Iodonium zwitterions

Journal of Fluorine Chemistry 122 (2003) 57–61

Iodonium zwitterions Darryl D. DesMarteau*, William T. Pennington, Vittorio Montanari, Brian H. Thomas Department of Chemistry, Clemson University, Box 340973, Clemson, SC 29634-0973, USA

Abstract The first example of a diaryl zwitterionic iodonium compound having the anionic function directly on the aromatic ring is described. Compound 2, Ph-I(þ)-C6H4-4-SO2N()SO2CF3, is obtained in excellent yield and its X-ray structure was determined. 2 and the many analogues that can be prepared have excellent potential as photoacid generators (PAGs) in microlithography. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Photoacids; Zwitterions; Iodonium compounds; Sulfonimides; Iodoarylsulfonyl fluoride

1. Introduction Perfluoroalkyl sulfonimides are of increasing interest for their high Brønsted acidity, electrochemical properties, high thermal and chemical stability and the ease of preparation resulting in a variety of structures. Our interest in these compounds has ranged from xenon compounds, selective fluorination, polymer membrane electrolytes, and most recently to the novel fluoroalkylation reagent CF3CH2I(Ph)N(SO2CF3)2 [1]. In the quest for new polymer electrolytes, we became interested in the preparation of iodophenyl perfluoroalkyl sulfonimides as precursors to new monomers. Unsymmetrical sulfonimides containing aromatic groups are not well known and procedures for making them are mostly claimed in patents [2]. The novel sulfonimides RfSO2N(Na)SO2C6H4I were especially attractive ionic starting materials to us for two reasons: firstly the iodine atom is a convenient handle for attaching vinyl groups; secondly, the compounds can be prepared easily from commercially available p-iodobenzenesulfonyl (‘‘pipsyl’’) chloride.

2. Results and discussion The synthesis of RfSO2N(Na)SOC6H4I is shown in Scheme 1. The first of the two routes shown is the reliable silicon-mediated synthesis of sulfonimides that we have used traditionally [1a,b]. The second, utilizing ‘‘pipsyl’’ amide provides a remarkable example of mesomeric effect. The 4-iodo substituent enables a reaction that is otherwise * Corresponding author. Tel.: þ1-864-656-4705; fax: þ1-864-656-0627. E-mail address: [email protected] (D.D. DesMarteau).

slow and impractical and can be used to easily introduce a variety of fluorocarbon substituents. From our work with CF3CH2I(Ph)N(SO2CF3)2, whose distinctive properties are due to its sulfonimide counterion [1d], it became an interest to us to see if CF3SO2NNaSO2C6H4I, 1, could be oxidized to a zwitterionic iodonium compound. Such a compound as Ph-I(þ)-C6H4-4-SO2N()SO2CF3, 2, was envisaged to have potential as a photoacid generator (PAG) in microlithography. Per se, a structure where the trivalent iodine cation and the counteranion are linked by an aromatic ring would be novel and interesting. Indeed, we found that 1 could be converted into 2 in a one step reaction by oxidation of 1 in sulfuric acid with potassium persulfate in the presence of benzene (Scheme 2). The synthetic method is essentially that devised by Meyer in 1893 to prepare the first diaryl iodonium salts, under conditions optimized by Beringer et al. in 1959 [3a,b]. Based on the fact that 1 has a strongly acidic function and on the literature, the prospects for conversion of 1 to an iodonium salt seemed unlikely. Diaryl iodonium salts have been studied and the subject has been reviewed many times [4]. Several preparative methods evolved to afford a wide range of structures. However, the synthesis of an iodonium zwitterion was eventually accomplished by Beringer and Falk only with difficulty [3c]. They did not obtain any compound where a strongly acidic group resides directly on an aromatic ring. The inherent difficulties in the synthesis of iodonium salts having strongly electronegative groups are well illustrated in a comparative study of preparative procedures [3b]. The example of 4-nitro iodobenzene was suggestive: it could be used as a starting material, if only in the persulfate/sulfuric acid system, analog to Scheme 2 [3b]. Based on this lone possible analogy, we reacted 1 with

0022-1139/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0022-1139(03)00080-0

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D.D. DesMarteau et al. / Journal of Fluorine Chemistry 122 (2003) 57–61

Scheme 1.

Scheme 2.

benzene accordingly and obtained a product whose insolubility in water and aqueous acids and bases indicated a zwitterion, rather than an iodonium sulfate with an additional ionic group. In such a case, the zwitterion form would be pH-dependent as in Beringer and Falk’s examples [3c]. Our structural hypothesis was confirmed by analysis, including X-ray diffraction. Crystals grown from DMSO/water were obtained solvent-free (Fig. 1a) or as DMSO co-crystals (Fig. 2a) depending on the DMSO/water ratio. In 2, the molecule has a cisoid conformation with respect to the R-groups of the sulfonimide (C4–S1    S2–C13 torsion angle of 10.68), while in 2DMSO the molecule has a transoid conformation (C4–S1    S2–C13 torsion angle of 145.28) [1e]. The structures of both are dominated by secondary bonding involving the iodine(III) center and either oxygen or nitrogen atoms. These interactions are similar to those seen in many related hypervalent iodine compounds [1e]. In 2, molecules related by a c-glide operation are linked into chains through an iodine    sulfonyl oxygen atom interaction ˚ ), and the chains are joined through (I1    O4B ¼ 2:926ð4Þ A an additional pair of iodine    sulfonyl oxygen atom inter˚ ) across an inversion center actions (I1    O1A ¼ 2:992ð4Þ A at (1 0 1) to form layers, which stack along the crystallographic a-axis (Fig. 1b). In 2DMSO, the molecules are linked into chains through an iodine    nitrogen atom inter˚ ), while the additional cooraction (I1    N1A ¼ 2:950ð7Þ A dination site of the iodine atom is occupied by the oxygen ˚ ). Two atom of the DMSO adduct (I1    O5 ¼ 2:691ð6Þ A chains related by two-fold rotational symmetry parallel to the b-axis (0 y 1/4) pack in a loosely-associated fashion to form square columns, which stack to complete the packing (Fig. 2b). Many modified structures based on 2 are possible. Substituted arenes can be used and a variety of perfluoroalkyl sulfonyl halides are readily available to build the sulfonimide moiety. The reaction of 1 with fluorobenzene, bromobenzene, toluene and phenylacetic acid was rapid,

slower with benzotrifluoride; with nitrobenzene no reaction occurred. Yields were in excess of 60%; no optimization study has been carried out at this time (Table 1). Possible applications of our novel materials in microlithography demand investigation. Onium salts, diaryl iodonium salts Ar1Ar2IþX in particular, generate the corresponding acid of the counteranion, HX, and various nonacid photoproducts under UV irradiation [5]. This property has found a significant use in the area of ‘chemically amplified’ photoresists, the lithographic procedure now employed to manufacture advanced integrated circuits [5]. In our case, a highly acidic sulfonimide is produced under conventional (254 nm) UV irradiation. With proper choice of the fluorinated chain and aromatic substitution both the size of the photoacid and the solubility of the salt can be tuned to specifications.

Table 1 Other examples of iodonium zwitterions Ar

Rf

Yield (%)

CF3, C4F9

84, 78

CF3, C4F9

80, 79

CF3, C4F9

84, 84

CF3, C4F9

0, 0

CF3

Decomposed by heat

CF3, C4F9

70 (90% meta), 65

D.D. DesMarteau et al. / Journal of Fluorine Chemistry 122 (2003) 57–61

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Fig. 1. (a) Thermal ellipsoid plot of 2 (50% probability ellipsoids). Dashed lines show extended interactions to atoms related by the following symmetry ˚ , I1–C7 2.103(5) A ˚, operations: (A) 2  x, y, 2  z; (B) x, 0:5  y, 0:5 þ z; (C) x, 0:5  y, 0:5 þ z. Selected distances and angles: I1–C1 2.088(5) A ˚ , I1    O4B 2:926ð4Þ A ˚ , C1–I1–C7 90.8(2)8, C1–I1    O1A 74:1ð1Þ8, C1–I1    O4B 166:1ð1Þ8, C7–I1    O1A 164:6ð1Þ8, I1    O1A 2:992ð4Þ A C7–I1    O4B 75:6ð1Þ8, O1A    I1    O4B 119:6ð1Þ8, S1–O1    I1A 129:3ð2Þ8, S2–O4    I1C 148:0ð2Þ8. (b) Crystal packing of 2, viewed down the b-axis.

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D.D. DesMarteau et al. / Journal of Fluorine Chemistry 122 (2003) 57–61

Fig. 2. (a) Thermal ellipsoid plot of 2DMSO (50% probability ellipsoids). Dashed lines show extended interactions to atoms related by the following symmetry ˚ , I1–C7 2.11(1) A ˚ , I1    O5 2:691ð6Þ A ˚, operations: (A) x, 1  y, 0:5 þ z; (B) x, 1  y, 0:5 þ z. Selected distances and angles: I1–C1 2.121(8) A ˚ , C1–I1–C7 93.7(4)8, C1–I1    O5 176:5ð3Þ8, C1–I1    N1A 85:7ð3Þ8, C7–I1    O5 83:5ð3Þ8, C7–I1    N1A 175:6ð3Þ8, I1    N1A 2:950ð7Þ A O5    I1    N1A 97:2ð3Þ8, S3–O5    I1 143:3ð4Þ8, S1–N1    I1B 117:8ð4Þ8, S2–N1    I1B 115:4ð4Þ8. (b) Crystal packing of 2DMSO, viewed down the c-axis.

Studies as PAGs for 193 and 157 nm photoresists will be reported in future work.

3. Experimental 3.1. Preparation of 1 4-Iodobenzenesulfonyl fluoride (26.2 g, 0.09 mol) and trimethylsilyl trifluoromethane sulfonamide Na-salt (19.8 g,

0.08 mol) were added to a 250 ml flask containing 200 ml of dry acetonitrile. The mixture was refluxed for 3 days under dry nitrogen and then N,N-diisopropylethylamine (5 ml, 0.028 mol) was added to the mixture and reflux continued for another 8 h. Evaporation of the solvent followed by sublimination of the excess p-iodobenzenesulfonyl fluoride out of the reaction mixture yielded 1 as a white powder (35.14 g, 98.5%) that was used directly. 19 F NMR, 188.31 MHz (CD3C(O)CD3) d(CF3) 78.11 (3F, s); 1 H NMR 200.13 MHz d ¼ 7:87 (dd, 3 JðHa  Hb Þ ¼ 9 Hz,

D.D. DesMarteau et al. / Journal of Fluorine Chemistry 122 (2003) 57–61

2H; Ha ortho-SO2NNaSO2CF3), 7.67 (dd, 2H; Hb ortho-I); IR(KCl): n ¼ 3522 (s), 1697 (s), 1569 (m), 1473 (m), 1387 (m), 1318 (s), 1254 (s), 1174 (s), 1061 (s), 964 (m), 820 (m), 784 (m), 749 (m), 720 (m). 3.2. Preparation of 2 1 (2.0 mmol) in sulfuric acid (15 ml) was cooled to 30 8C. Potassium persulfate (4.0 mmol) was added in one portion and the reaction mixture was allowed to warm to 15 8C with good stirring. Into the resulting suspension was added benzene (2.1 mmol). The reaction mixture became a dark solution and was allowed to return to 20 8C over 3 h. After 6 h at 20 8C the reaction was quenched in ice. The resulting suspension was filtered and washed with water (3 30 ml) on the filter. The dried solid weighed 0.83 g (84%).19 F NMR (CD3C(O)CD3) d(CF3) 77.39 (3F, s); 1 H NMR d ¼ 8:35 (dd, 3 JðHa  Hb Þ ¼ 8 Hz, 2H; Ha meta-SO2NNaSO2CF3), 8.26 (dd, 3 JðHc  Hd Þ ¼ 8 Hz, 2H; Hc ortho-IC6H4SO2R), 7.84 (dd, ¼8 Hz, 2H; Hb ortho-SO2NNaSO2CF3); 7.66 (dd, 3 JðHe  Hd Þ ¼ 7 Hz, 2H; He para-IC6H4SO2R), 7.55 (dd, 3 JðHa  Hb Þ ¼ 8 Hz, 2H; Hd meta-IC6H4SO2R). 3.3. Crystal data 2: C13H9NO4F3S2I, fw ¼ 491:23 g mol1; monoclinic, P21/c (no. 14), colorless parallelepiped, 0:16 mm  ˚ , b ¼ 8:0913ð9Þ A ˚, 0:22 mm  0:31 mm, a ¼ 15:445ð2Þ A ˚ ˚ c ¼ 13:484ð2Þ A, b ¼ 107:655ð9Þ8, V ¼ 1605:8ð3Þ A3, Z ¼ 4, Dcalc ¼ 2:03 Mg m3, m ¼ 2:30 mm1 (transmission coefficients ¼ 0:82–1.00). Total of 19,124 reflections collected on Rigaku AFC8 diffractometer with mercury CCD detector and graphite-monochromated Mo Ka radiation ˚ ); 3422 reflections unique (Rint ¼ 0:073). (l ¼ 0:71073 A Refinement on F2 gave final residuals of R1 ¼ 0:067 (based on 12,296 observed reflections ðI > 2sðIÞÞ) and wR2 ¼ 0:198 based on all data. Refinement was enhanced by treating crystal as a rotational twin (rotation about 1 0 0 vector in direct space). 2DMSO: C13H9NO4F3S2IC2H6OS, fw ¼ 569:37 g mol1; monoclinic, C2/c (no. 15), colorless parallelepiped, ˚, b ¼ 0:30 mm  0:30 mm  0:30 mm, a ¼ 19:000ð2Þ A ˚ , c ¼ 14:2545ð4Þ A ˚ , b ¼ 113:469ð2Þ8, V ¼ 16:713ð4Þ A ˚ 3, Z ¼ 8, Dcalc ¼ 1:82 Mg m3, m ¼ 1:90 mm1 4151:9ð7Þ A

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(transmission coefficients ¼ 0:87–1.00). Total of 30,421 reflections collected on Rigaku AFC8 diffractometer with mercury CCD detector and graphite-monochromated Mo ˚ ); 4407 reflections unique Ka radiation (l ¼ 0:71073 A ðRint ¼ 0:095Þ. Refinement on F gave final residuals of R ¼ 0:057 and Rw ¼ 0:069 (based on 2569 observed reflections ðI > 2:58sðIÞÞ).

Acknowledgements WTP thanks Dr. Thomas Cochilino of Rigaku/Molecular Structure Corporation for assistance with resolving the twinning in structure 2. Support of this research by the National Science Foundation (CHE-0109327) and for purchase of the CCD diffractometer (CHE-9808165) is gratefully acknowledged.

References [1] (a) D.D. DesMarteau, J. Fouropoulos Jr., J. Am. Chem. Soc. 104 (1982) 4260; (b) D.D. DesMarteau, J. Fouropoulos Jr., Inorg. Chem. 23 (1984) 3720; (c) D.D. DesMarteau, R.D. LeBlond, J. Chem. Soc. Chem. Commun. (1974) 555; (d) D.D. DesMarteau, V. Montanari, Chem. Lett. (2000) 1052; (e) V. Montanari, D.D. DesMarteau, W.T. Pennington, Synthesis and structure of novel perfluorinated iodinanes, J. Mol. Struct. 550–551 (2000) 337. [2] P. Baudry, H. Majestre, L. Reibel, S. Bayoud, Electricite de FranceService National, US Patent 5,837,400 (1998). [3] (a) A. Hartmann, V. Meyer, Ber. Dtsc. Chem. Ges. 26 (1893) 1727; (b) F.M. Beringer, R.A. Falk, M. Karniol, I. Lillien, G. Masullo, M. Mausner, E. Sommer, J. Am. Chem. Soc. 81 (1959) 342; (c) F.M. Beringer, R.A. Falk, J. Am. Chem. Soc. 81 (1959) 2997. [4] (a) R.B. Sandin, Chem. Rev. 32 (1943) 249; (b) D.F. Banks, Chem. Rev. 66 (1966) 243; (c) E.B. Merkushev, Russ. Chem. Rev. 56 (1987) 826. [5] (a) J.V. Crivello, J.H.W. Lam, Macromolecules 10 (1977) 1307; (b) S.A. MacDonald, C.G. Willson, J.M.J. Frechet, Acc. Chem. Res. 27 (1994) 151; (c) E. Reichmanis, O. Nalamasu, F.M. Houlihan, Acc. Chem. Res. 32 (1999) 659; (d) T. Aoai, K. Sato, K. Kodama, Fuji Photo, US Patent 5,945,250 (1999).