The “curly arrow” of Robinson and Ingold is the primary tool for describing and rationalizing reaction mechanisms. Despite this approach’s ubiquity and stellar success, its physical basis has never ...been clarified and a direct connection to quantum chemistry has never been found. Here we report that the bond rearrangements expressed by curly arrows can be directly observed in ab initio computations, as transformations of intrinsic bond orbitals (IBOs) along the reaction coordinate. Our results clarify that curly arrows are rooted in physical reality—a notion which has been challenged before—and show how quantum chemistry can directly establish reaction mechanisms in intuitive terms and unprecedented detail.
Curly arrows from ab initio calculations: Curly arrows in reaction mechanisms are shown to correspond to changes in intrinsic bond orbitals (IBOs) along reaction paths. With this quantum chemical basis, even complex reaction mechanisms can be derived and visualized in a simple, direct, and intuitive form.
Proton‐coupled electron transfer (PCET) events play a key role in countless chemical transformations, but they come in many physical variants which are hard to distinguish experimentally. While ...present theoretical approaches to treat these events are mostly based on physical rate coefficient models of various complexity, it is now argued that it is both feasible and fruitful to directly analyze the electronic N‐electron wavefunctions of these processes along their intrinsic reaction coordinate (IRC). In particular, for model systems of lipoxygenase and the high‐valent oxoiron(IV) intermediate TauD‐J it is shown that by invoking the intrinsic bond orbital (IBO) representation of the wavefunction, the common boundary cases of hydrogen atom transfer (HAT) and concerted PCET (cPCET) can be directly and unambiguously distinguished in a straightforward manner.
Proton‐coupled electron transfer (PCET) events are pivotal in many transformations, but variants are hard to distinguish. The boundary cases of hydrogen atom transfer (HAT) and concerted PCET (cPCET) could now be clearly identified in enzyme model complexes via theory. Key to this was an intrinsic bond orbital analysis of the PCET process along its intrinsic reaction coordinate.
The Stabilizing Effects in Gold Carbene Complexes Nunes dos Santos Comprido, Laura; Klein, Johannes E. M. N.; Knizia, Gerald ...
Angewandte Chemie (International ed.),
August 24, 2015, Letnik:
54, Številka:
35
Journal Article
Recenzirano
Bonding and stabilizing effects in gold carbene complexes are investigated by using Kohn–Sham density functional theory (DFT) and the intrinsic bond orbital (IBO) approach. The π‐stabilizing effects ...of organic substituents at the carbene carbon atom coordinated to the gold atom are evaluated for a series of recently isolated and characterized complexes, as well as intermediates of prototypical 1,6‐enyne cyclization reactions. The results indicate that these effects are of particular importance for gold complexes especially because of the low π‐backbonding contribution from the gold atom.
Is anybody there? Intrinsic bond orbital analyses based on DFT calculations on gold carbene complexes indicate little π backbonding from gold (A) and π stabilization from organic fragments even in cyclopropyl‐substituted gold carbene complex intermediates (B, C).
In a systematic study of the Au‐catalyzed reaction of o‐alkynylphenols with aryldiazonium salts, we find that essentially the same reaction conditions lead to a change in mechanism when a light ...source is applied. If the reaction is carried out at room temperature using a AuI catalyst, the diazonium salt undergoes electrophilic deauration of a vinyl AuI intermediate and provides access to substituted azobenzofurans. If the reaction mixture is irradiated with blue LED light, C−C bond formation due to N2‐extrusion from the diazonium salt is realized selectively, using the same starting materials without the need for an additional photo(redox) catalyst under aerobic conditions. We report a series of experiments demonstrating that the same vinyl AuI intermediate is capable of producing the observed products under photolytic and thermal conditions. The finding that a vinyl AuI complex can directly, without the need for an additional photo(redox) catalyst, result in C−C bond formation under photolytic conditions is contrary to the proposed mechanistic pathways suggested in the literature till date and highlights that the role of oxidation state changes in photoredox catalysis involving Au is thus far only poorly understood and may hold surprises for the future. Computational results indicate that photochemical activation can occur directly from a donor–acceptor complex formed between the vinyl AuI intermediate and the diazonium salt.
The Au‐catalyzed reaction of o‐alkynylphenols with aryldiazonium salts undergoes a change in mechanism when a light source is applied. If the reaction is carried out at room temperature using a AuI catalyst, the diazonium salt undergoes electrophilic deauration of a vinyl AuI intermediate generating substituted azobenzofurans. If the reaction mixture is irradiated with blue LED light, C−C bond formation due to N2‐extrusion from the diazonium salt is observed.
Our ability to understand and simulate the reactions catalyzed by iron depends strongly on our ability to predict the relative energetics of spin states. In this work, we studied the electronic ...structures of Fe
ion, gaseous FeO and 14 iron complexes using Kohn-Sham density functional theory with particular focus on determining the ground spin state of these species as well as the magnitudes of relevant spin-state energy splittings. The 14 iron complexes investigated in this work have hexacoordinate geometries of which seven are Fe(ii), five are Fe(iii) and two are Fe(iv) complexes. These are calculated using 20 exchange-correlation functionals. In particular, we use a local spin density approximation (LSDA) - GVWN5, four generalized gradient approximations (GGAs) - BLYP, PBE, OPBE and OLYP, two non-separable gradient approximations (NGAs) - GAM and N12, two meta-GGAs - M06-L and M11-L, a meta-NGA - MN15-L, five hybrid GGAs - B3LYP, B3LYP*, PBE0, B97-3 and SOGGA11-X, four hybrid meta-GGAs - M06, PW6B95, MPW1B95 and M08-SO and a hybrid meta-NGA - MN15. The density functional results are compared to reference data, which include experimental results as well as the results of diffusion Monte Carlo (DMC) calculations and ligand field theory estimates from the literature. For the Fe
ion, all functionals except M11-L correctly predict the ground spin state to be quintet. However, quantitatively, most of the functionals are not close to the experimentally determined spin-state splitting energies. For FeO all functionals predict quintet to be the ground spin state. For the 14 iron complexes, the hybrid functionals B3LYP, MPW1B95 and MN15 correctly predict the ground spin state of 13 out of 14 complexes and PW6B95 gets all the 14 complexes right. The local functionals, OPBE, OLYP and M06-L, predict the correct ground spin state for 12 out of 14 complexes. Two of the tested functionals are not recommended to be used for this type of study, in particular M08-SO and M11-L, because M08-SO systematically overstabilizes the high spin state, and M11-L systematically overstabilizes the low spin state.
PhI(OAc)2 is a common oxidant for Pd-catalyzed C−H bond functionalizations. Mechanistic hypotheses since the 1960s have suggested a Pd(II)/Pd(IV) mechanism. Here we present evidence for the relevance ...of bimetallic Pd(III) complexes to catalysis. A bimetallic Pd(III) acetate was isolated and can afford product by bimetallic reductive elimination.
In this contribution, we studied the OC-C bond in carbon suboxide and related allene compounds using the valence bond method. The nature of this bond has been the subject of debate, whether it is a ...regular, electron sharing bond or a dative bond. We compared the nature of this bond in carbon suboxide with the gold-CO bond in Au(CO)
2
+
, which is a typical dative bond, and we studied its charge-shift bond character. We found that the C-CO bond in carbon suboxide is unique in the sense that it cannot be assigned as either a dative or electron sharing bond, but it is an admixture of electron sharing and dative components, together with a high contribution of ionic character. These findings provide a clear basis for distinguishing the commonly found dative bonds between ligands and transition metals and the present case of what may be described as coordinative bonding to carbon.
Valence bond theory reveals the nature of the OC-C bond in carbon suboxide and related allene compounds.
This review describes transition‐metal‐catalysed and ‐mediated processes for the preparation of oxindoles from anilides through C(3)–C(3a) bond formation. Traditional methods, such as the Heck ...reaction, and recent developments, including direct Ar–H coupling processes, are presented, as are applications in natural product synthesis.
In this review we describe transition‐metal‐catalysed and ‐mediated processes for the preparation of oxindoles from anilides through C(3)–C(3a) bond formation. Traditional methods and recent developments are presented, including their applications in natural product synthesis.
A detailed analysis of the C(sp3)−H activation process by vinylidene AuI complexes is described based on an intrinsic bond orbital analysis. Based on our analysis this event can be divided into three ...phases: (i) hydride transfer, (ii) C−C bond formation, and (iii) σ to π rearrangement of the lone pair coordinated to Au. Small perturbations of the system lead to either a concerted asynchronous reaction, or a stepwise reaction featuring an intermediate with a C‐H‐C three‐centre two‐electron (3c–2e) bond. The role of π‐donating substituents is highlighted and provides a way of controlling reactions of this type in future experimental studies.
Detailed theoretical investigations reveal that C(sp3)‐H activation by vinylidene AuI complexes proceed either by a concerted asynchronous or a stepwise reaction featuring a C‐H‐C three‐centre two‐electron (3c‐2e) bond. Intrinsic bond orbital analysis uncovers that this type of reaction is greatly facilitated by π‐donating substituents.
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