Development of silica-supported frustrated Lewis pairs: highly active transition metal-free catalysts for the Z-selective reduction of alkynes

Abstract

A supported Lewis acid/base systems based on a triphenyl phosphine fragment and Piers' reagent (HB(C6F5)2) or BArF have been prepared and characterized. Both materials show unprecedented catalytic activity in Z-selective hydrogenation of 3hexyne to Z-3-hexene with a selectivity up to 87%. Other alkynes can also be hydrogenated Z-selectively, albeit with moderate yields. The activity of the supported phosphine/HB(C6F5)2 adduct is similar to the only homogeneous example reported thus far based on bridged B/N frustrated Lewis pairs under high pressure of hydrogen. Importantly, this transition metal-free supported catalyst was recycled five times in the challenging selective hydrogenation of a non-polar unactivated alkyne.

Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert

“…[3] An otable exception is the semihydrogenation of alkynes catalyzed by an intramolecular FLP that was reported by Repo et al [4] In that case, mechanistic investigationss howed that the protolysis of the FLP under the reaction conditions yields an amine-hydroborane that initiates the catalytic cycle by hydroboration of the alkyne. [5] Ap rotodeborylation of the alkenylborane yields then, in ah ighly stereoselective reaction, the cis-alkene. [6] We recently reported reversible H 2 activation by the boroxypyridine 3.…”

Metallomimetic Chemistry of Boron

“…A similar reaction has also been realized via a hydridoborane/silica-supported phosphine FLP. 83 Additionally, Wang and coworkers also have reported that the simple, highly Lewis acidic hydroborane HB(C6F5)2 can hydrogenate simple alkenes via a related hydroboration -hydrogenolysis mechanism, 84 which will be discussed in more detail in section 4.1. Overall, the wealth of FLP reactivity with H2 has uncovered two main hydrogenation mechanisms.…”

Solid Molecular Frustrated Lewis Pairs in a Polyamine Organic Framework for the Catalytic Metal‐free Hydrogenation of Alkenes

“…This FLP was characterized by DRIFT spectroscopy as well as MAS NMR spectroscopy. It shows a remarkable activity and selectivity in the hydrogenation of alkynes . In contrast, Xing et al.…”

“…Supported FLPs for heterogeneously catalyzed hydrogenation reactions are mentioned by Szeto et al. as well as Xing et al . Szeto et al.…”

“…The use of transition metal catalysts like organometallic Pd and Ni complexes as well as early transition metals such as Ti and Nb in hydrogenation reactions is widely known . However, even traces of metal are unfavorable in fine chemicals and pharmaceuticals . Stephan et al.…”