Transfer Hydrogenation of Alkenes Using Ethanol Catalyzed by a NCP Pincer Iridium Complex: Scope and Mechanism

Enable biomass-derived alcohols mediated alkylation and transfer hydrogenation

A single-atom catalyst with generally regarded inert Zn-N4 motifs derived from ZIF-8 is unexpectedly efficient for the activation of alcohols, enabling alcohol-mediated alkylation and transfer hydrogenation. C-alkylation of nitriles, ketones, alcohols, N-heterocycles, amides, keto acids, and esters, and N-alkylation of amines and amides all go smoothly with the developed method. Taking the α-alkylation of nitriles with alcohols as an example, the α-alkylation starts from the (1) nitrogen-doped carbon support catalyzed dehydrogenation of alcohols into aldehydes, which further condensed with nitriles to give vinyl nitriles, followed by (2) transfer hydrogenation of C=C bonds in vinyl nitriles on Zn-N4 sites. The experimental results and DFT calculations reveal that the Lewis acidic Zn-N4 sites promote step (2) by activating the alcohols. This is the first example of highly efficient single-atom catalysts for various organic transformations with biomass-derived alcohols as the alkylating reagents and hydrogen donors.

Iridium-catalyzed reductive β-alkylation of (iso)quinoline derivatives by an in situ enone-trapping strategy

By employing [IrCp*Cl2]2/Mg(OMe)2/(CH2O)n as an applicable catalyst system, we report a reductive β-alkylation of (iso)quinolinium salts with cost-effective and readily available β-chloro ketones, proceeding with good chemoselectivity, mild reaction conditions, and without the need for introduction of a substituent at position-3 of the quinolyl skeleton. Mechanistic investigations suggest that the reaction proceeds via a sequence of hydride transfer-initiated dearomatization of (iso)quinolinium salts, in situ enamine-trapping of enone and a second round of hydride transfer to the coupling adducts. The present work offers an important complement to the synthesis of functionalized (iso)tetrahydroquinolines.

Chemoselective Hydrogenation of α,β-Unsaturated Ketones Catalyzed by a Manganese(I) Hydride Complex

Here, we report the chemoselective hydrogenation of α,β-unsaturated ketones catalyzed by a well-defined Mn(I) PCNHCP pincer complex [(PCNHCP)Mn(CO)2H] (1). The reaction is compatible with a wide variety of functional groups that include halides, esters, amides, nitriles, nitro, alkynes, and alkenes, and for most substrates occurs readily at ambient hydrogen pressure (1-2 bar). Mechanistic studies and deuterium labeling experiments reveal a non-cooperative mechanism, which is further discussed in this report.

A Phosphine-Free Air-Stable Mn(II)-Catalyst for Sustainable Synthesis of Quinazolin-4(3H)-ones, Quinolines, and Quinoxalines in Water

The synthesis, characterization, and catalytic application of a new phosphine-free, well-defined, water-soluble, and air-stable Mn(II)-catalyst [Mn(L)(H2O)2Cl](Cl) ([1]Cl) featuring a 1,10-phenanthroline based tridentate pincer ligand, 2-(1H-pyrazol-1-yl)-1,10-phenanthroline (L), in dehydrogenative functionalization of alcohols to various N-heterocycles such as quinazolin-4(3H)-ones, quinolines, and quinoxalines are reported here. A wide array of multisubstituted quinazolin-4(3H)-ones were prepared in water under air following two pathways via the dehydrogenative coupling of alcohols with 2-aminobenzamides and 2-aminobenzonitriles, respectively. 2-Aminobenzyl alcohol and ketones bearing active methylene group were used as coupling partners for synthesizing quinoline derivatives, and various quinoxaline derivatives were prepared by coupling vicinal diols and 1,2-diamines. In all cases, the reaction proceeded smoothly using our Mn(II)-catalyst [1]Cl in water under air, affording the desired N-heterocycles in satisfactory yields starting from cheap and readily accessible precursors. Gram-scale synthesis of the compounds indicates the industrial relevance of our synthetic strategy. Control experiments were performed to understand and unveil the plausible reaction mechanism.

A bis(PCN) palladium pincer complex with a remarkably planar 2,5-diarylpyrazine core

A bimetallic Pd complex of a bis(pincer) with a diarylpyrazine core has been prepared. The complex demonstrates near-perfect coplanarity of the aromatic core, is fluorescent under UV irradiation, and displays two quasi-reversible reduction events.

Electroreduction of unactivated alkenes using water as hydrogen source

Herein, we report an electroreduction of unactivated alkyl alkenes enabled by [Fe]-H, which is provided through the combination of anodic iron salts and the silane generated in situ via cathodic reduction, using H2O as an H-source. The catalytic amounts of Si-additive work as an H-carrier from H2O to generate a highly active silane species in situ under continuous electrochemical conditions. This approach shows a broad substrate scope and good functional group compatibility. In addition to hydrogenation, the use of D2O instead of H2O provides the desired deuterated products in good yields with excellent D-incorporation (up to >99%). Further late-stage hydrogenation of complex molecules and drug derivatives demonstrate potential application in the pharmaceutical industry. Mechanistic studies are performed and provide support for the proposed mechanistic pathway.

Iridium-Catalyzed Enantioselective Transfer Hydrogenation of 1,1-Dialkylethenes with Ethanol: Scope and Mechanism

Despite half a century's advance in the field of transition-metal-catalyzed asymmetric alkene hydrogenation, the enantioselective hydrogenation of purely alkyl-substituted 1,1-dialkylethenes has remained an unmet challenge. Herein, we describe a chiral PCNOx-pincer iridium complex for asymmetric transfer hydrogenation of this alkene class with ethanol, furnishing all-alkyl-substituted tertiary stereocenters. High levels of enantioselectivity can be achieved in the reactions of substrates with secondary/primary and primary/primary alkyl combinations. The catalyst is further applied to the redox isomerization of disubstituted alkenols, producing a tertiary stereocenter remote to the resulting carbonyl group. Mechanistic studies reveal a dihydride species, (PCNOx)Ir(H)2, as the catalytically active intermediate, which can decay to a dimeric species (κ3-PCNOx)IrH(μ-H)2IrH(κ2-PCNOx) via a ligand-remetalation pathway. The catalyst deactivation under the hydrogenation conditions with H2 is much faster than that under the transfer hydrogenation conditions with EtOH, which explains why the (PCNOx)Ir catalyst is effective for the transfer hydrogenation but ineffective for the hydrogenation. The suppression of di-to-trisubstituted alkene isomerization by regioselective 1,2-insertion is partly responsible for the success of this system, underscoring the critical role played by the pincer ligand in enantioselective transfer hydrogenation of 1,1-dialkylethenes. Moreover, computational studies elucidate the significant influence of the London dispersion interaction between the ligand and the substrate on enantioselectivity control, as illustrated by the complete reversal of stereochemistry through cyclohexyl-to-cyclopropyl group substitution in the alkene substrates.

Air-Stable Coordinatively Unsaturated Ruthenium(II) Complex for Ligand Binding and Catalytic Transfer Hydrogenation of Ketones from Ethanol

Coordinatively unsaturated complexes are interesting from a fundamental level for their formally empty coordination site and, in particular, from a catalytic perspective as they provide opportunities for substrate binding and transformation. Here, we describe the synthesis of a novel underligated ruthenium complex [Ru(cym)(N,N')]+, 3, featuring an amide-functionalized pyridylidene amide (PYA) as the N,N'-bidentate coordinating ligand. In contrast to previously investigated underligated complexes, complex 3 offers potential for dynamic modifications, thanks to the flexible donor properties of the PYA ligand. Specifically, they allow both for stabilizing the formally underligated metal center in complex 3 through nitrogen π-donation and for facilitating through π-acidic bonding properties the coordination of a further ligand L to the ruthenium center to yield the formal 18 e- complexes [Ru(cym)(N,N')(L)]+ (4: L = P(OMe)3; 5: L = PPh3; 6: L = N-methylimidazole; 7: L = pyridine) and neutral complex [RuCl(cym)(N,N')] 8. Analysis by 1H NMR and UV-vis spectroscopies reveals an increasing Ru-L bond strength along the sequence pyridine <1-methylimidazole < PPh3 < P(OMe)3 with binding constants varying over 3 orders of magnitude with log(Keq) values between 2.8 and 5.7. The flexibility of the Ru(PYA) unit and the ensuing accessibility of saturated and unsaturated species with one and the same ligand are attractive from a fundamental point of view and also for catalytic applications, as catalytic transformations rely on the availability of transiently vacant coordination sites. Thus, while complex 3 does not form stable adducts with O-donors such as ketones or alcohols, it transiently binds these species, as evidenced by the considerable catalytic activity in the transfer hydrogenation of ketones. Notably, and as one of only a few catalysts, complex 3 is compatible with EtOH as a hydrogen source. Complex 3 shows excellent performance in the transfer hydrogenation of pyridyl-containing substrates, in agreement with the poor coordination strength of this functional group to the ruthenium center in 3.

BICAAC-Derived Covalent and Cationic Ir(I) Complexes: Application of Ir(BICAAC)Cl(COD) Complexes as Catalysts for Transfer Hydrogenation and Hydrosilylation Reactions

The ambiphilic bicyclic (alkyl)(amino)carbenes (Me/iPrBICAAC) upon reaction with [IrCl(COD)]2 smoothly afford mononuclear Ir(I) complexes that have been spectroscopically and structurally characterized. These complexes exhibit good catalytic activity for transfer hydrogenation (TH) of 4-chlorobenzaldehyde using isopropyl alcohol (iPrOH), with turnover frequency values ranging between 6269 and 8093 h-1. Choosing the covalent complex Ir(MeBICAAC)Cl(COD) as a catalyst, a wide array of carbonyls and imines functionalized with electron-withdrawing and electron-donating substituents have been surveyed and afforded their reduced products in moderate-to-good yields. No detachment of the BICAAC unit from the Ir center was observed upon prolonged heating of Ir(MeBICAAC)Cl(COD) in toluene-d8 or isopropyl alcohol-d8, which evidenced good thermal stability of the catalyst. Complex Ir(MeBICAAC)Cl(COD) was also found to be catalytically active for the hydrosilylation of a variety of aldehydes using triethylsilane (Et3SiH).

Electrochemical chemoselective hydrogenation of 1,4-enediones with HFIP as the hydrogen donor: scalable access to 1,4-diketones

A straightforward electrochemical protocol for efficient hydrogenation of unsaturated CC bonds has been reported in an undivided cell. A series of versatile 1,4-diketones are smoothly generated under metal-free and external-reductant-free electrolytic conditions. Moreover, the tolerance of various functional groups and decagram-scale experiments have shown the practicability and potential applications of this methodology. Moreover, a range of heterocyclic compounds were easily prepared through follow-up procedures of 1,4-diketones.

Hydrogenative alkene perdeuteration aided by a transient cooperative ligand

Deuterogenation of unsaturated organic compounds is an attractive route for installing C(sp3)-D bonds, but the existing methods typically use expensive D2 and introduce only two deuterium atoms per unsaturation. Herein we report the hydrogenative perdeuteration of alkenes using readily available H2 and D2O instead of D2, catalysed by an acridanide-based ruthenium pincer complex and resulting in the incorporation of up to 4.9 D atoms per C=C double bond in a single synthetic step. Importantly, adding a catalytic amount of thiol, which serves as a transient cooperative ligand, ensures the incorporation of deuterium rather than protium by balancing the rates of two sequential deuteration processes. The current method opens an avenue for installing perdeuteroalkyl groups at specific sites from widely available alkenes under mild conditions.

Deaminative bromination, chlorination, and iodination of primary amines

The primary amino group has been seldom utilized as a transformable functionality in organic synthesis. Reported herein is a deaminative halogenation of primary amines using N-anomeric amide as the nitrogen-deletion reagent. Both aliphatic and aromatic amines are competent substrates for direct halogenations. The mildness and robustness of the protocol are evidenced by the successful reactions of several complex- and functional group-enriched bioactive compounds or drugs. Elaboration of the resulting products provides interesting analogues of drug molecules.

Catalyst-Free Transfer Hydrogenation of Activated Alkenes Exploiting Isopropanol as the Sole and Traceless Reductant

Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of C=O and C=N bonds. However, selective transfer hydrogenation reactions of C=C bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents (i.e. primary and secondary alcohols), will mark a significant advancement towards the development of green transfer hydrogenation strategies. Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent. The reaction gives convenient synthetic access to a wide range of substituted malonic acid half oxyesters (SMAHOs) in moderate to good yields. Mechanistic investigations point towards an unprecedented hydrogen bond-assisted transfer hydrogenation process.

Electroreductively Induced Radicals for Organic Synthesis

Organic electrochemistry has attracted tremendous interest within the novel sustainable methodologies that have not only reduced the undesired byproducts, but also utilized cleaner and renewable energy sources. Particularly, oxidative electrochemistry has gained major attention. On the contrary, reductive electrolysis remains an underexplored research direction. In this context, we discuss advances in transition-metal-free cathodically generated radicals for selective organic transformations since 2016. We highlight the electroreductive reaction of alkyl radicals, aryl radicals, acyl radicals, silyl radicals, fluorosulfonyl radicals and trifluoromethoxyl radicals.

Microwave Assisted Esterification of Aryl/Alkyl Acids Catalyzed by N-Fluorobenzenesulfonimide

The susceptibility of the carbonyl group towards nucleophilic attack affords the construction of various organic compounds. Thus, investigations of carbonyl activation applying greener methodologies are highly important. In the present work, among the investigated N-halo compounds, N-fluorobenzenesulfonimide (NFSi) has been found as an efficient and selective catalyst in the reaction of direct esterification of aryl and alkyl carboxylic acids supported by microwave (MW) irradiation. The comprehensive esterification of different benzoic acids and mono-, di- and tri-carboxy alkyl derivatives was performed, whereby significant reaction time reductions were achieved. The presented method used NFSi as an easily manipulatable, non-metal, water- and air-tolerant catalyst, allowing simple synthetic and isolation procedures and energy saving, compared to conventional methodologies. Importantly, in contrast to esterification under thermal conditions, where N-halo compounds behave as pre-catalysts, in the MW-supported protocol, a distinct reaction mechanism has been proposed that assumes NFSi as a sustainable catalyst. Moreover, a scale-up of the industrially important derivative was performed.

A New Paradigm in Pincer Iridium Chemistry: PCN Complexes for (De)Hydrogenation Catalysis and Beyond

The discovery and development of organometallic catalysts is of paramount importance in modern organic synthesis, among which the ligand scaffolds play a crucial role in controlling the activity and selectivity. Over the past several decades, d⁸ transition-metal complexes of pincer ligands have been developed extensively thanks to their easy structural modification, versatile reactivities, and high stability. One paradigm is the bis(phosphine)-based pincer iridium complexes PCP-Ir, which are highly active for alkane dehydrogenation, partly due to their high thermostability. However, except for alkane dehydrogenation and related transformations, few applications of pincer iridium catalysis have been seen in organic synthesis. This mainly arises from the low functional-group compatibility and poor substrate scope and the limited catalytic chemistry that invariably involves Ir(I/III) redox processes initiated by oxidative addition of substrates to 14-electron (PCP)Ir fragments (the proposed catalytically active intermediates). In this Account, we describe our endeavor on the development of a new family of PCN-Ir complexes with initial intention on creating more efficient alkane dehydrogenation catalysts. The replacement of a soft, σ-donor phosphine arm in the PCP ligands by a harder, π-acceptor N-heteroarene (pyridine or oxazoline) not only provides an additional platform to modify the structural properties but also offers new modes of bond activation and novel reactivities and catalysis. One uniqueness of the PCN-Ir system lies in the formation, via ortho-C(sp²)-H cyclometalation of the pyridine unit in the PCN_Py ligand, of the neutral monohydride (PCC)Ir^IIIHL (L = neutral ligand), which catalyzes positional and stereoselective 1-alkene-to-(E)-2-alkene isomerization. Moreover, the PCN-Ir catalysts effect ethanol dehydrogenation without decarbonylation, allowing for transfer hydrogenation of unactivated alkenes and trans-selective semihydrogenation of internal alkynes with user-friendly ethanol as the H-donor. Another feature originates from the ability of the pentacoordinate hydrido chloride complex (PCN)Ir^IIIHCl to undergo reversible solvent-coordination-induced-ionization (SCII), furnishing a cationic monohydride [(PCN)Ir^IIIH(Sol)]⁺Cl^- bearing an uncoordinated Cl anion that effects selective hydrometalation of internal alkynes over the corresponding (Z)-alkenes; the resulting (PCN)Ir^III(vinyl)Cl complex undergoes amine-assisted formal alcoholysis involving the protonation of the Cl anion by the activated Ir^III-bound EtOH, again via the SCII pathway. Together these elementary reactions lay the foundation for cis-selective semihydrogenation of alkynes with EtOH. Further, the design of the oxazoline-containing chiral complexes (PCN_Oxa)Ir^IIIHCl enables asymmetric transfer hydrogenation of alkenes/ketones with ethanol. The efficient catalytic α-alkylation of unactivated esters/amides with alcohols is another case showing the benefit that the PCN-Ir catalyst can offer. These examples illustrate the profound impact of the pincer ligands on the reactivities and catalysis. We hope this Account will provide an in-depth view into the fundamentals of pincer iridium chemistry and ultimately broaden its applications in organic synthesis.

Iridium-Catalyzed Selective trans-Semihydrogenation of 1,3-Enynes with Ethanol: Access to (E,E)-1,4-Diarylbutadienes

A trans-semihydrogenation of 1,3-enynes with ethanol as the hydrogen source was developed using a new (PCN)Ir complex as the precatalyst and tBuNH₂ as the cocatalyst. This catalyst system provides an efficient and atom-economical access to unsymmetrical (E,E)-1,4-diarylbutadienes with high yields and stereoselectivities. Monitoring the process revealed that a sequence of cis-semihydrogenation of the triple bond of 1,3-enynes (to form (E,Z)-butadienes) and (E,Z)-to-(E,E) isomerization occurs to form (E,E)-butadienes.

E-Selective Manganese-Catalyzed Semihydrogenation of Alkynes with H2 Directly Employed or In Situ-Generated

Selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)₃(CH₂CH₂CH₃)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as a precatalyst is described. The required hydrogen gas is either directly employed or in situ-generated upon alcoholysis of KBH₄ with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl, and terminal alkynes was readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 60 °C for directly employed hydrogen or at 60-90 °C with in situ-generated hydrogen and catalyst loadings of 0.5-2 mol %. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups, including halides, phenols, nitriles, unprotected amines, and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations, including deuterium-labeling studies and density functional theory (DFT) calculations, were undertaken to provide a reasonable reaction mechanism, showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a...

Manganese-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes with iPrOH as hydrogen source

The Mn-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes is reported herein, along with Mn-catalyzed hydration of α-keto alkynes. Mechanistic studies displayed an asymmetrical Mn-hydride species performing the catalytic turnover.

Electrochemical Desaturative β-Acylation of Cyclic N-Aryl Amines

Herein, we disclose a straightforward, robust, and simple route to access β-substituted desaturated cyclic amines via an electrochemically driven desaturative β-functionalization of cyclic amines. This transformation is based on multiple single-electron oxidation processes using catalytic amounts of ferrocene. The reaction proceeds in the absence of stoichiometric amounts of electrolyte under mild conditions, affording the desired products with high chemo- and regioselectivity. The reaction was tolerant of a broad range of substrates and also enables late-stage β-C(sp³ )-H acylation of potentially valuable products. Preliminary mechanistic studies using cyclic voltammetry reveal the key role of ferrocene as a redox mediator in the reaction.

Chiral Iridium Complexes of Anionic NCP Pincer Ligand for Asymmetric Transfer Hydrogenation of 1,1-Diarylethenes with Ethanol

Chiral iridium complexes ligated by anionic oxazoline-bearing NCP-type pincer ligands were developed and applied to the asymmetric transfer hydrogenation (ATH) of diarylethenes using environmentally benign ethanol as the hydrogen donor. High enantioselectivities could be achieved for substrates bearing ortho-Me, ortho-Cl, or ortho-Br substituents on one of the aryl groups. The ATH of ortho-Br-substituted diarylethenes is particularly attractive due to the propensity of the C_(aryl)-Br bond to undergo various new bond-forming events.

Catalytic Transfer Deuteration and Hydrodeuteration: Emerging Techniques to Selectively Transform Alkenes and Alkynes to Deuterated Alkanes

Increasing demand for deuterium-labeled organic molecules has spurred a renewed interest in selective methods for deuterium installation. Catalytic transfer deuteration and transfer hydrodeuteration are emerging as powerful techniques for the selective incorporation of deuterium into small molecules. These reactions not only obviate the use of D₂ gas and pressurized reaction setups but provide new opportunities for selectively installing deuterium into small molecules. Commercial or readily synthesized deuterium donors are typically employed as easy-to-handle reagents for transfer deuteration and hydrodeuteration reactions. In this minireview, recent advances in the catalytic transfer deuteration and hydrodeuteration of alkenes and alkynes for the selective synthesis of deuterated alkanes will be discussed.

Recent Advances in Chemistry of Unsymmetrical Phosphorus-Based Pincer Nickel Complexes: From Design to Catalytic Applications

Pincer complexes play an important role in organometallic chemistry; in particular, their use as homogeneous catalysts for organic transformations has increased dramatically in recent years. The high catalytic activity of such bis-cyclometallic complexes is associated with the easy tunability of their properties. Moreover, the phosphorus-based unsymmetrical pincers showed higher catalytic activity than the corresponding symmetrical analogues in several catalytic reactions. However, in modern literature, an increasing interest in the development of catalysts based on non-precious metals is observed. For example, nickel, which is an affordable and sustainable analogue of platinum and palladium, known for its low toxicity, has attracted increasing attention in the catalytic chemistry of transition metals in recent years. Thus, this mini-review is devoted to the recent advances in the chemistry of unsymmetrical phosphorus-based pincer nickel complexes, including the ligand design, the synthesis of nickel complexes and their catalytic applications.

Highly Selective Hydrogenation of C═C Bonds Catalyzed by a Rhodium Hydride

Under mild conditions (room temperature, 80 psi of H₂) Cp*Rh(2-(2-pyridyl)phenyl)H catalyzes the selective hydrogenation of the C═C bond in α,β-unsaturated carbonyl compounds, including natural product precursors with bulky substituents in the β position and substrates possessing an array of additional functional groups. It also catalyzes the hydrogenation of many isolated double bonds. Mechanistic studies reveal that no radical intermediates are involved, and the catalyst appears to be homogeneous, thereby affording important complementarity to existing protocols for similar hydrogenation processes.

Highly Selective Vapor and Liquid Phase Transfer Hydrogenation of Diaryl and Polycyclic Ketones with Secondary Alcohols in the Presence of Magnesium Oxide as Catalyst

MgO has been shown to catalyze an almost quantitative hydrogen transfer from 2-octanol as the hydrogen donor to benzophenone to form benzhydrol, a useful intermediate product in the pharmaceutical industry. The hydrogen transfer from a series of alcohols to the carbonyl group of benzophenone, its ten derivatives, four polycyclic ketones, and 2-naphthyl phenyl ketone was carried out in liquid (LP) or vapor phase (VP). The dependence of reactivity on the structure of the hydrogen donor, reaction temperature, donor-acceptor ratio, amount of catalyst, and the type and position of substituents has been established. For both reaction modes, optimal conditions for selective synthesis of the alcohols were determined and side reactions were investigated. The results indicate that the reactivity of the ketone is suppressed by the presence of a methyl substituent in the ortho position to a much greater extent in LP mode. A scale-up was demonstrated in the liquid phase mode.

Enantioselective Hydrothiolation: Diverging Cyclopropenes through Ligand Control

In this article, we advance Rh-catalyzed hydrothiolation through the divergent reactivity of cyclopropenes. Cyclopropenes undergo hydrothiolation to provide cyclopropyl sulfides or allylic sulfides. The choice of bisphosphine ligand dictates whether the pathway involves ring-retention or ring-opening. Mechanistic studies reveal the origin for this switchable selectivity. Our results suggest the two pathways share a common cyclopropyl-Rh(III) intermediate. Electron-rich Josiphos ligands promote direct reductive elimination from this intermediate to afford cyclopropyl sulfides in high enantio- and diastereoselectivities. Alternatively, atropisomeric ligands (such as DTBM-BINAP) enable ring-opening from the cyclopropyl-Rh(III) intermediate to generate allylic sulfides with high enantio- and regiocontrol.

Iridium Complex-Catalyzed Transfer Hydrogenation of N-Heteroarenes and Tentative Asymmetric Synthesis

An iridium-catalyzed transfer hydrogenation of N-heteroarenes to access a series of substituted 1,2,3,4-tetrahydroquinoline derivatives in excellent yields is disclosed. This transformation is distinguished with water-soluble and air-stable iridium complexes as the catalyst, formic acid as the hydrogen source, mild reaction conditions, and broad functional group compatibility. Most importantly, a tentative chiral N,N-chelated Cp*Ir(III) complex-catalyzed enantioselective transfer hydrogenation is also presented, affording chiral products in excellent yields and good enantioselectivities.

Mild and Selective Rhodium-Catalyzed Transfer Hydrogenation of Functionalized Arenes

Diboron-mediated rhodium-catalyzed transfer hydrogenation of functionalized arenes is reported. In addition to good functional group tolerance, the reaction features operational simplicity and controllable chemoselectivity. The general applicability of this procedure is demonstrated by the selective hydrogenation of a range of arenes, including functionalized benzenes, biphenyls, and polyaromatics.

Transfer hydrogenation of N-heteroarenes with 2-propanol and ethanol enabled by manganese catalysis

A convenient well-defined manganese catalyzed transfer hydrogenation of N-heteroarenes using 2-propanol and ethanol as hydrogen sources is developed. DFT calculations support an outer sphere hydrogenation mechanism.

Ruthenium(ii)-catalyzed reductive N–O bond cleavage of N-OR (R = H, alkyl, or acyl) substituted amides and sulfonamides

A convenient method for the reductive cleavage of the N–O bonds of amide derivatives was developed using ruthenium(ii)-catalyzed transfer hydrogenation reaction.