Synthesis and molecular structure of boron-bridged constrained geometry complexes of zirconium and hafnium

Article abstract of DOI:10.1016/j.jorganchem.2005.08.004

The boron-bridged constrained geometry complexes [M{η⁵: η¹-(C₅H₄)B(NiPr₂)NPh}(NMe ₂)₂] (M = Zr (1), Hf (2)) and [Zr{η⁵: η¹-(C₉H₆)B(NiP

Full text of DOI:10.1016/j.jorganchem.2005.08.004

Journal of Organometallic Chemistry 690 (2005) 5000–5005
www.elsevier.com/locate/jorganchem
Note
Synthesis and molecular structure of boron-bridged
constrained geometry complexes of zirconium and hafnium
a,
a
a
Holger Braunschweig *, Frank M. Breitling a,b, Krzysztof Radacki , Fabian Seeler
a
Institut fu¨r Anorganische Chemie, Julius-Maximilians-Universita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg, Germany
b
Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom
Received 14 July 2005; accepted 12 August 2005
Available online 26 September 2005
Abstract
The boron-bridged constrained geometry complexes [M{g5:g1-(C5H4)B(NiPr2)NPh}(NMe2)2] (M = Zr (1), Hf (2)) and [Zr{g5:g1-
(C9H6)B(NiPr2)NPh}(NMe2)2] (3) have been prepared by reaction of the respective neutral ligand precursors (g1-C5H5)B(NiPr2)N(H)Ph
and (1-C9H7)B(NiPr2)N(H)Ph with [M(NMe2)4] (M = Zr, Hf) with elimination of two equivalents of HNMe2. All new compounds have
been characterised by means of multinuclear NMR spectroscopy and X-ray diffraction experiments.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Boron; Hafnium; Zirconium; Constrained geometry complex; Linked cyclopentadienyl-amido ligand
1. Introduction
PMe3
Linked cyclopentadienyl-amido ligands were first intro-
H
Cl
Sc
Sc
Ti
duced by Bercaw et al. [1] for the synthesis of scandium(III)
complexes, e.g. I. Shortly thereafter, research groups both
in academia [2] and industry [3] reported the utilization
of such ligands for the synthesis of corresponding Group
4 complexes, e.g. II. Frequently, complexes incorporating
ligands of the aforementioned type are referred to as con-
strained geometry complexes (CGCs), owing to the chelate
bite angle imposed by the cyclopentadienyl and amido do-
nors. When activated with suitable co-catalysts such as
MAO these CGCs serve as highly active olefin polymerisa-
tion catalysts [4] and produce polymers with exceptional
characteristics, e.g. long chain branching, resulting in low
density and advantageous mechanical properties [5]. Be-
sides the well-studied application of Group 4 CGCs in
olefin polymerisation, a number of reports on their cata-
lytic characteristics with regard to various organic transfor-
mations have appeared in the literature [6–9].
Si
Si
Si
Cl
H
N
N
N
PMe3
tBu
tBu
tBu
I
II
Me3Si
iPr
iPr
NMe2
NMe2
Cl
Cl
Ti
N
B
Ti
N
B
Me3Si
N
Ph
III
IV
Ph
N
iPr
iPr
B
N
Zr
N
B
iPr
iPr
N
*
Corresponding author. Tel.: +49 931 888 5260; fax: +49 931 888 4623.
Ph
E-mail address: h.braunschweig@mail.uni-wuerzburg.de (H. Braun-
V
schweig).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.004

H. Braunschweig et al. / Journal of Organometallic Chemistry 690 (2005) 5000–5005
5001
The presence of a bridging moiety between the cyclopen-
tadienyl and amido fragments in CGCs appears to be cru-
cial for the observed reactivity of these compounds [10].
The identity of the bridging element affects the Cp(cen-
troid)–M–N angle and may be utilised to fine tune the
activity. Introduction of a boranediyl bridge appeared to
be particularly interesting for several reasons [11]: (i) the
small size of the boron atom should result in a more acute
Cp(centroid)–M–N angle, a feature that was previously
associated with a higher polymerisation activity, and (ii)
in a more rigid ligand framework that may be advanta-
geous in the catalysis of asymmetric organic transforma-
tions, and (iii) the potentially Lewis acidic moiety in
proximity to the catalytically active centre may positively
affect its reactivity. Consequently, we extended the syn-
thetic method for the preparation of boron-bridged ligand
precursors [12] and corresponding metallocenes [13,14] that
are stabilized by an amino substituent, e.g., III, to the syn-
thesis of related boron-bridged CGC ligand precursors [15]
and corresponding titanium CGCs [16], e.g., IV. The latter
could be obtained by reaction of the respective ligand pre-
cursors with [Ti(NMe2)4] via amine elimination. Previ-
ously, we have not been able to isolate the zirconium or
hafnium congeners following this approach. Similarly, two-
fold deprotonation of a boron-bridged CGC ligand precur-
sor and reaction with ZrCl4 did not result in the formation
of the desired CGC, but yielded the bis-ligand metallocene
V [15a].
react with [Ti(NMe2)4] in toluene under reflux conditions
to give the corresponding titanium CGCs [16b]. In the light
of these positive results we re-examined our earlier findings
that isolation of boron-bridged CGCs of the higher homo-
logues zirconium and hafnium by a corresponding route is
not viable.
Indeed, reaction of (g1-C5H5)B(NiPr2)N(H)Ph with
[M(NMe2)4] (M = Zr, Hf) at reflux in toluene for several
hours and subsequent purification by means of recrystalli-
sation gave the corresponding CGCs [M{g5:g1-(C5H4)-
B(NiPr2)NPh}(NMe2)2] (M = Zr (1), Hf (2)) in reasonable
yields in the form of colourless crystals (Scheme 1). Under
very similar conditions, (1-C9H7)B(NiPr2)N(H)Ph reacted
with [Zr(NMe2)4] to yield the corresponding complex
[Zr{g5:g1-(C9H6)B(NiPr2)NPh}(NMe2)2] (3) as colourless
crystals (Scheme 2). It seems to be rather essential to per-
form these reactions under reflux conditions to oust the
amine formed and consequently drive the reactions to the
product side. NMR analyses of the crude products suggest
unbridged complexes to be the major side products. On the
other hand, decomposition of the formed CGCs due to the
high temperatures applied appears to be negligible.
Complexes 1–3 were characterised by multinuclear 1D
and 2D NMR spectroscopy. 11B NMR chemical shifts
for 1–3 very much resemble those of the respective ligand
precursors. 1H and 13C NMR spectra of 1–3 are unremark-
able. The resonances of the respective boron substituted
carbon atoms give rise to broad signals in the 13C NMR
spectrum of 1 and 2, while the corresponding signal in
the 13C NMR spectrum of 3 could not be detected at
À20 °C, due to quadrupolar 13C–11B coupling [17]. Apart
from that, all expected 1H and 13C resonances were
observed. The spectra closely resemble the spectra of the
respective titanium congeners [Ti{g5:g1-(C5H4)B(NiPr2)
NPh}(NMe2)2] and [Ti{g5:g1-(C9H6)B(NiPr2)NPh}(NMe2)2]
with only slight differences in chemical shifts [16]. As ob-
served for these diamino titanium complexes [18], the reso-
nances corresponding to the iPr2N moieties of 1–3 in the
In the present paper, we report the synthesis of the first
boron-bridged CGCs of zirconium and hafnium via amine
elimination and their structural characterisation by means
of X-ray diffraction.
2. Results and discussion
2.1. Synthesis and spectroscopic characterisation
We previously reported the synthesis of boron-bridged
titanium CGCs via amine elimination. Thus, (g1-C5H5)-
B(NiPr2)N(H)Ph reacts with [Ti(NMe2)4] at slightly ele-
vated temperature (40 °C) to give corresponding [Ti{g5:
g1-(C5H4)B(NiPr2)NPh}(NMe2)2] in high yield [16a]. Like-
wise, various related boron-bridged CGC ligand precursors
1
ambient temperature H and 13C NMR spectra are signif-
icantly broadened. Such line broadening may be ascribed
to rotation about the iPr2N–B linkage on the NMR time
1
scale. However, in H and 13C NMR spectra of 1–3 re-
corded at À20 °C the signals corresponding to the iPr2N
[M(NMe2)4] (M = Zr, Hf)
iPr
iPr
iPr
NMe2
NMe2
toluene, reflux, 4 h
M
N
B
N
B
- 2 HNMe2
iPr
N
H
N
Ph
Ph
+ isomer
M = Zr
M = Hf
1
2
Scheme 1.

5002
H. Braunschweig et al. / Journal of Organometallic Chemistry 690 (2005) 5000–5005
2.2. X-ray structure determination of complexes 1–3
The structures of CGCs 1–3 in the solid state could be
[Zr(NMe2)4]
iPr
iPr
iPr
iPr
NMe2
NMe2
determined by X-ray diffraction experiments. All three
toluene, reflux, 2 h
Zr
N
B
N
B
ꢀ
compounds crystallise in the triclinic space group P1. Table
- 2 HNMe2
N
H
N
1 compares selected structural parameters of 1–3. Fig. 1 de-
picts the molecular structure of 3 as a representative
example.
Ph
Ph
3
The gross structures of the new complexes 1–3 are very
similar with the structures of their respective titanium
analogues [Ti{g5:g1-(C5H4)B(NiPr2)NPh}(NMe2)2] and
[Ti{g5:g1-(C9H6)B(NiPr2)NPh}(NMe2)2] [16]. If one con-
siders the C5 aromatic rings in all these complexes as
g1-moieties, the geometry at the transition metal can be
viewed as a distorted tetrahedron. The main structural dif-
ferences between the complexes arise from the different
radii of the coordinated transition metals. The larger zirco-
nium and hafnium centres (when compared to the titanium
centres) result in a lengthening of all bonds involving
the metal centre. Concurrently, the N(1)–M–C5 angles be-
come more acute by ca. 5°, while the N(1)–B–C(1) angles
Scheme 2.
groups are sharp and the hyperfine structures of the signals
in the 1H NMR spectra (two doublets corresponding
to MeiPr and two heptets corresponding to CHiPr in the
spectra of the Cs symmetric Cp derivatives 1 and 2, four
doublets corresponding to MeiPr and two heptets corre-
sponding to CHiPr in the spectrum of the C1 symmetric
indenyl derivative 3) are clearly resolved. These observa-
tions are consistent with inhibition of the rotation about
the iPr2N–B bonds in 1–3 on the NMR time scale at low
temperatures.
Table 1
Comparative selected geometric parameters for complexes 1–3
1 [M = Zr, R1 = C(12), R2 = C(15)]
2 [M = Hf, R1 = C(12), R2 = C(15)]
3 [M = Zr, R1 = C(19), R2 = C(16)]
a
˚
M–C5 (A)
2.182
4.2
0.16
2.162
3.8
0.14
2.1233(18)
2.0225(19)
2.0415(19)
1.444(3)
1.414(3)
1.608(3)
2.196
4.3
0.16
/ (°)b
c
˚
d (A)
˚
M–N(1) (A)
2.1530(17)
2.0571(19)
2.0314(19)
1.438(3)
1.408(3)
1.614(3)
94.1
130.8(2)
105.08(18)
124.14(19)
360.0
2.1363(14)
2.0466(15)
2.0354(15)
1.446(2)
1.406(2)
1.607(2)
94.9
129.50(15)
105.45(13)
125.04(15)
360.0
˚
M–N(3) (A)
˚
M–N(4) (A)
˚
B–N(1) (A)
˚
B–N(2) (A)
˚
B–C(1) (A)
N(1)–M–C5 (°)a
N(1)–B–N(2) (°)
N(1)–B–C(1) (°)
94.9
130.7(2)
105.18(18)
124.2(2)
360.0
N(2)–B–C(1) (°)
P
[X–B–Y] (°)d
e
˚
DB (A)
0.007
0.006
0.006
B–N(2)–R1 (°)
B–N(2)–R2 (°)
122.89(18)
122.72(18)
114.38(17)
360.0
0.009
2.2
103.37(13)
123.15(13)
131.99(18)
358.5
0.110
29.4
123.14(18)
122.37(19)
114.45(17)
360.0
0.016
2.1
103.14(14)
123.88(14)
131.59(19)
358.6
0.106
30.4
122.52(14)
123.14(14)
114.30(13)
360.0
0.017
1.1
103.06(10)
124.70(10)
131.53(13)
359.3
0.076
30.5
R1–N(2)–R2 (°)
P
[X–N(2)–Y] (°)d
e
˚
DN(2) (A)
s[B–N(2)] (°)f
M–N(1)–B (°)
M–N(1)–Ph (°)
B–N(1)–Ph (°)
P
[X–N(1)–Y] (°)d
e
˚
DN(1) (A)
B–C(1)Á Á Á[C5] (°)g
h
˚
DB[C5] (A)
0.792
0.814
0.816
a
‘‘C5’’ refers to the centroid of the five-membered aromatic ring.
b
c
d
e
f
/ is the angle between the normal to the [C5] ring plane and the MÁ Á ÁC5 ring centroid vector.
d is the offset of the M centre away from a position perpendicularly beneath the C5 ring centroid.
Sum of the angles around the central atom.
DX is the deviation of atom X from the plane of its substituents.
Torsion angle about linkage.
g
h
Angle of B–C(1) bond to [C5] ring plane.
Deviation of B from [C5] plane.

H. Braunschweig et al. / Journal of Organometallic Chemistry 690 (2005) 5000–5005
5003
techniques. Solvents were dried utilising an M. Braun
Solvent Purification System and stored under argon over
molecular sieves. Deuterated solvents were degassed, dried
and stored over molecular sieves. (g1-C5H5)B(NiPr2)N(H)-
Ph [15c], (1-C9H7)B(NiPr2)N(H)Ph [15a], [Zr(NMe2)4] [19]
and [Hf(NMe2)4] [19] were prepared by previously pub-
lished methods.
C1
N2
1H and 13C–{1H} NMR spectra were recorded on a Bru-
ker DRX 300 spectrometer. 11B–{1H} NMR spectra were
recorded on a Bruker 200 Avance spectrometer. All chem-
B
1
Zr
ical shifts are reported in ppm. Chemical shifts for H and
N1
N3
13C–{1H} NMR spectra were referenced to internal solvent
resonances and are reported relative to SiMe4. Assignments
1
were made from the analysis of H, 13C–HMQC-COSY
N4
NMR experiments. Chemical shifts for 11B–{1H} NMR
spectra were referenced to BF3 Æ OEt2 as an external
standard.
4.2. Synthesis of [Zr{g5:g1-(C5H4)B(NiPr2)NPh}-
(NMe2)2] (1)
Fig. 1. ORTEP representation of the molecular structure of 3. Thermal
ellipsoids are drawn at a 50% probability level. Hydrogen atoms are
omitted for clarity.
Solutions of the ligand precursor (g1-C5H5)B(NiPr2)-
N(H)Ph (0.64 g, 2.39 mmol) and [Zr(NMe2)4] (0.64 g,
2.39 mmol), both in toluene (20 mL), were combined at
ambient temperature. During reflux for 4 h, the initially al-
most colourless solution became bright yellow in colour.
All volatiles were removed in vacuo, the dark yellow resi-
due was re-dissolved in hexane, concentrated and stored
for recrystallisation at ambient temperature. Large colour-
less crystals of 1 (0.74 g, 1.67 mmol, 70%) were obtained
after several hours. 1H NMR (300 MHz, CD2Cl2,
become more obtuse by ca. 1.5°. In all these structures,
both the B and N(2) centres have trigonal planar geome-
tries and these trigonal planes are almost coplanar in the
respective molecules. There are no noteworthy intermolec-
ular interactions in the crystals of 1–3.
Comparison of the structures of CGC 3 and the related
bis-ligand metallocene [Zr{g5:g1-(C9H6)B(NiPr2)NPh}2]
[15a] discloses only minor differences in the coordination
of the respective linked indenyl-amido ligands to the zirco-
nium centres. Most prominently, the Zr–C5 distance in 3 is
3
À20 °C): d = 0.86 (d, JH–H = 6.7 Hz, 6H, MeiPr), 1.40 (d,
3JH–H = 6.9 Hz, 6H, MeiPr), 2.75 (s, 12H, NMe2), 3.19
˚
significantly shorter (2.196 vs. 2.228 A) and presumably re-
3
3
sults from lower electron density at this zirconium centre.
Likewise, the slight shortening of the Zr–N(1) distance in
(m, JH–H = 6.9 Hz, 1H, CHiPr), 3.38 (m, JH–H = 6.7 Hz,
1H, CHiPr), 6.04 (pt, 2H, CHCp), 6.50 (pt, 2H, CHCp),
6.64–6.71 (m, 2H, o-CHPh), 6.77–6.85 (m, 1H, p-CHPh),
7.07–7.16 (m, 2H, m-CHPh). 13C NMR (75 MHz, CD2Cl2,
À20 °C): d = 21.2 (MeiPr), 26.8 (MeiPr), 43.1 (NMe2), 43.9
(CHiPr), 46.0 (CHiPr), 98.6 (BC), 113.6 (CHCp), 118.5
(CHCp), 120.3 (p-CHPh), 123.9 (o-CHPh), 128.2 (m-CHPh),
153.5 (ipso-CPh). 11B NMR (64 MHz, benzene-d6):
d = 27.8.
˚
3 may be rationalised (2.1363(14) vs. 2.1570 A). These dif-
ferences in bond lengths are accompanied by smaller
changes in the other structural parameters of the chelating
ligand, the most significant being the larger twist of the tri-
gonal planes surrounding B and N(2) in the bis-ligand
metallocene (5.1°) when compared with 3 (1.1°).
3. Conclusions
4.3. Synthesis of [Hf{g5:g1-(C5H4)B(NiPr2)NPh}-
(NMe2)2] (2)
The synthesis of the first boron-bridged CGCs of zirco-
nium and hafnium by reaction of the neutral ligand precur-
sors with [M(NMe2)4] (M = Zr, Hf) via amine elimination
is straightforward. X-ray diffraction experiments demon-
strated a close structural resemblance of the obtained com-
plexes with their titanium analogues.
Following the same procedure as for the preparation of
1, (g1-C5H5)B(NiPr2)N(H)Ph (0.86 g, 3.21 mmol) was trea-
ted [Hf(NMe2)4] (1.14 g, 3.21 mmol) in toluene (40 mL).
Recrystallisation from toluene at À30 °C yielded pure 2
(1.06 g, 1.99 mmol, 62%) in the form of colourless crystals
suitable for X-ray diffraction experiments. 1H NMR
4. Experimental
3
(300 MHz, CD2Cl2, À20 °C): d = 0.85 (d, JH–H = 6.7 Hz,
3
4.1. General methods
6H, MeiPr), 1.40 (d, JH–H = 6.9 Hz, 6H, MeiPr), 2.77 (s,
3
12H, NMe2), 3.20 (m, JH–H = 6.9 Hz, 1H, CHiPr), 3.36
3
All manipulations were performed under a dry atmo-
sphere of argon using standard Schlenk line and dry box
(m, JH–H = 6.7 Hz, 1H, CHiPr), 6.02 (pt, 2H, CHCp),
6.49 (pt, 2H, CHCp), 6.65–6.72 (m, 2H, o-CHPh),

5004
H. Braunschweig et al. / Journal of Organometallic Chemistry 690 (2005) 5000–5005
6.78–6.85 (m, 1H, p-CHPh), 7.08–7.16 (m, 2H, m-CHPh).
13C NMR (75 MHz, CD2Cl2, À20 °C): d = 21.1 (MeiPr),
26.7 (MeiPr), 43.0 (NMe2), 43.9 (CHiPr), 46.1 (CHiPr),
98.6 (BC), 113.2 (CHCp), 118.0 (CHCp), 120.6 (p-CHPh),
124.2 (o-CHPh), 128.1 (m-CHPh), 153.2 (ipso-CPh). 11B
NMR (64 MHz, benzene-d6): d = 27.2.
CInd), 128.2 (m-CHPh), 131.0 (quaternary CInd), 153.2
(ipso-CPh), BC resonance not observed. 11B NMR (64
MHz, benzene-d6): d = 28.5.
4.5. X-ray structure determination of compounds 1–3
A crystal of appropriate size was mounted on a glass
fiber with silicone grease. The crystal was transferred to
a Bruker SMART APEX diffractometer with CCD area
detector, centered in the beam, and cooled by a nitrogen
flow low-temperature apparatus to an appropriate tem-
perature. Preliminary orientation matrix and cell con-
stants were determined by collection of 100 frames,
followed by spot integration and least-squares refine-
ment. A hemisphere of data was collected [20]. The
raw data were integrated with SAINT [21]. Cell dimensions
were calculated from all reflections. Data analysis was
performed with XPREP [22]. The data were corrected for
Lorentz and polarization effects and an empirical absorp-
tion correction based on comparison of redundant and
equivalent reflections was applied with SADABS [23]. The
structures were solved via direct methods and refined
with the SHELX software package and expanded using
Fourier techniques [24]. All non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were assigned ide-
alized positions and were included in structure factor
calculations. The crystallographic data, parameters of
the X-ray experiments and refinements for compounds
1–3 are listed in Table 2.
4.4. Synthesis of [Zr{g5:g1-(C9H6)B(NiPr2)NPh}-
(NMe2)2] (3)
Following the same procedure as for the preparation of
1, (1-C9H7)B(NiPr2)N(H)Ph (0.61 g, 1.92 mmol) was trea-
ted with [Zr(NMe2)4] (0.51 g, 1.92 mmol) in toluene
(30 mL). Recrystallisation from hexane at À80 °C yielded
pure 3 (0.53 g, 1.08 mmol, 56%) in the form of a colourless
microcrystalline material. Recrystallisation from hexane at
4 °C yielded crystals of 3 suitable for X-ray diffraction
experiments. 1H NMR (300 MHz, CD2Cl2, À20 °C):
3
3
d = 0.94 (d, JH–H = 6.7 Hz, 3H, MeiPr), 0.99 (d, JH–H
=
3
6.7 Hz, 3H, MeiPr), 1.47 (d, JH–H = 6.8 Hz, 3H, MeiPr),
1.48 (d, JH–H = 6.8 Hz, 3H, MeiPr), 1.96 (s, 6H, NMe2),
2.89 (s, 6H, NMe2), 3.32 (m, JH–H = 6.8 Hz, 1H, CHiPr),
3.51 (m, JH–H = 6.7 Hz, 1H, CHiPr), 6.35–7.78 (m, 11H,
3
3
3
CHInd/Ph). 13C NMR (75 MHz, CD2Cl2, À20 °C):
d = 21.2 (MeiPr), 21.5 (MeiPr), 26.5 (MeiPr), 27.0 (MeiPr),
40.7 (NMe2), 43.9 (CHiPr), 44.3 (NMe2), 46.5 (CHiPr),
102.2 (CHInd-5-ring), 120.2 (p-CHPh), 122,8 (CHInd-6-ring),
123.1 (o-CHPh), 123.3 (CHInd-5-ring), 123.8 (CHInd-6-ring),
124.1 (CHInd-6-ring), 124.8 (CHInd-6-ring), 127.7 (quaternary
Table 2
Summary of the crystal data and details of data collection and refinement for compounds 1–3
Data
1
2
3
Empirical formula
Formula weight (g molÀ1
C
445.56
21H35BN4Zr
C21 H35BHfN4
532.83
C25H37BN4Zr
495.62
)
Temperature (K)
Radiation, k (A)
Crystal system
173(2)
Mo Ka, 0.71073
Triclinic
173(2)
Mo Ka, 0.71073
Triclinic
193(2)
Mo Ka, 0.71073
Triclinic
˚
ꢀ
ꢀ
ꢀ
Space group
P1
P1
P1
˚
a (A)
9.4986(8)
9.7515(8)
9.4684(11)
9.8068(13)
13.8449(19)
101.509(2)
103.455(2)
102.932(3)
1174.9(3)
9.735(2)
9.947(2)
13.809(3)
88.482(4)
80.798(5)
75.240(4)
1276.3(5)
˚
b (A)
˚
c (A)
13.8010(11)
101.5630(10)
103.7000(10)
102.6290(10)
1168.23(17)
2
a (°)
b (°)
c (°)
3
˚
V (A )
Z
2
2
Dcalc (Mg mÀ3
)
1.267
0.482
1.506
4.451
1.290
0.449
Absorption coefficient (mmÀ1
)
F(000)
468
532
520
h Range for data collection (°)
Reflections collected
1.58–26.18
24671
1.57–26.06
13292
2.12–27.53
12377
Independent reflections [Rint
Maximum/minimum transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
]
4659 [0.0271]
0.93/0.81231
Full-matrix least-squares on F2
4659/0/244
1.086
4628 [0.0200]
0.39/0.2651
Full-matrix least-squares on F2
4628/0/252
5821 [0.0182]
0.94/0.758
Full-matrix least-squares on F2
5821/0/288
1.065
1.051
Final R indices [I > 2sigma(I)]
R indices (all data)
R1 = 0.0315, wR2 = 0.0916
R1 = 0.0328, wR2 = 0.0927
0.655/À0.513
R1 = 0.0153, wR2 = 0.0390
R1 = 0.0159, wR2 = 0.0393
0.653/À0.361
R1 = 0.0283, wR2 = 0.0737
R1 = 0.0303, wR2 = 0.0750
0.498/À0.263
Minimum/maximum residual
À3
˚
electron density (e A
)

H. Braunschweig et al. / Journal of Organometallic Chemistry 690 (2005) 5000–5005
5005
[9] A.K. Dash, T.R. Jensen, C.L. Stern, T.J. Marks, J. Am. Chem. Soc.
126 (2004) 12528.
5. Supplementary data
[10] J.C. Stevens, Stud. Surf. Sci. Catal. 89 (1994) 277.
[11] For reviews on boron-bridged Group 4 metallocenes and related
compounds see: (a) P.J. Shapiro, Eur. J. Inorg. Chem. (2001)
321;
(b) H. Braunschweig, F.M. Breitling, E. Gullo, M. Kraft, J.
Organomet. Chem. 680 (2003) 31;
(c) S. Aldridge, C. Bresner, Coord. Chem. Rev. 244 (2003) 71.
[12] H. Braunschweig, C. von Koblinski, M. Neugebauer, U. Englert, X.
Zheng, J. Organomet. Chem. 619 (2001) 305.
Crystallographic data for the structures reported have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 278300 (1), 278304 (2) and 278301 (3).
Copies of this information may be obtained free of charge
from: The Director, CCDC, 12 Union Road, Cambridge,
CB21EZ, UK, fax(int)+44(1223)336033ore-mail:deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk.
[13] (a) H. Braunschweig, C. von Koblinski, R. Wang, Eur. J. Inorg.
Chem. (1999) 69;
Acknowledgements
(b) H. Braunschweig, C. von Koblinski, M. Mamuti, U. Englert, R.
Wang, Eur. J. Inorg. Chem. (1999) 1899;
(c) H. Braunschweig, M.O. Kristen, C. von Koblinski, Eur. Pat. Appl.
2000, EP-1140955;
(d) H. Braunschweig, M. Kraft, K. Radacki, S. Stellwag, Eur. J.
Inorg. Chem. (2005) 2754;
This work was supported by BMBF, DFG, EPSRC, R.
Soc. F.M.B. thanks the Fonds der Chemischen Industrie
for a doctoral scholarship.
(e) H. Braunschweig, M. Kraft, K. Radacki, S. Stellwag, Z. Anorg.
Allg. Chem. (in press).
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