C-H and C-F bond activation reactions of pentafluorostyrene at rhodium complexes

Article abstract of DOI:10.1039/c9dt03371h

The rhodium(i) complexes [Rh(Bpin)(PEt₃)₃] (1), [Rh(H)(PEt₃)₃] (5) and [Rh(Me)(PEt₃)₃] (14) were employed in reactions with pentafluorostyrene affording coordination of the olefin and C-F o

Full text of DOI:10.1039/c9dt03371h

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
C–H and C–F bond activation reactions of
pentafluorostyrene at rhodium complexes†‡
Cite this: Dalton Trans., 2019, 48,
16258
Conghui Xu, Maria Talavera,
Stefan Sander and Thomas Braun
*
The rhodium(I) complexes [Rh(Bpin)(PEt3)3] (1), [Rh(H)(PEt3)3] (5) and [Rh(Me)(PEt3)3] (14) were employed in
reactions with pentafluorostyrene affording coordination of the olefin and C–F or C–H bond activation.
Control of the reaction conditions allowed for selective activation reactions at different positions at the
fluorinated aromatic ring. The rhodacycle trans-[Rh(F)(CH2CH2(2-C6F4))(PEt3)2] (7) was identified as an
intermediate for an activation at the 2-position. Reactivity studies of the latter with CO led to the gene-
ration of trans-[Rh(F)(CH2CH2C6F4)(CO)(PEt3)2] (10). Stoichiometric and catalytic hydroboration reactions
were achieved using complexes 1 or 5 as catalysts.
Received 18th August 2019,
Accepted 9th October 2019
DOI: 10.1039/c9dt03371h
rsc.li/dalton
low
selectivity
when
employing
[Rh(acac)(κ2-o-
Introduction
Ph2PC6H4CHvN-2,6-iPr2C6H3)] as
a
catalyst. In 1993,
Introducing fluorine atoms to organic compounds not only Herrmann et al. reported a stoichiometric reaction using pen-
changes their chemical and biological properties but also pro- tafluorostyrene and osmium tetroxide to form a fluorinated
vides interesting building blocks for pharmaceuticals, agro- osmate ester quantitatively by a cycloaddition reaction.30 In
chemicals or in material science.1–3 In the last two decades it addition, Perutz and coworkers described the coordination of
was demonstrated that fluorinated olefins and aromatic com- pentafluorostyrene at nickel.31 However, to the best of our
pounds can undergo C–H or C–F bond activation reactions at knowledge, stoichiometric activation reactions of pentafluoro-
rhodium complexes, which opens up unique opportunities for styrene derivatives with rhodium complexes, which might be
functionalization.4–16
Perfluorinated styrene is an important starting material for are still unknown.
a lot of catalytic reactions, such as C–C coupling,17 epoxi-
Herein we describe the stoichiometric reactivities of
dation,18 hydrogenation,19,20 hydroformylation21
and [Rh(Bpin)(PEt3)3] (1), [Rh(H)(PEt3)3] (5) and [Rh(Me)(PEt3)3] (14)
crucial for an understanding of the conversions named above,
hydroboration.22–29 In the past, the hydroboration of penta- towards pentafluorostyrene. Reaction pathways are versatile
fluorostyrene mediated by rhodium complexes was achieved providing coordination, C–F bond activation or C–H bond acti-
with high selectivity.23–27 In these reactions, the borane source vation products. In addition, the hydroboration of pentafluor-
can be critical and Ramachandran et al.,23,27 Brown et al.25 ostyrene with HBpin and [Rh(Bpin)(PEt3)3] (1) or [Rh(H)(PEt3)3]
and Segarra et al.24 showed that HBcat (catechol borane) can (5) as a catalyst was studied to obtain fluorinated building
afford Markovnikov hydroboration products using [Rh(COD)- blocks by regioselective Markovnikov addition.
(dppb)]BF4, [Rh(Quinap)]OTf or [Rh(COD)(Binap)2]BF4 as cata-
lysts, respectively (dppb = 1,4-bis(diphenylphosphino)butane;
Quinap
Binap
=
1-(2-diphenylphosphino-1-naphthyl)isoquinoline;
Results and discussion
Coordination of fluorinated styrene derivatives
=
2,2′-bis(diphenylphosphino)-1,1′-binaphthyl).
However, Westcott and co-workers26 disclosed that HBpin
(pinacol borane) yields Markovnikov addition products in a
Treatment of the rhodium boryl complex [Rh(Bpin)(PEt3)3]
(1)32,33 with an excess amount of pentafluorostyrene (ratio
1 : 1.2) in d14-methylcyclohexane at room temperature for
5 min afforded the two complexes fac-[Rh(H)(η2-CH2CHC6F5)-
(PEt3)3] (2) and fac-[Rh(H)(η2-CH(Bpin)CHC6F5)(PEt3)3] (3) as
well as the borylated olefin E-BpinCHvCHC6F5 (4) in a ratio of
1.8 : 1 : 0.6 (based on the 19F NMR spectrum) (Scheme 1). In
contrast, when treating complex 1 with pentafluorostyrene in a
ratio of 2.5 : 1, complex 3 was generated together with the
rhodium hydrido complex [Rh(H)(PEt3)3] (5)34 (Scheme 1).
Humboldt-Universität zu Berlin, Department of Chemistry, Brook-Taylor-Straße 2,
12489 Berlin, Germany. E-mail: thomas.braun@cms.hu-berlin.de;
Tel: +49 30 2093 3913
†Dedicated to Prof. Robin Perutz on the occasion of his 70th birthday.
‡Electronic supplementary information (ESI) available: Synthesis and analytics
for all compounds, xyz coordinates for the DFT calculation optimized structure
and X-ray data. CCDC 1956127. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c9dt03371h
16258 | Dalton Trans., 2019, 48, 16258–16267
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
Scheme 1 Stoichiometric reactions of complex 1 with pentafluorostyrene.
Note that the complexes 2 and 3 (for their characterization see 1H NMR spectrum, for the rhodium-bound hydrido ligand, a
below) are in solution only stable at low temperature for long doublet of triplet of doublets with a coupling of 161.8 Hz to
periods of time and converted further by C–F bond activation the trans phosphine ligand, 19.8 Hz to the cis phosphine
(see below). Therefore, after their preparation at room tempera- ligands and 9.2 Hz to the rhodium atom appeared at
ture within 5 minutes, the characterization was performed at −14.64 ppm. The 19F NMR spectrum at room temperature also
213 K as recently reported for other similar rhodium com- reflects the dynamic process with three broad signals in a ratio
plexes such as fac-[Rh(H)(η2-CH2CHCF3)(PEt3)3]6 and fac-[Rh(H)- of 2 : 2 : 1. In the 19F NMR spectrum at 213 K, five resonances
(η2-CH2CFCF3)(PEt3)3].35
appeared in a ratio of 1 : 1 : 1 : 1 : 1. Signals at −146.0 and
1
In the H NMR spectrum of compound 4 (for the indepen- −146.7 ppm are presumably due to the two fluorine atoms in
dent synthesis see ESI‡) two doublet signals appeared at 7.48 the ortho position, while signals at −166.3 and −167.0 ppm
and 6.70 ppm which are assigned to the olefinic moiety. The belong to the two meta fluorine atoms and the signal at
coupling constant of 18.8 Hz is indicative of a trans arrange- −170.9 ppm can be assigned to the para fluorine atom.40–43
ment.36 In the 19F NMR spectrum three signals appeared as
The 31P{1H} NMR spectrum of 3 at 213 K showed three
multiplets at −144.0, −155.5 and −163.5 ppm, respectively, in signals comparable to the ones for complex 2 at 18.2, 15.3 and
a ratio of 2 : 1 : 2. A peak in the GC-MS of m/z 320 supports the 3.3 ppm. However, only two signals appeared at 3.97 and
proposed structure.
3.10 ppm in the 1H NMR spectrum with a proton–proton coup-
Three broad resonances for 2 were observed in the 31P{1H} ling constant of 12.0 Hz in the H{31P} NMR spectrum for the
NMR spectrum indicating a dynamic process, which is pre- protons of the coordinated olefin moiety. The absence of one
sumably associated with a rotation about the olefinic double proton suggests its substitution by the Bpin group. The
bond. The 31P{1H} NMR spectrum at 213 K revealed three hydrido ligand appeared as a doublet of triplet of doublets at
signals at 20.3, 13.7 and 5.8 ppm in a ratio of 1 : 1 : 1, which is −14.87 ppm. The resonance has a coupling constant of 163.0
consistent with the fac-configuration.6 The doublet of doublet Hz to the trans phosphorus atom, 18.2 Hz to the two cis phos-
1
of doublets (1J(P,Rh) = 139.8, J(P,P) = 42.6, J(P,P) = 24.2 Hz) at phorus atoms and 5.5 Hz to the rhodium atom. In the 19F
2
2
20.3 ppm and a doublet of doublet of doublets (1J(P,Rh) = 134.0, NMR spectrum, five signals, similar to the ones of complex 2,
2
2J(P,P) = 42.9, J(P,P) = 28.8 Hz) at 13.7 ppm were assigned to the appeared at −144.2, −145.0, −166.5, −167.1 and −170.4 ppm.
phosphine ligands in the trans position to the CHC6F5 and DFT calculations of 3 were performed (BP86/def2-SVP). The
CH2 moieties. The doublet of multiplets at 5.8 ppm with a structural optimization of the possible rotational isomers of
coupling of 95.8 Hz to the rhodium atom belongs to the phos- complex 3 showed that the isomer with the lower energy
phine ligand in trans position to the hydrido ligand. The large (favored by 21.2 kJ mol−1) has the Bpin group and hydrido
trans influence of the hydrido ligand is in accordance with the ligand orientated on the same side of a plane defined by the
smaller coupling constant.6,37,38 The values of the rhodium– rhodium center and the olefin, while the fluorinated moiety
phosphorus coupling constants suggest the presence of a Rh(I) remains positioned on the other side.
1
complex.5,6,32,39 In the H NMR spectrum of 2 at 213 K three
A conceivable mechanistic pathway for the observed reactiv-
broad signals appeared at 3.32, 3.05 and 1.83 ppm for the ole- ity is depicted in Scheme 2. After coordination of pentafluoros-
finic protons, which is consistent with data for the previously tyrene at complex 1 the insertion of the olefin into the Rh–B
reported complex fac-[Rh(H)(η2-CH2CHCF3)(PEt3)3].6 In the bond occurs. A β-hydride elimination would then lead to
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 16258–16267 | 16259

View Article Online
Paper
Dalton Transactions
Scheme 2 Possible mechanism for the formation of complexes 2 and 3.
complex 3 and subsequently 4 and 5 are formed initially and
results in 3 after olefin coordination. In the presence of an
excess of pentafluorostyrene, its coordination to 5 yields
complex 2. Note that a reaction of complex 1 with stoichio-
metric amounts of styrene leading to a dehydrogenative boryla-
tion at the double bond and complex 5 was reported,44 but the
coordination of the olefinic product was not observed.
C–F bond activation reactions
To confirm the structures of complexes 2 and 3 as well as the
proposed mechanism, independent reactions between penta-
fluorostyrene or the boryl derivative 4 and the rhodium
hydrido complex [Rh(H)(PEt3)3] (5) were performed.
Scheme 3 Independent stoichiometric reaction of complex
compound 4.
5 and
Indeed, treatment of 5 with the boryl derivative 4 (ratio
1.7 : 1) in d8-toluene at 213 K gave after 5 min fac-[Rh(H)(η2-CH-
(Bpin)CHC6F5)(PEt3)3] (3). Interestingly, after warming up the
reaction solution or performing the reaction directly at room
temperature for 30 min (ratio 1 : 1.4), the C–F bond activation at
the ortho position to the olefin moiety was observed yielding
[Rh(2-C6F4CHCH2)(PEt3)3] (6) as the main product, together
with another unidentified complex in a ratio of 13.5 : 1 (based
on the 31P{1H} NMR spectrum) (Scheme 3). The likely formation
of HF might induce deborylation reactions at the olefinic
moiety to give fluoroboronates. It is notable that the C–F bond
activation12,45–54 of the boryl derivative at 5 lead to the cleavage
of the C–F bond at the ortho position to the vinyl group.
Comparable ortho-directing effects have been observed before at
the {Rh(PEt3)3} fragment in C–F bond activation reactions of
fluorinated pyridines and the C–H bond activation of aromatic
SCF3 compounds.5,9,32,39,55
Fig. 1 The 31P{1H} NMR spectrum of complex 6; simulated (below)
1
observed (above) using the following coupling constants (Hz): J(Pa,Rh)
=
2
4
5
5
123.3, J(Pa,Pb) = 38.0, J(Pa,F2) = 14.6, J(Pa,F5) = 9.8, J(Pa,F3) = 6.6;
1J(Pb,Rh) = 143.3.
The signals in the 31P{1H} NMR spectrum for complex 6
were simulated and are depicted in Fig. 1. The coupling con- 11.8 Hz), a doublet (3J(H,H) = 18.1 Hz) and a doublet (3J(H,H)
=
stants shown in the 31P{1H} NMR spectrum between the 11.5 Hz) at 8.16, 6.38 and 5.40 ppm, respectively, due to the
rhodium and phosphorus atoms give evidence of a Rh(I) olefin moiety of the complex. Four signals were observed in
complex.5,6,32,39 The 1H NMR spectrum exhibited three reso- the 19F NMR spectrum, which was also simulated and is
3
nances as a doublet of doublets (3J(H,H) = 18.4, J(H,H)
=
depicted in Fig. 2. The assignment of the fluorinated moiety is
16260 | Dalton Trans., 2019, 48, 16258–16267
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
multiplets, respectively. For the phosphine ligands in a mutual
trans position, the coupling constant of 103.8 Hz to the
rhodium atom indicates the presence of a Rh(III) complex,32,61
while the coupling constants of 29.7, 17.9 Hz are due to coup-
lings to the phosphine and fluorido ligands, respectively. The
coupling constant of around 90 Hz for the resonance at
−2.8 ppm is due to the coupling to rhodium. Based on a
1H–1H COSY NMR spectrum, two signals at 3.04 and 1.42 ppm
Fig. 2 The 19F NMR spectrum of complex 6; simulated (below)
5
observed (above) using the following coupling constants (Hz): J(F2,F5)
=
3
4
3
3
43.8, J(F2,F3) = 14.6, J(F2,Pa) = 14.6, J(F2,Rh) = 14.6, J(F3,F4) = 20.3,
5J(F3,Pa) = 6.6, 4J(F3,Rh) = 4.0, 3J(F5,F4) = 20.3, 5J(F5,Pa) = 9.8, 4J(F5,Rh) = 5.2.
1
in the H NMR spectrum were assigned to the CH2 groups in
complex 8. Comparable to the data for complex 7, the 13C{1H}
NMR spectrum depicted two signals at 37.8 ppm and
based on the comparison with the literature.39,56–58 The chemi- 23.7 ppm for the β and α carbon atoms. The 19F NMR spec-
cal shifts resemble those found for trans-[Ni(F)(2,3,4,5-C6F4H)- trum displayed five signals, four in the fluoroaromatic region
(PEt3)2].43 In addition, liquid injection field desorption ioniza- and one at −385.1 ppm characteristic for the rhodium(III)
tion mass spectrometry (LIFDI MS) revealed a peak at m/z 632 bound fluorido ligand.10,62,63
consistent with the structure of complex 6.
Single crystals suitable for X-ray crystallography of complex
Similar to the formation of complex 3, complex 2 can be 8 were obtained from a concentrated solution in hexane by
also independently synthesized by the reaction of [Rh(H)- slow evaporation while letting the solution warm up from
(PEt3)3] (5) with pentafluorostyrene (ratio 1.4 : 1). Although, 193 K to 278 K (Fig. 3). The structure shows a distorted octa-
complex 2 is more stable, after 1 d at room temperature, it was hedral geometry of the metal-bound ligands at the rhodium
partially transformed (64% conversion) by cyclometallation center and the fluorido ligand occupies the trans position to
and C–F bond activation into the rhodaindane complex trans- the CH2 group. Note that the location of the fluorido ligand in
[Rh(F)(CH2CH2(2-C6F4))(PEt3)2] (7), free PEt3, traces of complex 7 and 8 is different, because in 7 we suggest the above men-
mer-[Rh(F)(CH2CH2(2-C6F4))(PEt3)3] (8) and minor amounts of tioned trans position of the fluorido ligand and the aromatic
the C–H bond activation complex [Rh(E-CHCHC6F5)(PEt3)3] ring. The Rh1–F1 distance is 2.1360(9) Å, which is slightly
(15) as well as the hydrogenation product ethylpentafluoroben- longer than in other Rh(III) fluorido complexes.62,64 Geometry
zene 9 (see below; the low temperature 19F NMR spectrum optimization performed by DFT calculations (BP86/def2-SVP)
shows that the ratio of 8 : 9 : 15 is 1 : 0.18 : 0.07)59 (Scheme 4). supports the obtained structure for 8 with an energy 12 kJ
Note that the formation of minor amounts of the C–H bond mol−1 lower than the isomer with the fluorido ligand trans to
activation product 15 promotes the hydrogenation of penta- the aromatic ring.
fluorostyrene to afford compound 9. Complex 7 and free phos-
Complex 7 can convert slowly into [Rh(2-C6F4CHCH2)-
phine are in equilibrium with 8, and by cooling down a solu- (PEt3)3] (6) and presumably HF. The presence of KPF6 can
tion at 233 K complex 7 can be converted into complex 8 com- accelerate the transformation to full conversion within 14 d.
pletely. In fact, after applying vacuum to remove the solvent The obtaining of complex 6 where the C–F bond activation
and some PEt3, complex 7 cannot be transformed completely occurs at the ortho position, supports the structural assign-
into complex 8 at low temperature.
ment of the rhodacycles.
In the 31P{1H} NMR spectrum of 7, a broad doublet of
Mechanistically, for the generation of 7 from complex 2, an
doublets appeared at 18.4 ppm with a coupling constant of initial insertion of the metal-bound olefin into the rhodium–
114.2 Hz to rhodium and 16.6 Hz to the metal-bound fluorido hydrogen bond is suggested (Scheme 4). Then, an intra-
ligand. The 1H NMR spectrum showed two broad signals at molecular oxidative addition of the C–F bond occurs. Note that
3.20 and 2.45 ppm that belong to the protons of the non-fluorinated metallaindanes have been previously
C6F4CH2CH2 moiety. Two signals appeared at 37.3 ppm and described at Pd and Ni by
a C–H orthometallation
23.2 ppm as a singlet and doublet with a coupling constant of reaction.65,66 However, the C–F bond oxidative additions at
32.6 Hz to the rhodium nucleus in the 13C{1H} NMR spectrum. rhodium are rare and were reported at cyclopentadienyl or tris-
They were assigned to the β and α carbon atoms of complex 7, pyrazolylborate complexes.10,67 Complex 6 can subsequently be
respectively. The APT NMR spectrum also confirmed the exist- formed by β-hydride elimination and a subsequent elimination
ence of the two CH2 moieties. In addition, five signals of HF. In the presence of KPF6 the latter reaction is promoted,
appeared at −130.6, −141.9, −162.5, −167.3 and −290.6 ppm because an initial production of KF can endorse a reductive
in the 19F NMR spectrum where the latter resonance corres- elimination and it can also trap HF by generation of a
ponds to the rhodium bound fluorido ligand.60 Geometry bifluoride.
optimization performed by DFT calculations (BP86/def2-SVP)
To confirm the structural assignment of 7 further, its reac-
revealed a trans arrangement of the fluorido ligand and the tivity towards carbon monoxide was tested, which could
aromatic ring.
occupy a vacant coordination site. Indeed, the 18-electron
In case of complex 8, the 31P{1H} NMR spectrum of 8 derivative trans-[Rh(F)(CH2CH2C6F4)(CO)(PEt3)2] (10) was
showed two signals at 7.9 and −2.8 ppm in a 2 : 1 ratio, which obtained under CO atmosphere. The isotopologue trans-[Rh(F)
appeared as a doublet of doublet of doublets and a doublet of (CH2CH2C6F4)(13CO)(PEt3)2] (10′) was generated after treatment
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 16258–16267 | 16261

View Article Online
Paper
Dalton Transactions
Scheme 4 Stoichiometric reactions of complex 5 with pentafluorostyrene.
of 7 with 13CO. Note that the formation of complex [Rh(H)(CO)- For complex 10′ an additional coupling to the labelled carbon
(PEt3)3] (11)68,69 (or the isotopologue [Rh(H)(13CO)(PEt3)3] (11′), atom of 10.9 Hz was detected. The coupling constant is in
see ESI‡ for characterization) was also observed. Complex 11 accordance with a cis-configuration of phosphine and CO
1
stems from the reaction of the remaining complex 2 with CO.
ligands.36,44 The H NMR spectrum shows a broad triplet (J =
A doublet of doublets at 16.9 ppm with a coupling constant 7.5 Hz) at 3.15 ppm that corresponds to the β carbon at
of 98.5 Hz to the rhodium atom and 17.3 Hz to the fluorido 33.4 ppm in the 13C domain of a 1H–13C HMQC NMR spec-
ligand can be observed in the 31P{1H} NMR spectrum of 10. trum. A multiplet at 2.56 ppm in the 1H domain correlates
16262 | Dalton Trans., 2019, 48, 16258–16267
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
The generation of a Rh–C bond furnishes initially HF, which
in turn can give with complex 5 the rhodium fluorido complex
13 and H2 or a dihydrido fluorido complex.60 Subsequently,
compound 9 can be generated by a hydrogenation reaction of
pentafluorostyrene in the presence of H2.
In the 31P{1H} NMR spectrum of complex 12 a doublet of
multiplets was observed at 18.4 ppm with rhodium–phos-
phorus coupling constant of 138.1 Hz for the phosphine
ligand in the trans position to the fluorinated moiety. A
doublet of doublets at 14.0 ppm showed a rhodium–phos-
phorus coupling constant of 141.1 Hz and phosphorus–phos-
phorus coupling constant of 40.1 Hz for the two phosphine
1
ligands in a mutually trans arrangement. In the H NMR spec-
Fig. 3 ORTEP diagram of complex 8. Ellipsoids are drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected dis-
tances [Å] and bond angles [°]: Rh1–C1 2.0775(15), Rh1–C8 2.0828(15),
Rh1–F1 2.1360(9), Rh1–P3 2.3470(4), Rh1–P1 2.3502(4), Rh1–P2 2.3836
(4), C1–C2 1.539(2), C1–Rh1–F1 173.53(5), C8–Rh1–F1 96.96(5), C1–
Rh1–P3 93.56(4), C8–Rh1–P3 87.01(4), F1–Rh1–P3 92.84(3), P3–Rh1–
P1 168.314(15), C1–Rh1–P2 90.47(4), C8–Rh1–P2 172.89(4), F1–Rh1–P2
90.08(3), P3–Rh1–P2 93.662(15), P1–Rh1–P2 92.732(16).
trum, three resonances appeared as a doublet of doublets
(3J(H,H) = 18.1, J(H,H) = 12.1 Hz), a doublet (3J(H,H) = 18.1 Hz)
3
and a doublet (3J(H,H) = 12.1 Hz) at 6.98, 6.20 and 5.33 ppm,
respectively, which are assigned to the olefinic moiety. The
coupling of 18.1 Hz confirms the existence of protons in the
trans position while 12.1 Hz is a typical coupling for protons in
the cis arrangement.72–74 Finally, in the 19F NMR spectrum,
two signals appeared as multiplets at −110.7 and −147.3 ppm
in a ratio of 1 : 1 due to the equivalent fluorine atoms, which
with a doublet of quartets (J = 19.9, 6.6 Hz) at 24.0 ppm in the confirms that the C–F bond activation takes place at the 4-posi-
13C{1H} NMR spectrum being assigned as the α carbon atom. tion of the perfluorinated ring.8,9,39,43,58
In the H{19F} NMR spectrum the proton resonances are sim-
plified to a triplet of pseudo triplets at 3.15 ppm and a triplet
1
C–H bond activation reaction
of triplets of doublets at 2.56 ppm. Similar data are obtained [Rh(Me)(PEt3)3] (14)75 is known to be a suitable precursor for
for complex 10′ where couplings to the labelled carbon atom C–H bond activation reactions.5,9,35,39 Therefore, it was also
are observed with values of 1.9 and 2.1 Hz for the β and α interesting to test its reactivity towards pentafluorostyrene in
carbon, respectively. These couplings might suggest a trans order to achieve a C–H bond activation instead of the C–F
arrangement to the carbonyl ligand which is consistent with bond activation described above. Indeed, treatment with
the fluorido ligand in the trans position to the aromatic ring pentafluorostyrene (ratio 1 : 1.1) in THF at room temperature
as described for complex 7; however a cis arrangement cannot afforded the C–H bond activation complex [Rh(E-CHCHC6F5)-
be excluded. The signal for the carbonyl ligand of complex 10′ (PEt3)3] (15) after 30 min as a brown oil (Scheme 5).
was revealed in the APT NMR spectrum at 189.5 ppm as a
After isolation, the 31P{1H} NMR spectrum of 15 depicted a
doublet of doublet of triplets due to couplings to rhodium, the doublet of triplets at 19.4 ppm (1J(Rh,P) = 115.7, 2J(P,P) = 36.1 Hz)
metal-bound fluorido ligand and the two phosphorus atoms and a doublet of doublets at 16.6 ppm (1J(Rh,P) = 156.7, J(P,P)
=
2
(41.3, 14.8 and 10.9 Hz, respectively). In the 19F NMR spectrum 36.1 Hz) in a integration ratio of 1 : 2. In the 1H NMR spec-
a signal for the rhodium bound fluorido ligand appeared as a trum, a doublet of multiplets and a doublet of doublet of
broad signal at −425.3 ppm for complex 10.63 In the IR spec- quadruplets, both as a broad doublets in the phosphorus
trum of complex 10 an absorption band at 2056 cm−1 can be decoupled NMR spectrum, appeared at 9.18 and 6.42 ppm,
assigned to the carbonyl ligand which is in agreement with respectively. The coupling constant between both resonances
data for other Rh(III) carbonyl complexes.70,71 The band of 18.6 Hz indicates an E-configuration at the double bond.
appears at 2002 cm−1 for the isotopologue 10′, where the isoto- Based on the data for [Rh(E-CHCHCF3)(PEt3)3],35 the signal at
pic shift is in accordance with literature data.36
lower field can be assigned to the proton at the α-position to
In contrast to all these observations, treatment of 5 with
pentafluorostyrene (ratio 1 : 1.3) at 333 K for 1 d led to a C–F
bond activation at the 4-position to yield [Rh(4-C6F4CHCH2)-
(PEt3)3] (12) and the fluorido complex [Rh(F)(PEt3)3] (13)60 as
well as the hydrogenation product ethylpentafluorobenzene
959 in a ratio of 1.5 : 1.6 : 1 (determined by 19F NMR spec-
troscopy) (Scheme 4). An independent experiment shows that
after an initial formation of 2 at room temperature (see above),
the generation of 12 is also observed after heating.
The observed C–F bond activation resembles a reaction
pathway, which was previously observed for other substrates.5,39,58 Scheme 5 Reaction of complex 14 with pentafluorostyrene.
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 16258–16267 | 16263

View Article Online
Paper
Dalton Transactions
the rhodium nucleus (J = 1.9 Hz), while the β-position proton species, the rhodium(III) complex fac-[Rh(H)2(Bpin)(PEt3)3]
showed a coupling constant of 6.7 Hz to the trans phosphorus (19)79 was identified as the only product after the catalytic reac-
ligand. Furthermore, LIFDI MS data revealed a peak with m/z tion was stopped (Scheme 6). Comparably, treatment of [Rh-
650 for complex 15.
(Bpin)(PEt3)3] (1), pentafluorostyrene and HBpin in a ratio of
1 : 1 : 1.25 in d14-methylcyclohexane at room temperature for
5 min gave the same organic compounds in a ratio of
Stoichiometric hydroboration reactions
Hydroboration reactions are widely employed to access bory- 49 : 14 : 22 : 15 as well as the rhodium(III) complex 19. It is
lated building blocks.28,76–84 Thus, [Rh(H)(PEt3)3] (5), penta- known that treating complex 5 with HBpin gives complex fac-
fluorostyrene and HBpin were reacted in a ratio of 1 : 1 : 2.5 in [Rh(H)2(Bpin)(PEt3)3] (19),79 whereas as described above a reac-
d8-toluene at room temperature for 5 min to afford the tion of 5 with pentafluorostyrene yields 2. However, in the
Markovnikov hydroboration compound [C6F5CH(Bpin)CH3] hydroboration reaction, introducing the reactants in different
(16),26 small amounts of the anti-Markovnikov product orders did not lead to different results (Scheme 6).
[C6F5CH2CH2(Bpin)] (17),26 the diborylated derivative
Two possible pathways can be proposed for the formation
[C6F5CH2CH(Bpin)2] (18)26 as well as the hydrogenation com- of the main hydroboration product, which are depicted in
pound 9 in a ratio of 92 : 2 : 4 : 2. Regarding the rhodium Scheme 7. They are consistent with plausible mechanisms pro-
Scheme 6 Stoichiometric hydroboration reactions using complexes 1 or 5.
Scheme 7 Possible pathways for the formation of the main hydroboration product.
16264 | Dalton Trans., 2019, 48, 16258–16267
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
Scheme 8 Catalytic reactions of pentafluorostyrene and HBpin.
posed for Ti or other Rh complexes.85–87 Treatment of complex
5 and pentafluorostyrene would yield complex 2, which after
Conclusion
insertion of the olefin into the Rh–H bond and a subsequent In summary, we reported stoichiometric reactions of the
oxidative addition of HBpin gives complex A. After reductive rhodium boryl complex [Rh(Bpin)(PEt3)3] (1) and the rhodium
elimination, the hydroboration product is formed regenerating hydrido complex [Rh(H)(PEt3)3] (5) towards pentafluorostyrene
complex 5. Alternatively, complex 5 and HBpin afford the oxi- or its borylated derivative, affording coordination and sub-
dative addition complex 19. Insertion of pentafluorostyrene sequent C–F bond activation. Aromatic C–F bond activation
might occur via an initial reductive elimination of H2 or a dis- occurred at the 4-position or 2-position depending on the reac-
sociation of a phosphine. After oxidative addition of H2 or tion temperature. The rhodacycle trans-[Rh(F)(CH2CH2(2-C6F4))-
rebinding of the phosphine, complex B might be generated. (PEt3)2] (7) was detected after treatment of 5 with pentafluoros-
Again, the product 16 is formed after a reductive elimination tyrene at room temperature. It converted very slowly into
reaction.
[Rh(2-C6F4CHCH2)(PEt3)3] (6). A C–H bond activation was
achieved when employing the rhodium methyl complex
[Rh(Me)(PEt3)3] (14) as the starting material. In stoichiometric
and catalytic hydroboration reactions, pentafluorostyrene and
HBpin were converted into the Markovnikov addition hydro-
boration product 16.
Catalytic hydroboration reactions
Considering previous work, in which complexes 1 and 5 were
used as catalysts for various reactions such as borylation, C–H
and C–F bond activation reactions,32,36,55,58,79 attention was
turned to the catalytic hydroboration reactions (Scheme 8).
The reaction of pentafluorostyrene, HBpin (ratio 1 : 1.5) and
the rhodium hydrido complex [Rh(H)(PEt3)3] (5) (3 mol% cata-
lyst based on pentafluorostyrene) as the catalyst in C6D6
was studied at room temperature. After 5 min, NMR spectro-
scopic data revealed full conversion of pentafluorostyrene into
the same organic products as found in the stoichiometric
hydroboration reaction in a ratio of 91 : 6 : 1 : 2 (according to
the 19F NMR spectrum) (Table 1 entry 1). The selectivity
towards compound 16 decreased to 81% when employing
[Rh(Bpin)(PEt3)3] (1) (3.7 mol%) as the catalyst (Table 1
entry 2) and Me3SiSiMe3 as solvent. Under neat condition, a
reaction with complex 5 (1.5 mol%) in pentafluorostyrene also
gave full conversion, but less selectively for compound 16
(75%) (Table 1 entry 3).
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We would like to acknowledge Dr Mike Ahrens for fruitful dis-
cussions and the China Scholarship Council for financial
support.
Notes and references
1 P. Jeschke, ChemBioChem, 2004, 5, 570–589.
2 K. Müller, C. Faeh and F. Diederich, Science, 2007, 317,
1881–1886.
3 Y. Zhou, J. Wang, Z. Gu, S. Wang, W. Zhu, J. L. Aceña,
V. A. Soloshonok, K. Izawa and H. Liu, Chem. Rev., 2016,
116, 422–518.
4 T. Braun and F. Wehmeier, Eur. J. Inorg. Chem., 2011, 2011,
613–625.
5 T. Ahrens, M. Ahrens, T. Braun, B. Braun and R. Herrmann,
Dalton Trans., 2016, 45, 4716–4728.
Table 1 Catalysts comparison of hydroboration reaction of
pentafluorostyrene
Conversiona
(%)
Ratiob
16 : 17 : 18 : 9
Catalyst
Solvent
mol%
5
1
5
C6D6
Me3SiSiMe3
Neat
3
3.7
1.5
>99
>99
>99
91 : 6 : 1 : 2
81 : 9 : 3 : 3c
75 : 13 : 4 : 8
a Based on pentafluorostyrene consumption. b Based on NMR measure-
ments. c 4% on an unknown product are present.
6 T. Ahrens, M. Teltewskoi, M. Ahrens, T. Braun and
R. Laubenstein, Dalton Trans., 2016, 45, 17495–17507.
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 16258–16267 | 16265

View Article Online
Paper
Dalton Transactions
7 A. L. Raza, M. F. Kuehnel, M. Talavera, M. Teltewskoi, 34 T. Braun, D. Noveski, M. Ahijado and F. Wehmeier, Dalton
M. Ahrens, P. Kläring, T. Braun and D. Lentz, J. Fluorine
Chem., 2018, 214, 80–85.
8 R. J. Lindup, T. B. Marder, R. N. Perutz and
A. C. Whitwood, Chem. Commun., 2007, 3664–3666.
9 A. L. Raza and T. Braun, Chem. Sci., 2015, 6, 4255–4260.
10 B. Procacci, Y. Jiao, M. E. Evans, W. D. Jones, R. N. Perutz
Trans., 2007, 3820–3825.
35 M. Talavera, C. N. von Hahmann, R. Müller, M. Ahrens,
M. Kaupp and T. Braun, Angew. Chem., Int. Ed., 2019, 58,
10688–10692.
36 C. N. von Hahmann, M. Talavera, C. Xu and T. Braun,
Chem. – Eur. J., 2018, 24, 11131–11138.
and A. C. Whitwood, J. Am. Chem. Soc., 2015, 137, 1258– 37 T. G. Appleton, H. C. Clark and L. E. Manzer, Coord. Chem.
1272.
Rev., 1973, 10, 335–422.
11 M. Aizenberg and D. Milstein, Science, 1994, 265, 359–361.
12 T. Ahrens, J. Kohlmann, M. Ahrens and T. Braun, Chem.
Rev., 2015, 115, 931–972.
13 T. Braun, F. Wehmeier and K. Altenhöner, Angew. Chem.,
Int. Ed., 2007, 46, 5321–5324.
38 B. J. Coe and S. J. Glenwright, Coord. Chem. Rev., 2000, 203,
5–80.
39 A. L. Raza, J. A. Panetier, M. Teltewskoi, S. A. Macgregor
and T. Braun, Organometallics, 2013, 32, 3795–3807.
40 J. A. Hatnean, M. Shoshani and S. A. Johnson, Inorg. Chim.
Acta, 2014, 422, 86–94.
14 L. Zámostná, S. Sander, T. Braun, R. Laubenstein,
B. Braun, R. Herrmann and P. Kläring, Dalton Trans., 2015, 41 M. W. Drover, L. L. Schafer and J. A. Love, Dalton Trans.,
44, 9450–9469. 2015, 44, 19487–19493.
15 W.-H. Guo, Q.-Q. Min, J.-W. Gu and X. Zhang, Angew. 42 T. Piou, F. Romanov-Michailidis, M. Romanova-
Chem., Int. Ed., 2015, 54, 9075–9078.
Michaelides, K. E. Jackson, N. Semakul, T. D. Taggart,
B. S. Newell, C. D. Rithner, R. S. Paton and T. Rovis, J. Am.
Chem. Soc., 2017, 139, 1296–1310.
16 J. F. Hartwig, Chem. Soc. Rev., 2011, 40, 1992–2002.
17 H. Li, K.-H. He, J. Liu, B.-Q. Wang, K.-Q. Zhao, P. Hu and
Z.-J. Shi, Chem. Commun., 2012, 48, 7028–7030.
18 J. P. Collman, Z. Wang, A. Straumanis, M. Quelquejeu and
E. Rose, J. Am. Chem. Soc., 1999, 121, 460–461.
43 S. A. Johnson, E. T. Taylor and S. J. Cruise, Organometallics,
2009, 28, 3842–3855.
44 S. I. Kalläne, T. Braun, B. Braun and S. Mebs, Dalton Trans.,
2014, 43, 6786–6801.
19 A. T. Normand, C. G. Daniliuc, B. Wibbeling, G. Kehr, P. Le
Gendre and G. Erker, J. Am. Chem. Soc., 2015, 137, 10796– 45 L. Keyes and J. A. Love, C-H and C-X Bond Functionalization:
10808.
Transition Metal Mediation, The Royal Society of Chemistry,
20 X. Xu, G. Kehr, C. G. Daniliuc and G. Erker, J. Am. Chem.
Soc., 2015, 137, 4550–4557.
21 I. Ojima, K. Kato, M. Okabe and T. Fuchikami, J. Am. Chem.
Soc., 1987, 109, 7714–7720.
2013.
46 E. Clot, O. Eisenstein, N. Jasim, S. A. Macgregor,
J. E. McGrady and R. N. Perutz, Acc. Chem. Res., 2011, 44,
333–348.
22 H. C. Brown, G.-M. Chen, M. P. Jennings and 47 M. K. Whittlesey and E. Peris, ACS Catal., 2014, 4, 3152–
P. V. Ramachandran, Angew. Chem., Int. Ed., 1999, 38,
2052–2054.
23 P. V. Ramachandran, M. P. Jennings and H. C. Brown, Org.
Lett., 1999, 1, 1399–1402.
24 A. M. Segarra, C. Claver and E. Fernandez, Chem. Commun.,
2004, 464–465.
25 A. Black, J. M. Brown and C. Pichon, Chem. Commun., 2005,
5284–5286.
26 D. I. McIsaac, S. J. Geier, C. M. Vogels, A. Decken and
S. A. Westcott, Inorg. Chim. Acta, 2006, 359, 2771–2779.
27 P. V. Ramachandran and M. P. Jennings, J. Fluorine Chem.,
2007, 128, 827–831.
3159.
48 T. Fujita, K. Fuchibe and J. Ichikawa, Angew. Chem., Int.
Ed., 2019, 58, 390–402.
49 M. F. Kuehnel, D. Lentz and T. Braun, Angew. Chem., Int.
Ed., 2013, 52, 3328–3348.
50 J.-D. Hamel and J.-F. Paquin, Chem. Commun., 2018, 54,
10224–10239.
51 J. L. Kiplinger, T. G. Richmond and C. E. Osterberg, Chem.
Rev., 1994, 94, 373–431.
52 H. Amii and K. Uneyama, Chem. Rev., 2009, 109, 2119–
2183.
53 H. Torrens, Coord. Chem. Rev., 2005, 249, 1957–1985.
28 S. Kisan, V. Krishnakumar and C. Gunanathan, ACS Catal., 54 N. A. LaBerge and J. A. Love, in Organometallic Fluorine
2017, 7, 5950–5954.
29 R. Xu, G.-p. Lu and C. Cai, New J. Chem., 2018, 42, 16456–
Chemistry, ed. T. Braun and R. Hughes, Springer, Cham,
2015, vol. 52.
16459.
55 S. I. Kalläne and T. Braun, Angew. Chem., Int. Ed., 2014, 53,
9311–9315.
56 T. Beweries, L. Brammer, N. A. Jasim, J. E. McGrady,
R. N. Perutz and A. C. Whitwood, J. Am. Chem. Soc., 2011,
133, 14338–14348.
30 W. A. Herrmann and S. J. Eder, Chem. Ber., 1993, 126, 31–
37.
31 L. Cronin, C. L. Higgitt, R. Karch and R. N. Perutz,
Organometallics, 1997, 16, 4920–4928.
32 M. Teltewskoi, J. A. Panetier, S. A. Macgregor and T. Braun, 57 Z. Chen, C.-Y. He, Z. Yin, L. Chen, Y. He and X. Zhang,
Angew. Chem., Int. Ed., 2010, 49, 3947–3951. Angew. Chem., Int. Ed., 2013, 52, 5813–5817.
33 M. Teltewskoi, S. I. Kalläne, T. Braun and R. Herrmann, 58 S. I. Kalläne, M. Teltewskoi, T. Braun and B. Braun,
Eur. J. Inorg. Chem., 2013, 2013, 5762–5768.
Organometallics, 2015, 34, 1156–1169.
16266 | Dalton Trans., 2019, 48, 16258–16267
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
59 Y. Sun, H. Sun, J. Jia, A. Du and X. Li, Organometallics, 74 A. Singh, C. J. Fennell and J. D. Weaver, Chem. Sci., 2016, 7,
2014, 33, 1079–1081. 6796–6802.
60 T. Braun, D. Noveski, B. Neumann and H.-G. Stammler, 75 P. Zhao and J. F. Hartwig, Organometallics, 2008, 27, 4749–
Angew. Chem., Int. Ed., 2002, 41, 2745–2748. 4757.
61 G. Meier and T. Braun, Angew. Chem., Int. Ed., 2011, 50, 76 H. C. Brown and B. C. S. Rao, J. Am. Chem. Soc., 1959, 81,
3280–3284. 6428–6434.
62 H. Baumgarth, G. Meier, T. Braun and B. Braun-Cula, 77 J. A. Soderquist, J. C. Colberg and L. Del Valle, J. Am. Chem.
Eur. J. Inorg. Chem., 2016, 2016, 4565–4572. Soc., 1989, 111, 4873–4878.
63 N. Pfister, T. Braun, P. Wittwer and M. Ahrens, Z. Anorg. 78 J. Schneider, C. P. Sindlinger, S. M. Freitag, H. Schubert
Allg. Chem., 2018, 644, 1064–1070.
and L. Wesemann, Angew. Chem., Int. Ed., 2017, 56, 333–
64 M. Wozniak, T. Braun, M. Ahrens, B. Braun-Cula,
337.
P. Wittwer, R. Herrmann and R. Laubenstein, 79 T. Braun, M. Ahijado-Salomon, K. Altenhöner,
Organometallics, 2018, 37, 821–828.
65 J. Cámpora, J. A. López, P. Palma, D. del Rio, E. Carmona,
M. Teltewskoi and S. Hinze, Angew. Chem., Int. Ed., 2009,
48, 1818–1822.
P. Valerga, C. Graiff and A. Tiripicchio, Inorg. Chem., 2001, 80 D. Noh, H. Chea, J. Ju and J. Yun, Angew. Chem., Int. Ed.,
40, 4116–4126. 2009, 48, 6062–6064.
66 J. Cámpora, M. a. del Mar Conejo, K. Mereiter, P. Palma, 81 E. E. Touney, R. Van Hoveln, C. T. Buttke, M. D. Freidberg,
C. Pérez, M. L. Reyes and C. Ruiz, J. Organomet. Chem.,
2003, 683, 220–239.
I. A. Guzei and J. M. Schomaker, Organometallics, 2016, 35,
3436–3439.
67 W. D. Jones, M. G. Partridge and R. N. Perutz, J. Chem. Soc., 82 M. Rauch, S. Ruccolo and G. Parkin, J. Am. Chem. Soc.,
Chem. Commun., 1991, 264–266. 2017, 139, 13264–13267.
68 J. K. MacDougall, M. C. Simpson, M. J. Green and D. J. Cole- 83 J. D. Hewes, C. W. Kreimendahl, T. B. Marder and
Hamilton, J. Chem. Soc., Dalton Trans., 1996, 1161–1172.
69 G. Gregorio, G. Pregaglia and R. Ugo, Inorg. Chim. Acta,
1969, 3, 89–93.
70 D. Noveski, T. Braun, B. Neumann, A. Stammler and
H.-G. Stammler, Dalton Trans., 2004, 4106–4119.
71 J. Rankin, A. C. Benyei, D. J. Cole-Hamilton and
A. D. Poole, Chem. Commun., 1997, 1835–1836.
72 T. Braun, J. Izundu, A. Steffen, B. Neumann and
H.-G. Stammler, Dalton Trans., 2006, 5118–5123.
73 X. Zhang, S. Fan, C.-Y. He, X. Wan, Q.-Q. Min, J. Yang and
Z.-X. Jiang, J. Am. Chem. Soc., 2010, 132, 4506–4507.
M. F. Hawthorne, J. Am. Chem. Soc., 1984, 106, 5757–
5759.
84 S. A. Westcott, H. P. Blom, T. B. Marder and R. T. Baker,
J. Am. Chem. Soc., 1992, 114, 8863–8869.
85 X. He and J. F. Hartwig, J. Am. Chem. Soc., 1996, 118, 1696–
1702.
86 S. A. Westcott, T. B. Marder and R. T. Baker,
Organometallics, 1993, 12, 975–979.
87 K. Burgess, W. A. Van der Donk, S. A. Westcott,
T. B. Marder, R. T. Baker and J. C. Calabrese, J. Am. Chem.
Soc., 1992, 114, 9350–9359.
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 16258–16267 | 16267