Metal complexes with two different hydrogen-bond donor ligands as anion hosts

Article abstract of DOI:10.1039/b823460d

The replacement of one pyrazole ligand by 2-aminopyridine in previously known rhenium tricarbonyl pyrazole complexes leads to more selective anion hosts.

Full text of DOI:10.1039/b823460d

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Metal complexes with two different hydrogen-bond donor ligands
as anion hostsw
a
a
a
a
b
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Sonia Nieto, Julio Perez,* Lucıa Riera,* Vıctor Riera and Daniel Miguel
Received (in Cambridge, UK) 5th January 2009, Accepted 25th March 2009
First published as an Advance Article on the web 24th April 2009
DOI: 10.1039/b823460d
The replacement of one pyrazole ligand by 2-aminopyridine in
previously known rhenium tricarbonyl pyrazole complexes leads
to more selective anion hosts.
do not experience a fast dissociation–recoordination process,
which would lead to the observation of a single methyl signal.
The presence of only one set of pyrazole resonances in 1H and
13C NMR, and only two carbonyl signals in 13C NMR for the
three CO ligands, indicate the presence of a molecular mirror
plane. Attempts to grow single crystals of 1ꢁBAr04 failed, but
anion exchange with [Bu4N][ClO4] afforded single crystals of
1ꢁClO4, which were used for the structural determination.6 The
results confirmed the formulation inferred from the spectro-
scopy data summarized above (see Fig. 1(a)). The 2-ampy
ligand binds Re through the NH2 group, a coordination mode
less frequently found in transition metal complexes than
binding through the pyridine nitrogen.7 This feature is attributed
to the presence of an intramolecular hydrogen bond between
the N–H group of one of the pyrazole ligands and the pyridine
nitrogen, characterized by N4ꢁ ꢁ ꢁN6 = 2.893(7) A and
N4–HꢁꢁꢁN6 = 162.3(6)1. The ClO4ꢀ anion forms weak hydrogen
bonds with N–H groups of pyrazole and 2-ampy ligands.
Fig. 1(a) shows, as dotted lines, the hydrogen bonds of the
perchlorate anion with one cationic host (for a more complete
view, showing also H-bonds with a second cation or the
structural packing, see ESIw).
When an equimolar amount of [Bu4N][ClO4] was added to a
solution of 1ꢁBAr04 in CD2Cl2, the 1H NMR signals of
the [Re(CO)3(Hdmpz)2(2-ampy)]+ complex did not change
appreciably. Therefore, the coordination mode of the 2-ampy
ligand in 1ꢁBAr04 must be the same as in 1ꢁClO4, in accord with
the low interacting ability of the perchlorate anion.
In contrast, in the structure of 2ꢁBAr04 (see Fig. 1(b)), the
3-ampy ligand is bonded to the rhenium atom through the
pyridine function.8 Compound 2ꢁClO4 was prepared by anion
exchange between 2ꢁBAr04 and [Bu4N][ClO4], and its structure
Metal complexes containing ligands functionalized with
hydrogen-bond donor groups can be used as anion hosts,
and their synthesis is often easier than those of purely organic
hosts.1 We have reported hosts of this type based on cationic
complexes of the fac-{Reꢀ(CO)3} fragment and three azole
ligands, as salts of BAr04 (Ar0 = 3,5-bis(trifluoromethyl)-
phenyl), more innocent and inert than the more widely used
anions PF6ꢀ or BF4ꢀ 2,3 The choice of the inert metal fragment
.
aimed to provide hosts stable against substitution of the
neutral ligands by the anionic guests, and the presence of
CO ligands makes IR spectroscopy a useful tool to detect such
a substitution, ligand deprotonation, etc.4 It occurred to us
that their modular synthesis,2 from a suitable metal precursor
and the free azoles, could allow the preparation of hosts
comprising more than one type of functionalized ligand. Such
a modification could afford a selectivity higher than that of the
more symmetric hosts. To test this idea we chose to modify the
fac-[Re(CO)3(Hdmpz)3]BAr04 (Hdmpz = 3,5-dimethylpyrazole)
compounds by replacing one of the pyrazole ligands by
an aminopyridine, a ligand employed by Steed et. al. in
ruthenium-based hosts.5
The reaction of [ReBr(CO)3(Hdmpz)2] (prepared by thermal
reaction of [ReBr(CO)5] with two equivalents of Hdmpz)
with AgOTf (to replace bromide by triflate), followed by
addition of the salt NaBAr04 and either 2-aminopyridine
(2-ampy) or 3-aminopyridine (3-ampy) afforded the new
compounds fac-[Re(CO)3(Hdmpz)2(2-ampy)]BAr04 (1ꢁBAr04)z
and fac-[Re(CO)3(Hdmpz)2(3-ampy)]BAr0 (2ꢁBAr04),y see
4
Scheme 1. Compounds 1ꢁBAr04 and 2ꢁBAr04 were characterized
by IR, NMR and microanalysis (C, H, N). The IR spectra
were typical of cationic complexes of the fac-{Re(CO)3}
fragment, with nCO values similar to those of the tris(pyrazole)
1
complexes mentioned above.2 The H NMR spectra featured
different signals for the two methyl groups in the 3 and 5
positions of the pyrazole ligands, indicating that these ligands
a
´
´
´
Departamento de Quımica Organica e Inorganica-IUQOEM,
Facultad de Quımica, Universidad de Oviedo-CSIC, 33006, Oviedo,
´
Spain. E-mail: rieralucia.uo@uniovi.es, japm@uniovi.es;
Fax: 34 9851 03446; Tel: 34 9851 03465
b Departamento de Quı´mica Inorga´nica, Facultad de Ciencias,
Universidad de Valladolid, 47005, Valladolid, Spain
w Electronic supplementary information (ESI) available: X-Ray
crystallographic data for compounds 1ꢁClO4, 2ꢁBAr04, 2ꢁClO4, 2ꢁBr
and 2ꢁNO3. 1H NMR titration profiles and experimental details.
CCDC 715278–715282. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b823460d
Scheme 1 Synthesis of compounds 1ꢁBAr04 and 2ꢁBAr04.
Chem. Commun., 2009, 3279–3281 | 3279
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and are shown in dashed lines in Fig. 2 (more detailed views of
these structures are given as ESIw).
The difference in stability is attributed to the different
coordination mode of the ampy ligand: the amine-ligated
2-ampy in 1ꢁBAr04 is labile, whereas the pyridine-ligated
3-ampy in 2ꢁBAr04 is stable. A higher stability of the s-donor
and p-acceptor pyridine compared with the only s-donor
amine is expected for a low oxidation organometallic fragment;
besides, 2-ampy is sterically more hindered than 3-ampy,
making its substitution by the anions more favored. As in
tris(pyrazole) hosts,2 fluoride deprotonated 2ꢁBAr04, as shown
by a 21 cmꢀ1 decrease in the nCO values of the IR bands.
Chloride, bromide and nitrate anions induced noticeable shifts
in the 1H NMR signals of the amine and pyrazole N–H groups
as well as in the ortho pyridine C–H groups of 2ꢁBAr04. The
signals of the pyrazole N–H groups underwent the larger
anion-induced shifts and these were used for the calculation
of binding constants. The exchange of the mentioned anions
was found to be fast; therefore, binding constants were
calculated from the variation of the chemical shifts of the
signals of 2ꢁBAr04 as a function of the amount of anion
added.11 Titration curves are given as ESI.w A good 1 : 1
fitting was found, and the calculated binding constants
in acetonitrile were: 104 (chloride), 142 (bromide) and 67
(nitrate). The selectivity (in this case, the large preference for
chloride), which for fast anion exchange is simply given by the
quotient of binding constants, is much higher than that found
in tris(pyrazole) hosts,2 likely reflecting that only the smaller
chloride can interact simultaneously with the hydrogen-bond
donor groups of the three N-donor ligands. These results
indicate that mixed complexes with two different types of
ligands functionalized with hydrogen-bond donor groups
can be prepared as single products in good yield with
the {Re(CO)3} fragment, and that such complexes show
promise as more selective anion hosts than the previously
known complexes with a single type of functionalized ligand.
Extension of these studies to other ligands is under way and
will be published in due course.
Fig. 1 (a) Molecular structure of the 1ꢁClO4 adduct. (b) Molecular
structure of [Re(CO)3(Hdmpz)2(3-ampy)]+ in 2ꢁBAr04.
was determined by X-ray diffraction (see ESIw). The cationic
complex [Re(CO)3(Hdmpz)2(3-ampy)]+ in 2ꢁClO4 is virtually
identical to that found in 2ꢁBAr04. The salt 2ꢁClO4 features
weak hydrogen bonding between the perchlorate anion and
amino N–H groups. The NH2 group is disordered between
two positions related by rotation about the Re–N(pyridine)
bond. Both 1ꢁBAr04 and 2ꢁBAr04 were found to be stable in
solution at room temperature during several days. Their
behavior toward the tetrabutylammonium salts of several
1
anions was investigated by IR and H NMR. With chloride,
bromide and nitrate, the IR bands of a CH2Cl2 solution of
1ꢁBAr04 shifted instantaneously some 10 cmꢀ1 toward lower
wavenumber values. In the case of chloride and bromide, the
products were found to be the known neutral complexes
[ReCl(CO)3(Hdmpz)2]2a and [ReBr(CO)3(Hdmpz)2],9 indicating
that the mentioned anions displaced the 2-ampy ligand. Unlike
1ꢁBAr04, 2ꢁBAr04 was found to be stable in the presence of
tetrabutylammonium chloride, bromide and nitrate. The 1 : 1
adducts formed by the cationic complex 2 and the anions
bromide (Fig. 2(a)) and nitrate (Fig. 2(b)) were crystallized
from equimolar solutions of 2ꢁBAr04 and the corresponding
tetrabutylammonium salt in CH2Cl2 via slow diffusion of
hexane at low temperature (ꢀ20 1C). The structures of these
adducts were determined by single-crystal X-ray diffraction,
and the results are displayed in Fig. 2.10 In both adducts
simultaneous hydrogen bonds between the anion and the N–H
groups of one pyrazole and the 3-ampy ligand, were found,
We gratefully acknowledge funding from the Ministerio de
´
Educacion y Ciencia (grant CTQ2006-07036/BQU and
Ramon y Cajal contract to L. R.) and the European Union
´
(grant ERG-516505 to L. R.).
Notes and references
z Synthesis of 1ꢁBAr04: [ReBr(CO)5] (0.100 g, 0.246 mmol) and Hdmpz
(0.047 g, 0.492 mmol) were refluxed in toluene (20 mL) for 30 min.
The solvent was evaporated under reduced pressure, the residue
redissolved in CH2Cl2 (20 mL), AgOTf (0.063 g, 0.246 mmol) was
added and the mixture was stirred in the dark for 1 h. The resulting
solution was filtered from the white solid through Celite, NaBAr0
4
(0.218 g, 0.246 mmol) and 2-ampy (0.023 g, 0.246 mmol) were added,
and the reaction mixture was allowed to stir at room temperature for
1 h. The solution was concentrated under vacuum to a volume of 5 mL
and addition of hexane (20 mL) caused the precipitation of a white
solid, which was washed with hexane (2 ꢃ 15 mL) and dried under
vacuum. Compound 1ꢁBAr04 was obtained as a white microcrystalline
solid. Yield: 0.272 g, 78%. IR (CH2Cl2): 2037vs, 1934s, 1917s (nCO).
1H NMR (CD2Cl2): d 10.71 [s, br, 2H, NH, Hdmpz], 7.73 [m, 9H, Ho
and CH, BAr04 and 2-ampy], 7.57 [m, 4H, Hp, BAr04], 7.44 [m, 1H,
CH, 2-ampy], 7.15 [m, 1H, CH, 2-ampy], 6.86 [m, 1H, CH, 2-ampy],
6.12 [s, 2H, CH, Hdpmz], 5.32 [s, br, 2H, NH2], 2.21 [s, 6H, CH3,
Hdmpz], 2.12 [s, 6H, CH3, Hdmpz]. 13C NMR (CD2Cl2): d 193.3 [CO],
Fig. 2 Molecular structure of 2ꢁBr (a) [selected distances (A) and
angles (1): N2ꢁ ꢁ ꢁBr 3.534(8), N2–Hꢁ ꢁ ꢁBr 146.1; N6ꢁ ꢁ ꢁBr 3.440(8),
N6–Hꢁ ꢁ ꢁBr 154.9], and 2ꢁNO3 (b) [selected distances (A) and angles
(1): N6ꢁ ꢁ ꢁO8 3.00(3), N6–Hꢁ ꢁ ꢁO8 154.0; N4–O7 2.93(2), N4–Hꢁ ꢁ ꢁO7
154.8] adducts.
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3280 | Chem. Commun., 2009, 3279–3281

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191.6 [2 ꢃ CO], 164.1 [q (1JCB = 50.0 Hz), Ci BAr04], 159.6 [C5(3),
Hdmpz], 155.8 [2-ampy], 151.7 [C3(5), Hdmpz], 144.5, 141.8 [2-ampy],
134.7 [Co BAr04], 128.8 [q (2JCF = 32.1 Hz), Cm BAr04], 124.5 [q (1JCF
= 272.9 Hz), CF3, BAr04], 117.5 [Cp BAr04], 116.5, 109.3 [2-ampy],
108.4 [CH, Hdmpz], 14.6, 10.8 [CH3, Hdmpz]. Anal. Calc. for
C50H37BF24N5O3Re: C 42.30, H 2.41, N 5.92. Found: C 41.97,
H 2.52, N 6.04%.
3 J. Pe
´
rez, L. Riera, L. Ion, V. Riera, K. M. Anderson, J. W. Steed
and D. Miguel, Dalton Trans., 2008, 878.
4 J. Perez and L. Riera, Chem. Soc. Rev., 2008, 37, 2658.
´
5 K. J. Wallace, R. Daari, W. J. Belcher, L. O. Abouderbala,
M. G. Boutelle and J. W. Steed, J. Organomet. Chem., 2003, 666,
63; S. J. Dickson, S. C. G. Biagini and J. W. Steed, Chem.
Commun., 2007, 4955; S. J. Dickson, M. J. Paterson,
C. E. Willans, K. M. Anderson and J. W. Steed, Chem.–Eur. J.,
2008, 14, 7296.
6 Selected crystallographic data for 1ꢁClO4: C18H22ClN6O7Re,
M = 656.07, monoclinic, P21/c, a = 13.002(12), b = 11.249(11),
c = 17.183(16) A, b = 106.685(17)1, V = 2407(4) A3, Z = 4, 296
K; 10476 reflections measured, 3458 independent (Rint = 0.0413);
R1 = 0.0264, wR2 = 0.0561 (all data).
7 M. M. Mashaly, Synth. React. Inorg. Met.-Org. Chem., 2004, 34,
115; C.-W. Su, C.-P. Wu, J.-D. Chen, L.-S. Liou and J.-C. Wang,
Inorg. Chem. Commun., 2002, 5, 215; R. Bosque, F. Maseras,
O. Eisenstein, B. P. Patel, W. Yao and R. H. Crabtree, Inorg.
Chem., 1997, 36, 5505; R.-E. Shepherd and S. Zhang, Transition
Met. Chem., 1994, 19, 146.
8 Selected crystallographic data for 2ꢁBAr04: C50H34BF24N6O3Re,
M = 1419.84, monoclinic, P21/n, a = 14.512(3), b = 25.848(5),
c = 15.739(3) A, b = 107.179(4)1, V = 5640.5(18) A3, Z = 4, 293
y Synthesis of 2ꢁBAr04: Prepared as described for 1ꢁBAr04, from
[ReBr(CO)5] (0.100 g, 0.246 mmol), Hdmpz (0.047 g, 0.492 mmol),
NaBAr04 (0.218 g, 0.246 mmol) and 3-ampy (0.023 g, 0.246 mmol).
Slow diffusion of hexane (20 mL) into a concentrated solution of
2ꢁBAr04 in CH2Cl2 afforded colorless crystals, one of which was used
for the X-ray determination. Yield: 0.261 g, 75%. IR (CH2Cl2):
2037vs, 1929s (nCO). 1H NMR (CD2Cl2): d 9.13 [s, br, 2H, NH,
Hdmpz], 7.89 [m, 1H, CH, 3-ampy], 7.73 [m, 9H, Ho and CH, BAr04
and 3-ampy], 7.57 [m, 4H, Hp, BAr04], 7.24 [m, 2H, CH, 3-ampy], 6.18
[s, 2H, CH, Hdpmz], 4.20 [s, br, 2H, NH2], 2.30 [s, 6H, CH3, Hdmpz],
2.23 [s, 6H, CH3, Hdmpz]. 13C NMR (CD2Cl2): d 196.0 [CO], 195.5
[2 ꢃ CO], 164.1 [q (1JCB = 49.9 Hz), Ci BAr04], 159.0, 148.7 [C5 and
C3, Hdmpz], 147.4, 143.6, 142.1, 137.2 [2-ampy], 134.4 [Co BAr04],
131.2 [q (2JCF = 31.3 Hz), Cm BAr04], 130.1, 127.2 [3-ampy], 127.0
[q (1JCF
=
272.3 Hz), CF3, BAr04], 119.9 [Cp BAr04], 111.3
[CH, Hdmpz], 17.6, 13.3 [CH3, Hdmpz]. Anal. Calc. for
C50H37BF24N5O3Re: C 42.30, H 2.41, N 5.92. Found: C 42.22, H
2.47, N 5.78%.
K;
25132
reflections
measured,
8094
independent
(Rint = 0.0417); R1 = 0.0574, wR2 = 0.1497 (all data).
9 G. A. Ardizzoia, G. LaMonica, A. Maspero, M. Moret and
N. Masciocchi, Eur. J. Inorg. Chem., 1998, 1503.
1 C. R. Rice, Coord. Chem. Rev., 2006, 250, 3190; M. H. Filby and
J. W. Steed, Coord. Chem. Rev., 2006, 250, 3200; P. D.
Beer and E. J. Hayes, Coord. Chem. Rev., 2003, 240, 167;
P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40,
486; M. G. Fisher, P. A. Gale, M. E. Light and S. J. Loeb, Chem.
Commun., 2008, 5695; I. D. Vega, P. A. Gale, M. E. Light and
S. J. Loeb, Chem. Commun., 2005, 4913; C. R. Bondy, P. A. Gale
and S. J. Loeb, J. Am. Chem. Soc., 2004, 126, 5030; C. R. Bondy,
P. A. Gale and S. J. Loeb, Chem. Commun., 2001, 729.
10 Selected crystallographic data for 2ꢁBr: C18H23BrN6O4Re,
ꢀ
M = 653.53, triclinic, P1, a = 8.3635(3), b = 8.9590(4),
c
=
16.4246(7) A,
107.713(4)1, V = 1131.21(9) A3, Z = 2, T = 150 K; 10083
reflections measured, 4179 independent (Rint = 0.0322); R1
0.0455, wR2 = 0.1375 (all data). 2ꢁNO3ꢁ1/8C6H4ꢁ1/8CH2Cl2:
18.88H24Cl0.25N7O6Re, M = 640.01, monoclinic, P21/c, a =
a = 104.396(4), b = 90.268(3), g =
=
C
17.1425(2), b = 18.6344(3), c = 19.2945(3) A, b = 108.678(2)1,
V = 5838.83(15), A3, Z = 8, T = 150 K; 29294 reflections
measured, 11272 independent (Rint = 0.0331); R1 = 0.0773,
wR2 = 0.2221 (all data).
2 S. Nieto, J. Pe
Commun., 2005, 546; S. Nieto, J. Pe
D. Miguel, Chem.–Eur. J., 2006, 12, 2244; S. Nieto, J. Pe
´
rez, V. Riera, D. Miguel and C. Alvarez, Chem.
rez, L. Riera, V. Riera and
rez,
´
´
L. Riera, V. Riera, D. Miguel, J. A. Golen and A. L. Rheingold,
Inorg. Chem., 2007, 46, 3407.
11 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311.
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