Anion Recognition by Redox-Responsive Ditopic Bis-Cobaltocenium

Abstract published in Advance ACS Abstracts, June 1, 1995. ... U.K. Electrochemical measurements were carried out using an E.G. and G. Princeton Appli...
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Organometallics 1995, 14, 3288-3295

3288

Anion Recognition by Redox-Responsive Ditopic Bis-CobaltoceniumReceptor Molecules Including a Novel Calix[4]arene Derivative That Binds a Dicarboxylate Dianion Paul D. Beer,* Dusan Hesek, Justine E. Kingston, David K. Smith, and Sally E. Stokes Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.

Michael G . B. Drew Department of Chemistry, The University, Whiteknights, P.O. Box 224, Reading RG6 2AD, U.K. Received February 23, 1995@

A series of novel ditopic bis-cobaltocenium receptor molecules containing alkyl, aryl, and calix[4]arene spacers have been synthesized via the reaction of the new synthon l4ethylcarboxy)-1’-(chlorocarbony1)cobaltocenium chloride (3)or 1-(chlorocarbony1)cobaltocenium chloride (9) with the appropriate diamine. Proton NMR halide anion coordination studies reveal that the ethyl- (4), propyl- (5), and butyl-linked (6) derivatives form 1:l stoichiometric complexes in acetonitrile solutions. Stability constant determinations suggest that the ethyl derivative 4 exhibits selectivity for the chloride anion in preference to bromide or iodide. Receptors containing larger aryl (7,8,10)and alkylamino (11)spacers form complexes of 2:l halide anion:receptor stoichiometry. An X-ray crystal structure of the bis-cobaltocenium calix[4]arene derivative 15 is described. This receptor forms extremely stable 1:l anion complexes with chloride, bromide, and HzP04- in dimethylsulfoxide solutions and with the dicarboxylate dianion adipate in acetone. All the bis-cobaltocenium systems were found to display electrochemical recognition of varied anion guests, as shown by cyclic voltammetric experiments. Receptor 15 was also found to redox-respond to the presence of adipate. Introduction The synthesis of positively charged1-2or neutra11x3 electron deficient abiotic receptor molecules designed to coordinate anionic guest species is an area of intense current research activity. This is because anions are known to play numerous fundamental roles in chemical and biochemical processes. For example, the majority of enzymes bind anions as either substrates or cofact o r ~and , ~ many anions act as nucleophiles, bases, redox agents, and phase transfer catalysts. We have recently reported the synthesis of the first redox-responsiveclass of anion receptor based on the redox-active, pHAbstract published in Advance ACS Abstracts, J u n e 1, 1995. (1)(a)Dietrich, B. Pure Appl. Chem. 1993,65,1457. t b Schmidtch~ en, F. P. Nachr. Chem. Tech. Lab. 1988,36,8. 12)ra)Park, C. H.; Simmons, H. E. J . Am. Chem. SOC.1968,90, 2431. ( b ) Lehn, J.-M.; Sonveaux, E.; Willard, A. K. J . A m . Chem. SOC. 1978, 100, 4914. (c) Dietrich, B.; Hosseini, M. W.; Lehn, J.-M.; Sessions, R. B. J . Am. Chem. SOC.1981, 103, 1282. ( d ) Gelb, R. I.; Lee, B. T.; Zompa, L. J. J . Am. Chem. SOC.1986,107,909. (el Heyer, D.; Lehn, J.-M. Tetrahedron Lett. 1986,27,5869. (DHosseini, M. W.; Lehn, J.-M. Helu. Chim. Acta. 1986,69,587. (g) Hosseini, M. W.; Blacker, A. J.; Lehn, J.-M. J . Am. Chem. SOC.1990,112,3896. ( h ) Sessler, J. L.; Furuta, H.; Kral, V. Supramol. Chem. 1993,1, 209 and references therein. 13)la) Katz, H. E. Organometallics 1987,6,1134. (bJ Wuest, J. D.; Zacharie, B. J . Am. Chem. SOC.1987,109,4714. I C ) Newcomb, M.; Horner, J. H.; Blanda, M. T. J . Am. Chem. SOC.1987,109,7878. ( d ) Jung, M. E.; Xia, H. Tetrahedron Lett. 1988,29, 297. le) Yang, X.; Johnson, S. E.: Khan, S. I.; Hawthorne, M. F. J . Am. Chem. SOC.1993, 115, 193. fh! Rudkevich, D. M.; Brzozka, Z.; Palys, M.; Visser, H.; Verboom, W.; Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1994, 33, 467-468. lil Scheerder, J.; Fochi, M.; Engbersen, J . F. J.; Reinhoudt, D. N. J . Org. Chem. 1994,59,7815. (4)Lang, L. G.; Riordon, J. F.: Vallee, B. L. Biochemistry 1974,13, 4361.

0

0

R = Alkyl, Aryl. calix[4]arene spacer

R = C02Et, H Figure 1. Schematic representation of anion recognition by a ditopic bis-cobaltocenium receptor. independent positively charged cobaltocenium moiety. Simple acyclic amide-linked cobaltocenium host molecules have been demonstrated to bind and electrochemically recognize halide, hydrogen sulfate, and dihydrogen phosphate guest anions5 via favorable mutual electrostatic interactions and ubiquitous amide -CONH- hydrogen-bonding effects. In an effort to impart selectivity and enhance complex stability for this class of anion receptor we describe here the synthesis, anion coordination, and electrochemical properties of novel ditopic bis-cobaltocenium receptor molecules. The two positively charged metallocene centers, linked via various alkyl, aryl, and calixL41arene spacers, may cooperate in the molecular recognition of mono- or dianionic guest substrates (Figure 1).

0276-733319512314-3288$09.00/00 1995 American Chemical Society

Anion Recognition by Bis-Cobaltocenium Receptors

Experimental Section Instrumentation. Nuclear magnetic resonance spectra were obtained on a Bruker AM300 instrument using the solvent deuterium signal as internal reference. Fast atom bombardment mass spectrometry was performed by the SERC mass spectrometry service a t University College, Swansea, U.K. Electrochemical measurements were carried out using an E.G. and G. Princeton Applied Research 362 scanning potentiostat. Elemental analyses were performed at the Inorganic Chemistry Laboratory, University of Oxford. Solvent and Reagent Pretreatment. Where necessary, solvents were purified prior to use and stored under nitrogen. Acetonitrile was predried over class 4A molecular sieves (4-8 mesh) and then distilled from calcium hydride. Unless stated to the contrary commercial grade chemicals were used without further purification. 1,l’-Bis(ethylcarboxy1)cobaltocenium hexafluorophosphate ( 1),61-(chlorocarbony1)cobaltoceniumchloride (9),6and 25,27dihydro~-26,28-dimethoxy-l1,23-dinitrocalix[4larene ( 13)’were prepared according to literature procedures. Syntheses. NJV’-Bis(1-carbonyl-1’4ethy1carboxy)cobaltoceniumyl)-1,2-diaminoethanebis(hexafluorophosphate)(4),N f l bis( 1-carbonyl-1’4ethylcarboxy)cobaltoceniumyl)-l,3-diaminopropane bis(hexafluorophosphate) ( 5 ) ,and N,”-bis( l-carbonyll’-~ethylcarboxy)cobaltoceniumyl~-l,4-diaminobutane bis(hexafluorophosphate) (6)were prepared using the following procedure. 1,l’-Bis(ethy1carboxy)cobaltocenium hexafluorophosphate (0.5 g, 1 mmol) was dissolved in ethanol with 1equiv of KOH (0.058g, 1mmol). The mixture was then refluxed for 6 h. The color was observed to change from yellow to red to green over this time. The mixture was evaporated to dryness, and the residue was dissolved in water (40 mL). The aqueous solution was filtered, and the filtrate acidified. The water was then removed in vacuo to yield cobaltocenium “monoacid-monoester” 2, which was thoroughly dried in vacuo and then refluxed with thionyl chloride for 12 h. The mixture was observed t o change color from yellow to green. The thionyl chloride was removed in vacuo, and the green product “mono acid chloride-monoester” 3 was dried in vacuo. A solution of this product in dry CH3CN was then added dropwise to a stirred solution of half an equivalent of the appropriate diamine in CH3CN. A color change was observed, and a precipitate formed. The solution was filtered and then evaporated to dryness. The resultant solid product was columned on Sephadex using MeOWCH3CN (50/50)as eluent. To each column fraction were added a few drops of aqueous ammonium hexafluorophosphate solution, and the products slowly crystallized as the solvent evaporated. Yields: 4, 2596, 5, 15%, and 6,20%. Analytical data for 4. ‘H NMR (CD3CN): d 1.38 (t,J = 7.1 Hz, 6H, CHZCH~), 3.53 (d, J = 5.7 Hz, 4H, N-CHz), 4.36 (q, J = 7.1 Hz, 4H, OCHZCH~), 5.84 (dd, J = 2.1 Hz, 4H, Cp H), 5.86 (dd, J = 2.1 Hz, 4H, Cp H), 6.09 (dd, J = 2.1 Hz, 4H, Cp H), 6.13 (dd, J = 2.1 Hz, 4H, Cp H), 7.47 (s, 2H, N-H). Anal. Found: C, 38.97; H, 3.33; N, 3.52. Calcd for coZc30H3zNz06PzFiz: C, 38.98; H, 3.49; N, 3.03. Ir v,,dcm-’: 3441 (N-H), 1728 (C=o,,,,), 1667 (c=oam&), 838 (PFs-). FAB MS mlz: 779 (M - PF#, 634 (M - 2PF6)+. Data for 5. ‘H NMR (CD3CN): d 1.37 (t, J = 7.2 Hz, 6H, CHzCHz), 3.42 (dt, J = 6.4 Hz, NCHz), 4.36 (q,J = 7.2 Hz, 4H, OCHZCH~) 5.85 (dd, J ( 5 )( a ) Beer, P. D.; Hesek, D.; Hodacova, J.; Stokes, S . E. J. Chem. Soc., Chem. Commun. 1992,270. tb, Beer, P. D.; Hazlewood, C.;Hesek, D.; Hodacova, J.; Stokes, S. E. J . Chem. Soc., Dalton Trans. 1993,1327. (CJ

Beer, P. D.; Drew, M. G. B.; Hazlewood, C.: Hesek, D.; Hodacova,

J.; Stokes, S. E. J . Chem. SOC.,Chem. Commun. 1993,229. rd) Beer, P. D.; Dickson, C. A. P.; Fletcher, N.; Goulden, A. J.; Grieve, A.; Hodacova, J.; Wear, T. J . Chem. Soc., Chem. Commun. 1993,828. ( e ) Beer, P. D.; Drew, M. G. B.; Graydon, A. R.; Smith, D. K.; Stokes, S . Dalton Trans. 1995,403. E. J. Chem. SOC., ( 6 )Sheats, J. E.; Rausch, M. D. J. Org. Chem. 1970,35,3245. (71 Loon, J.-D.; Arduini, A.; Coppi, A,; Verboom, W.: Pochini, A,; Ungaro, R.; Harkenna, S.; Reinhoudt, D. N. J. Org. Chem. 1990,55, 5639.

Organometallics, Vol. 14,No. 7, 1995 3289 = 2.1 Hz, 8H, Cp H), 5.88 (dd, J = 2.1 Hz, 4H, Cp H),6.13 (dd, J = 2.1 Hz, 4H, Cp H), 7.53 (s,2H, N-H). I3C NMR (CDy CN): b 14.27 (CHzCHs),29.23(NCHzCHz),37.96(NCHz),63.72 ( O C H ~ C H ~86.00 ), ( c p C-H), 87.47 ( c p C-HI, 88.04 ( c p C-H), 88.73 ( c p C-H), 91.4 ( c p c-c), 96.4 ( c p c-c), 161.4 (C=O), 163.4 (C=O). Anal. Found: C, 37.33; H, 3.43; N, 3.60. Calcd for C O Z C D ~ H ~ ~ N ~ C,~38.30; B P ~ H, F ~3.32; Z : N, 3.07. Ir vmU/cm-’: 3438 (N-HI, 1733 (C=Oester), 1678 (C=oam,de), 836 (PFs-). FAB MS m/z: 793 (M - PF6)+,648 (M - 2PFs)*. Data for 6. ‘H NMR (CD3CN): b 1.37 It, J = 7.2 Hz, 6H, CHzCHs), 1.66 (t, 4H, NCHzCHz), 3.37 (dt, 4H, NCHz), 4.35 (q, J = 7.2 Hz, 4H, OCH~CHS), 5.83 (m, 8H, Cp HI, 6.10 (m, 8H, Cp HI, 7.40 (s, 2H, N-H). I3C NMR (CDsCN): b 14.25 (CHZCH~), 27.09 ( N C H ~ C H ~40.42 ) , (NCH~), 63.69 ( O C H ~ C H ~86-00 ), ( c p C-H), 87.40 ( c p C-H), 87.95 ( c p C-H), 88.60 ( c p C-H), 91.40 (Cp C-C), 96.57 (Cp C-C), 161.12 (C-O), 163.35 (C-0). Anal. Found: C, 39.72; H, 3.68; N, 3.14. Calcd for COZC~ZH ~ ~ N z ~ ~ Pc ,z40.35; F ~ z H, : 3.81; N, 2.94. IR v,,/cm-’: 3436 (N-H), 1729 (C=Oe8ter),1668 (C=Oamlde), 834 (PFs-). FAB MS m/z: 807 (M - PF6)+, 662 (M - 2PF.5)+.

N,”-Bis( l-carbonyl-l’-(ethylcarboary)cobaltoceni)4,4’-diaminodiphenylmethaneBis(hexafluorophosphat4 (7). 4,4‘-Diaminodiphenylmethane(0.085 g, 4.2 x mol) was dissolved in dry CHsCN (60 mL) under a nitrogen atmosphere. To this solution was added 1-(ethy1carboxy)-1’(ch1orocarboxy)cobaltocenium chloride (3)(0.39 g, 8.4 x mol) in dry CH&N (50 mL) dropwise and under nitrogen. Once addition was complete, the mixture was stirred a t room temperature for 18 h. After this time the mixture was filtered to yield a small amount of cream-colored powder and a golden yellow filtrate. The filtrate was evaporated to dryness to give the crude product, which was purified by column chromatography on Sephadex LH20 using an eluting solvent system of CH&N/MeOH ( 1 : l j . To each of the seven fractions collected from the column were added a few drops of a dilute aqueous solution Of NH4PF6. On standing, the pure product crystallized out (as the more volatile solvent evaporated) as goldlyellow mol, yield: 45%). ‘H NMR (CD3crystals (0.20 g, 1.9 x CN): b 1.26 (t,J = 7.7 Hz, 6H, OCH2CH3), 3.99 (s,2H, ArCHzAr), 4.23 (q, J = 7.8 Hz, 4H, OCHZCH~), 5.87 (m, 8H, Cp H), 6.14 (t,J = 2.3 Hz, 4H, Cp H), 6.25 (t, J = 2.3 Hz, 4H, Cp H), 7.28 (d, J = 9.4 Hz, 4H, Ar H), 7.66 (d, J = 9.4 Hz, 4H, Ar H), 8.78 (s, 2H, N-H). I3C NMR (75.42 MHz, CD3CN): d 14.1 (CHZCH~), 41.2 (ArCH2Ar), 63.7 (CHZCH~), 86.2, 87.5, 88.1, a a . 7 ( c p c - ~ ) 91.5,97.0(cpc-c=0), , 1 2 ~ 7 , 1 3 0 .(A~c-H), 1 137 (Ar C-CHz), 139.5 (Ar C-N), 159.5, 163.0 tC=O). Anal. Found: C, 46.03; H, 3.7; N, 2.90. Calcd for C ~ & ~ N Z O ~ ConPaFlz: C, 46.35; H, 3.6; N, 2.64. IR v,,,/cm-’: 3410 (N-H), 1723 (C==Oester), 1684 (C=Oamlde), 852 (PF6-). FAB MS mlz: 772 (M - 2PFs)”+,917 (M - PFs)+.

N,”-Bis( l-carbonyl-l’-(ethylcarboxy)cobaltoceniu)4,4’-diaminodiphenylEther Bis(hexafluorophosphate) (8). 4,4’-Diaminodiphenyl ether (0.042 g, 2.1 x mol) was dissolved in dry CH3CN (50 mL) under a nitrogen atmosphere. To this solution was added 14ethy1carboxy)-1’4chlorocarboxy)cobaltocenium hexafluorophosphate (3)(0.2 g, 4.3 x mol) in dry CH&N (50 mL) dropwise and under nitrogen. Once addition was complete, the mixture was stirred a t room temperature for 24 h. After this time the mixture was filtered to yield a small amount of brown-colored powder and a golden brown filtrate. The filtrate was evaporated to dryness t o give the crude product, which was purified by column chromatography on Sephadex LH20 using an eluting solvent system of CH&N/MeOH (1:lj. Four major bands were eluted (yellow, orange, mid-brown, and r e a u r g a n d y ) , and to each of the fractions collected from the column were added a few drops of a dilute aqueous solution of NH4PF6. On standing, the pure product crystallized out of the last two fractions ( a s the more volatile solvent evaporated) to give r e a r o w n crystals (0.053 mol, yield: 23%). ‘H NMR (CDaCN): b 1.25 (t, J g, 5 x = 7.8 Hz, 6H, OCH~CHS), 4.23 (q, J = 7.8 Hz, 4H, OCHnCH3), 5.88(m,aH,CpH),6.14(t,J=2.22Hz,4H,CpH),6.26(t, J

3290 Organometallics, Vol. 14, No. 7, 1995

Beer et al.

[4larene 14 (0.49g, 1"011 was dissolved in dry DMF ( 5 mLj, = 2.4 Hz, 4H, Cp H), 7.27 (d, J = 7.6 Hz, 4H, Ar Hi, 7.66 (d, and acetonitrile ( 15 mL) was slowly added under nitrogen to J = 7.6 Hz, 4H, Ar H), 8.88 (s, 2H, N-HI. 13C NMR (75.42 14 chlorocarbonyl Jcobaltocenium chloride. The temperature MHz, CDsCN): d 14.1 (CH*CHs),63.7 tCH:!CH2), 86.1, 87.5, was raised to 40 "C for 0.5 h, and then triethylamine (0.45 87.9,88.6 (Cp C-H), 91.5, 97.0 (Cp C-C=OJ, 116.2, 123.4 (Ar ~ Lwas I added. The dark red solution was stirred for 5 h a t C HI, 130.9 (Ar C-OJ, 155.3 (Ar C-N), 159.4, 161.0 tC=O). room temperature. Methanol (10 mL) was added, and the Anal. Found: C, 44.48; H, 3.34; N, 2.85. Calcd for volatile components were evaporated under reduced pressure. C40H3&T207C02P2F12:C, 45.13; H, 3.41; N, 2.63. IR vma,/cm-': To the black oil was added water (80 mL), and the solid 3398 (N-H), 1728 (C=Oester), 1674 ( c = o a m , d e ) , 840 (PF6-1. precipitate was filtered off. After dissolving the crude sample FAB MS mlz: 774 (M - 2PFd', 919 (M - PFs)+. N,"-Bis( l-carbonylcobaltoceniumyl)-4,4'-diamino- in a minimum amount of DMF, the liquid phase was treated with NaPFs (0.3 g) and the mixture was filtered through a diphenylmethane Bis(hexafluorophosphate) (10). 4,4'short silica gel column with acetonitrile/dichloromethane (4: Diaminodiphenylmethane (0.15g, 6 x mol) and four drops 1 as eluent to give an orange powder of 15as the main fraction of triethylamine were dissolved in dry CH3CN (60 mLJ and in 61% (0.73 g ) yield. IH NMR (DMSO-&): 8 3.47 (d, J = J = stirred under a nitrogen atmosphere. To this solution was 13 Hz, 4H, CH2ie,),3.95 (s, 6H, CHs), 4.24 (d, 4H, CH2i,,), 5.90 added 1-(chlorocarbony1)cobaltoceniumchloride (9)(0.5 g, 1.3 (s, 10H, CH-CPJ,5.97 it, J = 2.0 Hz, 4H, CH-cp), 6.63 (dd, J = mmol) in CHsCN (50 mL), dropwise and under nitrogen. On 7.4 Hz, J = 7.6 Hz, 2H, CH-aromJ, 7.02 (d, 4H, CH-arom), 7.47 addition of the acid chloride, the solution changed from (s, 4H, CH-aromJ, 8.07 ( s , 2H, OH), 10.17 (s, 2H, -NHCO-1. colorless to yellow/orange and an orange precipitate formed. I3C NMR (DMSO-&): d 153.4, 149.6 (Ar C), 133.1, 129.3 (Ar The mixture was stirred for 12 h, and the crude product was Ci, 128.9 (Ar C), 127.0 (Ar C), 125.1 (Ar C), 121.3 (Ar C), 94 isolated as an orange solid. The crude product was taken up (Cp Ci, 85.9 (Cp C), 85.5 (d, Cp C), 84.0 (Cp C), 63.6 (CHs), in hot water, and a saturated solution of NH4PFs was added 30.5 (CH2). Anal. Found: C, 51.98; H, 3.84; N, 3.06. Calcd to precipitate the pure product as a bright orange powder (0.26 for C&&02N206P2F12: C, 52.30; H, 3.86; N, 2.40. FAB MS mol, yield: 47%). 'H NMR (CDsCNJ: b 3.98 ts, g, 2.8 x miz = 1192 (M+). 2H, ArCH2Ar), 5.60 (s, 10H, Cp HI, 5.74 (t, J = 2.3 Hz, 4H, CpH),6.13(t,J=2.3Hz,4H,CpH),7.28td,J=9.3Hz,4H, Crystal Structure Determination of 15. Crystal data for 15*2MeCN, C O ~ C S ~ N ~ O ~ HM,~ Y P 1243.2, ~ F ~ ~ ,a = Ar H), 7.65 (d,J = 9.3 Hz, 4H, Ar HI, 8.76 (s, 2H, N-H). Anal. Found: C, 45.72; H, 3.49; N, 3.31. Calcd for C ~ ~ H ~ O N ~ O : !20.117(16) A, b = 8.977(9)A, c = 34.288(23)A, p = 118.7(1)", U = 5431.4 A:j, F(000J = 2536, dm = 1.50-g ~ m - dc ~= , 1.52 g CoZP2F12: C, 45.77; H, 3.29; N, 3.05. FAB MS miz: 773 tM 2 = 4, Mo K radiation (A = 0.7107 A), p(Mo KaJ = 7.94 PF6)-, 628 (M - 2PFs)'. N,"-Bis( 1-carbonylcobaltoceniumy1)-N-methyl-N-pro- cm-', spacegroup C2/c. pylamine- 1,3-propanediamineBis(hexafluorophosphate) A crystal of approximate size 0.3 x 0.3 x 0.3 mm3 was mounted on a STOE-2 diffractometer to be rotated around the (11). Bis(N-methyl-N-propylamine 1-1,3-propanediamine(0.07 mol) a axis. Data were measured via w scan with a 28 maximum g, 3.24 x mol) and triethylamine (0.06 g, 5.9 x were dissolved in dry CHsCN (60 mL1 and stirred under a of 50". Background counts were for 20 s and a scan rate of nitrogen atmosphere. To this was added 14 chlorocarbony1)0.0333"/s was applied to a width of 11.5 + sin Idtan 0 ) . No cobaltocenium chloride (9) (0.24 g, 6.0 x mol) in CH3CN decay in intensity was observed for the standard reflections. (40 mL), dropwise and under nitrogen, and the yellow solution A total of 5200 independent reflections were measured of which that resulted was stirred overnight. The solvent was removed 1926 with Z > 28U) were used in subsequent calculations. The t o give the crude product as a yellow powder. The crude structure was solved by heavy atom methods. The cation product was purified by column chromatography using Sephacontains crystallographically imposed C:! symmetry. Hydrogen dex LH20 and CH3CN/MeOH (4:lJ as eluting solvent. Two atoms on the cation were placed in calculated positions. All fractions were collected, brown and bright yellow. The yellow non-hydrogen atoms in the cation and anion were refined fraction from the column was evaporated t o dryness, taken anisotropically. The acetonitrile solvent was given an ocup in hot water, and a saturated solution of NH4PF6was added cupancy of 5 0 8 and refined isotropically. The structure was refined by full matrix least squares with a weighting scheme to precipitate the pure product as a bright yellow powder (0.17 mol, yield: 80%). lH NMR tCDsCNJ: d [1.97 g, 1.8 x u: = l / [ 0 2 ( F+ ) 0.003F21. In the final cycle of refinement the (mJ, 2.87 (sj, 3.15 (t,J = 8 Hz), 3.43 it, J = 6.8 Hz), 24H, CH:! maximum shift error ratio was 0.1. In the final difference and CH31, 5.72 (s, 10H, Cp H), 5.78 (t, J = 2 Hz, 4H, Cp Hi, Fourier map, maximum and minimum peaks were a t 0.75 and 6.06 (t, J = 2 Hz, 4H, Cp H), 7.48 is, 2H, N-H). 13C NMR -0.53 e A-", respectively. Calculations were performed using (75.42 MHz, CDsCN): d 18.6 (CHs),23.6,36.6,52.1,53.4(CHz), SHELX7B8and some of our own programs on the Amdahl5870 83.8, 85.7, 85.9 (Cp C-H), 93.7 (Cp C-C=O), 161.6 (C=O). Computer at the University of Reading. The final R value was Anal. Found: C, 42.73; H, 4.01; N, 4.42. Calcd for 0.079 ( R , = 0.077). Positional coordinates, molecular dimenCs3H44N402C02P2F12:C, 42.32; H, 4.64; N, 4.74. IR v,,Jcm-l: sions, thermal parameters, and hydrogen atom positions are 3412 (NH), 1647 (C=O), 834 (PF6-J. FAB MS miz: 646 (M provided in the supporting information (formerly known as - 2PFs)', 791 (M - PFs)'. supplementary material). 11,23-Diamino-25,27-dihydroxy-26-28-dimethoxycalix[rllarene (14). Hydrazine hydrate was slowly added to a Results and Discussion stirred mixture of 13 ( 1.08 g, 2 mmol) and wet Raney nickel in methanol at 60 "C. After the reaction had changed to a Syntheses. 1,l'-Bis(ethy1carboxy)cobalteniumhexareddish color, the Raney nickel was separated and the filtrate fluorophosphate ( 1l6 was selectively monohydrolyzed by was concentrated to dryness in vacuo. The residue was addition of 1equiv of potassium hydroxide in refluxing dissolved in DMF and filtered with charcoal, and the volatile ethanol, Upon reaction with thionyl chloride the estercomponents were evaporated under reduced pressure. The 2 was converted to the ester-acid acid compound solid was treated with methanol to give a light red powder of chloride derivative 3. A 2 equiv amount of compound 3 14 in 55-70% yield. 'H NMR (CD2C12): 3.28 (d, J = 13 Hz, in an acetonitrile solution was added dropwise to 1equiv 4H, CH21,,), 3.95 (s,6H, CHaj, 4.26 td, 4H, CHala,),6.47 (s,4H, CH-arom),6.77 (t,2H, CH-arom),6.94 (d, 4H, J = 7.6 Hz, CHof an appropriate diamine in acetonitrile solution to arom),7.03 (br, 6H, N-H, 0-HJ. I T NMR (DMSO-&): 153.4, produce the respective crude ditopic bis-cobaltocenium 143.8 (Ar Ci, 140.7 CAr Ci, 128.6 (Ar Ci, 128.4 (Ar C), 124.8 receptor. This was typically purified via Sephadex (d, Ar CJ, 114.5 (Ar Ci, 63.2 (CHsj, 30.6 (CH2). 11,23-Bis~~~cobaltoceniumyl~carbonyl~amino)-25,27-di(81Sheldrick, G. M. SHELX-76. Programs for Crystallographic hydroxy-26,28-dimethoxycalix[4] arene ( 15). AminocalixCalculatiom: University of Cambridge: Cambridge, England. 1976.

Anion Recognition by Bis-Cobaltocenium Receptors

Organometallics, Vol. 14,No. 7,1995 3291 Scheme 1

&OEt PF;

(i) leq. KOH / EtOH

&OEt

* PFd Co'

Co' (ii) H'/ H20

0

1

(2)

SOClZ

dOEt PFi

Co'

=fC1 (3)

O

1

(i) 0.5 eq. HzNRNH2/

0

CHJCN

0

Scheme 2

column chromatography and converted to the bis(hexafluorophosphate) salt product using aqueous NH4PF6 (Scheme 1). The overall yields from 1 ranged between 10% and 25%, and all these new compounds 4-9 gave analytical and spectroscopic data in accordance with the proposed structures (See Experimental Section). The related ditopic receptors 10 and 11 were prepared in an analogous fashion via condensation of 2 equiv of (chlorocarbony1)cobaltoceniwn chloride (916with 1equiv of the respective diamine (Scheme 2). Sephadex column chromatography and conversion to the hexafluorophosphate salts gave 10 and 11 in 47% and 80% yields, respectively. The calixarenesg are attractive host molecules on which to construct additional recognition sites for target guests 2. Although the calix[4larene host structural unit has been modified at the lower rim for the recognition of metal cations,1° the design and synthesis of calix[4larene anion receptors is still relatively rare.l' The reaction of 1,3-dimethoxy-calix[4larene127 with nitric acid and acetic acid in dichloromethane produced the dinitro calixr41arene derivative 137in 50% yield. Reduction of 13 using Raney nickel and hydrazine hydrate gave the new diamino compound 14 in 70% yield. Condensation of 14 and 2 equiv of g6 in a dimethylformamide-acetonitrile solvent mixture ini-

tially produced a crude dark-red oil which, on treatment with an excess amount of sodium hexafluorophosphate

(9) Gutsche, C. D.Calixarenes; Stoddart, J. F., Ed.; Monographs in Supramolecular Chemistry; The Royal Society of Chemistry: Cambridge, England, 1989; Vol. 1.

(10) Ungaro, R.; Pochini, A. Calixarenes, A Versatile Class of Macrocyclic Compounds; Vicens, J., Bohmer, V., Eds.; Kluwer: Dordrecht, The Netherlands, 1990; p 133 and references therein.

&C]

( i ) 0.5eq.HzNRNH2/

Ieq. Et3N (ii) NH4PF6

R=

+o-

(10)

Beer et al.

3292 Organometallics, Vol. 14, No. 7, 1995 Scheme 3 NO2

02y

/

the Me

J

I

y

2

1

Me the

(9) ii, NaPFs

1 P F i co+

Co'

I

PF,'

I

c=o

o=c

I NH

I HN

I

I

Me Me

followed by silica gel column chromatography (acetonitrile-dichloromethane, 4:1), afforded 15 as a red crystalline solid in 61% yield (Scheme 3). X-ray Structural Investigation of 15. Crystals of 15 suitable for an X-ray structural determination were grown from an acetonitrile-methanol solvent mixture (Figure 2). The calix[4larene has the cone conformation stabilized by two 0-H 0 hydrogen bonds (2.80 A) around the bottom of the cone. The calix[4]arene is asymmetric in that the unique Car-Car-CH2-CH2 torsion angles are -81.4", -110.2", 98.5", and -71.5'. At the top of the cone the Ph-NH-CO-CSHS moieties are closely planar with torsion angles around the Car-

...

ill) ( a )Beer, P.D.; Chen, Z.; Goulden,A. J.;Graydon,A. R.; Stokes, S. E.; Wear, T. J . Chem. SOC.,Chem. Commun. 1993, 1834. ib) Morzherin, Y.;Rudkevich, D. M.; Verboom, W.; Reinhoudt, D. N. J . Org. Chem. 1993,88, 7602. ( C I Beer, P.D.; Chen, Z.; Goulden, A. J.; Grieve, A.; Hesek, D.; Szemes, F.; Wear, T. J . Chem. Soc.. Chem. Commun. 1994,1269.

N, N-C(O), and C(O)-Car bonds of -18.3", 178.9", and 3.6", respectively. The acetonitrile solvent molecules are positioned inside the cavity as shown in Figure 2 between the unattached cyclopentadienyl ring and the calixarene. The closest contacts are from N(81) to the cyclopentadienyl ring [C(61) at 3.44 and C(62) at 3.30 A] and to a phenyl ring of the calixarene [C(32) 3.42 and C(33) at 3.54 AI. In the Co(cyclopentadieny1h moiety, the Co-C distances are as expected, ranging from 1.94 to 2.06 A. The two rings are staggered across the metal atom. Anion Coordination Studies and Stability Constant Determinations from 'H NMR Titration Investigations. The addition of tetrabutylammonium halides to deuterated acetonitrile lH NMR solutions of 4-6 resulted in significant shifts of the respective protons of all three receptors. Remarkable downfield shifts of the amide and cyclopentadienyl protons are

Anion Recognition by Bis-Cobaltocenium Receptors

Organometallics, Vol. 14,No. 7, 1995 3293

3

Figure 2. Structure of 15 2MeCN.

.

1.5f

.

I , ,

-.

h ' " ' I ' " ' I " " I ' ' ' ~ i ' " ~ ~ 0

1

3

2

4

5

8.5

equivalmu added

Figure 3. Proton NMR titration curves of 4 with halide anions in CD3CN. Table 1. Stability Constant Data for 4-6 and Halide Anions in CD&N receptor 4 5 6

c1-

Wdm3 mol-' Br-

2500 1300 280

330 270 260

receptor 7 7

112)Hynes, M. J. J. Chrm. SOC.,Dalton Trans. 1993,311

I

I

I

I

k

Equivalents of anion added

I

k

Is

Table 2. Stability Constant Data for 7,8, 10, and 11 and Halide Anions in CDsCN"

I-

especially noteworthy, and the resulting titration curves suggest a stoichiometry of 1:1ditopic bis-cobaltocenium receptor:halide anion (Figure 3). The computer program EQNMR12was used to estimate stability constants from the 'H NMR titration data, and the results are summarized in Table 1. Receptor 4 clearly exhibits a degree of selectivity for chloride >> bromide x iodide. It is interesting that as the size of the methylene linker increases from ethyl (4) to propyl (5) or butyl (6) a dramatic reduction in the magnitude of the chloride anion stability constant value results. This is also observed for the bromide anion, although with the larger iodide anion all three receptors exhibit relatively low stability constant values of similar magnitudes. Consequently, whereas 4 is selective for chloride, receptors 5 and 6, within experimental error, exhibit virtually no selectivity for any of the halide anion guests. These observations may indicate the cavity of 4 being suf-

1

Figure 4. Proton NMR titration curves of 7 with C1- and Br- in CD?CN.

450 275 100

Errors estimated to be ~ 1 0 % .

e

8 8 10 10 llb llb a

anion c1Brc1Brc1Brc1Br-

Klldm3 mol-' 1260 1000 1260 800 2500

950 3160 3160

K2/dm3mol-' 250 65 400 130 130 50 90 50

log K overall 5.5 4.8 5.7 5.0 5.5 4.7 5.4 5.2

"'Errors estimated to be 5 15%. Titration performed in DMSO.

ficiently preorganized and of complementary size and shape for chloride but being relatively too small for the larger halide an'lons. With the more flexible and larger ditopic receptors 5 and 6 this degree of preorganization and cavity size selection is lost, and as a result little selectivity is observed. Analogous 'H NMR titrations of receptors 7 , 8, 10, and 11 with chloride and bromide anions were undertaken in deuterated acetonitrile solutions. It is noteworthy that EQNMR12 analysis of the titration data revealed 2:1 halide anion receptor stoichiometry (See Figure 41, the larger aryl and alkylamino spacers negating the possibility of cooperative 1:1stoichiometric binding. The resulting stability constants are shown in Table 2. As predicted on statistical and electrostatic grounds KIvalues are larger than those of Kz.Gener-

Beer et al.

3294 Organometallics, Vol. 14, No. 7, 1995

e '&

pFs

I

6.6

c=o

o=c

i

\ NH

6.0

/

HN

4 \

5.4 1.o

0.5

0.0

1.5

2.0

Equivalent of

TEA

2.5

3.0

3.5

Adipate

Figure 5. Proton NMR titration curve of 15 and adipate [-0&(CH2)4COyl in acetone-&. Table 3. Stability Constant Data for 15 and Various Anions in D M S O 4 anion c1-

BrHzP04HS04-02C(CH2)4C02-b a

Kldm3 mol-'

a

5035 1680 2800

K1= 990; K2 = 495 11510

Errors estimated to be 5 10%. Titration performed in acetone-

ds.

ally the overall log Kvalues are larger for C1- than Br-. Comparing the respective stability constant values for receptors 7 and 10 suggests the presence of the ester functionality has little effect on the halide anion recognition process. Disappointingly lH NMR titrations of 7, 8, 10, and 11 with other anions such as HS04- and HzP04- in acetonitrile or DMSO solutions led t o precipitation of the respective complexes. Consequently it was not possible to calculate stability constants from the resulting incomplete titration curves. 'H NMR titrations of the novel calix[4]arene receptor 15 with various anions were performed in deuteriated dimethyl sulfoxide solutions due t o solubility problems. Large downfield perturbations of the receptor's protons were observed on addition of halides, hydrogen sulfate, and dihydrogen phosphate anions. For example, with HS04- downfield shifts of A6 = 0.25 - 0.4 ppm for the aryl protons of the calix[4larene structural framework were observed, suggesting anion complexation takes place within the upper rim of the calix cavity of 15. EQNMRI2 analysis of the resulting titration curves suggested 1:l anion complexes are formed with C1-, Br-, and HzP04-. Hydrogen sulfate anions, however, formed a 1:2 host molecu1e:anion complex. The calculated stability constant values, shown in Table 3, are large in magnitude, especially considering they were determined in the highly polar D M s 0 - d ~solvent medium. With the dicarboxylate dianion adipate, although significant interactions were observed with acetonitrile,

oH

OCH,

OCH3 OH

Figure 6. Proposed solution complex structure of 15 and adipate.

acetone, and DMSO solutions of 7, 8, 10, and 11, precipitation problems of the resulting receptor-dianion complexes again thwarted their respective stoichiometries being elucidated. A 'H NMR titration curve of 15 and adipate was, however, obtained in acetoned6 solution (Figure 5). In addition to upfield perturbations of the substituted cyclopentadienyl protons, significant shifts of the calix aryl protons were observed, suggesting the adipate guest dianion coordinates within the confines of the upper rim cavity of 15 (Figure 6). The calculated stability constant of K = 11510 (Table 3) implies a thermodynamically stable 1:l 15-adipate complex exists in acetone solution. Disappointingly, repeated attempts a t obtaining crystals of X-ray quality of the 15-adipate complex from a variety of solvent mixtures failed. Electrochemical Anion Recognition Studies. The electrochemical properties of all these new bis-cobaltocenium receptor molecules were investigated in acetonitrile or acetone using cyclic voltammetry with Bu4NBF4 as the supporting electrolyte. Each compound exhibited a reversible two-electron redox reduction wave in the -0.8 to -1.1 V region (Table 4). Cyclic voltammograms were also recorded after progressively adding stoichiometric equivalents of anion guests to the electrochemical solutions, and the results are summarized

Anion Recognition by Bis-Cobaltocenium Receptors

Organometallics, Vol. 14, No. 7, 1995 3295

Table 4. Electrochemical Data

Conclusions

receptor EdV 4 5 8

7 8

10 11

le

-0.88 -0.89 -0.89 -0.85 -0.79 -0.90 -1.04 -0.85d

60 45 40 70

65 70 50 55d

40

30 30

65 35

3od

165 200

C

C

115

250

5od

C

Obtained in acetonitrile solution containing 0.2 mol of NBuJ3F4 per dm-3 as supporting electrolyte. Solutions were ca. 1 x mol dm-3 in receptor, and potentials were obtained with reference to a Ag/Ag+ electrode. Coulometric investigations suggest Ef values represent a two-electron reduction process. Cathodic shift in reduction potential produced by presence of anions (up to 4 equiv) added as their tetrabutylammonium salts. Precipitation of complex observed; no C.V.could be obtained. Obtained in acetone solution.

in Table 4. Substantial one-wave cathodic shifts of the respective cobaltoceniudcobaltocene redox couple are generally observed with most anionic guest species. The complexed anion effectively stabilizes the positive charge of the cobaltocenium unit. It is noteworthy that chloride, by virtue of its higher charge density, causes relatively larger cathodic perturbations than bromide (see examples of 4-6 in Table 4). Interestingly, as observed with monosubstituted cobaltocenium derivat i v e ~ the , ~ dihydrogenphosphate anion produces the largest magnitudes of cathodic shifts. The addition of tetrabutylammonium adipate to electrochemical solutions of 15 led to a cathodic shift of 50 mV, suggesting this receptor can electrochemically recognize this dianionic guest in acetone solution. Similar electrochemical experiments with the other biscobaltocenium receptors gave, because of solubility problems, inconclusive results.

A series of novel ditopic bis-cobaltocenium receptor molecules containing alkyl, aryl, and calix[4larene spacers have been synthesized, and a crystal structure of the calix[4larene derivative 15 has been determined. Proton NMR halide anion coordination studies revealed that the alkyl-linked derivatives 4-6 form 1:l stoichiometric complexes. Stability constant evaluations suggested that as the length of the alkyl chain increased the selectivity preference for chloride and the general stability of the halide complex decreased. Receptors 7 , 8, 10, and 11 containing larger linking moieties produced anion complexes of 2:1 halide anion:receptor stoichiometry. The bis-cobaltocenium calix[4larene derivative 15 forms thermodynamically stable 1:l anion complexes with C1-, Br-, and HzP04- in polar DMSO solutions and adipate in acetone. Electrochemical investigations showed all the bis-cobaltocenium systems can electrochemically recognize a variety of anions, including 15 sensing adipate. Acknowledgment. We thank the SERC for a postdoctoral fellowship to D.H., for studentships to J.E.K. and S.E.S., and for use of the mass spectrometry service at University College, Swansea, U.K. The University of Reading and the SERC are gratefully acknowledged for funding toward the crystallographic Image Plate System. Supporting Information Available: Tables of atom coordinates, bond distances and angles, and anisotropic thermal parameters for 15 (9 pages). Ordering information is given on any current masthead page. OM950147C