Polymerization of norbornadiene

The monomers dealt with can be polymerized by various mechanisms, not only by ROMP. For example, a rapid polymerization of norbornadiene occurs using a homogeneous catalytic system consisting of nickel acetylacetonate or a nickel-phosphine complex, such as nickel bis-(tri-n-butylphosphine) dichloride (NiCl2(TBP)2) or nickel bis-(tricyclohexylphosphine) dichloride (NiCl2(TBP)2). Nickel acetylacetonate as catalyst is known to initiate rather a classical vinyl polymerization (7). The classical vinyl polymerization... 

Two series of cationic complexes, [Mo(NO)2L4]2+ (L = RCN, py, etc.) and [MoCl(NO)2L3]+ have been prepared by halide abstraction from [MoCl2(NO)2L2] using silver salts in DME (method D). Some members of the series catalyze the polymerization of norbornadiene, whereas the uncharged parent compounds do not.29 The series [Mo(NO)2L4]2+ (L is a displaceable solvent such as THF) may also be obtained by treatment of [Mo(CO)6] with NO[PF6] followed by addition of further ligands such as bipy.29 This latter reaction also gives [ Mo(NO)2(PF6)2 ] which is assumed to be a polymer with weak PF6 bridges.29... 

No dimers were formed in the controlled thermal decomposition a binuclear ir complex Co2(CO)4(C7Hg)2(57). However, when the decomposition of this complex was performed in the presence of AlBrs, Binor-S was obtained in almost quantitative yield (52). Interaction of the complex with AlBrs may cause breaking of the bridging carbonyl groups and thus cause free rotation in the Co-Co axis, which may be necessary to obtain Binor-S selectivity. Similarly, CosfCOls becomes an effective Binor-S catalyst in the presence of as little as 0.5-1 mole of AlBi s or BFs O(C2H5)2 per mole of the carbonyl. These catalysts are very active and produce Binor-S essentially with quantitative conversion and selectivity (52). Other metal carbonyls and their mixtures with Lewis acids were evaluated as well. Low conversion to dimers other than Binor-S took place in some instances in the majority of cases, however, polymerization of norbornadiene occurred. The catalyst systems studied included Ni(CO)4, Fe(CO)5, Mn2(CO)io, Cr(CO)g, Mo(C0)fl, and W(CO)g in combination with BPg O(C2H5)2 cocatalyst (52). 

Stereospecific polymerization of 1,3-dienes (10-18) (to butadiene) and isoprene homo- and copolymers), dimerization of propene (19) and recently stereospecific polymerization of acetylene (20) to high cis-content polyacetylene have all been reported using lanthanide catalysts. Sen (21) has reported the preparation of cationic europium systems (which perhaps function as cationic initiators) for polymerization of norbornadiene and 1,3-cyclohexa-diene. 

The catalytic activities of both batches A and B of the polystyrene-supported phosphine Pd (II) chloride catalyst were found to be substantially less than that of the homogeneous analogue [ (C6H5)3P]2PdCl2 and to decrease with extended use. The precise cause of this loss of catalytic activity is unclear. Possible causes include oxidation of the pendant phosphine groups, leading to metal leaching, or polymerization of norbornadiene within the polystyrene matrix initiated by intermediates in such phosphine oxidation. 

An isomerization of bonds occurs in the transannular polymerization of norbornadiene ... 

Intramolecular transfer reactions are possible with cationic polymerizations. This leads to an isomerization of the monomeric unit. Since the monomeric unit of the resulting polymer often cannot be produced by polymerization of the monomer or unimer of this polymer, reactions of this type are also referred to as phantom or exotic polymerizations. At low temperatures, the isomerization polymerization is preferred to normal propagation, and here two types can occur. An isomerization of bonds occurs in the transannular polymerization of norbornadiene ... 

Polymerization of norbornadiene with cationic catalysts (e.g., AICI3) occurs readily at various temperatures leading to saturated polymers [139]. Thus, at low temperatures, soluble polymers having 2,6-disub-stituted nortricyclene structure were primarily obtained while at higher temperatures insoluble polymers with cross-linked structures, as a result of addition polymerization of the two double bonds, were formed [Eq. (70)]. 

A type of ring opening addition polymerization using transition metal catalysts not unlike Ziegler-Natta catalysts is called metathesis polymerization." Metathesis polymers, first made in the 1960s, are called polyalkenamers. Polymers made from cyclooctadiene and norbornadiene have applications as specialty elastomers. The polymerization of norbornadiene can be summarized as follows ... 

Scheme 1 ROMP of a 2,3-disubstituted norbornadiene, a 2-substituted norborn-5-ene and polymerization of a 1-alkyne via a- and /3-addition, respectively. A and B are initiator-and termination-derived endgroups, respectively...

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

The carbonylation of norbornadiene in benzene solution catalyzed by PdCl2 leads to the formation of a polymeric ketone.532 This unusual reaction is believed to have the complex [PdCl2(nbd)] as its catalyst precursor, and the mechanism proposed for it is given in Scheme 47. 

However, the fact that complexes in which R = Ph, F, M02CH, and C2F6 also initiate polymerization of acrylonitrile suggests that chemistry at cobalt may be involved instead. The displacement of carbon monoxide ligands by diolefins to give stable complexes of type RCCo3(CO)7(nor-bornadiene) in the case of norbornadiene has been reported (18, 76), so that such a process is entirely possible. 

The complex Mo(tfd)3 was reported by King and co-workers (86) to catalyze the conversion of quadricyclane to norbornadiene (Eq. 9), polymerization of quadricyclane or norbornadiene, as well as the addition of water to quadricyclane to give nortricyclanol (Eq. 15). The reactions appear to involve pseudo-[4 + 2] cycloaddition to the sulfur atoms in the dithioketone form of the metal... 

Chiral polymers have been applied in many areas of research, including chiral separation of organic molecules, asymmetric induction in organic synthesis, and wave guiding in non-linear optics [ 146,147]. Two distinct classes of polymers represent these optically active materials those with induced chirality based on the catalyst and polymerization mechanism and those produced from chiral monomers. Achiral monomers like propylene have been polymerized stereoselectively using chiral initiators or catalysts yielding isotactic, helical polymers [148-150]. On the other hand, polymerization of chiral monomers such as diepoxides, dimethacrylates, diisocyanides, and vinyl ethers yields chiral polymers by incorporation of chirality into the main chain of the polymer or as a pedant side group [151-155]. A number of chiral metathesis catalysts have been made, and they have proven useful in asymmetric ROM as well as in stereospecific polymerization of norbornene and norbornadiene [ 156-159]. This section of the review will focus on the ADMET polymerization of chiral monomers as a method of chiral polymer synthesis. 

Optically active polyacetylene derivatives 97 were synthesized through ring-opening polymerization of the corresponding cyclooctatetraene derivatives.25 A twisted conformation of the main chain was proposed on the basis of CD and UV absorptions. Various optically active polyacetylenes have also been prepared from chiral monomers.24,25,263,177-183 The examples include a phenylacetylene derivative (98),26a alkylacetylenes 99,24 propionic esters such as 100,177,178 a Si-containing monomer (101),179 and disubstituted monomers such as 102.180 Poly-(A)-98 synthesized using a [RhCl(norbornadiene)]2 catalyst shows intense CD bands in the UV—vis region, probably based on a predominant helical sense of the main chain.263 This polymer effectively resolves several racemic... 

Our search for a more active system led us to bis(pentafluorophenyl)nickel complexes originally reported by Klabunde and co-workers in the 1980s [56]. One of the more interesting complexes reported was (// -toluene)Ni(C6F5)2 (Fig. 4.26). Toluene can be readily replaced by a number of neutral electron donors including xylene, mesitylene, THF, PEtj, and norbornadiene. In fact, Klabunde noted that formation of (norbornadiene)Ni(C6F5)2 was accompanied by intractable polymer. Klabunde speculated that vinyl addition polymerization occurred with possible crosslinking. Unfortunately, the insolubility of the norbornadiene polymer prevented further analysis. 

The polymerization of phenylacetylene using the complex [(nbd) Rh(acac)] 9 (nbd = norbornadiene, acac = acetylacetonate) as a catalyst precursor was found to occur with considerably higher rates in compressed (liquid or supercritical) CO2 than in conventional solvent such as THF or hexane (Sche-... 

The first hving polymerization of cyclic olefins with a high ring strain [28], such as norbomenes, norbornadienes (bicyclohepta-2,5-dienes, NBDs) or the Feast-monomer 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 ]deca-3,7,9-triene (TCDTFj) by W(N-2,6 i Pr2 C6H3)(CH- Bu)(OCMe(CF3)2) [34] was re-... 

The new monomer cation then starts another polymer chain. If, on the other hand, isobutylene (or even norbornadiene) is polymerized with AICI3, saturated end groups and an unsaturated monomer cation are primarily formed. This cation then starts the polymerization of another polymer chain, whereby the unsaturated group formed in this way is aluminated by the initiator. Thus, each polymer molecule contains an aluminum atom, produced as in equation (18-98) or equation (18-101) ... 

During ring-opening metathesis polymerization (ROMP) of norbornadiene (NBD) with the Grubbs catalyst a free radical is also observed as a 1 2 1 triplet, which is also formed, but to a much weaker extent, with norbornene (NBE), cyclopentene and 1,7-octadiene. The identity of this triplet, and that of a transient doublet observed together with the triplet in the case of benzonorbornadiene, are discussed as well as the possible role of radicals in initiation of ROMP, crosslinking of ROMP products, and polymerization of a-methylstyrene. 

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