Hydroboration Of Alkenes Research Articles

Copper‐Photocatalyzed Hydroboration of Alkynes and Alkenes

AbstractThe photocatalytic hydroboration of alkenes and alkynes is reported. The use of newly‐designed copper photocatalysts with B2Pin2 permits the formation a boryl radical, which is used for hydroboration of a large panel of alkenes and alkynes. The hydroborated products were isolated in high yields, with excellent diastereoselectivities and a high functional group tolerance under mild conditions. The hydroboration reactions were developed under continuous flow conditions to demonstrate their synthetic utility. The reaction mechanism was studied and suggested an oxidation reaction between an in situ formed borate and the Cu‐photocatalyst in its excited state for the boryl radical formation.

Cover Picture: Recyclable Copper Nanoparticles‐Catalyzed Hydroboration of Alkenes and β‐Borylation of α,β‐Unsaturated Carbonyl Compounds with Bis(Pinacolato)Diboron (9/2021)

Cover Picture: Recyclable Copper Nanoparticles‐Catalyzed Hydroboration of Alkenes and β‐Borylation of α,β‐Unsaturated Carbonyl Compounds with Bis(Pinacolato)Diboron (9/2021)

Highly Selective Hydroboration of Terminal Alkenes Catalyzed by a Cobalt Pincer Complex Featuring a Central Reactive N-Heterocyclic Phosphido Fragment

The application of a cobalt pincer complex, (PPClP)CoCl2, as a precatalyst for the hydroboration of terminal alkenes with pinacolborane (HBPin) is described. The reactions proceed rapidly under mil...

B(C6F5)3‐Catalyzed Hydroboration of Alkenes with N‐Heterocyclic Carbene Boranes via B—H Bond Activation

Main observation and conclusionIn this work, a novel mode for the activation of N‐heterocyclic carbene boranes (NHC‐boranes) was developed by generating the highly reactive zwitterion species through hydride abstraction with Lewis acid B(C6F5)3 in an frustrated Lewis pairs manner. A broad range of alkenes including stilbenes, β‐methylstyrenes, styrenes, and alkyl‐alkenes were suitable substrates for the B(C6F5)3‐catalyzed hydroboration to furnish the desired products in good to high yields. Significantly, excellent regioselectivities were obtained in some cases. Mechanistic studies indicate that the B—H bond cleavage is likely involved in the rate‐determining step. In addition, an electrophilic addition of NHC‐borenium cation to alkenes and the subsequent formation of carbocation are also postulated. The current work provides a promising method for the activation of stable borane adducts, which might lead to some interesting transformations in the future.

Ligand Conformational Flexibility Enables Enantioselective Tertiary C-B Bond Formation in the Phosphonate-Directed Catalytic Asymmetric Alkene Hydroboration.

Conformationally flexible ancillary ligands have been widely used in transition metal catalysis. However, the benefits of using flexible ligands are often not well understood. We performed density functional theory (DFT) and experimental studies to elucidate the mechanisms and the roles of conformationally flexible α,α,α',α'-tetraaryldioxolane-4,5-dimethanol (TADDOL)-derived ligands on the reactivity and selectivity in the Rh-catalyzed asymmetric hydroboration (CAHB) of alkenes. DFT calculations and deuterium labeling studies both indicated that the most favorable reaction pathway involves an unusual tertiary C-B bond reductive elimination to give high levels of regio- and enantioselectivities. Here, the asymmetric construction of the fully substituted carbon center is promoted by the flexibility of the TADDOL backbone, which leads to two ligand conformations with distinct steric environments in different steps of the catalytic cycle. A pseudo-chair ligand conformation is preferred in the rate-determining tertiary benzylic C-B reductive elimination. The less hindered steric environment with this conformation allows the benzylic group to bind to the Rh center in an η3 fashion, which stabilizes the C-B reductive elimination transition state. On the other hand, a pseudo-boat ligand conformation is involved in the selectivity-determining alkene migratory insertion step, where the more anisotropic steric environment leads to greater ligand-substrate steric interactions to control the π-facial selectivity. Thus, using a conformationally flexible ligand is beneficial for enhancing both reactivity and enantioselectivity by controlling ligand-substrate interactions in two different elementary steps.

Recyclable Copper Nanoparticles‐Catalyzed Hydroboration of Alkenes and β‐Borylation of α,β‐Unsaturated Carbonyl Compounds with Bis(Pinacolato)Diboron

AbstractNano‐ferrite‐supported Cu nanoparticles (Fe‐dopamine‐Cu NPs) catalyzed anti‐Markovnikov‐selective hydroboration of alkenes with B2pin2 is reported under mild reaction conditions. This protocol can be applied to a broad range of substrates with high functional group compatibility. In addition, we demonstrated the use of Fe‐dopamine‐Cu NPs as a catalyst for the β‐borylation of α,β‐unsaturated ketones and ester, providing alkylboronate esters in up to 98% yield. Reuse of the magnetically recyclable catalyst resulted in no significant loss of activity in up to five reaction runs for both systems.magnified image

Synthesis and Catalytic Reactivity of Cobalt Pincer Nitrosyl Hydride Complexes.

The synthesis, characterization, and catalytic activity of low-spin {CoNO}8 pincer complexes of the type [Co(PCP)(NO)(H)] are described. These compounds are obtained either by reacting [Co(PCP)(κ2-BH4)] with NO and Et3N or, alternatively, by reacting [Co(PCP)(NO)]+ with boranes, such as NH3·BH3 in solution. The five-coordinate, diamagnetic Co(III) complex [Co(PCPNMe-iPr)(NO)(H)] was found to be the active species in the hydroboration of alkenes with anti-Markovnikov selectivity. A range of aromatic and aliphatic alkenes were efficiently converted with pinacolborane (HBpin) under mild conditions in good to excellent yield. Mechanistic insight into the catalytic reaction is provided by means of isotope labeling, NMR spectroscopy, and APCI/ESI-MS as well as DFT calculations.

4-Dimethylaminopyridine-Boryl Radical Promoted Regioselective Radical Hydroboration of Electron-Deficient Alkenes

4-Dimethylaminopyridine-Boryl Radical Promoted Regioselective Radical Hydroboration of Electron-Deficient Alkenes

Pyridylpyrrolido ligand in Ge(II) and Sn(II) chemistry: synthesis, reactivity and catalytic application.

In our previous communication, we have reported the synthesis of a new chlorogermylene (B) featuring a pyridylpyrrolido ligand. This study details the preparation of a series of new germylenes and stannylenes starting from B. A transmetallation reaction between B and SnCl2 led to the analogous chlorostannylene (1) with the simultaneous elimination of GeCl2. This is a very unusual example of transmetallation between two elements of the same group. The preparation of 1via lithiation led to the formation of 2 as a side product, where the ortho C-H bond of the pyridine ring was activated and functionalized with a nBu moiety. Subsequently, B and 1 were used as precursors to generate germylene (4) and stannylene (5) featuring tris(trimethylsilyl)silyl (hypersilyl) moieties. We also prepared tetrafluoropyridyl germylene (6) by reacting 4 with C5F5N with the simultaneous elimination of (Me3Si)3SiF by utilizing the fluoride affinity of the silicon atom. As there is scarcity of Sn(II) compounds as single-site catalysts, we investigated 5 as a catalyst towards the hydroboration of aldehydes, ketones, alkenes and alkynes. All the compounds have been characterized by single-crystal X-ray diffraction and by state of the art spectroscopic studies.

Selective electrocatalytic hydroboration of aryl alkenes

A CH3CN-involved electrochemical mono- or di-functional borylation reaction with alkenes and HBpin as substrates was reported. Functional group transformation and gram-scale synthesis demonstrated the utility of this method and showed great potential application.

Manganese-Catalyzed Hydroboration of Terminal Olefins and Metal-Dependent Selectivity in Internal Olefin Isomerization-Hydroboration.

In the past decade, the use of earth-abundant metals in homogeneous catalysis has flourished. In particular, metals such as cobalt and iron have been used extensively in reductive transformations including hydrogenation, hydroboration, and hydrosilylation. Manganese, on the other hand, has been considerably less explored in these reductive transformations. Here, we report a well-defined manganese complex, [Mn(iPrBDI)(OTf)2] (2a; BDI = bipyridinediimine), that is an active precatalyst in the hydroboration of a variety of electronically differentiated alkenes (>20 examples). The hydroboration is specifically selective for terminal alkenes and occurs with exclusive anti-Markovnikov selectivity. In contrast, when using the analogous cobalt complex [Co(iPrBDI)(OTf)2] (3a), internal alkenes are hydroborated efficiently, where a sequence of isomerization steps ultimately leads to their hydroboration. The contrasting terminal versus internal alkene selectivity for manganese and cobalt was investigated computationally and is further discussed in the herein-reported study.

ANIPE-Cu Catalyst Enables Highly Enantioselective Markovnikov Hydroboration of α-Olefins

AbstractAsymmetric hydroboration of simple and unactivated terminal alkenes (α-olefins), feedstock chemicals derived from the petrochemical industry, has not been efficiently realized for past decades. Using a bulky ANIPE ligand, we achieved a rare example of highly enantioselective copper-catalyzed Markovnikov hydroboration of α-olefins. The chiral secondary alkylboronic ester products were obtained in moderate to good yields and regioselectivities with excellent enantioselectivities.1 Introduction2 Conditions Optimization3 Substrate Scope4 Application5 Mechanistic Discussion6 Conclusions and Future Directions

ANIPE-Cu Catalyst Enables Highly Enantioselective Markovnikov Hydroboration of α-Olefins

AbstractAsymmetric hydroboration of simple and unactivated terminal alkenes (α-olefins), feedstock chemicals derived from the petrochemical industry, has not been efficiently realized for past decades. Using a bulky ANIPE ligand, we achieved a rare example of highly enantioselective copper-catalyzed Markovnikov hydroboration of α-olefins. The chiral secondary alkylboronic ester products were obtained in moderate to good yields and regioselectivities with excellent enantioselectivities.1 Introduction2 Conditions Optimization3 Substrate Scope4 Application5 Mechanistic Discussion6 Conclusions and Future Directions

Correction to Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex

Correction to Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex

Copper-Catalyzed Reactions of Alkylboranes

Abstract This account describes our work concerning the application of alkylboranes to addition reactions to unsaturated compounds, with catalysis by copper. Alkylboranes are readily obtained from standard alkene hydroboration reactions, which is an advantage of these processes. The substrates can contain a wide range of functional groups. The reactions described herein include the formation of alkylcopper(I) species via the catalytic B/Cu transmetallation of alkylboranes and subsequent addition to unsaturated carbon–carbon bonds or carbon dioxide.

Ligand-Free Iron-Catalyzed Regioselectivity-Controlled Hydroboration of Aliphatic Terminal Alkenes

The control of regioselectivities has been recognized as the elementary issue for alkene hydroboration. Despite considerable progress, the specificity of alkene substrates or the adjustment of liga...

Selective Hydroboration-Oxidation of Terminal Alkenes under Flow Conditions.

An efficient flow process for the selective hydroboration and oxidation of different alkenes using 9‐borabicyclo(3.3.1)nonane (9‐BBN) allows facile conversion in high productivity (1.4 g h−1) of amorpha‐4,11‐diene to the corresponding alcohol, which is an advanced intermediate in the synthesis of the antimalarial drug artemisinin. The in situ reaction of borane and 1,5‐cyclooctadiene using a simple flow generator proved to be a cost efficient solution for the generation of 9‐BBN.

Hydroboration of Alkenes Catalysed by a Nickel N-Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects.

The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η5 -C5 Me5 )Cl(IMes)] (IMes=1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in the presence of a catalytic amount of potassium tert-butoxide, and joins the very exclusive club of nickel catalysts for this important transformation. Interestingly, the regioselectivity can be reversed in some cases by using pinacolborane instead of catecholborane. Mechanistic investigations involving control experiments, 1 H and 11 B NMR spectroscopy, cyclic voltammetry, piezometric measurements and DFT calculations suggest an initial reduction of the NiII precursor to a NiI active species with the concomitant release of H2 . The crucial role of the alkoxo-catecholato-borohydride species resulting from the reaction of potassium tert-butoxide with catecholborane in the formation of an intermediate nickel-hydride species that would then be reduced to the NiI active species, is highlighted.

σ-Bond Hydroboration of Cyclopropanes.

Hydroboration of alkenes is a classical reaction in organic synthesis in which alkenes react with boranes to give alkylboranes with subsequent oxidation resulting in alcohols. The double bond (π-bond) of alkenes can be readily reacted with boranes owing to its high reactivity. However, the single bond (σ-bond) of alkanes has never been reacted. To pursue the development of σ-bond cleavage, we selected cyclopropanes as model substrates since they present a relatively weak σ-bond. Herein, we describe an iridium-catalyzed hydroboration of cyclopropanes, resulting in β-methyl alkylboronates. These unusually branched boronates can be derivatized by oxidation or cross-coupling chemistry, accessing "designer" products that are desired by practitioners of natural product synthesis and medicinal chemistry. Furthermore, mechanistic investigations and theoretical studies revealed the enabling role of the catalyst.

New Radical Borylation Pathways for Organoboron Synthesis Enabled by Photoredox Catalysis

AbstractRadical borylation using N‐heterocyclic carbene (NHC)‐BH3 complexes as boryl radical precursors has emerged as an important synthetic tool for organoboron assembly. However, the majority of reported methods are limited to reaction modes involving carbo‐ and/or hydroboration of specific alkenes and alkynes. Moreover, the generation of NHC‐boryl radicals relies principally on hydrogen atom abstraction with the aid of radical initiators. A distinct radical generation method is reported, as well as the reaction pathways of NHC‐boryl radicals enabled by photoredox catalysis. NHC‐boryl radicals are generated via a single‐electron oxidation and subsequently undergo cross‐coupling with the in‐situ‐generated radical anions to yield gem‐difluoroallylboronates. A photoredox‐catalyzed radical arylboration reaction of alkenes was achieved using cyanoarenes as arylating components from which elaborated organoborons were accessed. Mechanistic studies verified the oxidative formation of NHC‐boryl radicals through a single‐electron‐transfer pathway.