2830
Inorg. Chem. 1994, 33, 2830-2837
Metal Complexes with Tetrapyrrole Ligands, 67.' Synthesis and Spectroscopic Properties of Water-Soluble Cerium Bisporphyrinate Double-Decker Ions Johann W. Buchler. and Michaela Nawra Institut fiir Anorganische Chemie, Technische Hochschule Darmstadt, Hochschulstrasse 10, D-64289 Darmstadt, Germany
Received September 8. 1993' Reaction of cerium(II1) acetylacetonate with lithiated tetrakis(4-pyridyl)porphyrin, tetrakis(4-(dimethylamino)phenyl)porphyrin, and tetrakis (4-(methoxycarbonyl)phenyl)porphyrin in trichlorobenzene at 200 OC yields the corresponding neutral cerium(1V) bisporphyrinates Ce(TPyP)z, Ce(TMAP)z, and Ce(TMeCPP)z, respectively. Quaternarization of the former two double deckers with methyl tosylate, 2-chloroethanol, or methyl iodide produces salts of the octaalkylated cations [Ce1I1(TM4PyP)2l7+,[Ce1ii(TEpyP)~]7+, and [CeIv(TTM&P)2]*+, respectively. Ce1I1in the two heptacations is oxidized to CeIVwith bromine to obtain the corresponding octacations. The cations are isolated as halides or hexafluorophosphates. Saponification of the ester groups in Ce(TMeCPP)z with KOH gives the octacarboxylate [Ce1V(TCPP)z]8-,which is hydrolyzed to a dianion and precipitated as a bis(tripheny1phosphoranediy1)ammonium salt, ( P P N ) z [ C ~ ( T H ~ C P P ) ~The ] . ionic CelI1 and CeIV porphyrin double deckers including [CeIV(TH4PyP)2]*+, the octaprotonated form of Ce(TPyP)*, are identified by UV/Vis and 1H NMR spectra and gel electrophoresis at polyacrylamide or agarose gels in aqueous buffer solutions at pH 8.
Chert 1. Structural Formula and Specification of
1. Introduction
The reaction center of bacterial photosynthesis bears a bacteriochlorophyll b dimer. This dimer is called "Special Pair".2 Its photochemical oxidation is the first step of the light-induced decomposition of water. According to spectroscopic and electrochemical measurements and crystal structure analyses, sandwichlike bisporphyrinates of the lanthanoids3 and the early transition metals zirconium and hafnium4 may be regarded as structural and spectroscopic models of the Special Pair. So far, these bisporphyrinates are lipophilic, i.e. have just alkyl or aryl substituents in their periphery, as in the octaethylporphyrin derivative C ~ ( O E P ) Z tetraphenylporphyrin ,~~~~ derivative Ce(TPP)23f(Chart l), or Ce(OEP)(TPP)3f carrying two different porphyrin ligands. .Abstract published in Advance ACS Abstracts, May 15, 1994. (1) Part 66: Buchler, J. W.; Eiermann, V.; Hanssum, H.; Heinz, G.; RBterjans, H.; Schwarzkopf, M. Chem. Eer. 1994, 127, 589-595. (2) Deisenhofer,J.; Michel, H. Angew. Chem. 1989,101,872-892; Angew. Chem., Int. Ed. Engl. 1989, 28, 829-849. (3) (a) Buchlcr, J. W.; Kapcllmann, H.-G.; Knoff, M.; Lay, K.-L.; Pfeifer, S.2.Naturforsch. 1983, 386, 1339-1345. (b) Buchler, J. W.; KihnBotulinski, M.; Elsfisser, K.; Scharbert, B. Angew. Chem. 1986, 98, 257-258; Angew. Chem.,Int. Ed. Eng., 1986,25,286-287. (c) Buchler, J. W. Comments Inorg. Chem. 1987,6, 175-191. (d) Buchler; J. W.; Kihn-Botulinski,M.; Scharbert, B. Z . Naturforsch. 1988,436, 13711380. (e) Buchler,J. W.; De Cian, A.; Fischer, J.; Kihn-Botulinski,M.; Paulus, H.; Weiss, R. J . Am. Chem. Soc. 1986, 108, 3652-3659. (f) Buchler, J. W.; De Cian, A.; Fischer, J.; Hammerschmitt, P.; Lbffler, J.; Scharbert, B.; Weiss, R. Chem. Ber. 1989, 122, 2219-2228. (4) (a) Buchler, J. W.; De Cian, A.; Fischer, J.; Hammerschmitt, P.; Weiss, R. Chem. Ber. 1991,124,1051-1058. (b) Buchler,J. W.; DeCian, A.; Elschner, S.;Fischer, J.; Hammerschmitt, P.; Weiss, R. Chem. Ber. 1992, 125, 107-115. (c) Cho, S.-H.; Girolami, G. S.;Gorlin, P. A.; Kim, H.-J.; Kim, K.; Lee, W.; Suslick, K. S.Inorg. Chem. 1991, 30, 2652-2656, (5) Additionally to the ones given in Scheme 1, the following abbreviations are used: (P)z-, (OEP)S, (TTP)2-, (TH&PP)2-, (TH$PP)f, (TMelPyP)+, (2-TMe,PyP)2+, and (TC1P)z- for the species formed by deprotonation at the central N-atoms of a general porphyrin, 2,3,7,8,12.13,17,18-octaethylporphyrin, 5,10,15,2O-tetrakis(4-methylphenyl)porphyrin, 5,10,15,20-tetrakis(4-(hydroxycarbonyl)phenyl)porphyrin, 5-(4-carboxyphenyl)-IO, 15,20-tris(4-(hydroxycarbonyl)phenyl)porphyrin, 5-(4-pyridyl)-10,15,20-tris(4-methylpyridinio)porphyrin, 5,10,15,2O-tetrakis(2-methylpyridinio)porphyrin, and 5.10,15,20-tetrakis(4chlorophenyl)porphyrin,respectively;H(acac), acetylacetone;M, metal; PAA, polyacrylamide;PPN+,bis(triphenylphosphoranediy1)ammonium cation; TCB, 1,2,4-trichlorobenzene; TosOMe, 4-(methoxysulfony1)I-methylbenzene;TSP, sodium 3-(trimethylsilyl)propionate-2,2,3,3-& 0020- 166919411333-2830$04.50/0
Porphyrinate Ligands of Cerium Bisporphyrinates Ce(P)2 (Double Bonds Omitted)
Rl
Ce(P12 Substituents of the porphyrin ligands
R1
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-
(TPYP)~-
*-HI' -
(TH~PYP)~'
a -
Abbrevation of t h e porphyrin ligands
(TM,P~P)~*
CHsIf
*-CzH4OHI*
(TE*PYP)~'
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(TMAP)~-
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(TTMAP)2'
-02Me
(TM e C PP)2.
(C HS)S I'
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0 1994 American Chemical Society
(TH,CPP)~-
Metal Complexes with Tetrapyrrole Ligands In order toevaluate these bisporphyrinatesas functional models
of the Special Pair, they must be aggregated with appropriate electron acceptors like quinones. This could be achieved by covalently linking hydrophobic double-decker entities to organic acceptors as is being done with a variety of monoporphyrin systems: especially with zinc porphyrins? However, an access to functionalized metal bisporphyrinates appears to be difficult.' Under certain conditions, water-soluble porphyrins and metalloporphyrins form aggregates themselves.8 This aggregation tendency should also be exhibited toward other multicharged aromatic acceptor molecules in solution. Therefore, the synthesis of water-solublecerium(1V) bisporphyrinatesseemed worth being done. In this paper, experiments directed toward the synthesis of the water-soluble cerium(1V) bisporphyrinate ions [Ce(TH4PyP)2I8+, [Ce(TM4PyP)2I8+, [Ce(TEdPyP)#+, and [Ce(TCPP)2]8- are described (see Chart 1). The redox chemistry and aggregation behavior of such ions will be described in forthcoming publications. In a seminal paper? complexes of water-soluble tetraarylporphyrins with transition metal ions have been described by Pasternack et al., along with a comparison of spectroscopic properties of cationic and anionic metal-free porphyrins in water at different pH values. pK, values and aggregation states of water-soluble porphyrins have been discussed as well. Recently, their prospective application for industrial and medical purposes stimulated the interest in these substances. Manganese(II1) tetrakisb-sulfonatopheny1)porphyrinates have been used as oxidation catalysts for various purposes,1° e.g. as ligninase models." Paramagnetic water-soluble metalloporphyrins serve as contrast agents for N M R tomography.12 Water-soluble porphyrins accumulate in tumors and help in photodynamiccancer therapy.I3 Boron-containing porphyrins are used in neutroncapture therapy of cancer.14 Furthermore, the aggregation behavior of water-soluble porphyrins and phthalocyanines may become important for the creation of supramolecular assemblies.ls There is less knowledge about water-soluble lanthanoid porphyrinates. First, Horrocks et a1.'6 have reported on the synthesis and properties of sulfonated lanthanoid monoporphyrinates that could be used as shift reagents for tomographic measurements. Recently, the aggregation between cationic, anionic, and neutral metal-free and samarium porphyrins has been studied.17 The aggregate [Sm(TMPyP)I5+/[H2(TMPyP)I4+ has the largest formation constant. While this work was in progress, Machida and co-workers18 have described the preparation of a cerium bisporphyrinate double decker, Ce(TPyP)2, and its treatment with acid or methyl iodide giving a surprisingly stable octaprotonated cation [Ce(TH4PyP)218+or a salt with the alleged composition [Ce(TM4PyP)2]18. (6) Kriiger, C.; Dernbach, M.; Voit,G.;Carell,T.;Staab,H. A., Chem.Ber. 1993, 126, 811-821 and references cited therein. (7) For a review see: Gust, D.; Moore, T. A. Top. Curr. Chem. 1991,159, 103-151. ( 8 ) White, W. I. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol. 5, pp 303-341. (9) Pasternack, R. F.; Huber, P. R.; Boyd, P.;Engasser, G.; Francesconi, L.; Gibbs, E.; Fasella, P.; Cerio Venturo, G.; de C. Hinds, L. J. Am. Chem. SOC.1972, 94, 4511-4517. (10) For a review, see: Meunier, B. Chem. Reo. 1992, 92, 1411-1446. (11) Labat, G.; Meunier, B. J. Org. Chem. 1989, 54, 5008-5011. (12) Hoehn-Berlage,M.; Norris, 0.;Bockhorst, K.; Ernestus, R.-I.; Kloiber, 0.; Bonneholz, P.; Leibfritz, 0.;Hossman, K.-A. Magn. Reson. Med. 1992, 27, 201-213. (13) Dougherty, T. J. Photochem. Photobiol. 1987, 45, 879-889. (14) Hawthorne, M. F. Angew. Chem. 1993, IOS, 997-1033; Angew. Chem., Int. Ed. Engl. 1993. 32, 95G987. (15) Lipskier, J. F.; Tran-Thi, T. H. Inorg. Chem. 1993, 32, 722-731. (16) Horrocks, W. Dew.; Hove, E. G. J. Am. Chem. SOC.1978,100,43864389. (17) Radzki, S.; Krausz, P.;Gaspard, S.;Giannotti, C. Inorg. Chim. Acta 1987, 138, 139-143. (18) (a) Jiang, J.; Machida, K.;Yamamoto, E.; Adachi, G. Chem. Lett. 1991, 2035-2038. (b) Bull. Chem. Soc.Jpn. 1992,1990-1992. (c) Jiang, J.; Machida, K.; Adachi, G. J. Alloys Comp. 1993, 192, 296-299.
Inorganic Chemistry, Vol. 33, No.13, 1994 2831 2. Experimental Section 2.1. Instrumentrl Analysis. W / V i s Spectm Hewlett-Packard HP 8451 A (diode-array) and Bruins-Instruments Omega 10 spectrophotometers. Spectra were processed with SPECTRA CALC software (Galactic Industries Corp). IR Spectm Perkin-Elmer 397 (KBr pellets, 4000-400 cm-1). hlrssSpectm Varian MAT 311A (field desorptionmode). Molecular mass numbers, m / z , were calculated for 'We; for masses above m / z 1500, only doubly charged ions were looked for. 1H-NMR Spectra: Bruker WM-300 (300 MHz). Elemental Analyses: Mikroanalytisches Laboratorium, Institut fiir Organische Chemie, TH Darmstadt, Germany (given at the end of the protocols), and Analytische Laboratorien Malissa & Reuter, D-5 I753 Engelskirchen, Germany (Table 6). Electrophoresis Horizontal slab gel system type Despahor HE 200 andvertical tubegelsystemDesaphor VC 135(both Desaga/Heidelberg). Further details may be taken from previous publications.19 2.2. Materials. Chlorin-free tetraarylporphyrinsa and cerium(II1) acetylacetonateZ1were prepared according literature methods. The following chemicals were purchased from the companies indicated in parentheses: pyrrole and acetylacetone (both Merck, Darmstadt), 4-formylbenzoic acid methyl ester (Fluka), N,N-dimethylaminobenldehyde (Merck-Schuchardt), 4-formylpyridine (EGA-Chemic), cerium(111) chloride hydrate (Johnson-Matthey),p-toluenesulfonicacid methyl ester, propionic acid (99%), bis(triphenylphosphoranediy1)ammonium chloride (all Fluka), methyl iodide, n-butyllithium (1.6 M in n-hexane; both Merck), 2-chloroethanol (Riedel de HaZn). Solvents: tetrahydrofuran and dichloromethane (both Merck) were purified by passing an alumina column (basic, super I). 1,2,4-Trichlorobenzenc (TCB Janssen Chimica), chloroform-dl, dimethyl-& sulfoxide, deuteriomethanol-& and tetramethylsilane (all Merck),deuteriumoxidecontaining1%sodium 3-(trimethylsilyl)propionate2,2,3,3-d4(TSP Aldrich), and deionized water were used as received. 2.3. Stationary Phrses: Alumina, type W 200, super I, basic (ICN Chemicals Woelm). Lower activity grades were generated by addition of water. Amberlite IRA (Fluka) in the chloride form was used as an anion exchanger to prepare chlorides from salts with other anions. Polyacrylamide gels (8%) were prepared by a literature methodz2using (Fluka). a mixture of acrylamideand 5%N,"-methylenebis(acy1amide) Agarose (Fluka) was used as a 0.75% slurry in a tris/borate buffer pH 8 which was also used for all investigations with polyacrylamide gels. 2.4. Experimental Protocols. Protocol 1: Bi#,lO,lS,2O-tetrakis(4-pyridyl)porphyhto@rium(IV), Ce(TpyP)Z. To a solution of 124 mg (0.2 mmol) of Hz(TPyP) in 60 mL of TCB was added 1 mL of n-BuLi. The color of the solution turned from purple to green. After the solution was stirred under Nz for 20 min at 20 OC, 270 mg (0.6 mmol) of Ce(acac)3*HzOwas added and the mixture was heated to reflux under Nz for 5 h. After removal of the TCB in a high vacuum the resulting crude product A was dissolved in CHzClz and chromatographed at an alumina column (grade 111, basic, 4 X 20 cm). The following fractions were eluted: (1) a purple solution of unreacted Hz(TPyP) with CHIClZ/MeOH (955); (2) a purple solution of Hz(TPyP)/Ce(TPyP)z; (3) a brown solution of Ce(TPyP)Zwith CHzC12/MeOH (41). Evaporation of fraction 3 yielded 73 mg (53%) of a brown-violetpowder of Ce(TPyP)Z. IR (KBr): 3100, 3030 (m), 2960 (m), 1635 (m), 1600 (vs), 1440 (w), 1410 (s), 1330 (s), 1120 (vw), 980,800 (vs), 635 (m), 590 (m) cm-1. MS, m / z : calcd 1372 for [Ce(TPyP)z]+, found 1374 (100%). Anal. Calcd forCsoHaNl6Ce (mol wt 1373.51): C,69.96;H, 3.52;N, 16.32. Found: C, 67.77; H, 3.69; N, 14.24.
Protocol 2: B i s [ S , l O , l S , ~ t e ~ ( ~ , ~ - ~ ~ ~ y l - 4 - a ~ p ~ n y l ) porphyrinato]cerium(IV),Ce(TMAP)z. As described in protocol I , an
analogous crude product A was prepared from 157 mg (0.2 mmol) of Hz(TMAP). The formation of Cc(TMAP)z was followed by thin-layer chromatography because the UV/Vis spectra of metal-free and metalated (19) (a) Kiinzel, F. Dissertation Technische Hochschule Darmstadt, 1992. (b) Buchler, J. W.;KLlnzel, F.; Mayer, U.; Nawra, M. Fresenius J. Analyt. Chem. 1994,348,371-376. (c) Kiinzel, F.; Mayer, U.; Nawra, M.; Buchler, J. W . Abstracts, EUROBIC I , Metal Ions In Biological Systems; The Royal Society, Dalton Division: Newcastle upon Tyne, England, 8-12 July 1992; p 45. (20) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour, J.; Korsakoff, L. J. Org. Chem. 1%7,32, 1689-1693. (21) Stites, J. G.; McCarty, C. N.; Quill, L. L. J. Am. Chem. Soc. 1948,70, 3142-3 143. (22) Wagner,H.; Blasius, E. Praxis derelektrophoretischen Trennmethoden; Springer: Berlin, Heidelberg, 1989.
2832 inorganic Chemistry, Vol. 33, No. 13, 1994 porphyrins do not differ significantly. After removal of the TCB in a high vacuum the resulting crude product A was dissolved in CHzCIz, and the solution was chromatographed at an alumina column (grade 111, basic, 4 X 20 cm). The following fractions were eluted: (a) brownishgreen Ce(TMAP)2 with CH2C12; (2) an olive-green mixture of Hz(TMAP)/Ce(TMAP)2; at the top of the column remained CeIIIH(TMAP)2. After evaporation of the first fraction, 57 mg (45%) of a brownish-blackpowder of Ce(TMAP)z was obtained. IR (KBr): 2940, 2800 (m,b), 1730 (m),1610 (vs), 1520 (s, b), 1350 (s, vb), 1290 (m,b), 980,950 (s), 730 (m) cm-I. MS, m / z : calcd 855 for [Ce(TMAP)zlZ+, found 855 (100%). Anal. Calcd for Cl&%N&e (mol wt 1710.13): C, 73.04; H, 5.66; N, 13.10. Found: C, 70.70; H, 5.72; N, 10.62. Protocol3 BIs[5,10,15,20-tetrakis(4-(methoxycarbonyl)phenyl)porphyrinato]cerium(IV), Ce(TMeCPP)2. As described in protocol 1, an analogous crude product A was prepared from 847 mg (1.O mmol) of Hz(TMeCPP). After removal of the TCB in a high vacuum product A was dissolved in CHzCl2, and the solution was chromatographed at an alumina column (grade 111, basic, 4 X 20 cm). The following fractions were eluted: (1) a purple fraction of Hz(TMeCPP) with CHzC12; (2) a brown fraction of Ce(TMeCPP)2 with CH2Clz/MeOH (955) yielding 118 mg 68%) of a brownish-black powder of Ce(TMeCPP)z after evaporation of the solvent. IR (KBr): 2960 (m),1725 (b), 1610 (s), 1570(w), 1530(vw), 1115-1110(vs,vb),740(w)cm-~.MS,m/z: calcd (6%);calcd846forHz(TMeCPP), 914for [Ce(TMeCPP)2I2+,found914 found 846 (100%). Anal. Calcd for C1&7zN8016Ce (mol wt 1829.88): C, 68.26; H, 3.97; N, 6.12. Found: C, 65.05; H, 4.45; N, 4.75. Protocol 4 Bis[5,10,15,zete~(4-pyridinio)porphyrinato~rium(IV) HexafluoropLasphrte,[C~(THSyP)~](PF~),(xunknorm). A 10-
mg sample of solid Ce(TPyP)z was layered with 2 mL of Hz0, while the mixture was shaken, 0.5 N HCl was added dropwise until a clear brown solution of the hydrochloride [Ce1V(THSyP)2]Clswas obtained. (Such solutionswere used for electrophoresesand spectral measurements.)Then, an excess of a methanolic solution (5%) of NHJ'F6 was added dropwise until opacity. The precipitate (13 mg) was centrifuged and dried at 40 OC. Analysis indicated decompositionof the sampleon storage (see Table 6). Protocol 5: Bis[S,lO,lS,U)-tets( l-methyl-4-pyridinio)porphyrinasample tolcerium(II1) Heptachloride, [ c @ ( M P ) z f l 7 , A 30" (0.02 mmol) of Ce(TPyP)z and 300 mg (1.6 mmol) of p-toluenesulfonic acidmethylesterwerestirred5dat 100OC. Thecooledmeltwasdissolved in a mixture of 8 mL of CH& and 8 mL of HzO. Two phases were formed. The light-brown organic phase contained incompletely methylated material, and the clear dark brown aqueous phase the completely methylated product. After ion exchange of this phase on an Amberlite IRA column and evaporation, 37 mg (74%) of a black powder of [Ce1II(TM~PyP)2]Cl7.l6H20was obtained. Anal. Calcd for Cs8Hlo4Nl@l&eC17 (molwt 2030.18): c , 52.06; H, 5.16; N, 11.04; c1, 12.22. Found: C, 51.89; H, 4.10; N, 11.13; CI, 8.76. Protocol 6 Bicr[5,lO,l5,2O-tebPkis(l-(hydroxyethyl)-4-pyrididinio)porphyrinato]cerium(In) Heptachloride, C@(TE&P)$l7. A 43" sample of Ce(TPyP)2 was dissolved in 2 mL of 2-chloroethano1, and the solution was stirred 5 d at 100 OC. After removal of excess reagent at a high vacuum 41 mg (60%) of a black powder of [Ce1I1(TE4PyP)2]C1~16Hz0remained. Anal. Calcd for C~6H114Nl6OzoCeC17(mol wt 2200.34): C,52.40;H,5.22;N, 10.19;C1, 11.28. Found: C,51.37;H, 4.19; N, 9.99; CI, 9.86. Protocol 7: Bi~5,1O,l5,ZO-tetrakis(l-dkyl-4-pyri~)porphyrinato~ cerium(II1) Hexafluorophaephates. A methanolic solution (5%) of NHdPF6 was added dropwiseto an aqueous solution of 15 mg of the respective [Ce"'(TR&P)2]C18 (R = methyl, 2'-hydroxyethyl) until the mixture became turbid, which then was kept 1 d at 4OC. The precipitates (17-1 8 mg) were centrifuged and dried at 40 OC. For analyses, see Table 6. Protocol8: Bis[5,10,15,U)-tetrakis(l-elkyl-4-pyrldinio)~~to~ cerium(IV) HeptachlorideBromide, [CP(TR&P)zICl7Br (R = Methyl or 2'-Hydroxyethyl). A solution of bromine in CH2Cl2 (3 X lCzm) was added dropwise to an aqueous solution of [CeIIl(T&PyP)z]CI7 (about 10-5 M for UV/Vis, about lo-' M for NMR spectroscopy). The color of the mixture changed from greenish-brown due to the cerium(II1) complex to red brown for the cerium(1V) species. The completeness of the oxidation was proven by UV/Vis spectroscopy. Solutions prepared like this were used for physical measurements directly.
Protocol 9: B i ~ 5 , 1 0 , 1 5 , 2 0 - t e t m L f s ( e ( t r i " m o y l ) porphyrinato)cerium(IV) Octaiodide, [Ce(lT&fAP)Z&. A 0.5-mL portion (7.89 mmol) of CH31was added to a solution of 39 mg (0.023 mmol)of Ce(TMAP)z in 10 mL of CHCl'/EtOH (8:2) and the mixture
stirred for 2 h at 38 O C . The mixture was then kept 2 d at 20 OC. A
Buchler and Nawra 2 0 " volume of 2 N aqueous NH3 was added with shaking. The brown aqueous phase was separated and centrifuged. Small amounts (
