Handbook of Polymer Synthesis Second Edition Episode 6 pot

6 Metathesis Polymerization of Cycloolefins Ulrich Frenzel, Bettina K. M. Mu ¨ ller and Oskar Nuyken Technische Universita ¨ tMu ¨ nchen, Garching, Germany I. INTRODUCTION The term ‘olefin metathesis’ refers to an interchange reaction of alkylidene groups between alkenes. The total number of double bonds remains unchanged [1]. The history of olefin metathesis started in the mid 1950s, when Anderson and Merckling (Du Pont) – during their work on the Ziegler–Natta polymerization of norbornene (NBE) – received by means of TiCl 4 /EtMgBr catalysts a novel polymer [2,3]. In 1957 Eleuterio (Du Pont) filed a patent, which describes the polymerization of severa l cyclic olefins employing, among others, LiAlH 4 -activated MoO 3 /Al 2 O 3 catalysts [4]. Ozonolysis of a norbornene polymer yielded cis-cyclopentane-1,3-dicarboxylic acid, thus demonstrating the novel and unexpected nature of this polymerization reaction [4,5]. ð1Þ In the same year Peters and Evering patented a ‘disproportionation’ reaction of propene yielding ethene and 2-butene with Al(i-Bu) 3 þ MoO 3 /Al 2 O 3 -catalysts as the first metathetical conversion of acyclic alkenes [6]. The first report on the metathesis of acyclic olefins in the open literature appeared in 1964. It describes the ‘disproportionation’ of olefins into homologs of higher and lower molecular weight using Mo(CO) 6 /Al 2 O 3 catalysts [7]. At this time ring-opening metathesis polymerization and metathesis of acyclic olefins – originally considered as ‘olefin disproportionation’ [7] – were regarded as two different reactions. Calderon recognized in 1972 that these both are two sides of the same coin and introduced the term ‘olefin metathesis’ for this reaction type [8–11]. Copyright 2005 by Marcel Dekker. All Rights Reserved. From these very beginnings the olefin metathesis reaction is a central topic of industrial as well as academic research due to its great synthetic applicability. Many reviews and monographs about this topic were published since then [1,12–31]. The most important metathesis reaction pathways including cyclic olefins, ring-closing metathesis (RCM, [14–19]), ring-op ening metathesis (ROM, [17,18]) and ring-opening metathesis polymerization (ROMP, [4,20–29]) are schematically shown in structure (2). ð2Þ The present contribution deals primaril y with the polymer synthesis via ring-opening metathesis polymerization. Acyclic diene metathesis (ADMET) [20,32–38], the other metathetic route to polymers is omitted. This article intends to give a brief overview, for more details and further applications see, e.g., Refs. [1,4,20–29]. II. GENERAL MECHANISTIC ASPECTS As mentioned above, Calderon recognized in 1972 that metathesis polymerization and metathesis of acyclic olefi ns are two aspects of the same reaction [10]. As early as 1968 he had identified the double bonds as the reactive centers in the metathesis of acyclic olefins. Apart from the educts the metathesis reaction of d 8 -2-butene with 2-buten e yielded only d 4 -2-butene, so he could exclude the cleavage of any singl e bond [39,40]. Dall’ Asta and Motroni drew an analogous conclusion for ROMP by copolymerization of 1- 14 C- cyclopentene and cyclooctene (3). After ozonolytic degradation of the polymers the complete radioactivity was found in the C 5 -fraction, showing the exclusive cleavage of the double bonds (pathway (3b)) [41,42]. ð3Þ Copyright 2005 by Marcel Dekker. All Rights Reserved. In early mechanistic theories several pairwise mechanisms were proposed with, e.g., various quasi-cyclobutane (4b) [43–45], metal tetracarbene (4a) [46] or metallacyclo- pentane [47,48] intermediates respectively transition states [49]. ð4Þ Chauvin and He ´ risson found in 1970, that the initial product distribution in the cross metathesis of cyclopentene and 2-pentene is not in accordance with such a simple pairwise mechanism [30,50]. Therefore, they proposed a novel non-pairwise mechanism with metal carbene complexes as intermediates (5) [50]. This so-called metallacyclobutane mechanism is further supported by the fact that ROM polymerizations yield high molecular weight polymers already at low yields [51]. In the case of a step growth polymerization, as suggested by a simple pairwise mechanism, polymers with high molecular weight should yield only at high conversions. However, both findings may also be explained by a modified pairwise mechanism [30,49], but Katz et al. and Grubbs et al. demonstrated by highly sophisticated experiments using isoto pe labeled olefins that a pairwise mechanism is improbable [52–55]. ð5Þ Dolgoplosk’s finding that metal carbene-generating diazoalkanes [56] may act as highly efficient cocatalysts supported Chauvin’s mechanism [51]. The first metathesis polymerization using a well-defined metal carbene complex as initiator was performed in 1976 by Katz [57] with (CO) 5 W¼CPh 2 [58]. Since these initial investigations a broad variety of isolable metal carbene complexes has been synthesized and employed with great success as metathesis initiators. Furthermore, the metallacy clobutane mechanism was supported by many other investigations, e.g., the characterization of intermediate metall- acyclobutanes [59–61] or olefin-p-metal carbene complexes [62,63] and it is now generally accepted [1,30]. Four basic steps are proposed: coordination of the olefin to the metal center of a carbene complex, [2 þ 2]-cycloaddition forming the metallacyclobutane intermediate, cycloreversion and finally de-coordination of the olefin. All these reactions are reversible as shown in Scheme (5). In contrast to these success many details of the mechanism still remain unclear until now. For example Rooney et al. recently reported the presence of persistent metal anion radicals in metathesis reactions using the Grubbs catalyst (PCy 3 ) 2 Cl 2 Ru¼CHPh and Copyright 2005 by Marcel Dekker. All Rights Reserved. proposed for this initiator a novel mechanism involving radicals (Scheme 6) [64,65]. ð6Þ III. CATALYSTS A. General Aspects Most metathesis catalysts are based on compounds of Ti, Ta, Mo, W, Re, Ru, Os and Ir. Only a few reports on the use of Nb, Zr, V, Cr, Tc, Co and Rh systems appeared in literature [1]. But even MgCl 2 has been report ed recently to be an active catalyst for polymerization of strained olefins, i.e. norbornenes [66]. Metathesis catalysts may be divided formally into three groups: homogeneous, heterogeneous and immobilized homogeneous catalysts. In general the former are utilized for metathetic polymerizations and only few reports on ROMP with heterogeneous or immobilized catalysts were published until now (see, e.g., [6,7,67–72]). Early homogenous metathesis catalysts – often called ‘classical catalysts’ – are formed in situ from a transition metal halide and a main group metal alkyl co-catalyst. Typical examples of such multicomponent catalysts are carbonyl, nitr osyl, chlordie or oxychloride complexes of molybdenum, tungsten or rhenium in combination with lithium, aluminium or tin organyl compounds. Often also promoters, mostly containing oxygen, are added [1]. It has been reported that oxo ligands formed from traces of moisture or oxygen are of crucial importance for the activity of some classical catalysts, e.g., WCl 6 /BuLi [73,74]. Such binary and ternary catalyst systems including for example MoCl 5 /SnPh 4 [75], MoCl 2 (NO) 2 (C 2 H 5 N) 2 /EtAlCl 2 [76], the so-called Calderon catalyst WCl 6 /EtAlCl 2 /EtOH [11], ReCl 5 /Bu 4 Sn [77] or ReCl(CO) 5 /EtAlCl 2 [78], can catalyze metathesis reactions of cyclic and acyclic olefins with great success. However, also the monomer its elf may act as co-catalyst. Various mechanisms involving monomer molecules were proposed for the generation of the propagating species in these systems [1,79,80]. The catalyst systems mentioned above are widely used in the commercial applications of metathesis polymerization due to their low costs and simplicity of preparation (see Section VII). However, the harsh reaction conditions and strong Lewis acids often required limit the utility of such catalysts [81]. These may cause side-reactions and make them incompatible with most functional groups [82]. The propagating species are poorly defined and often neither quantitatively formed nor uniform. Hence, there is often a lack of reaction control using these systems. Moreover, for the polyme rization of functionalized monomers it is often necessary to use tin organyls instead of aluminium alkyls. These are more expensive and may cause severe injuries of health [25,83]. Copyright 2005 by Marcel Dekker. All Rights Reserved. As a consequence of a better unde rstanding the mechanistical aspects of olefin metathesis and the synthesis of the first metal carbene complexes by Fischer [84] and Schrock [85] the situation has dramatically changed. These findings triggered the development of highly active unicomponent homogeneous catalysts [81]. Early examples are (CO) 5 W¼CPh 2 reported by Katz and Casey [57,58,86], the Tebbe reagent (7a) [87–89] and the titanacyclobutanes developed by Grubbs (7b–e) [60,90]. This trend towards well-defined, isolable single component initiators continues in the field of olefin metathesis. The cocatalyst-free alkylidenes combine a fast initiation with high catalytic activitiy. Their high degree of reaction control allows to perform living polymerizations, i.e., precise adjusting of molecular weight by the monomer/initi ator-ratio and a low polydispersity [1]. An alternative approach using diazo compounds for the activation of suitable transition metal complexes is worth to be mentioned, too [51,91–98]. The formation of alkylidenes in situ avoids the expensive multi-step synthesis and isolation of well-defined initiators. However, these systems are also ill-defined and Noels reported for [RuCl 2 (p- cymene)] 2 /PCy 3 (2eq.)/trimethylsilyldiazomethane that only 15–20 mol% of the employed Ru become catalytically active [97]. Nevertheless, such systems can exhibit exceptionally high catalytic activities [94,95]. The development of highly active and robust catalysts, which tolerate additionally functional groups is an important goal in transition metal catalyzed polymerizations. In metathesis that may be gained by the use of catalysts which are based on late transition metals. As shown in the table, ruthenium has unique properties in this respect [1,81,99]. Due to their remarkable stability and activity ruthenium based catalysts were focused during the last decade. These catalysts are remarkable tolerant towards oxygen and mois- ture than early transition metals. Moreover, the polymerization of a broad variety of monomers bearing polar protic functionalities became possible. Some ruthenium systems even enable polymerizations in polar protic solvents, e.g., alcohols or water [94,100–109]. Also emulsion polymerizations by means of ROMP became possible with suitable Ru compounds, e.g., floc free lattices in high yields were obtained via emuls ion ROM polym- erization of norbornene using a water soluble Grubbs-type catalyst [98]. General trends in tolerance towards functional groups for transition metal based metathesis catalysts are listed in the following table [81,99]. Titanium Tungsten Molybdenum Ruthenium Acids Acids Acids Olefins Alcohols, water Alcohols, water Alcohols, water Acids x ? ? ? ? ? ? ? Increasing reactivityAldehydes Aldehydes Aldehydes Alcohols, water Ketones Ketones Olefins Aldehydes Ester, amides Olefins Ketones Ketones Olefins Esters, amides Easters, amides Easter, amides The catalytic activity of the originally employed RuCl 3 hydrate-based systems [110] was in comparison low, but the highly sophisticated modern Ru-alkylidene initiators can exhibit as high activities as Mo based systems [111]. B. Titanium-Based Initiators Grubbs et al. synthesized and characterized a series of titanacyclobutanes (e.g., 7b–e), which enabled for the first time living ROM polymerizations of cyclic olefins. For instance, the molecular weights were adjustable, the PDIs low and moreover, the chain carrying Copyright 2005 by Marcel Dekker. All Rights Reserved. intermediates were well characterize d [29,60,90,112,113]. These complexes were obtained by reaction of the Tebbe reagent (7a) [87–89] with suitable olefins in the presence of a Lewis base, e.g., pyridine or N,N-dimethylaminopyridine [60,90,112]. ð7Þ Living polymerization using titanacyclobutane initiators enabled also the prepara- tion of block copolmers by sequential addition of different monomers [114–116] and synthesis of highly conjugated polymers and block copolymers of 3,4-diisopropylidene- cyclobutene [116]. C. Tantalum-Based Initiators Schrock and co-workers reported a series of tantalum alkylidenes with the general formula Ta(¼CH-R)X 3 (solv) (R ¼ t-Bu, etc., X ¼ O-2,6-i-Pr 2 -C 6 H 3 , O-2,6-Me 2 -C 6 H 3 , S-2,4,6-i- Pr 3 -C 6 H 2 ; solv ¼ py, THF ). The complexes were used for ROM polymerizations of norbornene and additionally tantalacyclobutane intermediates were isolated and characterized [117]. Several other Ta based initiators were synthesized and characterized [118,119]. However, the propagating species of Ta-based catalysts are often short living [117,120] and may react with functional groups containing heteroatoms [29]. Ther efore, tantalum systems never gained the importance of well-defined Ru, Mo and W initiators. D. Molybdenum-Based Initiators The synthesis of high-oxidation-state molybdenum alkylidenes was reported by Schrock in 1987 [121]. Due to their improved tolerance towards functional groups (table) their better reaction profile and their lower costs well-defined molybdenum based initiators are now preferred over the related systems containing tungsten [122]. A broad variety of complexes with the general formula Mo(NAr)(CHR 1 )(OR 2 ) 2 (9) have been synthesized successfully, e.g., starting from Mo(NAr)(CHR 1 )(OTf) 2 (dme) (Tf ¼ SO 2 CF 3 ; dme ¼ 1,2-dimethoxyethane) (8) [20,121–124]. The ‘universal precursors’ of type (8) are readily accessible even in large-scale syntheses and storable under inert atmosphere at room temperature [122–124]. ð8Þ It is crucial to prevent a bimolecular decomposition of the 14e  -species’ Mo(NAr) (CHR 1 )(OR 2 ) 2 by sterical shielding of the metal center. Consequently, it is necessary to use bulky NAr, OR 2 and ¼CHR 1 ligands. Hence, neopentylidene and neophylidene Copyright 2005 by Marcel Dekker. All Rights Reserved. ligands are commonly employed, since these substituents generally yield stable, isolable species, as long as the NAr and OR groups themselves are relatively bulky (cf. Table 1, (9)) [122]. These Mo(NAr)(CHR 1 )(OR 2 ) 2 complexes (9) and the analogous tungsten systems are now commonly called ‘Schrock catalysts’ [20]. Schrock’s highly active Mo catalysts enable the polymerization of a broad variety of monomers often in a living manner. Variations of the electronic and steric properties of the particularly used ligands enable to tailor the microstructure of the resulting polymers [20,125,126,128–130]. Many reports dealing with this topic and with the influence of the imido or alkoxy ligands in particular appeared [20]. Even highly tactic all-cis ROM polymers can be accessible with initiators bearing suitable chiral ligands, e.g, BINO derivatives. Chiral Schrock systems were used not only in ROMP to yield highly tactic polymers [128,129,131,132], but also for asymmetric RCM (ARCM) and related metathesis reactions [133–141]. The major drawback of Schrock’s systems in their high sensitivity towards oxygen and moisture. On the other hand they possess a remarkable tolerance towards numerous functionalities and successful polymerizations of monomers with, e.g., cyano [59,142], ester [59,142], carboxylic acid anhydride [143], amide [144] and ether [59] functionalities were reported [20]. The addition of aldehydes allows for quenching the metathesis reaction and cleaves the polymer chain from the metal via a Wittig-like reaction (11a) [20]. Related coupling reactions involving molecular oxygen can cause a fraction of polymers having the double molecular weight as expected (11b) [1,20,145]. ð11Þ Table 1 Examples of well-defined molybdenum-based metathesis initiators. Complex Remarks Refs. # Ar ¼ Ph; 2,6-Me 2 -C 6 H 3 ; 2,6-I-Pr 2 -C 6 H 3 , etc. [121–124] R 1 ¼ CMe 2 Ph; t-Bu; SiMe 3 , etc. [121,122,123,124] (9) R 2 ¼ t-Bu, CMe 2 CF 3 , CMe(CF 3 ) 2 , C(CF 3 ) 3 , aryl, etc. Numerous combinations were realized [146] (10) Copyright 2005 by Marcel Dekker. All Rights Reserved. A related complex, Mo(N-t-Bu)(CH-t-Bu)(OCMe(CF 3 ) 2 ) 2 (10), was synthesized by Osborn et al. and investigated for the ROMP of norbornene and acyclic internal olefins [146]. Boncella performed metathesis reactions using tris(pyrazolyl)borate stabilized molybdenum complexes in combination with AlCl 3 [147]. Two further reports on Schrock-type catalysts are worth mentioning: Feher et al. used sesquisiloxanes as ligands [148] and Stelzer et al. heterogeneized them on a g-Al 2 O 3 support using hexafluorobisphenol-A linkers [70]. E. Tungsten-Based Initiators The first report on the use of an isolated alkylidene as initiator has been published by Katz in 1976 [57,86] using Casey’s (CO) 5 WCPh 2 [58] (Table 2). The first well-defined tungsten(VI) alkylidenes which serve as highly active metathesis inititors were reported by Osborn and co-workers in 1982 [149]. W(¼CH-t- Bu)(OCH 2 -t-Bu) 2 X 2 (13) in combination with AlBr 3 or GaBr 3 polymerizes a variety of cycloolefins [61,62,149–151]. Later it has been reported that the related cyclopentylidene complex W(¼C(CH 2 ) 4 )(OCH 2 -t-Bu) 2 Br 2 polymerizes numerous cycloolefins, e.g., various methoxycarbonyl derivatives of norbornene, even without addition of a Lewis acidic cocatalyst [152–154]. Early examples of well-defined Lewis acid-free initiators were reported by Basset in 1985: tungsten(VI) alkylidenes of the type W(¼CH-t-Bu)(OAr) 2 Cl(CH 2 -t-Bu)*(OR 2 ) (14) displayed high activity in metathesis of cyclic and acyclic olefins whilst avoiding the disadvantages of Lewis acid addition [155]. Basset et al. synthesized the highly active aryloxy-alkyloxy tungsten initiator (15) [156] and performed ROM polymerizations [156,157] and RCM reactions [158] with it. Oxoalkylidene complexes of the type (W¼CH-CH¼CPh 2 )(O)[OCMe(CF 3 ) 2 ] 2 *L (16) were obtained by Grubbs and utilized for ROMP of norbornene [159]. His synthetic strategy employed 3,3-diphenylcyclopropene for the synthesis of the alkylidene moiety [159,160]. This method was later adapted for the synthesis of the first well-defined ruthenium metathesis init iators [161]. Furthermore, (OAr) 2 W(CH-t-Bu)(O)(PMe 3 ) (17) was synthesized by Schrock et al. and reported to polymerize 2,3-dicarbomethoxynor- bornadiene in a living manner [162]. A broad variety of alkoxy-imido tungsten alkylidenes (NAr)W(CHR 1 )(OR 2 ) 2 (18) were developed by Schrock and coworkers since 1986 [163–165]. These complexes serve as highly active initiators and were utilized, e.g., for the living polymerization of endo,endo- 5,6-dicarbomethoxynorbornene [164] and other monomers [166]. But for most applica- tions these highly active metathesis initiators were replaced by the related molybdenum systems [122]. Similar tungsten-based systems ha ving an ether functionalized chelating benzylidene ligand were elaborated by Grubbs et al. (19) [167]. The diamido tungsten(VI) complex (20) was reported by Bonce lla et al. But this initiator exhibited only low metathesis activity, probably due to the high stability of the W–L bond [169]. A report by van der Schaaf et al. is further worth to be mentioned: [Me(CF 3 ) 2 CO] 2 (NPh)W(CH 2 SiMe 3 ) 2 and Cl(NPh)W(CH 2 SiMe 3 ) 3 are transformed into Schrock-type initiators by irridation and were used for the photoinduced ROMP (PROMP ) of norbornene and dicyclopentadiene [168]. The main advantage of these thermally very stable PROMP systems is their latency in pure monomers in the absence of light and the easier synthesis [26,27]. Copyright 2005 by Marcel Dekker. All Rights Reserved. Table 2 Examples of well-defined tungsten-based metathesis initiators. Complex Remarks Refs. # (CO) 5 W¼CPh 2 [57,58] (12) Cocatalyst: AlBr 3 or GaBr 3 X ¼ Cl,Br [149,151] (13) R ¼ t-Bu and others (OAr) 2 W(¼CH-t-Bu)Cl(CH 2 CMe 3 )(OR 2 )R¼ 2,6-Et, i-Pr [155] (14) Ar ¼ 2,6-Ph 2 -C 6 H 3 R ¼ 2,6-Ph 2 -C 6 H 3 [156] (15) L ¼ P(OMe) 3 , THF [159] (16) W(CH-t-Bu)(O)(OAr) 2 (PMe 3 )Ar¼ 2,6-Ph 2 -C 6 H 3 [162] (17) Ar ¼ 2,6-i-Pr 2 -C 6 H 3 , etc. R 1 ¼ CMe 2 Ph; t-Bu, etc. [163,164,165] (18) R 2 ¼ t-Bu, etc. Ar ¼ 2,6-Ph 2 -C 6 H 3 [167] (19) L ¼ PMe 3 ; PEt 3 ; TMS ¼ SiMe 3 [169] (20) W(NPh)[OCMe(CF 3 ) 2 ] 2 (CH 2 -SiMe 3 ) 2 Used for photoinduced ROMP [168] (21) W(NPh)Cl(CH 2 SiMe 3 ) 3 Used for photoinduced ROMP [168] (22) Copyright 2005 by Marcel Dekker. All Rights Reserved. F. Ruthenium-Based Initiators RuCl 3 hydrate is known to be a metathesis initiator since many years [170–172] and it is used in combination with HCl in butanol for the polymerization of norbornene in industrial scale (see Section VII) [81]. Its advantage is the tolerance towards functional groups, however, the induction periods are long and only a small amount of the employed Ru becomes catalytically active [100,171]. An important milestone in the way toward modern Ru initiators was the synthesis of Ru(tos) 2 (H 2 O) 6 . This Ru(II)-b ased initiator exhibited higher activity and much better initiation [80,100,102,103,173,174]. Even ROM polymerizations in water [103] an d CO 2 [175,176] were performed with this initiator. However, despite the characterization of some olefin-ruthenium(II) complexes, the actual propagating species in such systems is still ill-defined [20]. Later Noels reported the activation of, e.g., [Ru(p-cymene)Cl 2 ] 2 and RuCl 2 ( p-cymene)(PCy 3 ) with diazo compounds in situ. But as mentioned above only a part of the employed ruthenium becomes catalytically active [97]. The major breakthrough was the synthesis of (PPh 3 ) 2 Cl 2 Ru¼CH-CH¼CPh 2 as the first well-defined, unicomponent Ru based metathesis initiator by Grubbs et al. in 1992 [161]. Further investigations showed that benzylidene complexes of type (PR 3 ) 2 Ru(CHPh)Cl 2 initiate significantly faster than (PR 3 ) 2 Cl 2 Ru¼CH-CH¼CPh 2 [177,178]. Furthermore, the activity of these initiators could be strongly improved by using PCy 3 -ligands instead of PPh 3 [179]. Many other phosphines were tested, but PCy 3 substituted initiators were the optimal ones [81,180]. The reason for this behavior is probably the high e  -donation ability and optimal steric demand of PCy 3 . With this ligand stable, isolable complexes are formed and nevertheless the dissociation of one ligand during the formation of the propagating species is possible. Two pathways were considered for metathesis reactions with these catalysts: an associative one with both posphines bond to the metal center and a dissociative one with only one PR 3 -ligand [81,180]. There is now much evidence from NMR [181,182], MS [183–185] and theoretical [186,187] investigations that these catalysts propagate mainly or even exclusively via a dissociative mechanism. This is additionally supported by the facts that the addition of Cu(I)-salts which may act as phosphine scavengers improves catalytic activity and the presence of additional PCy 3 diminishes the metathesis activity [180,188]. The influence of the alkylidene moiety on metathesis activity has been studied in detail [177]. Grubbs’ catalysts were utilized for the ROM polymerizations of a broad variety of olefins. These reactions are not as controlled as with Schrock’s Mo based systems but a high degree of reaction control is generally given and PDIs are often low. Moreover, Grubbs’ versatile systems tolerate many functional groups and were successfully used even for ROM polymerizations in polar protic solvents. Especially complexes with ionic ligands (24) [106–109] are very useful in this respect and were employed for polymerizations in alcohols, water or emulsion [98,106–109]. A chain termination with aldehydes as with the Schrock systems is not possible if using Grubbs’ catalysts. Vinyleth ers are used to cleave the polymer chain from the metal via formation of Fischer-type carbene complexes, which are metathesis inactive as reported by Grubbs, and an olefinic end group [189,190]. Gibson reported that the analogous ruthenium complex bearing PCy 2 (CH 2 SiMe 3 ) ligands exhibits a better initiation/propagation ratio but much slower propagation than the parent Grubbs complex [191]. Copyright 2005 by Marcel Dekker. All Rights Reserved. [...]... 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 Mango, F D., and Schachtschneider, J H (1971) J Am Chem Soc., 93: 1123 Lewandos, G S., and Pettit, R (1971) J Am Chem Soc., 93: 7087 Grubbs, R H., and Brunck, T K (1972) J Am Chem Soc., 94: 2538 Biefield, C G., Eick, H A., and Grubbs, R H (1973) Inorg Chem., 12: 2 166 Calderon, N., Ofstead, E A., and Judy, W A (19 76) Angew Chem.,... ROMP of NBE with tungsten-based catalysts see [409] d For the Ru-based ROMP of NBE see [1,92–95,98,109,192,3 86, 439] b Ref [405] [ 166 ,4 06] c [142,4 06] [177,231]d ð38Þ ROMP of racemic (38a) yields a polymer with an all-HT-structure [57d] Strongly HT-biased polymers are reported for poly(38b) too [2 86, 2 96] ROMP of (38c) or (38d) leads to polymers with randomly oriented methyl-substituents [414–4 16] W(CO)3... [20,3 26 441]; polymers with bioactive oligopeptide side chains [344,345]; sugar-substituted poly(norbornenes) [3 46] ; polymers of porphyrazine benzonorbornadiene derivatives [347]; conjugated polymers [20,252–357]; stationary phases [143,358]; hydrogels and polyelectrolytes [359– 361 ]; photoresists [ 362 – 365 ]; high-temperature polymers [ 366 ]; polymerization from surfaces [ 367 , 368 ] SELECTED EXAMPLES FOR THE POLYMERIZATION... CHMePh, CHMe(Naphthyl), etc 2,4 ,6- Me3-C6H2, 4-Me-C6H4, 4-Cl-C6H4 2,4 ,6- Me3-C6H2 2 ,6- i-Pr2-C6H3 R ¼ 2,4 ,6- Me3-C6H2 Copyright 2005 by Marcel Dekker All Rights Reserved # [ 161 ] [177,178,180] [191] (23) [1 06 109] R1 ¼ CH ¼ CPh2; R2 ¼ Ph, Cy, etc R1 ¼ Ph; R2 ¼ Ph, Cy, etc R1 ¼ Ph; PR23 ¼ PCy2(CH2SiMe3) Refs (24) [192,195] (25) [193–195] [197] [1 96, 201,208] [202] ( 26) [198,199,203,205] (27) Several complexes... Various W-based/chlorobenzene No information given Schrock catalyst in toluene WCl6/Sn(CH3)4 in PhCl [ 263 ] [258] [ 264 ] [ 261 ] [ 265 ] [ 266 ] [ 267 ] [270–272] [ 264 ,273] Oligomers possess formula (C4H6)n Same equilibrium composition as starting from 1,5-cyclooctadiene b Copyright 2005 by Marcel Dekker All Rights Reserved polymerization of norbornene [274,275], probably due to steric shielding by the cyclopentylene... Ru(¼CHPh)(PCy3)2Cl2 ReCl5 RuCl3*3H2O (38a) all-HT polymer [57d] (38b) (CO)5W¼CPh2 High trans conformation [179]a [2 96] [2 86] [2 86] b all HT 1.00 RO¼OAc [1 56, 284] (38c) (38c) (38d) (38d) 1.00 0.52 1.00 0 .63 All cis polymer end with a fully syndiotactic ring sequence Atactic polymer [414,410] [411] [415] [415] (38f) WCl6/Me4Sn 0.22 1.00 0 (38b) ReCl5 WCl6/EtAlCl2 (1:4) ReCl5/PhCl WCl6/n-Bu4Sn (1:2) (38b) (38b) (38b)... discover of olefin metathesis see: (a) Eleuterio, H S (1991) J Mol Catal 65 : 55; (b) Banks, R L (19 86) CHEMTECH, 16: 112 and [1,4,5] Eleuterio, H S (1 960 ) US 3,074,918 1957, Ger 1,072,811, Du Pont de Nemours & Co., C.A 55: 160 05 Truett, W L., Johnson, D R., Robinson, I M., and Montague, B A (1 960 ) J Am Chem Soc., 82: 2337 Peters, E F., and Evering, B L (1 961 ) US 2, 963 , 447 1 960 , Standard Oil of Indiana,... and low prize this molecule became one of the standard monomers if testing the activity of a potential metathesis catalyst [1] Polymerizations were reported using a wide range of initiators from simple metal halides, e.g., TiCl4 [7], RuCl3 [ 161 ,400], MoCl5 [401] or MgCl2 [66 ] to well-defined carbene initiators [ 166 ,177,439] The first living ROMP was reported in 19 86 using a titanium metallacycle as catalyst... (e) (f) – – – – 0.25 [59] [ 466 ] (f)g – – (g)g Me – Meaendo/exo ¼ 3/1 H OMe OMe 0.07b OMed OMe 0.30b Various catalysts can be used ROMP in the presence of water; Ethanol/water; PDI ¼ 1.89 Insoluble products [170] [170]c [ 466 ] [ 467 ] [189] [189]h a Other rests are possible for the polymerization (R1 ¼ R2 ¼ CH2OH) [170, 469 ] The cis-content and the configuration of the resultant polymer is dependent on the... reaction In this case only the syn-isomer polymerizes, i.e., the polymer is completely free of the anti-isomer [152] Structure (38b) and a mixture of (38e) and (38f) were polymerized utilizing as well classical catalysts, e.g.,WCl6 in combination with SnBu4 or SnPh4 [2 86, 421], as the modern unicomponent initiator Ru(¼CHPh)(PCy3)2Cl2 [2 96] Examples of ROMP of the methyl substituted norbornenes (38a–f . 2 ,6- Et, i-Pr [155] (14) Ar ¼ 2 ,6- Ph 2 -C 6 H 3 R ¼ 2 ,6- Ph 2 -C 6 H 3 [1 56] (15) L ¼ P(OMe) 3 , THF [159] ( 16) W(CH-t-Bu)(O)(OAr) 2 (PMe 3 )Ar¼ 2 ,6- Ph 2 -C 6 H 3 [ 162 ] (17) Ar ¼ 2 ,6- i-Pr 2 -C 6 H 3 ,. 19 86 [ 163 – 165 ]. These complexes serve as highly active initiators and were utilized, e.g., for the living polymerization of endo,endo- 5 ,6- dicarbomethoxynorbornene [ 164 ] and other monomers [ 166 ] formula Ta(¼CH-R)X 3 (solv) (R ¼ t-Bu, etc., X ¼ O-2 ,6- i-Pr 2 -C 6 H 3 , O-2 ,6- Me 2 -C 6 H 3 , S-2,4 ,6- i- Pr 3 -C 6 H 2 ; solv ¼ py, THF ). The complexes were used for ROM polymerizations of norbornene and additionally