Regio- and Stereoselective Syn-Boronation of Terminal Alkynes Catalyzed by Copper Nanospheres on Graphene Nanosheets

Abstract

Evenly distributed copper nanospheres on reduced graphene oxide were prepared and showed high heterogeneous catalytic activity in converting varying terminal alkynes into (E)-β-styrene boronate esters. The excellent catalytic performance was achieved through the synergistic catalysis between Cu nanospheres and rGO. This work not only is a supplement for preparing (E)-β-styrene boronate esters but also provides a way for the rational designing of high-performance graphene-based catalysts. Meanwhile, the advancement of graphene-based nanomaterials will be motivated to promote their applications in the development of green catalytic chemistry.

Heterovalent Metal Pair Sites on Metal–Organic Framework Ordered Macropores for Multimolecular Co-Activation

“…And the universally used additives such as sodium alkoxide can smoothly cleave B−B bonds of B 2 Pin 2 to afford active copper-boryl species, directly or indirectly. [34][35][36]39,44,45 And thus the activation of alkyne bonds on Cu sites will contribute to increasing the reaction activity. 35,46,47 However, in the absence of additives, the activation of B 2 Pin 2 to nucleophilic copper-boryl species is driven by the copper ethoxide (Cu-OEt) species generated from the dissociation of EtOH molecules on Cu coordination bonds, 43,48 with the result that the efficient ethanol dissociation proves to be another dominating step for lowering the reaction energy barrier.…”

“…Generally, Cu-catalyzed hydroboration reactions of alkynes undergo a step of copper-boryl species formation, along with subsequent insertion of a C–C triple bond. And the universally used additives such as sodium alkoxide can smoothly cleave B–B bonds of B 2 Pin 2 to afford active copper-boryl species, directly or indirectly. − ,,, And thus the activation of alkyne bonds on Cu sites will contribute to increasing the reaction activity. ,, However, in the absence of additives, the activation of B 2 Pin 2 to nucleophilic copper-boryl species is driven by the copper ethoxide (Cu-OEt) species generated from the dissociation of EtOH molecules on Cu coordination bonds, , with the result that the efficient ethanol dissociation proves to be another dominating step for lowering the reaction energy barrier. Therefore, if ethanol dissociation and alkyne activation are conducted in parallel within an ideal distance, the hydroboration reaction will be definitely promoted.…”

“…In addition, it is worth noting that the steric hindrance among styrene moiety, BPin moiety, and Cu-HMP on TSA4 (Figure S44) is responsible for the high regioselectivity of 3a product, in which the insertion of the alkyne into the Cu−B bond in a syn fashion providing a lower steric hindrance effect finally gives (E)-β-styrene boronate ester. 35,44 As is well known, during the heterogeneous catalytic process, the adsorption of substrates on active sites is crucial for subsequent activation and reactions. Based on this, the adsorption energies of EtOH/phenylacetylene on relevant sites are calculated to evaluate the corresponding adsorption effect (Table S5 and Figure S45).…”

Aqueous hydroboration of alkynes via nonclassical generation of N-heterocyclic carbenes

“…48 Then the Petasis reaction of alkenylboronic acid with 1-benzhydrylpiperazine occurred to afford cinnarizine 3a in 78% yield. 49 With I 2 as a halogenated reagent, ( E )-(2-iodovinyl)benzene 3b was obtained in 94% yield. 50 The building block 2ff was prepared by the transborylation reaction of 2a with B 2 nep 2 .…”

“…48; (ii) 1-benzhydrylpiperazine (1 mmol), paraformaldehyde (1 mmol), 1,4-dioxane (4 mL), 90 °C, 24 h, see ref. 49; (iii) I 2 (2 mmol), NaOH (3 mmol), THF (4 mL), rt, 2 h, see ref. 50; (iv) B 2 nep 2 (2 mmol), MeOH (2 mL), 90 °C, 16 h, see ref.…”