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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. [ABSTRACT FROM AUTHOR]

Remote C(sp3)–H bond functionalization reactions are environmentally benign methods for not only acyclic molecules but also cyclic molecules. However, products in previous reports have been limited to aliphatic five-membered ring structures. Herein, we developed an unprecedented multitasking rhodium-catalyzed reaction that can synthesize benzene-fused heterocyclic compounds, 2,3-disubstituted dihydrobenzofurans, through a remote C(sp3)–H bond functionalization reaction (chain-walking/cycloisomerization/hydroboration reaction). This catalytic system promotes a twice-occurring chain-walking/functionalization set in one pot, thus allowing the synthesis of dihydrobenzofurans with various side chain lengths at the 2- and 3-positions. [ABSTRACT FROM AUTHOR]

The low-valent germanium and tin hydrides, [LMH; L = {(ArHN)(ArN)-C＝N–C＝(NAr)(NHAr); Ar = 2,6-Et2-C6H3}; M = Ge; (Ge-1), Sn (Sn-2)] bearing bis-guanidinato anions are employed as catalysts for chemoselective reduction of heterocumulenes via hydroboration reactions. This protocol demonstrates that a wide range of carbodiimides (CDI), isocyanates, isothiocyanates, and isoselenocyanates undergo partial reduction, yielding the corresponding N-boryl formamidine, N-boryl formamide, N-boryl thioformamide, and N-boryl selenoformamide products, respectively. Isocyanates and isothiocyanates are further converted into N-boryl methyl amines through hydrodeoxygenation (HDO) and hydrodesulfurization (HDS) reactions in the presence of catalyst Ge-1. Additionally, catalyst Sn-2 exhibits excellent inter and intra-molecular chemoselectivity over other functional groups. Based on stoichiometric experiments, a plausible catalytic cycle for chemoselective hydroboration of heterocumulenes is proposed. [ABSTRACT FROM AUTHOR]

Although cobalt(I) bis-phosphine complexes have been implicated in many selective C–C bond-forming reactions, until recently relatively few of these compounds have been fully characterized or have been shown to be intermediates in catalytic reactions. In this paper we present a new practical method for the synthesis and isolation of several cobalt(I)-bis-phosphine complexes and their use in Co(I)-catalyzed reactions. We find that easily prepared (in situ generated or isolated) bis-phosphine and (2,6-N-aryliminoethyl)pyridine (PDI) cobalt(II) halide complexes are readily reduced by 1,4-bis-trimethylsilyl-1,4-dihydropyrazine or commercially available lithium nitride (Li3N), leaving behind only innocuous volatile byproducts. Depending on the structures of the bis-phosphines, the cobalt(I) complex crystallizes as a phosphine-bridged species [(P∼P)(X)CoI[μ-(P∼P)]CoI(X)(P∼P)] or a halide-bridged species [(P∼P)CoI[μ-(X)]2CoI(P∼P)]. Because the side-products are innocuous, these methods can be used for the in situ generation of catalytically competent Co(I) complexes for a variety of low-valent cobalt-catalyzed reactions of even sensitive substrates. These complexes are also useful for the synthesis of rare cationic [(P∼P)CoI-η4-diene]+ X− or [(P∼P)CoI-η6-arene]+ X− complexes, which are shown to be excellent single-component catalysts for the following regioselective reactions of dienes: heterodimerizations with ethylene or methyl acrylate, hydroacylation and hydroboration. The reactivity of the single-component catalysts with the in situ generated species are also documented. [ABSTRACT FROM AUTHOR]

In this paper, we compare the reactivity of a series of triaryl borates B(OArx)3 as catalysts for the hydroboration of alkenes and alkynes. It was observed that commercially available B(OPh)3 performed the poorest, whereas catalysts with o-F atoms appeared to perform much better. [ABSTRACT FROM AUTHOR]

A series of tri-coordinated zinc alkyl complexes with the general molecular formula [κ2NE-{NHIRP(Ph)(E)N-Dipp}ZnEt] [R = Dipp (2,6-diisopropylphenyl), E = S (3a), Se (3b) and R = tBu (tert-butyl), E = S (4a), Se (4b)] bearing imino-phosphanamidinate chalcogenide ligands were prepared in good yields from the reaction between the protic imino-phosphanamidinate chalcogenide ligand [NHIRP(Ph)(E)NH-Dipp] [R = Dipp, E = S (1a), Se (1b) and R = tBu, E = S (2a), Se (2b)] and diethylzinc at room temperature. The molecular structures of all the zinc complexes were established by single-crystal X-ray diffraction analysis. In the solid state, all complexes exhibited a distorted trigonal planar geometry around the zinc ion. Metal-chalcogenide (Zn–S/Se) interactions were observed in the coordination sphere. These zinc alkyl complexes were employed as pre-catalysts in the hydroboration reaction of nitriles and esters to obtain the corresponding N,N-diborylamines and boronate esters, respectively, under ambient conditions. A wide substrate scope of nitriles and esters is presented. [ABSTRACT FROM AUTHOR]

Carbon substituted cobalt bis(dicarbollide) alkyl halides [(1-X-(CH2)n-1,2-C2B9H10)(1,2-C2B9H11)-3,3′-Co]Me4N (X = Br, I; n = 1–3) are prepared in high yields (>90%) from their corresponding alcohols without side skeletal substitutions. These species offer access to the synthesis of aromatic cobalt bis(dicarbollide) amines, however only for particular terminal halogen substitution, the propylene pendant arm, and under appropriately controlled reaction conditions. Thus, the compounds substituted at cage carbon atoms with a propylene linker and terminal aromatic amine groups could be prepared. In other cases, numerous irregular reaction pathways occur, undoubtedly as a consequence of the bulky anionic boron cage in close proximity to the reaction site. Among them, an unusual intramolecular hydroboration forming rigidified carbon-to-boron bridged isomeric anions with an asymmetric structure that correspond to formulae [(1,8′-μ-C2H4)-(1,2-C2B9H10)(1′,2′-C2B9H10)-3,3′-Co]− and [(1,7′-μ-C2H4)-(1,2-C2B9H10)(1′,2′-C2B9H10)-3,3′-Co]− is described herein and the former isomer is structurally characterized. This product with a restrained geometry is widely accessible through nucleophile and/or thermally induced decomposition of (pseudo)halides attached to the cage via an ethylene linker. Surprisingly enough, also doubly bridged isomeric species [(1,8-μ-C2H4-1,2-C2B9H9)2-3,3′-Co]− and [(1,7-μ-C2H4-1,2-C2B9H9)2-3,3′-Co]− are available in good yield using these methods. Furthermore, other more typical side reactions are discussed, i.e. nucleophilic reactions of propyl halides with Me3N formed apparently by disproportionation of Me4N+ at higher temperatures or with pyridine used as a base. [ABSTRACT FROM AUTHOR]

PNP pincers represent some of the most well-studied ligand systems in coordination chemistry owing to their high thermal and chemical stability, and the predictable metal coordination geometries of associated metal complexes. Examples of first-row transition metal complexes bearing acridine-based PNP pincer ligands are extremely rare. This study reports the preparation and structural authentication of acridine-based copper(I) PNP complexes, which reveal the profound effects that the steric bulk of methylene-tethered P-substituents has on metal centre coordination number and geometry. The capacity of these systems to mediate copper-catalysed alkyne hydroboration and the borylation of aryl halides is also investigated. [ABSTRACT FROM AUTHOR]

Iron complexes bearing new silyl-NHC bidentate ligands were synthesised by treating Fe3(CO)12 with a mixture of N-(hydrosilyl)methyl imidazolium salts and a base. These complexes showed high performance in the catalytic double hydroboration of nitrile with pinacolborane (HBpin) to produce N,N-bis(boryl)amine by a combination of UV irradiation and mild heating (60 °C). The product yields for the hydroboration of aromatic and aliphatic nitriles reached 85%–95% (NMR) using an iron complex (5 mol%). Reducing the loading amount of the iron complex to 0.5 mol% still afforded the products in high yields. An analogous ruthenium complex, which was similarly synthesised using Ru3(CO)12, showed lower activity. Stoichiometric reactions of the iron complex with nitriles afforded Fe(0)-N-silylimine complexes, which may be dormant states in nitrile hydroboration. A catalytic mechanism including Fe(0) N-silylimine species is proposed. [ABSTRACT FROM AUTHOR]

Reactions between the borane, HBpin (pin = pinacolato), and three magnesium(i) dimers, [{(ArNacnac)Mg–}2] (ArNacnac = [(ArNCMe)2CH]−; Ar = xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), have been carried out in 2 : 1, 5 : 1 and 20 : 1 ratios. In all cases, NMR spectroscopic studies have revealed complex mixtures of many known and novel products from these reactions. From extracts of the crude reaction mixtures, low yields of ten compounds, representing six different types of complexes between β-diketiminato magnesium fragments and boron containing ligands, have been isolated and crystallographically characterised. These include unprecedented examples of compounds in which the γ-carbon of the β-diketiminate ligand has been activated by boron hydride fragments. In addition, boryloxide (OBpin), borate ([B(pin)2]− or [(pin)BH2]−), B–O bond ruptured [pinBH2]−, a diborane(5) dianion, or BH3 have been shown to be incorporated into the isolated complexes. The complexity of the products of the reported reactions are discussed in light of recently published patents and papers which report that magnesium(i) dimers act as efficient catalysts, or as pre-catalysts to well defined catalysts, for the hydroboration of a variety of unsaturated substrates by HBpin. Our results strongly suggest that magnesium(i) dimers are not catalysts in these reactions, and that there are many more potential (pre-)catalysts that are generated in these reactions, than have previously been reported. [ABSTRACT FROM AUTHOR]

The conjugated bis-guanidinate (CBG)-supported zinc hydride {LZnH}2; L = {(ArHN)(ArN)–C＝N–C＝(NAr)(NHAr); Ar = 2,6-Et2-C6H3} (I) is utilized as a catalyst for the hydroboration of esters with pinacolborane (HBpin) under mild reaction conditions. Various aryl and alkyl substrates containing electron-donating, withdrawing, and cyclic groups of esters are effectively converted into alkoxy boronate esters as products upon hydroboration. Furthermore, stoichiometric experiments have been performed to understand the plausible reaction mechanism for the hydroboration of esters. Additionally, complex (I) was used for the hydroboration of carbonate, carboxylic acid, and anhydride substrates to showcase the broad substrate scope. [ABSTRACT FROM AUTHOR]

We herein report the regio- and chemoselective hydroboration of terminal alkynes with pinacolborane by a series of constrained-geometry catalyst-type or CGC-type rare earth metal monoalkyl complexes. This protocol offers a 100% atom-efficient and straightforward route for the synthesis of a variety of (E)-1-alkenylborons with the advantages such as high yield, high E-selectivity up to >99.9%, multiple metal center, broad substrate scope, broad functional-group tolerance, and no necessity for a solvent. A gram-scale synthesis and subsequent transformations of (E)-1-alkenylboron to several functional compounds suggest the practical applications of this synthetic methodology. The reaction mechanism has been explored through ESI-MS, isotopic labeling experiments, and in situ1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

A number of aryl building blocks for the synthesis of two xanthomonadin natural product pigments, as well as a related analogue, were accessed using a divergent hydroboration/bromoboration approach from a key alkynyl intermediate. A new approach towards substitution patterns around the ring was adopted following the isolation of an unexpected regioisomer from the bromination reaction. Potential coupling reactions onto these building blocks were explored, with a successful Sonogashira coupling performed on the key alkynyl intermediate, and with the key debrominated styrenyl boronate ester intermediate functionalised both by preliminary Suzuki–Miyaura coupling and by iododeboronation/Heck–Mizoroki coupling. Coupling reactions with brominated styrenyl intermediates proved much more challenging due to the instability of the intermediates to cross‐coupling, but some studies have shown promise. Several polyenyl pigments related to Xanthomonadin are known to be produced by some plant‐based bacteria, acting as inhibitors of UV‐mediated oxidative stress. This paper discusses these unusual, little known and long polyenes, and lays out a strategy to construct these unstable systems. [ABSTRACT FROM AUTHOR]

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Despite p-block clusters being known for over a century, their application as catalysts to mediate organic transformations is underexplored. Here, the boron functionalized [P7] cluster [(BBN)P7]2- ([1]²-; BBN = 9-borabicyclo[3.3.1]nonane) is applied in the dearomatized reduction of pyridines, as well as the hydroboration of imines and nitriles. These transformations afford amine products, which are important precursors to pharmaceuticals, agrochemicals, and polymers. Catalyst [1]2- has high stability in these reductions: recycling nine times in quinoline hydroboration led to virtually no loss in catalyst performance. The catalyst can also be recycled between two different organic transformations, again with no loss in catalyst competency. The mechanism for pyridine reduction was probed experimentally using variable time normalization analysis, and computationally using density functional theory. This work demonstrates that Zintl clusters can mediate the reduction of nitrogen containing substrates in a transition metal-free manner. [ABSTRACT FROM AUTHOR]

The hydroboration of alkynes with bis(pinacolato)diboron (B2pin2) using H2O or untreated H2O as a solvent is a challenging task. This work reports the aqueous N-heterocyclic carbene (NHC)-catalyzed hydroboration of alkynes with B2pin2, in which a wide range of alkynes with different functional groups are tolerated. The proposed NHC active species are formed through a nonclassical strategy in contrast to the traditional method involving deprotonation of the imidazolium salts in the presence of a base. The proposed NHC-catalyzed hydroboration process can be performed using untreated H2O as a solvent under an air atmosphere in the absence of exogenous bases. Mechanistic investigations, including control experiments, Fourier transform infrared spectroscopy, and density functional theory calculations revealed that the NHC generated in situ is the true active species. Moreover, an in situ generated diboron-NHC adduct, which acts as a reservoir of NHC and is critical for the stability of NHC in aqueous media, was isolated and fully characterized. [ABSTRACT FROM AUTHOR]

Various applications of bis(catecholato)germanes in catalysis were examined. The hydrosilylation of benzaldehydes, hydroboration of phenylacetylene derivatives, and Friedel–Crafts alkylation using arylalkenes and either diphenylamine or anisole was achieved. Furthermore, the recently reported oligomerization of α-methylstyrene catalyzed by bis(catecholato)germanes with weak donor ligands was examined further. The formation of a trimer species was observed in DCM. VTNA and Hammett analyses of the oligomerization reaction were conducted and an updated mechanism for bis(catecholato)germane catalysis is proposed. [ABSTRACT FROM AUTHOR]

The MOF material NU-1000 was employed to host Ni tripodal complexes prepared from new organometallic precursors [HNi(κ4(E,P,P,P)-E(o-C6H4CH2PPh2)3], E = Si (Ni-1), Ge (Ni-2). The new heterogeneous catalytic materials, Ni-1@NU-1000 and Ni-2@NU-1000, show the advantages of both homogeneous and heterogeneous catalysts. They catalyze the hydroboration of aldehydes and ketones more efficiently than the homogeneous Ni-1 and Ni-2, under aerobic conditions and show recyclability. [ABSTRACT FROM AUTHOR]

A crucial step in the formation of mono-aminoboranes (R2N–BH2) from the corresponding imine–BH3 adducts, under mild reaction conditions, is the 1,3-hydride shift. We offer experimental and theoretical insights into this molecular rearrangement according to two mechanistic pathways: intra-molecular (unimolecular) and inter-molecular (bimolecular). Even though a few experimental observations were inconclusive, an isotope-based experiment suggested that the 1,3-hydride shift occurs bimolecularly. In addition, the shape of the potential energy landscape, generated via the computational means, strongly suggests that these reactions are bimolecular. Relative energy gradient analysis enabled to identify the driving forces according to both scenarios and to explain the unusual shape of the minimum energy path in a unimolecular process. Our results imply that elevated temperature (60 °C) supplies the reactants with sufficient energy to cross the barrier, whereby each collision with properly oriented reactants results in mono-aminoborane formation. [ABSTRACT FROM AUTHOR]

The synthesis and full characterisation of two silver(I) amido complexes, stabilised by ancillary N-heterocyclic carbene (NHC) ligands is presented. The light stable complexes [Ag(IDipp)HMDS] 3 and [Ag(IAd)HMDS] 4 were explored as suitable pre-catalysts in the hydroboration and hydrosilylation of a range of carbonyl substrates, with complex 3 out-performing 4 and our previous phosphine-stabilised lead catalyst [Ag(PCy3)HMDS] 5. This study highlights that changing the stabilising Lewis donor in the silver(I)amide system has an influence on catalytic efficiency. Finally, to shed light on the catalytic differences of pre-catalysts 3–5, we used a suite of programs to examine the influence of steric bulk on the Lewis donor ligand including percent buried volume (%VBur), Solid-G and AtomAccess which revealed the most sterically protected Ag(I) metal centre correlated to the most effective pre-catalyst 3. [ABSTRACT FROM AUTHOR]

Preparation of catalytically active dinuclear transition metal complexes with an open coordination sphere is a challenging task because the metal sites tend to be "saturated" with excess donor atoms around during synthesis. By isolating the binding scaffolds with the metal–organic framework (MOF) skeleton and installing metal sites through post-synthetic modification, we succeed in constructing a MOF-supported metal catalyst, namely FICN-7-Fe2, with dinuclear Fe2 sites. FICN-7-Fe2 effectively catalyses the hydroboration of a broad range of ketone, aldehyde, and imine substrates with a low loading of 0.05 mol%. Remarkably, kinetic measurements showed that FICN-7-Fe2 is 15 times more active than its mononuclear counterpart FICN-7-Fe1, indicating that cooperative substrate activation on the two Fe centres significantly enhances the catalysis. [ABSTRACT FROM AUTHOR]

The catalysts used to catalyze the hydroboration of nitriles or carbodiimides usually have some disadvantages such as complex structure, high cost, large pollution of environment and so on. It is an important development direction to use the main group metals instead of the transition metals to reduce the costs and realize green catalysis. In this paper, using NaH or NaOH as a catalyst, an efficient reaction of nitrile or carbodiimide with pinacol borane (HBPin) has been achieved. It was found that 3.5 mol% of NaH participated in the hydroboration reaction in a simple and effective method under slight solvent‐free circumstances. In addition, intermolecular chemoselectivity hydroboration of nitrile and substrates with different functional groups was also investigated by employing three different catalysts. This reaction uses the inorganic alkali with simple structure, commercially available and low cost to synthesize organoborane compounds, which provides ideas for industrial development. [ABSTRACT FROM AUTHOR]

An efficient, simple, metal and ligand free, regioselective hydroboration of alkenes has been developed using pinacolborane (HBpin) as a reducing reagent and 1-ethyl-methylpyrrolidinium triflate [EMPyrr][OTf] as a non-corrosive and recyclable organocatalyst. The described protocol is scalable and compatible with a variety of alkenes offering the desired organoboron compounds in moderate-to-excellent yields. The system was reused in 30 cycles with comparable effectivity and stable selectivity of the process, increasing its sustainability. The utility of the obtained alkylboronates was checked in various subsequent transformations such as Suzuki–Miyaura coupling, Zweifel olefination and oxidation. Moreover, a reaction mechanism based on previously reported literature and NMR studies was proposed. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and catalytic application of six aluminum alkyl complexes supported by various imino-phosphanamidinate chalcogenide ligands are described. Six different unsymmetrical imino-phosphanamidinate chalcogenide ligands [NHIRP(Ph)(E)NH-Dipp] [R = 2,6-diisopropylphenyl (Dipp), E = S (2a-H), Se (2b-H); R = mesityl (Mes), E = S (3a-H), Se (3b-H); R = tert-butyl (tBu), E = S (4a-H), Se (4b-H)] were prepared by the oxidation of respective imino-phosphanamide ligands (1a, 1b and 1c) with elemental chalcogen atoms (S and Se). The aluminum complexes with imino-phosphanamidinate chalcogenide ligands with the general formulae [κ2NN-{NHIRP(Ph)(E)N-Dipp}AlMe2] [R = Dipp, E = S (5a), Se (5b); R = Mes, E = S (6a), Se (6b)] or [κ2NE-{NHIRP(Ph)(E)N-Dipp}AlMe2] [R = tBu, E = S (7a), Se (7b)] were synthesized in good yields from the reaction of the suitable protic ligands (2a,b-H–4a,b-H) and trimethylaluminum in a 1 : 1 molar ratio in toluene at room temperature. All the protic ligands and aluminum complexes were well characterized by multi-nuclear NMR spectroscopy, and the solid-state structures of 2a,b-H–4a,b-H, 5a,b–6a,b and 7b are established by single crystal X-ray diffraction analysis. The aluminum complexes 5a,b–7a,b were tested as catalysts for the hydroboration of nitriles, alkynes, and alkenes under mild conditions. The catalytic hydroboration reactions of nitriles, alkynes, and alkenes were accomplished with complex 5b at a mild temperature under solvent-free conditions to afford a high yield of the corresponding N,N-diborylamines, vinylboranes and alkyl boronate esters, respectively. [ABSTRACT FROM AUTHOR]

Triphosphinoboranes activated the B–H bond in the BH3 molecule without any catalysts at room temperature. Hydroboration reactions led to boraphosphacyloalkanes with diverse structures. The outcomes of reactions depend on the size of the phosphanyl substituent on the boron atom of the parent triphosphinoborane, where derivatives of boraphosphacyclobutane and boraphosphacyclohexane were obtained. Furthermore, the precursor of triphosphinoboranes, namely bromodiphosphinoborane, also exhibited high reactivity towards H3B·SMe2, yielding bromo-substituted boraphosphacyclobutane. The obtained products were characterized by heteronuclear NMR spectroscopy, single crystal X-ray diffraction, and elemental analysis. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the first repetitive batch selective hydroboration of terminal and internal alkynes in a series of poly(ethylene glycols) (PEGs), used as solvents and media for the immobilization of a Ru(CO)Cl(H)(PPh3)3 catalyst. The system based on 2 mol% of Ru−H complex and poly(ethylene glycol) with α‐methyl/ω‐trimethylsilyl ending groups (Mw=2000) was found to be the most efficient, and was able to carry out over 19 complete runs with the Z‐addition of pinacolborane to the phenylacetylene. With the use of one portion of the developed catalytic system, the hydroboration of five different alkynes was performed consecutively, and led to five different products being obtained with high yields and purities. The developed strategy was characterized by high TON values and it was found to be the best recyclable protocol, leading to alkenyl boronates in all reported cases. [ABSTRACT FROM AUTHOR]

A green and sustainable electrochemical hydroboration of carbonyl compounds with HBpin has been reported for the first time. Under catalyst-free and additive-free mild reaction conditions the corresponding boronic esters were obtained in excellent yields via the simple electrochemical hydroboration of various aldehydes and ketones with HBpin at room temperature. The scale-up reaction demonstrated potential practical applications. A plausible reaction mechanism was proposed based on the corresponding deuterium-labelling, radical inhibition and cyclic voltammetry experiments. [ABSTRACT FROM AUTHOR]

Six iron(0) tricarbonyl complexes (1a–f) with a η4-1-azadiene moiety were prepared and their performance in the hydroboration of unsaturated organic compounds was investigated. All the complexes exhibit catalytic activity towards hydroboration of ketones, aldehydes and aldimines with pinacolborane (HBpin) as a hydride source to lead to secondary alcohols, primary alcohols, and secondary amines, respectively, after hydrolysis of the hydroboration products. Of the iron(0) tricarbonyl complexes, complex 1e is the most robust one and was employed throughout the catalytic investigation. Its preference towards the three types of substrates is as follows: aldimines > aldehydes ≫; ketones. In total, 24 substrates were examined for the catalytic hydroboration reactivity and generally, isolation yields ranging from 40% to 95% were achieved. Mechanistic investigation suggests that the catalytic hydroboration of the substrates proceeds via intramolecular hydride transfer without going through an Fe–H intermediate. As indicated by 1H NMR spectroscopic monitoring, the substrates and the borane agent bind to the iron centre and the imine N atom, respectively, which facilitates the hydride transfer by activating the B–H bond and polarizing the double bond of the substrates. [ABSTRACT FROM AUTHOR]

A cheap and easily available ZnEt2 is an effective precatalyst, which can be used for the hydroboration reaction of various organic carbonates and esters with HBpin. The preliminary hydroboration reaction mechanism has been investigated via the corresponding DFT calculation. [ABSTRACT FROM AUTHOR]

The reductive functionalization of the C＝O unit of carbonates, carboxylic acids, esters, and CO2, respectively has received great attention since its introduction. This method is often used industrially for the synthesis of high value-added energy products in chemistry. This opens up a new way forward to reduce greenhouse gases and the consumption of traditional energy sources. Herein, we report an earth-abundant, cheap, and readily available aluminum dihydride, which can catalyze the reduction of a range of carbonates, esters, carboxylic acids, and CO2, respectively in the presence of pinacolborane as a reducing agent. Moreover, we demonstrate that the reaction can proceed to obtain good yield products under mild conditions, with low catalyst loading and solvent-free reactions. The mechanism of the catalytic reduction of carbonates has been investigated. [ABSTRACT FROM AUTHOR]

The heteroscorpionate zinc hydride complex LZnH 2, (L = (MePz)2CP(Ph)2NPh, MePz = 3,5-dimethylpyrazolyl), its formate complex 3, and magnesium hydride complex LMgH 5 with the same ligand were synthesized and detected for the catalytic hydroboration reaction of CO2. With BH3·SMe2 as the reductant, zinc-based hydride complex 2 and formate complex 3 show a similar capability of hydroboration of CO2, featuring excellent reactivity and selectivity. The conversion of BH3·SMe2 reached 84%, the highest TON of 252 compared to other zinc catalysts was achieved at room temperature and borate ester products at reduction levels of CH3OH were obtained. Magnesium-based hydride complex 5 showed inferior activity for the hydroboration reduction of CO2. [ABSTRACT FROM AUTHOR]

The push for environmentally benign and sustainable chemical processes has reinforced the demand to displace transition metals with cheap, nontoxic and naturally abundant metals. To fulfil this requirement, we endeavored to synthesize alkali- and alkaline earth-metal complexes and employ them as catalysts for organic transformations. Two lithium and one magnesium complexes, which are supported by pyridyl-pendanted unsymmetrical β-diketiminates, have been synthesized and characterized. They are formulated as [Li(L1)]2 (1), [Li(L2)]2 (2) and [Mg(L2)2]·0.5C6H14 (3) (HL1 = N{-4-[(2,6-diisopropylphenylamino)pent-3-en-2-ylidene]-6-methyl}pyridin-2-amine and HL2 = N-{4-[(2,6-diisopropylphenyl)imino]pent-2-en-2-yl}pyridin-2-amine). Complex 1 features two inequivalent Li(I) sites. One Li(I) center exhibits tetrahedral geometry, while the other Li(I) ion adopts a triangular coordination sphere. The catalytic activities of 1–3 toward the hydroboration of aldehydes and ketones by pinacolborane (HBpin) were investigated. Both dinuclear lithium complexes and homoleptic magnesium compound were found to be highly efficient catalysts for the hydroboration of aldehydes and ketones, affording the corresponding borate esters in good yields within a very short time. Synthetic application of the complexes was demonstrated by the gram-scale reduction of ketones via a one-pot two step reaction with only 0.2 mol% loading of 2. Mechanistic details for the hydroboration were revealed by DFT calculations. [ABSTRACT FROM AUTHOR]

Gallium hydrides stabilised by primary and secondary amines are scarce due to their propensity to eliminate dihydrogen. Consequently, their reactivity has received limited attention. The synthesis of two novel gallium hydride complexes HGa(THF)[ON(H)O] and H2Ga[μ2‐ON(H)O]Ga[ON(H)O] ([ON(H)O]2−=N,N‐bis(3,5‐di‐tert‐butyl‐2‐phenoxy)amine) is described and their reactivity towards aldehydes and ketones is explored. These reactions afford alkoxide‐bridged dimers through 1,2‐hydrogallation reactions. The gallium hydrides can be regenerated through Ga−O/B−H metathesis from the reaction of such dimers with pinacol borane (HBpin) or 9‐borabicyclo[3.3.1]nonane (9‐BBN). These observations allowed us to target the catalytic reduction of carbonyl substrates (aldehydes, ketones and carbon dioxide) with low catalyst loadings at room temperature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]