Asymmetric catalysts, whether metal complexes with chiral ligands, chiral organometallics, or chiral organic compounds (organocatalysts), achieve asymmetric induction by transferring chiral information from the catalyst to the substrate(s). [1] The source of the catalysts chirality therefore plays a crucial role for its mode of action, and is typically derived from one or more tetrahedral stereogenic centers (mostly carbon atoms, but also heteroatoms, such as sulfur or phosphorus), axial chirality, planar chirality, or a combination thereof (Scheme 1). In contrast, only few reports exist of asymmetric catalysts that derive their chirality exclusively from an octahedral stereocenter. [2][3][4] This seems surprising, considering the prevalence of the octahedral coordination geometry in chemistry and its ability to support the generation of structures with high complexity and, as a result of ligand crowding and chelate effects, often low conformational flexibility. [5] We recently demonstrated the use of chiral-atmetal octahedral complexes for the tailored design of a highly efficient asymmetric noncovalent catalyst that requires low catalyst loading by reporting an inert iridium(III)-based catalyst for the conjugate asymmetric transfer hydrogenation of b,b-disubstituted nitroalkenes. [6] However, excellent metal-, bio-, and organo-catalysts already exist for this transformation, [7] and we were therefore wondering whether an octahedral chiral-at-metal catalyst could be developed for a more challenging asymmetric conversion. In this respect, the asymmetric conjugate addition of carbon nucleophiles to b,b-disubstituted nitroalkenes constitutes a highly attractive reaction as it permits the construction of a stereogenic carbon atom bound to four other carbon substituents (all-carbon quaternary stereocenter). [8] Only a handful of studies are available dealing with this particular reaction, thereby presumably reflecting the involved challenge of overcoming a significant steric repulsion between the incoming carbon nucleophile and the carbon substituents of the nitroalkene electrophile. Nevertheless, Hoveyda and co-workers introduced a Cu-catalyzed dialkylzinc conjugate addition, [9] Arai and co-workers reported a Cu-catalyzed addition of indoles to isatin-derived nitroalkenes, [10] Jia and co-workers disclosed a Ni-catalyzed addition of indoles to b-CF 3 -b-disubstituted nitroalkenes, [11] Ricci and co-workers reported a phase-transfer asymmetric organocatalytic conjugate addition of cyanide to b,b-disubstituted nitroalkenes, albeit with only modest enantioselectivities, [12] Melchiorre and co-workers introduced the asymmetric vinylogous Michael addition of cyclic enones to nitroalkenes catalyzed by natural cinchona alkaloids, including one reaction using a b,b-disubstituted nitroalkene, [13] and finally Kastl and Wennemers introduced a proline-peptide-catalyzed asymmetric addition of aldehydes to b,b-disubstituted nitroalkenes under formation of g-nitroaldehydes. [14] The restricted scope of dialkylzinc reagents and t...

Extended pseudochalcogenides such as the solid-state carbodiimides (incorporating complex À N = C = N À units with D 1h symmetry) or cyanamides (with a less symmetrical N C À N 2À unit) have been extensively investigated, and a large number including alkali [1] and alkaline-earth metals, [2] main-group elements, [3] d 10 transition metals, [4] and also rare-earth metals [5] have been reported. The synthesis of the complete set of MNCN (M = Mn-Cu) phases with only partially filled 3d orbitals, however, looked far more difficult, because firstprinciples calculations [6] had predicted them to be unstable in terms of formation enthalpy DH f and Gibbs formation energy DG f , with the instability continuously rising from MnNCN to CuNCN, thereby mirroring the gradual filling of antibonding levels from 3d 5 to 3d 9 . Nonetheless, we have succeeded in finding new routes to synthesize the MNCN series of the divalent 3d metals as a prerequisite to determine their crystal structures. MnNCN, the first carbodiimide of a magnetic transition metal ever realized, is made by a metathesis around 600 8C involving ZnNCN and MnCl 2 [7] but this method is unsuitable for the later, more unstable compounds. FeNCN, [8] CoNCN, and NiNCN [9] are synthesized, instead, by a two-step route via the corresponding hydrogencyanamides M(HNCN) 2 at about 400 8C.[10] Finally, the most delicate carbodiimide, CuNCN, is obtained by the oxidation of a copper(I) cyanamide precursor under aqueous conditions at room temperature. [11] The magnetic properties of the carbodiimides involving divalent transition metals are similar to those of the isolobal oxides, in particular by indicating antiferromagnetic interactions. For example, the magnetic structure of MnNCN based on spin-polarized neutron diffraction reveals frustration between the high-spin (S = 5/2) Mn 2+ ions as a function of temperature [12] but also shows that the carbodiimide unit ensures a strong magnetic communication. Likewise, experimental as well as theoretical studies on the magnetic structure of CuNCN have shown a fascinating interplay between geometrical packing and exchange couplings. [13] Finally, UV/Vis measurements on MnNCN [14] stress the importance of the more covalent MnÀN bond and higher ligand-field splitting compared to Mn-O chromophores but a smaller nephelauxetic ratio. Also, the Mn À N bond lacks significant p interaction.In light of this information, the design of a carbodiimide that is not antiferromagnetic requires an alternative composition, for example, by moving towards a different oxidation state. The hypothetical chromium(III) carbodiimide, Cr 2 -(NCN) 3 , is such a synthetic target although its isolobal oxide Cr 2 O 3 is, in fact, antiferromagnetic. Because the electron configuration (3d 3 ) is even lower than in the MnNCN case, theory [6] implies that the synthetic route for MnNCN should also be applicable for Cr 2 (NCN) 3 . In addition, there is related information with respect to existing rare-earth metal(III) carbodiimides. Recent research on such Ln 2 (NCN) 3 ...

Strukturell gleich, magnetisch anders: Chrom(III)‐carbodiimid, das erste ferromagnetische Carbodiimid, wurde aus CrCl3 und ZnNCN synthetisiert und röntgenographisch charakterisiert. Trotz isostrukturellen Verhaltens zum antiferromagnetischen Cr2O3 weist Cr2(NCN)3 auf der Basis von SQUID‐Messungen und korrelierter DFT einen ferromagnetischen Grundzustand auf. Bei tiefen Temperaturen zeigt die Phase eine etwas größere Magnetisierung als Maghemit.

Multicomponent tandem polymerizations (MCTPs) of alkynes enjoying concise procedure, operational simplicity, synthetic efficiency, large structural diversity, high atom economy, and environmental benefit are recently developed as efficient strategies to synthesize functional conjugated polymers, which have attracted much attention from polymer scientists. In this work, through combination of Sonogashira coupling–Michael addition–cyclocondensation reactions in a one-pot procedure, an efficient three-component tandem polymerization of alkyne, carbonyl chloride, and hydrazine hydrate was reported to proceed smoothly under mild conditions at room temperature, affording polypyrazoles with high molecular weights (M w up to 19 400 g/mol) in excellent yields (up to 95%). This MCTP also applies to various aromatic diynes and aromatic hydrazines, producing polypyrazoles with improved solubility and processability, higher M ws of up to 30 700 g/mol, and high yields. Structural characterization of the polymers such as IR, 1H NMR, and 13C NMR spectra suggested total consumption of monomers and complete conversion of the polymer intermediate, proving the desired well-defined structure of polypyrazoles. These polypyrazoles generally enjoy good solubility and film-forming ability, high thermal stability, high light refractivity, and luminescence behavior. Such MCTPs are not just a simple reaction to connect functional units together in a polymer chain; they can also build functional units such as the newly formed multisubstituted heterocyclics embedded in the polymer main chain at the same time.

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