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1.
An oriented tetrahedron defined on four vertices is a set of four cyclic triples with the property that any ordered pair of vertices is contained in exactly one of the cyclic triples. A tetrahedral quadruple system of order with index , denoted by , is a pair , where is an ‐set and is a set of oriented tetrahedra (blocks) such that every cyclic triple on is contained in exactly members of . A is pure if there do not exist two blocks with the same vertex set. When , the spectrum of a pure TQS has been completely determined by Ji. In this paper, we show that there exists a pure if and only if and . A corollary is that a simple also exists if and only if and . 相似文献
2.
Patricia J. Nance Niklas B. Thompson Paul H. Oyala Jonas C. Peters 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(19):6286-6290
Species with 2‐center, 3‐electron (2c/3e?) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d9) trigonal pyramidal Rh and Ir complexes that feature 2c/3e? σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X‐ray diffraction, continuous wave and pulse electron paramagnetic resonance, density‐functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e? bonding framework with a σ*‐SOMO of metal 4‐ or 5dz2 parentage that is partially stabilized by significant mixing with Si (3pz) and metal (5‐ or 6pz) orbitals. Metal‐ligand covalency thus buffers the expected destabilization of transition‐metal (TM)‐silyl σ*‐orbitals by d–p mixing, affording well‐characterized examples of TM–main group, and hence polar, 2c/3e? σ “half‐bonds”. 相似文献
3.
Iridium-Catalyzed Enantioselective Hydrogenation of Oxocarbenium Ions: A Case of Ionic Hydrogenation
Tilong Yang Yongjie Sun Heng Wang Prof. Dr. Zhenyang Lin Dr. Jialin Wen Prof. Dr. Xumu Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6164-6170
Ionic hydrogenation has not been extensively explored, but is advantageous for challenging substrates such as unsaturated intermediates. Reported here is an iridium-catalyzed hydrogenation of oxocarbenium ions to afford chiral isochromans with high enantioselectivities. A variety of functionalities are compatible with this catalytic system. In the presence of a catalytic amount of the Brønsted acid HCl, an α-chloroether is generated in situ and subsequentially reduced. Kinetic studies suggest first-order kinetics in the substrate and half-order kinetics in the catalyst. A positive nonlinear effect, together with the half kinetic order, revealed a dimerization of the catalyst. Possible reaction pathways based on the monomeric iridium catalyst were proposed and DFT computational studies revealed an ionic hydrogenation pathway. Chloride abstraction and the cleavage of dihydrogen occur in the same step. 相似文献
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The LiRh-type crystal structure of the equiatomic intermetallic compound IrZn turns out to be a competitor to the otherwise energetically favored CsCl-type structures of congeneric transition metal zinc phases, thus enlightening the structural impact of element-specific factors beyond the Hume-Rothery concept. 相似文献
6.
Esmaeil Hosseini 《代数通讯》2019,47(9):3781-3788
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Xiao Liang Lei Shi Yipu Liu Hui Chen Rui Si Wensheng Yan Qi Zhang Guo‐Dong Li Li Yang Xiaoxin Zou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(23):7713-7717
Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium‐containing strontium titanates (Ir‐STO) as active and stable, low‐iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir‐STO contains 57 wt % less iridium relative to the benchmark catalyst IrO2, but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium‐based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites. 相似文献
10.
A new class of phenethylamine-derived tridentate P,N,N-ligands has been successfully developed. These ligands exhibited good performance in the Ir-catalyzed asymmetric hydrogenation of β-keto esters, affording the corresponding β-hydroxy esters in moderate to good enantioselectivities. 相似文献