Rhodium(I) silyl complexes for C-F bond activation reactions of aromatic compounds: Experimental and computational studies

Article abstract of DOI:10.1021/om400150p

The rhodium(I) silyl complexes [Rh{Si(OEt)₃}(PEt ₃)₃] (2a) and [Rh{Si(OMe)₃}(PEt ₃)₃] (2b) were synthesized by treatment of [Rh(CH ₃)(PEt₃)₃] (1) with the corresponding silanes HSi(OEt)₃ and HSi(OMe)₃ at low temperature. The intermediate oxidative addition products fac-[Rh(H)(CH₃){Si(OR) ₃}(PEt₃)₃] (R = Et, 6a; R = Me, 6b) were observed by low-temperature NMR spectroscopy. A reaction of 2a with CO afforded trans-[Rh(CO){Si(OEt)₃}(PEt₃)₂] (7) by the replacement of the phosphine ligand in the position trans to the silyl group. Treatment of 2a,b with pentafluoropyridine led to C-F activation reactions at the 2-position, yielding [Rh(2-C₅F₄N)(PEt ₃)₃] (11). The silyl complexes [Rh{Si(OR) ₃}(PEt₃)₃] (2a,b) gave with 2,3,5,6-tetrafluoropyridine the C-F activation product [Rh(2-C₅F ₃HN)(PEt₃)₃] (10), whereas complex 7 reacted by C-H activation to furnish trans-[Rh(CO)(4-C₅F₄N)(PEt ₃)₂] (12). The C-F activation of pentafluoropyridine at 2b was studied with density functional theory calculations using a [Rh{Si(OMe)₃}(PMe₃)₃] model complex (2′). The calculations indicate that a silyl-assisted C-F activation mechanism, analogous to related ligand-assisted processes at metal-phosphine and metal-boryl bonds, is more accessible than a C-F oxidative addition/Si-F reductive elimination pathway. The silyl-assisted process also proceeds with a kinetic preference for activation at the 2-position, as the transition state in this case derives extra stabilization through a Rh...N interaction. The C-F oxidative addition transition states show a significant degree of phosphine-assisted character and are not only higher in energy than the silyl-assisted process but also favor activation at the 4-position.

Full text of DOI:10.1021/om400150p

Article
pubs.acs.org/Organometallics
Rhodium(I) Silyl Complexes for C−F Bond Activation Reactions of
Aromatic Compounds: Experimental and Computational Studies
Anna Lena Raza,† Julien A. Panetier,‡,§ Michael Teltewskoi,† Stuart A. Macgregor,*,‡
and Thomas Braun*,†
†Department of Chemistry, Humboldt-Universitat zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany
̈
‡Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K.
S
* Supporting Information
ABSTRACT: The rhodium(I) silyl complexes [Rh{Si-
(OEt)3}(PEt3)3] (2a) and [Rh{Si(OMe)3}(PEt3)3] (2b)
were synthesized by treatment of [Rh(CH3)(PEt3)3] (1)
with the corresponding silanes HSi(OEt)3 and HSi(OMe)3 at
low temperature. The intermediate oxidative addition products
fac-[Rh(H)(CH3){Si(OR)3}(PEt3)3] (R = Et, 6a; R = Me, 6b)
were observed by low-temperature NMR spectroscopy. A
reaction of 2a with CO afforded trans-[Rh(CO){Si(OEt)3}-
(PEt3)2] (7) by the replacement of the phosphine ligand in the position trans to the silyl group. Treatment of 2a,b with
pentafluoropyridine led to C−F activation reactions at the 2-position, yielding [Rh(2-C5F4N)(PEt3)3] (11). The silyl complexes
[Rh{Si(OR)3}(PEt3)3] (2a,b) gave with 2,3,5,6-tetrafluoropyridine the C−F activation product [Rh(2-C5F3HN)(PEt3)3] (10),
whereas complex 7 reacted by C−H activation to furnish trans-[Rh(CO)(4-C5F4N)(PEt3)2] (12). The C−F activation of
pentafluoropyridine at 2b was studied with density functional theory calculations using a [Rh{Si(OMe)3}(PMe3)3] model
complex (2′). The calculations indicate that a silyl-assisted C−F activation mechanism, analogous to related ligand-assisted
processes at metal−phosphine and metal−boryl bonds, is more accessible than a C−F oxidative addition/Si−F reductive
elimination pathway. The silyl-assisted process also proceeds with a kinetic preference for activation at the 2-position, as the
transition state in this case derives extra stabilization through a Rh···N interaction. The C−F oxidative addition transition states
show a significant degree of phosphine-assisted character and are not only higher in energy than the silyl-assisted process but also
favor activation at the 4-position.
activation product [Rh(4-C5NF4)(PEt3)3]. In the presence of
H2 2,3,5,6-tetrafluoropyridine and [Rh(H)(PEt3)3] were
formed. The reaction is characterized by a selective C−F
activation at the 4-position at pentafluoropyridine.8 In contrast,
a unique reaction of the boryl complex [Rh(Bpin)(PEt3)3]
(HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolbor-
ane) with pentafluoropyridine afforded the activation of
pentafluoropyridine at the 2-position to give [Rh(2-C5NF4)-
(PEt3)3] and FBpin. Catalytic studies led to the development of
a process which involves the formation of the boronate ester 2-
C5N(Bpin)F4.9
Density functional theory (DFT) calculations have played a
significant role in both revealing the mechanistic complexity
and rationalizing the selectivity of aromatic C−F activation at
transition-metal complexes.4d,6m,q,10,11 For example, calcula-
tions showed that the C−F activation of pentafluoropyridine at
[Rh(Bpin)(PEt3)3] proceeds via a four-centered boryl-assisted
transition state in which C−F bond cleavage occurs over the
Rh−B bond. The unusual selectivity for the 2-position results
from the extra stabilization due to a Rh···N interaction
involving the pentafluoropyridine nitrogen (see Scheme 1).9
INTRODUCTION
■
Fluorinated organic compounds and building blocks play a key
role in a wide range of applications and can be found, for
example, in agrochemicals, pharmaceuticals, and refrigerants.1
The unique properties of these compounds can in part be
attributed to the strength of the carbon−fluorine bond.2 An
organometallic approach for the synthesis of fluorinated
compounds consists of a metal-mediated selective fluorination
of nonfluorinated precursors.3 However, a promising alternative
route to access fluorinated building blocks is represented by
selective C−F bond cleavage reactions at highly fluorinated
molecules.4 There are a variety of strategies to induce a C−F
activation step, such as an oxidative addition of a C−F bond at
a transition-metal center.5 In an alternative reaction pathway
hydrido complexes can also react with fluoroorganics to give
metal fluoro compounds and hydrodefluorination products.4,6
Other approaches involve the employment of metal hydrido,
boryl, or silyl complexes to yield on treatment with highly
fluorinated organics HF, fluoroboranes, or fluorosilanes,
respectively, as well as the corresponding organyl metal
complexes.5,7 Thus, a catalytic C−F activation and hydro-
defluorination of pentafluoropyridine was reported on using
[Rh(H)(PEt3)3] as catalyst. The stoichiometric reaction of the
heterocycle with the hydrido complex yielded the C−F
Received: February 22, 2013
Published: July 8, 2013
© 2013 American Chemical Society
3795
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
pentafluoropyridine proceeds via a silyl-assisted mechanism.
This process adds to the range of the general class of ligand-
assisted C−F activation processes.
Scheme 1. Boryl-Assisted C−F Activation Transition State
for the Reaction of Pentafluoropyridine at
[Rh(Bpin)(PR3)3] (R = Me, Computational; R = Et,
Experimental)9
RESULTS AND DISCUSSION
■
Experimental Studies. Synthesis of Rhodium(I) Silyl
Complexes. The methyl complex [Rh(CH3)(PEt3)3] (1) was
treated with a variety of silanes at room temperature as well as
at low temperatures. Reactions of 1 with HSiEt3, HSiPh3,
HSi(OEt)2Me, or HSiMePh2 led to the formation of the
hydrido complex [Rh(H)(PEt3)3] (4) and MeSiEt3, MeSiPh3,
Me2Si(OEt)2, or Me2SiPh2 (Scheme 2). The formation of 4
was also observed on using HSi(OEt)3 or HSi(OMe)3 at room
temperature. However, the latter reactions at 223 K gave the
rhodium(I) silyl complexes [Rh{Si(OEt)3}(PEt3)3] (2a) and
[Rh{Si(OMe)3}(PEt3)3] (2b) as well as methane (Scheme 2).
The complexes 2a,b could not be isolated and were only
characterized in solution, because of their high reactivity. The
31P{1H} NMR spectrum of 2a shows at room temperature a
doublet at δ 13.6 ppm for the phosphine ligands. The
rhodium−phosphorus coupling constant is 144 Hz. In addition,
silicon satellites with a coupling constant of 47 Hz can be seen
shouldering the main peak. The presence of only one signal for
the phosphine ligands can be explained by a dynamic behavior
which involves an intramolecular exchange of phosphine
ligands. Variable-temperature NMR measurements showed
that the presence of free phosphine has no influence on the
signal pattern and therefore on the dynamic behavior of
[Rh{Si(OEt)3}(PEt3)3] (2a). At 183 K the 31P{1H} NMR
spectrum shows the expected splitting patterns: a doublet of
doublets at δ 20.4 ppm (JRh,P = 151 Hz, JP,P = 34 Hz) for the
phosphine ligands in mutually trans positions and a doublet of
triplets at δ 3.2 ppm (JRh,P = 118 Hz, JP,P = 34 Hz) for the
phosphorus atom in the position trans to the silyl ligand
(Figure 1). The rhodium−phosphorus coupling constants are
characteristic for a rhodium(I) species.18 The coalescence
temperature is 233 K (121.5 MHz), at which the estimated
Gibbs activation energy is 9.3 kcal mol−1.19 A comparable
fluxional behavior has been observed for [Rh(H)(PEt3)3] (4)
and [Rh(Bpin)(PEt3)3],8,9,20 as well as for a range of
[Rh(X)(PPh3)3] complexes (X = H, CH3, CF3, Ph). In the
latter cases DFT calculations propose a role for an intermediate
with local C3 symmetry at Rh, the accessibility of which reflects
the trans influence of the ligand X.21 In the 29Si NMR spectrum
of 2a at 300 K a doublet of quartets at δ −11.3 ppm with a
Related phosphine-assisted C−F activation of fluoroaromatics,
ArF−F (ArF = C6F5, C5F4N), had previously been characterized
computationally at [LnM(PR3)] complexes (M = Ir,12a Pt,12b,c
Ni13). In such cases C−F activation has led to the location of
metallophosphorane intermediates, [LnM(ArF)(PR3F)],14 from
which subsequent R group transfer results in fluorophosphine
products.12 Alternatively, F transfer can take place to give
apparent oxidative addition products, [LnM(ArF)(F)(PR3)].
Such processes have been termed “phosphine-assisted C−F
oxidative addition” to reflect the masked role of the ligand in
promoting the reaction. An example was seen in the reaction of
[Ni(PEt3)2] with pentafluoropyridine to give trans-[Ni(2-
C5NF4)(F)(PEt3)2],13 in which DFT calculations accounted
for the unusual selectivity for the 2-position by a phosphine-
assisted C−F activation pathway.
Examples of the application of rhodium(I) silyl complexes for
C−F activation reactions are rare.15 Milstein et al. reported the
activation of hexafluorobenzene and pentafluorobenzene at
[Rh(SiR3)(PMe3)3] (R3 = Ph3, Me2Ph).16 Perutz and Marder et
al. published additional studies on the reactivity of [Rh(SiPh3)-
(PMe3)3] toward fluorinated pyridines.17 They showed that the
reaction with pentafluoropyridine gives C−F activation
products with the rhodium center at the 2- or 4-position of
the heterocycle in a 3:1 ratio. Treatment of [Rh(SiPh3)-
(PMe3)3] with 2,3,5,6-tetrafluoropyridine led to C−H
activation at the 4-position and C−F activation at the 2-
position in a ratio of 1:1.3.
In this paper we present the synthesis of the rhodium(I) silyl
complexes [Rh{Si(OR)3}(PEt3)3] (R = Et, 2a; R = Me, 2b) by
treatment of the methyl complex [Rh(CH3)(PEt3)3] (1) with
HSi(OR)3. Studies on the reactivity of the complexes 2a,b
toward fluorinated aromatics, 2,3,5,6-tetrafluoropyridine, and
pentafluoropyridine showed a unique reaction pattern. DFT
calculations revealed that the C−F activation step at
Scheme 2. Reactivity of the Methyl Complex 1 toward Silanes
3796
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Figure 1. 31P{1H} NMR spectra of [Rh{Si(OEt)3}(PEt3)3] (2a) at
room temperature and at 183 K (121.5 MHz, [D8]toluene).
Figure 2. 31P{1H} NMR spectrum of fac-[Rh(H)(CH3){Si(OEt)3}-
(PEt3)3] (6a) at 203 K (121.5 MHz, [D8]toluene).
rhodium−silicon coupling of 60 Hz and silicon−phosphorus
coupling of 47 Hz was observed. The NMR data of 2b are
comparable to those of 2a.
observed in the HMBC NMR spectrum. The NMR data of 6b
are comparable to those of 6a.
Monitoring the formation of [Rh{Si(OR)3}(PEt3)3] (2a,b)
by low-temperature NMR spectroscopy at 193 K revealed that
the methyl complex [Rh(CH3)(PEt3)3] (1) reacted with
HSi(OR)3 to give initially the oxidative addition products fac-
[Rh(H)(CH3){Si(OR)3}(PEt3)3] (R = Et, 6a; R = Me, 6b)
(Scheme 3). At 223 K the reductive elimination of methane and
the formation of 2a or 2b was observed. Addition of free
phosphine has no influence on the rate of the methane
elimination. Note also that in similar reactions of the rhodium
trimethylphosphine complexes [Rh(CH3)(PMe3)3,4] with other
silanes such as HSiEt3 or HSiPh3, intermediates such as 6a,b
were not observed.22
The reaction of [Rh(CH3)(PEt3)3] (1) with an excess of
HSi(OEt)3 gave the oxidative addition products 3 and 5a,
which were characterized by NMR spectroscopy. At low
temperature cis,fac-[Rh(H){Si(OEt)3}2(PEt3)3] (3) was fur-
nished, whereas at room temperature cis,fac-[Rh(H)2{Si-
(OEt)3}(PEt3)3] (5a) was generated (Scheme 2). In the
reaction of 1 with HSi(OMe)3 at room temperature the
formation of cis,fac-[Rh(H)2{Si(OMe)3}(PEt3)3] (5b) was
observed.23 The NMR data of 3 and 5a are in accordance
with the data of comparable complexes but bearing PMe3 or
Si(OMe)3 ligands, which were reported previously.22b,23
Treatment of a solution of [Rh{Si(OEt)3}(PEt3)3] (2a) in
C6D6 with CO afforded the replacement of the phosphine
ligand in the position trans to the silyl moiety by a carbonyl
ligand (Scheme 3). The silyl complex [Rh(CO){Si(OEt)3}-
(PEt3)2] (7) is stable in the solid state for a short time, but
under vacuum decomposition was observed. The 31P{1H}
NMR spectrum of 7 displays a doublet at δ 14.8 ppm with a
rhodium−phosphorus coupling constant of 108 Hz. The
The 31P{1H} NMR spectrum of 6a displays three doublets of
doublets of doublets at δ 12.2, 4.0, and −3.3 ppm with
rhodium−phosphorus coupling constants of 71−94 Hz which
reveal the presence of a rhodium(III) compound (Figure 2).18
This pattern is compatible with a fac configuration for 6a. A
31P,29Si HMBC NMR spectrum, which was optimized on a
large phosphorus−silicon coupling, shows that the signal at δ
−3.3 ppm can be assigned to the phosphorus atom in the
position trans to the silyl group. The 1H NMR spectrum shows
a broad multiplet at δ 0.04 ppm that can be assigned to the
methyl ligand. 31P decoupling experiments revealed a
rhodium−hydrogen coupling constant of 1.8 Hz. A doublet
of doublets of multiplets at δ −10.8 ppm confirms the presence
of a hydrido ligand. The coupling constant to the phosphorus
atom in the trans position is 144 Hz. 31P decoupling
experiments revealed a rhodium−hydrogen coupling constant
of 18 Hz. A 1H,29Si HMBC NMR spectrum exhibits a
resonance at δ −6.6 ppm in the 29Si domain, which correlates
with the signals for the hydrido ligand and the CH2 groups of
the ethoxy moieties. The coupling constant of the hydrido
ligand to the silicon atom is very small and could not be
29Si{1H} NMR spectrum shows a doublet of triplets (JRh,Si
=
25 Hz, JP,Si = 66 Hz,) at −10.3 ppm. This pattern is compatible
with a square-planar configuration with both phosphine ligands
in mutually trans positions. The 13C{1H} NMR spectrum
displays a doublet of triplets at δ 200.3 ppm with a coupling
constant of 67 Hz to the rhodium atom and a rather small
coupling constant of 0.21 Hz to the phosphorus atoms. The IR
spectrum of 7 shows an absorption band for the CO stretching
vibration of ν
̃
1922 cm−1.
C−F and C−H Activation of Fluorinated Aromatics. A
reaction of the silyl complex [Rh{Si(OEt)3}(PEt3)3] (2a) with
hexafluorobenzene led after 40 min at 303 K to the quantitative
generation of the C−F activation product [Rh(C6F5)(PEt3)3]
(8) and the fluorosilane FSi(OEt)3 (Scheme 4). As expected,
Scheme 3. Formation of Rhodium Silyl Complexes
3797
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Scheme 4. C−F and C−H Activation of Fluorinated Aromatics at 2a,b
the reaction of [Rh{Si(OMe)3}(PEt3)3] (2b) with hexafluor-
obenzene gave also 8. As already mentioned in the
introduction, Milstein et al. reported the C−F activation of
hexafluorobenzene at [Rh(SiR3)(PMe3)3] (R3 = Ph3, Me2Ph).16
Note that on reaction of hexafluorobenzene with 2a in the
presence of free phosphine no C−F activation was observed.
Although the phosphine exchange in 2a seems to be
intramolecular (see above), we suggest that phosphine
dissociation plays a crucial role along the reaction pathway.
This might occur either prior to or more likely after a
precoordination of the fluorinated substrate. This assumption is
also compatible with the behavior of the silyl carbonyl complex
7, which showed no activation of hexafluorobenzene at room
temperature. Phosphine dissociation is here more difficult,
because there is no phosphine ligand located in the position
trans to the strongly donating silyl group.
1
Compound 8 was characterized by H, 31P{1H}, and 19F
NMR spectroscopy. The 31P{1H} spectrum shows a doublet of
Figure 3. ORTEP diagram of complex 8. Ellipsoids are drawn at the
multiplets with a rhodium−phosphorus coupling of 132 Hz at δ
18.6 ppm for the phosphorus atom in the position trans to the
fluorinated ligand. The multiplet splitting is due to couplings to
the fluorine and phosphorus atoms. The phosphine ligands in a
mutually trans arrangement give a doublet of doublets at δ 14.1
ppm with coupling constants of 141 Hz to the rhodium atom
and of 40 Hz to the other phosphorus atom. The 19F NMR
spectrum displays three multiplets at δ −108.1, −164.1, and
−164.7 ppm, which integrate in the ratio 2:1:2. The molecular
structure of 8 in the solid state was determined by X-ray
diffraction analysis at 100 K (Figure 3). Suitable crystals were
grown from a benzene[D6] solution at room temperature.
Selected bond lengths and angles are summarized in Table 1.
The compound reveals a distorted-square-planar structure
similar to that reported by Milstein et al. for [Rh(C6F5)-
(PMe3)3].16 The Rh−P distances (Rh(1)−P(1) = 2.3304(3) Å,
Rh(1)−P(2) = 2.3000(3) Å, Rh(1)−P(3) = 2.2840(3) Å) and
the Rh−C distance to the pentafluorophenyl ligand (Rh(1)−
C(1) = 2.0863(13) Å) are in a range similar to that found for
[Rh(C6F5)(PMe3)3].
50% probability level; hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) in
[Rh(C6F5)(PEt3)3] (8) with Standard Deviations in
Parentheses
Rh(1)−C(1)
Rh(1)−P(1)
Rh(1)−P(2)
Rh(1)−P(3)
C(1)−C(2)
C(1)−C(6)
C(2)−F(1)
C(2)−C(3)
2.0863(13)
2.3304(3)
2.3000(3)
2.2840(3)
1.3859(19)
1.3888(18)
1.3595(16)
1.386(2)
C(3)−F(2)
C(3)−C(4)
C(4)−F(3)
C(4)−C(5)
C(5)−F(4)
C(5)−C(6)
C(6)−F(5)
1.3476(17)
1.380(2)
1.3443(18)
1.373(2)
1.3538(17)
1.384(2)
1.3645(17)
P(1)−Rh(1)−P(2)
P(2)−Rh(1)−P(3)
P(1)−Rh(1)−P(3)
C(1)−Rh(1)−P(1)
C(1)−Rh(1)−P(2)
C(1)−Rh(1)−P(3)
C(2)−C(1)−Rh(1)
163.403(12)
96.436(12)
95.372(13)
83.71(4)
C(6)−C(1)−Rh(1)
C(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(3)−C(4)−C(5)
C(4)−C(5)−C(6)
C(5)−C(6)−C(1)
C(2)−C(1)−C(6)
127.60(10)
125.02(13)
119.32(14)
118.60(14)
119.58(14)
124.89(14)
112.50(13)
86.79(4)
169.35(4)
119.85(10)
The reaction of silyl complex [Rh{Si(OEt)3}(PEt3)3] (2a)
and pentafluorobenzene gave the C−H activation product
3798
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
[Rh(C6F5)(PEt3)3] (8), even at 383 K (Scheme 4). In contrast,
Milstein et al. observed a selective C−F activation of
pentafluorobenzene at [Rh(SiMe2Ph)(PMe3)3] in the position
para to the hydrogen atom at higher temperatures (383 K).16
Note that we consider the silyl ligand in [Rh(SiMe2Ph)-
(PMe3)3] to be electronically very different in comparison to
the silyl ligand in 2a, which might be a reason for the difference
in selectivities. Treatment of a solution of 2a or 2b with
perfluorotoluene affords C−F activation in the position para to
the CF3 group to yield [Rh(4-C6F4CF3)(PEt3)3] (9) (Scheme
4). The 31P{1H} NMR spectrum of complex 9 displays a
doublet of doublets at δ 17.7 ppm (JRh,P = 140 Hz, JP,P = 41 Hz)
for the phosphine ligands in mutually trans positions and a
doublet of triplet of multiplets at δ 13.4 ppm (JRh,P = 130 Hz,
JP,P = 41 Hz) for the phosphorus atom in the position trans to
the fluorinated ligand. The 19F NMR spectrum exhibits a triplet
at δ −54.9 ppm for the CF3 group, a multiplet at δ −107.8 ppm
(JF,F = 20 Hz), and a triplet of multiplets at δ −145.8 ppm (JF,F
= 20 Hz) which integrate in a ratio of 3:2:2.
Note that the activation of 2,3,5,6-tetrafluoropyridine at 2a,b
is a spontaneous reaction at room temperature. In contrast, the
silyl carbonyl complex 7 reacted very slowly with 2,3,5,6-
tetrafluoropyridine and after 7 days the C−H activation
product [Rh(CO)(4-C5F4N)(PEt3)2] (12) was generated in
78% yield according to the 31P NMR spectrum (Scheme 6). An
alternative synthesis of 12 was previously reported by treatment
of [Rh(4-C5F4N)(PEt3)3] with CO.8a
Scheme 6. C−H Activation of Pentafluoropyridine at the
Silyl−Carbonyl Complex 7
On treatment of [Rh{Si(OR)3}(PEt3)3] (2a,b) with 2,3,5,6-
tetrafluoropyridine the C−F activation product [Rh(2-
C5F3HN)(PEt3)3] (10) was generated (Scheme 5). Complex
A reaction of [Rh{Si(OEt)3}(PEt3)3] (2a) with pentafluor-
opyridine at 243 K furnished the C−F activation product
[Rh(2-C5F4N)(PEt3)3] (11), which displays the rhodium
center at the position ortho to the nitrogen atom (Scheme
5). At room temperature activation of the C−F bond in the
position para to the nitrogen atom was observed as well. ortho
and para activation products [Rh(2-C5F4N)(PEt3)3] (11) and
[Rh(4-C5F4N)(PEt3)3] were generated in a 9:1 ratio according
to the 31P{1H} NMR spectrum. In contrast, the reaction of
[Rh{Si(OMe)3}(PEt3)3] (2b) with pentafluoropyridine at
room temperature as well as at low temperature afforded
selectively the activation product in an ortho position. The
presence of free phosphine led to C−F activation at 2b at a
comparable rate to yield 11. Thus, the reaction is not inhibited
by free phosphine. The generation of fluorophosphoranes and
2,3,5,6-tetrafluoropyridine was also observed, but at a slower
rate.24 However, the activation of pentafluoropyridine at 2a at
243 K is considerably slower in the presence of free phosphine,
suggesting that phosphine dissociation might play a role in the
mechanism of activation prior to or during the rate-determining
step.
Scheme 5. C−F Activation of 2,3,5,6-Tetrafluoropyridine
and Pentafluoropyridine at 2a,b
[Rh(2-C5F4N)(PEt3)3] (11) and [Rh(4-C5F4N)(PEt3)3]
were identified by comparison of their NMR spectroscopic
data with the literature.8,9 Note that metalation of penta-
fluoropyridine at the 2-position is usually very difficult to
achieve. However, this selectivity was previously observed in
the reaction of [Rh(Bpin)(PEt3)3] with pentafluoropyridine.9 A
comparison with a similar reaction at [Rh(SiPh3)(PMe3)3]
shows again that complexes 2a,b display a more selective
conversion. Treatment of [Rh(SiPh3)(PMe3)3] with penta-
fluoropyridine yields a mixture of the activation products in the
2- and 4-positions in a 3:1 ratio.17,24 Activation of
pentafluoropyridine at the 2-position was also reported at Ni,
Ti, and Zr complexes, whereas organic nucleophiles can show a
competitive pathway.13,25 However, in these cases the oxidative
addition of the C−F bond or fluoro complex formation was
observed. Similar to the reactivity pattern with hexafluor-
obenzene, no C−F activation of pentafluoropyridine at the silyl
carbonyl complex 7 was observed.
10 could not be isolated and was only characterized in solution
because of its low stability. The 31P{1H} NMR spectrum of
[Rh(2-C5F3HN)(PEt3)3] (10) displays a doublet of doublets at
δ 16.1 ppm for the phosphine ligands in mutually trans
positions and a doublet of triplets at δ 20.0 ppm with
rhodium−phosphorus couplings of 153 and 120 Hz and
coupling constants of 38 Hz between the phosphorus atoms.
The 19F NMR spectrum exhibits three doublets of multiplets at
δ −93.0, −103.0, and −153.8 ppm which integrate in a ratio of
1
1:1:1. In the H NMR spectrum a multiplet at δ 6.45 ppm can
be assigned to the hydrogen atom at the trifluoropyridyl ligand.
The formation of 10 is rather remarkable, because in
comparable reactions of 2,4,5,6-tetrafluoropyridine activation of
the C−H bond takes place. Thus, treatment of [Rh(H)(PEt3)3]
(4) or [Rh(Bpin)(PEt3)3] with 2,3,5,6-tetrafluoropyridine led
in both cases to the formation of [Rh(4-C5F4N)(PEt3)3].8,9 As
already mentioned in the introduction, Marder and Perutz et al.
investigated the reactivity of [Rh(SiPh3)(PMe3)3] toward
fluorinated pyridines. They observed a product mixture of
C−H and C−F activation products in a ratio of 1:1.3.17
Computational Studies. Density functional theory (DFT)
calculations have been performed to model the reaction of 2b
with C5F5N to give 11, and in particular, the competition
between C−F activation at the 2- and 4-positions. Two possible
3799
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Scheme 7. General Mechanisms Considered for C−F Activation of C5F5N at Rh Silyl Complexes (L = PMe3)
general pathways have been considered for these processes, as
illustrated in Scheme 7 for reaction at the 2-position. Along
pathway A initial C−F oxidative addition yields a Rh(III)
intermediate from which Si−F reductive elimination gives 11
and FSiR3. Alternatively, pathway B features a silyl-assisted
process in which C−F activation occurs over the Rh−Si bond
to give the products directly. Similar ligand-assisted processes
have been characterized for reactions of fluoroarenes12a,c and
fluoropyridines12b,13 at metal−phosphine bonds and for the
activation of C5F5N over the Rh−boryl bond in [Rh(Bpin)-
(PMe3)3].9 Note that for 2b the rate of C−F activation is not
affected by added phosphine and so we have not considered
alternative routes based on phosphine dissociation.
The calculations employed [Rh{Si(OMe)3}(PMe3)3] (2′) as
a model reactant, primarily to avoid the extreme conformational
flexibility of the PEt3 ligands in 2b (although extensive
conformational searching was still performed for each sta-
tionary point; see Computational Details). The computed
geometry of 2′ is shown in Figure 4 and shows good agreement
with the experimentally determined structure of the related
[Rh(SiPh3)(PMe3)3] system reported by Thorn and Harlow.22a
In particular, the observed deviation away from square-planar
geometry is reproduced in 2′, with average computed trans-L−
Rh−L angles of 151° in comparison to the experimental value
of 146°. While both the Rh−Si and the Rh−P distances are
somewhat overestimated, the elongation of the Rh−P1 bond
trans to Si(OMe)3 is well reproduced, reflecting the higher trans
influence of this ligand in comparison to PMe3. In the following
all energies are quoted relative to the combined energies of 2′
and C5F5N set to 0.0 kcal/mol.
The computed profiles for pathway A are shown in Figure 5
for the reactions of 2′ at both the 2- and 4-positions of C5F5N
to give 2-11 and 4-11, respectively. In principle, the initial
concerted C−F oxidative addition at 2′ can lead to three
different isomers of the [Rh(C5F4N)(F){Si(OMe)3}(PMe3)3]
intermediate: two mer forms, with either F (A2mer) or C5F4N
(A2mer′) trans to Si(OMe)3, and a fac form (A2fac). For both
C−F activations the most favored pathway, both kinetically and
thermodynamically, leads to A2mer. These pathways are
discussed here and shown in Figure 5, with the key C−F
activation transition states in Figure 6; details of all other
structures are provided in the Supporting Information.
Throughout the focus will be on the zero-point energy
corrected energies, although the computed free energies are
also provided in italics. As the key transition states in all
pathways involve an associative step, the inclusion of entropic
effects does not affect which pathway is preferred.
Activation at the 2-position proceeds via initial formation of a
trigonal-bipyramidal intermediate, 2-A1 (E = +0.4 kcal/mol),
with a barrier of only 5.9 kcal/mol. 2-A1 has Si(OMe)3 in an
equatorial position and features an η2-bound C5F5N ligand with
an elongated N−C2 bond (1.39 Å; cf. 1.33 Å in free C5F5N)
oriented in the equatorial plane, consistent with a degree of π
back-donation from the Rh center.26 C−F activation then
occurs via 2-TS(A1-A2mer) (E = +17.3 kcal/mol) to give 2-
A2mer at −27.1 kcal/mol. Isomerization of 2-A2mer is then
required to permit Si−F reductive elimination, and we have
characterized one possible mechanism (omitted from Figure 5)
involving dissociation of the PMe3 trans to the 2-C5F4N ligand.
This proceeds through a transition state at −12.5 kcal/mol and
is accompanied by spontaneous movement of F into the
vacated site. PMe3 reassociation then gives A2mer″ (where PMe3
is now trans to silyl; E = −24.4 kcal/mol), from which Si−F
Figure 4. Computed structure of [Rh{Si(OMe)3}(PMe3)3] (2′) with
selected distances (Å) and angles (deg). Hydrogen atoms are omitted
for clarity, and experimental data for [Rh(SiPh3)(PMe3)3] are shown
in italics.22a
3800
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Figure 5. Computed profiles (kcal/mol) for the reactions of 2′ with C5F5N to give 2-11 and 4-11 and FSiR3 via pathway A (L = PMe3 and R =
OMe). Values in plain text are zero-point energy corrected energies, and those in italics are free energies.
Figure 6. Computed structures for (a) 2-TS(A1-A2mer) and (b) 4-TS(2′-A2mer) with selected distances (Å) and angles (deg). Relative energies
(plain text, zero-point energy corrected energies; italics, free energies) are in kcal/mol, and H atoms are omitted for clarity.
bond formation readily occurs via 2-TS(A2mer″ -11) at −16.9
kcal/mol to give 2-11 and FSi(OMe)3 at −32.6 kcal/mol. The
isomerization/Si−F reductive elimination steps are therefore
much more accessible than the initial C−F oxidative addition.27
This, along with the exothermicity (and hence irreversibility) of
C−F oxidative addition, indicates that the C−F activation step
will control the overall reactivity (and selectivity) of the system.
The C−F oxidative addition transition state 2-TS(A1-A2mer) is
shown in Figure 6a. This structure exhibits a marked deviation
from that expected for a concerted oxidative addition at a
square-planar ML4 complex.28 Normally, the approach of a
substrate, X−Y, induces a narrowing of one trans-L−M−L
angle to accommodate the new M−X/M−Y bonds (see
Scheme 8): in the transition state the X−M−Y and L−M−L
planes are nearly coplanar with the angle between these planes
being close to 0°. In contrast, in 2-TS(A1-A2mer) the angle, α,
between the F2−Rh−C2 and the Si−Rh−P1 planes is 71.5°.
This and other features suggest a degree of phosphine
Scheme 8. Expected Geometric Changes upon Concerted
Oxidative Addition
3801
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Figure 7. Computed reaction profiles (kcal/mol) for the reactions of 2′ to give 2-11 and 4-11 and FSiR3 via pathway B (L = PMe3 and R = OMe).
Values in plain text are zero-point energy corrected energies, and those in italics are free energies.
Figure 8. Computed structures for (a) 2-TS(B1-B2) and (b) 4-TS(2′-B2) with selected distances (Å) and angles (deg). Relative energies (plain
text, zero-point energy corrected energies; italics, free energies) are in kcal/mol, and H atoms are omitted for clarity.
assistance in the C−F activation: 2-TS(A1-A2mer) exhibits a
short Rh−C2 distance of 2.08 Å but a very long Rh···F2
distance of 2.85 Å; F2 also shows a short contact of 2.46 Å with
P2, while the F2−C2−Rh−P2 torsion angle is only +23.3°. No
interaction with the pyridine N is apparent in this case, however
(Rh···N = 2.57 Å). Previous examples of phosphine-assisted
oxidative addition have involved metallophosphorane inter-
mediates,13,14 and a subsequent F → M transfer step has been
necessary to complete the overall oxidative addition process. In
addition transition state. The same trans-influence argument
explains why 2-TS(A1-A2mer) is the most stable C−F oxidative
addition transition state: 2-TS(2′-A2mer′) (E = +23.9 kcal/mol)
shows a similar square-pyramidal geometry at Rh but has PMe3
in the axial position and Si(OMe)3 trans to the developing Rh-
aryl bond; in 2-TS(2′-A2fac) (E = +20.4 kcal/mol) Si(OMe)3
lies trans to a PMe3 ligand (N.B.: no η2 intermediate was
located in these cases and so reaction proceeds directly from
2′) . The greater stability of intermediate 2-A2mer also reflects
the positioning of Si(OMe)3 trans to the weakly donating
fluoride (cf. 2-A2mer′, Si(OMe)3 trans to C5F4N, E = −24.4
kcal/mol, and 2-A2fac, Si(OMe)3 trans to PMe3, E = −25.3
kcal/mol).
the current case, however, characterization of 2-TS(A1-A2mer
)
shows that it leads directly to 4-A2mer, and all attempts to locate
a metallophosphorane species were unsuccessful. A further
feature of 2-TS(A1-A2mer) is the distorted-square-pyramidal
geometry around the Rh center, in which Si(OMe)3 occupies
the axial position. The high trans influence of this ligand favors
placing it opposite a vacant trans site, and the strong Si→Rh
donation can compensate for (and may even drive) the
movement of F2 toward P2 in the phosphine-assisted oxidative
Reaction at the 4-position of C5F5N via pathway A follows a
pattern similar to that described above for the 2-position. In
this case no η2 intermediate equivalent to 2-A1 was located and
C−F oxidative addition instead proceeded directly via 4-TS(2′-
A2mer) (E = +13.2 kcal/mol) to 4-A2mer (E = −34.9 kcal/mol).
3802
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Isomerization and Si−F reductive elimination then give 4−11
and FSi(OMe)3 with a combined energy of −45.6 kcal/mol,
13.0 kcal/mol more stable than 2-11 and FSi(OMe)3. The
overall reaction at the 4-position is therefore strongly favored
thermodynamically. Moreover the initial C−F activation step
also favors this process, both thermodynamically, 4-A2mer being
7.8 kcal/mol more stable than 2-A2mer, and kinetically, 4-
TS(2′-A2mer) being 4.1 kcal/mol more stable than 2-TS(A1-
A2mer). This is also reflected in an earlier transition state
geometry for 4-TS(2′-A2mer), which exhibits a shorter cleaving
C−F bond (1.61 Å) and a longer Rh···C2 distance (2.16 Å, see
Figure 6b). Phosphine assistance is still apparent, with F4 closer
to P2 (2.63 Å) than Rh (2.75 Å), and the twisting of the
{C5F5N} moiety (α = 64.0°; F4−C4−Rh−P2 = +29.2°).
Overall, all the computed results indicate that reaction via
pathway A should result in the formation of 4-11, a conclusion
clearly inconsistent with the observation of 2-11 experimen-
tally.
Computed reaction profiles for the activation of C5F5N at 2′
via pathway B are shown in Figure 7. The reaction at the 2-
position again proceeds by formation of an η2-bound adduct, 2-
B1 (E = +5.0 kcal/mol), an isomer of 2-A1 with Si(OMe)3 now
in an axial position. This ligand can now therefore participate in
a four-centered silyl-assisted C−F activation transition state, 2-
TS(B1-B2) (E = +10.2 kcal/mol, see also Figure 8a), in which
the C2−F2 bond (1.71 Å) adds over the Rh−Si bond (Rh−C =
2.07 Å, Si···F2 = 2.21 Å, F2−C2−Rh−Si = −14.3°).
Importantly, the Rh center maintains an interaction with the
{C5F4N} nitrogen, the Rh−N distance shortening to 2.17 Å (cf.
2.20 Å in 2-B1). The nature of the {C5F4N} ligand changes as
the C−F activation progresses, from an η2-arene in 2-B1 to
having benzyne character in 2-B2, the initial intermediate
formed (E = −5.2 kcal/mol; Rh−C2 = 2.02 Å, Rh−N = 2.21
Å). This change can be quantified by the angle between the
best-fit plane through the C5N ring and the C2−Rh−N plane
(2-B1, 56.4°; 2-TS(B1-B2), 30.6°; 2-B2, 3.2°). 2-B2 also
features a new Si−F2 bond (1.75 Å) and a residual Rh···Si
interaction (2.57 Å), resulting in the Si center exhibiting a
trigonal-bipyramidal geometry. Loss of FSi(OMe)3 and
formation of 2-11 entails a minimal barrier through 2-TS(B2-
11) (E = −4.1 kcal/mol) in which both the Rh−N and Rh−Si
distances lengthen to 2.69 and 3.01 Å, respectively.
Silyl-assisted C−F activation at the 4-position proceeds in
one step through 4-TS(2′-B2) (E = +11.9 kcal/mol). This links
directly to intermediate 4-B2 (E = −33.2 kcal/mol), in which
the newly formed {FSi(OMe)3} moiety interacts strongly with
the Rh center, through both Si (Rh−Si = 2.42 Å) and one
methoxy oxygen (Rh−O = 2.19 Å). 4-B2 is 27.0 kcal/mol more
stable than 2-B2, and these interactions also mean that
FSi(OMe)3 dissociation and product formation has a distinct
barrier of 8.7 kcal/mol via 4-TS(B2-11) at −24.4 kcal/mol.
The most important difference between the two reaction
profiles in Figure 7 lies in the two silyl-assisted C−F activation
transition states. The structure of 4-TS(2′-B2) (Figure 8b)
shows a four-centered geometry very similar to that of 2-
TS(B1-B2), with C4−F4 (1.70 Å) adding over the Rh−Si bond
(Rh−C4 = 2.08 Å; Si···F4 = 2.24 Å; F4−C4−Rh−Si = −14.6°).
One key difference, however, is the lack of any additional
interaction with the C5F4N ring: e.g., through a Rh−CFCF π
interaction. This is also reflected in a much wider P2−Rh−P3
angle of 148.4° (cf. 104.5° in 2-TS(B1-B2)) and in the lack of
any η2 intermediate prior to the silyl-assisted C−F activation
step. This was also a feature of C−F oxidative addition at the 4-
position, while in contrast, both pathways A and B for
activation at the 2-position feature Rh−η2-CFN intermedi-
ates. Interestingly, we were able to locate an alternative silyl-
assisted C−F activation transition state for reaction at the 2-
position which does not feature a short Rh···N contact. This
structure has an energy of +14.6 kcal/mol (G = +31.4 kcal/
mol) and resembles 4-TS(2′-B2), with a wide P2−Rh−P3
angle of 152.3° and a long Rh···N distance of 2.85 Å. This in
turn implies that the Rh···N stabilization in 2-TS(B1-B2) is
worth 4.4 kcal/mol, sufficient to take this structure 1.7 kcal/mol
below 4-TS(2′-B2). The reaction along pathway B is therefore
computed to be kinetically favored at the 2-position; moreover,
pathway B is more accessible than pathway A, and so the
calculations successfully rationalize the experimentally observed
selectivity for the 2-position by invoking a silyl-assisted C−F
activation process.
The characterization of silyl-assisted C−F activation adds to
the range of ligand-assisted C−F activation processes previously
reported at metal−phosphine12−14 and −boryl9 bonds. Both
silyl (X = Si(OMe)3) and boryl assistance (X = Bpin) have now
been characterized for the activation of pentafluoropyridine at
the 2-position at [Rh(X)(PMe3)3] species, allowing for direct
comparison of these two processes. Boryl-assisted C−F
activation also proceeds through an η2 intermediate, although
this is more stable (E = −2.3 kcal/mol) than 2-B1 located here
(E = +5.0 kcal/mol). The ligand-assisted C−F activation step
then proceeds with a very similar barrier (X = Bpin, ΔE⧧ = +6.4
kcal/mol; X = Si(OMe)3, ΔE⧧ = +5.2 kcal/mol), and this is
reflected in comparable transition state geometries. The overall
barrier to boryl assistance is therefore lower (+4.1 kcal/mol; cf.
+10.2 kcal/mol for silyl assistance), although this reflects the
energy of the η2 intermediate rather than different intrinsic
abilities of the two ligands to assist the C−F cleavage step. A
degree of Rh···N interaction is computed in both transition
states (X = Bpin, Rh···N = 2.22 Å; X = Si(OMe)3, Rh···N =
2.16 Å), and this accounts for the novel selectivity for the 2-
position in both cases.
CONCLUSIONS
■
The rhodium(I) silyl complexes 2a,b and 7 were synthesized
from the methyl complex 1. Reactions of the complexes 2a,b
with hexafluorobenzene and fluorinated pyridines result in C−F
activation products. Treatment of 2a or 2b with pentafluor-
opyridine led to the activation product at the 2-position. This
conversion is selective at 243 K for the triethoxysilyl-substituted
complex 2a and at room temperature for the trimethoxysilyl
complex 2b. Whereas the activation of hexafluorobenzene and
pentafluoropyridine at 2a is inhibited in the presence of free
phosphine, the activation of pentafluoropyridine at 2b is not
retarded by free phosphine.
DFT calculations using [Rh{Si(OMe)3}(PMe3)3] (2′) as a
model complex for 2b were performed. C−F oxidative addition
transition states are higher in energy and would imply that
activation at the 4-position of pentafluoropyridine is favored. In
contrast, a silyl-assisted C−F activation pathway is more
accessible and in this case the reaction at the 2-position is
preferred due to a stabilizing Rh···N interaction in the
transition state. The computational studies are in agreement
with the experimental results. A pathway based on phosphine
dissociation may also be close in energy to the silyl-assisted
reaction route, but for simplicity we only considered the
activation reaction at 2b computationally. Silyl-assisted C−F
activation is another example of the general process of ligand-
3803
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
Formation of [Rh(H){Si(OEt)3}2(PEt3)3] (3). HSi(OEt)3 (12 μL,
0.065 mmol) was added to a solution of [Rh(CH3)(PEt3)3] (1; 0.053
mmol) in n-pentane (0.5 mL) at 183 K. The solution was warmed to
233 K and then stirred for 4 h at this temperature. After the reaction
solution was warmed to room temperature, the solvent was removed
under vacuum. The red residue was dissolved in 0.3 mL of
[D6]benzene and the solution placed in a PFA NMR tube. The
NMR data reveal the formation of 2a and 3 in a ratio of 4:1. NMR data
for 3: 1H NMR (300.1 MHz, [D6]benzene, 300 K) δ −15.6 (dm, d in
the 1H{31P} NMR spectrum 1J(H,Rh) = 29 Hz, 1H, RhH). The signals
for the ethyl groups in 3 are covered by resonances of 2a; 31P{1H}
NMR (121.5 MHz, [D6]benzene, 300 K) δ 4.6 (dt, 1J(Rh,P) = 97 Hz,
assisted C−F activation which has been reported at phosphine
and boryl ligands.9,12−14 The favored four-membered transition
state that features a stabilizing Rh···N interaction and accounts
for activation at the 2-position of pentafluoropyridine is
comparable to previously reported boryl-assisted and phos-
phine-assisted oxidative addition C−F activation processes.
Note that radical-pair mechanisms for C−F activation reactions
have been discussed for conversions at ruthenium, rhodium and
iridium, but pentafluoropyridine should then be activated at the
para position.5b,29 In addition, we do not have any experimental
indication for such a mechanism. Thus, radical trapping
experiments with 9,10-dihydroanthracene showed no formation
of anthracene or tetrafluoropyridines.
1
2J(P,P) = 29 Hz, 1P), −2.4 (dd, J(Rh,P) = 71 Hz,2 J(P,P) = 29 Hz,
2P).
Formation of [Rh(H)(PEt3)3] (4). HSiEt3 (8.5 μL, 0.053 mmol)
was added to a solution of [Rh(CH3)(PEt3)3] (1; 0.053 mmol) in
[D6]benzene (0.5 mL). A quantitative conversion of 1 into complex 4
occurred. Complex 4 was identified by its NMR data.8
Formation of [Rh(H)2{Si(OEt)3}(PEt3)3] (5a). HSi(OEt)3 (9.8 μL,
0.053 mmol) was added to a solution of [Rh(H)(PEt3)3] (4; 0.053
mmol) in [D6]benzene (0.5 mL). The NMR spectroscopic data of the
EXPERIMENTAL SECTION
■
General Considerations. The synthetic work was carried out on a
Schlenk line. All solvents were dried and purified by conventional
methods and distilled under argon before use. [D6]Benzene,
[D8]toluene, [D14]methylcyclohexane, and [D8]THF were purified
by distillation from Na/K under argon. [Rh(CH3)(PEt3)3] (1) was
prepared according to the literature.30 In all experiments 1 was
employed in solution with a concentration of 0.106 mmol mL−1. PFA
NMR tubes were used for highly sensitive compounds to inhibit
reactions with OH groups at glass surfaces. PFA NMR tubes were
obtained from Roland Vetter Laborbedarf OHG.
1
reaction solution revealed the formation of 5a. NMR data for 5a: H
NMR (300.1 MHz, [D6]benzene, 300 K) δ 4.1 (q, 3J(H,H) = 6.9 Hz,
6H, SiOCH2CH3), 1.9 (m, 6H, PCH2CH3), 1.6 (m, 12H, PCH2CH3),
1.4 (t, 3J(H,H) = 6.9 Hz, 9H, SiOCH2CH3), 1.1 (m, 18H, PCH2CH3),
1.0 (m, 9H, PCH2CH3), −11.3 (ddm, d in the 1H{31P} NMR
spectrum, 1J(H,Rh) = 18 Hz, 2J(H,Ptrans) = 108 Hz, 1H, RhH);
31P{1H} NMR (121.5 MHz, [D6]benzene, 300 K) δ 16.0 (dd, 1J(Rh,P)
The NMR spectra were acquired on Bruker DPX 300, Bruker
Avance 300, and Bruker AV 400 NMR spectrometers. The H, 13C,
1
2
1
2
= 101 Hz, J(P,P) = 23 Hz, 2P), 7.2 (dt, J(Rh,P) = 83 Hz, J(P,P) =
and 29Si NMR spectra were referenced to external TMS at δ 0 ppm.
19F NMR spectra were referenced externally to C6F6 at δ −162.9 ppm,
and 31P NMR spectra were referenced externally to H3PO4 at δ 0 ppm.
Infrared spectra were recorded on a Bruker Vektor 22 spectrometer
which was equipped with a diamond ATR unit. Microanalyses were
carried out using a HEKAtech EURO EA 3000 elemental analyzer.
Synthesis of [Rh{Si(OEt)3}(PEt3)3] (2a). HSi(OEt)3 (9.8 μL,
0.053 mmol) was added to a solution of [Rh(CH3)(PEt3)3] (1; 0.053
mmol) in n-pentane (0.5 mL) at 183 K. The solution was warmed to
233 K and then stirred for 4 h at this temperature. After the reaction
solution was warmed to room temperature, the solvent was removed
under vacuum. The red residue was dissolved in 0.3 mL of
[D6]benzene and the solution placed in a PFA NMR tube. The
31P{1H} spectrum reveals a quantitative conversion of the methyl
complex 1 to 2a. NMR data for 2a: 1H NMR (300.1 MHz,
23 Hz, 1P); H,29Si HMBC NMR (300.1/59.6 MHz, [D6]benzene,
1
300 K) δ{29Si} 4/−3 (SiOCH2CH3), −11/−3 (HRhSi).
Formation of [Rh(H)2{Si(OMe)3}(PEt3)3] (5b). HSi(OMe)3 (6.8
μL, 0.053 mmol) was added to a solution of [Rh(H)(PEt3)3] (4; 0.053
mmol) in [D6]benzene (0.5 mL). A quantitative conversion of 4 into
complex 5b occurred. The latter was identified by its NMR data.8
Formation of fac-[Rh(H)(CH3){Si(OEt)3}(PEt3)3] (6a). HSi(OEt)3
(9.8 μL, 0.053 mmol) was added to a solution of [Rh(CH3)(PEt3)3]
(1; 0.053 mmol) in [D8]toluene (0.5 mL) at 183 K. After 15 min the
quantitative formation of 6a was observed by NMR spectroscopy.
NMR data for 6a: 1H NMR (300.1 MHz, [D8]toluene, 233 K) δ 4.0−
4.2 (m, 6H, SiOCH2CH3), 1.8−2.3 (m, br, 18H, PCH2CH3), 1.5−1.6
(m, 9H, SiOCH2CH3), 1.3−1.5 (m, 27H, PCH2CH3), 0.0 (m, br, d in
1
2
the H{31P} NMR spectrum J(H,Rh) = 1.8 Hz, 3H, RhCH3), −10.8
(ddm, d in the 1H{31P} NMR spectrum, 1J(H,Rh) = 18 Hz, 2J(H,Ptrans
)
3
[D6]benzene, 300 K) δ 4.1 (q, J(H,H) = 7.6 Hz, 6H, SiOCH2CH3)
= 144 Hz, 1H, RhH), the assignment of the signals is supported by a
1
3
1.8 (m, q in the H{31P} NMR spectrum, J(H,H) = 7.6 Hz, 18H,
1H,1H COSY NMR spectrum; 31P{1H} NMR (121.5 MHz, [D8]-
3
PCH2CH3), 1.4 (t, J(H,H) = 7.6 Hz, 9H, SiOCH2CH3), 1.0 (m, t in
1
2
1
3
the H{31P} NMR spectrum, J(H,H) = 7.6 Hz, 27H, PCH2CH3);
31P{1H} NMR (121.5 MHz, [D8]toluene, 300 K) δ 13.6 (d, 1J(Rh,P) =
144 Hz); 31P{1H} NMR (161.9 MHz, [D8]toluene, 183 K) δ 20.4 (dd,
toluene, 233 K) δ 12.2 (ddd, J(Rh,P) = 90 Hz, J(P,P) = 25 Hz,
2J(P,P) = 22 Hz, 1P), 4.0 (ddd, J(Rh,P) = 94 Hz, J(P,P) = 25 Hz,
1
2
2J(P,P) = 22 Hz, 1P), −3.3 (ddd, 1J(Rh,P) = 71 Hz, J(P,P) = 25 Hz,
2
2J(P,P) = 22 Hz, 1P, P trans Si,); H,29Si HMBC NMR (300.1/59.6
1
1J(Rh,P) = 151 Hz, J(P,P) = 34 Hz,2P), 3.2 (dt, J(Rh,P) = 118 Hz,
2
1
MHz, [D8]THF, 220 K) δ{29Si} 4/−7 (SiOCH2CH3), −11/−7
(HRhSi).
2J(P,P) = 34 Hz, 1P); 29Si{1H} NMR (59.6 MHz, [D6]benzene, 300
1
2
K) δ −11.3 (dq, J(Rh,Si) = 60 Hz, J(Si,P) = 47 Hz).
Formation of fac-[Rh(H)(CH3){Si(OMe)3}(PEt3)3] (6b). HSi-
(OMe)3 (6.8 μL, 0.053 mmol) was added to a solution of
[Rh(CH3)(PEt3)3] (1; 0.053 mmol) in [D14]methylcyclohexane (0.5
mL) at 183 K. After 15 min the quantitative formation of 6b was
Synthesis of [Rh{Si(OMe)3}(PEt3)3] (2b). HSi(OMe)3 (6.8 μL,
0.053 mmol) was added to a solution of [Rh(CH3)(PEt3)3] (1; 0.053
mmol) in n-pentane (0.5 mL) at 183 K. The solution was warmed to
218 K and then stirred for 4 h at this temperature. After the reaction
solution was warmed to room temperature, the solvent was removed
under vacuum. The red residue was dissolved in 0.3 mL of
[D14]methylcyclohexane and the solution placed in a PFA NMR
tube. The 31P{1H} spectrum reveals a quantitative conversion of the
1
observed by NMR spectroscopy. NMR data for 6b: H NMR (300.1
MHz, [D14]methylcyclohexane, 223 K) δ 3.1 (s, 9H, SiOCH3), 1.3−
1.5 (m, br, 6H, PCH2CH3), 1.3−1.1 (m, br, 12H, PCH2CH3), 0.7−0.8
1
(m, 27H, PCH2CH3), −0.7 (m, br, d in the H{31P} NMR spectrum
2J(H,Rh) = 1.8 Hz, 3H, RhCH3), −11.2 (ddm, d in the 1H{31P} NMR
1
methyl complex 1 to 2b. NMR data for 2b: H NMR (300.1 MHz,
1
spectrum, J(H,Rh) = 18 Hz,2J(H,Ptrans) = 144 Hz, 1H, RhH), the
[D14]methylcyclohexane, 300 K) δ 3.2 (s, 9H, SiOCH3), 1.5 (m, q in
the 1H{31P} NMR spectrum, 3J(H,H) = 7.6 Hz, 18H, PCH2CH3), 0.8
(m, t in the 1H{31P} NMR spectrum, 3J(H,H) = 7.6 Hz, 27H,
PCH2CH3); 31P{1H} NMR (121.5 MHz, [D14]methylcyclohexane,
assignment of the signals is supported by a 1H,1H COSY NMR
spectrum; 13C{1H} NMR (75.5 MHz, [D14]methylcyclohexane, 223
K) δ 55.4 (s, SiOCH3), 26.9 (m, PCH2CH3), 25.6 (m, PCH2CH3),
23.4 (m, PCH2CH3), 14.8 (s, PCH2CH3), 14.5 (s, PCH2CH3), 13.4 (s,
PCH2CH3), −14.3 (m, CH3); the assignment of the signals is
supported by a 1H,13C HMQC NMR spectrum; 31P{1H} NMR (121.5
MHz, [D14]methylcyclohexane, 223 K) δ 11.2 (ddd, 1J(Rh,P) = 90 Hz,
1
300 K) δ 13.7 (d, J(Rh,P) = 144 Hz); 31P{1H} NMR (121.5 MHz,
[D8]toluene, 183 K) δ 20.6 (dd, 1J(Rh,P) = 150 Hz, 2J(P,P) = 34 Hz,
2P), 2.7 (dt, 1J(Rh,P) = 119 Hz, 2J(P,P) = 34 Hz, 1P); 1H,29Si HMBC
NMR (30.1/59.6 MHz, [D14]methylcyclohexane, 300 K) δ 3/−8.
3804
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
2
1
2J(P,P) = 26 Hz, J(P,P) = 23 Hz, 1P), 4.3 (ddd, J(Rh,P) = 95 Hz,
[D8]toluene, 300 K) δ 6.5 (m, 1H, C5F3HN); 1.4 (m, br, 18H,
PCH2CH3), 1.0 (m, br, 27H, PCH2CH3); 31P{1H} NMR (121.5 MHz,
2
1
2J(P,P) = 26 Hz, J(P,P) = 23 Hz, 1P), −3.3 (ddd, J(Rh,P) = 72 Hz,
2J(P,P) = 26 Hz, 2J(P,P) = 23 Hz, 1P); 1H,29Si HMBC NMR (300.1/
59.6 MHz, [D14]methylcyclohexane, 223 K) δ{29Si} 3/−4
(SiOCH2CH3), −11/−4 (HRhSi).
1
2
[D8]toluene, 300 K) δ 20.0 (dt, J(Rh,P) = 120 Hz, J(P,P) = 38 Hz,
1
2
1P), 16.1 (dd, J(Rh,P) = 153 Hz, J(P,P) = 38 Hz, 2P); 19F NMR
(282.4 MHz, [D8]toluene, 300 K) δ −93.0 (dm, J(F,F) = 32 Hz, 1F),
−103.0 (dm, J(F,F) = 32 Hz, 1F), −153.8 (dm, J(F,F) = 32 Hz, 1F).
Formation of [Rh(2-C5F4N)(PEt3)3] (11). (a) Pentafluoropyridine
(5.8 μL, 0.053 mmol) was added to a solution of [Rh{Si(OEt)3}-
(PEt3)3] (2a; 0.053 mmol) in [D8]toluene (0.4 mL) at 243 K. After 3
h the quantitative formation of 11 and FSi(OEt)3 was observed by
31P{1H} NMR spectroscopy. Complex 11 was identified by
comparison of its NMR data with the literature.9
Synthesis of [Rh(CO){Si(OEt)3}(PEt3)2] (7). Carbon monoxide
was bubbled for 30 s into a solution of [Rh{Si(OEt)3}(PEt3)3] (2a;
0.053 mmol) in n-pentane (0.5 mL). The solvent was removed by
applying a moderate vacuum, and the resulting yellow oil was dissolved
in [D6]benzene. The NMR spectroscopic data revealed the
quantitative conversion of the silyl complex 2a into 7. NMR data
for 7: 1H NMR (300.1 MHz, [D6]benzene, 300 K) δ 4.7 (q, 3J(H,H) =
6.9 Hz, 6H, SiOCH2CH3), 1.5 (m, q in the 1H{31P} NMR
(b) Pentafluoropyridine (5.8 μL, 0.053 mmol) was added to a
solution of [Rh{Si(OMe)3}(PEt3)3] (2b; 0.053 mmol) in [D8]toluene
(0.4 mL). The quantitative formation of 11 and FSi(OMe)3 was
observed by 31P{1H} NMR spectroscopy. Complex 11 was identified
by comparison of its NMR data with the literature.9
spectrum,3J(H,H) = 7.7 Hz, 12H, PCH2CH3), 1.4 (t, J(H,H) = 6.9
3
Hz, 9H, SiOCH2CH3), 0.9 (m, t in the 1H{31P} NMR spectrum,
3J(H,H) = 7.7 Hz, 18H, PCH2CH3); 13C{1H} NMR (75.5 MHz,
1
[D6]benzene, 300 K) δ 200.3 (d, J(C,Rh) = 67 Hz, CO), 57.8 (m,
Formation of [Rh(CO)(4-C5F4N)(PEt3)3] (12). 2,3,5,6-Tetrafluor-
obenzene (5.3 μL, 0.053 mmol) was added to a solution of
[Rh(CO){Si(OEt)3}(PEt3)2] (4; 0.053 mmol) in [D6]benzene (0.4
mL). After 7 days 78% of [Rh(CO){Si(OEt)3}(PEt3)2] (4) was
converted into 12. Compound 12 was identified by its NMR data.8
Structure Determination. Red crystals of 8 were obtained at
room temperature from a solution of complex 8 in [D6]benzene. The
diffraction data were collected with a Stoe IPDS 2 Θ diffractometer for
a fragment with the dimensions of 0.36 × 0.28 × 0.16 mm3:
C24H45F5P3Rh, Mr = 624.42, monoclinic, space group P21/n, a =
9.3377(3) Å, b = 18.07909(4) Å, c = 16.7460(5) Å, V = 2826.55(14)
Å3, ρcalcd = 1.467 g cm−3, T = 100(2) K, Z = 4, μ(Mo Kα) = 0.818
mm−1, 30069 reflections measured, 7512 unique (R int = 0.0572); final
R1 and wR2 values on all data 0.0273 and 0.0652; R1 and wR2 values
for 7512 reflections with I0 > 2σ(I0) 0.0245 and 0.0639; residual
electron density +1.168/−1.515 e Å−3. CCDC-924071 contains the
supplementary crystallographic data. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Computational Details. DFT calculations were run with Gaussian
09 (Revision A.02)31 using the BP86 functional.32 Rh, P, and Si
centers were described with the Stuttgart RECPs and associated basis
sets,33 with added d-orbital polarization on P (ζ = 0.387) and Si (ζ =
0.284).34 6-31G** basis sets were used for all other atoms.35 All
stationary points were fully characterized via analytical frequency
calculations as either minima (all positive eigenvalues) or transition
states (one negative eigenvalue), and IRC calculations and subsequent
geometry optimizations were used to confirm the minima linked by
each transition state. Each stationary point was subjected to
conformational searching using our published protocol, and the
most stable conformation is reported in each case.36 All energies are
corrected for zero-point energy, while free energies are quoted at
298.15 K and 1 atm.
SiOCH2CH3), 21.0 (m, 1J(C,P) = 10.2 Hz, PCH2CH3), 18.4
(SiOCH2CH3), 7.7 (PCH2CH3), the assignment of the signals is
supported by a 1H,13C HMBC NMR spectrum; 31P{1H} NMR (121.5
MHz, [D6]benzene, 300 K) δ 14.8 (d, J(Rh,P) = 108 Hz). 29Si{1H}
1
NMR (59.6 MHz, [D6]benzene, 300 K) δ −10.3 (dt, 1J(P,Si) = 67 Hz,
̃
2J(Rh,Si) = 25 Hz). IR (ATR, ν/cm−1): 1922.
Synthesis of [Rh(C6F5)(PEt3)3] (8) via C−H Activation of
Pentafluorobenzene. [Rh{Si(OEt)3}(PEt3)3] (2a; 0.053 mmol)
was dissolved in benzene (0.3 mL) in a PFA NMR tube.
Pentafluorobenzene (20 μL, 0.180 mmol) was added. After 12 h the
formation of 8 was observed via NMR spectroscopy. Evaporation of
the solvent under vacuum gave a yellow solid. Yield: 31 mg (94%).
1
NMR data for 8: H NMR (300.1 MHz, [D6]benzene, 300 K) δ 1.4
(m, q in the 1H{31P} NMR spectrum, 3J(H,H) = 7.6 Hz, 6H,
PCH2CH3), 1.2 (m, q in the H{31P} NMR spectrum, J(H,H) = 7.6
1
3
Hz, 12H, PCH2CH3), 1.0 (m, t in the 1H{31P} NMR spectrum,
3J(H,H) = 7.6 Hz, 9H, PCH2CH3), 0.9 (m, t in the H{31P} NMR
1
spectrum, 3J(H,H) = 7.6 Hz, 18 H, PCH2CH3); 31P{1H} NMR (121.5
MHz, [D6]benzene, 300 K) δ 18.6 (dtm, 1J(Rh,P) = 132 Hz, 2J(P,P) =
40 Hz, 1P), 14.1 (dd, J(Rh,P) = 141 Hz, J(P,P) = 40 Hz, 2P). 19F
NMR (282.4 MHz, [D6]benzene, 300 K) δ −108.1 (m, 2F), −164.1
(m, 1F), −164.7 (m, 2F). Anal. Calcd for C24H45F5P3Rh: C, 46.16; H,
7.26. Found: C, 46.57; H, 7.30.
1
2
Formation of [Rh(C6F5)(PEt3)3] (8) via C−F Activation of
Hexafluorobenzene. [Rh{Si(OR)3}(PEt3)3] (2a or 2b; 0.053
mmol) was dissolved in hexafluorobenzene (0.3 mL) in a PFA
NMR tube. The NMR data revealed the quantitative formation of 8
and FSi(OR)3. Evaporation of the solvent under vacuum gave a yellow
solid. Yield: 32 mg (98%).
Synthesis of [Rh(4-C6F4CF3)(PEt3)3] (9). A solution of octa-
fluorotoluene (37 mg, 0.157 mmol) in [D14]methylcyclohexane (0.1
mL) was added to a solution of [Rh{Si(OR)3}(PEt3)3] (2a or 2b;
0.053 mmol) in hexane (0.5 mL). The formation of 9 and fluorosilane
was observed via NMR spectroscopy. Evaporation of the solvent under
ASSOCIATED CONTENT
1
■
vacuum gave a yellow oil. Yield: 35 mg (98%). NMR data for 9: H
NMR (300.1 MHz, [D6]benzene, 300 K) δ 1.4 (m, q in the H{31P}
S
1
* Supporting Information
3
NMR spectrum, J(H,H) = 7.5 Hz, 6H, PCH2CH3), 1.2 (m, q in the
Text, tables, and a CIF file giving crystallographic data,
computational details, and the full ref 32. This material is
available free of charge via the Internet at http://pubs.acs.org.
1H{31P} NMR spectrum, 3J(H,H) = 7.5 Hz, 12H, PCH2CH3), 1.0 (m,
t in the H{31P} NMR spectrum, J(H,H) = 7.5 Hz, 9H, PCH2CH3),
1
3
1
3
0.9 (m, t in the H{31P} NMR spectrum, J(H,H) = 7.5 Hz, 18 H,
PCH2CH3); 31P{1H} NMR (121.5 MHz, [D6]benzene, 300 K) δ 17.7
1
2
1
AUTHOR INFORMATION
(dtm, J(Rh,P) = 130 Hz, J(P,P) = 41 Hz, 1P), 13.4 (dd, J(Rh,P) =
■
140 Hz, J(P,P) = 41 Hz, 2P); 19F NMR (282.4 MHz, [D6]benzene,
2
Corresponding Author
300 K) δ −54.9 (t, J(F,F) = 20.4 Hz, 3F, CF3), −107.8 (m, 2F),
−145.8 (tm, J(F,F) = 20.4 Hz, 2F).
*E-mail: thomas.braun@chemie.hu-berlin.de (T.B.); s.a.
macgregor@hw.ac.uk (S.A.M.).
Formation of [Rh(2-C5F3HN)(PEt3)3] (10). 2,3,5,6-Tetrafluoro-
pyridine (5.3 μL, 0.053 mmol) was added to a solution of
[Rh{Si(OR)3}(PEt3)3] (2a or 2b; 0.053 mmol) in [D8]-toluene (0.4
mL). After 10 min the solvent was removed under vacuum. The yellow
residue was dissolved in 0.5 mL of [D8]toluene. The NMR
spectroscopic data of the reaction solution reveal the quantitative
formation of 10. NMR data for 10: 1H NMR (300.1 MHz,
Present Address
§Department of Chemistry, University of California, Berkeley,
CA 94720, United States.
Notes
The authors declare no competing financial interest.
3805
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
G. In Activation of Unreactive Bonds and Organic Synthesis; Murai, S.,
Ed.; Springer: New York, 1999; Vol. 3, pp 243−269. (n) Burdeniuc, J.;
Jedlicka, B.; Crabtree, R. H. Chem. Ber. 1997, 130, 145−154.
(o) Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.
1994, 94, 373−431. (p) Mazurek, U.; Schwarz, H. Chem. Commun.
2003, 1321−1326. (q) Meier, G.; Braun, T. Angew. Chem. 2009, 121,
1546−1548; Angew. Chem., Int. Ed. 2009, 48, 1575−1577. (r) Driver,
T. G. Angew. Chem. 2009, 121, 8116−8119; Angew. Chem., Int. Ed.
2009, 48, 7974−7976. (s) Ohashi, M.; Kambara, T.; Hatanaka, T.;
Saijo, H.; Doi, R.; Ogoshi, S. J. Am. Chem. Soc. 2011, 133, 3256−3259.
ACKNOWLEDGMENTS
■
Support from the research training group GRK 1582 “Fluorine
as a Key Element” funded by the Deutsche Forschungsge-
meinschaft is gratefully acknowledged, as well as Heriot-Watt
University and the EPSRC for provision of a DTA studentship
(J.A.P.). We thank Anna Eißler for the X-ray crystallographic
analysis.
REFERENCES
■
(t) Panisch, R.; Bolte, M.; Muller, T. J. Am. Chem. Soc. 2006, 128,
̈
(1) (a) Shine, K. P.; Sturges, W. T. Science 2007, 315, 1804−1805.
(b) Thayer, A. M. Chem. Eng. News 2006, 84, 15. (c) Muller, K.; Faeh,
C.; Diederich, F. Science 2007, 317, 1881−1886. (d) Begue, J.-P.;
́ ́
Bonnet-Deplon, D. Bioorganic and Medicinical Chemistry of Fluorine;
Wiley: Hoboken, NJ, 2008. (e) Banks, R. E., Ed. Fluorine Chemistry at
the Millenium. Fascinated by Fluorine; Elsevier: Amsterdam, 2000.
(f) Kirsch, P. Modern Fluoroorganic Chemistry. Synthesis, Reactivity,
Applications; Wiley-VCH: Weinheim, Germany, 2004. (g) Hiyama, T.
Organofluorine Compounds. Chemistry and Applications; Springer:
Berlin, 2000.
9676−9682. (u) Stahl, T.; Klare, H. F. T.; Oestreich, M. J. Am. Chem.
Soc. 2013, 135, 1248−1251. (v) Douvris, C.; Ozerov, O. V. Science
2008, 321, 1188−1190.
(5) (a) Jones, W. D.; Partridge, M. G.; Perutz, R. N. J. Chem. Soc.,
Chem. Commun. 1991, 264. (b) Braun, T.; Perutz, R. N. Chem.
̈
Commun. 2002, 2749−2757. (c) Breyer, D.; Braun, T.; Klaring, P.
̈
Organometallics 2012, 31, 1417−1421. (d) Fahey, D. R.; Mahan, J. E. J.
Am. Chem. Soc. 1977, 99, 2501−2508. (e) Cronin, L.; Higgitt, C. L.;
Karch, R.; Perutz, R. N. Organometallics 1997, 16, 4920−4928.
(f) Burling, S.; Elliott, P. I. P.; Jasim, N. A.; Lindup, R. J.; McKenna, J.;
Perutz, R. N.; Archibald, S. J.; Whitwood, A. C. Dalton Trans. 2005,
3686−3695. (g) Steffen, A.; Sladek, M. I.; Braun, T.; Neumann, B.;
Stammler, H. G. Organometallics 2005, 24, 4057−4064. (h) Keyes, L.;
Sun, A. D.; Love, J. A. Eur. J. Org. Chem. 2011, 3985. (i) Sladek, M. I.;
Braun, T.; Neumann, B.; Stammler, H. G. Dalton Trans. 2002, 297−
299. (j) Archibald, S. J.; Braun, T.; Gaunt, J. A.; Hobson, J. E.; Perutz,
R. N. Dalton Trans. 2000, 2013−2018. (k) Zhan, J. H.; Lv, H.; Yu, Y.;
Zhang, J. L. Adv. Synth. Catal. 2012, 354, 1529−1541. (l) Hatnean, J.
A.; Johnson, S. A. Organometallics 2012, 31, 1361−1373. (m) Braun,
T.; Izundu, J.; Steffen, A.; Neumann, B.; Stammler, H. G. Dalton Trans.
2006, 5118−5123. (n) Breyer, D.; Braun, T.; Penner, A. Dalton Trans.
2010, 39, 7513−7520. (o) Buckley, H. L.; Sun, A. D.; Love, J. A.
Organometallics 2009, 28, 6622. (p) Sun, A. D.; Love, J. A. Org. Lett.
2011, 13, 2750.
(2) (a) Smart, B. E. Mol. Struct. Eng. 1986, 3, 141. (b) Smart, B. E. In
Fluorocarbons Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1983; p
603. (c) Luo, Y.-R. Comprehensive Handbook of Chemical Bond
Energies; CRC Press: Boca Raton, FL, 2007.
(3) (a) Hughes, R. P. Eur. J. Inorg. Chem. 2009, 31, 4591−4606.
(b) Watson, D. A.; Su, M. J.; Teverovskiy, G.; Zhang, Y.; García-
Fortanet, J.; Kinzel, T.; Buchwald, S. L. Science 2009, 325, 1661−1664.
(c) Hollingworth, C.; Gouverneur, V. Chem. Commun. 2012, 48,
2929−2942. (d) Carreira, E. M.; Pagenkopf, B. L. Chem. Eur. J. 1999,
5, 3437−3442. (e) Grushin, V. V. Chem. Eur. J. 2002, 8, 1007−1014.
(f) Bobbio, C.; Gouverneur, V. Org. Biomol. Chem. 2006, 4, 2065−
2075. (g) Furuya, T.; Klein, J. E. M. N.; Ritter, T. Synthesis 2010, 11,
1804−1821. (h) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110,
1147−1169. (i) Furuya, T.; Kamlet, A. S.; Ritter, T. Nature 2011, 473,
470−477. (j) Brown, J. M.; Gouverneur, V. Angew. Chem. 2009, 121,
8762−8766; Angew. Chem., Int. Ed. 2009, 48, 8610−8614.
(6) (a) Kuhnel, M. F.; Lentz, D. Angew. Chem. 2010, 122, 2995−
̈
2998; Angew. Chem., Int. Ed. 2010, 49, 2933−2936. (b) Edelbach, B.
L.; Fazlur Rahman, A. K.; Lachicotte, J. R.; Jones, W. D.
Organometallics 1999, 18, 3170−3177. (c) Kraft, B. M.; Lachicotte,
R. J.; Jones, W. D. J. Am. Chem. Soc. 2001, 123, 10973−10979.
(d) Kraft, B. M.; Jones, W. D. J. Organomet. Chem. 2002, 658, 132−
(k) Hintermann, L.; Lang, F.; Maire, P.; Togni, A. Eur. J. Inorg.
̈
Chem. 2006, 1396−1412. (l) Hull, K. L.; Anani, W. Q.; Sanford, M. S.
J. Am. Chem. Soc. 2006, 128, 7134−7135. (m) Akana, J. A.;
Bhattacharyya, K. X.; Muller, P.; Sadighi, J. P. J. Am. Chem. Soc.
̈
2007, 129, 7736−7737. (n) Furuya, T.; Kaiser, H. M.; Ritter, T.
Angew. Chem. 2008, 120, 6082−6085; Angew. Chem., Int. Ed. 2008, 47,
5993−5996. (o) Furuya, T.; Ritter, T. J. Am. Chem. Soc. 2008, 130,
10060−10061. (p) Wang, X.; Mei, T.-S.; Yu, J.-Q. J. Am. Chem. Soc.
2009, 131, 7520−7521. (q) Wang, W.; Jasinski, J.; Hammond, G. B.;
Xu, B. Angew. Chem. 2010, 122, 7405−7410; Angew. Chem., Int. Ed.
2010, 49, 7247−7252. (r) Hollingworth, C.; Hazari, A.; Hopkinson,
M. N.; Tredwell, M.; Benedetto, E.; Huiban, M.; Gee, A. D.; Brown, J.
M.; Gouverneur, V. Angew. Chem. 2011, 123, 2661−2665; Angew.
Chem., Int. Ed. 2011, 50, 2613−2617. (s) Phipps, R. J.; Hiramatsu, K.;
Toste, F. D. J. Am. Chem. Soc. 2012, 134, 8376−8379. Rauniyar, V.;
Lackner, A. D.; Hamilton, G. L.; Toste, F. D. Science 2011, 334, 1681−
1684.
140. (e) Jager-Fiedler, U.; Klahn, M.; Arndt, P.; Baumann, W.;
̈
Spannenberg, A.; Burlakov, V. V.; Rosenthal, U. J. Mol. Catal. A: Chem.
2007, 261, 184−189. (f) Rieth, R. D.; Brennessel, W. W.; Jones, W. D.
Eur. J. Inorg. Chem. 2007, 2007, 2839−2847. (g) Kraft, B. M.;
Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc. 2000, 122, 8559−
́
8560. (h) Clot, E.; Megret, C.; Kraft, B. M.; Eisenstein, O.; Jones, W.
D. J. Am. Chem. Soc. 2004, 126, 5647−5653. (i) Kraft, B. M.; Clot, E.;
Eisenstein, O.; Brennessel, W. W.; Jones, W. D. J. Fluorine Chem. 2010,
131, 1122−1132. (j) Kraft, B. M.; Jones, W. D. J. Am. Chem. Soc. 2002,
124, 8681−8689. (k) Vela, J.; Smith, J. M.; Yu, Y.; Ketterer, N. A.;
Flaschenriem, C. J.; Lachicotte, R. J.; Holland, P. L. J. Am. Chem. Soc.
2005, 127, 7857−7870. (l) Reade, S. P.; Mahon, M. F.; Whittlesey, M.
K. J. Am. Chem. Soc. 2009, 131, 1847−1861. (m) Panetier, J. A.;
Macgregor, S. A.; Whittlesey, M. K. Angew. Chem. 2011, 123, 2835−
2838; Angew. Chem., Int. Ed. 2011, 50, 2783−2786. (n) Kuehnel, M.
(4) (a) Klahn, M.; Rosenthal, M. Organometallics 2012, 31, 1235−
1244. (b) Johnson, S. A.; Hatnean, J. A.; Doster, M. E. In Progress in
Inorganic Chemistry; Karlin, K. D., Ed.; Wiley: Hoboken, NJ, 2012; Vol.
57, pp 255−352. (c) Paquin, J.-F. Synlett 2011, 2011, 289−293.
(d) Clot, E.; Eisenstein, O.; Jasim, N.; Macgregor, S. A.; McGrady, J.
E.; Perutz, R. N. Acc. Chem. Res. 2011, 44, 333−348. (e) Braun, T.;
Wehmeier, F. Eur. J. Inorg. Chem. 2011, 2011, 613−625. (f) Sun, A. D.;
Love, J. A. Dalton Trans. 2010, 39, 10362−10374. (g) Amii, H.;
Uneyama, K. Chem. Rev. 2009, 109, 2119−2183. (h) Perutz, R. N.
Science 2008, 321, 1168−1169. (i) Macgregor, S. A. Chem. Soc. Rev.
2007, 36. (j) Perutz, R. N.; Braun, T. Transition Metal-Mediated C-F
Bond Activation. In Comprehensive Organometallic Chemistry III;
Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: Oxford, U.K.,
2007; pp 725−758. (k) Torrens, H. Coord. Chem. Rev. 2005, 249,
1957−1985. (l) Richmond, T. G. Angew. Chem. 2000, 112, 3378−
3380; Angew. Chem., Int. Ed. 2000, 39, 3241−3244. (m) Richmond, T.
F.; Holstein, P.; Kliche, M.; Kruger, J.; Matthies, S.; Nitsch, D.; Schutt,
̈
J.; Sparenberg, M.; Lentz, D. Chem. Eur. J. 2012, 18, 10701−10714.
(o) Kuehnel, M. F.; Schloder, T.; Riedel, S.; Nieto-Ortega, B.;
̈
́
Ramírez, F. J.; Lopez Navarrete, J. T.; Casado, J.; Lentz, D. Angew.
Chem. 2012, 124, 2261−2263; Angew. Chem., Int. Ed. 2012, 51, 2218−
2220. (p) Lentz, D.; Braun, T.; Kuehnel, M. Angew. Chem. 2013, 125,
5328−5332; Angew. Chem., Int. Ed. 2013, 52, 3328−3348. (q) Mac-
gregor, S. A.; McKay, D.; Panetier, J. A.; Whittlesey, M. K. Dalton
Trans. 2013, 42, 7386−7395.
(7) (a) Jones, W. D Dalton Trans. 2003, 21, 3991−3995.
(b) Aizenberg, M.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 8674−
8675. (c) Braun, T.; Noveski, D.; Neumann, B.; Stammler, H. G.
Angew. Chem. 2002, 114, 2870−2873; Angew. Chem., Int. Ed. 2002, 41,
3806
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807

Organometallics
Article
2745−2747. (d) Braun, T.; Ahijado Salomon, M.; Altenhoner, K.;
(23) Braun, T.; Wehmeier, F.; Altenhoner, K. Angew. Chem. 2007,
̈
̈
119, 5415−5418; Angew. Chem., Int. Ed. 2007, 46, 5321−5324.
(24) Braun, T.; Perutz, R. N.; Sladek, M. I. Chem. Commun. 2001,
2254−2255.
(25) (a) Archibald, S. J.; Braun, T.; Gaunt, J. A.; Hobson, J. E.;
Perutz, R. N. Dalton Trans. 2000, 2013−2018. (b) Piglosiewicz, I. M.;
Kraft, S.; Beckhaus, R.; Haase, D.; Saak, W. Eur. J. Inorg. Chem. 2005,
Teltewskoi, M.; Hinze, S. Angew. Chem. 2009, 121, 1850−1854;
Angew. Chem., Int. Ed. 2009, 48, 1818−1822. (e) Meier, G.; Braun, T.
Angew. Chem. 2009, 121, 1546−1548; Angew. Chem., Int. Ed. 2009, 48,
1546−1548.
(8) (a) Noveski, D.; Braun, T.; Neumann, B.; Stammler, A.;
Stammler, H.-G. Dalton Trans. 2004, 4106−4119. (b) Braun, T.;
Noveski, D.; Ahijado, M.; Wehmeier, F. Dalton Trans. 2007, 3820−
3825.
(9) Teltewskoi, M.; Panetier, J. A.; Macgregor, S. A.; Braun, T. Angew.
Chem. 2010, 122, 4039−4043; Angew. Chem., Int. Ed. 2010, 49, 3947−
3951.
(10) (a) Reinhold, M.; McGrady, J. E.; Perutz, R. N. J. Am. Chem. Soc.
2004, 126, 5268−5276. (b) Schaub, T.; Fischer, P.; Steffen, A.; Braun,
T.; Radius, U.; Mix, A. J. Am. Chem. Soc. 2008, 130, 9304−9317.
(c) Johnson, S. A.; Mroz, N. M.; Valdizon, R.; Murray, S.
Organometallics 2011, 30, 441−457. (d) Jakt, M.; Johannissen, L.;
Rzepa, H. S.; Widdowson, D. A.; Wilhelm, R. J. Chem. Soc., Perkin
Trans. 2 2002, 576−581. (e) Bahmanyar, S.; Borer, B. C.; Kim, Y. M.;
Kurtz, D. M.; Yu, S. Org. Lett. 2005, 7, 10111014. (f) Nova, A.; Mas-
938−945. (c) Jager-Fiedler, U.; Arndt, P.; Baumann, W.; Spannenberg,
̈
A.; Burlakov, V. V.; Rosenthal, U. Eur. J. Inorg. Chem. 2005, 2842−
2849. (d) Brooke, G. M. J. Fluorine Chem. 1997, 86, 1−76. (e) Coe, P.
L.; Rees, A. J. J. Fluorine Chem. 2000, 101, 45−60. (e) Adamson, A. J.;
Jondi, W. J.; Tipping, A. E. J. Fluorine Chem. 1996, 76, 67−78.
(f) Benmansour, H.; Chambers, R. D.; Hoskin, P. R.; Sandford, G. J.
Fluorine Chem. 2001, 112, 133−137.
(26) Albright, T. A.; Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J.
Am. Chem. Soc. 1979, 101, 3801−3812.
(27) Other mechanistic possibilities do exist for the isomerization/
Si−F reductive elimination steps. For example, a Si−F reductive
elimination transition state from the five-coordinate intermediate
formed after PMe3 loss from 2-A2mer was competitive (E = −15.7 kcal/
mol) with 2-TS(A2mer″ -11) and, because of the PMe3 dissociation,
actually favored in terms of free energy (G = −15.1 kcal/mol; cf. −1.9
kcal/mol for 2-TS(A2mer″ -11)). However, the PMe3 dissociation
transition state remains the highest point in this part of the profile,
whether in terms of E value (−12.5 kcal/mol) or free energy (G =
−0.1 kcal/mol).
Balleste,
2009, 5980−5988. (g) Beltran
Safont, V. S. Organometallics 2011, 30, 290−297. (h) Nova, A.; Mas-
Balleste, R.; Lledos, A. Organometallics 2012, 31, 1245−1256.
́
R.; Ujaque, G.; Gonzal
́ ́
ez-Duarte, P.; Lledos, A. Dalton Trans.
́
, T. F.; Feliz, M.; Llusar, R.; Mata, J. A.;
́
́
(i) Fischer, P.; Goetz, K.; Eichhorn, A.; Radius, U. Organometallics
2012, 31, 1374−1383. (j) Lv, H.; Zhan, J.-H.; Cai, Y.-B.; Yu, Y.; Wang,
B.; Zhang, J.-L. J. Am. Chem. Soc. 2012, 134, 16216−16227.
(11) For an example of C−F activation at lanthanide complexes see:
Maron, L.; Werkema, E. L.; Perrin, L.; Eisenstein, O.; Andersen, R. A.
J. Am. Chem. Soc. 2005, 127, 279−292.
(28) Saillard, J.-F.; Hoffmann, R. J. Am. Chem. Soc. 1984, 106, 2006−
2026.
(29) (a) Edelbach, B. L.; Jones, W. D. J. Am. Chem. Soc. 1997, 119,
7734−7742. (b) Blum, O.; Frolow, F.; Milstein, D. J. Chem. Soc., Chem.
Commun. 1991, 258−259. (c) Whittlesey, M. K.; Perutz, R. N.; Moore,
M. H. Chem. Commun. 1996, 787−788.
(30) Zhao, P.; Hartwig, J. F. Organometallics 2008, 27, 4749−4757.
(31) Frisch, M. J., et al.. Gaussian 09, Revision A.02; Gaussian Inc.,
Wallingford, CT, 2009.
(12) (a) Erhardt, S.; Macgregor, S. A. J. Am. Chem. Soc. 2008, 130,
15490−15498. (b) Nova, A.; Erhardt, S.; Jasim, N. A.; Perutz, R. N.;
Macgregor, S. A.; McGrady, J. E.; Whitwood, A. C. J. Am. Chem. Soc.
2008, 130, 15499−15511. (c) Jiao, E. Q.; Xia, F. T.; Zhu, H. Comput.
Theor. Chem 2011, 965, 92−100.
(13) Nova, A.; Reinhold, M.; Perutz, R. N.; Macgregor, S. A.;
McGrady, J. E. Organometallics 2010, 29, 1824−1831.
(14) Goodman, J.; Macgregor, S. A. Coord. Chem. Rev. 2010, 254,
1295−1306.
(15) (a) Peterson, A. A.; McNeill, K. Organometallics 2006, 25,
4938−4940. (b) Peterson, A. A.; Thoreson, K. A.; McNeill, K.
Organometallics 2009, 28, 5982−5991. (c) Ishii, Y.; Chatani, N.;
Yorimitsu, S.; Murai, S. Chem. Lett. 1998, 157−158.
(16) Aizenberg, M.; Milstein, D. Science 1994, 265, 359−361.
(17) Lindup, R. J.; Marder, T. B.; Perutz, R. N.; Whitwood, A. C.
Chem. Commun. 2007, 3664−3667.
(32) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098−3100. (b) Perdew,
J. P. Phys. Rev. B 1986, 33, 8822−8824.
(33) Andrae, D.; Haußermann, U.; Dolg, M.; Stoll, H.; Preuß, H.
̈
Theor. Chim. Acta 1990, 77, 123−141.
(34) Hollwarth, A.; Bohme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi,
̈
̈
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
̈
Chem. Phys. Lett. 1993, 208, 237−240.
(35) (a) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28,
213−222. (b) Hehre, W. J. Chem. Phys. 1972, 56, 2257−2261.
(36) Haller, L. J. L.; Page, M. J.; Erhardt, S.; Macgregor, S. A.;
̈
Mahon, M. F.; Naser, M. A.; Vel
Soc. 2010, 132, 18408−18416.
́
ez, A.; Whittlesey, M. K. J. Am. Chem.
(18) (a) Penner, A.; Braun, T. Eur. J. Inorg. Chem. 2011, 2579−2587.
(b) Meier, G.; Braun, T. Angew. Chem. 2011, 123, 3338−3342; Angew.
Chem., Int. Ed. 2011, 50, 3280−3284. (c) Ahijado-Salomon, M.; Braun,
T.; Penner, A. Angew. Chem. 2008, 120, 8999−9003; Angew. Chem.,
Int. Ed. 2008, 47, 8867−8871. (d) Ahijado; Braun, T. Angew. Chem.
2008, 120, 2996−3000; Angew. Chem., Int. Ed. 2008, 47, 2954−295.
(e) Ahijado, M.; Braun, T.; Noveski, D.; Kocher, N.; Neumann, B.;
Stalke, D.; Stammler, H.-G. Angew. Chem. 2005, 117, 7107−7111;
Angew. Chem., Int. Ed. 2005, 44, 6947−6951. (f) Meier, G.; Braun, T.
Angew. Chem. 2012, 124, 127323−12737; Angew. Chem., Int. Ed. 2012,
51, 12564−12569.
(19) Fribolin, H. Ein- und zweidimensionale NMR-Spektroskopie;
Wiley-VCH: Weinheim, Germany, 1999.
(20) Yoshida, T.; Thorn, D. L.; Okano, T.; Otsuka, S.; Ibers, J. A. J.
Am. Chem. Soc. 1980, 102, 6451−6457.
(21) (a) Goodman, J.; Grushin, V. V.; Larichev, R.; Macgregor, S. A.;
Marshall, W. J; Roe, D. C. J. Am. Chem. Soc. 2009, 131, 4236−4238.
(b) Goodman, J.; Grushin, V. V.; Larichev, R. B.; Macgregor, S. A.;
Marshall, W. J.; Roe, D. C. J. Am. Chem. Soc. 2010, 132, 12013−12026.
(22) (a) Thorn, D. L.; Harlow, R. L. Inorg. Chem. 1990, 29, 2017−
2019. (b) Aizenberg, M.; Ott, J.; Elsevier, C. J.; Milstein, D. J.
Organomet. Chem. 1998, 551, 81−92.
3807
dx.doi.org/10.1021/om400150p | Organometallics 2013, 32, 3795−3807