α‐Diamine Nickel Catalysts with Nonplanar Chelate Rings for Ethylene Polymerization

A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr₂, 1 : Ar=2,6‐diisopropylphenyl, 2 : Ar=2,6‐dimethylphenyl, 3 : Ar=phenyl), have been synthesized and characterized. X‐ray crystallographic analysis showed that the coordination geometry of the α‐diamine nickel complexes is markedly different from conventional α‐diimine nickel complexes, and that the chelate ring (N‐C‐C‐N‐Ni) of the α‐diamine nickel complex is significantly distorted. The α‐diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α‐diimine nickel catalyst. Increasing the steric hindrance of the α‐diamine ligand by substitution of the o‐methyl groups with o‐isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1 /Et₂AlCl at 35 °C or 2 /Et₂AlCl at 0 °C. The bulky α‐diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure.     

Beryllium(II) Complexes with Bis(dimethylamino)phosphorylfluoride: A Multinuclear NMR (31P, 19F,and 9Be) Characterization in Solution

Complexes of beryllium chloride and nitrate with (Me₂N)₂P(O)F were characterized in solution by multinuclear NMR spectroscopy and in some cases by IR spectroscopy and conductimetry. ³¹P and ¹⁹F NMR spectra were informative of changes associated with complex formation revealing resonances consistent with different species in solution and suggest an equilibrium between these species in both beryllium derivatives. These compounds show narrow lines in the solution ⁹Be NMR spectra, indicative of a highly symmetric environment for beryllium. The presence of the different species was more pronounced in beryllium chloride complexes. The results are compared to those reported in the literature for hexamethylphosphoramide (HMPA).     

New Organophosphorus Proligands and Amide Precursors: Crystal and Molecular Structures of Ph2P(X)NH(C6H3Pri 2-2,6) (X = O,S) and (OPPh2)(O2SMe)N(C6H3Pri 2-2,6)

The new organophosphorus proligand (OPPh₂)(O₂SMe)NR (R = C₆H₃Prⁱ ₂–2,6) (3) was prepared as a white crystalline solid by reacting the lithiated compound Li[Ph₂P(O)NR] with MeSO₂Cl in a 1:1 molar ratio. The precursor Ph₂P(O)NHR (1), as well as its thio analogue Ph₂P(S)NHR (2), were obtained in the reaction between the lithiated amine RNHLi and the corresponding organophosphorus chloride. All compounds were characterized by multinuclear (¹H, ¹³C, and ³¹P) NMR spectroscopy. The molecular structures of 1–3 were established by single-crystal X-ray diffraction. A zigzag polymeric chain is formed in the crystals of 1 and 2 by hydrogen N–H···X (X = O, S) bonding, while the crystal of 3 contains discrete monomeric units with a syn–syn conformation of the O?P(C)₂–N–S(C)(?O)₂ skeleton.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Sequential Alkylation of Tröger's Base. An Approach to New Chiral Ligands

Heterocycles derived from Tröger's base were shown to complex with metal salts in 2:1 ligand:salt ratios as monodentate or bidentate ligands depending on structure.