Hydroboration,haloboration and phenylboration polymerizations

A polyaddition between diene and monoalkylborane produced a polymer consisting of C-B bonds in the main chain. The resulting organoboron polymers can be used as a novel type of reactive polymers. On the other hand, hydroboration polymerization of dicyano compounds produced air-stable poly(cyclodiborazane)s having B-N four-membered rings via dimerization of iminoborane species. Poly(organoboron halide)s were prepared either by haloboration polymerization between diynes and boron tribromide or by hydroboration polymerization of dienes with monobromoborane. Furthermore, phenylboration polymerization of diynes or diisocyanates gave new organoboron mainchain polymers.     

The electrochemical behaviour and electron spin resonance spectroscopy of some heterocyclic organoboron compounds

Some heterocyclic organoboron compounds derived from the reaction of 1,2-disubstituted benzene with m-nitrophenyl boronic acid have been investigated electrochemically. All the compounds exhibit two irreversible reduction waves. Controlled-potential electrolysis at the plateau of the second wave leads to decomposition and formation of nitrophenyl boronic acid radical anions. Electron spin resonance spectroscopy has been carried out to investigate the nature of these radical anions.     

Generation of cationic indenyl silylamide gadolinium and scandium complexes [(Ind)Ln{N(SiMe3)2}]+[B(C6F5)4]- and their reactivity for 1,3-butadiene polymerization

Highly efficient cis-polymerization of butadiene was achieved by using new bis(indenyl) silylamide rare earth complexes with the cooperation of both a borate salt and i-Bu3Al; treatment of these complexes with organoboron compounds unexpectedly yielded new cationic mono(indenyl) amido species relevant to polymerization.     

A Chemoselective Polarity-Mismatched Photocatalytic C(sp3)−C(sp2) Cross-Coupling Enabled by Synergistic Boron Activation**

We report the development of a C(sp³)−C(sp²) coupling reaction using styrene boronic acids and redox-active esters under photoredox catalysis. The reaction proceeds through an unusual polarity-mismatched radical addition mechanism that is orthogonal to established processes. Synergistic activation of the radical precursor and organoboron are critical mechanistic events. Activation of an N-hydroxyphthalimide (NHPI) ester by coordination to boron enables electron transfer, with decomposition leading to a nucleofuge rebound, activating the organoboron to radical addition. The unique mechanism enables chemoselective coupling of styrene boronic acids in the presence of other alkene radical acceptors. The scope and limitations of the reaction, and a detailed mechanistic investigation are presented.     

Versatile Reactions of Organoboron Polymers Prepared by Hydroboration Polymerization

Hydroboration polymerization of dienes and thexylborane produces organoboron polymers, which can be regarded as a polymer homolog of trialkylboranes. In other words, the organoboron polymers obtained can be expected to be a novel type of reactive polymer. The present paper describes versatile reactions of organoboron polymers prepared by hydroboration polymerization. For example, reactions with carbon monoxide or with KCN were followed by oxidative treatment to produce the corresponding poly(alcohol)s or poly(ketone)s, respectively. The organoboron polymers were also reacted with bromopyridyl anion or with furyl anion to form cyano- or hydroxyl-containing polymers via ring-opening of pyridine or furan, respectively. Reductive treatment of the organoboron polymer gave the corresponding polymer after reductive cleavage of carbon—boron bonds.     

Organoboron chemistry comes to light: Recent advances in photoinduced synthetic approaches to organoboron compounds

Photoinduced synthetic approaches to organoboron compounds have attracted significant attention in the recent years. Photochemical activation of organic molecules enables generation of reactive intermediates from a variety of precursors, resulting in borylation methods with improved and broader substrate scopes. The review summarizes recent developments in the area of photoinduced reactions of organoboron compounds with an emphasis on borylation of haloarenes, amine derivatives, and redox-active esters of carboxylic acids, as well as photoinduced rearrangements of organoboron compounds and photoinduced synthesis of organoboron compounds from alkenes and alkynes.     

1,4-Phenylene-bis-((1-methyl-1H-pyrazol-5-yl)borinic 8-oxyquinolinate) as a photoredox catalyst in the atom transfer radical addition of iodoperfluoroalkanes to alkenyl groups bearing organoboron compounds

The key photocatalytic properties of a transition-metal-free heteroleptic complex derived from 1,4-phenyldiboronic acid were evaluated. This compound was utilized in the atom transfer radical addition of iodoperfluoroalkanes to a series of alkenyl group bearing organoboron compounds. The products of these reactions retained the BC bond, and Suzuki-Miyaura coupling of one product gave biphenyl derivatives. The X-ray analysis of one of the obtained perfluoroalkylated boronic acids revealed the presence of open star-shaped channels.     

Controlled Radical Polymerization

Various methods which lead to the control of molecular weight and polydispersities, and which allow for the preparation of block copolymers by radical polymerization are discussed. Thermal polymerizationof styrenes in the presence of stable radicals, polymerization of vinyl acetate and methyl methacrylate in the presence of chromium complexed by macrocyclic ligands polymerization of vinyl acetate initiated by organoaluminum compounds complexed by dipyridyl and activated by stable radicals, as well as in the presence of phosphites, are described in detail.     

Control of polymer structure by a chain-transfer reaction in the radical polymerization of acrylamide by β-mercaptopropionic acid and 1,2,6-hexanetriol trithioglycolate

 Star polymer synthesis by radical polymerization of acrylamide (AM) in the presence of thiol compounds was investigated. When 1,2,6-hexanetriol trithioglycolate (HTTG), as a trithiol compound, was used the molecular weights of the polymers were about 3 times those obtained in the presence of β-mercaptopropionic acid, as a monothiol compound, at the same concentration of thiol compounds in the feed. From viscosity measurements of the polymers and analysis of the ¹H NMR spectra of the polymers, we presumed that a star-shaped polymer of AM could be synthesized by radical polymerization in the presence of HTTG. Received: 9 June 2000 Accepted: 11 January 2001     

A General Approach to Deboronative Radical Chain Reactions with Pinacol Alkylboronic Esters

The generation of carbon‐centered radicals from air‐sensitive organoboron compounds through nucleohomolytic substitution at boron is a general method to generate non‐functionalized and functionalized radicals. Due to their reduced Lewis acidity, alkylboronic pinacol esters are not suitable substrates. We report their in situ conversion into alkylboronic catechol esters by boron‐transesterification with a substoichiometric amount of catechol methyl borate combined with an array of radical chain processes. This simple one‐pot radical‐chain deboronative method enables the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds through C?C bond formation using sulfonyl radical traps. The power of combining radical and classical boron chemistry is illustrated with a modular 5‐membered ring formation using a combination of three‐component coupling and protodeboronative cyclization.     

“Dormant” inhibitors of urethane type as controllers of temperature modes of styrene polymerization

Urethanes based on a series of monoisocyanates and phenolic inhibitors of styrene radical polymerization, which release the initial phenolic inhibitor at elevated temperatures, were prepared and characterized. Some of these compounds meet the requirements to “dormant” inhibitors: they sharply decelerate thermally initiated high-temperature polymerization of styrene and do not noticeably affect the rate of low-temperature polymerization in the presence of an inhibiting substance. The possibility of preventing uncontrollable emergency situations by adding these compounds to the initial monomer was confirmed experimentally.     

Macromonomers as well-defined building blocks in macromolecular engineering

The present work compares the efficiency of different polymerization methods to design well-defined comb-shaped structures based on macro monomers. Anionic polymerization remains the method of choice and allows the control of polymerization degree of the main chain and the length of the grafts. The presence of an active chain end on the backbone enabled the synthesis of a new type of hyperbranched polymers by reaction with appropriate low molar multifunctional compounds. Free radical polymerization is less efficient for the controlled homopolymerization of macromonomers but less sensitive to the presence of impurities. It requires in most cases long fractionation procedures to access well defined comb-shaped fractions characterized by high molar masses. The controlled free radical polymerization constitutes an interesting alternative. The homopolymerization of macromonomers with late transition metal catalysts was also examined and comb-shaped polymers characterized by a syndiotactic backbone and atactic grafts could be obtained.     

Radical Polymerization of Methyl Methacrylate in the Presence of Aromatic Nitroso Compounds

Features of radical polymerization of methyl methacrylate in the presence of various aromatic nitroso compounds (nitrosobenzene, nitrosodurene, 2,4,6-tribromonitrosobenzene) as potential sources of stable nitroxyl radicals controlling the chain propagation were studied.     

Studies of the polymerization of diallyl compounds. XI. Polymerization of styrene in the presence of diallyl compounds

Radical polymerization of styrene in the presence of various diallyl compounds was carried out at 60°C, with the use of 2,2′-azobisisobutyronitrile as an initiator. The chain transfer constant C_s of the styryl radical to diallyl compounds was determined graphically by solving the Mayo equation. The C_s values of diallyl esters are quite small compared to those of diallyl acetals. The polymerization mechanism of styrene in the presence of diallyl compounds was also discussed in connection with the results obtained previously.     

Radical CH Alkylation of BODIPY Dyes Using Potassium Trifluoroborates or Boronic Acids

A one‐step synthetic procedure for the radical C?H alkylation of BODIPY dyes has been developed. This new reaction generates alkyl radicals through the oxidation of boronic acids or potassium trifluoroborates and allows the synthesis of mono‐, di‐, tri‐, and tetraalkylated fluorophores in a good to excellent yield for a broad range of organoboron compounds. Using this protocol, multiple bulky alkyl groups can be introduced onto the BODIPY core thus creating solid‐state emissive BODIPY dyes.     

Synthesis of phenanthroimidazole-based four coordinate organoboron compounds

The synthesis of N,C-coordinated organoboron compounds (B1-B4) based on phenanthroimidazole described. All the compounds were characterized by various spectroscopic techniques. Single crystal X-ray diffraction analysis of the compounds B1 and B3 revealed that the vicinity around the boron atom adopts tetrahedral geometry. Except compound B4, other organoboron compounds (B1-B3) does not show solvatochromism. All our newly synthesized organoboron compounds exhibited moderate to good solution state quantum yields (0.07–0.88) and moderate solid state quantum yields.     

Polymer Inclusion Compounds by Polymerization of Monomers in β-Cyclodextrin Matrix in DMF Solution

The investigations of the synthesis of polyrotaxanes by the radical polymerization of monomers (vinylidene chloride, methyl acrylate, styrene, and methacrylonitrile) in DMF in the presence of β-cyclodextrin have been carried out. The possibility of formation β-cyclodextrin inclusion compounds with some vinyl monomers or some other organic substances in DMF solution has been established. We assume that the inclusion in presence of the solvent is related to the unusual phenomenon of β-cyclodextrin crystallization in hot DMF solutions. The polymerization of vinyl monomers in DMF solution at increased temperatures in the presence of β-cyclodextrin leads to compounds containing a great amount of cyclic compounds (up to 80%). Similar results have been obtained for monomers introduced as previously prepared adducts with β-cyclodextrin. Stable compounds of polymer and β-cyclodextrin have been obtained in the case of vinylidene chloride. The lack of carbohydrate moieties in the product obtained by polymerization of vinylidene chloride in the presence of linear dextrin suggest the inclusion character of the linkage between polymer and β-cyclodextrin molecules. The structure of a topological compound of polyrotaxane type is most feasible after dehydrochlorination.     

Polyhomologation: the living polymerization of ylides

The polymerization of dimethylsufoxonium methylide to produce linear polymethylene polymers is described. The reaction is catalyzed/initiated by trialkylboranes and gives organoboron star polymers as the primary product. The reaction is a living polymerization, providing control over molecular weight and functionality at the polymer chain ends. A variety of novel polymethylene architectures are available by this methodology.     

Quinone transfer radical polymerization of styrene: Synthesis of the actual initiator

ortho‐Quinones, such as phenanthrenequinone and 3,6‐dimethoxyphenanthrenequinone, added with a catalytic amount of metal complexes, impart control to styrene polymerization via the previously reported quinone transfer radical polymerization (QTRP) process. In this study, compounds that mimic the dormant species proposed in the QTRP mechanism have been synthesized and tested as initiators in the presence of cobalt(II) acetylacetonate. These compounds, and particularly 3,6‐dimethoxy‐10‐hydroxy‐10‐(1‐phenyl‐ethyl)‐phenanthren‐9‐one, are effective control agents for the radical polymerization of styrene, in agreement with the recently proposed mechanism. Moreover, the induction period, which has been systematically reported in the presence of ortho‐quinones, is no longer observed. The end capping of the polystyrene chains by the control agent has been confirmed by ¹H NMR analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1233–1244, 2006     

Synthesis of 3-aryl-4-chalcogen-2H-benzopyrans from 3-iodo-4-chalcogen-2H-benzopyrans using a Suzuki cross-coupling

The Suzuki cross-coupling reaction of 3-iodo-4-chalcogen-2H-benzopyran derivatives with a variety of organoboron compounds in the presence of catalytic amount of palladium salt is described. This cross-coupling reaction proceeded cleanly and was performed with aryl boronic acids bearing electron-withdrawing, electron-donating, and neutral substituents, furnishing the corresponding products in moderate to good yields.