Hydride ion abstraction from titanocene cyclic organohydroborates, Cp2Ti{(μ-H)2BR2} (R2 = C4H8, C5H10, C8H14), as a function of solvent

Article abstract of DOI:10.1021/om010267m

Hydride abstraction reactions of titanocene cyclic organohydroborate complexes Cp₂Ti{(μ-H)₂BR₂} (R₂ = C₄H₈, C₅H₁₀, C₈H₁₄) with B(C₆F₅)₃ were investigated as a function of solvent. It was determined that the coordinating ability of the solvent directed the course of these abstraction reactions. The reaction in toluene, a noncoordinating solvent, produced a metathesis product, Cp₂Ti{(μ-H)₂B(C₆F₅)₂} (1), in which the cyclic organohydroborate H₂BR₂ was substituted by H₂B(C₆F₅)₂. In diethyl ether and THF, the salts [Cp₂TiL₂] [HB(C₆F₅)₃] (2, L = Et₂O; 3, L = THF) consisting of titanocene cations with solvent ligands were isolated. Salt 2 is the first structurally characterized [Cp₂TiL₂]⁺ cation containing diethyl ether solvent ligands. The diethyl ether molecules of the cation in 2 are weakly coordinated and are labelized in THF and toluene. Dissolution of 2 in THF afforded 3. The complex Cp₂Ti{(μ-H)B(C₆F₅)₃} (OEt₂) (4) and the proposed 15-electron species Cp₂Ti{(μ-H)B(C₆F₅)₃} (5) were generated through the displacement of an ether molecule from 2 by the [HB(C₆F₅)₃]^- anion in toluene. Single-crystal X-ray structures of 1, 2, and 3 were determined.

Full text of DOI:10.1021/om010267m

Organometallics 2001, 20, 3599-3606
3599
Hyd r id e Ion Abstr a ction fr om Tita n ocen e Cyclic
Or ga n oh yd r obor a tes, Cp 2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10,
C8H14), a s a F u n ction of Solven t
Christine E. Plecˇnik, Fu-Chen Liu, Shengming Liu, J ianping Liu,
Edward A. Meyers, and Sheldon G. Shore*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
Received April 2, 2001
Hydride abstraction reactions of titanocene cyclic organohydroborate complexes Cp2Ti-
{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14) with B(C6F5)3 were investigated as a function of solvent.
It was determined that the coordinating ability of the solvent directed the course of these
abstraction reactions. The reaction in toluene, a noncoordinating solvent, produced a
metathesis product, Cp2Ti{(µ-H)2B(C6F5)2} (1), in which the cyclic organohydroborate H2-
BR2 was substituted by H2B(C6F5)2. In diethyl ether and THF, the salts [Cp2TiL2] [HB-
(C6F5)3] (2, L ) Et2O; 3, L ) THF) consisting of titanocene cations with solvent ligands were
isolated. Salt 2 is the first structurally characterized [Cp2TiL2]+ cation containing diethyl
ether solvent ligands. The diethyl ether molecules of the cation in 2 are weakly coordinated
and are labilized in THF and toluene. Dissolution of 2 in THF afforded 3. The complex Cp2-
Ti{(µ-H)B(C6F5)3}(OEt2) (4) and the proposed 15-electron species Cp2Ti{(µ-H)B(C6F5)3} (5)
were generated through the displacement of an ether molecule from 2 by the [HB(C6F5)3]-
anion in toluene. Single-crystal X-ray structures of 1, 2, and 3 were determined.
In tr od u ction
compounds stems from their unusual reactivity with the
strong Lewis acid and hydride ion abstracting reagent,
B(C6F5)3. B(C6F5)3 has been widely utilized as an alkyl
carbanion abstracting reagent9 to generate metallocene
cations10 for olefin polymerization, but in only a few
cases has B(C6F5)3 been utilized to abstract terminal
hydride from metallocenes.11 Our latest study reveals
that hydride ion abstraction from zirconocene organo-
hydroborates likewise results in the formation of zir-
conocene cations (Scheme 1).12 These reactions are
influenced by several factors. Although both terminal
and bridging hydrogens are present in Cp2ZrH{(µ-
H)2BC4H8}, the terminal hydride is more hydridic and
is preferentially abstracted by B(C6F5)3. Furthermore,
the abstraction product is a function of the coordinating
ability of the solvent. Abstraction in the noncoordinating
solvent benzene produces the salt, [(µ-H){Cp2Zr(µ-
H)2BC4H8}2] [HB(C6F5)3] (A of Scheme 1), while the
reaction in the coordinating solvent diethyl ether yields
the mononuclear cation in the salt, [Cp2Zr(OEt2)(OEt)]
[HB(C6F5)3] (B).
Recently there has been an increased effort in the
synthesis of low-valent titanocene compounds with
boron-containing ligands. Such compounds can be clas-
sified as Ti(II) σ-boranes, including Cp2Ti(HBCat)2 (Cat
) o-O2C6H4) and its derivatives1 and Ti(III) hydridobo-
rates Cp2Ti{(µ-H)2BR2} (R2 ) H2;2 (C6F5)2;3 C4H8, C5H10
,
C8H144). Only a handful of such compounds have been
synthesized; these complexes are structurally interest-
ing and they exhibit potentially useful chemical proper-
ties. For instance, the Ti(II) σ-boranes have demon-
strated catalytic activity in the hydroboration of alkenes
and alkynes.5
This laboratory has been involved in expanding the
number of early transition metal metallocene cyclic
organohydroborates. To date, zirconocene,6 hafnocene,6a-c
niobocene,4 and titanocene4 derivatives of the cyclic
organohydroborates H2BR2 (R2 ) C4H8,7 C5H10
,
6c C8H14
)
8
have been prepared. Our interest in these types of
(1) (a) Hartwig, J . F.; Muhoro, C. N.; He, X.; Eisenstein, O.; Bosque,
R.; Maseras, F. J . Am. Chem. Soc. 1996, 118, 10936. (b) Muhoro, C.
N.; Hartwig, J . F. Angew. Chem., Int. Ed. Engl. 1997, 36, 1510. (c)
Muhoro, C. N.; He, X.; Hartwig, J . F. J . Am. Chem. Soc. 1999, 121,
5033. (d) Lam, W. H.; Lin, Z. Organometallics 2000, 19, 2625.
(2) (a) No¨th, H.; Hartwimmer, R. Chem. Ber. 1960, 93, 2238. (b)
Lucas, C. R. Inorg. Synth. 1977, 17, 91. (c) Melmed, K. M.; Coucouvanis,
D.; Lippard, S. J . Inorg. Chem. 1973, 12, 232.
(3) (a) Chase, P. A.; Piers, W. E.; Parvez, M. Organometallics 2000,
19, 2040. (b) Douthwaite, R. E. Polyhedron 2000, 19, 1579.
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S. G. J . Organomet. Chem. 2001, 627, 109.
As an extension of this most recent work, we are
interested in the reactions of the titanocene systems
(7) (a) Clayton, W. R.; Saturnino, D. J .; Corfield, P. W. R.; Shore, S.
G. J . Chem. Soc., Chem. Commun. 1973, 377. (b) Saturnino, D. J .;
Yamauchi, M.; Clayton, W. R.; Nelson, R. W.; Shore, S. G. J . Am. Chem.
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(8) Ko¨ster, R.; Seidel, G. Inorg. Synth. 1983, 22, 198.
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references therein.
(5) (a) He, X.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118, 1696. (b)
Hartwig, J . F.; Muhoro, C. N. Organometallics 2000, 19, 30.
(6) (a) J ordan IV, G. T.; Shore, S. G. Inorg. Chem. 1996, 35, 1087.
(b) J ordan IV, G. T.; Liu, F.-C.; Shore, S. G. Inorg. Chem. 1997, 36,
5597. (c) Liu, J .; Meyers, E. A.; Shore, S. G. Inorg. Chem. 1998, 37,
496. (d) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. Inorg. Chem.
1998, 37, 3293. (e) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. Inorg.
Chem. 1999, 38, 2169. (f) Liu, F.-C.; Du, B.; Liu, J .; Meyers, E. A.;
Shore, S. G. Inorg. Chem. 1999, 38, 3228.
(10) 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.
(11) (a) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. (b) Antin˜olo, A.; Carrillo-Hermosilla, F.; Ferna´ndez-Baeza,
J .; Garc´ıa-Yuste, S.; Otero, A.; Sa´nchez-Prada, J .; Villasen˜or, E. J .
Organomet. Chem. 2000, 609, 123.
(12) Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Am. Chem.
Soc. 2000, 122, 6106.
10.1021/om010267m CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/04/2001

3600 Organometallics, Vol. 20, No. 16, 2001
Plecˇnik et al.
Sch em e 1
Sch em e 2
4
Cp2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14
)
that
contain only Ti(µ-H)2B bridges, with B(C6F5)3 as a
means of generating titanocene (Ti(III)) cations, about
which little is known.13-18 It is of interest to determine
whether the bridging hydrogens are sufficiently basic
for abstraction and if there is a similar unique depen-
dence on the solvent to affect the course of the reactions.
In the present contribution, we report the products of
these hydride abstraction reactions as a function of
solvent.
the 11B NMR spectra. The identity of the borane,
B(C6F5)(C8H14), was confirmed by GC-MS. A somewhat
similar reaction was described by Marks et al. with the
alkylation of Cp3UBH4 by BR3 (R ) C2H5, C6H5) to
afford Cp3UBH3R and HBR2.19
Resu lts a n d Discu ssion
A suggested mechanism for the formation of 1 is
illustrated in Scheme 2. Terminal B-H20 and metal-
H11,12 bonds can be abstracted as hydride ion. On the
other hand, bridge hydrogens tend to be acidic in
character and are less likely to be abstracted as hydride
ions,21 but double hydrogen-bridged systems of metal-
locene hydridoborates tend to be fluxional,22 which was
also observed in NMR studies of the organohydroborate
complexes Cp2ZrCl{(µ-H)2BC4H8},6a,b Cp2ZrCl{(µ-H)2-
BC5H10},6c and Cp2ZrH{(µ-H)2BC5H10},6d,23 in both co-
ordinating and noncoordinating solvents. Therefore, it
is likely that the hydrogen bridge bonds in Cp2Ti{(µ-
H)2BR2} readily open and close at room temperature
though this cannot be verified by NMR spectroscopy due
to the paramagnetism of the Ti(III) ion. With the bridge
open, a terminal hydride on titanium is accessible to
B(C6F5)3 but is not completely abstracted. It is presumed
that complete abstraction does not occur without as-
sistance from a coordinating solvent. Activation of a
Hyd r id e Ion Abstr a ction in a Non coor d in a tin g
Solven t: F or m a tion of Cp 2Ti{(µ-H)2B(C6F 5)2}, 1. In
reactions of the titanocene cyclic organohydroborates
Cp2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14), with
B(C6F5)3 in toluene, the unanticipated complex 1 is
produced in 57 to 68% yields (reaction 1). During the
(13) Coutts, R. S. P.; Kautzner, B.; Wailes, P. C. Aust. J . Chem. 1969,
22, 1137.
(14) Ohff, A.; Kempe, R.; Baumann, W.; Rosenthal, U. J . Organomet.
Chem. 1996, 520, 241.
(15) Seewald, P. A.; White, G. S.; Stephan, D. W. Can. J . Chem.
1988, 66, 1147.
(16) Borkowsky, S. L.; Baenziger, N. C.; J ordan, R. F. Organome-
tallics 1993, 12, 486.
(17) Merola, J . S.; Campo, K. S.; Gentile, R. A.; Modrick, M. A. Inorg.
Chim. Acta 1989, 165, 87.
(18) Allmann, R.; Ba¨tzel, V.; Pfeil, R.; Schmid, G. Z. Naturforsch.
1976, 31B, 1329.
(19) Marks, T. J .; Kolb, J . R. J . Am. Chem. Soc. 1975, 97, 27.
(20) Toft, M. A.; Leach, J . B.; Himpsl, F. L.; Shore, S. G. Inorg. Chem.
1982, 21, 1952.
(21) (a) Shore, S. G. Pure Appl. Chem. 1977, 49, 717. (b) Inkrott, K.
E.; Shore, S. G. J . Am. Chem. Soc. 1978, 100, 3954.
(22) Marks, T. J .; Kolb, J . R. Chem. Rev. 1977, 77, 263.
(23) Chow, A.; Liu, F.-C.; Fraenkel, G.; Shore, S. G. Magn. Reson.
Chem. 1998, 36, S145.
course of this metathesis reaction, the organohydrobo-
rate H2BR2 is replaced by bis(pentafluorophenyl)hydri-
doborate, H2B(C6F5)2. Titanium activates one of the
boron-carbon bonds from a pentafluorophenyl ring of
B(C6F5)3 to generate an organoborane that is believed
to be B(C6F5)R2, based on a downfield singlet (R2
)
C4H8, δ 81.8; R2 ) C5H10, δ 82.7; R2 ) C8H14, δ 85.0) in

Hydride Ion Abstraction from Titanocene Organohydroborates
Organometallics, Vol. 20, No. 16, 2001 3601
Sch em e 3
boron-carbon bond of B(C6F5)3 then takes place, with
transfer of the [C6F5]- moiety to BR2. Loss of B(C6F5)-
R2 occurs next with re-formation of the double hydrogen
bridge. The driving force of this metathesis reaction can
be discussed in terms of the relative acidities and
basicities of the reactants and products. The strong
Lewis acid, B(C6F5)3, incompletely abstracts a hydride
ion from the Lewis base, Cp2Ti{(µ-H)2BR2}, to produce
a weaker Lewis acid, B(C6F5)R2, and a weaker Lewis
base 1.
Compound 1 is paramagnetic and was identified by
single-crystal X-ray analysis. It has been previously
reported but prepared through different synthetic routes.
Piers et al. synthesized 1 by reacting Cp2TiR2 (R ) CH3,
CH2Ph) with 2.5 equiv of the borane, HB(C6F5)2.3a
Douthwaite, on the other hand, reacted 2 equiv of the
organohydroborate salt, [(Et2O)Li] [(µ-H)2B(C6F5)2], with
Cp2TiCl2 (or Cp2TiCl in a 1:1 ratio).3b The latter is
similar to the preparation of the starting materials, Cp2-
Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14).4 The IR and
19F NMR spectra obtained in this laboratory correlate
well with those of Piers et al. and Douthwaite.
Hyd r id e Ion Abstr a ction in Coor d in a tin g Sol-
ven ts: F or m a tion of [Cp 2Ti(OEt2)2] [HB(C6F 5)3], 2,
a n d [Cp 2Ti(THF )2] [HB(C6F 5)3], 3. Hydride ion ab-
stractions from Cp2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10
,
C8H14) with B(C6F5)3 in ether and THF solutions
produce the titanocene cations [Cp2Ti(OEt2)2]+ and [Cp2-
Ti(THF)2]+, with the [HB(C6F5)3]- counteranion (reac-
tion 2). A reasonable reaction pathway for the formation
B2(µ-H)2(µ-C4H8)2.24 The diborane B2(µ-H)2(µ-C4H8)2 was
verified by 11B NMR, with a broad unresolved triplet
appearing at 28.5 ppm in ether. Unlike the reaction of
Cp2Ti{(µ-H)2BC4H8}, the reactions of Cp2Ti{(µ-H)2BR2}
(R2 ) C5H10, C8H14) with B(C6F5)3 do not produce the
parent organodiboranes (µ-H)2(BC5H10)2 and (µ-H)2-
(BC8H14)2 (11B resonances at 26.0 and 28.3 ppm in ether,
respectively), because the latter are not as stable as B2-
(µ-H)2(µ-C4H8)2.24 The isolated boron-containing species
have 11B resonances appearing downfield as singlets at
53.7 (R2 ) C5H10) and 56.2 (R2 ) C8H14) ppm, charac-
teristic chemical shifts for trialkyl boranes.7b,25 Reaction
of Cp2Ti{(µ-H)2BC5H10} with B(C6F5)3 in THF produced
3 in 81% yield and an unidentified organoborane with
an 11B resonance at δ 54.0.
Since the opening and closing of the hydrogen bridge
bonds is a dynamic process, we expected reaction 2 to
be “slower” than the corresponding reaction of the
terminal hydride species Cp2ZrH{(µ-H)2BC4H8} with
B(C6F5)3 in ether (Scheme 1).12 Indeed, reaction 2, which
took several minutes to change color completely, was
observed to be qualitatively slower than the reaction of
Cp2ZrH{(µ-H)2BC4H8}, which is too rapid to observe
intermediates by NMR.
of 2 from Cp2Ti{(µ-H)2BC4H8} is depicted in Scheme 3.
The first step would be the opening of bridge bonds to
produce terminal hydrogens, either Ti-H or B-H, that
are susceptible to hydride ion abstraction. When hydride
ion is abstracted by B(C6F5)3, the resulting cationic
intermediate has a vacant coordination site on titanium
or boron accessible to diethyl ether. Next, the displace-
ment of the unsupported hydrogen bridge system occurs
by nucleophilic attack by ether. The resulting HBC4H8
ring then dimerizes to the stable neutral organodiborane
(24) (a) Young, D. E.; Shore, S. G. J . Am. Chem. Soc. 1969, 91, 3497.
(b) Breuer, E.; Brown, H. C. J . Am. Chem. Soc. 1969, 91, 4164.
(25) (a) Good, C. D.; Ritter, D. M. J . Am. Chem. Soc. 1962, 84, 1162.
(b) No¨th, H.; Wrackmeyer, B. In Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds; Springer-Verlag: Berlin, 1978; Table
9.3, pp 115-124.

3602 Organometallics, Vol. 20, No. 16, 2001
Plecˇnik et al.
Sch em e 4
Compounds 2 and 3 are more air sensitive than the
titanocene organohydroborates Cp2Ti{(µ-H)2BR2}. Trials
to obtain an IR spectrum of 2 with KBr did not succeed;
apparently, 2 reacts with KBr during the preparation
of the IR sample in the drybox to change color from blue
to yellow. A Nujol mull was prepared instead. Light blue
crystals of 2 and 3 were obtained from ether and a THF/
hexane solution mixture, respectively. Crystals of 2
evolve ether under a nitrogen atmosphere at room
temperature, turning dull blue in appearance. Pumping
on 2 for even a short period of time also removes
coordinated ether. Low carbon and hydrogen analyses
for 2 substantiated the loss of ether. Consequently,
yields of 2 from reaction 2 are not precise. This
complication was not encountered with 3. Salts 2 and 3
have characteristically different solubilities. Compound
2 is soluble in THF and toluene but is insoluble in ether,
and 3 is soluble in THF and pyridine but is insoluble in
ether and toluene.
Mononuclear titanocene (Ti(III)) salts with solvent
ligands, such as 2 and 3, are relatively rare, and to the
best of our knowledge, no diethyl ether coordinated
cations have been reported. Two of the earliest salts
prepared were the acetonitrile and pyridine coordinated
complexes [Cp2Ti(CH3CN)2][BPh4]13 and [Cp2Ti(Pyr)2]-
[BPh4].13,14 The [Cp2Ti(CH3CN)2]+ cation was later
prepared with the [ZnCl4]- anion.15 The mixed ligand
species [Cp2Ti(CH3CN)(THF)][BPh4]16 and [Cp2Ti(OC3-
H6)(THF)]2[Zn(B10H12)2]‚THF18 and the THF-coordinat-
ed compounds [Cp2Ti(THF)2] [BPh4]14 and [Cp2Ti-
(THF)2] [Co(CO)4]17 have also been synthesized.
THF coordinated salt, 3. The 11B NMR spectrum con-
sists of a doublet at δ -25.5 that is consistent with the
1
[HB(C6F5)3]- anion. The only signals observed in the H
NMR spectrum are the multiplets associated with the
free ether molecules. The cyclopentadienyl hydrogens
1
are H NMR silent due to the paramagnetism of the Ti-
1
(III) ion. Upon decoupling from 11B, the H{11B} spec-
trum showed sharpening of a peak at 3.75 ppm corre-
sponding to the hydride of the anion. Integration of this
hydride resonance vs the free ether signals indicated
that less than a molecule of ether remained. This is
further confirmation for the lability of the coordinated
ether under vacuum. Three sharp upfield resonances
at -132.1, -165.4, and -167.7 ppm in the 19F NMR
spectrum correlate with the three inequivalent fluorines
of the pentafluorophenyl rings of the anion. A compa-
rable displacement reaction occurs when the cation in
3 is transformed into the disubstituted [Cp2Ti(Pyr)2]+
cation by dissolution in pyridine.
When 2 is dissolved in d8-toluene, remarkably no 11
B
resonances are observed. The 1H NMR spectrum at
room temperature includes only two resonances due to
the free ether, but these appear as broad unresolved
signals rather than the expected multiplets. Increasing
the temperature to 94 °C gradually resolved the ether
resonances into sharp multiplets, without a change in
the chemical shifts. Decreasing the temperature to -70
°C significantly broadened the resonances, without a
substantial variation in the chemical shifts. Decoupling
from 11B did not affect the 1H spectra. Two broad upfield
resonances at -155.3 and -160.3 ppm for the para- and
meta-fluorines, respectively, are apparent in the 19F
NMR spectrum at room temperature. Sharpening of
these two resonances, without the appearance of new
ones, was evident in the variable temperature 19F NMR
spectra at higher temperatures.
Disp la cem en t Rea ctivity of 2. Through NMR spec-
troscopic studies, the ether molecules in 2 have been
found to be weakly coordinated and labilized in toluene
and THF (Scheme 4). In d8-THF, the ether molecules
are completely displaced from the cation to produce the

Hydride Ion Abstraction from Titanocene Organohydroborates
Organometallics, Vol. 20, No. 16, 2001 3603
The preceding observations signify the interaction of
the [HB(C6F5)3]- anion with the paramagnetic Ti(III)
ion. We propose that in toluene [HB(C6F5)3]- displaces
an ether molecule from the titanocene cation to form a
covalent compound, Cp2Ti{(µ-H)B(C6F5)3}(OEt2) (4),
containing an unsupported hydrogen bridge (see Scheme
4). The absence of the 11B and ortho-fluorine resonances
and the appearance of the two broad 19F singlets
substantiate this formulation. Furthermore, a compari-
son of the 19F NMR spectrum of 4 with 1 reveals that
the chemical shifts of the meta- and para-fluorines are
approximately the same. (The broad meta- and para-
fluorine resonances of 1 and 4 are shifted downfield
versus those of 2 and 3.) This indicates that 4 must have
structural features similar to those of 1. The cyclopen-
tadienyl protons, the bridging proton, and the coordi-
nated ether protons are not detected because they are
in close association with the paramagnetic Ti(III) ion.26
having an open coordination site on titanium. This
would constitute an uncommon but precedented 15-
electron configuration for the Ti(III) ion.27 Complex 5
is converted into 3 by addition of THF (Scheme 4). There
are no ether resonances in the 1H NMR spectrum, which
is further confirmation for the complete removal of the
coordinated ether by vacuum.
It was speculated that one of the fluorine atoms from
a pentafluorophenyl ring might donate a lone pair of
electrons to form a σ-bond with titanium to displace the
remaining coordinated ether in 4 or fill the vacant
coordination site in 5. Such σ-donation from fluorine
atoms on B(C6F5)3 to zirconium11a,28 and titanium29 has
been noted previously. However, the simplicity of the
solution 19F NMR spectra dismisses this hypothesis.
As with 2 and 3, the substitution of the solvent
ligands by nucleophiles has been documented with the
acetonitrile complex [Cp2Ti(CH3CN)2] [BPh4]. Recrys-
tallization of this salt in pyridine resulted in the
disubstituted cation [Cp2Ti(Pyr)2]+,13 and in THF the
monosubstituted cation [Cp2Ti(CH3CN)(THF)]+ 16 was
isolated. Cationic titanocene phosphines with the for-
mulations [Cp2Ti(CH3CN)(PMe3)]+ and [Cp2Ti(PMe3)2]+
were also prepared from [Cp2Ti(CH3CN)2] [BPh4].15
Substitution of the THF ligands in [Cp2Ti(THF)2] [BPh4]
occurred in the presence of pyridine to yield the cation,
[Cp2Ti(Pyr)2]+.14
H yd r id e Ion Ab st r a ct ion fr om Cp 2Ti{(µ-H )2-
B(C6F 5)2}, 1. Compared to the organohydroborates
Cp2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14), the bridg-
ing hydrogens of 1 should be less Lewis basic because
of the electron-withdrawing effect of the pentafluo-
rophenyl groups. Therefore, it was of interest to test
abstraction of the bridging hydrogens in 1 by B(C6F5)3
in coordinating and noncoordinating solvents. The me-
tathesis product 1 is soluble in THF and hydride ion
abstraction proceeded in a facile manner to afford 3
(reaction 3). The organoborane product of reaction 3 is
perceived to be the THF adduct of HB(C6F5)2 on the
basis of the resonance at -0.7 ppm in the 11B NMR
spectrum.30 The rate of hydride ion abstraction from 1
compared to the titanocene organohydroborates ap-
peared to be about the same order of magnitude despite
the lower basicity of the bridging hydrogens. Hydride
ion abstraction was not observed in diethyl ether due
to the insolubility of 1 in that solvent. Likewise,
abstraction did not occur in toluene even after heating
at 70 °C for 24 h.
The coordinated ether on 4 is labile and is exchanging
with the dissociated or free ether in solution, thus giving
rise to the broad free ether resonances at room temper-
ature. Since the protons on the coordinated ether are
1H NMR silent, there is no apparent chemical shift
averaging between the free and coordinated ether, that
is, the chemical shifts of the free ether resonances are
unvarying even though exchange is occurring. Increas-
ing the temperature drives the dissociation until all of
the coordinated ether has been completely dislodged to
produce Cp2Ti{(µ-H)B(C6F5)3}, 5 (Scheme 4). At 94 °C
the exchange process has ceased and only free ether is
present as evidenced by the distinctive ether multiplets.
This phenomenon is supported by the 19F NMR spectra.
At room temperature the two para- and meta-fluorine
resonances are broad due to ether exchange. At higher
temperatures the resonances sharpen because the dy-
namic process has ceased and the fluorine nuclei experi-
ence only one magnetic environment in 5.
Addition of THF to the NMR sample of 2 in toluene
(Scheme 4) causes the broad ether resonances to resolve
into their respective multiplets at room temperature and
a doublet to appear in the 11B NMR spectrum. The
substitution of the last weakly coordinated ether by THF
would take place initially followed by cleavage of the
unsupported hydrogen bridge to afford 3. This trans-
formation validates that the anion has not been altered
in toluene.
The variable temperature NMR experiment demon-
strated that the monocoordinated ether ligand of 4 is
labile. It is therefore not surprising that the ether ligand
is eliminated under vacuum by the following procedure
(Scheme 4). When complex 2 is twice dissolved in
toluene proceeded by removal of the volatile materials
under vacuum and the resulting blue solid is dissolved
in d8-toluene, 1H and 11B NMR spectra are silent. These
spectra reveal that all of the free ether has been
removed and suggest that the [HB(C6F5)3]- anion is in
intimate contact with the Ti(III) ion through an unsup-
ported hydrogen bridge. The 19F NMR spectrum still
contains only two broad signals at -155.2 and -160.2
ppm, which are identical to the chemical shifts of 4.
Although X-ray quality crystals could not be obtained
due to the extremely air-sensitive nature of the species,
the NMR evidence and elemental analyses point to a
system that is formulated as Cp2Ti{(µ-H)B(C6F5)3} (5),
Molecu la r Str u ctu r es of 1, 2, a n d 3. The molecular
structures of 1, 2, and 3 were determined by single-
crystal X-ray diffraction analysis. Structures of 2 and
3 are shown in Figures 1 and 2. Crystallographic data,
(26) The paramagnetism of the Ti(III) ion has been shown to affect
nuclei as far as four and five bonds away. Consequently, nuclei that
are in close vicinity to the Ti(III) ion are typically NMR silent. See ref
4 and NMR spectral data for Cp2Ti{(µ-H)2B(C6F5)2}, 1.
(27) (a) Klei, E.; Teuben, J . H. J . Organomet. Chem. 1980, 188, 97.
(b) Klei, E.; Telgen, J . H.; Teuben, J . H. J . Organomet. Chem. 1981,
209, 297.
(28) (a) Temme, B.; Erker, G.; Karl, J .; Luftmann, H.; Fro¨hlich, R.;
Kotila, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1755. (b) Ruwwe, J .;
Erker, G.; Fro¨hlich, R. Angew. Chem., Int. Ed. Engl. 1996, 35, 80. (c)
Karl, J .; Erker, G.; Fro¨hlich, R. J . Am. Chem. Soc. 1997, 119, 11165.
(29) Burlakov, V. V.; Troyanov, S. I.; Letov, A. V.; Strunkina, L. I.;
Minacheva, M. K.; Furin, G. G.; Rosenthal, U.; Shur, V. B. J .
Organomet. Chem. 2000, 598, 243.
(30) Parks, D. J .; Piers, W. E.; Yap, G. P. A. Organometallics 1998,
17, 5492.

3604 Organometallics, Vol. 20, No. 16, 2001
Plecˇnik et al.
F igu r e 1. Molecular structure of the cation in [Cp2Ti-
(OEt2)2] [HB(C6F5)3], 2, showing 15% probability thermal
ellipsoids. Hydrogens attached to carbon atoms are shown
with arbitrary thermal ellipsoids.
bond distances, and bond angles are given in Tables 1
and 2. Previously, the molecular structure of 1 was
determined by both Piers et al.3a and Douthwaite3b and
consequently, molecular structures, bond distances, and
angles are included only in the Supporting Information.
There are three unique molecules in the asymmetric
unit cell of 2. Since the cations in these independent
molecules of 2 are comparable, only the molecular
structure of one cation is shown.
The Ti- -B distances (2.433(4), 2.418(4) Å) in 1 deter-
mined by this laboratory are in agreement with those
of Piers et al. (2.450(10), 2.428(9) Å)3a and Douthwaite
(2.440(3), 2.454(3) Å).3b These Ti- -B distances are
generally longer than for Cp2Ti{(µ-H)2BH2} (2.37(1) Å)2c
and the titanocene organohydroborates Cp2Ti{(µ-H)2BR2}
(R2 ) C4H8, 2.409(4) Å; C5H10, 2.446(3) Å; C8H14, 2.428-
(2) Å).4 This lengthening of the Ti- -B distance is
attributed to the electron-withdrawing pentafluorophe-
nyl rings.
The molecular structures of 2 and 3 are similar to
each other. The coordination geometry about the tita-
nium center is best described as a distorted tetrahedron.
Occupying the corners of the tetrahedron are the centers
of the two cyclopentadienyl rings and the two oxygen
atoms of the ether and THF molecules. The Ti-O bond
distances range from 2.231(3) to 2.275(3) Å in 2, and
the distances are 2.199(1) and 2.223(2) for 3. It is not
surprising that 3 has shorter Ti-O distances because
THF is a stronger Lewis base than ether. This trend is
consistent with other titanocene cations coordinated to
THF, such as [Cp2Ti(CH3CN)(THF)] [BPh4] (2.175(4)
Å),16 [Cp2Ti(THF)2] [Co(CO)4] (2.190(5) to 2.219(6) Å),17
and [Cp2Ti(OC3H6)(THF)]2 [Zn(B10H12)2]‚THF (2.21(1)
and 2.13(1) Å).18 The O-Ti-O bond angles are 82.39-
(9), 83.5(1), and 79.5(1)o in 2 and 78.36(5)o in 3. These
are comparable to the cations in [Cp2Ti(THF)2] [Co-
(CO)4] (77.2(2) to 82.9(2)o)17 and [Cp2Ti(OC3H6)(THF)]2
[Zn(B10H12)2]‚THF (76.9 and 78.6°).18 The structural
features of the [HB(C6F5)3]- anions are not extraordi-
nary (see Table 2 and refs 11a and 12).
F igu r e 2. Molecular structure of the cation in [Cp2Ti-
(THF)2][HB(C6F5)3], 3, showing 15% probability thermal
ellipsoids. Hydrogens attached to carbon atoms are shown
with arbitrary thermal ellipsoids.
days, and finally distilled into a storage bulb containing
sodium/benzophenone. B(C6F5)3 was purchased from Aldrich
and used as received. B(C6F5)3 was also received as a gift from
Dr. J ohn Lee of Albemarle Corp. The titanocene organohy-
droborates Cp2Ti{(µ-H)2BR2} (R2 ) C4H8, C5H10, C8H14) were
prepared by literature procedures.4 Elemental analyses were
obtained by Galbraith Laboratories, Knoxville, TN. Proton
spectra (δ(TMS) 0.00 ppm) were recorded on a Bruker AM-
250 NMR spectrometer operating at 250.11 MHz and on a
Bruker DPX-400 NMR spectrometer operating at 400.13 MHz.
Boron-11 spectra (externally referenced to BF3‚OEt2 (δ 0.00
ppm)) were recorded at 128.38 or 80.25 MHz as noted.
Fluorine-19 spectra (externally referenced to CFCl3 (δ 0.00
ppm)) were recorded at 235.33 MHz. Infrared spectra were
recorded on a Mattson Polaris Fourier Transform spectrometer
with 2 cm-1 resolution.
X-r a y Str u ctu r e Deter m in a tion . Single-crystal X-ray
diffraction data were collected using graphite-monochromated
Mo KR radiation on a Nonius KappaCCD diffraction system.
Single crystals of 1, 2, and 3 were mounted on the tip of a
glass fiber coated with Fomblin oil (a perfluoro polyether).
Crystallographic data was collected at -70 °C for 1, -80 °C
for 2, and -123 °C for 3. Unit cell parameters were obtained
by indexing the peaks in the first 10 frames and refined
employing the whole data set. All frames were integrated and
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. Diethyl ether, tetrahydrofuran, and
toluene were dried over sodium/benzophenone and freshly
distilled prior to use. Hexane was stirred over concentrated
sulfuric acid for 2 days and then decanted and washed with
water. Next, the hexane was stirred over calcium hydride for
6 days, decanted and stirred over sodium/benzophenone for 5

Hydride Ion Abstraction from Titanocene Organohydroborates
Organometallics, Vol. 20, No. 16, 2001 3605
Ta ble 1. Cr ysta l a n d Str u ctu r e Refin em en t Da ta for 1, 2, a n d 3
1
2
3
empirical formula
formula wt. (amu)
T (°C)
radiation (λ, Å)
crystal system
space group
a (Å)
C
44H24B2F20Ti2
C108H93B3F45O6Ti3
2517.95
C36H27BF15O2Ti
835.29
1050.05
-70
-80
-123
Mo KR (0.71073)
Mo KR (0.71073)
monoclinic
P21/n
14.879(1)
52.512(2)
14.915(1)
Mo KR (0.71073)
monoclinic
P21/c
11.284(1)
13.584(1)
22.592(1)
triclinic
P1h
11.583(1)
12.634(1)
15.697(1)
90.62(1)
b (Å)
c (Å)
R (deg)
â (deg)
109.47(1)
110.54(1)
2006.7(3)
4
1.738
0.527
114.85(1)
102.52(1)
γ (deg)
V (Å3)
10574(1)
3380.7(4)
Z
12
4
density (calcd, g cm-3
)
1.582
1.641
µ (mm-1
)
0.356
0.371
crystal size (mm)
θ range (deg)
index ranges
0.12 × 0.15 × 0.15
2.38-25.06
-13 e he 13
-15 e k e 15
-18 e l e 18
14 090
0.31 × 0.38 × 0.38
2.33-25.03
-17 e h e 17
-62 e k e 62
-17 e l e 17
61 834
0.12 × 0.27 × 0.38
2.31-24.99
-13 e h e 13
-16 e k e 15
-26 e l e 26
19 006
reflections collected
independent reflections
Rint
7080
18 594
5924
0.0329
0.0509
0.0442
completeness to θ
99.5%
99.6%
99.7%
max/min transmission
data/restraints/parameters
goodness-of-fit on F2
final R indices [I g 2.0σ(I)]a,b
R indices (all data)
0.9395, 0.9252
7080/0/629
1.078
0.8976, 0.8766
18 594/0/1624
1.031
0.9568, 0.8719
5924/0/500
1.011
R1 ) 0.0526, wR2 ) 0.1232
R1 ) 0.0779, wR2 ) 0.1323
0.484 and -0.346
R1 ) 0.0663, wR2 ) 0.1563
R1 ) 0.1235, wR2 ) 0.1799
1.178 and -0.385
R1 ) 0.0377, wR2 ) 0.0778
R1 ) 0.0656, wR2 ) 0.0857
0.247 and -0.250
largest diff. peak and hole (e Å-3
)
a
b
R1 ) ∑|Fo| - |Fc|/∑|Fo|. wR2 ) {∑w(Fo2 - Fc2)2/∑w(Fo2)2}1/2
.
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
2 a n d 3
the flask at -78 °C. The flask was warmed to room temper-
ature and stirred for 2 h. The 11B NMR spectrum (80 MHz) of
the reaction solution showed the formation of an organoborane
(B(C6F5)(C4H8), δ 81.8 (br s)). The solvent was removed under
vacuum, and the solid was washed with a 1:1 toluene/hexane
mixture until the washings were colorless. The resulting
purple solid was dried under vacuum for 2 h, and 131 mg
(57.0%) of 1 was isolated. Crystals of 1 were grown from
toluene by slowly evaportating the solvent at room tempera-
ture. 1H NMR (250 MHz, C6D6): silent. 11B NMR (80 MHz,
C6D6): silent. 19F NMR (235 MHz, C6D6): δ -154.3 (br s, 1F,
p-F), -161.7 (br s, 2F, m-F). IR (Nujol mull): 3137 (w, br),
2730 (vw), 2129 (w), 2074 (m), 2008 (m), 1900 (w), 1829 (vw),
1645 (m), 1514 (s), 1401 (m), 1285 (m), 1178 (w), 1105 (s), 1093
(s), 1022 (m), 966 (s), 910 (m), 899 (m), 843 (w), 813 (s), 803
(s), 763 (m), 731 (w), 722 (w), 674 (w), 628 (w), 606 (w), 568
compound 2
compound 3
Bond Lengths (Å)
ave Ti(1)-C(11-15)
ave Ti(1)-C(16-10)
Ti(1)-O(11)
2.386
2.382
2.260(2) Ti(1)-O(1)
2.262(2) Ti(1)-O(2)
1.15(4) B(1)-H(1)
ave Ti(1)-C(11-15)
2.382
2.379
2.199(1)
2.223(2)
1.12(2)
ave Ti(1)-C(16-10)
Ti(1)-O(12)
B(1)-H(1)
Bond Angles (deg)
O(11)-Ti(1)-O(12) 82.39(9) O(1)-Ti(1)-O(2)
78.36(5)
125.3(1)
124.8(1)
125.2(1)
124.2(1)
Ti(1)-O(11)-C(11A) 121.0(2)
Ti(1)-O(11)-C(11D) 116.2(2)
Ti(1)-O(12)-C(12A) 121.3(2)
Ti(1)-O(12)-C(12C) 118.2(2)
Ti(1)-O(1)-C(1)
Ti(1)-O(1)-C(4)
Ti(1)-O(2)-C(5)
Ti(1)-O(2)-C(8)
(w) cm-1. Anal. Calcd for C22H12TiBF15
Found: C, 49.91; H, 2.31.
: C, 50.33; H, 2.30.
corrected for Lorentz and polarization effects using DENZO.31
The empirical absorption correction was applied with SOR-
TAV.32 Structures of 1, 2, and 3 were solved by direct methods
and refined using SHELXTL (difference electron density
calculations and full matrix least-squares refinements).33 For
each structure, non-hydrogen atoms were located and refined
anisotropically. For 2 and 3 the terminal hydrogen atoms of
the [HB(C6F5)3]- anions and the bridging hydrogens of 1 were
located and refined isotropically. All other hydrogen atoms
were calculated and fixed during the refinement. There are
two independent molecules in the asymmetric unit cell of 1.
For complex 2, the [HB(C6F5)3]- anions of two independent
molecules are disordered in the fluorine atom positions.
P r epar ation of Cp2Ti{(µ-H)2B(C6F5)2}, 1. A. Fr om Cp2Ti-
{(µ-H)2BC4H8}. A 50 mL flask was charged with 108 mg (0.437
mmol) of Cp2Ti{(µ-H)2BC4H8} and 227 mg (0.443 mmol) of
B(C6F5)3. Approximately 20 mL of toluene was condensed into
B. F r om Cp 2Ti{(µ-H)2BC5H10}. The preparation of 1 (86
mg, 68% yield) by reaction of Cp2Ti{(µ-H)2BC5H10} (63 mg, 0.24
mmol) and B(C6F5)3 (126 mg, 0.246 mmol) was similar to that
described above in A. The 11B NMR spectrum (80 MHz) of the
reaction solution showed the formation of an organoborane
(B(C6F5)(C5H10), δ 82.7 (br s)).
C. F r om Cp 2Ti{(µ-H)2BC8H14}. The preparation of 1 (252
mg, 68.1% yield) by reaction of Cp2Ti{(µ-H)2BC8H14} (211 mg,
0.700 mmol) and B(C6F5)3 (359 mg, 0.701 mmol) was similar
to that described above in A. The 11B NMR spectrum (80 MHz)
of the reaction solution displayed the appearance of an
organoborane (B(C6F5)(C8H14), δ 85.0 (br s)). A GC-MS analysis
of the reaction solution verified the product, B(C6F5)(C8H14).
GC-MS (EI): calcd for C14H14BF5, m/z ) 288.1; obsd, m/z )
288.1.
P r ep a r a tion of [Cp 2Ti(OEt2)2] [HB(C6F 5)3], 2. A. F r om
Cp 2Ti{(µ-H)2BC4H8}. A 194 mg (0.785 mmol) quantity of Cp2-
Ti{(µ-H)2BC4H8}, 402 mg (0.785 mmol) of B(C6F5)3, and 20 mL
of diethyl ether were charged into a 50 mL flask. After stirring
for 1 h, the 11B NMR spectrum (80 MHz) of the reaction
solution showed the appearance of the organodiborane, B2(µ-
H)2(µ-C4H8)2 (δ 28.5 (br t)). The solution was concentrated to
(31) 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,
Eds., R. R.; Academic Press: New York, 1997; pp 307-326.
(32) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(33) SHELXTL (version 5.10), Bruker Analytical X-ray Systems,
1997.

3606 Organometallics, Vol. 20, No. 16, 2001
Plecˇnik et al.
5 mL and light blue crystals formed. The crystals were washed
with a 1:1 ether/hexane mixture until the washings were
colorless. The crystals were dried under vacuum for 30 min.
Complex 2 was isolated as a powder blue solid (446 mg, 67.7%
yield). IR (Nujol mull): 3120 (vw), 2730 (vw), 2384 (w), 2348
(w), 2159 (vw), 2034 (vw), 1642 (m), 1604 (w), 1550 (w), 1513
(s), 1306 (w), 1272 (m), 1218 (vw), 1177 (w), 1113 (ms), 1105
(ms), 1071 (m), 1037 (m), 1013 (m), 962 (s), 945 (m, sh), 928
(w), 905 (m), 844 (w), 822 (s), 806 (m, sh), 786 (m), 760 (m),
722 (m), 670 (vw), 658 (w), 646 (w), 603 (w), 569 (w) cm-1. Anal.
Calcd for C36H31TiO2BF15: C, 51.52; H, 3.72. Found: C, 48.86;
H, 2.60.34
B. F r om Cp 2Ti{(µ-H)2BC5H10}. The preparation of 2 (663
mg, 79.0% yield) by reaction of Cp2Ti{(µ-H)2BC5H10} (261 mg,
1.00 mmol) and B(C6F5)3 (512 mg, 1.00 mmol) was similar to
that described above in A. The 11B NMR spectrum (80 MHz)
of the reaction solution displayed the appearance of an
unidentified organoborane (δ 53.7 (br s)).
final dissolution of the blue solid (5) in d8-THF. The NMR tube
was flame-sealed. H NMR (400 MHz, d8-THF): silent. (The
1
HB proton was not observed in the 1H NMR.) 11B NMR (128
MHz, d8-THF): δ -25.1 (d, 1J BH ) 86 Hz). 19F NMR (235 MHz,
d8-THF): δ -132.0 (br d, 2F, o-F), -164.8 (br t, 1F, p-F),
-167.6 (br t, 2F, m-F).
P r ep a r a tion of [Cp 2Ti(THF )2] [HB(C6F 5)3], 3. A 50 mL
flask was charged with 110 mg (0.421 mmol) of Cp2Ti{(µ-
H)2BC5H10} and 216 mg (0.422 mmol) of B(C6F5)3. Approxi-
mately 20 mL of THF was condensed into the flask at -78 °C.
The flask was warmed to room temperature and stirred for 1
h. The 11B NMR spectrum (80 MHz) of the reaction solution
indicated the presence of an organoborane (δ 54.0 (br s)). The
solvent was reduced under vacuum to about 5 mL, and dry
hexane was added to produce a blue oil phase. The solution
was decanted from the oil. The oil was dissoved in a minimum
amount of THF followed by addition of hexane. Recrystalli-
zation was repeated until blue crystals formed. The crystals
were dried under vacuum for 30 min producing 285 mg (81.0%
C. F r om Cp 2Ti{(µ-H)2BC8H14}. The preparation of 2 (294
mg, 59.3% yield) by reaction of Cp2Ti{(µ-H)2BC8H14} (178 mg,
0.591 mmol) and B(C6F5)3 (317 mg, 0.619 mmol) was similar
to that described above in A. The 11B NMR spectrum (80 MHz)
of the reaction solution displayed the appearance of an
unidentified organoborane (δ 56.2 (br s)).
1
yield) of 3. H{11B} NMR (400 MHz, d8-THF): δ ∼ 3.65 (br s,
shoulder of the most downfield d8-THF resonance, HB). 11B
NMR (128 MHz, d8-THF): δ -25.3 (d, 1J BH ) 86 Hz). 19F NMR
(235 MHz, d8-THF): δ -131.9 (br d, 2F, o-F), -165.2 (br t,
1F, p-F), -167.5 (br t, 2F, m-F). IR (KBr): 3128 (vw), 3001
(w), 2910 (vw), 2885 (vw), 2406 (w), 2381 (vw, sh), 1641 (w),
1510 (s), 1464 (vs), 1379 (w), 1276 (m), 1106 (m), 1074 (m),
1027 (m), 1014 (m), 970 (s), 902 (w), 861 (w), 816 (m), 807 (m),
760 (w), 726 (w), 673 (w), 678 (w), 601 (w), 567 (w) cm-1. Anal.
Calcd for C36H27TiO2BF15: C, 51.77; H, 3.26. Found: C, 51.40;
H, 3.17.
F or m a tion of [Cp 2Ti(d 8-THF )2][HB(C6F 5)3], 3, fr om 2.
Approximately 20 mg of 2 was dissolved in d8-THF in an NMR
tube that was flame-sealed. 1H{11B} NMR (400 MHz, d8-
3
THF): δ 3.75 (br s, 1H, HB), 3.38 (q, J HH ) 7.0 Hz, 3.6 H,
free ether), 1.04 (t, 3J HH ) 7.0 Hz, 4.7 H, free ether). 11B NMR
(128 MHz, d8-THF): δ -25.5 (d, 1J BH ) 90 Hz). 19F NMR (235
MHz, d8-THF): δ -132.1 (br d, 2F, o-F), -165.4 (br t, 1F, p-F),
-167.7 (br t, 2F, m-F).
Con ver sion of 3 in to [Cp 2Ti(d 5-P yr )2] [HB(C6F 5)3].
About 20 mg of 3 was dissolved in d5-pyridine producing an
olive green solution. 1H NMR (400 MHz, d5-pyridine): δ ∼ 4.6
F or m a tion of Cp 2Ti{(µ-H)B(C6F 5)3}(OEt2), 4, fr om 2.
Approximately 20 mg of 2 was dissolved in d8-toluene in an
NMR tube that was flame-sealed. 1H NMR (400 MHz, d8-
toluene): δ 3.32 (br s, 2H, free ether), 1.05 (br s, 3 H, free
ether). 11B NMR (80 MHz, d8-toluene): silent. 19F NMR (235
MHz, d8-toluene): δ -155.3 (v br s, 1F, p-F), -160.3 (v br s,
2F, m-F).
1
(br q, J BH ) 91 Hz, 1 H, HB), 3.64 (br s, 8 H, free THF), 1.61
1
(br s, 8 H, free THF). H{11B} NMR (d5-pyridine): δ 4.65 (br
s, 1H, HB). 11B NMR (128 MHz, d5-pyridine): δ -25.0 (d, 1J BH
) 91 Hz). 19F NMR (235 MHz, d5-pyridine): δ -129.9 (br d,
2F, o-F), -161.0 (br t, 1F, p-F), -163.9 (br t, 2F, m-F).
F or m a tion of 3 fr om 1. A 50 mL flask was charged with
115 mg (0.219 mmol) of 1 and 117 mg (0.229 mmol) of B(C6F5)3.
About 20 mL of THF was condensed into the flask at -78 °C.
The flask was warmed to room temperature and stirred for 2
h. The 11B NMR spectrum (80 MHz) of the reaction solution
indicated the presence of an organoborane THF adduct (δ -0.7
(br d)). The volume of the solution was reduced under vacuum
to approximately 5 mL and a blue oil phase formed upon
addition of hexane. Isolation of 3 (128 mg, 74.4%) was
performed in the same manner as described in the preparation
of 3. 1H NMR (400 MHz, d5-pyridine): δ ∼ 4.6 (br q, 1J BH ) 91
Con ver sion of 4 in to 3. Several drops of d8-THF were
added to a solution of 2 in d8-toluene. The NMR tube was
flame-sealed. 1H NMR (400 MHz, d8-toluene, d8-THF): δ 3.33
3
(q, 3J HH ) 7.0 Hz, 2 H, free ether), 1.14 (t, J HH ) 7.0 Hz, 3 H,
free ether). The HB proton resonance was not observed in the
1H NMR spectrum because it appears as a broad quartet
overlapping the most downfield d8-THF resonance. 11B NMR
1
(128 MHz, d8-toluene, d8-THF): δ -24.9 (d, J BH ) 86 Hz).
19F NMR (235 MHz, d8-toluene, d8-THF): δ -131.2 (br d, 2F,
o-F), -163.8 (br t, 1F, p-F), -166.3 (br t, 2F, m-F).
Hz, 1 H, HB), 3.65 (br s, 8 H, free THF), 1.63 (br s, 8 H, free
F or m a tion of Cp 2Ti{(µ-H)B(C6F 5)3}, 5, fr om 2. In an
NMR tube, 2 was dissolved in toluene followed by removal of
the volatile materials on the vacuum line for 15 min. This step
was repeated again with final dissolution of the blue solid in
d8-toluene. The NMR tube was flame-sealed. 1H NMR (250
MHz, d8-toluene): silent. 11B NMR (80 MHz, d8-toluene):
silent. 19F NMR (235 MHz, d8-toluene): δ -155.2 (v br s, 1F,
p-F), -160.2 (v br s, 2F, m-F). IR (Nujol mull): 3124 (vw), 2724
(vw), 2153 (m), 2115 (m), 2033 (m, br), 1984 (m), 1953 (m),
1643 (s), 1606 (w), 1518 (s), 1279 (s), 1179 (vw), 1098 (s, br),
1024 (s), 1009 (s, br), 971 (s, br), 945 (s), 915 (ms), 894 (ms),
820 (s, br), 787 (ms), 770 (ms), 759 (ms), 727 (ms), 694 (w),
686 (w), 669 (m), 654 (m), 641 (m), 611 (w), 601 (w), 569 (w)
cm-1. Anal. Calcd for C28H11TiBF15: C, 48.67; H, 1.60. Found:
C, 48.77; H, 1.93.
1
THF). 11B NMR (128 MHz, d5-pyridine): δ -23.7 (d, J BH
)
86 Hz).
Ack n ow led gm en t. This work was supported by the
National Science Foundation through Grants CHE 97-
00394 and CHE 99-01115. We thank Dr. Karl Vermil-
lion for assistance with the 19F NMR experiments. We
also thank Dr. J ohnie Brown of the Campus Chemical
Instrument Center for obtaining the GC-MS spectra.
Su p p or tin g In for m a tion Ava ila ble: Molecular struc-
tures of the two independent molecules of 1; molecular
structures of the two other independent cations and three
independent anions of 2; molecular structure of the anion of
3; tables of crystallographic data, positional and thermal
parameters, and interatomic distances and angles for 1, 2, and
3; relevant 1H, 11B, and 19F NMR spectra. Three X-ray
crystallographic files in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
Con ver sion of 5 in to 3. In an NMR tube, 2 was dissolved
in toluene followed by removal of the volatile materials on the
vacuum line for 15 min. This step was repeated again with
(34) See text for an explanation of the low carbon and hydrogen
analyses.
OM010267M