Synthesis and crystal structure of 1,3-Diphenyl-2-ferrocenyl-1,3,2- diazabora-[3]ferrocenophane

Article abstract of DOI:10.1515/znb-2008-0718

1,1′-Bis(phenylamino)ferrocene reacts with dibromo(ferrocenyl)borane to yield a [3]ferrocenophane. The experimental details as well as the crystal structure of the product are presented.

Full text of DOI:10.1515/znb-2008-0718

920
Note
atoms in the bridge are delocalized more efficiently
into the pz orbital of the boron atom, resulting in an
almost planar arrangement of the bridge (C–N–B–N–
C). In contrast, strong π donors lead to a constitution
with a considerable out-of-plane bending of the boron
center [10].
In continuation of our investigations on [1]-
and [2]boraferrocenophanes on the one hand [13– 15]
and ferrocenylboranes of the type [FcB(η1-C5H5)2],
[FcB(1-C9H7)2] [FcB(3-C9H7)2], [FcB(1-C9H7)N(H)-
Ph], [FcB(3-C9H7)N(H)Ph], [FcB(N(H)Ph)2], [FcB-
(Br)N(H)tBu] and [FcB(Br)N(H)Ph] (Fc = Ferrocenyl)
as ligands in organometallic compounds on the other
[16], we aimed to combine the two structural motifs,
thus providing an unusual example of a homodinuclear
ansa complex of iron.
Synthesis and Crystal Structure of
1,3-Diphenyl-2-ferrocenyl-1,3,2-di-
azabora-[3]ferrocenophane
Tanja-Corinna Aucha, Holger Braunschweigb,
Krzysztof Radackib, Rainer Sigritzb,
Ulrich Siemelinga, and Sascha Stellwagb
a Institut fu¨r Chemie, Universita¨t Kassel, Heinrich-Plett-
Straße 40, D-34132 Kassel, Germany
b
Institut fu¨r Anorganische Chemie, Julius-Maximilians-
Universita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg,
Germany
Reprint requests to Prof. Dr. Holger Braunschweig.
Fax: (+49) 931-888-4623. E-mail: h.braunschweig@mail.
uni-wuerzburg.de or Prof. Dr. Ulrich Siemeling.
Fax: (+49) 561-804-4777. E-mail: siemeling@uni-kassel.de
In the present paper we report on the experimen-
tal details of the reaction of 1,1ꢀ-bis(phenylamino)fer-
rocene with dibromo(ferrocenyl)boraneand the crystal
structure of the resulting dinuclear [3]ferrocenophane.
Z. Naturforsch. 2008, 63b, 920 – 922;
received February 28, 2008
1,1ꢀ-Bis(phenylamino)ferrocene reacts with dibromo(fer-
rocenyl)borane to yield a [3]ferrocenophane. The experimen-
tal details as well as the crystal structure of the product are
presented.
Results and Discussion
Synthesis
Key words: Ferrocenophane, Ferrocene, Boron, Chelating
Ligand
The synthesis of 1,3-diphenyl-2-ferrocenyl-1,3,2-
diazabora-[3]ferrocenophane(1) was carried out by re-
acting in a first step 1,1ꢀ-bis(phenylamino)ferrocene
◦
with 2 equivalents of LiBu at −78 C in hexane. A
yellow solid precipitated, when the mixture was al-
lowed to warm◦up to r. t. The suspension was again
cooled to −78 C, and in a second step a solution of
one equivalent of dibromo(ferrocenyl)borane in hex-
ane was added dropwise, according to Eq. 1.
Introduction
1,1ꢀ-Diaminoferrocene and in particular its benzyl-
ated [1, 2], arylated [3 – 5] and silylated [6] deriva-
tives ([Fe{(η5-C5H4)NHR}2]; R = CH2Ph, Ph, SiMe3)
have recently been in the focus of attention. Not only
have these compounds significant potential as building
blocks in polymers, they also have proven their propen-
sity as chelating ligands in combination both with main
group elements like phosphorus [7], aluminum [8, 9]
and boron [10, 11] and transition metals particularly of
group 4 [5]. The latter have attracted attention as suit-
After warming up the reaction mixture to ambient
temperature and stirring for further 12 h, 1 was isolated
as orange crystals in 85 % yield. The compound is sol-
uble in all common solvents and can be stored under
an atmosphere of argon. It shows no sign of decompo-
sition, neither in the solid state nor in solution.
1
The H NMR spectrum of the title compound dis-
able non-metallocene (pre-)catalysts for α-olefin poly- plays five signals: four pseudotriplets are located at
merization [12]. Especially a large number of 1,3,2-di- 4.18 (4H), 4.02 (4H), 3.83 (2H) and 3.52 (2H) ppm,
azabora[3]ferrocenophanes have been synthesized and and a singlet is found at 4.07 ppm. The former pair
structurally characterized by Wrackmeyer et al. [7 – of pseudotriplets can be assigned to the protons of the
11], who investigated the effect of tunable π donors at- ferrocenophane unit, while the latter pair as well as the
tached to the trigonal planar boron center on the overall singlet arise from the ferrocenyl moiety attached to the
structure of these [3]ferrocenophanes. Bearing weak boron atom. Additionally, the phenyl substituents are
π donors, the lone electron pairs of the two nitrogen characterized by rather complex signals in the aromatic
c
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Note
921
˚
Table 1. Selected bond lengths (A) and angles (deg) for 1
The boron center as well as both nitrogen atoms
are in a trigonal planar configuration. The B–N bond
with estimated standard deviations in parentheses.
˚
lengths are 1.443(5) and 1.458(5) A, and the B–C bond
Distances
˚
N(1)–C(31)
N(1)–C(51)
N(2)–C(41)
N(2)–C(61)
1.430(4)
1.446(4)
1.437(5)
1.436(4)
B(1)–N(1)
B(1)–N(2)
B(1)–C(21)
1.443(5)
1.458(5)
1.575(5)
length was found to be 1.575(5)A. The ferrocenyl moi-
ety is known to be a weak π donor, and thus, the lone
pairs of both nitrogen atoms are delocalized into the
empty pz orbital of the boron atom. Hence, an over-
all almost planar arrangement is imposed on the N–B–
N-bridge. This result is in full agreement with previ-
ously published data of related species [10]. The cy-
clopentadienyl rings of the [3]ferrocenophane unit are
slightly staggered (3.82◦) and tilted (13.32◦). Further-
more, the boron atom is bent towards the iron atom of
the ferrocenyl moiety (10.26◦) as observed for many
other ferrocenylboranes with Lewis-acidic boron cen-
ters [16 – 18].
Angles
N(1)–B(1)–N(2)
N(1)–B(1)–C(21)
N(2)–B(1)–C(21)
C(41)–N(2)–C(61)
C(41)–N(2)–B(1)
121.5(3)
120.4(3)
118.1(3)
110.4(3)
124.3(3)
C(61)–N(2)–B(1)
C(31)–N(1)–B(1)
C(31)–N(1)–C(51)
B(1)–N(1)–C(51)
125.1(3)
126.9(3)
110.5(3)
122.6(3)
Experimental Section
All manipulations were performed under an atmosphere
of argon using standard Schlenk or glove box techniques.
Solvents were dried according to standard procedures or by
using a MBraun solvent purification system (SPS) and stored
under argon over molecular sieves. Dibromo(ferrocenyl)bor-
ane [19] and 1,1ꢀ-bis(phenylamino)ferrocene [4] were pre-
pared according to literature procedures. LiBu was purchased
from Aldrich as a 2.5 mol L−1 solution in hexane. The NMR
spectra were recorded on a Bruker AMX 400 spectrometer.
Fig. 1. Molecular structure of 1 in the crystal. Displacement
ellipsoids are drawn at the 50 % probability level. Hydrogen
atoms and the toluene molecule have been omitted for clarity.
1
1H and 13C{ H} NMR spectra were referenced to external
TMS via the residual proton of the solvent (1H) or the sol-
1
vent itself (13C). 11B{ H} NMR spectra were referenced to
external BF3 · OEt2. Mass spectra were recorded on a Finni-
region of the spectrum. In the 11B NMR spectrum, a
resonance at 34.7 ppm occurs which is significantly
high-field shifted with respect to that of the starting
gan MAT 8200 spectrometer.
1,3-Diphenyl-2-ferrocenyl-1,3,2-diazabora-[3]ferroceno-
material (at 48.0 ppm), thus accounting for the Br/NR, phane
substitution.
0.54 mL of a solution of LiBu (2.5 mol · L−1 in hex-
ane, 1.34 mmol) was slowly added to a solution of 246 mg
(0.67 mmol) of 1,1ꢀ-bis(phenylamino)ferrocene in 30 mL of
hexane at −78 ◦C. The reaction mixture was stirred at −78 ◦C
for 1 h and was then allowed to warm up to r. t. and kept stir-
ring for further 30 min. The formation of a yellow precipitate
was observed during the reaction. The suspension was again
X-Ray structure determination
Single crystals suitable for X-ray diffraction analy-
sis were grown from toluene at −30 ◦C. The structure
of 1 in the solid state is shown in Fig. 1. Selected bond
lengths and angles are given in Table 1.
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922
Note
cooled to −78 ◦C, and a solution of 238 mg (0.67 mmol) of ture was solved with Direct Methods, expanded using Fourier
dibromo(ferrocenyl)borane in 20 mL of hexane was added. techniques, and refined with the SHELX [20] software pack-
The mixture was warmed up to r. t. and was stirred for 12 h. age. All non-hydrogen atoms were refined anisotropically.
The color changed slightly from yellow to orange. Insolu- Hydrogen atoms were assigned idealized positions and were
ble material was filtered off, and the solvent was removed included as fixed-atom contributions into structure factors
in vacuo. The residual orange oil was dissolved in a small calculations.
amount of toluene. The product was obtained at −30 ◦C
Crystal data for 1: C32H27BFe2N2 · 1/2(C7H8), Mr
=
as orange crystals (319 mg, 0.57 mmol, 85 %). – 1H NMR 608.13, orange block, 0.11 × 0.07 × 0.05 mm3, monoclinic
(400 MHz; C6D6; 25 ◦C): δ = 3.52 (pt, 2H, CHFc), 3.83 (pt, space group P21/c with a = 17.765(2), b = 9.2601(12), c =
◦
3
˚
˚
2H, CHFc), 4.02 (pt, 4H, CHCp−N), 4.07 (s, 5H, CHFc), 4.18 17.215(2) A, β = 99.328(3) , V = 2794.5(6) A , Z = 4,
ρcalcd = 1.45 g · cm−3, µ = 1.1 mm−1, F(000) = 1260 e,
T = 193(2) K, R1 = 0.0591, wR2 = 0.1073 for I ≥ 4σ(I),
for 5569 independent reflections [2θ ≤ 52◦] and 398 refined
parameters.
(pt, 4H, CHCp−N), 6.9 – 7.4 (m, 10H, CHPh). – 11B NMR
(64.2 MHz◦; C6D6; 25 ◦C): δ = 34.7. – 13C NMR (100 MHz;
C6D6; 25 C): δ = 69.04 (CHFc), 71.33, 77.11 (CHCp−N),
73.62, 74.85 (CHFc), 102.79 (CNFc), 124.27, 127.80, 128.87
(CHPh), 151.97 (CNPh). – MS (EI): m/z (%) = 562 (2) [M]+;
368 (100) [M – BFc]+.
CCDC 679421 contains 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.
Crystal structure determination
The crystal data of 1 were collected on a Bruker D8
APEX I diffractometer equipped with a CCD area detector
with graphite-monochromatized MoKα radiation. The struc-
Acknowledgement
This work was supported by the DFG and the FCI.
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