Temperature-Controlled Mono- and Diolefination of Arene Using Rh(III)/RTIL as an Efficient and Recyclable Catalytic System

Abstract

In this report, nonvolatile and chemically stable room-temperature ionic liquid [BMIM]­NTf2 was first developed as an excellent reaction medium in the Rh­(III)-catalyzed C–H bond-activated olefination. This reaction system is free of any organic solvents and is much safer without the need of pressure-tight equipment. Selective mono- and diolefination has been realized through temperature control for the first time. Room temperature gives mono-olefinated products predominantly with satisfactory yields, while 80 °C selectively generates a high yield of diolefinated products. A wide range of substrate scope with fine yields and satisfactory selectivity is achieved. The reaction can be scaled up to gram scale. Moreover, this catalytic system can be recycled at least 7 times with consistently high catalytic activity. This property reduces environmental contamination caused by the transition metal and saves costs significantly. This reaction approach can be applied in the synthesis of various valuable unsaturated aromatic compounds in academia and industry.

Recent advances in rhodium-catalysed cross-dehydrogenative-coupling between two C(sp2)–H bonds

“…Du and co-workers reported a reusable Rh( iii )/[BMIM]NTf 2 catalytic system for C–H olefination of arenes directed by N-containing heterocyclic groups (Scheme 14). 28 The replacement of conventional organic solvents with ionic liquids enabled a more environmentally sustainable approach whereas the high catalytic activity is still retained. The functionalisation can be selectively altered for mono- or di-olefination via reaction temperature control.…”

Recent development in transition metal-catalysed C–H olefination

“…Du and co-workers reported Rh( iii )/[BMIM]NTf 2 as a reusable catalytic system for the ortho -olefination of arenes at room temperature. 31 The ionic liquid used in the transformation is chemically stable and non-volatile accounting for an environment friendly protocol.…”

The C–H activated controlled mono- and di-olefination of arenes in ionic liquids at room temperature

“…Recently, our group realized the temperature-controlled mono- and di-olefination of arenes with good yield, excellent selectivity and satisfactory recyclability. 16 However, the generation of di-olefinated products required a high temperature, which was energy-consuming and unsafe in an industrial production process. To the best of our knowledge, a protocol for the selective synthesis of mono- and di-olefinated products at room temperature with full control is yet to be developed.…”

“…Up to now, ILs have been successfully employed in the Suzuki reaction, cross-coupling reaction, Heck reaction, C–H activated olefination and so on. 16,20 The employment of ILs in C–H activation is still rare and needs to be expanded.…”