Aminoferrocene derivatives in chloride recognition and electrochemical sensing

Full text of DOI:10.1021/ic990813s

5184
Inorg. Chem. 1999, 38, 5184-5186
Aminoferrocene Derivatives in Chloride
Recognition and Electrochemical Sensing
Konstantinos Kavallieratos, Sharon Hwang, and
Robert H. Crabtree*
Sterling Chemistry Laboratory, Department of Chemistry,
Yale University, 225 Prospect Street,
New Haven, Connecticut 06520-8107
ReceiVed July 8, 1999
Introduction
Redox-active anion receptors1-9 giving potential shifts on
binding are useful in chemical sensor applications:10-15
cobaltocenium,1-5,16,17 ferrocene,1-7,18-20 and transition-metal-
bipyridyl8,9 cases are known.
Our readily available isophthalamide (1)21 and disulfonamide
(2)22 receptors bind Cl- and other anions very strongly in CH2-
Cl2,21,22 suggesting the neutral diferrocenyl analogues 3 and 4
might act as Cl- sensors because the anion is closely coupled
to the ferrocenyl (Fc) group.23 Related aminomethylferrocene
diamide analogues have recently been reported by Beer et al.24
Amide receptors with two FcNH groups have not yet been
reported since FcNH2 is not commercially available and is
difficult to prepare.25-29
(1) Beer, P. D. Chem. Soc. ReV. 1989, 18, 409.
(2) Beer, P. D. AdV. Inorg. Chem. 1992, 39, 79.
(3) Beer, P. D.; Smith, J. K. Prog. Inorg. Chem. 1997, 46, 1 and references
therein.
We have synthesized 3-5, which, being neutral, are very
soluble in organic solvents. The chloride-binding properties of
4 are studied. We also report an improved synthesis of FcNH2.
(4) Beer, P. D.; Schnitt, P. Curr. Opin. Chem. Biol. 1997, 1, 475.
(5) Beer, P. D. Acc. Chem. Res. 1998, 31, 71.
Results and Discussion
(6) Jagessar, R. C.; Burns, D. H. Chem. Commun. 1997, 1685.
(7) Scherer, M.; Sessler, J. L.; Gebauer, A.; Lynch, V. Chem. Commun.
1998, 85.
Synthesis of FcNH2 and 3-5. FcNH2, synthesized by a
known route,25 but with an improved isolation procedure, gave
yields of 21-26% versus 8-14%.25,30 The disulfonamide 4,
synthesized in good yield (54%) in one step from FcNH2 and
1,3-benzenesulfonyl dichloride in EtOH,31 was isolated as a
yellow powder, soluble in CH2Cl2, and was characterized by
1H NMR, FT-IR, and elemental analysis. Attempts to synthesize
receptor 3 in CH2Cl2 gave only 8% of 3 but in EtOH gave a
24% yield of the amide ethyl ester 5; both were fully character-
ized.
(8) Beer, P. D.; Szemes, F.; Balzani, V.; Sala, C. M.; Drew, M. G. B.;
Bent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864.
(9) Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M. G. B.;
Goulden, A. J.; Graydon, A. R.; Grieve, A.; Mortimer, R. J.; Wear,
T.; Weightman, J. S.; Beer, P. D. Inorg. Chem. 1996, 35, 5868.
(10) Antonisse, M. M. G.; Reinhoudt, D. N. Chem. Commun. 1998, 443.
(11) Antonisse, M. M. G.; Snellink-Ruel, B. H. M.; Engbersen, J. F. J.;
Reinhoudt, D. N. J. Chem. Soc., Perkin Trans. 2 1998, 773.
(12) Ohyama, T.; Wang, D. Q.; Cowan, J. A. Chem. Commun. 1998, 467.
(13) Gale, P. A.; Chen, Z.; Drew, M. G. B.; Heath, J. A.; Beer, P. D.
Polyhedron 1998, 17, 405.
(14) Mathisson, S.; Bakker, E. Anal. Chem. 1998, 70, 303.
(15) Tsagatakis, J. K.; Chaniotakis, J. A.; Jurkschat, K. Quim. Anal. 1997,
16, 105.
(16) Beer, P. D.; Hesek, J.; Hodacova, J.; Stokes, S. E. J. Chem. Soc.,
Chem. Commun. 1992, 270.
(17) Atwood, J. L.; Hollman, K. T.; Steed, J. W. Chem. Commun. 1996,
1401.
(18) Beer, P. D.; Chen, Z.; Goulden, A. R.; Graydon, S. E.; Stokes, S. E.;
Wear, T. J. Chem. Soc., Chem. Commun. 1992, 270.
(19) Chen, Z.; Graydon, A. R.; Beer, P. D. J. Chem. Soc., Faraday Trans.
1995, 91, 295; 1996, 92, 97.
(1)
(2)
(20) Beer, P. D.; Szemes, F. Inorg. Chem. 1997, 36, 2112.
(21) Kavallieratos, K.; de Gala, S. R.; Austin, D. J.; Crabtree, R. H. J. Am.
Chem. Soc. 1997, 119, 2325.
(22) Kavallieratos, K; Bertao, C. M.; Crabtree, R. H. J. Org. Chem. 1999,
64, 1675.
(23) Beer, P. D.; Drew, M. G. B.; Jagessar, R. J. Chem. Soc., Dalton Trans.
1997, 881.
(24) Beer, P. D.; Smith, D. K. J. Chem. Soc., Dalton Trans. 1998, 417.
(25) Knox; G. R.; Paulson, P. L.; Willison, D. Organometallics 1990, 9,
301.
(26) Nesmeyanov A. N. Dokl. Akad. Nauk SSSR, Ser. Khim. 1955, 102,
535.
Anion Binding by 3-5 (1H NMR). Addition of Bu4NX
(X ) Cl-) to CD2Cl2 solutions of 3 and 4 caused large chemical
(29) Herberhold, M.; Ellinger, M.; Haumeier, L. Organometallic Syntheses;
King, R. B., Eisch, J. J., Eds.; Elsevier: Amsterdam, 1986; Vol. 3, p
81.
(27) Arimoto, F.; Haven, A. C. J. Am. Chem. Soc. 1955, 77, 6295.
(28) Herberhold, M.; Ellinger, M.; Kremnitz, W. J. Organomet. Chem.
1983, 241, 227.
(30) Details are given in the Experimental Section.
(31) Ertas, M.; Ahsen, V.; Gu¨l, A.; Bekaˆroglu, O. J. Organomet. Chem.
1987, 333, 383.
10.1021/ic990813s CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/06/1999

Notes
Inorganic Chemistry, Vol. 38, No. 22, 1999 5185
Figure 3. Titration curve of 5 with (n-Bu)4NCl at 19.4 °C in CD2Cl2.
Figure 1. 1H NMR spectra of 4 before and after addition of 10 equiv
of (n-Bu)4NCl. The resonance corresponding to the N-H (2H) shows
a dramatic downfield shift from 6.4 to 9.4 ppm. Similarly the 2-C-H
(1H) shows a smaller downfeld shift from 8.2 to 9.5 ppm. The other
aromatic protons are affected only slightly by anion addition.
Table 2. FT-IR νN-H Stretching Frequencies in CH2Cl2 Solution
and a Thin Film for the Free Receptors and Their Adducts (X ) Cl)
νN-H
νN-H
(thin
FT-IR
spectrum
of
νN-H
(thin
FT-IR
νN-H
(solution)
film) spectrum (solution)
film)
(cm-1
)
(cm-1
3228
)
of
(cm-1
)
(cm-1
)
4
3360 and 3228
(weak)
3360 and 3260
5
3434
3434
3263
3176
5‚X-
4‚X-
3258
As before,22 the self-associated sulfonamide band (3228 cm-1
)
does not appear in the solution or film spectra of 4‚X-. For the
monoamide ferrocenyl receptor we were able to observe the
free N-H band in solution at 3434 cm-1 and the self-associated
N-H band at 3263 cm-1 in a thin film. For 5‚Cl- only a broad
N-H‚‚‚Cl- band at 3175 cm-1 appeared in thin film, but the
solution spectra did not show many other differences from that
of free 5, suggesting a much weaker anion complexation.33
1H NMR Titrations. Association Constants. The association
constants, Ka, were determined for 4 and 5 with Cl- in a
CD2Cl2 solution, by a standard NMR titration34 monitoring
∆δ(N-H) and ∆δ(2-C-H) in a dilute receptor CD2Cl2 solution
of concentration range (0.5-1) × 10-3 M, with the addition of
1.0 × 10-2 to 1.0 × 10-1 M CD2Cl2 solutions of (n-Bu)4NCl
in the same receptor concentration. One to one binding curves
for the N-H protons (Figure 3) were analyzed using a nonlinear
regression method.35 The 1:1 binding isotherm34 of eq 3 gave
consistent fits for both 2-C-H and N-H.
Figure 2. Binding conformation of chloride-receptor complexes based
on the NMR data and previous work on similar receptors.21,22
Table 1. Chemical Shift Changes (∆δmax) for N-H and Aromatic
1
2-C-H Protons in the H NMR Spectrum upon Chloride Addition
∆δ (N-H) (R‚Cl-)
∆δ (2-C-H) (R‚Cl-)
compound
(ppm)
(ppm)
3
4
5
3.37
3.13
2.88
1.07
1.03
0.23
shift changes for protons (N-H and 2-C-H) affected by
hydrogen bonding (Figure 1 and Table 1).
Monoamide 5 gave smaller changes for the same protons.
The 2-C-H shift (0.23 ppm) being much smaller than the
4-C-H (0.50 ppm) suggests an anti binding conformation. On
the other hand, the large shift changes for the 2-C-H protons
of 3 and 4 suggest21,22 a syn-syn binding conformation is
adopted
∆δ ) ([R]t + [Cl-]t + Ka-1 - ((([R]t + [Cl-]t + Ka-1)2 -
4[Cl-]t[R]t)1/2))∆δmax/(2[R]t) (3)
(Figure 2).
Comparison of the data for Cl- binding (Ka ) 9500 M-1
((30%), 4‚Cl-; 30 M-1 ((5%), 5‚Cl-; ∆Gf ) -22.3 kJ/mol,
4‚Cl-; -8.3 kJ/mol, 5‚Cl-) demonstrates the importance of the
two convergent hydrogen-bonding groups;36-38 the second N-H
increases Ka by >300-fold and ∆Gf by >2-fold. In our previous
studies with the organic analogues 1 and 2,21,22 we found similar
binding constants for the two receptors, suggesting that the
higher acidity of the sulfonamide is a secondary factor.
No crystals were obtained for X-ray study of any complex
of 3 and 4, but previous studies21,22 with 1 and 2 strongly suggest
that all have a syn-syn binding conformation with two
convergent N-H‚‚‚Cl hydrogen bonds (Figure 2).
Solution and Thin Film FT-IR for Receptors and Adducts.
To compare Cl- binding of 4 and 5 in solution and the solid
state, we examined the solution and thin film32 FT-IR spectra
of the receptors and their adducts (Table 2). Free 4 (10-1 M),
gave νN-H bands at 3360 and 3228 cm-1 (w) for self-associated
N-H. The thin film spectrum shows only the 3228 cm-1 band.
With a slight excess of (n-Bu)4NCl, a new band appears for
N-H‚‚‚Cl- at 3260 cm-1 (thin film, 3258 cm-1).
(33) We have found that typically for association constants of <100 M-1
the hydrogen-bonded band is normally not observed in dilute solution.
(34) Connors, K. A. Binding Constants, 1st ed.; John Wiley & Sons: New
York, 1987.
(35) KaleidaGraph, Version 3.0.2, Synergy Software (PCS Inc.), Reading,
PA 19606; developed by Abelbeck Software Inc.
(36) Schmidtchen, F. P.; Berger, M. Chem. ReV. 1997, 97, 1609.
(32) The thin film is formed by slow evaporation on a NaCl plate of the
same solution used for the solution FT-IR study.

5186 Inorganic Chemistry, Vol. 38, No. 22, 1999
Notes
anhydrous Et2O (55 mL). Ferrocene (3.34 g, 18 mmol) was added and
the mixture refluxed (6 h) and then stirred (12 h). The mixture was
then cooled (-22 °C) and O-benzylhydroxylamine added dropwise over
15 min. The mixture was then warmed to room temperature for 45
min. HCl (30 mL, 0.1 N) was added at 0 °C and the acid layer (now
orange) discarded. Two more aliquots of HCl (30 mL, 0.1 N) were
added, and from the combined green-dark brown extract, an off-white
product was crystallized on addition of excess 12 M NaOH dropwise,
then filtered, and dried in vacuo. The product was spectroscopically
identical to the reported product (1H NMR) (yield 0.75-0.93 g,
21-26%).
N,N′-Bisferrocenyl 1,3-Benzenedicarboxamide (3). Aminoferro-
cene (100 mg, 0.5 mmol) was added to isophthaloyl dichloride (51
mg, 0.25 mmol) in distilled CH2Cl2 (20 mL). Triethylamine (0.05 mL,
0.5 mmoL) was added and the mixture stirred for 3 h. The mixture
was then washed with HCl (3 × 10 mL, 0.1 N), and then with water
(3 × 10 mL). The CH2Cl2 layer was dried with MgSO4. Dropwise
addition of hexanes precipitated a yellow solid (10.0 mg) which was
Figure 4. Cyclic voltammograms of 4 (‚‚‚), 4 + (n-Bu)4NCl (1 equiv)
(---), and 4 + (n-Bu)4NCl (5 equiv) (s). The total concentration of 4
is 5 × 10-4 M. The scan rate is 100 mV/s.
Electrochemical Study (Cyclic Voltammetry). The CVs of
5 × 10-4 M solutions of FeCp2 (standard), 4, and 5 in CH2Cl2
were recorded before and after addition of 1 and 5 equiv of
solid (n-Bu)4NCl (final concentrations 5 and 25 × 10-4 M Cl-).
(n-Bu)4NBF4 (0.1 M) was an inert electrolyte. All the waves
corresponded to quasi-reversible oxidations. In certain cases,19,20
Beer saw an EC mechanistic response, but our compounds and
conditions (including solvent) are somewhat different and 4
binds halides very strongly; in other cases23 Beer saw results
similar to our results. 4 showed a shift of -20.0 mV after
addition of 1 equiv of (n-Bu)4NCl increasing only marginally
for 5 equiv of (n-Bu)4NCl, as expected for anion binding23
(Figure 4). In contrast, control 5 gave only a weak negative
shift (<5 mV) for the solution containing 1 equiv of (n-Bu)4NCl
and no negative shift for the solution containing 5 equiv of
(n-Bu)4NCl, so the two convergent hydrogen-bonding groups
are very important for effective sensing. A small nonspecific
positive potential shift linearly dependent on [Cl-] for the
Cp2Fe standard explains why the voltammograms obtained for
solutions with 5 equiv of chloride for 4 and 5 show no further
increase (4) or reversal (5) of the previously observed negative
shift. The source of this shiftsonly expected in the case of an
interaction with a positive charge39sremains unexplained.
1
filtered and dried in vacuo (7.5% yield). H NMR (CD2Cl2, 19.2 °C):
δ (ppm) 8.58 (s, 1H, ar H-2), 8.04 (d, 2H, ar H-3, J3-1 ) 7.5 Hz), 7.63
(t, 1H, H-1, J1-3 ) 7.6 Hz), 7.42 (br s, 2H, N-H), 4.69 (s, 4H, Fc
H-4), 4.15 (s, 10H, Fc H-5), 4.03 (s, 4H, Fc H-6). Anal. Calcd for
C28H24N2O2Fe2: C, 63.20; H, 4.55. Found: C, 62.93; H, 4.70.
N,N′-Bisferrocenyl 1,3-Benzenedisulfonamide (4). Aminoferrocene
(100 mg, 0.5 mmol) was dissolved in EtOH (20 mL) containing
NaHCO3 (1 g) and MgSO4 (2 g). 1,3-Benzenedisulfonyl chloride (56
mg, 0.25 mmol) dissolved in ethanol (17 mL) was then added dropwise.
The mixture was refluxed for 20 h. The resulting dark brown solution
was cooled to room temperature, and after filtration of MgSO4 and
NaHCO3, the ethanol was evaporated. The dark brown residue was
redissolved in CH2Cl2 and the solution washed with HCl (3 × 20 mL,
0.1 N, or until the aqueous layer appeared colorless). The organic layer
was then washed with H2O (3 × 20 mL) and dried with MgSO4. After
filtration, slow evaporation of the CH2Cl2 gave a bright yellow powder
which was filtered and dried in vacuo (66.1 mg, 54% yield). 1H NMR
(CD2Cl2, 19.2 °C): δ (ppm) 8.19 (s, 1H, ar H-2), 7.75 (dd, 2H, ar H-3,
J3-1 ) 7.8 Hz, J3-2 ) 0.9 Hz), 7.50 (t, 1H, H-1, J1-3 ) 7.9 Hz), 6.38
(br s, 2H, N-H), 4.21 (s, 4H, Fc H-4), 4.11 (s, 10H, Fc H-5), 4.03 (s,
4H, Fc H-6). FT-IR (thin film, cm-1): 3228, 3090, 1492, 1178, 1157.
Anal. Calcd for C26H24N2S2O4Fe2: C, 51.70; H, 4.00; N, 4.64. Found:
C, 51.55; H, 3.99; N, 4.54.
(N-Ferrocenyl)-3-(ethylcarboxylate) Benzene-1-carboxamide (5).
The compound was prepared as above but from isophthaloyl dichloride
(51 mg, 0.25 mmol) and with 16 h of reflux. The product precipitated
Conclusion
1
as an orange powder (22.9 mg 24% yield). H NMR (CD2Cl2, 19.2
The new diferrocenyl sulfonamide receptor 4 is capable of
anion binding and electrochemical sensing. With its two
convergent N-H‚‚‚Cl H-bonds, disulfonamide 4 has a much
higher anion affinity than the monoamide analogue 5 (NMR,
e-chem).
°C): δ (ppm) 8.42 (s, 1H, ar H-2), 8.20 (d, 1H, ar H-3, J3-5 ) 7.5
Hz), 8.06 (d, 1H, ar H-4, J4-5) 7.3 Hz), 7.59 (t, 1H, H-5, J5-4,3 ) 7.6
Hz), 7.38 (br s, 1H, N-H), 4.74 (s, 2H, Fc H-6), 4.40 (q, 2H, H-8
-CH2-, J8-9 ) 7.0 Hz), 4.19 (s, 5H, Fc H-7), 4.07 (s, 4H, Fc H-8),
1.42 (t, 3H CH3-H-9, J9-8 ) 7.0 Hz). FT-IR (thin film, - cm-1):
3263, 3093, 1719, 1600, 1487. Anal. Calcd for C20H19NO3Fe: C, 63.70;
H, 5.08; N, 3.71. Found: C, 62.81; H, 4.91; N, 3.60. High-resolution
mass spectrometry (FAB): calcd 377.071 433, found 377.071 700.
Experimental Section
General Procedures. Solvents (analytical grade) and materials
(Aldrich Chemical Co.) were used as received. 1H NMR spectra
(GE-Omega 300 MHz) were referenced to residual solvent. FT-IR
spectra were recorded on a MIDAC M1200 FT-IR spectrophotometer.
Elemental analyses were performed by Atlantic Microlab Inc. (Norcross,
GA) or Robertson Microlit Laboratories Inc. (Madison, NJ). High-
resolution MS were obtained by Dr. S. Mullen (University of Illinois,
Urbana-Champaign). Electrochemical data were obtained using a
Princeton Model 243 potentiostat. O-Benzylhydroxylamine was pre-
pared25 from the hydrochloride and distilled.
1H NMR Titration Experiments. Solutions of 4 and 5 in CD2Cl2
(5 × 10-4 to 1 × 10-3 M) were titrated by the standard procedure
reported in ref 22, but dried (n-Bu)4NCl was used as a titrant (1.0 ×
10-2 and 1.0 × 10-1M).
Cyclic Voltammetry. Solutions (5 × 10-4 M) of 4, 5, and ferrocene
(control) were prepared in CH2Cl2 containing 0.1 M (n-Bu)4NBF4 as
supporting electrolyte. (n-Bu)4NCl was used as a Cl- source. The CVs
were recorded using a Pt working electrode and a Ag/AgCl reference
electrode before and after the addition of solid (n-Bu)4NCl in molar
ratios of 1:1 and 1:5.
Aminoferrocene. N-Butyllithium (15.9 mL of 2.5 M solution in
hexanes, 0.0339 mmol) was added using a gas-tight syringe to
Acknowledgment. We thank Professor Gary W. Brudvig
and Olaf Kievit for their kind help and the National Science
Foundation for funding.
(37) Seel, C.; de Mendoza, J. In ComprehensiVe Supramolecular Chemistry;
Vo¨gtle, F., Ed.; Pergamon: London, 1996; Vol. 2, p 519.
(38) Fan, E.; Van Arman, S. A.; Hamilton, A. D. J. Am. Chem. Soc. 1993,
115, 369.
(39) Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim, New York, 1995.
IC990813S