Qing-Chuan Yang

Synthesis, structural and spectroscopic study of polymeric copper(I) thiocyanato complexes [Cu(NCS)L]n (L=methyl nicotinate and ethyl nicotinate) and [HL][Cu(NCS)2] (HL=H-ethyl isonicotinate)

Abstract Three new copper(I) thiocyanato complexes [Cu(NCS)L]n (L=methyl nicotinate 1, ethyl nicotinate 2), and [HL][Cu(NCS)2] (HL=H-ethyl isonicotinate 3), have been prepared and characterized by spectroscopic and crystallographic methods. All three complexes display MLCT transitions in the visible region, as well as visible solid state emission spectra at room temperature. Their IR spectra are measured and discussed. In the structure of 1 each copper atom links two S atoms from two μ-S,S,N thiocyanato ligands and two nitrogen atoms from a pyridine nucleus and from a third μ-S,S,N thiocyanate group; the two S atoms bind another copper atom forming a Cu2S2 cyclic unit. The ladder propagates along the a axis of the unit cell. The structure of 2 features CuS2N2 coordination with approximate tetrahedral environment, μ-S,S,N bridging thiocyanate groups giving rise to corrugated layers at y=1/4. Complex 3 consists of an N-protonated ethyl isonicotinate cation and a polymeric [Cu(NCS)2]− anion. Each trigonal planar copper atom in the anion is coordinated by two S atoms from a μ-S,N thiocyanate bridge and a terminal S-thiocyanate group, and the third site is occupied by the end nitrogen of a μ-S,N thiocyanate bridge. The terminal NCS group forms a hydrogen bond of the type N–H⋯N with an N–H group of the [HL]+ cation. The planar ribbon which runs in the a direction is further stabilized by N–H⋯O hydrogen bonds.

[{[(η7-C2B10H12)(η6-C2B10H12)U][K2(thf)5]}2]: A Metallacarborane Containing the Novelη7-C2B10H124− Ligand

The tetranion ligand η7 -C2 B10 H124- has been observed for the first time in 1, which was obtained from the reaction of o-C2 B10 H12 with excess K metal followed by treatment with UCl4 . As shown in the picture (without K cations and coordinated THF molecules), 1 is a centrosymmetric dimer with a bent sandwich structure.

Synthesis and characterization of ruthenium complexes of 1,8-bis(diphenylphosphinomethyl)naphthalene (BDNA) and their catalytic hydrogenation reactions to α,β-unsaturated aldehydes

Abstract A new ligand BDNA [1,8-bis(diphenylphosphinomethyl)naphthalene] and three ruthenium complexes containing the new ligand, Ru2Cl4(BDNA)2 1, RuHCl(CO)(PPh3)(BDNA) 2, and RuH2(CO)(PPh3)(BDNA) 3, have been synthesized. Their compositions and structures were characterized by 31P{1H}-NMR, 1H-NMR, and elemental analysis. Molecular structure of 3 was also confirmed by single-crystal X-ray diffraction. The crystal belonged to the triclinic crystal system, P1 space group, a=10.7450(7), b=12.7100(7), c=18.1390(13) A, α=89.558(6), β=83.117(2), γ=80.859(5)°, V=2428.0(3) A3, and Z=2. The hydrogenation results of citral and cinnamaldehyde revealed that complex 2 had good catalytic activity and complex 3 had the high selectivity for the hydrogenation of CO bond in α,β-unsaturated aldehydes to form the corresponding allylic alcohols. In the presence of complex 3, very high selectivities of 99.5 and 95.1% were obtained for the hydrogenation of the carbonyl group in citral and cinnamaldehyde, respectively.

Anionic dichlorolanthanocene compounds. X-ray crystal structures of [{(Me3Si)2C5H3}2LnCl2][Li(THF)4] (Ln=Er, Yb) and {(Me3Si)2C5H3}2Yb(μ-Cl)2Li(THF)2

Abstract Treatment of LnCl3 with two equivalents of Cp″Li (Cp″=(Me3Si)2C5H3) in THF gave, after crystallization from a THF–n-hexane solution at −30°C, ionic compounds [Cp″2LnCl2][Li(THF)4] (Ln=Er (1), Yb (2)) in good yield. Recrystallization of 2 from a toluene solution afforded an ‘ate’ compound Cp″2Yb(μ-Cl)2Li(THF)2 (3). Interestingly, recrystallization of 3 from a mixed solvent of THF–n-hexane did not give compound 2, and only 3 was isolated, indicating that the dissociation of THF may be an irreversible process or 3 is a thermodynamically more stable compound. All three compounds were fully characterized by various spectroscopic date and single-crystal X-ray analyses. Compounds 1 and 2 are the rare structurally characterized examples of an anionic dichlorolanthanocene stabilized by an alkali metal complex ion.

Stereoisomeric Doubly Interpenetrating Three-Dimensional Networks of Tripodal Neodymium(III) Complexes from Spacer-Controlled Enantioselective Self-Assembly

Abstract Two three-dimensional frameworks composed of doubly interpenetrating networks of the same topology but different stereoisomeric structures have been constructed from self-assembly of the chiral building block, Δ- or Δ-[Nd(ntb)2]3+, with different spacers bipy and bpen (ntb = tris(2-benzimidazolylmethyl) amine, bipy = 4,4″-bipyridyl, bpen = trans-1,2-bis (4-pyridyl)ethylene). In the crystal structure of [Nd(ntb)2](ClO4)3·3bipy·2H2O the spacer bipy connects [Nd(ntb)2]3+ cations of the same handedness to generate a chiral network Δ3-Δ…(or Δ3-Δ…){[Nd(ntb)2](bipy)3}3+∞, which is interpenetrated further by another identical network. The crystal structure of [Nd(ntb)2](ClO4)3·3bpen·H2O shows a topologically similar but achiral framework in which non-planar and planar bpen spacers connect cations of the same chirality and a pair of enantiomers, respectively, thus generating a three-dimensional racemate Δ2Δ…(or Δ2Δ-Δ…){[Nd(ntb)2](bpen)3}3+∞. Aggregation of the molecular species is effected by N-H…N hydrogen bonds, and the observed enantioselective self-assembly can be rationalized by π…π interactions between aromatic rings.

Synthesis and structural characterisation of low-valent Group 14 metal complexes containing tridentate 2,6-pyridyl-bridged bis(1-azaallyl) ligands

Treatment of GeCl2(dioxane), SnCl2 and PbCl2 with appropriate alkali-metal compounds containing 2,6-pyridyl-bridged bis(1-azaallyl) dianionic ligands afforded bivalent Group 14 metal compounds [M{{N(SiMe3)C(R)CH}2C5H3N-2,6}] [R = Ph, M = Ge (1), Sn (2) and Pb (3); R = But, M = Sn (4) and Pb (5)]. The structures of the monomeric complexes 1, 2, 3 and 5 have been confirmed by single-crystal X-ray structure determination; it has been shown that the 2,6-pyridyl-bridged bis(1-azaallyl) ligand is bonded to the metal centre in a N,N,N′-chelate fashion.

Synthesis and molecular structure of a head-to-tail [4+4] dimer of a hexa-substituted anthracene

Two hexa-substituted anthracenes have been synthesised; the molecular structure of a [4+4] head-to-tail anthracene dimer has also been determined by X-ray diffraction analysis.

Mechanism of reduction of 1,1-diphenyl-2,2-dinitroethylene by 1-benzyl-1,4-dihydronicotinamide: transition state with partial diradical and partial covalent bonding character

The mechanism of reduction of 1,1-diphenyl-2,2-dinitroethylene (DPDN) by 1-benzyl-1,4-dihydronicotinamide (BNAH) in acetonitrile has been investigated. Based on product analysis, isotopic tracing and electrochemical analysis, the reaction takes place by a hydride transfer mechanism giving 1,1-diphenyl-2,2-dinitroethane (DPDNH). Single crystal X-ray analysis shows that DPDN conforms to idealized C2 symmetry, but steric repulsions between the bulky substituents result in an appreciable twist about the central bond, such that the phenyl rings make a dihedral angle of 77.7°and the planar C–NO2 fragments make a dihedral angle of 68.5°. A small kinetic H/D isotope effect was obtained, that we propose is due to steric hindrance. Reaction in oxygen-saturated acetonitrile produced DPDNH and benzophenone in the ratio of 59.2∶22.0 as the final products with a total yield of 68.6% by GC. Control experiments were performed, by stirring a solution of DPDN or DPDNH alone in oxygen-saturated acetonitrile, or by stirring a solution of DPDN or DPDNH alone in aqueous acetonitrile containing a small amount of hydrochloric acid or in acetonitrile containing triethylamine. These produced no benzophenone. The results clearly indicate the trapping of a radical species by oxygen in the reaction. A curve-crossing model for the reaction projects that the transition state has partial diradical and partial covalent bonding character. As DPDN has a low-lying π* orbital (LUMO), the radical anion DPDN−· is a stabilized radical. It is known that the reaction of alkyl and benzyl radicals with oxygen is exothermic with a rate close to the diffusion-controlled limit. Thus, with use of More O’Ferrall’s two-dimensional potential energy diagram, the results are rationalized by a mechanistic change induced by steric hindrance so that the transition state collapses in two directions leading to the formation of DPDNH (polar pathway) and benzophenone (ET pathway), respectively.

Synthesis and structural characterization of a novel asymmetric distannene [{1-[N(But)C(SiMe3)C(H)]-2-[N(But)(SiMe3)CC(H)]C6H4}Sn→Sn{1,2- [N(But)(SiMe3)CC(H)]2C6H4}]

The reaction of dilithium complex [{1,2-[N(But)C(SiMe3)C(H)]2C6 H4}{Li2(TMEDA)2}] 1 with SnCl2 yielded an unusual asymmetric distannene [{1-[N(But)C(SiMe3)C(H)]-2-[N(But)(S iMe3)CC(H)]C6H4}Sn→Sn{1,2- [N(But)(SiMe3)CC(H)]2C6H4 }] 2 resulting from intramolecular self-rearrangements of the ligands; 2 has a tin–tin bond distance of 3.0087(3) A.