Novel supramolecular architectures in group 13 perfluoroaryl complexes. Synthesis and structures of [AlMe(C6F5)(μ-Me)]2 and GaMe(C6F5)2

Article abstract of DOI:10.1039/b210024j

Novel supramolecular architectures are observed in the solid state structures of [AlMe(C₆F₅)(μ-Me)]₂ (1) and Ga(C₆F₅)₂Me (2) via π-π stacking between C₆F₅ rings and in

Full text of DOI:10.1039/b210024j

Novel supramolecular architectures in group 13 perfluoroaryl complexes.
Synthesis and structures of [AlMe(C6F5)(m-Me)]2 and GaMe(C6F5)2†
Gregory S. Hair, Alan H. Cowley,* John D. Gorden, Jamie N. Jones, Richard A. Jones* and Charles
L. B. Macdonald
The University of Texas at Austin, Chem. & Biochem. Dept., 1 University Station A5300, Austin, Texas
78712-0165, USA. E-mail: cowley@mail.utexas.edu; Tel: 512 471 7484. E-mail: rajones@mail.utexas.edu;
Tel: 512 471 1706
Received (in Columbia, MO, USA) 5th October 2002, Accepted 12th December 2002
First published as an Advance Article on the web 15th January 2003
¯
Novel supramolecular architectures are observed in the solid
state structures of [AlMe(C6F5)(m-Me)]2 (1) and
Ga(C6F5)2Me (2) via p–p stacking between C6F5 rings and
intermolecular aryl-F?Ga interactions, respectively.
in the triclinic space group P1 with two independent dimeric
molecules per unit cell.‡ The asymmetric unit contains two Al
atoms, each in a different dimer. Each dimer features an
inversion center located at the midpoint of the Al–Al vector. A
view of the atom numbering scheme for the two crystallo-
graphically independent molecules is shown in Fig. 1.
Noncovalent attractive forces such as hydrogen bonding and p–
p interactions are now recognized as key features in the self-
assembly of multicomponent molecular architectures.1,2 For the
group 13 elements, large supramolecular assemblies involving
dative covalent interactions between Lewis acid centers and
nitrogen or oxygen donor bases or halogens are well known.3
In this report we describe the synthesis and structures of two
group 13 organometallics which exhibit novel supramolecular
structures, namely [AlMe(C6F5)(m-Me)]2 (1) and GaMe(C6F5)2
(2). In 1, intermolecular p–p stacking between pairs of offset
C6F5 rings creates an unusual zig-zag one-dimensional chain. In
2, a linear chain-like supramolecular assembly is formed via
intermolecular aryl-F?Ga interactions.
Fig. 1 View of two independent molecules of [AlMe(C6F5)m-Me)]2 (1)
showing the atom numbering scheme.
Each dimeric unit of 1 bears two C6F5 groups and, as a
consequence, a novel supramolecular architecture is achieved
by offset p–p interactions between pairs of C6F5 groups from
different molecules. This creates a one-dimensional zig-zag
framework as shown in Fig. 2. There are two sets of offset p–p
interactions between C6F5 groups. In each case the dihedral
angle between the aryl rings is 7.6°. The distances between the
centroids of the p-stacked aryl rings are 3.713 Å and 4.465 Å.
The latter distance is consistent with significantly more offset
interactions between the fluoroaryl rings. These p–p inter-
actions are clearly supramolecular in nature and not simply the
result of unit cell packing. Calculations10 have shown that
intramolecular p–p interactions between C6F5 groups should be
favorable, although there appear to be few examples of such
interactions in organometallic chemistry. Thus similar close p–
p interactions are completely absent in the solid state structures
Strong group 13 Lewis acids such as B(C6F5)3 and Al(C6F5)3
are currently of significant interest as components of olefin
polymerization catalyst systems. The aluminium derivatives
Al(C6F5)3·(arene) (arene = benzene, toluene) may be conven-
iently prepared by the reaction of B(C6F5)3 with AlMe3 in an
arene solvent.4,5 This process no doubt occurs via a series of
mixed ligand species (eqn. 1,2).
(1)
2B(C6F5)3 + Al2Me6 Ù 2MeB(C6F5)2 + [AlMe2(C6F5)]2
2MeB(C6F5)2 + [AlMe2(C6F5)]2 Ù
(2)
2Me2B(C6F5) + [AlMe(C6F5)2]2
Recently Klosin et al. reported the detection of such dinuclear
aluminium species in these reaction mixtures.6 They were also
able to isolate and characterize the unsymmetrical aluminium
species (C6F5)3Al2Me3 when an excess of AlMe3 was used.
These kinds of mixed alkyl/perfluorophenyl aluminium com-
pounds are also of interest since it has been claimed that species
such as [Et(C6F5)2Al]x alone act as catalysts or catalyst
precursors for the polymerization of olefins.7
The initial products from the exchange reaction between
B(C6F5)3 and Al2Me6 should be MeB(C6F5)2 and Al-
2Me4(C6F5)2. In fact, the latter compound was isolated recently
by Roesky et al. from the reaction of C6F5Li with Me2AlCl in
hexane solution.8 Thermal decomposition results in a dis-
proportionation to give Al(C6F5)3 and Al2Me6.
We have prepared compound 1 by the direct reaction of
Al(C6F5)3·(toluene) with AlMe3 in toluene solution at room
temperature.9 It was recrystallized from toluene at 220 °C as
clear colorless crystals in 75% yield. The related gallium
complex GaMe(C6F5)2 2 was prepared via the exchange
reaction between B(C6F5)3 and GaMe3 in toluene solution at
room temperature and was isolated in pure form by sublimation
at 50 °C and 0.1 torr.9
6
of the related Al–C6F5 complexes (C6F5)3Al2Me3 and
Al(C6F5)3.PhMe.5 Mountford and coworkers have described
the titanium imide Ti(NC6F5)Cl2(NHMe2)2 in which both
C6F5–C6F5 p–p stacking as well as Ti–Cl…H–N interactions
are observed.11 In this compound the separation between the
C6F5 planes is 3.23 Å. Examples of intramolecular p–p
interactions between two C6F5 rings are also known for a few
ferrocene derivatives.12–14 For example, in Fe(C6F5Cp)2 the
14
distance between the aryl ring centroids is 3.58 Å and
intramolecular C–F distances of 3.23 and 3.27 Å are observed
between fluoroaryl rings. In 1 the closest C–F interactions are
3.190(3) Å (F35–C62) and 3.298(3) Å (F35–C63). A more
detailed view of these interactions in one of the p-stacked
fluoroaryl pairs is shown in Fig. 3 and full details of the other
interactions are given in the Supporting Information†.
The solution NMR data for 1 are consistent with a fluxional
system on the NMR time scale.9 In the solid state, 1 crystallizes
† Electronic supplementary information (ESI) available: Experimental
procedures for the preparation of 1 and 2 and X-ray experimental details.
See http://www.rsc.org/suppdata/cc/b2/b210024j/
Fig. 2 View of the p–p interactions that create the linear zig-zag
supramolecular structure in 1. Distances between ring centroids: X(1AD)–
X(1D) = 3.713(4) Å, X (1K)–X(1L) = 4.456(4) Å.
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CHEM. COMMUN., 2003, 424–425
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Fig. 3 View of p–p interactions in the C6F5 rings of 1. Close C–F
interactions are F(35)–C(62) 3.190(3) Å and F(35)–C(63) 3.298(3) Å.
Fig. 5 View of supramolecular framework structure of 2.
We are grateful for support from the Robert A. Welch
Foundation (Grants F135 and F816).
The related gallium complex 2 is essentially mononuclear,
possibly due to the presence of two bulky C6F5 groups per metal
vs. one in the case of 1. Thus, the presence of s-bonded C6F5
and Me groups in 2 results in a nearly planar three-coordinate
environment at gallium. However, in the solid state, there are
also two intermolecular aryl-F?Ga interactions from the m-F
atoms on each C6F5 group (F(25) and F(15)) (Fig. 4).‡ Thus, the
localized geometry around Ga is that of a pseudo trigonal
bipyramid and the overall supramolecular architecture com-
prises an interesting linear linked chain-like structure (Fig. 5).
The Ga…F contacts of 2.715(3) Å (Ga(1)–F(15)) and 2.727(3)
Å (Ga(1)–F(25)) are shorter than the sum of the van der Waals
radii (3.45 Å),15 but both are considerably longer than the sum
of the covalent radii (1.91 Å).15 These distances may be
compared with other short Ga…F interactions; for example the
intramolecular contacts in [2,4,6-(CF3)3C6H2]3 Ga fall within
the range 2.665–2.844 Å.16
Notes and references
‡ CCDC reference numbers 196548 and 196549. See http://www.rsc.org/
suppdata/cc/b2/b210024j/
1 L. F. Lindoy and I. M. Atkinson, Self-Assembly in Supramolecular
Systems, Cambridge University Press, UK, 2000.
2 I. Haiduc and F. T. Edelman, Supramolecular Organometallic Chem-
istry, Wiley-VCH, 1999.
3 See for example, F. P. Gabbaï, A. Schier and J. Riede, Angew Chem.,
Int. Ed., 1998, 37, 622; J. L. Atwood, J. E. D Davies, D. D. MacNicol,
F. Vögtle and K. S. Suslick, Comprehensive Supramolecular Chemistry,
Vol. 9, Pergamon, Oxford, 1996.
4 P. Biagini, G. Lugli, L. Abis and P. Andressi, U.S. Patent 5,602,269,
Enichem, 1997.
5 G. S. Hair, A. H. Cowley, R. A. Jones, B. G. McBurnett and A. Voigt,
J. Am. Chem. Soc., 1999, 121, 4922.
The use of novel supramolecular structures such as those
found in 1 and 2 to engineer the preparation of nanostructured
materials is currently under investigation.
6 J. Klosin, G. R. Roof, E. Y.-X. Chen and K. A. Abboud, Organome-
tallics, 2000, 19, 4684.
7 J. S. Kun, L. M. Wojcinski, S. Liu, J. C. Sworen and A. Sen, J. Am.
Chem. Soc., 2000, 122, 5668.
8 T. Belgardt, J. Storre, H. W. Roesky, M. Noltemeyer and H.-G.
Schmidt, Inorg. Chem., 1995, 34, 3821.
9 See Supplementary Information†.
10 S. Lorenzo, G. R. Lewis and I. Dance, New J. Chem., 2000, 24, 295.
11 N. Adams, A. R. Cowley, S. R. Dubberley, A. J. Sealey, M. E. G.
Skinner and P. Mountford, Chem. Commun., 2001, 2738.
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19, 1013.
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15 J. E. Huheey, E. A. Keiter and R. L. Keiter, Inorganic Chemistry
Principles of Structure and Reactivity, 4th ed., Harper Collins, New
York, 1993, p. 292.
Fig. 4 View of the molecular structure of GaMe(C6F5)2 (2) showing the
localized geometry about Ga and the atom numbering scheme. Ga(1)–C(1)
1.922(2) Å, Ga(1)–C(21) 1.978(2) Å, Ga(1)–C(11) 1.975(2) Å.
16 R. D. Schluter, H. S. Isom, A. H. Cowley, D. A. Atwood, R. A. Jones,
F. Olbrich, S. Corbelin and R. J. Lagow, Organometallics, 1994, 13,
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