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

Article abstract of DOI:10.3762/bjoc.13.246

The title molecules are sought in connection with various synthetic applications. The aliphatic fluorous alcohols R_fnCH₂OH (R_fn = CF₃(CF₂)_n-1; n = 11, 13, 15) are converted to the triflates R_fnCH₂OTf (Tf₂O, pyridine; 22-61%) and then to R_fnCH₂I (NaI, acetone; 58-69%). Subsequent reactions with NaOCl/HCl give iodine(III) dichlorides R_fnCH₂ICl₂ (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, R_fnI, are also inert, but additions of TMSCl to bis(trifluoroacetates) R_fnI(OCOCF₃)₂ appear to generate R_fnICl₂, which rapidly evolve Cl₂. The aromatic fluorous iodides 1, 3-R_f6C₆H₄I, 1, 4-R_f6C₆H₄I, and 1, 3-R_f10C₆H₄I are prepared from the corresponding diiodides, copper, and R_fnI (110-130 °C, 50-60%), and afford quite stable R_fnC₆H₄ICl₂ species upon reaction with NaOCl/HCl (80-89%). Iodinations of 1, 3-(R_f6)₂C₆H₄ and 1, 3-(R_f8CH₂CH₂)₂C₆H₄ (NIS or I₂/H₅IO₆) give 1, 3, 5-(R_f6)₂C₆H₃I and 1, 2, 4-(R_f8CH₂CH₂)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-(R_f8CH₂CH₂)₂C₆H₃ICl₂ (89%). The relative thermodynamic ease of dichlorination of these and other iodine(I) compounds is probed by DFT calculations.

Full text of DOI:10.3762/bjoc.13.246

Syntheses, structures, and stabilities of aliphatic and
aromatic fluorous iodine(I) and iodine(III) compounds:
the role of iodine Lewis basicity
Tathagata Mukherjee1,§, Soumik Biswas1, Andreas Ehnbom1, Subrata K. Ghosh1,
Ibrahim El-Zoghbi2, Nattamai Bhuvanesh1, Hassan S. Bazzi*2 and John A. Gladysz*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2017, 13, 2486–2501.
1Department of Chemistry, Texas A&M University, P.O. Box 30012,
College Station, Texas, 77842-3012, USA, and 2Department of
Chemistry, Texas A&M University at Qatar, P.O. Box 23874, Doha,
Qatar
doi:10.3762/bjoc.13.246
Received: 23 August 2017
Accepted: 25 October 2017
Published: 23 November 2017
Email:
Hassan S. Bazzi* - bazzi@tamu.edu; John A. Gladysz* -
gladysz@mail.chem.tamu.edu
This article is part of the Thematic Series "Organo-fluorine chemistry IV".
Guest Editor: D. O'Hagan
* Corresponding author
§ Present address: Dr. Tathagata Mukherjee, Intel Corporation, Hills-
boro, Oregon
© 2017 Mukherjee et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
chlorination; copper mediated perfluoroalkylation; crystal structure;
DFT calculations; fluorous; hypervalent iodine; nucleophilic
substitution; polar space group
Abstract
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.
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Introduction
A number of fluorous alkyl iodides, usually of the formula is an effective free radical chlorinating agent for hydrocarbons
RfnCH2CH2I or RfnI (Rfn = CF3(CF2)n–1), are commercially [26,27]. Importantly, the mechanism does not involve the liber-
available and have seen abundant use as building blocks in fluo- ation of Cl2, followed by the textbook sequence of steps.
rous chemistry [1-3]. Fluorous aryl iodides, such as RfnC6H4I or Rather, hydrogen abstraction is effected by a species other than
Rfn(CH2)mC6H4I species, are also often employed as intermedi- the chlorine radical Cl·, presumably PhICl· [26,27].
ates (typically m = 2, 3 and n ≥ 6 [1-3]), but only a few have
been commercialized [4]. Many research groups have de- One potential attraction of fluorous iodine(III) dichlorides as
scribed the syntheses of other types of fluorous alkyl [5-8] and chlorinating agents would be the recovery and recycling of the
aryl [9-12] iodides [13-17]. The former are ubiquitous by virtue fluorous iodide byproduct. Towards this end, higher fluorophi-
of the large number of perfluoroalkyl iodides RfnI that have licities are usually advantageous. To a first approximation, these
been shown to undergo free radical additions to alkenes [7,8]. are maximized by increasing the lengths and quantities of the
(CF2)n segments, and decreasing the lengths and quantities of
In previous papers, we have reported convenient preparations of any (CH2)m segments [1-3]. However, longer (CF2)n segments
a variety of fluorous alkyl iodides [13-15], aryl iodides [16,17], are often coupled with lower absolute solubilities [1,28], a
and hypervalent iodine(III) derivatives [16-19]. The latter have logical consequence as one approaches the macromolecular
included aliphatic iodine(III) bis(trifluoroacetates) [18,19] and limit of polytetrafluoroethylene. Fluorophilicities are typically
dichlorides [17], and aromatic iodine(III) bis(acetates) [16] and quantified by fluorous/organic liquid/liquid phase partition
dichlorides [17]. The bis(carboxylates) have been employed as coefficients [1-3]. The most common solvent combination is
recyclable reagents for oxidations of organic substrates perfluoro(methylcyclohexane) (CF3C6F11) and toluene.
[16,18,19], and some of the dichlorides are depicted in
Scheme 1. Others have described additional fluorous iodine(III) The objective of this study was to bridge several strategic gaps
species [11,20-22].
regarding highly fluorophilic building blocks for the formation
of (1) phosphorus–carbon bonded species, and (2) iodine(III)
Recently, our attention has been directed at two potential appli- dichloride reagents. For example, aliphatic species of the
cations of iodine containing fluorous compounds. One involves formula RfnCH2CH2ICl2 are unstable [17]. However, analogs
new approaches to phosphorus–carbon bond formation using with one less methylene group, RfnCH2ICl2, have been isolated
fluorous alkyl and aryl iodides [23,24]. The other involves the for n = 8 and 10 as depicted in Scheme 1 [17,20]. Although
use of fluorous iodine(III) dichlorides for free radical chlorina- partition coefficients are not available for the iodide Rf8CH2I
tions [25]. In this regard, phenyl iodine(III) dichloride (PhICl2) (the byproduct that would form in most chlorination reactions),
Scheme 1: Some previously reported iodine(III) dichlorides relevant to this work.
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they would fall between those of Rf8I (88.5:11.5 for CF3C6F11/ that is usually able to dissolve appreciable quantities of both
toluene [29]) and Rf8(CH2)3I (50.7: 49.3 [30]). These rather fluorous and non-fluorous solutes [33]. The reactions with
modest fluorophilicities would presumably be lower for the n = 11 and 13 were conducted at 0 °C, and work-ups gave the
more polar dichlorides RfnCH2ICl2 – a possible disadvantage expected triflates in 60–61% yields. In contrast, only traces of
for reactions in fluorous solvents. In any case, higher homologs product were obtained with n = 15, presumably due to the poor
that would have more biased partition coefficients were sought. solubility of the alcohol in virtually any medium. However, the
solubilities of fluorous compounds are often highly temperature
In the same vein, literature data prompted interest in certain dependent [28,34], and an analogous reaction at room tempera-
fluorous aromatic iodine(III) dichlorides. For example, the non- ture gave Rf15CH2OTf in 22% yield. The triflates were white
fluorous iodine(III) dichloride II-Me (Scheme 1) [31], which solids with some solubility in acetone. They were characterized
features two strongly electron-withdrawing nitro groups and a by IR and NMR (1H, 13C{1H}, 19F{1H}) spectroscopy and
mildly electron-donating methyl group, is easily isolated in ana- microanalyses as summarized in the experimental section.
lytically pure form from the reaction of the corresponding aryl
iodide and Cl2, even though the nitro groups render the iodine The triflates were treated with NaI in acetone at 75 °C. Over the
atom less Lewis basic and thermodynamically less prone to oxi- course of 24 h, high conversions to the corresponding fluorous
dation. The Hammett σ values associated with CF2CF3 and iodides RfnCH2I were realized, although at rates much slower
CF2CF2CF3 substituents (σp 0.52; σm 0.47–0.52 [32]) suggest than with non-fluorous analogs. Work-ups afforded the prod-
that Rfn groups are less electron withdrawing than nitro groups ucts as analytically pure white solids in 58–69% yields, which
(σp 0.81; σm 0.71). Therefore, similar fluorous compounds of were characterized analogously to the triflates. All were to some
the formula (Rfn)2C6H3ICl2 were seen as realistic targets. The degree soluble in acetone, but as the perfluoroalkyl group
less fluorophilic homologs III and IV (Scheme 1), which fea- lengthened, appropriate cosolvents were required to achieve sig-
ture three methylene or CH2CH2CH2 "spacers" that electroni- nificant concentrations. In order to obtain 13C NMR spectra
cally insulate the arene ring from the perfluoroalkyl groups, (n = 13, 15), C6F6 – which is technically a non-fluorous solvent
have been previously isolated [17].
[35] but is nonetheless often effective with fluorous solutes –
was employed.
As described below, the pursuit of the preceding objectives has
met with both success and some unanticipated speed bumps, for Importantly, these fluorous aliphatic iodides were more fluo-
which parallel computational studies have provided valuable rophilic than those mentioned in the introduction. Representa-
insight. Regardless, these efforts have resulted in a number of tive partition coefficients were determined as described in the
practical preparations that will soon be utilized in further appli- experimental section. Those for Rf15CH2I ranged from >99:<1
cations [23], and defined various physical properties and for CF3C6F11/toluene to 87:13 for CF3C6F11/acetone. The
stability limits that are useful guides for future research. CF3C6F11/toluene partition coefficient of Rf11CH2I was also
>99:<1.
Results
Syntheses and reactions, RfnCH2I (n = 11, 13, 15). To the Next, CH3CN/C6F6 solutions of the fluorous aliphatic iodides
authors' knowledge, no fluorous alkyl iodides of the formula (n = 11, 13) were treated with aqueous NaOCl and conc. HCl.
RfnCH2I are commercially available. Thus, as shown in The combination of HCl and a mild oxidant generates Cl2, pro-
Scheme 2, a sequence previously employed for lower homologs viding a "greener" synthetic approach to iodine(III) dichlorides
(n = 8, 10 [13]) was investigated. The commercially available [36-38]. Accordingly, the target molecules RfnCH2ICl2 precipi-
alcohols RfnCH2OH (n = 11, 13, 15) were first converted to the tated in 33–81% yields. However, the poor solubilities of these
triflates RfnCH2OTf using pyridine and triflic anhydride (Tf2O) pale yellow powders precluded further purification by the usual
in (trifluoromethyl)benzene (CF3C6H5), an amphoteric solvent protocols. Microanalyses confirmed the presence of chlorine.
Scheme 2: Syntheses of fluorous compounds of the formula RfnCH2X.
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When 1H NMR spectra were recorded in acetone-d6, new CH2 and isolated as analytically pure colorless oils in 84–93%
signals 1.37–1.38 ppm downfield of those of the precursors yields. Subsequent reactions with NaI in acetone (70–75 °C,
RfnCH2I were apparent. However, the NMR samples slowly be- x = 2,4,5) gave the corresponding iodides RfOxCH2I as color-
came greenish yellow, suggestive of dissolved Cl2, and the less liquids in 81–91% yields. Unfortunately, efforts to oxidize
starting iodides were usually evident. The use of Cl2 in place of these compounds to the corresponding iodine(III) dichlorides
NaOCl/HCl did not give better results.
using the conditions in Scheme 1 and Scheme 2 were unsuc-
cessful. NMR analyses of crude reaction mixtures showed only
Syntheses and reactions, RfOxCH2I (x = 2–5). There is an starting material.
ongoing effort in fluorous chemistry to decrease reliance on
perfluorooctyl containing building blocks, which are associated Attempted syntheses of RfnICl2. Prior to the efforts described
with a variety of environmental issues [39]. One approach is to in the previous sections, iodine(III) dichlorides derived from
switch to related ethereal phase tags or "ponytails" [40,41]. Ac- perfluoroalkyl iodides RfnI were considered as targets. Since
cordingly, oligomeric fluorous ethers that terminate in CH2OH these lack sp3 carbon–hydrogen bonds, they are not susceptible
groups, CF3CF2CF2O(CF(CF3)CF2O)xCF(CF3)CH2OH, are to possible chlorination or other degradation under free radical
commercially available. These are abbreviated RfOxCH2OH, chlorination conditions. However, no reactions were observed
and the ethereal oxygen atoms have essentially no Lewis base when RfnI were treated with Cl2 or NaOCl/HCl.
character. In some cases, CF2CF2OCF(CF3)CF2OCF(CF3)-
segments have been found to impart higher fluorophilicites than Nonetheless, perfluoroalkyl iodides RfnI (n = 6–8, 10, 12) can
similar perfluoroalkyl groups [42]. However, the multiple be oxidized using various recipes (e.g., 80% H2O2 in trifluoro-
CF(CF3) stereocenters are disadvantageous, as they render such acetic acid anhydride) to the iodine(III) bis(trifluoroacetates)
compounds mixtures of diastereomers, presenting an impedi- RfnI(OCOCF3)2 in high isolated yields [18,19,21]. It was
ment to crystallization. In some cases, NMR spectra do not thought that these might, in turn, react with TMSCl as sketched
differentiate the diastereomers, and in other cases more com- in Scheme 4 to provide "back door" entries to the target com-
plex signal patterns are evident.
pounds RfnICl2. Indeed, when these reactions were carried out,
the samples exhibited the appropriate characteristic bright
As shown in Scheme 3, the oligomeric alcohols (x = 2–5) were yellow colors (n = 6, 8). However, upon work-up only the orig-
elaborated as described for the non-ethereal alcohols inal perfluoroalkyl iodides RfnI were isolated. Hence, it is con-
RfnCH2OH and a previous report involving the lower non- cluded that the target compounds are thermodynamically and
oligomeric homolog RfO1CH2OH (x = 1 [5]). They were first kinetically unstable with respect to Cl2 elimination, consistent
converted to the triflates RfOxCH2OTf using pyridine and triflic with the failure of the direct reaction and a lower Lewis basicity
anhydride (Tf2O). These were soluble in hexane/ethyl acetate of the iodine atom as compared to RfnCH2I.
Scheme 3: Syntheses of fluorous compounds of the formula CF3CF2CF2O(CF(CF3)CF2O)xCF(CF3)CH2X'.
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Scheme 4: Attempted syntheses of aliphatic fluorous iodine(III) dichlorides RfnICl2.
After these experiments were carried out, we became aware of of C6H5Rf8 (77.5:22.5) or 1,4-(Rf8)2C6H4 (99.3:0.7) with the
the isolation of CF3ICl2 (Rf1ICl2) from the reaction of CF3IClF preceding examples [29]). Thus, in considering various fluo-
and TMSCl at −40 °C [43]. This route is conceptually similar to rous aryliodine(III) dichloride targets, initial efforts were
that shown in Scheme 4, and a crystal structure of CF3ICl2 directed at systems with at least two Rfn substituents per arene
could even be obtained. However, consistent with our observa- ring. Given the ready isolation of the dinitro-substituted aryl-
tions, the compound decomposed above −35 °C.
iodine(III) dichloride II-Me in Scheme 1 [31], this was seen as
a surefire objective.
Syntheses and reactions, aryl iodides with one perfluoro-
alkyl group. Aromatic compounds are challenging to render However, this was not to be, so the results in this and the
highly fluorophilic [16,30,44]. For example, the singly-phase- following section are presented in inverse chronological order,
tagged arene C6H5CH2CH2CH2Rf8 gives a 49.5:50.5 focusing first on arenes with one Rfn substituent. As shown in
CF3C6F11/toluene partition coefficient. Values for doubly Scheme 5 (top), the commercially available meta diiodide 1,3-
tagged analogs fall into the range (90.7–91.2):(9.3–8.8) C6H4I2 was treated with copper (1.0 equiv) and Rf6I (0.5 equiv;
(o, m, p-isomers), and that for the triply tagged species 1,3,5- a deficiency to help suppress dialkylation) in DMSO at 110 °C.
C6H3(CH2CH2CH2Rf8)3 is >99.7:<0.3 [30]. As noted above, Similar recipes have previously been used to couple aryl iodides
longer perfluoroalkyl segments increase fluorophilicities, as do and RfnI building blocks [45,46]. Work-up gave the target com-
shorter methylene segments (compare the partition coefficients pound 1,3-Rf6C6H4I in 60% yield (based upon limiting Rf6I).
Scheme 5: Syntheses of aromatic fluorous compounds with one perfluoroalkyl group.
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Some of the previously reported dialkylation product 1,3- yellow. Two aliquots were removed. The 1H NMR spectrum of
(Rf6)2C6H4 was also formed [47,48], but was easily separated one (Figure 1b) showed two downfield shifted signals
due to its differential fluorophilicity (extraction of a CH3CN (cf. Figure 1a), which were attributed to the target molecule
solution with perfluorohexane). An analogous procedure with 1,3,5-(Rf6)2C6H3ICl2. Integration indicated 77:23 and 75:25
Rf10I gave the higher homolog 1,3-Rf10C6H4I in 50% yield [9], ArICl2/ArI ratios prior to and after solvent removal (room tem-
and a lesser amount of what was presumed to be the dialkyla- perature, rotary evaporation). The isolated material was redis-
tion product. The analogous para diiodide 1,4-C6H4I2 gave solved in CF3C6H5 and kept at −35 °C. After 7 d, the solvent
parallel chemistry, as illustrated by the reaction with Rf6I to was again removed by rotary evaporation, giving a 65:35
give 1,4-Rf6C6H4I (50% [4,12]) in Scheme 5 (bottom).
ArICl2/ArI mixture (Figure 1d). The solvent was removed from
the second aliquot by oil pump vacuum at −40 °C. This gave a
The three aryl iodides RfnC6H4I thus obtained were treated with 35:65 ArICl2/ArI mixture as a pale white solid (Figure 1c). A
NaOCl/HCl per the sequence in Scheme 2. As shown in variety of attempts to achieve higher conversions or isolate pure
Scheme 5, work-ups gave the corresponding iodine(III) dichlo- 1,3,5-(Rf6)2C6H3ICl2 were unsuccessful. It was concluded that
rides RfnC6H4ICl2 as pale yellow powders in 80–89% yields. 1,3,5-(Rf6)2C6H3ICl2 was much more labile with respect to Cl2
Although these were clean by NMR, only one gave a correct evolution than the fluorous aryliodine(III) dichlorides shown in
microanalysis. As illustrated in Figure S1 (Supporting Informa- Scheme 5, and that the 75–80% conversions reflected a thermo-
tion File 1), CDCl3/C6F6 solutions of 1,3-Rf6C6H4ICl2 and 1,4- dynamic limit.
Rf6C6H4ICl2 containing an internal standard were monitored by
1H NMR. Slow partial evolution of Cl2 to give the iodides 1,3- Next, analogs of 1,3,5-(Rf6)2C6H3ICl2 with less electron-defi-
Rf6C6H4I and 1,4-Rf6C6H4I was observed (7% and 27% cient iodine atoms were sought. As shown in Scheme 1, related
conversion over 60 h, respectively).
fluorous aryliodine(III) dichlorides with three-methylene spac-
ers, (Rf8CH2CH2CH2)2C6H3ICl2, had been isolated (the
Syntheses and reactions, aryl iodides with two perfluoro- isomers III, IV) [17]. Recently, a potential precursor with two-
alkyl groups. In a previously reported procedure [48], the diio- methylene spacers, 1,3-(Rf8CH2CH2)2C6H4, became readily
dide 1,3-C6H4I2 was treated with copper (5.1 equiv) and Rf6I available [49]. Accordingly, it could be iodinated with
(2.2 equiv) in DMSO at 140 °C. As shown in Scheme 6 (top), I2/H5IO6 as shown in Scheme 6 (bottom) to give 1,2,4-
the bis(perfluorohexyl) adduct 1,3-(Rf6)2C6H4, which was the (Rf8CH2CH2)2C6H3I [50] in 93% yield after work-up. The
undesired byproduct in Scheme 5 (top), was isolated in 75% 1H NMR spectrum clearly indicated the regioisomer in which
yield. Subsequent iodination using NIS in fuming H2SO4/ the iodide is ortho and para to the two alkyl substituents. This
CF3CO2H afforded the "all meta" iodide 1,3,5-(Rf6)2C6H3I in contrasts with the iodination of 1,3-(Rf6)2C6H4, in which the
77% yield. The substitution pattern was evident from the substituents function as meta directing groups.
1H NMR spectrum.
As shown in Scheme 6, reactions of C6F6 or perfluoroheptane
When Cl2 gas was sparged through a CF3C6H5 solution of solutions of 1,2,4-(Rf8CH2CH2)2C6H3I and NaOCl/HCl
1,3,5-(Rf6)2C6H3I at −30 °C to −35 °C, the sample turned bright gave the corresponding iodine(III) dichloride 1,2,4-
Scheme 6: Syntheses of aromatic fluorous compounds with two perfluoroalkyl groups.
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Figure 1: Partial 1H NMR spectra (sp2 CH, 500 MHz, CDCl3) relating to the reaction of 1,3,5-(Rf6)2C6H3I and Cl2 in CF3C6H5 at −30 to −35 °C:
(a) starting 1,3,5-(Rf6)2C6H3I; (b) aliquot taken after 24 h and removing nearly all CF3C6H5 (* = residual signals) by rotary evaporation (75:25 ArICl2/
ArI); (c) aliquot taken after 24 h and removing all solvents by oil pump vacuum at −40 °C (35:65 ArICl2/ArI); (d) the sample from b, which was redis-
solved in CF3C6H5, kept at −35 °C for 7 d, and worked up as in b (65:35 ArICl2/ArI). The signals for the protons para and ortho to the iodine atoms are
denoted ° and ◊ (red = ArI; blue = ArICl2).
(Rf8CH2CH2)2C6H3ICl2 [50] as a white powder in 89% yield. were computed by DFT methods as described in the experimen-
This material was stable at room temperature and gave a micro- tal section and summarized in Table S1 (Supporting Informa-
analysis consistent with a monohydrate. Hence, the iodine atom tion File 1). The data are presented in "ladder format" in
in benzenoid compounds with two Rf8CH2CH2 substituents is Figure 4, with the substrates that undergo more exergonic chlo-
sufficiently Lewis basic to support a dichloride, but analogs rinations placed higher. The energy difference between any pair
with two Rf6 substituents are not.
of compounds is equal to that expressed by the corresponding
isodesmic equation:
Structural and computational data. Crystal structures of fluo-
rous compounds were virtually unknown 20 years ago [51], so
opportunities to acquire structural data are usually seized. Crys-
tals of 1,3,5-(Rf6)2C6H3I could be grown as described in the ex-
perimental section. X-ray data were collected, and the structure
(2)
determined, as summarized in Table 1 and the experimental The validity of the data was supported by the good agreement
section. Two views of the molecular structure and key metrical of the computed structure of 1,3,5-(Rf6)2C6H3I with the crystal
parameters are provided in Figure 2. Two perspectives of the structure (Figure 2). An overlay, provided in Figure S2 (Sup-
unit cell (Z = 8) are provided in Figure 3. There are some porting Information File 1), shows only very slightly increasing
unusual features associated with the packing and space group, conformational differences as the perfluorohexyl groups extend
and these are treated in the discussion section.
from the arene. For the aliphatic compounds (RfnI, RfnCH2I,
RfOxCH2ICl2), the free energies of chlorination were calculated
In order to help interpret the accessibilities and/or stabilities of for a series of chain lengths. As summarized in Figure 4 and
the various iodine(III) dichlorides described above, the gas tabulated in Table S1 (Supporting Information File 1), the
phase free energies of chlorination
ΔG values within each series varied by less than 0.5 kcal/mol.
In all cases, vertical ionization potentials (not presented) fol-
lowed analogous trends.
(1)
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Table 1: Summary of crystallographic data for 1,3,5-(Rf6)2C6H3I.
empirical formula
C18H3F26I
840.10
formula weight
diffractometer
Bruker GADDS X-ray (three-circle)
temperature [K]
110(2)
1.54178
tetragonal
I4
wavelength [Å]
crystal system
space group
unit cell dimensions
a [Å]
29.6474(9)
29.6474(9)
5.5976(2)
90
b [Å]
c [Å]
α [°]
β [°]
90
γ [°]
90
V [Å3]
4920.1(3)
8
Z
ρcalcd [Mg/m3]
µ [mm−1]
2.268
12.238
F(000)
3184
crystal size [mm3]
θ limit [°]
0.40 × 0.02 × 0.02
2.11 to 59.94
−33, 32; −33, 33; −6, 5
53384
index ranges [h, k, l]
reflections collected
independent reflections
R(int)
3568
0.0540
completeness (%) to θ (°)
max. and min. transmission
data/restraints/parameters
goodness-of-fit on F2
R indices (final) [I > 2σ(I)]
R1
99.8 (59.94)
0.7919 and 0.0843
3568/1/407
0.991
0.0156
0.0355
wR2
R indices (all data)
R1
0.0172
wR2
0.0357
largest diff. peak and hole [eÅ−3]
0.227 and −0.532
The iodine(III) dichlorides formed in the more exergonic reac- iodine(III) dichloride II-Me in pure form (Scheme 1), but not
tions (upper portion of Figure 4) would be expected to be more the bis(perfluorohexyl) species 1,3,5-(Rf6)2C6H3ICl2
stable with respect to Cl2 evolution. Thus, the data are consis- (Scheme 6, Figure 1). The latter is derived from a more Lewis
tent with the stability order RfnCH2ICl2 >> RfnICl2 evident basic aryl iodide, with Cl2 addition 0.83 kcal/mol more favor-
from Scheme 2 and Scheme 4. However, they also imply that able. The ortho methyl group in II-Me plays a moderately stabi-
the ethereal systems RfOxCH2ICl2 (Scheme 3; −0.65 kcal/mol, lizing role, with Cl2 addition to I-Me 0.73 kcal/mol more favor-
x = 1) should be more stable than RfnCH2ICl2 (−0.53 to able than I. Otherwise, the computations (carried out with Rf6
−0.59 kcal/mol, n = 4–8). All attempts to generate the former groups to aid comparability) nicely predict the relative stabili-
have been unsuccessful to date. Hence, there is either a kinetic ties of the fluorous aryliodine(III) dichlorides (1,2,4-
barrier to the formation of RfOxCH2ICl2 that is not overcome (Rf8CH2CH2)2C6H3ICl2 [50] > 1,4-Rf6C6H4ICl2 > 1,3-
under the conditions of Scheme 3, or an unrecognized, presum- Rf6C6H4ICl2 > 1,3,5-(Rf6)2C6H3ICl2).
ably non-electronic, destabilizing feature.
Discussion
In the same vein, there must be a mitigating factor, such as solu- The preceding experimental data define the stability limits asso-
bility, that allows the isolation of the dinitro-substituted aryl- ciated with a broad range of fluorous aliphatic and aromatic
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Beilstein J. Org. Chem. 2017, 13, 2486–2501.
Figure 2: Two views of the molecular structure of 1,3,5-(Rf6)2C6H3I with thermal ellipsoids at the 50% probability level. Key bond lengths (Å) and
angles (°): C1–I1 2.099(3), C1–C2 1.391(4), C2–C3 1.386(4), C3–C4 1.393(4), C4–C5 1.387(4), C5–C6 1.393(4), C6–C1 1.394(4), C3–C7 1.501(4),
C5–C13 1.508(4), average of 10 CF–CF 1.545(5), I1–C1–C2 119.0(2), C1–C2–C3 118.8(3), C2–C3–C4 121.0(3), C3–C4–C5 119.2(3), C4–C5–C6
121.1(3), C5–C6–C1 118.5(3), C6–C1–C2 121.4(3), C6–C1–I1 119.5(2), C2–C3–C7 119.7(2), C4–C3–C7 119.3(2), C4–C5–C13 119.6(2),
C6–C5–C13 119.3(2), average of 8 CF–CF–CF 115.0(10).
iodine(III) dichlorides. Aliphatic compounds of the formula (Rfn(CH2)m)2C6H3I (m = 2, 3) go to completion, as exempli-
RfnICl2 are clearly very unstable with respect to Cl2 loss, al- fied in Scheme 1 (bottom) and Scheme 6 (bottom). The inter-
though there is literature precedent for their synthesis and isola- vening methylene groups partially insulate the iodine atoms
tion from other iodine(III) precursors under exacting low tem- from the electron-withdrawing perfluoroalkyl segments,
perature conditions [43]. When an insulating methylene group enhancing Lewis basicities.
is introduced between the fluorous moiety and the ICl2 group,
the situation improves. Compounds of the formula RfnCH2ICl2 However, it has not yet proved possible to access related com-
can generally be isolated, although they are somewhat labile pounds with three Rfn(CH2)m groups, at least when two of them
towards Cl2 loss. In contrast, efforts to prepare the ethereal are ortho to the iodine atom, as exemplified by V in Scheme 1
systems RfOxCH2ICl2 by the chlorination of RfOxCH2I have [17]. To probe this point, the DFT calculations were extended to
been unsuccessful. This poses a conundrum with respect to the the Rf6 homologs of the precursors of the three aryliodine(III)
DFT calculations; they seemingly possess sufficient Lewis dichlorides in Scheme 1. These correspond to VII, VIII, and IX
basicity (Figure 4), but there appears to be a kinetic barrier. in Scheme 7 (top). The ΔG values obtained were −3.40, −3.75,
and −4.15 kcal/mol, respectively. Thus, the third Rfn(CH2)3
In contrast, fluorous aromatic iodine(III) dichlorides bearing a substituent enhances the exergonicity of Cl2 addition. Hence,
single perfluoroalkyl group, RfnC6H4ICl2, are easily isolated in the failure to observe a reaction must represent a kinetic phe-
analytically pure form (Scheme 5), although they are still nomenon. A second "ladder", augmented with the additional
subject to slow Cl2 loss in solution (Figure S1, Supporting alkyl and aryl iodides analyzed in the discussion section, is pro-
Information File 1). However, it has not yet proved possible to vided in Figure S3 (Supporting Information File 1).
quantitatively generate analogs with two perfluoroalkyl groups
by chlorinations of iodine(I) precursors (Scheme 6, top); Interestingly, isodesmic reactions corresponding to Equation 2
75–80% conversions are the maximum realized to date. In in the preceding section can actually be carried out. For exam-
contrast, chlorinations of the doubly substituted substrates ple, Cl2 can be transferred from the fluorous aliphatic
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Beilstein J. Org. Chem. 2017, 13, 2486–2501.
Figure 3: Ball-and-stick and space filling representations of the unit
cell of 1,3,5-(Rf6)2C6H3I.
iodine(III) dichloride Rf1CH2ICl2 (CF3CH2ICl2) to phenyl
iodide as shown in Scheme 7 (middle) [52]. The ΔG value for
the addition of Cl2 to phenyl iodide is computed to be
−3.86 kcal/mol, as compared to −0.72 kcal/mol for Rf1CH2I.
Curiously, the introduction of two Rfn(CH2)3 substituents that
are ortho/para or meta/para to iodine is thermodynamically
deactivating for Cl2 addition (VII/III and VIII/IV; −3.40 to
−3.75 kcal/mol), whereas the introduction of three that are
Figure 4: Free energies of chlorination of relevant aryl and alkyl
iodides to the corresponding iodine(III) dichlorides in the gas phase
(kcal/mol), presented in a ladder format (each iodide is more Lewis
basic than that shown below it).
ortho/para/ortho is activating (IX/V; −4.15 kcal/mol) but kinet- (Rfn)3CCH2I X (Scheme 7) would be strongly endergonic
ically inhibiting for steric reasons.
(ΔG = 3.36 kcal/mol, n = 6). Related species, such as (1)
(Rfn)3CCF2CF2CH2I, which features a more remote branch site,
As noted in the introduction, a long-standing goal has been to or (2) (RfnCH2)3CCH2I, which features additional insulating
realize highly fluorophilic aliphatic and aromatic iodine(I) com- methylene groups, would be more likely to give stabile
pounds and iodine(III) dichlorides. The preceding results raise iodine(III) dichlorides. Nonetheless, these types of species have
the question, "quo vadis?" When the compounds RfnCH2I and never been described in the literature. Silicon has been used as a
RfnCH2ICl2 reach n = 15 (Scheme 2), they are close to locus for branching, as exemplified by a variety of highly fluo-
approaching a practical solubility limit, although the former rophilic compounds of the formula (RfnCH2CH2)3SiZ (see XI
gives a highly biased CF3C6F11/toluene liquid/liquid partition in Scheme 7, Z = 4-C6H5X [53,54]). However, these feature
coefficient. Branched analogs may be more tractable. However, silicon–carbon and sp3 carbon–hydrogen bonds that may be
DFT calculations show that chlorinations of substrates such as sensitive towards Cl2.
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Beilstein J. Org. Chem. 2017, 13, 2486–2501.
Scheme 7: Other relevant fluorous compounds and reactions.
The fluorous aryl iodides that are precursors to III and IV have that are much smaller than the a and b values
rather modest fluorophilicities (CF3C6F11/toluene partition (29.6474(9)–29.5335(13) Å). As noted earlier and illustrated in
coefficients (69.5–74.7):(30.5–25.3) [16]), and simply length- Figure 2 (bottom), the sixteen perfluorohexyl groups associated
ening the Rf8 segments to Rf10 or even longer is unlikely to with the eight molecules in the unit cell lie roughly in the a/b
achieve biases of >99:<1. The same goes for 1,2,4- plane. They largely segregate, as seen for most fluorous mole-
(Rf8CH2CH2)2C6H3I in Scheme 6. Accordingly, we suggest cules [44,51,55,56], into fluorous domains.
that branched fluorous aryl iodides of the formula (Rfn)3CC6H4I
(XII, Scheme 7) have particular promise. DFT calculations The eight arene rings in the unit cell tilt distinctly out of the a/b
establish exergonic chlorinations, with ΔG values of −1.93 and plane (average angle 49.1°). Furthermore, the eight iodine
−1.59 kcal/mol for n = 6 and 8. This implies that the corre- atoms are oriented on the same "side" or a/b face of the unit
sponding iodine(III) dichlorides should have good stabilities, cell. In the neighboring unit cell that adjoins the a/b face, the
equal to or better than those of 1,3- and 1,4-Rf6C6H4ICl2 in iodine atoms are found on the opposite side (c direction). This
Scheme 5. However, this represents a currently unknown type represents the molecular basis for the polar nature of the crystal.
of compound, and the synthesis is potentially challenging.
Also, the C–C–C–C and F–C–C–F segments in the perfluoro-
hexyl groups do not exhibit the idealized antiperiplanar and
The following analysis of the crystal structure of 1,3,5- gauche conformations associated with saturated alkanes. Rather,
(Rf6)2C6H3I is kept brief, as this compound crystallizes in the the torsion angles for the roughly anti linkages average
same space group and crystal system (I4, tetragonal) as the cor- 164.4(1.6)° and 166.0(3.6)°, respectively. This leads to helical
responding bromide 1,3,5-(Rf6)2C6H3Br reported earlier [48]. motifs as shown in Figure 5, which are furthermore reproduced
The unit cell dimensions of the latter are virtually identical, by the computations. The basis for this deviation, as well as a
with the cell volume ca. 1.5% lower (4851.7(4) vs more detailed presentation of the torsional relationships, is pro-
4920.1(3) Å3), apropos to the smaller bromine atom. The space vided elsewhere [57-59]. In a given molecule, the C6F13 groups
group is both chiral and polar, and the unit cell dimensions of exhibit opposite helical chiralities (see Figure S2, Supporting
both compounds feature c values (5.5976(2)–5.5624 Å) Information File 1), affording a meso stereoisomer.
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Figure 5: Views of the helical motif of the perfluorohexyl segments in crystalline 1,3,5-(Rf6)2C6H3I (left) and the structure computed by DFT calcula-
tions (right).
Finally, attempts have been made to extend the preceding chem- in an ice bath. Then pyridine (1.0 mL, 1.0 g, 13 mmol) and
istry in several directions. In screening experiments, all of the (after 30 min) Tf2O (3.0 mL, 5.3 g, 14 mmol) were added drop-
fluorous iodine(III) dichlorides assayed, as well as PhICl2, were wise by syringe with stirring. The ice bath was allowed to warm
competent for the free radical chlorination of methane [25]. to room temperature. After 16 h, H2O (60 mL) was added. After
Under certain conditions, uncommon selectivities were 30 min, the organic phase was separated and dried (MgSO4).
apparent, but the fluorophilicities of the dichlorides or precur- The solvent was removed by rotary evaporation. The residue
sor iodides studied were insufficient for certain target recycling was dissolved in petroleum ether/ethyl acetate (4:1 v/v). The
strategies. As discussed above, it is not clear how to meet these solution was filtered through a silica pad (3 × 5 cm) and the sol-
challenges at this time, although the couple Rf13CH2ICl2/ vent was removed by rotary evaporation to give Rf11CH2OTf as
Rf13CH2I would be one of several with promise. Regardless, the a white solid (3.82 g, 5.21 mmol, 61%), mp 77.2–79.9 °C
fluorous iodides reported herein have numerous other uses, (capillary). Anal. calcd for C13H2F26O3S: C, 21.33; H, 0.28; F,
some of which will be communicated in the near future [23]. 67.46; S, 4.38; found: C, 21.44; H, 0.31; F, 67.21; S, 4.15;
1H NMR (500 MHz, acetone-d6) δ 5.55 (t, 3JHF = 13 Hz, 2H,
Conclusion
CH2); 19F{1H} NMR (470 MHz, acetone-d6) δ −75.5 (s, 3F,
The preceding experimental and computational data have estab- SO2CF3), −81.7 (t, 4JFF = 10 Hz [60-62], 3F, CF3), −120.2 (m,
lished a strong correlation between iodine atom Lewis basicity 2F, CF2), −122.2 (m, 12F, 6CF2), −123.2 (m, 4F, 2CF2), −126.7
and the feasibility of oxidizing fluorous and non-fluorous ali- (m, 2F, CF2); 13C{1H} NMR (125 MHz, acetone-d6, partial)
phatic and aromatic iodides to the corresponding iodine(III) δ 70.0 (t, 2JCF = 28 Hz, CH2); IR (powder film, cm−1): 2924
dichlorides. Although a few surprises are noted, these are attri- (w), 2855 (w), 1418 (m), 1202 (s), 1140 (s), 1103 (w), 1023
buted to special phenomena that can drive equilibria, such as (m), 854 (m), 822 (m).
precipitation (e.g., the conversion of I-Me to II-Me in
Scheme 1), or kinetic barriers (inertness of RfOxCH2I in Rf11CH2I. A round bottom flask was charged with
Scheme 3 or the precursor to V in Scheme 1). With the fluo- Rf11CH2OTf (3.01 g, 4.11 mmol), NaI (10.2 g, 68.0 mmol), and
rous iodides, the extent of chlorination generally provides a acetone (30 mL), and fitted with a condenser. The flask was
measure of the degree to which the electron-withdrawing per- placed in a 75 °C oil bath and the mixture was stirred. After 1 d,
fluoroalkyl or perfluoroether segments are insulated from the the bath was removed and the mixture was allowed to cool. The
Lewis basic site.
solvent was removed by rotary evaporation. Then Et2O (50 mL)
and H2O (40 mL) were added with stirring. After 5 min, the
dark brown organic phase was separated, washed with satu-
Experimental
Five syntheses that are representative of the types of transfor- rated aqueous Na2S2O3 until it became colorless, and dried
mations in this study are detailed in the main article. The (Na2SO4). The solvent was removed by rotary evaporation and
remaining preparations are described in Supporting Informa- the residue was dissolved in hexanes/ethyl acetate (20:1 v/v).
tion File 1, together with data on the solvents, starting materials, The solution was kept at −35 °C until a precipitate formed. The
and instrumentation employed.
solid was collected by filtration and washed with cold hexanes
to give Rf11CH2I as a white solid (2.00 g, 2.82 mmol, 69%), mp
Rf11CH2OTf. A Schlenk flask was flame dried, allowed to (capillary): 97.8–98.2 °C. Anal. calcd for C12H2F23I: C, 20.30;
cool, charged with Rf11CH2OH (5.10 g, 8.52 mmol) and an- H, 0.28; F, 61.54; I, 17.87; found: C, 20.20; H, 0.16; F, 61.29; I,
hydrous CF3C6H5 (50 mL) under a N2 flow, capped, and placed 17.68; 1H NMR (500 MHz, acetone-d6) δ 4.06 (t, 3JHF = 19 Hz,
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Beilstein J. Org. Chem. 2017, 13, 2486–2501.
2H, CH2); 19F{1H} NMR (470 MHz, acetone-d6) δ −81.6 (t, 2F, CF2), −122.3 (m, 2F, CF2), −123.5 (m, 2F, CF2), −127.0
4JFF = 10 Hz [60-62], 3F, CF3), −107.0 (m, 2F, CF2), −122.2 (m, 2F, CF2); 13C{1H,19F} (125 MHz, CD2Cl2) δ 141.9, 136.4,
(m, 14F, 7CF2), −123.2 (m, 2F, CF2), −126.7 (m, 2F, CF2); 130.8, 126.8, 118.0 (5 × s, C6H4), 116.1, 115.8, 112.0, 111.5,
13C{1H} NMR (125 MHz, acetone-d6, partial) δ −3.8 (t, 2JCF = 111.1, 109.3 (5 × s, 5CF2/CF3), 94.4 (s, CI).
25 Hz, CH2); IR (powder film, cm−1): 2986 (w), 2874 (w), 1422
(w), 1373 (w), 1348 (w), 1234 (s), 1200 (s), 1140 (s), 1040 (m), 1,3-Rf6C6H4ICl2. A round bottom flask was charged 1,3-
858 (m).
Rf6C6H4I (0.523 g, 1.00 mmol), C6F6 (1 mL), and CH3CN
(10 mL) with stirring. Aqueous NaOCl (2.5% w/w, 10 mL) fol-
Rf11CH2ICl2. A round bottom flask was charged with lowed by conc. HCl (10 mL) were slowly added. After 30 min,
Rf11CH2I (1.01 g, 1.42 mmol), C6F6 (1.4 mL), and CH3CN a pale yellow precipitate began to form. After 3 h, the mixture
(14 mL) with stirring. Aqueous NaOCl (2.5% w/w, 21 mL) and was filtered. The filter cake was washed with H2O (5 mL) and
then conc. HCl (10 mL) were slowly added. After 2 h, a pale hexane (10 mL) and air dried (2 d) to give 1,3-Rf6C6H4ICl2 as a
yellow precipitate began to form. After 5 h, the mixture was pale yellow powder (0.477 g, 0.804 mmol, 80%). Anal. calcd
filtered. The filter cake was washed with hexane (10 mL) and for C12H4F13Cl2I: C, 24.31; H, 0.68; F, 41.65; found: C, 23.89;
air dried (4–5 h) to give Rf11CH2ICl2 as a pale yellow powder H, 0.38; F, 49.81 [63]; 1H NMR (500 MHz, CDCl3/C6F6) δ
(0.90 g, 1.15 mmol, 81%), mp 122.1–125.4 °C (capillary). 8.54–8.52 (m, 2H), 7.94 (d, 3JHH = 8 Hz, 1H), 7.79 (t, 3JHH = 8
Anal. calcd for C12H2F23Cl2I: C, 18.46; H, 0.26; F, 55.96; Cl, Hz, 1H); 19F{1H} NMR (470 MHz, CDCl3/C6F6) δ −82.3 (t,
9.08; found: C, 16.76; H, 1.16; F, 50.15; Cl, 7.98 [63]; 1H NMR 4JFF = 9 Hz [60-62], 3F, CF3), −112.0 (t, 4JFF = 15 Hz [60-62],
(500 MHz, acetone-d6) δ 5.44 (t, 3JHF = 17 Hz, 2H, CH2); 2F, CF2), −124.4 (m, 4F, 2CF2), −123.7 (m, 2F, CF2), −127.3
19F{1H} NMR (470 MHz, acetone-d6, partial) δ −106.7 (m, 2F, (m, 2F, CF2).
CF2); IR (powder film, cm−1): 3030 (w), 2970 (w), 1392 (w),
1373 (w), 1348 (w), 1315 (w), 1202 (s), 1148 (s), 1046 (m), 860 Partition coefficients. The following is representative.
(m).
A 20 mL vial was charged with a CF3C6F11 solution of
RfnCH2I (n = 11, 15; 5.0 × 10−2 M, 4.0 mL) and toluene
1,3-Rf6C6H4I. A Schlenk tube was charged with copper (4.0 mL), capped, and vigorously stirred. After 10 min at room
(1.26 g, 20.0 mmol) and DMSO (30 mL) and placed in a 105 °C temperature (24 °C), aliquots were removed from the fluorous
oil bath. The mixture was sparged with N2 with stirring (2.0 mL) and organic (2.0 mL) phases. The solvent was evapo-
(30 min), and 1,3-diiodobenzene (6.60 g, 20.0 mmol) was rated from each, and the residues were dried under vacuum. A
added. After a second sparge, Rf6I (4.48 g, 10.0 mmol) was solution of Ph2SiMe2 (internal standard; 0.0055 mL) in acetone-
added in portions over 30 min under a N2 flow with stirring. d6/CF3C6H5 (1:1 v/v; 10.0 mL) was prepared. Each residue was
The tube was sealed and placed in a 110 °C oil bath. After 4 d, dissolved in 1.00 mL of this solution and 1H NMR spectra were
the mixture was cooled to room temperature and poured into recorded. The relative peak integrations gave the corresponding
H2O (100 mL). Then Et2O (100 mL) was added with stirring. partition coefficients.
After 1 h, the aqueous phase was separated and extracted with
Et2O (5 × 50 mL). The combined organic phases were dried Crystallography. A solution of 1,3,5-(Rf6)2C6H3I (ca. 0.05 g)
(Na2SO4) and the solvent was removed by rotary evaporation. in CHCl3/C6F6 (1.0 mL, 4:1 v/v) in an NMR tube was allowed
The residue was dissolved in CH3CN (10 mL). The sample was to concentrate. After 2 d, colorless needles with well defined
extracted with perfluorohexane (5 × 5 mL). The fluorous layers faces were obtained. Data were collected as outlined in Table 1.
were combined, concentrated to 2 mL, and extracted with ace- Integrated intensity information for each reflection was ob-
tone (5 × 3 mL). The solvent was removed from the extracts by tained by reduction of the data frames with the program APEX2
oil pump vacuum to give 1,3-Rf6C6H4I as a colorless oil [64]. Data were corrected for Lorentz and polarization factors,
(3.16 g, 6.05 mmol, 60% based upon Rf6I). Anal. calcd for and using SADABS [65] for absorption and crystal decay
C12H4F13I: C; 27.61; H, 0.77; F, 47.31; found: C, 28.09; H, effects. The structure was solved by direct methods using
0.67; F, 48.59 [63]. The solvent was removed from the concen- SHELXTL/XS [66,67]. Non-hydrogen atoms were refined with
trated perfluorohexane extract by oil pump vacuum to give 1,3- anisotropic thermal parameters. Hydrogen atoms were placed in
(Rf6)2C6H4 as a light yellow oil (1.07 g, 1.51 mmol, 15%) [48]. idealized positions and refined using a riding model. The struc-
The 1H NMR spectrum matched those in the literature [47,48]. ture was refined (weighted least squares refinement on F2) to
1H NMR (500 MHz, CD2Cl2) δ 8.01 (s, 1H), 7.96 (d, 3JHH = 8 convergence [66-68].
Hz, 1H), 7.61 (d, 3JHH = 8 Hz, 1H), 7.26 (t, 3JHH = 8 Hz, 1H);
19F{1H} (470 MHz, CD2Cl2) δ −82.0 (t, 4JFF = 9 Hz [60-62], Calculations. Computations were performed with the
3F, CF3), −111.7 (t, 4JFF = 15 Hz [60-62], 2F, CF2), −122.1 (m, Gaussian09 program package, employing the ultrafine grid
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Beilstein J. Org. Chem. 2017, 13, 2486–2501.
4. As of the submission date of this manuscript, a SciFinder search
(n ≥ 6) showed only 1,4-Rf6C6H4I (Hong Kong Chemhere Co.).
5. Kysilka, O.; Rybáčková, M.; Skalický, M.; Kvíčalová, M.; Cvačka, J.;
Kvíčala, J. Collect. Czech. Chem. Commun. 2008, 73, 1799–1813.
doi:10.1135/cccc20081799
(99,590) to enhance accuracy [69]. Geometries were optimized
using density functional theory (DFT). The B3LYP [70-72]
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 func-
tional 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).
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Full details and product characterization for all the
doi:10.1002/1099-0690(200103)2001:6<1121::AID-EJOC1121>3.0.CO
;2-3
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
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Supporting Information File 1
Experimental section continued.
doi:10.1002/1099-0682(200009)2000:9<1975::AID-EJIC1975>3.0.CO;
2-M
[http://www.beilstein-journals.org/bjoc/content/
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Supporting Information File 2
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Acknowledgements
The authors thank the Qatar National Research Fund for support
(project number 5-848-1-142), the Laboratory for Molecular
Simulation and Texas A&M High Performance Research
Computing for resources, Prof. Michael B. Hall and Dr. Lisa M.
Pérez for helpful discussions, and Dr. Markus Jurisch for pre-
liminary studies of Rf13CH2OTf and Rf13CH2I.
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ORCID® iDs
24.Cossairt, B. M.; Cummins, C. C. New J. Chem. 2010, 34, 1533–1536.
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Tathagata Mukherjee - https://orcid.org/0000-0002-6369-8923
Andreas Ehnbom - https://orcid.org/0000-0002-7044-1712
Hassan S. Bazzi - https://orcid.org/0000-0002-5702-0091
John A. Gladysz - https://orcid.org/0000-0002-7012-4872
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