Iron-terpyridine complexes, [Fe(terpyridine) 2](FeCl4)2 (1), FeCl3(terpyridine) (4), and FeCl3-(4,4′,4′′-tri-tert-butylterpyridine) (5), were found to display high catalytic activities for 1,2/3,4-polymerizations of isoprene and trans-1,4-polymerization of 1,3-butadiene in the presence of MMAO (modified methylalumoxane), whereas FeCl2(6,6′′-diarylterpyridine) complexes 2 and 3 exhibit no catalysis for polymerizations of these two monomers even in the presence of MMAO. The N,N,O-ligated N-(2-pyridyl)methyl-2-hydroxy-3,5-di-tert-butylbenzaldimine complex (6) of FeCl2 and the corresponding N-(2-pyridyl)-2-oxy-3,5-di-tert-butylbenzaldimine/FeCl (7) revealed more efficient catalysis for polymerization of isoprene and 1,3-butadiene. In sharp contrast to these N,N,N-donor or N,N,O-donor ligated complexes, N,N-ligated FeCl 2(sparteine) complex 8 shows much lower catalytic activities, although the stereospecifity is much higher.
A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2‘-Te(4-Me-6- t Bu-C6H2O)2}]2 (5: X = Cl; 6: X = O i Pr), catalyzed the ring-opening polymerization of cyclic esters such as ε-caprolactone, δ-valerolactone, and l-lactide. The strong dependence of polymerizations on the solvent was observed in this catalytic system. When the polymerizations of ε-caprolactone and l-lactide were carried out in toluene at 100 °C, tellurium-bridged bis(aryloxo)titanium complex 5 was found to give polymers with rather broad molecular weight distribution due to back-biting. When the polymerizations of ε-caprolactone and l-lactide was carried out in anisole or in dioxane at 100 °C, complex 5 was found to initiate the controlled polymerization, to result in quantitative polymer yields and narrow molecular weight distributions (living nature). The diblock copolymers of l-lactide and ε-caprolactone were also obtained with the catalyst system 5 in anisole. The diblock copolymers showed two melting endothermic at 44.7−53.5 °C derived from the ploy(ε-caprolactone) block and at 155.2−156.8 °C derived from the ploy(l-lactide) block.
A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands,), were prepared. 5b and 6b were determined by X-ray crystallography to have chloro-and isopropoxo-bridged dimeric structures. The structural data for these complexes indicated that the Ti-Te coordination bonds were stronger than the similar Ti-S coordination bonds in the corresponding sulfur-bridged complexes. The reaction of (C 5 R 5 )TiCl 3 (R ) H, Me) with 2,2′-Te(4-R-6-R′-C 6 H 2 OLi) 2 gave monocyclopentadienyl derivatives, (C 5 R 5 )TiCl{2,2′-Te(4-Me-6-t Bu-C 6 H 2 O) 2 } (7, R ) H; 8, R ) Me). The monomeric four-legged piano-stool geometry of 8 was revealed by X-ray analysis. Upon addition of methylaluminoxane (MAO), these complexes catalyzed the polymerization of ethylene. The activities of the tellurium-bridged complexes were found to be significantly higher than those of the corresponding methylene-bridged complex.
ROMP is a widespread tool to synthesize well-defined and highly functionalized polymers. 1 In particular, ruthenium initiators have been employed most often for the synthesis of polymers from a variety of cyclic olefins such as norbornenes and norbornadienes. 2 They tolerate a wide range of polar functionalities such as cyano 3 or ester 4 groups in norbornene derivatives. Additionally, some reports have been shown to produce polymers with well-defined microstructures in a living manner. 5 Recently, on the other hand, a detailed mechanistic investigation of the ROMP of endo-and exo-dicyclopentadiene has shown that the rate difference (>19 times) between exo/endoisomers is primarily due to steric interactions between the growing polymer chains and the incoming monomer. 6 Although there have been reports on the reactivity in ROMP using the exo/endo-isomers of norbornene derivatives bearing the polar groups, 7 in most cases these polar functional groups are the ester functionalities and a cyano group lie far from a norbornene skeleton, which may retard the appropriate evaluation of substituent effect by a cyano group toward the polymerization.It would be of great interest to evaluate reactivity for each of the isomerically pure exo-and endo-norbornene derivatives bearing both cyano and ester groups toward polymerization behavior. However, to the best of our knowledge, there are no reports in the literature on the ruthenium-initiated ROMP of such norbornenes including comparison of the reactivity between exo-and endo-monomers due to the rather limited synthetic methods for the simultaneous introduction of different two functional groups into the norbornene skeleton and isolation as pure isomeric exo-and endo-forms.Recently, we reported the palladium-catalyzed cyanoesterification of norbornadiene by ethyl cyanoformate, in which the cyano and ester groups can be introduced simultaneously and directly to a norbornene molecule, affording doubly functionalized exo-ethyl 3-cyanobicyclo[2.2.1]hept-5-ene-2-carboxylate (A) with excellent chemo-and stereoselectivities. 8 In addition, we prepared isomerically pure endo-form B by Diels-Alder reaction of freshly cracked cyclopentadiene and ethyl (Z)-3-cyano-2-propenoate followed by a careful separation by column chromatography on silica gel (Scheme 1). We herein describe ROMP of exo-isomer A, endo-isomer B, and the parent norbornene using the second-generation Grubbs' catalyst, (H 2 -IMes)(PCy 3 )Cl 2 RudCHPh (1) (H 2 IMes ) N,N-bis(mesityl)-4,5-dihydroimidazol-2-ylidene).
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