Experimentalists have recently achieved the first chemoselective aminocarbonylation of unactivated alkyl electrophiles, using the common cobalt reagent Co2(CO)8 as a catalyst. Here, we present a ...detailed density functional theory (DFT) mechanistic study on this remarkable reaction. Induced by the Lewis base morpholine (or MOR, the amine substrate), Co2(CO)8 disproportionates to Co(CO)3(MOR)2+ and Co(CO)4−. The active catalyst Co(CO)4− undergoes an SN2 reaction with the alkyl tosylate substrate to form an alkylcobalt(I) carbonyl intermediate with an inverted configuration at the α-carbon. The alkylcobalt(I) carbonyl complex favors CO migratory insertion over β-hydride elimination. The resulting acylcobalt(I) carbonyl intermediate, along with the MOR and CO substrates, could introduce several pathways for the amide C–N bond formation. The inner-sphere pathways involving Co(I)-bound MOR are ruled out. The outer-sphere pathway in which MOR attacks the Co(I)-bound acyl leads to the amide product and the regenerated Co(CO)4−. The SN2 process is the rate-determining step with the largest energy span (ΔG ⧺ = 22.8 kcal/mol). The side reaction of double CO insertion faces a higher selectivity-determining energy barrier and hence is less favorable. This DFT work provides deep mechanistic insights into the Co2(CO)8-promoted chemoselective aminocarbonylation of unactivated alkyl electrophiles, thereby having implications for organocobalt catalysis and transition-metal-catalyzed amide C–N bond-forming reactions.
Luminescent metal–organic frameworks (LMOFs) have been extensively studied for their potential applications in lighting, sensing and biomedicine-related areas due to their high porosity, unlimited ...structure and composition tunability. However, methodical development in systematically tuning the emission properties of fluorescent organic linker-based LMOFs to facilitate the rational design and synthesis of target-specific materials has remained challenging. Herein we attempt to build an emission library by customized synthesis of LMOFs with targeted absorption and emission properties using donor–acceptor–donor type organic linkers. By tuning the acceptor groups ( i.e. 2,1,3-benzothiadiazole and its derivatives), donor groups (including modification of original donors and use of donors with different metal–linker connections) and bridging units between acceptor and donor groups, an emission library is developed for LMOFs with their emissions covering the entire visible light range as well as the near-infrared region. This work may offer insight into well controlled design of organic linkers for the synthesis of LMOFs with specified functionality.
There is ongoing interest in catalysis with the earth-abundant metal copper (Cu). This density functional theory (DFT) study explores the detailed workings of the first CuH-catalyzed hydroarylation ...of alkenes with polyfluoroarenes involving C–F bond functionalization. The CuH complex undergoes Markovnikov hydrocupration with the aryl alkene substrate to give a Cu(i) benzyl intermediate, and the regioselectivity is due to a combination of orbital and dispersion interactions induced by the aryl alkene substrate. The benzyl ligand allows a 1,3-cupratropic shift for the Cu(i) complex to have an exposed carbonanionic atom facilitating nucleophilic aromatic substitution to the polyfluoroarene substrate. The distinct regioselectivity of para-C–F substitution is controlled by the noncovalent C(sp3)–H/π and C(sp2)–H⋯O interactions. These mechanistic insights can have implications for the development of new transition metal-catalyzed hydroarylation and C–F functionalization reactions.
The first catalytic hydrohalogenation of alkynes was recently achieved using a copper(I) N-heterocyclic carbene (NHC) complex, and the reaction was found to be syn and anti-Markovnikov selective. ...The present work is a density functional theory (DFT) computational study (B3LYP and M06) on the detailed mechanism of this remarkable catalytic reaction. The reaction begins with a phenoxide additive turning over the precatalyst (NHC)CuCl into (NHC)Cu(OAr), which subsequently transmetalates with the hydride source Ph2SiH2 to deliver the copper(I) hydride complex (NHC)CuH. (NHC)CuH undertakes hydrocupration of the substrate RCCH via alkyne coordination and subsequent migratory insertion into the Cu–H bond, forming (E)-(NHC)Cu(CHCHR). The migratory insertion step determines the syn selectivity because it occurs by a concerted pathway, and it also determines the anti-Markovnikov regioselectivity that arises from the charge distributions across the Cu–H and CC bonds. The brominating agent (BrCl2C)2 uses the bromonium end to attack the Cu-bound vinylic carbon atom of (E)-(NHC)Cu(CHCHR), leading to the final (E)-alkenyl bromide product (E)-RHCCHBr, as well as the copper(I) alkyl complex (NHC)Cu(CCl2CBrCl2), which undergoes β-bromide elimination to give the catalyst precursor (NHC)CuBr for the next cycle. (NHC)CuBr reacts with the phenoxide to regenerate the active catalyst (NHC)Cu(OAr). The computational results rationalize the experimental observations, reveal new insights into the mechanism of the Cu(I)-catalyzed hydrobromination of alkynes, and have implications for other catalytic functionalization reactions of alkynes involving active Cu–H intermediates.
The reaction of Co(II) with 5,15-dipyridyl-10,20-diphenylporphyrin (H2DPyP) produces the first metal-organic coordination polymer supported by a trans meso-bifunctional porphyrin ligand. Formulated ...empirically as Co3(DPyP)3·4DMF, this compound exhibits a ribbonlike coordination network consisting of tetranuclear metalloporphyrin cages. The DMF guest molecules fill the intra-ribbon cages as well as the inter-ribbon space. Evacuation of Co3(DPyP)3·4DMF at 130 °C generates Co3(DPyP)3 that retains crystallinity, as shown by its powder X-ray diffraction pattern, which is consistent with that of Co3(DPyP)3·4DMF.
Chemical bonding is at the heart of chemistry. Recent work on high bond orders between homonuclear transition metal atoms has led to ultrashort metal−metal (TM−TM) distances defined as dM−M<1.900 Å. ...The present work is a computational design and characterization of novel main group species containing ultrashort metal−metal distances (1.728–1.866 Å) between two beryllium atoms in different molecular environments, including a rhombic Be2X2 (X=C, N) core, a vertical Be−Be axis in a 3D molecular star, and a horizontal Be−Be axis supported by N‐heterocyclic carbene (NHC) ligands. The ultrashort Be−Be distances are achieved by affixing bridging atoms to attract the beryllium atoms electrostatically or covalently. Among these species are five global minima and one chemically viable diberyllium complex, which provide potential targets for experimental realization.
Short and sweet: High level ab initio calculations indicate that, with the aid of bridging atoms and supporting ligands, ultrashort Be−Be distances (1.728–1.866 Å) can be achieved that match the quintuple bond distances between two 3d transition metal atoms. Stability analyses suggest that the majority of these beryllium species are potential targets for experimental realization.
A novel complex comprising an ion pair of arginine–arginine carbamate is reported herein, which is isolated from an aqueous l-arginine solution after reacting with CO2. Its structure was ...unambiguously elucidated via single-crystal X-ray diffraction, and its phase purity was confirmed by powder X-ray diffraction (PXRD) analysis. Nuclear magnetic resonance (NMR) studies suggested that the arginine carbamate complex hydrolyzed in aqueous conditions with a rate directly proportional to its concentration. Furthermore, density functional theory (DFT) calculations revealed how the amino group acted as a nucleophile to attack CO2 to enable the ion-pair formation through a proton transfer between the arginine and arginine carbamate. The discovery of the arginine–CO2 adduct expands our understanding of CO2 fixation and can lead to the development of new methods of implementing l-arginine or other amino acids for CO2 capture technology.
The diagonal relationship between beryllium and aluminum and the isoelectronic relationship between BeH unit and Al atom were utilized to design a new series ppC- or quasi-ppC-containing species C5v ...CBe5H5(+), Cs CBe5H4, C2v CBe5H3(-), and C2v CBe5H2(2-) by replacing the Al atoms in previously reported global minima planar pentacoordinate carbon (ppC) species D5h CAl5(+), C2v CAl4Be, C2v CAl3Be2(-), and C2v CAl2Be3(2-) with BeH units. The three-center two-electron (3c-2e) bonds formed between Be and bridging H atoms were crucial for the stabilization of these ppC species. The natural bond orbital (NBO) and adaptive natural density partitioning (AdNDP) analyses revealed that the central ppCs or quasi-ppCs possess the stable eight electron-shell structures. The AdNDP analyses also disclosed that these species are all 6σ+2π double-aromatic in nature. The aromaticity was proved by the calculated negative nucleus-independent chemical shifts (NICS) values. DFT and high-level CCSD(T) calculations revealed that these ppC- or quasi-ppC species are the global minimum or competitive low-lying local minimum (Cs CBe5H4) on their potential energy surfaces. The Born-Oppenheimer molecular dynamic (BOMD) simulations revealed that the H atoms in C2v CBe5H3(-) and C2v CBe5H2(2-) can easily rotate around the CBe5 cores and the structure of quasi-planar C5v CBe5H5(+) will become the planar structure at room temperature; however, these interesting dynamic behaviors did not indicate the kinetic instability as the basic ppC structures were maintained during the simulations. Therefore, it would be potentially possible to realize these interesting ppC- or quasi-ppc-species in future experiments.
The subject of metal-metal bonding interactions in molecular systems continues to attract research interest. Chromium heretofore has been the only element known to afford metal-metal distances ...shorter than 1.700 Å in the form of Cr-Cr multiple bonds. In this computational study, the effect of a triple bond on reducing interatomic distances is simulated through forming three non-classical bonding orbitals between two beryllium atoms, thereby realizing the remarkably short Be-Be distances (1.692-1.735 Å) in kinetically stable global minimum species L → Be
2
H
3
← L
+
(L = NH
3
, PH
3
, and noble gases Ne-Xe). Such diberyllium complexes make promising candidates for experimental realization. In particular, the Be-Be distance of 1.692 Å in Ne → Be
2
H
3
← Ne
+
represents the first example of global minimum having a main group metal-metal distance under 1.700 Å. TEA → Be
2
H
3
← TEA
+
, which contains the bulky triethylamine (TEA) ligands, is designed as a more promising target for synthesis and isolation in condensed states.
Ne → Be
2
H
3
← Ne
+
represents the first global energy minimum having a main group metal-metal distance under 1.700 Å.
The Ni‐catalyzed decarbonylative borylation of (hetero)aryl carboxylic acids with B2cat2 has been achieved without recourse to any additives. This Ni‐catalyzed method exhibits a broad substrate scope ...covering poorly reactive non‐ortho‐substituted (hetero)aryl carboxylic acids, and tolerates diverse functional groups including some of the groups active to Ni0 catalysts. The key to achieve this decarbonylative borylation reaction is the choice of B2cat2 as a coupling partner that not only acts as a borylating reagent, but also chemoselectively activates aryl carboxylic acids towards oxidative addition of their C(acyl)−O bond to Ni0 catalyst via the formation of acyloxyboron compounds. A combination of experimental and computational studies reveals a detailed plausible mechanism for this reaction system, which involves a hitherto unknown concerted decarbonylation and reductive elimination step that generates the aryl boronic ester product. This mode of boron‐promoted carboxylic acid activation is also applicable to other types of reactions.
A Ni‐catalyzed direct decarbonylative borylation of aryl carboxylic acids with B2cat2 has been established. B2cat2 serves as a borylating agent, but also activates the carboxylic acid substrate towards decarbonylative coupling, playing a dual role in this reaction. A combination of experimental and computational studies reveals that the reaction proceeds through a hitherto unknown concerted decarbonylation and reductive elimination step.
