Reactivity of B(C6F5)3 with simple early transition metal alkoxides: Alkoxide-aryl exchange, THF ring-opening, or acetonitrile CC coupling

Article abstract of DOI:10.1021/om800234z

Treatment of the titanium(IV) and vanadium(IV) alkoxide complexes M(OPrⁱ)4 [M = Ti, V] with B(C₆F₅)3 results in alkoxide-aryl exchange and formation of the organometallic dimer complexes [M(OPrⁱ)₂(μ-OPrⁱ)(C₆F ₅)]₂ (M = Ti (1), V (2)). In comparison, the reaction between B(C₆F₅)₃ and Zr(OBu^t) ₄ in pentane, followed by recrystallization in acetonitrile-THF solutions, affords the unexpected trimeric zirconium salt [Zr ₃(OBu^t)₆(μ₂-OBu^t) ₃(μ₃-OBu^t)(μ₃-OCH ₂CH₂CH₂CH₃)][B(C₆F ₅)₄] (3), which proceeds through a redox reaction involving the borane and the THF solvent. In the presence of CH₃CN, a tetranuclear complex formulated as [Zr₂(OBu^t) ₅(μ-OBu^t)₂(μ-N,N′-N(H)C(CH ₃)=C(H)C≡N)]₂ (5) is obtained, which results from a C,C coupling reaction between two acetonitrile molecules. When Zr(OBu ^t)₄ is treated with (HO)B(C₆F₅) ₂, a dimer complex formulated as [Zr(OBu^t) ₂{μ-O-OB(OBu^t)(C₆F₅) ₂-κ²-O,O}]₂ (7) is formed that contains an unusual ligand bonding mode. The molecular structures of 1, 2, 3, 5, and 7 as well as the adduct B(C₆F₅)₃ THF (4) and [Zr(OBu^t)₃(μ-OBu^t)]₂(μ- N≡CCH₃) (6) have been determined by X-ray diffraction.

Full text of DOI:10.1021/om800234z

Organometallics 2008, 27, 5017–5024
5017
Reactivity of B(C6F5)3 with Simple Early Transition Metal
Alkoxides: Alkoxide-Aryl Exchange, THF Ring-Opening, or
Acetonitrile CC Coupling
Christian Lorber,* Robert Choukroun, and Laure Vendier
Laboratoire de Chimie de Coordination, CNRS UPR 8241 (Lie´ par ConVention a` l’UniVersite´ Paul Sabatier et
a` l’Institut National Polytechnique), 205 Route de Narbonne, 31077 Toulouse Cedex 04, France
ReceiVed March 12, 2008
Treatment of the titanium(IV) and vanadium(IV) alkoxide complexes M(OPri)4 [M ) Ti, V] with
B(C6F5)3 results in alkoxide-aryl exchange and formation of the organometallic dimer complexes
[M(OPri)2(µ-OPri)(C6F5)]2 (M ) Ti (1), V (2)). In comparison, the reaction between B(C6F5)3 and Zr(OBut)4
in pentane, followed by recrystallization in acetonitrile-THF solutions, affords the unexpected trimeric
zirconium salt [Zr3(OBut)6(µ2-OBut)3(µ3-OBut)(µ3-OCH2CH2CH2CH3)][B(C6F5)4] (3), which proceeds
through a redox reaction involving the borane and the THF solvent. In the presence of CH3CN, a
tetranuclear complex formulated as [Zr2(OBut)5(µ-OBut)2(µ-N,N′-N(H)C(CH3)dC(H)Ct N)]2 (5) is
obtained, which results from a C,C coupling reaction between two acetonitrile molecules. When Zr(OBut)4
is treated with (HO)B(C6F5)2, a dimer complex formulated as [Zr(OBut)2{µ-O-OB(OBut)(C6F5)2-κ2-O,O}]2
(7) is formed that contains an unusual ligand bonding mode. The molecular structures of 1, 2, 3, 5, and
7 as well as the adduct B(C6F5)3 · THF (4) and [Zr(OBut)3(µ-OBut)]2(µ-Nt CCH3) (6) have been determined
by X-ray diffraction.
Scheme 1. Alkoxide-Aryl Exchange Reaction
Introduction
The chemistry of the strongly Lewis acidic tris(pentafluor-
phenyl)borane B(C6F5)3 is the subject of numerous applications.
Although the main interest was its established role in the
formation of cationic derivatives for polymerization, different
organic, organometallic, and catalytic applications have been
reported in the past few years.1-4 In our group, we have used
B(C6F5)3 in conjunction with early transition metal group 4 and
5 precursors to afford new and original organometallic com-
plexes related to alkyl abstraction,5 reactivity of small molecules
(CO,6,7 water 8,9) and nitriles.10-15 During this research, while
attempting to generate metal-oxo · B(C6F5)3 adducts or cationic
species from oxo-vanadium(V) amido or alkoxo precursors
treated with B(C6F5)3, we found with others that in certain
alkoxide complexes an exchange reaction between a C6F5 group
of B(C6F5)3 and an alkoxy ligand attached to a metal can occur,
which results in the formation of an organometallic complex
containing a metal-C6F5 moiety, as depicted in Scheme 1.16-19
Particularly, the reaction of [VO(OCH2CF3)3]2 in pentane with
2 equiv of B(C6F5)3 afforded the organometallic vanadium dimer
complex [VO(µ-OCH2CF3)(OCH2CF3)2(C6F5)]2,16 a rare ex-
ample of a structurally established alkyl-vanadium(V) com-
plex.20 The alkoxide-aryl exchange reaction presumably pro-
ceeds through a zwitterionic [M-µ-OR-B(C6F5)3] adduct or a
cationic [M]+[B(OR)(C6F5)3]- intermediate (Scheme 1). Our
preliminary results prompted us to further investigate the
reactivity of other homoleptic early transition metal alkoxides
with B(C6F5)3; in particular, we were interested in attempting
to isolate the elusive intermediate in this reaction (zwitterionic
(11) Choukroun, R.; Lorber, C.; Vendier, L.; Donnadieu, B. Organo-
metallics 2004, 23, 5488–5492.
(12) Choukroun, R.; Lorber, C.; Vendier, L. Organometallics 2007, 26,
3784–3790.
(13) Choukroun, R.; Lorber, C. Eur. J. Inorg. Chem. 2005, 4683–4692.
(14) Choukroun, R.; Lorber, C.; Vendier, L. Organometallics 2007, 26,
3604–3606.
(15) Choukroun, R.; Lorber, C.; de Caro, D.; Vendier, L. Organome-
tallics 2006, 25, 4243–4246.
(16) Wolff, F.; Choukroun, R.; Lorber, C.; Donnadieu, B. Eur. J. Inorg.
Chem. 2003, 628–632.
(17) Hair, G. S.; Cowley, A. H.; Gorden, J. D.; Jones, J. N.; Jones, R. A.;
Macdonald, C. L. B. Chem. Commun. 2003, 424–425.
(18) Klosin, J.; Roof, G. R.; Chen, E. Y. X.; Abboud, K. A. Organo-
metallics 2000, 19, 4684–4686.
(19) Walker, D. A.; Woodman, T. J.; Hughes, D. L.; Bochmann, M.
Organometallics 2001, 20, 3772–3776.
(20) Lorber, C. Vanadium. In ComprehensiVe Organometallic Chemistry
III; Crabtree R. H., Mingos, D. M. P., Eds.; Elsevier: Oxford: 2007; Vol.
5, pp 1-60.
* Corresponding author. E-mail: lorber@lcc-toulouse.fr. Phone: (+33)
5 61 33 31 44. Fax: (+33) 5 61 55 30 03.
(1) Erker, G. Dalton Trans. 2005, 1883–1890.
(2) Focante, F.; Mercandelli, P.; Sironi, A.; Resconi, L. Coord. Chem.
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(4) Piers, W. E.; Chivers, T. Chem. Soc. ReV. 1997, 23, 345–354.
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10.1021/om800234z CCC: $40.75
2008 American Chemical Society
Publication on Web 09/04/2008

5018 Organometallics, Vol. 27, No. 19, 2008
Lorber et al.
Scheme 2. Synthesis of Complexes 1 and 2
or cationic species). Herein we report the reactivity of simple
early transition metal alkoxide complexes M(OR)4 (M ) Ti,
Zr, V) with B(C6F5)3. As part of this study, we also describe
the reaction of Zr(OBut)4 with (HO)B(C6F5)2 and the molecular
structure of the adduct B(C6F5)3 · (THF) and the complex
[Zr(OBut)3(µ-OBut)(µ-Nt CCH3)]2.
Alkoxide Exchange Reactions between M(OPri)4 (M )
Ti, V) and B(C6F5)3. Treatment of the tetra-alkoxides M(OPri)4
(M ) Ti, V) with 1 equiv of B(C6F5)3, at room temperature in
pentane, gives the related organometallic dimer complexes
[Ti(OPri)2(µ-OPri)(C6F5)]2 (1) and [V(OPri)2(µ-OPri)(C6F5)]2 (2),
as shown in Scheme 2. The reaction is accompanied by the
formation of B(OPri)(C6F5)2, which is easily removed by
filtration of the reaction mixtures (due to its higher solubility
Figure 1. Molecular structure of 1, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms
are omitted for clarity. Ti(1)-C(1) 2.1763(17), Ti(1)-O(1)
1.7651(13), Ti(1)-O(2) 1.7583(12), Ti(1)-O(3) 1.9420 (11),
Ti1-O3′ 2.0873(11), Ti(1) · · · Ti(1)′ 3.2299(6), O3-Ti1-O3′
73.53(5), Ti1-O3-Ti1′106.47(5), O(2)-Ti(1)-O(1) 101.98(6),
O(2)-Ti(1)-O(3) 99.93(5), O(1)-Ti(1)-O(3) 118.89(5), O-
(2)-Ti(1)-O(3)′ 167.35(6), O(1)-Ti(1)-O(3)′ 90.68(5), O(3)-
Ti(1)-O(3)′73.49(5),O(2)-Ti(1)-C(1)91.27(6),O(1)-Ti(1)-C(1)
108.61(7), O(3)-Ti(1)-C(1) 127.13(6).
1
in pentane), and identified by its characteristic signals in H,
19F, and 11B NMR spectroscopic studies. Complex 1 was
previously prepared from TiCl(OPri)3 and LiC6F5,21 whereas
the mixture of Ti(OPri)4/B(C6F5)3 was recently studied as
effective catalyst for ring-opening polymerization of propylene
oxide (from which B(OPri)(C6F5)2 appeared to be the active
species).22 Complex 2 is a paramagnetic d1-d1 complex
presenting in its solution EPR spectrum (RT, toluene) the
characteristic eight-band pattern for a V(IV) species (g ) 1.979,
a(51V) ) 54.1 G) and a magnetic moment µeff of 2.44 µB (per
dimer). These studies are in agreement with a d1-d1 species
with two noninteracting electrons.
species (19 F NMR: δ -131.2, -157.8, -164.4; 11B NMR: δ
-5). Unfortunately we were unable to obtain the intermediate
I in a pure form due to its high solubility in pentane. While we
expect this intermediate to be the zwitterionic [V(OiPr)3(µ-OiPr-
(B(C6F5)3)] or cationic [V(OiPr)3][(B(OiPr)(C6F5)3)],23 we can
probably rule out the second, as a cationic compound would
probably be insoluble in pentane. Moreover, both above
suggested zwitterionic or cationic possible intermediates would
certainly be paramagnetic; therefore we propose I to be a dimer
Under the above experimental conditions, the formation of
complex 1 is too rapid to allow an intermediate to be detected.
However, the analogous vanadium system proceeds differently.
Indeed, a light blue pentane solution of V(OPri)4 turned gray-
brown instantly upon addition of B(C6F5)3 to afford after a few
minutes a dark red solution. Later, brown crystals of complex
2 were formed upon standing for 2 weeks at room temperature.
Following the reaction by EPR spectroscopy in a sealed capillary
tube (both in pentane and in toluene solutions) showed the very
rapid decrease of the signal of paramagnetic V(OPri)4 (g )
1.971, a(51V) ) 70.7 G) after addition of B(C6F5)3 (95% of the
signal of V(OPri)4 has disappeared 4 min after the addition),
which implies the formation of an EPR-silent intermediate
species, which further evolved slowly (2 weeks), giving a new
signal for EPR-active complex 2 (g ) 1.979, and a(51V) ) 54.1
G). The formation of a diamagnetic intermediate was also
corroborated by following the same reaction by multinuclear
NMR spectroscopic methods (1H, 19F, 11B, 51V NMR in C6D6
solutions). After complete consumption of paramagnetic V(O-
Pri)4 (ca. after 10 min) it was possible to record spectra with
sharp signals corresponding to B(OPri)(C6F5)2 and a new
complex, I. The 51V NMR spectrum clearly demonstrates the
formation of only one vanadium compound [δ ) -742 ppm
(w1/2 ) 15 Hz) for I, as compared to -630 ppm (w1/2 ) 180
Hz) for V(OiPr)4]. This vanadium compound presents in its 1H
NMR spectrum signals characteristic of terminal and bridging
isopropoxides in a ratio of 3:1, while 19F and 11B NMR spectra
suggest the additional presence of a tetracoordinated boron
1
with bridging isopropoxides (as evidenced by H NMR stud-
ies).24
Crystals of 1 (colorless) and 2 (red-brown), suitable for X-ray
diffraction analysis, were obtained from cold pentane solutions
that allowed the determination of their molecular structure. The
molecular structures of complexes 1 and 2 are presented in
Figures 1 and 2, respectively, with selected bond distances and
angles. During the course of our studies, Johnson and Davidson
have reported the structure of 1 that crystallized in the same
monoclinic space group (P21/n).25 Therefore, we will discuss
only the structure of the vanadium complex 2, but details on
the structure of 1 are given in the Supporting Information (the
data are of better quality than those previously reported).
The molecular structure establishes that, in the solid state, 2
is a centrosymetric dimeric complex composed of two
V(OPri)2(C6F5) units linked by two bridging -OPri ligands. In
this respect, the overall structure of 2 resembles that of 1. The
coordination geometry of the vanadium centers is between a
(23) Chen et al. (see ref 22) showed that the aluminum analogue
Al(C6F5)3 forms the stable isopropoxy-bridged bimetallic adduct [Ti(O-
iPr)3(µ-OiPr)(Al(C6F5)3)], which is a monomer in the solid state.
(24) Selected examples of diamagnetic vanadium(IV) dimers: (a) Preuss,
F.; Becker, H.; Kaub, J.; Sheldrick, W. S. Z. Naturforsch. 1988, 43b, 1195–
1200. (b) Carrano, C. J.; Nunn, C. M.; Quan, R.; Bonadies, J. A.; Pecoraro,
V. L. Inorg. Chem. 1990, 29, 944–951. (c) Lorber, C.; Choukroun, R.;
Donnadieu, B. Inorg. Chem. 2002, 41, 4217–4226.
(21) Rausch, M. D.; Gordon, H. B. J. Organomet. Chem. 1974, 74, 85–
90.
(22) Rodriguez-Delgado, A.; Chen, E. Y. X. Inorg. Chim. Acta 2004,
357, 3911–3919.
(25) Johnson, A. L.; Davidson, M. G.; Mahon, M. F. Dalton Trans.
2007, 5405–5411.

ReactiVity of B(C6F5)3
Organometallics, Vol. 27, No. 19, 2008 5019
Scheme 3. Synthesis of Complex 3
OCH2CH2CH2CH3)][B(C6F5)4] (3) were obtained in low yield
and characterized by an X-ray structure determination. Com-
pound 3 crystallized in monoclinic P21/a space group, with half
a molecule of acetonitrile. The molecular structure of complex
3 is presented in Figure 3 with selected bond distances and
angles. Each zirconium atom is surrounded by six oxygen atoms
in a distorted octahedral geometry. Overall, the ionic structure
results from the coordination of a µ3-O(CH2)3CH3 group to three
metal center units, with loss of two of the 12 initial tert-butoxyde
ligands (as tert-butanol) of the three Zr(OBut)4. The formation
of the -O(CH2)3CH3 moiety is explained by ring-opening of a
THF molecule (see below). Zr-O bond distances are in the
expected range for terminal alkoxide-type ligands (average
1.91-1.92 Å), µ2-bridging alkoxide ligands (average 2.17-2.19
Å), and µ3-bridging alkoxide ligands (average 2.28-2.35 Å).
The three zirconium centers occupy an equilateral triangle, and
bridging oxygen atoms are contained in the Zr3 plane (average
Zr-O-Zr 102.18°, O-Zr-O 137.26°, values nearly expected
for a planar C3V-distorded regular hexagon). Terminal alkoxides
(OBut) are nearly situated perpendicular to this plane, and
oxygen atoms O(6) and O(8) are in apical location from this
plane.
Figure 2. Molecular structure of 2, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms are
omitted for clarity. V(1)-C(1) 2.1127(17), V(1)-O(1) 1.7980(12),
V(1)-O(2) 1.7970(13), V(1)-O(3) 1.9220(11), V(1)-O(3)′
2.0276(12), O(3)-V(1)-O(1) 119.91(6), O(3)-V(1)-O(2) 92.54(5),
O(1)-V(1)-O(2) 102.88(6), O(1)-V(1)-O(3)′ 95.68(6), O(2)
-V(1)-O(3)′161.16(5),O(3)-V(1)-O(3)′75.14(5),O(1)-V(1)-C(1)
108.03(7), O(2)-V(1)-C(1) 90.84(6), O(3)-V(1)-C(1) 129.71(6),
O(3)′-V(1)-C(1) 86.46(6).
five-coordinate distorted square pyramid and a trigonal bipyra-
mid (52% on the Berry pseudorotation path between D3h and
C4V, τ ) 0.52).26 Terminal and bridged V-O bond distances
and angles are in their expected range [ca. 1.71-1.81 Å and
1.92-2.03 Å, respectively] as well as the V-C bond distance
[2.1127(18) Å].16
Reactivity Studies between Zr(OBut)4 and B(C6F5)3. Simi-
larly, we studied the reactivity of Zr(OBut)4 with B(C6F5)3. First,
an NMR tube reaction of Zr(OBut)4 with 1 equiv of B(C6F5)3
carried out in CD2Cl2 shows that this reaction is not selective,
and a mixture of unidentified -OBut peaks is observed in the
1H NMR spectrum. 19F and 11B NMR spectra show the presence
of the unexpected [B(C6F5)4]- anion, as well as some
B(OBut)(C6F5)2, the latter being identified by its 19F and 11B
NMR spectra by analogy with known analogues B(OR)(C6F5)2
(R )Et,27 i-Pr,22 n-Bu28).29 The formation of B(OBut)(C6F5)2
demonstrates that alkoxide-aryl exchange reaction is not
prohibited by steric bulk of the tert-butyl group.
In order to isolate a zirconium species, Zr(OBut)4 was then
reacted with B(C6F5)3 in pentane solution (see Scheme 3). The
reaction afforded a white precipitate. Several attempts to grow
crystals of that compound failed, except when using CH3CN-
THF mixture of solvents. In CH3CN-THF (10:1), crystals of
the trinuclear zirconium salt [Zr3(OBut)6(µ2-OBut)3(µ3-OBut)(µ3-
Figure 3. Molecular structure of the cationic part of 3 (the anion
[B(C6F5)4]- and the solvent of crystallization (1/2 CH3CN) are
omitted for clarity), showing 50% probability ellipsoids and partial
atom-labeling scheme. Hydrogen atoms are omitted for clarity.
O(1)-Zr(2) 2.179(3), O(1)-Zr(1) 2.192(3), O(2)-Zr(2) 2.169(3),
O(2)-Zr(3) 2.175(3), O(3)-Zr(1) 2.184(3), O(3)-Zr(3) 2.192(3),
O(4)-Zr(2) 1.921(3), O(5)-Zr(2) 1.918(3), O(6)-Zr(2) 2.324(3),
O(6)-Zr(1) 2.334(3), O(6)-Zr(3) 2.352(3), O(7)-Zr(1) 1.922(3),
O(8)-Zr(1) 2.276(3), O(8)-Zr(3) 2.310(3), O(8)-Zr(2) 2.339(3),
O(9)-Zr(3) 1.921(3), O(10)-Zr(3) 1.924(3), O(11)-Zr(1) 1.914(3),
Zr(1) · · · Zr(3) 3.4083(6), Zr(1) · · · Zr(2) 3.4087(7), Zr(2) · · · Zr(3)
3.4079(6), O(11)-Zr(1)-O(7) 99.24(13), Zr(2)-O(1)-Zr(1)
102.49(12), Zr(2)-O(6)-Zr(3) 93.58(10), Zr(1)-O(6)-Zr(3)
93.33(10), Zr(1)-O(8)-Zr(3) 95.99(10), Zr(1)-O(8)-Zr(2)
95.21(10), O(11)-Zr(1)-O(1) 99.65(12).
(26) τ is the angular parameter commonly used to describe the geometry
around the metal center in pentacoordinate complexes and defined as τ )
(R-ꢀ)/60 (R and ꢀ are the two largest L-M-L bond angles,with R g ꢀ).
Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J. V. J. Chem. Soc.,
Dalton Trans. 1984, 1349–1356.
(27) Duchateau, R.; Lancaster, S. J.; Thornton-Pett, M.; Bochmann, M.
Organometallics 1997, 16, 4995–5005.
(28) Parks, D. J.; Piers, W. E.; Yap, G. P. A. Organometallics 1998,
17, 5492–5503.
(29) Piers et al. reported that diborane C6F4-1,2-[B(C6F5)2]2 rapidly
abstracts OCH3- from Cp2Zr(OCH3)2, but the cation in the resulting species
is not Very stable. Williams, V. C.; Irvine, G. J.; Piers, W. E.; Li, Z.; Collins,
S.; Clegg, W.; Elsegood, M. R. J.; Marder, T. B. Organometallics 2000,
19, 1619–1621.

5020 Organometallics, Vol. 27, No. 19, 2008
Lorber et al.
To better understand this reaction, we investigated the reaction
of Zr(OBut)4 and B(C6F5)3 by varying the ratio of the reactants
and using different solvents (in NMR tube reactions). Neverthe-
less, we were unable to explain more precisely this reaction
and the redox reaction leading to this salt (see Experimental
Section). The formation of an intermediate species [Zr(OBut)3-
(C6F5)] that would react with the borane present in the solution
to afford the transient salt [Zr(OBut)3][B(C6F5)4] could be
envisioned, but the determination of the mechanism of formation
of 3 was not elucidated. A titanium compound with a similar
structure (with a [Ti3(OPri)11]+ core) was recently reported from
the reaction of [Na][Ti(OPri)5] with FeCl3 that affords two
different products: the ionic compound [Ti3(OPri)6(µ2-OPri)3(µ3-
OPri)2][FeCl4] and the mixed oxide-alkoxide iron complex
[Fe5Cl5(µ5-O)(µ2-OPri)8].30 The main feature of the cationic
zirconium part in 3 is the opening of a THF molecule into a
n-butoxide group, µ3-bonded to the three zirconium atoms,
which involves the abstraction of a hydrogen atom from the
reaction medium. The THF ring-opening reaction that allows
the isolation of 3 may be explained by the presence in solution
of the transient cationic species [Zr(OBut)3]+, but may also be
due to other Lewis acids present in the reaction mixture
(B(C6F5)3 and B(OBut)(C6F5)2).31
Figure 4. Molecular structure of 4, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms are
omitted for clarity. B(1)-O(1) 1.5848(18), B(1)-C(14) 1.631(2),
B(1)-C(1) 1.637(2), B(1)-C(8) 1.645(2), O(1)-B(1)-C(14)
108.89(11), O(1)-B(1)-C(1) 107.96(11), O(1)-B(1)-C(8) 104.60-
(11), C(14)-B(1)-C(1) 105.26(11), C(14)-B(1)-C(8) 114.25(11),
C(1)-B(1)-C(8) 115.65(11).
1H and 13C NMR spectroscopic data (as well as 1H/1H
1
NOESY and H/13C HMQC chemical shift correlations) of 3
filtrate, after evaporation to dryness, gave a pale yellow solid,
which was analyzed by NMR spectroscopy in CD2Cl2 (1H, 19F,
and 11B) as being a mixture of B(OBut)(C6F5)2 and other Zr-
OBut peaks in the range 1.2-1.8 ppm. However, addition of
CH3CN to this solid caused evolution of H2 gas and formation
in the NMR tube of a few yellow crystals of a new complex, 5.
This compound was unambiguously characterized by an X-ray
structure analysis as being the tetrametallic neutral complex
[Zr2(OBut)5(µ-OBut)2(µ-N,N′-N(H)C(CH3)dC(H)Ct Ν)]2 (5).
Salient structural features for the zirconium complex 5 are
depicted in Figure 5, with selected bond distances and angles.
The crystal structure of 5 revealed a tetrametallic compound
composed of two dimeric [Zr2(OBut)5(µ-OBut)2] units held
together by two µ-N,N′-N(H)C(CH3)dC(H)Ct N moieties.
Dimerization of CH3CN molecules through C,C coupling
occurred to form the organic crotonylamido linker. The croto-
nylamido arrangement, also obtained by activation and dimer-
ization of acetonitrile, was recently reported by us for zirconium
chemistry (starting from Cp2ZrPh2, CH3CN, and B(C6F5)3)12
and by Teuben for yttrium chemistry.35 Zr-O bond lengths are
found in the expected range (ca. 1.91-1.95 Å), and the
crotonylamido linker has similar bond lengths and angles to
those found in the above-mentioned zirconocene and yttrium
complexes. At one side of the crotonylamido ligand, the nitrogen
atom [N(1)-H] of an imine functionality [the CN bond distance
is in agreement with a double bond: C(9)dN(1) 1.349(3) Å] is
bridging two distorded octahedral zirconium centers [Zr(1)-N(1)
2.413(2) Å, Zr(2)-N(1) 2.404(2) Å]. The second side of the
ligand contains a nitrile skeleton by which it is coordinated to
the zirconium center [Zr(2)′] of a symmetry-related dimeric unit
[Zr(2)′-N(2)′ 2.306(2) Å]. The Ct N bond distance of 1.154(3)
Å is consistent with a triple-bond character associated with a
nearly linear N(2)-C(33)-C(10) angle (175.0(3)°). As a result,
this crotonylamido fragment can be considered as a donor ligand
to the dimer form of Zr(OBut)4.
in THF-d8 show the peaks attributed to the different terminal
and bridged -OBut groups and to the -OBun group (see
Experimental Section). Attempts to generate 3 directly from
Zr(OBut)4, B(C6F5)3, and the borane adduct THF · B(C6F5)3 in
CD2Cl2 failed.32 In this case, the 11B NMR spectrum shows
mainly the presence of unreacted THF · B(C6F5)3 (δ 3.3 ppm),
together with a peak at 38 ppm attributed to B(OBut)(C6F5)2
(which demonstrates again that an aryl-alkoxide exchange
reaction occurs between the zirconium alkoxide precursor and
the borane) and other unattributed minor peaks (δ 23.3, -4.7,
and -13.0 ppm).
During our different attempts to get information on the above
reaction, the known3 adduct THF · B(C6F5)3 (4) was accidentally
obtained as crystals suitable for an X-ray structure determination.
The molecular structure of 4 is presented in Figure 4. The B-O
bond distance of 1.5847(18) Å has to be compared to that of
the related THF · B(C6H5)3 (1.6500(17) Å)33 and to Mes2P-
C6F4-B(C6F5)2 · THF (1.625 Å),34 reflecting again the stronger
Lewis acidity of B(C6F5)3.
In an other attempt to probe this reaction, but now using 2
or 3 equiv of Zr(OBut)4 and 1 equiv of B(C6F5)3 and in pentane
solution, we obtained a white precipitate. As above, the
precipitate was isolated by filtration and analyzed by 19F and
1H NMR spectroscopy, showing again the characteristic peaks
of the [B(C6F5)4]- anion and a broad signal in the range
1.30-1.90 ppm attributed to different Zr-OBut species. The
(30) Reis, D. M.; Nunes, G. G.; Sa, E. L.; Friedermann, G. R.; Mangrich,
A. S.; Evans, D. J.; Hitchcock, P. B.; Leigh, G. J.; Soares, J. F. New J. Chem.
2004, 28, 1168–1176.
(31) For selected examples of THF-ring-opening mediated by Lewis
acidic metal centers or main-group Lewis acids, see:(a) Guo, Z-Y.; Bradley,
P. K.; Jordan, R. F. Organometallics 1992, 11, 2690–2693. (b) Boisson,
C.; Berthet, J. C.; Lance, M.; Nierlich, M.; Ephritikhine, M. Chem. Commun.
1996, 2129–2130. (c) Borkowsky, S. L.; Jordan, R. F.; Hinch, G. D.
Organometallics 1991, 10, 1268–1274. (d) Welch, G. C.; Masuda, J. D.;
Stephan, D. W. Inorg. Chem. 2006, 45, 478–480.
(32) This experiment suggests that the solvent is the source of proton
in the reaction conducted in THF.
(33) Niehues, M.; Erker, G.; Meyer, O.; Fro¨hlich, R. Organometallics
2000, 19, 2813–2815.
(34) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Science
2006, 314, 1124–1126.
Although fortuitous, the issue of this reaction was confirmed
by the characterization of a few crystals of 5 (with identical
(35) Duchateau, R.; Tuinstra, T.; Brussee, E. A. C.; Meetsma, A.; van
Duijnen, P. T.; Teuben, J. H. Organometallics 1997, 16, 3511–3522.

ReactiVity of B(C6F5)3
Organometallics, Vol. 27, No. 19, 2008 5021
Figure 6. Molecular structure of 6, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms are
omitted for clarity. C(33)-N(1) 1.243(5), N(1)-Zr(1) 2.649(3),
O(1)-Zr(2)1.9662(18),O(1)-Zr(1)2.215(2),O(2)-Zr(1)2.1496(19),
O(2)-Zr(2) 2.2618(19), O(3)-Zr(1) 1.959(2), O(4)-Zr(1) 1.924(2),
O(5)-Zr(1) 2.037(2), O(6)-Zr(2) 2.072(2), O(7)-Zr(2) 2.074(2),
O(8)-Zr(2) 1.765(2), Zr(1) · · · Zr(2) 0.3.2902(4) N(1)-C(33)-
C(34) 179.5(5), Zr(2)-O(1)-Zr(1) 103.62(8), Zr(1)-O(2)-Zr(2)
96.43(8).
Figure 5. Molecular structure of 5, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms are
omitted for clarity. C(9)-N(1) 1.349(3), C(9)-C(10) 1.354(4),
C(9)-C(11) 1.514(4), C(10)-C(33) 1.392(4), C(33)-N(2)′ 1.154(3),
O(1)-Zr(2) 2.1832(18), O(1)-Zr(1) 2.2817(18), O(2)-Zr(2)
2.0852(18),O(2)-Zr(1)2.3353(18),N(1)-Zr(2)2.404(2),N(1)-Zr(1)
2.413(2), O(4)-Zr(1) 1.932(2), O(5)-Zr(1) 1.947(2), O(6)-Zr(1)
1.9449(19), O(7)-Zr(2) 1.9233(18), O(8)-Zr(2) 1.9168(19),
N(2)-Zr(2) 2.306(2), N(1)-C(9)-C(10) 121.7(3), N(1)-C(9)-
C(11) 118.2(3), C(10)-C(9)-C(11) 120.1(3), C(9)-C(10)-C(33)
122.7(3), N(2)′-C(33)-C(10) 175.0(3), Zr(2)-O(1)-Zr(1)
95.92(7), Zr(2)-O(2)-Zr(1) 97.07(7), C(9)-N(1)-Zr(2) 124.19-
(18), C(9)-N(1)-Zr(1) 123.84(19), Zr(2)-N(1)-Zr(1) 87.02(7),
C(33)′-N(2)-Zr(2) 161.3(2), O(4)-Zr(1)-O(6) 97.82(9),
O(4)-Zr(1)-O(5) 102.00(10), O(6)-Zr(1)-O(5) 102.13(9),
O(4)-Zr(1)-O(1) 94.73(8), O(6)-Zr(1)-O(1) 153.31(8),
O(5)-Zr(1)-O(1) 98.13(8), O(4)-Zr(1)-O(2) 160.39(8),
O(6)-Zr(1)-O(2) 90.75(8), O(5)-Zr(1)-O(2) 93.33(8), O(1)-
Zr(1)-O(2) 70.78(6), O(4)-Zr(1)-N(1) 92.09(9), O(6)-Zr(1)-
N(1) 86.01(8), O(5)-Zr(1)-N(1) 162.47(9), O(1)-Zr(1)-N(1)
70.04(7), O(2)-Zr(1)-N(1) 70.84(7), O(8)-Zr(2)-N(2) 85.62(8),
O(7)-Zr(2)-N(2) 89.99(8), O(2)-Zr(2)-N(2) 162.24(8), O(1)-
Zr(2)-N(2) 90.46(8), O(8)-Zr(2)-N(1) 87.77(9), O(7)-Zr(2)-
N(1) 171.88(8), O(2)-Zr(2)-N(1) 75.28(7), O(1)-Zr(2)-N(1)
71.83(7), N(2)-Zr(2)-N(1) 88.62(8).
centers is a six-coordinate distorted octahedron. Terminal Zr-O
bond distances span over 1.76-2.07 Å, whereas bridged Zr-O
bond distances are naturally longer [ca. 1.96-2.26 Å]. The
Zr-N bond distances amount to 2.649(3) and 2.886(3) Å.
In a last attempt of getting crystals of hypothetical transient
species [Zr(OBut)3(C6F5)] and [Zr(OBut)3][B(C6F5)4] from a
reaction mixture composed of Zr(OBut)4 and B(C6F5)3, but now
in CH2Cl2-pentane solutions, and due to the presence of
adventitious water during the crystallization process (that lasted
one month at RT and certainly resulted in hydrolysis of B(C6F5)3
into HOB(C6F5)2, see below), we obtained crystals of a new
compound (7). An X-ray crystallographic study of 7 reveals it
to be an unprecedented dimeric complex formulated as [Zr-
(OBut)2{µ-O-OB(OBut)(C6F5)2-κ2-O,O}]2 (see Figure 7).
The rather unusual OB(OBut) bonding mode in 7 prompted
us to prepare this compound in a more direct route. Thus, 7
was prepared more conveniently and in higher yield by the direct
reaction of Zr(OBut)4 and (HO)B(C6F5)2 (Scheme 5). However,
this reaction was not clean, as we also observed signals
corresponding to B(OBut)(C6F5)2. This could suggest the
formation of an intermediate [Zr-OH] species.36
Zirconium centers in complex 7 show a five-coordinate, very
distorted geometry (that is probably best described as a
tetrahedron with the fourth ligand being a chelating {OB(OBut)-
(C6F5)2-κ2-O,O} ligand). Within this new dianionic entity
{OB(OBut)(C6F5)2-κ2-O,O}, it is interesting to note the forma-
tion of an interaction between the oxygen of a tert-butoxide
group attached to the zirconium atom and the boron atom, the
corresponding B-O bond [B(1)-O(1) 1.533(4) Å] being
slightly longer than the B-O bond formed with the bridging
oxygen [B(1)-O(2) 1.480(4) Å]. This could suggest that the
B(1)-O(1) bond is better regarded as a dative bond, rather than
a covalent bond. A dative B-O bond is also more likely
according to 11B NMR spectroscopy of 7 (δ ) +5.0 ppm). To
our knowledge, this type of interaction between an alkoxide
cell parameters) from several experiments. The formation of
the minor byproduct 5 remains unclear and probably results from
a complex cascade of reactions.
In the course of our investigations, we noticed that liquid
Zr(OBut)4 was insoluble in acetonitrile. However, adding a few
drops of dichloromethane to liquid Zr(OBut)4, followed by
addition of CH3CN, afforded a gel, from which we were able
to obtain crystals of the µ-acetonitrile adduct of the dimeric
zirconate [Zr(OBut)3(µ-OBut)]2(µ-Nt CCH3) (6). The structure
of 6 (see Figure 6) is briefly described below, as it is related to
the structure of compound 5 and because no molecular structure
is known for “Zr(OBut)4”. It is important to note that compound
6 could not be isolated because the acetonitrile ligand is removed
during the vacuum drying step, giving back Zr(OBut)4. In the
solid state, 6 is a dimeric complex composed of two Zr(OBut)3
units linked by two bridging -OBut ligands and one N atom
of a CH3CN donor. The coordination geometry of the zirconium
(36) For a review on hydrolysis of metal alkoxides, see: Brinker, C. J.;
Scherer, G. W. In Sol-Gel Science, The Physics and Chemistry of Sol-Gel
Processing; Academic Press: New York, 1990.

5022 Organometallics, Vol. 27, No. 19, 2008
Lorber et al.
Conclusions
We have demonstrated the reactivity of the borane B(C6F5)3
with simple group 4 and 5 metal alkoxides. The reactions of
Ti(OPri)4 and V(OPri)4 with 1 equiv of B(C6F5)3 in pentane at
room temperature yielded dimeric organometallic complexes 1
and 2. Their formation can be regarded as an alkoxide-aryl
exchange reaction between [M-OPri] (M ) Ti, V) and B(C6F5)3,
from the elusive zwitterionic [M(OPri)3(µ-OPri)(B(C6F5)3] or
ionic [M(OPri)3][B(OPri)(C6F5)3] intermediate (that could not
be isolated). The reaction of Zr(OBut)4 and B(C6F5)3 proceeds
differently with formation of more complex products due to
further reaction with solvents (THF, acetonitrile). The formation
of 3 is the result of a more complex reaction, as demonstrated
by the presence of the [B(C6F5)4]- anion. The sterically crowded
tert-butoxide ligand could prevent the formation of a dimeric
species analogous to 1 or 2, leaving a transient species
([Zr(OBut)3(C6F5)] or [Zr(OBut)3][B(C6F5)4]) able to react with
the zirconate and the borane still present in the solution, thus
affording the polymetallic cationic zirconium alkoxide 3, with
an additional n-butoxide ligand due to ring-opening reaction of
THF. In acetonitrile, another unexpected tetrametallic complex
(4) was obtained that results from the dimerization of acetonitrile
molecules and coordination to dimers of Zr(OBut)4. Finally, we
could observe the formation of a new ligand bonding mode in
the reaction of Zr(OBut)4 with the boronic acid (HO)B(C6F5)2,
which leads to unprecedented complex 7. Future work will focus
on the isolation of stable zwitterionic or cationic species
generated during M-OR activation with B(C6F5)3, using ad-
ditional ancillary ligands.
Figure 7. Molecular structure of 7, showing 50% probability
ellipsoids and partial atom-labeling scheme. Hydrogen atoms
are omitted for clarity. C(1)-B(1) 1.633(4), C(7)-B(1) 1.658(5),
O(1)-B(1) 1.533(4), O(1)-Zr(1)′ 2.186(2), O(2)-B(1) 1.480(4),
O(2)-Zr(1) 2.068(2), O(2)-Zr(1)′ 2.208(2), O(4)-Zr(1) 1.885(2),
O(3)-Zr(1)1.909(2),B(1)-O(1)-Zr(1)′97.98(16),B(1)-O(2)-Zr(1)
151.30(19), B(1)-O(2)-Zr(1)′ 98.76(17), Zr(1)-O(2)-Zr(1)′
106.67(8), O(4)-Zr(1)-O(3) 104.62(10), O(4)-Zr(1)-O(2)
103.45(9), O(3)-Zr(1)-O(2) 107.48(9), O(4)-Zr(1)-O(1)′
101.37(9), O(3)-Zr(1)-O(1)′ 100.90(9), O(2)-Zr(1)-O(1)′
135.69(8), O(4)-Zr(1)-O(2)′ 113.77(9), O(3)-Zr(1)-O(2)′
140.41(9), O(2)-Zr(1)-O(2)′ 73.33(8), O(1)′-Zr(1)-O(2)′
63.18(8), O(2)-B(1)-O(1) 99.6(2), O(2)-B(1)-C(1) 107.6(2),
O(1)-B(1)-C(1) 114.3(3), O(2)-B(1)-C(7) 111.0(2), O(1)-B-
(1)-C(7) 105.6(2).
Experimental Section
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon. Solvents were refluxed and dried over
appropriate drying agents under an atmosphere of argon, collected
by distillation, and stored in a drybox over activated 4 Å molecular
sieves. Deuterated solvents were degassed and dried over activated
4 Å molecular sieves. NMR spectra were recorded on Bruker AC
200, AM 250, AMX 400, Avance 400, and Avance 500 spectrom-
eters, were referenced internally to residual protio-solvent (1H)
resonances, and are reported relative to tetramethylsilane (δ ) 0
ppm). 19F NMR spectra were recorded on a Bruker AC 200
(188.298 MHz) or Avance 400 spectrometer (376.441 MHz) and
referenced to CFCl3. 11B NMR (128.37 MHz; reference BF3 · Et2O)
spectra were recorded on a Bruker AMX 400 spectrometer.
Chemical shifts are quoted in δ (ppm). Multiplicities and peak types
are abbreviated: singlet, s; doublet, d; triplet, t; broad, br; Cq,
quaternary carbon. Infrared spectra were prepared as KBr pellets
under argon in a glovebox and were recorded on a Perkin-Elmer
Spectrum GX FT-IR spectrometer. Infrared data are quoted in
wavenumber (cm-1). EPR spectra were obtained by using a Bruker
ESP300E spectrometer. Magnetic susceptibilities were determined
by Faraday’s method. Elemental analyses (C, H, N) were performed
at the Laboratoire de Chimie de Coordination (Toulouse, France).
Ti(Oi-Pr)4 and Zr(Ot-Bu)4 were purchased from Aldrich Inc. or
Strem Inc. and used after distillation under reduced pressure. V(Oi-
Scheme 4. Synthesis of Complex 5
Scheme 5. Synthesis of Complex 7
ligand and a boron-containing ligand is unknown. The Zr-O
bond distances of the dissymmetric bridge are 2.068(2) Å
(Zr(1)-O(2)) and 2.208(2) Å (Zr(1)-O(2)′), while the alkox-
ide Zr-O bond distances are in the normal range (1.89-1.91
Å).
1
Consistent with the solid-state structure, the H NMR data
of 7 in CD2Cl2 exhibit two signals for the two types of Ot-Bu
groups (terminal and bridged alkoxy groups). Furthermore, the
19F NMR spectrum presents broad C6F5 signals for o-, p-, and
m-F atoms, indicative of a dynamical behavior of the C6F5
ligand.37 A dative Zr · · · o-F interaction is suggested in room-
temperature solution. Further studies on this interesting new
ligand bonding mode will be needed to clarify this point.
(37) For selected Zr-F interactions, see ref 12 and:(a) Pintado, G. J.;
Thornton-Pett, M.; Bouwkamp, M.; Meetsma, A.; Hessen, B.; Bochmann,
M. Angew. Chem., Int. Ed. Engl. 1997, 36, 2358–3831. (b) Pintado, G. J.;
Lancaster, S. J.; Thornton-Pett, M.; Bochmann, M. J. Am. Chem. Soc. 1998,
120, 6816–6817. (c) Siedle, A. R.; Newmark, R. A.; Lamanna, W. N.;
Huffman, J. C. Organometallics 1993, 12, 1491–1492. (d) Hannig, F.;
Fro¨hlich, R.; Bergander, K.; Erker, G.; Petersen, J. L. Organometallics 2004,
23, 4495–4502.

ReactiVity of B(C6F5)3
Organometallics, Vol. 27, No. 19, 2008 5023
Table 1. Crystallographic Data, Data Collection, and Refinement Parameters for Compounds 1-7
1
2
3
4
5
6
7
chemical formula
fw
cryst syst
space group
a, Å
C
30H42F10O6Ti2
C
30H42F10O6V2
C
138H201B2F20O22NZr6
C
22H8BF15
O
C
64H136N4O14Zr4
C
34H75NO8Zr2
C
48H54B2F20O8Zr2
784.38
monoclinic
P21/n
8.9690(7)
16.8220(14)
12.0463(10)
90
96.564(7)
90
1805.6(3)
2
790.52
3551.91
monoclinic
P21/a
20.2421(15)
20.2310(15)
21.0455(17)
90
112.960(8)
90
7935.7(11)
2
1.486
0.487
3638
584.09
monoclinic
P21/n
14.2611(13)
11.2276(8)
14.7056(12)
90
115.967(9)
90
2116.9(3)
4
1.833
0.202
1152
1550.65
monoclinic
P21/n
14.1142(5)
15.6865(5)
18.9583(6)
90
103.676(4)
90
4078.4(2)
2
1.263
0.551
1640
808.39
orthorhombic
Pbca
17.1407(5)
19.1840(6)
26.3148(8)
90
90
90
8653.0(5)
8
1.241
1342.97
triclinic
triclinic
j
j
P1
P1
9.4241(11)
9.5143(12)
11.2825
75.416(15)
67.418(14)
78.047(15)
897.05(19)
2
10.872(2)
11.866(3)
12.017(3)
110.37(2)
105.386(18)
98.153(18)
1353.3(5)
1
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
Dcalc, g cm-3
µ(Mo KR), mm-1
F(000)
1.443
0.532
808
1.463
0.611
406
1.648
0.505
676
0.523
3440
θ range (deg)
measd reflns
3.23 to 30.54
16 234
2.50 to 26.15
8723
2.69 to 26.37
57 500
3.08 to 32.06
21 453
2.69 to 32.10
43 674
2.55 to 28.28
74 061
3.20 to 24.71
8990
no. of unique reflns/Rint 5078/0.0466
3220/0.0352
223/0
16205/0.0779
986/2
7006/0.0298
352/0
13 539/0.0464
413/1
10 703/0.0479
431/0
4593/0.0460
370/0
no. of params/restraints
223/0
final R indices all data
R1 ) 0.0706,
R1 ) 0.0355,
wR2 ) 0.0920
R1 ) 0.0335,
wR2 ) 0.0904
1.062
R1 ) 0.1111,
wR2 ) 0.1191
R1 ) 0.0474,
wR2 ) 0.1018
0.869
R1 ) 0.0877,
wR2 ) 0.0971
R1 ) 0.0396,
wR2 ) 0.084
0.860
R1 ) 0.0916,
wR2 ) 0.1330
R1 ) 0.0370,
wR2 ) 0.0948
1.081
R1 ) 0.0728,
wR2 ) 0.1272
R1 ) 0.0357,
wR2 ) 0.0939
1.162
R1 ) 0.0488,
wR2 ) 0.1023
R1 ) 0.0404,
wR2 ) 0.0973
1.013
wR2 ) 0.0957
final R indices [I > σ2(I)] R1 ) 0.0390,
wR2 ) 0.0862
goodness of fit
0.928
∆Fmax, ∆Fmin
0.402 and -0.327 0.244 and -0.321 0.603 and -0.603
0.256 and -0.217 0.842 and -0.694 0.918 and -0.630 0.819 and -0.814
Pr)4,38 B(C6F5)3,39,40 and (HO)B(C6F5)241,42 were prepared accord-
ing to literature procedures.
temperature. The reaction mixture was stirred for 2 h at room
temperature and then cooled in the freezer (-18 °C) overnight.
Red crystals were filtered off, washed with pentane, and dried under
vacuum (152 mg, 64%). 1H NMR (C6D6): δ 4.60 (br m, 1H, CH),
1.16 (d, J ) 6.1 Hz, 3H, CH3). 19F NMR (C6D6): δ -119.7 (d,
o-F, C6F5), -157.3 (t, p-F, C6F5), -162.2 (br s, m-F, C6F5). Anal.
Calc for C15H21F5O3Ti: C, 45.94; H, 5.40. Found: C, 45.50; H, 5.32.
The 1H, 19F, and 11B NMR (C6D6) data of the filtrate (after
workup) showed signals corresponding to [B(OPri)(C6F5)2] (1H
NMR: δ 4.13 (sept, J ) 6.0 Hz, 1H, CH), 1.07 (d, J ) 6.0 Hz, 1H,
CH3). 19F NMR δ -132.8, -149.2, -160.8. 11B NMR: δ 39.7).
[V(OPri)2(µ-OPri)(C6F5)]2 (2). A suspension of B(C6F5)3 (281
mg, 0.35 mmol) in pentane (4 mL) was added dropwise to a blue
solution of [V(OPri)4] (100 mg, 0.35 mmol) in pentane (3 mL) at
room temperature, causing an immediate color change to brown.
The reaction mixture was stirred for 2 h at room temperature and
then left 2 weeks at RT. Brown crystals were filtered off, washed
with cold pentane, and dried under vacuum (94 mg, 68%). EPR
(toluene, RT): g ) 1.974; a(51V) 54.1 G. µeff ) 2.44 µB (per dimer).
51V NMR (C6D6): δ -554 (w1/2 ) 260 Hz). Anal. Calc for
C15H21F5O3V: C, 45.58; H, 5.36. Found: C, 45.41; H, 5.15.
Crystal Structure Determination. Crystal data collection and
processing parameters are given in Table 1. Crystals of 1 (colorless
blocks), 2 (brown-red blocks), 3 (colorless plates), 4 (colorless
blocks), 5 (colorless blocks), 6 (colorless blocks), and 7 (colorless
blocks) were obtained. The selected crystals, sensitive to air and
moisture, were mounted on a glass fiber using perfluoropolyether
oil and cooled rapidly to 180 K in a stream of cold N2. For all the
structures, data were collected at low temperature (T ) 180 K) on
a Stoe imaging plate diffraction system (IPDS), equipped with an
Oxford Cryosystems Cryostream cooler device or an Oxford
Diffraction Kappa CCD Excalibur diffractometer equipped with an
a cryojet from Oxford Instruments and using graphite-monochro-
mated Mo KR radiation (λ ) 0.71073Å). Final unit cell parameters
were obtained by means of a least-squares refinement of a set of
8000 well-measured reflections, and crystal decay was monitored
during data collection by measuring 200 reflections by image; no
significant fluctuation of intensities has been observed. Structures
have been solved by means of direct methods using the program
SIR9243 and subsequent difference Fourier maps, models were
refined by least-squares procedures on F2 by using SHELXL-9744
integrated in the package WINGX version 1.64,45 and empirical
absorption corrections were applied to the data.46 Details of the
structure solution and refinements are given in the Supporting
Information (CIF file). A full listing of atomic coordinates, bond
lengths and angles, and displacement parameters for all structures
has been deposited at the Cambridge Crystallographic Data Centre.
[Ti(OPri)2(µ-OPri)(C6F5)]2 (1). A solution of B(C6F5)3 (281 mg,
0.55 mmol) in pentane (4 mL) was added dropwise to a solution
of [Ti(OPri)4] (200 mg, 0.55 mmol) in pentane (3 mL) at room
The 1H, 19F, and 11B NMR (C6D6) data of the filtrate (after
workup) showed signals corresponding to [B(OPri)(C6F5)2] (see
synthesis of 1). This reaction was monitored by means of EPR (in
a sealed capillary tube, in pentane and in toluene solutions) and
NMR (1H, 19F, 11B, 51V, in C6D6) spectroscopic analyses, which
proved the reaction to proceed through an EPR-silent, red inter-
1
mediate species I. H NMR (C6D6): δ 4.86 (br m, 3H, CH), 4.30
(sept, J ) 6.0 Hz, 1H, CHbridged), 1.09 (d, J ) 6.0 Hz, 3H, CH3bridged),
0.87 (d, J ) 6.1 Hz, 3H, CH3). 19F NMR (C6D6): δ -131.2 (br s,
o-F, C6F5), -157.8 (s, p-F, C6F5), -164.4 (br s, m-F, C6F5).). 11
B
NMR (C6D6): δ -5.0. 51V NMR (C6D6): δ -742 (w1/2 ) 15 Hz).
[Zr3(OBut)6(µ2-OBut)3(µ3-OBut)(µ3-OCH2CH2CH2CH3)][B(C6-
F5)4], (CH3CN)0.5(3). A solution of B(C6F5)3 (120 mg, 0.23 mmol)
in pentane (6 mL) was added dropwise to a solution of [Zr(OBut)4]
(90 mg, 0.23 mmol) in pentane (5 mL) at room temperature. The
white precipitate obtained was filtered off and washed with pentane
(yield 110 mg). In THF-d8 the 1H NMR showed the characteristic
peaks of 3 (see below) with two other -OBut groups (one at 1.41
ppm related to B(OBut)(C6F5)2 and a second unattributed peak at
(38) Bradley, D. C.; Mehta, L. M. Can. J. Chem. 1962, 40, 1183–1188.
(39) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245–
250.
(40) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1966, 5, 218–
225.
(41) Chambers, R. D.; Chivers, T. J. Chem. Soc. 1965, 3933–3939.
(42) Beringhelli, T.; D’Alfonso, G.; Donghi, D.; Maggioni, D.; Mer-
candelli, D.; Sironi, A. Organometallics 2003, 22, 1588–1590.
(43) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(44) Sheldrick, G. M. SHELX97 [Includes SHELXS97, SHELXL97,
CIFTAB]-Programs for Crystal Structure Analysis (Release 97-2); Institu¨t
fu¨r Anorganische Chemie der Universita¨t: Go¨ttingen, Germany, 1998.
(45) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(46) Walker, N.; Stuart, D. Acta Crystallogr. A 1983, 39, 158–166.
1
1.27 ppm; for comparison the H NMR spectrum of [Zr(OBut)4]
in THF-d8 shows a peak at 1.37 ppm). Dissolution of the precipitate
in CH3CN and THF (10:1) allowed the formation of microcrystals
of 3. Yield: 32 mg (23% based on Zr).

5024 Organometallics, Vol. 27, No. 19, 2008
Lorber et al.
1H NMR (THF-d8): δ 4.13 (AA′B system, app. J ) 17.6 Hz,
OCH2CH2CH2CH3), 2.51 (m, OCH2CH2CH2CH3), 2.10 (s, 9H, µ3-
Ot-Bu), 2.07 (s, 3H, CH3CN), 1.90 (s, 27 H, µ2-Ot-Bu), 1.70 (s,
27 H, Ot-Bu terminal), 1.65 (s, 27 H, Ot-Bu terminal), 1.38 (m,
2H, OCH2CH2CH2CH3), 1.15 (t, J ) 14.7 Hz 2H, OCH2CH2-
CH2CH3). 13C NMR (THF-d8): δ 71.88 (OCH2CH2CH2CH3), 33.69
(OCH2CH2CH2CH3), 33.57 (µ2-Ot-Bu), 32.24 (Ot-Bu terminal),
32.15 (Ot-Bu terminal), 31.70 (µ3-Ot-Bu), 17.89 (OCH2CH2CH2-
CH3), 12.64 (OCH2CH2CH2CH3), 0.34 (CH3CN). 11B NMR (THF-
d8): δ -16.9. 19F NMR (THF-d8): δ -133.0 (d, o-F, C6F5), -165.2
(t,p-F,C6F5),-168.7(m,m-F,C6F5).Anal.CalcforC68H99BF20O11Zr3 · 1/
2CH3CN: C, 46.32; H, 5.70. Found: C, 46.75; H, 5.85.
The solution was left 3 more days at room temperature, during
which time a white precipitate was formed. The precipitate was
filtered off, washed with pentane, and dried under vacuum (see
above). The filtrate was dried under vacuum, giving an oil that
further solidified. Spectroscopic studies (1H, 19F, and 11B NMR)
showed signals corresponding to unreacted Zr(OBut)4, B(OBut)-
(C6F5)2, and other unidentified species. Addition of acetonitrile to
this solid caused gas evolution and formation of crystals of 5 in
very low yield (5-10 mg, which precluded further analysis),
suitable for X-ray diffraction studies.
[Zr(OBut)3(µ-OBut)(µ-Nt CCH3)]2 (6). A clear solution of
Zr(OBut)4 was obtained by addition of 40 mg of dichloromethane
to Zr(OBut)4 (150 mg, 0.3909 mmol), followed by addition of 2
mL of acetonitrile. This solution became more viscous and cloudy
within hours, and crystals of 6 suitable for X-ray diffraction analysis
were obtained. Complex 6 could not be isolated because it loses
the coordinated acetonitrile molecules upon vacuum, re-forming
Zr(OBut)4.
Attempts to Vary the Ratio Zr(OBut)4:B(C6F5)3. Reaction
between 1 equiv of Zr(OBut)4 and 2 equiv of B(C6F5)3 in pentane
and following the same procedure as the one described above for
3 led also to the formation of 3 (the filtrate containing
B(OBut)(C6F5)2 and an excess of free B(C6F5)3).
Reaction between 3 equiv of Zr(OBut)4 and 1 or 1.5 equiv of
B(C6F5)3 in pentane gave a white microcrystalline precipitate (see
also synthesis of compound 5). 19F and 11B NMR studies of the
above solution in pentane-CD2Cl2 showed the formation of
B(OBut)(C6F5)2. Nevertheless, the 1H NMR of the precipitate
showed signal attributed to different alkoxy groups in the range
1.30-1.90 ppm.
[Zr(OBut)2{µ-O(OBut)B(C6F5)2}]2 (7). Solid HOB(C6F5)2 (56
mg, 0.15 mmol) was added to a solution of Zr(OBut)4 (59 mg, 0.15
mmol) in CH2Cl2 (2 mL) at room temperature. The reaction mixture
was stirred for 24 h at room temperature. Slow evaporation afforded
white crystals of 7. The crystals were filtered off, washed with THF,
and dried under vacuum. Yield: 55 mg (55%). 1H NMR (CD2Cl2):
δ 1.41 (s, 9H, BOt-Bu); 1.27 (s, 18H, Ot-Bu). 19F NMR (CD2Cl2):
δ -54.8 (br, o-F, C6F5), -82.3 (p-F, C6F5), -88.6 (m-F, C6F5).
11B NMR (CD2Cl2): δ 5.0. Anal. Calc for C24H27BF10O4Zr: C,42.93;
H, 4.05. Found: C, 42.74; H, 3.83.
B(C6F5)3 · (THF) (4). This compound was crystallized by ac-
cident. It can be obtained in quantitative yield by the addition of 1
equiv of THF to a pentane solution of B(C6F5)3.
1H NMR (CD2Cl2): δ 4.25 (app. t, J ) 13.0 Hz, 4H), 2.10 (app.
t, J ) 13.1 Hz, 4H) (in C6D6, the signals are found at 3.23 and
0.91). 19F NMR (CD2Cl2): δ -133.8 (o-F, C6F5), -157.1 (p-F,
C6F5), -164.3 (m-F, C6F5) (in C6D6, the signals are found at δ
-132.9, -154.4 and -162.5). 11B NMR (CD2Cl2): δ 3.3.
[Zr2(OBut)5(µ-OBut)2(µ-N,N′-N(H)C(CH3)dC(H)Ct N)]2 (5).
This compound was obtained as a minor byproduct from a complex
mixture of compounds in the following reaction. A solution of
B(C6F5)3 (208 mg, 0.406 mmol) in pentane (5 mL) was added
dropwise to a solution of Zr(OBut)4 (313 mg, 0.816 mmol) in
pentane (5 mL) at room temperature and was stirred for 1 day.
Acknowledgment. We are grateful to the CNRS for
financial support.
Supporting Information Available: CIF files and tables of
atomic coordinates, bond distances, and angles for the X-ray crystal
structures of complexes 1-7. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM800234Z