Grubbs introduced (salicylaldimino)nickel methyl complexes [113], which
operate without requirement of a cocatalyst and allow the incorporation of bulky
cycloolefins such as norbornene as well as functionalities into polyethene. Some
promising results were reported on catalysts with nitrogen-based chelating ligands
(see Fig. 7). The functionalized monomers so far copolymerized with ethene by Ni
and Pd catalysts bearing nitrogen-based ligands are listed in Fig. 8. Copolymerization reactions of ethene with functionalized norbornene catalyzed by nickel
(salicylaldiminato)-based catalysts are summarized in Fig. 7.
Complexes VI-1 and VI-2 were early reported as single-component catalysts
for the copolymerization of ethene with functionalized norbornene derivatives
N OH and N COOMe , affording P(E-co-N OH ) with N OH incorporation of 22 wt%,
M w ¼ 17.2 kg mol
À1 , and M w /M n ¼ 1.6 and P(E-co-N COOMe ) with N COOMe
incorporation of 12 wt% and M w ¼ 73.8 kg mol
À1 , respectively. A more extensive
study revealed that acetonitrile-containing catalyst VI-2, owing to the easier activation, gives a higher activity than the phosphine-containing analogues VI-1 [114].
Copolymerization of ethene with functionalized norbornene derivatives was
extended to monomers N CH2OH and N OAc . Monomers bearing ester groups (N COOMe
and N OAc ) resulted in less poisoning than the protic N CH2OH , as showed by
productivities and molar masses. Moreover, the higher the steric demand of substituent the lower the incorporation (in the order N COOMe < N OAc < N CH2OH ). This trend
is ascribable to endo isomers of the monomer mixture, which after insertion are prone
to give chelated intermediates that block the vacant coordination site of catalysts.
Thus, tricyclononene-based functionalized monomers (TCN COOtBu , TCN (COOtBu)2 ,
TCN AN , TCN IM ) are more readily incorporated than bicyclic analogues because of
the longer distance between the polar functionality and the olefin double bond.
Interestingly, incorporation of monomer TCN COOtBu could be tuned from 2 to
31 mol% through TCN COOtBu /E feed ratio, though productivity dropped down with
decreasing ethene concentration.
Bimetallic catalysts, which are generally and intrinsically more active than their
monometallic analogues, can profit from cooperative effects arising from the close
proximity of two metal centers [115–118]. A positive effect of dinuclearity was
demonstrated by catalysts VII-1ÀVII-3/B(C 6 F 5 ) 3 in copolymerization of ethene
with functionalized norbornene derivatives N COOMe and N CH2OAc . A twofold higher
activity as well as higher incorporation of functionalized monomer was observed in a
series of E-co-N CH2OAc copolymerizations by dinuclear VII-1ÀVII-3/B(C 6 F 5 ) 3
with respect to the mononuclear analogues under the same conditions. Effect of
dinuclearity on activity, incorporation, and best performance of catalyst VII-3, which
possesses the terphenyl o-C 6 H 4 (C 6 H 4 ) 2 group as bridging unit between the two
salicylaldimine cores, was also confirmed for monomer N COOMe . Experimental
evidence and theoretical calculations suggested the effective action of a cooperative
effect between the two metal centers [118].
Binuclear naphthyloxydiiminato nickel catalysts VIII-1 and VIII-2 activated by
[Ni(cod) 2 ] efficiently copolymerize a variety of functionalized monomers from
norbornene derivatives [119, 120]. The effective occurrence of eventual cooperative effects in copolymerization of ethene with monomers N OH , N COOMe , and
132
L. Boggioni and I. Tritto
operate without requirement of a cocatalyst and allow the incorporation of bulky
cycloolefins such as norbornene as well as functionalities into polyethene. Some
promising results were reported on catalysts with nitrogen-based chelating ligands
(see Fig. 7). The functionalized monomers so far copolymerized with ethene by Ni
and Pd catalysts bearing nitrogen-based ligands are listed in Fig. 8. Copolymerization reactions of ethene with functionalized norbornene catalyzed by nickel
(salicylaldiminato)-based catalysts are summarized in Fig. 7.
Complexes VI-1 and VI-2 were early reported as single-component catalysts
for the copolymerization of ethene with functionalized norbornene derivatives
N OH and N COOMe , affording P(E-co-N OH ) with N OH incorporation of 22 wt%,
M w ¼ 17.2 kg mol
À1 , and M w /M n ¼ 1.6 and P(E-co-N COOMe ) with N COOMe
incorporation of 12 wt% and M w ¼ 73.8 kg mol
À1 , respectively. A more extensive
study revealed that acetonitrile-containing catalyst VI-2, owing to the easier activation, gives a higher activity than the phosphine-containing analogues VI-1 [114].
Copolymerization of ethene with functionalized norbornene derivatives was
extended to monomers N CH2OH and N OAc . Monomers bearing ester groups (N COOMe
and N OAc ) resulted in less poisoning than the protic N CH2OH , as showed by
productivities and molar masses. Moreover, the higher the steric demand of substituent the lower the incorporation (in the order N COOMe < N OAc < N CH2OH ). This trend
is ascribable to endo isomers of the monomer mixture, which after insertion are prone
to give chelated intermediates that block the vacant coordination site of catalysts.
Thus, tricyclononene-based functionalized monomers (TCN COOtBu , TCN (COOtBu)2 ,
TCN AN , TCN IM ) are more readily incorporated than bicyclic analogues because of
the longer distance between the polar functionality and the olefin double bond.
Interestingly, incorporation of monomer TCN COOtBu could be tuned from 2 to
31 mol% through TCN COOtBu /E feed ratio, though productivity dropped down with
decreasing ethene concentration.
Bimetallic catalysts, which are generally and intrinsically more active than their
monometallic analogues, can profit from cooperative effects arising from the close
proximity of two metal centers [115–118]. A positive effect of dinuclearity was
demonstrated by catalysts VII-1ÀVII-3/B(C 6 F 5 ) 3 in copolymerization of ethene
with functionalized norbornene derivatives N COOMe and N CH2OAc . A twofold higher
activity as well as higher incorporation of functionalized monomer was observed in a
series of E-co-N CH2OAc copolymerizations by dinuclear VII-1ÀVII-3/B(C 6 F 5 ) 3
with respect to the mononuclear analogues under the same conditions. Effect of
dinuclearity on activity, incorporation, and best performance of catalyst VII-3, which
possesses the terphenyl o-C 6 H 4 (C 6 H 4 ) 2 group as bridging unit between the two
salicylaldimine cores, was also confirmed for monomer N COOMe . Experimental
evidence and theoretical calculations suggested the effective action of a cooperative
effect between the two metal centers [118].
Binuclear naphthyloxydiiminato nickel catalysts VIII-1 and VIII-2 activated by
[Ni(cod) 2 ] efficiently copolymerize a variety of functionalized monomers from
norbornene derivatives [119, 120]. The effective occurrence of eventual cooperative effects in copolymerization of ethene with monomers N OH , N COOMe , and
132
L. Boggioni and I. Tritto