Non-covalent interactions between anions and a cationic rhenium diamine complex: Structural characterization of the supramolecular adducts

Article abstract of DOI:10.1039/b602907h

The behavior of the new cationic complex [Re(CN^tBu)(CO) ₃(N-N)]⁺ (N-N = 1,2-phenylenediamine) toward several inorganic anions (X^-) has been investigated both in solution (by ¹H NMR) and in the solid state (by X-ray diffraction), and the results show the formation of supramolecular adducts featuring N-H...X hydrogen bonds. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.

Full text of DOI:10.1039/b602907h

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Non-covalent interactions between anions and a cationic rhenium diamine
complex: structural characterization of the supramolecular adducts
a
a
a
a
b
´
´ ´
Sonia Nieto, Julio Perez,* Lucıa Riera, Vıctor Riera and Daniel Miguel
Received (in Durham, UK) 1st March 2006, Accepted 13th April 2006
First published as an Advance Article on the web 27th April 2006
DOI: 10.1039/b602907h
The behavior of the new cationic complex [Re(CNtBu)(CO)3
(N–N)]1 (N–N = 1,2-phenylenediamine) toward several inor-
donors compared with those of amides, pyrroles, etc. Amine-
based anion receptors are, in fact, protonated macrocyclic
polyamines, which interact with anions by a combination of
electrostatic attraction and hydrogen bonds (Fig. 1a illustrates
the encapsulation of halide anions by the diammonium poly-
macrocycles termed catapinands, the first synthetic organic
hosts for anionic species).8 Coordination as a chelate to a
cationic transition metal center closes the diamine ring and
provides the positive charge. The resulting complex can be
thought of as a simple model of the mentioned protonated
macrocyclic polyamines (Fig. 1b).
1
ganic anions (Xꢀ) has been investigated both in solution (by H
NMR) and in the solid state (by X-ray diffraction), and the
results show the formation of supramolecular adducts featuring
N–Hꢁ ꢁ ꢁX hydrogen bonds.
The hydrogen bond interactions between the N–H groups of
chelated diamine ligands and the negative end of polar mole-
cules have been found to be crucial in several instances. Thus,
such interactions stabilize the pericyclic transition state pro-
posed to occur in hydrogen transfer to ketones mediated by
Noyori-type catalysts1 and determine the nucleobase prefer-
ence displayed by the anti-cancer areneruthenium complexes
recently reported by Sadler.2 Regarding solid state structures,
Guilera and Steed have found that hydrogen bonds between
ethylenediamine (en) N–H groups and terephthalate (tph)
oxygens provide the inter-chain linkage in [Zn(en)(tph)]N
coordination polymers.3 The hydrogen bonds between the
keto oxygens of the ester groups and the N–H groups of 1,2-
phenylenediamine appear to be the major driving force in
determining the observed conformation of organometallic
[Mo(CO)2(MeOOC–CQC–COOMe)2(N–N)] fumarate and
maleate complexes.4
For our study, we have targeted the new compound fac-
[Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)]BAr04 (Ar04 = 3,5-bis(tri-
fluoromethyl)phenyl) (1), featuring (a) 1,2-phenylenediamine
ligand, more rigid than the more widely employed alkanedia-
mines such as ethylenediamine, (b) BAr04 as counteranion,
aiming to minimize its competition with the external anion
for the interaction with the N–H groups9 and, at the same time,
to afford a high solubility in low-polarity organic solvents, in
which the presumedly weak anion–diamine interactions could
be observed, (c) a cationic metal fragment, {Re(CO)3}1, rela-
tively inert regarding substitution reactions, without additional
strong hydrogen-bond donor groups, and devoid of ligands
able to engage in strong intra- or intermolecular hydrogen
bonding with the amine N–H groups, (i.e., ligands with high
hydrogen-bond acceptor character). t-Butyl isocyanide was
selected as the neutral monodentate ligand to block the remain-
ing coordination position because (d) it cannot act as a hydro-
gen-bond acceptor, and (e) exploratory experiments revealed
that it was more resistant to substitution by anions than other
monodentate ligands such as pyridines, phosphines, etc. The
choice of an organometallic complex with a hydrophobic
periphery, and whose preparation is carried out in anhydrous
organic solvents, helps to prevent the presence of molecules of
water and thus to limit the complexity of the structure.
Preparation of 1 was easily accomplished from [ReBr(CO)5]
via thermal reaction with the diamine to afford [Re-
Br(CO)3(1,2-(NH2)2C6H4)]. Reaction of this complex with
silver triflate afforded [Re(OTf)(CO)3(1,2-(NH2)2C6H4)], reac-
tion of which with NaBAr04 and t-butyl isocyanide yielded 1
(see Scheme 1).
Non-covalent interactions between chelated diamines and
external, i.e. non-coordinated, anions have been less studied,
although their occurrence in the solid state was noticed in
early works.5 Very recently, Yu, Xu and coworkers
reported the unusual photoelectric properties shown by
[Co(en)3]2(Zr2F12)(SiF6) ꢁ 4H2O, a compound containing a
hydrogen-bonded assembly of discrete [Co(en)3]31
,
(Zr2F12)4ꢀ, and (SiF6)2ꢀ ions, in which the N atoms serve as
H-bond donors and the F atoms as H-bond acceptors.6 The
study of second-sphere interactions between anions and metal
complexes of several ditopic ligands is an area of great current
interest.7
We set out to devise a simple system where such interactions
could be examined for the case of chelated diamines. There-
fore, we focused on mononuclear complexes with a single
diamine chelate. The N–H groups of amines are weak H-bond
Compound 1 was characterized analytically and by IR and
NMR (1H and 13C) spectroscopy. Its IR spectrum in the
2200–1800 cmꢀ1 region displayed, besides the pattern diag-
nostic of a fac-M(CO)3 moiety, a medium intensity band at
2187 cmꢀ1 (in CH2Cl2 solution) due to the coordinated
isocyanide.
a
´
Departamento de Quımica Organica e Inorganica-IUQOEM,
Facultad de Quımica, Universidad de Oviedo-CSIC, 33006 Oviedo,
´
´
´
Spain. E-mail: japm@uniovi.es; Fax: þ34 98510 3446; Tel: þ34
98510 3465
Departamento de Quımica Inorganica, Facultad de Ciencias,
b
´
Universidad de Valladolid, 47071 Valladolid, Spain
´
ꢂc
838 | New J. Chem., 2006, 30, 838–841 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006

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Fig. 1 Anion binding by (a) diammonium catapinand; (b) diamine
cationic metal complex.
The solution behavior of 1 toward several anions (added as
1
tetrabutylammonium salts) was studied by IR and H NMR.
Compound 1 was stable against ligand dissocꢀiation in thꢀe
presence of Clꢀ, Brꢀ, Iꢀ, HSO4ꢀ, NO3ꢀ, ReO4 and ClO4
anions. Dissociation of the monodentate isocyanide ligand
(found by us in other compounds)10 can be easily detected by
IR, since free NCtBu gives rise to a band at 2139 cmꢀ1 in
CH2Cl2 solution.
Fast anion exchange was found in every case, and the
titration profiles in CD3CN (attempts to study the anion
binding in CD2Cl2 were thwarted by precipitation of the
adducts), displayed in Fig. 2, were constructed plotting the
chemical shift of the midpoint of the AA0BB0 N–H multiplet
against the amount of anion added. These data were used to
calculate the 1 : 1 binding constants,11 which were found to be
very small, indicating weak interactions. The relative values of
the binding constants correlate with the ability of the different
anions to act as H-bond acceptors (Clꢀ: 77 ꢃ 15 Mꢀ1, Brꢀ: 48
Fig. 2 1H NMR titration plots of compound [Re(CNtBu)(CO)3
(1,2-(NH2)2C6H4)]BAr0 (1) in CD3CN with different anions.
4
ligand; thus, the bulky tBu group does not hinder the approach
of the anion to the N–H groups.ꢀ
ꢃ 6 Mꢀ1, Iꢀ: 20 ꢃ 2, HSO4ꢀ: 19 ꢃ 2 Mꢀ1, NO3ꢀ: 26 ꢃ 2 Mꢀ1
,
ReO4ꢀ: 24 ꢃ 2 Mꢀ1, ClO4ꢀ: 18 ꢃ 3 Mꢀ1). Attempts to study
the behavior of 1 towards more basic anions, such as fluoride,
dihydrogenphosphate or acetate led to the precipitation of a
black solid and the vanishing of the 1H NMR diamine signals,
indicating decomposition of the rhenium complex. Although
we have not studied this process, we note that 1,2-phenylene-
diamine transition metal complexes are prone to undergo
redox chemistry,12 which could account for the formation of
paramagnetic, NMR-invisible species. We are not aware of
previous solution studies of diamine complex–anion systems.
Single crystals of the nitrate and perchlorate adducts could
be grown by slow diffusion of hexane into saturated CH2Cl2
solutions. The solid state structures were determined by X-ray
diffraction, and the results are displayed in Fig. 3.13 The
neutral supramolecular adducts [Re(CNtBu)(CO)3(1,2-(NH2)2
C6H4)] ꢁ NO3 and [Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)] ꢁ ClO4
In the structure of the ClO4 adduct, each perchlorate
oxygen forms hydrogen bonds with one of the N–H groups
of a cationic complex, resulting in a tridimensional network
(Fig. 3a). In contrast, in the structure of the NO3ꢀ adduct, two
oxygen atoms of a nitrate anion interact each with one of the
exo-N–H groups of a single cationic complex, forming R22(8)
systems. The N(11)–O(11)ꢁ ꢁ ꢁH = 122.9(1)1, close to the
ideal value of 1201, and the small dihedral angle
Hꢁ ꢁ ꢁO(11)–N(11)–O(12) = 12.9(1)1 suggest hydrogen bonding
with the nitrate lone pair electrons.14 As can be seen in Fig. 3b,
the structure of the [Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)] ꢁ NO3
unit has space group imposed mirror symmetry. The resulting
[Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)] ꢁ NO3 adducts are linked
through hydrogen bonds between the same two oxygens and
N–H groups of adjacent similar units, resulting in zigzag
chains (Fig. 3b).
crystallized separately from the salt [Bu4N][BAr0 ], a fact
4
previously found by us in other instances.9 In both structures,
In summary, we have synthesized the compound fac-[Re
(CNtBu)(CO)3(1,2-(NH2)2C6H4)]BAr0 , designed to interact
the benzene ring of the diamine bends towards the CNtBu
4
with anions by a combination of coulombic attraction and
hydrogen bonds. Both in solution, where the interactions with
the Bu4N1 salts of the anions Xꢀ (Xꢀ = NO3ꢀ, ClO4ꢀ) are
very weak, albeit detectable, and in the solid state, the cationic
complex maintains its integrity and forms 1 : 1 adducts with a
number of anions. The neutral adducts [Re(CNtBu)(CO)3(1,2-
(NH2)2C6H4)] ꢁ X crystallize separately from [Bu4N][BAr0 ],
4
and their structures are dominated by the Xꢁ ꢁ ꢁH–N hydrogen
Scheme 1 Synthesis of [Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)]BAr04 (1).
bonds.
ꢂc
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New J. Chem., 2006, 30, 838–841 | 839

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during the titration) were injected through the septum using
Hamilton microsyringes (10–100 mL). Data were treated using
the WinEQNMR program.11
Crystal structure determination
General description. A crystal was attached to a glass fiber
and transferred to a Bruker AXS SMART 1000 diffractometer
with graphite monochromatized Mo Ka X-radiation and a
CCD area detector. A hemisphere of the reciprocal space was
collected up to 2y = 48.61. Raw frame data were integrated
with the SAINT15 program. The structures were solved by
direct methods with SHELXTL.16 An empirical absorption
correction was applied with the program SADABS.17 All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were set in calculated positions and refined as riding atoms
with a common thermal parameter. Calculations were made
with SHELXTL and PARST.18
Synthesis of [Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)]BAr04 (1).
A mixture of [ReBr(CO)5] (0.050 g, 0.123 mmol) and 1,2-
phenylenediamine (0.013 g, 0.123 mmol) was refluxed in
toluene (20 mL) for 4 h. The solvent was evaporated to
dryness, the residue redissolved in CH2Cl2 (20 mL) and AgOTf
(0.032 g, 0.123 mmol) was added. The resulting slurry was
stirred at room temperature in the dark for 1 h and then
filtered through Celite. To the colorless solution, NaBAr0
4
(0.109 g, 0.123 mmol) and CNtBu (0.014 mL, 0.123 mmol)
were added and the mixture was stirred for 30 min. The
solution was filtered by cannula, concentrated in vacuo and
upon addition of hexane, a white microcrystalline solid pre-
cipitated. Yield: 0.095 g, 77%. IR(CH2Cl2): n/cmꢀ1: 2187m
1
Fig. 3 (a) View of the crystalline structure of the [Re(CNtBu)
(CO)3(1,2-(NH2)2C6H4)] ꢁ ClO4 adduct. (b) View of the zig-zag chains
formed by the [Re(CNtBu)(CO)3(1,2-(NH2)2C6H4)] ꢁ NO3 adduct. The
additional letters A in the atom labels indicate that these atoms are
related to the original ones by the operation (x, 1/2 ꢀ y, z). In both
figures the probability of the thermal ellipsoids has been kept at 5%
for clarity.
(CN); 2044 s, 1962 vs, 1945 vs (CO). H NMR (CD3CN, 300
MHz): d 7.80 [m, 8H, Ho of BAr04], 7.77 [m, 4H, Hp of BAr04],
7.39 [m, 4H, C6H4], 5.94, 5.90, 5.79, 5.75 [AA0BB0system, 4H,
NH2], 1.34 [s, 9H, BuNC]. 13C {1H} NMR (CD3CN, 300
t
MHz): d 192.4 [2CO], 191.7 [CO], 161.1 [q (1JCB = 49.8 Hz),
Ci of BAr04], 140.5 [C6H4], 136.2 [Co of BAr04], 130.4 [q (2JCF
= 31.9 Hz), Cm of BAr04], 129.4, 128.2 [C6H4], 125.9 [q (1JCF
= 273.5 Hz), CF3 of BAr04], 119.2 [Cp of BAr04], 72.0
[(CH3)3CNC ], 32.1 [CH3 of tBuNC ]; the tBuNC signal could
not be observed. Anal. Calcd. for C46H29BF24N3O3Re: C,
41.71; H, 2.21; N, 3.17. Found: C, 41.85; H, 2.09; N, 3.14%.
Experimental
All manipulations were carried out under a nitrogen atmo-
sphere using Schlenk techniques. Tetrabutylammonium salts
were purchased from Fluka or Aldrich. Deuterated acetoni-
trile (Cambridge Isotope Laboratories, Inc.) was stored under
nitrogen in Young tubes. NMR spectra were recorded in
Bruker AC-300 and DPX-300 instruments. IR solution spectra
were obtained in a Perkin-Elmer FT 1720-X spectrometer
using 0.2 mm CaF2 cells. NMR samples were prepared under
nitrogen using Kontes manifolds purchased from Aldrich.
Oven-dried 5 mm NMR tubes were subjected to several
vacuum–nitrogen cycles, filled with the solution of the receptor
Acknowledgements
We thank Ministerio de Ciencia y Tecnologıa (grant BQU2003-
´
08649 and BQU2002-03414) and European Union (ERG to L.
R.) for support of this work. L. R. thanks Ministerio de
Educacion y Ciencia for a Ramon y Cajal contract.
´ ´
References
1 (a) R. Noyori and S. Hashiguchi, Acc. Chem. Res., 1997, 30,
97–102; (b) for related chemistry, see: K. Muniz, Angew. Chem.,
Int. Ed., 2005, 44, 6622–6627; (c) D. B. Grotjahn, Chem.–Eur. J.,
2005, 11, 7146–7153.
2 Y. K. Yan, M. Melchart, A. Habtemariam and P. J. Sadler, Chem.
Commun., 2005, 4764–4776.
3 G. Guilera and J. Steed, Chem. Commun., 1999, 1563–1564.
4 C.-H. Lai, C.-H. Cheng, W.-C. Chou and S.-L. Wang, Organome-
tallics, 1993, 12, 1105–1112 and 3418–3425.
(prepared separately in a Schlenk tube, typically in a 10ꢀ2
M
concentration in CD3CN) by means of a 1 mL syringe, and
1
stoppered with rubber septa. After the H NMR spectrum of
the receptor was recorded, successive aliquots of the tetra-
butylammonium salt (typically 4 ꢄ 10ꢀ2 M in CD3CN,
separately prepared and kept in a septum-stoppered vial
ꢂc
840 | New J. Chem., 2006, 30, 838–841 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006

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5 (a) M. Ul-Haque, C. N. Caughlan and K. Emerson, Inorg. Chem.,
1970, 9, 2421–2424; (b) D. A. Snyder and D. L. Weaver, Inorg.
Chem., 1970, 9, 2760–2767; (c) E. N. Duesler and K. N. Raymond,
Inorg. Chem., 1971, 10, 1486–1492.
6 Y. Du, M. Yang, J. Yu, Q. Pan and R. Xu, Angew. Chem., Int. Ed.,
2005, 44, 7988–7990.
7 (a) A. D. Burrows, D. M. P. Mingos, S. E. Lawrence, A. J. P. White
and D. J. Williams, J. Chem. Soc., Dalton Trans., 1997, 1295–1300;
(b) J. W. Canary and B. Gibb, Prog. Inorg. Chem., 1997, 45, 1–81;
(c) C. R. Bondy, P. A. Gale and S. J. Loeb, Chem. Commun., 2001,
729–730; (d) S. A. Dalrymple, M. Parvez and G. K. H. Shimizu,
Chem. Commun., 2001, 2672–2673; (e) K. J. Wallace, R. Daari, W. J.
Belcher, L. O. Abouderbala, M. G. Boutelle and J. W. Steed, J.
Organomet. Chem., 2003, 666, 63–74; (f) C. R. Bondy, P. A. Gale
and S. J. Loeb, J. Am. Chem. Soc., 2004, 126, 5030–5031.
8 (a) C. A. Ilioudis and J. W. Steed, J. Supramol. Chem., 2001, 1,
165–187; (b) J. M. Llinares, D. Powell and K. Bowman-James, Coord.
Chem. Rev., 2003, 240, 57–75; (c) Coord. Chem. Rev., ed. P. A. Gale,
2003, p. 240 (volume dedicated to anion receptor chemistry).
13 Crystal
data:
for
adduct
[Re(CNtBu)(CO)3(1,2-
(NH2)2C6H4)] ꢁ NO3, C14H17N4O6Re: crystal dimensions 0.14 ꢄ
0.11 ꢄ 0.06 mm3, monoclinic, space group P2(1)/m, a = 9.227(4)
A, b = 10.155(4) A, c = 10.156(4) A, b = 106.496(7)1, V =
912.4(7) A3, Z = 2, T = 296(2) K, Dc = 1.906 g cmꢀ3, Mo-Ka
radiation (l = 0.71073 A), 4105 reflections collected, 1404 inde-
pendent reflections (2.09 r y r 23.281), R1= 0.0412, wR2=
0.1078, GOF on F2 =1.057. For adduct [Re(CNtBu)(CO)3(1,2-
(NH2)2C6H4)] ꢁ ClO4, C14H17ClN3O7Re: crystal dimensions 0.26 ꢄ
0.10 ꢄ 0.09 mm3, orthorhombic, space group P2(1)2(1)2(1), a =
10.160(7) A, b = 12.354(9) A, c = 15.993(12) A, V = 2007(3) A3,
Z = 4, T = 296(2) K, Dc = 1.856 g cmꢀ3, Mo-Ka radiation (l =
0.71073 A), 17956 reflections collected, 2893 independent reflec-
tions (2.08 r y r 23.311), R1 = 0.0452, wR2 = 0.1085, GOF on
F2 =1.053. The XPREP routine of SHELXTL gave R(int) = 0.094
for a monoclinic lattice with b = 90.071 , and slightly higer R(int)
= 0.105 for orthorhombic space group P2(1)2(1)2(1), leading to
R1 = 0.0452, and wR2 = 0.1131 (all data) which are lower than
those obtained in the alternative choice of monoclinic P2(1) (R1 =
0.745, wR2 = 0.1839). CCDC reference numbers 292720 and
292721. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b602907h.
9 (a) S. Nieto, J. Pe
Commun., 2005, 546–548; (b) L. Ion, D. Morales, J. Pe
Riera, V. Riera, R. A. Kowenicki and M. McPartlin, Chem.
Commun., 2006, 91–93; (c) S. Nieto, J. Perez, L. Riera, V. Riera
´
rez, V. Riera, D. Miguel and C. Alvarez, Chem.
´
rez, L.
´
14 J. M. Mahoney, K. A. Stucker, H. Jiang, I. Carmichael, N. R.
Brinkmann, A. M. Beatty, B. C. Noll and B. D. Smith, J. Am.
Chem. Soc., 2005, 127, 2922–2928.
and D. Miguel, Chem.–Eur. J., 2006, 12, 2244–2251.
10 S. Nieto, PhD Thesis, Universidad de Oviedo, submitted.
11 (a) M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311–312.
Although the curves fit to a 1 : 1 binding model, the values of the
stability constants should be treated with caution as there may be
complexes of other stoichiometries in solution, as suggested by
sigmoidal shape of some curves.
15 SAINTþ. SAX area detector integration program. Version 6.02.
Bruker AXS, Inc., Madison, WI, 1999.
16 G. M. Sheldrick, SHELXTL, An integrated system for solving,
refining, and displaying crystal structures from diffraction data,
Version 5.1, Bruker AXS, Inc., Madison, WI, 1998.
12 A. L. R. Silva, M. O. Santiago, I. C. N. Dio
´
genes, S. O. Pinheiro,
17 G. M. Sheldrick, SADABS Empirical Absorption Correction Pro-
gram, University of Gottingen, Gottingen, Germany, 1997.
¨ ¨
18 (a) M. Nardelli, Comput. Chem., 1983, 7, 95–97; (b) M. Nardelli, J.
Appl. Crystallogr., 1995, 28, 659.
E. E. Castellano, J. Ellena, A. A. Batista, F. B. do Nascimento and
I. S. Moreira, Inorg. Chem. Commun., 2005, 8, 1154–1158 and
references therein.
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