Unprecedented η3-M3 coordination mode in a terpyridine ligand

Article abstract of DOI:10.1039/b502515j

The gold(I) complex [Au₃(C₆F₅) ₃(η³-Fcterpy)] (Fcterpy = 4′-ferrocenyl-2, 2′:6′,2″-terpyridine) represents the first example of a terpyridine ligand bonded to three different metals. The aurophilic interactions present in the molecule may contribute to the overall stability of the system, as was shown by DFT calculations. The positive Mayer indices (0.152 and 0.138), as well as the magnitude of the binding interaction between terpy and the Au(I)L fragments, support this interpretation. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b502515j

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Unprecedented g3-M3 coordination mode in a terpyridine ligand
Javier E. Aguado,a Maria Jose´ Calhorda,bc M. Concepcio´n Gimeno*a and Antonio Lagunaa
Received (in Cambridge, UK) 21st February 2005, Accepted 29th April 2005
First published as an Advance Article on the web 24th May 2005
DOI: 10.1039/b502515j
The gold(I) complex [Au3(C6F5)3(g3-Fcterpy)] (Fcterpy 5
49-ferrocenyl-2,29:69,20-terpyridine) represents the first example
of a terpyridine ligand bonded to three different metals. The
aurophilic interactions present in the molecule may
contribute to the overall stability of the system, as was shown
by DFT calculations. The positive Mayer indices (0.152 and
0.138), as well as the magnitude of the binding interaction
between terpy and the Au(I)L fragments, support this
interpretation.
The chemistry of terpyridine ligands has been the subject of
numerous studies with several metals induced by the exciting
ð1Þ
photophysical properties of metal–polypyridyl complexes.1 In
these compounds, the terpyridine acts as a chelating planar
tridentate ligand and only in some examples does it act as a
bidentate ligand with a non-coordinate residue.2 In the past,
interesting spiral arrays have been prepared with these ligands that
by twisting can accommodate more than one metal center. Thus,
some examples have been prepared with silver in which the terpy is
bonded to two different metal centers in a supramolecular
structure.3 However, the coordination mode in which the three
nitrogen atoms are bonded to three different metals is unknown.
Only a few complexes with terpyridine and gold have been
described and these are gold(III) derivatives, such as [AuX(Rterpy)]
(R 5 H, SMe, PhOMe),4–7 or [Au(CN)2Br(g2-terpy)].8 Here we
report the first example of a complex in which a substituted
terpyridine ligand, 49-ferrocenyl-2,29:69,20-terpyridine (Fcterpy),9
coordinates to three different gold atoms. The ligand twists the
external pyridine rings in opposite directions to accommodate the
three metals and these are also bonded through aurophilic
interactions that, clearly, contribute to the overall stability of the
complex. This compound also represents, to the best of our
knowledge, the first example of a gold(I) complex with a
terpyridine ligand.
The crystal structure of [Au3(C6F5)3(g3-Fcterpy)] has been
confirmed by X-ray diffraction methods and is shown in Fig. 1.{.
The pyridine rings are oriented in such a way as to minimize the
steric and probably the electronic repulsions among the three
pentafluorophenyl rings. The two outer pyridine rings are situated
almost perpendicular to the central one and with the nitrogen
…
atom pointing in opposite directions. The Au Au distances are
˚
3.0678(6) and 3.1559(7) A, which are typical values for aurophilic
interactions. The Au–N distances lie in the range 2.068(10)–
˚
2.106(8) A and are of the same order as those found in complexes
with a pentafluorophenyl ligand trans to a pyridine unit such as
10
[Au(C6F5)(Fcpy)] (2.124(15) A). The cyclopentadienyl rings are
˚
practically eclipsed. In the lattice there are several secondary
…
interactions of the type Au H about 2.7 A and F H about 2.5 A
…
˚
˚
which lead to a supramolecular structure.
DFT11 calculations (ADF12 program) were performed in a
model of the [Au3(C6F5)3(g3-Fcterpy)] complex where the C6F5
The reaction of the Fcterpy ligand with 3 equivalents of
[Au(C6F5)(tht)] in dichloromethane leads to the synthesis of the
compound [Au3(C6F5)3(g3-Fcterpy)] (Eqn. (1)). The IR spectrum
shows the absorptions arising at the pentafluorophenyl rings
bonded to gold(I) at 1506(s), 960(s) and 765(m) cm21. In the 19F
NMR spectrum the three pentaflorophenyl rings are equivalent
and consequently only three resonances appear for the ortho, meta
1
and para fluorine. The H NMR shows two multiplets for the a
and b protons of the substituted Cp ring, a singlet for the
protons of the unsubstituted Cp ring, and five resonances for
the five different terpyridine protons. In the mass spectrum
(LSIMS+) the molecular peak is not present but the peaks at
m/z 5 781 (40%, [M 2 (AuC6F5)2]+) and 1145 (8%, [M 2
(AuC6F5)]+) arising at the loss of one or two AuC6F5 fragments
appear.{
Fig. 1 Molecular structure of [Au3(C6F5)3(g3-Fcterpy)] in the crystal
showing the labelling scheme. Hydrogen atoms are omitted for clarity.
Radii are arbitrary.
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…
orbitals were frozen for Au ([1–4]s, [2–4]p, [3–4]d), Fe ([1–2]s, 2p), and C, N
and F (1s). Triple f Slater-type orbitals (STO) were used to describe the
valence shells of C, N, F (2s and 2p), Fe (3s, 3p, 3d, 4s) and Au (4f, 5d, 6s).
A set of two polarisation functions was added to C, N, F (single f, 3d, 4f),
Fe (single f, 4d, 4f), and Au (single f, 6p, 5f). Triple f STOs with one
polarisation function (single f, 2p) were used to describe the H (1s) valence
shell. Full geometry optimisations were performed without any symmetry
constraints.
groups were replaced by CF3.§ The Au Au distances, 3.156 and
˚
3. 217 A, are reproduced within ca. 0.05 A, the three Au–N bonds
˚
˚
ranging from 2.030 to 2.166 A, also very close to experimental
values. The calculated Mayer indices13 are 0.152 and 0.138,
respectively, for the two Au…Au contacts, indicating the existence
of the aurophilic interaction.14 The binding energy between
Fcterpy and three Au(CF3) groups is only 3.8 kcal mol21 higher
than the sum of the binding energies of py and Au(CF3) (twice)
and of ferrocenylpy and Au(CF3). These three pairs of fragments
build an analogue of the complex, without Au…Au interactions
and steric constraints. The small difference can be easily overcome
by the hydrogen bonding network in the supramolecular structure.
Also, three CF3 model ligands may be less suitable than C6F5 to
accommodate in the close proximity of the three gold atoms, the
real system being probably more stable. This particular bonding
mode of terpy allows the complete use of its binding capabilities,
keeping gold(I) in its favoured environment with aurophilic
interactions.14
1 E. C. Constable, Adv. Inorg. Chem. Radiochem., 1986, 30, 69.
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D. A. Tocher and J. V. Walker, Supramol. Chem., 1993, 3, 243; (d)
R. Chotalia, E. C. Constable, M. J. Hannon and D. A. Tocher,
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H. D. Abrun˜a and C. R. Arana, Inorg. Chem., 1993, 32, 4422; (b)
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4 L. S. Hollis and S. J. Lippard, J. Am. Chem. Soc., 1983, 105, 4293.
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This work was supported by the Ministerio de Educacio´n y
Ciencia-FEDER (No. CTQ2004-05495-C02-01/BQU).
Javier E. Aguado,a Maria Jose´ Calhorda,bc M. Concepcio´n Gimeno*a
and Antonio Lagunaa
aDepartamento de Qu´ımica Inorga´nica, Instituto de Ciencia de
Materiales de Arago´n, Universidad de Zaragoza-C.S.I.C., E-50009,
Zaragoza (Spain)
6 B. Pitteri, G. Marangoni, F. Visentin, T. Bobbo, V. Bertolasi and
P. Gilli, J. Chem. Soc., Dalton Trans., 1999, 677.
7 U. Sampath, W. C. Putnam, T. A. Osiek, S. Touami, J. Xie, D. Cohen,
A. Cagnolini, P. Droege, D. Klug, C. L. Bernes, A. Modak,
J. K. Bashkin and S. S. Jurisson, J. Chem. Soc., Dalton Trans., 1999,
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bDepartamento de Qu´ımica e Bioqu´ımica, Faculdade de Cieˆncias da
Universidade de Lisboa, 1749-016, Lisboa, Portugal.
E-mail: mjc@fc.ul.pt
cInstituto de Tecnologia Qu´ımica e Biolo´gica (ITQB), Av. da Repu´blica,
EAN, Apt 127, 2781-901, Oeiras, Portugal
8 V. Ferreti, P. Gilli, V. Bertolasi, G. Marangoni, P. Pitteri and G. Ghessa,
Acta Crystallogr. Sect. C, 1992, 48, 814.
Notes and references
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M. D. Villacampa, J. Organomet. Chem., 1999, 592, 258.
11 R. G. Parr and W. Yang, Density Functional Theory of Atoms and
Molecules, Oxford University Press: New York, 1989.
12 (a) G. te Velde, F. M. Bickelhaupt, S. J. A. van Gisbergen,
C. Fonseca Guerra, E. J. Baerends, J. G. Snijders and T. Ziegler,
‘Chemistry with ADF’, J. Comput. Chem., 2001, 22, 931–967; (b)
C. Fonseca Guerra, J. G. Snijders, G. te Velde and E. J. Baerends,
Theor. Chem. Acc., 1998, 99, 391; (c) ADF2004.01, SCM, Theoretical
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www.scm.com.
13 (a) I. Mayer, Chem. Phys. Lett., 1983, 97, 270; (b) I. Mayer, Int. J.
Quantum Chem., 1984, 26, 151; (c) MAYER version 1.2.3,
A. J. Bridgeman and C. J. Empson, The University of Hull, (2004).
Freely available from http://www.hull.ac.uk/php/chsajb/mayer/.
14 (a) P. Pyykko¨, Chem. Rev., 1997, 97, 597; (b) P. Pyykko¨, N. Runerberg
and F. Mendizabal, Chem. Eur. J., 1997, 3, 1451.
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8943.
19 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
{ Preparation: To a solution of [Au(C6F5)(tht)] (0.135 g, 0.3 mmol) in
20 cm3 of dichloromethane was added Fcterpy (0.041 g, 0.1 mmol) and the
mixture was stirred for 1 h. Evaporation of the solvent to ca. 2 cm3 and
addition of hexane gave [Au3(C6F5)3(g3-Fcterpy)] as a orange solid. Yield
59%. Analytical data: Found, C, 34.25; H, 1.32; N, 3.02. Calc. for
C43H19Au3F15FeN3: C, 34.21; H, 1.26; N, 2.78%. NMR: 1H, d: 4.01 (s, 5H,
C5H5), 4.32 (m, 2H, C5H4), 4.91 (m, 2H, C5H4), 8.81 (d, 2H, 6/60, J(HH)
4.64 Hz), 7.47 (m, 2H, 5/50), 7.95 (t, 2H, 4/40, J(HH) 7.69 Hz), 8.39 (m, 2H,
3/30), 8.42 (s, 2H, 39/59). 19F, 2116.6 (m, 6F, o-F), 2158.8 (t, 3F, p-F, J(FF)
21.3 Hz), 2162.8 (m, 6F, m-F).
{ Crystal Data for [Au3(C6F5)3(g3-Fcterpy)]?CH2Cl2:
C44H21Au3Cl2F15FeN3, M 5 1594.29, monoclinic, space group P21/n,
˚
a 5 11.5020(9), b 5 22.9336(19), c 5 16.6010(13) A, b 5 102.965(2)u,
3
V 5 4267.4(6) A , Z 5 4; Dc 5 2.481 Mg m23, m(MoKa) 5 10.845 mm21
,
˚
F(000) 5 2952, Bruker SMART Apex CCD difractometer, l(Mo–
Ka) 5 0.71073, T 5 100 K. An orange prism 0.20 6 0.20 6 0.12 mm
was used to collect 27998 intensities to 2hmax 5 57.4 from which 10107 are
independent (Rint 5 0.070). Scan type v. The structure was solved by direct
methods and subjected to anisotropic refinement on F2 (program
SHELXL-9719). H atoms were included using a riding model. The final
wR(F2) was 0.098 for 10107 reflections and 613 parameters, conventional
2
R(F) 0.049, S(F ) 0.826, max Dr 1.96 eA23. CCDC 264992. See http://
˚
www.rsc.org/suppdata/cc/b5/b502515j/ for crystallographic data in CIF or
other electronic format.
§ DFT calculations: Gradient-corrected geometry optimizations15 were
performed, using the Vosko, Wilk and Nusair local exchange correlation
potential,16 and the Generalized Gradient Approximation (PW9117).
Relativistic effects were treated with the ZORA approximation.18 Core
3356 | Chem. Commun., 2005, 3355–3356
This journal is ß The Royal Society of Chemistry 2005