Use of a smaller counterion results in an 'inverse sandwich' diindium cation

Article abstract of DOI:10.1016/S0022-328X(02)02034-X

Treatment of In(C₅Me₅) with [(toluene) H[[B(C₆F₅)₄] affords the salt [In(η⁵- which experiences a close contact with a meta-fluorine of a C₆F₅ group of a [B(C₆F₅) ₄]^- counterion. The other indium atom exhibits a weak η⁶-interaction with a C⁶F⁵ group of a different [B(C₆F₅)₄] ^- anion.

Full text of DOI:10.1016/S0022-328X(02)02034-X

Journal of Organometallic Chemistry 666 (2003) 3Á5
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www.elsevier.com/locate/jorganchem
Note
Use of a smaller counterion results in an ‘inverse sandwich’ diindium
cation
Jamie N. Jones, Charles L.B. Macdonald, John D. Gorden, Alan H. Cowley *
Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712-1167, USA
Received 1 August 2002
Dedicated to Professor Jerry Atwood in recognition of his many seminal contributions to main group and supramolecular chemistry
Abstract
Treatment of In(C5Me5) with [(toluene)H[[B(C6F5)4] affords the salt [In(h5-C5Me5)In][B(C6F5)4]. X-ray analysis indicates that the
cation possesses an inverse sandwich structure, one indium atom of which experiences a close contact with a meta-fluorine of a C6F5
group of a [B(C6F5)4]ꢀ counterion. The other indium atom exhibits a weak h6-interaction with a C6F5 group of a different
[B(C6F5)4]ꢀ anion.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Indium; Cation; Pentamethylcyclopentadienyl; Tetrakis(pentafluorophenyl)borate
ꢁ
˚
and 3.325(4) A for the toluene molecules in 2 , coupled
1. Introduction
with MO calculations on a model system that indicated
only very weak (ca. 7 kcal molꢀ1) indiumÁ
arene
In principle, the sandwiching of main group elements
between multihapto-bonding carbocyclic rings repre-
sents a viable means of supramolecular construction.
As an initial step in this direction, we recently reported
the synthesis and structural assay of the first examples of
triple decker main group cations, namely [(h5-
C5Me5)Sn(m-h5-C5Me5)Sn(h5-C5Me5)]ꢁ (1ꢁ) and [(h6-
C7H8)In(m-h5-C5Me5)In(h6-C7H8)]ꢁ (2ꢁ) [1]. Cations
1ꢁ and 2ꢁ were isolated as their [Ga(C6F5)4]ꢀ and
[(C6F5)3BO(H)B(C6F5)3]ꢀ salts, respectively. At the
time, we pointed out that although 2ꢁ could be
construed as a triple decker system, it could equally
well be thought of as an ‘inverse sandwich’ cation. The
distinction between these possibilities, of course, de-
pends on whether the capping h6-interacting toluene
molecules are considered to be bonded or not. Given the
/
interactions [1], we were inclined to the opinion that
2ꢁ is probably best viewed as an inverse sandwich
cation. However, in order to gain further insight into
this question, we decided to attempt replacement of the
voluminous [(C6F5)3BO(H)B(C6F5)3]ꢀ anion by a coun-
terion of more modest size.
2. Results and discussion
Treatment of two equivalents of In(h5-C5Me5) [2]
with one equivalent of [(toluene)H[B(C6F5)4] in toluene
solution at ꢀ78 8C resulted, after solvent removal, in a
/
thick brown oil that contained colorless, prismatic
crystals. The HRMS of the crystalline material was
consistent with the cation [In(m-C5Me5)In]ꢁ and there
was no indication of the presence of toluene on the basis
of 1H-NMR spectroscopy. Confirmation of the pro-
posed cation structure was provided by an X-ray
crystallographic study. The compound [In(m-h5-
C5Me5)In][B(C6F5)4] (3) crystallizes in the monoclinic
substantial indiumÃ
/
ring centroid distances of 3.490(4)
* Corresponding author. Tel.:
4716822
E-mail address: cowley@mail.utexas.edu (A.H. Cowley).
ꢁ
/
1-512-4747484; fax:
ꢁ/1-512-
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 2 0 3 4 - X

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J.N. Jones et al. / Journal of Organometallic Chemistry 666 (2003) 3Á5
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To our knowledge, this represents an unprecedented
mode of interaction for the [B(C6F5)4]ꢀ anion.
3. Experimental
All reactions were performed under a dry, oxygen-free
Ar atmosphere utilizing Schlenk manifold techniques or
a drybox. All solvents were dried and distilled under
nitrogen prior to use. NMR spectra were recorded on a
General Electric QE 300 spectrometer at 295 K (1H
300.16 MHz) and chemical shifts are reported relative to
SiMe4 (dꢂ0.00). High-resolution mass spectra were
/
obtained using a VG Analytical ZABZ-E mass spectro-
meter operating in the chemical ionization mode with
methane as the ionizing gas.
3.1. Preparation of [In(h5-C5Me5)In][B(C6F5)4]
Two equivalents of In(h5-C5Me5) (0.648 g, 2.59
mmol) in 50 ml of C6H5CH3 were treated with
[H(C7H8)][B(C6F5)4] (1.0 g, 1.30 mmol) in 50 ml of
Fig. 1. View of the structure of [In(h5-C5Me5)In]ꢁ showing the close
contacts with [B(C6F5)4]ꢀ anions. Important distances (A) and angles
˚
(8): C(1)Ã
C(5) 1.459(8), C(5)Ã
2.765(5), In(1)ÃC(3) 2.772(5), In(1)Ã
2.701(4), In(2)ÃC(1) 2.722(5), In(2)Ã
2.749(5), In(2)ÃC(4) 2.675(5), In(2)ÃC(5) 2.687(6); C(1)Ã
110.4(5), C(2)ÃC(3)ÃC(4) 107.1(5), C(3)ÃC(4)Ã
C(5)ÃC(1) 105.9(4), C(5)ÃC(1)ÃC(2) 108.1(5).
/
C(2) 1.406(7), C(2)Ã
C(1) 1.414(7), In(1)Ã
C(4) 2.730(6), In(1)Ã
C(2) 2.748(5), In(2)Ã
C(2)Ã
/
C(3) 1.388(8), C(3)Ã
/
C(4) 1.411(8), C(4)Ã
/
C6H5CH3 at ꢀ
at ꢀ78 8C for 2 h, after which the solvent and volatiles
were removed in vacuo from the cooled (ca. ꢀ20 8C)
/
78 8C. The resulting solution was stirred
/
/
C(1) 2.728(5), In(1)Ã
/
C(2)
/
/
/
C(5)
C(3)
C(3)
/
/
/
/
/
/
/
/
/
solution leaving a dark brown, thick oil that contained a
crop of colorless crystals. The product was then warmed
to ambient temperature to remove any additional traces
of C6H5CH3. The yield was 39%.
/
/
/
/
C(5) 108.5(4), C(4)Ã
/
/
/
/
space group P21/c with Zꢂ
/
8. The structure of the
cation features two In atoms that are h5-bonded to
3.1.1. Spectroscopic data
HRMS (CI, CH4): Calc. for C10H15In2, m/z 364.925.
1
Found: 364.926. H-NMR (C6D6): d 1.49 (ring Me).
either side of a C5Me5 group (Fig. 1). The In(1)Ã
/
ring
ring
centroidÃ
/
In(2) angle is 175.25(2)8 and the In(1)Ã
/
˚
centroid distance (2.4603(7) A) is slightly longer than
˚
3.1.2. Crystal data
that for In(2) (2.4350(7) A). In turn, each of these
distances is comparable to those in 2ꢁ which average
˚
2.486(4) A. All the foregoing distances are longer than
C10H15BF20In2, Mꢂ
P21/c, aꢂ10.065(2), bꢂ
bꢂ103.48(3)8, Vꢂ3728.7(13) A , Dcalc
cmꢀ3, Zꢂ
8, l(MoÁ
/
755.67, monoclinic, space group
˚
/
/
23.157(5), cꢂ
/
16.451(3) A,
2.692
0.71073 A, m(MoÁKa)ꢂ
3
˚
˚
those reported [2] for monomeric (2.288(4) A) and
/
/
ꢂ
/
g
5
˚
˚
/
/
Ka)ꢂ
/
/
/
hexameric (2.302(4) A) In(h -C5Me5).
2.665 mmꢀ1. A total of 8444 reflections was collected
on a Nonius Kappa diffractometer at 153(2) K with 2u
between 7.3 and 55.08. The structure was solved by
direct methods and refined by full-matrix least-squares
on F2 to R1 and wR2 values of 0.0897 and 0.2281,
respectively.
The replacement of [(C6F5)3BO(H)B(C6F5)3]ꢀ by the
smaller anion [B(C6F5)4]ꢀ has the effect of ‘squeezing’
the toluene molecules out of 2ꢁ and forming 3ꢁ.
However, this leaves 3ꢁ in a somewhat electrophilic
condition, a consequence of which is the existence of
some close cationÁ
/
anion contacts. Thus, a meta-fluor-
ine atom [F(32)] of one C6F5 group of a [B(C6F5)4]ꢀ
˚
anion is located 3.150(3) A from In(1 A). Although this
distance is less than the sum of van der Waals radii for
˚
4. Supplementary material
In and F (3.90 A), shorter InÁ Á ÁF contacts have, in fact,
been reported for In(2,4,6-(CF3)3C6H2)3 (average
˚
2.762(7) A) and In2(2,4,6-(CF3)3C6H2)4 (range
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 192393 for compound 3.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
˚
2.801(10)Á
/
2.957(13) A) [3]. Interestingly, the other
indium atom of 3ꢁ undergoes a weak h6-interaction
with one of the C6F5 groups of a second [B(C6F5)4]ꢀ
˚
anion; the In(2 A) to ring centroid distance is 3.588(4) A.
Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-336033;
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J.N. Jones et al. / Journal of Organometallic Chemistry 666 (2003) 3Á
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5
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
References
[1] A.H. Cowley, C.L.B. Macdonald, J.S. Silverman, J.D. Gorden, A.
Voigt, Chem. Commun. (2001) 175.
[2] In(h5-C5Me5) is a weakly-held hexamer in the solid state that
undergoes facile dissociation to the monomer in solution and in the
vapor phase: O.T. Beachley, Jr., R. Blom, M.R. Churchill, K.
Faegri, Jr., J.C. Fettinger, J.C. Pazik, L. Victoriano, Organome-
tallics 8 (1989) 346.
Acknowledgements
We are grateful to the Robert A. Welch Foundation
for generous financial support. One of us (J.N.J.) thanks
the National Defense Science and Engineering Graduate
Research Fellowship Program.
[3] R.D. Schluter, A.H. Cowley, D.A. Atwood, R.A. Jones, M.R.
Bond, C.J. Carrano, J. Am. Chem. Soc. 115 (1993) 2070.