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The detailed reaction mechanisms of rhodium-catalyzed cycloisomerization of benzylallene-terminal alkynes involving Csp2−H bond activation on the benzyl phenyl ring have been investigated with the aid of density functional theory calculations.

Derived from structurally similar precursors, two different azidodiboranes went through distinct aryl migration reactions triggered by different boron-boron separation distances. Biphenylene based diborane with a shorter boron-boron distance underwent heterolateral aryl migration to form a seven-membered azadiborepin, while xanthrene based diborane with a longer boron-boron distance afforded a stable bis-azidoborane scaffold. The pyrolysis of such a bis-azidoborane led to eight-membered oxazadiborocine through homolateral aryl migration and subsequent [3+2] cycloaddition. Density functional theory (DFT) calculations unveiled that the boron-boron separation distances were the intrinsic factors for the distinct migrations.

Among the parent borirane, benzoborirene and ortho-dicarbadodecaborane-fused borirane, the latter possesses the highest ring strain and the highest Lewis acidity according to our density functional theory (DFT) studies. The synthesis of this class of compounds is thus considerably challenging. The existing examples require either a strong π-donating group or an extra ligand for B-coordination, which nevertheless suppresses or completely turns off the Lewis acidity. The title compound, which possesses both features, not only allows the 1,2-insertion of P=O, C=O or C≡N to proceed under milder conditions, but also enables the heretofore unknown dearomative 1,4-insertion of Ar-(C=O)- into a B-C bond. The fusion of strained molecular systems to an o-carborane cage shows great promise for boosting both the ring strain and acidity.

The asymmetric hydroboration of alkenes has proven to be among the most powerful methods for the synthesis of chiral boron compounds. This protocol is well suitable for activated alkenes such as vinylarenes and alkenes bearing directing groups. However, the catalytic enantioselective hydroboration of O-substituted alkenes has remained unprecedented. Here we report a Rh-catalyzed enantioselective hydroboration of silyl enol ethers (SEEs) that utilizes two new chiral phosphine ligands we developed. This approach features mild reaction conditions and a broad substrate scope as well as excellent functional group tolerance, and enables highly efficient preparation of synthetically valuable chiral borylethers.

Highly efficient and straightforward access to enantioenriched five-membered ring-fused chromanones is developed via [3+2]-cycloaddition of 3-cyanochromones with Morita-Baylis-Hillman carbonates. Densely functionalized chiral cyclopenta[

Air-stable amine- and phosphine-boranes are discovered as donors to integrate with pyridinium acceptor for generating pho-toactive electron-donor-acceptor (EDA) complexes. Experimental results and DFT calculations suggest a dihydrogen bond bridging the donor and acceptor. Illuminating the EDA complex enables an intramolecular single electron transfer to give boron-centered radical for dehydrogenative borylation with no need of external photosensitizer and oxidant. The deproto-nation of Wheland-like radical intermediate rather than its generation is believed to determine the very good ortho-selectivity based on DFT calculations. A variety of α-borylated pyridine derivatives have been readily synthesized with good functional group tolerance.

Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels‐Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long‐established mechanistic picture of pericyclic rearrangements by demonstrating that seven‐membered borepins (i. e., heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels‐Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes., New insights into the reactivity of perarylated boroles toward alkynes have been derived from both experimental and computational studies. It is shown that borepins (the formal alkyne insertion products) can readily isomerize to the thermodynamically more favorable boranorbornadienes (the formal Diels‐Alder products), thus obscuring the mechanism of product formation (see Figure). In addition, the fluorescent nature of the tricyclic boracyclohexenes, the most stable isomers of the addition reactions, has been investigated by absorption and emission spectroscopy.

Highly reactive dicoordinate (i.e., mono-base-stabilized) borylenes of the form [LBR] (L = Lewis base) have recently shown intriguing reactivity with inert small molecules, including N2. However, t...

The reactions of the rhenium(III)-phosphine complex ReCl3(PMePh2)3 with organonitriles (NCR) were studied and found to give novel addition as well as simple substitution products. Refluxing ReCl3(P...

The detailed reaction mechanisms of gold-catalyzed reactions of 2,1-benzisoxazoles with propiolates and ynamides have been investigated with the aid of density functional theory calculations. Our investigation focused on the different selectivities observed for the reactions of the two different classes of substituted alkynes. Through our systematic calculations, we found that the catalytic reactions start with a nucleophilic nitrogen atom attacking one coordinated alkyne carbon. Then, an N–O bond cleavage takes place to give two different gold carbenoid intermediates, from which four possible pathways lead to different products (7-acylindolyl derivatives and quinolone oxides). In the reaction of 2,1-benzisoxazole (anthranil) with the propiolate PhCCCOOMe, the relevant N–O bond cleavage leading to the 7-acylindolyl product is only slightly less favorable than that leading to the quinolone oxide product. The steps following the N–O bond cleavage are all very facile. Therefore, the N–O bond cleavage step is responsible for the selective outcome observed experimentally. In the reaction of 2,1-benzisoxazole (anthranil) with the ynamide PhCCNMeMs, the N–O bond cleavages leading to the 7-acylindolyl product and the quinolone oxide have comparable barriers. However, the C–N coupling that followed has a very high barrier, making the pathway leading to the quinolone oxide product unfavorable. As a result, only the 7-acylindolyl product is experimentally observed.

A metal-free access to 3-allyl-2-alkoxychromanones by PPh3-catalyzed alkoxy allylation of chromones with MBH carbonates and alcohols is described. This reaction is performed under mild conditions and it shows good functional group tolerance, providing a series of functionalized chromanones in moderate to high yields with excellent diastereoselectivities. Deuterium-labeling experiments to probe a possible mechanism and scale-up reaction were also conducted.

[(η6-p-cymene)OsI2]2 was found to be a good catalyst for the cyclopropanation reaction of isobutyl vinyl ether with 3-tert-butyldiazoindene. In contrast, the complexes [(η6-p-cymene)OsX2]2 (X = Cl,...

Reactions of OsCl2(PPh3)3 with o-ethynylphenyl-carbonyl compounds o-HC≡CC6H4C(O)R (2, R = H (a) and Et (b)) produced the η3-o-ethynylphenyl-carbonyl complexes OsCl2(PPh3)2{η3-(o-HC≡CC6H4C(O)R)} (3)...

A highly efficient asymmetric synthesis of chiral thiochromanones is developed via Cu(I)/phosphoramidite catalyzed asymmetric alkynylation of thiochromones under mild reaction conditions. The catalyst system is tolerant of various thiochromone precursors and terminal alkynes. The established asymmetric transformation provides different enatiomeric-enriched thiochromanones with more molecular complexity and enables access to chiral thioflavanones, a subgroup of flavonoid by further functionalization.

We report a transition metal-free, regio- and stereo-selective, phosphine-catalyzed method for the trans hydroboration of 1,3-diynes with pinacolborane that affords (E)-1-boryl-1,3-enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3-diyne framework as unambiguously established by NMR and X-ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle.

Density functional theory calculations were carried out to study the reaction mechanisms of Ag(I)- and Zn(II)-catalyzed amination of unsaturated N-acylpyrazoles with azodicarboxylates. Our theoretical investigation focused on the origin of the metal-controlled regioselectivity (γ- versus α-amination). Through our calculations, it was found that the amination reactions occur via metal-dienolate intermediates, in which the Ag(I) center prefers to coordinate with the α-carbon or the pyrazolyl N-donor site of the dienolate ligand, while the Zn(II) center prefers to coordinate with the O-donor of the dienolate ligand. The different site preferences for coordination with dienolate between the Ag(I) and Zn(II) metal centers play the key roles in the different regioselectivity observed experimentally.

DFT calculations have been carried out to study the mechanisms and origin of regioselectivity in Rh- and Ir-catalyzed hydroalkynylation of enamides with terminal alkynes. The two reactions, despite...

Treatment of osmacyclopentadiene derivatives 1 with phenyl or isopropyl isothiocyanate gave the fused five and six-membered osmacycles 2-5 by a formal [4+2] cyclization. The facile protonation of the newly generated exocyclic imine in complexes 2-5 afforded conjugation-extended osmacycle derivatives 6-9. Compounds 2-9 each contain two main-group heteroatoms (N and S) in the fused six-membered ring located at the ortho (for S) and para (for N) positions relative to the osmium centre; these species can be regarded as rare osma-1,3-thiazine derivatives and represent the first fused metallathiazine derivatives. In contrast to the non-planar organic 6H-1,3-thiazine, nearly coplanar metallathiazines 8 and 9 can be achieved by tuning the groups on the two nitrogen atoms. These unique metal-bridged osma-1,3-thiazine derivatives exhibit remarkable stabilities, broad spectral absorptions spanning the visible spectra, and considerable photothermal properties, which suggests their potential applications in material science.

The reactions of [RhCl(COD)]2 with a series of diazoalkanes with different substitutents were investigated. The outcomes of the reactions were found to be substituent-dependent via four different pathways. (1) The reactions with diazoindenes produced η5-cyclopentadienyl complexes. (2) The reaction with diazofluorene produced a mixture of olefin and azine compounds. (3) The reactions with monosubstituted diazoalkanes RCHN2 (R = Ph, MeO2C) produced olefins RCH═CHR. (4) The reaction with the disubstituted diazoalkane Ph2CN2 produced the azine Ph2C═N–N═CPh2 only. Computational studies have been carried out to understand the interesting substituent effect by comparing the kinetics and thermodynamics of the reaction pathways. It was found that the reactions with diazocyclopentadiene, diazoindene, and Ph2CN2 are kinetically controlled, while the reactions with RCHN2 and diazofluorene are both thermodynamically and kinetically controlled.

DFT calculations have been carried out to study the reaction mechanism of copper-catalyzed three-component boracarboxylation of alkene with CO2 and diboron. The competing reaction pathways involving two components have also been investigated for comparison. Through this theoretical study deep mechanistic insight on this multicomponent reaction is provided.

Density functional theory calculations have been performed to study the diverse reactivity of pentaphenylborole toward different epoxides. We systematically investigated the effect of substituents on epoxides for the preference/competition of three experimentally observed pathways, that is, intramolecular proton transfer, direct ring expansion via insertion of one epoxide molecule, and ring expansion via insertion of two epoxide molecules. Our calculations also predicted a high competitivity between the proton transfer and direct ring expansion pathways for the epoxide containing both alkyl and aryl substituents.

We report a phosphine-catalyzed trans hydroboration of alkynoate esters and amides. The reaction proceeds under mild conditions with exclusive ( E)-selectivity to afford ( E)-β-boryl acrylates and ( E)-β-boryl acrylamides in good to excellent yields. The reaction is tolerant of a variety of functional groups and allows efficient access to novel oxaboroles as well as a pargyline derivative (MAO inhibitor). Theoretical calculations suggest an internal hydride generates a phosphonium allenoxyborane followed by the formation of a key phosphonocyclobutene intermediate that collapses in a stereoselective, rate-limiting step.

DFT calculations were performed to investigate the reactions of boroles with alkynes, in which boranorbornadiene, borepin and/or boracyclohexadiene can be formed depending on the substituents on the borole and alkyne. Our computational results indicated that formation of boranorbornadiene and borepin is generally kinetically favoured and that the products can interconvert. Formation of boracyclohexadiene is kinetically unfavourable in most reactions. However, certain substituents can promote the formation of boracyclohexadiene by stabilizing an energetically high-lying zwitterionic transition state that leads to boracyclohexadiene. Borafluorene reacted with most alkynes to give borepin exclusively due to its propensity to maintain its aromaticity. However, when it reacted with silyl-substituted alkyne(s), a novel product, different from boranorbornadiene, borepin and boracyclohexadiene was generated, which can be attributed to the well-known ability of silyl groups to migrate.

A series of new d2 Re (V) alkylidyne complexes were synthesized, including Re(≡CCH2Ph)Cl2(PR3)3 (PR3 = PMe3, and PMePh2), Re(≡CCH2Ph)I2(PMePh2)3, Re(≡CPh)(S2CNEt2)2(PMePh2), [CpRe(≡CPh)(PMePh2)2]Cl, and Re(≡CCH2Ph)(mnt)(PMePh2)2. The complexes Re(≡CCH2Ar)Cl2(PR3)3 (PR3 = PMe3, PMe2Ph, and PMePh2) as well as Re(≡CCH2Ph)I2(PMePh2)3 were found to undergo alkyne metathesis reactions with PhC≡CPh, while the other complexes are inactive. The activity of Re(≡CCH2Ar)Cl2(PR3)3 toward alkyne metathesis reactions with PhC≡CPh is in the order of PMe3 < PMe2Ph < PMePh2. The complex Re(≡CCH2Ph)I2(PMePh2)3 is slightly less reactive than its chloride analog. The difference in the reactivity of the alkylidyne complexes has been studied computationally.

The luminescent studies of cyclometalated Ir(III) complexes have attracted considerable interests in recent years. To fulfill the needs of emission wavelengths in various areas, the strategic emission color tuning of iridium(III) complexes is vital for their applications as phosphorescent materials. However, a feasible color-tuning method for iridacycles with fused carbon-rings (C∧C) has not been reported yet. Herein, a convenient color-tuning strategy for C∧C-based Iridacycles is accomplished with the aid of DFT calculations. The developed synthetic protocol allowed facile modifications on C∧C units and N∧N units via a one-pot synthesis starting from iridium vinyl complexes, accessing the novel phosphorescent iridapolycycles [(N∧N)Ir(C∧C)ClPPh3]+.

Reactions of silanes with transition-metal complexes are of interest because their relevance to Si–H bond activation, the structural properties of polyhydrides, and catalytic hydrosilylation reactions. This work presents the results derived from reactions of arylsilanes Ph2SiH2 and PhSiH3 with OsH3Cl(PPh3)3 (1). Reaction of 1 with 1 equiv or excess Ph2SiH2 affords OsH3(SiClPh2)(PPh3)3 (2) or OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3), respectively. These silyl complexes are formed via the oxidative addition of Si–H bonds and H/Cl exchange via silylene intermediates. Similarly, reaction of 1 with excess PhSiH3 produced the analogous bis(silyl) complex OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4). The bis(silyl) complexes are dodecahedral tetrahydride complexes containing weak Si···H interactions. The complex 3 reacts with PPh3 and CH3CN to selectively eliminate Ph2SiH2. Computational studies show that the preference for reductive eliminations from 3 follows the order Ph2SiH2 > H2 > Ph2SiHCl > Ph2HSi-SiClPh2.

Reactions of (cyclopentadienylidenehydrazono)triphenylphosphorane with RuCl2(PPh3)3 or (η6-cymene)RuCl2(PPh3) in toluene produced the chlorocyclopentadienyl complex (η5-C5H4Cl)RuCl(PPh3)2, which was likely formed through the cyclopentadienylidene intermediate RuCl2{═C(C4H4)}(PPh3)2. Treatment of (η6-cymene)RuCl2(PPh3) with (cyclopentadienylidenehydrazono)triphenylphosphorane in methanol gave [(η5-C5H4Cl)Ru(η6-cymene)]+. Computational studies reveal that the thermodynamic stability of the analogous chlororuthenium complexes RuCl2(═CRR′)(PPh3)2 and [RuCl(═CRR′)(PMe3)(η6-C6H6)]+, with respect to the formation of the corresponding η5-chloropentadienyl complexes via a migratory carbene-insertion reaction is in the order of cyclopentadienylidene < indenylidene < fluorenylidene < phenylcarbene.

Boroles undergo dimerization reactions to give Diels-Alder (DA) dimers, bridged-bicyclic (BB) dimers or spiro dimers (SD) depending on the substituents on the borole. We performed DFT calculations to investigate how different substituents at the carbon atoms of the butadiene backbone as well as at the boron atom influence the dimerization reaction pathways. The DFT results show that, in general, both the DA and BB dimers are easily accessible kinetically, and the DA dimers are thermodynamically more stable than the BB dimers. When the substituent-substituent repulsive steric interactions are alleviated to a certain extent, the BB dimers are more stable than the DA dimer, and become accessible. The SD dimers are generally kinetically difficult to obtain. However, we found that aryl substituents promote the formation of the SD dimers.

Density functional theory calculations have been performed to investigate how different nucleophiles and directing groups affect the preference of C–H versus C–O bond functionalization in the ruthenium-catalyzed coupling reactions of aryl ethers with organoboronates. Our results indicate that the preference depends on the relative stability of the transition state structures for the C–O bond activation in the C–O bond functionalization pathway and the transmetalation with boronate to form a Ru–C bond in the C–H bond functionalization pathway. When the transition state structure for the transmetalation with boronate lies lower in energy than that for the C–O bond activation, C–H bond functionalization is preferred, and vice versa. How different nucleophiles and directing groups affect the relative stability of the transition structures has been discussed in detail.

An unprecedented copper(I)-catalyzed asymmetric desymmetrization of 5-silylcyclopentadienes with in situ formed azoalkene was realized through an inverse-electron-demand aza-Diels-Alder reaction (IEDDA) pathway, in which 5-silylcyclopentadienes served as efficient enophiles. This new protocol provides a facile access to the biologically important heterocyclic tetrahydropyridazines containing a unique α-chiral silane motif and three adjoining stereogenic centers in generally good yield (up to 92 %) with exclusive regioselectivity, high diastereoselectivity (>20:1 diastereomeric ratio), and excellent enantioselectivity (up to 98 % enantiomeric excess). DFT calculations and control experiments further confirmed the proposed reaction mechanism.

Asymmetric copper-catalyzed intermolecular amino- and azidocyanation reactions of alkenes have been developed that proceed via a radical process in which a key benzylic radical intermediate is enantioselectively trapped by a chiral Box/CuII cyanide complex. A variety of enantiomerically enriched β-amino/azido alkylnitriles were efficiently synthesized. The β-azido alkylnitriles could be converted into a series of highly valuable optically active amine-based building blocks and bioactive compounds.

Density functional theory calculations have been performed to study the reaction mechanisms for the Rh(III)-catalyzed C–H functionalization versus deoxygenation of quinoline N-oxide (QNO) with diazo compounds, dimethyl diazomalonate and methyl phenyldiazoacetate. How different diazo compounds affect the reaction pathways has been analyzed and examined in detail. It was found that the stability of the Rh(III)-carbene intermediates derived from an N2 extrusion is crucial in determining the preferred reaction pathway.

The reactions of the trichloro carbyne complexes OsCl3(≡CR)(PPh3)2 (R = CH═CPh2, CH2Ar) with bromine and hydrogen peroxide were studied. Unlike monochloro carbyne complexes OsCl(≡CAr)(CO)(PPh3)2, the trichloro complexes OsCl3(≡CR)(PPh3)2 do not undergo oxidation reactions at the metal center or the metal–carbyne bond. Treatment of OsCl3(≡CCH═CPh2)(PPh3)2 with Br2/H2O and H2O2/HCl produced OsBr3(≡CCH═CPh2)(H2O)(PPh3) and OsCl3(≡CCCl═CPh2)(PPh3)2, respectively. Reactions of OsCl3(≡CCH2-C6H4-p-R)(PPh3)2 (R = H, CMe3) with H2O2/HCl or H2O2 gave OsCl3{≡CC(O)-C6H4-p-R}(PPh3)2. Computational studies suggest that the difference in the reactivity of OsCl(≡CAr)(CO)(PPh3)2 and OsCl3(≡CR)(PPh3)2 is mainly of thermodynamic origin.

The catalyst system of Pd(TFA)2/(S,S)-diPh-pyrox is reported to promote the highly efficient enantioselective oxidative cascade cyclization of alkene-tethered aliphatic acrylamides under mild aerobic conditions. A series of pyrrolizidine derivatives have been synthesized in good yield and excellent enantioselectivity. Deuterium-labeling experiments have revealed that the reaction proceeded through an anti-aminopalladation (anti-AP) pathway with high selectivity. The transition states for the anti-AP step have been calculated to account for the observed enantioselectivity.

A new building block ATVTA that uses stiff carbon-carbon triple bonds (A) on 1,2-di(2-thienyl)-ethene (TVT) has been developed. Oligothiophene derivatives S-01 with a TVT unit, S-02 with a 5,5'-diethynyl-2,2'-dithienyl (AT2) unit and S-03 with ATVTA were synthesized to compare their effects in a systematic study. Due to the better π-conjugation extension of the TVT unit, S-01 exhibits the most red-shifted absorption profile among them, whereas S-02 possesses the deepest HOMO level. While the HOMO level of S-03 is down-shifted by 0.02 eV relative to that of S-01, the alkyne linkages can effectively down-shift the HOMO level. By replacing the terminal units of S-03 with stronger electron acceptors, S-04 and S-05 exhibited broader absorption profiles and lower HOMO levels than those of S-03. Organic solar cells based on these molecules were fabricated and an S-03:PC60 BM (1:1, w/w) based device afforded the highest Voc value of 0.96 V and a power conversion efficiency (PCE) of 2.19 %.

Although alkyne metathesis reactions mediated by high-valent d0 carbyne complexes are well established, similar reactions mediated by well-defined low-valent (non-d0) carbyne complexes are rare. This work demonstrates that d2 Re(V) carbyne complexes Re(≡CR)Cl2(PMe2Ph)3 (R = CH2(o-C6H4Br), Ph, CO2Et) can undergo stoichiometric alkyne metathesis reactions. For example, reactions of Re{≡CCH2(o-C6H4Br)}Cl2(PMe2Ph)3 with TMSC≡CR (R = CO2Et, CH2Ph) and PhC≡CPh produced carbyne complexes Re(≡CR)Cl2(PMe2Ph)3 and Re(≡CPh)Cl2(PMe2Ph)3, respectively. Theoretical studies suggest that the metathesis reactions most likely proceed through six-coordinate alkyne-carbyne intermediates Re(≡CR)Cl2(η2-alkyne)(PMe2Ph)2 that undergo reversible cycloaddition reactions.

Treatment of [Re(dppm)3]I (dppm = PPh2CH2PPh2) with HC≡CPh produced the rhenium vinylidene complex ReI(═C═CHPh)(dppm)2. In the presence of HI, [Re(dppm)3]I reacted with HC≡CR (R = Ph, p-tolyl, C6H4-o-CHO, (CH2)5CH3) to give the rhenium carbyne complexes [ReI(≡CCH2R)(dppm)2]I and with HC≡CSiMe3 to give [ReI(≡CMe)(dppm)2]I. One-pot reactions of [Re(dppm)3]I, HC≡CC(OH)RR′ (RR′ = Ph2, Me2, PhMe), and HI produced the vinylcarbyne complexes [ReI(≡CCH═CRR′)(dppm)2]I.

Two copper salts (Cu(CF3CO2)2 and IMesCuCl) were identified as earth-abundant, inexpensive, but effective metal catalysts together with diazo malonate for chemo-/regioselective and stereospecific deoxygenation of various epoxides with tolerance of common functional groups (alkene, ketone, ester, p-methoxybenzyl, benzyl, tert-butyldimethylsilyl, and triisopropylsilyl). In particular, the unprecedented regioselectivity allowed for the first time monodeoxygenation of diepoxides to alkenyl epoxides. Density functional theory mechanistic studies showed that the deoxygenation occurred by collapsing the free ylide, unfavoring the possible intuitive pathway via cycloreversion of possible oxetane.

The carbene-stabilized electron-rich iminocarboranyl boron(I) compound [(Dipp)NC(But)C2B10H10]B(NHC) (1) (Dipp = 2,6-diisopropylphenyl, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is an excellent precursor for the preparation of the unprecedented carborane-fused azaborolyl radical cation [{(Dipp)NC(But)C2B10H10}B(NHC)]•+ ([2]•+) and dicarbollyl-fused azaborole 7,8-nido-C2B9H9-7,8-C(But)N(Dipp)B(NHC) (3) via controlled single-electron oxidation and two-electron oxidative deboration, respectively. Single-crystal X-ray analyses and DFT calculations indicate that the unpaired electron in [2]•+ is delocalized over the BNC unit, and the two fused five-membered rings in 3 form a sort of π-conjugated system.

An unsymmetrical diborane(4), pinB-BMes2, reacted with 2,6-dimethylphenyl isocyanide to give a spirocyclic 1,2-oxaboretane or isocyanide-coordinated boraalkene. The former product formed via ring contraction of the pinacolatoboryl group. DFT calculations revealed the ring contraction proceeded via a carbocationic intermediate. This new degradation pathway from the Bpin group would provide important information in Bpin-related chemistry.

In the absence of transition metal catalysts, the unsymmetrical diborane(4), pinB-BMes2, reacted with alkynes to afford diborylalkenes. The isomer ratio of the products could be controlled via temperature, solvent, and additive(s). A reaction mechanism was proposed on the basis of two isolated intermediates, and this reaction could furthermore be applied to synthesize a luminescent molecule.

Treatment of OsCl2(PPh3)3 with HC≡CAr (Ar = Ph, p-tolyl) produced the η3-allenylcarbene complexes OsCl2(═CAr-η2-CH═C═CHAr)(PPh3)2. Reactions of the η3-allenylcarbene complexes with gold alkynyls Au(C≡CR)(PPh3) (R = Ph, p-tolyl, TMS, nBu, CH(OEt)2) or copper(I) alkynyls Cu(C≡CR) (R = Ph, TMS) in the presence of HNEt3Cl produced the osmabenzynes Os{≡CC(R)═C(CH2Ar)CH═CAr}Cl2(PPh3)2. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt3Cl.

A metal-free borylation reaction of electron-rich aryl chlorides, fluorides, mesylates and phosphates under continuous-flow photolytic conditions is reported. The flow setup was designed to facilitate this process efficiently in comparison with the batch mode. Owing to its unique chemical selectivity, mild reaction conditions, good functional group tolerance and substrate scope, this reaction adds a complementary protocol to the current synthetic methods for boronic acid derivatives. The proposed reaction mechanism involves a photolytically generated triplet aryl cation, and DFT calculations suggest that the borylation product is formed in an anion-mediated single step process passing a minimum energy crossing point.