ABSTRACT
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 η5-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. In this context, the use of mono-cyclopentadienyl titanocene (mono-Cp'Ti) catalysts and mono-cyclopentadienyl rare-earth metal (mono-Cp'RE) metallocene catalysts for the syndiospecific polymerization of styrene is discussed. The effects of the mono-cyclopentadienyl ligand structure, cationic active metal types, and cocatalysts on the activity and syndiospecificity of mono-Cp' metallocene catalysts are briefly surveyed.
ABSTRACT
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. Treatment of 2 with 2 equiv. of chlorobis(isopropyl)phosphine afforded chloro-substituted silafluorene 4. The reaction of 8 which has a SiH-SiBr fragment with IiPr2Me2 (IiPr2: 2,5-diisopropyl-3,4-dimethylimidazol-1-ylidene) led to the formation of an Si-Si bond cleavage product, NHC-stabilized silacyclopentadienylidene 9.
ABSTRACT
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. In particular, complex 1 can be recycled and recovered from the reaction media after the catalytic reactions. Furthermore, it was found that complex 3 could catalyze the polymerization of styrene to yield atactic polystyrenes with low molecular weights. To the best of our knowledge, complex 1 represents the first rare-earth complex that can be recovered after catalytic reactions.
ABSTRACT
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.
ABSTRACT
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.
Subject(s)
Amines/chemistry , Organometallic Compounds/chemistry , Silanes/chemistry , Ytterbium/chemistry , Catalysis , Crystallography, X-Ray , Hydrogenation , Models, Molecular , Molecular StructureABSTRACT
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. DFT calculations indicate the 4,5-C-aryl substituents have significant contributions to the LUMOs.
Subject(s)
Aza Compounds/chemical synthesis , Boranes/chemical synthesis , Boron Compounds/chemistry , Luminescence , Tin Compounds/chemistry , Aza Compounds/chemistry , Boranes/chemistry , Models, Molecular , Molecular Structure , Quantum TheoryABSTRACT
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.
ABSTRACT
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.
