Bis-cyclopentadienyl nickel (Nickelocene): A convenient starting material for reactions catalyzed by Ni(O) phosphine complexes

Full text of DOI:10.1021/jo0158377

J . Org. Chem. 2001, 66, 7539-7541
7539
form M(0) complexes Ni(PR3)4.10 It is this reactivity that
we have exploited here for the in-situ generation of an
active catalyst.
Bis-Cyclop en ta d ien yl Nick el (Nick elocen e):
A Con ven ien t Sta r tin g Ma ter ia l for
Rea ction s Ca ta lyzed by Ni(0) P h osp h in e
Com p lexes
Nicholas E. Leadbeater
Department of Chemistry, King’s College London, Strand,
London, WC2R 2LS, United Kingdom
We find that the complexes are best formed by direct
reaction of nickelocene and the pure ligand in the absence
of solvent. The mixture is heated to around 80 °C in a
Schlenk tube under strictly anaerobic conditions for a few
minutes, which leads to a near quantitative yield of Ni-
(PR3)4. Alternatively, the preparation can also be effected
by addition of ligand to a degassed solution of nickelocene
followed by heating. Again, within a few minutes a near
quantitative yield of Ni(PR3)4 is obtained. The solution-
phase reaction works equally well in a range of hydro-
carbon-based media but some problems occur in solvents
bearing ether linkages. In the majority of cases we find
that it is better to prepare the Ni(0) complex by the direct
reaction route, as this is faster and yields are nearer
100%. Complexes have been prepared here with PPh3,
PCl3, and P(OiPr)3 yielding Ni(PPh3)4, Ni(PCl3)4, and Ni-
{P(OiPr)3}4, respectively, for the purposes of using them
in catalysis.11 To show that the Ni(0) complexes generated
from nickelocene are active in catalysis, each has been
used for a known reaction and the yields of product have
been compared with those reported in the literature.
For use in the coupling of aryl or zinc reagents with
aryl bromides,12 the reagents, namely the aryl zinc and
aryl bromide, can simply be added to a THF solution of
Ni(PPh3)4 prepared from NiCp2 and the resultant mixture
stirred at room temperature for 2 h. As shown in Table
1, the results obtained are almost identical to those
reported in the literature, as expected, since the active
complex is the same in both cases. The synthesis of Ni-
(PPh3)4 from NiCp2 for use in catalysis has significant
advantages over the conventional preparation which
involves reduction of nickel(II) acetylacetonate with
triethylaluminum in the presence of triphenylphosphine
where a yield of 55% of Ni(PPh3)4 is obtained.13 It is
therefore necessary to purify the phosphine complex
before use. With the NiCp2 route, no purification is
needed so all catalyses can be performed in the same
reaction vessel that the Ni(0) complex is prepared in.
nicholas.leadbeater@kcl.ac.uk
Received J une 14, 2001
Nickel(0)-catalyzed carbon-carbon bond forming reac-
tions are an extremely powerful tool in organic syn-
thesis.1-4 Using nickel(0) complexes it is often possible
to invoke reactivity with substrates that are not activated
by palladium analogues or else perform reactions using
less forcing conditions. In addition, as palladium is now
a very expensive metal commercially, nickel is a signifi-
cantly cheaper alternative. The big disadvantage of using
nickel(0) complexes is their air sensitivity, compounds
such as Ni(PPh3)4 and Ni(COD)2 [COD ) 1,5-cycloocta-
diene] having to be handled under strictly anaerobic
conditions, which affects their popularity as catalysts.
Chemists have tried to overcome this by reducing stable
Ni(II) complexes to Ni(0) analogues in situ by adding, for
example, an excess of zinc or butyllithium to the reaction
mixture or in a premixture.5,6 This is far from ideal, as a
large amount of waste can be produced and significant
byproduct formation often occurs especially when delicate
substrates are used. We report here the use of bis-
cyclopentadienyl nickel (nickelocene) as a starting mate-
rial for Ni(0)-catalyzed reactions and demonstrate its
applicability in a range of reactions with precedents in
the literature so direct comparisons between experimen-
tal procedures and yields can be made.
The chemistry of nickelocene (NiCp2) was explored in
the 1960s by Werner and others but its potential use as
a precatalyst for metal-mediated organic synthesis has
never been exploited.7 It is commercially available8 or else
readily prepared in high yield from cyclopentadiene and
NiCl2.9 It is air and moisture stable, although when
stored for prolonged periods of time should be kept under
a nitrogen atmosphere. Unlike other metallocenes such
as M(C5H5)2 [M ) V, Cr, Ru, Os], nickelocene reacts with
tertiary mono phosphine and phosphite ligands, PR3, to
(1) Bhaduri, S. Homogeneous Catalysis: Mechanisms and Industrial
Applications, Wiley-Interscience: New York, 2000.
(2) Diederich, F., Stang, P., Eds.; Metal-Catalysed Cross Coupling
Reactions, Wiley-VCH: Weinheim, 1998.
(3) Lipshutz, B. H.; Blomgren, P. A. J . Am. Chem. Soc. 1999, 121,
5819-5820.
(4) Chung, K.-G.; Miyake, Y.; Uemura, S. J . Chem. Soc., Perkin
Trans. 1 2001, 2725-2729.
The highly reactive complex Ni(PCl3)4 can be prepared
from NiCp2 and used successfully in the catalytic cyclo-
(5) Percec, V.; Bae, J .-Y.; Hill, D. H. J . Org. Chem. 1995, 60, 176-
185.
(6) Saito, S.; Oh-Tani. S.; Miyaura, N. J . Org. Chem. 1997, 62, 8024-
8030.
(7) For a discussion of early work on the chemistry of nickelocene,
see Werner, H. J . Organomet. Chem. 1980, 200, 335-348.
(8) Nickelocene can be purchased from a range of chemical manu-
facturers including Strem and Sigma-Aldrich.
(9) Barnett, K. W. J . Chem. Educ. 1974, 51, 422.
(10) Olechowski, J . R.; McAlister, C. G.; Clark, R. F. Inorg. Chem.
1965, 4, 246.
(11) On reaction of NiCp2 with phosphines, the cyclopentadiene
groups displaced dimerise to form pentafulvalene. In the cases we have
studied we find that this does not seem to partake in any further
reaction.
10.1021/jo0158377 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/04/2001

7540 J . Org. Chem., Vol. 66, No. 22, 2001
Notes
Ta ble 1. Com p a r a tive Yield s Usin g Liter a tu r e Meth od s a n d Usin g Nick elocen e a s Ca ta lyst P r ecu r sor
tetramerization of methyl propiolate. The yield of product
is slightly lower than that reported in the literature14
(Table 1), this being attributed to some decomposition
during the course of the reaction. Ni(PCl3)4 is highly
oxygen and water sensitive in solution, and its synthesis
by other routes involves either highly reactive Ni(0)
precursors such as Ni(allyl)2 or highly toxic Ni(CO)4.15,16
When preparing the Ni(PCl3)4, from nickelocene, to
minimize any decomposition we find that the best route
involves gentle heating (30 °C) of a pentane solution of
NiCp2 and PCl3 for a few minutes. Removal of the
pentane under reduced pressure gives a solid sample of
the complex to which another solvent and reagents can
be added for nickel-mediated catalysis, again making it
a one-pot reaction.
reaction of highly air and moisture sensitive Ni(COD)2
with P(OiPr)3.18
From our findings, the advantages of using nickelocene
as a starting material for metal-mediated catalysis are
clear, and its applicability runs much further than the
reactions presented here. Ni(0) complexes are used as
catalysts in a wide range of organic transformations,19
and we highlight here a route to their generation,
avoiding many of the problems encountered to date. Work
is currently underway to exploit this further.
Exp er im en ta l Section
Gen er a l. Reactions were carried out under a nitrogen atmo-
sphere in oven-dried glassware. Nickelocene, PPh3, PCl3, and
P(OiPr)3 were used as purchased. All liquid reagents for use in
catalysis were degassed before use. Solvents were distilled and
stored over molecular sieves. The 1H- and 31P{1H}-NMR spectra
were recorded in CDCl3 using a Bruker AVANCE 360 MHz
spectrometer at 293 K and are referenced to trimethylsilane and
phosphoric acid, respectively.
Gen er a l P r oced u r e for th e Dir ect Syn th esis of Ni(P R3)4
fr om Nick elocen e. A Schlenk tube was charged with nickel-
ocene and 4 equiv of PR3 (R ) Ph, OiPr). After the tube was
evacuated under vacuum and filled with nitrogen, the resultant
mixture heated to 80 °C for 10 min after which time the Ni-
(PR3)4 complex was formed. Reactions were performed using 50
mg, 0.26 mmol nickelocene. The products were characterized by
comparison of spectral and analytical data with that in the
literature.20
P r oced u r e for th e Syn th esis of Ni(P Cl3)4 fr om Nick el-
ocen e. A Schlenk tube was charged with nickelocene (50 mg,
0.26 mmol) and 4 equiv of PCl3 (143 mg, 0.09 mL, 1.04 mmol).
After the tube was evacuated under vacuum and filled with
nitrogen, freshly degassed dry pentane (10 mL) was added and
the resultant mixture was heated to 30 °C for 10 min after which
time the Ni(PCl3)4 complex was formed. The pentane was then
In another attempt to show the advantages of using
NiCp2 as a starting material for Ni(0) complexes, Ni{P-
(OiPr)3}4 was prepared by reaction with P(OiPr)3 and used
in the catalytic formation of nonconjugated alkenynes
from allylic esters of organic acids and alk-1-ynes. Again
yields using the NiCp2 route are analogous to those
reported in the literature,17 and again this route offers a
convenient method of preparing the active Ni(0) complex
which is otherwise most conveniently synthesized by the
(12) Negishi, E.-I.; King, A. O.; Okukado, N. J . Org. Chem. 1977,
42, 1821.
(13) Severson, S. J .; Cymbaluk, T. H.; Ernst, R. D.; Higashi, J . M.;
Parry, R. W. Inorg. Chem. 1983, 22, 3834.
(14) Leto, J . R.; Leto, M. F. J . Am. Chem. Soc. 1961, 83, 2944.
(15) Seel, F.; Ballreich, K.; Schmutzler, R. Chem. Ber. 1961, 94, 1173.
(16) Chiusoli, G. P.; Pallini, L.; Terenghi, G. Transition Met. Chem.
1983, 8, 189.
(17) Catellani, M.; Chiusoli, G. P.; Salerno, G.; Dallatomasina, F.
J . Organomet. Chem. 1978, 146, C19.
(18) Ittel, S. D. Inorg. Synth. 1990, 28, 98.
(19) See for example: Paqette, L. A., Ed. Encyclopedia of Reagents
for Organic Synthesis; Pergamon: Chichester, 1995.
(20) Ittel, S. D. Inorg. Synth. 1990, 28, 98.

Notes
J . Org. Chem., Vol. 66, No. 22, 2001 7541
removed under vacuum, leaving a solid sample of the product.
31P NMR: -172 ppm.
mixture was stirred at room temperature for 20 min after which
time the solvent was removed, hot ethanol added, and the
resultant mixture refluxed. On cooling, a cream colored precipi-
tate was formed which was collected and washed with ethanol.
Analysis of this by NMR in the presence of a standard showed
that tetracarbomethoxycyclooctatetraene was formed in 49%
Rep r esen ta tive P r oced u r e for th e Nick el-Ca ta lyzed
Cr oss-Cou p lin g of P h en yl a n d Ben zyl Zin c Ch lor id es w ith
Br om oben zon itr ile. A small Schlenk tube was charged with
nickelocene (38 mg, 0.2 mmol) and PPh3 (210 mg 0.8 mmol).
After the tube was evacuated under vacuum and filled with
nitrogen, the resultant mixture was heated to 80 °C for 10 min
after which time dry THF (5 mL) was added and the solution of
Ni(PPh3)4 allowed to cool to room temperature. To the cooled
solution was added p-bromobenzonitrile (728 mg, 4 mmol) and
a THF solution of phenylzinc chloride (4.4 mL of 1 M solution,
4.4 mmol). The reaction mixture was stirred at room tempera-
ture for 2 h after which time the mixture was worked up by
diluting with ether (30 mL), stirring with 1 M HCl (3 × 10 mL
additions), removing the organic layer, removing the solvent,
redissolving in ether, filtering the solution, drying the ether with
anhydrous MgSO4, and concentration. Analysis of the product
mixture by NMR in the presence of a standard showed that
p-phenylbenzonitrile was formed in 87% yield. 1H NMR: δ )
7.71 (m, 2H), 7.62 (m, 2H), 7.45 (m, 2H), 7.38 (m, 3H).
1
yield as a mixture of isomers. H NMR of isomer mixture: δ )
5.65 (m, 4 H), 3.25 (m, 4H).
Rep r esen ta tive P r oced u r e for th e Nick el-Ca ta lyzed
Syn th esis of Alk en yn es. A small Schlenk tube was charged
with nickelocene (38 mg, 0.2 mmol) and P(OiPr)3 (166 mg, 0.2
mL, 0.8 mmol). After the tube was evacuated under vacuum and
filled with nitrogen, the resultant mixture was heated to 80 °C
for 10 min after which time dry THF (10 mL) was added followed
by allyl acetate (670 mg, 0.72 mL, 6.7 mmol) and phenylacetyl-
ene (680 mg, 0.44 mL, 6.7 mmol). The reaction mixture was
stirred under reflux for 6 h after which time the mixture was
cooled, diluted with THF (30 mL), and filtered and the solvent
removed. Analysis of the crude product mixture by NMR in the
presence of a standard showed that 5-phenylpent-1-en-4-yne was
1
formed in 78% yield. H NMR: δ ) 7.40 (m, 2H), 7.28 (m, 3H),
P r oced u r e for th e Nick el-Ca ta lyzed Tetr a m er iza tion of
Meth yl P r op iola te. A small Schlenk tube was charged with
nickelocene (38 mg, 0.2 mmol) and PCl3 (110 mg, 0.069 mL, 0.8
mmol). After the tube was evacuated under vacuum and filled
with nitrogen, pentane was added and the resultant mixture
was heated to 30 °C for 20 min after which time the solvent
was removed. Dry cyclohexane (5 mL) was added followed by
methyl propiolate (4.53 g, 3.2 mL, 54 mmol). The reaction
5.91 (m, 1H), 5.39 (d, 1H), 3.2 (d, 2H).
Ack n ow led gm en t. The Royal Society is thanked for
a University Research Fellowship. Financial support
from King’s College London and Hoffmann La Roche is
acknowledged.
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