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Our study discovered a new stepwise mechanism for the oxidative addition of PhICl2 to LAuAr. Fewer electron-withdrawing substituents on the Ar ligand increase the energy of Au(i) dx2−y2 orbital, making the reaction easier to achieve.

Herein we report the B(3,4,5-F3H2C6)3-catalysed C3-allylation of indoles using allylic esters.

Publisher Copyright: © 2022 American Chemical Society. The 2-iodoxybenzoic acid (IBX)-controlled oxidative dearomatization of pyrroles occurs very slowly (or not all) in many organic solvents, including DMSO in which IBX is soluble. Interestingly, although IBX is only partially soluble in acetic acid, this solvent mediates the pyrrole oxidative dearomatization. With the aid of density functional theory (DFT) calculations, we have discovered a new mode of reactivity, termed the periodinane oxy-assisted (POA) oxidation mechanism, which explains this observation.

Funding Information: L.S. and X.T. are grateful to the CSC (China Scholarship Council) for a PhD fellowship. We gratefully acknowledge the generous allocation of computing time from the Australian National Computational Infrastructure and University of Tasmania, and the Australian Research Council (grant number DP180100904) for financial support. We thank Petra Krämer for her UV-vis measurements. Publisher Copyright: © 2023, The Author(s). Azepinone derivatives are privileged in organic synthesis and pharmaceuticals. Synthetic approaches to these frameworks are limited to complex substrates, strong bases, high power UV light or noble metal catalysis. We herein report a mild synthesis of azepinone derivatives by a photochemical generation of 2-aryloxyaryl nitrene, [2 + 1] annulation, ring expansion/water addition cascade reaction without using any metal catalyst. Among the different nitrene precursors tested, 2-aryloxyaryl azides performed best under blue light irradiation and Brønsted acid catalysis. The reaction scope is broad and the obtained products underwent divergent transformations to afford other related compounds. A computational study suggests a pathway involving a step-wise aziridine formation, followed by a ring-expansion to the seven-membered heterocycle. Finally, water is added in a regio-selective manner, this is accelerated by the added TsOH.

This report investigates the fundamental basis for rather surprising patterns of reactivity in Bronsted acid-mediated cyclizations of pyrrole substrates bearing pendant Michael acceptors that were identified during syntheses of Stemona alkaloids. Integrated experimental and theoretical studies reveal the profound influence that substituent effects have on the viability of these transformations. Additionally, we identify that electronic effects, in addition to barrier-lowering secondary orbital interactions within transition states, account for the exclusive preference for 7-endo-trig cyclizations over 6-exo-trig cyclizations.

In recent years, metal‐free organic synthesis using triarylboranes as catalysts has become a prevalent research area. Herein we report a comprehensive computational and experimental study for the highly selective synthesis of N‐substituted pyrazoles through the generation of carbenium species from the reaction between aryl esters and vinyl diazoacetates in the presence of catalytic tris(pentafluorophenyl)borane [B(C6F5)3]. DFT studies were undertaken to illuminate the reaction mechanism revealing that the in situ generation of a carbenium species acts as an autocatalyst to prompt the regiospecific formation of N‐substituted pyrazoles in good to excellent yields (up to 81 %)., Tris(pentafluorophenyl)borane‐catalyzed reactions between vinyl diazoacetates and aryl esters afforded highly regioselective N‐alkylated pyrazoles. These reactions involve an autocatalytic process in which in situ formed carbenium species act as a catalyst to regioselectively afford pyrazoles. Detailed DFT studies were carried out to explain the reaction mechanism.

In den letzten Jahren hat sich die metallfreie organische Synthese unter Verwendung von Triarylboranen als Katalysatoren zu einem weit verbreiteten Forschungsgebiet entwickelt. Hier berichten wir über eine umfassende theoretische und experimentelle Studie für die hochselektive Synthese von N-substituierten Pyrazolen durch die Erzeugung von Carbenium-Ionen aus der Reaktion zwischen Arylestern und Vinyldiazoacetaten in Gegenwart von katalytischem Tris(pentafluorphenyl)boran [B(C6F5)3]. DFT-Studien zum Reaktionsmechanismus zeigen, dass die In-situ-Generierung einer Carbenium-Spezies als Autokatalysator fungiert, welcher die regiospezifische Bildung von N-substituierten Pyrazolen in guter bis hervorragender Ausbeute (bis zu 81 %) auslöst.

Density functional theory computation indicates that bridge splitting of [PtII R2 (μ-SEt2 )]2 proceeds by partial dissociation to form R2 Pta (μ-SEt2 )Ptb R2 (SEt2 ), followed by coordination of N-donor bromoarenes (L-Br) at Pta leading to release of Ptb R2 (SEt2 ), which reacts with a second molecule of L-Br, providing two molecules of PtR2 (SEt2 )(L-Br-N). For R=4-tolyl (Tol), L-Br=2,6-(pzCH2 )2 C6 H3 Br (pz=pyrazol-1-yl) and 2,6-(Me2 NCH2 )2 C6 H3 Br, subsequent oxidative addition assisted by intramolecular N-donor coordination via PtII Tol2 (L-N,Br) and reductive elimination from PtIV intermediates gives mer-PtII (L-N,C,N)Br and Tol2 . The strong σ-donor influence of Tol groups results in subtle differences in oxidative addition mechanisms when compared with related aryl halide oxidative addition to palladium(II) centres. For R=Me and L-Br=2,6-(pzCH2 )2 C6 H3 Br, a stable PtIV product, fac-PtIV Me2 {2,6-(pzCH2 )2 C6 H3 -N,C,N)Br is predicted, as reported experimentally, acting as a model for undetected and unstable PtIV Tol2 {L-N,C,N}Br undergoing facile Tol2 reductive elimination. The mechanisms reported herein enable the synthesis of PtII pincer reagents with applications in materials and bio-organometallic chemistry.

Density functional theory (DFT) has been used to investigate the mechanism of the experimentally efficient hydroalkylation of styrene with acetylacetone in the presence of a bismuth catalyst. It is shown that the mechanism is fundamentally different to that of the analogous gold-catalysed reaction, even though it leads to the same product. Whereas gold prefers to coordinate to the π-bond of the enol isomer of acetylacetone, bismuth coordinates to the two oxygens to form a chelated complex. Furthermore, the overall reaction with bismuth via the enol isomer of acetylacetone occurs with a much lower activation energy compared to the ketone isomer. In addition, several bismuth catalysts were considered and two of these were shown to have no activity. All of these results have been rationalised in terms of the strength of binding of the metal centres to the acetylacetone. The stronger the binding, the greater the acidity of a proton on acetylacetone, and thus the lower the activation energy for the protonation of styrene, which turns out to be the rate-determining step in the overall reaction. In this way, good agreement is obtained with all the experimental data.

Computational studies support the key role of intramolecular coordination by a carboxylate group in the facile oxidative addition of the iodoarene 2,6-(HO2C)2C6H3I to a PdII center to form the pincer-PdIV motif Pd{2,6(O2C)C6H3-O,C,O}, Pd(OCO). Mechanisms of attack by an aryloxide nucleophile at the methylene group in a palladacycle PdIV(OCO)(CH2CRR′–E) to form ArOCH2CMe2–E (E = oxime) are examined; for RR′ = HEt and E = amine, it is mainly the formation of analogous ArOCH2CHEt–E together with CH2═CEt–E arising from β-hydrogen elimination. Computational results are in agreement with recent experimental results by Whitehurst, Gaunt. [J. Am. Chem. Soc. 2020, 142, 14169]. For β-hydrogen elimination, computation demonstrates that the conformational flexibility in the chelate ring is required to allow the hydrogen atom to be in an axial orientation relative to Pd–C, thus maximizing the dihedral angle Pd···C–C···H in the transition-state fragment Pd···CH2C(R)···H···OAr. Bulky substituents R′ at the β-position, CHR′, favor nucleophilic attack at the methylene carbon.

Density functional theory calculations were used to investigate the mechanisms of established hydroalkylation reactions of styrenes with 1,3-diketones that are promoted by either AuCl3/AgOTf or AgOTf catalyst systems. In the former case, our studies led us to propose an original mechanism that is initiated by the generation of highly electrophilic Au(OTf)3, which then coordinates the enol tautomer of the 1,3-diketone substrate. The ensuing highly Bronsted acidic π-complex serves to protonate the styrene to generate a relatively low-energy benzylic carbocation. Notably, this suggests that this benzylic carbocation represents the true catalytic species in the reaction, and thus, the role of the gold complex is solely to generate this active catalyst. AuCl3 alone does not serve as a good initiator for this process because it is not electrophilic enough to generate the relatively low-energy benzylic carbocation. Our investigation of the hydroalkylation facilitated by the slightly electron-deficient AgOTf catalyst revealed that an alternative mechanism predominates. Specifically, it is more likely that the reaction proceeds via a demetallation process directly mediated by the silver catalyst. We found a clear trend indicating that the electron deficiency of the metal center dictates which of these two mechanistic scenarios occurs. This article discusses these two mechanistic pathways in detail, providing key information for the experimental development of hydroalkylation processes.

Although Pd(OAc)2-catalysed alkoxylation of the C(sp3)–H bonds mediated by hypervalent iodine(III) reagents (ArIX2) has been developed by several prominent researchers, there is no clear mechanism yet for such crucial transformations. In this study, we shed light on this important issue with the aid of the density functional theory (DFT) calculations for alkoxylation of butyramide derivatives. We found that the previously proposed mechanism in the literature is not consistent with the experimental observations and thus cannot be operating. The calculations allowed us to discover an unprecedented mechanism composed of four main steps as follows: (i) activation of the C(sp3)–H bond, (ii) oxidative addition, (iii) reductive elimination and (iv) regeneration of the active catalyst. After completion of step (i) via the CMD mechanism, the oxidative addition commences with an X ligand transfer from the iodine(III) reagent (ArIX2) to Pd(II) to form a square pyramidal complex in which an iodonium occupies the apical position. Interestingly, a simple isomerization of the resultant five-coordinate complex triggers the Pd(II) oxidation. Accordingly, the movement of the ligand trans to the Pd–C(sp3) bond to the apical position promotes the electron transfer from Pd(II) to iodine(III), resulting in the reduction of iodine(III) concomitant with the ejection of the second X ligand as a free anion. The ensuing Pd(IV) complex then undergoes the C–O reductive elimination by nucleophilic attack of the solvent (alcohol) on the sp3 carbon via an outer-sphere SN2 mechanism assisted by the X− anion. Noteworthy, starting from the five coordinate complex, the oxidative addition and reductive elimination processes occur with a very low activation barrier (ΔG‡ 0–6 kcal mol−1). The strong coordination of the alkoxylated product to the Pd(II) centre causes the regeneration of the active catalyst, i.e. step (iv), to be considerably endergonic, leading to subsequent catalytic cycles to proceed with a much higher activation barrier than the first cycle. We also found that although, in most cases, the alkoxylation reactions proceed via a Pd(II)–Pd(IV)–Pd(II) catalytic cycle, the other alternative in which the oxidation state of the Pd(II) centre remains unchanged during the catalysis could be operative, depending on the nature of the organic substrate.

We thoroughly investigated mechanistic features of dichlorination of diazoacetates using PhICl2 catalysed by pyridine. We found that the pyridine serves as a catalyst for decomposition of PhICl2 to PhI and Cl2, leading to the dichlorination step being driven by the in situ generated Cl2. This type of activation was found to be applicable to other amine-catalysed chlorination reactions using PhICl2.

The synthesis of benzofurans by the reaction of the palladium(II) complex Pd{1-C

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di‐carboxamidation products and benzoxazolone compounds.

Density functional theory (DFT) was utilized to understand how bismuth(III) salts (BiX3) achieve greatest activation of organic Lewis bases in a catalytic reaction. It is reported in the literature that the BiX3 reactivity originates from its low lying Bi−X σ* orbital. In contrast to this belief, we will show here that for BiX3 to effectively serve as a catalyst, a p orbital of bismuth needs to be involved in activating organic substrates.

Density functional theory (DFT) at the SMD/M06‐2X/def2‐TZVP//SMD/M06‐2X/SDD,6‐31G(d) level was performed to interrogate the mechanistic details of two oxidative fluorination reactions mediated by hypervalent iodosoarenes (ArIO) in the presence of Lewis acid BF3: (i) formation of a 3‐fluoropyrrolidine from a homoallylic amine and (ii) formation of a fluorinated oxazoline from a benzamide. We found that in both cases, ArIO needs two Lewis acids to be sufficiently activated to mediate the oxidative reactions. When two Lewis acids bind to ArIO, its LUMO mainly centred on the iodine(III) atom becomes energetically more available, resulting in it interacting more strongly with the C–C π orbital of the organic substrate and thus the rate‐determining step of the reaction (an intramolecular nucleophilic attack) being accelerated. Finally, one of these Lewis acids serves as the catalyst and the other one supplies a fluorine atom to the organic substrate. A clear understanding of how ArIO reagents are activated in oxidation of organic substrates could be helpful in designing new oxidative reactions mediated by such hypervalent iodine compounds.

Efficient methods for the synthesis of fused-aromatic rings is a critical endeavour in the creation of new pharmaceuticals and materials. A direct method for preparing these systems is the tetradehydro-Diels–Alder reaction, however this is limited by the need for harsh reaction conditions. A potential, but underdeveloped, route to these systems is via transition metal-catalysed cycloaromatisation of ene-diynes. Herein, tethered unconjugated enediynes have been shown to undergo a facile room-temperature RhI-catalysed intramolecular tetradehydro-Diels–Alder reaction to produce highly substituted isobenzofurans, isoindolines and an indane. Furthermore, experimental and computational studies suggest a novel mechanism involving an unprecedented and complex RhI/RhIII/RhI/RhIII redox cycle involving the formation of an unusual strained 7-membered rhodacyclic allene intermediate and a RhIII-stabilized 6-membered ring allene complex.

A combination of iodosobenzene (PhIO) and molecular iodine (I2) is well-documented to produce a key species capable of conducting various organic reactions through radical mechanisms. This key species is identified here by density functional theory (DFT) calculations to be the hypoiodite radical (IO˙). The calculations show that two equivalents of IO˙ are generated when I2 reacts with two equivalents of PhIO. One of the ensuing IO˙ species acts as a hydrogen abstractor and thus forms an organic radical and the other one is involved in oxidation of the resultant organic radical to afford the final product.

Thermally induced cycloisomerization reactions of 1,6-allenynes gives α-methylene-γ-lactams via intramolecular Alder-ene reactions. The mechanism is supported by computational and deuterium labelling studies. This thermal, non-radical method enables the discovery of a hitherto unknown route that proceeds via a divergent mechanism distinct from the previous [2+2] cycloisomerization manifold.

Diazo compounds have been largely used as carbene precursors for carbene transfer reactions in a variety of functionalization reactions. However, the ease of carbene generation from the corresponding diazo compounds depends upon the electron donating/withdrawing substituents either side of the diazo functionality. These groups strongly impact the ease of N

This report investigates the fundamental basis for rather surprising patterns of reactivity in Brønsted acid-mediated cyclizations of pyrrole substrates bearing pendant Michael acceptors that were identified during syntheses of

We thoroughly investigated mechanistic features of dichlorination of diazoacetates using PhICl

Hypervalent iodine(V) (HVI) compounds are highly efficient reagents for the double oxidative dearomatization of electron-rich phenols to o-quinones. We recently reported that an underexplored class of iodine(V) reagents possessing bidentate bipyridine ligands, termed Bi(N)-HVIs, could efficiently dearomatize electron-poor phenols for the first time. To better understand the fundamental mechanistic basis of this unique reactivity, density functional theory (DFT) was utilized. In this way, different pathways were explored to determine why Bi(N)-HVIs are capable of facilitating these challenging transformations while more traditional hypervalent species, such as IBX cannot. Our calculations reveal that the first redox process is the rate-determining step, the barrier of which hinges on the identity of the ligands bound to the iodine(V) center. This crucial process is composed of three steps: (a) ligand exchange, (b) hypervalent twist, and (c) reductive elimination. We found that strong coordinating ligands disfavour these elementary steps and, for this reason, HVIs bearing such ligands cannot oxidize the electron-poor phenols. In contrast, the weakly coordinating triflate ligands in Bi(N)-HVIs allow for the kinetically favorable oxidation of such phenols {e.g., G‡ = ~22 kcal/mol where Bi(N) = Bi(4-CO2Etbipy)}. It was also identified that trapping triflic acid, which is generated in situ, is a key role played by the basic bidentate bipyridine ligands in Bi(N)-HVIs as this serves to minimize decomposition of the sensitive ortho-quinone product.

Strategies that enable intermolecular site-selective C–H bond functionalisation of organic molecules provide one of the cornerstones of modern chemical synthesis. In chloroalkane synthesis, such methods for intermolecular site-selective aliphatic C–H bond chlorination have, however, remained conspicuously rare. Here, we present a copper(I)-catalysed synthetic method for the efficient site-selective C(sp3)–H bond chlorination of ketones, (E)-enones and alkylbenzenes by dichloramine-T at room temperature. A key feature of the broad substrate scope is tolerance to unsaturation, which would normally pose an immense challenge in chemoselective aliphatic C–H bond functionalisation. By unlocking dichloramine-T’s potential as a chlorine radical atom source, the product site-selectivities achieved are among the most selective in alkane functionalisation and should find widespread utility in chemical synthesis. This is exemplified by the late-stage site-selective modification of a number of natural products and bioactive compounds, and gram-scale preparation and formal synthesis of two drug molecules., Organochlorides are widespread in natural products, therefore the methods for site-selective chlorination at specific C–H bonds are of great interest. Here, the authors report a copper(I)-catalysed synthetic method for the efficient site-selective C(sp3)–H bond chlorination of ketones, (E)-enones and alkylbenzenes by dichloramine-T at room temperature.

Precise control of the selectivity in organic synthesis is important to access the desired molecules. We demonstrate a regiospecific annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene derivatives for a geometry‐controlled synthesis of linear bispentalenes, which is one of the promising structures for material science. A gold‐catalyzed annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene could produce two isomeric pentalenes, but both electronic and steric effects on the aromatics at the terminal position of the alkyne prove to be crucial for the selectivity; especially a regiospecific annulation was achieved with sterically blocked substituents; namely, 2,4,6‐trimetyl benzene or 2,4‐dimethyl benzene. This approach enables the geometrically controlled synthesis of linear bispentalenes from 1,2,4,5‐tetraethynylbenzene or 2,3,6,7‐tetraethynylnaphthalene. Moreover, the annulation of a series of tetraynes with a different substitution pattern regioselectively provided the bispentalene scaffolds. A computational study revealed that this is the result of a kinetic control induced by the bulky NHC ligands., Give me five: The regiospecific annulation of unsymmetrically substituted 1,2‐di(arylethynyl)benzene derivatives is reported. Both electronic and steric effects on the aromatic moieties of the substrates are crucial for the selectivity. Moreover, the annulation of a series of differently substituted tetraynes regioselectively provided the corresponding bispentalenes (see scheme). The selectivity of this transformation is rationalized by computational studies, and the opto‐electronic properties of the obtained bispentalene derivatives are also reported.

This Article describes the development of a stable Ni(IV) complex that mediates C(sp(2))–H trifluoromethylation reactions. This reactivity is first demonstrated stoichiometrically and then successfully translated to a Ni(IV)-catalyzed C–H trifluoromethylation of electron-rich arene and heteroarene substrates. Both experimental and computational mechanistic studies support a radical chain pathway involving Ni(IV), Ni(III), and Ni(II) intermediates.

Density functional theory calculations were utilized to investigate a PdCl2-catalyzed transformation involving double-bond migration (alkene isomerization), followed by condensation with methanol s...

We have demonstrated the profound effect that the N-substituent steric bulk of ethylene-linked bis(N-heterocyclic carbene) (bis(NHC)) species has on the mechanism of their formation via Pd(OAc)2-assisted deprotometalations. The binding mode of an ethylene-linked bis(NHC) ligand is chelating when it bears N-2,4-Me2C6H3 substituents but forms a mono(NHC) with a pendant imidazolium group for N-2,6-iPr2C6H3. An N-mesityl-substituted bis(NHC), with steric bulk intermediate between the two aforementioned substituents, generates a mixture of two chelating homoleptic normal/normal and heteroleptic normal/abnormal bis(NHC) complexes, as predicted by DFT calculations. Interestingly, the latter was seen to undergo facile reductive elimination, affording a novel tricyclic monodentate NHC ligand.

In this study, we used density functional theory (DFT) to reinvestigate the mechanism proposed by Houk and Zhang et al. (J. Am. Chem. Soc. 2012, 134, 1078) for piperidinone formation through rearrangement of an acetylenic amine N-oxide catalysed by phosphine gold(I) complexes. For this rearrangement, the C-C coupling was proposed to be the rate-determining step with activation energy as high as 35.8 kcal/mol. Such a barrier seems inconsistent with the fact that the actual reaction proceeds under very mild conditions (0 °C, 1 h, in CH2Cl2). In the original report, it was proposed that the C-C coupling takes place via a mechanism which we called “front-side addition”. Interestingly, we found that the C-C coupling step becomes energetically more favourable if it occurs via another mechanism called “back-side addition”. We explored the effect of different phosphine ligands on all conceivable steps of the catalytic reaction and found that while the other steps are not highly sensitive to the phosphine identity, the C-C coupling one shows a considerable degree of dependency; the more electron-donating the phosphine ligand, the lower the rate-limiting step barrier.

We have demonstrated that air-stable cationic gold(I) cocatalysts have the capacity to enhance the efficiency of palladium-catalyzed cross-couplings. Specifically, we determined that a 1:1 [Pd{P(t-Bu)3}2]/[Au{P(t-Bu)3}(NTf2)] system provides superior reactivity relative to [Pd{P(t-Bu)3}2], across Suzuki–Miyaura, Stille, and Mizoroki–Heck reactions performed under mild conditions. Our results are consistent with cationic gold(I) species serving primarily as phosphine scavengers in this chemistry, as recently predicted by density functional theory (DFT).

Density functional theory (DFT) at the SMD/M06-2X/def2-TZVP//SMD/M06-2X/LANL2DZ,6-31G(d) level was employed to explore mechanistic aspects of BF3-catalyzed alcohol oxidation using a hypervalent iodine(III) compound, [ArI(OAc)2], to yield aldehydes/ketones as the final products. The reaction is composed of two main processes: (i) ligand exchange and (ii) the redox reaction. Our study for 1-propanol discovered that ligand exchange is preferentially accelerated if BF3 first coordinates to the alcohol. This coordination increases the acidity of the alcohol hydroxyl proton, resulting in ligand exchange between the iodane and the alcohol proceeding via a concerted interchange associative mechanism with an activation free energy of ∼10 kcal/mol. For the redox process, the calculations rule out the feasibility of the conventional mechanism (alkoxy Cα deprotonation) and introduce a replacement for it. This alternative route commences with α-hydride elimination of the alkoxy group promoted by BF3 coordination, which yields a BF3-stabilized aldehyde/ketone product and the iodane [ArI(OAc)(H)]. The ensuing iodane is extremely reactive toward reductive elimination to give ArI + HOAc in a highly exergonic fashion (ΔG = −62.1 kcal/mol). The reductive elimination reaction is the thermodynamic driving force for the alcohol oxidation to be irreversible. Consistent with the kinetic isotope effect reported experimentally, the α-hydride elimination is calculated to be the rate-determining step with an overall activation free energy of ∼24 kcal/mol.

Gas-phase ion trap mass spectrometry experiments and density functional theory calculations have been used to examine the routes to the formation of the 1,8-naphthyridine (napy) ligated geminally dimetallated phenyl complexes [(napy)Cu2(Ph)]+, [(napy)Ag2(Ph)]+ and [(napy)CuAg(Ph)]+ via extrusion of CO2 or SO2 under collision-induced dissociation conditions from their corresponding precursor complexes [(napy)Cu2(O2CPh)]+, [(napy)Ag2(O2CPh)]+, [(napy)CuAg(O2CPh)]+ and [(napy)Cu2(O2SPh)]+, [(napy)Ag2(O2SPh)]+, [(napy)CuAg(O2SPh)]+. Desulfination was found to be more facile than decarboxylation. Density functional theory calculations reveal that extrusion proceeds via two transition states: TS1 enables isomerization of the O, O-bridged benzoate to its O-bound form; TS2 involves extrusion of CO2 or SO2 with the concomitant formation of the organometallic cation and has the highest barrier. Of all the organometallic cations, only [(napy)Cu2(Ph)]+ reacts with water via hydrolysis to give [(napy)Cu2(OH)]+, consistent with density functional theory calculations which show that hydrolysis proceeds via the initial formation of the adduct [(napy)Cu2(Ph)(H2O)]+ which then proceeds via TS3 in which the coordinated H2O is deprotonated by the coordinated phenyl anion to give the product complex [(napy)Cu2(OH)(C6H6)]+, which then loses benzene.

Density functional theory (DFT) was utilized to investigate the mechanistic aspects of the oxidative dearomatization of phenols mediated by an iodine(iii) reagent. In this article, we will show that the conventional mechanism in which an iodine(iii) phenolate is proposed as the key intermediate is not operative, and the process is promoted if the phenolate ligand is dearomatized on the iodine(iii) center. The dearomatized phenolate is calculated to be a more potent reductant than phenolate itself. In such a case, the reaction is capable of proceeding via two competitive mechanisms (dissociative and associative). Consistent with the experimental findings, we found that while the less polar solvents considerably disfavor the dissociative mechanism, they have an insignificant effect on the associative one. The energetic order of these two mechanisms is calculated to be influenced by the nature of the counter anion coordinated to the iodine(iii) center.

Density functional theory (DFT) was used to investigate PR3AuOTf-catalyzed hydrofunctionalisation of nonactivated alkenes using acetic acid and phenol where OTf = triflate (CF3SO3−). The gold(I) complex itself is found to be unlikely to operate as the π-activator due to its relatively low electrophilicity. Instead, the concurrent coordination of two gold(I) complexes to a nucleophile (PhOH or AcOH) enhances the acidity of the latter's proton and causes the ensuing binuclear complex to serve as a strong proton supplier for activating the alkene π-bonds. Alternatively, the binuclear complex is also susceptible to produce a hidden HOTf. This hidden acid is accessible for hydrofunctionalization to occur but it is not in sufficient concentration to decompose the final product.

In contrast to early transition metal complexes of d0 electron configuration, their main group metal analogues are usually poor catalysts for ethylene polymerisation due to their diminished tendency to insert ethylene into an M-R bond. Interestingly, we found that ring strain in the transition structure of the insertion reaction is most likely responsible to set the ease of the process. Ethylene insertion into an M-R bond requires a four-membered ring transition structure. Strain in a four-membered ring was shown to be dependent on the metal identity (transition or main group/d or p block). For early transition metals, due to the presence of empty valence d orbitals, the strain is negligible but, for main group metals, the strain is significant and so destabilizes the corresponding transition structure. Our claim gains support from investigation of ethylene insertion into an M-allyl bond. In this case, the relevant insertion preferentially passes through a six-membered ring transition structure with an accessibly low activation barrier. In contrast to four-membered ring transition structures, six-membered ones do not suffer significantly from ring strain, causing the insertion activation barrier to become independent of the metal identity. It becomes obvious from our study that this previously undisclosed factor should play the pivotal role in determining the reactivity of many catalysts.

Although Pd(OAc)2-catalysed alkoxylation of the C(sp3)–H bonds mediated by hypervalent iodine(iii) reagents (ArIX2) has been developed by several prominent researchers, there is no clear mechanism yet for such crucial transformations. In this study, we shed light on this important issue with the aid of the density functional theory (DFT) calculations for alkoxylation of butyramide derivatives. We found that the previously proposed mechanism in the literature is not consistent with the experimental observations and thus cannot be operating. The calculations allowed us to discover an unprecedented mechanism composed of four main steps as follows: (i) activation of the C(sp3)–H bond, (ii) oxidative addition, (iii) reductive elimination and (iv) regeneration of the active catalyst. After completion of step (i) via the CMD mechanism, the oxidative addition commences with an X ligand transfer from the iodine(iii) reagent (ArIX2) to Pd(ii) to form a square pyramidal complex in which an iodonium occupies the apical position. Interestingly, a simple isomerization of the resultant five-coordinate complex triggers the Pd(ii) oxidation. Accordingly, the movement of the ligand trans to the Pd–C(sp3) bond to the apical position promotes the electron transfer from Pd(ii) to iodine(iii), resulting in the reduction of iodine(iii) concomitant with the ejection of the second X ligand as a free anion. The ensuing Pd(iv) complex then undergoes the C–O reductive elimination by nucleophilic attack of the solvent (alcohol) on the sp3 carbon via an outer-sphere SN2 mechanism assisted by the X− anion. Noteworthy, starting from the five coordinate complex, the oxidative addition and reductive elimination processes occur with a very low activation barrier (ΔG‡ 0–6 kcal mol−1). The strong coordination of the alkoxylated product to the Pd(ii) centre causes the regeneration of the active catalyst, i.e. step (iv), to be considerably endergonic, leading to subsequent catalytic cycles to proceed with a much higher activation barrier than the first cycle. We also found that although, in most cases, the alkoxylation reactions proceed via a Pd(ii)–Pd(iv)–Pd(ii) catalytic cycle, the other alternative in which the oxidation state of the Pd(ii) centre remains unchanged during the catalysis could be operative, depending on the nature of the organic substrate., This work uses DFT calculations to explore Pd(ii)-catalysed iodine(iii)-mediated alkoxylation of unactivated C(sp3)–H bonds and reveals how important the isomerization is in triggering the oxidative addition of ArIX2 to Pd(ii).

Efficient methods for the synthesis of fused-aromatic rings is a critical endeavour in the creation of new pharmaceuticals and materials. A direct method for preparing these systems is the tetradehydro-Diels–Alder reaction, however this is limited by the need for harsh reaction conditions. A potential, but underdeveloped, route to these systems is via transition metal-catalysed cycloaromatisation of ene-diynes. Herein, tethered unconjugated enediynes have been shown to undergo a facile room-temperature RhI-catalysed intramolecular tetradehydro-Diels–Alder reaction to produce highly substituted isobenzofurans, isoindolines and an indane. Furthermore, experimental and computational studies suggest a novel mechanism involving an unprecedented and complex RhI/RhIII/RhI/RhIII redox cycle involving the formation of an unusual strained 7-membered rhodacyclic allene intermediate and a RhIII-stabilized 6-membered ring allene complex., Room temperature Rh-catalysed tetradehydro-Diels–Alder reaction via an unusual Rh-stabilised allene.

The donor–acceptor ability of frustrated Lewis pairs (FLPs) has led to widespread applications in organic synthesis. Single electron transfer from a donor Lewis base to an acceptor Lewis acid can generate a frustrated radical pair (FRP) depending on the substrate and energy required (thermal or photochemical) to promote an FLP into an FRP system. Herein, we report the Csp3–Csp cross-coupling reaction of aryl esters with terminal alkynes using the B(C6F5)3/Mes3P FLP. Significantly, when the 1-ethynyl-4-vinylbenzene substrate was employed, the exclusive formation of Csp3–Csp cross-coupled products was observed. However, when 1-ethynyl-2-vinylbenzene was employed, solvent-dependent site-selective Csp3–Csp or Csp3–Csp2 cross-coupling resulted. The nature of these reaction pathways and their selectivity has been investigated by extensive electron paramagnetic resonance (EPR) studies, kinetic studies, and density functional theory (DFT) calculations both to elucidate the mechanism of these coupling reactions and to explain the solvent-dependent site selectivity.

Iodosobenzene (PhIO) is known to be a potent oxidant for alcohols in the presence of catalytic bromide in water. In order to understand this important and practical oxidation process, we have conducted density functional theory studies to shed light on the reaction mechanism. The key finding of this study is that PhIO is not the reactive oxidant itself. Instead, the active oxidant is hypobromite (BrO-), which is generated by the reaction of PhIO with bromide through an SN2-type reaction. Critically, water acts as a cocatalyst in the generation of BrO- through lowering the activation energy of this process. This investigation also demonstrates why BrO- is a more powerful oxidant than PhIO in the oxidation of alcohols. Other halide additives have been reported experimentally to be less effective catalysts than bromide - our calculations provide a clear rationale for these observations. We also examined the effect of replacing water with methanol on the ease of the SN2 reaction, finding that the replacement resulted in a higher activation barrier for the generation of BrO-. Overall, this work demonstrates that the hypervalent iodine(III) reagent PhIO can act as a convenient and controlled precursor of the oxidant hypobromite if the right conditions are present.

We have identified and extensively investigated the photochemical activation and reaction of a hydroxyquinone-derived phenyliodonium ylide in the presence of visible light using experiment and theory. These studies revealed that in its photoexcited state this iodonium is capable of facilitating a range of single-electron transfer (SET) processes, including hydrogen atom transfer (HAT), a Povarov-type reaction, and atom-transfer radical addition chemistry. Where possible, we have employed density functional theory (DFT) to develop a more complete understanding of these photoinduced synthetic transformations.

A combination of iodosobenzene (PhIO) and molecular iodine (I2) is well-documented to produce a key species capable of conducting various organic reactions through radical mechanisms. This key species is identified here by density functional theory (DFT) calculations to be the hypoiodite radical (IO˙). The calculations show that two equivalents of IO˙ are generated when I2 reacts with two equivalents of PhIO. One of the ensuing IO˙ species acts as a hydrogen abstractor and thus forms an organic radical and the other one is involved in oxidation of the resultant organic radical to afford the final product.

The oxidant diphenyldiselenide reacts with MIIMe2(bipy) (bipy = 2,2′-bipyridine) to form a pre-equilibrium involving weak adducts, from which [MMe2(bipy)]2·Ph2Se2 undergoes rate-limiting dissociation of phenylselenide preceded by the oxidative addition step to obtain [Me2(bipy)M-MMe2(bipy)(SePh)]+. Coordination of PhSe− gives the neutral MIII–MIII bonded dimers [MMe2(bipy)(SePh)]2. The dimers fragment in the presence of light to give radicals [MIIIMe2(bipy)(SePh)]˙. After reorientation in the solvent cage, the radicals interact to form triplet adducts [MIIIMe2(bipy)(SePh)·(bipy)MIIIMe2(SePh)]˙˙ with π-stacked ‘SePh·bipy’, followed by transformation via a Minimum Energy Crossing Point allowing [SePh]˙ transfer to give MIIMe2(bipy) and MIVMe2(bipy)(SePh)2. The regenerated MII reagent reacts with Ph2Se2 through the above sequence, allowing completion of reaction to give the MIV product only. The reaction of PtMe2(bipy) with diphenyldisulfide has been studied in an analogous manner to assist with interpretation of DFT results for reactions of diphenyldiselenide. In short, this study shows that photochemical cleavage of metal–metal bonds (Pd, Pt) via excitation to an M–M antibonding orbital facilates disproportionation of the MIII–MIII complex to MII and MIV complexes.

Density Functional Theory studies of square-planar PtII pincer structures, (4-Z-NCN)PtCl ([4-Z-NCN]- =[4-Z-2,6-(Me2 NCH2 )2 C6 H2 -N,C,N]- , Z=H, NO2 , CF3 , CO2 H, CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 , NMe2 ), enable characterisation of mesomerism for the pincer-Pt interaction. Relationships between Hammett σp substituent parameters of Z and DFT data obtained from NBO6 and AOMix computation are used to probe the interaction of the 5dyz orbital of platinum with π-orbitals of the arene ring. Analogous computation for 2,6-(Me2 CH2 )2 C6 H3 Z (Z=H, CF3 , CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 ) and (4-H-NCN)PtZ allows an estimation of the relative substituent effects of "(CH2 NMe2 )2 PtZ" on π-delocalisation in the pincer system.