Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

The industry-scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me_nSi₂Cl_6-n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono- and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride.     

Neodymium Catalyst for the Polymerization of Dienes and Polar Vinyl Monomers

Ziegler–Natta catalysts have played a major role in industry for the polymerization of dienes and vinyl monomers. However, due to the deactivation of the catalyst, this system fails to polymerize polar vinyl monomers such as vinyl acetate, methyl methacrylate, and methyl acrylate. Herein, a catalytic system composed of NdCl₃⋅3TEP/TIBA is reported, which promotes a quasi‐living polymerization of dienes and is also active for the homopolymerization of polar vinyl monomers. Additionally, this catalytic system generates polymyrcene‐b‐polyisoprene and poly(myrcene)‐b‐poly(methyl methacrylate) diblock copolymers by sequential monomer addition. To encourage the replacement of petroleum‐based polymers by environmentally benign biobased polymers, polymerization of β‐myrcene is demonstrated with a catalytic activity of ≈106 kg polymer mol Nd⁻¹ h⁻¹.     

Polymerization catalysis with transition metal amidinate and related complexes

Applications of transition metal amidinate [RC(NR′)₂], guanidinate and amidopyridine complexes to olefin coordination polymerization are reviewed. In addition, the use of complexes, featuring closely related ligands, such as phosphonamide or iminophosphonamide [R₂P(NR′)₂], in olefin polymerization is highlighted. Some of these complexes have also been investigated in the stereoregular polymerization of styrene and conjugated dienes, whereas more recent work has focused on controlled ring-opening polymerization of lactones and lactides.     

B(C6F5)3‐Catalyzed Transfer Hydrogenation of Imines and Related Heteroarenes Using Cyclohexa‐1,4‐dienes as a Dihydrogen Source

The strong boron Lewis acid tris(pentafluorophenyl)borane, B(C₆F₅)₃, is shown to abstract a hydride from suitably donor‐substituted cyclohexa‐1,4‐dienes, eventually releasing dihydrogen. This process is coupled with the FLP‐type (FLP=frustrated Lewis pair) hydrogenation of imines and nitrogen‐containing heteroarenes that are catalyzed by the same Lewis acid. The net reaction is a B(C₆F₅)₃‐catalyzed, i.e., transition‐metal‐free, transfer hydrogenation using easy‐to‐access cyclohexa‐1,4‐dienes as reducing agents. Competing reaction pathways with or without the involvement of free dihydrogen are discussed.     

Nitroxide‐Mediated Polymerization of Bio‐Based Farnesene with a Functionalized Methacrylate

Farnesene (Far) is a bio‐based terpene monomer that is similar in structure to commercially used dienes like butadiene and isoprene. Nitroxide‐mediated polymerization (NMP) is adept for the polymerization of dienes, but not particularly effective at controlling the polymerization of methacrylates using commercial nitroxides. In this study, Far is statistically copolymerized with a functional methacrylate, glycidyl methacrylate (GMA), by NMP using N‐succinimidyl modified commercial BlocBuilder (NHS‐BB) initiator. Reactivity ratios are determined to be r _Far = 0.54 ± 0.04 and r _GMA = 0.24 ± 0.02. The ability of the poly(Far‐stat‐GMA) chains to reinitiate for chain extension with styrene showed a clear shift in molecular weight and monomodal distribution. Copolymerizations using a new alkoxyamine, Dispolreg 007 (D7), is explored as it is shown to homopolymerize methacrylates, but not yet reported for statistical copolymerizations. Bimodal molecular weight distributions are observed when an equimolar ratio of Far and GMA is copolymerized with D7 due to slow decomposition of the initiator, but chain ends are active as shown by successful chain extension with styrene. Both NHS‐BB and D7 initiators are used to synthesize poly[Far‐b‐(GMA‐stat‐Far)] and poly(Far‐b‐GMA) diblock copolymers. While the NHS‐BB initiated polymer chains have lower dispersity, D7 exhibits more linear polymerization kinetics and maintains more active chain ends.     

Polymerization of 1‐Phosphaisoprene: Synthesis and Characterization of a Chemically Functional Phosphorus Version of Natural Rubber

Macromolecules derived from 1,3‐dienes, such as polyisoprene (or natural rubber), are of considerable importance in polymer science. Given the parallels between P=C and C=C bonds, the prospect of polymerizing P‐containing 1,3‐dienes, such as 1‐phosphaisoprene, is intriguing due to the unique chemical functionality imparted by the heavier element combined with their structural relationship to natural rubber. Herein, we report the synthesis, characterization and coordination chemistry of the first polymers derived from Mes*P=CR−CH=CH₂ (Mes*=2,4,6‐t‐Bu₃C₆H₂; R=H, Me). In the case of 1‐phosphaisoprene (R=Me), the monomer is isolable and its anionic polymerization affords a polymer that retains P=C bonds in its microstructure. The chemical functionality of these novel materials is demonstrated by forming the macromolecular gold(I) complex where the P=C bond is retained for further chemical elaboration.     

Tetradentate schiff base ligand/MCln initiating systems for the controlled cationic polymerization of isobutyl vinyl ether: Effects of the ligand framework

We investigated the cationic polymerization of vinyl ethers using metal complex catalysts with salen and salphen ligands. Metal complexes were generated in situ from the reaction of a ligand and a metal chloride. The choice of a ligand and a central metal was crucial for tuning the catalyst function such as catalytic activity and controllability of the polymerization. Among metal chlorides employed, ZrCl₄ was the most efficient for controlled polymerization. Cationic polymerization of isobutyl vinyl ether (IBVE) proceeded using the salen and salphen‐type ligand/ZrCl₄ initiating systems, yielding polymers with predetermined molecular weights and narrow molecular weight distributions. Importantly, the structural effects of the complex catalysts were responsible for the polymerization behavior. For example, the polymerization using the salen‐type ligand/ZrCl₄ system was much slower than that using the salphen‐type ligand/ZrCl₄ system. In addition, the polymerization of IBVE using the salen‐type ligand/FeCl₃ system proceeded in a controlled manner, which was in contrast to uncontrolled polymerization using the salphen‐type ligand/FeCl₃ system. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 989–996     

Ultrafast phosphazene‐promoted controlled anionic polymerization of styrenic monomers

The anionic polymerization of styrenic monomers with phosphazene bases as promoters, utilizing “seeding” technique in a nonpolar solvent and at room temperature was studied. In all experiments, the phosphazene base (t‐BuP₄, t‐BuP₂, and t‐BuP₁) was added in an equimolar amount to the organolithium initiator after the formation of oligomers (2 min) by conventional anionic polymerization. When t‐BuP₄ was used, the polymerization of styrene and 4‐methylstyrene was extremely fast (100 % conversion within 5 min) and the final homopolymers exhibited narrow molecular weight distribution and controlled molecular characteristics. Likewise, when weaker bases were employed, the polymerization was also controlled but showing slower reaction rate. To examine the “livingness” of this system, block copolymers were synthesized by sequential monomer addition. Further studies were conducted in order to extend this novel method to the anionic polymerization of dienes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 456–464     

Synthese funktionell substituierter Disilane auf der Basis von Triflatderivaten

Synthesis of Functional Substituted Disilanes on the Basis of Triflate Derivatives Functional substituted disilanes are prepared by reaction of phenylated disilanes with trifuloromethanesulfonic acid. Reduction of the triflate derivatives with LiAlH₄ leads to Si? H substituted disilanes. The chlorinated disilanes are obtained by reaction of the triflate derivatives with Et₃NHCl. Chloro-hydrogen substituted disilanes are prepared by combination of both reaction types. The preparation of these compounds in a high purity is difficult on other ways.     

Recent advances in the field of diolefin polymerization with transition metal catalysts

Recent advances in the field of catalysis for 1,3-diene polymerization and in the interpretation of the polymerization mechanism are examined. Catalysts prepared from methylaluminoxanes and soluble transition metal compounds are in general more active than the analogous systems prepared from AlR₃. With some catalysts, however, (e.g. lanthanide systems) a high activity is obtained only when transition metal compounds containing preformed metal-carbon bonds are used. Methylaluminoxanes affect also the stereospecificity of the polymerization. Active and stereospecific systems are obtained from monocyclopentadienyl derivatives of Ti and aluminoxanes. Recent views on the factors that determine stereospecificity are examined. Schemes are presented for the formation of iso- or syndiotactic polymers, with 1,2, cis-1,4 or trans-1,4 structure, from various dienes.     

Transition Metal Compounds in Combination with Alkylaluminoxanes as Catalysts for Olefin and Diene Polymerization

Catalytic systems based on Zr, Co, Ti, V, and Nd in combination with –(–RAlO–)– _n alkylaluminoxanes, where R = Me or iso-Bu, were used for the polymerization of olefins and dienes. The structure of methylaluminoxane (MAO) was studied with the use of theoretical calculations and experimentally by vibrational spectroscopy. It was found that only cis and trans conformations of linear MAO oligomers actually occurred at the active centers of olefin polymerization. The stereospecificity of catalytic systems for diene polymerization depends on the nature of the substituent at aluminum, as well as on the nature of the transition metal and its ligand environment.     

Formation of Tri‐ and Tetranuclear Titanacycles through Decamethyltitanocene‐Mediated Intermolecular C–C Coupling of Dinitriles

The reactions of [Cp*₂Ti(η²‐Me₃SiC₂SiMe₃)] (Cp*=η⁵‐pentamethylcyclopentadienyl) with various dicyano compounds were investigated. Nitrile–nitrile C? C couplings result in multinuclear complexes owing to the bifunctionality of the substrates. Applying 1,3‐ or 1,4‐dicyanobenzene led to tri‐ and tetranuclear complexes of the rare 1‐metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes. These are potential catalysts and were tested in the ring‐opening polymerization of ε‐caprolactone. The reaction with adiponitrile as alkyl dinitrile afforded a trinuclear 1‐metalla‐2,5‐diaza‐cyclopent‐3‐ene through additional protonation of the nitrogen atoms. The structure and bonding of the products were investigated by X‐ray crystallography and DFT analysis to understand the molecular organization in the macrocycles.     

A General Catalytic Hydroamidation of 1,3‐Dienes: Atom‐Efficient Synthesis of N‐Allyl Heterocycles,Amides, and Sulfonamides

Transition‐metal‐catalyzed hydroamination reactions are sustainable and atom‐economical C N bond‐forming processes. Although remarkable progress has been made in the inter‐ and intramolecular amination of olefins and 1,3‐dienes, related intermolecular reactions of amides are still much less known. Control of the regioselectivity without analogous telomerization is the particular challenge in the catalytic hydroamidation of alkenes and 1,3‐dienes. Herein, we report a general protocol for the hydroamidation of electron‐deficient N‐heterocyclic amides and sulfonamides with 1,3‐dienes and vinyl pyridines in the presence of a catalyst derived from [{Pd(π‐cinnamyl)Cl}₂] and ligand L7 or L10 . The reactions proceeded in good to excellent yield with high regioselectivity. The practical utility of our method is demonstrated by the hydroamidation of functionalized biologically active substrates. The high regioselectivity for linear amide products makes the procedure useful for the synthesis of a variety of allylic amides.     

A General Catalytic Hydroamidation of 1,3‐Dienes: Atom‐Efficient Synthesis of N‐Allyl Heterocycles,Amides, and Sulfonamides

Transition‐metal‐catalyzed hydroamination reactions are sustainable and atom‐economical C? N bond‐forming processes. Although remarkable progress has been made in the inter‐ and intramolecular amination of olefins and 1,3‐dienes, related intermolecular reactions of amides are still much less known. Control of the regioselectivity without analogous telomerization is the particular challenge in the catalytic hydroamidation of alkenes and 1,3‐dienes. Herein, we report a general protocol for the hydroamidation of electron‐deficient N‐heterocyclic amides and sulfonamides with 1,3‐dienes and vinyl pyridines in the presence of a catalyst derived from [{Pd(π‐cinnamyl)Cl}₂] and ligand L7 or L10 . The reactions proceeded in good to excellent yield with high regioselectivity. The practical utility of our method is demonstrated by the hydroamidation of functionalized biologically active substrates. The high regioselectivity for linear amide products makes the procedure useful for the synthesis of a variety of allylic amides.     

Direct Evidence for Intermolecular Oxidative Addition of σ(Si?Si) Bonds to Gold

Oxidative addition plays a major role in transition‐metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl₃, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative ³¹P and ²⁹Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si Si) bonds to gold and open promising perspectives for the development of new gold‐catalyzed redox transformations.     

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

Oxidative addition plays a major role in transition‐metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl₃, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative ³¹P and ²⁹Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si? Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si? Si) bonds to gold and open promising perspectives for the development of new gold‐catalyzed redox transformations.     

Spiro‐Bicyclic Bisborane Catalysts for Metal‐Free Chemoselective and Enantioselective Hydrogenation of Quinolines

A new series of spiro‐bicyclic bisborane catalysts has been prepared by means of hydroboration reactions of C₂‐symmetric spiro‐bicyclic dienes with HB(C₆F₅)₂ and HB(p‐C₆F₄H)₂. When used for hydrogenation of quinolines, these catalysts give excellent yields and enantiomeric excesses, and show turnover numbers of up to 460. The most attractive feature of these metal‐free hydrogenation reactions was the broad functional‐group tolerance, making this method complementary to existing methods for quinoline hydrogenation.     

Me3Si−SiMe2[oCON(iPr)2−C6H4]: An Unsymmetrical Disilane Reagent for Regio‐ and Stereoselective Bis‐Silylation of Alkynes

The air‐stable unsymmetrical disilane Me₃Si?SiMe₂[oCON(iPr)₂C₆H₄] has been developed for bis‐silylation of alkynes. This reagent tolerates a range of functional groups, providing Z‐vinyl disilanes in high yields. It is proposed that the phenyl‐ring‐tethered amide group directs oxidative addition of Pd⁰ into the Si?Si bond, which might facilitate formation of a six‐membered Pd cycle, generating products with good to excellent regioselectivity.     

Metal‐free anionic polymerization of methyl methacrylate in tetrahydrofuran using bis(triphenylphosphoranilydene)ammonium (PNP+) as counterion

Bis(triphenylphosphoranilydene)ammonium (PNP⁺) triphenylmethanide (Ph₃C^–) is a new metal‐free initiator for the living polymerization of methyl methacrylate (MMA). The kinetics of the polymerization strongly depend on the metal counterion of the initiator precursor. When the initiator is made from the metathesis reaction of Ph₃CK and PNPCl, the polymerization follows first‐order kinetics up to 0°C with half‐lives below 0.1 s. The propagation rate constants are much higher than those obtained with tetraphenylphosphonium (TPP⁺) cations, indicating a smaller fraction of dormant ylides. When the initiator is synthesized from Ph₃CLi, polymerization proceeds much slower and molecular weight distributions of the obtained polymers are broadened indicating that the active species are mostly lithium enolates in this case.     

Ring‐opening polymerization of lactides initiated by magnesium and zinc complexes based on NNO‐tridentate ketiminate ligands: Activity and stereoselectivity studies

Four metal benzylalkoxides, [L₂M₂(μ‐OBn)₂] (M = Mg or Zn), based on NNO‐tridentate ketiminate ligands are synthesized and characterized. X‐ray crystal structural studies of [(L¹)₂Mg₂(μ‐OBn)₂] ( 1a ) and [(L¹)₂Zn₂(μ‐OBn)₂] ( 1b ) (L¹‐H = (Z)‐4‐((2‐(dimethylamino)ethylamino)(phenyl)methylene)‐3‐methyl‐1‐phenyl‐pyrazol‐5‐one) reveal that both complexes 1a and 1b are dinuclear species whereas the geometry around the metal center is penta‐coordinated bridging through the benzylalkoxy oxygen atoms in the solid structure. The activities and stereoselectivities of these four complexes toward the ring‐opening polymerization of L ‐lactide and rac‐lactide are investigated. Polymerization of L ‐lactide initiated by these four metal benzyloxides proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. The kinetic studies for the polymerization of L ‐lactide with compound 1a show first order in both compound 1a and lactide concentrations with the polymerization rate constant, k, of 6.94 M/min. Besides, experimental results demonstrate that among these metal benzylalkoxides, complex 1a exhibits the highest stereoselectivity with a Pr up to 87% and complex 1b possesses the highest activity indicating that the terminal group of NNO‐tridentate ketimine ligands exerts a significant influence on both the reactivity and stereoselectivity of these complexes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2318–2329, 2009