Thallium Perfluorotetraphenylborate

Article abstract of DOI:10.1021/om0306729

Thallium perfluorotetraphenylborate, Tl-[B(C₆F₅) ₄], has been prepared by the reaction of thallium ethoxide with [H(OEt₂)₂][C₆F₅)₄]. Its use in the preparation of [(η<

Full text of DOI:10.1021/om0306729

Organometallics 2004, 23, 1459-1460
1459
Th a lliu m P er flu or otetr a p h en ylbor a te
Davide Alberti and Klaus-Richard Po¨rschke*
Max-Planck-Institut fu¨r Kohlenforschung, D-45466 Mu¨lheim an der Ruhr, Germany
Received November 25, 2003
Summary: Thallium perfluorotetraphenylborate, Tl-
[B(C6F5)4], has been prepared by the reaction of thallium
ethoxide with [H(OEt2)2][B(C6F5)4]. Its use in the prepa-
ration of [(η3-C3H5)Ni(Me2PC2H4PMe2)][B(C6F5)4] is de-
scribed.
by halide exchange with the silver or thallium salts, Ag-
[B(C6F5)4],8 Ag[TFPB],9 and Tl[TFPB].10 While the silver
salts are substantially less toxic, they sometimes un-
dergo unwanted redox side reactions. Thus, metathesis
with a thallium salt is usually more efficient and cleaner
to carry out.
Attempting the preparation of [(η3-C3H5)NiL]+ and
[(η3-C3H5)PdL]+ complexes with noncoordinating (or
weakly coordinating) counterions, we noticed that Tl-
[B(C6F5)4] (1), a potentially useful reagent in the context
of the above, is apparently not known. Here, we report
the synthesis and properties of the compound.
In tr od u ction
There is an enduring interest in the chemistry of
noncoordinating (or weakly coordinating) anions.1,2 In
many cases, classical anions such as ClO4-, SO3CF3
,
-
-
BF4-, BPh4-, and PF6 still act as weak nucleophiles
and thus bind to strong electrophiles. Anion nucleophi-
licity can, however, be further reduced when the charge
is delocalized by increasing ionic size and introducing
an array of electron-withdrawing fluorine substituents.
Typical developments, mainly over the last two decades,
are B(C6F5)4-, MeB(C6F5)3-, B{3,5-C6H3(CF3)2}4- (TFPB,
Exp er im en ta l Section
All manipulations were carried out under argon with
Schlenk-type glassware. Solvents were dried prior to use by
distillation from NaAlEt4 or P4O10. LiC6F5,3b,11a,c B(C6F5)3,3,11b,c
Li[B(C6F5)4],3a,b [H(OEt2)2][B(C6F5)4],6 and (η3-C3H5)Ni(dmpe)-
Br12a were prepared according to the literature. TlOEt (98%)
and C6F5I (99%) were obtained from Aldrich and used without
further purification. Additional information on the synthesis
and properties of some of the compounds is given below.
Microanalyses were performed by the local Mikroanalytisches
Labor Kolbe. NMR spectra were measured on Bruker AMX-
300 and DPX-300 instruments in CD2Cl2 as a solvent at 25
°C.
LiC6F 5. Synthesis was performed as described in ref 11a
but using C6F5I instead of C6F5Br: to a stirred solution of C6F5I
(29.4 g, 100 mmol) in 250 mL of diethyl ether was added
dropwise a 1.6 M solution of LinBu in n-hexane (62.5 mL, 100
mmol) at -78 °C. After the mixture was stirred for an
additional 1 h, the reaction was complete. The product was
used without isolation.
Li[B(C6F 5)4]. Following the protocol of ref 3b, the isolated
yield was increased to 83% (instead of a reported 43%) due to
the higher yield of the in situ prepared LiC6F5. Thus, the
solution of LiC6F5 (assumed to be 100 mmol) was added in
portions to a suspension of B(C6F5)3 (46.1 g, 90 mmol) in 250
mL of pentane at -40 °C. The mixture was stirred overnight
at ambient temperature. The resulting solid was isolated by
filtration, washed with pentane, and dried under vacuum:
yield 51.2 g (83%). ESIneg-MS (CH2Cl2): m/e (%) 679
([B(C6F5)4]-, 100).
BArF),1a,b and the carborane CB11H12 and its deriva-
-
tives.1c
Of these, B(C6F5)4-, discovered by Massey and Park,3
and Kobayashi’s TFPB4a are of particular interest, due
to their structural simplicity, high symmetry, and ready
-
availability. In a comparison of the two anions, B(C6F5)4
is more stable1c,5a than B{3,5-C6H3(CF3)2}4-, but the
latter seems to be less nucleophilic,5b,c though there is
also a contending view.5a Introduction of these anions
into a compound can typically occur by halide exchange
with an alkali-metal salt, e.g., Li[B(C6F5)4]3 and Na-
[TFPB],4 by protolysis with the corresponding oxonium
acids, [H(OEt2)2][B(C6F5)4]6 and [H(OEt2)2][TFPB],7 or
(1) Recent reviews: (a) Strauss, S. H. Chem. Rev. 1993, 93, 927. (b)
Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345. (c) Reed, C. A.
Acc. Chem. Res. 1998, 31, 133. (d) Piers, W. E. Chem. Eur. J . 1998, 4,
13. (e) Chen, E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(2) Recent developments: (a) LaPointe, R. E.; Roof, G. R.; Abboud,
K. A.; Klosin, J . J . Am. Chem. Soc. 2000, 122, 9560. (b) Al(ORF)4
-
:
Barbarich, T. J .; Miller, S. M.; Anderson, O. P.; Strauss, S. H. J . Mol.
Catal., A: Chem. 1998, 128, 289. Ivanova, S. M.; Nolan, B. G.;
Kobayashi, Y.; Miller, S. M.; Anderson, O. P.; Strauss, S. H. Chem.
Eur. J . 2001, 7, 503. Krossing, I. Chem. Eur. J . 2001, 7, 490. Krossing,
I.; Brands, H.; Feuerhake, R.; Koenig, S. J . Fluorine Chem. 2001, 112,
83.
(3) (a) Massey, A. G.; Park, A. J .; Stone, F. G. A. Proc. Chem. Soc.
1963, 212. (b) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964,
2, 245. (c) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1966, 5,
218. (d) Massey, A. G.; Park, A. J . In Organometallic Synthesis; King,
R. B., Eisch, J . J ., Eds.; Elsevier: New York, 1986; Vol. 3, p 461.
(4) (a) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Koba-
yashi, H. Bull. Chem. Soc. J pn. 1984, 57, 2600. (b) Bahr, S. R.;
Boudjouk, P. J . Org. Chem. 1992, 57, 5545.
(5) (a) Camire, N.; Nafady, A.; Geiger, W. E. J . Am. Chem. Soc. 2002,
124, 7262 and references therein. (b) Reference 1a, p 932. (c) Pfaltz,
A.; Blankenstein, J .; Hilgraf, R.; Ho¨rmann, E.; McIntyre, S.; Menges,
F.; Scho¨nleber, M.; Smidt, S. P.; Wu¨stenberg, B.; Zimmermann, N. Adv.
Synth. Catal. 2003, 345, 33.
(6) J utzi, P.; Mu¨ller, C.; Stammler, A.; Stammler, H.-G. Organome-
tallics 2000, 19, 1442.
(8) Mukaiyama, T.; Maeshima, H.; J ona, H. Chem. Lett. 2001, 388.
(9) (a) Golden, J . H.; Mutolo, P. F.; Lobkovsky, E. B.; DiSalvo, F. J .
Inorg. Chem. 1994, 33, 5374. (b) Hayashi, Y.; Rohde, J . J .; Corey, E.
J . J . Am. Chem. Soc. 1996, 118, 5502.
(10) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A.
Inorg. Chem. 1997, 36, 1726.
(11) (a) Coe, P. L.; Stephens, R.; Tatlow, J . C. J . Chem. Soc. A 1962,
3227. Uson, R.; Laguna, A. Inorg. Synth. 1982, 21, 72. (b) Pohlmann,
J . L. W.; Brinckmann, F. E. Z. Naturforsch., B 1965, 20, 5. (c)
Chernega, A. N.; Graham, A. J .; Green, M. L. H.; Haggitt, J .; Lloyd,
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(12) (a) Gemel, C.; Bu¨hl, M.; Goddard, R.; Rufin´ska, A.; Po¨rschke,
K.-R. To be submitted for publication. (b) Alberti, D. Dissertation,
projected for 2004.
10.1021/om0306729 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/17/2004

1460 Organometallics, Vol. 23, No. 6, 2004
Notes
[H(OEt2)2][B(C6F 5)4].6 13C NMR (75.5 MHz): δ 148.7 (d,
J (CF) ) 240 Hz, Cortho), 138.7 (d, J (CF) ) 245 Hz, Cpara), 136.8
(d, J (CF) ) 247 Hz, Cmeta), ∼125 (Cipso), 70.7 (CH2), 13.7 (CH3).
11B NMR (96.3 MHz): δ -16.7.
LiB(C6F5)4 HCl/Et O8
2
-LiCl
TlOEt
Tl[B(C F ) ]
[H(OEt2)2][B(C6F5)4] -EtOH8
(1)
6
5 4
1
Tl[B(C6F 5)4] (1). TlOEt (12.5 g, 50 mmol) was added
dropwise to a solution of [H(OEt2)2][B(C6F5)4] (41.4 g, 50 mmol)
in 250 mL of diethyl ether at ambient temperature. The
resulting light yellow reaction mixture was stirred for 1 h and
filtered to remove a small amount of an insoluble impurity
(presumably TlCl). Evaporating the solvent under vacuum
gave a white microcrystalline residue: yield 37.6 g (85%).
ESIpos-MS (CH2Cl2): m/e (%) 205 ([Tl]+, 100). ESIneg-MS
(CH2Cl2): m/e (%) 679 ([B(C6F5)4]-, 100). 13C NMR (75.5
MHz): δ 148.2 (d, J (CF) ) 242 Hz, Cortho), 138.3 (d, J (CF) )
246 Hz, Cpara), 136.4 (d, J (CF) ) 246 Hz, Cmeta), ∼124 (Cipso).
compound has so far not been amenable to single-crystal
X-ray analysis.13 The product contains small amounts
of diethyl ether and ethanol as solvates, which are
removed upon heating to 100 °C under vacuum. Accord-
ing to DSC, a phase transition occurs at about 140 °C,
but no melting or decomposition is observed up to 200
°C. The compound can be stored indefinitely at ambient
temperature. 1 has been characterized by its ESIpos-
MS and ESIneg-MS spectra, which gave single peaks
for [Tl]+ (m/z 205) and [B(C6F5)4]- (m/e 679). It dissolves
well in CH2Cl2, diethyl ether, and THF but not in
toluene or hydrocarbons. The solution NMR data agree
well with the previously reported data for the B(C6F5)4
anion.14
11B NMR (96.3 MHz): δ -16.7. 19F NMR (282.4 MHz):
δ
-132.8 (s, Fortho), -163.2 (t, Fpara), -167.0 (“t”, Fmeta). Anal.
Calcd for BC24F20Tl (883.4): C, 32.63; B, 1.22; F, 43.01; Tl,
23.14. Found: C, 32.82; B, 1.23; F, 42.59; Tl, 23.29.
[(η3-C3H5)Ni(Me2P C2H4P Me2)][B(C6F 5)4] (2). A solution
of (η3-C3H5)Ni(dmpe)Br (1.65 g, 5.00 mmol) in 15 mL of CH2-
Cl2 was stirred with solid 1 (4.42 g, 5.00 mmol) at -30 °C for
1 h. The light yellow precipitate of TlBr was removed by
filtration. After addition of an equal volume of diethyl ether
the solution was cooled to -60 °C to give yellow-orange
crystals, which were freed from the mother liquor by cannu-
lation, washed with a small volume of cold pentane (-78 °C),
and dried under vacuum (20 °C): yield 3.30 g (71%); mp 174
°C. ESIpos-MS (CH2Cl2): m/e (%) 249 ([(C3H5)Ni(dmpe)]+, 100).
ESIneg-MS (CH2Cl2): m/e (%) 679 ([B(C6F5)4]-, 100). 1H NMR
(300 MHz): δ 5.13 (m, 1H, Hmeso), 4.28 (m, 2H, Hsyn), 2.45 (m,
2H, Hanti), allyl; 1.97 (m, 4H, PCHaHb), 1.64, 1.52 (each d, 6H,
Me), dmpe. 13C NMR (75.5 MHz): δ 117.5 (s, 1C), 65.4 (m,
2C), allyl; 27.8 (m, 2C, PCH2), 13.5, 12.7 (each m, 2C, Me),
dmpe; 148.2 (d, Cortho), 138.3 (d, Cpara), 136.4 (d, Cmeta), ∼124
(Cipso), borate. 31P NMR (121.5 MHz): δ 36.9. Anal. Calcd for
C9H21NiP2‚BC24F20 (929.0): C, 42.67; H, 2.28; B, 1.16; F, 40.90;
Ni, 6.32; P, 6.67. Found: C, 42.52; H, 2.32; B, 1.13; Ni, 6.14;
P, 6.48.
The applicability of 1 as a reagent for the formation
of B(C6F5)4 salts is demonstrated by its reaction with
(η3-C3H5)Ni(dmpe)Br (dmpe ) Me2PC2H4PMe2) to afford
the ionic 2, which is easily separated from the insoluble
TlBr (eq 2). Complex 2 extends a series of likewise ionic
complexes [(η3-C3H5)Ni(dmpe)]X (X ) SO3CF3, PF6)12 to
X ) B(C6F5)4. For these complexes (in contrast to the
halides) the 1H and 13C NMR spectra in CD2Cl2 are
sharply resolved at ambient temperature, indicating a
rigid structure of the cation on the NMR time scale. We
conclude from the spectra that, despite substantial ion
pairing, the nucleophilicity of the anions toward the [(η3-
C3H5)Ni(dmpe)]+ cation is marginal.12
Resu lts a n d Discu ssion
LiC6F5 is prepared in quantitative yield from C6F5I
and LinBu in diethyl ether/n-hexane solution at -78 °C.
It reacts with B(C6F5)3 to afford Li[B(C6F5)4] (83%),
which in diethyl ether is converted with HCl into
[H(OEt2)2][B(C6F5)4], as described by J utzi et al.6 Reac-
tion of the oxonium acid with thallium(I) ethoxide by
the method of Hughes et al.10 afforded Tl[B(C6F5)4] (1)
in 85% yield (eq 1).
Ack n ow led gm en t. Financial support by the Fonds
der Chemischen Industrie is gratefully acknowledged.
OM0306729
(13) By the end of 2003 the Cambridge Structural Data File had
listed about 100 known structures of B(C6F5)4 salts.
(14) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., J r.; J ordan,
R. F. J . Am. Chem. Soc. 2001, 123, 8291.
Compound 1 crystallizes from cold diethyl ether in
large colorless chunks of microcrystalline material. The