A free boratriptycene-type Lewis superacid

An exceptionally strong ferrocene-containing, cationic boratriptycene-type Lewis acid is stabilized by a weak Fe⋯B through-space interaction.

Monomodal Ultrahigh-Molar-Mass Polycarbonate Homopolymers and Diblock Copolymers by Anionic Copolymerization of Epoxides with CO2

Whatever the chemistry used for the synthesis of aliphatic polycarbonates, in particular, those of high molar mass, the adventitious presence of water leads to bimodal GPC traces and affords polycarbonate samples of uncontrolled and unpredictable molar masses. It appears that among all reagents used in the copolymerization of CO₂ and epoxides, CO₂ is the most difficult one to dry. To address this issue, triisobutylaluminum (TiBA) was employed in this work to dry CO₂ through a bubbling method; its drying capability was investigated in the context of the copolymerization of CO₂ with epoxides initiated by onium chloride in the presence of triethylborane (TEB). It was then compared to the efficiency of other already reported drying agents such as phosphorus pentoxide, molecular sieves and commercially available CO₂ purifiers. With TiBA-dried CO₂, its copolymerizations respectively with propylene oxide (PO) and cyclohexene oxide (CHO) could be successfully achieved in a wide range of degrees of polymerization (DP), with the value of DP as high as 16000. Diblock copolymers poly(propylene carbonate-b-cyclohexene carbonate) (PPC-b-PCHC) could also be prepared through sequential addition of epoxide monomers. The polycarbonates obtained under the conditions were all well-defined as characterized by NMR, GPC, triple detector-GPC, and differential scanning calorimetry (DSC).

Chemoselective deoxygenation of ether-substituted alcohols and carbonyl compounds by B(C6F5)3-catalyzed reduction with (HMe2SiCH2)2

B(C6F5)3-catalyzed deoxygenation of ether-substituted alcohols and carbonyl compounds has been developed using (HMe2SiCH2)2 as the reductant. This unique reagent shows distinct superiority over traditional one silicon-centered hydrosilanes, giving the corresponding alkanes in high yields with good tolerance of ethers, aryl halides and alkenes. The control experiments suggest that (HMe2SiCH2)2 might facilitate the approach in an intramolecular Si/O activation manner.

A zwitterionic aluminabenzene–alkylzirconium complex having half-zirconocene structure: synthesis and application for additive-free ethylene polymerization

An aluminabenzene–alkylzirconium complex having a half-zirconocene structure was synthesized.

Discovering complexes containing a metal–metal quintuple bond: from theory to practice

Recent advances in quintuple bonding are highlighted based on theoretical predictions and experimental achievements.

The potassium hydride mediated trimerization of imines

A novel reaction, the potassium hydride mediated synthesis of fulvenes, is described. The synthesis utilizes N-aryl imines as an inexpensive starting material affording novel substituted aminofulvenes. It is proposed that the presence of the metalated enamine as well as the imine (ratio 2 : 1) leads to the formation of an initial dimerization and a transient trimerization product, which cyclizes, giving rise to the aminofulvene.

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Bis(1-methylethenyl-cyclopentadienyl)zirconium dichloride (7a) was prepared by a fulvene route. Photolysis at 0 degrees C with Pyrex-filtered UV light resulted in a rapid and complete intramolecular [2+2]cycloaddition reaction to yield the corresponding cyclobutylene-bridged ansa-zirconocene dichloride isomer (8a). This is one of the rare examples of an organic functional group chemistry that leads to carbon-carbon coupling at the framework of an intact sensitive group 4 bent metallocene complex. More sterically hindered open metallocenes that bear bulky isopropyl or tert-butyl substituents at their Cp rings in addition to the active 1-methylethenyl functional group undergo the photochemical ansa-metallocene ring closure reaction equally facile. The metallocene systems used and obtained in this study have served as transition metal components for the generation of active metallocene propene polymerization catalysts.

A remarkable inversion of structure–activity dependence on imido N-substituents with varying co-ligand topology and the synthesis of a new borate-free zwitterionic polymerisation catalyst

Ethylene polymerisation productivities of tris(pyrazolyl)methane-supported catalysts [Ti(NR){HC(Me2pz)3}Cl2] show a dramatically different dependence on the imido R-group compared to those of their TACN analogues, attributed to differences in fac-N3 donor topology; when treated with AliBu3, the zwitterionic tris(pyrazolyl)methide compound [Ti(N-2-C6H4tBu){C(Me2pz)3}Cl(THF)] also acts as a highly active, single site catalyst (TACN = 1,4,7-trimethyltriazacyclononane).

Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions

Tris(pentafluorophenyl)borane is best known for its role as an excellent activator component in homogeneous Ziegler-Natta chemistry. However, the special properties of B(C6F5)3 have made this strong boron Lewis acid an increasingly used catalyst or stoichiometric reagent in organic and organometallic chemistry. This includes catalytic hydrometallation reactions, alkylations and catalyzed aldol-type reactions. B(C6F5)3 catalyzes tautomerizations and can sometimes stabilize less favoured tautomeric forms by adduct formation. It induces some rather unusual reactions of early metal acetylide complexes and can help in stabilizing uncommon coordination geometries of carbon. The growing number of such examples indicates an increasing application potential of the useful Lewis acid B(C6F5)3 aside from its established role in olefin polymerization catalysis.

Formation of a bifunctional zirconocene complex that favours intramolecular –B(C6F5)2addition to a Cp ring over σ-ligand abstraction

The diphenyl-ansa-zirconocene complex 2 adds HB(C6F5)2 at the C=C double bond of its pendent Cp-allyl functional group to yield 3. During 3 days at room temperature the -B(C6F5)2 group takes part in an electrophilic substitution reaction at the adjacent Cp-ring to form 5 with formation of one equivalent of benzene. Complex 5 was characterized by X-ray diffraction.