Lewis Acid Organocatalysts

Activation of Isocyanides and Hydrosilanes by a Cationic [CCH] Subunit in a Tetrairon–Tetracarbon Cluster

“…Lewis acid catalysts based on carbenium or silyl cations have also been developed. 2 In the 1980s, Mukaiyama aldol reactions, Sakurai allylations, and Michael additions, catalyzed by trityl salts or N-acyliminium ions, were reported by Mukaiyama and his co-workers. 3 Franzén et al reported various organic transformations based on DielsAlder and Michael addition reactions using a catalytic amount of tritylium tetrafluoroborate.…”

“…6 The Lewis acid chemistry of an ethynyl cation bridged over a butterfly-type tetrairon core has been investigated recently by us, 7 generation of which has been postulated in heterogeneous catalytic reactions (FT process). 2 (1). The pyrazine moiety in 1 is labile and is easily replaced with substrates, indicating that 1 can act as a synthon for the cationic [CCH] subunit on the tetrairon core, applicable to reaction sites with high Lewis acidity.…”

“…Treatment of 1 with tertiary amine in acetonitrile afforded [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCC-CH 2 CN)](PF 6 ). The first step of the reaction involved the substitution of pyrazine with acetonitrile to generate [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCC-NCCH 3 )](PF 6 ) 2 , which was independently synthesized and characterized by X-ray diffraction study. Abstraction of a methyl proton in the fixed acetonitrile by a tertiary amine, followed by a 1,3-shift of the cyanomethyl group, afforded the desired product.…”

“…We report here the reactivity of 1 toward isocyanides and hydrosilanes, while some of the reactions with isocyanides have been reported in a communication form. (2), which was isolated as a dark green powder in 86% yield. From the reaction mixture, 1-tert-butylpyrazinium salt was isolated as a white solid in 32% yield (Scheme 1).…”

“…No formation of 2 was confirmed throughout the reaction. The N-xylyl amide cluster [(η 5 -C 5 H 4 Me) 4 Fe 4 (HCCH)(HCC-C(O)NHC 6 H 3 (CH 3 ) 2 )](PF 6 ) (10) was formed upon hydrolysis of 8. Work-up of the reaction mixture, including recrystallization from dichloromethane/ diethyl ether, afforded 10 as greenish brown crystals in 92% yield (Scheme 6).…”