Radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes: Synthesis and structures

Article abstract of DOI:10.1016/j.jorganchem.2011.08.014

Novel radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes were prepared by metal carbonyls free protocol of [2 + 2] cycloaddition reaction of 1,2-diferrocenyl- or 1,2-dicymantrenylethynes with chlorotris(triphenylphospine)cobalt(I) and carboethoxycyclopentadienide sodium with good yields. The molecular structure of these products was confirmed with X-ray analysis, and their electrochemical behavior was studied.

Full text of DOI:10.1016/j.jorganchem.2011.08.014

Journal of Organometallic Chemistry 696 (2011) 3822e3825
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes:
Synthesis and structures
,
,
a,b
Alexander S. Romanova b, Tatiana V. Timofeevab , Mikhail Yu. Antipin
*
a A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow GSP-1, Russian Federation
b Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel radial tetra(ferrocenyl)- and tetra(cymantrenyl)cyclobutadienecobalt complexes were prepared by
metalcarbonylsfreeprotocolof[2þ 2]cycloadditionreactionof1,2-diferrocenyl-or1,2-dicymantrenylethynes
with chlorotris(triphenylphospine)cobalt(I) and carboethoxycyclopentadienide sodium with good yields. The
molecular structure of these products was confirmed with X-ray analysis, and their electrochemical behavior
was studied.
Received 19 June 2011
Received in revised form
17 August 2011
Accepted 18 August 2011
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Sandwich complexes
Electrochemistry
Cobalt
Ferrocene
Cymantrene
1. Introduction
2. Results and discussion
The [2 þ 2] cycloaddition reaction of bulky acetylenes in coor-
dination sphere of cobalt atom was extensively used for preparation
of numerous Cb (Cb ¼ cyclobutadiene) complexes [1]. Nowadays,
the prospective CbCo complexes could be elaborated as building
blocks for design and synthesis of new materials or supramolecular
architectures: metallorganic dehydroannulenes [2], superphane
and ‘beltenes’ molecules [3], novel ligands for catalysis [4], organ-
ometallic dendrimers and polymers [5], and materials for electronic
devices [6]. Once the area has attracted considerable interest the
need of straightforward synthetic approaches to develop such
complicated systems arises.
2.1. Synthesis
The metal carbonyls free protocol of [2 þ 2] cycloaddition reaction
(Scheme 1) of two equivalents of 1,2-diferrocenyl- or 1,2-
dicymantrenylethynes, CoCl(PPh3)3, and Na(C5H4CO2Et) (1), was used
to prepare mixed metal compounds (h4eC4R4)Co(h5eC5H4CO2Et) (R ¼
(
h5eC5H5)Fe(h5eC5H4) (2) and R ¼ (CO)3Mn(h5eC5H4) (3)) with good
yields. Isolation of complexes 2 and 3 was carried out by column
chromatography with mixtures of hexane, CHCl3 and Et2O.
The compounds 2 and 3 are the orange solids, stable to air and
moisture both in the solid state and in the solution. They have been
characterized by the elemental analysis, IR, UVevis, and NMR (1H,
13C{1H}) spectroscopy, electrospray mass spectrometry and single-
crystal X-ray structure analysis. The IR spectrum of 2 and 3 has
absorption bands in the carbonyl region corresponding to the
eCO2Et substituent. Also, complex 3 shows two absorption bands
at 2018 and 1926 cmꢀ1 for carbonyl groups of cymantrene moieties
which are somewhat shifted to low frequencies in comparison with
CpMn(CO)3 (2026 and 1935 cmꢀ1) [8].
While complex {(h5eC5H5)Fe(h5eC5H4)}4(h4eC4)Co(h5eC5H5)
was first reported by Rausch and coworkers [7] we focused our
attention on synthesis of parent complexes with substituent in the
cyclopentadienyl(Co) ring. Herein, we report synthesis and charac-
terization of new tetra(ferrocenyl)- and tetra(cymantrenyl)cyclo-
butadienecobalt complexes. Introduction of eCO2Et group and its
further chemical modification offer more structural variability in the
constructing of the larger molecules (dendrimers).
2.2. Structures
In order to confirm the structures in the solid state we performed
the X-ray diffraction studies for 2 and 3 (Figs. 1 and 2). Summary of
* Corresponding author. Tel.: þ1 505 454 3362; fax: þ1 505 454 3202.
E-mail address: tvtimofeeva@nmhu.edu (T.V. Timofeeva).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.014

A.S. Romanov et al. / Journal of Organometallic Chemistry 696 (2011) 3822e3825
3823
Scheme 1. The [2 þ 2] cycloaddition reaction.
crystallographic data and structure refinement are given in Table 1.
The Cb- and Cp ligands in core unit CbCoCp are almost parallel for
complexes 2 and 3. The conformation of C5-rings in ferrocenyl
moieties is eclipsed for 2. All ferrocenyl and cymantrenyl moieties
possess similar structural characteristics. The metal atoms occupy
positions over the centroids of the rings. The Co/ring-centroid
distances (Co/C5 1.675(2) and 1.683(4); Co/C4 1.692(2) and
1.694(4) Å for compounds 2 and 3, respectively) show that intro-
duction of electron accepting group eCO2Et leads to the closer
position of C5- and C4-rings to the Co atom in comparison to
Fig. 2. The structure of compound 3. Ellipsoids are shown at the 50% level. Hydrogen
atoms are omitted for clarity.
{(h5eC5H5)Fe(h5eC5H4)}4(
h
4-C4)Co(h5eC5H5)
(Co/C5
1.681;
Co/C4 1.697 Å). The C4-ring is somewhat distorted from ideal
geometry due to the bulky substituents (ferrocenyl and cyman-
trenyl), namely one carbon atom is always 0.05 Å out of the plane
drawn through other three carbons for both molecules 2 and 3. The
ferrocenyl and cymantrenyl substituents mutually occupy the anti
and synpositions to the central core unit C4CoC5, thus Cp(M)-ligands
(M ¼ Fe or Mn) are almost coplanar (17.1ꢁ (CpFe4) and 17.6ꢁ
(CpMn3)) or almost perpendicaular (62.1ꢁ (CpFe1) and 69.6ꢁ
(CpMn2)) with respect to the Cb ligand.
oxidation processes with the values of E1/2 presented in Table 2
(measured versus Ag/AgCl reference electrode). We can compare
the oxidation potentials of complex 2 with those for the previously
reported compound {(h5eC5H5)Fe(h5eC5H4)}4(h4eC4)Co(h5eC5H5)
(measured versus E1/2(ferrocenium/ferrocene) 0.344 V) since they possess
Table 1
Crystal data, data collection and structure refinement parameters for 2 and 3.
2
3
2.3. Electrochemistry
Empirical formula
Molecular weight
Crystal system
Space group
Crystal color, habit
Crystal size (mm)
a (Å)
C52H45CoFe4O2
984.21
Triclinic
P-1
brown, plate
C44H25CoMn4O14
659.10
Triclinic
P-1
orange, plate
The cyclic and differential pulse voltametry for compounds 2 and
3 were recorded. All the complexes display three one-electron
0.19 ꢂ 0.11 ꢂ 0.08 0.29 ꢂ 0.18 ꢂ 0.09
11.173(2)
12.950(2)
14.248(2)
78.224(2)
85.438(3)
78.196(2)
1974.0(5)
2
9.6338(6)
11.0155(6)
20.815(1)
99.953(1)
96.214(2)
109.912(1)
2012.0(2)
2
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
V (Å3)
Z
Dcalc (g cmꢀ3
2
)
1.656
28.00
1.891
1.744
28.00
1.696
qmax (ꢁ)
Abs. coeff.,
m
(Mo-K
a
) (cmꢀ1
)
Absorption correction
Tmax/Tmin
Number of collected reflections
SADABS
0.8635/0.7152
26787
0.8623/0.6390
20603
Number of independent reflections 9493
9713
Number of observed reflections
(I > 2 (I))
Rint
7535
6741
s
0.0354
532
0.0332
0.0812
wꢀ1
0.0397
580
0.0532
0.1418
Number of parameters
R1 (on F for observed reflexions)a
wR2 (on F2 for all reflexions)b
Weighting scheme
ꢀ
ꢁ
¼
s2 F2o þ ðaPÞ2 þ bP, where
ꢀ
ꢁ
P ¼ 1=3 Fo2 þ 2Fc2 P ¼ 1/3(Fo2 þ 2F2c)
A
B
0.04
0.5
0.07
2.47
F(000)
GOF
1008
1.018
0.860/e0.413
1056
0.975
1.520/e1.202
Drmax
/
Drmax (e Åꢀ3
)
P
P
a
R1
¼
jFoj ꢀ jFck= ðFoÞ.
Fig. 1. The structure of compound 2. Ellipsoids are shown at the 50% level. Hydrogen
atoms are omitted for clarity.
n
o
1=2
2
ꢂ
ꢀ
ꢁ ꢃ
ꢀ
ꢁ
P
P
2
b
wR2
¼
w F2o ꢀ F2c
=
w F2o
.

3824
A.S. Romanov et al. / Journal of Organometallic Chemistry 696 (2011) 3822e3825
4.2. Synthesis of {(h5eC5H5)Fe(h5eC5H4)}4(h4eC4)
Co(h5eC5H4COOEt) (2)
Table 2
Formal electrode potentials exhibited by complexes 2, 3, and related analogs
{(h5eC5H5)Fe(h5eC5H4)}4(h4eC4)Co(h5eC5H5), cymantrene.
Complex
2a
Eꢁ0
Eꢁ0
Eꢁ0
Eꢁ0
0/þ
þ/2þ
2þ/3þ
3þ/4þ
6
ml of o-xylene was added to the mixture of 1,2-
þ0.47 þ0.64 þ0.74
þ1.29 þ1.44 þ1.54
e
e
diferrocenylethyne (0.220 g, 0.55 mmol) and CoCl(P(C6H5)3))
(0.120 g, 0.28 mmol) in 25 ml two-necked flask connected to the
argon supply. Another reaction vial was charged with Na(C5H4
3a
{(h5eC5H5)Fe(h5eC5H4)}4(h4eC4)Co(h5eC5H5)b ꢀ0.08 þ0.07 þ0.22 þ0.28
-
Cymantreneb
þ0.92 e
e
e
COOEt) (0.050 g, 0.31 mmol), dissolved in THF (2 ml) and added to
the above mentioned suspension via syringe. Then reaction
mixture was refluxed for 12 h. After cooling to room temperature
the reaction mixture was filtered through G4 frit. The residue was
additionally washed two times with 10 ml of Et2O and combined
with o-xylene filtrate. The solution was evaporated in vacuo with
small amount of silica gel (130/270). Chromatography on silica
column (2 ꢂ 25 cm) with hexane gave PPh3, elution with hexane/
CHCl3 ¼ 5/1 gave orange band of unreacted 1,2-diferrocenylethyne
(0.031 g) and elution with hexane/CHCl3 ¼ 1/1 gave red band of
product. All volatiles were removed under reduced pressure giving
brown-orange crystalline product (0.138 g, 51.3%). Anal. calcd. for
C52H45CoFe4O2: C 63.46, H 4.61. Found C 63.58, H 4.72. 1H NMR
a
V, vs. Ag/AgCl reference electrode, in CH2Cl2.
V, vs. E1/2(ferrocenium/ferrocene) 0.344 V, in CH2Cl2.
b
the same Cb-ligand [6]. An introduction of eCO2Et group in complex
2 shifts the oxidation potentials to the higher anodic values.
Comparison of oxidation potentials between compounds 2 and 3
demonstrates higher values for compound 3, apparently, due to 12
electron accepting carbonyl ligands in cymantrene moieties. At the
same time, we can compare first oxidationpotential for compounds 3
with that of cymatrene [9]. It is slightly shifted to the more anodic
values for the compound 3 (see Table 2), taking into account different
reference potentials. We suggest that [2]3þ/[2]4þ and [2]3þ/[2]4þ
couples might be detected in further experiments and were not
observed in this studies due to previously reported problems such as
absorption at the electrode surface [6].
(CDCl3, 300 MHz,
d
): 5.14 (t, J ¼ 2.1 Hz, 2H, C5H4(Co)), 4.89 (t,
J ¼ 2.1 Hz, 2H, C5H4(Co)), 4.83 (t, J ¼ 1.8 Hz, 8H, C5H4(Fe)), 4.33 (t,
J ¼ 1.8 Hz, 8H, C5H4(Fe)), 4.10 (s, 20H, C5H5(Fe)), 3.83 (quart,
J ¼ 7.2 Hz, 2H, eCO2CH2CH3), 1.08 (t, J ¼ 7.2 Hz, 3H, eCO2CH2CH3).
13C{1H} NMR (CDCl3, 100 MHz,
d): 166.8 (eCO2CH2CH3), 85.4 (Cipso,
Cp(Co)), 83.4 (Cp(Co)), 83.2 (Cp(Co)), 81.1 (C4), 70.1 (C5H4(Fe)), 69.4
(C5H5(Fe)), 69.0 (Cipso, C5H4(Fe)), 67.8 (C5H4(Fe)), 60.1 (eCH2e), 14.0
(eCH3). UV/Vis (CH2Cl2; lmax): 294, 465 nm. IR (KBr, cmꢀ1):
3. Conclusion
The metal carbonyls free protocol of [2 þ 2] cycloaddition
reaction gave first examples of substituted radial tetra(ferrocenyl)-
and tetra(cymantrenyl)cyclobutadienecobalt complexes 2 and 3
which are of interest for further use as building blocks for den-
drimer synthesis. Examination of their structural features showed
that the ferrocenyl and cymantrenyl substituents at C4-ring nearly
occupy the anti or syn conformations with respect to the central
core unit C4CoC5. The electrochemical behaviour display the
multiple electron transfers, namely, the sequences [2]3þ/[2]2þ/[2]þ/
[2]0 and [3]3þ/[3]2þ/[3]þ/[3]0 were found.
n(CO) ¼ 1701 (C]O, eCO2Et), 1279 (CeO, CO2Et), 921 (OeCH2,
59
eCO2Et). HRMS (ESI) m/z: calcd for [M]þ C52
H
Co56Fe4O2,
45
984.0149; found, 984.0178.
4.3. Synthesis of {(CO)3Mn(h5eC5H4)}4(h4eC4)Co(h5eC5H4COOEt) (3)
Complex 3 was prepared similarly to 2 from (CO)3Mn(h5eC5H4)
C^C(h5eC5H4)Mn(CO)3 (0.400 g, 0.93 mmol), CoCl(P(C6H5)3))
(0.210 g, 0.50 mmol) and Na(C5H4COOEt) (0.80 g, 0.50 mmol) in o-
xylene (15 ml) and THF (4 ml). Chromatography on silica column
(2 ꢂ 25 cm) with hexane/Et2O ¼ 9/1 gave PPh3 and elution with
hexane/Et2O ¼ 2/1 gave orange band of product. All volatiles were
removed under reduced pressure giving orange crystalline product
(0.304 g, 64.6%). Anal. calcd. for C44H25CoMn4O14: C 50.03, H 2.39.
4. Experimental
4.1. General
Found C 50.22, H 2.45. 1H NMR (CDCl3, 300 MHz,
d): 5.53 (t,
J ¼ 2.1 Hz, 2H, C5H4(Co)), 5.10 (t, J ¼ 2.1 Hz, 8H, C5H4(Mn)), 5.02 (t,
J ¼ 2.1 Hz, 2H, C5H4(Co)), 4.81 (t, J ¼ 2.1 Hz, 8H, C5H4(Mn)), 4.02
(quart, J ¼ 6.9 Hz, 2H, eCO2CH2CH3), 1.21 (t, J ¼ 6.9 Hz, 3H,
All reactions were carried out under argon in anhydrous
solvents which were purified and dried using standard procedures.
The isolation of products was conducted in air. Starting materials
eCO2CH2CH3). 13C{1H} NMR (CDCl3, 100 MHz,
d): 224.1 (12
were prepared as described in the literature:
(
h5eC5H5)
Mn(CO)), 166.3 (eCO2CH2CH3), 98.1 (Cipso, Cp(Mn)), 86.8 (Cipso,
Fe(h5eC5H4)C^C(h5eC5H4)Fe(h5eC5H5) [10], (CO)3Mn(h5eC5H4)
C^C(C5H4)Mn(CO)3 [11], CoCl(P(C6H5)3)) [12]. The Na(C5H4CO2Et)
was synthesized analogously to Na(C5H4CO2Me) [13] but instead of
(MeO)2CO the (EtO)2CO was used. The 1H and 13C NMR spectra were
recorded with a Bruker AMX-300 spectrometer. Chemical shifts are
given in ppm relative to either residual protons of the solvent
(CDCl3 d ¼ 7.25 (1H) and 77.0 (13C)) or Me4Si for 1H and 13C spectra.
High resolution mass spectra was recorded on a Waters LCT
Premier by Electrospray Ionisation in positive mode. The IR spectra
of the solid compounds were measured by Thermo Nicolet Magna
Cp(Co)), 85.9 (Cp(Co)), 84.7 (Cp(Co)), 83.8 (Cp(Mn)), 82.4 (Cp(Mn)),
71.0 (C4), 60.9 (eCH2e),14.0 (eCH3). UV/Vis (CH2Cl2; lmax): 273 nm.
IR (KBr, cmꢀ1): n(CO) ¼ 2018 (Mn(CO)3), 1926 (Mn(CO)3), 1700 (C]O,
eCO2Et), 1282 (CeO, CO2Et), 909 (OeCH2, eCO2Et). HRMS (ESI) m/z:
59
calcd for [M þ K]þ C44
H
25
Co39K55Mn4O14, 1094.7735; found,
1094.7749; [M þ Na]þ calcd for C44
H
25
Co55Mn243NaO14, 1078.7996;
59
found, 1078.8025.
4.4. X-ray crystallography of 2 and 3
IR 550 FTIR spectrometer in Nujol over the range 400e4000 cmꢀ1
.
The crystals of 2 and 3 suitable for X-ray study were grown by
slow diffusion of hexane into CHCl3/Et2O solutions in a desiccator.
The important crystallographic data and refinement parameters are
presented in Table 1. X-ray diffraction experiment was carried out
with a Bruker Apex II CCD area detector, using graphite mono-
UVevis absorption spectra were measured on a Hewlett Packard
8453 spectrophotometer. The following materials and apparatus
for electrochemistry were used: Fluka [NBu4][PF6] (electrochemical
grade) was used as supporting electrolyte (0.2 mol dmꢀ3), CHI620A
voltammetric analyzer with a glassy carbon working electrode, a Pt
wire auxiliary electrode, and a Ag/AgCl reference electrode.
chromated Mo Ka radiation (
correction was applied semi-empirically using APEX2 program [14].
l
¼ 0.71073 Å) at 100 K. Absorption

A.S. Romanov et al. / Journal of Organometallic Chemistry 696 (2011) 3822e3825
3825
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carbon atom of the methyl group in eCO2CH2CH3 of molecule 3
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Acknowledgements
This work was supported via grant Nos. CHE-0832622, DMR-
0120967, and DMR-0934212. The UNM Mass Spectrometry Facility
is gratefully acknowledged for HRMS analysis.
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Appendix A. Supplementary material
CCDC 829807 for 2 and CCDC 829808 for 3 contains the
supplementary crystallographic 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.
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Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.08.014.
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