Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP pincer complexes

Article abstract of DOI:10.1007/s00706-016-1706-x

A new asymmetric chiral PNP ligand based on the 2,6-diaminopyridine scaffold featuring a R-BINEPINE moiety was prepared. Treatment of anhydrous FeX₂ (X = Cl, Br) with 1 equiv of PNP-iPr,BIN at room temperature afforded the coordinatively unsatu

Full text of DOI:10.1007/s00706-016-1706-x

Monatsh Chem
DOI 10.1007/s00706-016-1706-x
ORIGINAL PAPER
Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP
pincer complexes
1
2
•
Christian Schroder-Holzhacker Nikolaus Gorgas1 Berthold Stoger Karl Kirchner1
•
•
¨
¨
Received: 8 January 2016 / Accepted: 11 February 2016
Ó The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract A new asymmetric chiral PNP ligand based on
the 2,6-diaminopyridine scaffold featuring a R-BINEPINE
moiety was prepared. Treatment of anhydrous FeX2
(X = Cl, Br) with 1 equiv of PNP-iPr,BIN at room tem-
perature afforded the coordinatively unsaturated
paramagnetic complexes [Fe(PNP-iPr,BIN)X2]. The struc-
ture of [Fe(PNP-iPr,BIN)Cl2] is described. Both complexes
react readily with the strong p-acceptor ligand CO in
solution to afford selectively the diamagnetic complexes
trans-[Fe(PNP-iPr,BIN)(CO)X2] in quantitative yield. Due
the lability of the CO ligand, these complexes are only
stable under a CO atmosphere and isolation in pure form
was not possible. The preparation of the carbonyl hydride
complex [Fe(PNP-iPr,BIN)(H)(CO)Br] was achieved albeit
in low yields via a one pot procedure by treatment of
[Fe(PNP-iPr,BINEP)Br2] with CO and subsequent reaction
with Na[HBEt3]. This complex was obtained as an insep-
arable mixture of two diastereomers in a ca. 1:1 ratio and
was tested as catalyst for the hydrogenation of ketones. The
catalyst showed acceptable activity under mild conditions
(5 bar H2, room temperature) with yields up to [99 %
within 18 h.
Graphical abstract
Keywords Iron Á Pincer ligands Á Chiral phosphines Á
Carbon monoxide
Introduction
In view of concerns regarding economy, environment, and
sustainable energy, there is a constant need for the dis-
covery of new catalytic reactions. A process we are
interested in is the catalytic hydrogenation of polar multi-
ple bonds via molecular hydrogen. This plays a significant
role in modern synthetic organic chemistry and is excel-
lently performed by many transition metal hydride
complexes containing noble metals such as ruthenium,
rhodium, or iridium [1–5]. The limited availability of
precious metals, their high price, and their toxicity lowers
the attractivity of these metals in the future and more
economical and environmentally friendly alternatives have
to be found which are in line with green chemistry
guidelines. In this respect, the preparation of well-defined
iron-based hydride catalysts of comparable or even higher
activity is desirable [6–12]. Iron is the most abundant
transition metal in the earth crust, and ubiquitously
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1706-x) contains supplementary
material, which is available to authorized users.
& Karl Kirchner
kkirch@mail.tuwien.ac.at
1
Institute of Applied Synthetic Chemistry, Vienna University
of Technology, Getreidemarkt 9/163-OC, 1060 Vienna,
Austria
2
Institute of Chemical Technologies and Analytics, Vienna
University of Technology, Getreidemarkt 9, 1060 Vienna,
Austria
123

¨
C. Schroder-Holzhacker et al.
Scheme 1
Results and discussion
H
n
Treatment of the mono-phosphinated ligand PNNH2-iPr (1)
with 1 equiv of BIN-PCl (2) (in the R-form) in the presence
of NEt3 afforded the new asymmetric chiral PNP ligand
PNP-iPr,BIN (3) in 64 % isolated yield (Scheme 2). The
optically pure ligand was isolated as air stable solid and
was characterized by elemental analysis, 1H, 13C{1H}, and
31P{1H} NMR spectroscopy.
H
N
PiPr2
CO
N
Fe
HN PiPr2
L
Treatment of anhydrous FeCl2 with 1 equiv of the PNP
ligand PNP-iPr,BIN (3) in THF at room temperature
afforded the coordinatively unsaturated complex [Fe(PNP-
iPr,BIN)Cl2] (4a) in 79 % isolated yields (Scheme 3). The
analogous bromide complex [Fe(PNP-iPr,BIN)Br2] (4b)
was obtained in similar fashion by straightforward com-
plexation of the respective free PNP ligand with anhydrous
ferrous dibromide (84 % yield). All complexes are ther-
mally robust pale yellow solids that are air sensitive in the
solid state and particularly in solution. They display large
paramagnetic shifted 1H and 13C{1H} NMR solution
spectra with broad and featureless signals which, due to the
complexity of the PNP ligands, were not assignable and
thus not informative. These complexes were characterized
by elemental analysis. In addition the molecular structure
of 4d was determined by X-ray crystallography. In this
case, the racemic BIN-PCl (2) was used, since all attempts
to grow crystals suitable for X-ray diffraction studies failed
for the chiral compounds. A structural view of 4a is
depicted in Fig. 1 with selected bond distances and angles
given in the caption. The coordination geometry of the iron
center is distorted square pyramidal. Bond distances and
angles are in good accord with the solid state structures of
similar complexes of the type [Fe(j3P,N,P-PNP)Cl2] [29].
Particularly characteristic for all these complexes are the
comparatively long Fe–N and Fe–P bonds which clearly
L = Br-, CH3CN, BH4
-
available. Accordingly, it is not surprising that the field of
iron catalyzed hydrogenations of polar multiple bonds is
rapidly evolving as shown by several recent examples [13–
27].
We are currently focusing on the synthesis and reactivity
of iron complexes containing PNP pincer ligands based on
the 2,6-diaminopyridine scaffold [28–38]. In these ligands
the aromatic pyridine ring and the phosphine moieties are
connected via NH, N-alkyl, or N-aryl linkers. Complexes
of the type [Fe(PNP-iPr)(H)(CO)(L)]n with labile ligands
(L = Br-, CH3CN, BH4-) and NH spacers were found to
be efficient catalysts for the hydrogenation of both ketones
and aldehydes to alcohols under mild conditions
(Scheme 1) [35].
Herein we report on the synthesis, characterization, and
preliminary catalytic activity of asymmetric chiral iron
pincer complexes where PiPr2 and BINEPINE moieties are
connected to the pyridine ring of the PNP ligand via NH
spacers. The iPr substituents were chosen to prevent the
coordination of two PNP ligands as found recently for
sterically little demanding PNP systems [34, 36].
Scheme 2
= BIN-PCl
Cl
P
2
1 equiv
N
HN
PiPr2
NH
P
N
HN
PiPr2
NH2
toluene
NEt3
1
3
123

Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP pincer complexes
Scheme 3
X
N
HN
PiPr2
NH
X
H
N
H
N
PR2
PR2
CO
3
PR2
CO
FeX2
N
Fe
N
Fe
THF
-CO
X
HN PiPr2
HN PiPr2
in CD2Cl2
X
4a X = Cl
4b X = Br
PR2 =
P
5a X = Cl
5b X = Br
NMR spectroscopy. In the 13C{1H} NMR spectrum the CO
ligands of 5a and 5b exhibit a single low-intensity triplet
2
resonance at 220.7 (t, JCP = 22.2 Hz) and 223.1 ppm (t,
2JCP = 21.9 Hz), respectively. The 31P{1H} NMR spectra
give rise to two doublets centered at 143.6/125.3 and 143.9/
125.1 ppm, respectively, with large JPP coupling constants
of 190 and 177 Hz which are consistent with a trans-P,P
configuration.
The preparation of carbonyl hydride complexes was
attempted via a one pot procedure by treatment of
[Fe(PNP-iPr,BINEP)Br2] (4b) with CO and subsequent
reaction with 1.1 equivs of Na[HBEt3] (Scheme 4). Com-
plex [Fe(PNP-iPr,BIN)(H)(CO)Br] (6) was obtained as an
inseparable mixture of two diastereomers in a ca. 1:1 ratio.
Together with 6, a considerable amount of free PNP-iPr,-
BIN ligand was detected in the 31P{1H} NMR spectrum,
and the yield was low (ca 50 %). In good agreement with
the experimental findings, also DFT/B3LYP calculations
showed that the energy difference between the two isomers
(denoted as 6A and 6B) is merely 10.5 kJ/mol (Fig. 2). In
both isomers, the hydride ligands are located trans to the
bromide ligand. Complex 6 turned out to be unstable in
solution and slow decomposition took place. Accordingly,
complete purification and characterization was unsuccess-
Fig. 1 Structural view of [Fe(PNP-iPr,BIN)Cl2] (4a) showing 50 %
thermal ellipsoids (most H atoms and solvent molecules omitted for
˚
clarity). Selected bond (A) and bond angles (°): Fe1–Cl1 2.3057(8),
Fe1–Cl2 2.3366(9), Fe1–P1 2.4853(9), Fe1–P2 2.5150(9), Fe1–N1
2.141(2), Cl1–Fe1–Cl2 130.99(3), Cl1–Fe1–P1 97.69(3), Cl2–Fe1–P2
92.32(3), P1–Fe1–P2 159.16(3), Cl1–Fe1–P1–N2 130.5(1), Cl2–Fe1–
P1–N2 97.0(1)
indicate that they are in high-spin state; low-spin Fe–PNP
˚
complexes have Fe–N and Fe–P bonds by ca. 0.2 A
shorter.
In order to obtain iron-based hydrogenation catalysts it
appears to be important to have diamagnetic complexes.
Accordingly, virtually all iron complexes that are active
catalysts feature the strong field CO and hydride ligands,
which seem to maintain a low spin configuration
throughout the catalytic cycle. Complexes 4a and 4b react
readily with the strong p-acceptor ligand CO in solution to
afford selectively the diamagnetic, octahedral complexes
trans-[Fe(PNP-iPr,BIN)(CO)Cl2] (5a) and trans-[Fe(PNP-
iPr,BIN)(CO)Br2] (5b), respectively, in quantitative yield
(Scheme 3). However, due the lability of the CO ligand,
these complexes are stable only under a CO atmosphere
and isolation in pure form was not possible. These com-
pounds slowly release CO thereby reforming the starting
materials 4a and 4b. Accordingly, complexes 5a and 5b
were fully characterized by 1H, 13C{1H}, and 31P{1H}
1
ful. The products were identified by H NMR where the
hydride signals of the two isomers 6A and 6B gave rise to
triplet resonances at -22.15 (2JPH = 61.6 Hz) and
-22.36 ppm (2JPH = 61.1 Hz), respectively (Fig. 3). The
assignments are based on DFT calculations.
Despite these facts, complex 6 (as mixture of two
diastereomers), prepared in situ, was tested as catalyst for
the hydrogenation of some ketones. Since the catalyst
could not be isolated in pure form, only preliminary tests
were performed with five substrates. These results are
depicted in Table 1. The catalyst showed acceptable activ-
ity under mild conditions (5 bar H2, room temperature)
with yields up to [99 % within 18 h indicating that in
123

¨
C. Schroder-Holzhacker et al.
Scheme 4
H
Br
Br
H
H
H
N
1. CO
2. Na[HBEt3]
PR2
CO
N
N
PR2
PR2
CO
N
Fe
N
Fe
N
Fe
THF
Br
HN PiPr2
HN PiPr2
HN PiPr2
Br
6 (two diastereoisomers)
H
4b
PR2 =
P
Fig. 2 DFT/B3LYP optimized structures and free energy difference of the two diasteromers of [Fe(PNP-iPr,BIN)(H)(CO)Br] (6)
Fig. 3 Hydride region of the 1H
NMR spectrum of 6A (left) and
6B (right) in CD3OD
further experiments the catalyst loadings and possibly
reaction times can be reduced significantly.
diaminopyridine scaffold featuring an R-BINEPINE moi-
ety. This ligand reacts with anhydrous FeX2 (X = Cl, Br)
to afford the coordinatively unsaturated paramagnetic
complexes [Fe(PNP-iPr,BIN)X2]. Both complexes react
In conclusion, we describe here the synthesis of a new
asymmetric chiral PNP ligand based on the 2,6-
123

Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP pincer complexes
and 31P{1H} NMR spectra were recorded on Bruker
Table 1 Hydrogenation of ketones catalyzed by [Fe(PNP-iPr,-
BIN)(H)(CO)Br] (6)
AVANCE-250, AVANCE-300 DPX, and AVANCE-400
1
spectrometers. H and 13C{1H} NMR spectra were refer-
H
2 (5 bar)
6
1.0 mol %
enced internally to residual protio-solvent, and solvent
resonances, respectively, and are reported relative to
tetramethylsilane (d = 0 ppm). 31P{1H} NMR spectra were
referenced externally to H3PO4 (85 %) (d = 0 ppm).
O
OH
2.0 mol % KOtBu
R
R
R'
18 RT
R'
EtOH,
Substrate
h,
Entry
1
Product
Yield/%a
O
OH
(1R)-N2-(3,5-Dihydro-4H-dinaphtho[2,1-c:10,20-e]phos-
phepin-4-yl)-N6-(diisopropylphosphanyl)pyridine-2,6-di-
amine (PNP-iPr,BIN) (3, C33H35N3P2)
89
O
OH
1 (1.00 eq, 6.55 mmol, 1.47 g) was dissolved in 100 cm3
toluene and 1.4 cm3 Et3N (1.50 eq, 9.83 mmol) was added.
After cooling to 0 °C, 2.50 g 2 (1.10 eq, 7.21 mmol) in
50 cm3 toluene was added and the reaction was stirred at
80 °Cfor12 h.Thesuspensionwasfilteredoverasmallpadof
CeliteÒ and the solvent was removed under reduced pressure.
The crude product was purified via flash chromatography
using silica gel (conditioned with 5 vol % NEt3) and 1:1 MC/
EE as eluent. Yield: 2.25 g (64 %). 1H NMR (CDCl3, 20 °C):
2
96
F
F
OH
O
3
>99
>99
>99
Cl
Br
Cl
Br
O
OH
4
R
OH
R
O
3
d = 7.89–7.79 (m, 4H, naph), 7.47 (d, JHH = 8.3 Hz, 1H,
5b
naph), 7.38–7.32 (m, 2H, naph), 7.31 (d, 3JHH = 8.3 Hz, 1H,
3
naph), 7.23 (m, 5H, py4, naph), 6.43 (dd, JHH = 8.0 Hz,
4JPH = 1.9 Hz, 1H, py5), 6.22 (d, 3JHH = 8.4 Hz, 1H, py3),
4.31 (d, 2JPH = 10.9 Hz, 1H, NHBIN), 4.08 (d,
a
1
Yields were determined by H NMR
2
2JPH = 10.7 Hz, 1H, NHiPr), 3.03 (dd, JHH = 17.0 Hz,
b
R = naphtyl
2
2JPH = 11.9 Hz, 1H, CH2), 2.70 (dd, JHH = 14.3 Hz,
2
2JPH = 2.8 Hz, 1H, CH2), 2.50 (dd, JHH = 18.2 Hz,
2
2JPH = 14.3 Hz, 1H, CH2), 2.29 (d, JHH = 11.9 Hz, 1H,
CH2), 1.68 (m, 2H, CH(CH3)2), 1.04–0.95 (m, 12H,
CH(CH3)2) ppm; 13C{1H} NMR (CDCl3, 20 °C):
d = 159.92 (d, 2JCP = 20.0 Hz, py6), 157.01 (d,
2JCP = 17.4, py2), 139.25 (s, py4), 133.79 (d, JCP = 4.1 Hz,
naph), 133.43 (s, naph), 133.08 (s, naph), 132.82 (d,
JCP = 1.5 Hz, naph), 132.72 (s, naph), 132.38 (s, naph),
132.28 (d, JCP = 1.8 Hz, naph), 132.15 (s, naph), 128.24 (s,
naph), 127.58 (s, naph), 127.23 (d, JCP = 2.1 Hz, naph),
126.69 (d, JCP = 10.8 Hz, naph), 126.06 (d, JCP = 11.5 Hz,
naph), 125.09 (d, JCP = 11.9 Hz, naph), 98.90 (d,
3JCP = 18.4 Hz, py5), 98.73 (d, 3JCP = 15.7, py3), 36.04 (d,
readily with the strong p-acceptor ligand CO in solution to
afford selectively and quantitatively trans-[Fe(PNP-
iPr,BIN)(CO)X2]. Due the lability of the CO ligand, these
complexes are only stable under a CO atmosphere. The
preparation of the carbonyl hydride complex [Fe(PNP-
iPr,BIN)(H)(CO)Br] was achieved albeit in low yields via a
one pot synthesis. This complex was obtained as an
inseparable mixture of two diastereomers and was suc-
cessfully tested as catalyst for the hydrogenation of
ketones.
1
1JCP = 15.0 Hz, CH2), 34.90 (d, JCP = 24.2 Hz, CH2),
26.43 (d, 1JCP = 11.5 Hz, CH(CH3)2), 16.34 (d,
Experimental
2
1JCP = 11.0 Hz, CH(CH3)2), 18.72 (d, JCP = 19.8 Hz,
2
CH(CH3)2), 17.22 (d, JCP = 10.6 Hz, CH(CH3)2), 17.14
All manipulationswere performed under an inert atmosphere
of argon by using Schlenk techniques or in an MBraun inert-
gas glovebox. The solvents were purified according to
standard procedures [39]. The deuterated solvents were
(d, 2JCP = 10.4 Hz, CH(CH3)2) ppm;31P{1H}NMR (CDCl3,
20 °C): d = 48.6 (s, iPr), 48.1 (s, BIN) ppm.
[(Dichloro)(1R)-N2-(3,5-dihydro-4H-dinaphtho[2,1-
c:10,20-e]phosphepin-4-yl)-N6-(diisopropylphos-
phanyl)pyridine-2,6-diamine)iron(II)] ([Fe(PNP-iPr,
BIN)Cl2]) (4a, C33H35Cl2FeN3P2)
˚
purchased from Aldrich and dried over 4 A molecular sieves.
The ligands N2-(diisopropylphosphanyl)pyridine-2,6-di-
amine (PNNH2-iPr) (1) and (1R)-4-chloro-4,5-dihydro-3H-
dinaphto[2,1-c:10,20-e]phosphepine (BIN-PCl) (2) were
A suspension of 71 mg anhydrous FeCl2 (0.56 mmol) and
300 mg 3 (0.56 mmol) was stirred in 15 cm3 of THF at
1
prepared according to the literature [37, 40]. H, 13C{1H},
123

¨
C. Schroder-Holzhacker et al.
room temperature for 12 h. The solvent was then removed
under vacuum and the remaining solid dissolved in 15 cm3
of CH2Cl2. Insoluble materials were removed by filtration.
The volume of the solution was reduced to 0.5 cm3 and the
product was precipitated by addition of 40 cm3 of n-
pentane. After filtration the yellow product was washed
with twice with 15 cm3 of n-pentane and dried under
vacuum. Yield: 324 mg (87 %) yellow solid.
Reaction of [Fe(PNP-iPr,BIN)Br2] (4b) with CO in CD2-
Cl2. Formation of trans-[(dibromo)(carbonyl)(1R)-N2-(3,5-
dihydro-4H-dinaphtho[2,1-c:10,20-e]phosphepin-4-yl)-N6-
(diisopropylphosphanyl)pyridine-2,6-diamine)iron(II)]
(trans-[Fe(PNP-iPr,BIN)(CO)Br2]) (5b, C34H35Br2
FeN3OP2)
CO was bubbled through a solution of 30 mg 4b
(39.9 lmol) in 0.6 cm3 of CD2Cl2 for 2 min, whereupon
the colour changed to dark violet. 1H NMR (CD2Cl2,
20 °C): d = 8.01–7.90 (m, 4H, naph), 7.80 (d,
[(Dibromo)(1R)-N2-(3,5-dihydro-4H-dinaphtho[2,1-
c:10,20-e]phosphepin-4-yl)-N6-(diisopropylphos-
phanyl)pyridine-2,6-diamine)iron(II)] ([Fe(PNP-iPr,
BIN)Br2]) (4b, C33H35Br2FeN3P2)
3
3JHH = 7.9 Hz, 1H, naph), 7.54 (d, JHH = 7.5 Hz, 1H,
3
naph), 7.41–7.36 (m, 3H, naph), 7.30 (d, JHH = 8.4 Hz,
1H, naph), 7.25–7.03 (m, 3H, naph, py4), 6.50 (bs, 1H,
This complex was prepared analogously to 4a with 121 mg
anhydrous FeBr2 (0.56 mmol) and 300 mg 3 (0.56 mmol)
as starting materials. Yield: 352 mg (84 %), yellow solid.
2
py5), 6.32 (d, JPH = 5.9 Hz, 1H, NHiPr), 5.83 (bs, 1H,
2
py3), 5.50 (d, JPH = 6.0 Hz, 1H, NHBIN), 4.67 (dd,
2
2JHH = 12.5 Hz, JPH = 3.9 Hz, 1H, CH2), 3.94 (dd,
2
Reaction of [Fe(PNP-iPr,BIN)Cl2] (4a) with CO in CD2-
Cl2. Formation of trans-[(dichloro)(carbonyl)(1R)-N2-(3,5-
dihydro-4H-dinaphtho[2,1-c:10,20-e]phosphepin-4-yl)-N6-
(diisopropylphosphanyl)pyridine-2,6-diamine)iron(II)]
(trans-[Fe(PNP-iPr,BIN)(CO)Cl2]) (5a, C34H35Cl2
FeN3OP2)
2JHH = 15.1 Hz, JPH = 8.8 Hz, 1H, CH2), 3.10 (m, 3H,
CH2,
CH(CH3)2),
2.73
(dd,
2JHH = 17.3 Hz,
3
2JPH = 13.3 Hz, 1H, CH2), 1.49 (dd, JHH = 5.8 Hz,
2JPH = 12.1 Hz,
3JHH = 6.8 Hz, JPH = 15.3 Hz, 3H, CH(CH3)2), 1.41
3H,
CH(CH3)2),
1.45
(dd,
2
3
2
(dd, JHH = 7.2 Hz, JPH = 16.9 Hz, 3H, CH(CH3)2),
1.32 (dd, 3JHH = 7.2 Hz, 2JPH = 16.6 Hz, 3H, CH(CH3)2)
ppm; 13C{1H} NMR (CD2Cl2, 20 °C): d = 223.05 (t,
CO cwas bubbled through a solution of 30 mg 4a (45.3 lmol)
in 0.6 cm3 of CD2Cl2 for 2 min, whereupon the colour changed
to dark violet. 1H NMR (CD2Cl2, 20 °C): d = 8.13–8.00 (m,
2
2JCP = 21.9 Hz, CO), 161.97 (dd, JCP = 12.6 Hz,
3
4H, naph), 7.79 (d, JHH = 7.9 Hz, 1H, naph), 7.66 (d,
3JCP = 5.3 Hz, py6), 160.60 (dd, 2JCP = 13.3 Hz,
3JCP = 5.1 Hz, py2), 140.11 (s, py4), 134.65 (s, naph),
134.12 (d, JCP = 5.0 Hz, naph), 133.67 (d, JCP = 10.9 Hz,
naph), 133.18 (d, JCP = 2.6 Hz, naph), 132.92 (d,
JCP = 1.3 Hz, naph), 132.44 (s, naph), 132.18 (d,
JCP = 2.4 Hz, naph), 131.61 (d, JCP = 2.9 Hz, naph),
129.08 (s, naph), 128.80 (d, JCP = 2.2 Hz, naph), 128.39
(d, JCP = 6.2 Hz, naph), 128.22 (d, JCP = 3.5 Hz, naph),
127.63 (d, JCP = 1.6 Hz, naph), 126.92 (d, JCP = 13.8 Hz,
naph), 126.41 (s, naph), 126.10 (s, naph), 125.61 (d,
3JHH = 7.5 Hz, 1H, naph), 7.41 (d, 3JHH = 8.4 Hz, 1H, naph),
7.34–7.15 (m, 6H, naph, py4), 6.62 (bs, 1H, py5), 6.41 (bs, 1H,
NHiPr), 6.03 (bs, 1H, py3), 5.56 (bs, 1H, NHBIN), 4.35 (dd,
2
2JHH = 12.3 Hz, JPH = 4.1 Hz, 1H, CH2), 3.76 (dd,
2
2JHH = 15.1 Hz, JPH = 9.1 Hz, 1H, CH2), 3.20 (d,
2JHH = 15.0 Hz, 1H, CH2), 2.99 (m, 2H, CH(CH3)2), 2.71
2
2
(dd, JHH = 17.0 Hz, JPH = 13.0 Hz, 1H, CH2), 1.62–1.37
(m, 12H, CH(CH3)2) ppm; 13C{1H} NMR (CD2Cl2, 20 °C):
d = 220.73 (t, 2JCP = 22.2 Hz, CO), 161.90 (dd,
2JCP = 13.2 Hz, 3JCP = 5.6 Hz, py6), 160.63 (dd,
3
JCP = 13.5 Hz, naph), 100.17 (d, JCP = 7.0 Hz, py5),
3
3
1
2JCP = 13.6 Hz, JCP = 5.1 Hz, py2), 140.16 (s, py4),
99.67 (d, JCP = 7.2 Hz, py3), 36.23 (d, JCP = 23.3 Hz,
1
CH2), 31.39 (d, JCP = 27.9 Hz, CH2), 28.48 (d,
1JCP = 22.6 Hz, CH(CH3)2), 28.01 (d, JCP = 23.3 Hz,
134.67 (d, JCP = 1.8 Hz, naph), 134.16 (d, JCP = 4.9 Hz,
naph), 133.21 (d, JCP = 2.6 Hz, naph), 132.91 (d, JCP = 1.6 -
Hz, naph), 132.82 (s, naph), 132.49 (s, naph), 132.24 (d,
JCP = 2.5 Hz, naph), 131.56 (d, JCP = 3.0 Hz, naph), 129.03
(s, naph), 128.81 (d, JCP = 2.1 Hz, naph), 128.45 (d,
JCP = 3.6 Hz, naph), 128.37 (d, JCP = 8.0 Hz, naph),
127.53 (s, naph), 126.96 (s, naph), 126.79 (s, naph), 126.40
(s, naph), 126.08 (s, naph), 125.65 (s, naph), 125.51 (s, naph),
99.88 (d, 3JCP = 7.7 Hz, py5), 99.52 (d, 3JCP = 7.2 Hz, py3),
1
2
CH(CH3)2), 18.97 (d, JCP = 4.5 Hz, CH(CH3)2), 18.52
(m, CH(CH3)2) ppm; 31P{1H} NMR (CD2Cl2, 20 °C):
d = 143.9 (d, 2JPP = 176.6 Hz, BIN), 125.1 (d,
2JPP = 176.5 Hz, iPr) ppm.
Reaction of [Fe(PNP-iPr,BIN)Br2] (4b) with CO and
Na[HBEt3].
Formation
of
[(bromo)(hydrido)(car-
bonyl)(1R)-N2-(3,5-dihydro-4H-dinaphtho[2,1-c:10,20-
e]phosphepin-4-yl)-N6-(diisopropylphosphanyl)pyridine-
2,6-diamine)iron(II)] ([Fe(PNP-iPr,BIN)(H)(CO)Br]) (6,
C34H36BrFeN3OP2)
1
1
33.05 (d, JCP = 21.9 Hz, CH2), 29.10 (d, JCP = 26.3 Hz,
1
CH2), 26.23 (d, JCP = 21.9 Hz, CH(CH3)2), 25.95 (d,
2
1JCP = 22.2 Hz, CH(CH3)2), 18.88 (d, JCP = 4.1 Hz,
2
CH(CH3)2), 18.86 (d, JCP = 4.0 Hz, CH(CH3)2), 17.95 (d,
A solution of 300 mg 4b (0.40 mmol) in 15 cm3 THF was
purged with CO for 3 min, whereupon the colour changed
to deep blue. The reaction mixture was then cooled to 0 °C
2JCP = 3.5 Hz, CH(CH3)2) ppm; 31P{1H} NMR (CD2Cl2,
2
20 °C): d = 143.6 (d, JPP = 189.7 Hz, BIN), 125.3 (d,
2JPP = 189.7 Hz, iPr) ppm.
123

Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP pincer complexes
and 0.44 cm3 Na[HBEt3] (0.44 mmol) was added slowly
performed to confirm the nature of the stationary points
via syringe. The solvent was then removed under reduced
pressure. The residue was redissolved in 15 cm3 of
CH2Cl2, filtered and the volume of the solution was
reduced to ca 0.5 cm3. The product was precipitated upon
addition of 40 cm3 of n-pentane, collected on a glass frit,
washed with 10 cm3 n-pentane and dried under vacuum for
2 h. The product could not be isolated in pure form and
was used for catalytic reactions as obtained.
yielding no imaginary frequency for the minima.
Acknowledgments Open access funding provided by Austrian
Science Fund (FWF). Financial support by the Austrian Science Fund
(FWF) is gratefully acknowledged (Project No. P24583-N28). The
X-ray center of the Vienna University of Technology is acknowl-
edged for financial support and for providing access to the single-
crystal diffractometer.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
X-ray structure determination
X-ray diffraction data of 4aÁxTHFÁ(2 - x)Et2O (CCDC
number 1445976) were collected at T = 100 K in a dry
stream of nitrogen on a Bruker Kappa APEX II diffrac-
tometer system using graphite-monochromatized MoKa
˚
radiation (k = 0.71073 A) and fine sliced u- and x-scans.
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improved residuals and twinning was ultimately dropped
from the refinement. Molecular graphics were generated
with the program MERCURY [45]. Crystal data are given
in Table S1.
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