Ferrocenyl- and octamethylferrocenyl-substituted phenylenevinylene-, thienylenevinylene-, and 1,1′-ferrocenylenevinylene spaced ethynes: Synthesis, metathesis polymerization, and polymer properties

Buchmeiser, Michael R.; Hallbrucker, Andreas; Kohl, Ingrid; Schuler, Norbert; Schottenberger, Herwig

doi:10.1163/156855500750206366

Cited by 20 publications

(20 citation statements)

References 51 publications

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“…In contrast to 18 , well‐defined molybdenum‐based Schrock‐type alkylidene complexes 19a – 19n and 19r – 19t (Fig. 3) have been proven to efficiently polymerize various monosubstituted acetylenes in a living manner, namely several ortho‐substituted phenylacetylenes,27, 46 metallocenyl‐substituted 1‐alkynes,33, 47, 48, 117 and 1,6‐heptadiynes 28, 29, 31, 32, 109–111. In general, the activity and selectivity of well‐defined molybdenum‐based alkylidenes can be fine‐tuned by the steric and electronic effects of the ligand sphere around the molybdenum center, and this leads to excellent initiators for the synthesis of conjugated polymers with highly defined microstructures 27–29, 46, 47, 109, 118…”

Section: Well‐defined Transition‐metal Alkylidene Initiatorsmentioning

confidence: 99%

Living polymerization of substituted acetylenes

Mayershofer

Nuyken

2005

J. Polym. Sci. A Polym. Chem.

121

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For many years, considerable research efforts have been dedicated to -conjugated polymers because of their extraordinary electronic, optical, and structural properties. The employed transition-metal-based initiating systems comprise not only simple transitionmetal salts but also rather sophisticated mixtures of two, three, or four compounds and even highly defined single-component systems such as transition-metal alkylidene complexes. Extensive fine-tuning of the electronic and steric properties of initiator-monomer systems eventually allowed the tailor-made synthesis of conjugated materials via living polymerization techniques. This article focuses on recent developments in the field of the living polymerization of substituted acetylene derivatives. Ill-defined group 5 and 6 transition metal halide-based initiators, well-

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Section: Well‐defined Transition‐metal Alkylidene Initiatorsmentioning

confidence: 99%

Living polymerization of substituted acetylenes

Mayershofer

Nuyken

2005

J. Polym. Sci. A Polym. Chem.

121

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“…18,[20][21][22][23][24]30,31 In that context not only the alkoxide but also the imido ligands played a predominant role in the control of the regioselectivity. 32,33 Recently, molybdenum−imidoalkylidene NHC bis(triflate) 34 and cationic tungsten−oxoalkylidene NHC complexes 35 have been developed in our group. Particularly molybdenum− imidoalkylidene NHC bistriflates display high reactivity for various norborn-2-enes, 7-oxanorborn-2-enes, and diynes and are also tolerant toward nitrile, amino, hydroxyl, and carboxylic acid groups.…”

Section: ■ Introductionmentioning

confidence: 99%

Mechanism of the Regio- and Stereoselective Cyclopolymerization of 1,6-Hepta- and 1,7-Octadiynes by High Oxidation State Molybdenum–Imidoalkylidene N-Heterocyclic Carbene Initiators

Herz¹,

Unold

Hänle³

et al. 2015

Macromolecules

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The regio-and stereoselective cyclopolymerization of a series of 1,6-heptadiynes and 1,7-octadiynes, i.(MAP3) is described. With initiators I1−I4, high regioselectivity >96% was observed in the polymerization of M1−M4, allowing for virtually selective α-insertion. These initiators displayed also high stereoselectivity, allowing for all-trans polyenes with up to 96% syndioselectivity. By contrast, the MAP initiators MAP1−MAP3 showed poor regioselectivity (26−62% α-selectivity). A polymerization mechanism is proposed that explains for the high stereo-and regioselectivity of the Mo− imidoalkylidene NHC complexes. ■ INTRODUCTIONThe cyclopolymerization of 1,6-hepta-and 1,7-octadiynes has been widely used for the syntheses of soluble, conjugated polymers possessing a rigid backbone. 1−29 Equally important, it can also be used as a probe to determine both the regio-and stereoselectivity of insertion and to come up with a polymerization mechanism for a specific initiator system. Two different pathways for the cyclopolymerization of α,ω-diynes with Schrock-type molybdenum carbenes exist (Scheme 1). 3,4 Thus, the monomer can undergo either α-or β-addition. The first addition step of the monomer to the metal alkylidene is decisive for the structure of the resulting repeat unit. In the absence of any backbiting, the polymer structure is a concise record of all previous insertion steps. For first-generation Schrock initiators, the concept of large and small alkoxides was developed by the Schrock group and allowed for the selective β-addition of monomer. 1,2 Our group was capable of extending this concept to selective α-addition by using first-generation Schrock initiators bearing small alkoxides, an additional coordinating base, and low temperatures. 18,[20][21][22][23][24]30,31 In that context not only the alkoxide but also the imido ligands played a predominant role in the control of the regioselectivity. 32,33 Recently, molybdenum−imidoalkylidene NHC bis(triflate) 34 and cationic tungsten−oxoalkylidene NHC complexes 35 have been developed in our group. Particularly molybdenum− imidoalkylidene NHC bistriflates display high reactivity for various norborn-2-enes, 7-oxanorborn-2-enes, and diynes and are also tolerant toward nitrile, amino, hydroxyl, and carboxylic acid groups. 34 We were interested in the polymerization mechanism that applies in the polymerization of α,ω-diynes with these novel initiators. Equally important, we wished to find out about the stereo-and regioselectivity of these novel complexes and therefore addressed the issues of tacticity and cis/trans selectivity in cyclopolymerization. Since the cationic species derived from Mo−imidoalkylidene NHC bis(triflate) complexes resemble to some extent molybdenum−imidoalkylidene monoalkoxide monopyrrolide (MAP) catalysts developed by the Schrock group, 36,37 and since these systems have

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“…From these data it becomes clear that (i) the original concept of large and small alkoxides developed by the Schrock group also applies to the cyclopolymerization of 4‐aza‐1,6‐heptadiynes,6, 30, 31 (ii) as outlined earlier,27, 32, 33 the size of the substituents in the 2‐ and 6‐position of the arylimido ligand does play a significant role, i.e. the larger the substituent, the more β ‐insertion is preferred, and (iii) addition of a base such as quinuclidine to an initiator favors α ‐insertion and thus the formation of five‐membered repeat units, presumably via stabilization of the anti ‐rotamer 15, 27.…”

Section: Resultsmentioning

confidence: 76%

“…Schrock catalyst initiated cyclopolymerizations were terminated after 3 h using ferrocene carbaldehyde (10 molequiv. with respect to the initiator) 32, 33, 39, 40. The solvent was evaporated almost to dryness and the polymer was precipitated by adding excess of pentane.…”

Section: Methodsmentioning

confidence: 99%