Ferrocenophanes with interannular boron-phosphorus bridges: Synthesis, structure, and reactivity toward nitrogen bases

Article abstract of DOI:10.1021/om970484g

Starting from readily available diborylferrocenes 1,1′-fc[B(Br)R]₂ (fc = (C₅H₄)Fe(C₅H₄); R: Br (1a), Me (1b), OEt (1d)), ferrocenophanes 1,1′-fc[B(μ-PPh₂)R]₂ (R = Br (2a), Me (2b

Full text of DOI:10.1021/om970484g

Organometallics 1997, 16, 4737-4745
4737
F er r ocen op h a n es w ith In ter a n n u la r Bor on -P h osp h or u s
Br id ges: Syn th esis, Str u ctu r e, a n d Rea ctivity tow a r d
Nitr ogen Ba ses
Eberhardt Herdtweck, Frieder J a¨kle, and Matthias Wagner*
Anorganisch-Chemisches Institut der Technischen Universita¨t Mu¨nchen,
Lichtenbergstrasse 4, D-85747 Garching, Germany
Received J une 9, 1997X
Starting from readily available diborylferrocenes 1,1′-fc[B(Br)R]2 (fc ) (C5H4)Fe(C5H4); R:
Br (1a ), Me (1b), OEt (1d )), ferrocenophanes 1,1′-fc[B(µ-PPh2)R]2 (R ) Br (2a ), Me (2b),
PPh2 (2d )) and 1,1′-fc[B(µ-PPh2)OEt][B(µ-PPh2)PPh2] (2c) are obtained upon reaction with
LiPPh2. In contrast, 1,1′-fc[B(Br)pyr]2 (pyr ) pyrrolidinyl, 1e) and 2 equiv of LiPPh2 give
an open-chain ferrocene 1,1′-fc[B(PPh2)pyr]2 (2e). The dynamic behavior of the B2P2-bridged
species has been investigated using variable-temperature NMR spectroscopy and the Forse´n-
Hoffman spin saturation transfer method. The reaction of 2a with Lipz (pz ) pyrazolide)
gives the ansa-ferrocene 1,1′-fc[B(µ-PPh2)PPh2][B(µ-pz)Br] (3a ), featuring an interannular
(BNNBP) heterocyclic bridge. When Lipz* (pz* ) 4-bromo-3,5-dimethylpyrazolide) was used
rather than Lipz, two products could be isolated: 3b, which is analogous to 3a , and 1,1′-
fc[B(µ-PPh2)Br][B(µ-pz)Br] (3c), which bears Br substituents at both bridgehead boron
centers. 2d and 3c have been characterized by X-ray crystallography. Treatment of 2a
with excess γ-picoline (pic) results in an ansa-bridge opening and bromide substitution with
the formation of the ionic species {1,1′-fc[B(PPh2)pic2]2}Br2 (5a ). The presence of three-
coordinate phosphorus centers in 5a was confirmed by showing their ability to bind Cr(CO)5
fragments, which afforded the trimetallic complex 5b.
Sch em e 1. F er r ocen op h a n es w ith a P yr a za bole (I)
a n d B2P 2 Br id ge (II)a
In tr od u ction
We have recently shown that the combination of
Lewis-acidic boron centers with Lewis-basic amino or
phosphino substituents in the ligand sphere of the same
ferrocene molecule can lead to interannular donor-
acceptor bonding and, thus, to ferrocenophanes I and
II (Scheme 1).1-4
This approach to ansa-bridged sandwich complexes
has an advantage due to the facile formation of dative
boron-nitrogen(phosphorus) links. Moreover, donor-
acceptor bonds may be broken and re-formed reversibly
without affecting the rest of the molecule. Our aim is
to make ferrocenophanes with “switchable” ansa-
bridges, which may be opened either by being thermally
induced or with the help of electrophilic or nucleophilic
additives (Scheme 1). While most ansa-ferrocenes I
with a pyrazabole5 bridge possess particularly rigid
molecular geometries, a continuous breaking and re-
forming of the interannular B2P2 ring of II (R ) Me)
was detected by NMR spectroscopy even at ambient
temperature.4
a
The monomer-dimer equilibrium of the phosphinoboryl
substituents in II (R ) Me) causes continuous breaking and
re-forming of the ansa-bridge.
on the strength of the interannular B-P bonds and to
investigate the reactivity of derivatives II toward
selected Lewis bases. Special emphasis will be put on
the relative stabilities of the bridging units in I and II.
The purpose of this paper is to give more detailed
information about the influence of substituents at boron
* Author to whom correspondence should be addressed.
Telefax: +49-89-28913473. E-mail: wagner@arthur.anorg.chemie.
tu-muenchen.de.
Resu lts a n d Discu ssion
X Abstract published in Advance ACS Abstracts, September 15, 1997.
(1) J a¨kle, F.; Priermeier, T.; Wagner, M. J . Chem. Soc., Chem.
Commun. 1995, 1765-1766.
Syn th eses. ansa-Ferrocenes 2a and 2b are prepared
by reaction of 1a and 1b with 2 equiv of LiPPh2 in 50%
and 80% yield, respectively (Scheme 2).4 ansa-Bridge
formation in 2a and 2b is the result of an intramolecular
dimerization of two phosphinoborane moieties via dative
B-P bonds. Such links are known to be weakened by
the presence of π donor substituents at boron.6 We
(2) Herdtweck, E.; J a¨kle, F.; Opromolla, G.; Spiegler, M.; Wagner,
M.; Zanello, P. Organometallics 1996, 15, 5524-5535.
(3) J a¨kle, F.; Priermeier, T.; Wagner, M. Organometallics 1996, 15,
2033-2040.
(4) J a¨kle, F.; Mattner, M.; Priermeier, T.; Wagner, M. J . Organomet.
Chem. 1995, 502, 123-130.
(5) Trofimenko, S. J . Am. Chem. Soc. 1967, 89, 4948-4952.
S0276-7333(97)00484-6 CCC: $14.00 © 1997 American Chemical Society

4738 Organometallics, Vol. 16, No. 21, 1997
Herdtweck et al.
Sch em e 2a
Sch em e 3a
a
Key: (i) 2a : 1a + 2LiPPh2; 2b: 1b + 2LiPPh2; 2c: 1c +
3LiPPh2; 2d : 1a + 4LiPPh2. (ii) 1e + 2LiPPh2. All reactions:
toluene, -78 °C to ambient temperature.
were, thus, interested in derivatives of 2 bearing ethoxy
(R ) R* ) OEt) and pyrrolidine substituents (R ) R* )
pyr) at boron (Scheme 2). These should gradually
increase the electron density at the boron centers and
in turn shift the equilibrium between the ansa-bridged
and the open-chain ferrocene to the right side (II;
Scheme 1).
An attempted synthesis of the ethoxy derivative from
1d and 2 equiv of LiPPh2 yielded a mixture of different
products. Only the unsymmetrically substituted 2c
could be isolated in pure form (Scheme 2). Similar
results were obtained when HPPh2/NEt3 was employed
instead of LiPPh2.
a
Key: (i) 3a : 2a + Lipz, toluene/THF, -78 °C to ambient
temperature; 3b,c: 2a + Lipz*, toluene/diethyl ether, ambient
temperature. (ii) 4a + 2LiPPh2, toluene, 12 h reflux.
ally give single crystals of particular good quality.1 To
gain detailed structural information about the unique
(BNNBP) heterocycle of 3, the reaction was, thus,
repeated using Lipz* instead of the parent Lipz. Two
products 3b and 3c were obtained in a ratio of 2:1, both
of them featuring the aimed-for unsymmetrical inter-
annular bridge. 3b, which bears two different exocyclic
boron substituents, results from the expected elimina-
tion of LiBr, while the minor product 3c is formed by
substitution of PPh2 (Scheme 3). Ferrocenophane 3c
gave crystals suitable for an X-ray crystal structure
investigation. Even with a large excess of the nucleo-
phile (2.5 equiv), the reaction of 3a with Lipz does not
proceed further to the pyrazabole derivative 4b. How-
ever, 4b is accessible in high yield via a different
pathway starting from 4a and 2 equiv of LiPPh2
(Scheme 3).
The yield of 2c could be increased considerably by
reacting 1c, which was prepared in situ from 1a and
one equiv of diethyl ether, with 3 equiv of LiPPh2.
Again, substitution of the ethoxy group for PPh2 took
place to some extent, leading to 2d as a byproduct. The
chemical composition of this material was confirmed by
preparing an authentic sample of 2d from 1a and 4
equiv of LiPPh2. Compared to 2a and 2b, which are
extremely moisture sensitive, 2c is much more stable
and 2d , which bears four sterically demanding PPh2
substituents, may even be handled in air for short
periods of time. X-ray quality crystals of 2d were grown
from toluene/hexane (1:1) at -25 °C. Finally, the
reaction of 1e with 2 equiv of LiPPh2 affords open-chain
2e in good yield.
Treatment of 2a with 1 equiv of lithium pyrazolide
(Lipz) in toluene/THF leads to the displacement of one
µ-PPh2 unit by a pyrazole ring to give the ferro-
cenophane 3a , which is the missing link between
structures I and II (Scheme 1, 3).
In our experience, ferrocenophanes I with bridging
pz* units (pz* ) 4-bromo-3,5-dimethylpyrazolide) usu-
While 2d does not react with γ-picoline, treatment of
the methyl derivative 2b with 2 equiv, 4 equiv, or a large
excess of this base led to slow ferrocenophane degrada-
tion (ambient temperature; toluene). In contrast, when
2a is dissolved in neat γ-picoline, the open-chain species
5a forms almost quantitatively within 30 min. Bromide
substitution takes place in addition to the cleavage of
(6) Paine, R. T.; No¨th, H. Chem. Rev. 1995, 95, 343-379.

Ferrocenophanes with Interannular B-P Bridges
Organometallics, Vol. 16, No. 21, 1997 4739
Sch em e 4a
four-coordinate boron centers.8 The 11B NMR signals
of 2c-e are broad (h1/2 between 250 and 500 Hz), thus
1J (B,P) coupling is not resolved. In the 31P NMR spectra
of 2c and 2d , the resonances for the µ-PPh2 units appear
at δ(31P) ) -14.1 and -4.3, respectively, which is the
region usually observed for dimeric phosphinoboranes.9-15
In both cases, the signals for the exocyclic PPh2 sub-
stituents are found at higher field compared to the
2
bridging phosphorus atoms (2c δ(31P) ) -55.3, J (P,P)
) 35 Hz; 2d δ(31P) ) -57.9, 2J (P,P) ) 31 Hz) with
integral ratios of exo-P:µ-P ) 1:2 and 2:2, respectively.
The 31P NMR spectrum of 2e shows one sharp resonance
at δ(31P) ) -39.8 (h1/2 ) 50 Hz), which is very close to
the value reported for the parent HPPh2 (δ(31P) )
-41.1).16 This again suggests an open-chain configu-
ration of 2e in solution.
Mutual assignments of the 1H and 13C resonance
signals are based on 2D heteronuclear shift correlations.
1
Together with H/1H COSY and NOE difference spectra,
an almost complete assignment of the resonances was
1
achieved. The H NMR signals of 2c-e appear in the
usually observed ranges. The ferrocene backbone of 2c
gives rise to three proton resonances (integral ratio 2:4:
2), whereas only two such signals are present in 2d and
2e. This finding can easily be explained by the reduced
symmetry of 2c, which bears two different substituents
at its bridgehead boron atoms. In the aromatic regions
of their 1H NMR spectra, three sets of signals are
observed for 2c (integral ratio 2:2:2) and 2d (integral
ratio 4:2:2). It may be concluded that in both cases the
exocyclic phenyl rings are magnetically equivalent. In
contrast, those of the bridging PPh2 units have different
chemical environments, because the phosphorus centers
are locked between two boron atoms. The NMR pattern
described is, thus, an important characteristic for the
a
Key: (i) 5a : 2a + excess γ-picoline, ambient temperature;
5b: 5a + excess Cr(CO)5THF, toluene/CH2Cl2/THF, ambient
temperature. (ii) 2a + 2bipy, CH2Cl2, ambient temperature.
two B-P bonds, generating tetracoordinate boronium
cations (Scheme 4).
The presence of three-coordinate phosphorus centers
in 5a was proven by showing their ability to bind
Cr(CO)5 fragments, which afforded the trimetallic com-
plex 5b . The stability of the proposed ferrocenyl-
boronium cations can be expected to increase when each
of the two picoline donors are substituted for one
chelating 2,2′-bipyridine ligand (bipy). We have, there-
fore, investigated the reaction of 2a with 2 equiv of bipy
both in toluene and in CH2Cl2 solution. From toluene,
a deep purple microcrystalline solid gradually precipi-
tated, which was poorly soluble in all common aprotic
solvents. Its 1H NMR data revealed a very complex
mixture of degradation products. In CH2Cl2, the reac-
tion is still rather unselective. Nevertheless, isolation
and characterization of one product (5c) was achieved
(Scheme 4). The chemical composition of the dication
5c was confirmed by a comparison of its NMR reso-
nances with those of an authentic sample prepared from
1a and 2 equiv of bipy.7 The fact that a PPh2 substitu-
ent may be replaced preferentially to Br by the bipy
ligand is reminiscent of the formation of 3c from 2a and
Lipz*.
NMR Sp ect r oscop y. The 11B NMR spectra of 2c
and 2d show resonances in a range characteristic for
tetracoordinate boron nuclei8 (2c, -8.4, 11.2 ppm; 2d ,
-2.4 ppm). The fact that two signals (integral ratio 1:1)
are observed in the case of 2c is in agreement with the
low symmetry of its proposed molecular structure. We
tentatively assign the resonance at -8.4 ppm to the
boron atom bearing an exo-PPh2 substituent, since this
value is closer to the one found for 2d (δ(11B) ) -2.4).
The pyrrolidine derivative 2e features only one signal
at δ(11B) ) 42.9, indicating three-coordinate rather than
1
rigid B2P2 ansa-structures. Consequently, the H NMR
spectrum of 2e features only one set of phenyl reso-
nances, which points toward a largely unrestricted
rotation about the B-P axis and is in agreement with
the proposed open-chain conformation of this compound.
Four different proton signals for the pyrrolidine sub-
stituents of 2e show the B-N rotation to be slow on the
NMR time scale as a result of pronounced N-B π
bonding to the three-coordinate boron nuclei. In the 13
C
NMR spectra of 2c-e, signal patterns very similar to
those discussed for the proton spectra are observed and
the same arguments hold for their interpretation.
The 11B NMR data of all derivatives 3 are symptom-
atic of boron centers coordinated by four substituents
(3a , -2.1 ppm; 3b, -2.3 ppm; 3c, -3.0 ppm).8 Spin-spin
coupling between the 11B and 31P nuclei is not resolved.
Two signals of equal intensity are apparent in the 31P
NMR spectra of 3a (-46.6, 0.9 ppm) and 3b (-43.7, -6.3
ppm), whereas only one resonance is found for 3c (-10.0
(9) No¨th, H. Z. Anorg. Allg. Chem. 1987, 555, 79-84.
(10) Ko¨ster, R.; Seidel, G.; Mu¨ller, G.; Boese, R.; Wrackmeyer, B.
Chem. Ber. 1988, 121, 1381-1392.
(11) Bartlett, R. A.; Dias, H. V. R.; Feng, X.; Power, P. P. J . Am.
Chem. Soc. 1989, 111, 1306-1311.
(12) Karsch, H. H.; Hanika, G.; Huber, B.; Riede, J .; Mu¨ller, G. J .
Organomet. Chem. 1989, 361, C25-C29.
(13) Frankhauser, P.; Driess, M.; Pritzkow, H.; Siebert, W. Chem.
Ber. 1992, 125, 1341-1350.
(14) No¨th, H.; Staude, S.; Thomann, M.; Paine, R. T. Chem. Ber.
1993, 126, 611-618.
(7) Fabrizi de Biani, F.; Gmeinwieser, T.; Herdtweck, E.; J a¨kle, F.;
Laschi, F.; Wagner, M.; Zanello, P. Organometallics, in press.
(8) No¨th, H.; Wrackmeyer, B. Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds. In NMR Basic Principles and Progress;
Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer: Berlin, 1978; Vol. 14.
(15) Groshens, T. J .; Higa, K. T.; Nissan, R.; Butcher, R. J .; Freyer,
A. J . Organometallics 1993, 12, 2904-2910.
(16) Berger, S.; Braun, S.; Kalinowski, H.-O. 31P-NMR-Spektrosko-
pie; G. Thieme Verlag: Stuttgart, New York, 1993.

4740 Organometallics, Vol. 16, No. 21, 1997
Herdtweck et al.
ppm). 31P-31P coupling leads to a doublet structure of
the more shielded 31P NMR signals of 3a and 3b, the
coupling constants being 50 and 40 Hz, respectively.
2J (P,P) coupling is not resolved in the case of the much
broader signals at δ(31P) ) 0.9 (h1/2 ) 300 Hz; 3a ) and
-6.3 (h1/2 ) 300 Hz; 3b). On the basis of their different
line shapes and by comparison with the 31P NMR shifts
of 2d (δ(µ-P) ) -4.3; δ(exo-P) ) -57.9), 3c (δ(µ-P) )
-10.0), and 4b (δ(exo-P) ) -39.3), the signals at higher
field most likely have to be assigned to the exocyclic
PPh2 groups of 3a and 3b whereas the signals at 0.9
ppm and -6.3 ppm correspond to the bridging phos-
1
phorus atoms. The H and 13C NMR spectra of 3a and
3b each reveal eight signals in the ferrocene region and,
thus, indicate that these molecules possess no elements
of symmetry. In contrast, 3c shows only four proton
and four carbon resonances due to a symmetry plane
that runs through the iron atom and is coplanar to the
cyclopentadienyl rings of the ferrocene backbone. The
1H chemical shifts of the ferrocene moieties in 3a -c
noticeably reflect the different nature of the two bridg-
ing units: Protons adjacent to µ-PPh2 are only slightly
more shielded than those of the parent ferrocene (e.g.
3c δ(1H) ) 3.82), which is consistent with the NMR data
of 2a -d . On the other hand, a considerable upfield shift
is observed for protons adjacent to the pyrazolyl frag-
ment (e.g., 3c δ(1H) ) 3.36). This anisotropy effect of
the amine heterocycle has already been shown to be
operative in ferrocenophanes with a pyrazabole bridge
(e. g. 4a ,b).1-3 In all three derivatives 3a -c the phenyl
rings of µ-PPh2 give rise to two sets of resonances both
1
in the H and in the 13C NMR spectra, whereas those
of exo-PPh2 are magnetically equivalent in 3a as well
as in 3b.
The 31P NMR signal of 4b at -39.3 ppm appears in
the same shift range as those of the exocyclic PPh2
substituents in 3a and 3b (-46.6 and -43.7 ppm,
respectively). The NMR spectroscopic data of 4b show
no peculiarities compared to other pyrazabole-bridged
ferrocenophanes1-3 and, thus, deserve no further dis-
cussion.
In the 11B NMR spectrum of 5a , the resonance at 7.3
ppm testifies to the presence of tetracoordinate boron
nuclei.8 Compared to the starting material 2a (δ(11B)
) -5.7),4 the boron signal of the picoline adduct 5a is
shifted to lower field by 13.0 ppm. A similar effect is
observed in the 31P NMR spectra of both compounds (2a ,
-36.4 ppm; 5a , -27.4 ppm). Moreover, the 31P NMR
signal sharpens up upon going from 2a (h1/2 ) 180 Hz)
to 5a (h1/2 ) 50 Hz). In contrast to 2a , the phenyl rings
F igu r e 1. PLATON plot of 2d (hydrogen atoms and
toluene molecules omitted for clarity; thermal ellipsoids at
the 50% probability level).
pic2]Br (Fc ) (C5H5)Fe(C5H4)), which has recently been
described by our group.7
1
of 5a are all magnetically equivalent in the H and 13C
The main difference between the NMR spectra of 5a
and the corresponding trimetallic complex 5b lies in a
46.7 ppm downfield shift of the 31P NMR signal upon
Cr(CO)5 coordination (5a δ(31P) ) -27.4; 5b δ(31P) )
19.3). Moreover, most 31P-13C coupling constants are
significantly smaller in 5b than in the free ligand 5a .
The NMR signal of the equatorial carbonyl groups in
5b is found at δ(13Ceq) ) 217.0 (2J (P,C) ) 7.8 Hz), and
the axial CO ligands resonate at δ(13Cax) ) 225.5.
Molecu la r Str u ctu r es of 2d a n d 3c. 2d crystallizes
from toluene/hexane with 1 equiv of toluene in the
monoclinic space group C2/c (Figure 1). Yellow crystals
of 3c (tetragonal; space group P42/m) were obtained by
layering its toluene solution with hexane. The com-
NMR spectra. From an inspection of the integral ratios
in the proton NMR of 5a , it may be deduced that two
PPh2 moieties and four γ-picoline ligands are present
in the molecule. This is in accord with the proposed
dicationic nature of 5a (Scheme 4). Due to spin-spin
coupling with one 31P nucleus, the signals of Cp-C2,5
(3J (P,C) ) 2.3 Hz) and pic-C2,6 (3J (P,C) ) 7.7 Hz)
appear as doublets in the 13C NMR spectrum. This
finding gives conclusive evidence for the open-chain
structure of 5a , since a triplet splitting is observed for
the resonances of Cp-C2,5 in ansa-2a (3J (P,C) ) 8.0 Hz)
and ansa-2b (3J (P,C) ) 9.0 Hz).4 Moreover, the chemical
shift values of 5a closely resemble those of Fc[B(Me)-

Ferrocenophanes with Interannular B-P Bridges
Organometallics, Vol. 16, No. 21, 1997 4741
interannular B2P2 ring is not planar but adopts a
butterfly conformation. The angle between the two
halves of the ring which meet in the P‚‚‚P line is 43.4°
(2b, 41.6°4); for the two halves meeting in the B‚‚‚B line,
an angle of 46.2° is found (2b, 45.0°4). Most impor-
tantly, the two cyclopentadienyl ligands of 2d deviate
only slightly from the coplanar arrangement found in
the parent ferrocene (C(11)-C(15)//C(21)-C(25) ) 7.8°).
It may, thus, be concluded that the ansa-bridge of 2d
is able to adjust almost perfectly to the steric require-
ments of the sandwich complex (for a more detailed
discussion of ring conformations in dimeric phosphino-
boranes see ref 4 and the literature cited therein). The
electron lone pairs of both pendant PPh2 moieties are
directed away from the ferrocene backbone in order to
minimize steric interactions between the phenyl rings
of exo-PPh2 on one hand and µ-PPh2 on the other. The
bond lengths between the boron centers and the three-
coordinate exo-phosphorus atoms are shorter (B(1)-P(3)
) 1.999(3) Å; B(2)-P(4) ) 2.001(3) Å) than those found
within the bridging B2P2 ring, which involve tetracoor-
dinate phosphorus atoms (B(1)-P(1) ) 2.034(3) Å; B(1)-
P(2) ) 2.033(3) Å; B(2)-P(1) ) 2.028(3) Å; B(2)-P(2) )
2.047(3) Å). Similar mean values of B-P(µ) ) 2.036(3)
Å and B-P(exo) ) 2.000(3) Å and differences ∆ between
B-P(µ) and B-P(exo) (∆ ) 0.036(3) Å) are found in 2d
and in the related unbridged phosphinoborane dimer
[B(PEt2)3]2 (B-P(µ) ) 2.018(6) Å; B-P(exo) ) 1.973(7)
Å); ∆ ) 0.045(7) Å).9,18,19 The sum of angles around P(3)
and P(4) in 2d is 313.8(1)° and 312.6(1)°, respectively.
F igu r e 2. PLATON plot of 3c (hydrogen atoms and
toluene molecules omitted for clarity; thermal ellipsoids at
the 50% probability level).
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for
2d ‚(tolu en e) a n d 3c‚0.5(tolu en e)‚0.25(h exa n e)
compd
formula
2d
3c
C58H48B2FeP4‚
C7H8
C27H24B2Br3FeN2P‚
0.5C7H8‚(0.25C6H14
770.72
)
fw
1038.45
cryst dimens, mm
cryst syst
space group
temp, K
a, Å
0.45 × 0.33 × 0.25 0.43 ×0.25 × 0.13
monoclinic
C2/c (No. 15)
253(2)
tetragonal
P42/m (No. 84)
193(2)
Compound 3c features one PPh2 and one pyrazolyl
unit in the ansa-bridge. The resulting five-membered
heterocycle adopts an envelope conformation with the
phosphorus atom deviating from the plane spanned by
the boron and nitrogen atoms. Again, the Cp rings of
the ferrocene backbone are essentially coplanar. The
bond lengths and angles within the B-(µ-pz)-B frag-
ment of 3c are very similar to those found in the related
pyrazabole-bridged derivative 4c (Table 2).1 In contrast,
the B-P bond lengths are shortened by 0.064 Å (0.060
Å) upon going from 2b (2d ) (B-P(µ) ) 2.040(4) Å
(2.036(3) Å)) to 3c (B(1)-P(1) ) 1.976(7) Å). The phenyl
ring, C(31)-C(36), of 3c is located in the symmetry
plane of the molecule, which results in an energetically
favorable edge-on conformation, both with respect to the
second phenyl ring (C(21)-C(26)) and the pyrazolyl
bridge. This arrangement is not possible in 2b,d due
to the presence of the second sterically demanding PPh2
moiety.
36.522(3)
13.566(1)
22.181(2)
90
15.8389(9)
15.8389(9)
12.6240(6)
90
b, Å
c, Å
R, deg
â, deg
96.133(7)
90
90
90
γ, deg
V, Å3
10926.8(16)
1.262
3167.0(3)
1.617
D
calcd, g cm-3
Z
8
4
F(000)
4336
1524
radiation
no. of total reflns
Mo KR, 0.710 73 Å Mo KR, 0.710 73 Å
61576
14259
no. of unique reflns 9100
2984
no. of obsd reflns
no. of params
µ, cm-1
7558 (I > 2σ(I))
1857 (I > 2σ(I))
685
200
4.3
43.3
a
final R1
0.0566 (all data)
0.1191 (all data)
1.096 (all data)
0.0811 (all data)
0.1483 (all data)
0.963 (all data)
final wR2 b
GOFc
a
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)2]1/2
.
c GOF ) [∑w(Fo - Fc2)2/(NO - NV)]1/2
.
2
Con clu sion
pound crystallizes together with 1 equiv of toluene and
a nonstoichiometric amount of hexane (ca. 0.25 equiv;
Figure 2).
A summary of crystallographic data and selected
geometrical parameters of 2d and 3c is given in Tables
1 and 2. The complete set of structural data is available
on request.17
Three different grades of B-P donor-acceptor bond
stability have to be distinguished in compounds 2. In
the case of derivatives 2a and 2d , the 11B and 31P NMR
resonances show essentially unaltered chemical shift
values in the temperature range between -60 and +100
°C (toluene-d8). Moreover, two (2a ) and three (2d )
magnetically different phenyl rings are always distin-
As already deduced from the NMR data, 2d bears two
ansa-bridging and two exocyclic PPh2 substituents. The
guishable in the variable-temperature H and 13C NMR
1
spectra. Employing the spin saturation transfer
(17) Further details of the crystal structure investigations are
available on request from the Fachinformationszentrum Karlsruhe,
Gesellschaft fu¨r wissenschaftlich-technische Information mbH, D-76344
Eggenstein-Leopoldshafen, Germany, on quoting the depository num-
bers CSD 407667 (2d ), CSD 407668 (3c), the names of the authors,
and the literature citation.
(18) Fritz, G.; Pfannerer, F. Z. Anorg. Allg. Chem. 1970, 373, 30-
35.
(19) Fritz, G.; Sattler, E. Z. Anorg. Allg. Chem. 1975, 413, 193-
228.

4742 Organometallics, Vol. 16, No. 21, 1997
Herdtweck et al.
Ta ble 2. Selected Bon d Len gth s (Å), An gles (d eg), a n d An gles betw een P la n es (d eg) of 2d , 3c, a n d th e
Refer en ce Com p ou n d 4ca
2d
3c
4c
B(1)-P(1)
B(1)-P(2)
B(2)-P(1)
B(2)-P(2)
B(1)-P(3)
B(2)-P(4)
B(1)-C(11)
B(2)-C(21)
2.034(3)
2.033(3)
2.028(3)
2.047(3)
1.999(3)
2.001(3)
1.603(4)
1.597(4)
B(1)-P(1)
1.976(7)
B(1)-Br(1)
B(1)-C(11)
2.040(7)
1.589(9)
B-C(Me)
B-C(Cp)
1.596
1.593
B(1)-N(41)
N(41)-N(41a)
1.574(8)
1.379(7)
B-N(pz)
N-N
1.599
1.379
P(1)-B(1)-P(2)
P(1)-B(2)-P(2)
B(1)-P(1)-B(2)
B(1)-P(2)-B(2)
81.9(1)
81.8(1)
89.4(1)
88.9(1)
B(1)-P(1)-B(1)a
91.0(3)
P(1)-B(1)-N(41)
B(1)-N(41)-N(41)a
95.9(4)
117.3(5)
N-B-N
B-N-N
105.0
121.2
P(1)B(1)P(2)//P(1)B(2)P(2)
B(1)P(1)B(2)//B(1)P(2)B(2)
C(11)-C(15)//C(21)-C(25)
43.4
46.2
7.8
B(1)P(1)B(1)a//B(1)N(41)N(41a)B(1a)
C(11)-C(15)//C(11a)-C(15a)
46.4
4.9
pz//pz′
Cp//Cp′
24.0
4.5
a
Mean values are given for 4c.
method,20-22 which provides a means for studying
moderately rapid exchange phenomena, it has also been
possible to exclude the dynamic behavior of the B-P(µ)
bonds in 2a and 2d on a slower time scale. This leads
to the conclusion that the ansa-bridge of these deriva-
tives remains intact under our experimental conditions.
In contrast, a very fast breaking and re-forming of B-P
bonds is already apparent at ambient temperature in
ansa-2b, even though no detectable stationary concen-
tration of open-chain 2b builds up.4 The different
dynamic behavior of 2a and 2b may be attributed to
the different electronegativities of the Br and CH3
substituents. The presence of electron-withdrawing
bromine atoms in 2a increases the Lewis acidity of the
bridgehead boron centers and in turn strengthens the
interannular B-P bonds.23 One may also anticipate
kinetic hindrance of the B2P2 bridge fluxionality to occur
when sterically demanding groups are attached to the
boron centers, and this factor certainly contributes to
the rigidity of ansa-2d .
apparently not existent. In contrast, the analogous
reaction of 4a with LiPPh2 leads to the incorporation of
PPh2 groups into the exo positions of 4b only. The
pyrazabole unit is fully maintained, and even after
prolonged heating in boiling toluene, no rearrangement
to the respective isomers 3 or 2 is observed. We,
therefore, conclude that the pyrazabole bridge is more
stable than an interannular B2P2 ring. The reaction of
2a with excess Lipz in THF/toluene (-78 °C to ambient
temperature) stops at the stage of 3a . Cleavage of the
residual B-P bonds is apparently hampered by the
presence of one pyrazole unit in the ansa-bridge.
Preliminary studies on the reactivity of compounds 2
toward transition metal Lewis acids reveal that the
chromium center of Cr(CO)5THF is not able to compete
successfully with the boron atoms of 2a , 2b, and 2d for
the bridging phosphorus donors. No indication for ansa-
bridge opening is found upon treatment of these com-
pounds with the Cr(CO)5 fragment, and in the case of
2d , not even the exocyclic PPh2 substituents act as
ligands to the metal atom. However, with the assist-
ance of a γ-picoline donor, ansa-2a is readily trans-
formed into the heterotrimetallic Cr2Fe complex 5b. The
potential of B-P-bridged ferrocenophanes as ligands to
transition metals is the subject of further investigations
in our laboratory.
The pyrrolidine derivative 2e maintains an open-
chain structure even upon cooling to -80 °C (NMR
spectroscopy; toluene-d8). A N-B π interaction obvi-
ously prevents effective attachment of the phosphine
bases to the boron centers and, thus, ansa-bridge
formation, although this would be a favorable intra-
molecular process.
Ferrocenophanes 2 with R ) R* ) OEt (Scheme 2)
have not been synthetically accessible in our hands. An
investigation of the relative energies of O-B π bonding
versus P-B adduct formation is, thus, restricted to 2c,
which bears an OEt substituent at only one of its boron
centers. This compound shows no sign of thermally-
induced ansa-bridge opening up to 100 °C (NMR spec-
troscopy; toluene-d8).
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions and manipulations
of air-sensitive compounds were carried out in dry, oxygen-
free argon using standard Schlenk ware or in an argon-filled
drybox. Solvents were freshly distilled under N2 from Na/K
alloy-benzophenone (toluene, hexane, THF, Et2O) or from
CaH2 (CH2Cl2, CH3CN) prior to use. NMR: J eol J MN-GX 400,
Bruker DPX 400. 11B NMR spectra are reported relative to
external BF3‚Et2O. 31P NMR shift values are given relative
to external H3PO4 (85%). Unless stated otherwise, all NMR
spectra were run at ambient temperature; abbreviations: s )
singlet; d ) doublet; tr ) triplet; vtr ) virtual triplet; q )
quartet; br ) broad; mult ) multiplet; n.r. ) multiplet ex-
pected in the 1H NMR spectrum but not resolved; n.o. ) signal
not observed; Cp ) cyclopentadienyl; bipy ) 2,2′-bipyridine;
pic ) γ-picoline; pz ) pyrazolyl; pz* ) 4-bromo-3,5-dimethyl-
pyrazolyl; the ipso, ortho, meta, and para positions of phenyl
When 2a is treated with Lipz, one bridging PPh2 unit
is displaced by the heterocyclic amine to give 3a .
Derivatives 2 with exocyclic pyrazole substituents are
(20) Forse´n, S.; Hoffman, R. A. J . Chem. Phys. 1963, 39, 2892-2901.
(21) Forse´n, S.; Hoffman, R. A. Acta Chem. Scand. 1963, 17, 1787-
1788.
(22) Forse´n, S.; Hoffman, R. A. J . Chem. Phys. 1964, 40, 1189-1196.
(23) Haaland, A. Angew. Chem. 1989, 101, 1017-1032; Angew.
Chem., Int. Ed. Engl. 1989, 28, 992-1007.

Ferrocenophanes with Interannular B-P Bridges
Organometallics, Vol. 16, No. 21, 1997 4743
3
rings are labeled as subscripts i, o, m, p (µ-PPh central), i′, o′,
m′, p′ (µ-PPh close to ferrocene), and ie, oe, me, pe (exocyclic
PPh2); the cyclopentadienyl, pyrazolyl, and γ-picoline rings are
numbered independently, following the numbering scheme of
the parent heterocycle (see Schemes 3 and 4). Mass spectra
(CI mode): Finnigan MAT 90. Elemental analyses: Micro-
analytical laboratory of the Technische Universita¨t Mu¨nchen.
The compounds 1a -e,3,24 2a ,b,4 and 4a 3 were synthesized
according to literature procedures.
) 7.3 Hz, Hp′), 7.17 (vtr, 4H, J (H,H) ) 7.3 Hz, Hm), 7.25 (tr,
2H, 3J (H,H) ) 7.3 Hz, Hp), 7.35 (vtr, 8H, 3J (H,H) ) 7.3 Hz,
3
H
me), 7.41 (tr, 4H, J (H,H) ) 7.3 Hz, Hpe), 8.02 (br, 8H, Hoe),
8.38 (br, 4H, Ho). 13C NMR (100.6 MHz, CDCl3): δ 70.2 (Cp-
C), 77.8 (tr, J (P,C) ) 8 Hz, Cp-C), 127.0 (vtr, 3J (P,C) ) 5J (P,C)
) 5 Hz, Cm), 127.9 (tr, 5J (P,C) ) 5 Hz, Cme), 128.1 (vtr, 3J (P,C)
) 5J (P,C) ) 5 Hz, Cm′), 128.5 (Cpe), 129.0 (Cp), 129.4 (Cp′), 133.1
1
3
2
(vtr, J (P,C) ) J (P,C) ) 19 Hz, Ci, Ci′), 133.5 (vtr, J (P,C) )
4J (P,C) ) 5 Hz, Co′), 135.3 (vtr, J (P,C) ) 3J (P,C) ) 35 Hz, Ci,
1
Ci′), 135.6 (m, Co), 137.4 (m, Coe), 139.4 (m, Cie), n.o. (Cp-C1).
Anal. Calcd for C58H48B2FeP4 (946.38): C, 73.61; H, 5.11, Fe
5.90, P 13.09. Found: C, 73.23; H, 5.31; Fe, 6.01; P, 12.85.
Syn th esis of 2c. Meth od 1: 1d (0.89 g, 1.95 mmol) in
toluene (30 mL) was added dropwise with stirring to a
suspension of LiPPh2 (0.75 g, 3.90 mmol) in toluene (20 mL)
at -78 °C. After 30 min, the orange-red slurry was allowed
to warm to ambient temperature, stirred for 12 h, and filtered
through a frit (G4). The insoluble precipitate was extracted
with toluene (2 × 10 mL). After all volatiles had been removed
from the combined filtrates under reduced pressure, the
orange-red oily residue was triturated with toluene/hexane (2:
1; 25 mL) to afford 2c as a yellow precipitate. 2c was isolated
by filtration and dried in vacuo. Yield: 0.55 g (35%).
Meth od 2: The ferrocene precursor 1c was prepared in situ
by adding diethyl ether (60 mg, 0.81 mmol) in toluene (10 mL)
at ambient temperature to 1a (0.42 g, 0.80 mmol) in toluene
(20 mL). The solution was stirred for 7 days and evaporated
to dryness under reduced pressure to remove bromoethane.
The remaining 1c was again dissolved in toluene (20 mL),
cooled to -78 °C, and added slowly with stirring to a slurry of
LiPPh2 (0.46 g, 2.39 mmol) in toluene (20 mL, -78 °C).
Further workup follows the procedure outlined above (method
1); the crude product was contaminated with 2d (15%). Pure
2c was obtained after recrystallization from toluene/hexane
(2:1) at -25 °C. Yield: 0.35 g (54%).
Syn th esis of 2e. 1e (0.74 g, 1.46 mmol) in toluene (10 mL)
was added slowly with stirring to a slurry of LiPPh2 (0.59 g,
3.07 mmol) in toluene (30 mL) at -78 °C. After 30 min, the
orange mixture was allowed to warm to ambient temperature
and stirred for 12 h. Insoluble LiBr was collected on a frit
(G4) and extracted with toluene (2 × 10 mL). From the
combined filtrates, the solvent was driven off under reduced
pressure. Trituration of the orange oily residue with hexane
(20 mL) afforded 2e as a yellow solid. The crude product was
isolated by filtration and recrystallized from toluene/hexane
(1:10). Yield: 0.75 g (72%).
11B NMR (128.3 MHz, CDCl3): δ 42.9 (h1/2 ) 250 Hz). 31P
NMR (161.9 MHz, CDCl3): δ -39.8 (h1/2 ) 50 Hz). 1H NMR
(400 MHz, CDCl3): δ 1.65, 1.77 (2 × m, 2 × 4H, NCH2CH2),
3.24, 3.64 (2 × tr, 2 × 4H, 3J (H,H) ) 7.0 Hz, NCH2CH2), 3.94,
4
4.05 (2 × vtr, 2 × 4H, 3J (H,H) ) J (H,H) ) 1.7 Hz, Cp-H),
7.19-7.24 (m, 12H, Hm, Hp), 7.36 (m, 8H, Ho). 13C NMR (100.6
MHz, CDCl3): δ 25.8, 26.5 (2 × d, 4J (P,C) ) 4 Hz, 6 Hz,
NCH2CH2), 50.9, 51.5 (2 × d, 3J (P,C) ) 4 Hz, 17 Hz, NCH2-
CH2), 71.8 (Cp-C), 75.8 (d, J (P,C) ) 5 Hz, Cp-C), 127.0 (Cp),
11B NMR (128.3 MHz, CDCl3): δ -8.4 (h1/2 ) 300 Hz, BP-
(exo)), 11.2 (h1/2 ) 400 Hz, BO). 31P NMR (161.9 MHz,
CDCl3): δ -55.3 (h1/2 ) 150 Hz, tr, 1P, 2J (P,P) ) 35 Hz, P(exo)),
-14.1 (h1/2 ) 200 Hz, 2P, P(µ)). 1H NMR (400 MHz, CDCl3):
δ 1.39 (tr, 3H, 3J (H,H) ) 6.7 Hz, OCH2CH3), 3.73 (n.r., 2H,
3
2
128.2 (d, J (P,C) ) 7 Hz, Cm), 134.5 (d, J (P,C) ) 17 Hz, Co),
138.1 (d, 1J (P,C) ) 8 Hz, Ci), n.o. (Cp-C1). Anal. Calcd for
42H44B2FeN2P2 (716.24): C, 70.43; H, 6.19; N, 3.91. Found:
C
C, 70.11; H, 6.22; N, 3.78.
Syn th esis of 3a . A cooled solution (-20 °C) of 2a ‚1toluene
(0.25 g, 0.30 mmol) in toluene (25 mL) was added dropwise
with stirring to a cold solution (-78 °C) of Lipz (0.03 g, 0.41
mmol) in toluene/THF (1:1; 10 mL). The mixture was slowly
warmed to ambient temperature, stirred for 12 h, and evapo-
rated to dryness under reduced pressure. The yellow residue
was washed with hexane (10 mL) and taken up in toluene (20
mL). Insoluble material was removed by filtration and the
filtrate evaporated in vacuo. Recrystallization of the residue
from toluene/hexane (1:1) afforded 3a ‚1toluene (NMR spec-
troscopy; elemental analysis) as a yellow microcrystalline solid.
Yield: 0.19 g (77%). The same product was obtained upon
reaction of 2a ‚1toluene with 2.5 equiv of Lipz.
3
Cp-H), 3.94 (q, 2H, J (H,H) ) 6.7 Hz, OCH2CH3), 3.95, 4.06
(2 × n.r., 4H, 2H, Cp-H), 6.91 (vtr, 4H, 3J (H,H) ) 7.3 Hz,
Hm), 6.99 (m, 10H, Ho′, Hm′, Hp), 7.17 (m, 2H, Hp′), 7.32 (vtr,
4H, 3J (H,H) ) 7.3 Hz, Hme), 7.38 (tr, 2H, 3J (H,H) ) 7.3 Hz,
H
pe), 8.00 (m, 4H, Hoe), 8.06 (br, 4H, Ho). 13C NMR (100.6 MHz,
CDCl3): δ 18.0 (OCH2CH3), 61.8 (br, OCH2CH3), 70.2, 70.9
(Cp-C), 76.3 (tr, J (P,C) ) 8 Hz, Cp-C), 77.0 (n.r., Cp-C),
127.0 (br, Cm, Cp), 127.9 (d, 3J (P,C) ) 8 Hz, Cme), 128.4 (br,
2
C
m′, Cpe), 129.3 (br, Cp′), 133.5 (br, Co′), 134.5 (d, J (P,C) ) 17
2
Hz, Co), 137.3 (d, J (P,C) ) 22 Hz, Coe), n.o. (Cp-C1, Cp-C1′,
Ci, Ci′,Cie). MS (CI): m/ z 807 (7, MH-), 729 (10, M- - Ph),
699 (20, MH- - PPh). Anal. Calcd for C48H43B2FeOP3
(806.26): C, 71.51; H, 5.38; P, 11.53. Found: C, 71.38; H, 5.68;
P, 11.13.
11B NMR (128.3 MHz, CDCl3): δ -2.1 (h1/2 ) 500 Hz). 31P
NMR (161.9 MHz, CDCl3): δ -46.6 (d, 2J (P,P) ) 50 Hz, P(exo)),
0.9 (h1/2 ) 300 Hz, P(µ)). 1H NMR (400 MHz, CDCl3): δ 3.11
(m, 1H, Cp-H2′), 3.41 (m, 1H, Cp-H2), 3.44 (m, 1H, Cp-H5),
3.79 (m, 1H, Cp-H5′), 3.92 (m, 1H, Cp-H4), 4.00 (m, 1H, Cp-
H3′), 4.03 (m, 1H, Cp-H3), 4.09 (m, 1H, Cp-H4′), 6.39 (m, 2H,
Ho), 6.61 (m, 1H, pz-H4), 7.07 (vtr, 4H, 3J (H,H) ) 7.3 Hz, Hme),
7.10-7.30 (m, 6H, Hpe, Hm, Ho′), 7.31 (tr, 1H, 3J (H,H) ) 7.3
Hz, Hp), 7.37 (m, 2H, Hm′), 7.44 (m, 4H, Hoe), 7.58 (tr, 1H,
Syn th esis of 2d . 1a (1.05 g, 2.00 mmol) in toluene (20 mL)
was added dropwise with stirring to a slurry of LiPPh2 (1.73
g, 9.00 mmol) in toluene (80 mL) at -78 °C. After 30 min,
the resulting reddish-brown mixture was allowed to warm to
ambient temperature and stirred for 12 h. Insoluble LiBr was
collected on a frit (G4) and extracted with toluene (2 × 10 mL).
The combined filtrates were concentrated to a volume of 15
mL and kept at -25 °C for several days, whereupon yellow
microcrystalline 2d gradually precipitated. After filtration,
2d was washed with cold toluene (10 mL, -78 °C) and dried
in vacuo (24 h, 50 °C). Yield: 1.64 g (87%). X-ray quality
crystals of 2d ‚1toluene were obtained from toluene/hexane (1:
1) at -25 °C.
3
3J (H,H) ) 7.3 Hz, Hp′), 7.63, 8.33 (2 × d, 2 × 1H, J (H,H) )
1.8 Hz, pz-H3, pz-H5). 13C NMR (100.6 MHz, CDCl3): δ 69.2
4
4
(d, J (P,C) ) 1 Hz, Cp-C3′), 70.5 (d, J (P,C) ) 1 Hz, Cp-C3),
3
71.1 (Cp-C4′), 71.3 (Cp-C4), 71.4 (d, J (P,C) ) 8 Hz, Cp-C2),
73.0 (d, 3J (P,C) ) 9 Hz, Cp-C2′), 73.3 (Cp-C5), 75.0 (Cp-C5′),
108.2 (d, 4J (P,C) ) 4 Hz, pz-C4), 127.5-128.0 (m, Cpe, Cme),
128.3, 128.8 (2 × d, 3J (P,C) ) 11 Hz, Cm, Cm′), 130.1 (d, 4J (P,C)
11B NMR (128.3 MHz, CDCl3): δ -2.4 (h1/2 ) 500 Hz). 31P
NMR (161.9 MHz, CDCl3): δ -57.9 (tr, 2J (P,P) ) 31 Hz,
P(exo)), -4.3 (n.r., h1/2 ) 100 Hz, P(µ)). 1H NMR (400 MHz,
CDCl3): δ 3.73, 4.10 (2 × n.r., 2 × 4H, Cp-H), 6.13 (m, 4H,
Ho′), 6.70 (vtr, 4H, 3J (H,H) ) 7.3 Hz, Hm′), 7.07 (tr, 2H, 3J (H,H)
4
2
) 1 Hz, Cp), 132.1 (d, J (P,C) ) 1 Hz, Cp′), 132.6 (d, J (P,C) )
2
3
6 Hz, Co), 135.3 (d, J (P,C) ) 20 Hz, Co′), 136.0 (d, J (P,C) ) 8
Hz, pz-C3, pz-C5), 136.3 (d, J (P,C) ) 20 Hz, Coe), 136.7 (br,
2
pz-C3, pz-C5), n.o. (Cp-C1, Cp-C1′, Ci, Ci′, Cie). Anal. Calcd
for C37H31B2BrFeN2P2‚1.0 C7H8 (815.13): C, 64.83; H, 4.82; N,
3.44. Found: C, 65.13; H, 5.03; N, 3.72.
(24) Ruf, W.; Renk, T.; Siebert, W. Z. Naturforsch. 1976, 31b, 1028-
1034.

4744 Organometallics, Vol. 16, No. 21, 1997
Herdtweck et al.
2
1
Syn th esis of 3b a n d 3c. 2a ‚1toluene (0.39 g, 0.47 mmol)
in toluene (30 mL) was added dropwise with stirring at
ambient temperature to a slurry of Lipz* (0.10 g, 0.55 mmol)
in diethyl ether (20 mL). The resulting yellow solution was
stirred for 12 h and evaporated to dryness. The yellow oil
obtained was treated with hexane (10 mL), whereupon it
solidified. The precipitate was extracted with toluene (20 mL),
and the volatiles were removed from the filtrate under reduced
pressure. Recrystallization of the solid residue from toluene/
hexane (1:1) at -20 °C gave yellow X-ray quality crystals of
3c‚0.5toluene‚0.25 hexane Yield: 0.10 g (27%). The mother
liquor was layered with half its volume of hexane and kept at
-20 °C to afford 3b‚1toluene as a microcrystalline yellow solid.
Yield: 0.21 g (48%).
Hz, Cm), 133.7 (d, J (P,C) ) 15 Hz, Co), 137.2 (d, J (P,C) ) 14
3
Hz, Ci), 137.6 (d, J (P,C) ) 15 Hz, pz-C3, pz-C5), n.o. (Cp-
C1, Cp-C1′). MS (CI): m/ z 526 (100, M+ - PPh2). Anal.
Calcd for C40H34B2FeN4P2 (710.15): C, 67.65; H, 4.83; N, 7.89;
P, 8.72. Found: C, 68.06; H, 4.88; N, 7.62; P, 8.38.
Syn t h esis of 5a . γ-Picoline (5 mL) was added to 2a ‚
1toluene (1.66 g, 2.00 mmol) at ambient temperature with
stirring. A clear red solution was obtained within 30 min, from
which a yellow microcrystalline solid gradually precipitated
over a period of several hours. The slurry was diluted with
toluene (20 mL), and all of the insoluble material was collected
on a frit, treated subsequently with toluene (2 × 20 mL) and
hexane (2 × 20 mL), and dried in vacuo. 5a ‚1toluene was
obtained in a yield of 2.09 g (87%).
3b: 11B NMR (128.3 MHz, CDCl3): δ -2.3 (h1/2 ) 400 Hz).
31P NMR (161.9 MHz, CDCl3): δ -43.7 (d, 2J (P,P) ) 40 Hz,
P(exo)), -6.3 (h1/2 ) 300 Hz, P(µ)). 1H NMR (400 MHz,
CDCl3): δ 2.18, 2.83 (2 × s, 2 × 3H, CH3), 3.02 (m, 1H, Cp-
H2′), 3.37 (m, 1H, Cp-H2), 3.46 (m, 1H, Cp-H5), 3.81 (m, 1H,
Cp-H5′), 3.92 (m, 1H, Cp-H4), 4.02, 4.04 (2 × m, 2 × 1H, Cp-
H3, Cp-H3′), 4.12 (m, 1H, Cp-H4′), 6.99 (vtr, 4H, 3J (H,H) )
7.3 Hz, Hme), 7.08 (m, 2H, Hpe), 7.15-7.35 (m, 9H, Ho, Hm, Hp,
Ho′, Hm′), 7.44 (m, 4H, Hoe), 7.61 (tr, 1H, 3J (H,H) ) 7.3 Hz,
Hp′). 13C NMR (100.6 MHz, CDCl3): δ 13.7 (d, 4J (P,C) ) 10
Hz, CH3) 14.6 (CH3), 69.7 (d, 4J (P,C) ) 2 Hz, Cp-C3′), 70.5
11B NMR (128.3 MHz, CDCl3): δ 7.3 (h1/2 ) 500 Hz). 31P
NMR (161.9 MHz, CDCl3): δ -27.4 (h1/2 ) 50 Hz). 1H NMR
(400 MHz, CDCl3): δ 2.67 (s, 12H, CH3), 3.23, 4.20 (2 × n.r.,
3
2 × 4H, Cp-H), 6.90 (vtr, 8H, 3J (H,H) ) J (H,P) ) 7.3 Hz,
Ho), 7.16 (vtr, 8H, 3J (H,H) ) 7.3 Hz, Hm), 7.28 (tr, 4H, 3J (H,H)
3
) 7.3 Hz, Hp), 7.72 (d, 8H, J (H,H) ) 5.8 Hz, pic-H3,5), 8.52
(d, 8H, 3J (H,H) ) 5.8 Hz, pic-H2,6). 13C NMR (100.6 MHz,
CDCl3): δ 21.7 (CH3), 72.0 (d, 3J (P,C) ) 2.3 Hz, Cp-C2,5), 73.3
(Cp-C3,4), 80.8 (br, Cp-C1), 127.5 (pic-C3,5), 127.8 (Cp), 128.1
(d, 3J (P,C) ) 7.7 Hz, Cm), 133.5 (d, 2J (P,C) ) 17.7 Hz, Co), 135.1
(d, 1J (P,C) ) 13.1 Hz, Ci), 144.8 (d, 3J (P,C) ) 7.7 Hz, pic-
3
(Cp-C3), 71.4 (d, J (P,C) ) 7 Hz, Cp-C2, Cp-C2′), 71.5, 71.5
C
2,6), 157.5 (pic-C4). Anal. Calcd for C58H56B2Br2FeN4P2‚C7H8
(Cp-C4, Cp-C4′), 71.7 (d, 3J (P,C) ) 9 Hz, Cp-C2, Cp-C2′),
(1200.48): C, 65.03; H, 5.37; N, 4.67; Br, 13.31. Found: C,
64.74; H, 5.40; N, 4.93; Br, 13.09.
4
73.3, 74.0 (Cp-C5, Cp-C5′), 99.8 (d, J (P,C) ) 6 Hz, pz-C4),
3
3
127.8 (d, J (P,C) ) 7 Hz, Cme), 128.2 (d, J (P,C) ) 10 Hz, Cm,
Syn th esis of 5b. 5a ‚1toluene (0.24 g, 0.20 mmol) was
dissolved in toluene/CH2Cl2 (1:1; 20 mL), and 28 mL (1.29
mmol) of a freshly prepared and calibrated solution of Cr(CO)5-
(THF) in THF was added at ambient temperature. The
mixture was stirred for 24 h, and the solvents were removed
under reduced pressure. Trituration of the yellow crude
product with toluene (2 × 10 mL) and hexane (2 × 10 mL)
afforded 5b as a yellow microcrystalline solid. Yield: 0.24 g
(80%).
3
C
m′), 128.5 (Cpe), 128.7 (d, J (P,C) ) 10 Hz, Cm, Cm′), 130.3 (d,
4J (P,C) ) 3 Hz, Cp), 132.1 (d, 4J (P,C) ) 3 Hz, Cp′), 133.1 (d,
2J (P,C) ) 6 Hz, Co), 134.0 (d, J (P,C) ) 16 Hz, Co′), 136.1 (m,
2
Coe), 146.7 (d, 3J (P,C) ) 8 Hz, pz-C3, pz-C5), 147.1 (d, 3J (P,C)
) 7 Hz, pz-C3, pz-C5), n.o. (Cp-C1, Cp-C1′, Ci, Ci′, Cie). Anal.
Calcd for C39H34B2Br2FeN2P2‚C7H8 (922.08): C, 59.92; H, 4.59;
N, 3.04. Found: C, 60.21; H, 4.50; N, 3.22.
3c: 11B NMR (128.3 MHz, CDCl3) δ -3.0 (h1/2 ) 400 Hz).
31P NMR (161.9 MHz, CDCl3): δ -10.0 (h1/2 ) 350 Hz). 1H
NMR (400 MHz, CDCl3): δ 2.76 (s, 6H, CH3), 3.36 (n.r., 2H,
Cp-H2, Cp-H2′), 3.82 (n.r., 2H, Cp-H5, Cp-H5′), 4.01 (n.r.,
2H, Cp-H4, Cp-H4′), 4.07 (n.r., 2H, Cp-H3, Cp-H3′), 6.73 (m,
2H, Ho), 7.27 (vtr, 2H, 3J (H,H) ) 7.4 Hz, Hm), 7.36 (tr, 1H,
11B NMR (128.3 MHz, CD2Cl2): δ 8.4 (h1/2 ) 500 Hz). 31P
NMR (161.9 MHz, CD2Cl2): δ 19.3 (h1/2 ) 80 Hz). 1H NMR
(400 MHz, CD2Cl2): δ 2.73 (s, 12H, CH3), 3.52, 3.78 (2 × br, 2
3
× 4H, Cp-H), 7.13 (br, 8H, Ho), 7.25 (vtr, 8H, J (H,H) ) 7.3
Hz, Hm), 7.41 (tr, 4H, 3J (H,H) ) 7.3 Hz, Hp), 7.78 (br, 8H, pic-
3
3J (H,H) ) 7.4 Hz, Hp), 7.69 (vtr, 2H, J (H,H) ) 7.4 Hz, Hm′),
H
3,5), 8.53 (br, 8H, pic-H2,6). 13C NMR (100.6 MHz, CD2Cl2):
7.77 (tr, 1H, 3J (H,H) ) 7.4 Hz, Hp′), 8.40 (m, 2H, Ho′). 13C NMR
(100.6 MHz, CDCl3): δ 13.9 (CH3), 70.4 (Cp-C3, Cp-C3′), 71.3
(d, 3J (P,C) ) 8 Hz, Cp-C2, Cp-C2′), 72.0 (Cp-C4, Cp-C4′), 73.4
δ 26.0 (CH3), 68.1, 73.0 (Cp-C), 128.7 (pic-C3,5), 129.0 (d,
3J (P,C) ) 7.8 Hz, Cm), 130.3 (Cp), 134.6 (d, J (P,C) ) 8.7 Hz,
2
Co), 146.2 (pic-C2,6), 160.5 (pic-C4), 217.0 (d, 2J (P,C) ) 7.8
Hz, COeq), 225.5 (COax), n.o. (Cp-C1, Ci). Mw for C68H56B2-
Br2Cr2FeN4O10P2: 1492.44.
4
(Cp-C5, Cp-C5′), 100.3 (d, J (P,C) ) 7 Hz, pz-C4), 128.5 (d,
3J (P,C) ) 10 Hz, Cm), 129.3 (d, 3J (P,C) ) 11 Hz, Cm′), 130.3 (d,
4J (P,C) ) 3 Hz, Cp), 132.4 (d, 2J (P,C) ) 7 Hz, Co), 133.1 (d,
4J (P,C) ) 2 Hz, Cp′), 135.6 (d, 2J (P,C) ) 7 Hz, Co′), 147.1 (d,
3J (P,C) ) 8 Hz, pz-C3, pz-C5), n.o. (Cp-C1, Cp-C1′, Ci, Ci′).
MS (CI): m/ z 722 (100, M+), 537 (74, M+ - PPh2). Anal.
Calcd for C27H24B2Br3FeN2P‚0.5 C7H8‚0.25C6H14 (792.28): C,
48.51; H, 3.98; N, 3.54. Found: C, 48.34; H, 3.99; N, 3.61.
Syn th esis of 4b. 4a (0.31 g, 0.62 mmol) in toluene (40 mL)
was added at ambient temperature with stirring to a slurry
of LiPPh2 (0.26 g, 1.35 mmol) in toluene (10 mL). The mixture
was refluxed for 12 h to afford a yellow solution and a white
precipitate, which was removed by filtration. The filtrate was
evaporated under reduced pressure, and the yellow solid
residue was washed with hexane (10 mL). Recrystallization
of the crude product from toluene/hexane (1:7) gave yellow
crystals of 4b. Yield: 0.36 g (82 %).
Cr ysta l Str u ctu r e Deter m in a tion of 2d (tolu en e).17
A
yellow crystal of 2d ‚toluene was selected in a perfluorinated
oil and mounted in a glass capillary on an image plate
diffraction system (IPDS, STOE). Final lattice parameters
were obtained by least-squares refinement of 1935 reflections
(graphite monochromator, λ ) 0.710 73 Å, MoKR). Empirical
formula C58H48B2FeP4‚C7H8, fw ) 1038.45, monoclinic system,
space group C2/c (No. 15); a ) 36.522(3) Å, b ) 13.566(1) Å, c
) 22.181(2) Å, â ) 96.133(7)°, V ) 10926.8(16) Å3, crystal size
0.45 × 0.33 × 0.25 mm, Dcalcd ) 1.262 g cm-3, Z ) 8, F(000) )
4336. Data were collected at 253 ( 2 K, distance from crystal
to image plate 75 mm (2.3° < θ < 24.7°), 270 images collected,
0° < æ < 270°, ∆æ ) 1°, exposure time 2.5 min. Data were
corrected for Lorentz and polarization effects.25 A decay and
absorption correction (µ ) 4.3 cm-1) was performed using the
program DECAY;25 61 576 data were measured, and 9100
independent reflections were used for refinement. The struc-
ture was solved by direct methods and refined with standard
difference Fourier techniques. All hydrogen atoms of 2d were
calculated in ideal positions (riding model); hydrogen atoms
of the disordered toluene molecules were not considered.
11B NMR (128.3 MHz, CDCl3): δ 0.7 (h1/2 ) 300 Hz). 31P
NMR (161.9 MHz, CDCl3): δ -39.3 (h1/2 ) 40 Hz). 1H NMR
(400 MHz, C6D6): δ 3.21 (vtr, 4H, 3J (H,H) ) 4J (H,H) ) 1.7
3
4
Hz, Cp-H2, Cp-H5), 4.04 (vtr, 4H, J (H,H) ) J (H,H) ) 1.7
3
Hz, Cp-H3, Cp-H4), 5.51 (tr, 2H, J (H,H) ) 1.8 Hz, pz-H4),
7.00 (tr, 4H, 3J (H,H) ) 7.3 Hz, Hp), 7.08 (m, 8H, Hm), 7.39 (m,
8H, Ho), 8.07 (d, 4H, 3J (H,H) ) 1.8 Hz, pz-H3, pz-H5). 13C
NMR (100.6 MHz, C6D6): δ 70.5 (Cp-C3, Cp-C4), 72.0 (Cp-
C2, Cp-C5), 106.2 (pz-C4), 127.0 (Cp), 128.4 (d, 3J (P,C) ) 6
(25) IPDS Operating System Version 2.6.; STOE&CIE; GmbH:
Darmstadt, Germany, 1995.

Ferrocenophanes with Interannular B-P Bridges
Organometallics, Vol. 16, No. 21, 1997 4745
Number of parameters refined: 685, 13.3 data per parameter,
correction (µ ) 43.3 cm-1) was performed using the program
DECAY;25 14 259 data were measured, and 2984 independent
reflections were used for refinement. The structure was solved
by direct methods and refined with standard difference Fourier
techniques. All hydrogen atoms of 3c and toluene were
calculated in ideal positions (riding model). The gross struc-
ture and location of the disordered hexane molecules were
confirmed. Further refinement to any satisfactory level was
not possible. We have, therefore, applied the “squeeze”
routine32 (ca. 15 e- suppressed) to cure this disordered solvent
problem. Number of parameters refined: 200, 14.9 data per
parameter, weighting scheme w ) 1/[σ2(Fo2) + (0.0873P)2],
weighting scheme w ) 1/[σ2(Fo2) + (0.0703P)2 + 10.5115P],
2
where P ) (Fo + 2Fc2)/3, shift/error < 0.001 in the last cycle
of refinement, residual electron density +0.92 e Å-3, -0.22 e
Å-3, R1 ) 0.0566 (all data), wR2 ) 0.1191 (all data), minimized
2
function was Σw(Fo - Fc2)2. Neutral atom scattering factors
for all atoms and anomalous dispersion corrections for the non-
hydrogen atoms were taken from the International Tables for
X-Ray Crystallography.26 All calculations were performed on
a DEC 3000 AXP workstation with the STRUX-V system,27
including the programs PLATON-92,28 PLUTON-92,28 SHELXS-
86,29 SIR-92,30 and SHELXL-93.31
2
where P ) (Fo + 2Fc2)/3, shift/error < 0.001 in the last cycle
Cr ysta l Str u ctu r e Deter m in a tion of 3c‚0.5(tolu en e)‚
0.25(h exa n e).17 A yellow crystal of 3c‚0.5toluene‚0.25 hexane
was selected in a perfluorinated oil and mounted in a glass
capillary on an image plate diffraction system (IPDS, STOE).
Final lattice parameters were obtained by least-squares
refinement of 1975 reflections (graphite monochromator, λ )
0.710 73 Å, MoKR). Empirical formula C27H24B2Br3FeN2P‚0.5
C7H8‚0.25C6H14, fw ) 770.72 + 0.25C6H14, tetragonal system,
space group P42/m (No. 84); a ) 15.8389(9) Å, b ) 15.8389(9)
Å, c ) 12.6240(6) Å, V ) 3167.0(3) Å3, crystal size 0.43 × 0.25
× 0.13 mm, Dcalcd ) 1.617 g cm-3, Z ) 4, F(000) ) 1524. Data
were collected at 193 ( 2 K, distance from crystal to image
plate 70 mm (2.1° < θ < 25.6°), 120 images collected, 0° < æ
< 120°, ∆æ ) 1°, exposure time 1 min. Data were corrected
for Lorentz and polarization terms.25 A decay and absorption
of refinement, residual electron density +1.57 e Å-3, -1.33 e
Å-3, R1 ) 0.0811 (all data), wR2 ) 0.1483 (all data), minimized
2
function was Σw(Fo - Fc2)2. Neutral atom scattering factors
for all atoms and anomalous dispersion corrections for the non-
hydrogen atoms were taken from the International Tables for
X-Ray Crystallography.26 All calculations were performed on
a DEC 3000 AXP workstation with the STRUX-V system,27
including the programs PLATON-92,28 PLUTON-92,28 SHELXS-
86,29 SIR-92,30 and SHELXL-93.31
Ack n ow led gm en t. We are grateful to Prof. Dr. W.
A. Herrmann (Technische Universita¨t Mu¨nchen) for his
generous support and to the “Deutsche Forschungsge-
meinschaft” and the “Fonds der Chemischen Industrie”
for financial funding.
(26) International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C, Tables 4.2.4.2, 4.2.6.8, 6.1.1.4, pp 193-199, 219-222, 500-502.
(27) Artus, G.; Scherer, W.; Priermeier, T.; Herdtweck, E. STRUX-
V, A Program System to Handle X-ray Data; TU Mu¨nchen: Mu¨nchen,
Germany, 1994.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
parameters, atomic coordinates and thermal parameters, and
bond distances and angles for 2d and 3c (18 pages). Ordering
information is given on any current masthead page.
(28) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
OM970484G
(29) Sheldrick, G. M. SHELXS-86: Program for Crystal Structure
Solutions; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1986.
(30) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. SIR-92; University of Bari: Italy.
(31) Sheldrick, G. M. J . Appl. Crystallogr., in press.
(32) Spek, A. SQUEEZE. An effective cure for the disordered solvent
syndrome in crystal structure refinement. ACA-94; Atlanta, GA, 1994;
Abstract M05, p 66.