Hydroboration Of Aldehydes Research Articles

Hydroboration of aldehydes with pinacolborane catalyzed by bulky 2‐iminopyrrolyl copper(I) triphenylphosphine complexes

Eight new copper(I) triphenylphosphine complexes of bulky 5‐substituted‐2‐iminopyrrolyl ligands [Cu{κ2N,N′‐5‐R‐NC4H2–2‐C(H) = N(2,6‐iPr2C6H3)}(PPh3)n] (for n = 2: R = 2,6‐Me2C6H3 (1), 3,5‐(CF3)2C6H3 (2); for n = 1: R = 2,4,6‐iPr3C6H2 (3), CPh3 (4), 2,6‐(OMe)2C6H3 (5), 2,4,6‐Ph3C6H2 (6), 2,6‐Me2C6H3 (7), 3,5‐(CF3)2C6H3 (8)) are presently reported. The complexes were prepared in good yields by: (1) the reaction of the previously reported binuclear complexes [Cu{κN,κN'‐5‐R‐NC4H2‐2‐C(H) = N(2,6‐iPr2C6H3)}]2 (D1–D6) with triphenylphosphine (PPh3); (2) the reaction of the respective 5‐R‐2‐iminopyrrolyl potassium salts (KL1–KL3 and KL5) and [Cu(NCMe)2(PPh3)2]BF4; or (3) the abstraction of one PPh3 ligand present in complexes 1 and 2 with one equivalent of tris(pentafluorophenyl)borane (only for complexes 7 and 8, respectively). All complexes were characterized by NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X‐ray diffraction. The single crystal X‐ray diffraction structures of 1, 3, and 5–7 displayed tetrahedral (for 1) and trigonal planar (for 3 and 5–7) coordination geometries. All complexes catalyzed the 1,4‐hydroboration of some α,β‐unsaturated (E)‐2‐enals with pinacolborane (HBPin), with 1,4:1,2‐addition selectivities as high as 29:1, the maximum turnover frequencies being equal to 9.9 min−1, and the 1,4‐hydroboration selectivity being favored by increasing steric protection of the 5‐substituted‐2‐iminopyrrolyl scaffold. Additionally, these complexes also catalyzed the hydroboration of an array of other aldehydes, reaching TOFs as high as 9.9 min−1. A combination of control experiments suggests that the catalyst system operates via a non‐classical copper‐hydride outer sphere route.

Synthesis, characterization and catalytic activities of Zn(II) and Cd(II) complexes supported by unsymmetrical aryl thiourea ligands

AbstractWe report a series of Zn(II) and Cd(II) metal complexes [L12(ZnCl2)] (1), [L12(ZnBr2)] (2), [L12(CdCl2)] (3), [L12(CdI2)] (4), [L22(ZnCl2)] (5), [L22(ZnBr2)] (6), [L22(ZnI2)] (7), [L22(CdCl2)] (8), [L32(CdCl2)] (9) and [L42(ZnBr2)] (10), synthesized using various unsymmetrical aryl thiourea ligands: 1‐(2,6‐diisopropylphenyl)‐3‐phenylthiourea (L1), 1‐mesityl‐3‐phenylthiourea (L2), 1‐(2‐fluorophenyl)‐3‐phenylthiourea (L3) and symmetrical 1,3‐bis(2‐fluorophenyl)thiourea (L4). The ligands and metal complexes were characterized by 1H, 13C{1H} NMR, FT‐IR analysis. Solid‐state structures of the zinc and cadmium metal complexes (1–8) were established using the single‐crystal diffraction analysis technique. Furthermore, the catalytic activities of the Zn(II) complexes towards hydroboration of aldehydes and ketones (‐C=O) as substrates were studied. Excellent yields of the corresponding boronate esters were achieved.

Synthesis and Characterization of Zinc, Lithium and Magnesium Complexes Containing Pyrrolyl Ligands, and Utilization as Catalysts in Borylation of Aryl Iodides and Hydroboration of Aldehydes and Ketones

Synthesis and Characterization of Zinc, Lithium and Magnesium Complexes Containing Pyrrolyl Ligands, and Utilization as Catalysts in Borylation of Aryl Iodides and Hydroboration of Aldehydes and Ketones

Reusable Iron/Iron Oxide-based Nanoparticles Catalyzed Organic Reactions

ABSTRACT:The last decade has witnessed a remarkable progress in the field of nanoscience and nanotechnology. Nanoparticles have been extensively used in diverse areas, including medicine, sensor, and catalysis. The easy accessibility of nanoparticles (NPs) with different shapes, sizes and compositions has inspired researchers to investigate their applications in catalysis. Recently, magnetic nanoparticles, such as iron-based nanoparticles, have attracted much consideration due to their unique properties, such as superparamagnetism, greater surface area, surface-to-volume ratio, and easy separation methodology. They increase the competence of organic reactions in terms of activity, selectivity, yield, simplicity, and sustainability. In this review, we focus on the developments of iron/iron oxide-based nanoparticles-catalyzed organic reactions and some examples of magnetic iron oxide nanoparticles as carriers/support for the main catalyst in organic reactions. Owing to magnetic properties, these nanocatalysts can be easily recovered from the reaction mixture by an external magnet and reused for several runs without loss of catalytic activity. Iron-based nanoparticles are used in a wide range of catalytic processes and applications. Notable focus has been on the hydrogenation of alkenes and alkynes, and also the hydrogenation of nitroarenes to aniline. Other catalyzed organic reactions, such as hydroboration of aldehydes and ketones, oxidative dehydrogenation of N-heterocycles, azide-alkyne cycloaddition reactions, synthesis of various heterocyclic compounds, multicomponent reactions, and crosscoupling reactions for C–C and C–heteroatom bond formation have been covered.

Hydroboration of aldehydes, ketones and CO2 under mild conditions mediated by iron(iii) salen complexes.

The hydroboration of aldehydes, ketones and CO2 is demonstrated using a cheap and air stable [Fe(salen)]2-μ-oxo pre-catalyst with pinacolborane (HBpin) as the reductant under mild conditions. This catalyst system chemoselectively hydroborates aldehydes over ketones and ketones over alkenes. In addition, the [Fe(salen)2]-μ-oxo pre-catalyst shows good efficacy at reducing "wet" CO2 with HBpin at room temperature.

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.

Catalytic and non-catalytic hydroboration of carbonyls: quantum-chemical studies.

The addition of hydroboranes across several unsaturated moieties is a universal synthetic tool for the reduction or functionalization of unsaturated moieties. Given the sustainable nature of this process, the development of more environmentally-benign approaches (main-group catalysis or uncatalysed approaches) for hydroboration has gained considerable recent momentum. The present paper examines both catalyst-free and KF-mediated hydroboration of carbonyl compounds with the use of quantum-chemical methods. The results of computations for several potential reaction pathways are juxtaposed with experiment-based calculations, which leads to stepwise mechanisms and energy profiles for the reactions of pinacolborane with benzaldehyde and acetophenone (in the presence of KF). For each step of these reactions, we provide an accurate description of the geometric and electronic structures of corresponding stationary points. Five different levels of theory are employed to select the most applicable theoretical approach and develop a computational protocol for further research. Upon selection of the best-performing methods, larger molecular systems are studied to explore possible more complex pathways at the M06-2X/6-311++G(2d,p) and ωB97XD/6-311++G(2d,p) levels of theory, which brings up multi-pathway, overlapping catalytic cycles. The mechanism of solvent-free, catalyst-free hydroboration of aldehydes is also revisited through the prism of the elaborated methodology, which leads to a whole new perspective on the pathways of this and similar reactions, with a multimolecular cascade of hydride transfers being more energetically favoured than a four-membered transition state.

Hydroboration of Aldehydes, Ketones, and Carbodiimides Promoted by Mono(imidazolin‐2‐iminato) Hafnium Complexes

Imidazolin‐2‐iminato hafnium complexes of the type [(ImRN)Hf(CH2Ph)3] were synthesized (ImtBuN = 1,3‐di‐tert‐butylimidazolin‐2‐iminato); ImDippN = 1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐iminato. The complexes were crystallized and structurally characterized. Despite the oxophilicity of the hafnium center, both hafnium complexes were catalytically active in the hydroboration of aldehydes, ketones, and carbodiimides. Herein, we present the influence of different substrates bearing electron‐withdrawing or electron‐donating groups on the catalytic reactions. Based on stoichiometric reaction in each process, plausible mechanistic scenarios are presented.

Potassium Fluoride‐Catalyzed Hydroboration of Aldehydes and Ketones: Facile Reduction to Primary and Secondary Alcohols

A catalytic hydroboration of various ketones and aldehydes can be achieved in the presence of inexpensive and commercially available inorganic salts containing fluoride anion. As a result, the reduction of carbonyl moieties to the corresponding primary and secondary alcohols can be achieved at room temperature under mild conditions.

N-Heterocyclic Germylene and Stannylene Catalyzed Cyanosilylation and Hydroboration of Aldehydes

Recent years have witnessed a significant growth in the area of low-valent main-group compounds due to their potential to activate small molecules. However, there is a paucity of examples of low-valent main-group compounds being used as single-site catalysts for organic transformations. This study represents the hydroboration and cyanosilylation reactions of a range of aldehydes by a benzannulated heavier N-heterocyclic germylene (1) and stannylene (2) under mild conditions. A wide variety of substrate scope was studied. The mechanistic pathway of the cyanosilylation reaction is initiated through the coordination of TMSCN with the catalyst followed by the attack of aldehydes. Conversely, hydroboration proceeds via formation of a donor–acceptor adduct between HBpin and the catalyst. Experimental and theoretical studies were performed to establish the mechanism.

Ge(ii) cation catalyzed hydroboration of aldehydes and ketones.

Well-defined germylene cations [(i-Bu)2ATI]GeOTf (4) and [(i-Bu)2ATIGe][GaCl4] (5) are isolated, and the catalytic utility of compound 4 for the hydroboration of a variety of aldehydes and ketones is reported (ATI = aminotroponiminate).

Alkaline Earth Metal Compounds of Methylpyridinato β-Diketiminate Ligands and Their Catalytic Application in Hydroboration of Aldehydes and Ketones

Ever increasing demand for green and sustainable chemical processes has set up a drive to replace transition metals with earth-abundant, nontoxic, and environmentally benign alternatives. In this regard, the alkaline earth metal complexes have attracted significant attention. Herein, we have used a β-diketiminato ligand with methyl-pyridine side arm to synthesize magnesium (1) and calcium (2) compounds. The constitutions of 1 and 2 have been confirmed by single crystal X-ray studies, which show that the magnesium and calcium atom in 1 and 2 possesses octahedral geometry. Subsequently, we have used them as catalysts (1 mol %) for hydroboration of a wide range of aldehydes using pinacolborane (HBpin) at room temperature. The strategy has further been extended to ketones with 2 mol % catalyst loading. DFT calculations have been performed to understand the mechanism.

Efficient and Selective Iron-Complex-Catalyzed Hydroboration of Aldehydes

An imine-coupled [Fe–N2S2]2 complex, prepared from a readily available benzothiazolidine ligand, catalyzes selectively the hydroboration of aliphatic and aromatic aldehydes at low catalyst loadings (0.1 mol %) using pinacolborane. Both mono- and disubstituted aromatic and aliphatic aldehydes are hydroborated selectively in the presence of ketones, nitriles, alkenes, amines, and halides. Reaction of the [Fe–N2S2]2 complex with CO and preliminary reaction progress kinetic studies point to a complex mechanism.

Titanium-Catalyzed Hydroboration of Aldehydes and Ketones

Titanium-Catalyzed Hydroboration of Aldehydes and Ketones

Diverse Activation Modes in the Hydroboration of Aldehydes and Ketones with Germanium, Tin, and Lead Lewis Pairs

AbstractIntramolecular germylene, stannylene, and plumbylene Lewis pairs were reacted with hexanal and yielded the cyclic addition products only with the germanium and tin reagents. In further reactivity studies, the hydroboration of aldehydes and ketones catalyzed by intramolecular germylene, stannylene, and plumbylene Lewis pairs was studied. In the case of the cyclic germylene Lewis pair, the product of the oxidative addition of pinacolborane at the germylene moiety was observed. According to stoichiometric as well as catalytic experiments, the intramolecular germylene Lewis pair acts as a catalyst in the hydroboration of aldehydes and ketones. The homologous stannylene Lewis pair forms a reactive tin hydride during the catalysis, which can also act as a catalyst in this transformation.

Diverse Activation Modes in the Hydroboration of Aldehydes and Ketones with Germanium, Tin, and Lead Lewis Pairs.

Intramolecular germylene, stannylene, and plumbylene Lewis pairs were reacted with hexanal and yielded the cyclic addition products only with the germanium and tin reagents. In further reactivity studies, the hydroboration of aldehydes and ketones catalyzed by intramolecular germylene, stannylene, and plumbylene Lewis pairs was studied. In the case of the cyclic germylene Lewis pair, the product of the oxidative addition of pinacolborane at the germylene moiety was observed. According to stoichiometric as well as catalytic experiments, the intramolecular germylene Lewis pair acts as a catalyst in the hydroboration of aldehydes and ketones. The homologous stannylene Lewis pair forms a reactive tin hydride during the catalysis, which can also act as a catalyst in this transformation.

ChemInform Abstract: Ruthenium Catalyzed Selective Hydroboration of Carbonyl Compounds.

AbstractThe Ru‐catalyzed hydroboration of aldehydes (I) and (III) followed by hydrolysis of the intermediate boronate esters with HCl affords primary alcohols (II) and (IV), resp., in high yields.

Mesoporous Silica-Supported Amidozirconium-Catalyzed Carbonyl Hydroboration

The hydroboration of aldehydes and ketones using a silica-supported zirconium catalyst is reported. Reaction of Zr(NMe2)4 and mesoporous silica nanoparticles (MSN) provides the catalytic material Zr(NMe2)n@MSN. Exhaustive characterization of Zr(NMe2)n@MSN with solid-state (SS)NMR and infrared spectroscopy, as well as through reactivity studies, suggests its surface structure is primarily ≡SiOZr(NMe2)3. The presence of these nitrogen-containing zirconium sites is supported by 15N NMR spectroscopy, including natural abundance 15N NMR measurements using dynamic nuclear polarization (DNP) SSNMR. The Zr(NMe2)n@MSN material reacts with pinacolborane (HBpin) to provide Me2NBpin and the material ZrH/Bpin@MSN that is composed of interacting surface-bonded zirconium hydride and surface-bonded borane ≡SiOBpin moieties in an approximately 1:1 ratio, as well as zirconium sites coordinated by dimethylamine. The ZrH/Bpin@MSN is characterized by 1H/2H and 11B SSNMR and infrared spectroscopy and through its reactivity wit...

Asymmetric Construction of (E)-δ-Stannyl Homoallylic Alcohols

The hydroboration of aldehydes with allylborane reagents usually gives homoallylic alcohols with terminal vinyl and β-substituents. In this work, the authors envisioned the β-carbocation-stabilizing effect of trialkyltin and succeeded the synthesis of (E)-δ-stannyl homoallylic alcohols in high stereoselectivities. These compounds could be very useful chiral synthetic building blocks upon further functionalization.