168704-96-9Relevant articles and documents
Polymerization of MMA by oscillating zirconocene catalysts, diastereomeric zirconocene mixtures, and diastereospecific metallocene pairs
Ning, Yalan,Cooney, Megan J.,Chen, Eugene Y.-X.
, p. 6263 - 6270 (2005)
Characteristics of methyl methacrylate (MMA) polymerization using oscillating zirconocene catalysts, (2-Ph-Ind)2ZrX2 (X = Cl, 1; X = Me, 2), mixtures of rac- and meso-zirconocene diastereomers, (SBI)ZrMe2 [3, SBI = Me2Si(Ind)2] and (EBI)ZrMe2 [4, EBI = C2H4(Ind)2], as well as diastereospecific metallocene pairs, rac-4/Cp2ZrMe 2 (5) and rac-4/CGCTiMe2 [6, CGC = Me 2Si(Me4C5)(t-BuN)], are reported. MMA polymerization using the chloride catalyst precursor 1 activated with a large excess of the modified methyl aluminoxane is sluggish, uncontrolled, and produces atactic PMMA. On the other hand, the polymerization by a 2/1 ratio of 2/B(C6F5)3 or 2/Ph3CB(C 6F5)4 is controlled and produces syndiotactic PMMA. Mixtures of diastereomeric ansa-zirconocenes 3 or 4 containing various rac/meso ratios, when activated with B(C6F5)3, yield bimodal PMMA; this behavior is attributed to the meso-diastereomer that, in its pure form, affords bimodal, syndio-rich atactic PMMA. For MMA polymerization using diastereospecific metallocene pairs, rac-4/5 and rac-4/6, the isospecific catalyst site dominates the polymerization events under the conditions employed in this study, and the aspecific and syndiospecific sites are largely nonproductive, thereby forming only highly isotactic PMMA.
Elusive silane-alane complex [Si-H...Al]: Isolation, characterization, and multifaceted frustrated Lewis pair type catalysis
Chen, Jiawei,Chen, Eugene Y.-X.
, p. 6842 - 6846 (2015)
Abstract The super acidity of the unsolvated Al(C6F5)3 enabled isolation of the elusive silane-alane complex [Si-H...Al], which was structurally characterized by spectroscopic and X-ray diffraction methods. The Janus-like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated-Lewis-pair-type catalysis. When compared with the silane-borane system, the silane-alane system offers unique features or clear advantages in the four types of catalytic transformations examined in this study, including: ligand redistribution of tertiary silanes into secondary and quaternary silanes, polymerization of conjugated polar alkenes, hydrosilylation of unactivated alkenes, and hydrodefluorination of fluoroalkanes. Al does it all: The elusive silane-alane complex [Si-H...Al] was isolated and structurally characterized by spectroscopic and X-ray diffraction methods. The Janus-like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated-Lewis-pair-type catalysis. Its use in four different reactions is described.
Round-Trip Oxidative Addition, Ligand Metathesis, and Reductive Elimination in a PIII/PVSynthetic Cycle
Lim, Soohyun,Radosevich, Alexander T.
supporting information, p. 16188 - 16193 (2020/10/26)
A synthetic cycle for aryl C-F substitution comprising oxidative addition, ligand metathesis, and reductive elimination at a Cs-symmetric phosphorus triamide (1, P{N[o-NMe-C6H4]2}) is reported. Reaction of 1 with perfluoroarenes (ArF-F) results in C-F oxidative addition, yielding fluorophosphoranes 1·[F][ArF]. The P-fluoro substituent is exchanged for hydride by treatment with DIBAL-H, generating hydridophosphoranes 1·[H][ArF]. Heating of 1·[H][ArF] regenerates 1 by C-H reductive elimination of ArF-H, where experimental and computational studies establish a concerted but highly asynchronous mechanism. The results provide well-characterized examples of the full triad of elementary mechanistic aryl C-X substitution steps at a single main-group site.
