Synthesis and 1H NMR spectroscopic properties of substituted (η4-tetraarylcyclobutadiene)(η5-cyclopentadienyl)cobalt metallocenes

Article abstract of DOI:10.1016/j.jorganchem.2008.09.004

The reaction of diarylacetylenes with CoCl(PPh₃)₃ and sodium cyclopentadienylide or sodium carbomethoxycyclopentadienylide gave (η⁴-tetra-arylcyclobutadiene)(η⁵-cyclopentadienyl)cobalt and (η⁴-tetra-arylcyclobutadiene)(η⁵-carbomethoxycyclopentadienyl)cobalt, respectively, where aryl = para-XC₆H₄ (X = CF₃, F, MeO). The reaction was unsuccessful for the synthesis of (η⁴-tetra(para-methoxyphenyl)cyclobutadiene)(η⁵-cyclopentadienyl)cobalt, which was synthesised instead from dicarbonyl(η⁵-cyclopentadienyl)cobalt. In all of the examples starting with CoCl(PPh₃)₃ an intermediate (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallography. Heating the (η⁵-cyclopentadienyl)- or (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complexes resulted in clean conversion to the corresponding metallocenes. The influence of the para-aryl substituents on the ¹H NMR of the cyclopentadienyl moiety is tabulated, together with the influence of a range of R substituents in (η⁴-tetraphenylcyclobutadiene)(η⁵-RC₅H₄)cobalt (R = CO₂Me, CH₂OH, Me, CHO, CCH, CO₂H, CN, CONHR¹, 2-oxazolinyl, NH₂, NHAc, HgCl, Br, I, SiMe₃, SnMe₃, Ph).

Full text of DOI:10.1016/j.jorganchem.2008.09.004

Journal of Organometallic Chemistry 693 (2008) 3668–3676
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1
Synthesis and H NMR spectroscopic properties of substituted
4-tetraarylcyclobutadiene)( 5-cyclopentadienyl)cobalt metallocenes
(g
g
Huy V. Nguyen, Mebuba R. Yeamine 1, Jahangir Amin 1, Majid Motevalli, Christopher J. Richards 1,
*
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 July 2008
Received in revised form 29 August 2008
Accepted 2 September 2008
Available online 10 September 2008
The reaction of diarylacetylenes with CoCl(PPh3)3 and sodium cyclopentadienylide or sodium carbometh-
oxycyclopentadienylide gave (
4-tetra-arylcyclobutadiene)( 5-cyclopentadienyl)cobalt and ( 4-tetra-
arylcyclobutadiene)(
5-carbomethoxycyclopentadienyl)cobalt, respectively, where aryl = para-XC6H4
(X = CF3, F, MeO). The reaction was unsuccessful for the synthesis of
4-tetra(para-methoxy-
phenyl)cyclobutadiene)(
5-cyclopentadienyl)cobalt, which was synthesised instead from dicar-
bonyl(
5-cyclopentadienyl)cobalt. In all of the examples starting with CoCl(PPh3)3 an intermediate
5-cyclopentadienyl)- or 5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraaryl-
cobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallog-
raphy. Heating the (
5-cyclopentadienyl)- or ( 5-carbomethoxycyclopentadienyl)(triphenylphosphine)-
g
g
g
g
(
g
g
g
Keywords:
(
g
(g
(g -
4-Tetraarylcyclobutadiene)(g5
cyclopentadienyl)cobalt
Metallocene
2,3,4,5-Tetraarylcobaltacyclopentadiene
NMR
g
g
2,3,4,5-tetraarylcobaltacyclopentadiene complexes resulted in clean conversion to the corresponding
metallocenes. The influence of the para-aryl substituents on the 1H NMR of the cyclopentadienyl moiety
is tabulated, together with the influence of a range of R substituents in (
ene)(
5-RC5H4)cobalt (R = CO2Me, CH2OH, Me, CHO, CCH, CO2H, CN, CONHR1, 2-oxazolinyl, NH2, NHAc,
HgCl, Br, I, SiMe3, SnMe3, Ph).
g
4-tetraphenylcyclobutadi-
g
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
of para-phenyl and cyclopentadienyl substituents on the 1H NMR
spectra of these complexes are tabulated and discussed.
Catalysts derived from bulky air-stable cobalt metallocenes 1a
[1] and 2a [2a] are of growing importance in asymmetric synthesis
(see Insert 1). Examples include 1,2-disubstituted planar chiral
derivatives such as palladacycles 3 [2], and the monosubstituted
chiral 4-aminopyridine derivative 4 [3]. This class of metallocene
has also been used as the basis of new carbon-rich organometallic
architectures [4]. Part of the attraction of these metallocenes is the
ease with which they may be synthesised utilising a metal-medi-
2. Results and discussion
Previous reactions starting with CoCl(PPh3)3, a cyclopentadienyl
salt and 2 equiv. of diphenylacetylene 8a have resulted in the iso-
lation of a
g
4-tetraphenylcyclobutadiene containing metallocene
after heating at reflux in toluene for several hours [7]. Similarly,
the use of sodium cyclopentadienylide 6 with a reaction time of
5 h resulted in the formation of 1a, isolated as a yellow crystalline
solid in 83% yield (Scheme 2, Table 1, entry 1). In contrast, shorten-
ing the reaction time to 30 min resulted in the isolation of a red
crystalline solid identified as the metallocyclopentadiene triphen-
ylphosphine adduct 9a (entry 2). The identity of 9a was confirmed
by an X-ray crystal structure analysis (Fig. 1). The use of di(para-
trifluoromethylphenyl)acetylene 8b with a reaction time of 5 h re-
sulted in the isolation of both the metallocyclopentadiene 9b and
the corresponding metallocene 1b. As before, the identity of the
former complex was confirmed by an X-ray crystal structure anal-
ysis (Fig. 1). The only significant difference between the two com-
plexes is the longer metallocyclopentadiene C(6)–Co bond in 9a
compared to 9b [1.987(4) versus 1.964(3)] and a shorter Co–P bond
in 9a compared to 9b [2.1914(13) versus 2.2011(8)]. Use of a 5 h
reaction time with di(para-fluorophenyl)acetylene 8c resulted pre-
dominantly in the isolation of metallocene 1c (entry 4), and
ated acetylene dimerisation to generate the
moiety. The first practical synthesis of 1a was reported by Rausch
and Genetti and started with dicarbonyl(
5-cyclopentadi-
enyl)cobalt, which also resulted in the formation of the cyclopen-
tadienone complex (Scheme 1) [5]. The formation of
g
4-cyclobutadiene
g
5
a
cyclopentadienone by-product is avoided by starting with
CoCl(PPh3)3 [6], which on combination with a sodium cyclopenta-
dienyl salt and diphenylacetylene gave 2a and related derivatives
in good yield [2a,7]. In this paper, we report in detail on the use
of this reaction for the synthesis of derivatives of 1 and 2 contain-
ing various para-phenyl substituents [8]. In addition, the influences
* Corresponding author. Tel.: +44 01603 593890.
E-mail address: Chris.Richards@uea.ac.uk (C.J. Richards).
Current address: School of Chemical Sciences and Pharmacy, University of East
1
Anglia, Norwich NR4 7TJ, UK.
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.004

H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
3669
metallocene 2a (entry 6 – although a 5 h reaction time has previ-
ously been reported to be sufficient for the formation of 2a [2a]).
Shortening the reaction time to 30 min resulted in the isolation
of the corresponding metallocyclopentadiene triphenylphosphine
adduct 10a (entry 7). The corresponding complex 10b was the ma-
jor product even after a reaction time of 15 hours with di(para-tri-
fluoromethylphenyl)acetylene 8b (entry 8), and 10c, together with
a greater yield of 2c, resulted from the 15 h reaction of di(para-
fluorophenyl)acetylene 8c (entry 9). Finally, and in contrast to
the result given in entry 5, di(para-methoxyphenyl)acetylene 8d
did result in the formation of the corresponding metallocene 2d
(entry 10).
2 x
Co
Co
O
1a (50%)
+
Ph
Ph
Ph
Ph
Ph
Ph
OC
CO
5 (10%)
Scheme 1. The synthesis of 1a [5a].
i-Pr
2
Me
X
Pd
Co
N
N
Me
Co
It has been observed previously that heating metallocyclopent-
adiene complex 9a above its melting point results in expulsion of
R
O
N
triphenylphosphine and formation of the corresponding
g
4-cyclo-
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
butadiene metallocene 1a [9]. In a similar way, all of the isolated
triphenylphosphine adducts 9a–9c and 10a–c were converted into
their corresponding
g
4-cyclobutadiene metallocenes by heating at
4
3 (X = Cl, OAc)
1a R = H
2a R = CO2Me
reflux in toluene (Scheme 2, Table 2, entries 1–6). These reactions
are essentially irreversible; heating a combination of 2b with a
fivefold excess of triphenylphosphine did not result in the detec-
tion of any of the corresponding metallocyclopentadienyl complex
10b.
Insert 1. Representative cobalt metallocenes.
The synthesis of complex 9a from CoCl(PPh3)3 has previously
been reported [10], an alternative to the related method starting
_
Na+
5-cyclopentadienyl)bis(triphenylphosphine)cobalt
11
R
from
(g
(R = H) [11]. As 11 (R = H) may itself be synthesised from
CoCl(PPh3)3 [10a,12], this first step in the reaction sequence
(Scheme 3) is followed by alkyne substitution reactions leading
sequentially to 12 and 13 [10a]. Oxidative cyclisation of the latter
to give 14 [13] is followed by either addition of triphenylphosphine
to this coordinatively unsaturated intermediate to give 9/10, or
6 (R = H)
7 (R = CO2Me)
(MeO)2CO
a Ar = C6H5
b Ar =
c Ar =
d Ar =
p
-CF3C6H4
p-FC6H4
CoCl(PPh3)3
PhCH3, Δ
Ar
Ar
p-MeOC6H4
8a-d
reductive elimination to the
g
4-cyclobutadiene complexes 1/2.
R
R
The slower rate of conversion of 9/10 into 1/2 where either Ar or
R contains an electron withdrawing group may be accounted for
by the slower rate of phosphine dissociation, presumably due to
the greater Lewis acidity of the cobalt atom.
Ar
Ar
Co
Co
+
PPh3
Ar
Ar
Ar
Ar
Ar
Ar
9a-d (R = H)
10a-d (R = CO2Me)
As the synthesis of metallocene 1d was unsuccessful using the
method described above, it was instead generated in low yield
by heating at reflux a solution of di(p-methyoxyphenyl)acetylene
1a-d (R = H)
2a-d (R = CO2Me)
with dicarbonyl(g
5-cyclopentadienyl)cobalt (Scheme 4). None of
PhCH3, Δ
the corresponding tetraarylcyclopentadienone metallocene was
observed. This outcome tallies with the absence of metallocyclo-
pentadiene complexes 9d and 10d in reactions of di(p-methyoxy-
phenyl)acetylene with CoCl(PPh3)3, suggesting that the aryl
para-methoxy substituents reduce the propensity of intermediate
sixteen electron metallocyclopentadiene complexes to coordinate
to either carbon monoxide or triphenylphosphine.
Scheme 2. Synthesis of metallocyclopentadiene complexes and
metallocenes.
g
4-cyclobutadiene
di(para-methoxyphenyl)acetylene 8d failed to give either complex
(entry 5).
Similar trends were observed with the carbomethoxy-substi-
tuted cyclopentadienyl salt 7 (prepared in situ by addition of dim-
The 1H NMR chemical shifts of the cyclopentadienyl singlets of
1a–d, and the
a and b signals of 2a–d, are listed in Table 3. The
ethylcarbonate to 6).
A longer reaction time of 15 h with
influence of the different aryl substituents on the chemical shifts
diphenylacetylene 8a resulted in the exclusive isolation of the
is approximately 1/10th of the chemical shift difference for the
Table 1
Synthesis of metallocyclopentadiene 9–10 complexes and
g
4-cyclobutadiene metallocenes 1–2
Entry
R
Ar
Reaction time (h)
Metallocyclopentadiene complex (yield)
g
4-Cyclobutadiene metallocene (yield)
1
2
3
4
5
6
7
8
9
10
H
H
H
H
Ph
Ph
5
0.5
5
5
5
15
0.5
15
15
15
9a (0%)
1a (83%)
1a (0%)
1b (34%)
1c (82%)
1d (0%)
2a (73%)
2a (66%)
2b (5%)
2c (47%)
2d (56%)
9a (90%)
9b (54%)
9c (6%)
p-CF3C6H4
p-FC6H4
p-MeOC6H4
Ph
H
9d (0%)
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
10a (0%)
10a (10%)
10b (88%)
10c (20%)
10d (0%)
Ph
p-CF3C6H4
p-FC6H4
p-MeOC6H4

3670
H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
Fig. 1. Representation of the X-ray crystal structure of 9a (left) and 9b. Selected bond lengths (Å) of 9a with the corresponding values for 9b in parenthesis: Co–C(6) 1.987(4)
[1.964(3)], C(6)–C(7) 1.355(6) [1.357(4)], C(7)–C(8) 1.467(6) [1.473(4)], C(8)–C(9) 1.359(6) [1.351(4)], C(9)–Co 1.975(5) [1.978], Co–P 2.1914(13) [2.2011(8)].
Table 2
Conversion of metallocyclopentadiene complexes 9 and 10 into
metallocenes 1 and 2
g
4-cyclobutadiene
Ar
Ar
Co
1d
PhCH3, Δ
Ar =
(CO)2
Entry
Metallocyclopentadienyl
complex
Reaction time
(h)
g
4-Cyclobutadiene
12%
p
-MeOC6H4
metallocene (yield)
Scheme 4. Synthesis of 1d.
1
2
3
4
5
6
9a
9b
9c
10a
10b
10c
5
1a (95%)
1b (81%)
1c (92%)
2a (82%)
2b (96%)
2c (97%)
15
15
15
15
15
extensive range of known and new monosubstituted derivatives
15–30 (see Insert 2).
Methyl ester 2a was reduced with LiAlH4 to the alcohol 15
[7b,16] which was further reduced with LiAlH4 in the presence of
AlCl3 to the methyl substituted derivative 16 (Scheme 5). Oxida-
tion of 15 with catalytic tetrapropylammonium perruthenate
(TPAP) and stoichiometric N-methylmorpholine-N-oxide (NMO)
proceeded cleanly to give aldehyde 17 [5a] which was transformed
into the 1-alkyne 18 as previously outlined [7b]. Hydrolysis of
methyl ester 2a gave the carboxylic acid 19 [2a] which was con-
verted into nitrile 20 using a literature procedure [17]. In addition,
acid 19 was transformed via amide 21 into the achiral oxazoline 22
using methodology previously employed for the synthesis of re-
lated chiral oxazolines [2a,2e]. Use of the Curtius rearrangement
as the key step resulted in the transformation of acid 19 into amine
23 [18] which was acetylated to give acetamide 24.
para-position of a corresponding substituted benzene (CF3: +0.05
versus +0.3; F: À0.02 versus À0.24; OMe: À0.05 versus À0.45).
The influence of a cyclopentadienyl substituent on the electronic
environment of the
g
5-ring, as manifested in the chemical shift
of the remaining protons, is somewhat more significant, as illus-
trated by the difference between the parent complexes 1a and 2a.
The effect of substituents on the chemical shifts of monosubsti-
tuted ferrocenes has previously been tabulated [14] and has
proved useful for the identification of related ferrocene derivatives,
including multiply substituted compounds [15]. To provide a sim-
ilar body of information for (g -
4-tetraphenylcyclobutadiene)(g5
cyclopentadienyl)cobalt metallocenes, we first synthesised an
R
R
_
Na+
Ar
Ar
R
Ar
Co
CoCl(PPh3)3
Co
+
Ph3P
Ph3P
PPh3
6/7
11
Ar
12
R
Ar
Co
PPh3
Ar
Ar
Ar
Ar
+ PPh3
R
R
9/10
Ar
- PPh3
Ar
Ar
Co
Co
Ar
Ar
R
Ar
Ar
13
Ar
Ar
14
Co
Ar
Ar
Ar
Ar
1/2
Scheme 3. A reaction pathway accounting for the formation of metallocyclopentadiene complexes and
g
4-cyclobutadiene metallocenes.

H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
3671
Table 3
1H NMR chemical shifts of substituted (
g
4-tetraarylcyclobutadiene)(
Ar
g
5-cyclopentadienyl)cobalt metallocenes
Metallocene
R
a
D
aa
Ferrocene
D
ab
b
D
ba
Ferrocene D
bb
1a
1b
1c
1d
2a
2b
2c
2d
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
H
H
H
H
Ph
4.62
4.67
4.60
4.57
5.19
5.21
5.16
5.15
4.71
4.53
5.22
4.79
5.22
4.90
5.02
5.11
4.39
4.86
4.69
4.73
4.76
4.66
4.65
4.99
0
–
–
–
–
4.62
4.67
4.60
4.57
4.77
4.82
4.75
4.72
4.59
4.46
4.88
4.62
4.78
4.66
4.70
4.77
4.13
4.54
4.86
4.55
4.56
4.75
4.72
4.69
0
–
–
–
–
p-CF3C6H4
p-FC6H4
p-MeOC6H4
Ph
p-CF3C6H4
p-FC6H4
p-MeOC6H4
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
+0.05
À0.02
À0.05
+0.57
+0.59
+0.54
+0.53
+0.09
À0.09
+0.60
+0.17
+0.60
+0.28
+0.40
+0.49
À0.23
+0.24
+0.07
+0.11
+0.14
+0.04
+0.03
+0.37
+0.05
À0.02
À0.05
+0.15
+0.2
+0.13
+0.1
À0.03
À0.16
+0.26
0
+0.16
+0.04
+0.08
+0.15
À0.49
À0.08
+0.24
À0.07
À0.06
+0.13
+0.10
+0.07
CO2Me
CO2Me
CO2Me
CO2Me
CH2OH
Me
+0.61
–
–
+0.20
–
–
–
–
0.00
À0.11
+0.55
+0.28
+0.68
+0.48
+0.50
+0.56
À0.17
+0.38
–
+0.23
+0.23
À0.06e
À0.12
+0.46
+0.03
À0.15
+0.36
+0.02
+0.28
+0.21
+0.18
+0.15
À0.32
À0.19
–
À0.08
À0.03
+0.17e
+0.19
+0.13
CHO
C„CH
CO2H
C„N
CONHRc
2-oxazolinyld
NH2
NHAc
HgCl
Br
I
SiMe3
SnMe3
Ph
a
Difference in chemical shift (d) relative to 1a.
From Ref. [14].
R = (CH2)2OH.
Derived from 21.
Figure from R = SnBu3.
b
c
d
e
A variety of other derivatives were obtained following transfor-
R
HgCl
HgCl
Ph
mation of 1a into the chloromercury derivative 25 [5a] (Scheme 6).
Reaction with N-bromosuccinimide and iodine gave the halogen
derivatives 26 and 27 [5a]. Addition of butyllithium to iodide 27 re-
sulted in halogen–lithium exchange, followed by the addition of
various electrophiles to give silane 28 [5a] and stannane 29. The
latter was employed in a Stille cross-coupling reaction to provide
the phenyl derivative 30 [5a].
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
31
15-30
Insert 2.
OH
NH2
Ph
CO2H
Me
LiAlH4
LiAlH4
AlCl3
Ref. 18
Ref. 17
Ref. 2a
2a
Co
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
19 (94%)
23
15 (98%)
16 (8%)
i) (COCl)2
ii) H2N(CH2)2OH
O
Ac2O
NEt3
TPAP
NMO
CN
OH
CHO
NHAc
Ph
N
H
Co
Co
Ph
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
24 (24%)
21 (55%)
17 (92%)
20
_
MsCl
NEt3
N
i)
Ph3P
Cl
ii) BuLi
O
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
22 (66%)
18 (45%)
Scheme 5. Synthesis of derivatives 15–24 from 2a.

3672
H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
para-substituent X on the 1H NMR chemical shift of the cyclopen-
HgCl
Br
Ph
tadienyl group is relatively small. The influence of an extensive
Ref. 5a
NBS
range of cyclopentadienyl substituents on the 1H NMR chemical
1a
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
shifts of the
a and b positions correlates well with the values of
the corresponding ferrocene derivatives.
Ph
26 (67%)
25 (65%)
4. Experimental
Ref. 5a
The following compounds were prepared as previously de-
scribed: 2a [2a], 19 [2a], 20 [17], 23 [18], 25 [5a] and 27 [5a]. All
reactions performed under a nitrogen atmosphere. Tetrahydrofuran
and diethyl ether were distilled from sodium benzophenone ketyl.
Dichloromethane and dimethylformamide were distilled from cal-
cium hydride. Toluene was distilled from sodium wire. Petroleum
ether refers to that fraction boiling in the range 40–60 °C. Column
SnMe3
I
i) BuLi
ii) Me3SnCl
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
29 (31%)
27
chromatography was performed on silica gel 40–63 lm.
i)
t
-BuLi
PdCl2/Pt-Bu3
CuI, CsF
PhBr
ii) TMSCl
4.1. General method for the synthesis of complexes 1 and 9
TMS
Ph
To a mixture of chlorotris(triphenylphosphine)cobalt (1 equiv.)
and diarylacetylene (2.3 equiv.) in toluene (5 mL/equiv.) was
added sodium cyclopentadienide (2.0 M in THF, 1.2 equiv.) and
the resulting mixture heated at reflux. After the specified reaction
time the solvent was removed in vacuo, the residue partially dis-
solved in CH2Cl2 (5 mL) and the black insoluble residue was re-
moved by filtration and washed with additional CH2Cl2 until the
washings were colourless. Following removal of the solvent, the
product complexes were isolated by column chromatography and
recystallised from CH2Cl2/petroleum ether.
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
28 (96%)
30 (79%)
Scheme 6. Synthesis of derivatives 25–30 from 1a.
The 1H NMR chemical shifts of the
tives 15–30 are listed in Table 1. For most of these compounds the
assignment of cyclopentadienyl proton signals as or b was made
by comparison to the corresponding ferrocene derivatives [14]. An
exception is the chloromercury derivative 25 (the ferrocene deriv-
ative of which is not listed in the previous study) [19]. Examination
of the 1H NMR of the 1,2-bis(chloromercury) derivative 31, the
relative stereochemistry of which has been unambiguously estab-
lished by X-ray crystallography [20], reveals two cyclopentadienyl
signals with a 2:1 ratio at 4.87 and 5.08 ppm. From this values of
Da and Db are calculated as +0.02 and +0.23, in good agreement
with the chemical shift differences observed in the mono-substi-
tuted derivative 25 (+0.07 and +0.24). It is of note that the magni-
Da and Db values are generally smaller than the
corresponding values found in the ferrocene series. For example,
for electron withdrawing substituents (i.e. where the values of
Da and Db are both positive), the average values for Da and Db
a and b positions of deriva-
a
4.1.1. (
[5a] and (
g
4-tetraphenylcyclobutadiene)(
g
g
5-cyclopentadienyl)cobalt 1a
5-cyclopentadienyl)(triphenylphosphine)-2,3,4,5-
tetraphenylcobaltacyclopentadiene 9a [10b]
Use of diphenylacetylene (0.400 g, 2.24 mmol) with a 5 h reac-
tion time, and column chromatography (petroleum ether) gave 1a
(0.390 g, 83% yield) as a yellow crystalline solid. Use of diphenyl-
acetylene (0.400 g, 2.24 mmol), a reaction time of 0.5 h, and col-
umn chromatography (30% CH2Cl2/70% petroleum ether) gave 9a
(0.652 g, 90% yield) as a red crystalline solid.
Compound 1a: 1H NMR (d, 270 MHz, CDCl3) 4.62 (5H, s, Cp),
7.14–7.23 (12H, m, Ph), 7.41–7.46 (8H, m, Ph); 13C NMR (d,
67 MHz, CDCl3) 74.9 (Cb), 83.3 (Cp), 126.2 (Ph), 128.0 (Ph), 128.9
(Ph), 136.5 (ipso-Ph).
tude of the
Compound 9a: 1H NMR (d, 270 MHz, CDCl3) 4.76 (5H, s, Cp),
6.41–6.53 (8H, m, Ph), 6.70–6.92 (12H, m, Ph), 7.13–7.42 (15H,
m, PPh3); 13C NMR (d, 67 MHz, CDCl3) 89.7 (Cp), 123.2, 123.7,
126.2, 126.8, 128.1, 128.3, 129.0, 129.8, 130.5, 133.6, 133.7,
142.1, 153.6, 157.7; 31P NMR (d{1H} 100 MHz, CDCl3) 52.2.
are approximately 80% and 50% of the corresponding ferrocene val-
ues, respectively.
3. Conclusion
(g
4-Tetraarylcyclobutadiene)(
locenes 1b–1c and
g
5-cyclopentadienyl)cobalt me-
4-tetraarylcyclobutadiene)(g5
4.1.2. (
g
4-tetra(para-trifluoromethylphenyl)cyclobutadiene)(g5
5-cyclopentadienyl)(triphenyl-
-
tal
(g
-
cyclopentadienyl)cobalt 1b and (g
carbomethoxycyclopentadienyl)cobalt metallocenes 2b–2d, where
aryl = para-XC6H4), were synthesised using CoCl(PPh3)3, a diaryl-
acetylene and the corresponding sodium cyclopentadienyl salt. In
all cases the intermediacy of metallocyclopentadiene triphenyl-
phosphine adducts (9b–9c, 10b–10d) were observed, and with uni-
form reaction conditions, the percentage of this intermediate
increased with the presence of electron-withdrawing groups in
the aryl group (X = CF3) and/or in the cyclopentadienyl group
(CO2Me). Use of di(para-methoxyphenyl)acetylene in this chemis-
try was only successful when the cyclopentadienyl group con-
tained the electron-withdrawing CO2Me group. Following
isolation of the metallocyclopentadiene triphenylphosphine
intermediates, subsequent heating resulted in conversion to the
corresponding metallocenes in high yield. The influence of the
phosphine)-2,3,4,5-tetra(para-trifluoromethylphenyl)cobaltacyclo-
pentadiene 9b
Use
of
di(p-trifluoromethylphenyl)acetylene
(0.500 g,
1.59 mmol), a reaction time of 5 h, and column chromatography
(10% CH2Cl2/petroleum ether) gave 1b (0.177 g, 34% yield) as a yel-
low crystalline solid, and 9b (0.379 g , 54% yield) as a red crystal-
line solid.
Compound 1b: m.p. 294 °C; Anal. Calc. for C37H21CoF12: C, 59.06;
H, 2.81. Found: C, 58.84; H, 2.70%. 1H NMR (d, 270 MHz, CDCl3) 4.67
(5H, s, 5H, Cp), 7.45–7.53 (16H, m, Ar); 13C NMR (d, 100 MHz,
CDCl3) 74.45 (Cb), 84.13 (Cp), 124.55 (q, J = 270, CF3), 125.72 (q,
J = 4, Ar), 129.18 (q, J = 32, Ar), 129.15 (Ar), 139.93 (Ar).
Compound 9b: m.p. 224 °C; 1H NMR (d, 270 MHz, CDCl3) 4.77
(5H, s, Cp), 6.51 (8H, t, J = 8, Ar), 6.86 (4H, t, J = 10, Ar), 7.02 (8H,

H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
3673
d, J = 7, Ar), 7.15–7.25 (6H, m, Ar), 7.28–7.50 (5H, m, Ar); 13C NMR
(d, 100 MHz, CDCl3) 90.15 (CpC), 123.35, 123.61, 124.05, 124.09,
124.37, 124.40, 125.85, 126.04, 126.17, 126.31, 126.61, 126.93,
128.48, 128.58, 128.85 128.90, 130.58, 130.79, 131.17, 133.61,
133.71, 133.84, 133.93, 135.37, 135.79, 144.54, 156.88, 170.34,
170.62; 31P NMR (d{1H} 100 MHz, CDCl3) 50.12; HRMS (EI) m/z;
Found for (MÀPPh3)+, 752.0782; Calc. for C37H21CoF12, 752.0778.
6.83 (17H, m, Ph), 7.01–7.45 (13H, m, Ph); 13C NMR (d,
100 MHz, CDCl3) 52.11 (Me), 84.83 (ipso-Cp), 89.64 (Cp), 98.99
(Cp), 123.54, 123.81, 126.24, 126.71, 127.93, 128.03, 128.28,
129.30, 130.30, 133.91, 134.00, 141.97, 152.94, 158.44, 164.79,
165.06, 167.44 (C„O); 31P NMR (d{1H} 100 MHz, CDCl3) 49.99;
HRMS (FAB) m/z; Found for M+, 800.2252; Calc. for C53H42Co
O2P, 800.2249.
4.1.3. (
dienyl)cobalt 1c and (
2,3,4,5-tetra(para-fluorophenyl)cobaltacyclopentadiene 9c
g
4-tetra(para-fluorophenyl)cyclobutadiene)(
g
5-cyclopenta-
4.2.2. (g
4-tetra(para-trifluoromethylphenyl)cyclobutadiene)-
g
5-cyclopentadienyl)(triphenylphosphine)-
(
(
g
g
5-carbomethoxycyclopentadienyl)cobalt 2b and
5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-
Use of di(p-fluorophenyl)acetylene (0.510 g, 2.38 mmol), a reac-
tion time of 5 h, and column chromatography (10%CH2Cl2/petro-
leum ether) gave 1c (0.469 g, 82% yield) as a yellow crystalline
solid, and 9c (0.051 g, 6% yield) as a red crystalline solid.
Compound 1c: m.p. 250 °C. Anal. Calc. for C33H21F4Co Á H2O: C,
69.48; H, 4.06. Found: C, 69.29; H, 3.70%; 1H NMR (d, 270 MHz,
CDCl3) 4.60 (5H, s, Cp), 6.91 (8H, t, J = 9, Ar), 7.34 (8H, dd, J = 9,5,
Ar); 13C NMR (d, 100 MHz, CDCl3) 73.78 (Cb), 83.15 (CC), 115.24
(d, J = 22, Ar), 130.16 (d, J = 8, Ar), 131.70 (d, J = 4, Ar), 161.35 (d,
J = 245, Ar).
Compound 9c: m.p. 200 °C; Anal. Calc. for C51H36CoF4P: C, 75.18;
H, 4.45. Found: C, 75.19; H, 4.41%; 1H NMR (d, 270 MHz, CDCl3)
4.73 (5H, s, Cp), 6.29–6.58 (18H, m, Ar), 6.85–7.00 (3H, m, Ar),
7.10–7.50 (10H, m, Ar); 13C NMR (d, 100 MHz, CDCl3) 89.98 (Cp),
113.52, 113.72, 113.87, 114.08, 128.22, 128.32, 128.65, 128.74,
130.29, 130.36, 130.75, 130.78, 131.92, 132.00, 133.76, 133.86,
133.96, 134.02, 134.06, 136.13, 136.55, 137.97, 138.00, 138.03,
149.52, 149.55, 156.85, 156.87, 158,72, 159.01, 161.14, 161.42,
167.19, 167.46; 31P NMR (d{1H} 100 MHz, CDCl3) 51.79.
tetra(para-trifluoromethylphenyl)cobaltacyclopentadiene 10b
Use of di(p-trifluoromethylphenyl)acetylene (1.240 g, 3.95
mmol), a reaction time of 15 h, and column chromatography
(25% CH2Cl2/petroleum ether) gave 2b (0.070 g, 5% yield) as a yel-
low crystalline solid, and 10b (1.620 g , 88% yield) as a red crystal-
line solid.
Compound 2b: m.p. 172 °C; Anal. Calc. for C39H23CoF12O2: C,
57.79;
H
2.86. Found: C, 57.75; H, 2.80%, IR (CDCl3) mmax
;
1713 cmÀ1
1H NMR (d, 270 MHz, CDCl3) 3.21 (3H, s, Me), 4.82
(2H, brs, Cp), 5.21 (2H, brs, Cp), 7.46 (8H, d, J = 8, Ar), 7.53 (8H, d,
J = 8, Ar); 13C NMR (d, 100 MHz, CDCl3) 51.38 (Me), 75.40 (Cb),
84.91 (Cp), 86.79 (Cp) 87.19 (ipso-Cp), 124.08 (q, J = 270, CF3),
125.47 (q, J = 4, Ar) 128.80 (Ar), 129.37 (q, J = 32, Ar), 138.13 (Ar),
165.63 (C@O).
Compound 10b: m.p. 182 °C; Anal. Calc. for C57H38CoF12O2P: C,
63.82; H, 3.57. Found: C, 63.39; H, 3.53%; IR (CDCl3) mmax
1706 cmÀ1 1H NMR (d, 270 MHz, CDCl3) 3.84 (3H, s, Me), 4.71
;
(2H, brs, Cp), 5.39 (2H, brs, Cp), 6.50 (4H, d, J = 7, Ar), 6.73 (4H,
d, J = 7 Ar), 6.90–7.10 (14H, m, Ar), 7.18 (3H, brs, Ar), 7.38 (6H,
brs, Ar); dC{1H} (100 MHz, CDCl3) 52.73 (Me), 84.42 (ipso-Cp),
90.13 (Cp), 99.73 (Cp), 120.56, 120.86, 123.26, 123.56, 124.19,
124.23, 124.40, 124.43, 125.92, 125.97, 126.24, 126.27, 126.56,
126.89, 127.21, 127.53, 128.74, 128.83, 129.25, 130.43, 130.97,
131.60, 133.93, 134.02, 134.57, 135.00, 144.62, 156.40, 157.63,
167.36 (C@O), 168.23, 168.52; 31P NMR (d{1H} 100 MHz, CDCl3)
48.51.
4.2. General method for the synthesis of complexes 2 and 10
To a solution of sodium cyclopentadienylide (2.0 M in THF,
1.14 equiv.) in THF (3.3 mL/equiv.) was added dimethyl carbonate
(3.45 equiv.) and the resulting mixture heated at reflux for 4 h.
After cooling to room temperature to the reaction vessel was added
toluene (26.5 mL/equiv.), chlorotris(triphenylphosphine)cobalt
(1 equiv.) and the diarylacetylene (2.3 equiv.). The resulting mix-
ture heated at reflux and after the specified reaction time the sol-
vent was removed in vacuo, the residue partially dissolved in
CH2Cl2, and the black insoluble residue was removed by filtration
and washed with additional CH2Cl2 until the washings were col-
ourless. Following removal of the solvent in vacuo, the product
complexes were isolated by column chromatography or
recrystallisation.
4.2.3. (g
4-tetra(para-fluorophenyl)cyclobutadiene)-
(
(
g
g
5-carbomethoxycyclopentadienyl)cobalt 2c and
5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-
tetra(para-fluorophenyl)cobaltacyclopentadiene 10c
Use of di(p-fluorophenyl)acetylene (2.300 g, 10.74 mmol), a
reaction time of 15 h, and column chromatography (30% CH2Cl2/
petroleum ether) gave 2c (1.339 g, 47% yield) as a yellow crystal-
line solid, and 10c (0.815 g , 20% yield) as a red crystalline solid.
Compound 2c: m.p. 212 °C; Anal. Calc. for C35H23O2F4Co: C,
68.86; H, 3.80. Found: C, 68.80; H, 3.77%. IR (CDCl3) mmax
4.2.1. (
g
4-tetraphenylcyclobutadiene)(
g
g
5-carbomethoxy-
5-carbomethoxy-
cyclopentadienyl)cobalt 2a [2a] and (
cyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraphenyl-
1704 cmÀ1 1H NMR (d, 270 MHz, CDCl3) 3.28 (3H, s, Me), 4.75
;
(2H, brs, Cp), 5.16 (2H, brs Cp), 6.93 (8H, t, J = 9, Ar), 7.34 (8H,
dd, J = 5, 9, Ar); 13C NMR (d, 100 MHz, CDCl3) 51.27 (Me), 75.24
(Cb), 84.45 (Cp), 86.37 (Cp) 86.53 (ipso-Cp), 115.42 (d, J = 22, Ar),
130.24 (d, J = 8, Ar) 130.37 (d, J = 3, ipso-Ar), 161.69 (d, J = 246,
ipso-Ar), 166.33 (C@O).
cobaltacyclopentadiene 10a
Use of diphenylacetylene (0.340 g, 1.91 mmol), a reaction time
of 0.5 h, and column chromatography (20–50% CH2Cl2/petroleum
ether) gave 2a (0.295 g, 66% yield) as a yellow crystalline solid,
and 10a (0.066 g, 10% yield) as a red crystalline solid. Use of
diphenylacetylene (0.40 g, 2.24 mmol) with a 15 h reaction time
gave only 2a (0.384 g, 73% yield) as a yellow crystalline solid.
Compound 2a: 1H NMR (d, 270 MHz, CDCl3) 3.22 (3H, s, 3H, Me),
4.77 (2H, t, J = 2, Cp), 5.19 (2H, t, J = 2, Cp), 7.15–7.40 (12H, m, Ph),
7.40–7.46 (8H, m, Ph); 13C NMR (d, 100 MHz, CDCl3) 51.16 (Me),
76.44 (Cb), 84.54 (Cp), 86.37 (Cp), 86.72 (ipso-Cp), 126.70 (Ph),
128.06 (Ph), 128.87 (Ph), 135.12 (ipso-Ph), 166.35 (C@O).
Compound 10a: m.p. 168 °C; Anal. Calc. for C53H42CoO2P: C,
79.49; H, 5.29. Found: C, 79.00; H, 5.19%; IR (CH2Cl2) mmax
Compound 10c: Mp 152 °C; IR (CDCl3) m
max 1712 cmÀ1; 1H NMR
(d, 270 MHz, CDCl3) 3.81 (3H, s, Me), 4.66 (2H brs, Cp), 5.36 (2H, t,
J = 3 Hz, Cp), 6.32–6.42 (4H, m, Ar), 6.42–6.52 (8H, m, Ar), 6.52–
6.61 (4H, m, Ar), 6.92–7.04 (3H, m, Ar), 7.12–7.28 (8H, m, Ar),
7.32–7.42 (4H, m, Ar); 13C NMR (d, 100 MHz, CDCl3) 52.57 (Me),
84.56 (ipso-Cp), 90.09 (Cp), 99.56 (Cp), 113.69, 113.90, 113.92,
114.12, 128.53, 130.54, 130.70, 130.77, 131.75, 131.83, 134.19,
137.90, 137.93, 137.96, 148.95, 148.98, 157.61, 157.65, 158.95,
159.12, 161.37, 161.53, 165.35, 165.64, 167.74 (C@O); 31P NMR
(d{1H} 100 MHz, CDCl3) 49.82; HRMS (EI) m/z; Found: (MÀPPh3)+
610.0959; Calc. for C35H23CoF4O2, 610.0961.
;
1720 cmÀ1 1H NMR (d, 270 MHz, CDCl3) 3.81 (3H, s, Me), 4.68
(2H, brs, Cp), 5.42 (2H, brs, Cp), 6.46–6.48 (5H, m, Ph), 6.64–

3674
H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
4.2.4. (
g
4-tetra(para-methoxyphenyl)cyclobutadiene)-
Compound 15: 1H NMR (d, 270 MHz, CDCl3) 4.08 (s, 2H, CH2),
4.59 (brs, 2H, Cp), 4.71 (brs, 2H, Cp), 7.15–7.40 (m, 12H, Ph),
7.40–7.46 (m, 8H, Ph); 13C NMR (d, 100 MHz, CDCl3) 59.8 (CH2),
75.3 (Cb), 81.9 (Cp), 84.1 (Cp), 126.9 (para-Ph), 128.6 (Ph), 129.1
(Ph), 136.5 (ipso-Ph), ipso-Cp not observed.
(g
5-carbomethoxycyclopentadienyl)cobalt 2d
Use of di(p-methyoxyphenyl)acetylene (1.420 g, 5.96 mmol), a
reaction time of 15 h, and recrystallisation (CH2Cl2) gave 2d
(0.956 g, 56% yield) as an orange powder.
Compound 2d: m.p. 192 °C; Anal. Calc. for C39H35CoO6.H2O: C,
69.23; H, 5.51. Found: C, 69.05; H, 5.24%; IR (nujol) mmax
4.3.2. (g
5-Methylcyclopentadienyl)-
1702 cmÀ1
;
1H NMR (d, 270 MHz, CDCl3) 3.25 (3H, s, CO2Me),
(g
4-tetraphenylcyclobutadiene)cobalt 16
3.77 (12H, s, OMe), 4.72 (2H, t, J = 2, 2H, Cp), 5.15 (2H, t, J = 2,
Cp), 6.76 (8H, d, J = 9, Ar), 7.35 (8H, d, J = 9, Ar); 13C NMR (d,
100 MHz, CDCl3) 51.15 (CO2Me), 55.23 (OMe), 75.76 (Cb), 84.13
(Cp), 86.08 (Cp), 86.16 (ipso-Cp), 113.59 (Ar), 127.37 (ipso-Ar)
129.90 (Ar), 158.31 (ipso-Ar), 166.83 (C@O).
To a solution of 15 (0.081 g, 0.16 mmol) in Et2O (20 mL) was
added AlCl3 (0.021 g, 0.16 mmol) with vigorous stirring. To the
reaction was added LiAlH4 (0.006 g, 0.16 mmol) and stirring was
maintained 15 h. The resulting mixture was quenched with 1 M
NaOH (3 mL) and filtered through celite, washing with Et2O. The
organic layer was dried (MgSO4), filtered and solvent removed in
vacuo. Column chromatography (1:5 Et2O/petroleum ether) gave
16 as a yellow crystalline solid (0.006 g, 8%).
4.2.5. (
5-cyclopentadienyl)cobalt 1d
solution of cyclopentadienylcobaltdicarbonyl (0.038 g,
g
4-tetra(para-methoxyphenyl)cyclobutadiene)-
(g
A
Compound 16: m.p. 88–91 °C. 1H NMR (270 MHz, CDCl3) d 0.86
(3H, s, Me), 4.45 (2H, t, J = 2, Cp), 4.51 (2H, t, J = 2, Cp), 7.13–7.35
(12H, m, Ph), 7.35–7.52 (8H, m, Ph). 13C NMR (100 MHz, CDCl3) d
14.5 (Me), 74.9 (Cb), 83.1 (Cp), 84.0 (Cp), 126.4 (Ph), 128.3 (Ph),
129.2 (Ph), 136.9 (ipso-Ph), ipso-Cp not observed. HRMS (ES) m/z;
Found for MH+: 494.1437; Calc. for C34H27Co: 494.5205.
0.21 mmol), di(p-methoxyphenyl)acetylene (0.100 g, 0.42 mmol)
in toluene (2 mL) was heated at reflux for 48 h. After cooling the
crude reaction mixture was filtered through a plug of SiO2, washing
with CH2Cl2, followed by removal of the solvent removed in vacuo,.
Column chromatography (50% CH2Cl2/petroleum ether) gave 1d
(0.015 mg, 12%) and recovered di(p-methoxyphenyl)acetylene
(0.070 g, 70%).
4.3.3. (g
5-Formylcyclopentadienyl)-
Compound 1d: m.p. 272 °C; 1H NMR (d, 270 MHz, CDCl3) 3.80
(12H, s, Me), 4.57 (5H, s, Cp), 6.75 (8H, d, J = 8.4, Ar), 7.36 (8H, d,
J = 8.9, Ar). 13C NMR (d, 100 MHz, CDCl3) 55.69 (Me), 75.40 (Cb),
83.12 (Cp), 113.84 (Ar), 130.25 (Ar), ipso-Ar not observed;
HRMS (EI) m/z; Found for M+, 600.1709; Calc. for C37H33CoO4,
600.1705.
(
g
4-tetraphenylcyclobutadiene)cobalt 17 [5a]
To a solution of 15 (0.396 g, 0.78 mmol) in CH2Cl2 (10 mL) con-
taining 4 Å molecular sieves was added N-methylmorpholine-N-
oxide (0.159 g, 1.36 mmol) followed by tetrapropylammonium
perruthenate (0.014 g, 0.04 mmol). The reaction mixture darked
quickly and was stirred for 1 h at room temperature before wash-
ing with sodium sulfite solution (10 mL), brine (10 mL) and satu-
rated CuSO4 solution (10 mL). The solution was dried (Na2SO4),
filtered and evaporated, then redissolved in the minimum volume
of CH2Cl2 and a dark solid precipitated on the addition of petro-
leum ether. After separation the filtrate was evaporated to give
17 as an orange yellow solid (0.364 g, 92%).
4.3. General method for the conversion of metallocyclopentadienyl
complexes 9 and 10 into g
4-cyclobutadiene metallocenes 1 and 2
A solution of the metallocyclopentadienyl complex (3 or 5) in
toluene was heated at reflux until the starting material could no
longer be detected by thin layer chromatography. The solvent
was removed in vacuo and the product purified by column
chromatography.
Synthesis of 1a. Compound 9a (0.150 g, 0.2 mmol), toluene
(2 mL), a reaction time of 5 h, and column chromatography (100%
petroleum ether) gave 1a (0.092 g, 95%).
Compound 17: 1H NMR (d, 270 MHz, CDCl3) 4.88 (brs, 2H, Cp),
5.22 (brs, 2H, Cp), 7.10–7.40 (m, 12H, Ph), 7.40–7.50 (m, 8H, Ph),
9.30 (s, 1H, CHO); 13C NMR (d, 100 MHz, CDCl3) 77.52 (Cb), 83.53
(Cp), 89.18 (Cp), 92.78 (ipso-Cp), 127.46 (para-Ph), 128.59 (Ph),
129.19 (Ph), 135.23 (ipso-Ph), 191.48 (CHO).
Synthesis of 1b. Compound 9b (0.050 g, 0.05 mmol), toluene
(5 mL), a reaction time of 15 h, and column chromatography (10%
CH2Cl2/petroleum ether) gave 1b (0.030 g, 81%).
4.3.4. (g
5-Ethynylcyclopentadienyl)-
(g
4-tetraphenylcyclobutadiene)cobalt 18 [16]
To a solution of (chloromethyl)triphenylphosphonium chloride
Synthesis of 1c. Compound 9c (0.040 g, 0.05 mmol), toluene
(4 mL), a reaction time of 15 h, and column chromatography (10%
CH2Cl2/petroleum ether) gave 1c (0.025 g, 92%).
Synthesis of 2a. Compound 10a (0.650 g, 0.81 mmol), toluene
(10 mL), a reaction time of 15 h, and column chromatography
(30% CH2Cl2/petroleum ether) gave 2a (0.358 g, 82%).
Synthesis of 2b. Compound 10b (0.110 g, 0.10 mmol), toluene
(5 mL), a reaction time of 15 h, and column chromatography (30%
CH2Cl2/petroleum ether) gave 2b (0.080 g, 96%).
(4.82 g, 13.9 mmol) in THF (50 mL) cooled to À78 °C was added
BuLi (10.1 mL, 1.38 M in hexanes, 13.9 mmol). The solution was
warmed to room temperature and then re-cooled to À78 °C. To
the deep red-orange solution of the resulting ylide was added a
solution of 17 (7.17 g, 14.1 mmol) in THF (50 mL) via cannula over
a period of 5 min. The resulting reaction mixture was warmed to
room temperature and stirred for 15 h. After evaporation of the
solvent the residue was partitioned between 10% aqueous NH4Cl
(50 mL) and Et2O (30 mL), the organic layer separated and the
aqueous layer extracted with further Et2O (30 mL). The combined
organic layers were dried (MgSO4) filter and evaporated, and the
residue purified by precipitation from CH2Cl2/hexane to give a
Synthesis of 2c. Compound 10c (0.03 g, 0.03 mmol), toluene
(5 mL), a reaction time of 15 h, and column chromatography (30%
CH2Cl2/petroleum ether) gave 2c (0.020 g, 97%).
1:1 mixture of E and Z isomers of (
g
5-1-chloroethenylcyclopenta-
4.3.1. (
g
5-Hydroxymethylcyclopentadienyl)-
dienyl)(
g
4-tetraphenylcyclobutadiene)cobalt (5.43 g, 72%): 1H
(g
4-tetraphenylcyclobutadiene)cobalt 15 [5a]
NMR (d, 400 MHz, CDCl3) 4.53 (2H, brs, Cp), 4.58 (2H, brs, Cp),
4.63 (2H, brs, Cp), 4.98 (2H, brs, Cp), 5.71 (1H, d, J = 7.8, CH), 5.75
(1H, d, J = 7.8, CH), 5.76 (1H, d, J = 13.5, CH), 5.86 (1H, d, J = 13.5,
CH), 7.10–7.25 (24H, m, Ph), 7.30–7.40 (16H, m, Ph).
This mixture of isomers was dissolved in THF (100 mL) and the
resulting solution cooled to approximately À30 to À40 °C. To this
was added BuLi (21.6 mL, 1.38 M in hexanes, 29.8 mmol) and the
To a solution of 2a (0.420 g, 0.80 mmol) in THF (25 mL) was
added LiAlH4 (0.132 g, 3.5 mmol) and the resulting mixture stirred
at room temperature for 15 hours. The reaction was quenched with
H2O (100 mL) and extracted with EtOAc (2 Â 100 mL). The com-
bined organic layers were dried (MgSO4), filtered and evaporated
to give 15 as a dark yellow solid (0.390 g, 98%).

H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
3675
resulting solution slowly darkened. After 15 min the reaction mix-
ture was cooled to À84 °C and to this added H2SO4 (from 4:1 H2O/
conc. H2SO4) which resulted in the solution instantly changing col-
our from black to orange. After warming to room temperature, the
solvent was evaporated and the residue partitioned between Et2O
(50 mL) and brine (50 mL). The organic layer was separated, dried
(MgSO4) and evaporated, and the product column chromato-
graphed (CH2Cl2/petroleum ether) to give 18 as a yellow solid
(3.18 g, 63%).
4.3.7. (
4-tetraphenylcyclobutadiene)cobalt 24
To a solution of (
5-aminocyclopentadienyl)(
clobutadiene)cobalt 23 [18] (0.200 g, 0.40 mmol) in CH2Cl2 (10 mL)
was added acetic anhydride (0.05 mL, 0.5 mmol), NEt3 (0.07 mL,
g
5-Acetamidocyclopentadienyl)-
(g
g
g
4-tetraphenylcy-
0.5 mmol) and DMAP (2.4 mg, 20 lmol). The reaction mixture
was stirred for 15 h, washed with NaHCO3 (10 mL), followed by
water (10 mL). The combined organic fractions was dried (Na2SO4),
filtered, the solvent removed in vacuo and the residue column
chromatographed (25% Et2O/petroleum ether) to give 24 (0.053 g,
24%).
Compound 18: 1H NMR (400 MHz, CDCl3) d 2.43 (1H, s, CCH),
4.62 (2H, brs, Cp), 4.79 (2H, brs, Cp), 7.21–7.29 (12H, m, Ph),
7.45–7.50 (8H, m, Ph). 13C{1H} NMR (100 MHz, CDCl3) d 76.25
(Cb), 78.00 (CCH), 79.36 (CCH), 84.69 (Cp), 86.45 (Cp), 87.69 (Cp),
126.63 (Ph), 128.16 (Ph), 139.08 (Ph), 135.65 (ipso-Ph).
The 1H and 13C NMR date for 20 [17] is included here as it has
not been previously reported in full.
Compound 24: m.p. 266–268 °C. Anal. Calc. for C35H28CoNO: C,
78.20: H, 5.25. Found: C, 78.19: H, 5.17. IR (film) mmax 3365,
3058, 1662 cmÀ1 1H NMR (270 MHz, CDCl3) d 1.59 (3H, s, Me),
.
4.54 (2H, brs, Cp), 4.86 (2H, brs, Cp), 5.92 (1H, brs, NH), 7.14–
7.33 (12H, m, Ph), 7.33–7.53 (8H, m, Ph). 13C{1H} NMR (100 MHz,
CDCl3) d 24.08 (CH3), 75.70 (Cp), 76.89 (Cb), 102.35 (Cp), 104.14
(Cp), 126.64 (Ph), 128.52 (Ph), 129.16 (Ph), 136.32 (ipso-Ph), C@O
not observed.
Compound 20: 1H NMR (400 MHz, CDCl3) d 4.66 (2H, brs, Cp),
4.90 (2H, brs, Cp), 7.10–7.25 (12H, m, Ph), 7.30–7.45 (8H, m, Ph).
13C{1H} NMR (100 MHz, CDCl3) d 66.90 (ipso-Cp), 77.76 (Cb),
86.39 (Cp), 86.90 (Cp), 117.33 (CN), 127.46 (Ph), 128.55 (Ph),
129.02 (Ph), 134.58 (ipso-Ph).
4.3.8. (g
5-Bromocyclopentadienyl)-
(g
4-tetraphenylcyclobutadiene)cobalt 26
To a solution of 25 [5a] (0.143 g, 0.20 mmol) in CH2Cl2 (20 mL)
4.3.5. (g
5-N-2-(1-Hydroxyethyl)carboxamidocyclopentadienyl)-
was added N-bromosuccinimide (0.046 mg, 0.26 mmol) with vig-
orous stirring. The reaction flask was wrapped in foil and stirring
was maintained for 15 h. The resulting dark mixture was quenched
with 1 M NaOH (10 mL) and extracted with CH2Cl2 (10 mL). The or-
ganic layer was dried (MgSO4), filtered and the solvent removed in
vacuo. Column chromatography (1:4 CH2Cl2/petroleum ether)
(1:4) followed by recrystallisation (CH2Cl2/petroleum ether) gave
26 as a yellow crystalline solid (0.075 g, 67% yield).
Compound 26: m.p. 185–185 °C. Anal. Calc. for C33H24CoBr: C,
70.86: H, 4.32. Found: C, 70.88: H, 4.31%. 1H NMR (270 MHz, CDCl3)
d 4.54 (2H, t, J = 2.1, Cp), 4.72 (2H, t, J = 2.1, Cp), 7.19–7.28 (12H, m,
Ph), 7.33–7.51 (8H, m, Ph). 13C NMR (68 MHz, CDCl3) d 76.41 (Cb),
82.79 (ipso-Cp), 83.34 (Cp), 84.92 (Cp), 126.62 (Ph), 128.08 (Ph),
129.05 (Ph), 135.40 (ipso-Ph).
(g
4-tetraphenylcyclobutadiene)cobalt 21
To a solution of 19 (0.980 g, 1.87 mmol) in CH2Cl2 (15 mL) was
added oxalyl chloride (0.32 mL, 3.7 mmol) and a couple of drops of
DMF. Gas evolution was observed and the reaction mixture stirred
for 30 min, after which time the solvent was removed in vacuo to
give the crude acid chloride as a red oil. To a portion of this (0.56 g,
1.0 mmol) in CH2Cl2 (10 mL) was added 2-aminoethanol (0.09 mL,
1.5 mmol) and triethylamine (0.31 mL, 2.2 mmol). The solution
was stirred for 15 h, quenched with water (18 mL), and extracted
with EtOAc (3 Â 30 mL). The combined organic phases were dried
(MgSO4), filtered, the solvent removed in vacuo and the residue
column chromatographed (3% MeOH/CH2Cl2) to give 21 as a yellow
crystalline solid (0.32 g, 55 %).
Compound 21: m.p. 200–204 °C. Anal. Calc. for C36H30CoNO2: C,
76.18: H, 5.33: N, 2.47. Found: C, 75.93: H, 5.34: N, 2.39%. IR (film)
m
4.3.9. (g
5-Trimethylsilylcyclopentadienyl)-
(
max 3380, 1624 cmÀ1. 1H NMR (270 MHz, CDCl3) d 2.46 (1H, s, OH),
g
4-tetraphenylcyclobutadiene)cobalt 28 [5a]
2.96 (2H, m, CH2), 3.46 (2H, m, CH2), 4.70 (2H, t, J = 2, Cp), 5.02 (2H,
d, J 2, Cp), 7.16–7.28 (12H, m, Ph), 7.39–7.48 (8H, m, Ph). 13C{1H}
NMR (100 MHz, CDCl3) d 43.59 (CH2), 62.98 (CH2), 76.64 (Cb),
82.67 (Cp), 86.96 (Cp), 90.15 (Cp), 127.18 (Ph), 128.88 (Ph),
132.38 (Ph), 135.63 (ipso-Ph), 167.50 (C@O).
A solution of 27 (0.100 g, 0.16 mmol) in THF (5 mL) was cooled
to 0 °C before tert-BuLi (0.13 mL of a 1.7 M in THF, 0.22 mmol) was
added. The reaction mixture was stirred for 30 min before trimeth-
ylsilylchloride (0.046 mL, 0.4 mmol) was added. After stirring for
an additional 30 min at room temperature, the reaction was
quenched with H2O, diluted with CH2Cl2 (10 mL) and washed with
sodium hydrogen carbonate (2 Â 15 mL). The organic fraction was
dried (MgSO4), the solvent removed in vacuo, and the residue puri-
fied by column chromatography (petroleum ether) to give 28
(0.082 g, 96%) as a yellow crystalline solid.
4.3.6. (g
5-2-Oxazolinylcyclopentadienyl)-
(g
4-tetraphenylcyclobutadiene)cobalt 22
To an ice-bath cooled solution of 21 (0.220 g, 0.39 mmol) and
28: 1H NMR (270 MHz, CDCl3) d À0.17 (6H, s, 3 Â Me), 4.66 (2H,
d, J = 1.7, Cp), 4.74 (2H, d, J = 1.7, Cp), 7.13–7.27 (12H, m, Ph), 7.41–
7.52 (8H, m, Ph). 13C{1H} NMR (100 MHz, CDCl3) d 0.00 (Me), 75.14
(Cb), 87.40 (Cp), 87.88 (Cp), 126.80 (Ph), 128.61 (Ph), 129.58 (Ph),
137.19 (ipso-Ph), ipso-Cp not observed.
triethylamine (0.60 mL, 4.3 mmol) in CH2Cl2 (10 mL) was added
methanesulfonylchloride (0.08 mL, 1.0 mmol). The solution was
allowed to warm to room temperature, diluted with additional
CH2Cl2 (10 mL), and washed with NaHCO3 (2 Â 10 mL) followed
by aqueous saturated sodium chloride (10 mL). The organic
phrase was dried (Na2SO4), filtered, the solvent removed in va-
cuo and the residue column chromatographed (2% MeOH/CH2Cl2)
to give 22 as a dark yellow crystalline solid (0.140 g, 66 %).
Compound 22: m.p. 192–194 °C. Anal. Calc. for C36H28Co-
NO Á H2O: C, 76.18: H, 5.33: N, 2.47. Found: C, 76.12: H, 5.16: N,
4.3.10. (g
5-Trimethylstannylcyclopentadienyl)-
(g
4-tetraphenylcyclobutadiene)cobalt 29
To a solution of 27 (0.900 g, 1.48 mmol) in THF (20 mL) at
À78 °C was added BuLi (0.76 mL of a 2.5 M solution in THF,
1.9 mmol). The reaction mixture was stirred at À78 °C for
30 min, trimethyltinchloride (2.66 mL of a 1.0 M solution in hex-
anes, 2.66 mmol) added, and the reaction mixture allowed to warm
to room temperature. To the reaction mixture was added H2O
(1 mL) and CH2Cl2 (20 mL), and the organic phase washed with sat-
urated aqueous NaHCO3- (2 Â 20 mL) followed by drying (MgSO4)
2.21%. IR (film) mmax 1651 cmÀ1 1H NMR (270 MHz, CDCl3) d 3.48
.
(2H, m, CH2), 3.64 (2H, m, CH2), 4.78 (2H, d, J = 2, Cp), 5.11 (2H,
d, J = 2, Cp), 7.13–7.32 (12H, m, Ph), 7.39–7.52 (8H, m, Ph).
13C{1H} NMR (100 MHz, CDCl3) d 54.86 (CH2), 66.96 (CH2), 76.37
(Cb), 84.03 (Cp), 85.32 (Cp), 85.63 (Cp), 126.81 (Ph), 128.32 (Ph),
129.27 (Ph), 132.32 (ipso-Ph), 161.44 (C@O).

3676
H.V. Nguyen et al. / Journal of Organometallic Chemistry 693 (2008) 3668–3676
and removal of the solvent in vacuo. Column chromatography
(petroleum ether) gave 29 as a yellow crystalline solid (0.280 g,
31%).
Centre, University of Wales, Swansea. HVN and JA (EP-C511034-
01) thank the EPSRC for support.
Compound 29: m.p. 175–176 °C. Anal. Calcd for C36H33CoSn: C,
67.21: H, 5.17. Found: C, 67.33: H, 5.18%. 1H NMR (270 MHz, CDCl3)
d À0.11 (6H, s, 3 Â Me), 4.66 (2H, d, J = 1.7, Cp), 4.72 (2H, d, J = 1.7,
Cp), 7.13–7.27 (12H, m, Ph), 7.41–7.52 (8H, m, Ph). 13C{1H} NMR
(100 MHz, CDCl3) d À8.76 (Me), 74.74 (cb), 85.70 (ipso-Cp), 86.87
(Cp), 89.08 (Cp), 126.36 (Ph), 128.18 (Ph), 129.15 (Ph), 136.89
(ipso-Ph).
References
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4.3.11. (
4-tetraphenylcyclobutadiene)cobalt 30 [5a]
mixture of 29 (0.100 g, 0.16 mmol) and bromobenzene
g
5-Phenylcyclopentadienyl)-
(g
A
[5] (a) M.D. Rausch, R.A. Genetti, J. Org. Chem. 35 (1970) 3888;
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(0.017 mL, 0.2 mmol) was dissolved in DMF (4 mL). To this was
added caesium fluoride (0.047 g, 0.31 mmol), PdCl2 (0.0005 g,
3 lmol), P(t-Bu)3 (0.0012 g, 6 lmol), and CuI (0.0012 g, 6 lmol).
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The mixture was heated at 100 °C for 15 h, cooled and diluted with
CH2Cl2 (10 mL) and H2O (2 mL). After vigorous shaking, the mix-
ture was filtered through celite with a CH2Cl2/EtOAc solvent mix-
ture. The organic layer was separated, dried (MgSO4), the solvent
removed in vacuo, and the residue purified by column chromatog-
raphy (30% CH2Cl2/petroleum ether 40–60 °C) to give 30 (0.072 g,
79%).
(b) A.M. Stevens, C.J. Richards, Tetrahedron Lett. 38 (1997) 7805;
(c) Y. Ortin, K. Ahrenstorf, P. O’Donohue, D. Foede, H. Müller-Bunz, P. McArdle,
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(d) C.-P. Chang, R.G. Kultyshev, F.-E. Hong, J. Organomet. Chem. 691 (2006)
5831.
30: 1H NMR (270 MHz, CDCl3) d 4.68 (2H, t, J = 2 Hz, Cp), 4.99
(2H, t, J = 2Hz, Cp), 7.03–7.16 (5H, m, Ph), 7.16–7.29 (12H, m, Ph),
7.42–7.53 (8H, m, Ph). dC{1H}(100 MHz, CDCl3) d 75.40 (Cb),
80.16 (Cp), 83.43 (ipso-Cp), 84.98 (Cp), 125.98 (Ph), 126.13 (Ph),
126.27 (Ph), 128.07 (Ph), 128.40 (Ph), 128.88 (Ph), 134.36 (ipso-
Ph), 136.12 (ipso-Ph).
[8] During the preparation of this manuscript a report appeared on the synthesis
of various
complexes containing
(
g g
4-tetraarylcyclobutadiene)( 5-formylcyclopentadienyl)cobalt
a
variety of para-phenyl substituents. The
intermediacy of metallocyclopentadienes of type 9/10 was not discussed.
See: S. Dabek, M.H. Prosenc, J. Heck, J. Organomet. Chem. 692 (2007)
2216.
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[13] Y. Watatsuki, O. Nomura, K. Kitaura, K. Morokuma, H. Yamazaki, J. Am. Chem.
Soc. 105 (1983) 1907.
Supplementary material
CCDC 656493 and 656492 contain the supplementary crystallo-
graphic data for 9a and 9b. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[14] T.E. Pickett, C.J. Richards, Tetrahedron Lett. 40 (1999) 5251.
[15] C. Pichon, B. Odell, J.M. Brown, Chem. Commun. (2004) 598.
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[18] D.C.D. Butler, C.J. Richards, Organometallics 21 (2002) 5433.
[19] The 1H NMR
a, b and Cp chemical shifts of chloromercurioferrocene are 4.11,
Acknowledgements
4.47 and 4.24 ppm, respectively. See: A.F. Cunningham, Organometallics 16
(1997) 1114.
We thank Greg Coumbarides for assistance with recording the
NMR spectra and the EPSRC National Mass Spectrometry Service
[20] A.C. Villa, L. Coghi, A.G. Manfredotti, C. Guastini, Acta Crystallogr. B 30 (1974)
2101.