Copper and iron complexes as visible‐light‐sensitive photoinitiators of polymerization

The utilization of visible lights for the fabrication of polymeric materials is recognized as a promising and environmentally friendly approach. This process relies on the photochemical generation of reactive species (e.g., radicals, radical cations, or cations) from well‐designed photoinitiators (PIs) or photoinitiating systems (PISs) to initiate the polymerization reactions of different monomers (acrylates, methacrylates, epoxides, and vinyl ethers). In spite of the fact that metal complexes such as ruthenium‐ or iridium‐based complexes have found applications in organic and polymer synthesis, the search of other low‐cost metal‐based complexes as PISs is emerging and attracting increasing attentions. Particularly, the concept of the photoredox catalysis has appeared recently as a unique tool for polymer synthesis upon soft conditions (use of light emitting diodes and household lamp). This highlight focuses on recently designed copper and iron complexes as PI catalysts in the application of photoinduced polymerizations (radical, cationic, interpenetrated polymer networks, and thiol‐ene) or controlled radical polymerization under visible light irradiation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2673–2684     

Main-Group Metal Complexes in Selective Bond Formations Through Radical Pathways

Recent years have witnessed remarkable advances in radical reactions involving main-group metal complexes. This includes the isolation and detailed characterization of main-group metal radical compounds, but also the generation of highly reactive persistent or transient radical species. A rich arsenal of methods has been established that allows control over and exploitation of their unusual reactivity patterns. Thus, main-group metal compounds have entered the field of selective bond formations in controlled radical reactions. Transformations that used to be the domain of late transition-metal compounds have been realized, and unusual selectivities, high activities, as well as remarkable functional-group tolerances have been reported. Recent findings demonstrate the potential of main-group metal compounds to become standard tools of synthetic chemistry, catalysis, and materials science, when operating through radical pathways.     

后过渡金属配合物催化乙烯齐聚与聚合的研究进展

后过渡金属配合物催化乙烯齐聚和聚合研究,不仅拓展了后过渡金属配合物的应用 ,而且为探求烯烃聚合催化剂提供了新机遇,成为当前催化研究中的热点课题.本文综述了后过渡金属铁、钴、镍配合物催化乙烯齐聚和聚合的国内外最新研究进展.     

Thio-Pybox and Thio-Phebox complexes of chromium, iron, cobalt and nickel and their application in ethylene and butadiene polymerisation catalysis

A series of bis(thiazolinyl)- and bis(thiazolyl)pyridine Thio-Pybox ligands and their metal complexes of chromium(III), iron(II), cobalt(II) and nickel(II) has been prepared, as well as a nickel(II) complex containing a monoanionic bis(thiazolinyl)phenyl Thio-Phebox ligand. These new metal complexes have been characterised and used as catalysts, in combination with the co-catalyst MAO, for the polymerisation of ethylene and for the polymerisation of butadiene. In the case of ethylene polymerisation, the Thio-Pybox and Thio-Phebox metal complexes have shown relatively low polymerisation activities, much lower compared to the related bis(imino)pyridine complexes of the same metals. In the polymerisation of butadiene, several Thio-Pybox cobalt(II) complexes show very high activities, significantly higher than the other metal complexes with the same ligand. It is the metal, rather than the ligand, that appears to have the most profound effect on the catalytic activity in butadiene polymerisation, unlike in the polymerisation of ethylene, where bis(imino)pyridine ligands provide highly active catalysts for a range of 1st row transition metals.     

In situ‐generated Ru(III)‐mediated ATRP from the polymeric Ru(III) complex in the absence of activator generation agents

Past research has examined the atom transfer radical polymerization (ATRP) with high oxidation state metal complexes and without the need for any additives such as reducing agent or free radical initiator. To extend this research, half‐metallocene ruthenium(III) (Ru(III)) catalysts were used for the polymerization of methyl methacrylate (MMA) for the first time. These catalysts were generated in situ simply by mixing phosphorus‐containing ligand and pentamethylcyclopentadienyl (Cp*) Ru(III) polymer ((Cp*RuCl₂)_n). The complexes in their higher oxidation state such as Cp*RuCl₂(PPh₃) were air‐stable, highly active, and removable catalysts for the ATRPs of MMA with both precision control of molecular weight and narrow polydispersity index. The addition of ppm amount of metal catalyst contributed to the formation of very well‐defined homopolymers and copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Our variations on iron and cobalt catalysts toward ethylene oligomerization and polymerization

Iron and cobalt complexes are a new family of catalysts for ethylene oligomerization and polymerization. The extensive researches on bis(imino)pyridyl metal complexes have been carried out with the aim of synthesizing their derivatives and finding suitable reaction parameters for the optimum activity. Beyond the modification works of bis(imino)pyridyl metal complexes, several alternative models with similar coordination sphere have been developed in our group. This review article describes our experiences in innovating new models of iron and cobalt complexes as catalysts for ethylene oligomerization and polymerization.     

Metal complexes with polymeric ligands: Chelation and metalloinitiation approaches to metal tris(bipyridine)‐containing materials

Synthetic approaches to metal complexes with polymeric ligands are described. The development of efficient methods for preparing simple bipyridine (bpy) derivatives and their corresponding metal complexes has facilitated their use as initiators and coupling agents in polymer syntheses. Ligand reagents were utilized as initiators in controlled polymerization reactions to form poly(2‐R‐2‐oxazolines) (R = methyl, ethyl, phenyl, undecyl), polystyrenes, poly(methyl methacrylates) (PMMA)s, poly(ϵ‐caprolactone)s, and poly(lactic acid)s with bipyridine chelates at the end or centers of the chains. Poly(ethylene glycol) macroligands were formed by a chain‐coupling method. Detailed studies of reaction kinetics were performed to determine the scope and limitations of each reaction type with different catalysts and reaction conditions. These results are illustrated for bpyPMMA_n (n = 1 or 2), which was prepared by atom transfer radical polymerization with a CuBr/1,4,4,7,7,10‐hexamethyltriethylenetetraamine catalyst system. Results of the kinetics investigations performed with other ligands and metalloinitiators are summarized. Macroligands thus prepared were coordinated to a labile metal ion, Fe(II), with standard protocols. Ultraviolet–visible spectral data for selected Fe‐centered polymers are provided that confirm the production of the targeted polymeric iron complex products. An inert metal, Ru(II), was used as a template for generating architectural diversity; polymeric complexes with one to six chains emanating from the central core, as well as different heteroarm star products, were prepared. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4704–4716, 2000     

Effect of catalyst transition metal and ancillary ligand on syndiospecific polymerization of styrene

In the coordination polymerization of styrene, selected transition metal complexes of metals other than group 4 elements and non-metallocenes have been investigated in comparison to a known half-metallocene titanium complex with regard to the catalytic activity as well as to the thermal and molecular properties of the polymers synthesized. Whereas iron catalysts lead to syndiotactic polystyrenes, catalysts with nickel as the transition metal result only in atactic polymers with an enhanced isotactic content.In addition to the influence of the transition metal, the effect of a broad variation of the ancillary ligands of a specific half-sandwich titanocene, octahydrofluorenyl titanium trimethoxide, on polymerization activity and polymer properties has been investigated and discussed in detail.     

Formation of cationic peptide radicals by gas-phase redox reactions with trivalent chromium, manganese, iron, and cobalt complexes

The collision-induced dissociation (CID) of a series of gas-phase complexes [M(III)(salen)(P)](+) [where M = Cr, Mn, Fe, and Co; P = hexapeptides YGGFLR, WGGFLR, and GGGFLR; and salen = N,N'-ethylenebis(salicylideneaminato)] has been examined with respect to the ability of the complexes to form the corresponding cationic peptide radical ions, P(+)(*), by homolytic cleavage of the metal peptide bond. This is the first example of the use of gas-phase ternary metal peptide complexes to produce the corresponding cationic peptide radical for a metal other than copper(II). The fragmentation reactions competing with radical formation are highly dependent on the metal ion used. In addition, examination of modified complexes in which the periphery of the salen was substituted allowed evaluation of electronic effects on the CID process, presumably without significant change in the geometry surrounding the metal. This substitution demonstrates that the ligand can be used to tune the dissociation chemistry to favor radical formation and suppress unwanted further fragmentation of the peptide radical that is typically observed immediately following its dissociation from the complex.     

Aqueous Catalytic Polymerization of Olefins

Catalytic conversions in aqueous environments by transition metal complexes have become a well‐established field over the past two decades. However, the vast majority of investigations have focussed on small‐molecule synthesis. This may appear somewhat surprising as water is a particularly attractive reaction medium, especially for polymerization reactions. For example, aqueous emulsion and suspension polymerization is carried out today on a large scale by noncatalytic free‐radical routes. Polymer latices can be obtained as a product, that is, stable aqueous dispersions of polymer particles in the size range of 50 to 1000 nm. Such latices possess a unique property profile. Amongst other advantages, the use of water as a dispersing medium is particularly environmentally friendly. In comparison to these free‐radical reactions, aqueous catalytic polymerizations of olefinic monomers have received less attention. However, considerable advances and an increased awareness of this field have emerged during the past few years. A variety of high molecular weight polymers ranging from amorphous or semicrystalline polyolefins to polar‐substituted hydrophilic materials have now been prepared by catalytic polymerization of olefinic monomers in water. Polymer latices based on a number of readily available monomers are accessible and catalytic activities as high as 10⁵ turnovers per hour have already been reported. As another example, materials prepared by aqueous catalytic polymerization have been investigated as protein inhibitors. A versatile field spanning colloids, polymer, and coordination chemistry has emerged.     

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     

Effect of water on copper mediated living radical polymerization

The use of water as a solvent for copper mediated living radical polymerization has been further investigated. Optimal conditions for effective living radical polymerization using catalyst complexes based on CuBr and N-(n-alkyl)-2-pyridylmethanimine ligands were found, leading to well defined polymer structures. The effect of water on the rate of polymerization was studied, and it was found that competitive complexation of ligand and water occurs at copper in addition to an enhanced polymerization rate on increasing the polarity of the medium.     

Oxygen binding and activation by the complexes of PY2- and TPA-appended diphenylglycoluril receptors with copper and other metals

The copper(I) complexes of diphenylglycoluril basket receptors and , appended with bis(2-ethylpyridine)amine (PY2) and tris(2-methylpyridine)amine (TPA), respectively, and their dioxygen adducts were studied with low-temperature UV-vis and X-ray absorption spectroscopy (XAS). The copper(I) complex of, [.Cu(I)2] or, forms a micro-eta2:eta2 dioxygen complex, whereas the copper(I) complex of, [.Cu(I)2] or, does not form a well defined dioxygen complex, but is oxidized to Cu(II). Dioxygen is bound irreversibly to and the formed complex is stable over time. The coordination geometries of the above complexes were determined by XAS, which revealed that pyridyl groups and amine N-donors participate in the coordination to Cu(I) ions in the complexes of both receptors. The catalytic activities of various metal complexes of and , that were designed as mimics of dinuclear copper enzymes that can activate dioxygen, were investigated. Phenolic substrates that were expected to undergo aromatic hydroxylation, showed oxidative polymerization without insertion of oxygen. The mechanism of this polymerization turns out to be a radical coupling reaction as was established by experiments with the model substrate 2,4-di-tert-butylphenol. In addition to Cu(II), the Mn(III) complex of and the Fe(II) complex of were tested as oxidation catalysts. Oxidation of catechol was observed for the Cu(II) complex of receptor but the other metal complexes did not lead to oxidation.     

Driving Polymer Brushes from Synthesis to Functioning

The great success of controlled radical polymerizations has encouraged researchers to develop more facile and robust approaches for surface-initiated polymerizations (SIPs) to fabricate polymer brushes, even for non-experts. In recent years, external-stimuli-mediated radical polymerization methods have come to the fore as SIPs because of their less rigorous synthetic procedures and high controllability, which expand the opportunities for synthesizing macromolecules with desired chemical compositions and structures, as well as tailor-made polymers and bioconjugates that show broad applicability and physiological compatibility. This review discusses the latest developments in surface-initiated polymerization methods, in particular, external-stimuli mediated atom transfer radical polymerization (ATRP), photo-induced polymerizations, and reversible addition-fragmentation chain transfer (RAFT) polymerization, as well as other methods and their combination for the application in surface grafting. The implementation of these methods is of great interest due to their unique possibilities to temporally control a polymerization process, fast and straightforward polymerization, and environmentally benign features, which lead to established and emerging applications in biolubrication, antifouling, and biosensing.     

IVB金属配合物催化烯烃聚合的研究进展

IVB金属配合物催化烯烃聚合的研究,不仅为工业界提供大量新型高效的催化剂模型,同时也为探索烯烃配位聚合机理提供了可能.更为重要的是,这些新型的配合物催化剂,可以制备具有优异性能的新型聚烯烃树脂.研究的核心仍然是新型聚烯烃催化剂,基于配合物中配位原子种类的不同,将催化剂的种类分为氮配位和氧配位催化剂.文中综述了近年来IVB金属配合物作为烯烃聚合催化剂的研究进展,集中讨论催化剂结构的变化对催化性能的影响.     

Fluoropolymer materials and architectures prepared by controlled radical polymerizations

This review initially summarizes the mechanisms, merits and limitations of the three controlled radical polymerizations: nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP) or metal catalyzed living radical polymerization, and reversible addition-fragmentation chain transfer (RAFT) polymerization. This is followed by two parts, one dealing with homo- and copolymerizations of fluorinated methacrylates and acrylates, and a second where fluorinated styrenes, alone or in combination with other monomers, are the main issues. In these parts, initiators (including multifunctional and macroinitiators), ligands and other reaction conditions as well as some kinetics and conversions are discussed. Numerous possibilities for preparation of a variety of different block copolymers where one or more blocks are fluorinated are devoted particular attention. The advantageous properties and functionalities that can be obtained from these novel fluorinated materials and architectures are especially emphasized. Thus, various amphiphilic, biocompatible or low energy materials, fluorinated nanoparticles and nanoporous films/membranes as well as materials for submicron and nanolevel electronics have been fabricated. In addition, the possible fluorination of various surfaces through surface initiation is highlighted. A final part deals with the use of fluorine containing initiators and macroinitiators, and the applications on the novel materials derived thereof.     

Copper‐Mediated Reversible Deactivation Radical Polymerization in Aqueous Media

Key advances within the past 10 years have transformed copper‐mediated radical polymerization from a technique which was not very tolerant of protic media into a range of closely related processes capable of controlling the polymerization of a wide range of monomers in pure water at ppm catalyst loadings. This approach has afforded water‐soluble macromolecules of desired molecular weight, architecture, and chemical functionality, with applications ranging from drug delivery to oil processing. In this Review we highlight and critically evaluate the synthetic methods that have been developed to control radical polymerization in water by using copper complexes as well as identify future areas of interest and challenges still to be overcome.     

Radical polymerization of styrene controlled by half-sandwich Mo(III)/Mo(IV) couples: all basic mechanisms are possible

Density functional calculations of bond dissociation energies (BDEs) have been used as a guide to the choice of metal system suitable for controlling styrene polymerization by either the stable free radical polymerization (SFRP) or the atom transfer radical polymerization (ATRP) mechanism. In accord with the theoretical prediction, CpMo(eta(4)-C(4)H(6))(CH(2)SiMe(3))(2), 2, is not capable of yielding SFRP of styrene. Still in accord with theoretical prediction, CpMo(eta(4)-C(4)H(6))Cl(2), 1, CpMo(PMe(3))(2)Cl(2), 3, and CpMo(dppe)Cl(2) (dppe = 1,2-bis(diphenylphosphino)ethane), 4, yield controlled styrene polymerization by the SFRP mechanism in the presence of 2,2'-azobisisobutyronitrile (AIBN). This arises from the generation of a putative Mo(IV) alkyl species from the AIBN-generated radical addition to the Mo(III) compound. The controlled nature of the polymerizations is indicated by linear M(n) progression with the conversion in all cases and moderate polydispersity indices (PDIs). Controlled polymerization of styrene is also given by compounds 3 and 4 in combination with alkyl bromides. These complexes then operate by the ATRP mechanism, again in accord with the theoretical predictions. Controlled character is revealed by linear increase of M(n) versus conversion, low PDIs, a stop-and-go experiment, and (1)H NMR and MALDI-TOF analyses of the polymer end groups. The same controlled polymerization is given by a "reverse" ATRP experiment, starting from AIBN and CpMo(PMe(3))(2)Cl(2)Br, 5. On the other hand, when compound 1 or 2 is used in combination with an alkyl bromide (as for an ATRP experiment), the isolated polystyrene shows by M(n), (1)H NMR, and MALDI-TOF analyses that catalytic chain transfer (CCT) radical polymerization takes place in this case. Kinetics simulations underscore the conditions regulating the radical polymerization mechanism and the living character of the polymerization. The complexes herein described are ineffective at controlling the polymerization of methyl methacrylate.     

Tailored covalent grafting of hexafluoropropylene oxide oligomers onto silica nanoparticles: toward thermally stable, hydrophobic, and oleophobic nanocomposites

The modification of silica nanoparticles with hexafluoropropylene oxide (HFPO) oligomers has been investigated. HFPO oligomers with two different average degrees of polymerization (DPn = 8 and 15) were first prepared by anionic ring-opening polymerization, deactivated by methanol, and in some cases postfunctionalized by aminopropyl(tri)ethoxysilane or allylamine. The "grafting onto" reactions of these oligomers were then carried out either on bare silica (reaction between a silanol surface and ethoxy-silanized HFPO) or on silica functionalized by amino groups (in an amidation reaction with methyl ester-ended HFPO) or mercapto groups (via the radical addition of allyl-functionalized HFPO). Hybrid nanoparticles thus obtained were characterized by solid-state (29)Si NMR and FTIR spectroscopies as well as elemental and thermogravimetric analyses. The results assessed a significant yield of covalent grafting of HFPO oligomers when performing the hydrolysis-condensation of ethoxylated HFPO on the bare silica surface, compared to the other two methods that merely led to physically adsorbed HFPO chains. Chemically grafted nanohybrids showed a high thermal stability (up to 400 °C) as well as a very low surface tension (typically 5 mN/m) compared to physisorbed complexes.     

Catalytic aerobic radical polymerization in typical redox-non-innocent solvents as potential low-efficiency initiators

Abstract

Certain complexes of some transition metal cations in the high oxidation state could oxidize some organic substrates with labile C-H moieties, leading to the corresponding cations in the lower" oxidation state and some carbon-centered radicals. The former would form oxidative complexes with molecular dioxygen to continuously oxidize organic substrates, while the latter would initiate polymerization of vinylic monomers. Such catalytic oxidation is adopted to initiate radical polymerization of methyl methacrylate (MMA) and styrene (St) with cyclohexanone (CyHO) and benzylic hydrocarbons as both the solvent and the substrate. Although, a large array of complexes could trigger the polymerization, Cu^II/2,2′-bipyridine complexes display a maximum turnover frequency above 200?h^–1 during the catalytic aerobic radical polymerization of MMA in CyHO at 70–80?°C, but only less than 0.4% of CyHO is involved in chain formatting. Cu^II/ligand-catalyzed aerobic radical polymerization of St in CyHO exhibit comparable behaviors. Only Co^II complexes could catalyze the aerobic radical polymerization of MMA in para-xylene and cumene at 90?°C, but only 0.1% of PX and 0.3% of cumene are involved in chain forming.