Syntheses, Structures and Reactivity of Terminal Phosphido Complexes of Iron(II) Supported by a β-Diketiminato Ligand

Article abstract of DOI:10.1002/ejic.201800850

We report the synthesis of the first series of terminal phosphido iron complexes supported by a β-diketiminato ligand (Dippnacnac) and their catalytic activity in dehydrocoupling of secondary phosphines. Anionic and neutral mono- or diphosphido complexes were obtained from the reaction of [(Dippnacnac)FeCl₂Li(dme)₂] with the R₂PLi (R = iPr, tBu, Cy, Ph) phosphides by tuning the stoichiometric ratio, polarity of the solvent, and the bulkiness of the substituents at the P-atom. The structures of the synthesized compounds were determined by single-crystal X-ray diffraction, which revealed that the iron sites of the anionic complexes are four-coordinate, whereas those of the neutral complexes are three-coordinate with almost planar geometry. These phosphido iron complexes were also characterized by ¹H NMR and zero-field M?ssbauer spectroscopy. The thermal stability and reactivity of selected complexes were studied. The catalytic properties of the phosphido complexes were confirmed by investigating the conversion of diphenylphosphine to symmetrical 1,1,2,2-teraphenyldiphosphane.

Full text of DOI:10.1002/ejic.201800850

A Journal of
Accepted Article
Title: Syntheses, structures and reactivity of terminal phosphido
complexes of iron(II) supported by a β-diketiminato ligand
Authors: Kinga Kaniewska, Alina Dragulescu-Andrasi, Łukasz
Ponikiewski, Jerzy Pikies, Sebastian Stoian, and Rafał
Grubba
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
Syntheses, structures, and reactivity of terminal phosphido
complexes of iron(II) supported by a β-diketiminato ligand
[
a]
[b]
[a]
[a]
Kinga Kaniewska , Alina Dragulescu-Andrasi , Łukasz Ponikiewski , Jerzy Pikies , Sebastian A.
[c]
[a]
Stoian * and Rafał Grubba *
Abstract: We report the synthesis of the first series of terminal
phosphido iron complexes supported by a β-diketiminato ligand
design, low coordination environments. Examples of ligands
that support distinctive, low-coordinate environments include
the N-containing β-diketiminates (e.g., nacnac)[10–13].
Depending on the N-atom substituents, the properties of
β-diketiminates can vary considerably which, in turn,
(Dippnacnac) and their catalytic activity in the dehydrocoupling of
secondary phosphines. Anionic and neutral mono- or
diphosphido complexes were obtained from the reaction of
[
(Dippnacnac)FeCl
2
Li(dme)
2
] with the R
2
PLi (R = iPr, tBu, Cy, Ph)
substantially influence the properties and reactivity of their
complexes[
14,15]
. β-diketiminates with sterically demanding
groups have been successfully employed in the synthesis of
low-coordinate iron complexes. In contrast to a large number
phosphides by tuning the stoichiometric ratio, polarity of the
solvent, and the bulkiness of the substituents at the P-atom. The
structures of the synthesized compounds were determined by
single-crystal X-ray diffraction, which revealed that the iron sites
of the anionic complexes are four-coordinate, whereas those of
the neutral complexes are three-coordinate with almost planar
of heteroleptic β-diketiminato iron complexes with alkyl, aryl,
vinyl, amido, and imido co-ligands[
16–26]
, the chemistry of iron
β-diketiminato complexes featuring phosphido co-ligands is
largely unexplored[27]
Notably, the closest analogs of
phosphido complexes reported by Holland and co-workers
geometry. These phosphido iron complexes were also
.
1
characterized by
H
NMR and zero-field Mössbauer
spectroscopy. The thermal stability and reactivity of selected
complexes were studied. The catalytic properties of the
phosphido complexes were confirmed by investigating the
conversion of diphenylphosphine to symmetrical 1,1,2,2-
teraphenyldiphosphane.
2
are iron complexes with NR groups, which exhibit interesting
structural properties and reactivity[20].
Metal complexes featuring phosphido ligands have
attracted interest due to their great potential as effective
catalysts, especially in promoting the formation of P-P[
and P-C[31–40] bonds [41,42]. Moreover, these compounds are
also catalytically active in the dehydrocoupling of amino- and
phosphino-boranes, which are regarded as versatile
28–30]
Introduction
storage[43]. In this context, special attention
processes for H
2
should be given to terminal low-coordinated phosphido
One of the main research areas in the field of catalysis
is primarily directed towards finding more efficient catalysts
that are not based on rare, expensive metals such as
ruthenium, palladium or platinum but rather on cheap,
biologically benign, and earth abundant elements. Among the
cheapest, non-toxic, and plentiful transition metals a special
place is taken by iron - an element which is at the center of
many biological processes including the well-known example
of the bacterial dinitrogen fixation[1–3]. Due to its wide
availability as well as the occurrence in a plethora of
biological catalytic sites, iron has been viewed as an
essential component of the next generation of sustainable
complexes with pyramidal or planar geometry[44–56]. In these
cases, the phosphorus atom is connected only to one metal
center and can exhibit either pyramidal geometry with one
lone pair or planar geometry with the lone pair participating in
π bonding[41,57–65]. It should be noted that, among the high
number of bridged phosphido complexes[44,66–71], there are
many reports of transition metal complexes featuring non-
bridging, terminal phosphido ligands[44,46–55,72–79], including
some supported by nacnac ligands[80–85]. However, only
a handful of known terminal phosphido complexes[31,86–97]
incorporate iron and, in most cases, these complexes are
supported by carbonyl or cyclopentadienyl co-ligands.
Reports of the use of an iron(II) β-diketiminato pre-
catalysts[4–9]
.
The utility of synthetic iron complexes as catalysts is
predicated on both: the redox properties of the central metal
as well as the ability to stabilize, with appropriate ligand
2
catalyst, [(Dippnacnac)Fe(CH TMS)], by Webster et al.
[14,27,43,98–102]
to carry out the hydrophosphination of
unsaturated hydrocarbons and dehydrocoupling of primary
and secondary phosphines, postulated the formation of
an intermediate terminal phosphido complex. In the case of
hydrophosphination, the authors proposed that the active
catalyst is a monomeric phosphido complex; however, the
[
a]
Department of Inorganic Chemistry, Chemical Faculty, Gdańsk
University of Technology, 11/12 Gabriela Narutowicza Str. 80-233
Gdańsk, Poland.
E-mail: grubba@pg.edu.pl
active species was isolated as bridging complex,
a
https://chem.pg.edu.pl/kchn/grubba-group
Department of Chemistry and Biochemistry, Florida State University.
Tallahassee, FL 32306, USA.
Department of Chemistry, University of Idaho. Moscow, ID 83844,
USA.
[
(Dippnacnac)Fe(PRH(CH CH=CH Worth
2
)
3
2 2
)] [27].
[
[
b]
c]
emphasizing is that this compound is not only the first
β-diketiminate iron complex bridged by phosphido groups,
but also a perfect example highlighting the catalytic potential
of low-coordinate iron compounds. The hydrophosphination
and dehydrocoupling processes are both ideally suited for
the synthesis of novel P-containing compounds and their
catalytic improvements will expand the access to
E-mail: sstoian@uidaho.edu
https://www.uidaho.edu/sci/chem/people/faculty/stoian
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
functionalized phosphines, diphosphanes, and other
P-containing derivatives.
with tBu
2
PLi did not result in the formation of isolable anionic,
2
terminal phosphido Fe(II) complex. Cy PLi yielded an isolable
Recently, we have reported a new synthetic method to
access iron(II) phosphanylphosphido complexes using as
product, however, to our surprise, it was not the anticipated
anionic complex but rather the contact ion pair 3, where Li is
+
starting
[
diphosphanes, R
propensity of the diphosphorus ligand to undergo P-P bond
cleavage, these iron(II) phosphanylphosphido complexes
have rather limited catalytic potential. Considering this
limitation, we directed our attention to iron(II) complexes with
materials
(Dippnacnac)FeCl Li(dme)
P-P(SiMe
the
β-diketiminato
complex
not separated by solvent molecules (Scheme 2). Reaction
with two equivalents of Cy PLi produced only the anionic
2
complex 4 (Scheme 2), which exhibits a structure analogous
to those of 1 and 2.
][103] and lithium salts of
2
2
)Li (R= iPr, tBu)[ . Due to the
104]
2
3
2
phosphido R P ligands. In this paper, we detail the syntheses,
structures, and spectroscopic characterization of the first
series of terminal phosphido Fe(II) complexes stabilized by
β-diketiminates. We also discuss their thermal stability and
catalytic activity in promoting the dehydrocoupling of
secondary phosphines.
Results and Discussion
Syntheses
We
have
explored
the
reactivity
of
PLi
[
(Dippnacnac)FeCl
2
Li(dme)
2
][103] towards phosphides R
2
Scheme 2. Syntheses of complexes 3 and 4.
(
R= iPr, tBu, Cy, Ph). The outcome of the reaction between
PLi is strongly influenced by the
the iron(II) complex and R
2
donor properties of the solvent. The main products of
reactions performed with equimolar amounts of starting
materials in DME are anionic, terminal phosphido complexes
of iron(II) (1-2) (Scheme 1).
Attempts to obtain a Fe(II) complex bearing two
terminal phosphido ligands were successful only when
Ph
2
PLi
was
employed. Reaction
of
[(Dippnacnac)FeCl
2
Li(dme) ] with Ph PLi in DME in 1:2 molar
2
2
ratio gave a mixture of mono- (2) and diphosphido (5)
complexes. Exclusive formation of 5 was achieved only for a
threefold excess of Ph
2
PLi (Scheme 3). Excess of Ph
2
PLi is
noticeable in the 31P{ H} NMR spectra of reaction mixtures
and this excess of phosphide accelerates the second stage
of the reaction leading to product 5. Complete conversion of
the monophosphido derivative 2 to the diphosphido derivative
1
5
was reached by keeping the reaction mixture at room
temperature for several days. Dark brown crystals of 5 were
isolated from concentrated reaction mixtures at low
temperature with a 37% yield.
Scheme 1. Syntheses of anionic phosphido complexes 1 and 2.
Compounds 1-2 were isolated from concentrated
reaction mixtures at low temperature (first crop at +4 °C and
second crop at -20 °C) as dark violet (1) or dark red (2)
crystals. The yields of reactions were 46% and 29% for 1 and
2, respectively. These species are solvent-separated ionic
compounds where a Li cation is surrounded by three DME
molecules and the anion is the Fe(II) complex bearing
β-diketiminato, chlorido, and phosphido ligands. Reactions
Scheme 3. Synthesis of complex 5.
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
The addition of 12-crown-4 to the DME solutions of
either 1 or 5 led to the complexation of lithium cations by the
crown ether, which resulted in the isolation of crystalline
We note that all terminal phosphido complexes (1-9)
are extremely moisture and oxygen sensitive and were
handled with great care to prevent their decomposition. In
contact with air, for example, dark red, dark violet or dark
green hydrocarbon solutions of 1-9, underwent a color
change to dark brown within seconds. Moreover, crystals of
1-9 disintegrate within minutes into yellow powders when
exposed to air. Notably, the most air-sensitive compounds of
the whole series of terminal phosphido complexes are those
complexes [(Dippnacnac)FeCl(PiPr
and [(Dippnacnac)Fe(PPh [Li(12-crown-4)(dme)][Li(dme)
5’).
2
)][Li(12-crown-4)
2
]
(1’)
3
]
2
)
2
]
2
(
The nature of the solvent exerted a strong influence on
outcomes of reactions between
(Dippnacnac)FeCl Li(dme) ] and R PLi (R= iPr, tBu, Cy, Ph).
the
[
2
2
2
In contrast to the reactions run in DME, we observed that
reactions in toluene at a 1:1 molar ratio proceeded with the
exclusive formation of neutral terminal phosphido complexes
2
bearing iPr P groups (1, 6), due to the smallest steric
protection compared to other isolated compounds with R
ligands.
2
P
(
6-9) (Scheme 4).
During our studies on Fe(II) β-diketiminato complexes
we observed that addition of phosphides to the Fe(III)
III
complex [(Dippnanac)Fe Cl
2
] leads to the formation of Fe(II)
complexes and compounds containing P-P bond. An
example of such reactivity is the reaction of
III
[
(Dippnanac)Fe Cl
2
] with Ph
2
PLi in either DME or toluene
P-PPh and the corresponding
leading to the formation of Ph
Fe(II) complex (Scheme 6).
2
2
Scheme 4. Syntheses of neutral phosphido complexes 6, 7, 8 and 9.
Reactions carried out in toluene gave isolable products
in moderate yields (28-55% for 7-9), with the exception of 6
isolated in low yield (5%). Dark green (6, 8-9) and dark violet
2 2
Scheme 6. Reaction of [(Dippnanac)FeCl ] with Ph PLi.
(
7) crystals of the neutral complexes were obtained via
crystallization in pentane at low-temperatures (first crop at
4 °C and second crop at -20 °C). The neutral phosphido
+
II
[
(Dippnacnac)Fe Cl
2
Li(dme)
2
] was isolated in crystalline
complexes can be also obtained from the corresponding
anionic complexes (Scheme 5). For example, dissolution of
form when the reaction was performed in DME, whereas in
II
toluene a possibly dimeric complex [(Dippnacnac)Fe Cl]
2
crystalline
corresponding neutral complex 9. However, the direct
syntheses of neutral complexes from
(Dippnacnac)FeCl Li(dme) ] and R PLi in toluene were more
effective.
3 in toluene led to the formation of the
might form. Because of this oxidative dimerization of
phosphides, it was not possible to obtain the β-diketiminato
phosphido complexes of Fe(III) in this direct way.
[
2
2
2
Crystal Structures
The monophoshido anionic complexes 1, 1’, 2, 4 and
contact ion pair 3 exhibit similar structural features and are
discussed together. The solid-state structures of anions of 1-
4
are presented in Figure 1, whereas the structure of 1’ is
shown in Figure S1 (ESI). The Fe-site geometry of these
compounds is distorted pseudotetrahedral with
a coordination sphere composed of two N atoms of the
β-diketiminato ligand, one P atom of phosphido ligand and
one chlorido ligand. The Fe center is located out of the plane
of the Dippnacnac ligand. The phosphido ligand is situated
opposite to the β-diketiminato ligand, whereas the Fe-Cl
bond is perpendicular to the Dippnacnac plane. The N1-Fe1-
Scheme 5. Synthesis of neutral phosphido complex 9 from complex 3.
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
N2 bite angles and N-Fe1 bond lengths in complexes 1-4 are
typical for low-coordinated Fe-diketiminato compounds
Table 1)[ . The Fe1-P1 bond distances are in the range
20]
(
2
.371(1)-2.407(1) Å, longer than those observed for
tetrahedral phosphanylphosphido complex
(Dippnacnac)Fe(η -iPr The
)] (2.3638(9)Å)[104]
2
[
2
P-P-SiMe
3
.
elongation of the Fe1-P1 bonds together with the pyramidal
geometry around P1 atoms (Table 1) indicate a single-bond
character for the Fe1-P1 bonds in 1-4.
Figure 2. X-ray structure of complex anion 5. Ellipsoids are shown at 50%
probability. H atoms are omitted for clarity.
Table 1. Selected bond lengths and geometries around iron and
phosphorus atoms for compound 1-9.
ƩFe1a
ƩP1
ƩP2
Complex
Fe1-P1
Fe1-P2
Fe1-N1
Fe1-N2
Fe1-Cl
Fe1-O1
(Å)
(Å)
(Å)
(°)
(°)
1
2.4054(8)
2.371(1)
2.3827(6)
2.3771(9)
2.407(1)
2.366(1)
2.073(2)
2.3623(8)
322.36
316.50
2
.070(2)
2.064(3)
.057(3)
2.042(1)
.045(2)
2.026(2)
.041(2)
2.062(4)
.064(3)
1
2
3
4
5
5
6
7
8
9
’
2.361(1)
2.3012(5)
2.377(1)
2.345(1)
320.32
320.84
326.23
325.22
315.74
314.51
357.08
359.25
334.50
358.39
321.49
322.13
320.94
323.06
2
2
2
2
2.072(4)
2.038(4)
338.85
337.44
2
.473(1)
2.375(2)
.454(2)
’
2.047(4)
2.088(4)
332.36
333.88
2
2.372(1)
1.989(3)
333.73
345.34
325.75
327.68
Figure 1. X-ray structures of complex anions 1, 2, 4, and of the neutral
complex 3 showing the atom-numbering scheme. Ellipsoids are shown at
2.011(3)
2
.001
.001
50% probability. H atoms are omitted for clarity.
2.366
2
2.3663(6)
2.328(2)
2.026(2)
.024(2)
1.990(5)
.988(5)
2
2.129(2)
The diphosphido anionic complexes 5 and 5’ possess
similar structural features as their monophosphido
counterparts 1-4. The molecular structures of 5 and 5’ are
shown in Figure 2 and Figure S2 (ESI), respectively. The
Fe1-P2 bond in both diphosphido complexes 5 and 5’ is
situated perpendicular to the plane of Dippnacnac ligand –
similarly to the Fe1-Cl bond in 1-4 – and is significantly
1
aSum of angles: N1-Fe1-N2, N2-Fe1-P1, P1-Fe1-N2
The X-ray structures of compounds 6, 7, and 9 are
shown in Figure 3. These neutral phosphido complexes differ
in many aspects from 1-4. The geometry around the Fe
center is trigonal planar with two N atoms and one P atom
coordinated to the metal atom. In contrast to 1-4, the Fe atom
is located in the Dippnacnac plane. Similar spatial alignment
of the iron atom was observed for terminal amido complexes
supported by nacnac ligands[20]. When we compared the
longer
.366(1)/2.473(1) for
Moreover, the geometries of both phosphorus atoms in 5 and
’ exhibit a higher degree of planarity than the P atoms in 1-4
Table 1).
than
Fe1-P1
bond
(Fe1-P1/Fe1-P2
=
2
5 and 2.375(2)/2.454(2) for 5’).
5
(
2
anionic and neutral complexes possessing the same R P
groups we noticed that the Fe-P distances are shorter in
case of neutral complexes (Table 1). Compound 8 stands out
from the series of neutral phosphido complexes. Its X-ray
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
structure, shown in Figure 3, indicates additional coordination
of the O atom of the DME molecule to the metal center.
Because of this, the structural features of 8 resemble
a greater degree than those observed for the anionic
complexes 1-4.
resonances, the spectra recorded for the anionic tetrahedral
complexes 1-5 were difficult to interpret. In contrast, the
resonances observed for the neutral species 7-9 (Figures S3-
S8, ESI) were separated and discernible from one another,
which allowed us to rationalize these spectra. These spectra
exhibit resonances within a wide range of chemical shifts
extending
from
+105.78
to
-112.70
ppm.
A comparable wide range of chemical shifts was observed for
Fe(II)-amido[
20]
and
Fe(II)-
β-diketiminate-supported
phosphanylphosphido complexes[ . The chemical shifts
observed for 7-9 depend strongly on the position of the
respective protons relative to the Dippnacnac plane. Protons
located in the plane of the β-diketiminato ligand are shifted
downfield, whereas those normal to the plane resonate at
higher fields. Spectral integration was necessary to
unequivocally assign the observed peaks. The spectra
obtained for the phosphido complexes 7 and 8 exhibit many
similarities to those observed for the planar, trigonal amido
complexes synthesized by Holland group[ . Thus, the
signals of the four isopropyl groups of the Dippnacnac ligand,
as well as those of the two methyl groups of the nacnac
backbone, and accordingly aromatic para and meta protons
are equivalent. Moreover, the signals assigned to the tBu and
Ph groups of 7 and 8, respectively, are also equivalent. This
observation suggests that in solution compounds 7 and 8
adopt a C2v point group symmetry. Furthermore, the solution-
104]
20]
1
based H NMR spectra of 8 do not exhibit signals that can be
associated with a DME molecule, which in the solid-state
X-ray structure was found to be coordinated to the iron atom.
This observation, together with the high symmetry of 8 in
solution, indicates that the DME molecule was removed upon
exposure of crystals to vacuum prior to the preparation of the
NMR sample. Most likely, the loss of the crystal-bound DME
molecule results in a trigonal planar geometry at the metal
Figure 3. X-ray structures of 6-9 showing the atom-numbering scheme.
Ellipsoids are shown at 50% probability. H atoms are omitted for clarity.
1
center. In contrast to the H NMR spectra recorded for 7-8,
the spectrum of 9 exhibits many more signals. Incorporating
the Cy groups in the phosphido ligand of 9 leads not only to
non-equivalent Cy groups but also to a loss of molecular
symmetry and thus to a splitting of the Dippnacnac ligand
resonances.
The coordination geometry of Fe in 8 can be described
as distorted pseudotetrahedral with the coordination sphere
completed by N1, N2, O1 and P1 atom of Ph P ligand.
2
However, the angles N1-Fe1-N2, N2-Fe-P1, P1-Fe1-N1 are
somewhat widened in 8 (ƩFe1 = 334.50° omitting the Fe1-O1
bond) in comparison to anionic complex 2 (ƩFe1 = 320.84°
omitting the Fe1-Cl1 bond) bearing the same phosphido
ligand. Similarly to 1-4, the Fe atom in complex 8 is out of the
plane of Dippnacnac ligand. As indicated by microanalysis of
crystals of 8, the DME ligand can be effectively removed from
the metal center coordination sphere by keeping crystals of 8
57Fe Mössbauer Spectroscopy
To assess the oxidation state of the iron sites we have
recorded a series of 4.2 K, zero-field Mössbauer spectra. The
four-coordinate complexes 1, 2, 4, and 5 exhibit well-defined
quadrupole doublets (Figure 4). These spectra are
characterized by isomer shifts δ = 0.69-0.78 mm/s and
-3
under vacuum (10 Torr) for several hours.
Q
quadrupole splittings E = 2.52-2.67 mm/s, values that are
1H NMR Spectroscopy
typical of high-spin iron(II) sites[105]. In contrast, the 4.2 K
spectrum of the three-coordinate complex 9 (not shown)
exhibits magnetic hyperfine splitting, which collapses into
a broad quadrupole doublet at 100 K. This behavior
demonstrates that the ground state of 9 consists of a quasi-
doublet with a vanishing zero-field splitting[106]. For three-
Solutions of the anionic, 1-5, and neutral, 7-9, terminal
phosphido Fe(II) complexes were studied using H NMR
1
spectroscopy. Despite of their paramagnetic character, many
Fe(II) β-diketiminato complexes can be successfully
characterized by H NMR spectroscopy[15,26]. However, due
to the broadness and overlap of many of the observed
1
coordinate complexes supported by β-diketiminato ligands
such as 9, this behavior originates from the presence of
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
a {z /yz} orbital degeneracy[107]. The zero-field Mössbauer
parameters of 9 determined at 100 K are very similar to those
observed for 7 and 8 at 4.2 K for which we observe well-
defined quadrupole doublets even at low-temperature.
2
Table 2. Zero-field Mössbauer parameters.
Complex
CN

E
Q

L/R
[
mm/s]
[mm/s]
2.644(3)
2.532(3)
2.526(4)
2.676(3)
1.033(3)
1.497(5)
1.21(2)
[mm/s]
1
2
4
4
4
4
3
3
3
0.746(4)
0.778(3)
0.735(4)
0.690(4)
0.552(5)
0.575(6)
0.54(2)
0.31/0.29
0.34/0.30
0.31/0.30
0.31/0.28
0.29/0.29
0.40/0.42
0.51/0.53
4
5
7
8a
9b
aspectrum recorded for a sample exposed to high-vacuum
b
parameters determined at 100 K
Reactivity studies
It was previously postulated that transient terminal
phosphido complexes play a crucial role in the catalytic
dehydrocoupling (DHC) of secondary phosphines[98]. Having
access to multigram quantities of this class of compounds
allowed us to test this hypothesis. In order to get a boarder
and deeper insight into the forms of catalysts under
dehydrocoupling conditions, we studied the thermal stability
of a toluene solutions of phosphido complexes 1, 2, 4, 5, 7, 8
and 9. Heating these solutions to 120°C for 24 hours leads
to the decomposition of the title compounds. The various
diamagnetic decay products were identified using 31P NMR
spectroscopy (for details see ESI). Complexes 2, 5 and 8,
which incorporate Ph
formation of Ph P(p-tol) and diphosphane, Ph
Symmetrical diphosphanes iPr P-PiPr (together with iPr
and Cy P-PCy were also obtained by heating toluene
solutions of 1 (iPr P co-ligand) and 4 and 9 (Cy P co-ligand),
respectively. For a solution of complex 7 (tBu P co-ligand)
only a strong signal of tBu PH was observed. It is worth
2
P co-ligands, decomposed with the
P-PPh
PH)
2
2
2
.
2
2
2
Figure 4. Zero-field 57Fe Mössbauer spectra recorded at 4.2 K for 1, 2, 4,
2
2
5, 7, 8 and at 100 K for 9. The solid red lines are simulations obtained
2
2
using the parameters listed in Table 2.
2
2
mentioning that, albeit much slower, the decomposition of the
phosphido complexes also takes place at room temperature,
with the same phosphorus-based products being identified.
These results suggest that the phosphido complexes can act
The decrease in the isomer shift values δ = 0.54-0.58
mm/s is consistent with the decrease in the coordination
number and is concomitant with a sizable drop in the
quadrupole splitting to E
Q
= 1.0-1.5 (Table 2).
The
as sources of phosphanyl radicals. Whereas the Ph
iPr PH, and tBu PH can be viewed as products of the
reaction of R P· radicals with the solvent (toluene), the
2
P(p-tol),
spectrum recorded for 8 was obtained after exposing the
sample to high-vacuum at room-temperature for several days.
Unlike for all other samples for which the major spectral
component (theoretical simulation shown in red) accounts for
more than 95% of the iron present in the sample, the major
component in the spectrum of 8 accounts for only 75% of the
iron. The remaining amount can be represented by a
quadrupole doublet with parameters analogous to those of
the four-coordinate complexes studied here. This observation
suggests that upon exposure to vacuum 8 loses the DME
solvent molecule incorporated in the crystal leading to a
three-coordinate iron site. Finally, the zero-field Mössbauer
parameters of 7-9 are similar to those of other three-
coordinate ferrous ions supported by β-diketiminato
complexes[108].
2
2
2
symmetrical diphosphanes are formed by the coupling of
phosphanyl radicals. We anticipate that in solution the
coupling of radicals to be far less likely than the reaction of
those radicals with the solvent. The amount of symmetrical
diphosphanes identified in these reaction mixtures is
surprisingly large and can be explained only if the coupling of
the phosphanyl radicals takes place in the inner coordination
sphere of the iron atoms. We anticipate that the starting
phosphido complex
intermediate two-core iron complex possessing bridging
phosphido ligands. This complex can further eliminate Ph P-
PPh to form a dinuclear Fe(I) complex. Very important in this
context is the comparison of thermal reactions of 5 and 8. For
in the reaction solution only Ph P(p-tol) is visible. Because
of its structural features, 5 has no tendency to dimerization
8 dimerizes yielding a short-lived
2
2
5
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
and a symmetrical diphosphane is not formed at all. Similarly,
in the case of decomposition of complex 7 containing more
dilution of the reaction mixture reduced the conversion rate
from 89% to 64% and 44%, respectively (Figure S18, ESI).
Furthermore, we have also tested the catalytic activity
of the toluene solution of 8 after heating this solution at
120°C for 24 hours. Despite decomposition of 8 (with the
crowded phosphido ligand tBu
prevented the formation of dimeric Fe intermediates,
whereas tBu P radical is released into solution and reacts
only with the solvent yielding tBu PH.
2
P, a steric interaction
2
2
formation of Ph
probably diiron complexes) this solution exhibited high DHC
catalytic conversion of Ph PH (Table 3, run 9, 90%). This
2
P(p-tol), diphosphane Ph
2
P-PPh
2
and
We investigated the catalytic activity of phosphido
iron(II) complexes possessing different geometries, anionic
2
or neutral character, and diverse R
have tested the scope and the extent of the DHC for the
following secondary phosphines: Ph PH, tBuPhPH, tBu PH,
Cy PH, and (iPr N) PH. All runs were carried out under the
2
P ligands (1-5, 7-9). We
behavior together with the lack of catalytic activity of
investigated complexes at room temperature, suggests that
the diiron complexes could play an important role in DHC of
2
2
2
2
2
Ph
2
PH. Additionally, we tested this reaction with catalytic
Li(dme) ] (Table 3, run 10),
same reaction conditions: 5 mol% of phosphido complex in
amounts of [(Dippnacnac)FeCl
2
2
toluene heated at 120°C in a closed Schlenk tube for 24 h.
the starting material for the syntheses of all phosphido
complexes. However, this compound exhibits no catalytic
activity in DHC of secondary phosphines.
3
1
The reaction progress was monitored by
spectroscopy. We have identified the formation of
diphosphane R P-PR only in runs involving Ph PH. A similar
P
NMR
2
2
2
For previously reported dehydrocoupling of secondary
phosphanes with Zr-catalysts, a mechanism of σ-bond
metathesis was postulated[30]. However, in contrast to the
Fe(II) catalysts, the Zr-catalyzed reactions proceed both with
aryl and alkyl substituted phosphines. Moreover, our
reactivity studies of phoshido Fe(II) complexes indicates that
they also act as a source of phosphanyl radicals. This
observation suggests a radical-mediated mechanism for
dehydrocoupling reactions involving Fe(II) complexes. Our
DFT calculations also support a radical-based mechanism.
Thus, it was found that the stability of phosphanyl radicals is
strongly dependent on the size and type of the P-substituent
[
98]
reactivity was observed recently in the dehydrocoupling
and hydrophosphination[
31]
reactions catalyzed by Fe(II)
complexes, which were also limited to the aromatic
derivatives of phosphines. Catalytic activity in the
2
dehydrocoupling of Ph PH (Scheme 7) was observed for all
tested Fe(II) complexes.
and decreases such that: Ph
2
P·> tBuPhP· > (iPr
2 2
N) P· >
tBu P· (for details see ESI). The Ph
2
2
P· radical exhibits the
highest degree of spin density delocalization due to the
presence of aromatic rings. Furthermore, it has the highest
value of radical stabilization energy (RSE)[109] of the entire
series of studied radicals. These results can explain the lack
of reactivity of alkyl- and amino- substituted secondary
phosphines in our DHC experiments.
2
Scheme 7. Dehydrocoupling (DHC) of Ph PH.
2
Table 3. The extent of conversion of Ph PH using Fe(II) phosphido
complexes.
Conversion of Ph
2
PH
Run
Complex [Fe]
to Ph
2
PPPh
89
88
86
90
88
98
89
86
90
0
2
(%)
It is important to stress that the monomeric complex 8
is not stable under our reaction conditions (see stability
studies) and the most plausible explanation for its observed
catalytic activity is the formation of a dimeric species in the
catalytic cycle. The perfect examples confirming this
hypothesis are the visible-light and thermal driven catalytic
reactions employing the commercially available diiron
1
2
3
4
5
6
7
8
9
1
2
3
4
5
7
8
9
8 (after heating)
(Cp = η5-C
compound [CpFe(CO)
recently reported by Waterman and co-workers[110,111]
2
]
2
5 5
H ) as precatalyst
10
2 2
[(Dippnacnac)FeCl Li(dme) ]
.
Moreover, the Fe(I)-Fe(I) dimers play crucial roles in
biologically important systems including [Fe-Fe]
hydrogenases. Such moieties are electron rich and favor
oxidative additions in catalytic cycles [112]. The low oxidation
We observed a high conversion of Ph
86-98%) for all runs involving phosphido complexes (run
entries 1-8 in Table 3). It is worth mentioning that small
amounts of Ph P(p-tol) (5-8 mol%) were also detected in all
DHC experiments catalyzed by phosphido complexes (run
entries 1-9), which is the most probable product of a side
2 2 2
PH to Ph P-PPh
(
state in the postulated Fe(I) dimers strongly suggests the
formation of a Fe-Fe bond. Isolated complexes of iron with
unsupported Fe-Fe bond not involving CO ligands are,
2
however, extremely rare[113]
.
reaction of Ph
reaction of complex 8 and Ph
2
P· radicals with the solvent. Moreover, for the
PH, we have also tested the
2
effect of varying the dilutions of the reaction mixture on the
conversion of secondary phosphines to symmetrical
diphosphanes. We observed that the two- and four-fold
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
Conclusions
parameters; hydrogen atoms were usually refined using the isotropic
model with Uiso(H) values fixed to be 1.5 times Ueq of C atoms for
–
3 2
CH or 1.2 times Ueq for –CH, –CH groups and aromatic H. The
We found that a series of terminal phosphido complexes of
crystallographic details together with ORTEP drawings of obtained
compounds are placed in ESI. For the structure of 7, the P atom and
tert-buthyl groups were refined as positional disordered over two
positions (special position for the mentioned atoms, glade plane) by
using the PART -1 command (in this model the occupancies were
refined to 0.5 and 0.5). The anisotropic displacement parameters of
the methyl carbon atoms (c17 c18 c19 c21 c22 c23) were each
constrained to be identical. The two carbon atoms P1, c16 and c20
were refined isotopically, by using ISOR command. All bond
distances C-C and P-C in the disordered sections were restrained to
be the same within a standard deviation of 0.002 Å.
Fe(II) supported by
straightforwardly synthesized
(Dippnacnac)FeCl Li(dme) ] with phosphides R
2
a
β-diketiminato ligand can be
via the reaction of
PLi (R= iPr,
[
2
2
tBu, Cy, Ph). The nature of the reaction products is dictated
by solvent and reaction stoichiometry. This new series of
terminal phosphido complexes includes neutral trigonal
planar complexes, which are coordinatively unsaturated;
anionic tetrahedral complexes; and species featuring two
phosphido ligands. The reactivity studies of selected terminal
phosphido Fe(II) complexes revealed that such compounds
can act as sources of phosphanyl radicals. A preliminary
investigation of the catalytic activity of these phosphido
complexes showed that they are good catalysts for
dehydrocoupling of phosphines. We proposed that the DHC
Crystallographic data for the structures of 1, 1’, 2, 3, 4, 5, 5’, 6, 7, 8,
and 9 reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication No.
CCDC 1560588-1560598. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: (+44) 1223-336-033; E-mail: deposit@ccdc.cam.ac.uk). For
more crystallographic details see ESI.
2
of Ph PH undergoes through a radical-mediated mechanism.
Additional studies on the reactivity of terminal phosphido
complexes of Fe(II) are in progress and will be published in
due course.
The temperature-dependent, zero-field 57Fe Mössbauer spectra were
recorded using a spectrometer operated in a constant acceleration
mode. The instrument was fitted with a flow-type cryostat cooled with
liquid helium. The source consisted of 100 mCi 57Co dispersed in
Experimental Section
rhodium foil. The isomer shifts are reported against the centroid of a
spectrum of α-iron metal foil recorded at room temperature.
Materials and methods
All manipulations were performed under an Ar atmosphere in flame-
dried Schlenk-type glassware on a vacuum line or in a dry box.
Solvents 1,2-dimethoxyethane (DME) and toluene were dried over
K/benzophenone and distilled under argon. Pentane was dried over
Na/benzophenone/diglyme and distilled under argon, while petroleum
Synthetic procedures
General procedure for the synthesis of phosphides: 5 mol%
excess of nBuLi (2.5 M in hexane) or tBuLi (1.7 M in pentane) was
added dropwise to a solution of R PH in petroleum ether at -30°C.
2
The resulting reaction mixture was then slowly allowed to warm to RT
and stirred overnight at this temperature. Afterwards, obtained
2
precipitation of R PLi, with the yield higher than 90%, was filtered off
ether was dried over sodium-potassium alloy and also distilled under
argon. 31P{ H} NMR (external standard 85% H
1
PO
), 1H (internal
3
4
standard Me
4
Si) spectra were recorded on a Bruker AV400 MHz
spectrometer at room and low temperature. 31P NMR and 31P{ H}
NMR spectra used for quantitative integration were recorded at 25 °C
using an inverse-gated decoupling pulse sequence in case of 31P{ H}
NMR spectra, with 64 scans, using a -250 to 150 ppm spectral width,
1
in an inert atmosphere.
1
General procedure for the synthesis of anionic phosphido iron
complexes supported by β-diketiminates: To the stirred
suspension of [(Dippnacnac)FeCl
16 K data points, with a relaxation delay of 80 s. Data were
2 2
Li(dme) ] in DME, the solution of
processed using Bruker’s Topspin 3.5 software. The accuracy of the
2
R PLi in DME at -30°C was added. The temperature of the reaction
method was determined by integration of 31P NMR and 31P{ H} NMR
1
was maintained at -30°C to -20°C for half hour. A color change from
light yellow to almost black was observed. The reaction mixture was
stirred overnight at RT. Afterwards, the resulting solution was
concentrated to the half of volume and the precipitated LiCl was
filtered off. First of all, the solution was stored at +4°C to yield dark
crystals, which was isolated, washed with cold pentane at -50°C and
dried in vacuo. Cooling to -20°C of the mother liquor gave an
additional crop.
spectra of reference samples containing Ph
PPh , where the biggest error was 2%. Ph PH, Cy
were purchased from Aldrich and used as received. Literature
methods were used to prepare i-Pr and
PH[114]
(Dippnacnac)FeCl Li(dme)
][103]. All obtained compounds are very
moisture and air-sensitive.
2
PH, Ph
3
P, and Ph
2
P-
PH
2
2
2
PH, and t-Bu
2
2
[
2
2
Diffraction data of complexes 1’, 2, 3, 5, 5’, 6, 7, 8, and 9 were
collected on diffractometer equipped with a STOE image plate
detector using MoKα radiation with graphite monochromatization (λ
[
(Dippnacnac)FeCl(PiPr
1 mmol) of [(Dippnacnac)FeCl
PLi in 3 mL of DME yielded 0.415 g (0.459 mmol,
6%) dark violet crystals. Crystals were dried under high vacuum
resulting in the removal of non-coordinated DME. Elemental Analysis
Found: C, 62.31; H, 9.006; N, 3.41. Calc for C47 85ClFeLiN P: C,
2.49; H, 9.484; N, 3.10%).
(Dippnacnac)FeCl(PPh )][Li(dme)
mmol) [(Dippnacnac)FeCl Li(dme) ] in 2.5 mL of DME with 0.096 g
0.5 mmol) Ph PLi in 1.5 mL of DME yielded 0.140 g (0.144 mmol,
9%) dark red crystals. Elemental Analysis (Found: C, 65.02; H,
2
)][Li(dme)
3
]·dme (1): Reaction of 0.732 g
(
2
Li(dme)
2
] in 5 mL of DME with 0.124
g (1 mmol) of iPr
2
=
0.71073 Å). The experimental diffraction data of 1 and 4 were
4
collected with a KM4CCD kappa-geometry diffractometer equipped
with a Sapphire2 CCD detector using MoKα radiation source with a
graphite monochromator (λ = 0.71073 Å). Determination of the unit
cells and data collection was carried out at 120 K for 5, 6, 7, 8 and 9,
at 130 K for 2 and 3, at 150 K for 1, 1’ and 5’ and at 298K for 4. The
(
H
2 6
O
6
[
2
3
] (2): Reaction of 0.366 g (0.5
2
2
2
structures were solved by direct methods and refined against F
(
2
using the Shelxs-97 and Shelxl-97 programs[115] run under WinGX[116]
Non-hydrogen atoms were refined with anisotropic displacement
.
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201800850
FULL PAPER
8
.000; N, 3.29. Calc. for C53
H
81ClFeLiN
2
O
6
P: C, 65.53; H, 8.404; N,
1H NMR (400 MHz; toluene-d
77.22 (4H, Cy P), 58.12 (1H, Cy
nacnac), 31.74 (2H, Cy P), 20.90 (3H, Me nacnac), 19.67 (2H, m-H),
10.41 (2H, m-H), 6.45 (6H, iPr methyl), 1.33 (4H + 4H, broad signal,
Cy P), -9.51 (6H + 6H, broad signal, Me nacnac), -1.33 (4H, Cy P) -
8
; Me
4
Si; 25°C): δ = 105.78 (2H, Cy
2
P),
2.88%).
2
2
P), 50.33 (1H, Cy
2
P), 35.50 (3H, Me
[(Dippnacnac)FeCl(PCy
(1 mmol) [(Dippnacnac)FeCl
(1 mmol) Cy PLi in 3 mL of DME yielded 0.517 g (0.526 mmol, 53%)
2
)Li(dme)
2
]·(dme) (3): Reaction of 0.732 g
2
2
Li(dme)
2
] in 5 mL of DME with 0.204 g
2
2
2
dark crystals. Elemental Analysis (Found: C, 64.42; H, 9.309; N, 3.09.
Calc for C53 93ClFeLiN P: C, 64.72; H, 9.531; N, 2.84%).
(Dippnacnac)FeCl(PCy
g (1 mmol) [(Dippnacnac)FeCl
2 mmol) Cy
45.04 (2H, broad signal, iPr methine), -59.31 (1H, p-H), -75.35 (1H,
p-H), -88.88 (6H, iPr methyl), -99.89 (2H, broad signal, iPr methine)
ppm. The resonance of methine proton of the Dippnacnac ligand was
not observed.
H
2 6
O
[
2
)][Li(dme)
3
](dme)1.5 (4): Reaction of 0.732
Li(dme) ] in 5 mL of DME and 0.408 g
2
2
(
2
PLi in 6 mL of DME yielded 0.560 g (0.521 mmol, 52%)
dark crystals. Drying under high vacuum resulted in the removal of
non-coordinated DME. Elemental Analysis (Found: C, 63.28; H,
General procedure for the dehydrocoupling of phosphines: To
the solutions containing
complexes stabilized by β-diketiminato co-ligand in 0.35 mL of
toluene, the phosphine Ph PH was added dropwise at room
temperature. The reaction mixture was stirred at 120 °C for 24 h.
5 mol% of selected phosphido iron
2 8
9.228; N, 2.53 Calc for C57H103ClFeLiN O P: C, 63.76; H, 9.670; N,
2.61%).
2
[
(Dippnacnac)Fe(PPh
mmol) [(Dippnacnac)FeCl
1.5 mmol) Ph PLi in 4.5 mL of DME yielded 0.217 g (0.186 mmol,
7%) dark brown crystals (co-crystallization with LiCl in ratio 1:1). To
2
)
2
][Li(dme)
3
] (5): Reaction of 0.366 g (0.5
] in 2.5 mL of DME and 0.288 g
2
Li(dme)
2
2 2 2
Conversion of Ph PH to Ph P-PPh was confirmed by signal
(
3
2
31
31
1
integration in the P and P{ H} NMR spectra.
In the case of run entry 9, a solution of complex 8 (0.021 g, 0.03
mmol) in 0.35 mL of toluene was stirred at 120°C for 24h. After this
achieve full conversion in this reaction, the mixture was allowed to
react for a few days at room temperature. Elemental Analysis (Found:
time, the solution was cooled to RT and Ph
2
PH (0.111 g, 0.6 mmol)
2 6 2
C, 67.40; H, 7.825; N, 2.63. Calc. for C65H91FeLiN O P + LiCl: C,
was added dropwise. The reaction mixture was stirred again at 120°C
6
7.10; H, 7.883; N, 2.41%).
for 24 h. Conversion of Ph
2
PH to Ph
2
P-PPh
2
was confirmed by signal
integration in the 31P and 31P{ H} NMR spectra.
1
General procedure for the synthesis of neutral phosphido iron
complexes supported by β-diketiminates: To the stirred
suspension of [(Dippnacnac)FeCl
Ph
Ph
2
PH: 31P{ H} NMR (400 MHz, C
1
6
D
6 3
, H PO
4
, 25°C): δ = -40.6 ppm
: 31P{ H} NMR (400 MHz, C
1
PO , 25°C): δ = -14.9
2
P-PPh
2
6 6
D , H
3
4
117]
2
Li(dme)
2
]
in toluene, the
ppm[
suspension of R PLi in toluene at -30°C was added. The temperature
2
of the reaction was maintained at -30°C to -20°C for half hour. A color
change from light yellow to almost black occurred. The reaction
mixture was stirred overnight at RT. Afterwards, the solvent was
evaporated under vacuum and the residue was washed with pentane
Table 4. Experimental details for the dehydrocoupling of phosphines
catalyzed by phosphido iron complexes.
Mass of
iron
Conversion
of Ph PH
to
Mass of
Ph PH
2
(20 mL). The solution was concentrated to the half of volume and LiCl
Run #
Complex
complex
catalyst
2
was filtered off. The solution was then stored at +4°C to yield dark
crystals, which were isolated, washed with cold pentane at -50°C and
dried in vacuo. Cooling to -20°C of the mother liquor gave an
additional crop.
(g)
Ph
2
P-PPh
(%)
89
2
(g)
1
2
3
4
5
6
7
8
9
1
0.027
0.026
0.027
0.028
0.030
0.018
0.020
0.019
0.021
0.111
0.100
0.101
0.098
0.096
0.107
0.106
0.107
0.111
2
88
[
[
(Dippnacnac)Fe(PiPr
(Dippnacnac)FeCl Li(dme)
PLi in 3 mL of toluene yielded 0.015 g (0.025 mmol, 5%)
2
)] (6): Reaction of 0.366
g (0.5 mmol)
3
86
2
2
] in 2.5 mL of toluene and 0.062 g (0.5
4
90
mmol) i-Pr
2
5
88
dark green crystals.
(Dippnacnac)Fe(PtBu
(Dippnacnac)FeCl Li(dme)
PLi in 6 mL of toluene yielded 0.337 g (0.545 mmol, 55%) dark
7
98
[
2
)] (7): Reaction of 0.732
g (1 mmol)
8
89
[
2
2
] in 5 mL of toluene and 0.152 g (1 mmol)
9
86
t-Bu
2
8 (after heating)
90
violet crystals. Elemental Analysis (Found: C, 71.69; H, 9.630; N,
Not
1
0
[LFeCl
2
Li(dme)
2
]a
0.018
0.093
4
.76. Calc for C37
H
59FeN
2
P: C, 71.83; H, 9.612; N, 4.53%).
; Me Si; 25°C): δ = 57.28 (6H, Me
P), 48.02 (1H, CH nacnac), 9.99 (4H, m-H),
.66 (12H, iPr methyl), -46.02 (12H, iPr methyl), -46.52 (4H, iPr
methine), -112.42 (2H, p-H) ppm.
(Dippnacnac)Fe(PPh )(dme)] (8): Reaction of 0.732 g (1 mmol)
(Dippnacnac)FeCl Li(dme) ] in 5 mL of toluene and 0.192 g (1 mmol)
PLi in 6 mL of toluene yielded 0.256 g (0.365 mmol, 37%) dark
observed
1
H NMR (400 MHz; toluene-d
nacnac), 50.78 (18H, tBu
1
8
4
aL = Dippnacnac
2
General procedure for the thermal stability investigation of
phosphido complexes supported by β-diketiminates: In the case
of all discussed complexes, two solutions were prepared as the result
of the dilution of the pure crystals (0.025 mmol) in 0.35 mL. Part of
them was stirred at room temperature for 24 h, while the other part
was heated to 120°C and stirred at that temperature for 24 h.
[
[
Ph
2
2
2
2
green needle-shape crystals (co-crystallization with LiCl in 1:1 ratio).
Drying under high vacuum resulted in the removal of the DME
molecule. Elemental Analysis (Found: C, 70.22; H, 7.357; N, 3.99.
Reaction progress was monitored by 31P and
spectroscopy.
31
P{ H} NMR
1
Calc for C41
H NMR (400 MHz; toluene-d
nacnac), 35.52 (8H, Ph
H
51FeN
2
P + LiCl: C, 70.24; H, 7.332; N, 3.99%).
; Me Si, 25°C): δ = 79.69 (1H, CH
P), 34.77 (2H, Ph P), 33.02 (6H, Me
nacnac), -11.96 (12H, iPr methyl), -12.10 (4H, m-H), -74.02 (2H, p-H),
PH: 31P{ H} NMR (400 MHz, C
1
PO
, 25°C): δ = -15.0 ppm
, 25°C): δ = 19.6 ppm
iPr
tBu
iPr
2
6 6
D , H
3
4
1
8
4
PH: 31P{ H} NMR (400 MHz, C
1
2
6 6
D , H
3
PO
4
2
2
: 31P{ H} NMR (400 MHz, C
1
D
6
D
6
D
6
, H
, H
, H
, 25°C): δ = -12.1
, 25°C): δ = -14.9
, 25°C): δ = -21.7
2
P-PiPr
2
6
6
6
3
PO
3
PO
3
PO
4
4
4
ppm[
118]
-
[
94.92 (12H, iPr methyl), -99.68 (4H, iPr methine) ppm.
(Dippnacnac)Fe(PCy )] (9): Reaction of 0.732
Li(dme) ] in 5 mL of toluene and 0.204 g (1 mmol)
PLi in 6 mL of toluene yielded 0.187 g (0.279 mmol, 28%) dark
1
Ph
2
P-PPh
2
: 31P{ H} NMR (400 MHz, C
2
g (1 mmol)
ppm[
117]
[
(Dippnacnac)FeCl
2
2
1
Cy
2
P-PCy
2
: 31P{ H} NMR (400 MHz, C
Cy
2
ppm[
117]
green crystals. Elemental Analysis (Found: C, 73.42; H, 9.563; N,
.24. Calc for C41 P: C, 73.41; H, 9.467; N, 4.18%).
31
1
PPh2(p-tol)
ppm[119]
:
6 6 3 4
P{ H} NMR (400 MHz, C D , H PO , 25°C): δ = -5.3
4
H63FeN
2
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European Journal of Inorganic Chemistry
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FULL PAPER
102, 3031–3065.
Table 5. Experimental details for the thermal stability investigations of
phosphido iron complexes.
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Mass of iron complex
Iron complex
Identified products
(g)
iPr
iPr
Ph P-PPh
PPh
Cy P-PCy
PPh
tBu
Ph P-PPh
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0.023
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Reaction of [(Dippnacnac)FeCl
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2 2
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.113 mmol, 23%).
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Acknowledgements
R.G., K.K. and Ł.P. thank the National Science Centre NCN,
Poland (Grant 2016/21/B/ST5/03088) for financial support.
K.K. thanks Prof. Hans-Jörg Krüger and Dr. Harald Kelm for
an internship opportunity (Project ‘Inter PhD’ no.
POKL.04.01.01-00-368/09) and for their guidance and
supervision. R.G. and K.K. thank Natalia Szynkiewicz for
DFT calculations of radicals. The authors thank TASK
Computational Center for the access to computational
resources. Mössbauer spectra were recorded at NHMFL
which is supported by the NSF award DMR-1157490 and by
the State of Florida. S.A.S. acknowledges partial support
from the University of Idaho. Partial support for A.D.-A from
the NSF (CHE 1464955) is also acknowledged.
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
The facile synthesis of a novel family
of iron(II) complexes supported by
terminal phosphido ligands is
presented. The structures of the
Phosphido complexes
Kinga Kaniewska, Alina Dragulescu-
Andrasi, Łukasz Ponikiewski, Jerzy
Pikies, Sebastian A. Stoian* and Rafał
Grubba*
terminal
phosphido
complexes
described here could be easily tuned
by a judicious choice of solvent and
by a change in the stoichiometry of
Page No. – Page No.
the
reaction.
A
preliminary
Syntheses, structures and reactivity
of terminal phosphido complexes of
iron(II) supported by a
investigation of the catalytic activity
of these phosphido complexes
showed that they exhibit good
β-diketiminato ligand
catalytic
activity
in
the
dehydrocoupling of phosphines.
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