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Subrata Chakraborty, Gregory Leitus, David Milstein
The first example of a base-metal-catalyzed homogeneous hydrogenative coupling of nitriles and amines to selectively form secondary cross-imines is reported. The reaction is catalyzed under mild conditions by a well-defined (iPr-PNP)Fe(H)Br(CO) pincer pre-catalyst and catalytic tBuOK.
January 12, 2017: Angewandte Chemie
Nicklas Deibl, Rhett Kempe
The development of catalytic reactions for synthesizing different compounds from alcohols to save fossil carbon feedstock and reduce CO2 emissions is of high importance. Replacing rare noble metals with abundantly available 3d metals is equally important. We report a manganese-complex-catalyzed multicomponent synthesis of pyrimidines from amidines and up to three alcohols. Our reaction proceeds through condensation and dehydrogenation steps, permitting selective C-C and C-N bond formations. β-Alkylation reactions are used to multiply alkylate secondary alcohols with two different primary alcohols to synthesize fully substituted pyrimidines in a one-pot process...
January 12, 2017: Angewandte Chemie
Jeffrey A Therrien, Michael O Wolf
The effect of modifying the pyridyl para position of lutidine-linked bis(N-heterocyclic carbene) Pd pincer complexes is studied both experimentally (R = OMe, H, Br, and COOR) and computationally, showing a strong effect on the first reduction potential of the complex and allowing the reduction potential to be tuned over a wide range in relation to the Hammett σp constant of the para substituent. The effect of the pyridyl para substituent on electron density of the metal center, frontier orbital energies, and dissociation energy of the trans ligand are also investigated in the context of reactivity with CO2 through electrochemical characterization of the complexes under N2 and CO2 and controlled potential electrolysis experiments where CO2 is reduced to CO...
January 10, 2017: Inorganic Chemistry
Stacey A Morris, Dmitry G Gusev
Pincer-type complexes [OsH2 (CO){PyCH2 NHCH2 CH2 NHPtBu2 }] and [OsH2 (CO){HN(CH2 CH2 PiPr2 )2 }] catalyze the disproportionation reaction of aldehydes via an outer-sphere bifunctional mechanism achieving turnover frequencies up to 14 000 h(-1) . The N-H group of the catalysts is a key player in this process, elucidated with the help of DFT calculations.
January 9, 2017: Angewandte Chemie
Fernando Comba, Carlos Yacuzzi, Pablo J Ali, Gerardo Zanotti, Martin Buttaro, Francisco Piccaluga
BACKGROUND: The purpose of this study is to evaluate the clinical outcomes, radiological degenerative progression and the joint preservation rate in a series of patients with Femoroacetabular Impingement (FAI) treated with hip arthroscopy at a minimum follow-up of 7 years. The predictive factors for total hip arthroplasty (THA) requirement were analyzed. MATERIALS AND METHODS: Between February 2008 and February 2009, 42 consecutive patients treated with hip arthroscopy due to FAI syndrome were included...
July 2016: Muscles, Ligaments and Tendons Journal
Yan-Zhi Liu, Kun Yuan, Liu Liu, Zhao Yuan, Yuan-Cheng Zhu
Anion recognitions between common anions and a novel pincer-like receptor (N, N'-bis-(five-fluoro-benzoyl-oxyethyl)-urea, BFUR) were theoretically explored, particularly on geometric features of the BFUR@X (X = F-, Cl-, Br-, I-, CO32-, NO3- and SO42-) systems at a molecular level in this work. Complex structures show that two N-H groups as a claw and two -C6F5 rings on BFUR as a pair of tweezers simultaneously interact with captured anions through cooperative double-dentate hydrogen bond and double-side anion-π interactions...
January 6, 2017: Journal of Physical Chemistry. A
Robert H Crabtree
The different types of acceptorless alcohol dehydrogenation (AAD) reactions are discussed, followed by the catalysts and mechanisms involved. Special emphasis is put on the common appearance in AAD of pincer ligands, of noninnocent ligands, and of outer sphere mechanisms. Early work emphasized precious metals, mainly Ru and Ir, but interest in nonprecious metal AAD catalysis is growing. Alcohol-amine combinations are discussed to the extent that net oxidation occurs by loss of H2. These reactions are of potential synthetic interest because they can lead to N heterocycles such as pyrroles and pyridines...
January 4, 2017: Chemical Reviews
Yulei Wang, Chuan Qin, Xiangqing Jia, Xuebing Leng, Zheng Huang
A unique Ir complex ((tBu) NC(C) P)Ir with the pyridine-phosphine pincer as the sole ligand, featuring a dual agostic interaction between the Ir and two σ C-H bonds from a tBu substituent, has been prepared. This complex exhibits exceptionally high activity and excellent regio- and stereoselectivity for monoisomerization of 1-alkenes to trans-2-alkenes with wide functional-group tolerance. Reactions can be performed in neat reactant on a more than 100 gram scale using 0.005 mol % catalyst loadings with turnover numbers up to 19000...
January 2, 2017: Angewandte Chemie
Lucía Álvarez-Rodríguez, Javier Brugos, Javier A Cabeza, Pablo García-Álvarez, Enrique Pérez-Carreño, Diego Polo
A PGeP pincer-type germylene, Ge(NCH2P(t)Bu2)2C6H4, which contains two phosphane groups hanging from the N atoms of an N-heterocyclic germylene fragment, has been isolated for the first time. This compound has already furnished a rich transition metal derivative chemistry (Co, Rh, and Pd) that includes complexes containing bridging P,Ge,P-, chelating P,Ge- and pincer P,Ge,P-ligands.
December 23, 2016: Chemical Communications: Chem Comm
Zhizhou Liu, Rakesh Ganguly, Dragoslav Vidović
Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Brønsted acids (HBAs). Finally, the control experiments conducted in order to eliminate HBA activity that involve a bulky pyridine base should be performed with caution as the corresponding protonated pyridinium salt could also serve as a proton source...
December 19, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
Shaojin Gu, Jiehao Du, Jingjing Huang, Yun Guo, Ling Yang, Weilin Xu, Wanzhi Chen
This report describes the synthesis and characterization of a family of unsymmetrical NCN pincer Ni(ii) complexes 2-8 with NHC-triazole arms. All of these complexes have been fully characterized by X-ray single crystal analysis, NMR spectroscopy, and elemental analysis. Complexes 2 and 4-6 were square planar with a chloride trans to the carbene carbon atoms. Complex 3 was a paramagnetic octahedral complex with its central metal surrounded by two NCN pincer ligands. Complexes 7 and 8 contain [(NHC)2Ni2-OH] moieties bearing a OH bridge...
January 3, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Jonathan O Bauer, Gregory Leitus, Yehoshoa Ben-David, David Milstein
Azines (2,3-diazabuta-1,3-dienes) are a widely used class of compounds with conjugated C=N double bonds. Herein, we present a direct synthesis of azines from alcohols and hydrazine hydrate. The reaction, catalyzed by a ruthenium pincer complex, evolves dihydrogen and can be run in a base-free version. The dehydrogenative coupling of benzylic and aliphatic alcohols led to good conversions and yields. Spectroscopic evidence for a hydrazine-coordinated dearomatized ruthenium pincer complex was obtained. Isolation of a supramolecular crystalline compound provided evidence for the important role of hydrogen bonding networks under the reaction conditions...
December 2, 2016: ACS Catalysis
David A Ahlstrand, Alexey V Polukeev, Rocio Marcos, Mårten Sg Ahlquist, Ola F Wendt
Cyclometallation of 8-methylquinoline and 2-(dimethylamino)-pyridine in an iridium based pincer complex is described. The C-H activation of 2-(dimethylamino)pyridine is not chelation assisted, which has not been described before for Csp³-H bonds in cyclometallations. The mechanism of the cyclometalation of 2-(dimethylamino)pyridine was studied through DFT calculations and kinetic measurements.
December 16, 2016: Chemistry: a European Journal
Nikolaus Johannes Wachter, Martin Mentzel, Raphaela Hütz, Gert D Krischak, Joachim Gülke
INTRODUCTION: In the assessment of hand and upper limb function, grip strength is of major importance. Use of the JAMAR dynamometer has been an accepted test of grip strength and routinely part of the physical examination. PURPOSE OF THE STUDY: The aim of this study was to determine by means of a median nerve block simulating a patient group if the measurement of different types of grip force can improve the quantification of impairment of the hand beyond the sole power grip measurements...
December 12, 2016: Journal of Hand Therapy: Official Journal of the American Society of Hand Therapists
George Kleinhans, Max M Hansmann, Gregorio Guisado-Barrios, David C Liles, Guy Bertrand, Daniela I Bezuidenhout
We report the synthesis and reactivity of unusual T-shaped (LXL)Au(I)-pincer complexes, based on a carbazole framework flanked by two mesoionic carbenes (MICs). In contrast to other Au(I) complexes, these complexes react with electrophiles. Protonation and alkylation occur either at the metal or the ligand, depending on steric factors. Of particular interest, protonation at gold leads to an unprecedented cationic Au(III) hydride, which gives a (1)H NMR resonance at δ -8.34 ppm. The reactivity of this "hydride", however, shows protic and not hydridic behavior...
December 14, 2016: Journal of the American Chemical Society
Grazia Pozzi, Ezio Lanza, Cleber Garcia Parra, Ilaria Merli, Luca Maria Sconfienza, Alberto Zerbi
OBJECTIVES: We evaluated the incidence of greater trochanter pain syndrome (GTPS) in patients who underwent magnetic resonance arthrography (MRA) of the hip for a suspected femoroacetabular impingement (FAI) syndrome. METHODS: Hip MRA performed at our institution (3/2012-1/2014) were reviewed. The absence/presence of FAI (cam, pincer, and mixed) was noted. GTPS diagnosis was based on gluteus medius/minimus tendinopathy/tears, trochanteric bursitis, fascia lata thickening, and trochanter bone oedema/erosion...
December 9, 2016: La Radiologia Medica
Chee Koon Ng, Jie Wu, T S Andy Hor, He-Kuan Luo
Correction for 'A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide' by Chee Koon Ng et al., Chem. Commun., 2016, 52, 11842-11845.
December 22, 2016: Chemical Communications: Chem Comm
G Dautel
Congenital thumb anomalies are common and have a major impact given the specific functional role of the thumb. They may occur alone or as part of a multiple congenital anomaly syndrome. The primary goal of surgical management is to improve or restore pincer grip. In patients with 'congenital' trigger thumb, the A1 pulley must be released if the interphalangeal joint remains in fixed flexion. Thumb duplication is generally managed by reconstruction of the thumb from the predominant (ulnar-based) digit; the accessory (radial-based) digit is excised after collection of its tissue components needed for the reconstruction programme...
December 8, 2016: Orthopaedics & Traumatology, Surgery & Research: OTSR
Toni Hille, Torsten Irrgang, Rhett Kempe
New reactions that convert alcohols into important classes of compounds are becoming increasingly important as their development contributes to the conservation of our fossil carbon feedstock and the reduction of CO2 emissions. Two key catalytic alcohol conversion concepts are borrowing hydrogen or hydrogen autotransfer and acceptorless dehydrogenative condensation. Herein, we combined both concepts to synthesize meta-functionalized pyridines. First, diols and amines were linked to β-amino alcohols, which can then undergo a selective dehydrogenative heterocondensation with γ-amino alcohols...
January 2, 2017: Angewandte Chemie
Arumugam Vignesh, Nattamai S P Bhuvanesh, Nallasamy Dharmaraj
A convenient synthesis of a library of tetrazoles through a novel and operationally simple protocol effecting the direct conversion of arylboronic acids catalyzed by a new ONO pincer-type Pd(II) complex under mild reaction conditions using the readily available reagents is reported. The palladium complex was reused up to four cycles in an open-flask condition.
December 9, 2016: Journal of Organic Chemistry
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