Praseodymium Metallacrown-Based NMR Probe for Enantioselective Discrimination of Mandelate Anions in Water.

Recently, the enhanced interest in water-soluble aminohydroximate Ln(III)-Cu(II) metallacrowns (MC) is largely due to their fascinating structural chemistry, diverse properties and ease of synthesis. We examined the water-soluble praseodymium(III) alaninehydroximate complex Pr(H2O)4[15-MCCu(II)Alaha-5]·3Cl (1) as a highly effective chiral lanthanide shift reagent for NMR analysis of the biologically relevant (R/S)-mandelate (MA) anions in aqueous media. The R-MA and S-MA enantiomers can be easily discriminated in the presence of small (1.2-6.2 mol %) amounts of MC 1 by the 1H NMR signals of multiple protons exhibiting an enantiomeric shift difference (ΔΔδ) of 0.06 ppm up to 0.31 ppm. Additionally, a possibility of coordination of MA to the metallacrown was investigated by the ESI-MS technique and a Density Functional Theory modeling of the molecular electrostatic potential and noncovalent interactions.

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands.

The fused 1,3-dithiole spacer seems to be very suitable for the functionalization of sterically hindered o-quinones with additional groups capable of coordination of metal ions and/or possessing a redox activity. An effective method for the synthesis of sterically hindered o-quinones containing 1,3-diketonate, dinitrile and p-quinone-methide functional groups at the periphery of the ligand has been developed. The novel compounds have rigid and conjugated structures and exhibit properties typical of o-quinones. A study of their monoreduced semiquinone derivatives reveal that the spin density is delocalized across the whole molecule, including peripheral fragments. The first stable o-quinone derivative bearing an annulated thiete heterocycle has been isolated and characterized.

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds.

A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [( p- tBu-C6H4)2CH]2M(L n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2(THF) n ( n = 0-2) and [( p- tBu-C6H4)2CH]-Na+. In complex 1, the benzhydryl ligands are bound to the metal center in η2-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η3-fashion. In complex 2, one ligand is η3-coordinated while the second one is η4-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 °C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal C═C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb(II) complex as a catalyst.

Trinuclear alkyl hydrido rare-earth complexes supported by amidopyridinato ligands: synthesis, structures, C-Si bond activation and catalytic activity in ethylene polymerization.

The reaction of Ap(9Me)Lu(CH2SiMe3)2(thf) (Ap(9Me) = (2,4,6-trimethylphenyl)[6-(2,4,6-triisopropylphenyl)pyridine-2-yl]amido ligand) with two molar equivalents of PhSiH3 affords a trinuclear alkyl-hydrido cluster [(Ap(9Me)Lu)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2]. The analogous reactions with Ap(9Me)Ln(CH2SiMe3)2(thf) (Ln = Y, Yb) are more complex and result in the formation of mixtures of two types of trinuclear alkyl-hydrido complexes [(Ap(9Me)Ln)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2] and [(Ap(9Me)Ln)3(µ(2)-H)3(µ(3)-H)2(CH2SiH2Ph)(thf)2] differing in the alkyl group. The DFT calculations of [(Ap*Y)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2] (Ap* = (2,6-diisopropylphenyl)[6-(2,4,6-triisopropylphenyl)pyridine-2-yl]amido ligand) confirm localization of the HOMO on the Ap*-Y(1A)-CH2SiMe3 fragment, thus explaining its enhanced reactivity. Analysis of the electron density distribution reveals the Y-H and H-H bonding interactions in the (Y)3(µ(2)-H)3(µ(3)-H)2 moiety. The NMR studies of diamagnetic complexes [(Ap(9Me)Lu)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2] and [(Ap*Y)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2] demonstrated that the trinuclear cores are retained in the solution and revealed exchange between µ(3)- and µ(2)-bridging hydrido ligands. Complexes [(Ap*Ln)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2], the cationic yttrium hydrido cluster [(Ap*Y)3(µ(2)-H)3(µ(3)-H)2(thf)3](+)[B(C6F5)4](-) as well as [(Ap(9Me)Ln)3(µ(2)-H)3(µ(3)-H)2(CH2SiMe3)(thf)2] proved to be active in catalysis of ethylene polymerization under mild conditions.

Cascade synthesis of polyoxygenated 6H,11H-[2]benzopyrano-[4,3-c][1]benzopyran-11-ones.

2-(methoxymethoxymethyl)aryllead triacetates, obtained in situ from the corresponding arylboronic acids, reacted with 4-hydroxycoumarins, leading to 3-(2-methoxymethoxymethyl)aryl-4-hydroxycoumarin derivatives in good to high yields. These compounds underwent a cascade sequence of reactions, deprotection-halogenation-annulation, to afford polyoxygenated tetracyclic 6H,11H-[2]benzopyrano-[4,3-c] [1]benzopyran-11-ones in good yields. Some compounds showed a moderate cytotoxicity against human epithelial mammary HBL100 cells.