Solvent-free oligomerization of phenylacetylene catalyzed by (cyclopentadienyl)nickel complexes

Article abstract of DOI:10.1039/a905854k

The solvent-free reaction of phenylacetylene at 115°C in the presence of nickelocene, [(η-Cp)Ni]₂(PhC≡CH), [(η-Cp)Ni(CO)]₂, (η-Cp)Ni(NO), (η-Cp)Ni(GeBr₃)(CO), (η-Cp)Ni[(P(OMe₃)]Cl, (η-Cp)Ni(Ph₃P)Cl, (η-Cp)Ni(Bu₃ⁿP)I, or (Ph₃P)₂Ni(CO)₂ gives rise to a mixture of cyclotrimers, linear oligomers and poly(phenylacetylene), no reaction being observed in the case of internal acetylenes. Cyclotrimer formation is favoured by the presence of (a) added phosphine (2 equiv.), or (b) (cyclopentadienyl)nickel catalysts bearing a chloro substituent at Ni. A reduction in reaction temperature results in lower conversion but favours linear oligomer and polymer formation. The extent of reaction is greatly reduced in the case of (a) nickelocene in the presence of 2 equiv. PBu₃ⁿ, (b) (η-Cp)Ni(GeBr₃)(CO), or (c) (η-Cp)Ni(NO). The main effect of the presence of solvent, regardless of whether it is potentially coordinating (toluene) or not (n-octane), is to suppress almost completely reactions catalyzed by nickelocene. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a905854k

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Solvent-free oligomerization of phenylacetylene catalyzed by
(cyclopentadienyl)nickel complexes
William E. Douglas
CNRS UMR 5637, Case 007, Université de Montpellier II, 34095 Montpellier Cedex 5, France
Received 20th July 1999, Accepted 28th October 1999
᎐
The solvent-free reaction of phenylacetylene at 115 ЊC in the presence of nickelocene, [(η-Cp)Ni] (PhC᎐CH), [(η-
᎐
2
Cp)Ni(CO)]2, (η-Cp)Ni(NO), (η-Cp)Ni(GeBr3)(CO), (η-Cp)Ni[(P(OMe3)]Cl, (η-Cp)Ni(Ph3P)Cl, (η-Cp)Ni(Bu3nP)I,
or (Ph3P)2Ni(CO)2 gives rise to a mixture of cyclotrimers, linear oligomers and poly(phenylacetylene), no reaction
being observed in the case of internal acetylenes. Cyclotrimer formation is favoured by the presence of (a) added
phosphine (2 equiv.), or (b) (cyclopentadienyl)nickel catalysts bearing a chloro substituent at Ni. A reduction in
reaction temperature results in lower conversion but favours linear oligomer and polymer formation. The extent of
reaction is greatly reduced in the case of (a) nickelocene in the presence of 2 equiv. PBu3n, (b) (η-Cp)Ni(GeBr3)(CO),
or (c) (η-Cp)Ni(NO). The main effect of the presence of solvent, regardless of whether it is potentially coordinating
(toluene) or not (n-octane), is to suppress almost completely reactions catalyzed by nickelocene.
2 months), lit.8 red oil; Mϩ 452 [FAB: m-nitrobenzylalcohol])
Introduction
and (η-Cp)Ni(NO)9 [Mϩ 153 (EI)] were prepared as described.
During a previous study concerning the catalyzed cure of
acetylene-terminated resins it was discovered that nickelocene
is an effective catalyst for the polymerization of terminal
acetylenes, but the reaction occurs only under solvent-free con-
ditions.1 In the case of phenylacetylene the products consist of
a mixture of cyclotrimers, linear oligomers and trans-cisoidal
poly(phenylacetylene).2,3 Here are reported the results of an
investigation into this reaction and its generalization to a
variety of (cyclopentadienyl)nickel catalysts. It is shown that the
nature and distribution of the products can be monitored by
the use of size exclusion chromatography (SEC).
Preparation of tetraphenylcyclooctatetraene isomers
The previously described10 mixture of cyclooctatetraene iso-
mers (in which no trace of trimers was detected)10 was prepared
from phenylacetylene in the presence of chlorotrimethylsilane
and Pd/C. The SEC trace of the crude reaction product showed
only three peaks (retention times 37.90, 39.37 and 40.64 min).
Preparation of 1,2,4-triphenylbenzene. The title compound
was prepared from phenylacetylene and Hg[Co(CO)4]2 as
11
described12 and recrystallized from n-heptane (mp 101.1–
101.6 ЊC, lit.13 two forms 100 ЊC and 119–120 ЊC). The IR
spectrum showed no bands characteristic of linear trimers. A
solution of KMnO4 in acetone was not decolourized by the
compound thus confirming the absence of non-aromatic alkene
groups.13 The SEC trace showed a single peak with a retention
time of 42.03 min, identical to that for 1,3,5-triphenylbenzene
(Aldrich). The SEC trace for a mixture of the two isomers also
showed only a single peak with a retention time of 42.03 min.
Experimental
Phenylacetylene (Aldrich or Acros) was redistilled before use.
The mass spectra were obtained by use of a JEOL JMS-DX300
instrument (EI or FAB). Elemental analyses [% Found (% Cal-
culated)] were done at the CNRS Service Central d’Analyse.
SEC was carried out in THF at a flow rate of 0.9 ml minϪ1 by
use of a Waters 510 system equipped with 100, 500, 1000 and
10000 Å columns and a UV detector operating at 254 nm.
᎐
Preparation of PhC᎐C–CH᎐CHPh. β-Bromostyrene (ca.
᎐
᎐
Catalyst preparation/purification
85% trans and 15% cis) was coupled with phenylacetylene under
the published conditions, Et3N being used in place of Et2NH.14
The SEC trace of the reaction product (containing mainly
E-1,4-diphenylbut-1-en-3-yne with some Z-isomer14) showed
a single peak with a retention time of 43.64 min. An identical
trace was obtained after leaving the material to stand for 4 d.
The complex (PPh3)2Ni(CO)2 (Aldrich) was used as received,
(η-Cp)Ni(PPh3)Cl (Aldrich) was recrystallized from CH2Cl2–
pentane to give the pure compound [C 65.52 (65.53), H 4.90
(4.78)%], and nickelocene (Strem) was re-sublimed. Technical
grade [(η-Cp)Ni(CO)]2 from Aldrich (containing much
nickelocene) was fractionally vacuum-sublimed at 100 ЊC to
give a small quantity (<20%) of fine dark-red crystals of the
desired compound.
Preparation of PhC᎐C–CPh᎐CH . The unstable15,16
᎐
᎐
᎐
2
branched enyne was prepared starting from α-bromostyrene
under the same conditions as for the preceding reaction. After
6 h at RT the SEC trace for the reaction mixture showed a peak
with a retention time of 43.64 min assigned to the compound
together with a peak resulting from the monomer (retention
time 46.20 min). There was also a barely perceptible peak with a
retention time of 40.54 min. After 5 d, the magnitude of the
4
᎐
The dimer [(η-Cp)Ni] (PhC᎐CH), prepared as described
᎐
2
from crude [(η-Cp)Ni(CO)]2, was isolated by chromatography
followed by recrystallization from n-pentane at Ϫ78 ЊC to give
dark-green crystals [mp 133–134 ЊC (blackening above 100 ЊC),
lit.4 132–133 ЊC; Mϩ 348 (EI)].
(η-Cp)Ni(GeBr3)(CO) [Mϩ 464 (EI)] was prepared as
described5 from pure [(η-Cp)Ni(CO)]2 in toluene. The com-
plexes (η-Cp)Ni[P(OMe)3]Cl6 [Mϩ 282 (EI)], (η-Cp)Ni[P-
(n-Bu)3]I7 (mp 50–52 ЊC (waxy crystals formed over a period of
᎐
peak for PhC᎐C–CPh᎐CH (retention time 43.64 min) had
᎐
᎐
2
decreased, the peak with a retention time of 40.54 min having
become the most important (ratio of areas ca. 1:2).
J. Chem. Soc., Dalton Trans., 2000, 57–62
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57

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Polymerization procedure
Unless otherwise stated (Tables 1 and 2), the catalyst (ca. 0.1
mol% [Ni]) was added to degassed phenylacetylene (0.930 g
[1 ml]; 9.105 mmol) under dinitrogen. The stirred mixture was
placed in a bath at 115 ЊC and the reaction tube was closed to
prevent loss of material. In most cases there was a colour
change to dark orange-red after a short period. The reaction
mixture was cooled to RT after 6 h to give a dark red solid
or viscous liquid. The SEC traces of the product mixtures
thus obtained showed peaks resulting from some or all of the
following: poly(phenylacetylene) (retention time ca. 32 min),
linear oligomers of phenylacetylene (retention time ca. 40
min), 1,2,4- and/or 1,3,5-triphenylbenzene (retention time 42.03
min), unchanged phenylacetylene (retention time 45.00 min).
Results and discussion
The (Ph3P)2Ni(CO)2-catalyzed polymerization of acetylenes in
solution was reported many years ago.17 With phenylacetylene
in alcohol at 70 ЊC a violent reaction occurs giving a gum
containing triphenylbenzene.13,18 The reaction in inert solvents
such as refluxing cyclohexane has been extensively studied by
Meriwether et al.19–22 In particular, the results of experiments
with deuterated acetylenes are consistent with a hydrogen
transfer step for both linear and cyclic polymerization of phenyl-
acetylene, the suggested mechanism [Scheme 1 with (Ph3P)2 in
Fig. 1 SEC trace for product mixture from reaction of phenylacety-
lene in the presence of nickelocene under the standard conditions
(Table 1, entry 1).
hexasubstituted cyclotrimer in this case,22 but it should be noted
that 2-butyne-1,4-diol undergoes spontaneous dimerization
and cyclotrimerization in protic solvents.24 The Meriwether
mechanism has also been applied in the case of Ni(acac)2–
AliBu3 for which the intermediate ethynyl hydride complex of
Ni has been isolated.25
Previously, we have reported that under solvent-free condi-
tions nickelocene catalyzes terminal-acetylene polymerization,1
in the case of phenylacetylene giving cyclotrimers and linear
polyenes but no cyclotetramers.2,3 In solution, nickelocene,
᎐
and also [(η-Cp)Ni] (RC᎐CRЈ), catalyze the polymerization of
᎐
2
acetylenes but only in the presence of an aromatic heterocyclic
27
amine (e.g. pyridine)26 or AlBr3 (nickelocene with F CC᎐
᎐
᎐
3
CCF3 in solution has been reported to give traces of the
cyclotrimer28).
Product SEC retention times
In order to investigate the feasibility of using SEC for monitor-
ing the polymerization reaction, the polymerization of phenyl-
acetylene in the presence of nickelocene was repeated under the
same conditions as those used previously when the reaction
products were separated and analyzed.3 The SEC trace showed
four peaks (Fig. 1 and Table 1, entry 1) corresponding to the
four components previously separated from the reaction
mixture and characterized:3 (i) retention time 32.01 min; trans-
cisoidal poly(phenylacetylene) (Mw ca. 3000 [polydispersity 1.6]
with respect to polystyrene standards), (ii) 40.30 min; linear
oligomers of phenylacetylene (that with n = 4.5 has been
previously isolated3), (iii) 42.03 min; 1,2,4- and 1,3,5-tri-
phenylbenzene, and (iv) 45.00 min; unchanged phenylacetylene.
However, there are some discrepancies between the relative
amounts of each component determined by the two methods;
isolated3 (found by SEC), (i) 39 (50), (ii) 30 (9), (iii) 24 (30), and
(iv) 8 (8)%. These differences can be explained by variations in
sensitivity of the UV detector, and also by the fact that some of
the material isolated in the linear oligomer fraction is not
included in the area measured for the SEC peak with a
retention time of 40.30 min.
It having been established that the components in the
reaction mixture could be distinguished by SEC, various other
possible products were synthesized in order to check for any
coincidence of retention times.
Scheme 1 Reaction mechanism for nickelocene-catalyzed polymeriz-
ation and cyclotrimerization of phenylacetylene in the absence of
solvent.
The mixture of tetraphenylcyclooctatetraene isomers (possi-
bility of 7 isomers29), prepared in such a way as to contain no
trace of cyclotrimers,10 showed three SEC peaks with retention
times 37.90, 39.37 and 40.64 min. In particular, the peak at
37.90 min allows tetraphenylcyclooctatetraene formation in the
place of (η-Cp)] accounting for both processes.22 Of the many
disubstituted acetylenes investigated only 2-butyne-1,4-diol
reacted.19 A disputed23 second mechanism involving a nickelole
intermediate was put forward to explain the formation of the
58
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J. Chem. Soc., Dalton Trans., 2000, 57–62
59

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reaction mixture to be distinguished by SEC (cf. Fig. 1 for the
case where the absence of cyclotetramers has been established
by other means3).
D which re-forms A by reductive elimination of linear polymer
E. The cyclotrimers F can be formed by reductive elimination
from D when n = 2.
The SEC trace of pure 1,2,4-triphenylbenzene contained a
single peak with a retention time of 42.03 min, identical to that
for 1,3,5-triphenylbenzene, thus showing that the two cyclo-
In order to investigate the effect of solvents, the nickelocene-
catalyzed reaction was carried out at 100 ЊC for 7 h in the
presence of 5 ml of toluene or n-octane, the concentration of
the phenylacetylene solution being ca. 17% v/v. In each case,
the mixture became yellow almost immediately and after 1 h
orange-red. Evaporation of the reaction mixtures gave traces of
reddish-brown oils, the weights obtained corresponding to 8%
and 5% overall reaction (Table 1, entries 3 and 4), respectively.
The main effect of the presence of solvent, regardless of
whether it is potentially coordinating (toluene) or not (n-
octane), is to suppress almost completely reactions catalyzed
by nickelocene. In the case of nickelocene, coordination of a
solvent molecule occurs at the expense of an acetylene molecule
in the 19-electron catalytic species A (Scheme 1) thus inhibiting
the reaction. This is in contrast to (Ph3P)2Ni(CO)2 where
the corresponding catalytic species is 18-electron and can co-
ordinate a molecule of solvent in addition to the acetylene
molecules.
trimer isomers cannot be distinguished by SEC.
᎐
The stable tail-to-tail dimer PhC᎐C–CH᎐CHPh was pre-
᎐
᎐
pared from a commercial sample of β-bromostyrene (ca. 85%
trans and 15% cis) by Pd-catalyzed coupling with phenylacet-
ylene.14 The SEC trace of the reaction product (containing
mainly E-1,4-diphenylbut-1-en-3-yne with some Z-isomer)
showed a single peak with a retention time of 43.64 min. An
identical trace was obtained after leaving the material to stand
for 4 d. SEC can therefore be used to distinguish the presence of
the dimer in the reaction mixture.
Starting from α-bromostyrene, the unstable15,16 head-to-tail
᎐
dimer PhC᎐C–CPh᎐CH was prepared in the same way, the
᎐
᎐
2
SEC trace of the product mixture showing peaks at 43.64 min
for the head-to-tail dimer and at 46.20 min for unchanged
monomer. There was also a barely perceptible peak with a
retention time of 40.54 min. After 5 d, the magnitude of the
The presence of 1 equiv. of PBu3n (high electron-donating
ability and moderate cone angle38) per (η-Cp)2Ni (Table 1,
entry 5) had little effect. In contrast, with 2 equiv. PBu3n per (η-
Cp)2Ni the extent of conversion fell to 54% (Table 1, entry 6).
This was accompanied by an increase in the proportion of
cyclotrimers suggesting that the phosphine is present in the
coordination sphere of the catalytic species. Previously it has
been found that the electronic and steric factors of the phos-
phorus ligand play an important rôle in product distribution
in the solution oligomerization of phenylacetylene catalyzed
by rhodium() complexes,39,40 the presence of excess electron-
donating phosphites inhibiting the reaction.40 Indeed, the
sterically-hindered complex (tBu2PC2H4PtBu2)Ni(C2H2) does
not catalyze cyclooligomerization or polymerization of
acetylenes.41
The addition of 2 equiv. PPh3 (moderate electron-donating
ability and large cone angle38) per (η-Cp)2Ni had a very
different result, the extent of reaction being almost complete
(98.5%) with selective formation of cyclotrimers in 77% yield
(Table 1, entry 7). Presumably, triphenylphosphine is present
in the coordination sphere of Ni replacing one acetylene
group, thus favouring reductive elimination of the cyclotrimers.
Nickelocene reacts with PPh3 in cyclohexane to give Ni(PPh3)4
quantitatively,42 but (η-Cp)Ni(PPh3)Cl and CpCl are formed in
the presence of CCl4.32,33 Analogous reactions occur in the case
of phosphites.43 The intermediate species (η-Cp)Ni(PPh3)-
(σ-Cp) may be formed by a π to σ rearrangement of a cyclo-
pentadienyl ligand.32,44 In the presence of excess phosphine,
ionic species such as [(η-Cp)Ni(PR3)2]ϩClϪ are formed.45,46
Alkyl compounds of the type (η-Cp)Ni(PPh3)R are sufficiently
stable to be isolated and characterized, an investigation of the
n-alkyl derivatives suggesting reversible olefin β-elimination
accompanied by nickel hydride formation.47 Nineteen-electron
complexes (η-Cp)Ni(PR3)2 have been isolated and character-
ized, and have been shown to be most probably intermediates in
the reactions of nickelocene with phosphines.48
᎐
peak for PhC᎐C–CPh᎐CH had decreased and the peak for the
᎐
᎐
2
decomposition product at 40.54 min had become the most
important (ratio of areas ca. 1:2). The retention time of the
decomposition product is consistent with it being a mixture of
linear oligomers of phenylacetylene. Thus, SEC allows dimer
formation to be distinguished in the reaction mixture but no
differentiation between the tail-to-tail and head-to-tail isomers
is possible.
The preliminary studies showed the feasibility of using SEC
to follow the effects of catalysts on product distribution.
Indeed, the absence of SEC peaks with retention times of ca.
37.9 min or ca. 43.6 min rules out any significant cyclotetramer
or dimer formation. In all cases only the four products previ-
ously isolated and characterized for nickelocene are formed,
their distribution being dependent on the nature of the nickel
catalyst and reaction conditions.
Nickelocene-catalyzed polymerization of phenylacetylene
Treatment of phenylacetylene with nickelocene under the
standard conditions (115 ЊC, 6 h) in the absence of solvent
resulted in 92% conversion, the final reaction mixture con-
taining 50% polymer (Table 1, entry 1). The initial deep
green solution became rapidly olive-green and after 5 min
the mixture was orange-red. The reaction was unaffected by
the presence of the radical scavenger 2,6-di-tert-butyl-4-
methylphenol. Lowering the reaction temperature to 65 ЊC for
24 h resulted in a much reduced degree of conversion (26%), the
product mixture becoming poorer in cyclotrimers (Table 1,
entry 2).
᎐
᎐
No reaction of internal acetylenes (Me SiC᎐CSiMe , PhC᎐
᎐
᎐
3
3
᎐
CSiMe3, PhC᎐CPh) occurred under solvent-free conditions in
᎐
the presence of nickelocene or the other (cyclopentadienyl)nickel
catalysts. This suggests that, as with (Ph3P)2Ni(CO)2, the reac-
tion mechanism includes an acetylene hydrogen transfer step
rather than involving nickelole or other such intermediates.30,31
Probably the mechanism operating in this case is that of
Meriwether (Scheme 1), the catalytic species A being formed by
loss of a cyclopentadienyl ring, a reaction which is known to
Solvent-free polymerization in the presence of other (cyclopenta-
dienyl)nickel catalysts
occur readily.32,33 Indeed, a variety of 19-electron (η-Cp)NiL2
Use of the green phenylacetylene-bridged binuclear compound
᎐
᎐
complexes, including (η-Cp)NiPPh (HC᎐CPh) and (η-Cp)-
[(η-Cp)Ni] (PhC᎐CH) or the carbonyl-bridged binuclear
᎐
᎐
3
2
᎐
Ni(HC᎐CPh) , have been studied in benzene solution and are
complex [(η-Cp)Ni(CO)]2 (Table 2, entries 1 and 2) gave
᎐
2
surprisingly stable.34 The following step in the catalytic cycle
is the oxidative addition of phenylacetylene giving B, such
intermediate ethynyl hydride complexes of Ni having been
previously isolated.25 The next step is the insertion of phenyl-
acetylene into the Ni–C bond, a reaction which has been
previously observed.35–37 This step is repeated (n Ϫ 1)-fold giving
results very similar to those with nickelocene. In the case of
[(η-Cp)Ni(CO)]2 most probably the known reaction4 to give
᎐
[(η-Cp)Ni] (PhC᎐CH) takes place initially. Indeed, when the
᎐
2
᎐
internal acetylene PhC᎐CPh was treated with 0.35 mol% [(η-
᎐
Cp)Ni(CO)]2 at 115 ЊC in the absence of solvent, the initially
red solution turned deep green within 2 min consistent with
60
J. Chem. Soc., Dalton Trans., 2000, 57–62

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᎐
formation of [(η-Cp)Ni] (PhC᎐CPh) (no oligomerization of
Ni(GeBr3)(CO), or (c) nickelocene in the presence of 2 equiv.
᎐
2
the acetylene was observed). The kinetics of the reaction of
PBu3n. The main effect of the presence of solvent, regardless
of whether it is potentially coordinating (toluene) or not
(n-octane), is to suppress almost completely reactions catalyzed
by nickelocene. It can be concluded that under solvent-free
conditions (cyclopentadienyl)nickel compounds in general are
active catalysts for the polymerization of terminal acetylenes.
᎐
[(η-Cp)Ni(CO)] with acetylenes to give [(η-Cp)Ni] (RC᎐CRЈ)
᎐
2
2
have been extensively investigated,49,50 and it was found that at
very high acetylene concentrations a second order mechanism is
important.50 Green acetylene-bridged binuclear compounds are
readily formed on reaction of acetylenes with nickelocene,51
and the complexes are stable up to 70–80 ЊC in an inert
solvent.52 Most probably the nickelocene-catalyzed reaction
References
᎐
involves an initial conversion step to give [(η-Cp)Ni] (PhC᎐CH)
᎐
2
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which then subsequently forms the catalytic species
(Scheme 1). This is consistent with the shorter times for the
A
colour-change to orange-red in the case of [(η-Cp)Ni]2-
᎐
(PhC᎐CH) or [(η-Cp)Ni(CO)] the binuclear intermediates
᎐
2
being present initially in the reaction mixture.
The complex (η-Cp)Ni(NO) gives only 35% conversion at
115 ЊC. Decrease in the reaction temperature to 65 ЊC results in
a reduction in both the extent of reaction (to 5%) and, as with
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nickelocene, the proportion of cyclotrimers (Table 2, entry 3).
᎐
Loss of the NO ligand enabling formation of [(η-Cp)Ni] (PhC᎐
᎐
2
CH) occurs only with difficulty. Indeed, it has been found that
nitrosyl exchange with 15NO did not occur for (η-Cp)Ni(NO) in
10 d at 120 ЊC.53
The complex (η-Cp)Ni(GeBr3)(CO) gave very similar results
(Table 2, entry 4) to those for (η-Cp)Ni(NO), suggesting that
although the CO ligand is readily lost (as shown by the initially
green solution turning orange-red after only 1 min at 115 ЊC),
the presence of the electron-withdrawing GeBr3 substituent5
hinders subsequent reactions with phenylacetylene. The reac-
tion mechanism may involve 20-electron species (Scheme 1 with
15 L. Carlton and G. Read, J. Chem. Soc., Perkin Trans. 1, 1978, 1631.
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(η-Cp)(GeBr3)Ni in place of (η-Cp)Ni). No reaction was
᎐
observed with PhC᎐CPh.
᎐
In the case of (η-Cp)Ni(Bu3nP)I, the product distribution and
extent of reaction (Table 2, entry 5) were very similar to those
for nickelocene (Table 1, entry 1), but the reaction mixture
did not pass through a green stage. Here too the reaction
mechanism may involve 20-electron species [Scheme 1 with
(η-Cp)NiI in place of (η-Cp)Ni].
20 L. S. Meriwether, E. C. Colthup and G. W. Kennerly, J. Org. Chem.,
1961, 26, 5163.
21 E. C. Colthup and L. S. Meriwether, J. Org. Chem., 1961, 26, 5169.
22 L. S. Meriwether, M. F. Leto, E. C. Colthup and G. W. Kennerly,
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23 V. O. Reikhsfel’d and K. L. Makovetskii, Usp. Khim., 1966, 35, 1204;
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24 M. d’Amboise, D. Mathieu and D. L. Piron, Talanta, 1988, 35, 763.
25 G. A. Chukhadzhyan, Z. I. Abramyan and G. A. Gevorkyan,
Zh. Obshch. Khim., 1973, 43, 2012; J. General Chem. USSR (Engl.
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26 M. Dubeck and A. H. Filbey, US Pat., 3256260, 1966 (Chem. Abstr.,
1966, 65, 7307a).
27 V. O. Reikhsfel’d, B. I. Lein and K. L. Makovetskii, Dokl. Akad.
Nauk SSSR, 1970, 190, 125 (Proc. Acad. Sci. USSR, 1970, 190, 31).
28 J. L. Davidson and D. W. A. Sharp, J. Chem. Soc., Dalton Trans.,
1976, 1123.
The complexes (η-Cp)Ni[(P(OMe3)]Cl and (η-Cp)Ni(PPh3)-
Cl (Table 2, entries 6 and 7) gave very similar results, the
product mixtures being much richer in cyclotrimers than in the
case of nickelocene. Since the phosphorus ligands are quite
different in nature,38 the phosphine groups are probably not
present in the active catalytic species. The reaction mechanism
in each case may involve 20-electron species [Scheme 1 with (η-
Cp)NiCl in place of (η-Cp)Ni]. Indeed, in neither case was a
green stage observed corresponding to formation of [(η-Cp)-
29 R. Diercks, L. Stamp and H. tom Dieck, Chem. Ber., 1984, 117,
᎐
Ni] (PhC᎐CH). This is in contrast to the case of nickelocene
᎐
2
1913.
in the presence of 2 equiv. PPh3 (Table 1, entry 7) where
cyclotrimer formation is favoured, the phosphine presumably
playing a rôle in the co-ordination sphere of Ni (vide supra).
Finally, for comparison, the effect of (Ph3P)2Ni(CO)2 was
investigated in the absence of solvent (Table 2, entry 8). Unlike
the reaction in benzene where only cyclotrimer and linear
trimer are afforded,19 the solvent-free reaction of phenyl-
acetylene in the presence of (Ph3P)2Ni(CO)2 gives linear
polymer in addition to cyclotrimer consistent with the much
greater concentration of phenylacetylene favouring a larger
30 R. E. Colborn and K. P. C. Vollhardt, J. Am. Chem. Soc., 1986, 108,
5470.
31 J. J. Eisch, J. E. Galle, A. A. Aradi and M. P. Boleslawski,
J. Organomet. Chem., 1986, 312, 399.
32 Y. T. Ustynyuk, T. I. Voevodskaya, N. A. Zharikova and N. A.
Ustynyuk, Dokl. Akad. Nauk SSSR, 1968, 181, 372; Dokl. Chem.
(Engl. Transl.), 1968, 181, 640.
33 C. Moberg and M. Nilsson, J. Organomet. Chem., 1973, 49, 243.
34 A. Becalska, J. D. Debad, H. K. Sanati and R. H. Hill, Polyhedron,
1990, 9, 581.
35 J. M. Huggins and R. G. Bergman, J. Am. Chem. Soc., 1979, 101,
4410.
value of n in intermediate D [Scheme 1 with (Ph3P)2 in place
36 S. J. Tremont and R. G. Bergman, J. Organomet. Chem., 1977, 140,
᎐
of (η-Cp)]. No reaction was observed with PhC᎐CPh.
᎐
C12.
In summary, the oligomerization and cyclotrimerization of
phenylacetylene with high conversion is catalyzed under
solvent-free conditions by a wide variety of cyclopentadienyl-
nickel complexes, internal acetylenes being unreactive. Cyclo-
trimer formation is favoured by the presence of (a) 2 equiv. of
phosphine in the reaction mixture, or (b) (cyclopentadienyl)-
nickel catalysts bearing a chloro substituent at Ni. A reduction
in reaction temperature results in lower conversion but favours
linear oligomer and polymer formation. The extent of reaction
is greatly reduced in the case of (a) (η-Cp)Ni(NO), (b) (η-Cp)-
37 L. M. Zubritskii, T. N. Fomina, V. A. Kalinina and K. V. Bal’yan,
Zh. Org. Khim., 1979, 15, 2213; J. Org. Chem. USSR (Engl. Transl.),
1979, 15, 2006.
38 C. A. Tolman, Chem. Rev., 1977, 77, 313.
39 S. Yoshikawa, J. Kiji and J. Furukawa, Makromol. Chem., 1977, 178,
1077.
40 J. Wendt, U. Klinger and H. Singer, Inorg. Chim. Acta, 1991, 183,
133.
41 K.-R. Pörschke, C. Pluta, B. Proft, F. Lutz and C. Krüger, Z.
Naturforsch., Teil B, 1993, 48, 608.
42 H. Behrens and K. Meyer, Z. Naturforsch., Teil B, 1966, 21, 489.
J. Chem. Soc., Dalton Trans., 2000, 57–62
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