The Effects of Internal Electron Donors on MgCl-Supported Ziegler-Natta Catalysts for Isotactic PP.

The electron donors (ED) in Ziegler-Natta (Z-N) catalysis are classified as internal electron donors (IED) and external electron donors (EED), and both IED and EED are indispensable components for enhancing the catalytic reactivity and regulating the stereoregularity of polyolefinic materials in a typical industrial Z-N catalytic process. With the intensive research on ED, the Z-N catalyst performances have experienced successive progress in the last few decades. Polypropylenes (PP) as a commodity polyolefin material, especially the isotactic PP (iPP), are produced in multi-billion pounds per annum by utilization of the various IED- and EED-assisted Z-N catalysts systems.

High-Efficiency Mono-Cyclopentadienyl Titanium and Rare-Earth Metal Catalysts for the Production of Syndiotactic Polystyrene.

Syndiotactic polystyrene (SPS) refers to a type of thermoplastic material with phenyl substituents that are alternately chirally attached on both sides of an aliphatic macromolecular main chain. Owing to its excellent physical and mechanical properties, as well as its chemical stability, high transparency, and electrical insulation characteristics, SPS is used in a wide variety of technical fields. SPS is commonly produced via the stereoselective transition metal-catalyzed coordination polymerization method mediated by stereospecific catalysts, which consists of anionic mono-cyclopentadienyl derivative η-coordinated single active metal centers (referred to as "mono-Cp'-M"), with active center metals involving Group 4 transition metals (with an emphasis on titanium) and rare-earth (RE) metals of the periodic table.

Synthesis and study of an unprecedented 1-hydro-1-lithio-1-silafluorene anion.

The 1-hydro-1-lithio-silafluorene anion 2 has been isolated and characterized by single-crystal X-ray analysis for the first time. Three tetrahydrofuran molecules coordinate with lithium atoms in the crystal structure of 2. 2 was reacted with a number of electrophilic reagents and it can be used as a useful reagent for generating various functional hydrogen-substituted silafluorenes.

N-Heterocyclic Carbene-Ytterbium Amide as a Recyclable Homogeneous Precatalyst for Hydrophosphination of Alkenes and Alkynes.

The N-heterocyclic carbene-ytterbium(II) amides (NHC)2Yb[N(SiMe3)2]2 (1: NHC: 1,3,4,5-tetramethylimidazo-2-ylidene (IMe4); 2: NHC: 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr)) and the NHC-stabilized rare-earth phosphide (IMe4)3Yb(PPh2)2 (3) have been synthesized and fully characterized. Complexes 1-3 are active precatalysts for the hydrophosphination of alkenes, alkynes, and dienes and exhibited much superior catalytic activity to that of the NHC-free amide (THF)2Yb[N(SiMe)2]2. Complex 1 is the most active precursor among the three complexes.

Isolable 1,1-disubstituted silole dianion: a homogeneous two-electron-transfer reducing reagent.

The 1,1-disubstituted silole dianion 2 has been isolated and characterized by single-crystal X-ray analysis for the first time. 2 can be used as a two-electron-transfer reducing reagent for the reduction of organic compounds and inorganic salts with regeneration of the corresponding neutral silole in nearly quantitative yields, indicating that it is an excellent reducing reagent. Reduction of (Mes)2SiCl2 with 2 selectively yielded the cyclotrisilane (Mes2Si)3 in high yield, which has not been isolated in pure form with the existing methods.

[(NHC)Yb{N(SiMe3)2}2]-catalyzed cross-dehydrogenative coupling of silanes with amines.

Top cat: [(NHC)Yb{N(SiMe(3))(2)}(2)] adducts (NHC = N-heterocyclic carbene) are efficient catalysts for catalytic cross-dehydrogenative coupling of silanes with a range of primary and secondary amines to yield silylamines in high yields (82-100%) under mild reaction conditions. The catalytic activity and selectivity of the rare-earth-metal silylamides are modulated by altering the steric bulk of the NHC.

One-step access to luminescent pentaaryldiazaboroles via C-C double bond formation from imidoylstannanes.

A series of pentaaryl-substituted diazaboroles have been prepared for the first time by a novel strategy based on the C-C double bond formation from imidoylstannane reagents in the presence of dibromophenylboranes. The aryl substituents on the 4,5-position of the planar C(2)N(2)B core have substantial effects on their electronic structures. All the new diazaboroles are luminescent both in solution and in the solid state.

The reactivity of a silacyclopentadienylidene towards aldehydes: silole ring expansion and the formation of base-stabilized silacyclohexadienones.

Tossing aldehydes into the ring: The reaction of a silacyclopentadienylidene with aldehydes leads to C=O bond cleavage with the formation of base-stabilized silanones and cyclopropanation of the adjacent C=C bond, followed by silole ring expansion to give silicon analogues of cyclohexadienones.

Access to B=S and B=Se double bonds via sulfur and selenium insertion into a B-H bond and hydrogen migration.

Stable compounds with a boron-chalcogen (S or Se) valence double bond have been prepared via sequences involving insertion of the chalcogen into a B-H bond and subsequent hydrogen migration. X-ray diffraction studies and density functional theory calculations on the resulting compounds provide convincing evidence for the boron-chalcogen multiple bonding.