Cycloaliphatic polyolefins with functional groups were
obtained by Pd(II)-catalyzed homo-
and copolymerizations of norbornene derivatives.
Bicyclo[2.2.1]hept-5-ene-2-carboxylic acid, the
corresponding methyl ester,
2-(hydroxymethyl)bicyclo[2.2.1]hept-5-ene, and the
corresponding octanoate and
decanoate were used as the monomers in these addition polymerizations.
Pd(II)−nitrile catalysts [Pd(RCN)4][BF4]2 (with R =
CH3 and C2H5) quite selectively
polymerized the exo isomers of the esters of
2-(hydroxymethyl)bicyclo[2.2.1]hept-5-ene.
Monomer mixtures containing an 80/20 ratio of
endo/exo
isomers were converted into polymers containing more than 50% of exo
units. 1H NMR studies showed
that the predominant fraction of the endo isomer remained unreacted.
The nitrile based Pd catalysts
were not sufficiently active to polymerize the monomers with
electron-withdrawing substituents linked
to the bicyclic unit at ambient temperature. In-situ prepared
(η3-allyl)palladium complexes with
associated
tetrafluoroborate and hexafluoroantimonate ions were found to be
substantially more active. They were
able to catalyze the addition polymerization of norbornene derivatives
containing a large proportion of
endo isomers. Quantitative monomer conversions were achieved for
aliphatic esters of 2-(hydroxymethyl)bicyclo[2.2.1]hept-5-ene. Random copolymers of
norbornene and the latter esters with molecular weights
M
n(GPC) above 100 000 were prepared.
The (η3-allyl)palladium compounds were suitable
for the
polymerization of bicyclo[2.2.1]hept-5-ene-2-carboxylic
acid methyl ester; high molecular weight materials
were obtained via copolymerization with norbornene. Furthermore,
addition polymers containing 0.2
carboxylic acid group per repeating unit were prepared by the
copolymerization of norbornene and bicyclo[2.2.1]hept-5-ene-2-carboxylic acid. The
hexafluoroantimonate-based (η3-allyl)Pd(II)
catalyst had a higher
polymerization activity than the Pd compound with the smaller
BF4
- counterion which was
rationalized
by a slightly stronger association of BF4
-
with the (η3-allyl)Pd(II) unit.
Cycloaliphatic polyolefins with functional groups were prepared by the Pd(II)‐catalyzed addition polymerization of norbornene derivatives. Homo‐ and copolymers containing repeating units based on bicyclo[2.2.1] hept‐5‐en‐2‐ylmethyl decanoate (endo/exo‐ratio = 80/20), bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylic acid methyl ester (exo/endo = 80/20), bicyclo[2.2.1]hept‐5‐ene‐2‐methanol (endo/exo = 80/20), and bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylic acid (100% endo) were prepared in 49–99% yields with {(η3‐allyl)Pd(BF4)} and {(η3‐allyl)Pd(SbF6)} as catalysts. The catalyst containing the hexafluoroantimonate ion was slightly more active than the tetrafluoroborate based Pd‐complex.
Palladium complexes of cross‐linked polyvinylpyridine and poly(acryl‐amide‐methacrylic acid) copolymer coated on silica gel have been used as catalysts for the hydrogenation of azo and nitro groups under 101 kPa hydrogen pressure at 30°C. Nitro aromatics were selectively and almost completely reduced to the corresponding amines. A rate equation of the type, rate = k[cat][H2] has been derived for the hydrogenation of nitrobenzene on the basis of the experimental results and kinetic data. Also the selective hydrogenation of azobenzene to hydrazobenzene could be achieved with these catalysts.
Palladium complexes of polyvinyl pyridine coated silica gel have been prepared and used as hydrogenation catalysts for alkenes and alkynes under ambient conditions. The kinetics of hydrogenation for a few substrates have been studied and a possible mechanism proposed. The kinetic and mechanistic aspects of the hydrogenation of the substrates, effect of additives on the rate of hydrogenation, selectivity of the catalyst and recycling efficiency of the catalyst are presented in this paper.
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