Deamination of 1-aminoethylferrocene and the crystal structure of ethenylferrocene

Article abstract of DOI:10.1016/j.ica.2007.10.035

Ethenylferrocene, C₁₂H₁₂Fe, was an unexpected product of the thermolysis of 1-aminoethylferrocene in a melt reaction with naphthalene-2,3-dicarboxylic acid. It was characterized by single crystal X-ray diffraction which revealed that the cyclopentadiene rings are slightly staggered and the ethenyl substituent lies approximately in the plane of the substituted cyclopentadiene ring. In the crystal structure C-H?π interactions link molecules into parallel rows.

Full text of DOI:10.1016/j.ica.2007.10.035

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 2172–2175
www.elsevier.com/locate/ica
Note
Deamination of 1-aminoethylferrocene and the crystal structure
of ethenylferrocene
*
C. John McAdam , Brian H. Robinson, Jim Simpson
Department of Chemistry, University of Otago, P.O. 56, Dunedin 9001, New Zealand
Received 7 August 2007; received in revised form 9 October 2007; accepted 21 October 2007
Available online 1 November 2007
Abstract
Ethenylferrocene, C12H12Fe, was an unexpected product of the thermolysis of 1-aminoethylferrocene in a melt reaction with naph-
thalene-2,3-dicarboxylic acid. It was characterized by single crystal X-ray diffraction which revealed that the cyclopentadiene rings
are slightly staggered and the ethenyl substituent lies approximately in the plane of the substituted cyclopentadiene ring. In the crystal
structure C–Hꢀ ꢀ ꢀp interactions link molecules into parallel rows.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Deamination; Ferrocene; X-ray crystal structure
1. Introduction
Using this strategy to prepare N-1-(ferrocenyl)ethyl-2,3-
naphthalimide (2) from 1-aminoethylferrocene (Scheme 1)
[2] led also to the isolation of ethenylferrocene, 1 in yields
of up to 50% (based on excess starting amine).
It is more than fifty years since the first reported synthe-
sis of ethenylferrocene (1) by Arimoto and Haven [1]. The
literature now contains thousands of papers utilising this
versatile small molecule and covering its extensive polymer
chemistry. We report here the crystal structure of this fun-
damental organometallic building block and the unconven-
tional synthesis that led to its preparation.
Ethenylferrocene has been previously prepared by a vari-
ety of routes. The seminal work involved dehydration of
ferrocenylethanol at elevated temperature with Al2O3 [1].
Other thermal preparations utilise acetylferrocene [4]
and formylferrocene [5], the latter being our preferred syn-
thetic route. A methyl iodide quaternisation of the amine in
Fc–CHMe–NMe2, and a multistep synthesis from Fc–
CH2–NMe2 also lead to the preparation of 1 [6,7]. Comple-
mentary to this, a reaction in the reverse direction provides
convenient synthesis of (2-aminoethyl)ferrocenes from
ethenylferrocene and lithium amides [8].
To our knowledge this is the first report of an acid-catal-
ysed deamination for the preparation of 1. The proposed
course of the reaction leading to the observed product is
shown in Scheme 2, with a driving force provided by the
intermediate formation of an a-ferrocenyl carbenium ion,
well known for its particular stability [9–11], following pro-
tonation and deamination of the starting material.
The structure of the unexpected product 1 had, surpris-
ingly, not been reported previously and was investigated by
single crystal X-ray diffraction (Fig. 1).
2. Results and discussion
N-Ferrocenylnaphthalimides have been prepared by the
reaction of 1,8-naphthalic anhydrides with ferrocenyl
amines or, in the case of 2,3-napthalimides, by the direct
reaction between the amines and naphthalene-2,3-dicar-
boxylic acid [2]. The latter synthesis is based on the well
known synthetic strategy for N-phenyl-2,3-naphthalimides
from naphthalene-2,3-dicarboxylic acid and a four molar
excess of aniline, at elevated temperature [3].
*
Corresponding author.
E-mail address: mcadamj@alkali.otaga.ac.nz (C.J. McAdam).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.10.035

C.J. McAdam et al. / Inorganica Chimica Acta 361 (2008) 2172–2175
2173
H
HOOC
O
CH3
CH
H
C
CH3
CH
HOOC
C
N
(0.2 mole)
+
H
Fe
Fe
NH2
Fe
O
o
170 C
2
1
Scheme 1.
of the C3ꢀ ꢀ ꢀC7 cyclopentadiene ring, with the maximum
CH3
CH3
CH
˚
H+
deviation 0.158(5) A for C1a. A search of the Cambridge
CH
database [12] (V 5.28 to January 2007) reveals 11 other
ethenylferrocene complexes [13–16]. The C@C distances
observed here in Table 1 for the two disorder components
are similar to those in other ethenylferrocene compounds
+
Fe
Fe
NH3
NH2
˚
(mean C@C 1.32(3) A).
H2
C
In the crystal structure C11–H11ꢀ ꢀ ꢀCg1i (C11ꢀ ꢀ ꢀCg1i =
H
i
˚
H
C
3.6474(18) A; C11–H11ꢀ ꢀ ꢀCg1 = 136.4°; i = x, ꢁy ꢁ 1/2,
H
-H+
z ꢁ 1/2) and C2a–H2aꢀ ꢀ ꢀCg2ii interactions (C2aꢀ ꢀ ꢀCg2ii =
C+
C
ii
˚
3.881(2) A; C2a—H2aꢀ ꢀ ꢀCg2 = 170.4°; ii = x, 1/2 ꢁ y, 1/
H
H
Fe
Fe
2 + z) [17] link adjacent molecules into parallel rows along
diagonals of the bc plane, Fig. 2, Table 2 (Cg1 and Cg2 are
the centroids of the C3ꢀ ꢀ ꢀC7 and C8ꢀ ꢀ ꢀC12 cyclopentadie-
nyl rings, respectively).
Scheme 2.
3. Experimental
1-Aminoethylferrocene (1.15 g, 5 mmol) was added to
naphthalene-2,3-dicarboxylic acid (0.22 g, 1 mmol) and
the mixture heated at 170 °C for 15 min. Orange 1 sub-
limed out of the heating zone. The residue in the flask
was chromatographed (SiO2/CH2Cl2) to give additional 1
(total yield 0.43 g, 50% based on excess amine) and N-1-
(ferrocenyl)ethyl-2,3-naphthalimide, 2 (yield 0.30 g, 73%
based on the dicarboxylic acid).
Orange-yellow plate-like crystals of 1 sublimed from this
1
oil over an extensive period at ambient temperature. H
NMR (CDCl3) d: 6.45 [dd (J = 11, 17 Hz), 1H, –CH@CH2]
5.34 [dd (J = 2, 17 Hz), 1H, –CH@CHtrans], 5.03 [dd (J = 2,
11 Hz), 1H, –CH@CHcis], 4.36 (m, 2H, C5H4-a) 4.21 (m,
2H, C5H4-b), 4.11 (s, 5H, C5H5). 13C NMR (CDCl3) d:
134.7 (–CH@CH2), 111.1 (–CH@CH2), 83.6 (C5H4-ipso),
69.3 (C5H5), 68.7 (C5H4-b), 66.7 (C5H4-a).
Fig. 1. The molecular structure of 1 with atom labels and 50% probability
displacement ellipsoids for non-H atoms. Bonds to atoms of the minor
disorder component are drawn as dashed lines.
4. Crystal structure determination
Crystal data for 1 is given in Table 2. An orange-yellow
plate-like crystal was mounted on a plastic loop and data
were collected at 90(2) K on a Bruker APEXII CCD
The cyclopentadienyl rings of the ferrocene vary some-
what from an eclipsed orientation, with a mean cyclopenta-
dienyl twist angle of 10.0(2)°; the relatively high
uncertainty in this value may reflect the possible unresolved
disorder in the vinyl substituted cyclopentadienide ring.
The dihedral angle between the Cp ring planes is 2.1(2)°.
The ethenyl substituent is disordered over two sites (a
and b) but each component lies approximately in the plane
Table 1
˚
Selected bond distances (A) and angles (°) for 1
C1a–C2a 1.329(4)
C1b–C2b 1.320(7)
C1a–C2a–C3 119.7(3)
C2a–C3 1.494(3)
C2b–C3 1.568(4)
C1b–C2b–C3 115.5(4)

2174
C.J. McAdam et al. / Inorganica Chimica Acta 361 (2008) 2172–2175
Fig. 2. Part of the packing of 1, with C–Hꢀ ꢀ ꢀp interactions drawn as dashed lines. The circles represent centroids of the C3ꢀ ꢀ ꢀC7 (Cg1) and C8ꢀ ꢀ ꢀC12 (Cg2)
rings. Only the major component of the disordered ethenyl group is shown.
Table 2
gesting possible disorder. However, a suitable disorder
model could not be developed for this case. All non-hydro-
gen atoms were assigned anisotropic temperature factors,
with hydrogen atoms included in calculated positions using
a riding model. The final difference Fourier map was essen-
Crystal data and structure refinement for 1
Compound
Fc–CH@CH2 (1)
C12H12Fe
212.07
90(2)
monoclinic
P21/c
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
tially flat with no peaks higher than 0.648 e Aꢁ3. Molecular
˚
plots were made with ORTEP3 [21] and MERCURY [22].
Lattice parameters
˚
a (A)
11.4962(4)
7.6740(3)
10.7562(4)
99.269(2)
936.54(6)
4
1.504
1.553
440
Acknowledgements
˚
b (A)
˚
c (A)
We are grateful to the New Zealand Foundation for Re-
search Science and Technology for a Postdoctoral Fellow-
ship to C.J.M. and the University of Otago for purchase of
the diffractometer.
b (°)
Cell volume (A )
3
˚
Z
Dcalc (g cmꢁ3
)
l (mmꢁ1
F(000)
)
Appendix A. Supplementary material
h Range (°)
3.58–33.12
ꢁ17 ! h ! 17
ꢁ11 ! k ! 11
ꢁ15 ! l ! 15
16440
3307 (0.0305)
2823
0.776/0.940
3307/0/137
1.057
R1 = 0.0321,
wR2 = 0.0690
R1 = 0.0414
wR2 = 0.0737
0.648 and ꢁ0.778
Index ranges
CCDC 649191 contains the supplementary crystallo-
graphic data for 1. 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 the online
version, at doi:10.1016/j.ica.2007.10.035.
Reflections collected
Independent reflections (Rint
Reflections observed
Tmin/Tmax
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
)
References
R indices (all data)
[1] F.S. Arimoto, A.C. Haven Jr., J. Am. Chem. Soc. 77 (1955) 6295.
[2] C.J. McAdam, B.H. Robinson, J. Simpson, Organometallics 19
(2000) 3644.
ꢁ3
˚
Largest difference in peak and hole (e A
)
´
´
[3] V. Wintgens, P. Valat, J. Kossanyi, A. Demeter, L. Biczok, T. Berces,
J. Photochem. Photobiol. A 93 (1996) 109.
diffractometer, processed using APEXII and SAINT [18] with
empirical absorption corrections applied using SADABS [18].
The structure was solved with SHELXS-97 [19] and refined
with SHELXL-97 [19] and TITAN2000 [20] by full-matrix least
squares on F2. Atoms of the ethenyl group are disordered
over two position with site occupancies that refined to
0.582(5) and 0.418(5), respectively. The ellipsoids of the
C3ꢀ ꢀ ꢀC7 atoms of the vinyl substituted cyclopentadienide
ring are somewhat polarised in the plane of the ring sug-
[4] E.A. Zimakova, E.A. Chernyshev, Z. Obshchei Khim. 45 (1975) 1132.
[5] W.-Y. Liu, Q.-H. Xu, Y.-X. Ma, Y.-M. Liang, N.-L. Dong, D.-P.
Guan, J. Organomet. Chem. 625 (2001) 128.
[6] P. Dixneuf, R. Dabard, Bull. Soc. Chim. France 7 (1972) 2838.
[7] C.R. Hauser, J.K. Lindsay, D. Lednicer, J. Org. Chem. 23 (1958) 358.
[8] K.M. Joly, R.M. Gleixner, S.M.E. Simpkins, D.M. Coe, L.R. Cox,
Tetrahedron 63 (2007) 761.
[9] M. Cais, S. Dani, F.H. Herbstein, M. Kapon, J. Am. Chem. Soc. 100
(1978) 5554.
[10] U. Behrens, J. Organometal. Chem. 182 (1979) 89.

C.J. McAdam et al. / Inorganica Chimica Acta 361 (2008) 2172–2175
2175
[11] M. Watanabe, I. Motoyama, T. Takayama, Bull. Chem. Soc. Jpn. 69
(1996) 2877.
[18] Bruker AXS Inc. APEXII Version 2.0-2, SAINT Version 7.23A and
SADABS 2004/1, Madison, Wisconsin, USA, 2004.
[12] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
[13] T.-Y. Dong, M.-Y. Hwang, T.L. Hsu, C.-C. Schei, S.-K. Yeh, Inorg.
Chem. 29 (1990) 80.
[14] A. Togni, G. Rihs, Organometallics 12 (1993) 3368.
[15] A. Bertogg, A. Togni, Organometallics 25 (2006) 622.
[19] G.M. Sheldrick, SHELXS
Germany, 1997.
[20] K.A. Hunter, J. Simpson, TITAN2000, University of Otago, New
Zealand, 1999.
[21] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[22] I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler, C.F. Macrae, P.
McCabe, J. Pearson, R. Taylor, Acta Crystallogr., Sect. B 58 (2002)
389.
& SHELXL97, University of Go¨ttingen,
ˇ
´
[16] P. Steˇpnicˇka, I. Cısarˇova´, Collect. Czech. Chem. Commun. 71 (2006)
215.
[17] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.