Substituted ferrocenylboranes - Potential ligand precursors for ansa-metallocenes, constrained geometry complexes and ansa-diamido complexes

Article abstract of DOI:10.1002/zaac.200500365

A wide range of potential ligand precursors and related compounds have been synthesized from ferrocenyldibromoborane and ferrocenylenebis(dibromoborane) via salt elimination reactions. These comprise ligand precursors suitable for the preparation of (i) ansa-metallocenes such as [FcB(η¹-C ₅H₅)₂] (2), [FcB(1-C₉H ₇)₂] (3), [FcB(3-C₉H₇)₂] (4) and [1,1′-fc{B(3-C₉H₇)₂}₂] (11), (ii) constrained geometry complexes such as [FcB(1-C₉H ₇)N(H)Ph] (7) and [FcB(3-C₉H₇)N(H)Ph] (8), (iii) ansa-diamido complexes such as [FcB(N(H)Ph)₂] (9) as well as (iv) the related compounds [FcB(Br)N(H)tBu] (5), [FcB(Br)N(H)Ph] (6), [1,1′-fc{B(Br)N(SiMe₃)₂}₂] (12) and [1,1′-Fc(B(Br)NiPr₂}₂] (13) (Fc = ferrocenyl, fc = ferrocenylene, C₅H₅ = cyclopentadienyl, C ₉H₇ = indenyl). All new compounds have been characterised by multinuclear NMR spectroscopic techniques and in the case of 7 and 12 by X-ray diffraction methods.

Full text of DOI:10.1002/zaac.200500365

DOI: 10.1002/zaac.200500365
Substituted Ferrocenylboranes ؊ Potential Ligand Precursors for ansa-
Metallocenes, Constrained Geometry Complexes and ansa-Diamido Complexes
Holger Braunschweiga,*, Frank M. Breitlinga,b, Katharina Krafta, Mario Krafta, Fabian Seelera, Sascha
Stellwaga, and Krzysztof Radackia
a Würzburg, Institut für Anorganische Chemie der Julius-Maximilians-Universität
b London / United Kingdom, Imperial College, Department of Chemistry
Received August 17th, 2005.
Abstract. A wide range of potential ligand precursors and related
compounds have been synthesized from ferrocenyldibromoborane
and ferrocenylenebis(dibromoborane) via salt elimination reactions.
These comprise ligand precursors suitable for the preparation of (i)
ansa-metallocenes such as [FcB(η1-C5H5)2] (2), [FcB(1-C9H7)2] (3),
[FcB(3-C9H7)2] (4) and [1,1Ј-fc{B(3-C9H7)2}2] (11), (ii) constrained
geometry complexes such as [FcB(1-C9H7)N(H)Ph] (7) and
[FcB(3-C9H7)N(H)Ph] (8), (iii) ansa-diamido complexes such as
[FcB(N(H)Ph)2] (9) as well as (iv) the related compounds
[FcB(Br)N(H)tBu] (5), [FcB(Br)N(H)Ph] (6), [1,1Ј-fc{B(Br)N-
(SiMe3)2}2] (12) and [1,1Ј-fc{B(Br)NiPr2}2] (13) (Fc ϭ ferrocenyl,
fc ϭ ferrocenylene, C5H5 ϭ cyclopentadienyl, C9H7 ϭ indenyl).
All new compounds have been characterised by multinuclear NMR
spectroscopic techniques and in the case of 7 and 12 by X-ray dif-
fraction methods.
Keywords: Boron; Boranes; Ferrocene; Ligand
1 Introduction
Such complexes play an important role in areas such as
the synthesis of novel organometallic polymers and the
homogeneous Ziegler-Natta type polymerization of olefins.
The incorporation of a boron bridge has been associated
with a number a beneficial characteristics, i.e. an improved
catalytic activity of [n]bora-metallocenophanes (n ϭ 1, 2)
[3]. Furthermore, the potential of a Lewis-acidic boron
centre in ansa-metallocenes to activate the pendant tran-
sition metal centre without the need for added Lewis-acidic
co-catalysts has been envisaged [7a]. However, the Lewis-
acidity of the boron atom in currently known boron-
bridged ansa-metallocenes of the types II and III is moder-
ated either by π-donation from an amino group or by the
formation of base adducts.
Boron-bridged ansa-ligands have recently attracted con-
siderable attention in the chemistry of strained (I) [1, 2] and
unstrained (II, III) [3Ϫ5] metallocenophanes, constrained
geometry complexes (CGCs, IV) [6, 7] and ansa-diamido
complexes (V) [8].
Consequently, we attempted to synthesize corresponding
complexes with more Lewis-acidic boron bridges, i.e. less
stabilization of the electron deficient boron atoms. Ligands
based on substituted ferrocenylboranes appeared to be a
suitable starting point since the ferrocenyl group is known
to provide only a weak stabilisation of the boron centre. [9]
Moreover, the introduction of the redox-active ferrocenyl
moiety may have the additional effect to allow fine tuning
of the ligation characteristics and/or catalytic performance
of derived complexes. Based on the versatile chemistry of
ferrocenyldibromoborane, [FcBBr2], the synthesis of tris(-
pyrazol-1-yl)borate ligands („scorpionates“) and derived
complexes [10] and a variety of other ferrocenylboranes and
borates was previously reported [11]. In our group,
[FcBBr2] has already been successfully utilized for the syn-
thesis of various new boryl and borylene complexes [12].
In the present paper we report on a series of substitution
reactions on ferrocenyldibromoborane and ferrocenylene-
Illustration 1
* Prof. Dr. Holger Braunschweig
Institut für Anorganische Chemie
Julius-Maximilians-Universität Würzburg
Am Hubland
DϪ97074 Würzburg
Fax: ϩ49 931 888 4623.
E-mail: h.braunschweig@mail.uni-wuerzburg.de
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H. Braunschweig, F. M. Breitling, K. Kraft, M. Kraft, F. Seeler, S. Stellwag, K. Radacki
bis(dibromoborane). The obtained ferrocenylboranediyl
metric substitution pattern (va/va or vh/vh) while the other
one is the unsymmetrically substituted isomer (va/vh). In
bridged ligand precursors may find application in the prep-
aration of new ansa-metallocenes, CGCs and ansa-diam-
ido complexes.
1
the H and 13C NMR spectra, the symmetric isomer exhib-
its only one resonance corresponding to the methylene
groups of the cyclopentadienyl rings, while the unsymmetric
isomer displayed two resonances corresponding to the two
chemically distinct methylene fragments. In the 13C NMR
spectrum, the methine groups of the boron bound C5H5
fragments give rise to three resonances for the symmetric
isomer, but six resonances for the unsymmetric isomer. For
both isomers the 13C NMR resonances corresponding to
the boron bound carbon atoms could not be detected due
to quadrupolar 13C-11B coupling [14]. In the 11B NMR
spectrum of 2, a single resonance at δ ϭ 53.5 is observed,
i.e. shifted to low field by 7.5 ppm compared to the
11B NMR of 1.
2 Results and Discussion
2.1 Substitution reactions involving
ferrocenyldibromoborane
2.1.1 ansa-Metallocene ligand precursors
The salt elimination reaction between [FcBBr2] (1) and two
equivalents of Na[C5H5] (C5H5 ϭ cyclopentadienyl) or
Li[C9H7] (C9H7 ϭ indenyl) gave cleanly the ferrocenylbor-
anes 2 and 3 in quantitative yields as orange amorphous
solids (Scheme 1).
Scheme 1
2 is obtained as a mixture of isomers as is apparent from
3 is obtained as the kinetically favoured product, in which
the boron atom is linked to the sp3 hybridized carbon atoms
of the indenyl substituents, i.e. in the 1-position, resulting
in two chiral centres in the molecule. Therefore, 3 is ob-
tained as a mixture of two diastereomers (rac and meso)
1
the H and 13C NMR spectra. For related aminobis(cyclo-
pentadienyl)boranes, we have earlier found isomers that dif-
fer with respect to the connectivity of the double bonds in
the cyclopentadienyl rings relative to the boryl substituent.
At ambient temperature, generally only the vinylic-allylic
(va) and vinylic-homoallylic (vh) isomers, i.e. where the
boryl moiety is bound to an sp2-hybridized carbon atom,
are observed. Consequently, for bis(cyclopentadienyl)bor-
anes up to three isomers are anticipated (va/va, va/vh and
vh/vh) [13]. However, in the case of 2 we observed only two
1
and the interpretation of the H and 13C NMR spectro-
scopic data proved difficult. The 11B NMR spectrum
showed a single resonance at δ ϭ 68.4, i.e. low field shift
by ca. 23 ppm relative to that of 1. As was previously re-
ported for other (indenyl)boranes [3b, 15], the 1-indenyl iso-
mer 3 can be isomerized to the thermodynamically more
stable 3-indenyl isomer 4, i.e. the isomer in that the boron
atom is bound to an sp2 hybridized carbon atom, in the
1
1
isomers. H,1H and H,13C correlation NMR spectroscopy
enabled us to determine that one of the isomers has a sym-
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Substituted Ferrocenylboranes
Scheme 2
presence of catalytic amounts of a base, e.g. NEt3
(Scheme 2).
ligand precursor prior to introduction of the NHR frag-
ment was found to be essential in performing these synth-
eses. However, initial attempts to react [FcBBr2] with
Na[C5H5] and Li[C9H7], respectively, in a 1:1 fashion failed
and always resulted in mixtures of several products. Conse-
quently, we reversed the order of the substitution reactions
and attempted the introduction of the NHR moiety prior
to the introduction of the cyclopentadienyl moiety.
4 does not possess any chiral centres and, therefore, is
1
obtained as a single isomer. The H and 13C NMR spectra
of 4 are significantly simplified when compared to the
corresponding spectra of 3 and all observed signals can be
assigned. In the 13C NMR spectrum of 4, one signal corre-
sponding to the methylene moiety and five resonances
corresponding to the methine fragments of the indenyl sub-
stituent are observed, suggesting free rotation about the
BϪC bonds despite the bulkiness of the substituents. The
isomerization results in a shielding of the boron atom that
is reflected by an 11B NMR signal at δ ϭ 58.0, which is
shielded by ca. 10 ppm when compared to the correspond-
ing resonance of 3. A similar shift was previously observed
for the 1-indenyl and 3-indenyl isomers of (Me3Si)2NB-
(C9H7)2 [3b].
Precursor 1 was reacted with Li[NHR] (R ϭ tBu, Ph) to
give [FcB(Br)N(H)R] (R ϭ tBu (5), Ph (6)) via salt elimin-
ation (Scheme 3). 11B NMR spectra of 5 and 6 displayed
singular resonances at δ ϭ 35.3 and 36.7, respectively, that
are significantly high-field shifted relative to the corre-
1
sponding signal for 1. The H and 13C NMR spectra of 5
at ambient temperature showed two sets of signals in an
1
integral ratio of ca. 10:1. Resonances of 6 in the H and
13C NMR spectra at ambient temperature were very broad;
however, at low temperature (Ϫ30 °C) resonances were well
resolved. Again, two sets of signals were observed in an
integral ratio of ca. 5:2, indicating the presence of two iso-
mers.
2.1.2 Constrained geometry complex ligand precursors
We have previously reported the synthesis of boron-bridged
CGC ligand precursors employing aminodihaloboranes
[6, 16]. Introduction of the cyclopentadienyl moiety into the
The observation of two isomers of 5 and 6 is almost cer-
tainly the result of π-donation from the nitrogen lone pair
Scheme 3
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H. Braunschweig, F. M. Breitling, K. Kraft, M. Kraft, F. Seeler, S. Stellwag, K. Radacki
into the empty p-orbital on boron and hence, a strong
of signals in an integral ratio of ca. 5:2, indicating the pres-
ence of two distinct isomers in solution. This observation
may be likewise attributed to the presence of E and Z iso-
mers with respect to the substituents on the BϪN linkage
in 7. The 11B NMR spectrum of 7 displayed a single reson-
ance at δ ϭ 42.9 that falls in the expected range for the
substitution pattern of the compound.
double bond character of the BϪN bond. Given four differ-
ent substituents on the BϭN linkage and hindered rotation
about this bond, two distinguishable isomers E and Z are
possible. There is no easy way to identify whether the E or
Z isomers are predominant in the mixtures, however, the Z
isomers (where the Fc and R groups are positioned in trans
position relative to each other) may be expected to be lower
in energy and therefore predominant on steric grounds. The
lower barrier for rotation about the BϪN bond in 6 com-
pared to 5, as indicated by the resolution of the signals for
the two isomers in the former only at low temperature, can
be explained by a modest electron withdrawing effect of the
phenyl group that moderates π-donation from nitrogen to
boron.
Isomerisation of the 1-indenyl isomer 7 to the thermo-
dynamically more stable 3-isomer isomer 8 was achieved in
1
the presence of NEt3 (Scheme 5). Surprisingly, the H and
13C NMR spectra of 8 displayed only one set of signals.
Presumably, π-donation from the indenyl fragment to the
boron atom results in a reduced double bond character of
the BϪN linkage and in turn facilitates fast interconversion
of E and Z isomers on the NMR timescale. The 11B NMR
resonance observed for the 3-indenyl isomer 8 at δ ϭ 41.5
is slightly high-field shifted compared to the corresponding
resonance in the 1-indenyl isomer 7 at δ ϭ 42.9. This shift
is significantly smaller than in the di(indenyl)ferrocenyl-
boranes 3 and 4, apparently due to the strong influence of
the amino moiety in 7 and 8 on the shielding of the boron
centre.
Reaction of 6 with Li[C9H7] afforded 7 after work-up as
a red oil that solidified at ambient temperature (Scheme 4).
Recrystallization from toluene at Ϫ30 °C yielded pure 7.
While the crystalline solid was identified as the Z isomer
(where the Fc and Ph groups are positioned in cis position
relative to each other) by an X-ray diffraction experiment
1
(vide infra), H and 13C NMR spectra displayed two sets
Scheme 4
Scheme 5
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Substituted Ferrocenylboranes
Scheme 6
2.1.3 ansa-Diamido complex ligand precursors
scribed above to the substitution of the related precursor
[1,1Ј-fc(BBr2)2] (fc ϭ ferrocenylene) (10) [17]. In the pro-
spective products, suitable substituents should provide co-
ordination sites to ligate two transition metal centres in
close proximity to each other as well as to the redox active
iron centre.
[FcBBr2] was reacted with two equivalents of Li[NHPh] to
give the symmetrically substituted diamino boron com-
pound [FcB{N(H)Ph}2] (9) (Scheme 6). Ambient tempera-
1
ture H and 13C NMR spectra of 9 exhibit only one set of
signals corresponding to the target compound, consistent
with facile rotation about the BϪN bonds, whose bond or-
ders are expected to be 1.5 at most. As anticipated, the 11B
NMR chemical shift of δ ϭ 31.5 for 9 is high-field shifted
by ca. 6 ppm compared to the chemical shift for the corre-
sponding monoamino ferrocenyl borane 6 and is consistent
with the proposed substitution pattern at the boron centre.
The reaction of 10 with four equivalents of Li[C9H7]
results in the clean formation of the corresponding tetra-
indenyl substituted diborylated ferrocene. As described in
the synthesis of 3 (vide supra), the compound is initially
obtained as the kinetically favoured 1-indenyl isomer, which
can be isomerized quantitatively to the corresponding 3-
indenyl isomer 11 in the presence of catalytic amounts of
NEt3 (Scheme 7).
1
The resonances observed in the H, 13C and 11B NMR
2.2 Substitution reactions involving 1,1Ј-
ferrocenylenebis(dibromoborane)
spectra of 11 very much resemble the signals displayed in
the corresponding spectra of 4. Accordingly, in the 13C
NMR spectrum of 11, one signal corresponding to the
methylene moiety and five signals corresponding to the
methine fragments of the indenyl substituents are observed,
again indicating free rotation about all BϪC bonds. For the
ferrocenylene fragment in 11, two pseudo triplets are found
In the literature on transition metal catalysis, several ex-
amples of the beneficial effect of close proximity of two
catalytically active sites, e.g. through incorporation in the
same molecule, are documented. Therefore, we explored the
potential to extend the substitution chemistry of 1 as de-
Scheme 7
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H. Braunschweig, F. M. Breitling, K. Kraft, M. Kraft, F. Seeler, S. Stellwag, K. Radacki
in the 1H NMR spectrum as well as two corresponding res-
The crystal structure confirms the proposed constitution
with the boron atom attached to the sp3-hybridized carbon
atom of the indenyl system. The Cp rings of the ferrocenyl
unit are oriented in an eclipsed fashion with a minor tilt of
1.1° between the two virtually planar ring systems (r.m.s.
onances in the 13C NMR spectrum, indicating approximate
C2 symmetry of the molecule in solution.
Reaction of 10 with two equivalents of Li[NR2] (R ϭ
SiMe3, iPr) results exclusively in the substitution of one
bromide substituent per boron centre and formation of 12
and 13, respectively (Scheme 8).
˚
˚
deviation of 0.0030 A for C5H4 and 0.0004 A for C5H5,
respectively). The boron centre is situated in a trigonal
Scheme 8
Surprisingly, the respective 1H and 13C NMR spectra
show only one signal corresponding to the SiMe3 groups of
12, but two sets of signals (two septets and two doublets)
corresponding to the iPr moieties of 13. In analogy to the
bonding situation found in 5؊7 one might expect a strong
double bond character of the BϪN linkage in 12 and 13
rendering the two R substituents of the NR2 moiety chemi-
cally non-equivalent, hence, giving rise to two sets of signals
in the respective 1H and 13C NMR spectra. However,
N(SiMe3)2 is known to be a comparably weaker π-donor
[18], therefore apparently facilitating rotation about the
BϪN bond in 12 even at ambient temperature.
2.3 X-ray structure determination of complexes 7 and
12
Crystal data and structure refinement details for 7 and 12
are compiled in the experimental section. Single crystals of
7 suitable for X-ray crystallographic analysis were grown
from a concentrated toluene solution at Ϫ30 °C. Com-
Figure 1 ORTEP representation of 7 in the solid state; thermal
ellipsoids are drawn at the 50 % probability level; hydrogen atoms
˚
are omitted for clarity. Selected bond lengths /A and angles /°:
¯
N(1)ϪB(1) 1.406(3), B(1)ϪC(21) 1.609(3), B(1)ϪC(31) 1.549(3),
pound 7 crystallizes in the triclinic space group P1 with two
C(32)ϪC(31)ϪB(1)
N(1)ϪB(1)ϪC(21)
123.32(19),
117.16(19),
C(35)ϪC(31)ϪB(1)
N(1)ϪB(1)ϪC(31)
130.76(19),
125.14(19),
formula units per unit cell; the molecules being without site
symmetry (C1) (Fig. 1).
C(31)ϪB(1)ϪC(21) 117.70(18).
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Substituted Ferrocenylboranes
planar environment (sum of angles between respective sub-
stituents is 360.0°). The BϪN distance of 1.406(3) A is in
The crystal structure confirms the proposed constitution
of 12. The Cp rings of the ferrocenyl unit are displaced by
ca. 18.5° from an eclipsed orientation with a minor tilt of
0.5° between the two virtually planar ring systems (r.m.s.
˚
the expected range of BϪN double bonds. The phenyl
group is oriented in trans position with respect to the inde-
nyl moiety. The BϪC(21) and BϪC(31) bond lengths of
˚
˚
deviation of 0.0017 A for C5H4 (1) and 0.0012 A for C5H4
(2), respectively). Most notably, the constitution in the solid
state reveals a torsion of the r.m.s. planes defined by the
three respective substituents of the boron (sum of angle ϭ
360.0° and 359.8°) and nitrogen (sum of angles ϭ 359.7°
and 359.8°) centres of 49.7° and 39.0°. This twist is, how-
ever, not accompanied by any significant lengthening of the
˚
1.609(3) and 1.549(3) A differ significantly and reflect the
difference in hybridization of the two carbon atoms.
The short BϪC(31) distance, together with the almost co-
planar arrangement of the CpϪBϪNϪC11 linkage (re-
flected by the torsion angles C(35)ϪC(31)ϪBϪN and
C(31)ϪBϪNϪC(11) of Ϫ0.8(4) and 0.9(4)° respectively),
may indicate some π-delocalisation via the BϪ(C31) bond.
The most interesting feature of the X-ray structure is the
positioning of the boryl moiety relative to the ferrocenyl
fragment. The boryl substituent is moderately bent out of
the Cp plane towards the iron centre, a disposition that is
frequently observed in ferrocenylboranes with Lewis-acidic
boron centres [9]. As the boron atom is significantly re-
placed from the virtual mirror plane dissecting the ferro-
cenyl unit in C(31) (indicated by angles C(32)ϪC(31)ϪB
and C(35)ϪC(31)ϪB of 123.3(2) and 130.8(2)° respec-
tively), the usually applied method for the calculation of
the dip angle α* (α* ϭ 180°Ϫα, with α being the angle
Cp(centroid)-Cipso-B) [10a] as a measure for the bending is
invalid. Therefore, the angle between the r.m.s. plane of the
substituted Cp ring and the r.m.s. plane calculated for bo-
ron and its three substituents is determined to be 9.8°. This
value is slightly smaller than α* found in FcB(OH)Me
(10.3°, 10.8°, and 12.9°, respectively, for three crystallo-
graphically independent molecules), another example for a
ferrocenylborane in which the Lewis-acidity of the boron
centre is partially cancelled by a neighbouring π-donor [9e].
Single crystals of 12 suitable for X-ray diffraction analy-
sis were obtained by recrystallization from a concentrated
hexane solution at Ϫ30 °C. Compound 12 crystallizes in the
˚
BϪN bonds (1.416(4) and 1.406(4) A) that are of similar
length as the BϪN bond in 7. Notwithstanding, the torsion
about the BϪN linkages in 12 in the solid state agrees with
the possibility for free rotation about these bonds in solu-
tion that was concluded from NMR spectroscopic evidence
(vide supra). Dip angles α* of 0.8° and 5.0° were calculated,
reflecting the influence of crystal packing effects rather than
interactions between the boron atom and the ferrocenyl li-
gand. This interpretation is supported by the twist of the
planes defined by the respective substituents of the boron
centre and the plane defined by the respective ring system
of 18.3° and 33.0°. As a result of this twist, the pz-orbitals
of the respective boron centres are positioned in such a way
that a stabilizing interaction with iron based orbitals can
be excluded.
3 Conclusions
We have prepared a range of ferrocenyl- and ferrocenylene-
based ligand precursors and related compounds. Investi-
gations to utilise these precursors for the synthesis of new
ansa-metallocenes, CGCs and ansa-diamido complexes are
in progress.
¯
triclinic space group P1 with two formula units per unit
cell; the molecules being without site symmetry (C1) (Fig-
ure 2).
4 Experimental
4.1 General considerations
All manipulations were performed under a dry atmosphere of ar-
gon using standard Schlenk line and dry box techniques. Solvents
were dried utilising an M. Braun Solvent Purification System and
stored under argon over molecular sieves. Deuterated solvents were
degassed, dried and stored over molecular sieves. [FcBBr2] (Fc ϭ
Ferrocenyl) [19], [1,1Ј-fc(BBr2)2] (fc ϭ ferrocenylene) [19] and
Na[C5H5] [20] were prepared by previously published methods.
Lithium indenide and lithium amides were prepared by depro-
tonation of indene and corresponding amines, respectively, utilising
butyl lithium.
1H and 13C NMR spectra were recorded on either a Bruker 200
Avance spectrometer, a Bruker DRX 300 spectrometer, a Bruker
400 Avance spectrometer or a Bruker 500 Avance spectrometer.
11B-{1H} NMR spectra were recorded on a Bruker 200 Avance
spectrometer. All chemical shifts are reported in ppm. Chemical
shifts for 1H and 13C-{1H} NMR spectra were referenced to in-
ternal solvent resonances and are reported relative to SiMe4. As-
Figure 2 ORTEP representation of 12 in the solid state; thermal
ellipsoids are drawn at the 50 % probability level; hydrogen atoms
˚
are omitted for clarity. Selected bond lengths /A, angles /° and tor-
sion angles /°:
B1ϪN1 1.406(4), B2ϪN2 1.416(4), B1ϪC11 1.535(5), B2ϪC21 1.539(5),
B1ϪBr1 1.993(4), B2ϪBr2 1.988(4), C11ϪB1ϪN1 126.12, C11ϪB1ϪBr1
114.82, Br1ϪB1ϪN1 119.02, C21ϪB2ϪN2 126.74, C21ϪB2ϪBr2 114.13,
Br2ϪB2ϪN2 119.04.
1
signments were made from the analysis of 13C APT, H,1H-COSY
1
and H,13C-HMQC-COSY NMR experiments. Chemical shifts for
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H. Braunschweig, F. M. Breitling, K. Kraft, M. Kraft, F. Seeler, S. Stellwag, K. Radacki
11B-{1H} NMR spectra were referenced to BF3·OEt2 as an external
in toluene (30 mL) was added dropwise over a 45 min period. After
stirring the mixture for 1 h at Ϫ80 °C, it was allowed to warm to
ambient temperature and stirred for a further 1 h. The pale yellow
precipitate was removed by centrifugation. All volatiles were then
removed in vacuo to yield 5 (1.32 g, 3.79 mmol, 94 %) as an iso-
meric mixture (isomer ratio ca. 10:1) in the form of a red oil that
crystallized on standing at ambient temperature.
standard. All NMR spectra were recorded in benzene-D6 as a sol-
vent at ambient temperature unless stated otherwise. Abbreviations
used for the description of 1H NMR signals are as follows: s ϭ
singlet, d ϭ doublet, pt ϭ pseudo triplet, pq ϭ pseudo quartet,
h ϭ heptet, m ϭ multiplet, br ϭ broad. Mass spectra were recorded
on a Finnigan MAT 8200.
1H NMR (400 MHz): [major isomer]: δ ϭ 1.29 (s, 9H, tBu), 4.06 (s, 5H,
CHC H ), 4.23 (pt, 2H, CHC H B), 4.32 (pt, 2H, CHC H B), 4.54 (br s, 1H,
5
5
5
5
4
NH); [minor isomer]: δ ϭ 1.274(s, 9H, tBu), 4.06 (s, 5H, CHC H ), 4.22 (pt,
4.2 Preparation of [FcB(η1-C5H5)2] (2)
5
2H, CHC H B), 4.31 (pt, 2H, CHC H B), 4.59 (br s, 1H, NH).5 13C NMR
5
5
(101 MHz):4[major isomer]: δ ϭ 32.0 4(CH3), 51.4 (C(CH3)), 69.5 (CHC H ),
[FcBBr2] (1.00 g, 2.81 mmol) was dissolved in toluene (20 mL) and
added at 0 °C to a suspension of Na[C5H5] (0.53 g, 6.00 mmol) in
toluene (20 mL). After stirring the mixture for 16 h the insoluble
material was removed by centrifugation and all volatiles were re-
moved in vacuo to yield 2 (0.90 g, 2.78 mmol, 99 %) as an orange
amorphous material. 1H and 13C NMR spectra showed two sets of
signals corresponding to an isomeric mixture.
5
5
72.6, 73.6 (CHC H B), BC resonance not observed; [minor isomer]: δ ϭ 31.9
5
4
(CH3), 50.8 (C(CH3)), 69.4 (CHC H ), 72.5, 73.2 (CHC H B), BC resonance
5
5
5
4
not observed. 11B NMR (64 MHz): [mixture of isomers]: δ ϭ 35.3.
4.6 Preparation of [FcB(Br)N(H)Ph] (6)
Following essentially the same procedure as for the synthesis of 5,
[FcBBr2] (2.19 g, 6.16 mmol) was reacted with Li[NHPh] (0.61 g,
1H NMR (500 MHz): [symmetrical isomer]: δ ϭ 3.35 (pq, 4H, CH2C H B),
3.90 (s, 5H, CHC H ), 4.45, 4.51 (pt, 4H, CHC H B), 6.72, 6.77, 7.27 (m5, 6H,
5
5
5
5
4
6.16 mmol) in toluene (80 mL). After work-up,
6 (2.02 g,
CHC H B); [unsymmetrical isomer]: δ ϭ 2.98, 3.37 (pq, 4H, CH2C H B), 3.92
5
5
5
(s, 5 H, CHC H ), 4.48, 4.60 (pt, 4H, CHC H B), 6.4 Ϫ 7.6 (m, 6H, 5CHC H B).
5
5
4
5
5.49 mmol, 89 %) was obtained in the form of a red oil. The 1H
and 13C NMR spectra at ambient temperature showed very broad
signals. At low temperatures, two sets of signals were resolved in
the 1H and 13C NMR spectra, corresponding to two isomers in
approximately a 5:2 ratio.
13C NMR (1256 MHz): [symmetrical isomer]: δ ϭ 47.8 (CH2C H B),5 69.7
(CHC H ), 75.2, 78.7 (CHC H B), 134.3, 140.0, 146.9 (CHC H B), 5BC reson-
5
ances5not observed; [unsym5metrical isomer]: δ ϭ 44.1, 47.3 5(CH2C H B), 69.8
5
4
5
5
5
(CHC H ), 75.7, 78.4 (CHC H B), 132.3, 134.5, 139.2, 141.8, 142.3, 151.0
5
5
5
4
(CHC H B), BC resonance not observed. 11B NMR (64 MHz): [mixture of
5
isome5rs]: δ ϭ 53.5. MS m/z (%): 326 (54) [Mϩ], 261 (60) [Mϩ Ϫ Cp], 186
1H NMR (dichloromethane-D2, 300 MHz, Ϫ30 °C): [major isomer]: δ ϭ 4.24
(63) [C10H10Feϩ], 121 (100) [C5H5Feϩ], 66 (72) [CpHϩ].
(s, 5H, CHC H ), 4.53 Ϫ 4.58 (m, 4H, CHC H B), 6.59 (br s, 1H, NH), 7.16
5
5
4
Ϫ 7.40 (m, 5H5, CHPh). [minor isomer]: δ ϭ 4.11 (pt, 2H, CHC H B), 4.14 (s,
5H, CHC H ), 4.42 (pt, 2H, CHC H B), 6.50 (br s, 1H, NH), 57.16 Ϫ 7.40
4
5
5
5
4
4.3 Preparation of [FcB(1-C9H7)2] (3)
(m, 5H, CHPh). 13C NMR (dichloromethane-D2, 75 MHz, Ϫ30 °C ): [major
isomer]: δ ϭ 69.2 (CHC H ), 73.2 (CHC H B), 73.5 (CHC H B), 123.7 (o-CHPh),
125.0 (p-CHPh), 128.7 5(m-CHPh), 141.44 (ipso-CPh), B5C 4resonance not ob-
5
5
In analogy to the synthesis of 2, [FcBBr2] (1.00 g, 2.81 mmol) was
dissolved in toluene (20 mL) and added at 0 °C to a suspension of
Li[C9H7] (0.68 g, 5.60 mmol) in toluene (20 mL). After stirring the
mixture for 16 h the insoluble material was removed by centrifug-
ation. All volatiles were removed in vacuo to yield 3 (1.18 g,
2.78 mmol, 99 %) as a red amorphous solid.
served. [minor isomer]: δ ϭ 69.5 (CHC H ), 73.0 (CHC H B), 76.1 (CHC H B),
5
5
4
124.1 (o-CHPh), 125.0 (p-CHPh), 128.95(m-CHPh), 1415.54(ipso-CPh), BC res-
onance not observed. 11B NMR (dichloromethane-D2, 64 MHz): [mixture of
isomers]: δ ϭ 36.7.
1H NMR (200 MHz): [mixture of isomers]: δ ϭ 3.61, 3.67 (m, 4H, BCH),
3.95, 3.97 (s, 10H, CHC H ), 3.8 Ϫ 4.3 (m, 8H, CHC H B), 6.4 Ϫ 7.5 (m, 24H,
4.7 Preparation of [FcB(1-C9H7)N(H)Ph] (7)
5
5
5
4
CHInd). 13C NMR (50 MHz): [mixture of isomers]: δ ϭ 51.0 (br, BCH), 75.1,
75.4, 75.5, 75.6, 75.7, 76.6 (CpFc), 121.4, 121.5, 124.5, 124.5, 124.6, 124.9,
125.7, 125.9, 131.0, 131.3, 137.8, 138.0 (CHInd), 145.9, 146.2, 147.6, 148.3
(quaternary CInd), BCC H B resonance not observed. 11B NMR (64 MHz):
A solution of 6 (0.78 g, 2.11 mmol) in 40 mL toluene was cooled
to Ϫ70 °C and added to neat LiInd (0.26 g, 2.11 mmol). The mix-
ture was allowed to come to ambient temperature and subsequently
stirred for 16 h. Precipitated LiBr was removed by centrifugation,
all volatiles were removed in vacuo to yield a red oil that solidified
at ambient temperature. Pure 7 (0.68 g, 1.68 mmol, 80 %) was ob-
tained by recrystallisation from toluene at Ϫ30 °C as orange col-
oured crystals, that were suitable for X-ray structure determination.
At ambient temperature, the 1H and 13C NMR spectra showed the
presence of two isomers in an approximate ratio of 5:2.
5
4
[mixture of isomers]: δ ϭ 68.4. MS m/z (%) (EI): 426 (58) [Mϩ], 311 (75)
[Mϩ Ϫ Ind], 186 (100) [C10H10Feϩ], 121 (50) [C5H5Feϩ], 116 (73) [Indϩ];
(CI): 426 (33) [Mϩ], 311 (51) [Mϩ Ϫ Ind], 186 (54) [C10H10Feϩ], 116 (56)
[Indϩ].
4.4 Preparation of [FcB(3-C9H7)2] (4)
A catalytic amount of NEt3 was added to a solution of 3 (0.98 g,
2.65 mmol) in toluene (30 mL). The mixture was stirred for 16 h at
ambient temperatures, then all volatiles were removed in vacuo to
yield 4 (0.98 g, 2.65 mmol) quantitatively in the form of a red
amorphous solid.
1H NMR (500 MHz): [major isomer]: δ ϭ 4.02 (s, 5H, CHC H ), 4.11 (br s,
5
5
1H, BCH), 4.15 (s, 1H, CHC H B), 4.18 (s, 1H, CHC H B), 4.19 (s, 2H,
5
4
5
4
CHC H B), 5.41 (s, 1H, NH), 6.6 Ϫ 7.7 (m, 11H, CHPh/Ind); [minor isomer]:
5
4
δ ϭ 3.67 (s, 1H, CHC H B), 3.84 (s, 1H, CHC H B), 3.93 (s, 5H, CHC H ), 4.03
5
5
4
5
5
(s, 2H, CHC H B), 4.264(br s, 1H, BCH), 6.27 (s, 1H, NH), 6.9 Ϫ 7.5 (m,
11H, CHPh/Ind)4. 13C NMR (126 MHz): [major isomer]: δ ϭ 49.7 (BCH), 69.0
5
1H NMR (500 MHz): δ ϭ 3.35 (m, 4H, CH2 Ind), 3.99 (s, 5H, CHC H ), 4.52
(CHC H ), 72.7, 72.8, 75.5, 75.9 (CHC H B), 121.9, 124.0, 124.7, 124.9, 126.0,
5
5
5
5
5
4
(pt, 2H, CHC H B), 4.62 (pt, 2H, CHC H B), 6.99 (pt, 2H, CHInd), 7.00 Ϫ
126.3, 128.7, 130.4, 138.9 (CHPh/Ind), 143.5, 145.6 (quaternary CInd), 148.1
(ipso-CPh), BCC H B resonance not observed; [minor isomer]: δ ϭ 46.2
5
4
4
7.15 (m, 4H, CHInd), 7.40 (m, 2H, CHI5nd), 7.60 (m, 2H, CHInd). 13C NMR
5
4
(126 MHz): δ ϭ 41.4 (CH2 Ind), 70.2 (CHC H ), 76.7, 78.7(CHC H B), 123.9,
(BCH), 69.0 (CHC H ), 71.8, 71.9, 72.4, 73.1 (CHC H B), 121.3, 124.3, 124.4,
5
5
4
124.4, 125.2, 127.0, 143.1 (CHInd), 145.0, 149.52 (quaternary CInd), BC reson-
ances not observed. 11B NMR (64 MHz): δ ϭ 58.0. MS m/z (%) : 426 (80)
[Mϩ], 311 (100) [Mϩ Ϫ Ind], 121 (34) [C5H5Feϩ], 116 (33) [Indϩ].
5
5
5
124.5, 124.8, 125.9, 128.6, 129.4, 130.8 (CHPh/Ind), 1443.3, 146.0 (quaternary
CInd), 148.7 (ipso-CPh), BCC H B resonance not observed. 11B NMR
5
4
(64 MHz): [mixture of isomers]: δ ϭ 42.9.
4.5 Preparation of [FcB(Br)N(H)tBu] (5)
4.8 Preparation of [FcB(3-C9H7)N(H)Ph] (8)
[FcBBr2] (1.44 g, 4.05 mmol) was dissolved in toluene (30 mL), co-
Compound 7 (0.15 g, 0.37 mmol) was dissolved in 20 mL toluene,
oled to Ϫ80 °C and a suspension of Li[NHtBu] (0.32 g, 4.05 mmol)
neat NEt3 (0.05 mL, 0.37 mmol) was added and the reaction mix-
276
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© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 269Ϫ278

Substituted Ferrocenylboranes
ture was stirred for 16 h at ambient temperature. All volatiles were
removed in vacuo to yield 8 (0.15 g, 100 %) in the form of a red oil.
1H and 13C NMR spectra showed the presence of a single isomer.
sequently stirred for a further 2 h. The precipitate was removed by
centrifugation and the recovered supernatant concentrated in va-
cuo. Cooling to Ϫ30 °C yielded 13 (4.59 g, 8.11 mmol, 72 %) in the
form of an orange coloured microcrystalline material.
1H NMR (500 MHz): δ ϭ 3.31 (m, 2H, CH2 Ind), 4.05 (s, 5H, CHC H ), 4.29
5
5
1H NMR (500 MHz): δ ϭ 0.92, (d, 3J ϭ 6.62 Hz, 12H, CH3iPr), 1.55 (d, 3J ϭ
6.94 Hz, 12H, CH3iPr), 3.26 (h, 3J ϭ 6.62 Hz, 2H, CHiPr), 3.38 (h, 3J ϭ
6.94 Hz, 4H, CHiPr), 4.49 (pt, 4H, CHC H B), 4.56 (pt, 4H). 13C NMR
(m, 2H, CHC H B), 4.31 (m, 2H, CHC H B), 6.33 Ϫ 7.40 (m, 10H, CHPh/Ind),
5
4
5
NH resonance not observed. 13C NMR 4(126 MHz): δ ϭ 41.0 (CH2 Ind), 68.9
(CHC H ), 72.8, 74.0 (CHC H B), 121.7, 122.9, 123.2, 123.9, 124.6, 126.4,
5
5
4
129.1, 1540.2 (CHPh/Ind), 144.1, 144.4 (quaternary CInd), 147.9 (ipso-CPh), BC
5
4
(126 MHz): δ ϭ 22.7, 25.9 (CH3iPr), 46.4, 47.3 (CHiPr), 73.2, 76.8 (CHC H B),
5
4
resonances not observed. 11B NMR (64 MHz): δ ϭ 41.5.
BC resonances not observed. 11B NMR (64 MHz): δ ϭ 35.8.
4.9 Preparation of [FcB{N(H)Ph}2] (9)
4.13 X-ray crystal structure determination of
compounds 7 and 12
[FcBBr2] (0.62 g, 1.74 mmol) was dissolved in 40 mL toluene and
cooled to Ϫ80 °C. 2 equivalents of Li[NHPh] (3.48 mmol) (as a
suspension in 40 mL toluene) were added dropwise and the re-
sulting mixture was stirred for 2 h at Ϫ80 °C, then 16 h at ambient
temperature. Precipitated LiBr was removed by centrifugation and
all volatiles were removed in vacuo to yield 9 (0.60 g, 1.57 mmol,
91 %) as a red oil.
The crystal data of 7 and 12 were collected at Bruker APEX dif-
fractometer with CCD area detector and graphite monochromated
MoKα radiation. The structure was solved using direct methods,
refine with shelx software package (G. Sheldrick, University of
Göttingen 1997) and expanded using Fourier techniques. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
assigned idealized position and were included in structure factor
calculations.
1H NMR (500 MHz): δ ϭ 3.98 (s, 5H, CHC H ), 4.14 (pt, 2H, CHC H B), 4.18
5
5
5
4
(pt, 2H, CHC H B), 5.42 (br s, 2H, NH), 6.30 Ϫ 7.10 (m, 10H, CHPh). 13C
5
4
NMR (126 MHz): δ ϭ 69.1 (CHC H ), 71.1, 74.1 (CHC H B), 115.1 (p-CHPh),
5
5
5
121.9 (o-CHPh), 129.3 (m-CHPh), 144.3 (ipso-CPh), BC4 resonance not ob-
served. 11B NMR (64 MHz): δ ϭ 31.5.
Crystal data for 7: C25H22BFeN, Mr ϭ 403.10, yellow plate,
˚
0.22ϫ0.20ϫ0.08, triclinic space group P-1, a ϭ 7.4676(17) A, b ϭ
˚
˚
3
11.346(3) A, c ϭ 12.538(3) A, α ϭ 77.333(4)°, β ϭ 82.899(5)°, γ ϭ
75.143(4)°, V ϭ 999.2(4) A , Z ϭ 2, ρcalcd ϭ 1.340 g·cmϪ3, μ ϭ
˚
4.10 Preparation of [1,1Ј-fc{B(3-C9H7)2}2] (11)
0.764 cmϪ2, F(000) ϭ 420, T ϭ 173(2) K, R1 ϭ 0.0419, wR2
ϭ
In analogy to the synthesis of 4, a solution of 1,1Ј-fc(BBr2)2 (2.24 g,
4.27 mmol) in toluene (20 mL) was added at 0 °C to a suspension
of Li[C9H7] (2.20 g, 18.0 mmol) in toluene (30 mL). The resulting
red mixture was stirred for 16 h at ambient temperature, the insol-
uble material removed by centrifugation and a catalytic amount of
NEt3 added to the supernatant. After 16 h all volatiles were re-
moved in vacuo to yield 11 (2.28 g, 3.42 mmol, 80 %) in the form
of an amorphous solid.
0.1023, 3952 independent reflections [2θՅ52.26°] and 253 para-
meters.
Crystal data for 12: C22H44B2Br2FeN2Si4, Mr ϭ 686.24, red block,
˚
0.26ϫ0.23ϫ0.19, triclinic space group P-1, a ϭ 9.2239(8) A, bϭ
˚
˚
˚
12.8962(11) A, c ϭ 14.6589(13) A, α ϭ 97.847(2)°, β ϭ 93.099(2)°,
γ ϭ 110.139(2)°, V ϭ 1612.2(2) A , Z ϭ 2, ρcalcd ϭ 1.414 g·cmϪ3
,
3
μ ϭ 3.109 cmϪ2, F(000) ϭ 704, T ϭ 173(2) K, R1 ϭ 0.0413, wR2 ϭ
0.1050, 6357 independent reflections [2θՅ52.24°] and 298 para-
meters.
1H NMR (500 MHz): δ ϭ 3.20 (m, 8H, CH2 Ind), 4.68 (pt, 4H, CHC H B),
5
4
4.73 (pt, 4H, CHC H B), 6.95 (pt, 4H, CHInd), 7.00 Ϫ 7.17 (m, 8H, CHInd),
5
4
7.35 (m, 4H, CHInd), 7.49 (m, 4H, CHInd). 13C NMR (126 MHz): δ ϭ 41.3
(CH2 Ind), 77.4, 79.2(CHC H B), 123.7, 124.4, 125.3, 126.9, 144.2 (CHInd),
5
145.0, 148.7 (quaternary CI4nd), BC resonances not observed. 11B NMR
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication no.
CCDC-280929 (7) and CCDC-280930 (12). These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data request/cif.
(64 MHz): δ ϭ 60.0.
4.11 [1,1Ј-fc{B(Br)N(SiMe3)2}2] (12)
A solution of [1,1Ј-fc(BBr2)2] (2.34 g, 4.45 mmol) in toluene
(20 mL) was added to a suspension of Li[N(SiMe3)2] (1.44 g,
8.90 mmol) in toluene (20 mL) at Ϫ80 °C. The reaction mixture
was allowed to come to ambient temperature and subsequently
stirred for a further 2 h. The formed precipitate was removed by
centrifugation and the supernatant concentrated to in vacuo. Cool-
ing to Ϫ30 °C yielded 12 (3.37 g, 4.23 mmol, 95 %) as an orange
coloured crystalline material.
Acknowledgements. This work was supported by BMBF, DFG,
EPSRC, R. Soc. F.M.B. thanks the Fonds der Chemischen Indus-
trie for a doctoral scholarship.
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