Recently, 2D versions of metamaterials, metasurfaces, have attracted more attention, [11] due to their advantages of low cost, low profile, and strong abilities to manipulate spatial and surface waves. Novel generalized sheet transition condition method [12] and transverse resonance method [13] were first presented to analyze the EM performance of metasurfaces. Then generalized Snell's law [14] was proposed to introduce the concept of abrupt phase when designing metasurfaces. By changing the size, shape, or orientation of unit cells, the abrupt phase provided by the metasurface can be tailored accordingly, and the outgoing EM waves are engineered arbitrarily. Metasurfaces have offered more convenience and freedom for manipulating EM wavefronts, and have been widely applied in the microwave, [15][16][17][18][19][20] terahertz, [21][22][23][24] visible, [25][26][27][28] and even acoustic [29,30] frequencies.Metamaterials and metasurfaces described by continuously effective medium parameters and phase distributions have powerful capabilities in controlling EM waves, but in static ways. That is to say, once a metamaterial or metasurface is fabricated, its function will be fixed. In order to reach real-time controls to EM waves, digital coding characterization has been proposed to describe metamaterial, resulting in the concepts of coding, digital, and programmable metamaterials. [31] The binary 1-bit digital codes "0" and "1" are adopted to indicate the reflection phases of 0° and 180°, from which one can manipulate EM waves using different coding sequences. The digital codes have been extended to 2-bit and more to bring more freedom for controlling scattering beams. The digital states "0." "1," "2," and "3" represent the reflection phases of 0°, 90°, 180°, and 270°, respectively.By designing a unit cell controllable by a diode to achieve either "0" or "1" state, the digital and programmable metamaterials have been realized to reach real-time manipulations to EM waves. [31] The digital coding representation links the traditional metamaterials to information theory, giving us an opportunity to control EM performance through discrete digital states. Based on these concepts, many kinds of functions such as beam steering [31][32][33] and reduction of radar crosssections [34] have been achieved by switching coding sequences on coding metamaterials in microwave and terahertz regions. Recently, the concept of anisotropic coding metamaterials has been demonstrated, which can achieve two independent coding behaviors for different polarizations. [35] Furthermore, convolution operations on coding metasurfaces were presented to Coding representation of metamaterials builds up a bridge between the physical world and the digital world, making it possible to manipulate electromagnetic (EM) waves by digital coding sequences and reach field-programmable metamaterials. Here, the coding space is extended to complex domain and proposed complex digital codes to provide closer essence of EM-wave propagation. Based on the analytic geometr...

Coding metasurfaces are aimed at representing digital information of the metasurface, usually by programing digital unit cells to control electromagnetic waves. However, some information sequences cannot be recognized by the receiver, because of nonorthogonality of the usual phase codes. Here, new coding method is proposed to encode information with orthogonal parameters in the emitting beam, which reduces information loss in the system. A vector beam modulator is proposed by combining orthogonal polarizations and orbital angular momentum (OAM) modes. A normal incident wave can be modulated by OAM‐mode bit and polarization bit, which are regarded as specific information by the receiver. A polarization converter is used to realize the polarization selection (polarization bit) and phase control, independently. The phase patterns on the coding metasurfaces can be programed to realize the designed OAM modes (OAM bits) in the microwave frequency. Three schemes are presented to emit multiple OAM modes in dual polarizations, one of which is manufactured and measured for near and far fields. The simulations and experiments are in outstanding agreement, verifying the excellent performance of the proposed schemes. This work has great potential in communication applications of coding metasurfaces.

The chemistry of transition metal-containing metallabenzenes has attracted considerable attention.[1] Previous studies have led to the isolation and characterization of a number of stable metallabenzenes, especially those of osmium, [2][3][4] iridium, [5][6][7][8] platinum, [9] ruthenium, [10,11] and rhenium. [12] Many interesting chemical properties of metallabenzenes have also been discovered. For example, it has been demonstrated that metallabenzenes can undergo electrophilic substitution reactions, [2a, 5d] cycloaddition reactions, [8d, 9c] nucleophilic addition reactions, [13] and nucleophilic aromatic substitution of hydrogen. [14] Another common reactivity of metallabenzenes is that they can undergo migratory insertion reactions to give cyclopentadienyl complexes. The transformation has been demonstrated with well-characterized metallabenzenes [2e, 6b,-d,e, 10b] as well as a spectroscopically characterized ruthenabenzene, [15] and it has been proposed as a key step in the formation of cyclopentadienyl complexes.[1]Compounds closely related to metallabenzenes are metallabenzynes.[16] Compared with the chemistry of metallabenzenes, that of metallabenzynes is much less developed, which is partly due to the lack of convenient methods to synthesize such compounds.[17] Structurally, metallabenzynes are similar to metallabenzenes in that both have a delocalized structure. Thus it might be expected that metallabenzynes should have properties similar to those of metallabenzenes. Indeed, previous studies have demonstrated that metallabenzynes, like metallabenzenes, can also undergo electrophilic substitution reactions [18] and nucleophilic addition reactions.[17c] As formation of cyclopentadienyl complexes from metallabenzenes by migratory insertion reactions is well-known, one might expect that metallabenzynes could also undergo migratory insertion reactions to give carbene complexes. However, such reactions have not been previously observed. Herein, we present a reliable method to prepare osmabenzynes along with the first examples of conversion of metallabenzynes into carbene complexes.We recently observed that reaction of zinc with the osmium vinyl carbyne complex [OsCl 3 { C À CH = C(2-ClC 6 H 4 ) 2 }(PPh 3 ) 2 ] produced a osmanaphthalyne complex. [19] The reaction was proposed to proceed through a 16e fourcoordinate square planar osmium carbyne complex, which undergoes an oxidative addition reaction involving a CÀCl bond. Inspired by the observation, we envisioned that reactions of zinc with carbyne complexes of the type [OsCl 3 { C À CH = CR À CR' = CClR''}(PPh 3 ) 2 ] might lead to the formation of new osmabenzynes.To test this hypothesis, we first prepared the meridional osmium carbyne complex 1 and then treated it with zinc in THF at room temperature. An in situ 31 P NMR study showed that osmabenzyne 2 with substituents on the C3 and C5 positions was produced as the major phosphorus-containing product (Scheme 1), which can be isolated in 62 % yield after column chromatography.The osmabenzyne 2 has bee...

Axially chiral compounds play an important role in areas such as asymmetric catalysis. The tyrosine click-like reaction is an efficient approach for synthesis of urazoles with potential applications in pharmaceutical and asymmetric catalysis. Here we discover a class of urazole with axial chirality by restricted rotation around an N–Ar bond. By using bifunctional organocatalyst, we successfully develop an organocatalytic asymmetric tyrosine click-like reaction in high yields with excellent enantioselectivity under mild reaction conditions. The excellent remote enantiocontrol of the strategy originates from the efficient discrimination of the two reactive sites in the triazoledione and transferring the stereochemical information of the catalyst into the axial chirality of urazoles at the remote position far from the reactive site.

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties.

No abstract

The catalytic activity of a series of ruthenium complexes lacking cyclopentadienyl ligands has been evaluated for the cycloaddition of terminal alkynes and azides to give selectively 1,4-disubstituted 1,2,3-triazoles. The complex RuH(η 2 -BH 4 )(CO)(PCy 3 ) 2 was found to be an effective catalyst for the cycloaddition reactions. In the presence of RuH(η 2 -BH 4 )(CO)(PCy 3 ) 2 , primary and secondary azides reacted with a range of terminal alkynes containing various functionalities to selectively produce 1,4-disubstituted 1,2,3triazoles. The ruthenium-catalyzed azide−alkyne cycloaddition appears to proceed via a Ru−acetylide species as the key intermediate, which undergoes formal cycloaddition with an azide to give a ruthenium triazolide complex. The 1,4-disubstituted 1,2,3-triazole product is generated by metathesis of the triazolide complex with a terminal alkyne. In support of the reaction mechanism, the acetylide complex Ru(CCCMe 3 ) 2 (CO)(PPh 3 ) 3 reacts cleanly with benzyl azide to give a ruthenium triazolide complex, which reacts with excess tert-butylacetylene in the presence of PPh 3 to give 4-tert-butyl-1-benzyl-1,2,3-triazole and the diacetylide complex Ru(CCCMe 3 ) 2 (CO)(PPh 3 ) 3 . The mechanism is also supported by DFT calculations.

Asymmetric hydrogenation of α,β-unsaturated acids catalyzed by noble metals has been well established, whereas, the asymmetric hydrogenation with earth-abundant-metal was rarely reported. Here, we describe a cobalt-catalyzed asymmetric hydrogenation of α,β-unsaturated carboxylic acids. By using chiral cobalt catalyst bearing electron-donating diphosphine ligand, high activity (up to 1860 TON) and excellent enantioselectivity (up to >99% ee) are observed. Furthermore, the cobalt-catalyzed asymmetric hydrogenation is successfully applied to a broad spectrum of α,β-unsaturated carboxylic acids, such as various α-aryl and αalkyl cinnamic acid derivatives, α-oxy-functionalized α,β-unsaturated acids, α-substituted acrylic acids and heterocyclic α,β-unsaturated acids (30 examples). The synthetic utility of the protocol is highlighted by the synthesis of key intermediates for chiral drugs (6 cases). Preliminary mechanistic studies reveal that the carboxy group may be involved in the control of the reactivity and enantioselectivity through an interaction with the metal centre.