Selective Hydroboration Research Articles

Markovnikov-Selective Co(I)-Catalyzed Hydroboration of Vinylarenes and Carbonyl Compounds.

An NHC-supported Co(I) catalyst has been developed for selective Markovnikov hydroboration of vinylarenes under mild reaction conditions. The hydroboration allows highly selective synthesis of a wide range of secondary and tertiary alkyl boronates in excellent yields. Our protocol also enables hydroboration of aldehydes and ketones with diverse functional groups to access the corresponding borate esters.

Ir-Catalyzed Selective Hydroboration of 2-Substituted 1,3-Dienes: A General Method to Access Homoallylic Boronates

An operationally simple protocol for the 4,3-selective hydroboration of 2-substituted 1,3-dienes using an iridium catalyst is described. Independently of the nature (alkyl, aryl, heteroaryl) and the size of the substituent in the 2-position, it provides access to a variety of homoallylic boronates featuring a 1,1-disubstituted olefin in high yield and chemo- and regioselectivity. An array of potentially sensitive functional groups is well-tolerated, and the method can be extend to 1,2-disubstituted 1,3-dienes. Derivatization of the homoallylic boronates is also demonstrated using contemporary catalytic and enantioselective processes.

Enantioselective Synthesis of α-Amidoboronates Catalyzed by Planar-Chiral NHC-Cu(I) Complexes.

The first highly selective catalytic hydroboration of alkyl-substituted aldimines to provide medicinally relevant α-amidoboronates is disclosed. The Cu(I)-catalyzed borylation proceeds with excellent facial selectivity when a set of planar-chiral N-heterocyclic carbenes (NHCs) were employed as ligands. Density functional theory computations suggest that interactions between BPin and the planar-chiral catalyst are responsible for the observed stereoselectivity. Important pharmacophores, such as the boronate analogue of isoleucine, can be prepared using a chromatography-free protocol starting from commercially available reagents. The application of these NHC ligands in these Cu(I)-catalyzed processes offers a significant contribution to existing strategies for laboratory-scale preparation of enantioenriched α-amidoboronates.

N-Butyllithium Catalyzed Selective Hydroboration of Aldehydes and Ketones.

Highly efficient and selective hydroboration of aldehydes and ketones with HBpin is achieved by using the simple and convenient n-BuLi as a catalyst. The reaction proceeds rapidly with low catalyst loading (0.1-0.5 mol %) under mild conditions. Key features include the high catalytic efficiency, exceptional functional group compatibility, ample substrate scope, and high selectivity for aldehydes over ketones. Computational studies were carried out to provide a mechanistic insight into the n-BuLi catalyzed hydroboration of aldehydes/ketones with HBpin.

Cobalt(II) Coordination Polymer as a Precatalyst for Selective Hydroboration of Aldehydes, Ketones, and Imines.

Highly effective hydroboration precatalyst is developed based on a cobalt(II)-terpyridine coordination polymer (CP). The hydroboration of ketones, aldehydes, and imines with pinacolborane (HBpin) has been achieved using the recyclable CP catalyst in the presence of an air-stable activator. A wide range of substrates containing polar C═O or C═N bonds have been hydroborated selectively in excellent yields under ambient conditions.

Efficient and selective carbonyl hydroboration catalyzed by a lithium NCN-Pincer magnesiate complex [Li(THF)4][NCN-MgBr2

The well-defined lithium NCN-Pincer magnesiate complex [Li (THF)4][NCN-MgBr2] 2 based on a bis(imino)aryl ligand has been successfully prepared, crystallographic characterized and employed as an efficient catalyst for hydroboration of a wide range of aldehydes and ketones with pinacolborane (HBpin) at room temperature. Both aldehyde and ketone hydroboration proceeded efficiently (>99% conversion in <15 min) and could be directly carried out in a CDCl3 solution. In addition, chemoselective hydroboration of aldehydes over ketones was also achieved under these conditions.

Reusable Fe2O3-nanoparticle catalysed efficient and selective hydroboration of carbonyl compounds

We present readily accessible Fe2O3 nanoparticles as an efficient catalyst for the selective hydroboration of carbonyl compounds, which represents the first example of the use of nanoparticles as a catalyst for this process.

4-Cyanopyridine-catalyzed anti-Markovnikov selective hydroboration of alkenes

4-Cyanopyridine catalyzed anti-Markovnikov selective hydroboration of alkenes with B2pin2 affords the corresponding alkylboronates in good yields via a radical pathway.

Lewis acid catalysis: regioselective hydroboration of alkynes and alkenes promoted by scandium triflate.

The first commercially available scandium-catalysed selective hydroboration of alkynes and alkenes with HBpin (pin = OC-Me2CMe2O) in the presence of a catalytic amount of NaHBEt3 has been developed. This protocol can be applicable to a wide range of substrates including aromatic, aliphatic with cyclic and acyclic side chains, and heteroaryl systems with broad functional-group compatibility. Mechanistic studies revealed that the reaction occurs in a syn fashion via the σ-bond metathesis between the alkenyl scandium species and HBpin.

Selective Double Hydroboration and Dihydroborylsilylation of Organonitriles by an Iron-indium Cooperative Catalytic System.

Organonitriles (RC≡N) were selectively converted into the corresponding diborylamines (RCH2N(Bpin)2) in reactions with pinacolborane (pinBH) in the presence of a catalytic amount of the iron-indium complex [Fe(CH3CN)6][cis-Fe(CO)4(InCl3)2]. The catalytic reaction mechanism was tentatively proposed. In addition, this catalytic system was found to be applicable for the synthesis of borylsilylamine in high yield when organonitrile was treated with hydroborane and hydrosilane simultaneously.

Selective Ni-Catalyzed Hydroboration of CO2 to the Formaldehyde Level Enabled by New PSiP Ligation

The synthesis and characterization of group 10 metal pincer complexes supported by a new bis(indolylphosphino)silyl ligand are described, including the synthesis of Ni, Pd, and Pt hydride species. Solution NMR and single-crystal X-ray data revealed that a significant amount of structural variability is possible for such hydride complexes, particularly in the case of Ni, where terminal Ni-H as well as complexes involving η2-SiH coordination are both accessible and may even coexist, in ratios dependent on factors such as the nature of additional coligands, including N2 from the reaction atmosphere, as well as solvent and temperature. Nickel and palladium hydride complexes of this new ligand were found to exhibit divergent selectivity in the catalytic hydroboration of CO2 with pinacolborane (HBPin). While the Pd catalyst exhibited moderate activity for CO2 hydroboration to the formate level, the analogous Ni species exhibited unprecedented selectivity (97%) for hydroboration of CO2 to the formaldehyde level ...

Ruthenium-Catalyzed Anti-Markovnikov Selective Hydroboration of Olefins

Ruthenium-catalyzed selective hydroboration of styrenes and aliphatic olefins with pinacolborane (HBpin) is reported. This efficient transformation provided products with exclusive anti-Markovnikov selectivity, and this hydroboration protocol is compatible with olefins having electronic and steric divergence as well as diverse functional groups. Hydroboration occurred at room temperature under solvent-free conditions with minimal catalyst load (0.05 mol %) and provided high TON (>1980; >990 per Ru). Mechanistic studies confirmed the involvement of intermediate [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] (2). A catalytic cycle including a mononuclear ruthenium intermediate is proposed. The rationale for observed anti-Markovnikov selectivity is provided from reversible 1,3-hydride transfer leading to the regioselective 1,2-insertion on olefins.

Stable, Yet Highly Reactive Nonclassical Iron(II) Polyhydride Pincer Complexes: Z-Selective Dimerization and Hydroboration of Terminal Alkynes.

The synthesis, characterization, and catalytic activity of nonclassical iron(II) polyhydride complexes containing tridentate PNP pincer-type ligands is described. These compounds of the general formula [Fe(PNP)(H)2(η2-H2)] exhibit remarkable reactivity toward terminal alkynes. They efficiently promote the catalytic dimerization of aryl acetylenes giving the corresponding conjugated 1,3-enynes in excellent yields with low catalyst loadings. When the reaction is carried out in the presence of pinacolborane, vinyl boronates are obtained. Both reactions take place under mild conditions and are highly chemo-, regio-, and stereoselective with up to 99% Z-selectivity.

Transition-metal-free PhI(OAc)2-promoted highly selective hydroboration of terminal alkynes under air

A new transition-metal-free PhI(OAc)2-promoted highly selective hydroboration of terminal alkynes with bis(pinacolato)diboron has been developed at room temperature under air.

Magnesium amide catalyzed selective hydroboration of esters.

Magnesium amide complexes such as Mg{N(SiMe3)2}2 (1) xylLMgN(SiMe3)2·THF (2) [xylL = ArNC(NiPr2)NAr; (Ar = 2,6-Me2-C6H3)] and dippLMgN(SiMe3)2·THF (3) [dippL = ArNC(NiPr2)NAr; (Ar = 2,6-iPr2-C6H3)] are reported as highly efficient pre-catalysts for the hydroboration of a wide range of esters using pinacolborane (HBpin) under mild reaction conditions. Moreover, we have shown compound 1 catalyzed chemoselective reduction of esters in the presence of other reducible functional groups such as alkene, alkyne and nitro.

Cobalt-catalysed Markovnikov selective hydroboration of vinylarenes.

A bipyridiyl-oxazoline cobalt catalyst tBuBPOCoCl2 has been developed for the Markovnikov selective hydroboration of alkenes using pinacolborane and NaOtBu as the in situ activator with up to >98 : 2 branched : linear selectivity (24 examples, 45-92% isolated yield).

Correction: A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide.

Correction for 'A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide' by Chee Koon Ng et al., Chem. Commun., 2016, 52, 11842-11845.

Ruthenium-Catalyzed Selective Hydroboration of Nitriles and Imines.

Ruthenium-catalyzed hydroboration of nitriles and imines is attained using pinacolborane with unprecedented catalytic efficiency. Chemoselective hydroboration of nitriles over esters is also demonstrated. A simple [Ru(p-cymene)Cl2]2 complex (1) is used as a catalyst precursor, which upon reaction with pinacolborane in situ generates the monohydrido-bridged complex [{(η6-p-cymene)RuCl}2(μ-H-μ-Cl)] 2. Further oxidative addition of pinacolborane to intermediate 2 leading to the formation of mononuclear ruthenium hydride species is suggested. Mass spectral analysis of the reaction mixture and independent experiments with phosphine-ligated ruthenium complexes indicated the involvement of mononuclear ruthenium intermediates in the catalytic cycle. Consecutive intramolecular 1,3-hydride transfers from the ruthenium center to coordinated nitrile and boronate imine ligands, leading to the reduction and resulting in the formation of diboronate amines, are proposed as a plausible reaction mechanism.

Highly Selective Hydroboration of Alkenes, Ketones and Aldehydes Catalyzed by a Well‐Defined Manganese Complex

AbstractWell‐defined manganese complexes based on inexpensive, readily available ligands, 2,2′:6′,2′′‐terpyridine and its derivatives have been prepared and employed for the selective hydroboration of alkenes, ketones and aldehydes. Highly Markovnikov regioselective hydroboration of styrenes as well as excellent chemoselective hydroboration of ketones over alkenes were achieved, for the first time, by an earth‐abundant manganese catalyst.

Highly Selective Hydroboration of Alkenes, Ketones and Aldehydes Catalyzed by a Well‐Defined Manganese Complex

Well-defined manganese complexes based on inexpensive, readily available ligands, 2,2':6',2''-terpyridine and its derivatives have been prepared and employed for the selective hydroboration of alkenes, ketones and aldehydes. Highly Markovnikov regioselective hydroboration of styrenes as well as excellent chemoselective hydroboration of ketones over alkenes were achieved, for the first time, by an earth-abundant manganese catalyst.