Synthesis and structure of iron (II) complexes of functionalized 1,5-diaza-3,7-diphosphacyclooctanes

Article abstract of DOI:10.3390/molecules25173775

In order to synthesize new iron (II) complexes of 1,5-diaza-3,7-diphosphacyclooctanes with a wider variety of the substituents on ligands heteroatoms (including functionalized ones, namely, pyridyl groups) and co-ligands, it was found that these ligands with relatively small phenyl, benzyl, and pyridin-2-yl substituents on phosphorus atoms in acetonitrile formed bis-P,P-chelate cis-complexes [L₂Fe(CH₃CN)₂]²⁺ (BF₄)₂^?, whereas P-mesityl-substituted ligand formed only monoligand P,P-complex [LFe(CH₃CN)₄]²⁺ (BF₄)₂^?. 3,7-dibenzyl-1,5-di(1⁰-(R)- phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane reacted with hexahydrate of iron (II) tetrafluoroborate in acetone to give an unusual bis-ligand cationic complex of the composition [L₂Fe(BF₄)]⁺ BF₄^?, where two fluorine atoms of the tetrafluoroborate unit occupied two pseudo-equatorial positions at roughly octahedral iron ion, according to X-ray diffraction data. 1,5-diaza-3,7-diphosphacyclooctanes replaced tetrahydrofurane and one of the carbonyl ligands of cyclopentadienyldicarbonyl(tetrahydrofuran)iron (II) tetrafluoroborate to form heteroligand complexes [CpFeL(CO)]⁺BF₄^?. The structural studies in the solid phase and in solutions showed that diazadiphosphacyclooctane ligands of all complexes adopted chair-boat conformations so that their nitrogen atoms were in close proximity to the central iron ion. The redox properties of the obtained complexes were performed by the cyclic voltammetry method.

Full text of DOI:10.3390/molecules25173775

molecules
Article
Synthesis and Structure of Iron (II) Complexes of
Functionalized 1,5-Diaza-3,7-Diphosphacyclooctanes
Yulia S. Spiridonova, Yulia A. Nikolaeva, Anna S. Balueva *, Elvira I. Musina , Igor A. Litvinov ,
Igor D. Strelnik, Vera V. Khrizanforova, Yulia G. Budnikova and Andrey A. Karasik
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of
Sciences, Arbuzov str. 8, 420088 Kazan, Russia; aik79@iopc.ru (Y.S.S.); nikolaeva@iopc.ru (Y.A.N.);
elli@iopc.ru (E.I.M.); litvinov@iopc.ru (I.A.L.); igorstrelnik@iopc.ru (I.D.S.);
KhrizanforovaVera@yandex.ru (V.V.K.); yulia@iopc.ru (Y.G.B.); karasik@iopc.ru (A.A.K.)
*
Correspondence: balueva62@mai.ru; Tel.: +78-43-272-7392
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: György Keglevich
Received: 24 July 2020; Accepted: 17 August 2020; Published: 19 August 2020
ꢀ
ꢁꢂꢃꢄꢅꢆ
Abstract: In order to synthesize new iron (II) complexes of 1,5-diaza-3,7-diphosphacyclooctanes with
a wider variety of the substituents on ligands heteroatoms (including functionalized ones, namely,
pyridyl groups) and co-ligands, it was found that these ligands with relatively small phenyl, benzyl,
and pyridin-2-yl substituents on phosphorus atoms in acetonitrile formed bis-P,P-chelate cis-complexes
2
+
−
[
[
L Fe(CH CN) ] (BF ) , whereas P-mesityl-substituted ligand formed only monoligand P,P-complex
2
3
2
2
4 2
−
+
0
LFe(CH CN) ] (BF ) . 3,7-dibenzyl-1,5-di(1 -(R)- phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane
3
4
4 2
reacted with hexahydrate of iron (II) tetrafluoroborate in acetone to give an unusual bis-ligand cationic
+
−
complex of the composition [L Fe(BF )] BF , where two fluorine atoms of the tetrafluoroborate
2
4
4
unit occupied two pseudo-equatorial positions at roughly octahedral iron ion, according to X-ray
diffraction data. 1,5-diaza-3,7-diphosphacyclooctanes replaced tetrahydrofurane and one of the
carbonyl ligands of cyclopentadienyldicarbonyl(tetrahydrofuran)iron (II) tetrafluoroborate to form
+
−
heteroligand complexes [CpFeL(CO)] BF4 . The structural studies in the solid phase and in solutions
showed that diazadiphosphacyclooctane ligands of all complexes adopted chair-boat conformations
so that their nitrogen atoms were in close proximity to the central iron ion. The redox properties of
the obtained complexes were performed by the cyclic voltammetry method.
Keywords: 1,5-diaza-3,7-diphosphacyclooctane; iron; complex; synthesis; structure; redox properties
1
. Introduction
The complexes of aminomethylphosphines with earth-abundant metals, such as nickel, cobalt,
and iron, draw permanent attention as molecular catalysts and electrocatalysts for the activation
of small molecules (H , N , CO , etc.) [ ]. The metal complexes of cyclic and acyclic
1–6
2
2
2
aminomethylphosphines-containing amine centers in the main framework of a diphosphine ligand as
proton relay act as the mimetics of the [FeFe]- and [NiFe]-hydrogenases, which are fast and efficient
catalysts for the oxidation/generation of H2 [1–4]. The most studied objects are the nickel (II) complexes
of 1,5-diaza-3,7-diphosphacyclooctanes, which show the high effectiveness in the electrocatalysis,
both of the reduction of protons to generate H and of the oxidation of H [
1–
3,
7], and have been
2
2
successfully used as both the cathode and anode catalysts in fuel cells [
4
,8
,9
]. A very wide variation of
the substituents on the ligands heteroatoms has been performed for these nickel-containing complexes
in order to find the most effective and convenient catalysts for different applications [2,7,8,10–13].
It has been shown that the nature of the central ion could essentially influence on the
type of the complexes formed on the basis of 1,5-diaza-3,7-diphosphacyclooctanes. In particular,
the interaction of these ligands with chromium dichloride leads to the unexpected ring expansion
Molecules 2020, 25, 3775; doi:10.3390/molecules25173775
www.mdpi.com/journal/molecules

Molecules 2020, 25, 3775
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and the formation of the chromium (II) complexes of 12-membered P N and 16-membered P N
4
3
3
4
macrocyclic aminomethylphosphines [14]. Another example of the ring expansion of 1,5-di-p-tolyl-3,7-
0
di(pyridine-2 -yl)-1,5-diaza-3,7-diphosphacyclooctane on Au3 cluster into 16-membered P N
4
4
macrocycle has been observed [15]; it should be mentioned that this ligand transformation does
not take place, both for other diazadiphosphacyclooctane ligands [15] and for other gold cores [16 17].
,
These data indicate that the formation of the metal complexes of diazadiphosphacyclooctanes cannot
be considered a completely predictable process.
The iron complexes of 1,5-diaza-3,7-diphosphacyclooctanes are less studied in spite of their
promising activity in H splitting and electrooxidation [3, –20] and N binding and activation [5].
18
In particular, the set of substituents on phosphorus atoms of the investigated P N ligands is
2
2
2
2
restricted and includes phenyl [21
groups [24], whereas the nitrogen atoms bear phenyl or benzyl groups. These diphosphines are
used for the synthesis of bis-ligand iron (II) complexes [21 23] or more often for the preparation of
heteroligand complexes containing cyclopentadienyl [19 20 22 25] or benzenedithiolate ligands [24].
The cyclopentadienyl-containing complexes draw the main interest due to their activity in hydrogen
–24], tert-butyl [19,20,24,25], cyclohexyl [21,24], and benzyl
,
,
, ,
electrooxidation [
3
,
19
,
20
,
25]. The only additionally functionalized diazadiphosphacyclooctane
0
ligand, namely, 1,5-diphenyl-3,7-bis(2 -diphenylphosphinoethyl)-1,5-diaza-3,7-diphosphacyclooctane,
has been used for the synthesis of unusual square planar iron complexes stabilized by the
coordination with exocyclic phosphino groups, which are able to activate both hydrogen and nitrogen
molecules [5,18].
It should be mentioned that the varying of the substituents on the nitrogen atoms of acyclic P N
2
ligands, namely, bis(diethylphosphinomethyl)organylamines, has shown the essential influence of the
nature of these substituents on the activity of the corresponding iron (II) complexes in the hydrogen
electrooxidation [26]. These data indicate that the wider variety of the diazadiphosphacyclooctane
ligands of iron complexes and the further study of their structures and properties is expedient for the
search of new catalysts on the basis of these compounds.
The synthesis of various types of homo- and heteroligand new iron (II) complexes of
1,5-diaza-3,7-diphosphacyclooctanes, including additionally functionalized P-pyridyl substituted
ligands, and the results of our study of their structures and redox properties were reported in
this contribution.
2
. Results
,5-Diaza-3,7-diphosphacyclooctanes
atoms, namely, phenyl, benzyl, and pyridin-2-yl groups, reacted with hexa(acetonitrile)iron (II)
1
1–4 with relatively small substituents on phosphorus
2
+
tetrafluoroborate in acetonitrile to give yellow or orange bis-ligand complexes [L Fe(CH CN) ]
2
3
2
−
(BF4)2
6–9, according to the data of elemental analysis. In ESI or MALDI mass-spectra of all these
complexes, the peaks of ions containing two diazadiphosphacyclooctane moieties, iron ion, and in
31
some cases, various co-ligands were observed. P-NMR spectra of complexes 6–9 showed two
complex second-order multiplets of the equal intensity in the ranges 25.6–34.7 and 34.2–41.2 ppm.
This spectral pattern is typical for AA’BB’ spin system of cis-iron (II) complexes with the strongly
distorted octahedral configuration of the central ion-containing two P,P-chelating diphosphine ligands
and two acetonitrile co-ligands, which occupy formally equatorial positions [21], so it indicated the
1
analogous cis-structures of the complexes
6–9
(Scheme 1). Their H-NMR spectra also indicated the
highly asymmetric structures of the complexes. The substituents on phosphorus atoms were mutually
nonequivalent; the substituents on nitrogen atoms provided two sets of the corresponding signals,
which probably corresponded to the chair-boat conformation of the cyclic diphosphine ligands so that
two halves of the ligand molecule were in the different spatial environment (Figure 1). One of the
nitrogen atom (and the corresponding substituent) of each ligand was in close proximity to the second
diazadiphosphacyclooctane ligand, whereas the other nitrogen atom and its substituent were located

Molecules 2020, 25, 3775
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on the side of acetonitrile ligand and took the remote positions. The very complex spectral patterns
observed for the protons of P-CH -N fragments were in accordance with these conformations.
2
R2
2
N
R1
R2
R1
R2 R2
P
Fe
1
/
2
[Fe(CH
CH CN
3
CN)
6
](BF
4
)
2
P
[
CpFe(CO)
2
(THF)]BF
4
C
N
P
P
R2
P
N
N
P
BF
4
R1
O
N
N
R1
2
BF
4
H
H
3
CCN
toluene,
60-70 C
P
R1
Fe
3
R1
R2
1 - 5
3
CCN
P
R1
R1
N
[Fe(CH
3
CN)
6
](BF
4
)
2
1/2 [Fe(H
acetone
2 6 4 2
O) ](BF )
R2
12, 13
3
CH CN
N
R2
6 - 9
R2
R2
2
R2
2
N
N
N
R1
R1
R1
R1
P
P
R1
R2
NCCH3
NCCH
P
P
R2
P
P
H
2
O
N
N
2 BF
4
+
F
F
F
N
N
BF
4
P
P
Fe
B
Fe
3
2
BF
Fe
4
R2
F
R2
2
H O
NCCH
NCCH3
3
P
R1
R1
P
R1
R1
R1
N
N
N
R2
R2
R2
1
0
11a
11b
R1 = Ph, R2 = C
H
6 4
OMe-4 (1, 6);
R) Ph
(
R1 = Bn: R2 = Ph (2, 7),
(3, 8, 11, 12);
R1 = Py-2, R2 = Tol-p (4, 9, 13);
R1 = Mes, R2 = Tol-p (5, 10)
Scheme 1. The synthesis of iron (II) complexes of 1,5-diaza-3,7-diphosphacyclooctanes.
1
Figure 1. The H-NMR spectrum of complex 9 in CD CN (400 MHz).
3
The singlets of methyl groups of coordinated acetonitrile molecules were observed near 1.96 ppm
in the spectra of complexes . It indicated that the exchange between coordinated and uncoordinated
6–9

Molecules 2020, 25, 3775
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acetonitrile molecules was not fast. However, it should be mentioned that all complexes
6–
9
were
sensitive to the solvent nature, and their partial decomposition was observed in dimethylformamide
DMF), alcohols, and even in acetone or dichloromethane. In the last solvents, the decomposition
(
was probably caused by the presence of traces of water or hydrogen chloride, which led to the
partial substitution of acetonitrile co-ligands, so these ligands might be considered as relatively labile.
The solvent sensitivity of these complexes restricted the possibility of their variable-temperature
NMR studies.
The proposed structure of the complex
8
was confirmed by X-ray diffraction analysis. A single
in methylene chloride.
crystal of was grown by the gas-phase diffusion of acetonitrile to the solution of
8
8
The iron ion had a distorted octahedral configuration (Figure 2a). The acetonitrile ligands occupied the
formally equatorial positions. As a result, bonds P7-Fe and P7B-Fe were formally apical (a bond angle
◦
P7-Fe1-P7B is 175.4(1) ), and the other P-Fe bonds were formally equatorial. The selected bond lengths
and angles of complex
8 are presented in Table 1. There was not a noticeable difference between the
lengths of apical bonds Fe1-P7, Fe1-P7B (2.232(3) and 2.242(3) Å) and equatorial bonds Fe1-P3, Fe1-P3B
(
1
2.233(3) and 2.246(3) Å). The equatorial bond lengths N40-Fe1 and N43-Fe1 were 1.960(10) and
◦
.940(9) Å, the bond angle N40-Fe1-N43 was only 82.9(4) , whereas the bond angle P3-Fe1-P3B was
◦
enlarged up to P3-Fe1-P3B 104.09(1) . The similar structure was observed for the previously described
cis-[bis(1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane)di(acetonitrile)-iron(II)]
tetrafluoroborate [21].
Table 1. Selected bond lengths and angles of complexes 8 and 11b.
Parameter
Complex 8
Bond
Complex 11b
Bond Length (Type)
d, Å
Bond
Fe1-P3
Fe1-P3
d, Å
Fe1-P7
Fe1-P7B
2.232(3)
2.242(3)
2.267(3)
2.267(3)
d Fe-Pa
d Fe-Peq
d Fe-Xeq
0
Fe1-P3
Fe1-P3B
2.233(3)
2.246(3)
Fe1-P7
Fe1-P7
2.209(4)
2.209(4)
0
Fe1-N40
Fe1-N43
1.960(10)
1.940(9)
Fe1-F1
Fe1-F1
Angle
2.050(8)
2.050(8)
0
◦
◦
Bond Angle (Type)
Pa—Fe-Pa
Angle
0
0
P7-Fe1-P7B
P3-Fe1-P3B
175.4(1)
P3-Fe1-P3
P7-Fe1-P7
176.5(2)
101.1(2)
Peq-Fe-Peq
104.09(1)
P7-Fe1-P3
P7B-Fe1-P3B
P7B-Fe1-P3
P7-Fe1-P3B
79.1(1)
79.3(1)
98.5(3)
97.4(1)
P3-Fe1-P7
79.96(13)
79.96(13)
102.28(14)
102.28(14)
0
0
P3 -Fe1-P7
Pa—Fe-Peq
0
P3-Fe1-P7
0
P3 -Fe1-P7
0
Xeq-Fe-Xeq
X-Fe-Pa
N40-Fe1-N43
82.9(4)
F1-Fe1-F1
70.1(4)
N40-Fe1-P7B
N43-Fe1-P7
N40-Fe1-P7
N43-Fe1-P7B
93.5(3)
94.0(3)
89.6(3)
89.8(3)
F1-Fe1-P3
85.4(3)
85.4(3)
91.7(3)
91.7(3)
0
0
F1 -Fe1-P3
0
F1-Fe1-P3
0
F1 -Fe1-P3
0
N40-Fe1-P3
N43-Fe1-P3B
N40-Fe1-P3B
N43-Fe1-P3
164.0(3)
165.7(3)
88.6(3)
86.6(3)
F1-Fe1-P7
159.5(2)
159.5(2)
95.9(2)
95.9(2)
0
F1 -Fe1-P7
F1-Fe1-P7
X-Fe-Peq
0
0
F1 -Fe1-P7

Molecules 2020, 25, 3775
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(
a)
) The molecular structure of the cation of the complex
and solvate molecules (acetonitrile) were omitted for clarity; Bond distances Fe1-P3 2.233(3), Fe1-P7
.232(3), Fe1-P3B 2.246(3), Fe1-P7B 2.242(3), Fe1-N40 1.960(10), Fe1-N43 1.940(9) Å, ( ) The molecular
(b)
Figure 2.
(a
8. Hydrogen atoms, anions BF4,
2
b
structure of the cation of the complex 11b. Hydrogen atoms, disordered anions, and solvate molecules
were omitted for clarity. Bond distances Fe1-P3 2.267(3), Fe1-P7 2.209(4), Fe1-F1 2.050(8) Å.
Both diazadiphosphacyclooctane ligands (N(1)P(3)N(5)P(7) and N(1B)P(3B)N(5B)P(7B)) had
chair-boat conformations, so the substituents on nitrogen atoms in the chair and boat parts of the
heterocycles were in an essentially different environment. That explained the nonequivalence of these
substituents in NMR spectra. It should be mentioned that the high asymmetry of the complex and the
nonequivalence of two halves of the ligand cycle had to take place even in the case of conformational
exchange between two chair-boat conformations of diazadiphosphacyclooctane. The endocyclic
nitrogen atoms of the boat parts of both ligands were in the proximity to the iron ion (the distances Fe
.
. . N5 and Fe . . . N5B are 3.552(8) and 3.566(8) Å respectively). This arrangement was favorable for
the secondary interactions, similar to ones observed in natural hydrogenases [3].
Theinteractionofhexa(acetonitrile)iron(II)tetrafluoroboratewith1,5-diaza-3,7-diphosphacyclooctane
5
bearing bulky mesityl groups on phosphorus atoms led only to monoligand P,P-chelate complex
2+
−
[
LFe(CH CN) ] (BF ) 10 (L =
5
) (Scheme 1), even in the presence of the excess of the ligand.
The exclusive formation of complexes with metal-ligand ratio 1:1 has been earlier shown for
,5-diaza-3,7-diphosphacyclooctane with bulky substituents on phosphorus atoms and other transition
metal (Pt (II), Pd (II), Ni(II)) derivatives [ 27 29]. Both MALDI and ESI mass-spectra of 10 showed
a peak with m/z 621 corresponding to [LFe] ion (L = 10). Only one narrow signal at
3
4
4 2
1
7
, –
+
δ
55.56 ppm
P
was observed in its 31P-NMR spectrum. Unlike the spectra of the complexes 6–9, the H-NMR
spectrum of 10 showed only one set of signals for every group of ligand’s protons. The spectral
pattern was typical for the chair-boat conformation of diazadiphosphacyclooctane ligand in the case
of the fast conformational exchange in the NMR time scale in the solutions [29]. The absence of
the signal of coordinated acetonitrile molecules indicated also the fast exchange and the lability of
acetonitrile co-ligands.
1
The acetonitrile co-ligands are considered as ones, which form relatively strong coordination
bonds with iron (II) ion [21], so in order to obtain the iron complex with less coordinating co-ligands or
even coordinationally unsaturated iron complex of 1,5-diaza-3,7-diphosphacyclooctane, the hydrate
iron complex was used as the starting reagent in a low-coordinating solvent. Ligand
3 readily reacted
with iron (II) tetrafluoroborate hexahydrate [Fe(H O) ](BF ) in acetone to give a mixture of two
2
6
4 2
31
bis-ligand cis-complexes 11a and 11b (Scheme 1). In the P-NMR spectrum of the reaction mixture,
2
2JPP
two pairs of doublets at
δ
38.21 and 31.03 ppm ( J
≈
≈
70.7 Hz) (11a), 37.30 and 29.94 ppm
P
PP
2
2
(
JPP
≈
JPP
≈
71.8 Hz) (11b) with a ratio of intensities of 1.4:1 were observed. Nevertheless, after the
concentration of the reaction mixture and the crystallization of the residue at
◦
−
15 C, only the minor

Molecules 2020, 25, 3775
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product 11b was isolated as small dark-red crystals in the yield of 41%. The elemental analysis data of
1
1b corresponded to the composition L Fe(BF ) (L =
3
). Its mass-spectrum showed peaks with m/z
2
4 2
+
+
1
132 and 1162 corresponding to the ions [L Fe] and [L FeBF] . Unexpectedly, the bands of hydroxyl
2
2
groups were absent in the IR-spectrum of 11b, whereas the characteristic very strong broadband of BF
4
−1
2
2
anion was observed at 1057 cm . Two doublets at 37.30 and 29.94 ppm ( J = J = 71.8 Hz) were
PP
PP
observed in its 31P-NMR spectrum. Like the spectra of complexes
6–9, the H-NMR spectrum of 11b
1
demonstrated the pairwise nonequivalence of all protons of the heterocyclic fragments, of the benzylic
methylene groups, and 1-phenylethyl substituents on nitrogen atoms, which indicated the chair-boat
conformations of diazadiphosphacyclooctane rings. The absence of the signals of the coordinated
water in the spectrum was in accordance with the data of IR-spectroscopy and confirmed the absence
of water co-ligands in the coordination sphere of the iron.
The structure of the complex 11b was finally established by X-ray diffraction analysis. Unfortunately,
despite numerous attempts to grow a crystal of satisfactory quality, it was not possible, and the
crystal structure of the compound was established with large experimental errors; nevertheless,
the structure of the complex cation was established reliably. Therefore, in this work, we presented
only the conformation and selected geometry parameters of the cation, but not the crystal structure
of this compound. The dark-red single crystal of 11b was grown by the gas-phase diffusion of
acetone to the solution of 11b in methylene chloride. It should be mentioned that the crystal is an
acetone solvate and contains an undetermined solvent. Molecule 11b appeared to be a bis-ligand
+
−
monocationic complex of the composition [L Fe(BF )] BF , where two fluorine atoms of one of the
2
4
4
tetrafluoroborate unit were included in the coordination sphere of the iron ion and occupied two
pseudo-equatorial positions (Figure 2b). A similar coordination mode was described for the complexes
of bis- and tetrakis-phosphines with iron (II) sulfate and carbonate [30,31], but for the low-coordinating
tetrafluoroborate anion, it was unexpected. The molecule 11b in this crystal was on the special position
on the two-fold axis 2 (atoms Fe and B lied on the two-fold axis 2). In the unit cell of the crystal,
3
8
88 Å free volumes remained, in which other solvate molecules could not be identified. As a result,
the refinement of the structure was carried out using the SQUEEZE procedure. It should be mentioned
that a simultaneous TG/DSC analysis of the single crystals of 11b showed a loss of two water molecules
and a half of acetone molecule per one molecule of the complex in the temperature range 60–138
◦
C (Figure S26, Supplementary Materials), so the undetermined disordered solvent was the water
and acetone.
The central iron ion had the strongly distorted octahedral configuration: the dihedral angle
0
0
◦
0
between P(7)-Fe-P(7 ) and F(1)-Fe-F(1 ) planes was 20(1) , and the bond angles P(7)-Fe-P(7 ) and
0
◦
0
F(1)-Fe-F(1 ) were 101.1(2) and 70.4(4) , respectively, (P(7 ) and all atoms with ‘ were symmetry-related
atoms, symmetry operation 2
0 ◦
−
x, 1
−
x + y, 1
−
z). The bond angle P(3)-Fe-P(3 ) was 176.5(2) .
P,P-chelating diazadiphosphacyclooctane ligands had chair-boat conformations; phosphorus atoms of
every ligand coordinated the iron atom in pseudo-equatorial and pseudo-apical positions. Bond lengths
of equatorial bonds Fe1-P7 were 2.209(4), and the axial bonds Fe1-P3 were 2.267(3) Å (the selected
bond lengths and angles of complex 11b are presented in Table 1). Nitrogen atoms of the boat
parts of the heterocycles were directed to the coordinated tetrafluoroborate fragment so that they
were in the proximity, both to the central ion (the shortest distance Fe1 . . . N5 was 3.314(11) Å)
and to the coordinated fluorine atoms (the shortest distance F . . . N was only 2.59(2) Å and less
than a sum of van der Waals radii). Their lone electron pairs were directed to the metal iron. This
structure might be favorable for the small molecules activation due to the secondary interactions of
the metal-coordinated substrates with amine centers of the ligands. The comparison of the structural
parameters of complexes
of iron ion in 11b, namely, the small value of F1-Fe-F1 bond angle and some lengthening of apical
8
and 11b showed more noticeable distortion of the octahedral geometry
0
Fe–P bonds in comparison with equatorial ones (2.267(3) vs. 2.209(4) Å), whereas Fe–P distances
of complex
8 varied in the narrow range of 2.232(3)–2.246(3) Å (Table 1). The bond lengths Fe–F
were close (2.050(9) Å). The bonds B–F with the coordinated fluorine atoms were slightly longer

Molecules 2020, 25, 3775
7 of 17
than the corresponding bonds with uncoordinated ones (1.49(2) Å vs. 1.39(2) Å). The Fe–F bond
lengths were within the typical range of few known BF -ligated iron (II) complexes (1.96–2.26 Å),
4
1
which contained only terminally
complexes-containing bidentate
η
-coordinated tetrafluoroborate anions [32
-bound tetrafluoroborate ligands were silver (I) complexes with
–
39]. The most of known
2
κ
weakly coordinated BF anions, where the Ag–F distances were relatively long (2.79–3.01 Å) [40
–
43].
4
2
Only two examples of an almost covalent
κ
-F BF bonding of tetrafluoroborate anion had been
2
2
−
described, namely, the silver (I) complex of cyclodextrine-based diphosphine, where BF4 counterion
lied deep inside the cavity, and Ag–F distances were only 2.53–2.62 Å [44], and dimolibdenum complex
2
[
Mo Cp (k -F BF )(
µ
-PPh ) (CO)](BF ), which showed close and short Mo–F distances (2.18(1) Å) [45].
2
2
2
2
2 2
4
1
These values were quite close to the metal-fluorine distances measured for related
η -FBF coordinated
3
tungsten and molybdenum complexes [45]. According to these structural criteria, namely, the usual
lengths of two Fe–F bonds in the cation of 11b and a small difference between them, the Fe/BF4
interaction might be considered as relatively strong and close to the covalent one.
The complex 11a was not isolated, but most probably it was the corresponding dihydrate complex
with uncoordinated tetrafluoroborate anions; the easy replacement of two water ligands by bidentate
sulfate or carbonate ligand from the outer sphere was described for the iron (II) complexes of 1,5-di[di
(hydroxymethyl)phosphinomethyl]-3,7-di(hydroxymethyl)-1,5-diaza-3,7-diphosphacyclooctane [30].
The attempt to register NMR spectra of 11b in CD CN showed the fast change of the solution
3
color from red to yellow and the appearance of the signals of corresponding bis-acetonitrile complex
(multiplets at 25.6 and 34.2 ppm) along with other signals in close ranges, which presumably
corresponded to the products of the incomplete ligand replacement. The possibility of the exchange
of tetrafluoroborate ligand to acetonitrile led to the attempt to synthesize complex directly from
the more accessible and less sensitive iron (II) tetrafluoroborate hexahydrate. Its interaction with the
ligand in acetonitrile indeed led finally to the complex , but the reaction was very slow, and its
completion required about 50 days vs. 12 h in the case of starting from [Fe(CH CN) ](BF ) , so this
8
8
3
8
3
6
4 2
route was inadvisable.
The interaction of P-benzyl-substituted ligand 3 with cyclopentadienyldicarbonyl(tetrahydrofuran)
iron (II) tetrafluoroborate in toluene at ambient temperature for 1 day smoothly led to the replacement
of tetrahydrofuran (THF) and one of the carbonyl ligand by the diphosphine ligand and to the
3
formation of cationic complex 12 (Scheme 1) in a yield of 82%. A similar complex containing chloride
counter-ion was isolated in relatively low yield (20%) during the early stages of the photolysis of a
mixture of CpFe(CO) Cl and 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane, whereas
2
Ph
Bn
the final and main product of the photolysis was the complex CpFe(P 2N 2)Cl [22]. The reaction of
−
the ligand
4
with [CpFe(CO) (THF)]BF4 proceeded slowly, probably due to a decreased nucleophilicity
2
of phosphorus atoms bearing relatively electron-withdrawing pyridyl substituents. The completion
◦
of the reaction required the heating of the reaction mixture at 60–70 C for 4 days, and the formation
of the analogous complex 13 (Scheme 1) was complicated by the precipitation of a large amount of
low-soluble and paramagnetic dark resin, so the yield of 13 was only 9%. Presumably, the prolonged
heating led to a loss of its carbonyl ligand. According to elemental analysis data, the complexes 12
+
−
and 13 had the composition [CpFeL(CO)] BF , and their ESI mass-spectra showed the peaks of
4
+
corresponding cations [CpFeL(CO)] (L =
3
,
4
) with m/z 687.3 and 633.4, respectively. Two bands
−
1
of the carbonyl group vibrations at 1940 and 1950–1951 cm were observed in the IR spectra of 12
and 13. In the 31P-NMR spectrum of 13, one narrow signal at 59.14 ppm was observed, whereas the
spectrum of 12 showed two close doublets of AB system at 55.55 and 56.27 ppm ( J = 116.4 Hz)
2
PP
because two phosphorus atoms were nonequivalent due to the presence of the chiral substituents on
1
nitrogen atoms [46]. In the H-NMR spectrum of 13, the nonequivalence of the p-tolyl substituents on
nitrogen atoms and the pairwise nonequivalence of the methylene groups in the heterocyclic fragment
were observed as a result of the chair-boat conformation of the diazadiphosphacyclooctane ligand.
1
In the H-NMR spectrum of 12, the presence of chiral substituents on nitrogen atoms led additionally
to the nonequivalence of benzyl substituents on phosphorus atoms and to the nonequivalence of all

Molecules 2020, 25, 3775
8 of 17
four methylene groups of the chair-boat diazadiphosphacyclooctane fragment, which formed complex
overlapped multiplets. The protons of cyclopentadienyl ligands were registered as a singlet at 5.18 ppm
2
for 12 and as a triplet at 5.05 ppm ( J = 1.4 Hz) for 13.
PH
The redox properties of synthesized iron complexes 6–13 were studied by the cyclic voltammetry
in MeCN. The results are presented in Table 2 and Figure 3. One reduction and oxidation peaks were
observed for all iron complexes. One irreversible reduction peak, as we supposed, corresponding
to FeII/I couple, was observed on cyclic voltammograms (CVs) at range from
for complexes 10) and depended on substituents at phosphorus and nitrogen atoms of ligands.
The reversible oxidation peak corresponding FeII/III couple was observed at 0.25–0.34 V in these
cases. In the case of complexes 12 and 13, slightly negative shift to 1.60–1.80 V of reduction potential
) and irreversible oxidation peaks at 1.10–1.23 V were observed on CVs.
−1.37 to
−1.74 V
(
6–
−
(vs. bis-chelated complexes 6–9
Table 2. Electrochemical data for iron complexes 6–13 in MeCN (potentials vs. Ag/AgCl reference
electrode).
Complex
Reduction Potential, V
Oxidation Potential, V
6
7
8
9
−1.74
−1.50
−1.48
−1.37
−1.64
−1.80
−1.60
0.34
0.30
0.25
0.30
0.32
1.23
1.10
1
1
1
0
2
3
Figure 3. Cyclic voltammograms for complexes
8 and 13 in MeCN. Conditions: working electrode-glassy
carbon, auxiliary electrode-Pt, supporting electrolyte-Bu NBF .
4
4
3
. Discussion
,5-Diaza-3,7-diphosphacyclooctanes
substituents on phosphorus atoms reacted with hexa(acetonitrile)iron (II) tetrafluoroborate in
1
1–4 with relatively small phenyl, benzyl, and pyridin-2-yl
2
+
−
acetonitrile as P,P-chelating ligands to give bis-ligand cis-complexes [L Fe(CH CN) ] (BF ) (6
4 2
whereas the P-mesityl-substituted ligand
–
9
),
2
3
2
2
+
5
formed only monoligand P,P-complex [LFe(CH CN) ]
3
4
−
(BF4)2
(10). The interaction of the ligand 3 with hexahydrate of iron (II) tetrafluoroborate
+
in acetone unexpectedly led to a bis-ligand cationic complex of the composition [L Fe(BF )]
2
4
−
BF4
into the coordination sphere of the iron ion and occupied two pseudo-equatorial positions.
,5-diaza-3,7-diphosphacyclooctane ligands were able to replace tetrahydrofurane and one of the carbonyl
ligands of cyclopentadienyldicarbonyl(tetrahydrofuran)iron (II) tetrafluoroborate to form heteroligand
(11b), where two fluorine atoms of one of the tetrafluoroborate unit were included
1
+
−
complexes 12 and 13 of the composition [CpFeL(CO)] BF4 . The diazadiphosphacyclooctane ligands
of all complexes adopted chair-boat conformations so that their nitrogen atoms were in close proximity
to the central iron ion. In spite of the favorable disposition of the metal center and pendant amine

Molecules 2020, 25, 3775
9 of 17
centers, the redox properties of the obtained complexes (in particular, the presence of the irreversible
reduction peaks) were not promising for the application of these complexes as electrocatalysts.
4
. Materials and Methods
4
.1. General
All the reactions and manipulations with phosphines
1–
5
were carried out under a dry argon
atmosphere using standard vacuum-line techniques. All manipulations with complexes 6–13,
excluding the electrochemical measurements, were carried out under normal conditions without inert
atmosphere. Solvents were purchased from Acros Organics (Geel, Belgium) and were purified, dried,
deoxygenated, and distilled before use. Iron (II) tetrafluoroborate hexahydrate, hexa(acetonitrile)iron
(II) tetrafluoroborate and cyclopentadienyldicarbonyl(tetrahydrofuran)iron (II) tetrafluoroborate were
purchased from Sigma-Aldrich (St. Louis, MO, USA) and used as received.
ESIpos MS were recorded with an AmazonX (Bruker Daltonics GmbH, Bremen, Germany)
spectrometer at a capillary voltage of 4500 V. DataAnalysis 4.0 (Bruker Daltonics GmbH, Bremen,
Germany) program was used to process the mass spectrometry data. MALDI MS was recorded
with an Ultraflex III TOF/TOF (Bruker Daltonics, Germany) spectrometer on the p-nitroaniline (pNA)
matrix. FlexAnalysis 3.0 (Bruker Daltonics GmbH, Bremen, Germany) program was used to process
1
the mass spectrometry data. The mass spectra are reported as m/z values. H-NMR (400 MHz and
6
00 MHz) and 31P-NMR (162 and 242 MHz) spectra were obtained with Bruker Avance-DRX 400
(
BrukerBioSpin, Billerica, MA, USA) and Bruker Avance-600 spectrometers (BrukerBioSpin, Billerica,
1
MA, USA). The chemical shifts are reported in ppm relative to SiMe ( H, internal standard) and 85%
H PO (aq) ( P, external standard). The coupling constants (J) are reported in Hz. The IR spectra
4
31
3
4
were obtained on a spectrometer “Vector-22” (Bruker Optics GmbH, Bremen, Germany) in the range
−1
4
00–4000 cm in Nujol mulls. Determination of the CHN content was carried out on CHN analyzer
“CHN-3 KBA”. The determination of the phosphorus content was provided by combustion in an
oxygen stream. Simultaneous thermogravimetry and differential scanning calorimetry (TG/DSC)
analysis of samples of 11b (solvate) (10.7 mg) were performed using the STA 449F1 Jupiter (Netzsch,
◦
◦
Selb, Germany) thermoanalyzer (in the range of temperatures from 40 to 200 C in aluminum crucible
under a dynamic atmosphere of argon 75 mL/min). The heating rate was 10 C/min.
Starting phosphines
1 [47], 2 [48], and 4 [2] were prepared according to the literature procedures.
4
.2. X-ray Crystallography Data
The data of were collected on a Bruker SmartApex II (Bruker AXS GmbH, Karlsruhe,
Germany) using the -scan mode, and the data of 11b were collected on a Bruker KappaApex
II diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) ( (MoK ) = 0.71073 Å), at temperature
00(2) K. The performance mode of the sealed X-ray tube was 50 kV, 30 mA. A suitable crystal of
8
ω
λ
α
1
appropriate dimensions was mounted on a glass fiber in a random orientation. Data collection:
images were indexed and integrated using the APEX3 data reduction package (v2018.7-2, Bruker AXS,
Madison, WI, USA). Final cell constants were determined by the global refinement of reflections from
the complete data set. Data were corrected for systematic errors and absorption using SADABS-2016/2
(v2016-2, Bruker AXS, Madison, WI, USA). XPREP-2014/2 (v2014-2, Bruker AXS, Madison, WI, USA)
and the Assign Space group routine of WinGX-2018.3 (v2018-3, Bruker AXS, Madison, WI, USA) were
used for the analysis of systematic absences and space-group determination. The structures were
solved by the direct method using SHELXT-2018/2 (v2018-2, Bruker AXS, Madison, WI, USA) [49] and
2
refined by the full-matrix least-squares on F using SHELXL-2018/3 (v2018-3, Bruker AXS, Madison,
2
WI, USA) [50] and refined by the full-matrix least-squares on F using SHELXL-2018/3 (v2018-3, Bruker
AXS, Madison, WI, USA) [50]. Calculations were mainly performed using the WinGX-2018.3 suite of
programs [51]. Non-hydrogen atoms were refined anisotropically. The hydrogen atoms were inserted

Molecules 2020, 25, 3775
10 of 17
at the calculated positions and treated as riding atoms. The absolute structure of crystals was confirmed
by the Flack parameter [52].
4
.2.1. Crystal Data and Structure Refinement for Compound 8
C H FeN P42+, 2(BF4 ), 2(C H N) ; M = 1470.93, orthorhombic, space group P2 2 2 ,
−
−
72
86
6
2
3
1
1
1
−3
3
a = 13.7178(14), b = 20.452(2), c = 27.659(3) Å, V = 7759.9(14) Å , Z = 4, D
= 1.259 g cm ;
calc
−1
◦
µ
(MoKα) = 0.342 mm ; ΘMax = 25.8 , 134,467 reflections were measured, 14,690 were independent
reflections. Final R = 0.0791, R = 0.1537, goodness of fit 1.007 for 7289 reflections with I (I),
= 0.2081 for all reflections; flack parameter (absolute structure parameter) 0.006(12).
w
≥
2σ
1
and R = 0.2051, R
w
1
4
.2.2. Crystal Data and Structure Refinement for Compound 11b
−
−
3
(C H BF FeN P4+), 2(BF4 ), 15(C H O), [+ solvent], one BF anion was not solved;
68 68 4 4 3 6 4
3
M = 4704.49, trigonal, space group P321, a = b = 22.651(2), c = 15.3431(17) Å, V = 6817.4(16) Å ,
−
3
−1
Z = 1, Dcalc = 1.146 g cm ;
µ
(MoKα) = 0.297 mm ; 29,199 reflections were measured, 8934 were
independent reflections. Final R = 0.1040, R
w
= 0.2221 for 4109 reflections with I (I), and R1
≥
2σ
1
=
0.2191, R
w
= 0.2794 for all reflections, goodness of fit 0.978, flack parameter (absolute structure
parameter)
−
0.04(4). Organometallic cation was on a special position on the two-fold axis; BF anion
4
−
was on a special position on the trifold axis; molecules disordered on 6 positions BF4 anion were
disordered by two-fold and trifold axes and were not solved from different Fourier maps, and one of
the solvate molecules of acetone was on a special position on the two-fold axis. In this crystal, the total
potential solvent-accessible void volume (SOLV-Map Value) 926 Å was found, but solvate molecules
and those disordered on 6 positions of BF4 anion were not found from the different Fourier maps
3
−
of electron density, and the final stages of structure refinement were performed using the SQUEEZE
procedure of program PLATON [53].
CCDC 2000581 (8), CCDC 2000582 (11b) contained the crystallographic data. These data could
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44)-1223-336-033;
or deposit@ccdc.cam.uk).
4
.3. Electrochemical Measurements
Cyclic voltammetry measurements were performed with an E2P potentiostat of BASi Epsilon (USA)
composed of a measuring block, a Dell Optiplex 320 computer with an installed EpsilonES-USB-V200
program, and a C3 electrochemical cell. A stationary glassy-carbon electrode (with a diameter of
3.0 mm) was used as a working electrode. Ag/AgCl was used as a reference electrode. A platinum
wire of 0.5 mm diameter was used as an auxiliary electrode. Measurements were performed under an
inert argon atmosphere.
0
3
,7-Dibenzyl-1,5-di(1 -(R)-phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane (
3). 1-(R)-phenylethylamine
(
0.83 g, 6.85 mmol) in dry ethanol (7 mL) was added to a solution of bis(hydroxymethyl)benzylphosphine,
obtained by the stirring of the mixture of benzylphosphine (0.85 g, 6.85 mmol) and paraformaldehyde
◦
(
0.41 g, 13.70 mmol) at 100–110 C up to homogenization in dry ethanol (8 mL). The reaction mixture
◦
was stirred at 70–80 C for 6 h and cooled. The precipitate formed was filtered off, washed with
−
2
◦
ethanol, and dried for 5 h at 2
·
10 torr to give
3
as a white powder (1.07 g, 58%). M.p. 130–132 C.
1
3
2
H-NMR (CDCl ):
δ
1.14 (d, J
= 6.4 Hz, 6H, CH ), 2.06 (d, JHH = 13.0 Hz, 2H, P-CH -Ph), 2.19
3
HH
3
2
2
2
2
(br. d, J
= 13.0 Hz, 2H, P-CH -Ph), 2.91 (d, J
= 14.8 Hz, 2H, P-CH -N), 3.06 (d, J
= 14.4 Hz,
HH
= 14.8 Hz, 2H, P-CH -N),
HH 2
HH
2
HH
2
2
2
2
4
H, P-CH -N), 3.27 (br. d, J
= 14.4 Hz, 2H, P-CH -N), 3.69 (br. d, J
2
HH
2
3
3
.64 (q, J
= 6.4 Hz, 2H, CH(Me)Ph), 7.07 (t, J
= 7.8 Hz, 2H, Har), 7.10–7.26 (m, 14H, Har), 7.48
HH
HH
3
31
1
(
d, J
= 7.8 Hz, 4H, Har). P{ H} NMR (CDCl ):
δ
P
-67.54 (s). Anal. Calc. for C H P N (538.64):
HH
3
34 40
2
2
C 75.81, H 7.49, N 5.20, P 11.50%. Found: C 75.60, H 7.57, N 5.16, P 11.61%.

Molecules 2020, 25, 3775
11 of 17
3,7-Dimesityl-1,5-di(p-tolyl)-1,5-diaza-3,7-diphosphacyclooctane (
5).
5
was prepared like
3
from
mesitylphosphine (0.91 g, 5.99 mmol), paraformaldehyde (0.36 g, 12.00 mmol), and p-toluidine
◦
(
(
4
0.64 g, 5.99 mmol). The reaction time was 10 h, and the yield of
5
was 1.05 g (62%). M.p. > 200 C
1
decomp.). H-NMR (CDCl ):
δ
2.18 (s, 6H, NC H CH ), 2.34 (s, 6H, CH3Mes-p), 2.53 (s, 12H, CH3Mes-o),
3
6
4
3
2
2
2
.43 (br.d, J
= 15.0 Hz, 4H, P-CH -N), 4.51 (dd, J
= 15.0 Hz, J = 3.2 Hz,4H, P-CH -N), 6.27
HH PH 2
= 8.4 Hz, 4H, NC H CH -m), 6.96 (s, 4H, HMes).
HH 6 4 3
HH
2
3
3
(
d, J
= 8.4 Hz, 4H, NC H CH -o), 6.92 (d, J
HH
6
4
3
3
1
1
P{ H} NMR (CDCl ): δ −44.41 (s). Anal. Calc. for C H P N (566.70): C 76.30, H 7.83, N 4.94, P
3
P
36 44
2
2
1
0.93%. Found: C 76.18, H 7.92, N 4.75, P 10.78%.
Bis(3,7-Diphenyl-1,5-di(p-methoxyphenyl)-1,5-diaza-3,7-diphosphacyclooctane)-bis(acetonitrile)iron(II)]
tetrafluoroborate ( ). [Fe(CH CN) ](BF ) (0.088 g, 0.19 mmol) in dry acetonitrile (4 mL) was added
to (0.200 g, 0.38 mmol) in dry chlorophorm (4 mL). The reaction mixture was stirred at room
6
3
6
4 2
1
temperature for 12 h. The ligand was completely dissolved, and the reaction mixture turned dark-red.
The reaction mixture was concentrated to ca. 3 mL under reduced pressure, the precipitate was
−
2
filtered off, washed with diethyl ether, and dried for 3 h at 2 10 torr to give complex 6 as a brown
·
◦
1
powder (0.112 g, 43%). Decomposed at 160 C. H-NMR (CD CN):
δ 1.96 (s, 6H, CH CN), 3.62 (s, 6H,
3
3
2
-
(
(
OCH ), 3.74 (d, J
= 6.5 Hz, 4H, P-CH -N), 3.79 (m, 4H, P-CH -N), 3.88 (s, 6H, -OCH ), 4.06–4.11
HH 2 2 3
3
3
m, 4H, P-CH -N), 4.32–4.35 (m, 4H, P-CH -N), 6.68 (d, J
= 9 Hz, 4H, N-C H OCH -o), 6.78
= 8 Hz, 4H, N-C H OCH -m), 6.97 (d,
H, N-C H OCH -m), 7.51–7.55 (m, 4H, Har), 7.70 (br s, 7H, Har), 7.82 (br s, 9H, Har). P{ H} NMR
CD CN): δ 30.52–31.46 (m), 34.23–35.20 (m). ESI MS: m/z 542 [6-2 BF -2 CH CN] , 1103 [6-2 BF -2
3 P 4 3 4
2
2
3
HH
6
4
3
3
3
d, JHH = 8 Hz, 4H, N-C H OCH -o), 6.80 (d, J
J
= 9 Hz,
6
4
3
HH
6
4
3
HH
1
3
1
4
(
6
4
3
2
+
+
CH CN + H O] . Anal. Calc. for C H P N O FeB F (1340.63): C 57.34, H 5.26, N 6.27, P 9.24%.
3
2
64 70
4
6
4
2 8
Found: C 57.03, H 5.41, N 6.49, P 9.08%.
[
Bis(3,7-Dibenzyl-1,5-diphenyl-1,5-diaza-3,7-diphosphacyclooctane)-bis(acetonitrile)iron(II)] tetrafluoroborate
(
2
3
7). [Fe(CH CN) ](BF ) (0.0953 g, 0.215 mmol) in dry acetonitrile (6 mL) was added to a suspension of
(0.2081 g 0.43 mmol) in dry acetonitrile (70 mL) at 70 C. The reaction mixture was stirred at 70 C for
.5 h and then at room temperature for 12 h. The ligand was completely dissolved, and the reaction
3
6
4 2
◦
◦
mixture turned yellow-orange. The reaction mixture was concentrated to ca. 25 mL under reduced
◦
pressure, and the residue was crystallized at
−
15 C for 24 h. The precipitate was filtered off, washed
−2
twice with cold acetonitrile and then with diethyl ether, and dried for 3 h at 2
as yellow crystals (0.110 g, 40%). M.p. > 200 C (decomp.)
·10 torr to give complex
◦
7
1
2
H-NMR (CD CN):
δ
1.96 (s, 6H, CH CN), 2.39 (d, J
= 12.8 Hz, 2H, P-CH -Ph), 2.78
HH 2
3
3
(
d, 2JHH = 13.6 Hz, 2H, P-CH -Ph), 3.32–3.68 (m, 10H, P-CH -Ph + P-CH -N), 3.96–4.24 (m, 8H,
2 2 2
3
3
P-CH -N), 4.34–4.44 (m, 2H, P-CH -N), 6.50 (d, J
= 8.0 Hz, 4H, N-C H -o), 6.56 (br d, JHH = 7.2 Hz,
6 5
= 7.8 Hz, 2H, N-C H -p), 7.02 (br d, J
2
2
HH
2
3
4
7
H, N-C H -o), 6.83 (t, J
= 8.4 Hz, 4H, P-CH - C H -o),
HH 2 6 5
6
5
HH
6
5
31
1
.07–7.15 (m, 6H, Har), 7.19–7.28 (m, 6H, Har), 7.42–7.49 (m, 6H, Har), 7.54–7.64 (m, 8H, Har). P{ H}
+
NMR (CD CN):
δ
P
31.44 (m), 35.57 (m). MALDI MS: m/z: 1019.7 [
7
-2 BF -2 CH CN] , 1050.7
3
4
3
+
−1
[7-2BF 2CH CN-H + 2O] . IR (Nujol, ν, cm ): 1060 vs. br. (BF ). Anal. Calc. for C H P N FeB F
4- 3 4 64 70 4 6 2 8
(1276.63): C 60.21, H 5.53, N 6.58, P 9.70%. Found: C 60.06, H 5.64, N 6.71, P 9.56%.
0
[
Bis(3,7-Dibenzyl-1,5-di(1 -(R)-phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane)-bis(acetonitrile)iron(II)]
tetrafluoroborate (8). [Fe(CH CN) ](BF ) (0.0371 g, 0.085 mmol) in dry acetonitrile (1 mL) was added to
3 6 4 2
a solution of
3 (0.0904 g, 0.17 mmol) in 10 mL dry acetonitrile. The reaction mixture was stirred at
room temperature for 12 h and turned yellow-brown. The reaction mixture was concentrated to ca.
3
mL under reduced pressure, and the diethyl ether (5 mL) was added to precipitate the product.
−2
The precipitate was filtered off, washed twice with diethyl ether, and dried for 3 h at 2
complex 8 as a yellow powder (0.131 g, 56%). Decomposed at 140 C.
·
10 torr to give
◦

Molecules 2020, 25, 3775
12 of 17
1
δ
0.55 (d, 3JHH = 6.6 Hz, 6H, CH(Me)Ph), 1.74 (d, 3JHH = 7.2 Hz, 6H,
H-NMR (CD CN):
3
CH(Me)Ph), 1.96 (s, 6H, CH CN), 2.14–2.29 (m, 8H, P-CH -Ph), 2.81–2.85 (m, 2H, P-CH -N), 2.96–3.02
3
2
2
(
m, 2H, P-CH -N), 3.09–3.19 (m, 4H, P-CH -N), 3.24–3.32 (m, 4H, P-CH -N + CH(Me)Ph), 3.62 (d.m,
2
2
2
2J
= 15.0 Hz, 2H, P-CH -N), 3.74 (br.d, J
= 7.2 Hz, 2H, CH(Me)Ph), 6.69 (m, 4H, Har), 7.07–7.45 (m, 36H, Har). P{ H} NMR (CD CN):
HH 3
25.61 (m), 34.19 (m). ESIpos MS: m/z 1208 [8-2 BF -CH CN + F + O] , 1192 [8-2 BF -CH CN + F] .
4 3 4 3
2
= 15.0 Hz, 2H, P-CH -N), 3.88 (m, 2H, P-CH -N), 4.18
HH
3
2
HH
2
2
31
1
(
q, J
+
+
δ
P
−
ν, cm ): 1060 vs. br. (BF ). Anal. Calc. for C H N P FeB F [1388.84]: C 62.27, H 6.24, N
4 72 86 6 4 2 8
1
IR (Nujol,
.05, P 8.92%. Found: C 61.96, H 6.40, N 6.36, P 8.74%.
6
0
[
Bis(3,7-Di(pyridine-2 -yl)-1,5-di(p-tolyl)-1,5-diaza-3,7-diphosphacyclooctane)-bis(acetonitrile)iron(II)]
tetrafluoroborate ( ). as an orange powder was obtained like from 4 (0.0985 g, 0.203 mmol) and
Fe(CH CN) ](BF ) (0.0447 g, 0.101 mmol), except that 4 was used as a suspension. The yield of 9
9
9
8
[
3
6
4 2
◦
1
was 0.079 g (61%). Decomposed at 160 C. H-NMR (CD CN):
NC H CH ), 2.32 (s, 6H, NC H CH ), 2.90–2.99 (m, 2H, P-CH -N), 3.28 (br.d, J
P-CH -N), 3.34 (br.d, J
.73–3.83 (m, 2H, P-CH -N), 4.13 (br.d, J
δ
1.96 (s, 6H, CH CN), 2.11 (s, 6H,
3
3
2
= 12.8 Hz, 2H,
= 11.6 Hz, 2H, P-CH -N),
HH 2
6
4
3
6
4
3
2
HH
2
2
= 14.2 Hz, 2H, P-CH -N), 3.41 (br.d, J
2
HH
2
2
3
4
= 14.2 Hz, 2H, P-CH -N), 4.24–4.33 (m, 2H, P-CH -N),
2
HH
2
2
3
3
.38–4.48 (m, 2H, P-CH -N), 6.52 (d, J
= 8.6 Hz, 4H, NC H CH -o), 6.71 (d, J
= 8.6 Hz, 4H, NC H CH -m), 6.95 (m, 2H, H pyr), 7.11 (d, J
= 8.4 Hz, 4H,
2
HH
6
4
3
HH
3
4
3
NC H CH -o), 6.91 (d, J
= 8.4Hz,
6
4
3
HH
6
4
3
HH
3
H, NC H CH -m), 7.36 (m, 2H, H pyr), 7.51 (m, 2H, H pyr), 7.70 (m, 2H, H5pyr), 7.95 (br.d, J
4
5
= 8.0
4
6
4
6
3
HH
3
= 4.4 Hz, 2H, H3pyr), 8.16 (m, 2H, H6pyr), 9.03 (br.d, 3JHH = 3.6 Hz, 2H,
Hz, 2H, H pyr), 8.13 (br.d, J
HH
3
31
1
2+
H
1
pyr). P{ H} NMR (CD CN): δ 34.69 (m), 41.13 (m). ESIpos MS: m/z 512.4 [9-2 BF -2 CH CN] ,
3 P 4 3
+
−1
059.6 [9-2 BF - 2 CH CN + F + O] . IR (Nujol, ν, cm ): 1060 vs. br. (BF ). Anal. Calc. for
4 3 4
C H N P FeB F [1280.58]: C 56.27, H 5.19, N 10.94, P 9.67%. Found: C 56.09, H 5.31, N 11.17,
60
66 10
4
2 8
P 9.49%.
[(3,7-Dimesityl-1,5-di(p-tolyl)-1,5-diaza-3,7-diphosphacyclooctane)tetrakis-(acetonitrile)iron(II)]
tetrafluoroborate (10). [Fe(CH CN) ](BF ) (0.240 g, 0.53 mmol) in dry acetonitrile (2 mL) was
3
6
4 2
added to a solution of
5 (0.300 g, 0.53 mmol) in dry acetonitrile (6 mL). The reaction mixture was
stirred at room temperature for 48 h. The ligand was completely dissolved, and the reaction mixture
turned brown. The reaction mixture was concentrated to ca. 3 mL under reduced pressure, and the
◦
residue was crystallized at
−
15 C for 12 h. The precipitate was filtered off, washed with diethyl ether,
−2
and dried for 3 h at 2
at 130 C. H-NMR (CD CN):
·
10 torr to give complex 10 as a dark-red powder (0.116 g, 28%). Decomposed
2.18 (s, 6H, NC H CH ), 2.38 (s, 6H, CH3Mes-p), 2.44 (s, 12H, CH
.77–4.82 (m, 4H, P-CH -N), 4.93–4.97 (m, 4H, P-CH -N), 6.54 (br s, 4H, NC H CH -o), 6.99 (br.d, J
2 2 6 4 3 HH
6 Hz, 4H, NC H CH -m), 7.17 (s, 4H, HMes). P{ H} NMR (CD CN):
10-2 BF -4 CH CN] . ESIpos MS: m/z 621 [10-2 BF -4 CH CN] . IR (Nujol,
◦
1
δ
-o),
3
6
4
3
3Mes
3
4
31
1
=
δ
P
55.56. MALDI MS: m/z 621
6
4
3
3
+
+
−1
[
ν
, cm ): 1059 vs. br. (BF4).
4
3
4
3
Anal. Calc. for C H N P FeB F [960.36]: C 55.03, H 5.88, N 8.75, P 6.45%. Found: C 54.87, H 6.01,
44
56
6
2
2 8
N 8.97, P 6.28%.
0
[
Bis(3,7-Dibenzyl-1,5-di(1 -(R)-phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane)- tetrafluoroboratoiron(II)]
tetrafluoroborate (11b). [Fe(H O) ](BF ) (0.0314 g, 0.095 mmol) was added to a solution of
3
(0.100 g,
2
6
4 2
0
.19 mmol) in dry acetone (10 mL). The reaction mixture was stirred at room temperature for 12 h
31
and turned dark-red. In P-NMR spectrum, two pairs of doublets were observed at 38.21 and 31.03
ppm ( J
of intensities of 1.4:1. The reaction mixture was concentrated to ca. 2 mL under reduced pressure,
and the residue was crystallized at
cold acetone, and dried for 3 h at 2
2
2
2
2
≈
JPP
≈
70.7 Hz) (11a), 37.30 and 29.94 ppm ( J
≈
JPP
≈
71.8 Hz) (11b) with a ratio
PP
PP
◦
−
15 C for 12 h. The precipitate was filtered off, washed with
−2
·
10 torr to give complex 11b as dark-red small crystals (0.054
◦
1
3
g, 44%). M.p. > 140 C (decomp.) H-NMR (acetone-d ):
δ
1.10 (d, JHH= 6.8 Hz, 6H, CH(Me)Ph),
6
3
2
1
.58 (d, J
= 6.8 Hz, 6H, CH(Me)Ph), 1.84 (br. d, J
= 14.2 Hz, 2H, P-CH -Ph), 1.94–1.99 (m, 2H,
HH
HH
2
2
P-CH -Ph), 2.44–2.52 (m, 2H, P-CH -N), 2.65 (br d, 2H, J
P-CH -N), 3.04–3.11 (m, 4H, P-CH -N), 3.22 (br d, J
= 14.2 Hz, P-CH -Ph), 2.91–2.98 (m, 2H,
2
2
HH
2
2
= 13.2 Hz, 2H, P-CH -N), 3.54–3.63 (m, 2H,
2
2
2
HH

Molecules 2020, 25, 3775
13 of 17
3
P-CH -N), 3.68 (q, J
= 6.8 Hz, 2H, CH(Me)Ph), 3.84–3.94 (m, 4H, P-CH -N), 4.01 (m, 2H, P-CH -N),
2
HH
2
2
3
4
3
.14 (q,
J
= 6.8 Hz, 2H, CH(Me)Ph), 6.74–6.79 (m, 4H, Har), 6.85–6.90 (m, 4H, Har), 7.10–7.55 (m,
HH
2H, Har). P{ H} NMR (acetone-d ):
Hz). MALDI MS: m/z 1132 [11b-2 BF ] , 1162 [11b-BF -3 F] . IR (Nujol,
31
1
2
2
2
2
δ
+
37.30 (dd, J = J = 71.8 Hz), 29.94 (dd, J = J = 71.8
6
P
PP
PP
+
PP
PP
−1
ν
, cm ): 1057 vs. br. (BF ).
4
4
4
Anal. Calc for C H N P FeB F [1306.74]: C 62.50, H 6.17, N 4.29, P 9.48%. Found: C 62.39, H 6.31,
68
80
4
4
2 8
N 4.18, P 9.23%.
0
[
(Cyclopentadienyl)carbonyl(3,7-dibenzyl-1,5-di(1 -(R)-phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane)iron(II)]
tetrafluoroborate (12 A solution of (0.1036 g, 0.192 mmol) in dry toluene (10 mL) was added to solid
CpFe(CO) (THF)]BF (0.0646 g, 0.192 mmol). The reaction mixture was stirred at room temperature
)
.
3
[
2
4
for 24 h and turned yellow-orange. The small amount of a sticky dark resin was removed by the
centrifugation, the volatiles were removed from the filtrate under reduced pressure, and the residue
was crystallized from diethyl ether. The precipitate was filtered off, washed twice with diethyl ether,
−
2
◦
and dried for 3 h at 2
·
10 torr to give complex 12 as a yellow powder (0.122 g, 82%). M.p. 177–180 C
1
3
3
(
decomp.) H-NMR (acetone-d ):
δ
1.19 (d, J = 7.2 Hz, 3H, CH(Me)Ph), 1.44 (d, JHH= 6.8 Hz, 3H,
6
HH
2
2
CH(Me)Ph), 2.58 (d, J = 13.5 Hz, 1H, P-CH -Ph), 2.61 (d, J = 12.8 Hz, 1H, P-CH -Ph), 2.73–2.89
HH
2
HH
2
2
(
1
m, 4H, P-CH -N, partially overlapped with the signal of H O in (CD ) C(O)), 3.12 (d, JHH= 13.5 Hz,
2 2 3 2
2
H, P-CH -Ph), 3.18 (d, J = 12.8 Hz, 1H, P-CH -Ph), 3.53–3.64 (m, 2H, P-CH -N), 3.66–3.78
2 HH 2 2
3
(
(
(
m, 3H, P-CH -N + CH(Me)Ph), 4.05 (q, J = 7.2 Hz, 1H, CH(Me)Ph), 5.18 (s, 5H, C H ), 7.01–7.05
2 HH 5 5
31
1
m, 2H, Har), 7.15–7.24 (m, 6H, Har), 7.25–7.36 (m, 12H, Har). P{ H} NMR (acetone-d ):
d, JPP= 116.4 Hz), 56.27 (d, JPP= 116.4 Hz). ESIpos MS: m/z 687.3 [12 -BF ] . IR (KBr, ν, cm ): 1047
δ 55.55
P
6
2
2
+
−1
4
vs. br. (BF ), 1940 s (CO), 1951 s (CO). Anal. Calc for C H N OP FeBF [744.40]: C 62.04, H 5.86, N
4
40 45
2
2
4
3
.62, P 8.00%. Found: C 61.91, H 5.97, N 3.58, P 7.68%.
0
[
(Cyclopentadienyl)carbonyl(3,7-di(pyridine-2 -yl)-1,5-di(p-tolyl)-1,5-diaza-3,7-diphosphacyclooctane)iron(II)]
tetrafluoroborate (13). A solution of 4 (0.0656 g, 0.135 mmol) in dry toluene (5 mL) was added to solid
CpFe(CO) (THF)]BF (0.0456 g, 0.136 mmol) in dry toluene (1 mL). The reaction mixture was stirred
[
2
4
◦
at 60–70 C temperature for 4 days and turned yellow-orange. The formation of a noticeable amount
of a sticky dark resin was observed. The resin was removed by the centrifugation, the volatiles were
removed from the filtrate under reduced pressure, and the residue was crystallized from diethyl ether.
The precipitate was filtered off, washed twice with diethyl ether, and dried for 3 h at 2 10 torr to
give complex 13 as a yellow powder (0.042 g, 9%). Decomposed at 160 C. H-NMR (acetone-d ):
−
2
·
◦
1
δ
6
2
2
2
.24 (s, 3H, CH ), 2.28 (s, 3H, CH ), 4.04 (d, J = 13.6 Hz, 2H, P-CH -N), 4.22 (dm, J
= 13.6 Hz,
3.4 Hz, 2H, P-CH -N),
= 9.0 Hz, 2H,
HH
= 8.8 Hz, 2H, NC H CH -o),
HH 6 4 3
3
3
HH
2
2
HH
2
4
2
4
JPH
≈
J
≈
3.4 Hz, 2H, P-CH -N), 4.44 (dm, J
= 14.0 Hz, J
≈
JHH
≈
HH
2
HH
PH
2
2
3
3
4
.58 (d, J = 14.0 Hz, 2H, P-CH -N), 5.05(t, J = 1.4 Hz, 5H, C H ), 7.10 (d, J
HH
2
PH
5
3
5
3
NC H CH -o), 7.15 (d, J
= 9.0 Hz, 2H, NC H CH -m), 7.20 (d, J
6
4
3
HH
6
4
3
3
3
3
4
7
8
5
.29 (d, J
= 8.8 Hz, 2H, NC H CH -m), 7.64 (ddm, J
= 7.2 Hz, J
= 4.8 Hz, 2H, H pyr),
HH
= 4.8 Hz, 2H, H pyr). P{ H} NMR (acetone-d ): δ
6 P
, cm ): 1050 vs. br. (BF ), 1940 s (CO), 1950 s (CO).
HH
6
4
3
HH
5
6
3
3
31
1
.06–8.15 (m, 4H, H pyr + H pyr), 8.91 (d, J
9.14. ESIpos MS: m/z 633.4 [12 -BF ] . IR (KBr,
HH
+
−1
ν
4
4
Anal. Calc for C H N OP FeBF [720.27]: C 56.70, H 4.90, N 7.78, P 8.60%. Found: C 56.58, H 5.07, N
34
35
4
2
4
4
.79, P 8.43%.
1
31
Supplementary Materials: The following are available online. H-NMR, P-NMR, mass spectra of synthesized
3
1
compounds, and TG/DSC curve of complex 11b; CIF data for complexes
8
and 11b. Figure S1: P-NMR spectrum
5
; Figure S7: ESI-MS spectrum of
1
31
1
of
3
; Figure S2: H-NMR spectrum of
3
; Figure S3: P-NMR spectrum of
; Figure S6: H-NMR spectrum of
; Figure S10: MALDI-MS spectrum of
; Figure S13: H-NMR spectrum of
protons of P-CH -N, P-CH -Ph, CH(Ph)Me fragments); Figure S14: ESI-MS spectrum of 8; Figure S15: P-NMR
; Figure S17: H-NMR spectrum of
; Figure S19: P-NMR spectrum of 10; Figure S20: H-NMR spectrum
of 10; Figure S21: ESI-MS spectrum of 10; Figure S22: P-NMR spectrum of 11b; Figure S23: H-NMR spectrum
; Figure S4: H-NMR spectrum of
5
;
3
1
1
Figure S5: P-NMR spectrum of
P-NMR spectrum of
P-NMR spectrum of
6
6
6
; Figure S8:
; Figure S11:
(the region of
3
3
1
1
1
7
8
; Figure S9: H-NMR spectrum of
; Figure S12: H-NMR spectrum of
7
8
7
1
1
8
3
1
2
2
1
1
spectrum of
9
; Figure S16: H-NMR spectrum of
protons; Figure S18: ESI-MS spectrum of
9
9, the region of aromatic
3
1
1
9
3
1
1

Molecules 2020, 25, 3775
14 of 17
1
of 11b; Figure S24: H-NMR spectrum of 11b (the region of aliphatic protons); Figure S25: MALDI-MS spectrum
3
1
1
of 11b; Figure S26: TG/DSK diagram of 11b; Figure S27: P-NMR spectrum of 12; Figure S28: H-NMR spectrum
1
of 12; Figure S29: H-NMR spectrum of 12 (the region of aliphatic protons); Figure S30: ESI-MS spectrum of 12
Figure S31: P-NMR spectrum of 13; Figure S32: H-NMR spectrum of 13; Figure S33: H-NMR spectrum of 13
the region of aromatic protons); Figure S34: ESI-MS spectrum of 13.
;
3
1
1
1
(
Author Contributions: Conceptualization, E.I.M. and A.A.K.; Funding acquisition, A.A.K.; Investigation, Y.S.S.,
Y.A.N., A.S.B., I.A.L., I.D.S., and V.V.K.; Methodology, E.I.M., I.A.L., and Y.G.B.; Project administration, A.A.K.;
Supervision, A.A.K.; Writing—original draft, A.S.B.; Writing—review and editing, A.A.K. All authors have read
and agreed to the published version of the manuscript.
Funding: This research was funded by RFBR, grant number 18-03-00833_a.
Acknowledgments: Authors gratefully acknowledge A.V. Gerasimov and V.V. Gorbachuk from Alexander
Butlerov Institute of Chemistry of Kazan Federal University for the TG/DSC analysis, which has been performed
in the frame of subsidy allocated to Kazan Federal University for the state assignment in the sphere of scientific
activities NO 0671-2020-006. The NMR, IR, mass spectra were obtained, and X-ray diffraction analysis and
elemental analysis were performed at the Assigned Spectral-Analytical Center of FRC Kazan Scientific Center
of RAS.
Conflicts of Interest: The authors declare no conflict of interest.
References
1
.
DuBois, D.L.; Bullock, R.M. Molecular Electrocatalysts for the Oxidation of Hydrogen and the Production
of Hydrogen—The Role of Pendant Amines as Proton Relays. Eur. J. Inorg. Chem. 2011, 2011, 1017–1027.
[CrossRef]
2
.
Musina, E.I.; Khrizanforova, V.V.; Strelnik, I.D.; Valitov, M.I.; Spiridonova, Y.S.; Krivolapov, D.B.; Litvinov, I.A.;
Kadirov, M.K.; Lönnecke, P.; Hey-Hawkins, E.; et al. New Functional Cyclic Aminomethylphosphine Ligands
for the Construction of Catalysts for Electrochemical Hydrogen Transformations. Chem. Eur. J. 2014
0, 3169–3182. [CrossRef] [PubMed]
,
2
3
4
.
.
Bullock, R.M.; Helm, M.L. Molecular Electrocatalysts for Oxidation of Hydrogen Using Earth-Abundant
Metals: Shoving Protons Around with Proton Relays. Acc. Chem. Res. 2015, 48, 2017–2026. [CrossRef]
[PubMed]
Kadirov, M.K.; Karasik, A.A.; Nizameev, I.R.; Strelnik, I.D.; Kholin, K.V.; Kadirov, D.M.;
Ismaev, T.I.; Budnikova, Y.G.; Sinyashin, O.G. Organometallic Polymer Electrolyte Membrane Fuel Cell
Bis-Ligand Nickel(II) Complex of 1,5-Di-P-Tolyl-3,7-Dipyridine-1,5,3,7-Diazadiphosphacyclooctane Catalyst.
Energy Technol. 2018, 6, 1088–1095. [CrossRef]
5
6
7
8
.
.
.
.
.
Prokopchuk, D.E.; Wiedner, E.S.; Walter, E.D.; Popescu, C.V.; Piro, N.A.; Kassel, W.S.; Bullock, R.M.;
Mock, M.T. Catalytic N Reduction to Silylamines and Thermodynamics of N Binding at Square Planar Fe.
2
2
J. Am. Chem. Soc. 2017, 139, 9291–9301. [CrossRef]
Burgess, S.A.; Grubel, K.; Appel, A.M.; Wiedner, E.S.; Linehan, J.C. Hydrogenation of CO at Room
2
Temperature and Low Pressure with a Cobalt Tetraphosphine Catalyst. Inorg. Chem. 2017, 56, 8580–8589.
[CrossRef]
Karasik, A.A.; Balueva, A.S.; Musina, E.I.; Sinyashin, O.G. Chelating cyclic aminomethylphosphines and
their transition metal complexes as a promising basis of bioinspired mimetic catalysts. Mendeleev Commun.
2
013, 23, 237–248. [CrossRef]
Shaw, W.J.; Helm, M.L.; DuBois, D.L. A modular, energy-based approach to the development of nickel
containing molecular electrocatalysts for hydrogen production and oxidation. Biochim. Biophys. Acta. 2013
827, 1123–1139. [CrossRef]
,
1
9
1
Bullock, R.M.; Das, A.K.; Appel, A.M. Surface Immobilization of Molecular Electrocatalysts for Energy
Conversion. Chem. Eur. J. 2017, 23, 7626–7641. [CrossRef]
0. Klug, C.M.; Cardenas, A.J.P.; Bullock, R.M.; O’Hagan, M.; Wiedner, E.S. Reversing the Tradeoff Between
Rate and Overpotential in Molecular Electrocatalysts for H 2 Production. ACS Catal. 2018, 8, 3286–3296.
[CrossRef]
1
1. Lense, S.; Dutta, A.; Roberts, J.A.S.; Shaw, W.J. A proton channel allows a hydrogen oxidation catalyst
to operate at a moderate overpotential with water acting as a base. Chem. Commun. 2014, 50, 792–795.
[CrossRef] [PubMed]

Molecules 2020, 25, 3775
15 of 17
1
1
2. Klug, C.M.; Dougherty, W.G.; Kassel, W.S.; Wiedner, E.S. Electrocatalytic Hydrogen Production by a Nickel
Complex Containing a Tetradentate Phosphine Ligand. Organometallics 2019, 38, 1269–1279. [CrossRef]
3. Khrizanforova, V.V.; Musina, E.I.; Khrizanforov, M.N.; Gerasimova, T.P.; Katsyuba, S.A.; Spiridonova, Y.S.;
Islamov, D.R.; Kataeva, O.N.; Karasik, A.A.; Sinyashin, O.G.; et al. Unexpected ligand effect on the
catalytic reaction rate acceleration for hydrogen production using biomimetic nickel electrocatalysts with
1
,5-diaza-3,7-diphosphacyclooctanes. J. Organomet. Chem. 2015, 789–790, 14–21. [CrossRef]
1
1
1
1
4. Mock, M.T.; Chen, S.; O’Hagan, M.; Rousseau, R.; Dougherty, W.G.; Kassel, W.S.; Bullock, R.M. Dinitrogen
Reduction by a Chromium (0) Complex Supported by a16-Membered Phosphorus Macrocycle. J. Am. Chem. Soc.
2013, 135, 11493–11496. [CrossRef] [PubMed]
5. Strelnik, I.D.; Dayanova, I.R.; Poryvaev, T.M.; Gerasimova, T.P.; Litvinov, I.A.; Katsyuba, S.A.; Musina, E.I.;
Karasik, A.A.; Sinyashin, O.G. Rearrangement of two 8-membered 1,5-diaza-3,7-diphosphacyclooctane rings
into 16-membered P N ligand on the gold(I) template. Mendeleev Commun. 2020, 30, 40–42. [CrossRef]
4
4
6. Strelnik, I.D.; Gurzhiy, V.V.; Sizov, V.V.; Musina, E.I.; Karasik, A.A.; Tunik, S.P.; Grachova, E.V.
A stimuli-responsive Au(I) complex based on an aminomethylphosphine template: Synthesis, crystalline
phases and luminescence properties. Cryst. Eng. Comm. 2016, 18, 7629–7635. [CrossRef]
7. Elistratova, J.; Strelnik, I.; Brylev, K.; Shestopalov, M.; Gerasimova, T.; Babaev, V.; Kholin, K.; Dobrynin, A.;
Musina, E.; Katsyuba, S.; et al. Novel water soluble cationic Au(I) complexes with cyclic PNNP ligand
as building blocks for heterometallic supramolecular assemblies with anionic hexarhenium cluster units.
J. Lumin. 2018, 196, 485–491. [CrossRef]
1
1
2
8. Prokopchuk, D.E.; Chambers, G.M.; Walter, E.D.; Mock, M.T.; Bullock, R.M. H Binding, Splitting, and Net
2
Hydrogen Atom Transfer at a Paramagnetic Iron Complex. J. Am. Chem. Soc. 2019, 141, 1871–1876. [CrossRef]
9. Liu, T.; DuBois, D.L.; Bullock, R.M. An iron complex with pendent amines as a molecular electrocatalyst for
oxidation of hydrogen. Nat. Chem. 2013, 5, 228–233. [CrossRef]
0. Liu, T.; Liao, Q.; O’Hagan, M.; Hulley, E.B.; DuBois, D.L.; Bullock, R.M. Iron Complexes Bearing Diphosphine
Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H . Organometallics 2015
,
2
3
4, 2747–2764. [CrossRef]
2
2
2
2
2
2
2
2
1. Jacobsen, G.M.; Shoemaker, R.K.; McNevin, M.J.; Rakowski DuBois, M.; DuBois, D.L. Syntheses and Structural
Characterizations of Iron (II) Complexes Containing Cyclic Diphosphine Ligands with Positioned Pendant
Nitrogen Bases. Organometallics 2007, 26, 5003–5009. [CrossRef]
2. Liu, T.; Chen, S.; O’Hagan, M.J.; Rakowski DuBois, M.; Bullock, R.M.; DuBois, D.L. Synthesis, Characterization,
and Reactivity of Fe Complexes Containing Cyclic Diazadiphosphine Ligands: The Role of the Pendant Base
in Heterolytic Cleavage of H . J. Am. Chem. Soc. 2012, 134, 6257–6272. [CrossRef] [PubMed]
2
3. Liao, Q.; Liu, T.; Johnson, S.I.; Klug, C.M.; Wiedner, E.S.; Bullock, R.M.; DuBois, D.L. Evaluation of attractive
interactions in the second coordination sphere of iron complexes containing pendant amines. Dalton Trans.
2
019, 48, 4867–4878. [CrossRef] [PubMed]
4. Orthaber, A.; Karnahl, M.; Tschierlei, S.; Streich, D.; Stein, M.; Ott, S. Coordination and conformational
isomers in mononuclear iron complexes with pertinence to the [FeFe] hydrogenase active site. Dalton Trans.
2
014, 43, 4537–4549. [CrossRef] [PubMed]
5. Liu, T.; Wang, X.; Hoffmann, C.; DuBois, D.L.; Bullock, R.M. Heterolytic Cleavage of Hydrogen by an Iron
Hydrogenase Model: An Fe-H···H-N Dihydrogen Bond Characterized by Neutron Diffraction. Angew. Chem.
Int. Ed. 2014, 53, 5300–5304. [CrossRef]
6. Kumar, N.; Darmon, J.M.; Weiss, C.J.; Helm, M.L.; Raugei, S.; Bullock, R.M. Outer Coordination Sphere
Proton Relay Base and Proximity Effects on Hydrogen Oxidation with Iron Electrocatalysts. Organometallics
2
019, 38, 1391–1396. [CrossRef]
7. Karasik, A.A.; Naumov, R.N.; Balueva, A.S.; Spiridonova, Y.S.; Golodkov, O.N.; Novikova, H.V.; Belov, G.P.;
Katsyuba, S.A.; Vandyukova, E.E.; Lönnecke, P.; et al. Synthesis, Structure, and Transition Metal Complexes
of Amphiphilic 1,5-Diaza-3,7-diphosphacyclooctanes. Heteroat. Chem. 2006, 17, 499–513. [CrossRef]
8. Ignatieva, S.N.; Balueva, A.S.; Karasik, A.A.; Latypov, S.K.; Nikonova, A.G.; Naumova, O.E.; Lönnecke, P.;
Hey-Hawkins, E.; Sinyashin, O.G. First Representative of Optically Active P-L-Menthyl-Substituted
(Aminomethyl)phosphine and Its Borane and Metal Complexes. Inorg. Chem. 2010, 49, 5407–5412.
[CrossRef]

Molecules 2020, 25, 3775
16 of 17
2
3
3
9. Latypov, S.K.; Strelnik, A.G.; Ignatieva, S.N.; Hey-Hawkins, E.; Balueva, A.S.; Karasik, A.A.; Sinyashin, O.G.
Structure and Dynamics of P, N-Containing Heterocycles and Their Metal Complexes in Solution. J. Phys.
Chem. A 2012, 116, 3182–3193. [CrossRef]
0. Burrows, A.D.; Dodds, D.; Kirk, A.S.; Lowe, J.P.; Mahon, M.F.; Warren, J.E.; Whittlesey, M.K. Substitution
and derivatization reactions of a water soluble iron (II) complex containing a self-assembled tetradentate
phosphine ligand. Dalton Trans. 2007, 570–580. [CrossRef]
1. Burrows, A.D.; Harrington, R.W.; Kirk, A.S.; Mahon, M.F.; Marken, F.; Warren, J.E.; Whittlesey, M.K.
Synthesis, Characterization, and Electrochemistry of a Series of Iron(II) Complexes Containing Self-Assembled
1,5-Diaza-3,7-diphosphabicyclo[3.3.1]nonane Ligands. Inorg. Chem. 2009, 48, 9924–9935. [CrossRef] [PubMed]
3
3
3
2. Landau, S.E.; Morris, R.H.; Lough, A.J. Acidic Dicationic Iron (II) Dihydrogen Complexes and Compounds
Related by H Substitution. Inorg. Chem. 1999, 38, 6060–6068. [CrossRef] [PubMed]
2
3. Halfen, J.A.; Moore, H.L.; Fox, D.C. Synthetic Models of the Reduced Active Site of Superoxide Reductase.
Inorg. Chem. 2002, 41, 3935–3943. [CrossRef] [PubMed]
4. Vela, J.; Smith, J.M.; Yu, Y.; Ketterer, N.A.; Flaschenriem, C.J.; Lachicotte, R.J.; Holland, P.L. Synthesis and
Reactivity of Low-Coordinate Iron (II) Fluoride Complexes and Their Use in the Catalytic Hydrodefluorination
of Fluorocarbons. J. Am. Chem. Soc. 2005, 127, 7857–7870. [CrossRef] [PubMed]
3
5. Quesada, M.; de la Peña-O’Shea, V.A.; Aromí, G.; Geremia, S.; Massera, C.; Roubeau, O.; Gamez, P.;
Reedijk, J. A Molecule-Based Nanoporous Material Showing Tuneable Spin-Crossover Behavior near Room
Temperature. Adv. Mater. 2007, 19, 1397–1402. [CrossRef]
3
6. Zhang, Q.; Xiang, L.; Deng, L. Dinuclear Iron Imido Complexes with N-Heterocyclic Carbene Ligation:
−
Synthesis, Structure, and Redox Reactivity. Organometallics 2012, 31, 4537–4543. [CrossRef]
3
7. Ke, C.-H.; Chen, C.-H.; Tsai, M.-L.; Wang, H.-C.; Tsai, F.-T.; Chiang, Y.-W.; Shih, W.-C.; Bohle, D.S.; Liaw, W.-F.
9
{
Fe(NO) } Dinitrosyl Iron Complex Acting as a Vehicle for the NO Radical. J. Am. Chem. Soc. 2017, 139, 67–70.
2
[
CrossRef]
8. Hemming, E.B.; Chan, B.; Turner, P.; Corcilius, L.; Price, J.R.; Gardiner, M.G.; Masters, A.F.; Maschmeyer, T.
Fe(C Ar )(CO) Br] complexes as hydrogenase mimics for the catalytic hydrogen evolution reaction.
3
[
5
5
2
Appl. Catal. B Environ. 2018, 223, 234–241. [CrossRef]
3
9. Narwane, M.; Chang, Y.-L.; Ching, W.-M.; Tsai, M.-L.; Hsu, S.C.N. Investigation on the coordination behaviors
of tris(2-pyridyl) pyrazolyl borates iron (II) complexes. Inorg. Chim. Acta. 2019, 495, 118966. [CrossRef]
0. Horn, E.; Snow, M.R.; Tiekink, E.R.T. A Polymeric Silver Lutidine Tetrafluoroborate Compound,
4
[Ag(lut)2(µ4-BF )]N, with Weak µ4-Tetrafluoroborate Coordination to Silver. Aust. J. Chem. 1987, 40, 761–765.
4
[CrossRef]
4
1. Blake, A.J.; Brooks, N.R.; Champness, N.R.; Cunningham, J.W.; Hubberstey, P.; Schröder, M. Thioether ligands
as molecular rods in silver(I) coordination networks: 1,4-dithiane as an analogue of pyrazine. CrystEngComm
2
000, 6, 41–45. [CrossRef]
4
4
2. Fenton, H.; Tidmarsh, I.S.; Ward, M.D. Hierarchical self-assembly of heteronuclear co-ordination networks.
Dalton Trans. 2010, 39, 3805–3815. [CrossRef] [PubMed]
3. Kilduff, B.; Pogozhev, D.; Baudron, S.A.; Hosseini, M.W. Heterometallic Architectures Based on the Combination
of Heteroleptic Copper and Cobalt Complexes with Silver Salts. Inorg. Chem. 2010, 49, 11231–11239. [CrossRef]
[PubMed]
4
4
4
4
4. Poorters, L.; Armspach, D.; Matt, D.; Toupet, L.; Jones, P.G. A Metallocavitand Functioning as a Container
for Anions: Formation of Noncovalent Linear Assemblies Mediated by a Cyclodextrin-Entrapped NO Ion.
3
Angew. Chem. Int. Ed. 2007, 46, 2663–2665. [CrossRef] [PubMed]
5. Cimadevilla, F.; Garc
í
a, E.M.; Garc
í
a-Viv
ó
, D.; Ruiz, M.A.; Rueda, M.T.; Halut, S. Protonation reactions
5
of the oxo complex cis-[Mo (h -C H ) (O)(
µ-PPh2)2(CO)]. Hydroxo and tetrafluoroborate derivatives.
2
5
5 2
J. Organomet. Chem. 2012, 699, 67–74. [CrossRef]
6. Musina, E.I.; Karasik, A.A.; Balueva, A.S.; Strelnik, I.D.; Fesenko, T.I.; Dobrynin, A.B.; Gerasimova, T.P.;
Katsyuba, S.A.; Kataeva, O.N.; Lönnecke, P.; et al. Synthesis and Stereoselective Interconversion of Chiral
1
-Aza-3,6-diphosphacycloheptanes. Eur. J. Inorg. Chem. 2012, 2012, 1857–1866. [CrossRef]
7. Kilgore, U.J.; Roberts, J.A.S.; Pool, D.H.; Appel, A.M.; Stewart, M.P.; Rakowski DuBois, M.; Dougherty, W.G.;
Kassel, W.S.; Bullock, R.M.; DuBois, D.L. [Ni(PPh2NC6H4X ) ] Complexes as Electrocatalysts for H Production:
2+
2 2
2
Effect of Substituents, Acids, and Water on Catalytic Rates. J. Am. Chem. Soc. 2011, 133, 5861–5872. [CrossRef]

Molecules 2020, 25, 3775
17 of 17
4
8. Kilgore, U.J.; Stewart, M.P.; Helm, M.L.; Dougherty, W.G.; Kassel, W.S.; Rakowski DuBois, M.; DuBois, D.L.;
Bullock, R.M. Studies of a Series of [Ni(PR2NPh ) (CH3CN)]2+ Complexes as Electrocatalysts for H Production:
2 2
2
Substituent Variation at the Phosphorus Atom of the P N Ligand. Inorg. Chem. 2011, 50, 10908–10918. [CrossRef]
2
2
4
5
9. Sheldrick, G.M. SHELXT-Integrated space-group and crystal-structure determination. Acta Crystallogr. Sect.
A Found. Adv. 2015, 71, 3–8. [CrossRef]
0. Sheldrick, G.M. Crystal structure refinement with SHELXL Acta Crystallogr. Sect. C Struct. Chem. 2015
1, 3–8. [CrossRef]
,
7
5
5
1. Farrugia, L.J.J. WinGX and ORTEP for Windows: An update. Appl. Crystallogr. 2012, 45, 849–854. [CrossRef]
2. Flack, H.D.; Bernardinelli, G. Reporting and evaluating absolute-structure and absolute-configuration
determinations. J. Appl. Crystallogr. 2000, 33, 1143–1148. [CrossRef]
5
3. Spek, A.L. Structure validation in chemical crystallography. Acta Crystallogr. Sect. D Struct. Biol. 2009
5, 148–155. [CrossRef] [PubMed]
,
6
Sample Availability: Samples of the compounds 6–13 are available from the authors.
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