematic in giving either no reaction products or mixtures of compounds displaying various degrees of substitution. Partial decomposition (2–7%) to the disulfide was observed for both the bismuth thiolates derived from 2-mercaptopyrimidine and thiosalicylic acid on storage of a solution over several weeks.