Sheng-Di Bai

Intramolecular NMe2H Elimination and Fulvene Coupling Leading to Novel Allyl‐Bridged Zirconocene and Hafnocene Complexes

Deprotonation of the aminofulvene 1 with LiCH(SiMe3)2 provides 2, which reacts with MCl4 (M=Zr or Hf) by intramolecular NMe2H elimination and coupling of the fulvene moieties to form complex 3 or 4. This reaction is a useful synthetic pathway to allyl-bridged ansa-metallocenes, especially those with a conjugated 14 π electron system. R′=dimethylamino.

Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: synthesis, structures and ethylene polymerization behaviors of the group 4 complexes

Lithium N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamidate (2) was prepared from the reaction of new compound N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamine (1) and LiBu(n). Treatment of the lithium salt (2) with an equal equivalent of MgBr(2)(THF)(2), FeCl(2) and CoCl(2) afforded the corresponding dinuclear complexes , , and , in which metal atoms possess similar trigonal bipyramidal geometries and each ligand functions as a bimetallic bridging binding aminopyridinato moiety with N-donation from the dimethylamino group. While the stoichiometric reaction of with ZrCl(4) gave the mononuclear zirconium complex (6); the seven coordinated zirconium atom adopts a distorted pentagonal bipyramid geometry and the ligand acts as monoanionic η(2)-aminopyridinato moiety with the pendant arm coordinated via N(CH(3))(2). The reaction of with one equivalent of TiCl(4)(THF)(2) produced the interesting dinuclear titanium complex (7) owing to the elimination of a (N,N-dimethylamino)dimethylsilyl group from the original ligand, and the two titanium centers present different coordination geometries. The molecular structures of the crystalline metal complexes have been confirmed by X-ray single crystal diffraction analysis. Upon activation with methylaluminoxane (MAO), both complexes and exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylenes with broad molecular weight distributions.

Group IV compounds bearing a novel tridentate N-donor ligand: synthesis, structures and ethylene polymerization

Treatment of the mixed amidinate-amido-lithium, [PhN(CH2)3NC(Ph)NSiMe3]2Li4·2Et2O, with group IV metal chlorides yields the corresponding compounds 3–5. Their structures were confirmed by X-ray diffraction analysis, showing a distorted octahedral geometry. The catalytic behaviors of compounds 3–5 were investigated in the presence of MAO as a co-catalyst. Compounds 3 and 4 showed high activities for ethylene polymerization.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

The dimer lithium complex 3 and zirconium complexes 4–6 were synthesized and characterized. Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. Their structures were confirmed by X-ray diffraction analysis, which showed a distorted octahedral geometry. Complexes 5 and 6 were zirconium trichloride compounds, while complex 4 was not a zirconium chloride species. The catalytic behaviors of complexes 4–6 were investigated in the presence of MAO as a cocatalyst. It was found that the catalytic activities of these zirconium complexes toward ethylene polymerization were closely related to the bonding patterns (η3:η1, η3 or η1), the number of chlorine atoms in the procatalysts and the availability of the coordination site in the molecule. Zirconium trichloride complex 5 showed the highest catalytic activity mainly because of its η1 bonding pattern.

Trichlorozirconium η 2-hydrazonides: Synthesis, characterization and their catalytic behavior toward ethylene polymerization

The trichlorozirconium η2-hydrazonides (R=H, A; R=CH3, B) were synthesized through the finely controlled stoichiometrical reactions of anhydrous zirconium tetrachloride with the lithium salt of either 1-(furan-2-ylmethylene)-2-phenylhydrazonide or 1-(furan-2-ylethylidene)-2-phenyl hydrazonide in the solvent tetrahydrofuran (THF), respectively. These complexes were highly sensitive to air and moisture due to solely using less bulky ligand of hydrazonides. The molecular structures of the title complexes, determined by means of single crystal X-ray diffraction, were found to be the distorted pentagonal bipyramid geometry around zirconium atom, with three chlorides and the hydrazonato ligand acting as the η2-coordination mode as well as two incorporated THF molecules. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), both complexes A and B exhibited catalytic activities toward ethylene polymerization, producing polyethylenes with ultra-high molecular weights.

N-Cyclo-hexyl-3-methyl-benzamidine.

The title amidine compound, C14H20N2, prepared by a one-pot reaction, is asymmetric as only one N atom has an alkyl substituent. The terminal cyclohexyl group connected to the amino N atom is located on the other side of the N—C—N skeleton to the 4-methylbenzene ring and has a chair conformation. The dihedral angle between the phenyl ring and the NCN plane is 47.87 (12)°. In the crystal, molecules are linked via N—H⋯N hydrogen bonds, forming chains propagating along the a-axis direction.

Tetra­chlorido­[N2,N2′-(di­methyl­silanedi­yl)bis­(N-tert-butyl-3-methyl­benzimid­amid­ato)-κ2N2,N2′]hafnium(IV)

The symmetric title molecule, [Hf(C26H40N4Si)Cl4], lies about a twofold rotation axis. The HfIV and Si atoms lie on the rotation axis with all other atoms being in general positions. The HfIV atom is six-coordinated by two N atoms from the N 2,N 2′-(dimethylsilanediyl)bis(N-tert-butyl-3-methylbenzimidamidate) ligand and four Cl− ions in a slightly distorted octahedral geometry. The two amidinate moieties are connected through the central Si atom with Si—N bond length of 1.762 (3) Å, generating the characteristic N—C—N—Si—N—C—N skeleton of a silyl-linked ansa-bis(amidine) species.

Synthesis and structural characterization of electrochemically reversible bisferrocenes containing bis(acyl-thiourea)s: enantiomers and conformers

Two chiral bisferrocenyl-modified bis(acyl-thiourea) enantiomers, (1R,2R)-bis(ferrocenylcarbonylthioureido)cyclohexane (1) and (1S,2S)-bis(ferrocenylcarbonylthioureido)cyclohexane (2), were synthesized by the reactions of 2.2 equivalents of ferrocenoyl isothiocyanate with (1R,2R) and (1S,2S)-1,2-diaminocyclohexane (1,2-DACH) via a nucleophilic addition reaction, respectively. The two new compounds were fully characterized by 1H NMR, 13C NMR, IR, UV-Vis, elemental analyses and single-crystal X-ray diffraction. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) experiments of compounds 1 and 2 showed roughly similar single reversible redox waves when using nBu4NClO4 (TBAP) as the supporting electrolyte, whereas two CV and DPV waves were observed when using nBu4NBArF4 [ArF4 = 3,5-bis(trifluoromethyl)phenyl]. Furthermore, both compounds 1 and 2 displayed potential antitumor activity against human HepG2 cells. When compounds 1 and 2 were crystallized from diethyl ether, the solvent-free enantiomers (1 and 2) were obtained, respectively. Molecules of both solvent-free enantiomers (1 and 2) assemble into a three-dimensional network structure through hydrogen-bonding and C–H⋯π (cyclopentadienyl rings) interactions. On the other hand, crystallization of compound 1 from benzene produced a benzene disolvate, 1·(C6H6)2. Molecules of the solvent-free and disolvated forms of compound 1 exhibit different molecular conformations and packing arrangements.

meso‐Bis{η5‐1‐[1‐(dimethylamino)ethenyl]‐3‐(trimethylsilyl)cyclopentadienyl}iron(II) and the cobalt(II) analogue

The two title crystalline compounds, viz. meso-bis{η(5)-1-[1-(dimethylamino)ethenyl]-3-(trimethylsilyl)cyclopentadienyl}iron(II), [Fe(C(12)H(20)NSi)(2)], (II), and meso-bis{η(5)-1-[1-(dimethylamino)ethenyl]-3-(trimethylsilyl)cyclopentadienyl}cobalt(II), [Co(C(12)H(20)NSi)(2)], (III), were obtained by the reaction of lithium 1-[1-(dimethylamino)ethenyl]-3-(trimethylsilyl)cyclopentadienide with FeCl(2) and CoCl(2), respectively. For (II), the trimethylsilyl- and dimethylaminoethenyl-substituted cyclopentadienyl (Cp) rings present a nearly eclipsed conformation, and the two pairs of trimethylsilyl and dimethylaminoethenyl substituents on the Cp rings are arranged in an interlocked fashion. In the case of (III), the same substituted Cp rings are perfectly staggered leading to a crystallographically centrosymmetric molecular structure, and the two trimethylsilyl and two dimethylaminoethenyl substituents are oriented in opposite directions, respectively, with the trimethylsilyl group of one Cp ring and the dimethylaminoethenyl group of the other Cp ring arranged more closely than in (II).

A convenient route to silyl linked bis(amidinate) ligands and synthesis of group(I) metal derivatives

A novel type of linked bis(amidinate) ligands (D) were developed successfully. Their lithium derivatives 1-4 were synthesized by treating the silyl-bridged diamines I-IV with two equivalents of LiBu(n) and PhCN in sequence, which underwent a silyl-bridge migration process. In addition, the linked bis(amidinate) configuration proved to be the thermodynamically stable form rather than the mono(amidinate) type by contrasting reaction of I with one equivalent of LiBu(n) and PhCN in sequence.