Hydroboration Reaction Research Articles

Copper‐Catalyzed Ring‐Opening Hydrosilylation and Hydroboration of Arylidenecyclopropanes

Comprehensive SummaryArylidenecyclopropanes (ACPs) are highly strained substrates that can be readily utilized for diverse transformations. This study showcases the outcomes of copper‐catalyzed ring‐opening hydrosilylation and hydroboration reactions of ACPs, showcasing precise cleavage of C—C bonds. The reaction presents an effective and convenient method for producing homoallylic silanes and boronates.

Hidden Boron Catalysis: A Cautionary Tale on TMEDA Inhibition.

Hidden boron catalysis plagues catalyzed hydroboration reactions, with the "catalyst" acting to mediate the decomposition of HBpin/HBcat to BH3 which is the actual (hidden) catalyst. N,N,N',N'-Tetramethylethylenediamine (TMEDA) has been used to identify hidden boron catalysis through trapping/inhibition. Kinetic analyses showed that TMEDA inhibition is only applicable below 60 °C and that other amine traps are likewise ineffective. Awareness of this temperature limitation reveals widespread hidden catalysis in previous methods and should limit future false negative tests.

Mechanism for Site-Selective Hydroboration of C70 Fullerene with Borane by DFT-D3 Study.

We studied the hydroboration of the C70 fullerene using both B3LYP-D3(BJ)/6-311G(d,p) and M06-2X-D3/6-311G(d,p) levels of theory, incorporating the empirical dispersion interaction, and Fukui index calculations. Potential energy surfaces (PESs) and Gibbs free energy surfaces (GFESs) were calculated for the pathways from four BH3 adducts (located at the AB, CC, D, and E sites) on the C70 to eight products formed by the 1,2-addition of BH3 across the four [6,6]-ring fused bonds (AB, CC, DE, and EE) and across the two [5,6]-ring fused bonds (AA and DD). These pathways are two-step consecutive reactions. We denoted the positions on the fullerene cage as A through E, from the pole to the equator, based on the D5h symmetry of the C70 fullerene. In the first step reaction, the product ratios for the four adduct intermediates should be as the primary intermediate BH3(D), the secondary intermediate BH3(AB), the tertiary intermediate BH3(CC), and the minor intermediate BH3(E), based on the Fukui indices. In addition, in the second step reaction, transition states (TSs) from four adduct intermediates to eight product isomers, namely, BH2(A)H (B) to BH2(E)H (E), were obtained using the QST2 method. The calculated reaction coordinates showed exothermic reactions for all bonds except the EE bond. We also confirmed the transition states by frequency calculations and intrinsic reaction coordinate (IRC) analyses. The PESs and GFESs suggest spontaneous processes for the four isomers, of which the primary products are BH2(A)H (B) and its isomer BH2(B)H (A), the secondary product is BH2(C)H (C), and the tertiary product is BH2(D)H (D), all formed through adduct intermediates. Therefore, through the hydroboration reaction of C70, we could predict and design the site selectivity of C70 by controlling the energy barrier of the transition state in the second step of the reaction. This implies that we could selectively synthesize mainly BH2(B)H (A) isomers across the AB-[6,6]-ring fused bond and also design BH2(D)H(D) isomers across the DD-[5,6]-ring fused bond. Also, the calculations of formation rate constants can well simulate the experimental ratio of two C70H2 isomers by the hydrolysis of BH2(A)H(B), BH2(B)H(A), and BH2(C)H(C) products at room temperature.

Flexible Coordination of SacNac Ligands in Iridium Complexes and their Application to Catalytic Hydroboration

AbstractHerein, we report the synthesis and characterization of a small family of Ir(I) and Ir(III) complexes supported by β‐thioketoiminates (SacNac) ligands. All complexes were fully characterized by IR, 1D and 2D NMR, and Elemental Analysis (e.a.) experiments. X‐ray diffraction studies were carried out to corroborate the structure of compounds [Ir(cod)(SacNac)] (1) (cod=1,5‐cyclooctadiene), [Ir(dmb)(SacNac)] (2) (dmb=2,3‐dimethyl‐1,3‐butadiene) and [IrCp*(SacNac‐H)(Cl)2] (8) (Cp*=pentamethyl‐cyclopentadienyl). Complexes 1 and 2 are Ir(I) species and have square‐planar geometry in solid state, with bond angles and distances that suggest semi‐aromaticity in the six‐membered ring. To the best of our knowledge, we report the first mono‐coordination mode of a SacNac ligand via sulfur atom in complex 8. Also, we report the first application of iridium‐SacNac complexes as catalytic precursors in hydroboration reactions, where Ir(III) species give the best results.

Atomically precise Cu32 nanoclusters with selenide doping: Synthesis, bonding, and catalysis

AbstractCopper nanoclusters with stable compositions and precise structures have long been sought after, as they possess properties that are absent in gold and silver counterparts. However, the creation of copper nanoclusters with novel compositions, structures, and functionalities remains largely unexplored in the literature. In this study, we demonstrate that selenide doping is an effective method for fabricating stable copper nanostructures through controlled synthesis and structure determination of a copper–selenide nanocluster. The nanocluster of [Cu32Se7(BnSe)18(PPh3)6]+ (denoted as Cu32Se7, Bn is benzyl) has been prepared by reducing copper salts in the presence of organic diselenides. The atomic structure of the Cu32Se7 cluster, accurately determined through single‐crystal X‐ray diffraction, reveals a core–shell arrangement of Cu20Se7@Cu12(BnSe)18(PPh3)6, where Se2− anions are well dispersed in the Cu20 framework. Notably, this cluster represents a rare example of copper–selenide semiconductor nanoclusters. Experimental and theoretical analysis shows strong interactions between Se ligands and metal atoms, resulting in high stability of the Cu32Se7 cluster. Furthermore, the cluster exhibits excellent catalytic performance in the hydroboration reaction of alkynes, producing a range of vinylboron compounds with adjustable structures and functions. Importantly, the cluster undergoes no structural or nuclearity changes during the reaction, as confirmed by extended X‐ray absorption fine structure and X‐ray photoelectron spectroscopy studies. This study not only presents a molecular cluster model highlighting the effectiveness of selenide dopants in fabricating new copper nanostructures but also paves the way for utilizing stable copper nanoclusters in diverse and exciting areas beyond catalysis.

Alkylaluminum Complexes Featuring Bridged Bis-Formylfluorenimide Ligands for Hydroboration of Aldehyde, Ketone, and Imines.

Three bis-formylfluorenimide ligands with different bridging groups were designed and synthesized, leading to the successful preparation of six novel alkylaluminum complexes through their reaction with alkylaluminum reagents (AlMe3 or AlEt3). Complexes 1 and 2 were obtained by the reaction of 1,2-propylene-bridged diamine (L1) with AlMe3 or AlEt3. By reacting 1,2-cyclohexylene-bridged diamine (L2) with AlMe3 or AlEt3 to obtain complexes 3 and 4. The above ligands formed a bidentate four-coordinate structure with alkylaluminum, which involved the elimination of one alkyl group as the ligand reacted with alkylaluminum. The complexes 5 and 6 were synthesized through the reaction of 1,2-phenylene-bridged diamine (L3) with AlEt3 in toluene or tetrahydrofuran. Notably, L3 exhibited unique reactivity compared with the other ligands, which formed a tridentate four-coordinated structure when reacting with alkylaluminum. The formation of the tridentate complex resulted from the introduction of a benzimidazole derivative or tetrahydrofuran (THF) molecule along with the elimination of two alkyl groups during its coordination with alkylaluminum. All complexes were characterized via 1H NMR, 13C NMR, and elemental analysis, with structural determination confirmed through X-ray. Furthermore, the catalytic activity in the hydroboration reaction of aldehyde, ketone, and imines was investigated with these complexes as catalysts. Among them, complex 1 demonstrated excellent catalytic performance (up to 99% yield) and broad substrate compatibility (more than 30 substrates) at low catalyst loading (1 mol %) under mild reaction conditions.

Access to 1,2- and 1,3-Amino Alcohols via Cu-Catalyzed Enantioselective Borylations of Allylamines.

We report Cu-catalyzed enantioselective borylation/oxidation sequences that afford either enantioenriched 1,2- or 1,3-amino alcohols starting from N,N-protected allylamines as a common platform. The approach is based on the mechanistic specificities of catalytic hydroboration and protoboration reactions, which formally install a boron unit and a hydrogen atom at opposite positions of a C═C bond. The nature of the substituents of the carbon-carbon double bond also exerts a determining influence on the regioselectivity of insertion of the catalytically active Cu species. Both protocols are regio- and enantioselective and applicable to a broad range of substrates. Homoallylamines are also competent substrates, providing access to 1,3- and 1,4-amino alcohols.

Hydroboration of Acid Anhydrides Catalyzed by Aluminumhydride Supported by β-diketimines Ligand

Abstract The hydroboration reaction was historically catalyzed by transition metals. Nevertheless, the known aluminum hydride catalyst supported by β-diketimines ligand for catalyzing the hydroboration reaction of acid anhydride compounds reduces pollution and the cost associated with those heavy metals while broadening the synthesis pathway of organoboranes. Most importantly, this innovative substance has not been previously reported. In this regard, this research investigates the excellent performance of the aluminum hydride catalyst in the hydroboration of acid anhydrides, observing short reaction times and high yields. Furthermore, we found long-term stability as well as recyclability in LAlH2, proven to be an environmentally friendly green catalyst.

Synthesis and structural characterization of 2,2′:6,2″-Terpyridine zinc Formate: Hydroboration and hydrosilylation of CO2 and carbonyl compounds

The zinc formate compound (terpy)Zn(O2CH)2 is obtained via the reaction of Zn(O2CH)2 with 2,2′:6′,2″-terpyridine (terpy) and has been structurally characterized by X-ray diffraction as possessing formate ligands that coordinate via a κ1-monodentate coordination mode, which is in accord with IR spectroscopic studies. In terms of reactivity, (terpy)Zn(O2CH)2 participates in catalytic transformations involving CO2 and carbonyl compounds via hydrosilylation and hydroboration reactions. For example, (terpy)Zn(O2CH)2 achieves hydroboration of Me2CO and Ph2CO by HBpin to afford R2C(H)OBpin, and triple insertion of Ph2CO, PhC(O)Me, Me2CO and PhCHO into the Si–H bonds of PhSiH3 to afford PhSi[OCH(R)R’]3. In addition, CO2 also undergoes hydroboration and hydrosilylation by HBpin and (MeO)3SiH in the presence of (terpy)Zn(O2CH)2 to afford HCO2Bpin and HCO2Si(OMe)3, respectively.

2,6-Bis(pyrazol-1-yl)pyridine cobalt-catalyzed high selective hydroboration of alkenes

A novel series of cobalt (II) catalysts featuring 2,6-bis(pyrazol-1-yl)pyridine ligands have been synthesized for the purpose of achieving high selectivity in hydroboration reactions of alkenes. These catalysts function effectively under mild, solvent-free conditions, demonstrating contrasting selectivities: Markovnikov-type selectivity for vinylarenes and anti-Markovnikov-type selectivity for alkyl alkenes. This dual-selectivity system offers a versatile platform for the controlled hydroboration of a diverse range of alkene substrates.

Predicting Activation of Small Molecules Including Dinitrogen via a Carbene with a σ0π2 Electronic Configuration.

Although the main group species in the s and p blocks have begun to gain prominence in the field of dinitrogen (N2) activation in recent years, reports of carbene-mediated N2 activation remain particularly rare, especially for carbenes with a σ0π2 electronic configuration. Herein, we demonstrate examples of N2 activation initiated by a carbene with a σ0π2 electronic configuration and consequent N2 hydroboration reaction (with a reaction barrier as low as 19.9 kcal/mol) via density functional theory calculations. Meanwhile, the "push-pull" electronic effect upon introduction of a hydroborenium complex facilitates the generation of a thermodynamically and kinetically more stable product. In addition, such a σ0π2 carbene can also activate a series of H-X (X = H, CH3, or Bpin) bonds through an oxidative addition process with activation energies ranging from 6.0 to 18.0 kcal/mol. Our findings highlight the importance of σ0π2 carbenes in the field of small molecule activation, especially N2 activation.

Hydrogenolysis of Haloboranes: from Synthesis of Hydroboranes to Formal Hydroboration Reactions.

Hydroboranes are versatile reagents in synthetic chemistry, but their synthesis relies on energy-intensive processes. Herein, we report a new method for the preparation of hydroboranes from hydrogen and the corresponding haloboranes. Triethylamine (NEt3) form with dialkylchloroboranes a Frustrated Lewis Pair (FLP) able to split H2 and afford the desired hydroborane with ammonium salts. Unreactive haloboranes were unlocked using a catalytic amount of Cy2BCl, enabling the synthesis of commonly used hydroboranes such as pinacolborane or catecholborane. The mechanisms of these reactions have been examined by DFT studies, highlighting the importance of the base selection. Finally, the system's robustness has been evaluated in one-pot B-Cl hydrogenolysis/hydroboration reactions of C=C unsaturated bonds.

Hydrogenolysis of haloboranes: from synthesis of hydroboranes to formal hydroboration reactions

Hydroboranes are versatile reagents in synthetic chemistry, but their synthesis relies on energy‐intensive processes. Herein, we report a new method for the preparation of hydroboranes from hydrogen and the corresponding haloboranes. Triethylamine (NEt3) form with dialkylchloroboranes a Frustrated Lewis Pair (FLP) able to split H2 and afford the desired hydroborane with ammonium salts. Unreactive haloboranes were unlocked using a catalytic amount of Cy2BCl, enabling the synthesis of commonly used hydroboranes such as pinacolborane or catecholborane. The mechanisms of these reactions have been examined by DFT studies, highlighting the importance of the base selection. Finally, the system's robustness has been evaluated in one‐pot B‐Cl hydrogenolysis/hydroboration reactions of C=C unsaturated bonds.

Hydroboration of Terminal Alkynes Catalyzed by a Mn(I) Alkyl PCP Pincer Complex Following Two Diverging Pathways.

A stereo- and regioselective Mn(I)-catalyzed hydroboration of terminal alkynes with pinacolborane (HBPin) is described. The hydroboration reaction is highly Z-selective in the case of aryl alkynes and E-selective in the case of aliphatic alkynes. The reaction requires no additives or solvents and proceeds with a catalyst loading of 1 mol % at 50-70 °C. The most active precatalyst is the bench-stable alkyl Mn(I) complex cis-[Mn(PCP-iPr)(CO)2(CH2CH2CH3)]. The catalytic process is initiated by the migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate. This species undergoes C-H and B-H bond cleavage of the alkyne (aromatic alkynes) and HBPin (in the case of aliphatic alkynes) forming the active Mn(I) alkynyl and boryl catalysts [Mn(PCP-iPr)(CO)(C≡CR)] and [Mn(PCP-iPr)(CO)(BPin)], respectively. A broad variety of aromatic and aliphatic alkynes was efficiently and selectively borylated. Mechanistic insights are provided based on experimental data and DFT calculations. The functionalized alkenes can be used for further applications in cross-coupling reactions.

Multisite Amino‐Allylidene Ligands from Thermal CO Elimination in Diiron Complexes and Catalytic Activity in Hydroboration Reactions

AbstractThe new diiron(I) complexes [Fe2Cp2(μ‐CO){μ‐k3C,kN‐C(R1)C(R2)C(CN)NMe(R)}], 3 a–o (R=alkyl or 4‐C6H4OMe; R1=alkyl, aryl, ferrocenyl (Fc), thiophenyl, CO2Me or SiMe3; R2=H, Me or CO2Me) were synthesized in moderate to high yields from the thermal decarbonylation of the bis‐carbonyl precursors 2 a–o, and were structurally characterized by IR and NMR spectroscopy, and single crystal X‐ray diffraction in four cases. Electrochemical behavior of one complex was also investigated. Complexes 3 a–o comprise a highly functionalized, multisite amino‐(cyano)allylidene ligand, including metal coordination of a tertiary amine group. Selected complexes displayed negligible to moderate catalytic activity in CO2/propylene oxide coupling, working under ambient conditions. Additionally, they were investigated as catalysts for the conversion of benzaldehyde to the corresponding borate ester 6 a, using pinacolborane (HBpin) as the borylating agent. Most complexes achieved good conversions at room temperature with 1 % catalyst loading, and data highlight the significant influence of the multisite ligand substituents on the catalytic performance. Notably, complex 3 m (featuring R=4‐methoxyphenyl, R1=Fc, R2=H) displayed the highest activity and effectively catalyzed the hydroboration of various aldehydes and ketones. A plausible mechanistic cycle involves metal coordination of the carbonyl substrate, its activation being possibly facilitated by intramolecular interactions.

Cobalt-Catalyzed Reduction of Aldehydes to Alcohols via the Hydroboration Reaction.

A method for the reduction of aldehydes with pinacolborane catalyzed by pincer cobalt complexes based on a triazine backbone is developed in this paper. The presented methodology allows for the transformation of several aldehydes bearing a wide range of electron-withdrawing and electron-donating groups under mild conditions. The presented procedure allows for the direct one-step hydrolysis of the obtained intermediates to the corresponding primary alcohols. A plausible reaction mechanism is proposed.

Cu(II)-Catalyzed Hydroboration Reactions of 1,1-Disubstituted α,β-Unsaturated Ketones, Esters, and Amides in Pure Water.

Here, a Cu2(OH)2CO3-catalyzed hydroboration reaction of 1,1-disubstituted α,β-unsaturated compounds has been developed. The reaction was carried out using water as a solvent at room temperature except for N-monosubstituted α,β-unsaturated amides. This method is applicable to diverse 1,1-disubstituted α,β-unsaturated ketones, esters, and amides, showing excellent reactivity (up to 98% yield). Gram-scale experiments and functional group transformations further demonstrated the practicality of this method.

Synthesis, Characterization, and Catalytic Performance of a New Heterobimetallic Y/Tb Metal-Organic Framework with High Catalytic Activity.

A three-dimensional heterobimetallic porous structure with the formula {[Y3.5Tb1.5L6(OH)3(H2O)1.5 (DMF)1.5] n ·1.5H2O·DMF} n (L = 3-amino-4-hydroxybenzoate) (Y/Tb-MOF) has been synthesized and characterized by single crystal and powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), electrophoretic mobility, and Fourier transform infrared (FTIR) spectroscopy. The structure presents two metal environments: a bioaugmented isosceles wedge (mm2) MO8 and a tricapped trigonal prism (-6m2) MN3O6. These configurations facilitate the creation of channels with a diameter of 10.7 Å, enabling its utilization as an active catalyst where the heterobimetallic nature of the assembly will be explored. This mixed-metal metal-organic framework has been tested in the cycloaddition of epoxides with carbon dioxide as well as in the cyanosilylation and hydroboration reactions of carbonylic substrates. Additionally, a monometallic Tb-MOF analogue has been synthesized for comparative evaluation of their catalytic performances. Both the mixed metal and monometallic variants exhibit outstanding activity in the cyanosilylation and hydroboration of carbonyls and in the synthesis of carbonates under CO2 pressure. However, only the latter exhibits high recyclability.

Planar Core and Macrocyclic Shell Stabilized Atomically Precise Copper Nanocluster Catalyst for Efficient Hydroboration of C-C Multiple Bond.

Atomically precise metal nanoclusters (NCs) have become an important class of catalysts due to their catalytic activity, high surface area, and tailored active sites. However, the design and development of bond-forming reaction catalysts based on copper NCs are still in their early stages. Herein, we report the synthesis of an atomically precise copper nanocluster with a planar core and unique shell, [Cu45(TBBT)29(TPP)4(C4H11N)2H14]2+ (Cu45) (TBBT: 4-tert-butylbenzenethiol; TPP: triphenylphosphine), in high yield via a one-pot reduction method. The resulting structurally well-defined Cu45 is a highly efficient catalyst for the hydroboration reaction of alkynes and alkenes. Mechanistic studies show that a single-electron oxidation of the in situ-formed ate complex enables the hydroboration via the formation of boryl-centered radicals under mild conditions. This work demonstrates the promise of tailored copper nanoclusters as catalysts for C-B heteroatom bond-forming reactions. The catalysts are compatible with a wide range of alkynes and alkenes and functional groups for producing hydroborated products.

Cobalt-Catalyzed Selective Hydroboration of 1,3-Enynes with HBpin toward 1,3-Dienylboronate Esters.

An efficient cobalt-catalyzed selective hydroboration of 1,3-enynes with HBpin toward 1,3-dienylboronate esters is disclosed. With a commercially available catalytic system of Co(acac)2 and dppf, the hydroboration reactions proceeded well to afford a wide range of 1,3-dienylborates in moderate to high yields. This protocol features a cheap base-metal catalytic system, broad substrate scope, excellent selectivity, easy gram-scale preparation, and good functional group tolerance and provides access to synthetically valuable 1,3-dienylborates.