Synthesis and anti‐inflammatory effect of morachalcone B,morachalcone C,and analogs

An efficient method to synthesize morachalcones B and C ( 1 and 2 ) is described. Rap?Stoermer condensation and 1,3‐prenyl rearrangement were used as two key synthetic methods. Morachalcone C was obtained by photo‐oxygenation of morachalcone B. Morachalcones B and C showed moderate anti‐inflammatory activity.     

Chromium to chromium quintuple bonds in a trigonal lantern configuration

A new family of the quintuply bonded dichromium complexes [Cr₂{μ‐κ²‐HC(N‐2,6‐R₂C₆H₃)₂}₂(μ‐κ²‐HC[NAr]₂)] (R = ⁱPr, Ar = 4‐MeC₆H₄ ( 5 ), Ar = 3,5‐Me₂C₆H₃ ( 6 ), and Ar = 2,6‐Me₂C₆H₃ ( 7 ); R = Et, Ar = 4‐MeC₆H₄ ( 8 ), Ar = 3,5‐Me₂C₆H₃ [ 9 ], and Ar = 2,6‐Et₂C₆H₃ ( 10 )) with a heteroleptic lantern configuration was obtained upon the addition of one equivalent of amidinate to the quintuply bonded dichromium amidinates [Cr{μ‐κ²‐HC(N‐2,6‐R₂C₆H₃)₂}]₂ (R = ⁱPr, Et). Additionally, the same approach was applied to the preparation of the acetate derivative [Cr₂{μ‐κ²‐HC(N‐2,6‐ ⁱPr₂C₆H₃)₂}₂(μ‐κ²‐CH₃CO₂)] ( 11 ), which represents the first example that the quintuply bonded dinuclear complex contains an oxygen‐containing ligand. Of particular interest is that the Cr‐Cr bond lengths in these new trigonal paddlewheel quintuple Cr‐Cr bond species are comparable with those in their precursor compounds. They show ultrashort Cr‐Cr bond lengths in a narrow range of 1.740–1.755 å on the basis of single‐crystal X‐ray crystallography. The small Mayer bond orders of the long Cr‐N bonds as well as divergent, C_2v and D_3h, structural conformations in 5 – 11 suggest that the metal–ligand interactions possess minor covalent character and the electrostatic interactions play a dominant role. As a result, these extremely short Cr‐Cr quintuple bonds are caused by the overlap between five pairs of d orbitals that do not involve much in metal–ligand bonding. Additionally, anionic lantern dichromium trisamidinates 5 – 10 can be chemically oxidized by one electron, supported by electrochemistry, and their ease to undergo oxidation is presumably associated with their neutral lantern dichromium trisamindinate products, whose structures inherently display a Jahn‐Teller distortion, exemplified by the structure of the homoleptic dichromium complex [Cr₂{μ‐κ²‐HC(N‐2,6‐Et₂C₆H₃)₂}₃] [ 12 ] determined by X‐ray crystallography. These results unambiguously support the Cr‐Cr quintuple bonding in these novel anionic lantern dichromium complexes.     

Development of dipyridine‐based coordinative polymers for reusable heterogeneous catalysts

Poly(di(pyridin‐2‐yl)methyl acrylate) (PDPyMA), which was obtained by the free radical polymerization of designed coordinative monomer of di(pyridin‐2‐yl)methyl acrylate, is able to coordinate with various metal ions to form heterogeneous catalysts for diverse catalytic reactions. The Pd and Cu complexes supported by PDPyMA were developed for the heterogeneous Suzuki‐Miyaura reaction and Friedel‐Crafts alkylation, respectively. The PDPyMA‐based catalysts showed no significant decline of reactivity after five times recycling. However, the hydrolysis of the PDPyMA backbone under alkaline conditions limited the catalytic efficiency of this heterogeneous catalyst so that the coordinative monomer was redesigned as 1,1‐di(pyridine‐2‐yl)‐2‐(4‐vinylphenyl)ethan‐1‐ol and then 2,2′‐(1‐methoxy‐2‐(4‐vinylphenyl)ethane‐1,1‐diyl)dipyridine (MVPhDPy). With copolymerization of N‐isopropyl acrylamide (NIPAM), the efficiency of polymer‐based heterogeneous catalysts could be further raised, demonstrated by the increased turn over number in the Suzuki‐Miyaura reaction, which approached 5,260 by using the catalyst formed from poly(MVPhDPy‐co‐NIPAM) and Pd(OAc)₂. poly(MVPhDPy‐co‐NIPAM) copolymer, therefore, could be a versatile platform to support different metal ions for various heterogeneous catalytic reactions.     

Anion‐ and Solvent‐Induced Assembly and Reversible Structural Transformation of d10‐Metal Coordination Architectures Containing N‐(4‐(4‐Aminophenyloxy)phenyl)isonicotinamide

We set out studies on anion‐ and solvent‐induced assembly based on the ligand N‐(4‐(4‐aminophenyloxy)phenyl)isonicotinamide (papoa), which is synthesized to show a bent and flexible backbone. Reactions of papoa with ZnX₂ (X=Cl, Br, and I) gave the dinuclear macrocycles ([ZnX₂(papoa)]₂; X=Cl ( 1 a ), Br ( 2 a ), I ( 3 )), the structure of which was determined by X‐ray diffraction. Notably, the less bulky Cl and Br compounds afforded the coordinated imine in acetone (i.e., [ZnX₂(papoi)]₂, papoi=N‐(4‐(4‐(propan‐2‐ylideneamino)phenoxy)phenyl)isonicotinamide; X=Cl ( 1 b ), Br ( 2 b )), whereas the iodine one only gave the coordinated amine compound 3 under the same reaction condition. In fact, the coordinated imine can return to the amine analogue upon exposure to air or in DMSO, which has been monitored by ¹H NMR spectroscopy and powder X‐ray diffraction. Both the dinuclear [Zn(papoa)(NO₃)₂]₂ ( 4 a ) and the 1D [Zn(papoa)₂(NO₃)₂]_n ( 4 b ) were formed from the reaction of Zn(NO₃)₂ and papoa in mixed solvents with acetone and acetonitrile, respectively. In addition, Cd(ClO₄)₂ can react with papoa to give the 1D framework {[Cd(papoa)₂(CH₃CN)₂](ClO₄)₂}_n ( 5 a ) and the 2D framework [Cd(papoa)₂(ClO₄)₂]_n ( 5 b ), depending on the solvent used, that is, MeOH and CH₃CN, respectively. Importantly, the 1D framework with axially coordinated CH₃CN molecules and the 2D framework with axially coordinated ClO₄^? ions can be interconverted by heating and grinding in the presence of CH₃CN, respectively. Such a reversible structural transformation process was proven by PXRD studies.     

Robust Limit Cycle Suppression for Control Systems with Parametric Uncertainty and Nonlinearity

A systematic limit cycle suppression method is presented to predict and suppress the sustained limit cycles persisting in a class of uncertain control systems containing inherent nonlinearity. The aim is to determine the feasible controller parameter sets in the parameter plane for the entire uncertain system. A family of constant limit cycle amplitude loci is plotted. Successful application to pitch orientation control system with parametric uncertainties and nonlinearity is demonstrated. System output response is further investigated.