Direct synthesis of dicarbonyl PCP-iron hydride complexes and catalytic dehydrogenative borylation of styrene

Article abstract of DOI:10.1039/c6dt01149g

A new and efficient method based on the simple metalating reagent Fe(CO)₅ has been developed for the straightforward synthesis of well defined cyclometalled PCP iron carbonyl pincer complexes. The reaction proceeds cleanly under mild conditions

Full text of DOI:10.1039/c6dt01149g

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Direct synthesis of dicarbonyl PCP-iron hydride
complexes and catalytic dehydrogenative
borylation of styrene†
Cite this: DOI: 10.1039/c6dt01149g
a
a
b
b
Shi Jiang,‡ Samuel Quintero-Duque,‡ Thierry Roisnel, Vincent Dorcet,
c,d
c,d
a
Mary Grellier,* Sylviane Sabo-Etienne,* Christophe Darcel* and
Jean-Baptiste Sortais*
a
5
A new and efficient method based on the simple metalating reagent Fe(CO) has been developed for the
Received 23rd March 2016,
Accepted 14th June 2016
straightforward synthesis of well defined cyclometalled PCP iron carbonyl pincer complexes. The reaction
proceeds cleanly under mild conditions at 30 °C and UV irradiation. Four hydride pincer complexes are
synthesized and fully characterized as well as an intermediate dinuclear species. The new iron complexes
are active and selective catalytic precursors for the dehydrogenative borylation of styrene with HBpin.
DOI: 10.1039/c6dt01149g
www.rsc.org/dalton
5
e,f,i,j,7
on POCOP pincer type ligands.
In particular, Guan et al.
Introduction
have recently found that the POCOP-iron hydride complexes,
5
i,j
Cyclometalated complexes with iron are relatively rare com- originally applied in hydrosilylation reactions
could be
pared to cyclometaled complexes based on other late tran- efficient catalysts for the dehydrogenation of ammonia–
1
8
sition metals. For several decades, from the early work of borane.
2
3
Hübel and Braye in 1959 to the work of Klein in 2005, cyclo-
metalation with iron has remained a curiosity.
development of a methodology based on Fe(PMe ) for the iron hydride complex in good yield. Consecutive PMe3
orthometalation of imines, iron(0) and related iron(II) exchanges by carbonyl ligands only occurred after extended
precursors bearing phosphine ligands, namely (Fe(PMe reaction times, leading ultimately to the stable dicarbonyl
Fe(PMe Ph) and Fe(PMe ) (Me) ) were found to promote the iron hydride complex 1c (Scheme 1). Manning has demon-
The bis-phosphinite POCOP, such as 1 (Scheme 1) has
After the been metalated with Fe(PMe ) leading to the corresponding
3 4
1
d,4
5
i
3
4
3
3 4
) ,
5
i,j
2
4
3 4
2
5
orthometalation of a series of ligands. Alternatively, carbonyl strated that the closely related iron tricarbonyl bis-phosphite
iron(0) precursors have been used to promote the C–H acti- complex Fe(P(OPh)
vation on a few Schiff bases derived from heterocycles.
3
)
2
(CO)
3
, led to a cyclometalated complex
6
Cyclometalated iron complexes have been scarcely applied
in catalysis. The majority of the complexes have been tested in
hydrosilylation reactions of carbonyl derivatives and are based
a
Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes
1, Team Organometallics: Materials and Catalysis, Centre for Catalysis and Green
Chemistry, Campus de Beaulieu, 263 av. du Général Leclerc, 35042 Rennes Cedex,
France. E-mail: christophe.darcel@univ-rennes1.fr,
jean-baptiste.sortais@univ-rennes1.fr
b
Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes
1, Centre de Diffractométrie X, Campus de Beaulieu, 263 av. du Général Leclerc,
3
5042 Rennes Cedex, France
c
CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP
44099, F-31077 Toulouse Cedex 4, France. E-mail: mary.grellier@lcc-toulouse.fr,
sylviane.sabo@lcc-toulouse.fr
d
Université de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
†
Electronic supplementary information (ESI) available: NMR spectra of the com-
pounds and additional data. CCDC 1469695–1469701. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c6dt01149g
Scheme 1 Previous synthesis of [(POCOP)Fe(H)(CO)
2
] as described by
‡
These authors have contributed equally to this work.
Guan.
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3
1
1
under UV irradiation, albeit the orthometalated species structure of complex 1d, whose P{ H} NMR spectrum dis-
HFe(CO) {P(OPh) }{(PhO) POC H } was only found stable at played only one signal at 217.1 ppm in C D , was confirmed by
2
3
2
6
4
6 6
9
low temperature.
X-ray diffraction (Fig. 1). The related complex 2d was also pre-
1
0
Due to the importance of pincer complexes, and of iron pared from the 1,3-bis(diphenylphosphinito)benzene 2, follow-
phosphine complexes in catalysis, coupled with our experi- ing the same procedure (see ESI†).
ence in iron carbonyl complexes in catalysis, we envisioned
1
1
1
2
Unfortunately, the two complexes 1c and 1d could not be
that the cyclometalated complexes could be directly obtained separated by crystallisation, and thus 1c could not be isolated
in one step starting from the commercially available Fe(CO)5 in pure analytical form by this route. We thus changed the
precursor and the pincer compound. Here, we report the ratio 1 : Fe(CO)
5
from 1 : 1.1 to 1 : 0.9 to prevent the formation
straightforward synthesis of a series of iron dicarbonyl pincer of complex 1d. The reaction was also monitored over time by
3
1
1
complexes, and their use as catalyst precursors for the catalytic
dehydrogenative borylation of styrene.
P{ H} NMR spectroscopy (Fig. 2). After 1 h of reaction at
room temperature, the cyclometalated complex 1c was already
formed (ca. 50%) in addition to unreacted starting ligand
(
ca. 20%), along with 1d (ca. 5%) and other unidentified
1
4
iron–phosphine complexes. Remarkably, after 10 h, only the
signals of the expected iron complex 1c and of the free ligand
1
Results and discussion
Synthesis of the PCP-iron complexes
3
1
1
appeared in the P{ H} NMR spectrum with a ratio 90 : 10.
Compound 1, namely 1,3-bis(diisopropylphosphinito)benzene,
The remaining ligand could be removed easily during the
recrystallization step, and complex 1c was isolated in good
yield, 85%.
was selected as a model and reacted with Fe(CO)
5
as a metalat-
ing agent. In a first attempt, a solution of 1.1 equiv. of Fe(CO)
5
and 1 equiv. of 1 in toluene was irradiated under UV (350 nm)
1
at room temperature for 20 h. The H NMR spectrum of the
6 6
crude mixture in C D confirmed the presence of the charac-
teristic hydride signal for complex 1c which appeared as a
5
i
31
1
triplet at −9.42 ppm (JHP = 52.3 Hz). The P{ H} NMR spec-
1
trum was consistent with the H NMR spectrum, as the main
5
i
signal at 230.6 ppm matched the previously reported data.
The presence of a by-product at 217.1 ppm was also detected
(
vide infra).
This first promising experiment prompted us to optimize
the reaction conditions. The course of the reaction, performed
3
1
1
in a Young NMR tube, was monitored by P{ H} NMR spec-
troscopy in C D (Fig. S1†). After only 2 h of irradiation, the
6
6
signal of the free ligand 1 (δ = 147.11 ppm) had disappeared,
and complex 1c was already formed, as well as the by-product
1
d (δ = 217.18 ppm), with a relative ratio 1c : 1d of 75 : 25. After
Fig. 1 ORTEP view of the molecular structure of complex 1d with
1
0 h, the relative ratio 1c : 1d had evolved in favour of the thermal ellipsoids drawn at 50% probability. Hydrogens are omitted for
desired product 1c (85 : 15). The nature of the by-product 1d
clarity.
was first elucidated. As a slight excess of Fe(CO) (1.1 equiv.)
5
was used and as the formation of the by-product started from
the early stage of the reaction, we assumed that the by-product
resulted from the coordination of two Fe(CO)4 fragments to
each of the phosphorus atoms of 1. In order to validate this
hypothesis, compound 1d was independently synthesized fol-
1
3
lowing the methodology described by Coville, by reacting 1
with an excess of Fe(CO) (4 equiv.) in the presence of 2 mol%
of [Cp*Fe(CO) in toluene at 70 °C (Scheme 2). The molecular
5
2 2
]
31
1
Fig. 2 Monitoring over time by P{ H} NMR spectroscopy of the crude
5
reaction in the presence of a slight excess of ligand (ratio 1 : Fe(CO) =
Scheme 2 Synthesis of [(CO)
4
Fe(POCOP)Fe(CO)
4
]] (1d).
1 : 0.9, toluene, rt, UV (350 nm)).
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2
Scheme 3 General synthesis of [(PXCYP)Fe(H)(CO) )] complexes. Iso-
lated yields indicated in parenthesis.
The same methodology was applied for the synthesis of
1
5
various PCP complexes (Scheme 3). Starting from the bis-
phosphinite pincer 2 bearing two phenyl groups on the phos-
phorus atoms, the cyclometalated complex 2c was obtained in
satisfactory yield (65%). In the case of the bulkier phosphinite
3
bearing tBu substituents, the expected reaction did not
proceed and after irradiation, no hydride signal was detected
1
31
1
by H NMR whereas the P{ H} NMR spectrum displayed a
main signal assigned to the free ligand. Nevertheless, after
work-up, complex 3d analogue to 1d, with two iron centres,
could be obtained in very low yield (5%) as a microcrystalline Fig. 3 Top: ORTEP view of the molecular structure of complex 2c with
thermal ellipsoids drawn at 50% probability. Hydrogens atoms, except
the hydride, were omitted for clarity. Bottom: Optimized DFT structure
of 2c.
solid. The molecular structure was confirmed by X-ray diffrac-
tion (see ESI†). The procedure was successfully extended to the
1
6
dissymmetric diphosphino compound 4, based on 3-amino-
1
7
phenol, and to 5, based on 1,3 diaminobenzene, the corres-
ponding pincer complexes, 4c and 5c, being obtained in 30
and 60% yields, respectively.
1
(
1890 cm− ) was reported by Guan for the related bis(dimethyl-
8
phenyl)phosphine complex.
The molecular structure of complexes 1c, 2c, 4c, and 5c was
confirmed by X-ray diffraction studies (Fig. 3, 4, S30, and S31
in ESI† and Table 2). Suitable single crystals were obtained for
Characterization of the complexes
1
The four pincer complexes were fully characterized by H,
1
3
1
31
1
1c and 2c at −20 °C from a saturated solution in toluene–
C{ H}, P{ H} NMR studies, IR, elemental analysis, X-ray
diffraction and DFT calculations.
methanol, for 4c from hexane at −30 °C and for 5c from a satu-
rated solution of toluene–hexane at −30 °C. The iron centre
adopts a distorted octahedral geometry, with the PCP and one
carbonyl ligand in the equatorial plane. The hydride was loca-
lized by Fourier difference map analysis with a Fe–H distance
of 1.45 (3), 1.49 (2), and 1.40 (4) Å for 1c, 2c, and 4c, respec-
tively. In the case of 5c, some disorder prevented an accurate
location. DFT calculations on the four complexes provided dis-
tances dcalc(Fe–H) of 1.508, 1.508, 1.506 and 1.505 Å for 1c, 2c,
1
The presence of the hydride is ascertained by H NMR, with
a hydride signal around −9 ppm (−9.42 ppm, t, J = 52.3 Hz;
−
−
8.22 ppm, t, J = 52.6 Hz; −9.47 ppm, dd, J = 54.2, 50.8 Hz and
9.50 ppm, t, J = 52.8 Hz, for 1c, 2c, 4c and 5c, respectively).
The stretching IR frequencies of the carbonyl ligands and
the Fe–H bonds are reported in Table 1. The IR spectra,
recorded in the solid state using an ATR equipment, display
−
1
three bands: two between 2011–1929 cm and one between
1
4c and 5c, respectively (Fig. 3 and 4, bottom) showing that the
1
890–1867 cm− , assigned to the carbonyl and the Fe–H
nature of the pincer ligand has almost no effect on the Fe–H
bond, the hydride keeping the same ligand (a carbonyl) in
trans position. The Fe–CO distance for the carbonyl trans to
the hydride is longer (1.780 to 1.800 Å) than those of the carbo-
nyl cis to the hydride (1.768–1.780 Å) which reflects the greater
trans influence of the hydride compared to the aryl ring.
Similar features were already observed in the case of cyclo-
stretching frequencies, respectively, by comparison with DFT
calculations conducted on each complex. A similar Fe–H band
Table 1 Summary of relevant IR spectroscopic data (cm−
1 a
)
calcd b
CO
calcd b
ν
Fe–H
Complex
ν
CO
ν
ν
Fe–H
5
i
metalated complexes bearing PMe ligands.
3
1c
2c
4c
5c
1980, 1930
2011, 1954
1975, 1929
1961, 1917
2088, 2055
2113, 2070
2091, 2052
2088, 2051
1867
1890
1867
1876
1971
1958
1969
1985
Catalytic study
POCOP-iron complexes bearing phosphine ligands had
been already tested for catalytic hydrosilylation and
a
b
Solid state ATR measurements. Non-corrected DFT values.
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Scheme 4 Dehydrogenative borylation of styrene with HBpin catalysed
by iron.
5
mol% of catalyst, without any solvent. To our delight, full
1
1
conversion of HBpin was detected by B NMR spectroscopy,
and H NMR as well as GC analysis of the crude mixture
1
showed the formation of styrylboronate as the main compound
(
88% NMR yield) with only 6% of 7 and 8 (Table 3, entry 1). 6
was isolated in 80% yield.
The parameters of the reaction were further optimized
(
Table 3). Interestingly, with 2 equiv. of styrene, the conver-
sion and the selectivity were not altered (entry 2). It was
possible to decrease the quantity of styrene to 1.5 equiv.,
however the reaction time needed to be increased to 80 h in
order to reach a satisfying conversion (entry 3). Lowering the
quantity of styrene to 1 equiv. led to a lower conversion of
HBpin (56%, entry 4). It is noteworthy that dehydrogenative
borylation of styrene could be performed in toluene as
Fig. 4 Top: ORTEP view of the molecular structure of complex 4c with
thermal ellipsoids drawn at 50% probability. Hydrogen atoms, except the solvent keeping the same activity and selectivity as under
hydride and NH, were omitted for clarity. Two molecules of 4c were
present in the unit cell, only one is depicted. Bottom: Optimized DFT
structure of 4c.
neat conditions and that no borylation of toluene was
detected (entries 5 and 6). Furthermore, the irradiation with
UV light (350 nm) was crucial for the reaction to occur as no
conversion was detected after 60 h under thermal conditions
(
50 °C, entry 7).
Complexes 2c, 4c and 5c were also tested as catalyst precur-
5
i–k,8
dehydrogenation of ammonia–borane.
Based on our inter-
est in iron catalysis involving hydroboranes, namely hydro- sors (entries 8–11). In the case of 2c, containing less basic
1
2d
18
boration of alkenes,
C–H borylation of arenes, and CO
2
phosphine substituents, even if full conversion of HBpin was
1
9
functionalization, we decided to test the newly prepared obtained after 48 h, the selectivity of the reaction was modest
complexes in the reaction of styrene with pinacolborane as 6, 7, and 8 were detected in a ratio 47 : 17 : 36 (entry 8). The
(
HBpin). Indeed, selective dehydrogenative borylation of dissymmetrical pincer 4c displayed a very low activity as only
2
0
21
alkenes is unknown to date with iron catalysts. Styryl- 26% conversion was achieved after 48 h (entry 9). Notably,
boronate 6 was detected as a side-product during the course of complex 5c with the amino linkages exhibited an activity and a
1
2d
styrene hydroboration yielding 7 as reported by us
and selectivity comparable with 1c (entries 10 and 11).
2
2
Huang, together with ethylbenzene 8 resulting from the
The catalytic activity of the dinuclear complex 1d was finally
hydrogenation of styrene (Scheme 4).
examined under the same conditions (entry 12). Compared to
In a preliminary test, we selected complex 1c [(iPr
2
POCO- the pincer complex 1c, the dinuclear complex 1d is more active
PiPr )Fe(H)(CO) ] as catalyst precursor, and used the con- as full conversion of HBpin was observed after 24 h of reaction
2
2
ditions previously optimized for the C–H borylation of but the selectivity toward the dehydrogenative borylated
1
8
arenes, i.e. 3 equiv. of styrene and 1 equiv. of HBpin, stirring product 6 dropped to 68% whereas 7 and 8 were both formed
under UV irradiation for 2 days at 30 °C, in the presence of in 16% yield.
Table 2 Selected X-ray and DFT bond distances (Å) for the pincer complexes
Complex
d
Fe–H
dFe–H calcd
d
Fe–C
dFe–CO trans H
dFe–CO cis H
d
Fe–P1
d
Fe–P2
1c
2c
4c
5c
1.45 (3)
1.49 (2)
1.40 (4)
n.d.
1.508
1.508
1.506
1.505
1.998 (2)
1.981 (2)
2.017 (3)
2.019 (3)
1.800 (2)
1.797 (3)
1.781 (3)
1.780 (3)
1.777 (2)
1.774 (2)
1.780 (3)
1.768 (4)
2.1903 (6)
2.1710 (5)
2.1836 (1)
2.198 (1)
2.1861 (6)
2.174 (5)
2.209 (1)
2.193 (4)
a
a
In the case of 5c, the Fe–H distance was not determined by X-ray diffraction as a result of some disorder.
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Table 3 Optimization of the parameters for the iron catalysed boryla- spectra were calibrated against an external
3 4
H PO and
1
1
tion of styrene
B NMR spectra against an external BF ·OEt standard. Chemical
3
2
shift (δ) and coupling constants (J) are given in ppm and
in Hz, respectively. The peak patterns are indicated as follows:
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet, and br.
for broad.
IR spectra were measured by Shimadzu IR-Affinity 1 with
ATR equipment. HR-MS spectra and microanalysis were
carried out by the corresponding facilities at the CRMPO
(Centre Régional de Mesures Physiques de l’Ouest), University
of Rennes 1.
a
Selectivity (%)
a
Styrene
(equiv.)
Time
(h)
Conv.
(%)
Entry
Catalyst
6
7
8
1
2
3
4
1c
1c
1c
1c
1c
1c
1c
2c
4c
5c
5c
1d
3
2
1.5
1
2
1
3
2
2
48
48
80
72
72
72
60
48
48
72
48
24
98 (80)
98
90 (78)
56
88
86
88
90
89
88
—
47
12
85
88
68
6
7
6
5
5
6
6
7
6
5
6
6
b
5
>98
50
0
98
b
6
c
7
17
76
7
5
16
36
12
8
UV irradiation were performed in a Rayonet RPR-100
apparatus at 350 nm.
26
2
2
2
98 (78)
98
7
b
98
16 Synthetic procedures
a
Synthesis of complex 1c. Fe(CO) (330 μL, 2.51 mmol) was
5
typical reactions conditions: catalyst (5 mol%), neat conditions, UV
(
350 nm), rt, the conversion of styrene and the selectivity were deter- added to a solution of m-C H (OP(iPr) ) (900 mg, 2.63 mmol)
6 4 2 2
1 b
mined by GC and H NMR. Isolated yield in parenthesis. Toluene
c
in toluene (25 mL) in a Schlenk tube. The mixture was
irradiated under UV (350 nm) for 14 h at room temperature.
The solution was concentrated under vacuum, then methanol
(0.5 mL). 50 °C, no irradiation.
(
15 mL) was added. After crystallization at −20 °C (one night),
the mother liquor was discarded and the white solid was
recrystallized from toluene and methanol (1 : 4) at −30 °C
precursor, we affording the pure complex 1c as a white solid (968 mg, 85%).
Conclusions
In conclusion, starting from the simple Fe(CO)
5
report herein the straightforward synthesis of four iron pincer Single crystals suitable for X-ray diffraction studies were grown
complexes bearing a hydride and two carbonyl ligands. The from toluene and methanol (1 : 4) at −20 °C.
1
cyclometalated complexes serve as catalysts for the selective
6 6
H NMR (400 MHz, C D ): δ 6.83 (t, J = 7.8 Hz, 1H, Ar), 6.72
dehydrogenative borylation of styrene using pinacolborane. (d, J = 7.8 Hz, 2H, Ar), 2.41–2.32 (m, 2H, CH), 2.22–2.13
The reaction proceeds under mild conditions with only 2 (m, 2H, CH), 1.30–1.17 (m, 12H, CH ), 1.06–0.95 (m, 12H,
3
equiv. of styrene at 30 °C under UV irradiation. Of notable CH ), −9.42 (t, J = 52.3 Hz, 1H, Fe–H).
3
1
3
1
interest, the dehydrogenative borylation occurred in absence
of any hydrogen acceptor and with very little styrene 212.8 (t, J = 13.7 Hz, CO), 164.3 (t, J = 8.8 Hz, Ar), 136.2 (t, J =
6 6
C{ H} NMR (126 MHz, C D ) δ 214.6 (t, J = 11.1 Hz, CO),
hydrogenation.
17.7 Hz, Ar), 126.1 (s, Ar), 105.1 (t, J = 5.5 Hz, Ar), 34.5 (t, J =
1.3 Hz, CH), 33.0 (t, J = 14.7 Hz, CH), 17.8 (s, CH ), 17.6
s, CH ), 17.4 (s, CH ), 17.1 (t, J = 3.3 Hz, CH ).
1
(
3
3
1
3
3
3
1
P{ H} NMR (162 MHz, C
6
D
6
) δ 230.58.
IR (ATR, ν, cm− ): 1980, 1930, 1867.
Anal. Calc. (%). for (C H FeO P ): C, 52.88; H, 7.10.
Experimental
Materials and methods
1
2
0
32
4 2
All reactions were carried out with oven-dried glassware using Found: C, 52.94; H, 7.05.
standard Schlenk techniques under an inert atmosphere of dry Synthesis of complex 2c. Complex 2c was prepared following
argon or in an argon-filled glove-box. Toluene, THF, diethyl the same method as for complex 1c but starting with
ether (Et O), and CH Cl were dried over Braun MB-SPS-800 m-C (OPPh (197 mg, 0.41 mmol) and Fe(CO) (50 μL,
2
2
2
6
H
4
2
)
2
5
solvent purification system and degassed by thaw-freeze cycles. 0.37 mmol). The complex was obtained after recrystallization
Technical grade pentane, diethyl ether were used for chro- as a white solid (142 mg, yield: 65%).
matography column. Analytical TLC was performed on Merck
Single crystals suitable for X-ray diffraction studies were
6
0
F
254 silica gel plates (0.25 mm thickness). Column chromato- grown from toluene and methanol (1 : 4) at −20° C.
1
graphy was performed on Across Organics Ultrapure silica gel
H NMR (400 MHz, C D ) δ 7.93–7.80 (m, 8H, Ar), 7.03–6.92
6 6
(
mesh size 40–60 μm, 60 Å). All reagents were obtained from (m, 16H, Ar), −8.22 (t, J = 52.6 Hz, 1H, Fe–H).
1
3
1
commercial sources and liquid reagents were dried on mole-
6 6
C{ H} NMR (100 MHz, C D ) δ 214.4 (t, J = 12.3 Hz, CO),
cular sieves and degassed prior to use.
208.9 (t, J = 14.4 Hz, CO), 163.4 (t, J = 10.6 Hz, Ar), 140.7 (t, J =
3
or 27.0 Hz, Ar), 140.4 (t, J = 24.2 Hz, Ar), 137.7 (t, J = 19.4 Hz, Ar)
1
13
31
11
H, C, P and B NMR spectra were recorded in CDCl
C
6
D
6
at 298 K, on Bruker AVANCE 500, AVANCE 400 and 131.4 (t, J = 6.9 Hz, Ar), 131.1 (s, Ar), 130.7 (s, Ar), 130.1 (t, J =
1
13
AVANCE 300 spectrometers. H and C NMR spectra were cali- 6.6 Hz, Ar), 128.8 (t, J = 5.1 Hz, Ar), 128.6 (t, J = 5.3, Ar),
brated using the residual solvent signal as internal standard 126.4 (s, Ar), 106.5 (t, J = 6.3, Ar).
1
13
31
1
(
H: CDCl
3
7.26 ppm, C
6
D
6
7.16 ppm, C: CDCl
3
, central peak
P{ H} NMR (162 MHz, C
6
D
6
) δ 192.2.
31
−1
at 77.00 ppm, C D , central peak at 128.06 ppm). P NMR
IR (ATR, ν, cm ): 2011, 1954, 1890.
6
6
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Anal. Calc. (%). for (C32
H
24FeO
4
P
2
)(C
7
H
8
)0.5: C, 67.00;
Anal. Calc. (%). for C20
H
34FeN
2
O
2
P
2
: C, 53.11; H, 7.58;
H, 4.43. Found: C, 67.00; H, 4.52. Note: toluene was detected N, 6.19. Found: C, 52.90; H, 7.45; N, 5.95.
1
−1
by H NMR spectroscopy with a ratio 0.5, see ESI.†
Synthesis of complex 4c. Fe(CO) (250 μL, 1.22 mmol) was
IR (ATR, ν, cm ): 1961, 1917, 1876.
Synthesis of complex 1d. Fe(CO)
5
5
(1.6 mL, 12.6 mmol,
added to a solution of m–C H (NHP(iPr) )(OP(iPr) ) (437 mg, 4 equiv.) was added to a solution of 1 (1.02 g, 3.0 mmol) in
6
4
2
2
1
2 2
.28 mmol) in toluene (13 mL) in a Schlenk tube. The mixture toluene (50 mL), then [Cp*Fe(CO) ] (30 mg, 2 mol%) was
was exposed to UV irradiation (350 nm) for 14 h at room temp- added. The reaction mixture was heated at 70 °C for 14 h. After
erature. The obtained product was dried under vacuum and cooling down to room temperature, the product was dried
extracted with distilled hexane (3 × 5 mL). The solution was fil- under vacuum and washed with methanol. The obtained
tered by cannula and concentrated under vacuum. The white brown solid was purified by column chromatography (eluent:
solid was then recrystallized from hexane at −30 °C (165 mg, petroleum ether/dichloromethane 9 : 1), yielding 1d (300 mg,
3
0% yield).
15% yield). Single crystals suitable for X-ray diffraction studies
Cl
H NMR (400 MHz, C D ) δ 7.08 (s, 1H, Ar), 6.97 (t, J =
Single crystals suitable for X-ray diffraction studies were were obtained by slow evaporation of a solution in CH
2
2
.
1
grown from hexane.
6
6
1
H NMR (400 MHz, C
6
D
6
) δ 6.90 (t, J = 7.7 Hz, 1H, Ar), 6.69 7.7 Hz, 1H, Ar), 6.81 (d, J = 7.7 Hz, 2H, Ar), 2.43–2.18 (m, 4H,
), 1.03 (dd, J = 16.6,
(d, J = 7.9 Hz, 1H, Ar), 6.20 (d, J = 7.6 Hz, 1H, Ar), 3.49 (s, 1H, CH), 1.14 (dd, J = 16.2, 6.9 Hz, 12H, CH
3
NH), 2.53–2.32 (m, 1H, CH), 2.29–2.12 (m, 1H, CH), 2.09–1.93 7.0 Hz, 12H, CH ).
3
1
3
1
(m, 1H, CH), 1.78–1.69 (m, 1H, CH), 1.34–1.22 (m, 6H, CH
3
),
6 6
C{ H} NMR (101 MHz, C D ) δ 213.6 (d, J = 17.8 Hz, CO),
1
.17–0.97 (m, 15H, CH
3
), 0.90–0.84 (m, 3H, CH
3
), −9.47 (dd, 154.0 (d, J = 7.7 Hz, Ar), 130.2 (s, Ar), 119.1 (s, Ar), 117.6 (s, Ar),
35.2 (d, J = 27.8 Hz, CH), 17.7 (s, CH ), 17.4 (s, CH ).
J = 54.2, 50.8 Hz, 1H, Fe–H).
3
3
1
3
1
31
1
C{ H} NMR (126 MHz, C
6
D
6
) δ 215.6 (t, J = 12.3 Hz, CO),
P{ H} NMR (162 MHz, C
6
D
6
) δ 217.18.
IR (ATR, ν, cm− ): 2048, 1979, 1917 (br.)
1
2
13.6 (t, J = 13.7 Hz, CO), 164.2 (dd, J = 10.4, 6.5 Hz, Ar), 155.0
+
56
(
(
(
dd, J = 20.3, 5.8 Hz, Ar), 134.4 (dd, J = 18.0, 15.3 Hz, Ar), 125.4
s, Ar), 103.4 (d, J = 12.9 Hz, Ar), 102.9 (d, J = 12.4 Hz, Ar), 34.7 701.0061, found 701.0060 (0 ppm); m/z [M + K] calcd for
d, J = 22.7 Hz, CH), 33.1 (dd, J = 27.2, 2.0 Hz, CH), 32.5 (d, J =
HR MS (ESI): m/z [M + Na] calcd for C H O NaP Fe2
2
6
32 10
2
+
5
6
C
26
H
32
O
10
P
2
K Fe
Synthesis of complex 2d. Fe(CO)5 (165 μL, 1.26 mmol,
, 2C), 4 equiv.) was added to a solution of 2 (150 mg, 0.315 mmol) in
toluene (15 mL), then [Cp*Fe(CO) (3.0 mg, 2 mol%) was
P{ H} NMR (162 MHz, C D ) δ 229.41 (d, J = 115.0 Hz), added. The reaction mixture was heated at 70 °C for 14 h. After
2
716.9801 m/z found 716.9798 (0 ppm).
26.1 Hz, CH), 31.8 (dd, J = 24.7, 1.0 Hz, CH), 18.6 (s, CH3),
18.5 (d, J = 2.3 Hz, CH ), 18.0–17.9 (m, 2C), 17.8 (s, CH
17.5 (s, CH ), 17.3 (d, J = 6.7 Hz, CH ).
3
3
3
3
2 2
]
3
1
1
6
6
1
58.58 (d, J = 115.0 Hz).
Anal. Calc. (%). for C20H33FeNO P
3 2
cooling down to rt, the product was dried under vacuum and
: C, 53.00; H, 7.34; washed with methanol. The obtained brown solid was purified
by column chromatography (eluent: petroleum ether/dichloro-
N, 3.09. Found: C, 53.09; H, 7.44; N, 3.03.
IR (ATR, ν, cm− ): 1975, 1929, 1867.
1
methane 9 : 1), yielding 2d (150 mg, 60% yield). Single crystals
Synthesis of complex 5c. Fe(CO)
5
(220 μL, 1.67 mmol) was suitable for X-ray diffraction studies were obtained by slow
added to a solution of m-C H (NHPiPr ) (600 mg, 1.76 mmol) evaporation of a solution in CH Cl .
6
4
2 2
2
2
1
in toluene (18 mL) in a Schlenk tube under argon. The mixture
6 6
H NMR (400 MHz, C D ) δ 7.71 (br. m, 8H, Ar), 7.00 (br. m,
was set to UV irradiation (350 nm) for 14 h at room tempera- 12H, Ar), 6.93 (br. s, 1H, Ar), 6.66 (br. m, 3H, Ar).
1
3
1
ture. The solvent was evaporated under vacuum. The complex
C{ H} NMR (101 MHz, C D ) δ 212.8 (d, J = 19.3 Hz, CO),
6 6
was extracted with hexane (15 mL). The mixture was filtered 153.4 (d, J = 6.9 Hz, Ar), 138.6 (d, J = 55.9 Hz, Ar), 131.8 (d, J =
by cannula transfer and the clear solution was put into 2.2 Hz, Ar), 131.6 (d, J = 12.3 Hz, Ar), 128.9 (d, J = 11.1 Hz, Ar),
the freezer for 24 h. The obtained yellow solid was recrystal- 119.7 (d, J = 2.8 Hz, Ar), 117.7 (t, J = 4.1 Hz, Ar).
3
1
1
lized from toluene and hexane (1 : 4) at −30 °C (434 mg, 60%
yield).
P{ H} NMR (162 MHz, C
6
D
6
) δ 181.95.
IR (ATR, ν, cm− ): 2054, 2048, 1994, 1952 (br.), 1917 (br.).
1
Single crystals suitable for X-ray diffraction studies were
Anal. Calc. (%). for C H Fe O P : C, 56.05; H, 2.97.
3
8
24
2 10 2
grown from toluene and hexane (1 : 4) at −30 °C.
Found: C, 56.01; H, 2.98.
1
6 6
H NMR (400 MHz, C D ): δ = 6.95 (t, J = 7.6 Hz, 1H, Ar),
6
.18 (d, J = 7.6 Hz, 2H, Ar), 3.48 (s, 2H, NH), 2.08–1.99 (m, 2H,
CH), 1.82–1.71 (m, 2H, CH), 1.19–1.13 (m, 12H, CH ),
), −9.50 (t, J =
General procedure for the dehydrogenative borylation
of styrene
3
1
5
.10–0.97 (m, 6H, CH3), 0.97–0.84 (m, 6H, CH
2.8 Hz, 1H, Fe–H).
3
In an argon filled glove box, a Schlenk flask was charged with
1
3
1
C{ H} NMR (126 MHz, CDCl
CO), 213.4 (t, J = 13.3 Hz, CO), 154.3 (t, J = 12.9 Hz, Ar), 133.7 (0.5 mL) (see Table 3), styrene (1–3 equiv.) and pinacolborane
t, J = 15.7 Hz, Ar), 124.0 (s, Ar), 100.3 (s, Ar), 32.2 (t, J = (1 equiv.). The mixture was stirred under UV (350 nm) at room
3
) δ = 215.7 (t, J = 13.8 Hz, the iron complex (5.0 mol%), followed eventually by toluene
(
1
(
2.7 Hz, CH), 31.5 (t, J = 14.5 Hz, CH), 18.5 (s, 2 CH
s, CH ), 17.7 (s, CH ).
P NMR (162 MHz, C D ) δ = 158.6 (br. d, J = 50 Hz).
3
), 18.0 temperature for 24–72 hours. The solution was diluted with
diethyl ether and filtered through a small pad of silica (2 cm
in a Pasteur pipette). The silica was washed with diethyl ether.
3
3
3
1
6
6
Dalton Trans.
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Paper
The filtrate was evaporated and the crude residue was purified
by column chromatography.
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(a) H. F. Klein, S. Camadanli, R. Beck, D. Leukel and
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2
3
(
1
E)-4,4,5,5-Tetramethyl-2-styryl-1,3,2-dioxaborolane
H NMR (400 MHz, C D ) δ 7.74 (d, J = 18.4 Hz, 1H), 7.31 (dd,
J = 7.8, 1.5 Hz, 2H), 7.07–6.93 (m, 3H), 6.43 (d, J = 18.4 Hz,
6
6
1
H), 1.12 (s, 12H).
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1
1
B{ H} NMR (128 MHz, C D ) δ 30.36.
C{ H} NMR (101 MHz, C
6
6
1
3
1
6
D
6
, the carbon attached to the
boron atom was not observed due to low intensity): δ 150.2,
38.0, 129.0, 128.8, 127.4, 83.2, 25.0.
1
Crystallography
X-ray diffraction data were collected on an APEXII, Bruker-AXS
diffractometer equipped with a CCD detector, using graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at T = 150(2) K.
The structures were solved by direct methods using the SIR97
program, and then refined with full-matrix least-square
methods based on F (SHELXL-97) with the aid of the
WINGX program.
Complete details of the X-ray analyses reported herein have
been deposited at the Cambridge Crystallographic Data Center
2
4
2
25
2
6
(CCDC 1469695–1469701).
4556–4559.
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(a) L. Wang, H. Sun and X. Li, Eur. J. Inorg. Chem., 2015,
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Calculations methods
2
7
DFT calculations employing the B3PW91 functional with D3
2
8
version of Grimme’s dispersion were performed with the
(
6
d) G. Xu, H. Sun and X. Li, Organometallics, 2009, 28,
090–6095; (e) S. Huang, H. Zhao, X. Li, L. Wang and
2
9
GAUSSIAN 09 series of programs, D01 version. The iron and
phosphorous atoms were represented by the relativistic
effective core potential (RECP) from the Stuttgart group and
their associated basis set, augmented by polarization functions
H. Sun, RSC Adv., 2015, 5, 15660–15667; (f) H. Zhao,
H. Sun and X. Li, Organometallics, 2014, 33, 3535–3539;
(
metallics, 2010, 29, 364–377; (h) R. Beck, H. Sun, X. Li,
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3
g) E. C. Volpe, P. T. Wolczanski and E. B. Lobkovsky, Organo-
(
α = 2.462, Fe; α = 0.387, P ). The remaining atoms (C, O, N,
f d
3
0
H) were represented by 6-31G(d,p) basis sets. Full optimi-
zations of geometry without any constraint were performed.
Calculations of harmonic vibrational frequencies were per-
formed to determine the nature of each extremum.
253–3257; (i) P. Bhattacharya, J. A. Krause and H. Guan,
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Acknowledgements
6
We thank the CNRS and the ANR agency (program blanc
(
b) W.-S. Hwang, T.-S. Tzeng, D.-L. Wang and M. Y. Chiang,
1
0
2-BS07-0011-01 “Ironhyc” and program JCJC ANR-15-CE07-
001 “Ferracycles”). C. D. and J.-B. S. thank the University of
Polyhedron, 2001, 20, 353–362; (c) S.-Y. Jin, C.-Y. Wu,
C.-S. Lee, A. Datta and W.-S. Hwang, J. Organomet. Chem.,
Rennes 1 and the Fondation Rennes 1 (grant to S. Q.-D.).
Computer time was given by the HPC resources of CALMIP
supercomputing center (Toulouse, France) under the allocation
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015-[P0909].
2
(
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3
1
1
1
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CO) fragment to one phosphorus atom. Unfortunately, we
4
were unable to selectively synthesize and fully characterize
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1
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This journal is © The Royal Society of Chemistry 2016