Cyclopropane systems, polymerization

Prior knowledge has shown the value of introducing cyclopropane systems into macromolecules. A number of isolated studies have been carried out on the polymerization of such structures (10, 14, 28), principally on cyclopropane (28) and isopropylcyclopropane. Attention was directed toward three types of structures—i.e., the 1,1-dichlorocyclopro-panes, the bicyclo[n.l.0]alkanes, and the spiro [2.n] alkanes. In each case, the effects involved appeared highly complex the polymers formed have not yet all been characterized, and it is thought that a comparison with the model structures expected from rupture of one or the other of the cyclopropane bonds may be of value. 

With some catalyst systems, selectivity to primary metathesis products is near 100%, but side reactions (double-bond migration, dimerization, cyclopropanation, polymerization) often reduce selectivity. Such side reactions, such as oligomerization and double-bond shift over oxide catalysts, may be eliminated by treatment with alkali and alkaline-earth metal ions.26... 

Rhodium-based catalysis suffers from the high cost of the metal and quite often from a lack of stereoselectivity. This justifies the search for alternative catalysts. In this context, ruthenium-based catalysts look rather attractive nowadays, although still poorly documented. Recently, diruthenium(II,II) tetracarboxylates [42], polymeric and dimeric diruthenium(I,I) dicarboxylates [43], ruthenacarbor-ane clusters [44], and hydride and silyl ruthenium complexes [45 a] and Ru porphyrins [45 b] have been introduced as efficient cyclopropanation catalysts, superior to the Ru(II,III) complex Ru2(OAc)4Cl investigated earlier [7]. In terms of efficiency, electrophilicity, regio- and (partly) stereoselectivity, the most efficient ruthenium-based catalysts compare rather well with the rhodium(II) carboxylates. The ruthenium systems tested so far seem to display a slightly lower level of activity but are somewhat more discriminating in competitive reactions, which apparently could be due to the formation of less electrophilic carbenoid species. This point is probably related to the observation that some ruthenium complexes competitively catalyze both olefin cyclopropanation and olefin metathesis [46], which is at variance with what is observed with the rhodium catalysts. 

Benzyloxy(cyano)carbene would be expected to be electrophilic by virtue of the calculated selectivity index, Wp -HjOccN 111- This has not yet been experimentally proved as 3-bcnzyloxy-3-cyano-3//-diazirine is rather labile and cannot be isolated if it is synthesized by the substitution of chlorine by a cyano group in 3-benzyloxy-3-chloro-3if-diazirine consequently, this substitution reaction is carried out in the presence of an alkene, hence, preparing 1-benzyloxy-cyclopropane-l-carbonitrile derivatives. However, the cyanide ion present in the system induces the polymerization of electrophilic alkenes, such as acrylonitrile or methyl acrylate. 

Although no new types of bonds are formally formed, (alk-l-enyl)cyclopropane formation occurred during the polymerization of tricyclo[3.1.0.0 ]hex-3-ene in the presence of the Schrock and Osborn catalytic systems. ... 

The reactivity of this vinylcyclopropane compound toward cationic or Ziegler-Natta initiators is greater than that of purely cyclopropane-type monomers. This stems from the conjugation of the two unsaturated systems the results obtained agree with work carried out on the polymerization of vinyl cyclopropane itself. 

Polymerization of Bicyclo[6.1.0]non-4-ene and 9,9-Dihalobicyclo-[6.1.0]non-4-ene. Bicyclo[6.1.0]non-4-ene and 9,9-dihalobicyclo [6.1.0]-non-4-ene (M26, Equation 32) have the special feature of having two unsaturated sites that can react separately or simultaneously—that is, one C=C double bond and a cyclopropane (47-50) 9,9-dihalobicyclo [6.1.0]-non-4-ene was synthesized by adding dihalocarbene to 1,5-cyclooctadiene (yield 56%). Reduction of the dihalocyclopropane group with a Na/ hydrated methanol system yielded bicyclo[6.1.0]non-4-ene (yield 85%). 

For the cyclopropanation of styrene with EDA, Cu-polymerized 82 complexes afforded similar results than the non supported Box. In the first case 61% and 60% yield, 67/33 and 71/29 dr in favour of the trans, 93% and 94% ee were respectively observed. The catalytic system could be reused without loss of its catalytic properties. Moreover, it is noteworthy that the immobilization method did not influence the catalytic behaviour catalytic systems formed with copolymerized (route A) [84] or graft methodology (route B) [85] were substantially equivalent (variation of about 1 to 2% of the yield, ee or dr). 

The emphasis is put only on the facts that (a) when the substituted olefins are metathesized with classical Friedel-Crafts catalytic systems the pathways for carbene formation (initiation) are in most cases unresolved [16] (b) in this cases it is difficult to avoid the cationic processes [17] and (c) metallacyclobutanes are discussed as transition states not only for OM but for cyclopropanation and addition polymerization as well [14]. 

The tungsten carbene system, Ph2C—W(CO)5/TiCl4 induced polymerization of bicyclo[5.1.0]oct-2-ene to polyalkenamers having cyclopropane rings along the polymer chain [144] [Eq. (80)]. 

A special case of stereoelectivity has been encountered in polymerizing a racemic monomer with an optically active one. Minoura et al. (158) carried out the ring-opening copolymerization of propylene oxide with d-camphoric acid anhydride using diethyl zinc and triethyl amine as catalyst. It was found that the products were alternating copolymers which were optically active. The propylene oxide recovered from the copolymerization system was also optically active. An attempt to incorporate preferentially in a polyamide chain one of the optical antipodes of trans-cyclopropane-1,2-dicarbonyl chloride, by polycondensing this racemic monomer with optically active 1,2-propylene diamine failed (159). 

---