Electrophilic fluorination of organoplatinum(II) iodides: Iodine and platinum atoms as competing fluorination sites

Article abstract of DOI:10.1021/ja3039272

A series of diphosphine Pt(II) aryl iodo complexes were reacted with XeF₂ to cleanly produce the corresponding Pt(II) difluoro complexes and free iodoarenes. However, when aryl ligands bearing fluoro substituents in the ortho positions were used, the formation of the corresponding Pt(II) aryl fluoro complexes was observed in the reaction with XeF₂. In the case of the Pt-C₆F₅ complex, the products of the fluoride-for-iodide exchange were the only products observed by means of ³¹P and ¹⁹F NMR spectroscopy. The experimental and theoretical studies suggest that the formation of iodine-fluorine bond may accompany this transformation. The plausible I-F species could be trapped by electron-richer organoplatinum complexes to give a Pt(IV) transient which subsequently eliminates the corresponding aryl iodide. Hence, in some cases a pathway involving an attack of XeF₂ at the iodo ligand of Pt(II) aryl iodo complexes to generate I-F species can be operative in addition to or instead of the XeF₂ attack at the metal center. Our DFT studies demonstrate that the electrophilic attacks of XeF₂ at both sites, platinum and iodide, can be competitive.

Full text of DOI:10.1021/ja3039272

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Article
Electrophilic Fluorination of Organoplatinum(II) Iodides:
Iodine and Platinum Atoms As Competing Fluorination Sites
Ina S. Dubinsky-Davidchik, Shay Potash, Israel Goldberg, Arkadi Vigalok, and Andrei N Vedernikov
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja3039272 • Publication Date (Web): 20 Jul 2012
Downloaded from http://pubs.acs.org on August 2, 2012
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Electrophilic Fluorination of Organoplatinum(II)
Iodides: Iodine and Platinum Atoms As Competing
Fluorination Sites
Ina S. Dubinsky-Davidchik,1 Shay Potash,1 Israel Goldberg, 1 Arkadi Vigalok1* and Andrei N.
Vedernikov2*
1- School of Chemistry, The Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978,
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Israel. 2- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742,
USA
Email: avigal@post.tau.ac.il; avederni@umd.edu
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
ABSTRACT. A series of diphosphine Pt(II) aryl iodo complexes were reacted with XeF2 to cleanly
produce the corresponding Pt(II) difluoro complexes and free iodoarenes. However, when aryl ligands
bearing fluoro substituents in the ortho-positions were used, the formation of the corresponding Pt(II)
aryl fluoro complexes was observed in the reaction with XeF2. In the case of the Pt-C6F5 complex, the
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products of the fluoride-for-iodide exchange were the only products observed by means of P and F
NMR spectroscopy. The experimental and theoretical studies suggest that the formation of iodine-
fluorine bond may accompany this transformation. The plausible 'I-F' species could be trapped by
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electron-richer organoplatinum complexes to give a Pt(IV) transient which subsequently eliminates the
corresponding aryl iodide. Hence, in some cases a pathway involving an attack of XeF2 at the iodo
ligand of Pt(II) aryl iodo complexes to generate 'I-F' species can be operative in addition to or instead of
the XeF2 attack at the metal center. Our DFT studies demonstrate that the electrophilic attacks of XeF2
at both sites, platinum and iodide, can be competitive.
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Introduction
In recent years, the electrophilic fluorination of organometallic complexes became an important area
of research.1-4 The major driving force behind this expansion is the central role of organofluorine
compounds in the development of new pharmaceuticals and agrochemicals.5 The electrophilic
fluorination can be viewed as a complementary tool to the commonly used nucleophilic fluorination
techniques that allows for the direct conversion of C-H bonds into C-F bonds.6-8 Electrophilic
fluorination was also applied in the formation of the carbon-carbon bonds,9 including the Ar-CF3
bond,10 as well as C-I bonds.11 This last reaction was observed upon treatment of a series of (P~P)Pd(II)
aryl iodo complexes with XeF2 and proceeded under very mild conditions giving the products, iodoarene
and (P~P)PdF2, in a quantitative yield. The reaction was very general in scope and even (P~P)Pd(C6F5)I
was found to be reactive giving pentafluoroiodobenzene as the organic product.
The accepted general mechanism for the formation of new bonds under the electrophilic fluorination
conditions is shown in Scheme 1. This mechanism involves the initial reaction of an electrophilic
reagent acting as a source of “F+” with the M(II) atom giving the M(IV) intermediate that undergoes
subsequent reductive elimination1,2 to produce the C-F, C-C or C-X bonds.
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Scheme 1.
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F
L
R
F
M
"F+"
F
X
L
R
X
R
X
L
L
L
M
M
M
+
L
L
L
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R-X
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X= Hydrocarbyl or Halide
M= Pd, Pt
C-X bond formation
X
L
M
+
R-F
L
C-F bond formation
Notably, when an M(II) complex contains other relatively electron-rich atoms, such as an iodine atom at
the metal center, the electrophilic fluorine might react with the coordinated halide. This reaction
direction, known in the chemistry of organic iodides,12 was not previously considered in organometallic
chemistry. Herein, we present the first experimental and theoretical studies suggesting the formation of
intermediates with a fluorine-iodine bond resulting from electrophilic fluorination with XeF2 of Pt(II)
aryl iodo complexes and discuss some potential implications of this reaction for group 10
organometallic chemistry.
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Results and Discussion
Complexes 1a-d, f-g and 2b-d were prepared following the standard procedures.13 Typically, the
corresponding (Ph3P)2Pt(Ar)I was prepared by reacting (Ph3P)4Pt with the corresponding iodoarene and
treated with dcpe (1,2-dicyclohexylphosphinoethane) in hot benzene for 24 hrs (Scheme 2). The
products were obtained in 70-90% yields. In the case of 1e and 2a, (COD)2Pt(Mes)I and
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(COD)2Pt(C6F5)I were used as the precursors, respectively. The P NMR spectra of complexes 1 show
two singlets with the 195Pt satellites without the observed coupling due to the inequivalent phosphorus
atoms in the mutual cis-position. The presence of the ortho-F substituents in 2a-d results in the splitting
of the 31P NMR signal of the phosphine ligand trans to the aryl group. This signal appears as a doublet in
2d, triplet in 2b,c and multiplet (due to additional two meta-F atoms) in 2a with JFP-s of ca. 14 Hz.
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Scheme 2.
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Cy2
dcpe
L
P
Aryl
I
Aryl
I
2 L
+
Pt
L
Pt
C6H6, ꢀ
P
Cy2
L= Ph3P or 0.5 COD
1: Aryl= 4-FC6H4 (a), 4-OMeC6H4 (b), 4-CF3C6H4 (c)
2-MeC6H4 (d), 2,4,6-Me3C6H2 (e), 3,5-(CF3)2C6H3 (f)
3,5-(NO2)2C6H3 (g)
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2: Aryl= C6F5 (a), 2,4,6-F3C6H2 (b), 2,6-F2C6H3 (c),
2,4-F2C6H3 (d)
The X-ray structure of 1e (Figure 1a) shows the metal center in a square planar geometry. The bond
angles at the Pt atom are close to the ideal 90 deg. Stronger trans-influence of the mesityl group over
iodide is manifested in a longer Pt(1) – P(4) distance of 2.3088(14) Å compared with 2.2455(14) Å for
the Pt(1) – P(3) distance. The Pt(1) – I(2) bond length of 2.6570(4) Å compares well with other Pt-I
distances in similar complexes.14 The crystallographic features of complex 2b, crystallized from CH2Cl2
(Figure 1b), are nearly identical to those in 1e. The presence of the electron-withdrawing 2,4,6-F3C6H2
group has little effect on the bond lengths of the Pt center. For example, the Pt(1) – P(3) (trans to the
aryl) and Pt(1) – P(4) bonds of 2.2908(18) and 2.2375(18) Å, respectively, correspond well to the
platinum-phosphine distances in 1e. Similarly, the Pt(1) – C(31) bond length of 2.086(7) Å in 2b is
insignificantly shorter than that in 1e (2.093(5) Å). Yet, when compared with the bond distances in 2a
(Figure 1c), one can see a trend in the electron density influence on the bonds at the metal center. For
instance, the Pt(1) – C(31) bond of 2.075(5) Å is again slightly shorter in 2a than in 1e and 2b, and so is
the Pt(1) – P(4) bond trans to the aryl of 2.2881(12) Å.
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(a)
(b)
(c)
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Figure 1. X-ray crystal structures of complexes 1e (a), 2b (b) and 2a (c). Hydrogen atoms and solvent
are omitted for clarity.
Upon reaction of complexes 1 with XeF2 in CH2Cl2 at room temperature, their complete conversion to
complex (dcpe)PtIIF2 (3) and the corresponding free iodoarenes was observed at room temperature
(Scheme 3). The reactions proceeded rapidly with both electron-rich and electron-poor aryl derivatives,
as well as with the sterically hindered ones (o-tolyl, 1d or mesityl, 1e). Cooling the reactions down to –
78°C did not enable us to find evidence for the involvement of any intermediates that could be detected
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by means of F or P NMR spectroscopy. In some cases, the formation of small amounts (< 5%) of
(dcpe)Pt(I)F (4) and (dcpe)Pt(Ar)F (5) complexes could be observed, likely as a result of the Pt(II)
difluoro complexes acting as a source of a strongly nucleophilic F- anion.15 Indeed, the addition of a
CH2Cl2 solution of 3 to a solution of 1a led to the formation of 4 and 5a (eq. 1).
Scheme 3.
Cy2
P
Cy2
P
XeF2
Aryl
I
F
F
Pt
Pt
Aryl-I
+
CH2Cl2, -30oC - RT
P
P
Cy2
Cy2
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(dcpe)PtF2 (3) + (dcpe)Pt(4-C6H4)I (1a) ꢀ (dcpe)Pt(I)F (4) + (dcpe)Pt(4-C6H4)F (5a)
( 1 )
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Interestingly, the addition of 1 equiv. of XeF2 to a solution of the pentafluorophenyl complex 2a did
not lead to the formation of either 3 or C6F5-I. Instead, the slightly yellowish solution turned dark pink
and a nearly quantitative formation of the fluoro aryl complex 6a was observed (Scheme 4). As in the
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o
case of complexes 1, the reaction with XeF2 proceeded extremely fast even at -78 C or just above the
CH2Cl2 melting point (-96 C). No other products besides 6a were observed in either 19F or 31P{1H}
o
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NMR spectra when the reaction was performed in a PTFE (Teflon) NMR liner, although the F NMR
analysis was significantly obstructed by strong absorbance of PTFE in the aromatic fluorine region of
the spectrum. In a regular NMR tube, small amounts (ca. 10%) of a by-product were also observed. The
by-product most likely contains HF2 anion, which appears in the 19F NMR spectrum as a small hump at
-
ca. -180 ppm at room temperature and as a broad doublet of doublets at -78ºC. In addition, a small broad
signal at 11.5 ppm, expected for HF2 , also appeared in the H NMR spectrum.16 Furthermore, upon
-
1
standing of the reaction mixture for several days at room temperature in a regular NMR tube, the signals
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due to the reactant 2a started to re-appear in the NMR spectra. The F NMR spectrum of complex 6a,
which can be prepared independently from 2a and AgF, shows a broad signal at – 277.1 ppm due to the
platinum-bound fluoro ligand, as well as the signals of the pentafluorophenyl group. In its 31P{1H}
NMR spectrum, the phosphorus atom trans to the fluoro ligand gives rise to a doublet at 48.1 ppm (JFP=
160 Hz). The X-ray structure of 6a (Figure 2) shows features similar to those in 2a except that the Pt(1)
– P(2) distance (trans to the fluoro ligand) of 2.1987(19) Å is now shorter than in the parent compound
(2.2354(12) Å), indicating the smaller trans-influence of the fluoro ligand vs. iodide. The Pt(1) – F(4)
bond length of 2.035(4) Å is in the right region for an organometallic Pt(IV) fluoride.8, 17
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Scheme 4.
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Cy2
P
Cy2
P
C6F5
F
C6F5
I
XeF2
Pt
Pt
+ 'I-F'
P
CH2Cl2
P
Cy2
Cy2
2a
6a
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Figure 2. X-ray crystal structure of complex 6a. Hydrogen atoms are omitted for clarity.
As the stoichiometry of the reaction in Scheme 4 suggests the formation of xenon and an "I-F"
species, we decided to check the reaction mixture for the presence of a product with an iodine-fluorine
bond in it. Iodine monofluoride is known to form a polymer in dilute solutions18 and is relatively
unstable giving free iodine and IF3, which in turn decomposes to I2 and IF5.19 Being a source of a
strongly electrophilic iodine, I-F is also known to react rapidly with hydrazones, giving the
difluoromethylene compounds, dinitrogen and HI (Scheme 5).20 To verify the formation of the
product(s) containing I-F bond, we treated the solution containing 6a and presumed "I-F" species,
prepared at –78ºC, with a slight excess of benzophenone hydrazone. To our delight, instantaneous
appearance of a signal at -89 ppm due to the formation of Ph2CF2 was observed in the 19F NMR
spectrum, which was confirmed by comparison with the authentic sample of Ph2CF2. The released H-I
converts 6a to 2a within seconds (Figure 3), which was verified independently. It is possible that slow
production of I- is responsible for the re-generation of 2a upon leaving the reaction mixture in Scheme 4
for several days at room temperature.
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Scheme 5.
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2
3
4
5
NH2
N
F2
C
+ 2 I-F
+ 2 H-I
+ N2
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8
Aryl
R
Aryl
R
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Figure 3. The F{1H} NMR spectrum of: (a) 2a in CH2Cl2; (b) after the reaction with XeF2; (c) after
the addition of Ph2C=N-NH2.
The apparent formation of products with the I-F bond in the reaction between 2a and XeF2 raises the
question about the possible pathways that can be involved in the reaction between XeF2 and
aryliodoplatinum(II) complexes. The most commonly anticipated reaction direction involves oxidative
addition of an "F+" to a Pt(II) center in 2a that gives the coordinatively unsaturated Pt(IV) species 7
(path a, Scheme 6).21,22 The latter may undergo the isomerization that puts the iodo ligand in the axial
position (8) and form products of the subsequent C-I reductive elimination. Another plausible
mechanism (path b) includes direct attack of XeF2 at the coordinated iodo ligand in 2a23,24,12 to form an
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I-coordinated Pt(II) I-F complex 9 which can subsequently produce either 6a and free "I-F" as a result of
F-for-I-F ligand substitution, or 8 as a result of intramolecular oxidative addition of I-F to the Pt(II)
center.
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Scheme 6.
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F
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Ar
I
L
Pt
L
(a)
-Xe, -F-
I
7
Ar
F
L
Ar
I
L
Pt
+ XeF2
Pt
2a
L
L
(b)
8
-Xe, -F-
L
Ar
I
Pt
F-
L
F
F-
9
F
L
Pt
L
Ar
L
F
Pt
L
F
+ Ar-I
3
+ "I-F"
6a
The second mechanism (path b) allows one to account for the observed behavior of complexes such as
2a that are too sterically congested and/or electron poor to accept an electrophilic attack by XeF2 onto
the metal atom (path a). In such a case, an attack by XeF2 onto the much more sterically accessible iodo
ligand in 2a (path b) may lead to the accumulation of 6a and "I-F" at low temperatures if it occurs at a
faster rate than the oxidative addition of “I-F’ to form 8.
To check the viability of path b for complex 2a we performed a crossover experiment. A fresh mixture
of 6a and "I-F" species was prepared in the reaction between 2a and XeF2 and was kept at -78 °C. Then
it was combined with an electron-richer aryl fluoride complex (dcpe)Pt(4-FC6H4)F, 5a. With ‘I-F’
species present in the former mixture we expected formation of para-fluoroiodobenzene as a result of
the reaction between ‘I-F’ and 5a. Indeed, para-fluoroiodobenzene formed instantaneously along with 3,
thus supporting the viability of path b.
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In addition, we also prepared iodine monofluoride by reacting I2 with F2 at -78ºC.20 The addition of a
small amount25 of the polymeric I-F to a solution of 5a in CH2Cl2 at this temperature led to the
formation of 3 and 4-IC6H4F.26
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4
5
6
7
8
9
Analyzing the reactivity of sterically bulky mesityl complex 1e and electron-poor complexes 1f and 1g
that all undergo an exclusive aryl-I elimination reaction upon treatment with XeF2, we propose that the
fluoro substituents present in the aryl ligand play a crucial role in directing the attack of XeF2 at the iodo
ligand in Pt(II) aryl iodo complex 2a. To check this hypothesis, we studied fluorination of
polyfluorophenyl complexes 2b-d with XeF2. Importantly, the reaction outcome was found to be
dependent on the number and position of the fluoro substituents in the aromatic ring. With 2,4,6-
trifluorophenyl complex 2b and 2,6-difluorophenyl complex 2c, both complex 3 (along with the
corresponding aryliodide) and complex 6 were obtained in a 4:6 and 7:3 ratio, respectively, whereas
with 2,4-difluorophenyl complex 2d, only the aryl-iodide reductive elimination products were observed.
The presence of "I-F" in the reaction mixture of 2b and XeF2 was also evident from the formation of
Ph2CF2 observed upon combination of this mixture with Ph2C=N-NH2. Thus, the presence of at least
two ortho-fluoro substituents was crucial for directing the electrophilic attack of XeF2 at the iodo ligand
leading to the formation of 6 and "I-F" species.
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Scheme 7.
Cy2
P
Cy2
P
Cy2
P
Aryl
I
F
F
Aryl
F
XeF2
Pt
Pt
Pt
+
P
CH2Cl2
P
P
Cy2
Cy2
Cy2
2
3
6
+ Aryl-I
+ 'I-F'
Complex
Products ratio
Aryl= C6F5 (2a)
0
100
58
30
0
2,4,6-F3C6H2 (2b)
2,6-F2C6H3 (2c)
2,4-F2C6H3 (2d)
42
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100
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The effect of the ortho-fluoro substituents at the aryl ligand on the reactivity of late transition metal
complexes has previously been reported.27 In particular, it was demonstrated that, in a rhodium complex,
two ortho-F substituents increase the barrier for the Aryl-H reductive elimination by ca. 5 kcal/mol
compared with the single fluorine.28
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ꢀGo298, kcal/mol
CH2Cl2 solution
Ar = C6F5/C6F3H2/C6F2H3
I
Cy2
P
+ Xe + F-
Cy2
P
Ar
F
Pt
Ar
I
P
F
I
Pt
Xe
Cy2
P
Cy2
P
Ar
F
Cy2
Cy2
P
Pt
F
P
TSArI
Ar
F
Xe
Cy2
11.6
Pt
+ Xe + F-
I
P
8
F
Cy2
TSPt
9.0
TSI
Cy2
P
6.9/5.9/3.7
6.8/6.9/7.1
Ar
I
Pt
P
F
Cy2
5.1
+ Xe + F-
9
(0)
Pt
F
Pt
I
Cy2
P
0
Ar
P
Cy2
P
Cy2
+ Xe + F-
Ar
I
10
P
Cy2
+ XeF2
2
Cy2
TS-X
P
Ar
I
Cy2
P
-42.9
Pt
Pt
P
F
F
F
Cy2
Pt
F
-45.0
P
Cy2
+ Xe
Cy2
P
3
-79.4
Ar
+ Xe + ArI
IF2
P
Cy2
P
-48.0
Cy2
Ar
F
11
+ Xe
Pt
P
Cy2
6
+ Xe + IF
Figure 4. DFT calculated Gibbs energy profile for reaction between complex 2 and XeF2 in
dichloromethane solutions, ꢀGo298, kcal/mol.
To get a better understanding of the reactivity of polyfluorophenyl complexes 2a, 2b and 2c towards
XeF2, both reaction paths a and b shown in Scheme 6 were analyzed using DFT calculations for
dichloromethane solutions (Fig. 4).
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For the pentafluorophenyl complex 2a, path a includes the electrophilic attack of XeF2 at the PtII
center via the transition state TSPt (6.9 kcal/mol) to form intermediate 10 (isomer 7 in Scheme 6 could
not be located on the potential energy surface). The intermediate 10 can isomerize to 8 leading to facile
reductive elimination of C6F5-I. The corresponding transition state TSArI is the highest energy point
(11.6 kcal/mol) on the reaction energy profile. Path b for complex 2a includes a relatively low-energy
transition state TSI (6.8 kcal/mol) corresponding to the electrophilic attack of XeF2 at the iodo ligand in
2a. This transition state leads to an I-coordinated I-F PtII complex 9 that, upon reaction with fluoride
anion, can give rise to the observed 6 and free I-F. Another possible site of the attack of fluoride anion at
the intermediate 9 might include the iodine atom. In this case the resulting intermediate is the PtII – I-
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3
4
5
6
7
8
9
10
11
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coordinated difluoroiodide complex (dcpe)Pt(C6F5)(κI-IF2), 11; this reaction direction is also very
favorable (-45.0 kcal/mol). Complex 11 can reductively eliminate I–F with very low activation energy of
2.1 kcal/mol relative to 11 to form complex 6. Either of the two reaction mechanisms leading to 6 and
I-F may be operational. Importantly, based on very similar energies of TSI and TSPt both reaction
directions, fluorination at the iodine atom and at the PtII center, look almost equally probable. Taking
into account a possible error associated with DFT calculations, this prediction agrees satisfactorily with
the experimental data given in Scheme 7. Interestingly, the formation of an F-coordinated I-F complex
(dcpe)Pt(C6F5)(κF-IF), 12 can also occur as a result of F-I bond reductive elimination from intermediate
8 but with the Gibbs activation energy of 12.4 kcal/mol (see SI).
Finally, the barriers corresponding to the electrophilic attack of XeF2 at the PtII center and the iodo
ligand in complexes 2b and 2c were also found. As the number of fluorine atoms in the aryl ligand
decreases the Gibbs activation energy for the attack of XeF2 at the iodine atom remains almost the same
(6.8, 6.9 and 7.1 kcal/mol for 2a, 2b and 2c respectively) whereas the barrier corresponding to the attack
of XeF2 at the PtII center decreases noticeably (6.9, 5.9 and 3.7 kcal/mol for 2a, 2b and 2c respectively),
reflecting well the experimental trend shown in Scheme 7.
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Conclusion
1
2
3
4
5
6
7
8
We provided strong evidence for the existence of an alternative pathway of electrophilic fluorination
of organometallic iodo Pt(II) complexes with XeF2, in addition to the commonly accepted pathway
including electrophilic attack of XeF2 at the PtII center. The new reaction pathway involves the
unprecedented, for organometallic chemistry, formation of an I-F bond via the direct fluorination of the
coordinated iodo ligand. Evidence for the generation of such a bond was obtained from the reactions
between the (dcpe)Pt(Ar)I complexes 2a-c and XeF2, where the aryl ligand of complex 2 bears two
ortho-fluoro substituents. In the case of the complex 2a containing the pentafluorophenyl ligand, the
formation of (dcpe)Pt(C6F5)F and putative I-F was the only documented reaction pathway. As the steric
environment at the Pt center should be similar for all three complexes, electronic effects seem to play
the major role in determining the reaction outcome. DFT calculations are in qualitative agreement with
the experimental data and show the trend of the diminishing activation barrier corresponding to the
attack of XeF2 at the PtII center in the series 2a > 2b > 2c whereas the activation barrier corresponding to
the attack at the iodine atom remains unchanged.
9
10
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ACKNOWLEDGMENTS: We thank the US-Israel Binational Science Foundation for supporting this
work.
Supporting Information Available. Experimental and computational details (PDF), X-ray crystal
data for complexes 1e, 2a, b and 6a (CIF).
REFERENCES.
1. Engle, K. M.; Mei, T.-S.; Wang, X.; Yu, J.-Q. Angew. Chem. Int. Ed. 2011, 50, 1478-1491.
2. Vigalok, A. Organometallics 2011, 30, 4802-4810.
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3. (a) Furuya, T.; Klein, J. E. M. N.; Ritter, T. Synthesis 2010, 11, 1804–1821. (b) Furuya, T.; Kamlet,
A. S.; Ritter, T. Nature 2011, 473, 470-477.
1
2
3
4
5
4. Kirk, K. L. Org. Proc. Res. & Develop. 2008, 12, 305–321.
6
7
8
9
5. Chambers, R. D. Fluorine in Organic Chemistry, CRC Press, Boca Raton, 2004.
6. Hull, K. L.; Anani, W. Q.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 7134-7135.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7. (a) Wang, X.; Mei, T.-S.; Yu, J.-Q. J. Am. Chem. Soc. 2009, 131, 7520-7521. (b) Chan, K. S. L.;
Wasa, M.; Wang, X.; Yu, J.-Q. Angew. Chem. Int. Ed. 2011, 50, 9081-9084.
8. Kaspi, A. W.; Goldberg, I.; Vigalok, A. J. Am. Chem. Soc. 2010, 132, 10626-10627.
9. Yahav, A.; Goldberg, I.; Vigalok, A. J. Am. Chem. Soc. 2003, 125, 13634-13635.
10. (a) Ball, N. D.; Kampf, J. W.; Sanford, M. S. J. Am. Chem. Soc. 2010, 132, 2878–2879. (b) Ball,
N. D.; Gary, J. B.; Ye, Y.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 7577–7584.
11. Kaspi, A.; Yahav-Levi, A.; Goldberg, I.; Vigalok, A. Inorg. Chem. 2008, 47, 5-8.
12. (a) Zupan, M.; Pollak, A. J. Fluor. Chem. 1976, 7, 445-447. (b) Ruppert, I. J. Fluor. Chem. 1980,
15, 173-178. (c) Della, E. W.; Head, N. J. J. Org. Chem. 1992, 57, 2850-2855.
13. (a) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-428. (b) Eaborn, C.; Odell, K.
J.; Pidcock, A. J. Chem. Soc., Dalton Trans. 1978, 357-368. (c) Kuniyasu, H.; Yamashita, F.; Hirai, T.;
Ye, J.-H.; Fujiwara, S.; Kambe, N. Organometallics 2006, 25, 566-570.
14. Yahav-Levi, A.; Goldberg, I.; Vigalok, A.; Vedernikov, A. N. J. Am. Chem. Soc. 2008, 130, 724-
731.
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15. See for example, (a) Grushin, V. V. Angew. Chem. Int. Ed. 1998, 37, 994-996. (b) Gorol, M.;
Moesch-Zanetti, N.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Eur. J. Inorg. Chem. 2004, 13,
2678-2682. (c) Yahav, A.; Goldberg, I.; Vigalok, A. Inorg. Chem. 2005, 44, 1547-1153.
1
2
3
4
5
6
7
8
9
16. (a) Coulson, D. R. J. Am. Chem. Soc. 1976, 98, 3111-3119. (b) Jasim, N. A.; Perutz, R. N. J. Am.
Chem. Soc. 2000, 122, 8685-8693.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
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34
35
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
17. (a) Yahav-Levi, A.; Goldberg, I.; Vigalok, A. J. Fluor. Chem. 2010, 131, 1100-1102. (b) Zhao, S.-
B.; Wang, R.-Y.; Nguyen, H.; Becker, J. J.; Gagne, M. R. Chem. Commun. 2012, 48, 443–445.
18. Rozen, S. e-EROS Encyclopedia of Reagents for Organic Synthesis 2001, DOI:
10.1002/047084289X.ri015.
19. Schmeisser, M.; Sartori, P.; Naumann, D. Chem. Ber. 1970, 103, 880-884.
20. (a) Rozen, S.; Brand, M.; Zamir, D.; Hebel, D. J. Am. Chem. Soc. 1987, 109, 896-897. (b) Rozen,
S.; Zamir, D. J. Org. Chem. 1991, 56, 4695-4700. (c) Rozen, S.; Zamir, D. J. Org. Chem. 1990, 55,
3552-3555.
21. Similar platinum intermediate was proposed for the C(alkyl)-F reductive elimination: Zhao, S.-B.;
Becker, J.; Gagne, M. R. Organometallics 2011, 30, 3926-3929.
22. For the proposed C-F elimination from a similar Pd(IV) complex see: Furuya, T.; Benitez, D.;
Tkatchouk, E.; Strom, A. E.; Tang, P.; Goddard, W. A. III; Ritter, T. J. Am. Chem. Soc. 2010, 132,
3793–3807. See also ref. 11.
23. For a review describing deiodinative fluorination of alkyl iodides see: Tius, M. A. Tetrahedron
1995, 51, 6605-6634.
24. For an example of generation of X-F bonds from alkali metal halides see: Robins, M. J.;
Manfredini, S. Tetrahedron Lett. 1990, 31, 5633-5636.
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25. Due to rapid decomposition of polymeric I-F outside the cold (-78ºC) suspension in a Freon,
accurate determination of its amount was extremely challenging.
1
2
3
4
5
6
7
8
26. Similar results were obtained with the "I-F" prepared from N-Iodosuccinimide and Et3N-3HF,
however, other sources of an electrophilic iodine can also be present in this homogeneous mixture:
Alvernhe, G.; Laurent, A.; Haufe, G. Synthesis 1987, 562-564.
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10
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27. Clot, E.; Eisenstein, O.; Jasim, N.; Macgregor, S. A.; Mcgrady, J. E.; Perutz, R. N. Acc. Chem.
Res. 2011, 44, 333-348 and references therein.
28. (a) Evans, M. E.; Burke, C. L.; Yaibuathes, S.; Clot, E.; Eisenstein, O.; Jones, W. D. J. Am. Chem.
Soc. 2009, 131, 13464-13473. (b) Tanabe, T.; Brennessel, W. W.; Clot, E.; Eisenstein, O.; Jones, W. D.
Dalton Trans. 2010, 39, 10495–10509.
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SYNOPSIS TOC. The formation of an I-F bond followed by its oxidative addition to a Pt(II) center is
proposed as an alternative to the direct fluorine attack at the metal in the reductive elimination of
iodoarenes under electrophilic fluorination conditions.
1
2
3
4
5
6
7
8
9
F
L
Ar
I
Pt
Fluorination at Pt center
L
(a)
-Xe, -F-
(b)
-Xe, -F-
I
10
11
12
13
14
15
16
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L
Ar
F
Ar
I
L
Pt
+ XeF2
Pt
L
L
-F-
L
Ar
I
Pt
F-
L
F
F-
Proposed in this work
Fluorination at iodo ligand
L
F
Pt
L
Ar
F
L
F
Pt
L
+ Ar-I
+ "I-F"
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