The preparation, spectroscopy, structure and electrochemistry of some [Co(η4-C4Ph4)(η5-C 5H4R)] complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.12.026

[Co(η⁴-C₄Ph₄)(η⁵-C ₅H₄R)] (R = CO₂Me, 2; and CHO, 3), prepared by the reactions of [Co(η⁵-C₅H₄R)(PPh ₃)₂] with Ph₂C₂, were used as precursors for complexes where R = CH₂OH, 4; CH₂Cl, 5; CH₂P(O)(OEt)₂, 6; CH₂PPh₃ ⁺, [7]⁺; C(O)Fc, 8 (Fc = ferrocenyl); CFc₂OH, 9; CHC(CN)₂, 10; syn and anti-CHNNH-C₆H ₃(NO₂)₂-2,4, 11; CH(Fc)OH, 12; CHFc ⁺, [13]⁺; and CFc₂⁺, [14] ⁺. Most new compounds have been characterised by elemental analyses, and all by spectroscopy. Their spectra are consistent with their formulae; of particular interest is the UV-Vis spectrum of [14]⁺ which shows two very strong absorption bands at 389 and 835 nm. X-ray diffraction techniques were used to determine the structures of 1 (R = Me), 4, 6, [7]Cl, 8, 9, 10, 11a (syn isomer), and 12. All have the same basic structure with the Co atom sandwiched between ca. planar η⁵-C₅H₄R and η⁴-C₄Ph₄ rings. The Ph groups do not lie in the C₄ planes, and the C₄Ph₄ ligands constitute four-bladed propellers. The two rings are close to parallel with interplanar angles of 0.4-4.4° except where R = CH(Fc)OH (6.6°) and CFc₂OH (12°) which is attributed to steric crowding though this does not affect the ferrocenyl groups to the same extent. When the C atom α to the C₅H₄ ligand is sp³ hybridised, it is usually displaced out of the C₅ plane away from Co, but when C_α is sp² hybridised (in 8 and 10) it is displaced out of the C₅ plane towards Co. This is attributed to the contribution that η⁶-fulvene mesomers make towards a description of the structure of the latter compounds but not the former. In the primary and secondary alcohols 4 and 12 there is H-O?H-O hydrogen bonding, but in the tertiary alcohol 9 there is evidence of an intramolecular Fe?HO bond to one ferrocenyl group Fe?H = 2.965(1) and an angle of 5.1° between its two cyclopentadienyl ligands. Electrochemical studies are reported for 8-11 and the known compound triferrocenylcarbinol; this last is compared with the mixed cobalt/ferrocenyl systems 8 and, particularly, 9. The Co(η⁴- C₄Ph₄)(η⁵-C₅H₄-) centre is always more difficult to oxidise than Fe(η⁵-C ₅H₅)(η⁵-C₅H₄-).

Full text of DOI:10.1016/j.jorganchem.2010.12.026

Journal of Organometallic Chemistry 696 (2011) 1496e1509
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The preparation, spectroscopy, structure and electrochemistry of some
[Co(
h
4-C4Ph4)(
h
5-C5H4R)] complexes
,
a
a
a
Paul O’Donohue a, C. John McAdam b , Donagh Courtney , Yannick Ortin , Helge Müller-Bunz ,
*
Anthony R. Manning a, Michael J. McGlincheya, Jim Simpson b
a School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland.
b Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054, New Zealand
a r t i c l e i n f o
a b s t r a c t
4-C4Ph4)(
h
5-C5H4R)] (R ¼ CO2Me, 2; and CHO, 3), prepared by the reactions of [Co(
h
5-C5H4R)
Article history:
[Co(
h
Received 1 November 2010
Received in revised form
15 December 2010
(PPh3)2] with Ph2C2, were used as precursors for complexes where R ¼ CH2OH, 4; CH2Cl, 5; CH2P(O)
(OEt)2, 6; CH2PPhþ3 , [7]þ; C(O)Fc, 8 (Fc ¼ ferrocenyl); CFc2OH, 9; CH]C(CN)2, 10; syn and anti-CH]NNH
eC6H3(NO2)2-2,4, 11; CH(Fc)OH, 12; CHFcþ, [13]þ; and CFcþ2 , [14]þ. Most new compounds have been
characterised by elemental analyses, and all by spectroscopy. Their spectra are consistent with their
formulae; of particular interest is the UVeVis spectrum of [14]þ which shows two very strong absorption
bands at 389 and 835 nm. X-ray diffraction techniques were used to determine the structures of
1 (R ¼ Me), 4, 6, [7]Cl, 8, 9, 10, 11a (syn isomer), and 12. All have the same basic structure with the Co
Accepted 20 December 2010
Keywords:
Cobalt
Tetraphenylcyclobutadiene
Ferrocenyl
atom sandwiched between ca. planar h h
5-C5H4R and 4-C4Ph4 rings. The Ph groups do not lie in the C4
planes, and the C4Ph4 ligands constitute four-bladed propellers. The two rings are close to parallel with
interplanar angles of 0.4e4.4ꢀ except where R ¼ CH(Fc)OH (6.6ꢀ) and CFc2OH (12ꢀ) which is attributed to
steric crowding though this does not affect the ferrocenyl groups to the same extent. When the C atom
a
to the C5H4 ligand is sp3 hybridised, it is usually displaced out of the C5 plane away from Co, but when
Ca is sp2 hybridised (in 8 and 10) it is displaced out of the C5 plane towards Co. This is attributed to the
contribution that
h
6-fulvene mesomers make towards a description of the structure of the latter
compounds but not the former. In the primary and secondary alcohols 4 and 12 there is H-O/H-O
hydrogen bonding, but in the tertiary alcohol 9 there is evidence of an intramolecular Fe/HO bond to
ꢀ
ꢀ
one ferrocenyl group Fe/H ¼ 2.965(1) A and an angle of 5.1 between its two cyclopentadienyl ligands.
Electrochemical studies are reported for 8e11 and the known compound triferrocenylcarbinol; this last is
compared with the mixed cobalt/ferrocenyl systems 8 and, particularly, 9. The Co(
centre is always more difficult to oxidise than Fe(
5-C5H5)( 5-C5H4-).
Ó 2010 Elsevier B.V. All rights reserved.
h h
4-C4Ph4)( 5-C5H4-)
h
h
1. Introduction
to attack by many electrophiles. For example, although it reacts with
mercuric acetate/perchloric acid and then lithium chloride to give [Co
It is fifty years since [Co(
h
4-C4Ph4)(
h
5-C5H5)] was first reported by
(h h
4-C4Ph4)( 5-C5H4HgCl)] ingoodyields, thisisa reagentand product
Nakamura and Hagihara [1], and there are now over four hundred
papers and patents relating to (cyclobutadiene)(cyclopentadienyl)
cobalt derivatives. A lot of recent work has been application driven,
with several different foci: asymmetric synthesis and catalysis [2],
molecularrotors[3]andasaTamoxifenanalogue[4]. Thechemistryof
that are probably best avoided if possible; its Vilsmeier formylation
with POCl3/HC(O)N(Me)Ph gives a disappointing 8% yield of the more
desirable [Co(
h
4-C4Ph4)(
h
5-C5H4CHO)] [5].
[Co(h
4-C4Ph4)(
h
5-C5H4CHO)] and [Co( 4-C4Ph4)( 5-C5H4CO2Me)]
h h
are readily prepared from Na[C5H4R], [Co(PPh3)3Cl] and then Ph2C2
(R ¼ CHO and CO2Me) [6e9], and we have found them to be effective
entry compounds. Here they are used in a variety of reactions to
[Co(
oped as that of the ferrocenyl analogues. One reason for this is that,
compared with ferrocene, [Co(
4-C4Ph4)( 5-C5H5)] is less susceptible
h h
4-C4Ph4)( 5-C5H5)] complexes however is not as well-devel-
h
h
prepare a diverse range of [Co(h h
4-C4Ph4)( 5-C5H4R)] complexes,
some of which have been foreshadowed in our study of [Co(h
4-C4R4)
(
h
5-C5H4R)] (R ¼ Me and Et) derivatives [10]. They include donore
p
-
-
acceptor systems, and mixed cobalt/ferrocene alcohols [Co(h4
C4Ph4){
h
5-C5H4CHn(Fc)2ꢁnOH}] (Fc ¼ ferrocenyl; n ¼ 0, 1). These
* Corresponding author. Tel.: þ64 3 479 4897; fax: þ64 3 479 7906.
E-mail address: mcadamj@alkali.otago.ac.nz (C.J. McAdam).
alcohols are readily dehydroxylated to the di- and triarylmethyl
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.12.026

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1497
cation analogues [Co(
h
4-C4Ph4)(
h
5-C5H4CHFc)]þ and [Co(
h
4-C4Ph4)
2.2. Synthesis of [Co(h h
4-C4Ph4){ 5-C5H4CH2P(O)(OEt)2}], 6
(h
5-C5H4CFc2)]þ isolated as their [BF4]ꢁ salts. The cations are the
counterparts of the previously reported [Co(
h
4-C4Ph4)( 5-C5H4CHR)]þ
h
Diethyl phosphite (0.21 ml, 1.57 mmol) and excess sodium (0.2 g)
in toluene (30 ml) was stirred at 0 ꢀC for 30 min, refluxed for 90 min,
and cooled. The excess sodium solidified to a single ball and was
removed manually. 4 (0.40 g, 0.78 mmol) was added to the refluxing
reaction mixture in small portions over 10 min and reflux main-
tained for 4 h. The mixture was cooled, and quenched with a 20% w/
v solution of sodium bicarbonate. After 20 min the organic layer was
separated, washed with water, dried over MgSO4, filtered, concen-
trated, and chromatographed (silica). Dichloromethane eluted
unreacted 4 and THF-dichloromethane (1/19) eluted the product 6.
This crystallised as a brown solid from a dichloromethaneepentane
solution (yield 0.24 g, 49%). M.p. 156e158 ꢀC. Found: C 71.93, H 5.73,
P 4.74, Co 9.58; C38H36O3PCo requires C 72.38, H 5.75, P 4.91, Co
(R ¼ But and Ph) and [Co(
h h
4-C4Ph4)( 5-C5H4CPh2)]þ [11,12].
Additionally, this work has resulted in two versatile new syn-
thons, the Wittig and HornereWadswortheEmmons reagents [Co
(h h h h
4-C4Ph4)( 5-C5H4CH2PPh3)]Cl and [Co( 4-C4Ph4){ 5-C5H4CH2P
(O)(OEt)2}] respectively. These provide access to organometallic
functionalised alkenes, research area currently attracting
much attention [13]. This work will be covered in a subsequent
paper [14].
a
2. Experimental
2 and 3 were prepared as reported previously [8], and the same
procedure was used to prepare 1 [15]. A procedure for the
synthesis of 4 has been published [9] since our original synthetic
work; our similar methodology offers similar yield but reduced
reaction time and is available in the Electronic Supplementary
Information.
9.35%. IR
(P]O) 1248 (KBr). 1H NMR (CDCl3):
and 4.50 (m, 2H, C5H4), 3.81 (dq, 3JH,P 7 Hz, 3JH,H 7 Hz, 4H, CH2CH3),
2.14 (d, 2JH,P 19 Hz, 2H, C5H4CH2), 1.09 (t, 3JH,H 7 Hz, 6H, CH2CH3). 13
NMR (CDCl3): 136.1, 128.8, 128.1, 126.3 (C4Ph4), 88.7 (Cipso, C5H4),
y
/cmꢁ1
:
y(C]C) 1598, 1497 (CH2Cl2);
y(C]C) 1596, 1498, y
d
7.34e7.11 (m, 20H, Ph), 4.52
C
d
2
83.9 and 83.5 (CH, C5H4), 75.0 (C4Ph4), 62.0 (d, JC,P 6 Hz, CH2CH3),
Tributyltin-ferrocene was prepared according to the literature
[16]. TMEDA was dried from n-BuLi and then distilled under
reduced pressure [17]. All other reagents were purchased from
commercial sources unless otherwise stated. Column chromatog-
raphy was performed on alumina (activity II or III) or silica (Merck
7734). All reactions were carried out under an atmosphere of
nitrogen. IR spectra were recorded on a Perkin Elmer Paragon 1000
FTIR spectrometer having a resolution of 4 cmꢁ1. NMR spectra were
recorded on Varian Inova 300, 400 or 500 MHz spectrometers. 1H
(300 and 400 MHz) and 13C (75 and 100 MHz) chemical shifts are
reported downfield from tetramethylsilane as the internal stan-
dard; 31P (121 MHz) from H3PO4. All coupling constants are given in
Hz. UV/Visible spectra were recorded on a UNICAM UV2 spec-
trometer. Elemental analyses were carried out in the Microanalyt-
ical Laboratory, University College Dublin.
24.6 (d, 2JC,P 138 Hz, C5H4CH2), 16.4 (CH2CH3).
2.3. Preparation of [Co(h h
4-C4Ph4)( 5-C5H4CH2PPh3)]Cl, [7]Cl
A mixture of triphenylphosphine (3.17 g, 12.1 mmol) and 5
(0.640 g, 1.21 mmol) in dry toluene (60 ml) was refluxed overnight,
cooled, and filtered. The precipitate was washed with toluene and
pentane, and recrystallised from chloroform-pentane solution to
give yellow crystals of [7]Cl (yield 0.72 g, 75%). M.p. 262e265 ꢀC.
Found: C 78.65, H 5.18, Cl 4.80; C52H41PClCo requires C 78.93, H
5.22, Cl 4.48%. IR y : y(C]C) 1597,1497 (CH2Cl2); y(C]C) 1595,
/cmꢁ1
1498 (KBr). 1H NMR (CDCl3):
d 7.80e7.25 (m, 35H, Ph), 4.67 and 4.33
(m, 2H, C5H4), 3.48 (d, 2JH,P 12 Hz, 2H, CH2). 31P NMR (CDCl3):
d
20.4.
4
13C NMR (CDCl3):
d
135.7 (d, JC,P 3 Hz, Cpara, PPh3), 135.2, 128.9,
2
128.6 and 127.0 (C4Ph4), 133.8 (d, JC,P 10 Hz, Cortho, PPh3), 130.5
Cyclic voltammetric experiments were carried out at 20 ꢀC in
CH2Cl2 solutions degassed with nitrogen. A three-electrode cell was
used with CypressSystems 1 mm diameter Ptor 1.4 mm glassycarbon
working, Ag/AgCl reference and platinum wire auxiliary electrodes.
Solutions were w10ꢁ3 M in electroactive material and contained
0.1 M[Bu4N][PF6] as the supportingelectrolyte. Voltammograms were
recorded using a Powerlab/4sp computer-controlled potentiostat. All
potentials are referenced to the reversible formal potential (taken as
3
1
(d, JC,P 12 Hz, Cmeta, PPh3), 117.3 (d, JC,P 86 Hz, Ci2pso, PPh3), 85.7
3
(d, JC,P 3 Hz, CH, C5H4), 84.7 (CH, C5H4), 82.9 (d, JC,P 2 Hz, Cipso
C5H4), 76.4 (C4Ph4), 25.7 (d, 1JC,P 50 Hz, CH2).
,
2.4. Preparation of [Co(h h
4-C4Ph4){ 5-C5H4C(O)Fc}], 8, and [Co
(h
4-C4Ph4)(
h
5-C5H4CFc2OH)], 9 {Fc ¼ Fe(
h h
5-C5H5)( 5-C5H4-)}
The addition of n-BuLi (0.81 ml, 1.3 mmol) to a solution of
[Fe(
5-C5H5)( 5-C5H4SnBun3)] (0.78 g, 1.63 mmol) in dry THF
E0 ¼ 0.00 V) for the [Fe(
h
5-C5Me5)2]þ/0 process [18] where E0 was
h
h
calculated from the average of the oxidation and reduction peak
potentials under conditions of cyclic voltammetry. Under the same
(30 ml) at ꢁ78 ꢀC gave an orange solution and precipitate of LiFc
[16]. After 30 min, to this was added a solution of 2 (0.35 g,
0.65 mmol) in THF (5 ml). The mixture turned red and was stirred
overnight. It was quenched with water (2 ꢂ 10 ml), and extracted
with CH2Cl2. The organic layer was dried over magnesium sulphate,
evaporated to dryness at reduced pressure, and the residue chro-
matographed on alumina (pentaneetoluene; 1/1). The tertiary
alcohol 9 eluted as the second band and the ketone 8 as the third.
Both products were isolated and crystallised from dichloro-
methaneepentane solutions to give red-brown 8 (yield 0.087 g,
20%) and yellow-brown 9 (yield 0.074 g, 13%).
conditions, E0 calculated for [Fe( 5-C5H5)2]þ/0 was 0.55 V.
h
2.1. Synthesis of [Co(h h
4-C4Ph4)( 5-C5H4CH2Cl)], 5
Thionyl chloride (0.21 g, 3.44 mmol) was added dropwise over
one hour to a cooled solution (0 ꢀC) of 4 (0.82 g, 1.6 mmol) and
pyridine (0.27 g, 3.44 mmol) in toluene (50 ml). The mixture was
allowed to return to room temperature, stirred overnight and then
filtered through a glass frit to remove the precipitate. The mixture
was evaporated to dryness under a vacuum. The residue was
recrystallised froma dichloromethaneepentane solution togive 5 as
a yellow powder (yield 0.70 g, 85%). M.p. (dec) 160e162 ꢀC. Found: C
76.95, H 4.85, Cl 6.25;C34H26ClCorequiresC 77.20, H4.95, Cl6.70%. IR
2.4.1. [Co(
M.p. 175e178 ꢀC. Found: C 75.82, H 4.78, Co 8.13, Fe 7.92;
C44H33OFeCo requires C 76.31, H 4.80, Co 8.51, Fe 8.06%. IR
/cmꢁ1
(C]O) 1618,
7.60e7.25 (m, 20H, Ph)
h h
4-C4Ph4){ 5-C5H4C(O)Fc}], 8
y
:
y
/cmꢁ1
819 (KBr).1H NMR (CDCl3):
3JH,H 2 Hz, 2H, C5H4), 3.94 (s, 2H, CH2). 13C NMR (CDCl3):
:
y
(C]C) 1597, 1498 (CH2Cl2);
7.46e7.19 (m, 20H, Ph), 4.71 and 4.62 (t,
135.8,
y(C]C) 1595, 1497;
y(CeCl)
y
(C]O) 1625,
y(C]C) 1596, 1499, 1455 (CH2Cl2); y
d
y
(C]C) 1605, 1499 (KBr). 1H NMR (CDCl3):
d
d
5.54 and 4.94 (t, 3JH,H 2 Hz, 2H, C5H4Co), 4.62 and 4.39 (t, 3JH,H 2 Hz,
128.8, 128.2 and 126.6 (C4Ph4), 93.2 (Cipso, C5H4), 84.8 and 83.2 (CH,
C5H4), 75.5 (C4Ph4), 42.0 (CH2).
2H, C5H4Fe), 4.19 (s, 5H, C5H5). 13C NMR (CDCl3):
129.2, 128.4 and 127.0 (C4Ph4), 95.4 (Cipso, C5H4Co), 87.0 and 84.5
d 194.3 (CO), 135.5,

1498
P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
Table 1
Crystal data for (a) 1, 4, 6, [7]Cl and 8 and (b) 9, 10, both forms of 11a and 12.
Compound
1
4
6
[7]Cl.2H2O.CHCl3
8
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C
34H27Co
C34H27OCo
510.49
C38H36O3PCo
630.57
C53H46O2PCl4Co
946.60
C44H33OCoFe
692.48
494.49
293(2) K
0.71073 A
Orthorhombic
Pbcn
293(2) K
100(2) K
100(2) K
100(2) K
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.71073 A
0.71073 A
0.71073 A
0.71073 A
Monoclinic
Cc
Triclinic
P ꢁ 1
Monoclinic
C2/c
Triclinic
P ꢁ 1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Unit cell dimensions
a ¼ 20.9888(17) A
a ¼ 20.976(2) A
a ¼ 10.6221(9) A
a ¼ 24.5903(8) A
a ¼ 11.3276(7) A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
b ¼ 14.8096(12) A
b ¼ 28.010(3) A
b ¼ 17.4465(14) A
b ¼ 12.5321(4) A
b ¼ 11.4871(7) A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
c ¼ 32.301(3) A
c ¼ 9.3932(9) A
c ¼ 17.9525(15) A
c ¼ 30.0100(10) A
c ¼ 12.3527(8) A
a
b
g
¼ 90ꢀ
¼ 90ꢀ
¼ 90ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 75.414(2)ꢀ
¼ 75.766(1)ꢀ
¼ 85.727(2)ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 82.521(1)ꢀ
¼ 77.025(1)ꢀ
¼ 87.221(1)ꢀ
¼ 108.036(2)ꢀ
¼ 100.6070(10)ꢀ
¼ 90ꢀ
¼ 90ꢀ
3
3
3
3
3
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
10 040.2(14) A
16
5247.6(9) A
8
3120.6(4) A
4
9090.1(5) A
8
1552.68(17) A
2
1.309 Mg/m3
0.704 mmꢁ1
4128
1.292 Mg/m3
0.678 mmꢁ1
2128
1.342 Mg/m3
0.638 mmꢁ1
1320
1.383 Mg/m3
0.690 mmꢁ1
3920
1.481 Mg/m3
1.038 mmꢁ1
716
Crystal size (mm)
0.20 ꢂ 0.10 ꢂ 0.05
1.20 ꢂ 0.20 ꢂ 0.15
0.50 ꢂ 0.40 ꢂ 0.20
0.60 ꢂ 0.50 ꢂ 0.50
0.20 ꢂ 0.10 ꢂ 0.05
q
range for data collection
1.80e24.00ꢀ
2.04e25.00ꢀ
1.90e26.00ꢀ
1.83e33.00ꢀ
1.70e27.00ꢀ
Index ranges
e 24 <¼ h <¼ 23,
e 16 <¼ k <¼ 16,
e 36 <¼ l <¼ 36
e 24 <¼ h <¼ 24,
e 33 <¼ k <¼ 33,
e 11 <¼ l <¼ 11
e 13 <¼ h <¼ 13,
e 21 <¼ k <¼ 21,
e 22 <¼ l <¼ 22
e 37 <¼ h <¼ 37,
e 19 <¼ k <¼ 19,
e 45 <¼ l <¼ 45
e 14 <¼ h <¼ 14,
e 14 <¼ k <¼ 14,
e 15 <¼ l <¼ 15
Reflections collected
63 258
37 310
50 562
81 147
25 805
Independent reflections
7880 [R(int) ¼ 0.0468]
9200 [R(int) ¼ 0.0396]
12 234 [R(int) ¼ 0.0324]
16 884 [R(int) ¼ 0.0210]
6769 [R(int) ¼ 0.0338]
Completeness to
q
¼ 24.0ꢀ
99.9%
99.9%
99.7%
98.5%
99.7%
Absorption correction
Semi-empirical from
equivalents
Semi-empirical
from equivalents
0.9051 and 0.7186
Full-matrix
Semi-empirical
from equivalents
0.8830 and 0.7513
Full-matrix
Semi-empirical
from equivalents
0.7243 and 0.6406
Full-matrix
Semi-empirical
from equivalents
0.9499 and 0.8284
Full-matrix
Max. and min. transmission
Refinement method
0.9656 and 0.8255
Full-matrix
least-squares on F2
7880/0/623
least-squares on F2
9200/2/651
least-squares on F2
12 234/0/1019
1.064
least-squares on F2
16 884/6/589a
1.041
least-squares on F2
6769/0/556
Data/restraints/parameters
Goodness-of-fit on F2
1.019
1.043
1.046
Final R indices [I > 2sigma(I)]
R1 ¼ 0.0351,
wR2 ¼ 0.0792
R1 ¼ 0.0483,
wR2 ¼ 0.0853
R1 ¼ 0.0387,
wR2 ¼ 0.0833
R1 ¼ 0.0489,
wR2 ¼ 0.0878
R1 ¼ 0.0432,
wR2 ¼ 0.1144
R1 ¼ 0.0504,
wR2 ¼ 0.1217
R1 ¼ 0.0391,
wR2 ¼ 0.0995
R1 ¼ 0.0449,
wR2 ¼ 0.1034
R1 ¼ 0.0353, wR2 ¼ 0.0878
R indices (all data)
R1 ¼ 0.0443, wR2 ¼ 0.0942
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
Largest diff. peak and hole
Compound
0.590 and ꢁ0.344 e A
0.420 and ꢁ0.176 e A
0.806 and ꢁ0.390 e A
1.132 and ꢁ1.139 e A
0.526 and ꢁ0.233 e A
9.CH2Cl2
10
11a.CH2Cl2
11a.½CHCl3
12
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C
55H45OCl2Fe2Co
C37H25N2Co
556.52
C41H31N4O4Cl2Co
773.53
C81H59N8O8Cl3Co2
1496.57
C44H35OCoFe
694.50
963.44
100(2) K
150(2) K
100(2) K
100(2) K
293(2) K
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.71073 A
Triclinic
P ꢁ 1
0.71073 A
0.71073 A
0.71073 A
0.71073 A
Monoclinic
P21/c
Monoclinic
P21/n
Triclinic
Triclinic
P ꢁ 1
P ꢁ 1
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Unit cell dimensions
a ¼ 10.570(3) A
a ¼ 11.0164(10) A
a ¼ 15.7015(16) A
a ¼ 10.910(3) A
a ¼ 11.487(8) A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
b ¼ 11.658(3) A
b ¼ 14.3726(13) A
b ¼ 11.1903(12) A
b ¼ 10.987(3) A
b ¼ 12.978(9) A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
c ¼ 18.863(7) A
c ¼ 17.1720(16) A
c ¼ 20.930(2) A
c ¼ 15.218(4) A
c ¼ 13.216(10) A
a
b
g
¼ 104.222(7)ꢀ
¼ 103.098(7)ꢀ
¼ 95.925(5)ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 107.282(4)ꢀ
¼ 98.832(5)ꢀ
¼ 99.518(4)ꢀ
a
b
g
¼ 73.228(12)ꢀ
¼ 65.870(12)ꢀ
¼ 67.095(13)ꢀ
¼ 98.0540(10)ꢀ
¼ 90ꢀ
¼ 109.596(2)ꢀ
¼ 90ꢀ
3
ꢀ
3
ꢀ
3
3
ꢀ
3
ꢀ
ꢀ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
2163.3(12) A
2
2692.1(4) A
4
3464.5(6) A
1677.5(7) A
1637(2) A
4
1
2
1.479 Mg/m3
1.205 mmꢁ1
992
1.373 Mg/m3
0.667 mmꢁ1
1152
1.483 Mg/m3
0.700 mmꢁ1
1592
1.481 Mg/m3
0.682 mmꢁ1
770
1.409 Mg/m3
0.985 mmꢁ1
720
Crystal size (mm)
0.20 ꢂ 0.10 ꢂ 0.03
1.83e20.94ꢀ.
e 10 <¼ h <¼ 10,
e 11 <¼ k <¼ 11,
e 18 <¼ l <¼ 18
8681
0.70 ꢂ 0.50 ꢂ 0.50
1.86e28.29ꢀ.
e 14 <¼ h <¼ 14,
e 19 <¼ k <¼ 18,
e 22 <¼ l <¼ 22
44 689
0.80 ꢂ 0.40 ꢂ 0.20
1.98e25.00ꢀ.
e 18 <¼ h <¼ 18,
e 13 <¼ k <¼ 13,
e 24 <¼ l <¼ 24
23 424
0.30 ꢂ 0.05 ꢂ 0.03
1.94e23.50ꢀ.
e 12 <¼ h <¼ 12,
e 12 <¼ k <¼ 12,
e 17 <¼ l <¼ 17
10 636
0.20 ꢂ 0.15 ꢂ 0.05
1.71e24.00ꢀ.
e 13 <¼ h <¼ 13,
e 14 <¼ k <¼ 14,
e 15 <¼ l <¼ 15
21 619
q
range for data collection
Index ranges
Reflections collected
Independent reflections
4521 [R(int) ¼ 0.0500]
6448 [R(int) ¼ 0.0296]
6093 [R(int) ¼ 0.0425]
4929 [R(int) ¼ 0.0433]
5131 [R(int) ¼ 0.0662]
Completeness to
q
¼ 24.0ꢀ
97.9%
96.6%
99.9%
99.3%
100.0%
Absorption correction
Semi-empirical
from equivalents
0.9647 and 0.4044
Full-matrix
Numerical
Semi-empirical
from equivalents
0.8726 and 0.6300
Full-matrix
Semi-empirical
from equivalents
0.9798 and 0.6637
Full-matrix
Semi-empirical
from equivalents
0.9524 and 0.8163
Full-matrix
Max. and min. transmission
Refinement method
0.7314 and 0.6524
Full-matrix
least-squares on F2
4521/0/551
least-squares on F2
6448/0/461
least-squares on F2
6093/0/473
least-squares on F2
4929/0/482
least-squares on F2
5131/0/436
Data/restraints/parameters

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1499
Table 1 (continued)
Compound
9.CH2Cl2
10
11a.CH2Cl2
11a.½CHCl3
12
Goodness-of-fit on F2
Final R indices
[I > 2sigma(I)]
1.002
1.039
1.055
1.079
1.163
R1 ¼ 0.0481,
wR2 ¼ 0.1043
R1 ¼ 0.0714,
wR2 ¼ 0.1118
R1 ¼ 0.0312,
wR2 ¼ 0.0796
R1 ¼ 0.0359,
wR2 ¼ 0.0824
R1 ¼ 0.0513,
wR2 ¼ 0.1244
R1 ¼ 0.0628,
wR2 ¼ 0.1308
R1 ¼ 0.0541,
wR2 ¼ 0.1144
R1 ¼ 0.0707,
wR2 ¼ 0.1230
R1 ¼ 0.0633,
wR2 ¼ 0.1325
R1 ¼ 0.0898,
wR2 ¼ 0.1423
R indices (all data)
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
ꢀꢁ3
Largest diff. peak
and hole
0.590 and ꢁ0.506 e A
0.379 and ꢁ0.240 e A
0.922 and ꢁ0.613 e A
0.556 and ꢁ0.367 e A
0.436 and ꢁ0.424 e A
(CH, C5H4Co), 81.1 (Cipso, C5H4Fe), 76.9 (C4Ph4) 71.3 and 70.9 (CH,
C5H4Fe), 70.2 (C5H5). lmax/nm (
/dm3 molꢁ1 cmꢁ1) (CH2Cl2): 279
(41 000); 335 (sh, 15 000); 385 (sh, 5700); 450 (sh, 2800).
and 127.2 (C4Ph4), 129.9, 123.5 and 116.8 {C5, C3 and C6, C6H3(NO2)2},
88.4 and 83.6 (CH, C5H4), 85.9 (Cipso, C5H4), 76.8 (C4Ph4). lmax/nm (
dm3 molꢁ1 cmꢁ1) (CH2Cl2): 270 (45 000); 315 (22 000); 386 (19 000).
3
3/
2.4.2. [Co(
h
4-C4Ph4)(
h
5-C5H4CFc2OH)], 9
2.6.2. Anti-[Co(h h
4-C4Ph4){ 5-C5H4CH]NNHC6H4(NO2)2-2,4}], 11b
M.p. 178e181 ꢀC. Found: C 70.06, H 4.84, Co 5.98, Fe 11.43;
M.p. 177e178 ꢀC. Found C 69.63, H 4.52, N 7.69, Co, 8.16;
C40H29O4N4Co requires C 69.77, H 4.24, N 8.14, Co 8.56%. IR
/cmꢁ1
(C]N)
C54H43OCoFe2.CH2Cl2 requires C 68.56, H 4.71, Co 6.12, Fe 11.59%. IR
y
:
y
/cmꢁ1
:
y
(C]C) 1594, 1499 (CH2Cl2);
1498 (KBr). 1H NMR (CDCl3):
7.50e7.20 (m, 20H, Ph), 4.80, 4.40
(m, 2H, C5H4Co), 4.05 (s, 10H, C5H5Fe), 4.02, 3.96, 3.88, 3.32 (m, 2H,
C5H4Fe), 2.34 {s, 1H, C(OH)}. 13C NMR (CDCl3):
136.9, 129.4, 128.3
y(OH) 3680,
y(C]C) 1594,
y
(C]N) 1615,
y
(C]C) 1585,1498,
y
(NO2) 1517, 1337 (CH2Cl2);
y
d
1613,
(399.8 MHz, CDCl3):
y(C]C) 1583, 1495,
y
(NO2) 1512, 1333 (KBr). 1H NMR
4
d
10.53 (s, 1H, NH), 9.14 {d, JH,H 2 Hz, 1H, H3,
4
3
d
C6H3(NO2)2}, 8.32 {dd, JH,H 3 Hz and JH,H 10 Hz, 1H, H5,
and 126.6 (C4Ph4), 111.7 (Cipso, C5H4Co), 99.6 (Cipso, C5H4Fe), 83.2,
82.1 (CH, C5H4Co), 75.1 (C4Ph4), 72.6 {C(OH)}, 69.0 (C5H5), 68.2, 67.4,
67.2, 66.7 (CH, C5H4Fe). lmax/nm (
C6H3(NO2)2}, 7.83 {d, 3JH,H 10 Hz, 1H, H6, C6H3(NO2)2}, 7.46e7.14 (m,
20H, Ph), 7.08 (s,1H, CH]N), 5.10 and 4.91 (t, 3JH,H 2 Hz, 2H, C5H4).13
C
3
/dm3 molꢁ1 cmꢁ1) (CH2Cl2): 294
NMR (125.7 MHz, CDCl3): d 145.9 (CH]N),144.3,137.8 and 128.3 {C1,
(sh, 28 000); 384 (sh, 4000); 450 (sh, 2000).
C2 and C4 C6H3(NO2)2}, 135.5, 129.0, 128.3 and 127.0 (C4Ph4), 130.0,
123.9 and 116.8 {C5, C3 and C6, C6H3(NO2)2}, 89.5 (Cipso, C5H4), 86.3
and 82.9 (CH, C5H4), 76.9 (C4Ph4). lmax/nm (
(CH2Cl2): 259 (41000); 315 (23 000); 414 (21000).
3 )
/dm3 molꢁ1 cmꢁ1
2.5. Preparation of [Co(h h
4-C4Ph4){ 5-C5H4CH]C(CN)2}], 10
Two drops of triethylamine were added to a solution of malono-
nitrile (0.02 g, 0.27 mmol) and 3 (0.10 g, 0.20 mmol) in dry dichloro-
methane (30 ml), and the mixture stirred overnight. When the
solvent was removed at reduced pressure, it gave a deep red residue
which was chromatographed on silica (dichloromethaneepentane;
1/1). Deep red crystals of 10 were grown from dichloromethane/
pentane mixtures (yield 0.085 g, 77%). M.p. 203e204 ꢀC. Found:
C 79.61, H 4.55, N, 5.06; C37H25N2Co requires C 79.85, H 4.53, N 5.03%.
2.7. Preparation of [Co(
5-C5H5)( 5-C5H4-)}
h h
4-C4Ph4){ 5-C5H4CH(Fc)OH}], 12 {Fc]Fe
(h
h
n-BuLi (0.32 ml, 0.5 mmol) and then TMEDA (0.08 ml, 0.5 mmol)
were added dropwise to a cooled solution (0 ꢀC) of ferrocene (0.112 g,
0.6 mmol) in dry diethyl ether, and the mixture stirred overnight
[19]. This solution was cooled to ꢁ78 ꢀC and a solution of 3 (0.100 g,
0.2 mmol) in THF (20 ml) added dropwise to it. The mixture was
allowed to return to room temperature and stirred for a further 3 h. It
was cooled to ꢁ78 ꢀC, hydrolysed with water (10 ml), and extracted
with dichloromethane. The dichloromethane solution was washed
with brine, dried over magnesium sulphate, concentrated and
chromatographed on silica (pentaneedichloromethane; 2/3). The
product was crystallised from pentaneedichloromethane to give
yellow-brown 12 (yield 0.040 g, 29%). Found: C 75.00, H 5.14, Co 8.02,
IR
(C]C) 1569, 1498 (KBr). 1H NMR (CDCl3):
6.87 (s, 1H, CH]C(CN)2), 5.35 and 5.07 (t, JH,H 2 Hz, 2H, C5H4).
13C NMR (CDCl3):
157.4 (CH]C(CN)2), 134.3, 128.9, 128.8 and 127.8
(C4Ph4), 114.9 and 114.2 (CN), 90.4 and 85.2 (CH, C5H4), 87.9 (Cipso
C5H4), 78.9 (C4Ph4). lmax/nm (
/dm3 molꢁ1 cmꢁ1) (CH2Cl2): 277
(35 000); 322 (sh,16 000); 360 (sh, 8400); 421 (7700), 500 (sh, 3500).
y
/cmꢁ1
:
y(C^N) 2225,
y(C]C) 1577, 1499 (CH2Cl2);
y(C^N) 2218,
y
d
7.42e7.25 (m, 20H, Ph),
3
d
,
3
2.6. Preparation of syn and anti-[Co(h h
4-C4Ph4){ 5-C5H4CH]
NNHC6H4(NO2)2-2,4}], 11a and 11b
Fe 7.70; C44H35OCo Fe requires C 76.09, H 5.08, Co 8.49, Fe 8.04%. IR
cmꢁ1
(C]C) 1605, 1492 (CH2Cl2); (OH) 3671, (C]C) 1603, 1493
(KBr). 1H NMR (CDCl3):
y/
:
y
y
y
d
7.50e7.24 (m, 20H, Ph), 4.92, 4.58, 4.56 and
4.53 (m,1H, C5H4Co), 4.82 {d, 3JH,H 3 Hz,1H, CH(OH)}, 4.05, 4.02, 4.01
and 3.80 (m,1H, C5H4Fe), 4.03 (s, 5H, C5H5),1.64 {d, 3JH,H 3 Hz,1H, CH
ꢀ
Molecular sieves (4 A) were added to a solution of 3 (0.25 g,
0.49 mmol) and dried 2,4-dinitrophenylhydrazine (0.15 g, 0.74 mmol)
in dry dichloromethane (50 ml), and the mixture refluxed overnight. It
was allowed to cool, filtered and the filtrate concentrated. Syn and anti
isomers of the product (11a and 11b respectively) were separated by
chromatography (silica; pentaneedichloromethane; 5/2) and each
crystallised from dichloromethane/pentane mixtures to give red 11a
(yield 0.071 g, 21%) and 11b (yield 0.094 g, 28%).
(OH)}.13C NMR (CDCl3):
d 136.5,129.0,128.4 and 126.6 (C4Ph4),103.4
(Cipso, C5H4Co), 93.1 (Cipso, C5H4Fe), 83.7, 82.4, 80.9, 80.9 (CH, C5H4Co),
75.1 (C4Ph4), 68.8 (C5H5), 67.9, 67.8, 67.1, 66.4 (CH, C5H4Fe), 66.7
{CH(OH)}.
2.8. The reaction of [Co(
HBF4.OEt2. The formation of [Co(
[13][BF4] {Fc ¼ Fe(
5-C5H5)( 5-C5H4-)}
h
4-C4Ph4){
h
5-C5H4CH(Fc)OH}], 12, with
5-C5H4CH(Fc)}][BF4],
h
4-C4Ph4){
h
2.6.1. Syn-[Co(
M.p. 228e230 ꢀC. Found C 69.21, H 4.37, N 7.79, Co, 7.86;
C40H29O4N4Co requires C 69.77, H 4.24, N 8.14, Co 8.56%. IR
/cmꢁ1
(C]N)
(NO2) 1514, 1331 (KBr). 1H NMR (CDCl3):
h
4-C4Ph4){
h
5-C5H4CH]NNHC6H4(NO2)2-2,4}], 11a
h
h
y
:
When two drops of HBF4.Et2O were added to a solution of 12 in
dichloromethane at room temperature, the colour changed from
yellow to deep green/blue. The solution was washed with water
(5 ml) to remove any excess acid, and the organic layer passed
through a pad of pre-dried Celite. The eluant, a solution of [13][BF4],
y(C]N) 1616,
y(C]C)1592,1498,
y(NO2)1518,1336(CH2Cl2);
y
1616,
y
(C]C) 1593, 1495, y
d
11.13 (s, 1H, NH), 9.06 {d, 4JH,H 2 Hz, 1H, H3, C6H3(NO2)2}, 8.28 {dd,
4JH,H 3 Hz and 3JH,H 10 Hz, 1H, H5, C6H3(NO2)2}, 7.86 {d, 3JH,H 10 Hz, 1H,
H6, C6H3(NO2)2}, 7.46e7.14 (m, 20H, Ph), 7.04 (s,1H, CH]N), 5.29 and
was concentrated and analysed. 1H NMR (CDCl3):
d 8.09 (s, 1H, CH),
4.93(t, 3JH,H 2 Hz, 2H, C5H4).13C NMR (75.4 MHz, CDCl3):
d
145.3, 138.2
7.38e7.18 (m, 20H, Ph), 5.92, 5.73, 4.84 and 4.34 (m, 1H, C5H4Fe),
and 128.1 {C1, C2 and C4 C6H3(NO2)2},143.3(CH]N),135.1,128.9,128.4
5.76, 5.35, 5.25 and 5.06 (m,1H, C5H4Co), 4.65 (s, 5H, C5H5). 13C NMR

1500
P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
(125.7 MHz, CDCl3):
d
148.0 (CH, Ca), 133.3, 128.7, 128.6 and 127.9
structures were solved by direct methods using SHELXS-97 and
refined by full-matrix least-squares on F2 using SHELXL-97 [21]. All
non-hydrogen atoms were assigned anisotropic temperature
factors. For compounds 1, 4, [7]Cl, 9, 11a and 12 all hydrogen atoms
were added at calculated positions and refined using a riding
model. Their isotropic temperature factors were fixed to 1.2 times
(1.5 times for methyl groups) the equivalent isotropic displacement
parameters of the carbon/nitrogen atom to which the H atom is
attached. For compounds 6, 8 and 10 all hydrogen atoms were
located in the difference Fourier map and allowed to refine freely
with isotropic temperature factors. For [7]Cl, the OeH distances in
the water molecules of crystallization were restrained to 0.9 A.
ORTEX [22] and Mercury [23] were used to calculate some inter-
plane angles and interatomic separations.
Crystal data for 1, 4, 6, [7]Cl, 8, 9, 10, both types of 11a and 12 are
given in Table 1. Their molecular structures and atom labeling are
shown in Figs. 1e9 which also include some selected molecular
dimensions.
(C4Ph4), 93.4 (Cipso, C5H4Co), 90.6 (Cipso, C5H4Fe), 94.9, 94.9, 90.0 and
80.9 (CH, C5H4Co), 87.9, 87.5, 80.8 and 73.4 (CH, C5H4Fe), 81.2
(C4Ph4), 78.5 (C5H5).
2.9. The reaction of [Co(
HBF4.OEt2. The formation of [Co(
[BF4], {Fc ¼ Fe(
5-C5H5)( 5-C5H4-)}
h
4-C4Ph4)(
h
5-C5H4CFc2OH)], 9, with
5-C5H4CFc2)][BF4], [14]
h
4-C4Ph4)(
h
h
h
When two drops of HBF4.Et2O or aqueous HBF4 were added to
a solution of 9 in dichloromethane at room temperature, the colour
changed from yellow-brown to deep green/blue. The solution was
washed with water (5 ml) to remove any excess acid, and the
organic layer passed through a pad of pre-dried Celite. The eluant,
a solution of [14][BF4], was evaporated to dryness and the residue
analysed. The UV/Visible spectrum of this compound was obtained
by carrying out this reaction in a suitable cell. Found: C 58.77, H
4.06, Co 5.57, Fe 9.49; C54H42 BF4CoFe2.(CH2Cl2)2.H2O requires C
ꢀ
59.20, H 4.26, Co 5.19, Fe 9.83%. 1H NMR (CDCl3):
(m, 20H, Ph), 5.83 (s, br, 2H, C5H4) 5.36 (s, br, 6H, C5H4), 5.16 (s, br,
4H, C5H4), 4.38 (s, 10H C5H5). 13C NMR (125.7 MHz, CDCl3):
196.9
d 7.40e7.20
3. Results and discussion
d
(Ca), 132.9, 128.4, 128.1 and 127.8 (C4Ph4), 102.7 (Cipso, C5H4Co), 88.3
(Cipso, C5H4Fe), 94.1 and 89.6 (CH, C5H4Co), 81.3 (C4Ph4), 80.5 and
78.8 (CH, C5H4Fe), 75.0 (C5H5). lmax/nm
(CH2Cl2): 389 (13 000); 555 (2600); 616 (2800); 835 (7700).
The reactions carried out in the course of this work are
summarized in Schemes 1 and 2. All compounds 1e12 are air-stable
solids soluble in the appropriate solvents. Most are yellow to red-
brown except where the groups R ¼ CH]C(CN)2 (10) and CH]
NNHC6H3(NO2)2-2,4 (11) which are deep red. The merocyanine [13]
[BF4] and [CPh3]þ analogue [14][BF4] are deep blueegreen.
(3 )
/dm3 molꢁ1 cmꢁ1
2.10. [{Fe(
h
5-C5H5)( 5-C5H4)}3C][BF4]
h
The UV/Visible spectrum of this compound was obtained by
adding a drop of aqueous HBF4 to a solution of [{Fe(
5-C5H5)
5-C5H4-)}3COH] in dichloromethane in a suitable cell. Work-up of
this solution as per [14][BF4] afforded a sample for electrochemical
studies. lmax/nm (
/dm3 molꢁ1 cmꢁ1) (CH2Cl2): 395 (24 000); 585
R
R
Co(PPh3)3Cl
+
Na[C5H4R]
h
(i)
(ii)
(iii)
Co
Co
red
?
Ph
Ph
Ph
Ph
(h
Ph3P
PPh3
green
3
(sh, 900); 855 (12 000).
Scheme 1. (i) Tetrahy2drofuran solution, 20 ꢀC. (ii) Add 2 equivalents of C2Ph2 in
toluene, 20 ꢀC. (iii) Reflux for 16 h.
2.11. Crystal structure determinations
[Co(
shown in Scheme 1 from [Co(PPh3)3Cl] and Na[C5H5] via red [Co(h5
C5H5)(PPh3)2] which reacts with two equivalents of Ph2C2 to give
h h
4-C4Ph4)( 5-C5H5)] is efficiently prepared in a single pot as
The structures of 1, 4, 6, [7]Cl, 8, 9, 10, 11a, and 12 were deter-
mined by X-ray crystallography in the X-ray laboratory of Univer-
sity College Dublin. Crystals were grown by slow diffusion and
evaporation methods using CDCl3epentane, CH2Cl2epentane and
tolueneepentane mixtures. Data were collected on a Bruker SMART
Apex CCD diffractometer. Semi-empirical absorption corrections
based on redundant reflections were made using SADABS [20]. The
-
a green unidentified intermediate which is converted on heating to
yellow-brown [Co(h h
4-C4Ph4)( 5-C5H5)] [11]. However, unlike
ferrocene, this does not undergo facile electrophilic substitution
reactions at the cyclopentadienyl ligand and is not, in general,
a suitable precursor for other [Co(
It has been shown that these are best prepared by the same route as
[Co(
4-C4Ph4)( 5-C5H5)] but with Na[C5H4R] salts in step 1, and
h h
4-C4Ph4)( 5-C5H4R)] complexes.
h
h
C34
C29
proceeding to the desired complex utilising conventional organic
chemistry to modify R as necessary [7e9,11]. However, yields of
C33
C30
[Co(h h
4-C4Ph4)( 5-C5H4R)] vary considerably as a function of R and
C32
although both 2 and 3 are desirable entry compounds, the yield of 2
(R ¼ CO2Me)at 67%is greaterthanthatof3 (R ¼ CHO)at 16%. 3 canbe
prepared from 2 in much higher yields (60% based on [Co(PPh3)3Cl])
by reduction to the primary alcohol 4 (Scheme 2) and subsequent
oxidation to 3 [9,24].
In the current work we converted the primary alcohol 4 to the
chloromethyl complex 5 by reaction with thionyl chloride and pyri-
dine. We had hoped to prepare the bromo-analogue of 5 directly from
1 by reaction with N-bromosuccinimide and dibenzoylperoxide or
azobisisobutyronitrile (AIBN), but both reactions failed. 5 proved an
excellent precursor for the triphenyl phosphonium salt [7]Cl, but it
failed to react with P(OEt)3. The HornereWadswortheEmmons
reagent 6 [25] was obtained in the same way as its ferrocene coun-
terpart [26] by a modification of the basic Michaelis reaction [27] in
which Na[P(O)(OEt)2] is reacted with the alcohol 4.
C31
Co1
C5
C11
C6
C2
C3
C1
C4
C12
C17
C18
C23
C24
Fig. 1. Molecular structure and atom labelingof [Co(
h
4-C4Ph4)(
h
5-C5H4Me)],1 (molecule 1
ꢀ
illustrated). Selected bond lengths (A) C29eC34 1.501(4); CoeC4Ph4(cent) 1.689(1),
CoeC5H4(cent) 1.669(1). Selected bond angles (ꢀ) C5H4(cent)eCoeC4Ph4(cent) 179.22
(2); C4eC5(Co) (interplane angle between C4 and C5 ligands on Co) 0.5.

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1501
N
O2N
NNH
C
Fc
Fc
NO2
CN
H
H
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Fc
H
11
[14]+
(x)
10
Co
Ph
Ph
Ph
Ph
(viii)
(ix)
CHO
[13]+
Fc
(x)
Fc
H
H
Co
O
Fc
H
Co
(vii)
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
O
Co
Ph
Ph
Ph
Ph
12
O
3
9
Fc
Co
Ph
Ph
Ph
Ph
(vii)
8
CO2Me
CH2Cl
Ph
CH2OH
(i)
(iii)
(iv)
Co(PPh3)3Cl
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4
2
5
(v)
(vi)
EtO
Ph
P
OEt
O
Ph
Ph
(ii)
P
CH3
Cl
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
1
7
6
Scheme 2. (i) See Scheme 1. (ii) N-bromosuccinimide (NBS)/PhCOO2COPh/hv or NBS/AIBN. (iii) LiAlH4/Et2O. (iv) SOCl2/pyridine. (v) Na[P(O)(OEt)2/toluene/
(vii) LiFc/THF. (viii) CH2(CN)2/Et3N. (ix) 2,4-C6H3(NO2)2NHNH2. (x) HBF4.OEt2/CH2Cl2.
D. (vi) Ph3P/toluene/D.
The reaction of 2 with Li[Fe(
products, the mixed ketone 8, [Co(
the tertiary alcohol 9, [Co(
4-C4Ph4){
4-C4Ph4){ 5-C5H4CPh2OH}] counterpart of 9 was prepared by the
reaction of [Co(
4-C4Ph4)( 5-C5H4Li)] with Ph2CO [8,9]. 8 has been
previously prepared in lower yield by a Friedel-Crafts type reaction
of [Co(
4-C4Ph4){ 5-C5H4C(O)}]þ with ferrocene [28].
The aldehyde 3 undergoes many conventional reactions such as
the base-promoted Knoevenagel condensation with CH2(CN)2/Et3N
[29] which gives the dicyanoethene derivative 10, and the conden-
sation reaction with 2,4-dinitrophenylhydrazine to give the hydra-
zone 11 as separable syn and anti isomers 11a and 11b respectively. It
h
5-C5H5)(
4-C4Ph4){
5-C5H4CFc2OH}]. The [Co
h
5-C5H4)], LiFc, gives two
also reacts with LiFc to give the secondary alcohol 12, [Co(h
4-C4Ph4)
h
h
5-C5H4C(O)Fc}], and
{h
5-C5H4CH(Fc)OH}]; we have previously reported similar reactions
h
h
of 3 with LiR (R ¼ tBu and Ph) which give the secondary alcohols [Co
(h
h
(h h
4-C4Ph4){ 5-C5H4CH(R)OH}] [11].
h
h
Both the secondary alcohol 12 and the tertiary alcohol 9 react
with HBF4.OEt2 to give very intensely coloured green-blue products
which, on the basis of their spectra are judged to be respectively the
h
h
merocyanine salt [Co(
the triarylmethyl cation counterpart, [Co(
[BF4], [14][BF4], similar to the [Co(
4-C4Ph4)(
and [Co(
4-C4Ph4)( 5-C5H4CPh2)][BF4] salts previously described
h h
4-C4Ph4)( 5-C5H4CHFc)][BF4], [13][BF4], and
h
4-C4Ph4)(
h
5-C5H4CFc2)]
h
h
5-C5H4CHR)][BF4]
h
h
[11,12]. Although these are reasonably stable compounds, they did
not afford crystals suitable for X-ray diffraction.
3.1. Spectroscopy
O2
The most important bands in the IR spectra of 5e12 are those due
to the vibrations of the phenyl groups of the h
4-C4Ph4 ligands, espe-
C42
C44
C39
C43
cially the y(C]C) modes which give rise to two strong absorption
bands at ca. 1498 and 1595 cmꢁ1. There are few differences between
them except where an IR-active ancillary group R is present. Thus its
C41
C40
Co2
C35
y
(CO) vibrations give rise to a strong absorption bands in the spec-
C51
C45
C36
trum of the ferrocenyl ketone 8 (1625 cmꢁ1). This frequency is
comparable to that reported for the analogous ferrocene derivative
diferrocenyl ketone (1612 cmꢁ1 [30]) and is shifted to higher energy
C52
C57
C58
C37
C38
C46
C63
C64
relative to [Co(
h
4-C4Ph4){
h
5-C5H4C(O)CH3}] (1672 cmꢁ1) [11] and
(CN) vibrations of
ferrocenecarboxaldehyde (1690 cmꢁ1 [31]). The
y
the dicyanoethene 10 give rise to a strong absorption band at
2220 cmꢁ1 which is higher than the 2185/2170 cmꢁ1 pair observed
for its ferrocenyl counterpart [32] but both are lower than that of
CH2(CN)2, 2274 cmꢁ1 [33]. The absorption bands at ca. 1616 cmꢁ1 in
the IR spectra of the hydrazones 11a and 11b are assigned to their
Fig. 2. Molecular structure and atom labeling of [Co(h h
4-C4Ph4)( 5-C5H4CH2OH)], 4
ꢀ
(molecule 2 illustrated). Selected bond lengths (molecules 1/2, A) CoeC4Ph4(cent)
1.692(1)/1.684(1); CoeC5H4(cent) 1.674(1)/1.667 (1); C33eC34/C67eC68 1.522(6)/
1.471(5); C34eO1/C68eO2 1.377(6)/1.429(4); O2-H2O.O1#1 1.85; O1-H1O.O2#2
1.80. Selected bond angles (molecules 1/2, ꢀ) C34eO1eH10/C68eO2eH2O 109.5/109.5;
C5H4(cent)eCoeC4Ph4(cent) 178.66(2)/176.65(3); C4eC5(Co) 0.4/3.1.
y
(C]N) vibrations, but also present are bands at ca.1336 and
1518 cmꢁ1 due to their
(NO2) vibrations, frequencies close to those
observed for C6H5NO2 (1347 and 1521 cmꢁ1) [34]. There is a strong
y

1502
P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
C38
C35
C37
O1
O3
O2
C36
P1
C29
C30
C34
C33
C31
C7
C32
C8
Co1
C9
C25
C24
C6
C26
C5
C10
C4
C23
C1
C12
C16
C27
C28
C13
C15
C2
C18
C3
C17
C14
C11
C22
C19
C20
C21
h
4-C4Ph4){h5-C5H4CH2P(O)(OEt)2}], 6 (molecule 1 illustrated). Selected bond lengths (molecules 1/2, A) CoeC4Ph4(cent) 1.682
ꢀ
Fig. 3. Molecular structure and atom labeling of [Co(
(1)/1.689(1); CoeC5H4(cent) 1.667(1)/1.671(1); C33eC34 1.501(3)/1.501(3); C34eP(1) 1.794(2)/1.795(2); P(1)eO(1) 1.4638(16)/1.4643(16); P(1)eO(2) 1.5820(16)/1.5727(16); P(1)eO
ꢀ
(3) 1.5759(16)/1.5799(15). Selected bond angles (molecules 1/2,
) C32eC33eC34 126.4(2)/126.8(2); C29eC33eC34 126.0(2)/125.6(2); C33eC34eP1 110.74(15)/113.04(15);
O1eP1eC34 114.78(10)/114.11(10); O3eP1eC34 101.70(10)/106.22(10); O2eP1eC34 106.65(10)/104.73(9); C5H4(cent)eCoeC4Ph4(cent) 176.62(2)/178.29(2); C4eC5(Co) 4.4/2.4.
absorption band at 819 cmꢁ1 in the spectrum of the chloromethyl
complex 5 which is assigned to its (CeCl) vibration, and one at
1248 cmꢁ1 in the spectrum of the phosphonate which is assigned to
its (P]O) mode. The (OH) vibrations of the primary alcohol 4, the
though readily identified absorption bands in their spectra at 3401,
3671 and 3680 cmꢁ1 respectively. The first of these is broad but the
other two are sharp. This suggests that the OH group of 4 partakes of
hydrogen bonding but those of 12 and 9 do not. Additional evidence
for this comes from X-ray crystallographic studies, and is discussed in
Section 3.2.
y
y
y
secondary alcohol 12 and the tertiary alcohol 9 give rise to weak
The 1H NMR spectra of 5e12 are consistent with their known or
anticipated structures. The complex multiplet due to the twenty
protons of the
cyclopentadienyl protons of the
h
4-C4(C6H5)4 ligand are not greatly affected by R. The
h
5-C5H4R ligands where R is not
chiral give rise to two triplets or unresolved broad resonances, each
integrating for two protons. If R has inherent chirality as in 12,
all four Co(h
5-C5H4) protons are magnetically inequivalent and
C35
give rise to a distinctive set of four multiplets each integrating
for a single proton. The introduction of ferrocenyl groups into
R increases the number of cyclopentadienyl resonances. The singlet
P
C41
C47
C33
C32
C31
and two triplets due to the Fe(
generally found upfield of their Co(
the Co(
5-C5H4) resonances, the chiral molecule 12, shows four Fe
5-C5H4) multiplets. The Fe( 5-C5H5) remains a singlet. The spec-
trum of 9 is unusual. Symmetry generated inequivalence about the
Ca pyramid generates two Co(
5-C5H4) and one Fe( 5-C5H5) reso-
nance, but four due to Fe(
5-C5H4) as illustrated in Fig. 10.
h
h
h
5-C5H5) and Fe( 5-C5H4) are
C34
5-C5H4) counterparts. As with
C29
C1
C30
h
Co
(h
h
C11
C2
C3
C4
C23
h
h
C17
h
C5
Other 1H NMR resonances for 5e12 show the anticipated
chemical shifts and multiplicity associated with coupling to adja-
cent protons or, in the case of 6 and 7, 31P atoms. The spectra of 11a
and 11b do not allow either to be defined, but the X-ray diffraction
shows 11a to be the syn isomer so 11b is assumed to be the anti. The
spectra for these compounds also feature very broad signals at
Fig. 4. Molecular structure and atom labeling of the cation of [Co(h -
4-C4Ph4)(h5
ꢀ
C5H4CH2PPh3)]Cl.2H2O.CHCl3, [7]Cl.2H2O.CHCl3. Selected bond lengths (A)
CoeC4Ph4(cent) 1.695(1); CoeC5H4(cent) 1.680(1); C29eC34 1.5032(15); C34eP 1.8111
(11). Selected bond angles (ꢀ) C33eC29eC34 124.27(10); C30eC29eC34 128.05(10);
C29eC34eP 113.88(7); C35ePeC34 112.03(5); C47ePeC34 107.43(5); C41ePeC34
108.27(5); C5H4(cent)eCoeC4Ph4(cent) 177.73(1); C4eC5(Co) 3.8.
d
11.13 and 10.53 respectively. They disappear on treatment with
D2O and so are attributed to the NH protons. For most hydrazones,
these are found at 7e8; here the downfield shift and the broad-
ened signal suggest that the amine protons are engaged in hydrogen
d

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1503
C40
C44
C41
C42
C43
O
Fe
C36
C39
C32
C33
C37
C38
C34
C35
C31
C30
C29
C19
C20
C25
C23
Co
C24
C18
C26
C28
C17
C27
C3
C21
C4
C1
C22
C11
C6
C7
C8
C2
C12
C16
C5
C10
C15
C9
C13
C14
Fig. 5. Molecular structure and atom labeling of [Co(h
4-C4Ph4){h5-C5H4C(O)Fc}], 8. Selected bond lengths (A) CoeC4Ph4(cent) 1.697(1); CoeC5H4(cent) 1.681(1); C33eC34 1.474(3);
ꢀ
C34eC35 1.482(3); FeeC5H4(cent) 1.648(1); FeeC5H5(cent) 1.653(1). Selected bond angles (ꢀ) C33eC34eO1 120.23(19); C35eC34eO1 121.25(19); C5H4(cent)eFeeC5H4(cent) 178.15
(2); C5eC5(Fe) 3.5(1); C5H4(cent)eCoeC4Ph4(cent) 177.10(2); C4eC5(Co) 3.5(2).
bonding with the oxygen of the ortho-positioned nitro groups as
found in the solid state for 11a.
The salts [13][BF4] and [14][BF4] are formed when yellow solu-
tions of the alcohols 12 and 9 are respectively treated with
HBF4.OEt2 or aqueous HBF4. They are an intense green-blue in
colour. For the latter this is due to the presence of strong absorption
bands in its UV/Visible spectra at 389 and 835 nm and much
weaker ones at 555 and 616 nm which are not present in the
spectrum of the alcohol 9. The analogous triferrocenylmethyl cation
[36] has a similar spectrum, but the strong bands are more intense
and appear at longer wavelength at 395 and 855 nm, and the
absorption in the visible region 550e620 nm is barely discernible.
However, it is their NMR spectra which give the most structural
information about these salts. The cation formation is accompanied
by a marked deshielding of many but not all 1H resonances. Thus
The 13C NMR spectra of 5e12 contain the expected
h
4-C4Ph4
h
5-C5H4)
ligand signals, again largely independent of R. The Co(
ligands give rise to three resonances unless R is chiral when five are
observed. Introduction of ferrocenyl groups leads the presence of
further four resonances or six in a chiral molecule. These generally
lie upfield of those due to Co(
gives rise to three resonances as expected but the Fe(
h
5-C5H4). In 9, the Co(
h
5-C5H4R) moiety
5-C5H4R)
h
groups give rise to five each for the reasons outlined above (Fig. 10).
The resonances due to other groups in R are as expected with
coupling to 31P in both 6 (1JC,P ¼ 138 Hz) and 7 (1JC,P ¼ 50 Hz) as
well as coupling to OEt and Ph groups respectively. In all solid
state structures (see below) the C4Ph4 ligand acts as a four-bladed
propeller and a source of molecular chirality. However, this
chirality is not maintained in solution (see above) as the single
13C NMR signals for both o and m C6H5 atoms confirms that rotations
about the C-C6H5 and Co-C4Ph4/C5H4R axes are fast on the NMR
timescale.
the (
when M ¼ Co and
the cation [13]þ whilst the (
4.65. The most dramatic effect is noted for the exocyclic Ca-H
resonance which moves from 4.82 to 8.09, whereas the
C4(C6H5)4 protons are unaffected. Similar changes in chemical shifts
are observed for the 9/[14]þ pair of
3.32e4.80 to 5.15e5.83 for
the ( 4.05 to 4.38 for (
5-C5H4), and 5-C5H5)Fe, whilst the
C4(C6H5)4 protons are, again, unaffected.
h
5-C5H4e)M protons of 12 which lie between
3.80e4.05 when M ¼ Fe, shift to
5-C5H5)Fe signal shifts from
d
4.53e4.92
4.34e5.92 in
4.03 to
d
d
h
d
d
d
The UV/Visible spectra of most of 5e12 are very similar to that of
d
d
[Co(
h
4-C4Ph4)(
h
5-C5H5)] which shows a very intense absorption
h
d
d
h
band below 250 nm, a strong band at 274 nm and a very weak band
at 412 nm [35]. Thus when the C5H4-Ca carbon atom is sp3 hybri-
The dehydroxylation of the alcohols has similar consequences
dised, the observed spectrum is the summation of the [Co(h4
-
for the 13C NMR spectra. For each C atom there is a change of
C4Ph4)(
contain ferrocenyl groups. However, when this carbon atom is sp2
hybridised and R is a eCH]X group, the [Co(
4-C4Ph4)( 5-C5H4e)]
moiety is part of a potential donore eacceptor system, extra or
h
5-C5H4e)] and eR parts e.g. in the alcohols 9 and 12 which
chemical shift Dd
¼
dcation
ꢁ
dalcohol which is generally positive as
most become more deshielded on cation formation, but this is not
h
h
universally the case. For the 12/[13]þ pair the largest Dd (81.4 ppm)
p
is for Ca; the others are much smaller with those for Co(
5-C5H4e) < Fe( 5-C5H5)( 5-C5H4e). However, the Dd for the ipso
carbon atoms of both Co(
5-C5H4e) and Fe( 5-C5H4e) are negative
i.e. the resonances of the cation lie upfield of those of the alcohol.
This has been observed previously in the [Co(
4-C4Ph4){ 5-C5H4CH
(OH)Ph}]/[Co(
4-C4Ph4)( 5-C5H4CHPh)]þ pair, where Dd for Cipso of
Ph is negative though that for Cipso of the Co(
5-C5H4e) moiety is
h
5-C4Ph4)
red-shifted absorption band appear in the electronic spectra and
such compounds are a much darker red, e.g. 10, {R ¼ eCH]C(CN)2}
shows a strong absorption band at 421 nm and a shoulder at ca.
500 nm. The better electron donor properties of ferrocene are
evident in the ferrocenylogue [FceCH]C(CN)2] where the maxima
are observed at longer wavelengths, 395 and 521 nm [32].
(h
h
h
h
h
h
h
h
h
h

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P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
Cl1
C38
C55
C43
C42
Cl2
C37
C39
Fe1
C41
C44
C40
C36
C35
C51
C52
C50
Fe2
C34
C53
C46
C45
C33
C47
C48
C29
C31
C54
O
C49
C32
C4
C30
C5
C7
Co
C28
C6
C9
C27
C8
C1
C26
C25
C18
C24
C10
C23
C11
C16
C2
C3
C15
C19
C17
C12
C13
C20
C22
C14
C21
Fig. 6. Molecular structure and atom labeling of [Co(h
4-C4Ph4)(h5-C5H4CFc2OH)].CH2Cl2, 9.CH2Cl2. Selected bond lengths (A) CoeC4Ph4(cent) 1.707(7); CoeC5H4(cent) 1.682(6);
ꢀ
C33eC34 1.530(8); C34eC35/C34eC45 1.524(8)/1.511(8). Selected bond angles (ꢀ) C33eC34eC35 110.4(4); C33eC34eC45 108.0(5); C35eC34eC45 109.4(4); Fee(C5H4)(cent) 1.656
(5)/1.647(4); FeeC5H5(cent) 1.662(5)/1.648(4); C5H4(cent)eFeeC5H4(cent) 175.82(6)/177.94(7); C5eC5(Fe) 5.1(5)/0; C5H4(cent)eCoeC4Ph4(cent) 172.23(5); C4eC5(Co) 11.9(4).
N13
C13
C9
C8
C5
C11
C12
N12
C10
C7
C1
C6
C35
C16
C15
C36
C32
Co
C37
C17
C18
C34
C33
C14
C19
C4
C27
C21
C2
C3
C28
C22
C20
C26
C29
C24
C31
C23
C25
C30
Fig. 7. Molecular structure and atom labeling of [Co(h
4-C4Ph4){h5-C5H4CH]C(CN)2}], 10. Selected bond lengths (A) CoeC4Ph4(cent) 1.693(1); CoeC5H4(cent) 1.677(1); C5eC10 1.432
ꢀ
(2); C10eC111.356(2); C11eC12/C11eC13 1.356(2)/1.437(3). Selected bond angles (ꢀ) C10eC5eC6 122.90(13); C10eC5eC 130.32(14); C5eC10eC11128.72(16); C10eC11eC12 119.43
(17); C10eC11eC13 122.31(16); C5H4(cent)eCoeC4Ph4(cent) 175.4; C4eC5(Co) 4.4.

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1505
C33
C32
C31
d
d
C34
N1
Co
Cα
C29
c
c
C40
C30
C35
C36
C37
C39
N4
N2
N3
O1
a'
a'
Co
C3
C38
O2
C2
O4
C17
C23
b'
O3
b'
Fe
Fe
C11
a
a
C5
C1
b
b
C4
Fig. 10. The inequivalence of the (
axis of 9, or the perpendicular to the trigonal plane of [14]þ
h
5-C5H4)Fe protons. A projection down the OeCa
.
more effectively delocalized on to the metal when M ¼ Fe(
than when M ¼ Co(
4-C4H4) [37], and also with the oxidation
potentials of the metallocenyl groups (see below).
When the alcohol 9 is converted to the cation [14]þ, the number of
h
5-C5H5)
h
Fig. 8. Molecular structure and atom labeling of syn-[Co(
h
4-C4Ph4){ 5-C5H4CH]
h
ꢀ
NNHC6H4(NO2)2-2,4}], 11a. Selected bond lengths (A) for 11a.CH2Cl2 {for 11a.½CHCl3}
CoeC4Ph4(cent) 1.692(1) {1.692(3)}; CoeC5H4(cent) 1.679(1) {1.683(3)}; C29eC34
1.460(5) {1.455(5)}; C34eN1 1.296(5) {1.317(5)}; N1eN2 1.376(4) {1.383(4)};
N2eH2N.O1 1.95(4) {1.77(3)}. Selected bond angles (ꢀ) for 11a.CH2Cl2 {for
11a.½CHCl3} C33eC29eC34 120.5(4) {119.3(3)}; C30eC29eC34 133.2(4) {106.5(3)};
C29eC34eN1 133.6(4) {134.2(3)}; C34eN1eN2 116.8(3) {114.3(3)}; C5H4(cent)e
CoeC4Ph4(cent) 177.39(3) {179.20(3)}; C4eC5(Co) 1.2 {1.8}.
resonances due to the Fe(h
5-C5H4e) moieties declines from five to three
and there is one due to the Fe(h5-C5H5). Thus the a/a0 and b/b0 pairs of
the two ferrocenyl groups in the cation are no longer in different NMR
environments. This is a consequence of planar coordination about Ca in
[14]þ and rapid rotation about its Ca-Cipso bonds. The chemical shift of
the Ca resonance at
Dd of 124.3 ppm is much larger and comparable to that observed for the
Ph3COH/Ph3Cþ system (128 ppm) [38]. The Dd for the ( 5-C5H4)Fe
carbon atoms are larger than those for (
5-C5H4)Co. However the Dd for
both these and (
5-C5H5)Fe are smaller than those for the 12/[13]þ pair.
d
196.9 is much lower than that found in [13]þ but its
positive Dd [11]. We do not understand the reasons for this, but the
general import of the spectral data is that the positive charge of the
h
cation is delocalized from Ca into the adjacent Co(
5-C5H4e) and Fe( 5-C5H5)( 5-C5H4e) substituents, and, given
that DdFe DdCo, the ferrocenyl group is the more effective donor of
the two. It is generally accepted that carbocations are stabilized by
adjacent metal centres, and there is much evidence that in [(h5
h
5-C4Ph4)
h
(h
h
h
h
>
The ipso C atoms for all three C5H4 groups show negative Dd values.
Taken as a whole this suggests that, as in [13]þ, the positive charge is
delocalized away more effectively by the Fe centres than the Co, but
because [14]þ contains two ferrocenyl groups, the effect on each is less
pronounced than on the single ferrocenyl group of [13]þ. When the
structure of [14]þ is represented by a resonance hybrid of four meso-
mers, each of the equivalents of II in Fig.11 makes a smaller contribution
than does II itself to [13]þ, and so the Ca-ferrocenyl bonds have a lower
order in [14]þ than in [13]þ.
-
C5H4CaHR)Fe(h
5-C5H5)]þ this happens by direct interaction of the
metal atom with the Cþa (See the Introduction section of ref. [11]).
The structure of [13]þ may thus be represented by a hybrid of three
mesomers, I, II and III (Fig. 11) with II predominating over III. These
conclusions are consistent with work of Gleiter et al. who
concluded that in [M(
h
-C5H4CPh2)] systems the positive charge is
C44
O1
C39
C43
O2
C34
C38
C40
C32
C31
C35
Fe
C42
C33
C29
C37
C41
C30
C18
C36
Co
C3
C13
C19
C20
C12
C11
C2
C17
C14
C24
C16
C15
C25
C1
C4
C9
C10
C23
C21
C26
C22
C28
C5
C8
C7
C6
C27
Fig. 9. Molecular structure and atom labeling of [Co(h
4-C4Ph4){h5-C5H4CH(Fc)OH}], 12. Selected bond lengths (A) CoeC4Ph4(cent) 1.70(1); CoeC5H4(cent) 1.68(1); C33eC34 1.503
ꢀ
(8); C(34)eC(35) 1.497(8); FeeC5H4(cent) 1.641(6); FeeC5H5(cent) 1.641(6). Selected bond angles (ꢀ) C33eC34eO1/O2 109.8(6)/117(1); C35eC34eO1/O2 117.6(7)/120.6(8);
C5H4(cent)eFeeC5H4(cent) 177.06(9); C5eC5(Fe) 0; C5H4(cent)eCoeC4Ph4(cent) 174.92(6); C4eC5(Co) 6.6.

1506
P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
Y
Y
Y
Fe
Fe
Fe
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
III
I
II
[13]+, Y = H; [14]+, Y = ferrocenyl
X
X
X
Y
Y
Y
Co
Co
Co
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
IV
V
VI
3 {Y, X = H, O}; 8 {Y, X = Fc, O}; 10 {Y, X = H, C(CN)2}; 11a {Y, X = H, NNHC6H3(NO2)2-2,4}
Fig. 11. Resonance forms of the [Co(
h
4-C4Ph4)(
h
5-C5H4CYFc)]þ cations [13]þ (Y ¼ H) and [14]þ (Y ¼ Fc), and of various [Co(
h
4-C4Ph4)(
h
5-C5H4CY ¼ X)] complexes.
3.2. Crystal structures
amounts. They lie between 19.0ꢀ and 66.5ꢀ with an average of 35.4ꢀ.
Due to this synchronized tilting of the phenyl rings the molecules
are inherently chiral and pack in the unit cells in symmetry
generated rac pairs.
The crystal and molecular structures of 1, 4, 6, [7]Cl, 8, 9, 10, 11a
and 12 have been determined by X-ray diffraction techniques; that
of 3 was reported previously [11]. They are shown in Figs. 1e9
together with the atom labeling. In the cases of 1, 4 and 6 there
are two molecules per asymmetric unit. Molecule 2 of 1 has
With the exception of 9, and to a lesser extent 12, normal bond
lengths are observed for CoeCCb (Cb ¼ cyclobutadiene){1.968(2)e
ꢀ
ꢀ
2.002(1) A}, CoeCCp {2.035(3)e2.098(1) A}, CCbeCCb {1.455(3)e
5-C5H4Me ring plane. The secondary alcohol 12 has
1.479(5) A}and CCpeCCp {1.370(9)e1.457(8) A}. For 9 the steric
interactions which cause the anomalous angle between the Cp and
Cb planes also bring about a lengthening of the Co bond to the ipso
ꢀ
ꢀ
disorder in the
h
H/OH disorder (55:45) at Ca. The structure of 11a was determined
twice, once with crystals grown from CH2Cl2/pentane (structure 1)
and the other with crystals grown from CHCl3/pentane mixtures
(structure 2); both define 11a as the syn isomer and, hence, 11b as
the anti isomer.
ꢀ
C5H4 atom, CoeC33 {2.116(6) A} but not of CoeC29 or CoeC32
{2.068(5) and 2.095(5) A} or of CoeC30 or C31 {2.032(5) and 2.050
(5) A} whilst retaining the planarity of the C5 ring. There is also
ꢀ
ꢀ
All compounds adopt a sandwich structure with the Co atoms
a lengthening of the bond from Co to C4 of the C4Ph4 ligand {2.029
(5) A} which is almost eclipsed by C33. Similar but far less signifi-
5-C5H4R and
h
4-C4Ph4 ligands. These rings
ꢀ
coordinated by planar
h
are ca. parallel with angles of 0.4e4.4ꢀ between their planes except
cant effects are also observed for 12.
for 12 (6.6ꢀ) and 9 (12ꢀ). This distortion is probably a consequence
of steric interactions between the
8, 9 and 12 contain ferrocenyl (Fc) groups. Their ca. planar h
5-C5
h
4-C4Ph4 and CH(OH)Fc or C(OH)
rings are close to parallel with interplanar angles varying from 1.8ꢀ
in 12 to 5.1ꢀ for the Fc1 of 9. They are almost exactly staggered in 8
(rotated by ca. 3.5ꢀ from the ideal), otherwise they are closer to
eclipsed being rotated by 15ꢀ in 12 and by 6.2ꢀ/10ꢀ for Fc1/Fc2 in 9.
Fc2 groups respectively. The relative orientations of the cyclo-
pentadienyl and cyclobutadiene rings (Fig. 12) is configuration e in
1, 3, and 4 (molecule 1), b in 4 (molecule 2), b/e in 6, (molecule 1),
d in 6 (molecule 2), c/e in [7]þ, c in 8 and 9, a in 10, d in 11a
(structure 1), f in 11a (structure 2) and 12.
ꢀ
The FeeC and CeC distances lie in the range 2.023(6)e2.062(2) A
ꢀ
ꢀ
ꢀ
(average 2.042 A) and 1.389(9)e1.439(8) A (av. 1.419 A) for the C5H4
ligand, and 2.006(7)e2.062(2) A (av. 2.041 A) and 1.357(11)e1.449
(9) A (av. 1.411 A) for the C5H5 ligand. There is only limited distor-
4-C4Ph4 ligands do not lie in the C4
ꢀ
ꢀ
The phenyl groups of the
h
ꢀ
ꢀ
plane. The C-C6H5 bonds point away from the Co atom atoms with
centroid-C-CPh angles of 169.0(4)e178.9(2)ꢀ (average ¼ 173.8ꢀ).
Furthermore, the phenyl rings are tilted with respect to the C4 plane
so that C4Ph4 constitutes a four-bladed propeller. The angles
between the C4 and C6 planes are not the same in any one structure,
though generally each of the trans pairs are tilted by comparable
tion of the ferrocenyl groups in 9 and 12 (but see below) where the
consequences of steric crowding are borne by the Co(
h
4-C4Ph4)
(h
5-C5H4) moiety.
In general, the bond lengths and angles within the R groups are
normal. When the Ca of R is sp3 hybridised, it generally lies close to
the C5H4(Co) plane being displaced from it away from Co by
ꢀ
between ꢁ0.024 and þ0.057 A, but in 12 the displacement is
ꢀ
ꢀ
þ0.104 A and in 9 it is þ0.158 A away from Co, again probably due to
steric effects. The projection along the CaeCipso(Co) bond shows that
in most cases these molecules adopt one of the two conformations
shown in Fig. 13 or close to them. A with X, Y ¼ H is adopted by one
molecule of 4, both molecules of 6 and [7]þ, and A with Y ¼ Fc by 12.
9 is midway between A and B with Y ¼ OH. One molecule of 4 and of
1 are closer to B than A, X, Y ¼ H. Similarly for the ferrocenyl groups
in 9 and 12, Ca do not lie in the planes of the ferrocenyl C5H4 groups,
a
b
e
c
f
d
Fig. 12. Relative orientations of cyclobutadiene and cyclopentadienyl ligands in [Co
4-C4Ph4)( 5-C5H4R)] complexes.
(
h
h

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1507
There are a number of H-bonding interactions of note in these
structures. In the primary alcohol 4 intermolecular/O2eH2/O1
eH1/O2eH2/O1eH1/interactions form molecular ribbons
Z
Z
C
ꢀ
running through the lattice with H2/O1/H2/O1eH1 ¼1.ꢀ848(4) A/
C
Y
174.5(2)ꢀ and H1/O2/H1/O2eH2 ¼1.796(3) A/167.7(3) . In the
ꢀ
Y
secondary alcohol 12 the situation is more complicated. The diaste-
reomer based on O2eH2 forms an H-bonded dimer with an adjacent
O2- diastereomer though the H2/O20 distances are much longer
X
X
Co
Co
0
0
ꢀ
ꢀ
A
B
than in 4, H2/O2 ¼ 2.305 A and O2-H2/O2 ¼ 131.1 . The only
ꢀ
other possible interactions are >3 A. There are no similar interactions
Fig. 13. Projection down the CipsoeCa axis of [Co(
h
4-C4Ph4)(
h
5-C5H4CaXYZ)] molecules.
apparent in the structure of the tertiary alcohol 9, but it does have an
ꢀ
intramolecular Fe1/H1 separation of 2.965(1) A with Fe1/H1-
O1 ¼127.2(2)ꢀ. The Fe1/H axis enters the ferrocenyl group between
the C40eC44 and C35ipsoeC39 bonds though closer to the latter.
Because the two C5 rings are not parallel (dihedral angle 5.11ꢀ) it is at
about this point that their separation is at its greatest with
ꢀ
but are displaced from them away from the metal atom by 0.07 A in
12, 0.11 A for Fc1 in 9, and 0.18 A for Fc2 in 9. The projection along
ꢀ
ꢀ
the CaeCipso(Fe) is close to B in 12 with Z ¼ Co(
h
h
4-C4Ph4)( 5-C5H4e),
h
5-C5H5)( 5-C5H4e)/
h
whilst in 9 it is between A and B with Z ¼ Fe2(
ꢀ
ꢀ
C35/C40 ¼ 3.416(7) A. By comparison C38/C43 ¼ 3.219(6) A whilst
Y ¼Co(
h
4-C4Ph4)(
h
5-C5H4e) for Fc1, and Z ¼ Co(
h -
4-C4Ph4)(h5
the Fe2(
h
5-C5H4)(
h
5-C5H5) moiety has near parallel rings (dihedral
C5H4e)/Y ¼ Fe1(
h
5-C5H5)(
h
5-C5H4e) for Fc2. As a consequence of
angle 2.3ꢀ) and an average CCp/CCp separation of 3.301 A. It is
tempting to regard the situation as the early stages of an electrophilic
attack (protonation) on the Fe atom of a ferrocene. Intramolecular
Fe/HO contacts are a common feature of 1-ferrocenyl alcohols
ꢀ
the orientations adopted, the angles between the planes of the C5H4
ligands are all close to 90ꢀ; 86.7ꢀ in 12, and 83ꢀ, 88ꢀ and 87.5ꢀ in 9 for
Co/Fe1, Co/Fe2 and Fe1/Fe2 ligands respectively.
arrangement is found in [{Fe(
A similar
h
5-C5H5)( 5-C5H4-)}3COH] where the
h
[40,41]. For example in [Fe(h h
5-C5H5){ 5-C5H4C(Ph)(Me)OH}] the two
ferrocenyl groups are close to eclipsed and the three CpeFeeCp
axes are essentially orthogonal to one another with C5H4 interplane
angles of 95.4ꢀ, 90.9ꢀ and 92.7ꢀ [39].
cyclopenatadienyl rings have a dihedral angle of 4.31ꢀ and Fe/H 2.94
ꢀ
(3) A [40]. There are similar though weaker Fe/HO interactions in 12
(Fe/HO ¼ 3.226(1) A and Fe/H-O ¼ 117.07ꢀ with a C5H4/C5H5
ꢀ
When Ca is sp2 hybridised in Co{
h
5-C5H4C(Y) ¼ X } systems it is
ꢀ
ꢀ
interplane angle of 1.8 ) and [Fc3COH] [39] (Fe1/HO ¼ 3.2454(4) A
and Fe1/H-O ¼ 115.4(2)ꢀ) with a C5H4/C5H5 interplane angle of
4.59ꢀ. Interplane angles for the Fe2 and Fe3 ferrocenyl components
are 2.84 and 3.33ꢀ respectively. Here the Fe1/H axis enters the fer-
normally displaced from the C5H4 plane by between ꢁ0.031 and
ꢀ
ꢀ
ꢀ
0.114 A i.e. towards Co decreasing 3 (0.114 A) > 8 (0.108 A) > 10
ꢀ
ꢀ
(0.06 A) > 11a (ꢁ0.031 A). This distortion may be a consequence of
some C /Co interactions as in mesomer VI (Fig.11). A similar series is
a
ꢀ
rocenyl group close to the C1ipsoeC6 (separation 3.406(4) A) with the
also observed for the angle between the C5H4 and CipsoeC(X)eYplanes
which is 5.1ꢀ in the aldehyde 3, 6.95ꢀ in the ketone 8, 3.7 and 6.4ꢀ in
the two structures of the hydrazone 11a and 12.8ꢀ in the dicyanoe-
thene 10. Bothof the series, butparticularly the first, correlate with the
decreasing electron-withdrawing nature of the C(Y)]X group C(H)]
O > C(Fc)]O > C(H)]C(CN)2 > C(H)]NNHC6H3(NO2)2, and the
increasing importance of mesomer IV over mesomers V and VI in
ꢀ
shortest interplanar contact between C4 and C9 ¼ 3.218(5) A.
11a shows an intramolecular hydrogen bond of NH with an O
atom of the o-NO2 group. In the 11a.½CHCl3 structure (2) this is
ꢀ
relatively long with O1/H(2N) ¼ 1.95(3) A and O1/H-N2 ¼130
(3)ꢀ, whereas in the 11a.CH2Cl2 structure (1) it is shorter with
ꢀ
ꢀ
O1/H(2N) ¼ 1.77(3) A and O1/H-N2 ¼144(2) .
ꢀ
Fig. 11. For 8, Ca lies 0.027 A out of the C5H4(Fe) plane away from Fe,
and the angle between this plane and the CeC(O)Ce plane is 41.6ꢀ.
This suggests that any Ca/Fe interaction is limited, and that the
contribution that mesomers such as III (X ¼ Oꢁ) makes towards
3.3. Electrochemistry
Electrochemical data for 8e11 are given in Table 2 which also
a description of the overall structure is not important. For 8, the Fe(h5
-
includes that for other compounds relevant to our discussion. In
dichloromethane solution [Co(h h
4-C4Ph4)( 5-C5H5)] undergoes a ch-
C5H5) moietylies on the opposite side of the CeCa(O)eC plane from Co
emically reversible oxidation at E0 ¼ 0.98 V (plus a second irreversible
(h
5-C4Ph4), and the angle between the two h5-C5H4 planes is 45ꢀ.
Table 2
Electrochemical dataa for 8e11, [Fc3COH] and various ferrocenyl derivatives for comparison.
Compoundb
Co(h
4-C4Ph4)(
h
5-C5H4) oxidation
Fe(h h
5-C5H5)( 5-C5H4)
oxidation
E0/V
ipc/ipa
E0/V
c
8
9
10
11a
11b
[Co(
[Co(
[Co(
Syn-[Co(
Anti-[Co(
[Fc3COH]
h
h
h
4-C4Ph4){
4-C4Ph4){
4-C4Ph4){
h
h
h
5-C5H4C(O)Fc}]
1.22
1.12
1.25
1.16
1.08
0.6
1.0
0.3
0.8
0.7
0.72
0.49, 0.69
5-C5H4CFc2(OH)}]
5-C5H4CH¼C(CN)2}]
h
h
4-C4Ph4)(
h
5-C5H4CH¼NNHC6H4(NO2)2-2,4})]
4-C4Ph4)(
h
5-C5H4CH¼NNHC6H4(NO2)2-2,4})]
0.47, 0.66, 0.76d
[Co(h
4-C4Ph4)(
h
5-C5H5)]
0.98
1.0
[Fe(
h
5-C5H5)2] [44]
0.55
0.66, 0.85
0.45, 0.64
[Fc2CO] [45],e
[PhFc2COH] [45],e
a
1 ꢂ 10ꢁ3 M in CH2Cl2/0.1 M [Bu4N][PF6]/100 mV sꢁ1/internal [Fe(
h
5-C5Me5)2]0/þ reference.
b
c
Fc ¼ Fe(
h h
5-C5H5)( 5-C5H4).
ipc/ipa at 100 mV sꢁ1
.
d
e
Em calculated from the average of the oxidation and reduction potentials.
Converted from original SCE reference.

1508
P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
oxidation process at higher anodic potentials) [42,43]. [Co(
h
4-C4Ph4)
supporting electrolyte. In both of these cases, substitution of [PF6]ꢁ
with the large and weakly coordinating fluorinated aryl borate
counter anion, [B(C6F5)4]ꢁ [49] brought about normal solution-
based, diffusion controlled electrochemical behaviour. We have not
performed the cyclic voltammetry of triferrocenylcarbinol with the
Geiger anion, but predict a similar result. In contrast, the triply
charged 93þ cation remains in the CH2Cl2 solution even in the
presence of the [Bu4N][PF6] supporting electrolyte. We suggest that
the bulky tetraphenylcyclobutadiene ligand interferes with the
formation of the solid salt on the electrode surface.
Cyclic voltammetry shows that in dichloromethane solution [14]
[BF4] undergoes a quasi-reversible reduction to the [14]∙ radical
(E0 ¼ ꢁ0.28 V, ipa/ipc ¼ 0.2). It also showed multiple oxidations on
application of an anodic potential > 0.5 V, but these species were
unstable and could not be characterised. [Fc3C][BF4] also under-
went a reduction to its radical (E0 ¼ ꢁ0.27 V) but this was chemi-
cally reversible as was an oxidation at 0.96 V. For both [14][BF4] and
[Fc3C][BF4] salts the decamethylferrocene reference was non-
innocent and gave rise to broad features between 0.5 and 0.7 V in
the votammograms. This is the region for the oxidation of the
alcohol precursors 9 and [Fc3COH] which suggests that the cations
decompose to neutral species.
(h
5-C5H4R)], 8e11, undergo a similar oxidation but at higher E0, and it is
only for 9 (R ¼ CFc2OH) that this is reversible. For other compounds it is
quasi-reversible with the reverse to forward current ratio, ipc/ipa,
decreasing to 0.3 for 10.
The ferrocenyl ketone 8 shows an additional wave associated
with the fully chemically reversible Fcþ/0 couple (ipc/ipa ¼ 1.0). Its E0
of 0.72 V lies between the first and second oxidations reported for
diferrocenyl ketone [45] (Table 2), consistent with the relatively
poor electron donor ability of the Co(
Furthermore its peak-to-peak potential separation is about the
same as that of the internal decamethylferrocene, [Fe(
5-C5Me5)2]0/þ
reference in this medium, which suggests that the wave can be
considered Nernstian, the deviation from a 60 mV Ep waveform
h h
4-C4Ph4)( 5-C5H4) fragment.
h
,
D
being associated with uncompensated resistance as typically
encountered in CH2Cl2 solution.
For 9, two distinct chemically reversible ferrocenyl oxidations
(E0 ¼ 0.49, 0.69 V;
D
Eox ¼ 200 mV) are observed before the cobalt
based oxidation at 1.12 V (Fig. 14). This suggests that the electronic
communication between the two ferrocenyl groups is well defined
despite the saturated link. Similar behaviour has been noted previ-
ously for PhFc2COH(
compounds, and was attributed to a through-space mechanism
[45,46].
D
Eox ¼ 190 mV),Fc2COandrelatedpolyferrocenyl
4. Conclusions
We wished to compare the electrochemistry of 9 with that of its
ferrocenyl counterpart triferrocenylcarbinol, [{Fe(
h
5-C5H5)(h5
-
The previously reported and readily preparedester 2 and aldehyde
3 are shownto beexcellent precursors for the preparation of other [Co
C5H4-)}3COH]^[Fc3COH]. However this has not been reported
despite [Fc3COH] being first prepared in 1962 [47] and studied
intensively more recently [36,39,48], though there have been
investigations of the electrochemistry of other multiferrocenyl
compounds [45,49]. We were able to carry out our comparison
because of a gift of [Fc3COH]. The cyclic voltammograms of the two
compounds, recorded in CH2Cl2 solution under identical sweep
conditions, are illustrated in Fig. 14. The oxidations of the first two
(h h h h
4-C4Ph4)( 5-C5H4R)] complexes. The Co( 4-C4Ph4)( 5-C5H4e)
radicalissufficientlyrobusttowithstand thechemicaldemandsmade
on it during our transformations, the products are air-stable, and the
reactions are specific to the h
5-C5H4R ligand and do not appear to
affect other parts of the molecules e.g. the phenyl groups.
The diethylphosphonate 6 and the triphenyl phosphonium salt
[7]Cl are particularly useful synthons. In another paper from these
laboratories they are used in the HornereWadswortheEmmons or
Wittigreactionsto preparefunctionalised alkenes of thegeneraltype
ferrocenyl groups of [Fc3COH] (E0 ¼ 0.47, 0.66 V;
D
Eox ¼ 190 mV)
occur at potentials similar to those of
9
(E0 ¼ 0.49, 0.69 V;
D
Eox ¼ 200 mV). Application of increased anodic potential to
[Co(
to be a ligand in its own right (cf. Ref. [51]) and the precursor to the
phosphonic acid [Co(
4-C4Ph4)( 5-C5H4CH2PO3H2)] which could be
h h
4-C4Ph4)( 5-C5H4CH]CHR)]. Furthermore, 6 has the potential
[Fc3COH]2þ generates the distinctive adsorption/stripping wave-
form. This is a consequence of low solubility of the salts of the
multiply charged cation and resultant precipitation on the elec-
trode surface. Reversal of the potential regenerates soluble species
which redissolve, and thus repeat scans overlay. Similar behaviour
has been observed for terferrocene [49] and ferrocenyl polyesters
[50] when using the low polarity solvent CH2Cl2 and [Bu4N][PF6]
h
h
used to prepare metal-organometallic arrays.
The alcohols 12 and 9 contain ferrocenyl as well as Co(h
4-C4Ph4)
(h
5-C5H4-) groups. They are analogues of Ph2CHOH, Fc2CHOH,
Ph3COH and Fc3COH and like them are precursors of stable cations
i.e. [13]þ and [14]þ which were isolated as their [BF4]ꢁ salts. As well
as being analogues of diaryl and triarylmethyl cations, [13]þ and
[14]þ could be used as precursors of other [Co( 4-C4Ph4){ 5-C5H4CH
h h
(Fc)X}] and [Co(h h
4-C4Ph4)( 5-C5H4CFc2X)] complexes where the
hydroxyl groups have been replaced by different groups X (cf. ref.
[36]). This would open the way to the incorporation of the chiral {Co
(h h h h
4-C4Ph4)( 5-C5H4)}(Fc)(H)C- and bulky {Co( 4-C4Ph4)( 5-C5H4)}
10
(Fc)2C- moieties into molecules with possible applications in
asymmetric syntheses, chiral catalysis and non-symmetric molec-
ular machines. On the basis of our observations, it is reasonable to
Fc*
5
suggest that the Co(
a degree of oxidative (air) and thermal stability on such systems.
The electrochemical studies show that [Co(
4-C4Ph4)(h5
h h
4-C4Ph4)( 5-C5H4) group would confer
0
I / μA
h
-
C5H4R)] complexes are always more difficult to oxidise than their
ferrocenyl counterparts, and that in most instances the oxidation is
not fully reversible. This resistance to oxidation may well be an
advantage in situations such as those described above.
-5
-10
Acknowledgements
E / V
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
We thank the New Economy Research Fund (grant No. UOO-
X0808) for support of this work (CJM). We are also grateful to
Fig. 14. Cyclic voltammograms of 9 (upper) and Fc3COH (lower) in CH2Cl2 solution;
0.1 M [Bu4N][PF6]/100 mV sꢁ1/internal [Fe( 5-C5Me5)2]þ/0 reference (Fc*).
h

P. O’Donohue et al. / Journal of Organometallic Chemistry 696 (2011) 1496e1509
1509
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CCDC 798676e798685 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
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