Turning up the spin, turning on single-molecule magnetism: from S = 1 to S = 7 in a [Mn(8)] cluster via ligand induced structural distortion

The spin ground state of a [Mn(III)(6)Mn(II)(2)] cluster has been deliberately switched from S = 1 to S = 7 upon designed ligand substitution.     

Copper-catalyzed asymmetric conjugate addition of trialkylaluminium reagents to trisubstituted enones: construction of chiral quaternary centers

Me3Al, Et3Al, and vinylalane species undergo enantioselective conjugate addition to a wide range of 2- or 3-substituted enones (cyclopent-2-enones, cyclohex-2-enones, 3-methyl cyclohept-2-enone) in the presence of catalytic amount of copper salt (copper thiophene carboxylate, [Cu(CH3CN)4]BF4 or [CuOTf]2C6H6) and tropos-phosphoramidite-based ligand. Thus, chiral quaternary centers can be built, with up to 98% ee after rigorous optimization of experimental conditions. It was shown that the main important parameter was the order of the introduction of the reagents. Then, the generated enantioenriched aluminium enolates and the chiral conjugate adducts were functionalized and used for subsequent reactions.     

Acetate/di-2-pyridyl ketone oximate "blend" as a source of high-nuclearity nickel(II) clusters: dependence of the nuclearity on the nature of the inorganic anion present

The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2.4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state.     

The supramolecular chemistry of metal complexes with heavily substituted imidazoles as ligands: Cobalt(II) and zinc(II) complexes of 1-methyl-4,5-diphenylimidazole

An investigation of the M^II/X⁻/L [M^II = Co, Ni, Cu, Zn; X⁻ = Cl⁻, Br⁻, I⁻, NCS⁻, NO₃⁻, N₃⁻, CH₃COO⁻; L = 1-methyl-4,5-diphenylimidazole] general reaction system towards the detailed study of the intermolecular interactions utilized for controlling the supramolecular organization and the structural consequences on the structures produced has been initiated. Three representative complexes with the formulae [Co(NO₃)₂(L)₂] (1), [Zn(NO₃)₂(L)₂] (2) and [Co(NCS)₂(L)₂]·EtOH (3·EtOH) have been synthesized and characterized by spectroscopic methods and single-crystal X-ray analysis. Compounds 1 and 2 are isomorphous (tetragonal, I4₁cd) with their metal ions in a severely distorted octahedral Co/ZnN₂O₄ environment, while 3·EtOH crystallizes in P2₁/c with a tetrahedral CoN₄ coordination. The structural analysis of 1, 2 and 3·EtOH reveals a common mode of packing among neighbouring ligands (expressed through intramolecular π–π interactions between the 4,5-diphenylimidazole moieties), enhancing thus the rigidity and stability of the complexes. The bent coordination of the two isothiocyanates in 3 [Co–NCS angles of 173.8(2) and 160.8(2)°] seems to be caused by intermolecular hydrogen bonding and crystal packing effects.     

Complexes derived from the general copper(II)/maleamic acid/N,N′,N′′-chelate reaction systems: Synthetic,reactivity, structural and spectroscopic studies

The synthetic investigation of the Cu^II/maleamate(−1) ion (HL⁻)/N,N′,N′′-chelate general reaction system has allowed access to compounds [Cu₂(HL)₂(bppy)₂](ClO₄)₂·H₂O (1·H₂O), [Cu(HL)(bppy)(ClO₄)] (2) and [Cu(HL)(terpy)(H₂O)](ClO₄) (4) (bppy = 2,6-bis(pyrazol-1-yl)pyridine, terpy = 2,2′;6′,2′′-terpyridine). In the absence of externally added hydroxides, compound [Cu₂(L′)₂(bppy)₂](ClO₄)₂ (3) was obtained from MeOH solutions; L′⁻ is the monomethyl maleate(−1) ligand which is formed in situ via the Cu^II-assisted HL⁻ → L′⁻ transformation. In the case of tptz-containing (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) reaction systems, the Cu^II-assisted hydrolysis of tptz to pyridine-2-carboxamide (L1) afforded complex [Cu(L1)₂(NO₃)₂] (5). The crystal structures of 1–5 are stabilized by intermolecular hydrogen bonding and π–π stacking interactions. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Enantioselective Organocatalytic Conjugate Addition of Aldehydes to Vinyl Sulfones and Vinyl Phosphonates as Challenging Michael Acceptors

Chiral framework : Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.

     

Improvement of source and wind field input of atmospheric dispersion model by assimilation of concentration measurements: Method and applications in idealized settings

The problem of correcting the pollutant source emission rate and the wind velocity field inputs in a puff atmospheric dispersion model by data assimilation of concentration measurements has been considered. Variational approach to data assimilation has been used, in which the specified cost function is minimized with respect to source strength and/or wind field. The analyzed wind field satisfied the constraints derived from the conditions of mass conservation and linearized flow equations for perturbations from the first guess wind field. ‘Identical twin’ numerical experiments have been performed for the validation of the method. The first guess estimation errors of source emission rate and wind field were set to a factor of up to 10 and up to 6 m/s respectively. The calculations results showed that in most studied cases an improvement of vector wind difference (VWD) error by about 0.7–1 m/s could be achieved. The resulting normalized mean square error (NMSE) of concentration field was also reduced significantly.     

Copper-catalyzed asymmetric conjugate addition of Grignard reagents to trisubstituted enones. Construction of all-carbon quaternary chiral centers

The copper-catalyzed asymmetric conjugate addition of Grignard reagents to trisubstituted cyclic enones affords enantioenriched all-carbon quaternary centers with up to 96% ee. The chiral ligand is a diaminocarbene, directly generated in situ. The combination of Grignard reagent and diaminocarbene is unprecedented in conjugate addition, and the additon of the phenyl group, on such enones, cannot be done by other conjugate addition methods.