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Robbert van Putten, Evgeny A Uslamin, Marcel Garbe, Chong Liu, Angela Gonzalez-de-Castro, Martin Lutz, Kathrin Junge, Emiel J M Hensen, Matthias Beller, Laurent Lefort, Evgeny A Pidko
Catalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub-stoichiometric amounts of KO(t) Bu base.
April 21, 2017: Angewandte Chemie
T H V Azevedo, C L S Neiva, R V Consoli, A C D Couto, A F M P Dias, E J R Souza
Pincer nail is a transverse overcurvature of the nail plate that may appear in association with a variable number of diseases. We present a case report of a 28-year-old woman with pincer nail deformity associated with systemic lupus erythematosus. A renal biopsy confirmed class V lupus nephritis and treatment had included systemic steroids and cyclophosphamide. After 6 months there was a marked improvement of nail deformities.
January 1, 2017: Lupus
Thomas Simler, Andreas A Danopoulos, Pierre Braunstein
New non-symmetrical, redox-active imino NHC pyridine pincer ligands, 2-(R(1)-imidazol-2-ylidene)-6-(R(2)N[double bond, length as m-dash]CH)-pyridine (R(1) = 2,6-diisopropylphenyl (DiPP), R(2) = 2,4,6-trimethylphenyl (Mes), 4B; R(1) = R(2) = DiPP, 4C), have been accessed by a Zn(II)-promoted modular synthesis involving the quaternization of R(1)-imidazole by [Zn(κN(imine)κN(pyridine))(2-(R(2)N[double bond, length as m-dash]CH)-6-bromo-pyridine)Cl2], followed by Zn(II) removal and deprotonation of imidazolium pro-ligands...
April 18, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Matthias Mastalir, Ernst Pittenauer, Berthold Stöger, Günter Allmaier, Karl Kirchner
An air-stable, thermally robust, and well-defined Cu(I) PNP pincer complex based on the 2,6-diaminopyridine scaffold is described. This complex is an active catalyst for the cross-couplings of a range of aryl and heteroaryl (including benzoxazole, thiazole, pyridine, and thiophene) halides with different organomagnesium reagents, alkynes, and aryl-amines giving excellent to good isolated yields.
April 13, 2017: Organic Letters
Josh Abbenseth, Martin Diefenbach, Sarah C Bete, Christian Würtele, Christian Volkmann, Serhiy Demeshko, Max C Holthausen, Sven Schneider
Reduction of the pincer complex [Os(III)Cl2(PNP)] (PNP = N(CHCHPtBu2)2) affords the isolation and full characterization of an osmium(ii) complex with square-planar coordination geometry, i.e. [Os(II)Cl(PNP)]. Spectroscopic, structural and magnetic data in combination with multireference computations indicate strong temperature independent paramagnetism, which arises from an energetically well separated ground state that mixes with excited states through spin-orbit coupling.
April 13, 2017: Chemical Communications: Chem Comm
Nikolay V Lukashev, Gennadii A Grabovyi, Dmitry A Erzunov, Alexey V Kazantsev, Gennadij V Latyshev, Alexei D Averin, Irina P Beletskaya
Cu- and Pd-catalyzed arylation of aminocholanes has been described for the first time. While this Cu-catalyzed protocol provides high yields in reactions of aminocholanes with iodoarenes, Pd catalysis was found to be preferable for the reactions of aminocholanes with dichloroanthraquinones. UV-vis titration of bis(cholanylamino)anthraquinones with a series of cations demonstrated their high binding affinity to Cu(2+), Al(3+), and Cr(3+).
2017: Beilstein Journal of Organic Chemistry
Rong Zeng, Moran Feller, Yehoshoa Ben-David, David Milstein
Due to its significant contribution to stratospheric ozone depletion and its potent greenhouse effect, nitrous oxide has stimulated much research interest regarding its reactivity modes and its transformations, which can lead to its abatement. We report the homogeneously catalyzed reaction of nitrous oxide (N2O) with H2. The reaction is catalyzed by a PNP pincer ruthenium complex, generating efficiently only dinitrogen and water, under mild conditions, thus providing a green, mild methodology for removal of nitrous oxide...
April 12, 2017: Journal of the American Chemical Society
Matthew R Kita, Alexander J M Miller
Rapid, selective, and highly controllable iridium-catalyzed allylbenzene isomerization is described, enabled by tunable hemilability based on alkali metal cation binding with a macrocyclic "pincer-crown ether" ligand. An inactive chloride-ligated complex can be activated by halide abstraction with sodium salts, with the resulting catalyst [κ(5) -((15c5) NCOP(iPr) )Ir(H)](+) exhibiting modest activity. Addition of Li(+) provides a further boost in activity, with up to 1000-fold rate enhancement. Ethers and chloride salts dampen or turn off reactivity, leading to three distinct catalyst states with activity spanning several orders of magnitude...
April 12, 2017: Angewandte Chemie
Brian M Lindley, Quinton J Bruch, Peter S White, Faraj Hasanayn, Alexander J M Miller
The conversion of metal nitride complexes to ammonia may be essential to dinitrogen fixation. We report a new reduction pathway that utilizes ligating acids and metal-ligand cooperation to effect this conversion without external reductants. Weak acids such as 4-methoxybenzoic acid and 2-pyridone react with nitride complex [(H-PNP)RuN](+) (H-PNP = HN(CH2CH2P(t)Bu2)2) to generate octahedral ammine complexes that are κ(2)-chelated by the conjugate base. Experimental and computational mechanistic studies reveal the important role of Lewis basic sites proximal to the acidic proton in facilitating protonation of the nitride...
April 6, 2017: Journal of the American Chemical Society
Aya Eizawa, Kazuya Arashiba, Hiromasa Tanaka, Shogo Kuriyama, Yuki Matsuo, Kazunari Nakajima, Kazunari Yoshizawa, Yoshiaki Nishibayashi
Intensive efforts for the transformation of dinitrogen using transition metal-dinitrogen complexes as catalysts under mild reaction conditions have been made. However, limited systems have succeeded in the catalytic formation of ammonia. Here we show that newly designed and prepared dinitrogen-bridged dimolybdenum complexes bearing N-heterocyclic carbene- and phosphine-based PCP-pincer ligands [{Mo(N2)2(PCP)}2(μ-N2)] (1) work as so far the most effective catalysts towards the formation of ammonia from dinitrogen under ambient reaction conditions, where up to 230 equiv...
April 4, 2017: Nature Communications
Ming-Jia Yu, Shi-Lu Chen
Lactate racemase (LarA), a new Ni enzyme discovered recently, catalyzes the racemization between D- and L-lactates via a novel Ni pincer cofactor (Ni-PTTMN) derived from nicotinic acid. Here, using DFT and a 200-atom active-site model, LarA is revealed to employ a modified proton-coupled hydride transfer mechanism where a hydride is transferred to a cofactor pyridine carbon from the substrate α-carbon along with a proton transfer from the substrate hydroxyl to a histidine, and then moved back from the opposite side...
April 4, 2017: Chemistry: a European Journal
L Rocchigiani, J Fernandez-Cestau, P H M Budzelaar, M Bochmann
Selective Au-C bond cleavage and arene-C-H activation in (C^N^C)Au(iii) pincer complexes are reversible, leading to a solvent-dependent proton shuttling process. The ether-free cleavage products are non-fluxional and show weak gold(iii)-arene interactions commensurate with intermediates postulated for CMD-type arene activation.
April 4, 2017: Chemical Communications: Chem Comm
Shilu Xu, Peng Zhang, Xiaoyan Li, Benjing Xue, Hongjian Sun, Olaf Fuhr, Dieter Fenske
Four silyl [P,Si]-chelate cobalt complexes (2-5) have been synthesized through the chelate-assisted Si-H activation of bidentate preligand ortho-HSi(Me)2 (PPh2 )C6 H4 (1) with CoMe(PMe3 )4 and CoCl(PMe3 )3 . The silyl Co(I) complex, Co(PMe3 )3 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (2), was synthesized by Si-H activation of 1 with CoMe(PMe3 )4 or by combining complex 5 with MeLi and PMe3 . Complex 2 was treated with CH3 I or EtBr, generating the silyl Co(II) products CoI(PMe3 )2 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (3) and CoBr(PMe3 )2 (1-Si(Me)2 -2-(PPh2 )C6 H4 ) (4)...
March 16, 2017: Chemistry, An Asian Journal
Alexander V Polezhaev, Chun-Hsing Chen, Yaroslav Losovyj, Kenneth G Caulton
A pyridyl pincer ligand is introduced to incorporate steric bulk, via a PtBu2 arm, and proton responsivity, via a pyrazole pincer ligand arm, together with reactivity at benzylic hydrogen and redox activity within a 1,4 diazabutadiene moiety. Binding it to CoCl2 yields square pyramidal (PNNH)CoCl2, that is deprotonated with Li[N(SiMe3)2] forming [Li(THF)2PNN]CoCl2. Reduction of this LiCl adduct with KC8 under CO atmosphere leads to formation of Co(I) mono- and dicarbonyls, which can be protonated but also be further deprotonated, at the benzylic CH, leading to a dearomatized pyridyl functionality...
March 28, 2017: Chemistry: a European Journal
Jan Wenz, Hubert Wadepohl, Lutz H Gade
Bench-stable nickel fluoride complexes bearing NNN pincer ligands have been employed as precursors for the regioselective hydrosilylation of epoxides at room temperature. A nickel hydride assisted epoxide opening is followed by the cleavage of the newly formed nickel oxygen bond by σ-bond metathesis with a silane.
April 3, 2017: Chemical Communications: Chem Comm
Kotaro R Shibata, Shuichi Matsuda, Marc R Safran
BACKGROUND: Few studies have published the results of hip arthroscopic surgery in elite athletes and none studying a significant number of elite female athletes. PURPOSE: (1) To compare sex-based differences in the ability to return to prior competitive sports activity after arthroscopic hip surgery. (2) To compare sex-based differences in the type of sports activity, diagnosis, and treatment in athletes requiring hip arthroscopic surgery. STUDY DESIGN: Cohort study; Level of evidence, 3...
March 1, 2017: American Journal of Sports Medicine
Jun Takaya, Ko Miyama, Chuan Zhu, Nobuharu Iwasawa
A PGeP-pincer palladium-catalyzed hydrocarboxylation of styrenes to obtain pharmaceutically important α-arylpropionic acid derivatives was achieved using a formate salt as both a reductant and a CO2 source. The reaction was also applicable to vinylsulfone and acrylates. Isotope labeling experiments demonstrated that a CO2-recycling mechanism is operative through generation and reaction of a benzylpalladium complex as a carbon nucleophile. This protocol has realized a mild and atom economical CO2-fixation reaction without the necessity of using strong metallic reductants...
March 23, 2017: Chemical Communications: Chem Comm
Luis F Schettino, Sergei V Adamovich, Eugene Tunik
Our understanding of reach-to-grasp movements has evolved from the original formulation of the movement as two semi-independent visuomotor channels to one of interdependence. In spite of a number of important contributions involving perturbations of the reach or the grasp, some of the features of the movement, such as the presence or absence of coordination between the digits during the pincer grasp and the extent of spatio-temporal interdependence between the transport and the grasp are still unclear. In this study, we physically perturbed the index finger into extension during grasping closure, on a minority of trials, to test whether modifying the movement of one digit would affect the movement of the opposite digit, suggestive of an overarching coordinative process...
March 22, 2017: Journal of Neurophysiology
Deepak Bansal, Rajeev Gupta
Amide-based ligands (H2L(1-6)) with assorted functional groups appended to them have been used for the synthesis of dicopper(ii) complexes 1-6 having a Cu(μ-OH)Cu core. The crystal structures of 1-6 show that while every Cu(ii) ion is ligated within the N3 pincer cavity of a potentially multidentate ligand, two Cu(ii) centers are bridged by a hydroxide group. Notably, the Cu(μ-OH)Cu core is encased within the secondary coordination sphere intricately created by the appended groups. While complexes 1 and 2 exhibit the presence of an H-bond acceptor in the proximity of the Cu(μ-OH)Cu core, complexes 3 and 4 display the occurrence of both the H-bond donor as well as H-bond acceptor groups in the vicinity of the Cu(μ-OH)Cu core...
March 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Robert Harold Morris, Samantha Alizabeth Michelle Smith, Paraskevi Olympia Lagaditis, Alan J Lough, Anne Lüpke
The reductive amination of -dialkylphosphine acetaldehydes with enantiopure -aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P'. Four new ligands PR2CH2CH2NHCHR'CHR''PPh2 (R = iPr, Cy, R' = Ph, CH(CH3)2, R'' = Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P') and mer-FeCl(H)(CO)(P-NH-P'). The hydride complex with the rigid ligand with R'= R''= Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst...
March 21, 2017: Chemistry: a European Journal
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