A mild approach to the synthesis of 1,2-diferrocenylethanedione from ferrocenealdehyde

The synthesis of 1,2-diferrocenylethanedione (II) was achieved through metal-free route. Trögerʹs-base functionalized pre-N-heterocyclic carbenes, TB–[CH2–Im–CH2–Mes]2+2X¯, where TB = 6H,12H-5,11-methano-dibenzo[b,f][1,5]diazocine; Im = imidazolium; Mes = 2,4,6-trimethylbenzene; X = Br (4), BF4 (5) and PF6 (6) were synthesized in very good yield through simple synthetic route. 4–6 were characterized by FT-IR and multinuclear NMR. These new molecules, 4–6 were used as an organocatalyst to study the ferrocenealdehyde condensation reactions. 4–6 mediated condensation of ferrocenealdehyde resulted the mixture of 2-hydroxy-1,2-diferrocenyl-ethan-1-one (major product, I) to 1,2-diferrocenylethanedione (minor product, II). II was conveniently separated from reaction mixture by hexane wash, while the purification of I using silica loaded column chromatography resulted the quantitative oxidation of I to II. Catalysts [{2,6-Me2C6H3N(CH)2N(CH2Mes)}CH]+Br− (7) and [{CH2CHN(CH)2N(CH2Mes)}CH]+Br− (8) as well as 7–8 in the presence of 2,8-dibromo tröger base also showed similar catalytic behavior, however yield of II was very poor. Among 4–8, catalyst 4 in THF gave the best conversion.