Mechanistic Studies of Carbonyl Allylation Mediated by (NHC)CuH: Isoprene Insertion, Allylation, and ß-Hydride Elimination.

The ability of Cu-H complexes to undergo selective insertion of unsaturated hydrocarbons under mild conditions has rendered them valuable, versatile catalysts. The direct formation of Cu allyl intermediates from unfunctionalized 1,3-dienes and transient Cu hydrides is an appealing strategy for upgrading conjugated diene feedstocks. However, empirical mechanistic studies of the underlying elementary steps and characterization of key intermediates in Cu-H catalysis are sparse. Using [(NHC)CuH]2 (NHC = N-heterocyclic carbene), we examined the steric effects of NHC ligands on two key elementary steps of CuH-catalyzed carbonyl allylation: the insertion of a diene into the Cu-H bond to produce a Cu-allyl complex, and the formation of C-C bonds from stoichiometric allylations of ketones and aldehydes. The resulting allyl and homoallylic alkoxide complexes have been characterized by NMR spectroscopy and single-crystal X-ray diffraction. Employing isolable (NHC)Cu-allyl complexes, we further evaluated the roles of the ligand size, electronic properties of carbonyl substrates, coordinating groups within the substrate, and solvent on the regioselectivity, diastereoselectivity, and relative rate of the C-C bond formation step. In contrast to the clean allylation of ketones, allylation of aldehydes provided a rare example of a formal ß-hydride elimination reaction from a secondary homoallylic alkoxide species. Mechanistic studies of key elementary steps provide insights for a range of catalytic reactions of dienes mediated by hydride complexes.

Single-Crystal to Single-Crystal Transformations: Stepwise CO2 Insertions into Bridging Hydrides of [(NHC)CuH]2 Complexes.

Mechanistic studies of substrate insertion into dimeric [(NHC)CuH]2 (NHC=N-heterocyclic carbene) complexes with two bridging hydrides have been shown to require dimer dissociation to generate transient, highly reactive (NHC)Cu-H monomers in solution. Using single-crystal to single-crystal (SC-SC) transformations, we discovered a new pathway of stepwise insertion of CO2 into [(NHC)CuH]2 without complete dissociation of the dimer. The first CO2 insertion into dimeric [(IPr*OMe)CuH]2 (IPr*OMe=N,N'-bis(2,6-bis(diphenylmethyl)-4-methoxy-phenyl)imidazole-2-ylidene) produced a dicopper formate hydride [(IPr*OMe)Cu]2 (µ-1,3-O2 CH)(µ-H). A second CO2 insertion produced a dicopper bis(formate), [(IPr*OMe)Cu]2 (µ-1,3-O2 CH)(µ-1,1-O2 CH), containing two different bonding modes of the bridging formate. These dicopper formate complexes are inaccessible from solution reactions since the dicopper core cleanly ruptures to monomeric complexes when dissolved in a solvent.

Isolation of a Cu-H Monomer Enabled by Remote Steric Substitution of a N-Heterocyclic Carbene Ligand: Stoichiometric Insertion and Catalytic Hydroboration of Internal Alkenes.

Transient Cu-H monomers have long been invoked in the mechanisms of substrate insertion in Cu-H catalysis. Their role from Cu-H aggregates has been mostly inferred since ligands to stabilize these monomeric intermediates for systematic studies remain limited. Within the last decade, new sterically demanding N-heterocyclic carbene (NHC) ligands have led to isolable Cu-H dimers and, in some cases, spectroscopic characterization of Cu-H monomers in solution. We report an NHC ligand, IPr*R, containing para R groups of CHPh2 and CPh3 on the ligand periphery for the isolation of a Cu-H monomer for insertion of internal alkenes. This reactivity has not been reported for (NHC)CuH complexes despite their common application in Cu-H-catalyzed hydrofunctionalization. Changing from CHPh2 to CPh3 impacts the relative concentration of Cu-H monomers, rate of alkene insertion, and reaction of a trisubstituted internal alkene. Specifically, for R = CPh3, monomeric (IPr*CPh3)CuH was isolated and provided >95% monomer (10 mM in C6D6). In contrast, for R = CHPh2, solutions of [(IPr*CHPh2)CuH]2 are 80% dimer and 20% (IPr*CHPh2)CuH monomer at 25 °C based on 1H, 13C, and 1H-13C HMBC NMR spectroscopy. Quantitative 1H NMR kinetic studies on cyclopentene insertion into Cu-H complexes to form the corresponding Cu-cyclopentyl complexes demonstrate a strong dependence on the rate of insertion and concentration of the Cu-H monomer. Only (IPr*CPh3)CuH, which has a high monomer concentration, underwent regioselective insertion of a trisubstituted internal alkene, 1-methylcyclopentene, to give (IPr*CPh3)Cu(2-methylcyclopentyl), which has been crystallographically characterized. We also demonstrated that (IPr*CPh3)CuH catalyzes the hydroboration of cyclopentene and methylcyclopentene with pinacolborane.

Mechanistic Studies on the Insertion of Carbonyl Substrates into Cu-H: Different Rate-Limiting Steps as a Function of Electrophilicity.

We report mechanistic studies on the insertion reactions of [(NHC)Cu(µ-H)]2 complexes with carbonyl substrates by UV-vis and 1 H NMR spectroscopic kinetic studies, H/D isotopic labelling, and X-ray crystallography. The results of these comprehensive studies show that the insertion of Cu-H with an aldehyde, ketone, activated ester/amide, and unactivated amide consist of two different rate limiting steps: the formation of Cu-H monomer from Cu-H dimer for more electrophilic substrates, and hydride transfer from a transient Cu-H monomer for less electrophilic substrates. We also report spectroscopic and crystallographic characterization of rare Cu-hemiacetalate and Cu-hemiaminalate moieties from the insertion of an ester or amide into the Cu-H bond.

Cyclo-P3 Complexes of Vanadium: Redox Properties and Origin of the ³¹P NMR Chemical Shift.

The synthesis and characterization of two high-valent vanadium-cyclo-P3 complexes, (nacnac)V(cyclo-P3)(Ntolyl2) (1) and (nacnac)V(cyclo-P3)(OAr) (2), and an inverted sandwich derivative, [(nacnac)V(Ntolyl2)]2(µ2-η(3):η(2)-cyclo-P3) (3), are presented. These novel complexes are prepared by activating white phosphorus (P4) with three-coordinate vanadium(II) precursors. Structural metrics, redox behavior, and DFT electronic structure analysis indicate that a [cyclo-P3](3-) ligand is bound to a V(V) center in monomeric species 1 and 2. A salient feature of these new cyclo-P3 complexes is their significantly downfield shifted (by ∼300 ppm) (31)P NMR resonances, which is highly unusual compared to related complexes such as (Ar[(i)Pr]N)3Mo(cyclo-P3) (4) and other cyclo-P3 complexes that display significantly upfield shifted resonances. This NMR spectroscopic signature was thus far thought to be a diagnostic property for the cyclo-P3 ligand related to its acute endocyclic angle. Using DFT calculations, we scrutinized and conceptualized the origin of the unusual chemical shifts seen in this new class of complexes. Our analysis provides an intuitive rational paradigm for understanding the experimental (31)P NMR spectroscopic signature by relating the nuclear magnetic shielding with the electronic structure of the molecule, especially with the characteristics of metal-cyclo-P3 bonding.

Addition of Si-H and B-H bonds and redox reactivity involving low-coordinate nitrido-vanadium complexes.

In this study we enumerate the reactivity for two molecular vanadium nitrido complexes of [(nacnac)V≡N(X)] formulation [nacnac = (Ar)NC(Me)CHC(Me)(Ar)(-), Ar = 2,6-(CHMe2)2C6H3); X(-) = OAr (1) and N(4-Me-C6H4)2 (Ntolyl2) (2)]. Density functional theory calculations and reactivity studies indicate the nitride motif to have nucleophilic character, but where the nitrogen atom can serve as a conduit for electron transfer, thus allowing the reduction of the vanadium(V) metal ion with concurrent oxidation of the incoming substrate. Silane, H2SiPh2, readily converts the nitride ligand in 1 into a primary silyl-amide functionality with concomitant two-electron reduction at the vanadium center to form the complex [(nacnac)V{N(H)SiHPh2}(OAr)] (3). Likewise, addition of the B-H bond in pinacolborane to the nitride moiety in 2 results in formation of the boryl-amide complex [(nacnac)V{N(H)B(pinacol)}(Ntolyl2)] (4). In addition to spectroscopic data, complexes 3 and 4 were also elucidated structurally by single-crystal X-ray diffraction analysis. One-electron reduction of 1 with 0.5% Na/Hg on a preparative scale allowed for the isolation and structural determination of an asymmetric bimolecular nitride radical anion complex having formula [Na]2[(nacnac)V(N)(OAr)]2 (5), in addition to room-temperature solution X-band electron paramagnetic resonance spectroscopic studies.

Copper-catalyzed intermolecular amidation and imidation of unactivated alkanes.

We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C-H bonds over tertiary C-H bonds and even occur at primary C-H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from ß-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C-H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C-H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product.

Copper-catalyzed oxidative dehydrogenative carboxylation of unactivated alkanes to allylic esters via alkenes.

We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV-vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C-H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C-H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper-carboxylate, copper-amidate, and copper-imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)-amidate > Cu(II)-imidate > Cu(II)-benzoate. Consistent with this trend, Cu(II)-amidates and Cu(II)-benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products.

Direct observation of ß-alkynyl eliminations from unstrained propargylic alkoxide Cu(i) complexes by C-C bond cleavage.

ß-Carbon eliminations of aryl, allylic, and propargylic alkoxides of Rh(i), Pd(ii), and Cu(i) are key elementary reactions in the proposed mechanisms of homogeneously catalysed cross-coupling, group transfer, and annulation. Besides the handful of studies with isolable Rh(i)-alkoxides, ß-carbon eliminations of Pd(ii)- and Cu(i)-alkoxides are less definitive. Herein, we provide a comprehensive synthetic, structural, and mechanistic study on the ß-alkynyl eliminations of isolable secondary and tertiary propargylic alkoxide Cu(i) complexes, LCuOC(H)(Ph)C[triple bond, length as m-dash]CPh and LCuOC(ArF)2C[triple bond, length as m-dash]CPh (L = N-heterocyclic carbene (NHC), dppf, S-BINAP), to produce monomeric (NHC)CuC[triple bond, length as m-dash]CPh, dimeric [(diphosphine)CuC[triple bond, length as m-dash]CPh]2, and the corresponding carbonyl. Selective ß-alkynyl over ß-hydrogen elimination was observed for NHC- and diphosphine-supported secondary propargylic alkoxide complexes. The mechanism for the first-order reaction of ß-carbon elimination of (IPr*Me)CuOC(ArF)2C[triple bond, length as m-dash]CPh is proposed to occur through an organized four-centred transition state via a Cu-alkyne π complex based on Eyring analysis of variable-temperature reaction rates by UV-vis kinetic analysis to provide ΔH ‡ = 24(1) kcal mol-1, ΔS ‡ = -8(3) e.u., and ΔG ‡ (25 °C) = 27 kcal mol-1 over a temperature range of 60-100 °C. Additional quantitative UV-vis kinetic studies conclude that the electronic and steric properties of the NHC ligands engendered a marginal effect on the elimination rate, requiring 2-3 h at 100 °C for completion, whereas complete ß-alkynyl eliminations of diphosphine-supported propargylic alkoxides were observed in 1-2 h at 25 °C.

[A multi-dimensional analysis of pollen broadcasting concerns in Chinese population: a large-scale multi-center cross-sectional survey].

Objective: To investigate the concern about pollen broadcasting in Chinese population from multiple dimensions and to understand the information about allergic rhinitis (AR) in China by analyzing related factors. Methods: From March 1 to September 30, 2022, a large-scale multi-center cross-sectional survey was conducted based on the Questionnaire Star platform in 21 Chinese hospitals. A total of 7 056 subjects from 7 regions in China: Northeast, North, East, Central, South, Southwest, and Northwest China were included. Basic characteristics (including social demographic characteristics and disease characteristics of AR patients), concern about pollen broadcasting, the willingness of pollen-induced AR (PiAR) patients to receive pollen broadcasting, and the treatment satisfaction rate of AR patients were collected. The chi-square test, multivariate linear regression model, and Logistic regression analysis were used to analyze the concern about pollen broadcasting in the Chinese population and related factors from multiple dimensions. Results: Among 7 056 subjects, 23.02% were concerned about pollen broadcasting. Among 3 176 self-reported AR and 1 019 PiAR patients, 25.60% and 39.16% were concerned about pollen broadcasting, respectively, which was higher than that of non-AR or non-PiAR subjects (χ2 value was 21.74 and 175.11, respectively, both P<0.001). Among AR patients, the proportion of spring and autumn allergen-positive patients concerned about pollen broadcasting was higher than that in perennial allergen-positive patients (χ2 value was 20.90 and 19.51, respectively, both P<0.001). The proportion of AR patients with asthma, sinusitis, allergic conjunctivitis, and cardiovascular and cerebrovascular diseases was higher than those without complications (χ2 value was 50.83, 21.97, 56.78, 7.62, respectively, all P<0.05). The proportion of AR patients in North China who could find pollen broadcasting locally was 31.01%, significantly higher than those in other regions (all P<0.05). Multivariate linear regression model analysis showed that among PiAR patients, those with higher per capita household income and higher AR disease cognition levels had been concerned about pollen broadcasting in the past, and those complicated with allergic conjunctivitis had stronger intention to receive pollen broadcasting (B value was 0.24, 0.13, 0.66, 0.47, respectively, all P<0.05). The higher the disease cognition level of PiAR patients, the stronger their willingness to actively participate in treatment (R2=0.72, P<0.001). Only 18.89% of AR patients felt satisfied with the treatment effect. Logistic regression analysis showed that in AR patients, the treatment satisfaction rate was significantly higher among those concerned about pollen broadcasting compared to those who were not (OR=1.83, P<0.001). Conclusions: Currently, the dissemination of pollen broadcasting in China is hindered by various factors such as disease cognition level. The treatment satisfaction among AR patients remains unsatisfactory.

3d early transition metal complexes supported by a new sterically demanding aryloxide ligand.

The bulky aryloxide 2,6-bis(diphenylmethyl)-4-tert-butylphenol [HOAr(tBu)] (1) can be synthesized from 4-tert-butylphenol and benzhydrol in solvent-free conditions and obtained pure in 91% yield. Deprotonation of HOAr(tBu) is accomplished with M(N(SiMe3)2) (M = Na, Li), yielding the corresponding salts of the aryloxide [MOAr(tBu)] (M(+) = Na (2), Li(3)) in 83% and 73% yield, respectively. Facile salt formation of the aryloxide ligand allows for transmetalation to a variety of metal halides. Through transmetalation reactions involving two aryloxides, mononuclear complexes of the type [M'(OAr(tBu))2Cl(THF)2] (M' = Sc (4), V (5), Cr (6), Ti (7)) can be prepared from the corresponding metal halide precursor MCl3(THF)3. Additionally, two aryloxides can be coordinated to Ti(IV) via a protonolysis route of Ti(NMe2)2Cl2 and 2 equiv of HOAr(tBu) to yield [Ti(OAr(tBu))2Cl2(NHMe2)] (8) in 72% isolated yield. Single-crystal X-ray diffraction studies of 1, 2, and the 3d metal complexes 5-8 clearly show the steric demand of the bulky ligand, whereas in transition metal complexes we do not observe the formation of mononuclear tris-aryloxide complexes.

Uranium(III) complexes with bulky aryloxide ligands featuring metal-arene interactions and their reactivity toward nitrous oxide.

We report the synthesis and use of an easy-to-prepare, bulky, and robust aryloxide ligand starting from inexpensive precursor materials. Based on this aryloxide ligand, two reactive, coordinatively unsaturated U(III) complexes were prepared that are masked by a metal-arene interaction via δ-backbonding. Depending on solvent and uranium starting material, both a tetrahydrofuran (THF)-bound and Lewis-base-free U(III) precursor can easily be prepared on the multigram scale. The reaction of these trivalent uranium species with nitrous oxide, N2O, was studied and an X-ray diffraction (XRD) study on single crystals of the product revealed the formation of a five-coordinate U(V) oxo complex with two different molecular geometries, namely, square pyramidal and trigonal bipyramidal.

[Incidence and prognosis of olfactory and gustatory dysfunctions related to infection of SARS-CoV-2 Omicron strain: a national multi-center survey of 35 566 population].

Objective: This cross-sectional investigation aimed to determine the incidence, clinical characteristics, prognosis, and related risk factors of olfactory and gustatory dysfunctions related to infection with the SARS-CoV-2 Omicron strain in mainland China. Methods: Data of patients with SARS-CoV-2 from December 28, 2022, to February 21, 2023, were collected through online and offline questionnaires from 45 tertiary hospitals and one center for disease control and prevention in mainland China. The questionnaire included demographic information, previous health history, smoking and alcohol drinking, SARS-CoV-2 vaccination, olfactory and gustatory function before and after infection, other symptoms after infection, as well as the duration and improvement of olfactory and gustatory dysfunction. The self-reported olfactory and gustatory functions of patients were evaluated using the Olfactory VAS scale and Gustatory VAS scale. Results: A total of 35 566 valid questionnaires were obtained, revealing a high incidence of olfactory and taste dysfunctions related to infection with the SARS-CoV-2 Omicron strain (67.75%). Females(χ2=367.013, P<0.001) and young people(χ2=120.210, P<0.001) were more likely to develop these dysfunctions. Gender(OR=1.564, 95%CI: 1.487-1.645), SARS-CoV-2 vaccination status (OR=1.334, 95%CI: 1.164-1.530), oral health status (OR=0.881, 95%CI: 0.839-0.926), smoking history (OR=1.152, 95%CI=1.080-1.229), and drinking history (OR=0.854, 95%CI: 0.785-0.928) were correlated with the occurrence of olfactory and taste dysfunctions related to SARS-CoV-2(above P<0.001). 44.62% (4 391/9 840) of the patients who had not recovered their sense of smell and taste also suffered from nasal congestion, runny nose, and 32.62% (3 210/9 840) suffered from dry mouth and sore throat. The improvement of olfactory and taste functions was correlated with the persistence of accompanying symptoms(χ2=10.873, P=0.001). The average score of olfactory and taste VAS scale was 8.41 and 8.51 respectively before SARS-CoV-2 infection, but decreased to3.69 and 4.29 respectively after SARS-CoV-2 infection, and recovered to 5.83and 6.55 respectively at the time of the survey. The median duration of olfactory and gustatory dysfunctions was 15 days and 12 days, respectively, with 0.5% (121/24 096) of patients experiencing these dysfunctions for more than 28 days. The overall self-reported improvement rate of smell and taste dysfunctions was 59.16% (14 256/24 096). Gender(OR=0.893, 95%CI: 0.839-0.951), SARS-CoV-2 vaccination status (OR=1.334, 95%CI: 1.164-1.530), history of head and facial trauma(OR=1.180, 95%CI: 1.036-1.344, P=0.013), nose (OR=1.104, 95%CI: 1.042-1.171, P=0.001) and oral (OR=1.162, 95%CI: 1.096-1.233) health status, smoking history(OR=0.765, 95%CI: 0.709-0.825), and the persistence of accompanying symptoms (OR=0.359, 95%CI: 0.332-0.388) were correlated with the recovery of olfactory and taste dysfunctions related to SARS-CoV-2 (above P<0.001 except for the indicated values). Conclusion: The incidence of olfactory and taste dysfunctions related to infection with the SARS-CoV-2 Omicron strain is high in mainland China, with females and young people more likely to develop these dysfunctions. Active and effective intervention measures may be required for cases that persist for a long time. The recovery of olfactory and taste functions is influenced by several factors, including gender, SARS-CoV-2 vaccination status, history of head and facial trauma, nasal and oral health status, smoking history, and persistence of accompanying symptoms.

A mononuclear Fe(III) single molecule magnet with a 3/2↔5/2 spin crossover.

The air stable complex [(PNP)FeCl(2)] (1) (PNP = N[2-P(CHMe(2))(2)-4-methylphenyl](2)(-)), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh(3), displays an unexpected S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveal complex 1 to have frequency dependence on the out-of-phase signal and thus being a single molecular magnet with a thermally activated barrier of U(eff) = 32-36 cm(-1) (47-52 K). Variable-temperature Mössbauer data also corroborate a significant temperature dependence in δ and ΔE(Q) values for 1, which is in agreement with the system undergoing a change in spin state. Likewise, variable-temperature X-band EPR spectra of 1 reveals the S = 3/2 to be likely the ground state with the S = 5/2 being close in energy. Multiedge XAS absorption spectra suggest the electronic structure of 1 to be highly covalent with an effective iron oxidation state that is more reduced than the typical ferric complexes due to the significant interaction of the phosphine groups in PNP and Cl ligands with iron. A variable-temperature single crystal X-ray diffraction study of 1 collected between 30 and 300 K also reveals elongation of the Fe-P bond lengths and increment in the Cl-Fe-Cl angle as the S = 5/2 state is populated. Theoretical studies show overall similar orbital pictures except for the d(z(2)) orbital, which has the most sensitivity to change in the geometry and bonding, where the quartet ((4)B) and the sextet ((6)A) states are close in energy.

A planar three-coordinate vanadium(II) complex and the study of terminal vanadium nitrides from N2: a kinetic or thermodynamic impediment to N-N bond cleavage?

We report the first mononuclear three-coordinate vanadium(II) complex [(nacnac)V(ODiiP)] and its activation of N2 to form an end-on bridging dinitrogen complex with a topologically linear V(III)N2V(III) core and where each vanadium center antiferromagnetically couples to give a ground state singlet with an accessible triplet state as inferred by HFEPR spectroscopy. In addition to investigating the conversion of N2 to the terminal nitride (as well as the microscopic reverse process), we discuss its similarities and contrasts to the isovalent d(3) system, [Mo(N[(t)Bu]Ar)3], and the S = 1 system [(Ar[(t)Bu]N)3Mo]2(µ2-η(1):η(1)-N2).

Thermal stability and structural studies on the mixtures of Mg(BH4)2 and glymes.

Coordination complexes of Mg(BH4)2 are of interest for energy storage, ranging from hydrogen storage in BH4 to electrochemical storage in Mg based batteries. Understanding the stability of these complexes is crucial since storage materials are expected to undergo multiple charging and discharging cycles. To do so, we examined the thermal stabilities of the 1 : 1 mixtures of Mg(BH4)2 with different glymes by DSC-TGA, TPD-MS and powder XRD analysis. Despite their structural similarities, these mixtures show diverse phase transitions, speciations and decomposition pathways as a function of linker length.

Challenges to developing materials for the transport and storage of hydrogen.

Hydrogen has the highest gravimetric energy density of any energy carrier and produces water as the only oxidation product, making it extremely attractive for both transportation and stationary power applications. However, its low volumetric energy density causes considerable difficulties, inspiring intense efforts to develop chemical-based storage using metal hydrides, liquid organic hydrogen carriers and sorbents. The controlled uptake and release of hydrogen by these materials can be described as a series of challenges: optimal properties fall within a narrow range, can only be found in few materials and often involve important trade-offs. In addition, a greater understanding of the complex kinetics, mass transport and microstructural phenomena associated with hydrogen uptake and release is needed. The goal of this Perspective is to delineate potential use cases, define key challenges and show that solutions will involve a nexus of several subdisciplines of chemistry, including catalysis, data science, nanoscience, interfacial phenomena and dynamic or phase-change materials.

The association between bacterial colonization and inflammatory pattern in Chinese chronic rhinosinusitis patients with nasal polyps.

BACKGROUND: Chronic rhinosinusitis with nasal polyps (CRSwNP) can be subdivided according to the mucosal inflammatory patterns. In mainland China, apart from interleukin (IL)-5-positive and IL-17-positive polyps, a large group of patients with IL-5/IL-17/interferon-gamma (IFNγ)-negative nasal polyps (referred to as key cytokine-negative (KCN) polyps) can be found. OBJECTIVE: To further study the KCN polyps and evaluate the associations between bacterial colonization and mucosal inflammatory pattern in KCN vs IL-5-positive nasal polyps. METHODS: Nasal polyp or nasal turbinate tissue was obtained from 89 Chinese CRSwNP patients and 36 nonatopic control subjects during surgery. Samples without and after SEB exposure were processed for the assessment of pro-inflammatory cytokines and mediators by immunoassay. Prior to surgery, nasal swabs were taken from each patient for microbiological evaluation. RESULTS: Overall, 80% polyp tissue did not express IL-5, with about 70% (49/71) of these being KCN. Key cytokine-negative nasal polyps were characterized by the synthesis of mediators promoting neutrophilic inflammation (myeloperoxidase (MPO), IL-1ß, IL-6 and IL-8), whereas IL-5-positive nasal polyps were characterized by the synthesis of mediators promoting eosinophilic inflammation (IL-5, ECP, total IgE and SE-IgE). Key cytokine-negative nasal polyps were associated with greater Gram-negative bacterial load compared with controls, while IL-5-positive nasal polyps were associated with greater Gram-positive bacterial colonization vs controls and KCN polyps. CONCLUSION: Our findings suggest that the bacteria colonizing nasal polyps of CRSwNP patients may impact on or be determined by the presence/absence of IL-5.

Accelerating the insertion reactions of (NHC)Cu-H via remote ligand functionalization.

Most ligand designs for reactions catalyzed by (NHC)Cu-H (NHC = N-heterocyclic carbene ligand) have focused on introducing steric bulk near the Cu center. Here, we evaluate the effect of remote ligand modification in a series of [(NHC)CuH]2 in which the para substituent (R) on the N-aryl groups of the NHC is Me, Et, t Bu, OMe or Cl. Although the R group is distant (6 bonds away) from the reactive Cu center, the complexes have different spectroscopic signatures. Kinetics studies of the insertion of ketone, aldimine, alkyne, and unactivated α-olefin substrates reveal that Cu-H complexes with bulky or electron-rich R groups undergo faster substrate insertion. The predominant cause of this phenomenon is destabilization of the [(NHC)CuH]2 dimer relative to the (NHC)Cu-H monomer, resulting in faster formation of Cu-H monomer. These findings indicate that remote functionalization of NHCs is a compelling strategy for accelerating the rate of substrate insertion with Cu-H species.

Low-coordinate and neutral nitrido complexes of vanadium.

Two neutral and four-coordinate vanadium(V)-nitrido complexes have been prepared via the thermolysis of metastable vanadium(III)-azido precursors. All complexes have been fully characterized by multinuclear NMR, FT-IR, isotopic labeling, and, in most instances, single crystal X-ray diffraction. On the basis of activation parameters, N(2) extrusion to form the V[triple bond]N moiety is proposed to occur via an ordered and early transition state having three- or four-triazametallacycle frameworks. In addition, we demonstrate the nitrido ligand to undergo incomplete N-atom transfer to CO and CN{2,6-Me(2)-C(6)H(3)) to form the bent V-N=C=X (X = O, N{2,6-Me(2)-C(6)H(3)}) ligands with concomitant 2e(-) reduction at the vanadium center.