Coordinatively unsaturated ruthenium complexes as efficient alkyne-azide cycloaddition catalysts

The performance of 16-electron ruthenium complexes with the general formula Cp*Ru(L)X (in which L = phosphine or N-heterocyclic carbene ligand; X = Cl or OCH2CF3) was explored in azide−alkyne cycloaddition reactions that afford the 1,2,3- triazole products. The scope of the Cp*Ru(PiPr3)Cl precatalyst was investigated for terminal alkynes leading to new 1,5-disubstituted 1,2,3-triazoles in high yields. Mechanistic studies were conducted and revealed a number of proposed intermediates. Cp*Ru- (PiPr3)(η2-HCCPh)Cl was observed and characterized by 1H, 13C, and 31P NMR at temperatures between 273 and 213 K. A rare example of N,N-κ2-phosphazide complex, Cp*Ru(κ2-iPr3PN3Bn)Cl, was fully characterized, and a single-crystal X-ray diffraction structure was obtained. DFT calculations describe a complete map of the catalytic reactivity with phenylacetylene and/or benzylazide.Publisher PDFPeer reviewe

Extended endoscopic endonasal transsphenoidal approach to the suprasellar area: Anatomic considerations - Part I

INTRODUCTION: Interest in using the extended endonasal transsphenoidal approach for management of suprasellar lesions, with either a microscopic or endoscopic technique, has increased in recent years. The most relevant benefit is that this median approach permits the exposure and removal of suprasellar lesions without the need for brain retraction. MATERIALS AND METHODS: Fifteen human cadaver heads were dissected to evaluate the surgical key steps and the advantages and limitations of the extended endoscopic endonasal transplanum sphenoidale approach. We compared this with the transcranial microsurgical view of the suprasellar area as explored using the bilateral subfrontal microsurgical approach, and with the anatomy of the same region as obtained through the endoscopic endonasal route. RESULTS: Some anatomic conditions can prevent or hinder use of the extended endonasal approach. These include a low level of sphenoid sinus pneumatization, a small sella size with small distance between the internal carotid arteries, a wide intercavernous sinus, and a thick tuberculum sellae. Compared with the subfrontal transcranial approach, the endoscopic endonasal approach offers advantages to visualizing the subchiasmatic, retrosellar, and third ventricle areas. CONCLUSION: The endoscopic endonasal transplanum sphenoidale technique is a straight, median approach to the midline areas around the sella that provides a multiangled, close-up view of all relevant neurovascular structures. Although a lack of adequate instrumentation makes it impossible to manage all structures that are visible with the endoscope, in selected cases, the extended endoscopic endonasal approach can be considered part of the armamentarium for surgical treatment of the suprasellar area

Mechanistic features of isomerizing alkoxycarbonylation of methyl oleate.

The weakly coordinated triflate complex [(P∧P)Pd(OTf)]+(OTf)− (1) (P∧ P = 1,3-bis(di-tert-butylphosphino) propane) is a suitable reactive precursor for mechanistic studies of the isomerizing alkoxcarbonylation of methyl oleate. Addition of CH3OH or CD3OD to 1 forms the hydride species [(P∧P)PdH(CH3OH)]+(OTf)− (2-CH3OH) or the deuteride [(P∧P)PdD(CD3OD)]+(OTf)− (2DCD3OD), respectively. Further reaction with pyridine cleanly affords the stable and isolable hydride [(P∧P)PdH- (pyridine)]+(OTf)− (2-pyr). This complex yields the hydride fragment free of methanol by abstraction of pyridine with BF3·OEt2, and thus provides an entry to mechanistic observations including intermediates reactive toward methanol. Exposure of methyl oleate (100 equiv) to 2D-CD3OD resulted in rapid isomerization to the thermodynamic isomer distribution, 94.3% of internal olefins, 5.5% of α,β-unsaturated ester and <0.2% of terminal olefin. Reaction of 2-pyr/BF3·OEt2 with a stoichiometric amount of 1-13C-labeled 1-octene at −80 °C yields a 50:50 mixture of the linear alkyls [(P∧P)Pd13CH2(CH2)6CH3]+ and [(P∧P)PdCH2(CH2)6 13CH3]+ (4a and 4b). Further reaction with 13CO yields the linear acyls [(P∧P)Pd13C(=O)12/13CH2(CH2)6 12/13CH3(L)]+ (5-L; L = solvent or 13CO). Reaction of 2-pyr/ BF3·OEt2 with a stoichiometric amount of methyl oleate at −80 °C also resulted in fast isomerization to form a linear alkyl species [(P∧P)PdCH2(CH2)16C(=O)OCH3]+ (6) and a branched alkyl stabilized by coordination of the ester carbonyl group as a four membered chelate [(P∧P)PdCH{(CH2)15CH3}C(=O)OCH3]+ (7). Addition of carbon monoxide (2.5 equiv) at −80 °C resulted in insertion to form the linear acyl carbonyl [(P∧P)PdC(=O)(CH2)17C(=O)OCH3(CO)]+ (8-CO) and the fivemembered chelate [(P∧P)PdC(=O)CH{(CH2)15CH3}C(=O)OCH3]+ (9). Exposure of 8-CO and 9 to 13CO at −50 °C results in gradual incorporation of the 13C label. Reversibility of 7 + CO ⇄ 9 is also evidenced by ΔG = −2.9 kcal mol−1 and ΔG‡ = 12.5 kcal mol−1 from DFT studies. Addition of methanol at −80 °C results in methanolysis of 8-L (L = solvent) to form the linear diester, 1,19-dimethylnonadecandioate, whereas 9 does not react and no branched diester is observed. DFT yields a barrier for methanolysis of ΔG‡ = 29.7 kcal mol−1 for the linear (8) vs ΔG‡ = 37.7 kcal mol−1 for the branched species (9)

Lewis pair polymerization by classical and frustrated Lewis pairs: acid, base and monomer scope and polymerization mechanism

Classical and frustrated Lewis pairs (LPs) of the strong Lewis acid (LA) Al(C6F5)3 with several Lewis base (LB) classes have been found to exhibit exceptional activity in the Lewis pair polymerization (LPP) of conjugated polar alkenes such as methyl methacrylate (MMA) as well as renewable α-methylene- γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone (γ-MMBL), leading to high molecular weight polymers, often with narrow molecular weight distributions. This study has investigated a large number of LPs, consisting of 11 LAs as well as 10 achiral and 4 chiral LBs, for LPP of 12 monomers of several different types. Although some more common LAs can also be utilized for LPP, Al(C6F5)3-based LPs are far more active and effective than other LA-based LPs. On the other hand, several classes of LBs, when paired with Al(C6F5)3, can render highly active and effective LPP of MMA and γ-MMBL; such LBs include phosphines (e.g., PtBu3), chiral chelating diphosphines, N-heterocyclic carbenes (NHCs), and phosphazene superbases (e.g., P4-tBu). The P4-tBu/Al(C6F5)3 pair exhibits the highest activity of the LP series, with a remarkably high turn-over frequency of 9.6 × 104 h−1 (0.125 mol% catalyst, 100% MMA conversion in 30 s, Mn = 2.12 × 105 g mol−1, PDI = 1.34). The polymers produced by LPs at RT are typically atactic (PγMMBL with ∼47% mr) or syndio-rich (PMMAwith ∼70–75% rr), but highly syndiotactic PMMAwith rr ∼91% can be produced by chiral or achiral LPs at −78 °C. Mechanistic studies have identified and structurally characterized zwitterionic phosphonium and imidazolium enolaluminates as the active species of the current LPP system, which are formed by the reaction of the monomer·Al(C6F5)3 adduct with PtBu3 and NHC bases, respectively. Kinetic studies have revealed that the MMA polymerization by the tBu3P/Al(C6F5)3 pair is zero-order in monomer concentration after an initial induction period, and the polymerization is significantly catalyzed by the LA, thus pointing to a bimetallic, activated monomer propagation mechanism. Computational study on the active species formation as well as the chain initiation and propagation events involved in the LPP of MMAwith some of the most representative LPs has added our understanding of fundamental steps of LPP. The main difference between NHC and PR3 bases is in the energetics of zwitterion formation, with the NHC-based zwitterions being remarkably more stable than the PR3-based zwitterions. Comparison of the monometallic and bimetallic mechanism

Regression analysis of properties of [Au(IPr)(CHR2)] complexes

The European Research Council (ERC) and the Engineering and Physical Sciences Research Council (EPSRC), UK, are gratefully acknowledged for their support. L.C., and S.P.N. thank the King Abdullah University of Science and Technology (KAUST) and Kind Saud University (KSU) for support.New [Au(IPr)(CHR2)] complexes have been synthesised through protonolysis reactions of [Au(IPr)(OH)] with moderately acidic substrates, CH2R2. An array of spectroscopic (IR and NMR), structural (X-ray), electronic (DFT) and experimental (reactivity) parameters was collected to quantify the variation in stereoelectronic properties of these new and previously reported [Au(IPr)(CHR2)] complexes. Variation of the R substituents on the carbanion ligands (CHR2–) was found to have a crucial impact on parameters characterising the resulting gold complexes. A regression analysis of both experimental and modelled parameters, guided by network analysis techniques, produced linear models that supported trends within the [Au(IPr)(CHR2)] complexes.PostprintPeer reviewe

Age of Onset of Mood Disorders and Complexity of Personality Traits

Objective. The aim of the present study is to evaluate the link between the age of onset of mood disorders and the complexity of the personality traits. Methods. 209 patients with major depressive or manic/hypomanic episodes were assessed using the Structured Clinical Interview for DSM Axis I diagnoses and the Millon Clinical Multiaxial Inventory-III (MCMI-III). Results. 17.2% of the patients had no elevated MCMI-III scores, 45.9% had one peak, and 36.9% had a complex personality disorder with two or more elevated scores. Mood disorders onset of 29 years or less was the variable most related to the complexity of personality disorders as indicated from a recursive partitioning analysis. Conclusions. The relationship between mood disorders and personality traits differ in reference to age of onset of the mood disorder. In younger patients, maladaptive personality traits can evolve both in a mood disorder onset and in a complex personality disorder, while the later development of a severe mood disorder can increase the personality symptomatology. Our results suggest a threshold of mood disorder onset higher compared to previous studies. Maladaptive personality traits should be assessed not only during adolescence but also in young adults to identify and treat potential severe mood disorders

Synthesis and reactivity of [Au(NHC)(Bpin)] complexes

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), AstraZeneca (Studenship to C.M.Z) and VLAIO (CO2PERATE) for support of this work. We thank King Saud University (DSF Program) and KAUST (Award No.OSR-2015-CCF-1974-03) for support.A new class of [Au(NHC)(Bpin)] complexes has been synthesized and their unusual reactivity was investigated using computational and experimental methods. The gold-boryl complexes exhibit unexpected high stability and reactivity.PostprintPeer reviewe

Electronic effects in mixed N-heterocyclic carbene/phosphite indenylidene ruthenium metathesis catalysts

The authors gratefully acknowledge the Royal Society (University Research Fellowship to CSJC), the EC (CP-FP 211468-2 EUMET and CIG09-GA-2011-293900) and the MICINN (PGC2018-097722-B-I00 to AP) for funding.Five new complexes [RuCl2(SIMes)(Ind)(O-pXC5H4)] bearing different para-substituted triphenylphosphites (X = H, OCH3, CF3, Cl, SF5 and CN) were synthesised and used to study the effect of the electronic properties of the phosphite on olefin metathesis activity. Investigations of the physical properties of the new ligands and complexes were performed using physicochemical and DFT calculations. The catalytic activity of the complexes was benchmarked in challenging ring closing metathesis transformations featuring the formation of tetra-substituted double bonds. Complex [RuCl2(SIMes)(Ind)P(O-pCF3C5H4)3] (3c) exhibited a particularly high catalytic activity, superior to state-of-the-art catalysts, and was further tested on a wide range of substrates.PostprintPeer reviewe