Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity

The title molecules are sought in connection with various synthetic applications. The aliphatic fluorous alcohols RfnCH2OH (Rfn = CF3(CF2)n–1; n = 11, 13, 15) are converted to the triflates RfnCH2OTf (Tf2O, pyridine; 22–61%) and then to RfnCH2I (NaI, acetone; 58–69%). Subsequent reactions with NaOCl/HCl give iodine(III) dichlorides RfnCH2ICl2 (n = 11, 13; 33–81%), which slowly evolve Cl2. The ethereal fluorous alcohols CF3CF2CF2O(CF(CF3)CF2O)xCF(CF3)CH2OH (x = 2–5) are similarly converted to triflates and then to iodides, but efforts to generate the corresponding dichlorides fail. Substrates lacking a methylene group, RfnI, are also inert, but additions of TMSCl to bis(trifluoroacetates) RfnI(OCOCF3)2 appear to generate RfnICl2, which rapidly evolve Cl2. The aromatic fluorous iodides 1,3-Rf6C6H4I, 1,4-Rf6C6H4I, and 1,3-Rf10C6H4I are prepared from the corresponding diiodides, copper, and RfnI (110–130 °C, 50–60%), and afford quite stable RfnC6H4ICl2 species upon reaction with NaOCl/HCl (80–89%). Iodinations of 1,3-(Rf6)2C6H4 and 1,3-(Rf8CH2CH2)2C6H4 (NIS or I2/H5IO6) give 1,3,5-(Rf6)2C6H3I and 1,2,4-(Rf8CH2CH2)2C6H3I (77–93%). The former, the crystal structure of which is determined, reacts with Cl2 to give a 75:25 ArICl2/ArI mixture, but partial Cl2 evolution occurs upon work-up. The latter gives the easily isolated dichloride 1,2,4-(Rf8CH2CH2)2C6H3ICl2 (89%). The relative thermodynamic ease of dichlorination of these and other iodine(I) compounds is probed by DFT calculations.

Recently, our attention has been directed at two potential applications of iodine containing fluorous compounds. One involves new approaches to phosphorus-carbon bond formation using fluorous alkyl and aryl iodides [23,24]. The other involves the use of fluorous iodine(III) dichlorides for free radical chlorinations [25]. In this regard, phenyl iodine(III) dichloride (PhICl 2 ) is an effective free radical chlorinating agent for hydrocarbons [26,27]. Importantly, the mechanism does not involve the liberation of Cl 2 , followed by the textbook sequence of steps. Rather, hydrogen abstraction is effected by a species other than the chlorine radical Cl·, presumably PhICl· [26,27].
One potential attraction of fluorous iodine(III) dichlorides as chlorinating agents would be the recovery and recycling of the fluorous iodide byproduct. Towards this end, higher fluorophilicities are usually advantageous. To a first approximation, these are maximized by increasing the lengths and quantities of the (CF 2 ) n segments, and decreasing the lengths and quantities of any (CH 2 ) m segments [1][2][3]. However, longer (CF 2 ) n segments are often coupled with lower absolute solubilities [1,28], a logical consequence as one approaches the macromolecular limit of polytetrafluoroethylene. Fluorophilicities are typically quantified by fluorous/organic liquid/liquid phase partition coefficients [1][2][3]. The most common solvent combination is perfluoro(methylcyclohexane) (CF 3 C 6 F 11 ) and toluene.
The objective of this study was to bridge several strategic gaps regarding highly fluorophilic building blocks for the formation of (1) phosphorus-carbon bonded species, and (2) iodine(III) dichloride reagents. For example, aliphatic species of the formula R fn CH 2 CH 2 ICl 2 are unstable [17]. However, analogs with one less methylene group, R fn CH 2 ICl 2 , have been isolated for n = 8 and 10 as depicted in Scheme 1 [17,20]. Although partition coefficients are not available for the iodide R f8 CH 2 I (the byproduct that would form in most chlorination reactions), Scheme 2: Syntheses of fluorous compounds of the formula R fn CH 2 X. they would fall between those of R f8 I (88.5:11.5 for CF 3 C 6 F 11 / toluene [29]) and R f8 (CH 2 ) 3 I (50.7: 49.3 [30]). These rather modest fluorophilicities would presumably be lower for the more polar dichlorides R fn CH 2 ICl 2 -a possible disadvantage for reactions in fluorous solvents. In any case, higher homologs that would have more biased partition coefficients were sought.
In the same vein, literature data prompted interest in certain fluorous aromatic iodine(III) dichlorides. For example, the nonfluorous iodine(III) dichloride II-Me (Scheme 1) [31], which features two strongly electron-withdrawing nitro groups and a mildly electron-donating methyl group, is easily isolated in analytically pure form from the reaction of the corresponding aryl iodide and Cl 2 , even though the nitro groups render the iodine atom less Lewis basic and thermodynamically less prone to oxidation. The Hammett σ values associated with CF 2 CF 3 and CF 2 CF 2 CF 3 substituents (σ p 0.52; σ m 0.47-0.52 [32]) suggest that R fn groups are less electron withdrawing than nitro groups (σ p 0.81; σ m 0.71). Therefore, similar fluorous compounds of the formula (R fn ) 2 C 6 H 3 ICl 2 were seen as realistic targets. The less fluorophilic homologs III and IV (Scheme 1), which feature three methylene or CH 2 CH 2 CH 2 "spacers" that electronically insulate the arene ring from the perfluoroalkyl groups, have been previously isolated [17].
As described below, the pursuit of the preceding objectives has met with both success and some unanticipated speed bumps, for which parallel computational studies have provided valuable insight. Regardless, these efforts have resulted in a number of practical preparations that will soon be utilized in further applications [23], and defined various physical properties and stability limits that are useful guides for future research.

Results
Syntheses and reactions, R fn CH 2 I (n = 11, 13, 15). To the authors' knowledge, no fluorous alkyl iodides of the formula R fn CH 2 I are commercially available. Thus, as shown in Scheme 2, a sequence previously employed for lower homologs (n = 8, 10 [13]) was investigated. The commercially available alcohols R fn CH 2 OH (n = 11, 13, 15) were first converted to the triflates R fn CH 2 OTf using pyridine and triflic anhydride (Tf 2 O) in (trifluoromethyl)benzene (CF 3 C 6 H 5 ), an amphoteric solvent that is usually able to dissolve appreciable quantities of both fluorous and non-fluorous solutes [33]. The reactions with n = 11 and 13 were conducted at 0 °C, and work-ups gave the expected triflates in 60-61% yields. In contrast, only traces of product were obtained with n = 15, presumably due to the poor solubility of the alcohol in virtually any medium. However, the solubilities of fluorous compounds are often highly temperature dependent [28,34], and an analogous reaction at room temperature gave R f15 CH 2 OTf in 22% yield. The triflates were white solids with some solubility in acetone. They were characterized by IR and NMR ( 1 H, 13 C{ 1 H}, 19 F{ 1 H}) spectroscopy and microanalyses as summarized in the experimental section.
The triflates were treated with NaI in acetone at 75 °C. Over the course of 24 h, high conversions to the corresponding fluorous iodides R fn CH 2 I were realized, although at rates much slower than with non-fluorous analogs. Work-ups afforded the products as analytically pure white solids in 58-69% yields, which were characterized analogously to the triflates. All were to some degree soluble in acetone, but as the perfluoroalkyl group lengthened, appropriate cosolvents were required to achieve significant concentrations. In order to obtain 13 C NMR spectra (n = 13, 15), C 6 F 6 -which is technically a non-fluorous solvent [35] but is nonetheless often effective with fluorous soluteswas employed.
Importantly, these fluorous aliphatic iodides were more fluorophilic than those mentioned in the introduction. Representative partition coefficients were determined as described in the experimental section. Those for R f15 CH 2 I ranged from >99:<1 for CF 3 C 6 F 11 /toluene to 87:13 for CF 3 C 6 F 11 /acetone. The CF 3 C 6 F 11 /toluene partition coefficient of R f11 CH 2 I was also >99:<1.
Next, CH 3 CN/C 6 F 6 solutions of the fluorous aliphatic iodides (n = 11, 13) were treated with aqueous NaOCl and conc. HCl. The combination of HCl and a mild oxidant generates Cl 2 , providing a "greener" synthetic approach to iodine(III) dichlorides [36][37][38]. Accordingly, the target molecules R fn CH 2 ICl 2 precipitated in 33-81% yields. However, the poor solubilities of these pale yellow powders precluded further purification by the usual protocols. Microanalyses confirmed the presence of chlorine. When 1 H NMR spectra were recorded in acetone-d 6 , new CH 2 signals 1.37-1.38 ppm downfield of those of the precursors R fn CH 2 I were apparent. However, the NMR samples slowly became greenish yellow, suggestive of dissolved Cl 2 , and the starting iodides were usually evident. The use of Cl 2 in place of NaOCl/HCl did not give better results.
Syntheses and reactions, R fOx CH 2 I (x = 2-5). There is an ongoing effort in fluorous chemistry to decrease reliance on perfluorooctyl containing building blocks, which are associated with a variety of environmental issues [39]. One approach is to switch to related ethereal phase tags or "ponytails" [40,41]. Accordingly, oligomeric fluorous ethers that terminate in CH 2 OH groups, CF 3 CF 2 CF 2 O(CF(CF 3 )CF 2 O) x CF(CF 3 )CH 2 OH, are commercially available. These are abbreviated R fOx CH 2 OH, and the ethereal oxygen atoms have essentially no Lewis base character. In some cases, CF 2 CF 2 OCF(CF 3 )CF 2 OCF(CF 3 )segments have been found to impart higher fluorophilicites than similar perfluoroalkyl groups [42]. However, the multiple CF(CF 3 ) stereocenters are disadvantageous, as they render such compounds mixtures of diastereomers, presenting an impediment to crystallization. In some cases, NMR spectra do not differentiate the diastereomers, and in other cases more complex signal patterns are evident.
As shown in Scheme 3, the oligomeric alcohols (x = 2-5) were elaborated as described for the non-ethereal alcohols R fn CH 2 OH and a previous report involving the lower nonoligomeric homolog R fO1 CH 2 OH (x = 1 [5]). They were first converted to the triflates R fOx CH 2 OTf using pyridine and triflic anhydride (Tf 2 O). These were soluble in hexane/ethyl acetate and isolated as analytically pure colorless oils in 84-93% yields. Subsequent reactions with NaI in acetone (70-75 °C, x = 2,4,5) gave the corresponding iodides R fOx CH 2 I as colorless liquids in 81-91% yields. Unfortunately, efforts to oxidize these compounds to the corresponding iodine(III) dichlorides using the conditions in Scheme 1 and Scheme 2 were unsuccessful. NMR analyses of crude reaction mixtures showed only starting material.
Attempted syntheses of R fn ICl 2 . Prior to the efforts described in the previous sections, iodine(III) dichlorides derived from perfluoroalkyl iodides R fn I were considered as targets. Since these lack sp 3 carbon-hydrogen bonds, they are not susceptible to possible chlorination or other degradation under free radical chlorination conditions. However, no reactions were observed when R fn I were treated with Cl 2 or NaOCl/HCl. Nonetheless, perfluoroalkyl iodides R fn I (n = 6-8, 10, 12) can be oxidized using various recipes (e.g., 80% H 2 O 2 in trifluoroacetic acid anhydride) to the iodine(III) bis(trifluoroacetates) R fn I(OCOCF 3 ) 2 in high isolated yields [18,19,21]. It was thought that these might, in turn, react with TMSCl as sketched in Scheme 4 to provide "back door" entries to the target compounds R fn ICl 2 . Indeed, when these reactions were carried out, the samples exhibited the appropriate characteristic bright yellow colors (n = 6, 8). However, upon work-up only the original perfluoroalkyl iodides R fn I were isolated. Hence, it is concluded that the target compounds are thermodynamically and kinetically unstable with respect to Cl 2 elimination, consistent with the failure of the direct reaction and a lower Lewis basicity of the iodine atom as compared to R fn CH 2 I. After these experiments were carried out, we became aware of the isolation of CF 3 ICl 2 (R f1 ICl 2 ) from the reaction of CF 3 IClF and TMSCl at −40 °C [43]. This route is conceptually similar to that shown in Scheme 4, and a crystal structure of CF 3 ICl 2 could even be obtained. However, consistent with our observations, the compound decomposed above −35 °C.
However, this was not to be, so the results in this and the following section are presented in inverse chronological order, focusing first on arenes with one R fn substituent. As shown in Scheme 5 (top), the commercially available meta diiodide 1,3-C 6 H 4 I 2 was treated with copper (1.0 equiv) and R f6 I (0.5 equiv; a deficiency to help suppress dialkylation) in DMSO at 110 °C. Similar recipes have previously been used to couple aryl iodides and R fn I building blocks [45,46]. Work-up gave the target compound 1,3-R f6 C 6 H 4 I in 60% yield (based upon limiting R f6 I).
Scheme 6: Syntheses of aromatic fluorous compounds with two perfluoroalkyl groups.
Some of the previously reported dialkylation product 1,3-(R f6 ) 2 C 6 H 4 was also formed [47, 48], but was easily separated due to its differential fluorophilicity (extraction of a CH 3 CN solution with perfluorohexane). An analogous procedure with R f10 I gave the higher homolog 1,3-R f10 C 6 H 4 I in 50% yield [9], and a lesser amount of what was presumed to be the dialkylation product. The analogous para diiodide 1,4-C 6 H 4 I 2 gave parallel chemistry, as illustrated by the reaction with R f6 I to give 1,4-R f6 C 6 H 4 I (50% [4,12]) in Scheme 5 (bottom).
The three aryl iodides R fn C 6 H 4 I thus obtained were treated with NaOCl/HCl per the sequence in Scheme 2. As shown in Scheme 5, work-ups gave the corresponding iodine(III) dichlorides R fn C 6 H 4 ICl 2 as pale yellow powders in 80-89% yields. Although these were clean by NMR, only one gave a correct microanalysis. As illustrated in Figure S1 (Supporting Information File 1), CDCl 3 /C 6 F 6 solutions of 1,3-R f6 C 6 H 4 ICl 2 and 1,4-R f6 C 6 H 4 ICl 2 containing an internal standard were monitored by 1 H NMR. Slow partial evolution of Cl 2 to give the iodides 1,3-R f6 C 6 H 4 I and 1,4-R f6 C 6 H 4 I was observed (7% and 27% conversion over 60 h, respectively).
When Cl 2 gas was sparged through a CF 3 C 6 H 5 solution of 1,3,5-(R f6 ) 2 C 6 H 3 I at −30 °C to −35 °C, the sample turned bright yellow. Two aliquots were removed. The 1 H NMR spectrum of one ( Figure 1b) showed two downfield shifted signals (cf. Figure 1a), which were attributed to the target molecule 1,3,5-(R f6 ) 2 C 6 H 3 ICl 2 . Integration indicated 77:23 and 75:25 ArICl 2 /ArI ratios prior to and after solvent removal (room temperature, rotary evaporation). The isolated material was redissolved in CF 3 C 6 H 5 and kept at −35 °C. After 7 d, the solvent was again removed by rotary evaporation, giving a 65:35 ArICl 2 /ArI mixture (Figure 1d). The solvent was removed from the second aliquot by oil pump vacuum at −40 °C. This gave a 35:65 ArICl 2 /ArI mixture as a pale white solid (Figure 1c). A variety of attempts to achieve higher conversions or isolate pure 1,3,5-(R f6 ) 2 C 6 H 3 ICl 2 were unsuccessful. It was concluded that 1,3,5-(R f6 ) 2 C 6 H 3 ICl 2 was much more labile with respect to Cl 2 evolution than the fluorous aryliodine(III) dichlorides shown in Scheme 5, and that the 75-80% conversions reflected a thermodynamic limit.
As shown in Scheme 6, reactions of C 6 F 6 or perfluoroheptane solutions of 1,2,4-(R f8 CH 2 CH 2 ) 2 C 6 H 3 I and NaOCl/HCl gave the corresponding iodine(III) dichloride 1,2,4- (R f8 CH 2 CH 2 ) 2 C 6 H 3 ICl 2 [50] as a white powder in 89% yield. This material was stable at room temperature and gave a microanalysis consistent with a monohydrate. Hence, the iodine atom in benzenoid compounds with two R f8 CH 2 CH 2 substituents is sufficiently Lewis basic to support a dichloride, but analogs with two R f6 substituents are not.
Structural and computational data. Crystal structures of fluorous compounds were virtually unknown 20 years ago [51], so opportunities to acquire structural data are usually seized. Crystals of 1,3,5-(R f6 ) 2 C 6 H 3 I could be grown as described in the experimental section. X-ray data were collected, and the structure determined, as summarized in Table 1 and the experimental section. Two views of the molecular structure and key metrical parameters are provided in Figure 2. Two perspectives of the unit cell (Z = 8) are provided in Figure 3. There are some unusual features associated with the packing and space group, and these are treated in the discussion section.
In order to help interpret the accessibilities and/or stabilities of the various iodine(III) dichlorides described above, the gas phase free energies of chlorination (1) were computed by DFT methods as described in the experimental section and summarized in Table S1 (Supporting Information File 1). The data are presented in "ladder format" in Figure 4, with the substrates that undergo more exergonic chlorinations placed higher. The energy difference between any pair of compounds is equal to that expressed by the corresponding isodesmic equation: The validity of the data was supported by the good agreement of the computed structure of 1,3,5-(R f6 ) 2 C 6 H 3 I with the crystal structure ( Figure 2). An overlay, provided in Figure S2 (Supporting Information File 1), shows only very slightly increasing conformational differences as the perfluorohexyl groups extend from the arene. For the aliphatic compounds (R fn I, R fn CH 2 I, R fOx CH 2 ICl 2 ), the free energies of chlorination were calculated for a series of chain lengths. As summarized in Figure 4 and tabulated in Table S1 (Supporting Information File 1), the ΔG values within each series varied by less than 0.5 kcal/mol. In all cases, vertical ionization potentials (not presented) followed analogous trends. The iodine(III) dichlorides formed in the more exergonic reactions (upper portion of Figure 4) would be expected to be more stable with respect to Cl 2 evolution. Thus, the data are consistent with the stability order R fn CH 2 ICl 2 >> R fn ICl 2 evident from Scheme 2 and Scheme 4. However, they also imply that the ethereal systems R fOx CH 2 ICl 2 (Scheme 3; −0.65 kcal/mol, x = 1) should be more stable than R fn CH 2 ICl 2 (−0.53 to −0.59 kcal/mol, n = 4-8). All attempts to generate the former have been unsuccessful to date. Hence, there is either a kinetic barrier to the formation of R fOx CH 2 ICl 2 that is not overcome under the conditions of Scheme 3, or an unrecognized, presumably non-electronic, destabilizing feature.

Discussion
The preceding experimental data define the stability limits associated with a broad range of fluorous aliphatic and aromatic iodine(III) dichlorides. Aliphatic compounds of the formula R fn ICl 2 are clearly very unstable with respect to Cl 2 loss, although there is literature precedent for their synthesis and isolation from other iodine(III) precursors under exacting low temperature conditions [43]. When an insulating methylene group is introduced between the fluorous moiety and the ICl 2 group, the situation improves. Compounds of the formula R fn CH 2 ICl 2 can generally be isolated, although they are somewhat labile towards Cl 2 loss. In contrast, efforts to prepare the ethereal systems R fOx CH 2 ICl 2 by the chlorination of R fOx CH 2 I have been unsuccessful. This poses a conundrum with respect to the DFT calculations; they seemingly possess sufficient Lewis basicity (Figure 4), but there appears to be a kinetic barrier.
In contrast, fluorous aromatic iodine(III) dichlorides bearing a single perfluoroalkyl group, R fn C 6 H 4 ICl 2 , are easily isolated in analytically pure form (Scheme 5), although they are still subject to slow Cl 2 loss in solution ( Figure S1, Supporting Information File 1). However, it has not yet proved possible to quantitatively generate analogs with two perfluoroalkyl groups by chlorinations of iodine(I) precursors (Scheme 6, top); 75-80% conversions are the maximum realized to date. In contrast, chlorinations of the doubly substituted substrates (R fn (CH 2 ) m ) 2 C 6 H 3 I (m = 2, 3) go to completion, as exemplified in Scheme 1 (bottom) and Scheme 6 (bottom). The intervening methylene groups partially insulate the iodine atoms from the electron-withdrawing perfluoroalkyl segments, enhancing Lewis basicities.
However, it has not yet proved possible to access related compounds with three R fn (CH 2 ) m groups, at least when two of them are ortho to the iodine atom, as exemplified by V in Scheme 1 [17]. To probe this point, the DFT calculations were extended to the R f6 homologs of the precursors of the three aryliodine(III) dichlorides in Scheme 1. These correspond to VII, VIII, and IX in Scheme 7 (top). The ΔG values obtained were −3.40, −3.75, and −4.15 kcal/mol, respectively. Thus, the third R fn (CH 2 ) 3 substituent enhances the exergonicity of Cl 2 addition. Hence, the failure to observe a reaction must represent a kinetic phenomenon. A second "ladder", augmented with the additional alkyl and aryl iodides analyzed in the discussion section, is provided in Figure S3 (Supporting Information File 1).
Interestingly, isodesmic reactions corresponding to Equation 2 in the preceding section can actually be carried out. For example, Cl 2 can be transferred from the fluorous aliphatic iodine(III) dichloride R f1 CH 2 ICl 2 (CF 3 CH 2 ICl 2 ) to phenyl iodide as shown in Scheme 7 (middle) [52]. The ΔG value for the addition of Cl 2 to phenyl iodide is computed to be −3.86 kcal/mol, as compared to −0.72 kcal/mol for R f1 CH 2 I. Curiously, the introduction of two R fn (CH 2 ) 3 substituents that are ortho/para or meta/para to iodine is thermodynamically deactivating for Cl 2 addition (VII/III and VIII/IV; −3.40 to −3.75 kcal/mol), whereas the introduction of three that are ortho/para/ortho is activating (IX/V; −4.15 kcal/mol) but kinetically inhibiting for steric reasons.
As noted in the introduction, a long-standing goal has been to realize highly fluorophilic aliphatic and aromatic iodine(I) compounds and iodine(III) dichlorides. The preceding results raise the question, "quo vadis?" When the compounds R fn CH 2 I and R fn CH 2 ICl 2 reach n = 15 (Scheme 2), they are close to approaching a practical solubility limit, although the former gives a highly biased CF 3 C 6 F 11 /toluene liquid/liquid partition coefficient. Branched analogs may be more tractable. However, DFT calculations show that chlorinations of substrates such as (R fn ) 3 CCH 2 I X (Scheme 7) would be strongly endergonic (ΔG = 3.36 kcal/mol, n = 6). Related species, such as (1) (R fn ) 3 CCF 2 CF 2 CH 2 I, which features a more remote branch site, or (2) (R fn CH 2 ) 3 CCH 2 I, which features additional insulating methylene groups, would be more likely to give stabile iodine(III) dichlorides. Nonetheless, these types of species have never been described in the literature. Silicon has been used as a locus for branching, as exemplified by a variety of highly fluorophilic compounds of the formula (R fn CH 2 CH 2 ) 3 SiZ (see XI in Scheme 7, Z = 4-C 6 H 5 X [53,54]). However, these feature silicon-carbon and sp 3 carbon-hydrogen bonds that may be sensitive towards Cl 2 . The fluorous aryl iodides that are precursors to III and IV have rather modest fluorophilicities (CF 3 C 6 F 11 /toluene partition coefficients (69.5-74.7):(30.5-25.3) [16]), and simply lengthening the R f8 segments to R f10 or even longer is unlikely to achieve biases of >99:<1. The same goes for 1,2,4-(R f8 CH 2 CH 2 ) 2 C 6 H 3 I in Scheme 6. Accordingly, we suggest that branched fluorous aryl iodides of the formula (R fn ) 3 CC 6 H 4 I (XII, Scheme 7) have particular promise. DFT calculations establish exergonic chlorinations, with ΔG values of −1.93 and −1.59 kcal/mol for n = 6 and 8. This implies that the corresponding iodine(III) dichlorides should have good stabilities, equal to or better than those of 1,3-and 1,4-R f6 C 6 H 4 ICl 2 in Scheme 5. However, this represents a currently unknown type of compound, and the synthesis is potentially challenging.
The following analysis of the crystal structure of 1,3,5-(R f6 ) 2 C 6 H 3 I is kept brief, as this compound crystallizes in the same space group and crystal system (I4, tetragonal) as the corresponding bromide 1,3,5-(R f6 ) 2 C 6 H 3 Br reported earlier [48].
The unit cell dimensions of the latter are virtually identical, with the cell volume ca. 1.5% lower (4851.7(4) vs 4920.1(3) Å 3 ), apropos to the smaller bromine atom. The space group is both chiral and polar, and the unit cell dimensions of both compounds feature c values (5.5976(2)-5.5624 Å) that are much smaller than the a and b values (29.6474(9)-29.5335(13) Å). As noted earlier and illustrated in Figure 2 (bottom), the sixteen perfluorohexyl groups associated with the eight molecules in the unit cell lie roughly in the a/b plane. They largely segregate, as seen for most fluorous molecules [44,51,55,56], into fluorous domains.
The eight arene rings in the unit cell tilt distinctly out of the a/b plane (average angle 49.1°). Furthermore, the eight iodine atoms are oriented on the same "side" or a/b face of the unit cell. In the neighboring unit cell that adjoins the a/b face, the iodine atoms are found on the opposite side (c direction). This represents the molecular basis for the polar nature of the crystal. Also, the C-C-C-C and F-C-C-F segments in the perfluorohexyl groups do not exhibit the idealized antiperiplanar and gauche conformations associated with saturated alkanes. Rather, the torsion angles for the roughly anti linkages average 164.4(1.6)° and 166.0(3.6)°, respectively. This leads to helical motifs as shown in Figure 5, which are furthermore reproduced by the computations. The basis for this deviation, as well as a more detailed presentation of the torsional relationships, is provided elsewhere [57][58][59]. In a given molecule, the C 6 F 13 groups exhibit opposite helical chiralities (see Figure S2, Supporting Information File 1), affording a meso stereoisomer. Finally, attempts have been made to extend the preceding chemistry in several directions. In screening experiments, all of the fluorous iodine(III) dichlorides assayed, as well as PhICl 2 , were competent for the free radical chlorination of methane [25]. Under certain conditions, uncommon selectivities were apparent, but the fluorophilicities of the dichlorides or precursor iodides studied were insufficient for certain target recycling strategies. As discussed above, it is not clear how to meet these challenges at this time, although the couple R f13 CH 2 ICl 2 / R f13 CH 2 I would be one of several with promise. Regardless, the fluorous iodides reported herein have numerous other uses, some of which will be communicated in the near future [23].

Conclusion
The preceding experimental and computational data have established a strong correlation between iodine atom Lewis basicity and the feasibility of oxidizing fluorous and non-fluorous aliphatic and aromatic iodides to the corresponding iodine(III) dichlorides. Although a few surprises are noted, these are attributed to special phenomena that can drive equilibria, such as precipitation (e.g., the conversion of I-Me to II-Me in Scheme 1), or kinetic barriers (inertness of R fOx CH 2 I in Scheme 3 or the precursor to V in Scheme 1). With the fluorous iodides, the extent of chlorination generally provides a measure of the degree to which the electron-withdrawing perfluoroalkyl or perfluoroether segments are insulated from the Lewis basic site.

Experimental
Five syntheses that are representative of the types of transformations in this study are detailed in the main article. The remaining preparations are described in Supporting Information File 1, together with data on the solvents, starting materials, and instrumentation employed. Partition coefficients. The following is representative. A 20 mL vial was charged with a CF 3 C 6 F 11 solution of R fn CH 2 I (n = 11, 15; 5.0 × 10 −2 M, 4.0 mL) and toluene (4.0 mL), capped, and vigorously stirred. After 10 min at room temperature (24 °C), aliquots were removed from the fluorous (2.0 mL) and organic (2.0 mL) phases. The solvent was evaporated from each, and the residues were dried under vacuum. A solution of Ph 2 SiMe 2 (internal standard; 0.0055 mL) in acetoned 6 /CF 3 C 6 H 5 (1:1 v/v; 10.0 mL) was prepared. Each residue was dissolved in 1.00 mL of this solution and 1 H NMR spectra were recorded. The relative peak integrations gave the corresponding partition coefficients.

Crystallography.
A solution of 1,3,5-(R f6 ) 2 C 6 H 3 I (ca. 0.05 g) in CHCl 3 /C 6 F 6 (1.0 mL, 4:1 v/v) in an NMR tube was allowed to concentrate. After 2 d, colorless needles with well defined faces were obtained. Data were collected as outlined in Table 1. Integrated intensity information for each reflection was obtained by reduction of the data frames with the program APEX2 [64]. Data were corrected for Lorentz and polarization factors, and using SADABS [65] for absorption and crystal decay effects. The structure was solved by direct methods using SHELXTL/XS [66,67]. Non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were placed in idealized positions and refined using a riding model. The structure was refined (weighted least squares refinement on F 2 ) to convergence [66][67][68].

Calculations.
Computations were performed with the Gaussian09 program package, employing the ultrafine grid (99,590) to enhance accuracy [69]. Geometries were optimized using density functional theory (DFT). The B3LYP [70][71][72] functional was employed with an all-electron 6-311+G(d,p) [73] basis set on all atoms except iodine, which was treated using an effective core potential, SDD [74]. The optimized structures were subjected to frequency calculations (using the same functional and basis set as before) to confirm that all structures were local minima and to obtain the free energies of chlorination ( Figure 4 and Table S1, Supporting Information File 1).

Supporting Information
Full details and product characterization for all the syntheses described in Schemes 2, 3, 5, and 6, information on the solvents, starting materials, and instrumentation employed, and additional spectroscopic, structural, and computational data, including a molecular structure file that can be read by the program Mercury [75] and contains the optimized geometries of all computed structures [76].