Effect of solvent in the reaction of Cp2ZrH{(μ-H)2BR2} (R2 = C4H14, C 8H14) with B(C6F5)3: Formation of [HB(C6F5)3]- salts of the unsupported hydrogen-bridged cations [(μ-H){Cp2Zr(μ-H)(2)Br(2)}(2)](+) (R(2) = C (4)H(8), C(8)H(14)) and [Cp(2)Zr(OEt(2))X](+) (X = OEt, {(μ-H)(2)BC(8)H(14)})

Article abstract of DOI:10.1021/om030692a

Hydride abstraction reactions of the zirconocene cyclic organohydroborate complexes Cp₂ZrH{(μH)₂BR₂} (R₂ = C₄H₈,1; C₃H₁₄, 2) with B(C ₈F₅)₃ were observed as a function of solvent. The reaction in poorly coordinating solvents, benzene and toluene, forms [HB(C₆F₅)₃]^- salts of Zr-H-Zr hydrogen-bridged cations [(μ-H){Cp₂Zr(μ-H)₂BR ₂}₂]⁺ (R₂ = C₄H ₈, 3; C₈H₁₄, 4), in which there is no direct metal-metal bonding between the bridged metals. The unsupported hydrogen-bridged bond in complex 4 was cleaved when it was dissolved in the coordinating solvent THF to produce the neutral complex 2 and the ionic complex [Cp ₂Zr(THF){(μ-H)₂BC₆H₁₄}][HB(C ₆F₅)₃]. In the coordinating solvent, diethyl ether, the salts of [Cp₂Zr(OEt₂)X]⁺[HB(C ₆F₅)₃]^- (X = OEt, 5; {(-H) ₂BC₈H₁₄}, 6) consisting of zirconocene cations with coordinated solvent ligands were isolated. The formation of 5 involves hydride insertion from zirconium into the carbon oxygen bond of one the coordinated ethers, resulting in the liberation of ethane and the formation of an ethoxyl group coordinated to zirconium. The diethyl ether molecules in the cations 5 and 6 are weakly coordinated to Zr and are displaced in THF solution. Single-crystal X-ray structures of 3, 4, and 5 were determined.

Full text of DOI:10.1021/om030692a

2100
Organometallics 2004, 23, 2100-2106
Effect of Solven t in th e Rea ction of Cp 2Zr H{(µ-H)2BR2}
(R2 ) C4H8, C8H14) w ith B(C6F 5)3: F or m a tion of
[HB(C6F 5)3]- Sa lts of th e Un su p p or ted Hyd r ogen -Br id ged
Ca tion s [(µ-H){Cp 2Zr (µ-H)2BR2}2]+ (R2 ) C4H8, C8H14) a n d
[Cp 2Zr (OEt2)X]+ (X ) OEt, {(µ-H)2BC8H14})
Xuenian Chen, Fu-Chen Liu, Christine E. Plecˇnik, Shengming Liu, Bin Du,
Edward A. Meyers, and Sheldon G. Shore*
Evans Laboratory, Department of Chemistry, The Ohio State University,
Columbus, Ohio 43210
Received December 23, 2003
Hydride abstraction reactions of the zirconocene cyclic organohydroborate complexes Cp2-
ZrH{(µ-H)2BR2} (R2 ) C4H8, 1; C8H14, 2) with B(C6F5)3 were observed as a function of solvent.
The reaction in poorly coordinating solvents, benzene and toluene, forms [HB(C6F5)3]- salts
of Zr-H-Zr hydrogen-bridged cations [(µ-H){Cp2Zr(µ-H)2BR2}2]+ (R2 ) C4H8, 3; C8H14, 4),
in which there is no direct metal-metal bonding between the bridged metals. The
unsupported hydrogen-bridged bond in complex 4 was cleaved when it was dissolved in the
coordinating solvent THF to produce the neutral complex 2 and the ionic complex [Cp2Zr-
(THF){(µ-H)2BC8H14}][HB(C6F5)3]. In the coordinating solvent, diethyl ether, the salts of
[Cp2Zr(OEt2)X]+[HB(C6F5)3]- (X ) OEt, 5; {(µ-H)2BC8H14}, 6) consisting of zirconocene cations
with coordinated solvent ligands were isolated. The formation of 5 involves hydride insertion
from zirconium into the carbon oxygen bond of one the coordinated ethers, resulting in the
liberation of ethane and the formation of an ethoxyl group coordinated to zirconium. The
diethyl ether molecules in the cations 5 and 6 are weakly coordinated to Zr and are displaced
in THF solution. Single-crystal X-ray structures of 3, 4, and 5 were determined.
In tr od u ction
of bridging hydrogens (M-H-B) and terminal hydrogen
(M-H) of the cyclic organohydroborate. A recent report
from this laboratory shows that terminal metal hydride
assumes a required role in the process of intramolecular
hydrogen exchange between Cp and Zr-H-B hydro-
gens.2b,3 Exchange between bridging and Cp-hydrogens
in zirconocene cyclic organohydroborates does not occur
when there is no terminal M-H bond. However, a
terminal hydrogen on zirconium in the complexes Cp2-
ZrH{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14) participates
in intramolecular exchange with bridging and Cp-
hydrogens. The order of exchange as a function of
increasing temperature is as follows: bridging hydro-
gens interchange; then bridging hydrogens and terminal
Zr-hydrogen exchange; then terminal Zr-hydrogen, bridg-
ing hydrogens, and Cp-hydrogens exchange.
Recently, group IV and V transition metal metal-
locene complexes of the cyclic organohydroborate anions
[H2B2(µ-H)(µ-C4H8)2]- (a transannular hydrogen-bridged
10-membered ring anion), [H2BC5H10]-, and [H2BC8H14]-
(the hydroborate anion of the 9-BBN dimer) were
investigated.1 A common structural feature of all those
complexes is the M-H-B (3c-2e) bond, like that ob-
served in transition metal tetrahydroborate complexes,
but the reactivity and fluxional behavior of cyclic
organohydroborate complexes are unlike those of the
tetrahydroborate analogues.2 Without the contribution
of hydrogen exchange between M-H-B and B-H bonds
that occurs in tetrahydroborate derivatives, it is possible
to isolate and investigate the reactivity and interchange
Another point of interest with respect to the reactivity
of the hydrogen bridge systems of the cyclic organohy-
droborates of the group IV and V metals is their
reactions with a hydride abstraction reagent such as
B(C6F5)3.4 The question of interest is whether the
(1) (a) Ho, N. N.; Bau, R.; Plecˇnik, C. E.; Shore, S. G.; Wang, X.;
Schultz, A. J . J . Organomet. Chem. 2002, 654, 216. (b) Liu, F.-C.;
Plecˇnik, C. E.; Liu, S.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Organomet.
Chem. 2001, 627, 109. (c) Liu, F.-C.; Du, B.; Liu, J .; Meyers, E. A.;
Shore, S. G. Inorg. Chem. 1999, 38, 3228. (d) Liu, F.-C.; Liu, J .; Meyers,
E. A.; Shore, S. G. Inorg. Chem. 1999, 38, 2169. (e) Liu, J .; Meyers, E.
A.; Shore, S. G. Inorg. Chem. 1998, 37, 496. (f) J ordan, G. T., IV; Liu,
F.-C.; Shore, S. G. Inorg. Chem. 1997, 36, 5597. (g) J ordan, G. T., IV;
Shore, S. G. Inorg. Chem. 1996, 35, 1087.
(2) (a) Chen, X.; Lim, S.; Plecˇnik, C. E.; Liu, S.; Bin, D.; Meyers, E.
A.; Shore, S. G. Inorg. Chem. 2004, 43, 692. (b) Chen, X.; Liu. S.;
Plecˇnik, C. E.; Liu, F.-C.; Fraenkel, G.; Shore, S. G. Organometallics
2003, 19, 275. (c) White, J . P., III; Deng, H.; Shore, S. G. Inorg. Chem.
1991, 30, 2337. (d) Marks, T. J .; Kolb, J . R. J . Am. Chem. Soc. 1975,
97, 3397.
(3) (a) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. Inorg. Chem.
1998, 37, 3293. (b) Shore, S. G.; Liu, F.-C. Cationic Metallocenes
Derived from Cyclic Organohydroborate Metallocene Complexes. In
Contemporary Boron Chemistry; Davidson, M. G., Hughes, A. K.,
Marder, T. B., Wade, K., Eds.; The Royal Society of Chemistry: London,
2000; pp 28-35. (c) Chow, A.; Liu, F.-C.; Fraenkel, G.; Shore, S. G.
Magn. Reson. Chem. 1998, 36, 145.
10.1021/om030692a CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/30/2004

Formation of [HB(C6F5)3]- Salts
Organometallics, Vol. 23, No. 9, 2004 2101
Sch em e 1
bridging hydrogen in the M-H-B (3c-2e) bond is
sufficiently basic for it to be abstracted to generate a
metallocene cation. The reagent B(C6F5)3 has been wide-
ly employed as an alkyl carbanion abstracting reagent
to produce metallocene cations for olefin polymeriza-
tion,5 and weakly coordinating anions containing boron
and aluminum can greatly improve the activity of met-
allocene catalysts used in industrial olefin polymeriza-
tion.6 We found that the bridging hydrogens are suf-
ficiently basic for abstraction to produce ionic complexes
in the reaction of B(C6F5)3 with the complexes Cp2Ti-
{(µ-H)2BR2}and Cp2Nb{(µ-H)2BR2} (R2 ) C4H8, C5H10
,
C8H14), which possess only bridging hydrogens but no
terminal M-H hydrogens.4b,c Furthermore, it was ob-
served that the abstraction product is a function of the
coordinating ability of the solvent. The reaction of ti-
tanocene cyclic organohydroborates Cp2Ti{(µ-H)2BR2}
(R2 ) C4H8, C5H10, C8H14) with B(C6F5)3 in the poorly
coordinating solvent toluene produces the covalent
metathesis product Cp2Ti{(µ-H)2B(C6F5)}, while in the
coordinating solvent diethyl ether, the [HB(C6F5)3]- salt
of the titanocene cation, [Cp2Ti(OEt2)2]+, is formed.4c On
the other hand, the reaction of niobocene cyclic orga-
BC4H8}2][HB(C6F5)3], 3, and [(µ-H){Cp2Zr(µ-H)2BC8H14}2]-
[HB(C6F5)3], 4, are produced (reaction 1). Each complex
2 Cp2ZrH{(µ-H)2BR2} + B(C6F5)3
(R2 ) C4H8, 1; C8H14, 2)
f
[(µ-H){Cp2Zr(µ-H)2BR2}2][HB(C6F5)3]
(R2 ) C4H8, 3; C8H14, 4)
(1)
nohydroborates Cp2Nb{(µ-H)2BR2} (R2 ) C4H8, C5H10
,
C8H14) with B(C6F5)3 is much more complicated. In the
poorly coordinating solvent toluene, the product is the
[HB(C6F5)3]- salt of the triniobocene cation [Cp2Nb(µ-
H )(η5-η1-C5H 4)Nb(η5-η1-C5H 4)2Nb{(µ-H )(η5-C5H 4B-
(C6F5)2)}]+, but the neutral complex CpNb(C6F5){(µ-
H)(η5-C5H4B(C6F5)2)} is obtained in the coordinating
solvent diethyl ether.4b
For the zirconocene complex Cp2ZrH{(µ-H)2BC4H8},
1, although both terminal and bridging hydrogens are
present, the terminal hydrogen is more hydridic and is
preferentially abstracted by B(C6F5)3 in the poorly
coordinating solvent benzene to form the [HB(C6F5)3]-
salt of the unsupported hydrogen-bridged cation [(µ-H)-
{Cp2Zr(µ-H)2BC4H8}2]+. However, in the coordinating
solvent diethyl ether the [HB(C6F5)3]- salt of the mono-
nuclear cation [Cp2Zr(OEt2)(OEt)]+ is produced.4d In this
paper we provide new examples of hydride abstraction
reactions from the zirconocene complex Cp2ZrH{(µ-
H)2BC8H14}, 2, and provide additional details of hydride
abstractions from 1.
contains a Zr-H-Zr hydrogen-bridged cation. These
cations are unusual since unsupported hydrogen-
bridged systems are usually either neutral or anionic.7
Marks and co-workers showed that the reaction of
Cp*ZrH2 with B(C6F5)3 generates the ionic complex
[(Cp*2 ZrH][HB(C6F5)3] in the solid state.8 A dinuclear
unsupported Zr-H-B bridge was not observed in the
solid state. In the formation of 3 and 4 the reactants
react in a 2:1 ratio, irrespective of their initial ratio.
When the initial reactant ratio is 1:1, the excess
B(C6F5)3 does not react with either 3 or 4. It should be
noted that the reaction of L2ZrMe2 (L ) C5H5, 1,2-
Me2C5H3, Me5C5) with B(C6F5)3 in a 1:1 ratio always
-
produces ion-paired complexes L2ZrMe+MeB(C6F5)3
.
Even when the B(C6F5)3 is in excess, the second methyl
group is still not removed.8 In contrast, the reaction of
L2ZrMe2 (L ) C5H5, 1,2-Me2C5H3, Me5C5) with PBB
(tris(2,2′,2′′-perfluorobiphenyl)borane) in 2:1 ratios gives
the methyl-bridged complexes [L2Zr(Me)(µ-Me)MeZrL2]-
[MePBB]-.9
A possible pathway for the formation of 3 and 4 is
shown in Scheme 1. The terminal Zr-H hydrogen in
complexes 1 and 2 is abstracted by B(C6F5)3 to first
produce a 16-electron Zr cation [Cp2Zr{(µ-H)2BR2}]+.
Then the terminal hydrogen of the second molecule Cp2-
ZrH{(µ-H)2BR2} (R2 ) C4H8, C8H14) adds to the vacant
site on the cation to form the unsupported hydrogen-
bridged cation of 3 and 4. On the basis of the fact that
the product is not influenced by the reactant ratio, it is
believed that the first step of the reaction, hydride
abstraction by B(C6F5)3, is slower than the second step,
hydride addition by Cp2ZrH{(µ-H)2BR2). Moreover, the
Resu lts a n d Discu ssion
F or m a tion of [(µ-H){Cp 2Zr (µ-H)2BR2}2] [HB(C6-
F 5)3] (R2 ) C4H8, 3; C8H14, 4). In reactions of 1 and 2
with B(C6F5)3 in the poorly coordinating solvents ben-
zene and toluene, the complexes [(µ-H){Cp2Zr(µ-H)2-
(4) (a) Ding, E.; Liu, F.-C.; Liu, S.; Meyers, E. A.; Shore, S. G. Inorg.
Chem. 2002, 41, 5329. (b) Liu, S.; Liu, F.-C.; Renkes, G.; Shore, S. G.
Organometallics 2001, 20, 5717. (c) Plecˇnik, C. E.; Liu, F.-C.; Liu, S.;
Liu, J .; Meyers, E. A.; Shore, S. G. Organometallics 2001, 20, 3599.
(d) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Am. Chem. Soc.
2000, 122, 6106.
(5) (a) Chen, E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391, and
references therein. (b) Chen, E. Y.-X.; Abboud, K. A. Organometallics
2000, 19, 5541. (c) Abbenhuis, H. C. L. Angew. Chem., Int. Ed. 1999,
38, 1058. (d) Mcknibht, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98,
2587. (e) Kaminsky, W. J . Chem. Soc., Dalton Trans. 1998, 1413. (f)
Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255. (g) Guram, A.
S.; J ordan, R. F. In Comprehensive Organometallic Chemistry, II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier Science, Ltd.: New
York, 1995; Vol. 4, Chapter 12.
(7) (a) Albinati, A.; Chaloupka, S.; Eckert, J .; Venanzi, L. M.; Wolfer,
M. K. Inorg. Chem. Acta 1997, 259, 305. (b) Bau, R.; Drabnis, M. H.
Inorg. Chim. Acta 1997, 259, 27.
(8) (a) Yang, X.; Sterm, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. (b) Yang, X.; Sterm, C. L.; Marks, T. J . J . Am. Chem. Soc.
1991, 113, 3623.
(6) (a) LaPointe, R. E.; Roof, G. R.; Abboud, K. A.; Klosin, J . J . Am.
Chem. Soc. 2000, 122, 9560. (b) Choukroun, R.; Douziech, B.; Don-
nadieu, B. Organometallics 1997, 16, 5517.
(9) (a) Chen, Y.-X.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J . J .
Am. Chem. Soc. 1998, 120, 6287. (b) Chen, Y.-X.; Stern, C. L.; Yang,
S.; Marks, T. J . J . Am. Chem. Soc. 1996, 118, 12451.

2102 Organometallics, Vol. 23, No. 9, 2004
Chen et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta for 4a
Ta ble 1. Com p a r ison of P r oton Ch em ica l Sh ifts of
2, 3, 4, a n d 6 in Differ en t Solven ts
formula
C54H54B3F15Zr2
H(Cp) Zr-H H(anion)
Zr-H-B
Zr-H-Zr
mol wt
1202.84
monoclinic
P21/c
21.6948(2)
10.2050(1)
24.4983(2)
114.05
4952.97(8)
4
1.613
2432
2.12-27.48
-28 28,-13 13,-31 31
0.27 × 0.23 × 0.12
0.516
0.9407, 0.8733
22 011
11 341
0.0309
99.9%
11 341/0/707
R1 ) 0.0387; wR2 ) 0.1025
R1 ) 0.0642; wR2 ) 0.1438
1.106
cryst syst
space group
a (Å)
b (Å)
c (Å)
3 in toluene
4 in toluene
4 in THF
5.70
5.85
6.65;
6.02
6.64
6.02
4.09
4.38
3.73
-2.03; -3.86
-1.64; -3.60
0.30; -2.21;
-3.34; -4.20
0.32; -2.19
-5.55
-5.20
3.85
3.85
6 in THF
2 in THF
3.74
â (deg)
-3.34; -4.07
volume (Å3)
Z
precipitation of products 3 and 4 from benzene or
toluene prevents reversal of the reaction. The ability of
the Zr-H bond to act as an electron donor in the
formation of a three-center hydrogen bridge was dem-
onstrated in the formation of Cp2Zr{(µ-H)BC4H8(CH2-
Ph)}{µ-H)2BC4H8}.1d
Dc (g/cm3)
F(000)
θ range (deg)
h k l ranges
cryst size (mm)
µ(Mo KR) (mm-1
transmission: max., min.
no. of reflns collected
no. of indep reflns
Rint
completeness to θ
no. of data/restraints/params
final R indices [I g 2σ(I)]b
R indices (all)
)
Complexes 3 and 4 are white solids that are stable
at room temperature under nitrogen. Their 1H NMR
spectra in d8-toluene indicate bridge hydrogen reso-
nances of Zr-H-Zr at δ -5.55 and -5.20 ppm and
bridge hydrogen resonances of Zr-H-B at δ -2.03,
-3.86 and -1.64, -3.60 ppm, respectively. The 1H{11B}
NMR spectra of 3 and 4 show that the proton in the
anion [HB(C6F5)3]- resonates at δ 4.09 and 4.38 ppm,
respectively. The 11B NMR spectrum of complex 3 in
d8-toluene displays one broad signal from Zr-H-B at
δ 36.59 ppm and one broad doublet from [HB(C6F5)3]-
at δ -25.27 ppm. The 11B NMR spectrum of complex 4
in d8-toluene contains one broad doublet at δ -23.44
ppm produced by [HB(C6F5)3]-. The 11B signal from the
cation was not observed, consistent with a report by
Choukroun and co-workers.6b However, in d2-methylene
chloride, in which complex 4 is significantly more
soluble, the 11B NMR spectrum clearly displays two
signals, a broad signal at δ 38.62 ppm (B-H-Zr) and a
doublet at -25.48 ppm ([HB(C6F5)3]-). Its proton NMR
spectrum is consistent with that of 4 in d8-toluene.
GOF
largest diff peak, e/Å3
1.040/-0.911
a
Features common to all determinations: λ(Mo KR) ) 0.71073
Å. R1 ) ∑||Fo| - |Fc||/∑||Fo|; wR2 ) {∑w(Fo - Fc2)2/∑w(Fo2)2}1/2
.
b
2
Ta ble 3. Selected Bon d Dista n ces a n d An gles
for 4a
Bond Distances (Å)
Zr1-Zr2
Zr1-H
Zr2-H
Zr1-B1
Zr2-B2
Zr1-H(1A)
Zr1-H(1B)
3.9755(4)
2.00(4)
2.01(4)
2.578(4)
2.580(4)
1.95(3)
Zr2-H(2A)
Zr2-H(2B)
Zr1-Cpcentroid(C1-C5)
Zr1-Cpcentroid(C6-C10)
Zr2-Cpcentroid(C11-C15)
Zr2-Cpcentroid(C16-C20)
B3-H(3A)
1.95(3)
1.99(3)
2.185(2)
2.190(2)
2.194(2)
2.190(2)
1.21(3)
1.90(3)
Bond Angles (deg)
Zr1-H-Zr2
164(2)
130.86(7)
105(1)
99(1)
100(1)
108.45(9)
108.6(1)
131.39(6)
103(1)
100(1)
103(1)
When 4 is dissolved in THF, on the basis of 11B and H
1
Cpcentroid(C1-C5)-Zr1-Cpcentroid(C6-C10)
H-Zr1-Cpcentroid(C1-C5)
H-Zr1-Cpcentroid(C6-C10)
H-Zr1-B1
NMR spectra, the Zr-H-Zr hydrogen bridge is cleaved
to produce the previously reported neutral complex Cp2-
ZrH{(µ-H)2BC8H14}, 2,2b and the ionic complex [Cp2Zr-
(THF){(µ-H)2BC8H14}][HB(C6F5)3], which also forms
when 6 is dissolved in THF. Comparisons of the proton
chemical shifts of 2, 3, 4, and 6 are given in Table 1.
Molecu la r Str u ctu r es of 3 a n d 4. The molecular
structures of 3 and 4 were determined by single-crystal
X-ray diffraction analysis. The structure of 3 is very
similar to 4 and has been reported simply as a com-
munication, and Supporting Information is available.4d
Crystallographic data for 4 are given in Table 2, and
selected bond distances and bond angles for 4 are given
in Table 3. The structure of the cation of 4 is depicted
in Figure 1. Two structural units of Cp2Zr{(µ-H)2B-
(C8H14)} are connected by a single bridged hydrogen.
Four Cp and two {(µ-H)2B(C8H14)} groups are in a
staggered conformation, Figure 2, with respect to the
Zr-H-Zr axis. The coordination geometry of each
zirconium atom can be described as a distorted tetra-
hedron, consisting of B, H, and the centroids of two Cp
rings at the corners of the tetrahedron.
B1-Zr1-Cpcentroid(C1-C5)
B1-Zr1-Cpcentroid(C6-C10)
Cpcentroid(C11-C15)-Zr2-Cpcentroid(C16-C20)
H-Zr2-Cpcentroid(C11-C15)
H-Zr2-Cpcentroid(C16-C20)
H-Zr2-B2
B2-Zr2-Cpcentroid(C11-C15)
B2-Zr2-Cpcentroid(C16-C20)
108.39(9)
107.52(9)
a
Centroid, Cp, parameters were calculated as unweighted
averages, p , of the corresponding cyclopentadiene carbon param-
eters. Their standard deviations, S p , for the Cp centroids were
estimated from the individual carbon standard deviations: S
)
p
(∑Si2)1/2/N, N ) 5. The geometric relations involving Cp were then
obtained with PARST (Nardelli, M. J . J . Appl. Crystallogr. 1995,
28, 659) in its implementation in WINGX (Farrugia, L. J . J . Appl.
Crystallogr. 1999, 32, 837).
M-H-M bonds, with the exception of the Ru-H-Ru
bond in {Ru2H(µ-H)Cl(syn-Me4[14]aneS4)2}Cl.14b,d The
angle of Zr-H-Zr is 163(2)° for 3 and 164(2)° for 4, and
the Zr‚‚‚Zr distance is 3.8983(9) Å for 3 and 3.9755(4)
Å for 4. A noteworthy feature of both structures is that
the Zr‚‚‚Zr distance is 0.2-0.3 Å longer than the sum
[2radii Zr(cov) + 2radii H(cov)] ) 3.70 Å for a bond angle
of about 164°.16 These results suggest that the Zr-H-
To our knowledge these are the first examples of
unsupported M-H-M hydrogen-bridged bonds of group
IV10-15 even though numerous complexes containing
three-center two-electron M-H-M bonds of groups V,11
VI,12 VII,13 and VIII14 are well known. The Zr-H-Zr
bond is bent, consistent with previously reported
(10) (a) Venanzi, L. M. Coord. Chem. Rev. 1982, 43, 251. (b) Bau,
R.; Teller, R. G.; Kirtley, S. W.; Koetzle, T. F. Acc. Chem. Res. 1979,
12, 176.

Formation of [HB(C6F5)3]- Salts
Organometallics, Vol. 23, No. 9, 2004 2103
F igu r e 1. Molecular structure of the cation of 4, showing
50% probability thermal ellipsoids. Bridging hydrogens are
drawn with arbitrary thermal ellipsoids. All other hydrogen
atoms are omitted for clarity.
Zr bond is an open three-center bond in which there is
no significant overlap of metal orbitals.10,12
As indicated above, the Zr-H-Zr bond in complexes
3 and 4 represents the second type of hydrogen-bridged
bond in which a terminal Zr-H functions as an electron
pair donor in the formation of the bond. In earlier work
from this laboratory it was shown that a Zr-H-B bond
is formed in the reaction of 1 with B(C4H8)CH2Ph to
form Cp2Zr{(µ-H)BC4H8(CH2Ph)}{µ-H)2BC4H8}. The Zr-
H-B bond in this complex is weaker than that of 3 and
4. NMR spectra in benzene indicate that it is dissociated
into 1 and B(C4H8)CH2Ph at room temperature but
exists in solution at -60 °C. It crystallizes as the
hydrogen-bridged species, and its molecular structure
was determined from data obtained at -60 °C. It is of
interest to compare the structural parameters of the Zr-
H-Zr bond with those of the Zr-H-B bond. The bond
F igu r e 2. Staggered configuration of the cation viewed
through the Zr-H-Zr axis in complexes 3 and 4.
angle of the Zr-H-B bond is 159.9(2)°. As in the case
of the Zr-H-Zr bond, the Zr‚‚‚B distance is longer,
3.263 (4) Å, than the calculated Zr‚‚‚B distance, [radius
Zr(cov) + radius B(cov) + 2radii H(cov)] ) 3.09 Å, for
an angle of 159.9(2)°.16
F or m a tion of [Cp 2Zr (OEt2)X] [HB(C6F 5)3] (X )
OEt, 5; X ) {(µ-H)2BC8H14}, 6). Reactions of 1 and 2
with B(C6F5)3 in diethyl ether produce ionic complexes:
[Cp2Zr(OEt2)(OEt)] [HB(C6F5)3], 5, and [Cp2Zr(OEt2){(µ-
H)2BC8H14}][HB(C6F5)3], 6, respectively. Note that in
complex 5 the unit {(µ-H)2BC4H8} has been eliminated
as the organodiborane B2(µ-H)2(µ-C4H8)2, but this unit
is retained in complex 6. Products are formed rapidly
in these reactions; observation of intermediates is
precluded. Reasonable pathways for the formation of 5
and 6 are shown in Scheme 2.
(11) (a) Herrmann, W. A.; Biersack, H.; Ziegler, M. L.; Wulknitz, P.
Angew. Chem., Int. Ed. Engl. 1981, 20, 388. (b) Labinger, J . A.; Wong,
K. A.; Scheidt, W. R. J . Am. Chem. Soc. 1978, 100, 3254.
(12) (a) Hart, D. W.; Bau, R.; Koetzle, T. F. Organometallics 1985,
4, 1590. (b) Petersen, J . L.; Brown, R. K.; Williams, J . M. Inorg. Chem.
1981, 20, 158. (c) Petersen J . L.; Brown, R. K.; Williams, J . M.;
McMullan, R. K. Inorg. Chem. 1979, 18, 3493. (d) Petersen, J . L.;
J ohnson, P. L.; O’Connor, J .; Dahl, L. F.; Williams, J . M. Inorg. Chem.
1978, 17, 3460. (e) Roziere, J .; Williams, J . M.; Stewart, R. P., J r.;
Petersen, J . L.; Dahl, L. F. J . Am. Chem. Soc. 1977, 99, 4497. (f) Love,
R. A.; Chin, H. B.; Koetzle, T. F.; Kirtley, S. W.; Whittlesey, B. R.;
Bau, R. J . Am. Chem. Soc. 1976, 98, 4491. (g) Wilson, R. D.; Graham,
S. A.; Bau, R. J . Organomet. Chem. 1975, 91, C49. (h) Olsen, J . P.;
Kirtley, S. W.; Kirtiey, S. W.; Andrews, M.; Tipton, D. L.; B. R.; Bau,
R. J . Am. Chem. Soc. 1974, 96, 6621. (i) Handy, L. B.; Ruff, J . K.; Dahl,
L. F. J . Am. Chem. Soc. 1970, 92, 7312.
(13) (a) Bullock, R. M.; Brammer, L.; Schultz, A. J .; Albinati, A.;
Koetzle, T. F. J . Am. Chem. Soc. 1992, 114, 5125. (b) Foust, A. S.;
Graham, W. A. G.; Stewart, R. P., J r. J . Organomet. Chem. 1973, 54,
C22.
(14) (a) Yoshida, T.; Adachi, T.; Ueda, T.; Goto, F.; Baba, K.; Tanaka,
T. J . Organomet. Chem. 1994, 473, 225. (b) Albinati, A.; Chaloupka,
S.; Demartin, F.; Koetzle, T. F.; Ruegger, H.; Venanzi, L. M.; Wolfer,
M. K. J . Am. Chem. Soc. 1993, 115, 169. (c) Yoshida, T.; Adachi, T.;
Tanaka, T. J . Organomet. Chem. 1992, 428, C12. (d) Albinati, A.;
Naegeli, R.; Togni, A.; Venanzi, L. M. J . Organomet. Chem. 1987, 330,
35. (e) Albinati, A.; Naegeli, R.; Togni, A.; Venanzi, L. M. Organome-
tallics 1983, 2, 926.
The first step, like in the situation of poorly coordi-
nating solvent benzene or toluene, is the abstraction of
the terminal Zr-H hydrogen by B(C6F5)3 to produce a
16-electron cation [Cp2Zr{(µ-H)2BR2}]+ and [HB(C6F5)3]-.
A solvent molecule of diethyl ether then adds to the
vacant site on zirconium to form the cation [Cp2Zr-
(OEt2){(µ-H)2BR2}]+. For the reaction of 2 with B(C6F5)3,
the reaction is complete and the final product is [Cp2-
Zr(OEt2){(µ-H)2BC8H14}][HB(C6F5)3], 6. However, the
cation produced in the reaction of 1 with B(C6F5)3
undergoes symmetrical cleavage of the hydrogen bridge
bond by the attack of diethyl ether solvent, resulting in
the formation of a terminal Zr-H hydrogen and addition
of a second molecule of diethyl ether to the zirconium.
(15) (a) Takusagawa, F.; Fumagalli, A.; Koetzle, T. F.; Shore, S. G.;
Schmitkons, T.; Fratini, A. V.; Morse, K. W.; Wei, C.-Y.; Bau, R. J .
Am. Chem. Soc. 1981, 103, 5165.
(16) (a) Howard, W. A.; Parkin, G. J . Am. Chem. Soc. 1994, 116,
606. (b) Howard, W. A.; Waters, M.; Parkin, G. J . Am. Chem. Soc. 1993,
115, 4917. (c) Pauling, L. The Nature of the Chemical Bond, 3rd ed.;
Cornell University Press: Ithaca, NY, 1960.
17
The organodiborane B2(µ-H)2(µ-C4H8)2 is also formed
in this reaction. With time it is converted to a trialkyl
borane, based on 11B NMR spectroscopy. The terminal

2104 Organometallics, Vol. 23, No. 9, 2004
Chen et al.
Sch em e 2
determination, the single-crystal X-ray structure of 5
was determined.4d Because of the limited amount of data
that could be obtained and because of severe disorder
with respect to rotation of the Cp rings and the angle
between the rings, a number of restraints were applied
in the solution of the structure. Details are given in the
Experimental Section, and the RES file is in Supporting
Information. Despite the difficulties, the structure of the
molecule is clear.
The coordination geometry about the zirconium center
in 5 is best described as a distorted tetrahedron.
Occupying the corners of the tetrahedron are the centers
of two cyclopentadienyl rings and the two oxygen atoms
of the diethyl ether molecule and the ethoxyl group. The
zirconium-oxygen distance in the Zr-OEt2 linkage,
2.209(8) Å, is consistent with the sum of the covalent
radii, 2.16 Å.16 On the other hand the zirconium-oxygen
distance in the Zr-OEt linkage is significantly shorter,
1.884(8) Å. It is intermediate between a single and
double bond of Zr-O. In the complex CpEt*2Zr(O)-
(NC5H5), which has a zirconium-oxygen double bond,
the Zr-O distance is 1.804(4) Å, the shortest Zr-O
distance reported16a,b to date.
Zr-H hydrogen of the cation inserts into a carbon-
oxygen bond of a coordinated ether to liberate ethane
and form a coordinated ethoxyl group, resulting in the
ionic product [Cp2Zr(OEt2)(OEt)][HB(C6F5)3], 5. The
ethane liberated was identified by GS-mass spectrom-
etry. The insertion of a terminal metal hydride into the
carbon-oxygen bond of a coordinated ether has been
established in earlier work,4d with results most relevant
to this study being the conversion of coordinated THF
to a butoxyl group in the formation of [(C5H4Me)2Zr(O-
n-Bu)(THF)]+.18
Possibly, the short distance in the Zr-O bond in the
Zr-OEt linkage of 5 can be attributed to two contribu-
tions to the bonding in addition to σ character: pπ-dπ
bonding and partial ionic bonding (Zrδ+-Oδ-) between
Zr and O. On the basis of the angles around the oxygen
of the diethyl ether, Zr1-O1-C12, Zr1-O1-C14, and
C12-O1-C14 of 120.3(9)°, 123.0(9)°, and 111.2(11)°,
and the angle around the oxygen of the ethoxyl group,
Zr1-O2-C16 of 153.4(9)°, pπ-dπ bonding between Zr
and O2 of the ethoxyl group can be considered to be a
factor because the large angle of Zr1-O2-C16 implies
more sp character for oxygen.
Both of 5 and 6 are white solids in which the diethyl
ether coordinated to Zr is partially removed by pumping
under vacuum. There is no apparent sign of decomposi-
tion in diethyl ether. In THF solvent, the diethyl ether
in both of 5 and 6 is displaced by THF to give free
diethyl ether. The 11B NMR spectrum of 5 in d8-THF
displays only one boron doublet signal at δ -26.43 ppm
However, after comparing the distance of Zr-O in
different zirconocene complexes, it is concluded that
partial ionic contribution to the bonding (Zrδ+-Oδ-) is
a persuasive factor for short Zr-O distances in the Zr-
OEt linkage.15,16a,b,19-21 When a neutral ligand, like THF
or diethyl ether, coordinates to zirconium, the Zr-O
distance is always longer than the Zr-O distance when
the ligand is an anion (see Table 4).19,20 Undoubtedly,
the electrostatic contribution to bonding is larger when
the anionic ligand is employed. Thus the length of the
Zr-O2 bond (oxygen in the anion of the ethoxyl group)
is significantly shorter than that of the Zr-O1 bond
distance (oxygen in the neutral molecule diethyl ether).
When the anionic ligand is involved, the Zr-O-C angle
is observed to vary from 125.2(3)° 20c to 177(2)° 20q even
though the Zr-O distance is relatively unchanged in
zirconocene complexes.20 This variability of angle, lack
of a directional effect, is consistent with an ionic
contribution to the bonding.
1
(J B-H ) 93 Hz). The H NMR spectrum of 5 consists of
the signal of the Cp hydrogens at δ 6.59, two signals of
the ethoxyl group at δ 4.30 (q, J ) 7 Hz) and 1.21 (t, J
) 7 Hz), and two signals of free diethyl ether, which is
displaced from the cation of 5 by d8-THF in the NMR
tube, at δ 3.38 (q, J ) 7 Hz) and 1.11 (t, J ) 7 Hz). The
1H{11B} NMR spectrum of 5 in d8-THF shows the proton
signal of [HB(C6F5)3]- at δ 3.80 ppm. The 11B NMR
spectrum of 6 in d8-THF consists of two boron signals
at δ 27.60 (br) assigned to boron in the cation (B-H-
Zr) and -26.50 (d, J B-H ) 88 Hz) assigned to boron in
1
[HB(C6F5)3]-. In the H NMR spectrum of 6, the signal
of the Cp hydrogens appears at δ 6.64 (s), and two
signals at δ 3.38 (q, J ) 7 Hz) and 1.11 (t, J ) 7 Hz) are
consistent with free diethyl ether. The multiple reso-
nances at δ 1.90-1.43 are assigned to the R-, â-, and
γ-hydrogens in a group of BC8H14. The hydrogen reso-
nance in [HB(C6F5)3]- appears at δ 3.74 ppm, and the
signal of two bridged hydrogens appears at δ 0.32 and
A thorough study by Parkin and co-workers16a,b,20c,d
indicates that both the Zr-O single and double bond
lengths in two series of chalcogenido and hydrochalco-
genido complexes are anomalously short on the basis
of the sum of the covalent radii of Zr and O with respect
1
-2.19 in the H{11B} spectrum of 6.
Molecu la r Str u ctu r e of 5. While suitable crystals
of 6 could not be obtained for an X-ray structure
(19) (a) This work. (b) J ordan, R. F.; LaPointe, R. E.; Bradley, P.
K.; Baenziger, N. Organometallics 1989, 8, 2892. (c) J ordan, R. F.;
Bajgur, C. S.; Willett, R.; Scott, B. J . Am. Chem. Soc. 1986, 108, 7410.
(d) Rosenthal, U.; Ohff, A. Michalik, H. G.; Burlakov, V. V.; Shur, V.
B. Angew. Chem. 1993, 32, 1193.
(17) Young, D. E.; Shore, S. G. J . Am. Chem. Soc. 1969, 91, 3497.
(18) Guo, Z.-Y.; Bradley, P. K.; J ordan, R. F. Organometallics 1992,
11, 2690.

Formation of [HB(C6F5)3]- Salts
Organometallics, Vol. 23, No. 9, 2004 2105
Ta ble 4. Dista n ces of Zr -O a n d An gles of Zr -O-C in Zir con ocen e Der iva tives a n d Mon ocyclop en ta d ien yl
Zir con iu m Der iva tives*
d(Zr-O)/Å
Zr-O-C/deg
ref
ZrdO (double bond)
CpEt*2Zr(O)(NC5H5)
1.804(4)
18a,b
Zr-O (neutral ligand)
[{Cp2Zr(OEt2)(OEt)][HB(C6F5)3]
[(Cp′)2Zr(Me)CC(Me)(nPr)(THF)]+
[Cp2ZrMe(THF)][BPh4]
2.209(8)
2.289(6)
2.122(14)
2.390(5)
123.0(9); 120.3(9)
19a
19b
19c
19d
Cp2Zr(THF)(Me3SiC/CSiMe3)
Zr-O (anion ligand)
[{Cp2Zr(OEt2)(OEt)][HB(C6F5)3]
Cp*Zr{2,6-OC6H3(CH3)2}3
Cp*2Zr[η2-OCH(But)OCH(But)O]
Cp*2Zr(OH)[η1-OC(But)dCH2]
Cp*2Zr(OH)(NHPh)
1.884(8)
153.4(9)
20a
20b
20c
20c
20c
20c
20d
20d
20d
20h
1.940(4); 1.947(4); 1.950(4)
2.011(4); 2.007(3)
2.001(6); 2.006(5)
2.061(7)
2.067(2)
2.010(2); 1.993(2)
1.987(3)
167.5(4); 155.3(4); 166.1(5)
126.4(3); 125.2(3)
169.9(6)
Cp*2Zr(η2-O2CMe)(η1-OCOMe)
Cp*2Zr(OH)[η1-OC(Ph)dCH2]
Cp*2Zr(SH)[η1-OC(Ph)dCH2]
Cp*2Zr(SeH)[η1-OC(Ph)dCH2]
Cp2Zr(OPh)(η2-S2CNMe2)
161.8(2)
174.6(2)
168.8(3)
168.5(4)
159.7(8)
2.012(5)
2.023(8)
a
The data for aryloxy and alkoxy zirconocene derivatives have been summarized by G. Parkin in ref 20d.
ether, toluene, and benzene were dried over sodium/benzophen-
one and freshly distilled prior to use. Methylene chloride was
stirred over P2O5 for 10 days before being distilled for use.
Hexane was stirred over concentrated sulfuric acid for 2 days
and then decanted and washed with water. Next the hexane
was stirred over sodium/benzophenone for 1 week, followed
by distillation into a storage bulb containing sodium/benzophen-
one. Celite was dried by heating at 150 °C under dynamic
vacuum for 5 h. B(C6F5)3 was purchased from Aldrich and used
as received. The zirconocene organohydroborates Cp2ZrH{(µ-
H)2BR2} (R2 ) C4H8, 1; C8H14, 2) were prepared by literature
procedures.1c,2b Elemental analyses were performed by Gal-
braith Laboratories, Inc. of Knoxville, TN. NMR spectra were
to the other chalcogens (S, Se, and Te). They compare
the Zr-O distance and the Zr-O-C angle in a number
of alkoxy and aryloxy zirconocene complexes and provide
evidence that short Zr-O bond lengths and linear Zr-
O-C units are not necessarily a consequence of a strong
pπ-dπ lone pair donation from oxygen to the zircon-
ium.20d Furthermore, Parkin and co-workers point out
that such a shortening of the Zr-O single and double
bonds is believed to be a consequence of partial ionic
character in the zirconium oxygen bond (Zrδ+-Oδ-
)
mainly due to the greater electronegativity of oxygen
with respect to the other chalcogens and the smaller
size of oxygen, both of which serve to increase the
Coulombic stabilization associated with the dipolar
1
recorded on a Bruker AM-250 spectrometer. H NMR spectra
were obtained at 250.1 MHz and referenced to residual solvent
protons. 11B NMR spectra were obtained at 80.3 MHz and
externally referenced to BF3‚OEt2 in C6D6 (δ ) 0.00 ppm).
Infrared spectra were recorded on a Mattson-Polaris FT-IR
spectrometer with 2 cm-1 resolution.
moiety Zrδ+-Oδ- 20d
The fact that the Zr-O distances
.
in neutral ligand complexes are significantly longer than
the Zr-O distance in anion ligand complexes (Table 4)
and the sum of the covalent radii of zirconium and
oxygen is in accord with the Zr-O distance in neutral
ligand complexes are consistent with substantial ionic
contribution to the short Zr-O bonding.
X-r a y Str u ctu r e Deter m in a tion . Single-crystal X-ray
diffraction data were collected on a Nonius Kappa CCD
diffraction system, which employs graphite-monochromated
Mo KR radiation (λ ) 0.71073). A single crystal of 3, 4, and 5
was mounted on the tip of a glass fiber coated with Fomblin
oil (a pentafluoropolyether). Unit cell parameters were ob-
tained by indexing the peaks in the first 10 frames and refined
employing the whole data set. All frames were integrated and
corrected for Lorentz and polarization effects using the DENZO-
SMN package (Nonius BV, 1999).22 The empirical absorption
correction was applied with the SORTAV program23 provided
by MaXus software.24 The positions of the heavy atoms were
revealed by the Patterson method. The structures were refined
using the SHELXTL-97 (difference electron density calcula-
tions and full-matrix least-squares refinements) structure
solution package.25 Data merging was performed using the
data preparation program supplied by SHELXTL-97.
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations were carried out
on a standard high-vacuum line or in a drybox under an
atmosphere of nitrogen or argon. Tetrahydrofuran, diethyl
(20) (a) This work. (b) AntiAÄ olo, A.; Carrillo-Hermosilla, F.; Corro-
chano, A.; Ferna´ndez-Baeza, J .; Lara-Sanchez, A.; Ribeiro, M. R.;
Lanfranchi, M.; Otero, A.; Pellinghelli, M. A.; Portela, M. F.; Santos,
J . V. Organometallics, 2000, 19, 2837. (c) Howard, W. A.; Trnka, T.
M.; Waters, M.; Parkin, G. J . Organomet. Chem. 1997, 528, 95. (d)
Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34, 5900.
(e) Amor, J . I.; Burton, N. C.; Cuenca, T.; Go´mez-Sal, P.; Royo, P. J .
Organomet. Chem. 1995, 485, 153. (f) Miquel, L.; Basso-Bert, M.;
Choukroun, R.; Madhouni, R.; Eichhorn, B.; Sanchez, M.; Mazieres,
M.-R.; J aud, J . J . Organomet. Chem. 1995, 490, 21. (g) Gau, H.-M.;
Chen, C.-T.; Schei, C.-C. J . Organomet. Chem. 1992, 424, 307. (h)
Femec, D. A.; Groy, T. L.; Fay, R. C. Acta Crystallogr. 1991, C27, 1811.
(i) Veya, P.; Florriani, C.; Chiesi-Villa, A.; Guastini, C. Organometallics
1991, 10, 2991. (j) Veya, P.; Florriani, C.; Chiesi-Villa, A.; Guastini,
C. J . Chem. Soc., Chem. Commun. 1991, 1166. (k) Steffey, B. D.;
Truong, N.; Chebi, D. E.; Kerschner, J . L.; Fanwick, P. E.; Rothwell,
I. P. Polyhedron 1990, 9, 839. (l) Heppert, J . A.; Boyle, T. J .;
Takusagawa, F. Organometallics 1989, 8, 461. (m) Gambarotta, S.;
Strologo, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem.
1985, 24, 654. (n) Lappet, M. F.; Raston, C. L.; Engellhardt, l. M.;
White, A. H. J . Chem. Soc., Chem. Commun. 1985, 521. (o) Wenrui,
C.; J inbi, D.; Shoushan, C. J . Struct. Chem. 1982, 1, 73. (p) J inbi, D.;
Meizhen, L.; J iping, Z.; Shoushen, C. J . Struct. Chem. 1982, 1, 63. (q)
Qingchuan, Y.; Xianglin, J .; Xiaojie, X.; Genpei, L.; Youqi, T.; Shoushan,
C. Sci. Sin., Ser. B (Engl. Ed.) 1982, 25, 356.
For molecular structures 3 and 4, after all non-hydrogen
atoms were located and refined anisotropically, hydrogen atom
positions were calculated assuming standard geometries.
Bridge hydrogens and the terminal B-H hydrogens of the
anions were located and refined isotropically. The molecular
structure of the cation [Cp2Zr(OEt2)(OEt)]+ in 5 was highly
disordered. Two sets of coordinates for carbon and oxygen
atoms were located. The SADI and SAME instructions were
used to restrain the bond distances between the carbon atoms
and carbon-oxygen atoms such that all carbon-carbon dis-
tances are equal and carbon-oxygen distances are equal
within effective standard deviations. Extra constraints for
common site occupation factors were also applied. The carbon
and oxygen in OEt2 and OEt groups were refined isotopically,

2106 Organometallics, Vol. 23, No. 9, 2004
Chen et al.
and all other non-hydrogen atoms were refined anisotopically.
The hydride atom on boron in the anion was located and
refined isotopically, and other hydrogen atoms were calculated.
P r ep a r a tion of [(µ-H){Cp 2Zr (µ-H)2BC4H8}2][HB(C6F 5)3],
3. In a drybox 147 mg (0.50 mmol) of 1 and 128 mg (0.25 mmol)
of B(C6F5)3 were put in a flask. After degassing, 5 mL of
benzene was transferred to the flask, After stirring for 10 min,
hexane was transferred to the system to produce a white
precipitate, which was washed with hexane twice, and a 215
mg (mmol), 78% yield of white product was isolated. 11B NMR
(d8-toluene): δ 36.59 (br, (B-H-Zr)), -25.27 (d, [HB(C6F5)3]-)
1464(vs), 1437(sh), 1420(sh), 1374(sh), 1350(w), 1331(w),
1314(w), 1277(m), 1210(m), 1173(w), 1114(m), 1093(s), 1069(sh),
1924(m), 969(vs), 925(m), 912(m), 889(w), 809(vs), 768(w),
754(w), 680(w), 632(w), 568(w).
P r ep a r a tion of [Cp 2Zr (OEt2)(OEt)][HB(C6F 5)3], 5. In a
drybox 294 mg (1 mmol) of 1, 512 mg (1 mmol) of B(C6F5)3,
and 15 mL of ether were put in a flask. The reaction was
monitored by 11B NMR. The anion [HB(C6F5)3]- (-26.9 ppm,
d, J B-H ) 88 Hz) and organodiborane B2(µ-H)2(C4H8)2 (28.5
ppm) were formed in less than 5 min. But with increasing time
B2(µ-H)2(µ-C4H8)2 diminished in concentration while a new
signal at 58.0 ppm (singlet) appeared, indicative of a trialkyl
borane. After stirring this system for 1 h, the ether solution
was removed by filtration, and 583 mg (68.3% yield) of white
solid was isolated. Complex 5 has limited solubility in Et2O.
For the NMR spectra in THF the Et2O in 5 is replaced by THF
solvent. 11B NMR (d8-THF): δ -26.43 (d, J B-H ) 93 Hz) ppm.
1H NMR (d8-THF): δ 6.59 (s, Cp), 4.30 (2H, q, J ) 7 Hz), 3.38
(4H, q, J ) 7 Hz), 1.21 (3H, t, J ) 7 Hz), and 1.11 (6H, t, J )
1
ppm. H NMR (d8-toluene): δ 5.70 (s, Cp), 1.62 (br, 8H, â-H),
0.89 (br, 8H, R-H), -2.03 (br, 2 µ-H), -3.86 (br, 2 µ-H), and
1
-5.55 (br, 1 µ-H) ppm. H{11B} NMR (d8-toluene): δ 4.09 (br,
HB). Anal. Calcd: C, 50.47; H, 3.87. Found: C, 50.36; H, 4.01.
IR (KBr): 3114(s), 3099(sh), 2912(s), 2845(s), 2809(m), 2659(w),
2649(w), 2367(s), 1898(sh), 1873(s), 1850(s), 1822(m), 1708(m),
1640(s), 1604(w), 1548(w), 1510(vs), 1465(vs), 1427(vs), 1416(vs),
1373(s), 1343(s), 1327(m), 1275(s), 1224(s), 1203(m), 1167(w),
1099(vs), 1075(s), 1039(w), 1924(s), 1017(s), 995(w), 970(vs),
910(m), 897(w), 841(s), 811(vs), 759(m), 731(w), 696(w), 659(m),
649(m), 603(m), 587(w), 568(m).
7 Hz) ppm. 1H{11B} NMR (d8-THF): δ 3.80 (m, HB, J H-B
)
4.6 Hz). Anal. Calcd: C, 47.84; H, 3.07. Found: C, 47.01; H,
3.09. IR (KBr): 3123(m), 2982(s), 2940(m), 2884(m), 2734(w),
2373(s), 1643(s), 1606(w), 1551(w), 1511(vs), 1466(vs), 1412(w),
1384(s), 1328(w), 1274(s), 1185(w), 1108(vs), 1078(vs), 1020(s),
968(vs), 930(m), 914(m), 893(w), 881(w), 866(m), 840(sh), 825-
(s), 787(w), 765(m), 757(m), 733(w), 688(w), 664(m), 637(m),
605(m), 569(m), 542(m), 524(w).
P r epar ation of [Cp2Zr (OEt2){(µ-H)2BC8H14}][HB(C6F5)3],
6. In a drybox 345 mg (1 mmol) of 2, 512 mg (1 mmol) of
B(C6F5)3, and 15 mL of ether were put in a flask. The reaction
was monitored by 11B NMR. The anion [HB(C6F5)3]- (-27.0
ppm, d, J B-H ) 88 Hz) and 9-BBN dimer (µ-H)2(BC8H14)2 (27.3
ppm) were formed in less than 5 min. But with increasing time
P r epar ation of [(µ-H){Cp2Zr (µ-H)2BC8H14}2][HB(C6F5)3],
4. In a drybox 173 mg (0.50 mmol) of 2 and 128 mg (0.25 mmol)
of B(C6F5)3 were put in a flask. After degassing, 5 mL of toluene
was transferred to the flask and stirred for 10 min, and hexane
was transferred to the system to produce a white precipitate,
which was washed with hexane twice, producing a 220 mg
(mmol), 73% yield of white product. 11B NMR (d8-toluene): δ
1
-23.44 ([HB(C6F5)3]-, br) ppm. H NMR (d8-toluene): δ 5.85
(s, Cp), 2.05-1.20 (m, 28H, R-,â-, and γ-H in C8H14 group),
-1.64 (br, 2 µ-H), -3.60 (br, 2 µ-H), and -5.20 (br, 1 µ-H) ppm.
1H{11B} NMR (d8-toluene): δ 4.38 (br, HB). 11B NMR (d2-
methylene chloride): δ 38.62 ((B-H-Zr), br), -25.48 ([HB(C6-
F5)3]-, d, J B-H ) 80 Hz) ppm. 1H NMR (d2-methylene chlo-
ride): δ 6.33 (s, Cp), 2.34-1.48 (m, 28H, R-,â-, and γ-H in C8H14
group), -1.36 (br, µ-H), -3.14 (br, 2 µ-H), and -4.90 (br, 1
(µ-H)2(BC8H14
) diminished in concentration, while a new
2
signal at 59.4 ppm (singlet) appeared, indicative of a trialkyl
borane. After stirring this system for 1 h, the ether solution
was removed by filtration, and 610 mg (70.5% yield) of white
solid was isolated. Complex 6 has limited solubility in Et2O.
For the NMR spectra in THF the Et2O in 6 is replaced by THF
solvent. 11B NMR (d8-THF): δ 27.60 ((B-H-Zr)2, br), -26.50
([HB(C6F5)3]-, d, J B-H ) 88 Hz) ppm. 1H NMR (d8-THF): δ
6.64 (s, Cp), 3.38 (4H, q, J ) 7 Hz), 1.90-1.43 (14H, m), and
1.11 (6H, t, J ) 7 Hz) ppm. 1H{11B} NMR (d8-THF): δ 3.74
(m, HB), 0.32 (br, 1 µ-H), and -2.19 (br, 1 µ-H). Complex 2
was dried under vacuum overnight, and part of the ether
ligand was lost. Anal. Calcd: C, 50.55; H, 3.26 for [Cp2Zr-
(OEt2)0.1{(µ-H)2BC8H14}][HB(C6F5)3]. Found: C, 50.08; H, 3.68.
IR (KBr): 3117(m), 2984(s), 2890(s), 2836(s), 2373(m), 1982(w),
1965(w), 1941(w), 1642(s), 1511(vs), 1463(vs), 1390(s), 1312(w),
1276(s), 1209(w), 1097(s), 1016(s), 969(vs), 924(w), 817(s),
760(m), 678(w), 600(w), 566(m), 524(w).
1
µ-H) ppm. H{11B} NMR (d2-methylene chloride): δ 3.72 (br,
HB). 11B NMR (d8-THF): δ 31.82 ((B-H-Zr), s, in neutral
complex), 29.20 ((B-H-Zr), br, in ionic complex), and -25.46
1
([HB(C6F5)3]-, d, J B-H ) 90 Hz) ppm. H{11B}NMR (d8-THF):
δ 6.65 (s, Cp), 6.02 (s, Cp), 3.85 (m, HB(C6F5)3]-), 3.73 (br, Zr-
H), 2.04-1.23 (m, 28H, R-,â-, and γ-H in C8H14 group), 0.30
(br, µ-H), -2.21 (br, µ-H), -3.34 (br, µ-H), and -4.20 (br, µ-H)
ppm. Anal. Calcd: C, 53.92; H, 4.53. Found: C, 53.39; H, 4.45.
IR (KBr): 3108(m), 2984(sh), 2919(s), 2888(s), 2836(m), 2689(w),
2665(w), 2365(s), 1869(m), 1845(s), 1652(sh), 1644(s), 1510(vs),
(21) (a) Bai, G.; Roesky, H. W.; Li, J .; Labahn, T.; Cimpoesu, F.;
Magull, J . Organometallics 2003, 22, 3034. (b) Niehues, M.; Erker, G.;
Meyer, O.; Fro¨hlich. Organometallics 2000, 19, 2813. (c) Blaschke, U.;
Erker, G.; Nissinen, M.; Wegelius, E.; Fro¨hlich Organometallics 1999,
18, 1224. (d) Rosenthal, U.; Ohff, A.; Michalik, M.; Go¨rls, H.; Burlakov,
V. V.; Shur, V. B. Organometallics 1993, 12, 5016. (e) Fachinetti, G.;
Florian, C.; Chiesi-Villa, A.; Guastini, C. J . Am. Chem. Soc. 1979, 101,
1766.
Ack n ow led gm en t. This work was supported by the
National Science Foundation through Grants CHE99-
01115 and CHE02-13491.
(22) Otwinowsky, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology, Vol. 276:
Macromolecular Crystallography, Part A; Carter, C. W., J r., Sweet, R.
M., Eds.; Academic Press: New York, 1997; pp 307-326.
(23) (a) Blessing, R. H. Acta Crystallogr. 1995, 51A, 33. (b) Blessing,
R. H. J . Appl. Crystallogr. 1997, 30, 421.
(24) Mackay, S.; Gilmore, C. J .; Edwards, C.; Tremayne, M.; Stuart,
N.; Shankland, K. MaXus: A Computer Program for the Solution and
Refinement of Crystal Structures from Diffraction Data; University of
Glasgow: Scotland, Nonius BV: Delft, The Netherlands, and Mac-
Science Co. Ltd.: Yokohama, J apan, 1998.
Su p p or tin g In for m a tion Ava ila ble: Molecular structure
of the anion in 3, 4, and 5; the second set of structures of the
cation [Cp2Zr(OEt2)(OEt)]+ and disordered [Cp2Zr(OEt2)(OEt)]+
in 5; tables of crystallographic data, positional and thermal
parameters, and interatomic distances and angles for 3, 4, and
1
5; relevant additional H, 11B NMR spectra for 3, 4, 5, and 6.
Three X-ray crystallographic files in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
(25) Sheldrick, G. M. SHELXTL-97: A Structure Solution and
Refinement Program; University of Go¨ttingen: Germany, 1998.
OM030692A