Contribution to the chemistry of boron, 245: Deprotonation of B,B'-Di- tert-butyl-b,b'-difluorenyldiborane(4) and the structure of the Di-tert- butyl-difluorenylidenediborate(2-) anion

Article abstract of DOI:10.1002/1099-0682(200007)2000:7<1571::AID-EJIC1571>3.0.CO;2-4

In contrast to the deprotonation of the diorganyl(fluorenyl)boranes tBu₂B(fl-H) and Me₂B(fl-H), which cannot be achieved uniformly, the deprotonation of B₂(tBu)₂(fl-H)₂ in THF proceeds smoothly to give the anion B₂(tBu)₂(fl)₂^2-. The isolated salts have been identified as [Na(thf)(n)]₂[B₂tBu₂(fl)₂] and [Na(thf)(OEt₂){Na(OEt₂)₂}][B₂tBu₂(fl)₂]. The X-ray structure of the latter compound reveals a longer B-B bond [1.744(9) A] than that in the parent compound B₂(tBu₂)(fl-H)₂ [1.687(7) A]. One sodium center is coordinated to the five-membered ring of one fluorenylidene substituent, while the other is coordinated to three C atoms of one of the six-membered rings. This results in a rather asymmetric structure. Each sodium center is also coordinated by two ether ligands.

Full text of DOI:10.1002/1099-0682(200007)2000:7<1571::AID-EJIC1571>3.0.CO;2-4

FULL PAPER
Contribution to the Chemistry of Boron, 245[‡]
Deprotonation of B,BЈ-Di-tert-butyl-B,BЈ-difluorenyldiborane(4) and the
Structure of the Di-tert-butyl-difluorenylidenediborate(2؊) Anion
Ralf Littger,[a] Heinrich Nöth*[a] and Max Suter[a]
Dedicated to Prof. Dr. D. Walther on the occasion of his 60th birthday
Keywords: Boranes / Borates / Deprotonation / Anions / Alkali metals
˚
[1.744(9) A] than that in the parent compound B2(tBu2)(fl-H)2
In contrast to the deprotonation of the diorganyl(fluorenyl)-
boranes tBu2B(fl-H) and Me2B(fl-H), which cannot be [1.687(7) A]. One sodium center is coordinated to the five-
˚
achieved uniformly, the deprotonation of B2(tBu)2(fl-H)2 in
THF proceeds smoothly to give the anion B2(tBu)2(fl)22−. The
isolated salts have been identified as [Na(thf)n]2[B2tBu2(fl)2]
and [Na(thf)(OEt2){Na(OEt2)2}][B2tBu2(fl)2]. The X-ray struc-
ture of the latter compound reveals a longer B−B bond
membered ring of one fluorenylidene substituent, while the
other is coordinated to three C atoms of one of the six-mem-
bered rings. This results in a rather asymmetric structure.
Each sodium center is also coordinated by two ether ligands.
Introduction
ison purposes, we have also investigated the deprotonation
of some related monoboranes, specifically fluorenyldime-
thylborane, Me2B(fl-H), and di-tert-butyl-fluorenylborane,
tBu2B(fl-H).
We have recently reported on the synthesis, molecular
structures,[2] and synthetic potential[3] of the alkali and al-
kaline earth metal salts of bis(dimethylamino)difluorenyldi-
borane(4),[4] (Me2N)2B2(fl-H)2 (fl-H ϭ fluorenyl ϭ C13H9).
A common feature of these compounds is a bent metallo-
cene-type structure, in which the metal cations (Li, K, or
Ca) are complexed by the two fluorenylidene ligands of the
[(Me2N)2B2(fl)2]2Ϫ unit. The two fluorenylidene ligands are
connected by a diborane(4)-ansa-bridge. The boron centers
of (Me2N)2B2(fl-H)2 are shielded electronically by NϪB π-
bonding. Thus, in the dianion [(Me2N)2B2(fl)2]2Ϫ, the lone
pairs on the dimethylamino groups and the π-systems of
the deprotonated fluorenyl substituents compete for the va-
cant pz orbitals at the boron centers. The π-interactions of
the fluorenylidene substituents with the boron centers are,
however, reduced by the complexation of the countercat-
ions, resulting in larger angles between the planes at the
boron atoms and the planes of the fluorenylidene substitu-
ents than one might observe in the free dianions. Our inter-
est has now been drawn to how substitution of the di-
methylamino groups of [(Me2N)2B2(fl)2]2Ϫ by non-π-donor
ligands affects the degree of π-interaction between the an-
ionic fluorenyl groups and the boron centers and how this
influences the ligand capacity of the [R2B2(fl)2]2Ϫ unit (R ϭ
organyl group). To answer these questions, we have synthe-
sized di-tert-butyl-difluorenyldiborane(4), (tBu)2B2(fl-H)2,
and have studied its deprotonation by sodium. For compar-
Synthesis
In order to obtain a stable difluorenyl-diorganyldibor-
ane(4), we decided to replace the dimethylamino groups of
(Me2N)2B2(fl-H)2 (1-H2) by tert-butyl groups. This group is
known[5,6] to be sufficiently bulky to prevent redox dispro-
portionation, which occurs in diborane(4) compounds that
lack adequate electronic shielding. Indeed, di-tert-butyl-di-
fluorenyldiborane(4) (2-H2) could be readily prepared by
the stepwise substitution of the bromine atoms of dibromo-
di-tert-butyldiborane(4)[7] by the flϪ anion. Unexpectedly,
however, MeO substitution of (tBu)2B2(OMe)2, which has
been successfully employed for the preparation of the tetra-
alkyldiborane(4) derivatives (tBu)2B2(tBu)R (R ϭ Me,[5]
CH2SiMe3,[5] CH2CMe3[6]) and (tBu)2B2(CH2CMe3)2,[6] did
not work in the present case. No reaction occurred between
(tBu)2B2(OMe)2 and fluorenyllithium. On the other hand,
(tBu)2B2(fl-H)Br (3), could be obtained almost quantitat-
ively from the reaction of (tBu)2B2Br2 with one equivalent
of fluorenyllithium [Scheme 1, (1)]. The reaction of pure 3
with a further equivalent of fluorenyllithium also proceeded
quantitatively [Scheme 1, (2)], as shown by the 11B-NMR
spectrum of the reaction mixture. The diborane(4) com-
pounds 2-H2 and 3 were isolated as colorless solids. At
room temperature, they were found to be stable in solution
as well as in the solid state.
[‡]
Part 244: Ref.[1]
[a]
Department of Chemistry, Inorganic Chemistry, University of
The syntheses of di-tert-butyl-fluorenylborane (4-H) and
fluorenyl-dimethylborane (5-H) proved to be straightfor-
Munich,
Butenandtstraße 5Ϫ13, Haus D, 81377 München, Germany
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ1948/00/0707Ϫ1571 $ 17.50ϩ.50/0
1571

R. Littger, H. Nöth, M. Suter
FULL PAPER
boron atoms in this compound. The disodium salt of the
dianion [2]2Ϫ was isolated as an orange solid as a THF solv-
ate [Na(thf)x]2[2] and was characterized by multinuclear
NMR spectroscopy. The dimetallation of 2-H2 was further
confirmed by performing a single-crystal X-ray structure
analysis on the related solvate [Na(thf)(OEt2)][Na-
(OEt2)2][2].
The lithium monoborate, containing the anion
[tBu2B(fl)]Ϫ ([4]Ϫ) is the main product of the reaction be-
tween tBu2B(fl-H) (4-H) and one equivalent of LiNtBu-
(SiMe3) in tetrahydrofuran solution [Scheme 2, (5)]. The
11B-NMR spectrum of the reaction mixture not only shows
a signal due to this anion (δ ϭ 77.9), but further signals at
δ(11B)
ϭ
87.9 [tBu2B(fl-H)] and 54.0 [possibly
tBu2BϪNtBu(SiMe3), 8%] and minor signals in the region
δ(11B) ϭ ϩ10.0 to 0.0 (tetracoordinated borates, 5%). The
lithium salt [Li(thf)2][4] was recovered as a 4:1 mixture with
fluorenyllithium. All attempts to separate these compounds
by crystallization were unsuccessful. The formation of fluo-
renyllithium leads us to believe that the fluorenyl ligand of
4-H is substituted by the amide [NtBu(SiMe3)]Ϫ in a com-
peting reaction [Scheme 2, (6)]. This hypothesis is sup-
ported by the 11B-NMR signal at δ(11B) ϭ 54.0, which
Scheme 1
is
consistent
with
an
amino-diorganylborane
ward. These compounds could be obtained by treating fluo- tBu2BϪNtBu(SiMe3), a compound that could be formed
renyllithium with one equivalent of tBu2BCl or Me2BBr, through such a substitution reaction [cf. the 11B resonance
respectively [Scheme 2, (4)], and were isolated as colorless, of Me2BϪNtBu(SiMe3): δ(11B) ϭ 56.2].[9] The deborylation
crystalline solids. Other diorganyl-fluorenylboranes, R2B(fl- of alkylboranes upon treatment with strong bases is well
H) (R ϭ Et, Ph), have been reported previously.[8]
known for Et2B(Cp),[10,11] a compound akin to 4-H.
Scheme 2
On treatment with two equivalents of NaN(SiMe3)2 in
The lithium salt [Li(thf)2][4] has been characterized by
tetrahydrofuran solution, 2-H2 is doubly deprotonated multinuclear NMR spectroscopy. Its data are especially in-
[Scheme 1, (3)]. According to the 11B-NMR spectrum of the teresting with regard to the interpretation of the NMR data
reaction mixture, the dianion [(tBu)2B2(fl)2]2Ϫ (22Ϫ) is the of the title dianion [2]2Ϫ. These will be discussed later.
main product (90%). Unidentified boron species give rise to
The deprotonation of Me2B(fl-H) (5-H) which contains
signals in the region δ (11B) ϭ ϩ5 to Ϫ20 (altogether 10%). a sterically and electronically poorly shielded boron center
This indicates that the steric shielding of the boron centers is difficult. As yet, we have been unable to extract any useful
of 2-H2 is insufficient to completely suppress the nucleo- information from the NMR spectra of the reaction mixture
philic attack of Li(H)fl. On the other hand, the double de- generated when 5-H is treated with alkali metal amides or
protonation of the sterically less shielded 1-H2 is quantitat- sodium metal. From the reaction of Et2B(fl-H) with
ive as a result of the additional electronic shielding of the Na[BHEt3], a compound claimed[8] to be [Na(digly-
1572
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579

Contribution to the Chemistry of Boron, 245
FULL PAPER
me)1.5][Et2B(fl)] has been isolated. However, its NMR data ents as well. Such additional stabilization is naturally not
are not compatible with a tricoordinated boron atom (vide possible for a CH2Ϫ group, even less so for a PhCHϪ group.
infra).
In this context, it seems unlikely that the anion of [Na(dig-
lyme)1.5][Et2B(fl)][8] has the structure of a deprotonated tri-
alkylborane with a trigonal-planar coordinated boron
atom. For the system Et2B(fl-H) [δ(11B, THF) ϭ 50.9]/
[Et2B(fl)]Ϫ [δ(11B, THF) ϭ Ϫ25.5], a shielding difference of
NMR Spectra
The NMR-spectroscopic data of compounds 3, 2-H2, 4- ∆δ11B ϭ 76.4 has been reported. However, the 11B reson-
H, 5-H, Na2[2], and [Li(thf)2][4] are reported in the Experi- ance for [Et2B(fl)]Ϫ would be consistent with a tetracoord-
mental Section. The 11B-NMR resonance of 2-H2 at inated borate anion (dimeric species?).[15]
δ(11B) ϭ 102.5 is indicative of a tetraalkyldiborane(4) com-
Compared to the corresponding resonances in Na2[(-
pound.[5,6] However, only a single, albeit broad resonance Me2N)2B2(fl)2], Na2[1],[2] the 13C nuclei of the fluorenyl
at δ(11B) ϭ 92.9 is observed for the two different boron substituents are seen to be deshielded in Na2[(tBu)2B2(fl)2],
atoms of 3, this chemical shift being intermediate between Na2[2], on average by 2.4 ppm (see Table 1), thus indicating
those of the resonances of the corresponding symmetric a stronger π interaction between the fluorenyl substituents
species 2-H2 [δ(11B) ϭ 102.5] and (tBu)2B2Br2 [δ(11B) ϭ and the boron centers in the latter compound.
88.0].[7] The asymmetric structure of 3 is, however, reflected
Even more deshielded are the C atoms in fluorenylidene-
1
in its H- and 13C-NMR spectra, which show discrete sig- (tetramethylpiperidino)borane,[17] tmpϪBϭfl (tmp
ϭ
nals due to the two different tert-butyl groups. The fluor- 2,2,6,6-tetramethylpiperidyl), a compound related to Na2[2]
enyl substituents of both 3 and 2-H2 give rise to double sets containing a true BϭCfl double bond. In this case, one ob-
of signals. In the case of 3, all the nuclei of the single fluor- serves a ∆δ(13C) value of 2.3 ppm (average for C2 to C13)
enyl group are chemically inequivalent, but the two fluor- compared to Na2[2].
enyl substituents of 2-H2 should be equivalent. At the pre-
Despite the partial BϭCfl double-bond character in
sent time, the question as to whether the observed inequi- Na2[2], the fluorenyl substituents give rise to single sets of
valence is due to hindered rotation about the BϪB bond signals in the 1H- and 13C-NMR spectra. This indicates that
and/or about the BϪCfl bonds remains unclear. Most prob- the rotation about the BϪCfl bond is still a fast process on
ably, the barrier associated with rotation about the BϪB the NMR time scale. On the other hand, the signals due to
bond is higher than that for rotation about the BϪC bond C-2,13, C-4,11, and 5-,10-H are significantly broader, show-
and hence diastereomers arise. Indeed, diastereomers have ing the onset of coalescence.
been found for much less sterically demanding substituted
diborane(4) derivatives, such as (Me2N)2B2iPr2 and by just 8.4 ppm compared with that of protonated 4-H.
The 11B resonance of [Li(thf)2][4] is shifted to higher field
(Me2N)2B2(benzyl)2 (room temperature, 400 MHz).[12]
This is surprising as deprotonation of the fluorenyl sub-
The NMR data of the monoboranes 4-H and 5-H are stituents in the related 2-H2/[2]2Ϫ system leads to a down-
unexceptional: 4-H shows two sets of signals due to the two field shift in the resonance of the 11B nuclei by 28 ppm.
1
tert-butyl groups in the H- and 13C-NMR spectra and a In comparison with Na2[2], the 13C-NMR signals of the
single set of signals due to the fluorenyl substituent. This fluorenyl substituents in [Li(thf)2][4] are upfield shifted by
corresponds to a preferred conformation in which the plane an average of 2.6 ppm (see Table 2). These observations are
of the fluorenyl substituent is oriented perpendicular to the consistent with a lesser degree of BϪCfl-π interaction in the
plane at the boron center, with hindered rotation about the monoborane case, with more electron density residing in
BϪCfl bond. The two methyl groups of 5-H are chemically the fluorenyl system. This complies with a noncoplanar ori-
equivalent and the observation of one set of signals due to entation of the plane of the fluorenyl substituent and the
the fluorenyl group indicates free rotation about the BϪCfl plane about the boron center in [4]Ϫ due to the presence of
bond. This difference between 4-H and 5-H (one signal in the two bulky tert-butyl substituents at the boron atom. The
1
the H- and 13C-NMR spectra due to the B-methyl groups small difference in shielding can then readily be explained
for the latter) can therefore be attributed purely to steric in terms of an essentially perpendicular arrangement of the
factors.
fl-H and flϪ group with respect to the tBu2B moiety.
1
The boron atoms in the disodium salt Na2[2] [δ(11B) ϭ
The H- and 13C-NMR data of [Li(thf)2][4] are strongly
74.0] are better shielded by 28 ppm than in the protonated solvent-dependent. In C6D6 solution, the 13C nuclei of the
2-H2 [δ(11B) ϭ 102.5]. This can be rationalized in terms of central five-membered ring (C-1, C-2,13, C-7,8) of the fluo-
a strong π interaction between the deprotonated fluorenyl renyl substituent are better shielded by 4.5 ppm (average)
substituents and the boron centers. Even larger shielding than in THF solution (see Table 2). On the other hand, the
effects have been observed in other cases, e.g. ∆δ ϭ 43.2 for protonated benzoid 13C nuclei of the fluorenyl substituent
the couple Mes2BϪCH3 [δ(11B, THF)
ϭ
83.6]/ are deshielded by 2.4 ppm (average) in C6D6 solution. The
[Mes2BϪCH2]Ϫ [δ(11B, THF) ϭ 40.4] (Mes ϭ 2,4,6-trime- same is true for the 1H nuclei, which are deshielded by
thylphenyl)[13] and ∆δ ϭ 38.6 for the couple Mes3B/ 0.53 ppm (average) in C6D6 solution as compared to their
[Mes2BϪ(3,5-Me2)C6H2CH2]Ϫ.[14] We assume that the resonances in THF solution. This behavior is not unusual
negative charges in Na2[2] are not only stabilized by the for alkali metal fluorenides and can be explained in terms
boron centers, but by the π system of the fluorenyl substitu- of a solvent dependency of the formation of contact ion
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579
1573

R. Littger, H. Nöth, M. Suter
Table 1. Comparison of the 13C-NMR data of the fluorenyl substituents of Li2[flϪ(CH2)2Ϫfl], Na2[1], Na2[2], and tmpϪBϭfl
FULL PAPER
Li2[(CH2)2(fl)2][16]
[D8]THF
∆
Na2[1][2]
THF
∆
Na2[2]
THF
∆
tmpϪBϭfl[17]
CDCl3
Solvent
C-2,13
C-7,8
C-4,11
C-6,9
C-3,12
C-5,10
∆
135.9
123.4
118.9
118.9
114.8
107.2
ϩ5.2
ϩ2.3
ϩ1.7
ϩ0.8
ϩ3.7
ϩ3.5
ϩ2.9
141.1
125.7
120.6
119.7
118.5
110.7
ϩ4.9
ϩ4.5
ϩ1.9
ϩ1.3
Ϫ0.4
ϩ2.1
ϩ2.4
146.0
130.2
122.5
121.0
118.1
112.8
Ϫ1.9
ϩ3.5
ϩ2.3
Ϫ1.2
ϩ2.9
ϩ8.1
ϩ2.3
144.1
133.7
124.8
119.8
121.0
120.9
Table 2. Comparison of the 13C-NMR data of the fluorenyl group the sterically demanding tert-butyl groups in this com-
of [Li(thf)2][4] (solvent-dependent) with those of the fluorenyl
groups of Na2[2]
pound. Despite the bulky substitution of 2-H2, the B1ϪB2
distance is quite short at 1.688(8) A and, indeed, is the
˚
shortest yet found for a neutral tetraorganyldiborane(4).
[Li(thf)2][4]
∆
[Li(thf)2][4]
∆
Na2[2]
Solvent
C6D6
THF
THF
Comparable diborane(4) derivatives are Mes2BϪBMesPh
[20]
[20]
˚
˚
[1.706(12) A],
Mes2BϪBMes(CH2SiMe3) [1.71(2) A],
C-2,13
C-7,8
C-4,11
C-6,9
C-3,12
C-5,10
C-1
137.4
122.0
121.6
121.5
120.3
112.6
100.7
ϩ4.7
ϩ4.4
Ϫ1.2
Ϫ2.3
Ϫ2.0
Ϫ3.9
142.1
126.4
120.4
119.2
118.3
108.7
105.2
ϩ3.9
ϩ3.8
ϩ2.1
ϩ1.8
Ϫ0.2
ϩ4.1
146.0
130.2
122.5
121.0
118.1
112.8
n.b.
[21]
˚
Mes2B2[CH(SiMe3)2]2 [1.739(7) A],
tioned diboracyclopentane [1.729(8), 1.709(9) A].
and the afore-men-
[19]
˚
The
two fluorenyl substituents of 2-H2 show significantly differ-
˚
ent BϪCfl bond lengths [B1ϪC1 ϭ 1.609(6) A, B2ϪC14 ϭ
˚
1.641(6) A] and two different orientations with respect to
∆
ϩ2.6
the diborane(4) unit, as indicated by the dihedral angles
C31ϪB2ϪC14ϪH14a ϭ 171.6° and C27ϪB1ϪC1ϪH1a ϭ
9.4°. For the trialkylborane 4-H (Figure 2), a BϪCfl dis-
pairs (CIPs) and solvent-separated ion pairs (SSIPs).[18] In
the poorly solvating solvent C6D6, CIPs are formed be-
tween [Li(thf)2]ϩ and [4]Ϫ. The cation [Li(thf)2]ϩ is located
above the five-membered ring of the fluorenyl substituent,
polarizing the π electrons towards this central ring, thereby
accounting for the enhanced shielding of the central 13C
nuclei and the deshielding of the nuclei of the peripheral
carbon atoms. In the strongly solvating solvent THF, an
equilibrium exists between CIPs and SSIPs, as a result of
which the polarizing effect of the cation [Li(thf)2]ϩ towards
the fluorenyl substituent is somewhat diminished.
˚
tance of 1.612(8) A is found. The most significant feature
of the molecular structure of 4-H is the perpendicular ar-
rangement of the plane at the boron center and the plane
of the fluorenyl substituent (C1ϪC14ϪC18/C1 to C13 ϭ
89.0°), which has already been established on the basis of
1H- and 13C-NMR data.
We were unable to obtain single crystals of a THF solvate
of Na2[2] from THF or THF/hexane mixtures. However,
crystals suitable for X-ray crystallography were formed
when [Na(thf)x]2[2] (Figure 3) was crystallized from diethyl
Molecular Structures
In order to obtain further information on the degree of
CflϪB-π bonding in the dianion [2]2Ϫ, an X-ray structure
determination of [Na(thf)(Et2O)][Na(Et2O)2][2] was per-
formed. The protonated compounds 2-H2 (Figure 1)
and 4-H were also subjected to X-ray structure analyses for
comparison purposes. To the best of our knowledge, the
crystal structure of 2-H2 represents the first solid-state
structure of a noncyclic tetraalkyldiborane(4). A structure
useful for making comparisons is that of the cyclic dibor-
ane(4) derivative [ϪB(Me)ϪB(Me)ϪC(SiMe3)2ϪSi(Me)2Ϫ
C(SiMe3)2Ϫ], in which all the atoms connected to the di-
borane(4) unit are C(sp3) atoms.[19] The most striking fea-
ture of 2-H2 is that the planes at B1 and B2 are arranged
Figure 1. Molecular structure of (tBu)2B2(fl-H)2 (2-H2); thermal
ellipsoids are drawn at a 25% probability level; hydrogen atoms,
except those on atoms C-1 and C-14, have been omitted for the
perpendicularly
to
one
another
(C1ϪB1ϪC27/
˚
sake of clarity; selected bond lengths [A]: B1ϪB2 1.687(7), B1ϪC1
C14ϪB2ϪC31 ϭ 89.2°). Normally, the planes at the boron
atoms in diborane(4) derivatives form angles in the range
60Ϫ80°. The orthogonal orientation of the planes at the
1.609(6), B2ϪC14 1.641(6), B1ϪC27 1.615(6), B2ϪC31 1.586(6);
selected angles [°]: B2ϪB1ϪC1 124.1(3), B2ϪB1ϪC27 120.4(4),
C1ϪB1ϪC27 115.1(4), B1ϪB2ϪC14 116.2(3), B1ϪB2ϪC31
121.6(3), C14ϪB2ϪC31 122.2(3), C1ϪB2ϪC27/C14ϪB1ϪC31
boron atoms in 2-H2 can be attributed to the presence of 89.3, C1ϪB2ϪC27/C1 to C13 81.5, C14ϪB1ϪC31/C14 to C26 82.8
1574 Eur. J. Inorg. Chem. 2000, 1571Ϫ1579

Contribution to the Chemistry of Boron, 245
FULL PAPER
is evident from the sum of the bond angles about these
atoms (C1: 359.7°; C14: 360.0°). The dianion [2]2Ϫ and the
two sodium cations form a monomeric contact ion triple.
The sodium cations are complexed by one (Na2) or both
(Na1) fluorenyl substituents of the dianion and by two ad-
ditional ether molecules.
The angles between the planes at the boron atoms and
the planes of the fluorenyl substituents are 12.7° and 13.8°,
respectively. In the related dimetallated derivatives of 1-H2,
the corresponding angles are 40.2 and 49.4°. The BϪCfl
distances in Na2[2] are 10 pm shorter [1.529(8) and 1.533(9)
˚
A] than those in the protonated 2-H2. These distances are
also significantly shorter than those in (Me2N)2B2Ph2, a re-
lated compound with a BϪCsp2 bond (average BϪC dis-
˚
tance ϭ 1.585 A), but shorter than those in the analogous
M2[1] compounds (M2 ϭ Li2, K2, Ca) (average BϪCfl dis-
˚
tance of 1.547 A). Together with the almost coplanar ar-
rangement of the planes at the boron atoms and the fluor-
enyl planes, this gives an additional indication of significant
BϪCfl-π bonding in Na2[2].
Figure 2. Molecular structure of tBu2B(fl-H) (4-H); thermal ellips-
oids are shown at a 25% probability level; hydrogen atoms, except
that on atom C-1, have been omitted for the sake of clarity; selected
The BϪCfl distances in Na2[2] are best compared with
[22]
˚
the BϪC distance of 1.52(1)
A
in the anion
˚
bond lengths [A]: BϪC1 1.616(3), BϪC14 1.594(3), BϪC18
[Mes2BϪ(3,5-Me2)C6H2CH2]Ϫ, as the boron atom has a
similar acidity and the negative charge is also stabilized by
an organic π system. In Na2[2], steric repulsion between the
fluorenyl substituents and the tert-butyl groups connected
to the same boron atom is to be expected, and this indeed
becomes apparent on comparing the pairs of angles
1.607(4); selected angles [°]: C1ϪBϪC14 113.6(2), C1ϪBϪC18
120.7(2), C14ϪBϪC18 125.7(2), C1ϪC14ϪC18/C1 to C13 89.0
B1ϪC1ϪC2/B1ϪC1ϪC13
ϭ
122.5°/134.7°
and
B2ϪC14ϪC26/B2ϪC14ϪC15 ϭ 122.5°/133.9° (see Fig-
ure 4). The two fluorenyl substituents are forced apart by
the tert-butyl group connected to the same boron atom.
This most probably accounts for the fact that the BϪCfl
distances in Na2[2] are longer than they would be in a
sterically less strained system. The two planes form an angle
of 82.1°. Like the similar planes in the C2BB starting mat-
erial 2-H2, these are oriented almost perpendicularly to one
˚
another. The BϪB distance in the dianion is 1.744(9) A,
which is 5.7 pm longer than the BϪB distance in the parent
˚
protonated compound 2-H2 [1.687(7) A]. An even more
˚
elongated BϪB bond [1.859(8) A] occurs in the less twisted
(43°)
diborane(4)
unit
of
the
related
Li2[Mes2B2{C(SiMe3)2}2].[23]
Figure 3. Molecular structure of [Na(thf)(OEt2)][Na(OEt2)2][2];
thermal ellipsoids are shown at a 25% probability level; carbon
atoms of the ether ligands and hydrogen atoms, except those at
atom C-32, have been omitted for the sake of clarity; selected bond
It is interesting to compare the rather unusual coordina-
tion modes of Na2 and especially of Na1 in Na2[2] (Fig-
ure 4) with those observed in other fluorenyl sodium com-
pounds.
˚
lengths [A]: B1ϪB2 1.744(9), B1ϪC1 1.529(8), B1ϪC27 1.615(9),
B2ϪC14 1.533(9), B2ϪC31 1.626(9), Na1ϪC25 2.720(6), Na1ϪC3
2.818(6), Na1ϪC26 2.822(6), Na1ϪC4 2.987(7), Na1ϪC24
Na2 is bonded in an asymmetric η5 mode to the central
3.071(7), Na1ϪO1 2.301(6), Na1ϪO2 2.329(5), Na2ϪC13 2.599(6), five-membered ring of the fluorenyl substituent C1 to C13
Na2ϪC1 2.671(6), Na2ϪC8 2.898(6), Na2ϪC2 2.912(6), Na2ϪC7
(see Figure 4, top). It is not located centrally above the fluo-
3.075(7), Na2ϪO4 2.242(6), Na2ϪO3 2.250(5), Na2ϪH32A 2.495;
renyl substituent, but is rather shifted towards C13 and C1,
resulting in shorter contacts between Na2 and these carbon
selected angles [°]: B2ϪB1ϪC1 121.6(5), B2ϪB1ϪC27 115.6(5),
C1ϪB1ϪC27 122.8(5), B1ϪB2ϪC14 121.0(5), B1ϪB2ϪC31
116.0(5), C14ϪB2ϪC31 122.9(5), C27ϪB2ϪC1/C31ϪB1ϪC14
82.1, C27ϪB2ϪC1/C1 to C13 13.8, C31ϪB1ϪC14/C14 to C26
12.7, O1ϪNa1ϪO2 109.4(2), O3ϪNa2ϪO4 96.4(2)
˚
˚
atoms [Na2ϪC13 ϭ 2.599(6) A, Na2ϪC1 ϭ 2.671(6) A]. A
similar shift and similar NaϪC distances have been re-
ported for monomeric Nafl·PMDTA.[24] In both cases, the
ether at Ϫ20 °C. The structure determination confirmed the two shortest NaϪC contacts are those to C1 and one of its
dimetallation of 2-H2 by sodium. The absence of protons neighbors. The coordination sphere about Na2 is completed
at the fluorenyl carbon atoms bonded to the boron atoms by two ether molecules (one molecule of tetrahydrofuran
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579
1575

R. Littger, H. Nöth, M. Suter
FULL PAPER
coordinated by the benzoid carbon atoms of the fluorenyl
substituents instead. It shows three contacts to the fluorenyl
substituent C14 to C26 with NaϪC distances of
˚
˚
Na1ϪC25 ϭ 2.720(6) A, Na1ϪC26 ϭ 2.822(6) A, and
˚
Na1ϪC24 ϭ 3.071(7) A, and two contacts to the fluorenyl
substituent C1 to C13 with NaϪC distances of Na1ϪC3 ϭ
˚
˚
2.818(6) A and Na1ϪC4 ϭ 2.987(7) A (see Figure 4). If
Na1 is projected perpendicularly onto the fluorenyl plane
defined by the carbon atoms C1 to C13, it can be seen that
this cation lies outside of the area of this fluorenyl substitu-
ent (see Figure 4, bottom). This coordination is strongly re-
miniscent of that of one of the sodium atoms in the cyclic
tetramer [Na(fl)·TMPDA]4, in which the NaϪC distances
[24]
˚
measure 3.025(5) and 3.032(5) A.
Similar ‘‘out-of-ring
coordination’’ has been observed in the dipotassium salt
[K(DME)]2[1].[2] The coordination sphere of Na1 is com-
pleted by two molecules of diethyl ether. The average
˚
NaϪO distance is 2.315 A, 7 pm longer than for Na2; the
OϪNaϪO angle is 13° wider for Na1 (O1ϪNa1ϪO2 ϭ
109.4°) compared to that at Na2 (O3ϪNa2ϪO4 ϭ 96.4°).
Conclusion
The present study has again shown that the quantitative
deprotonation of alkylboranes is not easily achieved. Even
in the case of the compounds 2-H2 and 4-H, in which the
boron centers are sterically very shielded, the action of the
weak nucleophilic bases NaN(SiMe3)2 and LiNtBu(SiMe3)
leads to products in which significant numbers of boron
atoms are tetracoordinated. As expected, the dianion [2]2Ϫ
displays a higher degree of CϪB-π bonding than the related
dimethylamino derivative [1]2Ϫ, as has been established on
the basis of the following criteria: the BϪCfl bond lengths
are shorter, the angles between the planes at the boron
atoms and the planes of the corresponding fluorenyl sub-
Figure 4. Plots showing the positions of the sodium cations Na1
and Na2 in [Na(thf)(OEt2)][Na(OEt2)2][2] with respect to the
planes of the fluorenyl substituents C1 to C13 (top) and C14 to
C26 (bottom); distances between the sodium cations and the fluor-
1
˚
enyl planes [A]: Na2Ϫ(C1 to C13) 2.401, Na1Ϫ(C1 to C13) 2.642,
stituents are smaller, and NMR studies show the H and
Na1Ϫ(C14 to C26) 2.673
the 13C nuclei of the fluorenyl substituents to be more de-
shielded. In [2]2Ϫ, the π system is not delocalized over the
CflϪBϪBϪCfl unit as might be expected for an isoelec-
tronic butadiene system. This is obvious as the planes at the
boron atoms adopt an almost perpendicular arrangement.
Therefore, [2]2Ϫ is best described as a system in which two
borylated carbanions are connected by a BϪB single bond
without BϪC-π bond character. The question remains as to
why butadiene-like structures are not realized for [2]2Ϫ and
the related anion [Mes2B2{C(SiMe3)2}2]2Ϫ, i.e. whether this
is due to steric reasons or also due to the electronic situ-
ation.
and one molecule of diethyl ether) and there is a weak inter-
˚
action (Na2ϪH32a ϭ 2.495 A) between Na2 and a methyl
group of the tert-butyl substituent bonded to B2. In con-
trast to monomeric [Na(thf)(OEt2)][Na(OEt2)2][2], solvates
of fluorenylsodium in which the sodium cation is also co-
ordinated to the fluorenyl anion and two donor atoms are
either polymeric, such as [Na(fl)·TMEDA]ϱ, or oligomeric,
such as [Na(fl)·TMPDA]4. A monomeric solvate of fluoren-
ylsodium is only formed with the tridentate PMDTA li-
gand.[24]
Na1 interacts with both fluorenyl substituents of the di-
anion [2]2Ϫ. The fluorenyl substituents do not coordinate
Na1 through the carbon atoms of the central five-mem-
bered rings as has been observed for alkali metal com-
pounds of the analogous dianion [1]2Ϫ. Such a di-η5 coor-
dination is impossible in the case of [2]2Ϫ because of the
almost perpendicular orientation of the planes at the boron
atoms and the small angles between the planes at the boron
Experimental Section
General: All manipulations were carried out under N2 using
Schlenk techniques. Solvents were dried by standard procedures.
Commercial chemicals were purified prior to use as necessary;
(tBu)2B2Br2,[25] (tBu)2BCl,[26] Me2BBr,[27] Li(fl),[28] NaN(SiMe3)2,
and LiNtBu(SiMe3)[29] were prepared according to literature pro-
atoms and the planes of the fluorenyl substituents. Na1 is cedures. Ϫ NMR: Bruker AC-P 200 (11B), Jeol EX 400 (1H, 13C);
1576 Eur. J. Inorg. Chem. 2000, 1571Ϫ1579

Contribution to the Chemistry of Boron, 245
FULL PAPER
standards: ext. BF3·Et2O (11B), int. TMS or C6D6 (1H, 13C). Ϫ IR:
a second crop of crystals (1.32 g). Ϫ Yield: 1.82 g of 4-H (51%);
PerkinϪElmer 325. Ϫ MS: Varian CH7 (70 eV). Ϫ X-ray structure m.p. 70Ϫ72 °C. Ϫ C21H27B (290.3): calcd. C 86.90, H 9.38; found
determinations: Siemens P4 or Nicolet R3m diffractometer, Mo-Kα
radiation, graphite monochromator.
C 83.69, H 7.77. Ϫ 11B NMR (64.2 MHz, C6D6): δ ϭ 86.3 (h1/2
ϭ
670 Hz). Ϫ 1H NMR (400 MHz, C6D6): δ ϭ 7.75 [d, 2 H,
3J(H,H) ϭ 7.3 Hz, 6-,9-H], 7.28 [pseudo-t, 3J(H,H) ϭ 7.3 Hz, 2 H,
4-,11-H or 5-,10-H], 7.23 [d, 2 H, 3J(H,H) ϭ 6.8 Hz, 3-,12-H], 7.18
[pseudo-t, 2 H, 3J(H,H) ϭ 7.3 Hz, 4-,11-H or 5-,10-H], 4.41 (s, 1 H,
1-H), 1.24, 0.53 [2 s, 2 ϫ 9 H, 2C(CH3)3]. Ϫ 13C NMR (100.6 MHz,
C6D6): δ ϭ 147.9 (C-2,13), 143.2 (C-7,8), 126.8, 126.2 (C-
4,5,10,11), 124.4 (C-3,12), 120.6 (C-6,9), 48.8 (C-1), 30.3, 29.9
[C(CH3)3], 28.6, 27.6 [C(CH3)3].
1-Bromo-1,2-di-tert-butyl-2-(1-fluorenyl)diborane(4) (3): A suspen-
sion of fluorenyllithium (0.69 g, 4.01 mmol) in toluene (20 mL) was
added dropwise to a solution of (tBu2)B2Br2 (1.18 g, 3.99 mmol) in
toluene (25 mL) at Ϫ78 °C. The mixture was allowed to warm to
room temperature, stirred for 6 h, and then the insoluble material
(0.32 g) was removed by centrifugation. The solution was concen-
trated to dryness, the residue was redissolved in hexane (12 mL),
and this solution stored for 20 h at Ϫ20 °C. A colorless solid separ-
ated, which was filtered off, washed with cold hexane, and dried in
vacuo. Ϫ Yield: 0.40 g of 3 (26%); m.p. 92Ϫ93 °C. Ϫ C21H27B2Br
(381.0): calcd. C 66.21, H 7.14; found C 64.74, H 6.37. Ϫ MS
(1-Fluorenyl)dimethylborane (5-H): A suspension of fluorenylli-
thium (3.37 g, 19.6 mmol) in toluene (20 mL) was added dropwise
to a stirred solution of Me2BBr (2.37 g, 19.6 mmol) in toluene
(20 mL) at Ϫ78 °C. The mixture was allowed to warm to ambient
(70 eV); m/z (%): 380 (100) [M•ϩ], 233 (45) [M•ϩ Ϫ B(fl-H)Br], 165 temperature, stirred for a further 3 d, and then the insoluble mat-
(56) [fl-H]. Ϫ 11B NMR (64.2 MHz, CDCl3): δ ϭ 92.9 (h1/2
940 Hz). Ϫ 1H NMR (400 MHz, CDCl3): δ ϭ 7.84, 7.78, 7.50, tracted with toluene (7 mL) and the toluene solutions were com-
ϭ
erial (1.75 g) was separated by centrifugation. This solid was ex-
3
3
7.45 [d, 1 H, J(H,H) ϭ 7.3 Hz; d, 1 H, J(H,H) ϭ 7.3 Hz; d, 1 H,
bined. Removal of all volatile compounds in vacuo left a red oil
3J(H,H) ϭ 6.8 Hz; d, 1 H, 3J(H,H) ϭ 7.3 Hz, 3-,6-,9-,12-H], 7.32 (3.45 g), heating of which at 110Ϫ130 °C/10Ϫ3 Torr resulted in the
(m, 4 H, 4-,5-,10-,11-H), 4.57 (s, 1 H, 1-H), 1.29, 0.37 [2 s, 2 ϫ 9 H, formation of very thin, colorless needles. Ϫ Yield: 2.79 g of 5-H
2 C(CH3)3]. Ϫ 13C NMR (100.6 MHz, CDCl3): δ ϭ 147.1, 143.9 (69%); m.p. 49Ϫ50 °C. Ϫ C15H15B (206.1): calcd. C 87.42, H 7.34;
(C-2,13), 142.2, 140.5 (C-7,8), 126.7, 126.6, 126.5, 126.3, 126.1, found C 86.67, H 7.87. Ϫ 11B NMR (64.2 MHz, C6D6): δ ϭ 83.8
1
125.8 (C-3,4,5,10,11,12), 120.4, 119.9 (C-6,9), 49.3 (C-1), 30.1, 29.3
[C(CH3)3], 27.5, 26.2 [C(CH3)3].
(h1/2 ϭ 310 Hz). Ϫ H NMR (400 MHz, C6D6): δ ϭ 7.74 [d, 2 H,
3J(H,H) ϭ 7.3 Hz, 6-,9-H], 7.22 (m, 6 H, 3-,4-,5-,10-,11-,12-H),
4.29 (s, 1 H, 1-H), 0.53 (s, 6 H, CH3). Ϫ 13C NMR (100.6 MHz,
C6D6): δ ϭ 145.4 (C-2,13), 142.1 (C-7,8), 126.8, 126.3 (C-
4,5,10,11), 124.8 (C-3,12), 120.5 (C-6,9), 53.8 (C-1), 13.0 (CH3).
1,2-Di-tert-butyl-1,2-bis(1-fluorenyl)diborane(4) (2-H2): A suspen-
sion of fluorenyllithium (0.40 g, 2.32 mmol) in toluene (15 mL) was
slowly added to a stirred solution of 3 (0.87 g, 2.28 mmol) in tolu-
ene (10 mL) at Ϫ78 °C. The mixture was allowed to warm to room
temperature, stirred for 20 h, and then the insoluble material was
[Na(thf)x]2[(tBu)2B2(fl)2] {[Na(thf)x]2[2]}:
A solution of NaN-
(SiMe3)2 (0.31 g, 1.69 mmol) in tetrahydrofuran (7 mL) was added
separated by centrifugation. The solution was then concentrated to dropwise to a stirred solution of 2-H2 (0.41 g, 0.88 mmol) in tetra-
dryness in vacuo and the residue was redissolved in hexane
(10 mL). Storing this solution for 3 d at Ϫ25 °C gave colorless,
microcrystalline 2-H2, which was filtered off, washed with cold hex-
ane (3 mL), and dried in vacuo for several hours. Ϫ Yield: 0.44 g
hydrofuran (10 mL) at room temperature. During the addition of
the base, the color of the reaction mixture turned orange. Stirring
was continued for 20 h and then the deep-red mixture was concen-
trated to dryness in vacuo. On treating the residue with hexane
of 2-H2 (41%); m.p. 138Ϫ139 °C. Ϫ C34H36B2 (466.3): calcd. C (10 mL), an orange powder formed, which was collected by filtra-
87.58, H 7.78; found C 85.47, H 7.57. Ϫ MS (70 eV); m/z (%): 466
tion (0.28 g), washed with hexane (3 mL), and dried in vacuo. 11B-
(11) [M•ϩ], 409 (5) [M•ϩ Ϫ C(CH3)3], 301 (91) [M•ϩ Ϫ C13H9], , 1H-, and 13C-NMR spectroscopy showed the product to be a THF
233 (34) [M•ϩ/2], 176 (77) [B(fl-H)], 165 (100) [fl-H]. Ϫ 11B NMR
solvate of the disodium salt [Na(thf)x]2[2]. Crystals of the solvate
(64.2 MHz, C6D6): δ ϭ 102.5 (h1/2 ϭ 2250 Hz). Ϫ 1H NMR [Na(thf)(OEt2)][Na(OEt2)2][2] suitable for X-ray crystallography
3
(400 MHz, C6D6): δ ϭ 7.76 [d, 2 H, J(H,H) ϭ 7.3 Hz, 6-H], 7.68
were obtained by recrystallizing the orange powdery [Na(thf)x]2[2]
3
3
[d, 2 H, J(H,H) ϭ 7.3 Hz, 9-H], 7.57 [d, 2 H, J(H,H) ϭ 6.4 Hz, from diethyl ether at Ϫ20 °C. Ϫ 11B NMR (64.2 MHz, THF/C6D6):
3-H], 7.28 (pseudo-t, 2 H, 5-H), 7.19 (pseudo-t, 2 H, 10-H), 7.14
(pseudo-t, 2 H, 4-H), 7.04 (pseudo-t, 2 H, 11-H), 6.35 (m, very
δ ϭ 72.0 (h1/2 ϭ 4100 Hz). Ϫ 1H NMR (400 MHz, THF/C6D6):
δ ϭ 8.27 [d, 4 H, 3J(H,H) ϭ 8.3 Hz, 6-,9-H], 7.88 [d, 4 H,
broad, 12-H), 4.66 (s, 2 H, 1-H), 0.75 [s, 18 H, C(CH3)3]. Ϫ 13C 3J(H,H) ϭ 7.3 Hz, 3-,12-H], 6.77 [(at ϩ55 °C, t), 4 H, 4-,11-H],
NMR (100.6 MHz, C6D6): δ ϭ 147.2, 145.6 (C-2,13), 142.9, 142.6
6.60 (pseudo-t, 4 H, broad, 5-,10-H), 1.44 [s, 18 H, C(CH3)3]. Ϫ
(C-7,8), 127.0 (C-4), 126.4 (C-5,10,11,12), 125.6 (C-3), 120.6 (C-6),
13C NMR (100.6 MHz, THF/C6D6): δ ϭ 146.0 (broad, C-2,13),
120.3 (C-9), 50.5 (C-1), 32.5 [C(CH3)3], 28.7 [C(CH3)3]. The 1H and 130.2 (C-7,8), 122.5 (broad, C-4,11), 121.0 (C-6,9), 118.1 (C-3,12),
1
13C NMR resonances were assigned on the basis of H-1H-COSY 112.8 (C-5,10); (C-1) and [C(CH3)3] could not be detected; 34.7
1
and H-13C-HETCOR NMR experiments.
[C(CH3)3].
Di-tert-butyl-(1-fluorenyl)borane (4-H): A suspension of fluorenylli-
Reaction of 4-H with LiN(tBu)(SiMe3): A solution of LiNtBu(S-
thium (2.14 g, 12.43 mmol) in toluene (30 mL) was slowly added to iMe3) (0.51 g, 3.37 mmol) in tetrahydrofuran (15 mL) was added
a stirred solution of tBu2BCl (1.99 g, 12.40 mmol) in toluene
(20 mL) at Ϫ78 °C. The mixture was allowed to warm to room
temperature, in the course of which a brown-red color developed.
After stirring for a further 20 h at room temperature, the insoluble
material was separated by centrifugation and this solid was ex-
tracted with toluene (10 mL). The toluene solutions were combined
and concentrated to dryness in vacuo. The residue (3.31 g) was re-
dropwise to a solution of 4-H (0.96 g, 3.31 mmol) in tetrahydrofu-
ran (15 mL) at room temperature. The mixture was stirred for 1 d,
in the course of which a deep-red color developed. After removing
all volatile material in vacuo, a dark-red resinous residue (1.88 g)
remained. Addition of hexane (20 mL) produced an orange powder
(0.75 g), which was collected by filtration, washed with hexane
1
(5 mL), and dried in vacuo. H-, 13C-, and 11B-NMR spectroscopy
dissolved in hexane (15 mL) and storage of this solution at Ϫ25 °C showed this powder to consist of a 4:1 mixture of [Li(thf)2][4] and
led to the deposition of large, colorless needles (0.50 g). Concentra-
tion of the mother liquor and further storage at Ϫ25 °C furnished
fluorenyllithium. The powder proved to be very soluble in THF
and benzene and moderately soluble in hexane. Separation of the
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579
1577

R. Littger, H. Nöth, M. Suter
FULL PAPER
Table 3. Crystallographic data for the structures of 2-H2, 4-H, and [Na(thf)(Et2O)][Na(Et2O)2][2] and details relating to data collection
and structure refinement
2-H2
4-H
[Na(thf)(Et2O)][Na(Et2O)2][2]
Empirical formula
Molecular mass
Crystal size [mm]
Crystal system
Space group
C34H36B2
466.28
C21H27B
290.24
C50H72B2Na2O4
804.68
0.35 ϫ 0.20 ϫ 0.35
Orthorhombic
P212121
9.269(2)
14.470(3)
20.579(8)
90
0.6 ϫ 0.4 ϫ 0.4
Monoclinic
P2(1)/c
13.967(3)
14.502(3)
8.999(2)
90.119(4)
1822.9(7)
4
0.50 ϫ 0.45 ϫ 0.42
Monoclinic
P2(1)/n
12.282(4)
25.00(1)
16.04(1)
103.15(4)
4796(5)
4
˚
a [A]
˚
b [A]
˚
c [A]
β [°]
3
˚
V [A ]
2760.1(15)
4
Z
ρ(calcd.) [Mg/mm3]
1.122
1.058
1.114
µ [mmϪ1
F(000)
]
0.062
0.058
0.083
1000
632
1744
Index range
Ϫ1 Յ h Յ 10
Ϫ1 Յ k Յ 16
Ϫ22 Յ l Յ 23
4.0 to 47.0
203
Ϫ17 Յ h Յ 17
Ϫ18 Յ k Յ 18
8 Յ l Յ 12
5.34 to 57.88
193(2)
0 Յ h Յ 12
Ϫ1 Յ k Յ 25
Ϫ16 Յ l Յ 16
3.08 to 43.00
173
2θ [°]
T [K]
Refl. collected
Refl. unique
Refl. observed (4σ)
No. of variables
GooF
5285
10492
6033
4073
3397
5404
2451
2085
2766
325
208
559
0.88
0.987
1.085
R
0.0551
0.0599
0.0729
wR2
0.0663
0.1714
0.1580
3
˚
[e/A ]
0.25
0.223
0.297
two components by fractional crystallization could not be achieved.
riding on the respective C-atoms. Selected crystallographic data
Ϫ NMR Data for [Li(thf)2][4]: 11B NMR (64.2 MHz, THF/C6D6): and data related to the structure solution and refinement are sum-
δ ϭ 77.9 (h1/2 ϭ 950 Hz). Ϫ 1H NMR (400 MHz, THF/C6D6): δ ϭ
marized in Table 3. Programs used: SHELXTL and SHELXL-93.
3
7.76 [d, 2 H, J(H,H) ϭ 7.3 Hz, 6-,9-H], 7.19 [d, 2 H, 3J(H,H) ϭ Crystallographic data (excluding structure factors) for the structure
3
8.3 Hz, 3-,12-H], 6.71 [pseudo-t, 2 H, J(H,H) ϭ 7.1 Hz, 4-,11-H],
reported in this paper have been deposited with the Cambridge
6.35 [pseudo-t, 2 H, 3J(H,H) ϭ 7.3 Hz, 5-,10-H], 1.15 [s, 18 H, Crystallographic Data Centre as supplementary publication no.
C(CH3)3]. Ϫ 13C NMR (100.6 MHz, THF/C6D6): δ ϭ 142.1 (C- CCDC-143688 to -143690. Copies of the data can be obtained free
2,13), 126.4 (C-7,8), 120.4 (C-4,11), 119.2 (C-6,9), 118.3 (C-3,12),
of charge on application to the CCDC, 12 Union Road, Cambridge
1
108.7 (C-5,10), 105.2 (C-1), 31.0 [C(CH3)3], 30.3 [C(CH3)3]. Ϫ H CB2 1EZ, U.K. [Fax: (internat.) ϩ 44-1223/336-033; E-mail:
3
NMR (400 MHz, C6D6): δ ϭ 8.27 [d, 2 H, J(H,H) ϭ 7.8 Hz, 6-
,9-H], 7.61 [d, 2 H, 3J(H,H) ϭ 8.3 Hz, 3-,12-H], 7.25 [pseudo-t,
deposit@ccdc.cam.ac.uk].
3
3
2 H, J(H,H) ϭ 7.6 Hz, 4-,11-H], 6.99 [pseudo-t, 2 H, J(H,H) ϭ
7.3 Hz, 5-,10-H], 2.66 (m, 8 H, THF), 1.35 [s, 18 H, C(CH3)3], 1.04
(m, 8 H, THF). Ϫ 13C NMR (100.6 MHz, C6D6): δ ϭ 137.4 (C-
2,13), 122.0 (C-7,8), 121.6 (C-4,11), 121.5 (C-6,9), 120.3 (C-3,12),
112.6 (C-5,10), 100.7 (C-1), 67.6 (THF), 30.9 [C(CH3)3], 29.4
[C(CH3)3], 25.0 (THF). Ϫ NMR Data for Fluorenyllithium: 1H
NMR (400 MHz, THF/C6D6): δ ϭ 7.85 (d, 2 H, 6-,9-H), 7.24 (d,
2 H, 3-,12-H), 6.75 (pseudo-t, 2 H, 4-,11-H), 6.37 (pseudo-t, 2 H,
5-,10-H), 5.87 (s, 1 H, 1-H). Ϫ 13C NMR (100.6 MHz, THF/C6D6):
δ ϭ 138.0 (C-2,13), 123.4 (C-7,8), 119.4 (C-4,11), 118.9 (C-6,9),
116.5 (C-3,12), 108.4 (C-5,10), 81.4 (C-1).
Acknowledgments
We thank the Fonds der Chemischen Industrie and Chemetall
GmbH for support of this work. Thanks are also due to Mr. P.
Mayer for recording many NMR spectra, and to the team in the
microanalytical laboratory for performing the analyses.
[1]
W. Lippert, H. Nöth, W. Ponikwar, T. Seifert, Eur. J. Inorg.
Chem. 1999, 817Ϫ824.
[2]
R. Littger, N. Metzler, H. Nöth, M. Wagner, Chem. Ber. 1994,
127, 1901Ϫ1908.
[3]
R. Littger, H. Nöth, M. Thomann, M. Wagner, Angew. Chem.
1993, 105, 275Ϫ277; Angew. Chem. Int. Ed. Engl. 1993, 32,
X-ray Structure Determination: Single crystals were coated with
perfluoroether oil and mounted on glass fibres. They were cooled
to Ϫ80 °C on the goniometer head. Cell dimensions were deter-
mined by automatically centering reflections taken from rotation
photographs. Data collections were performed in the ω/2θ mode
with variable scan speeds and adjusted scan widths. After data re-
duction (Lorentz and polarization correction), direct methods were
applied for structure solution. The model was initially refined after
atom assignment with isotropic temperature parameters, and then
the positions of the atoms were refined using an anisotropic de-
scription. Hydrogen atom positions were calculated and included
in the final calculation with fixed isotropic thermal parameters as
295Ϫ297.
[4]
H. Nöth, M. Wagner, Chem. Ber. 1991, 124, 1963Ϫ1972.
W. Biffar, H. Nöth, H. Pommerening, Angew. Chem. 1980, 92,
63Ϫ64; Angew. Chem. Int. Ed. Engl. 1980, 19, 56.
K. Schlüter, A. Berndt, Angew. Chem. 1980, 92, 64Ϫ65; Angew.
Chem. Int. Ed. Engl. 1980, 19, 57.
H. Pommerening, Ph.D. Thesis, University of Munich, 1979.
P. Paetzold, B. Boeke, Chem. Ber. 1976, 109, 1011Ϫ1016.
H. Nöth, W. Tinhof, B. Wrackmeyer, Chem. Ber. 1974, 107,
518.
H. Grundke, P. I. Paetzold, Chem. Ber. 1971, 104, 1136Ϫ1146.
E. Herberich, B. Schmidt, U. Englert, Organometallics 1995,
14, 471Ϫ480.
[5]
[6]
[7]
[8]
[9]
[10]
[11]
1578
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579

Contribution to the Chemistry of Boron, 245
FULL PAPER
A. Berndt, see reference [18] in: A. Moezzi, M. M. Olmstead,
R. A. Bartlett, P. P. Power, Organometallics 1992, 11,
2383Ϫ2388.
[12]
[21]
R. Littger, Ph.D. Thesis, University of Munich, 1996.
[13]
M. M. Olmstead, P. P. Power, K. J. Weese, J. Am. Chem. Soc.
1987, 109, 2541Ϫ2542.
[22]
[23]
[14]
R. A. Bartlett, P. P. Power, Organometallics 1986, 5,
B. G. Ramsey, L. M. Isabelle, J. Org. Chem. 1981, 46, 179.
[15]
1916Ϫ1917.
H. Nöth, B. Wrackmeyer, NMR Spectroscopy of Boron Com-
M. Pilz, J. Allwohn, P. Willershausen, W. Massa, A. Berndt,
Angew. Chem. 1990, 102, 1085Ϫ1087; Angew. Chem. Int. Ed.
Engl. 1990, 29, 1030Ϫ1032.
pounds, vol. 14 (NMR Basic Principles and Applications; Eds.:
P. Diehl, E. Fluck, R. Kosfeld), Springer Publ., Heidelberg,
Berlin, New York, 1978.
[24]
[16]
S. Corbelin, J. Kopf, E. Weiss, Chem. Ber. 1991, 124,
B. Becker, V. Enkelmann, K. Müller, Angew. Chem. 1989, 101,
2417Ϫ2422.
501Ϫ503; Angew. Chem. Int. Ed. Engl. 1989, 28, 458.
[25]
[26]
[27]
[17]
H. Pommerening, Dissertation, University of Munich, 1979.
U. Höbel. H. Nöth, H. Prigge, Chem. Ber. 1986, 119, 325Ϫ327.
H. Nöth, H. Vahrenkamp, J. Organomet. Chem. 1968, 11,
399Ϫ405.
B. Glaser, H. Nöth, Chem. Ber. 1986, 119, 3253Ϫ3267.
[18] [18a]
[18b]
U. Edlund, Org. Magn. Reson. 1979, 12, 661Ϫ666. Ϫ
J. B. Grutzner, J. M. Lawlor, L. M. Jackman, J. Am. Chem.
Soc. 1972, 94, 2306Ϫ2315.
[19]
[20]
[28]
[29]
U. Englert, R. Finger, P. Paetzold, B. Redenz-Stormanns, Z.
Pawelec, W. Wojnowski, Organometallics 1995, 14, 1507Ϫ1509.
A. Moezzi, M. M. Olmstead, R. A. Bartlett, P. P. Power, Or-
ganometallics 1992, 11, 2383Ϫ2388.
M. Wagner, Dissertation, University of Munich, 1992.
C. R. Krüger, H. Niederprüm, Inorg. Synth. 1966, 8, 15Ϫ19.
Received December 30, 1999
[I99477]
Eur. J. Inorg. Chem. 2000, 1571Ϫ1579
1579