Synthesis, Crystal Structure, and Application of the Oxonium Acid [H(OEt2)2]+[B(C6F5) 4]-

Article abstract of DOI:10.1021/om990612w

The reaction of LiB(C₆F₅)₄ with HCl in diethyl ether afforded the new oxonium acid [H(OEt₂)₂]⁺-[B(C₆F₅) ₄]^- (1) as a colorless crystalline solid, which was characterized by NMR spectroscopy, by elemental analysis, and by single-crystal X-ray diffraction. The application of 1 is demonstrated in the generation of the complex {[η⁵-C₅H₃(CH₂CH ₂NMe₂)CMe₂-η⁵-C ₁₃H₈]ZrCH₃}⁺-[B(C₆F ₅)₄]^- (3), containing an intramolecularly donorstabilized alkylzirconocene cation.

Full text of DOI:10.1021/om990612w

1442
Organometallics 2000, 19, 1442-1444
Syn th esis, Cr ysta l Str u ctu r e, a n d Ap p lica tion of th e
Oxon iu m Acid [H(OEt2)2]+[B(C6F 5)4]-
Peter J utzi,* Christian Mu¨ller, Anja Stammler, and Hans-Georg Stammler
Faculty of Chemistry, University of Bielefeld, Universita¨tsstrasse 25,
D-33615 Bielefeld, Germany
Received August 2, 1999
Sch em e 1
Summary: The reaction of LiB(C6F5)4 with HCl in di-
ethyl ether afforded the new oxonium acid [H(OEt2)2]+-
[B(C6F5)4]- (1) as a colorless crystalline solid, which was
characterized by NMR spectroscopy, by elemental analy-
sis, and by single-crystal X-ray diffraction. The applica-
tion of 1 is demonstrated in the generation of the complex
{[η5-C5H 3(CH 2CH 2NMe2)CMe2-η5-C13H 8]Zr CH 3}+-
[B(C6F5)4]- (3), containing an intramolecularly donor-
stabilized alkylzirconocene cation.
In tr od u ction
Cationic species with main group and transition metal
centers have attracted considerable interest because of
their activity in certain catalytic C-C bond formation
reactions;1 their detailed investigation has led to a much
better understanding of the interaction between catalyst
and substrate. For the stabilization of highly electro-
philic cations, unreactive and noncoordinating (or weakly
coordinating) counteranions are prerequisite.
[B(C6F5)4]-, [HNR3]+[B(C6F5)4]-, [HNMe2Ph]+[B(C6F5)4]-,
[C5Me5Sn]+[B(C6F5)4]-,
or
[H(OEt2)2]+[3,5-(CF3)2-
C6H3)4B]-.4-6 We now wish to report on the synthesis
and crystal structure of an oxonium salt containing the
cation [H(OEt2)2]+ and the anion [B(C6F5)4]-. Further-
more, we describe an application of this compound in
zirconocene chemistry.
Anions such as [PF6]-, [BF4]-, [SO3CF3]-, [SbF6]-, and
[BPh4]- are regarded as noncoordinating (or weakly
coordinating) counterions, but they react with highly
Resu lts a n d Discu ssion
According to the procedure described by Massey and
Park, LiB(C6F5)4 was prepared by reaction of LiC6F5
with B(C6F5)3 in pentane.3 This compound, which is
soluble in diethyl ether, reacted with HCl under pre-
cipitation of LiCl to give the desired product [H(OEt2)2]+-
[B(C6F5)4]- (1) (Scheme 1). By crystallization from a
concentrated ether solution at -60 °C, 1 was obtained
as colorless crystals. 1 is slightly air- and moisture-
sensitive but can be handled in air for a short period of
time. It is stable at room temperature and soluble in
electrophilic cations.2 The hexabromo carborane anion
- 2d
CB12H6Br6
and the perfluorinated tetraarylborate
[B(C6F5)4]-,3 however, are very poorly coordinating,
fairly nonreactive anions. [B(C6F5)4]- is much more
stable than the chemically labile tetraphenylborate or
the related tetrakis[3,5-bis(trifluoromethyl)phenyl)-
borate.2d,e Thus, it is frequently used as counteranion
for electrophilic cations. In the chemistry of transition
metal alkyl and olefin complexes, the tetraarylborate
anion can be introduced by reaction with reagents such
as [Ag]+[B(C6F5)4]-, [Cp2Fe]+[B(C6F5)4]-, [Ph3C]+-
(4) For example see: (a) Piers, W. E.; Chivers, T. Chem. Soc. Rev.
1997, 26, 345-354, and references therein. (b) Turner, H. W. European
Patent No. 277 004, 1988. (c) Turner, H. W. United States Patent No.
5 599 761, 1997. (d) Bochmann, M.; Lancaster, S. J . J . Organomet.
Chem. 1992, 434, C1-C5. (e) Bochmann, M. J . Chem. Soc., Dalton
Trans. 1996, 255-270. (f) J ordan, R. F. Adv. Organomet. Chem. 1991,
32, 325-387, and references therein. (g) Chien, J . C. W.; Tsai, W.-M.;
Rausch, M. D. J . Am. Chem. Soc. 1991, 113, 8570-8571. (h) Rhodes,
B.; Chien, J . C. W.; Rausch, M. D. Organometallics 1998, 17, 1931-
1933. (i) J ia, L.; Yang, X.; Stern, C. L.; Marks, T. J . Organometallics
1997, 16, 842-857. (j) Brookhart, M.; Grant, B.; Volpe, A. F. Organo-
metallics 1992, 11, 3920-3922. (k) Taube, R.; Wache. S. J . Organomet.
Chem. 1992, 428, 431-442.
(1) For example see: (a) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt,
R.; Rieger, B.; Waymouth, R. Angew. Chem., Int. Ed. Engl. 1995, 34,
1143, and references therein. (b) Britovsek, G. J . P.; Gibson, V. C.;
Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428-447. (c) Aulbach,
M.; Ku¨ber, F. Chem. Unserer Zeit 1994, 28, 197-208. (d) Coles, M. P.;
J ordan, R. F. J . Am. Chem. Soc. 1997, 119, 8125-8126. (e) Bochmann,
M.; Dawson, D. M. Angew. Chem., Int. Ed. Engl. 1996, 35, 2226-2228.
(2) For weakly coordinating anions see for example: (a) Strauss, S.
H. Chem. Rev. 1993, 93, 927-942, and references therein. (b) Noiret,
M. D.; Anderson, O. P.; Strauss, S. H. Inorg. Chem. 1987, 26, 2216-
2223, and references therein. (c) Shelley, K.; Reed, C. A.; Lee, Y. J .;
Scheidt, W. R. J . Am. Chem. Soc. 1986, 108, 3117-3118. (d) Reed, C.
A. Acc. Chem. Res. 1998, 3, 133-139. (e) Reed, C. A. Acc. Chem. Res.
1998, 6, 325-332. (f) Seppelt, K. Angew. Chem., Int. Ed. Engl. 1993,
32, 1025. (g) Bochmann, M. Angew. Chem., Int. Ed. Engl. 1992, 31,
1181-1182. (h) Lambert, J . B.; Zhan, S. J . Chem. Soc., Chem.
Commun. 1993, 383-384. (i) Reedijk, J . Comm. Inorg. Chem. 1982, 1,
379. (j) J ordan, R. F.; Dasher, W. E.; Echols, S. F. J . Am. Chem. Soc.
1986, 108, 1718. (k) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J .
Am. Chem. Soc. 1989, 111, 2728-2729.
(5) The strong Brønstedt acid [C6Me3H4]+[B(C6F5)4]- might also be
a suitable reagent for protonolysis of M-CH3 bonds or protonation of
metal olefin complexes: Reed, C. A.; Fackler, N. L. P.; Kim, K.-C.;
Stasko, D.; Evans, D.; Boyd, P. D. W.; Rickard, C. E. F. J . Am. Chem.
Soc. 1999, 121, 6314-6315.
(6) The related anions [RB(C6F5)3]- (R ) alkyl) and [(C6F5)3B(µ-
OH)B(C6F5)3]- are obtained upon reaction of metal alkyl complexes
with B(C6F5)3 or metal complexes with B(C6F5)3 in the presence of H2O.
See for example ref 4a and: Danopoulos, A. A.; Galsworthy, J . R.;
Green, M. L. H.; Cafferkey, S.; Doerrer, L. H.; Hursthouse, M. B. J .
Chem. Soc., Chem. Commun. 1998, 2529-2530.
(3) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1962, 2, 245.
10.1021/om990612w CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/03/2000

Notes
Organometallics, Vol. 19, No. 7, 2000 1443
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1
Sch em e 2
empirical formula
fw
cryst size, color and habit
C32H21BF20O2
828.30
0.8 × 0.5 × 0.3 mm3, colorless
needles
cryst syst, space group
temperature
orthorhombic Pbca
173(2) K
wavelength
0.71073 Å
unit cell dimens
a ) 18.714(9) Å, R ) 90°
b ) 16.871(10) Å, â ) 90°
c ) 21.315(9) Å, γ ) 90°
6730(6) Å3
volume
Z, calcd density
abs coeff
8, 1.635 Mg/m3
0.176 mm-1
θ range for data collection
1.89-25.02°
index ranges
0 e h e 22, 0 e k e 20,
-25 e l e 0
1 is a useful reagent for the preparation of ionic species
containing the [B(C6F5)4]- counteranion. Concerning
metallocene chemistry, the lack of proton resonances in
the aromatic region is valuable for monitoring reactive
species in NMR tube experiments. As an example, 1 was
reacted with the 2-(N,N-dimethylamino)ethyl-function-
alized zirconocene dimethyl 2 to give complex 3, con-
taining an intramolecularly donor-stabilized 16-VE
zirconocene cation (Scheme 2).9
no. of reflns collected/unique 5928/5927 [R(int) ) 0.0367]
abs corr
no. of data/restraints/params 5927/0/504
none
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
diffractometer used
programs used
1.006
R1 ) 0.0812, wR2 ) 0.1587 [2780]
R1 ) 0.1843, wR2 ) 0.2054
0.433 and -0.392 e A-3
Siemens P2(1) difractometer
Siemens SHELXTL plus/
SHELXL-97
refinement method
full-matrix least-squares on F2
Exp er im en ta l Section
Ta ble 2. Selected Bon d Len gth s a n d Atom ic
Dista n ces [Å] for 1
Gen er a l Da ta . All manipulations were carried out under
a purified argon atmosphere using standard Schlenk tech-
niques. The solvents were commercially available, purified by
conventional means, and distilled immediately prior to use.
The melting point determination was performed using a Bu¨chi
510 melting point apparatus. The elemental analyses were
performed by the Microanalytical Laboratory of the Univer-
sita¨t Bielefeld. The NMR spectra were recorded on a Bruker
Avance DRX 500 spectrometer (1H 500.1 MHz; 13C{1H} 125.8
MHz; 19F{1H} 470.6 MHz). Chemical shifts are reported in ppm
and are referenced to the solvent as internal standard.
B(1)-C(1)
B(1)-C(7)
B(1)-C(13)
B(1)-C(19)
O(1)‚‚‚O(2)
O(1)‚‚‚F(6)
1.657(9)
1.651(9)
1.665(8)
1.673(9)
2.445(9)
3.460(7)
P r ep a r a tion of [H(OEt2)2]+[B(C6F 5)4]- (1). A solution of
LiB(C6F5)4 (3.00 g, 4.25 mmol) in diethyl ether (12 mL) was
transferred via syringe to a 500 mL Schlenk flask containing
HCl(g) (25.0 mmol) at -30 °C. Immediately LiCl precipitated,
and the flask was allowed to stand at -30 °C for 4 h. After
filtration the solution was concentrated to 10 mL and stored
at -60 °C. Colorless crystals (2.30 g, 2.78 mmol, 65%) of 1
were formed and isolated by decanting the supernatant and
by evaporating the residual solvent under reduced pressure.
Mp: 148 °C.
1H NMR (CD2Cl2 T ) 298 K): δ 15.50 (v br, 1 H, Et2OH),
7.55 (q, 3J ) 7.2 Hz, 8 H, CH2), 1.42 (t, 3J ) 7.2 Hz, 12 H,
CH3). 13C NMR (CD2Cl2): δ 148.5 (d, 1J C-F ) 240.83 Hz), 138.6
(d, 1J C-F ) 244.72 Hz), 136.7 (d, 1J C-F ) 241.58 Hz), 124.5 (br),
F igu r e 1. Molecular structure of [H(OEt2)2]+[B(C6F5)4]-
(1) (ORTEP diagram; 50% probability ellipsoids).
(7) (a) Kolesnikov, S. P.; Sizov, A. I.; Soleveichik, G. L.; Bulychev,
B. M. Izv. Akad. Nauk SSSR, Ser. Khim. 1985, 1, 79-86. (b) Mootz,
D.; Steffen, M. Z. Anorg. Allg. Chem. 1981, 482, 193-299. (c) Cotton,
F. A.; Fair, C. K.; Lewis, G. E.; Mott, G. N.; Ross, F. K.; Schultz, A. J .;
Williams, J . M. J . Am. Chem. Soc. 1984, 106, 5319-5323.
polar organic solvents such as ethers and dichlo-
romethane. H NMR spectroscopy as well as elemental
1
analysis indicate that 1 is a dietherate. This is con-
firmed by an X-ray crystal structure determination.
Crystallographic data for 1 are presented in Table 1;
selected bond length and atomic distances are given in
Table 2. The molecular structure of 1 is depicted in
Figure 1. The R factor of the crystal structure and the
thermal parameters of the C atoms of the ether mol-
ecules do not allow a definite predication whether the
proton is located symmetrically or unsymmetrically
between O(1) and O(2).7
(8) For the application of [H(OEt2)2]+[3,5-(CF3)2C6H3)4B]- see: (a)
J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc. 1995,
117, 6414-6415. (b) Ca´mpora, J .; Lo´pez, J . A.; Palma, P.; Valerga, P.;
Spillner, E.; Carmona, E. Angew. Chem., Int. Ed. 1999, 38, 147-151.
(c) Widenhoefer, R. A.; Vadehra, A.; Cheruvu, P. K. Organometallics
1999, 18, 4614-4618.
(9) Mu¨ller, C.; J utzi, P. Manuscript in preparation. NMR spectro-
scopic data for 3: 1H NMR (CD2Cl2, T ) 298 K): δ -0.70 (s, 3 H, Zr-
CH3), 0.21 (s, 4 H, CH4), 1.18 (t, 3J ) 7.1 Hz, (CH3CH2)2O), 1.22, 1.97,
2.17, 2.38 (4×s, 4×3 H, C(CH3)2, N(CH3)2), 2.39, 2.42, 2.70, 3.25, (4×m,
4×1 H, -CH2-CH2-), 3.52 (q, 3J ) 7.1 Hz, (CH3CH2)2O), 5.42, 5.69,
6.65 (3×m, 3×1 H, Cp-H), 7.36, 7.46, 7.53 (3×m, 3×1 H, fluorenyl-
H), 7.67 (d, 3J ) 8.9 Hz, 1 H, fluorenyl-H), 7.75 (m, 1 H, fluorenyl-
H), 8.07 (d, 3J ) 8.8 Hz, 1 H, fluorenyl-H), 8.30 (d, 3J ) 8.2 Hz, 1 H,
fluorenyl-H), 8.33 (d, 3J ) 8.4 Hz, 1 H, fluorenyl-H).
The application of 1 in organometallic and organic
chemistry seems to be promising.8 Due to its easy access,

1444 Organometallics, Vol. 19, No. 7, 2000
Notes
70.4 (CH2), 13.9 (CH3). 19F NMR (CD2Cl2): δ 76.78 (s, br, o-F),
46.30 (t, J F-F ) 20.28 Hz, p-F), 42.36 (m, m-F). 11B NMR (CD2-
Cl2): δ -17.28. Anal. Calcd for C32H21BF20O2: C, 46.40; H,
2.56. Found: C, 46.20; H, 2.74.
gratefully acknowledged. We thank the Witco GmbH,
Bergkamen, Germany, for generous gifts of B(C6F5)3.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and selected bond
lengths and angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. Financial support provided by
the Deutsche Forschungsgemeinschaft, the Universita¨t
Bielefeld, and the Fonds der Chemischen Industrie is
OM990612W