N2 Activation by an Iron Complex with a Strong Electron-Donating Iminophosphorane Ligand

Article abstract of DOI:10.1021/acs.inorgchem.5b00536

A new tridentate cyclopentane-bridged iminophosphorane ligand, N-(2-diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine (NpNP^iPr), was synthesized and used in the preparation of a diiron

Full text of DOI:10.1021/acs.inorgchem.5b00536

Forum Article
pubs.acs.org/IC
N Activation by an Iron Complex with a Strong Electron-Donating
2
Iminophosphorane Ligand
†
,‡
†
†
†
†
Tatsuya Suzuki, Yuko Wasada-Tsutsui, Takahiko Ogawa, Tomohiko Inomata, Tomohiro Ozawa,
§
,‡
,†
Yoichi Sakai, Michael D. Fryzuk,* and Hideki Masuda*
†Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya
66-8555, Japan
4
‡
Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
§Department of Chemistry, Daido University, Takiharu-cho, Minami-ku, Nagoya 457-8530, Japan
S Supporting Information
*
ABSTRACT: A new tridentate cyclopentane-bridged iminophosphorane
ligand, N-(2-diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-
iPr
diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine (NpNP ),
was synthesized and used in the preparation of a diiron dinitrogen
iPr
complex. The reaction of the iron complex FeBr(NpNP ) with KC8
under dinitrogen yielded the dinuclear dinitrogen Fe complex [Fe-
iPr
(
NpNP )] (μ-N ), which was characterized by X-ray analysis and
2 2
resonance Raman and NMR spectroscopies. The X-ray analysis revealed a
diiron complex bridged by the dinitrogen molecule, with each metal
iPr
center coordinated by an NpNP ligand and dinitrogen in a trigonal-
monopyramidal geometry. The N−N bond length is 1.184(6) Å, and
resonance Raman spectra indicate that the N−N stretching mode
1
4
15
−1
ν( N / N ) is 1755/1700 cm . The magnetic moment of [Fe-
(
2
2
iPr
1
NpNP )] (μ-N ) in benzene-d solution, as measured by H NMR spectroscopy by the Evans method, is 6.91μ (S = 3).
2
2
6
B
The Mo
̈
ssbauer spectrum at 78 K showed δ = 0.73 mm/s and ΔE = 1.83 mm/s. These findings suggest that the iron ions are
Q
2
−
divalent with a high-spin configuration and that the N molecule has (NN) character. Density functional theory calculations
2
iPr
performed on [Fe(NpNP )] (μ-N ) also suggested that the iron is in a high-spin divalent state and that the coordinated
2
2
dinitrogen molecule is effectively activated by π back-donation from the two iron ions (dπ) to the dinitrogen molecule (π* and
x
πy*). This is supported by cooperation between a large negative charge on the iminophosphorane ligand and strong electron
donation and effective orbital overlap between the iron dπ orbitals and N π* orbitals supplied by the phosphine ligand.
2
INTRODUCTION
complexes with β-diketiminate ligands (nacnac), which have a
low coordination number for the iron centers with coordinated
■
(
The first dinitrogen metal complex was identified as [Ru-
2+
1
N
, similar to that suggested in the nitrogenase active site of
2
NH ) (N )] by Allen and Senoff in 1965. Subsequently, a
3 5 2
FeMoco, activate N2 more effectively than five- or six-
wide variety of transition-metal complexes with coordinated
dinitrogen have been studied by inorganic and organometallic
8
d,e
coordinate iron−N complexes.
These reports suggest that
2
2
a coordinatively unsaturated electron-rich iron complex can
effectively capture and activate dinitrogen.
chemists. The chemical conversion of N2 to ammonia
promoted by a well-defined catalyst precursor has also been
studied using mainly Mo and Fe complexes from the viewpoint
of the structure−function relationships identified in the
nitrogenase FeMoco active center (which includes Fe and
The coordinated dinitrogen molecule in dinitrogen-bridged
diiron complexes can in general be formally considered as
2−
either a neutral N or as a N2 dianion, depending whether π
2
back-bonding from the metal to the dinitrogen moiety is
operative. Thus, the coordinated dinitrogen molecule can be
activated if the metal ion is stabilized by a strong σ-donating
ancillary ligand system, which in turn enhances overlap of the
metal dπ and dinitrogen π* orbitals. Recently, Peters and co-
3
Mo). In this context, molybdenum dinitrogen complexes have
been studied and examples of crystal structures have been
4
reported. Catalytic conversion of dinitrogen to ammonia by
molybdenum complexes has been investigated mainly by
5
6
Schrock and Nishibayashi. Capture and activation of
dinitrogen using base-metal complexes have been studied by
7
8
9
Special Issue: Small Molecule Activation: From Biological Principles
to Energy Applications
the groups of Chirik, Holland, and Peters using low-valent
iron and cobalt complexes.
Additionally, Holland and co-workers recently published a
Received: March 11, 2015
report indicating that the three- and four-coordinate iron−N2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
Scheme 1. Synthesis of LiNpNPiPr and HNpNPiPr
workers investigated iron complexes with tris(phosphino)silyl,
bis(phosphino)(thioether)silyl, and bis(thioether)(phosphino)-
9
b
silyl ligands.
complexes were found to bind dinitrogen, while the bis-
thioether)(phosphino)silyl ligands could not. Instead, it was
The former two mononuclear iron(II)
(
found that the latter complex traps dinitrogen in the presence
of hydride anion. These findings indicate that strong σ donation
from the ancillary ligands to the metal ion is essential to
facilitate capture of dinitrogen.
Building on the above findings, in this paper we describe the
design and synthesis of a new tridentate NpNP ligand, N-(2-
diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-
diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine
iPr
(
NpNP ), that incorporates an iminophosphorane unit (R −
3
PN−R), an electron-rich phosphine, and an aryl imine. This
combination was chosen to mimic the nacnac donor set by the
10
combination of the imine and iminophosphorane moieties
and enhance it by the presence of the phosphine donor. We
anticipated that this combination of donors would provide an
electron-rich metal center, which in turn would allow increased
activation of the dinitrogen moiety upon coordination. We also
report the synthesis and characterization of a formally
monovalent diiron(I) dinitrogen complex with NpNP and
discuss the activation of the coordinated dinitrogen.
Figure 1. ORTEP drawing of the crystal structure of LiNpNPiPr with
ellipsoids at the 30% probability level. All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): P(1)−
N(2) 1.6202(13), P(1)−C(17) 1.757(2), P(2)−C(29) 1.825(3),
N(1)−C(13) 1.3348(19), N(2)−C(24) 1.398(3), C(13)−C(17)
iPr
1
.395(3), C(24)−C(29) 1.421(2), N(1)−C(13)−C(17) 129.10(16),
P(1)−C(17)−C(13) 131.57(11), N(2)−P(1)−C(17) 110.53(9),
P(1)−N(2)−C(24) 125.75(14), N(2)−C(24)−C(29) 119.55(18),
P(2)−C(29)−C(24) 118.95(14), P(2)−Li(1)−N(1) 155.4(2),
P(2)−Li(1)−N(2) 87.56(15), N(1)−Li(1)−N(2) 117.03(17).
RESULTS AND DISCUSSION
■
iPr
Synthesis and Characterization of the HNpNP
iPr
Ligand and the LiNpNP Complex. The synthesis of the
iPr
iPr
compounds HNpNP and LiNpNP is illustrated in Scheme
iPr
1
. The cyclopentylidene-based phosphine−amine starting
structure of HNpNP , which contains two independent
iPr
material 2,6-diisopropyl-N-(2-diisopropylphosphinocyclo-
HNpNP molecules in the unit cell, is shown in Figure 2. In
iPr
iPr
pentylidene)aniline (HNP ), which contains a bulky 2,6-
the crystal structure of LiNpNP (Figure 1), the lithium ion is
diisopropylphenyl group on the amine nitrogen, was synthe-
coordinated to the anilide nitrogen, the phosphine phosphorus,
and the phosphoranimine nitrogen of NpNP to form a
11
iPr
sized according to literature procedures. The reaction of
iPr
HNP with 2-bromophenyl azide (2-Br-Ar-N ) gave the
trigonal plane. The sum of the bond angles at the lithium ion is
close to 360° (P(2)−Li(1)−N(1) = 155.4(2)°, P(2)−Li(1)−
N(2) = 87.56(15)°, N(1)−Li(1)−N(2) = 117.03(17)°). The
3
iPr
12
phosphazide HNpN Br in high yield as previously reported.
3
Subsequent heating of the product at 80 °C overnight produced
iPr
iPr
the iminophosphorane HNpNBr in excellent high yield. The
molecular structure of the protonated derivative HNpNP is
iPr
reaction of HNpNBr with 2 equiv of n-BuLi followed by the
bent from the N−P−N plane containing the cyclopentyl ring,
iPr
iPr
reaction with iPr PCl yielded LiNpNP . The crystal structure
although it is essentially the same as the structure of LiNpNP .
2
iPr
of LiNpNP is shown in Figure 1. The lithium salt was
This indicates that the π electrons in the N−P−N ring in
iPr
protonated with Me NHCl in tetrahydrofuran (THF) to form
LiNpNP are delocalized compared with the π electrons of
3
iPr
iPr
the neutral ligand HNpNP . Colorless block crystals of
HNpNP were obtained after storage at −35 °C. The crystal
HNpNP , which adopts the enamine tautomeric form. This
iPr
iPr
interpretation is supported by the bond lengths of the NpNP
B
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
Figure 2. ORTEP drawing of the crystal structure of HNpNPiPr with ellipsoids at the 30% probability level. All hydrogen atoms except for H(1) and
H(3) have been omitted for clarity. Selected bond lengths (Å) and angles (deg): P(1)−N(2) 1.5855(11), P(1)−C(17) 1.7726(17), P(2)−C(29)
1
1
.839(3), P(3)−N(4) 1.5900(11), P(3)−C(52) 1.7687(15), P(4)−C(64) 1.837(3), N(1)−C(13) 1.3609(19), N(2)−C(24) 1.383(3), N(3)−C(48)
.3570(18), N(4)−C(59) 1.385(3), C(13)−C(17) 1.364(3), C(24)−C(29) 1.4222(19), C(48)−C(52) 1.362(2), C(59)−C(64) 1.4172(19),
N(1)−C(13)−C(17) 128.20(15), P(1)−C(17)−C(13) 124.24(11), N(2)−P(1)−C(17) 113.82(7), P(1)−N(2)−C(24) 128.13(13), N(2)−
C(24)−C(29) 118.06(18), P(2)−C(29)−C(24) 117.81(15), N(3)−C(48)−C(52) 128.14(14), P(3)−C(52)−C(48) 123.56(11), N(4)−P(3)−
C(52) 113.50(7), P(3)−N(4)−C(59) 126.72(13), N(4)−C(59)−C(64) 117.99(17), P(4)−C(64)−C(59) 117.21(15).
Scheme 2. Synthesis of the Iron Complex with the NpNPiPr Ligand and Reduction To Generate the Dinitrogen Complex
ligands of LiNpNPiPr and HNpNPiPr as follows; for LiNpNPiPr,
structure of FeBr(NpNP ) (Figure 3) revealed a distorted
iPr
the P(1)−N(2), P(1)−C(17), C(17)−C(13), and N(1)−
trigonal-monopyramidal geometry (τ = 0.64; the value of τ was
13
C(13) bond lengths are 1.6202(13), 1.757(2), 1.395(3), and
calculated by using eq 1 in the Experimental Section) with the
Br, anilide nitrogen, and phosphine in the basal plane and the
phosphoranimine nitrogen at the apex. The sum of the angles
in the basal trigonal plane is 353.0° (i.e., close to 360°)
(Br(1)−Fe(1)−N(1) = 121.06(5)°, Br(1)−Fe(1)−P(2) =
113.575(14)°, and P(2)−Fe(1)−N(1) = 118.29(5)°). The
average angle of the axial ligands from the basal plane is close to
90° (N(2)−Fe(1)−Br(1) = 109.24(5)°, N(2)−Fe(1)−N(1) =
102.49(7)°, and N(2)−Fe(1)−P(2) = 83.67(5)°). The bond
iPr
1
.335(2) Å, respectively, while for HNpNP , the P(1)−N(2)/
P(3)−N(4), P(1)−C(17)/P(3)−C(52), C(17)−C(13)/
C(52)−C(48), and N(1)−C(13)/N(3)−C(48) bond lengths
are 1.5855(1)/1.5900(11), 1.7726(17)/1.7687(15), 1.364(3)/
1
.362(2), and 1.3609(19)/1.3570(18) Å, respectively. Fur-
iPr
thermore, for compound HNpNP , a hydrogen bond extends
between the enamine NH and the phosphoranimine (N(1)···
N(2)/N(3)···N(4) = 3.006/2.990 Å), which likely stabilizes the
1
iPr
enamine tautomer. Evidence for this is also provided by the H
lengths between the ligands and the metal in FeBr(NpNP )
and 31P NMR spectra of HNpNP (Figures S3 and S4 in the
Supporting Information), which show that there is only one
species present in solution.
iPr
are Fe(1)−Br(1) = 2.4323(4), Fe(1)−P(2) = 2.4037(5), and
Fe(1)−N(1) = 2.0004(16) for the basal plane and Fe(1)−N(2)
= 2.0515(19) Å for the axial ligand. These bond lengths and the
geometry at the metal center are very similar to those of a
previously reported high-spin Fe(II) complex with a pyridine-
Preparation and Characterization of the Fe(II)
iPr
Complex with the NpNP Ligand. Treatment of the
iPr
14
lithium salt LiNpNP with FeBr (THF) in Et O yielded the
linked bis(anilide) pincer ligand. The π electrons of the ligand
2
2
2
iPr
iron bromide complex FeBr(NpNP ), which acts as a
precursor to the diiron dinitrogen complex, as shown in
Scheme 2. The iron monobromide complex could be obtained
as single crystals suitable for X-ray analysis. The crystal
backbone are also delocalized on the N−P−N ring, as
understood from the bond lengths (P(1)−N(2) =
1.6275(14), P(1)−C(17) = 1.769(2), C(17)−C(13) =
1.384(4), and N(1)−C(13) = 1.362(3) Å). As expected, the
C
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
5
.06μ , which indicates that the complex is paramagnetic and
B
has four unpaired electrons, consistent with high-spin Fe(II).
Preparation and Characterization of the Diiron
Dinitrogen Complex. Reduction of the iron(II) bromide
iPr
complex FeBr(NpNP ) with KC8 under a dinitrogen
atmosphere produced a color change from yellow to dark
brown. Fortunately, we obtained dark-red single crystals under
a dinitrogen atmosphere from n-pentane, which were found to
be highly sensitive to air. X-ray crystal structure analysis
revealed a dinuclear iron complex bridged by μ-N , [Fe-
2
iPr
(
NpNP )] (μ-N ) (Figure 4). In the crystal structure, the two
2 2
iron sites were found to be rotated with respect to each other
about the μ-N molecule with a N(2)−Fe(1)−Fe(2)−N(4)
2
torsion angle of 92.07°. Each iron complex has a distorted
trigonal-monopyramidal geometry (τ = 0.64 and 0.65 for Fe(1)
and Fe(2), respectively) with the μ-N2 nitrogen, anilide
nitrogen, and phosphine phosphorus atoms in the basal
trigonal plane and the phosphoranimine nitrogen at the apex.
For the Fe(1) site, the sum of the angles in the basal plane,
Figure 3. ORTEP drawing of the crystal structure of FeBr(NpNPiPr)
with ellipsoids at the 30% probability level. All hydrogen atoms have
been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Br(1)−Fe(1) 2.4323(4), Fe(1)−P(2) 2.4037(5), Fe(1)−N(1)
3
53.02°, is close to 360° (N(5)−Fe(1)−N(1) = 122.33(16)°,
N(5)−Fe(1)−P(2) = 104.55(13)°, and P(2)−Fe(1)−N(1) =
26.14(14)°). The average angle of the axial ligand from the
1
2
.0004(16), Fe(1)−N(2) 2.0515(19), P(1)−N(2) 1.6275(14),
basal plane is close to 90° (N(2)−Fe(1)−N(5) = 116.23(17),
N(2)−Fe(1)−N(1) = 99.19(14), and N(2)−Fe(1)−P(2) =
80.30(12)°). For the Fe(2) site, the sum of the angles in the
basal plane, 353.17°, is close to 360° (N(6)−Fe(2)−N(3) =
P(1)−C(17) 1.769(2), C(13)−C(17) 1.384(4), C(24)−C(29)
1
.417(3), P(2)−C(29) 1.812(3), Br(1)−Fe(1)−P(2) 113.575(14),
Br(1)−Fe(1)−N(1) 121.06(5), Br(1)−Fe(1)−N(2) 109.24(5),
P(2)−Fe(1)−N(1) 118.29(5), P(2)−Fe(1)−N(2) 83.67(5), N(1)−
Fe(1)−N(2) 102.49(7).
1
22.29(14)°, N(6)−Fe(2)−P(4) = 105.16(13)°, and P(4)−
Fe(2)−N(3) = 125.72(10)°). The average angle of the axial
ligand from the basal plane is close to 90° (N(4)−Fe(2)−N(6)
= 113.38(16), N(4)−Fe(2)−N(3) = 101.56(16), and N(4)−
Fe(2)−P(4) = 79.96(10)°). The bond lengths of the ligands to
1
iPr
H NMR spectra of FeBr(NpNP ) in C D included
6
6
broadened signals in the paramagnetic region (Figure S5).
The magnetic moment of FeBr(NpNP ) in the solution state,
as measured by the Evans method, was found to be μeff
iPr
iPr
the Fe(1) ion in the trigonal plane for [Fe(NpNP )] (μ-N )
2
2
1
5
=
are Fe(1)−N(1) = 1.983(4), Fe(1)−N(2) = 2.117(4), Fe(1)−
iPr
Figure 4. ORTEP drawing of the crystal structure of [Fe(NpNP )] (μ-N ) with ellipsoids at the 30% probability level. All hydrogen atoms have
2
2
been omitted for clarity. Selected bond lengths (Å) and angles (deg): Fe(1)−P(2) 2.3486(16), N(5)−N(6) 1.186(6), Fe(1)−N(1) 1.983(4),
Fe(1)−N(2) 2.117(4), Fe(1)−N(5) 1.800(4), Fe(2)−P(4) 2.3466(13), Fe(2)−N(3) 1.992(4), Fe(2)−N(4) 2.125(4), Fe(2)−N(6) 1.812(4),
P(1)−N(2) 1.614(4), P(1)−C(17) 1.758(5), P(2)−C(29) 1.823(5), P(3)−N(4) 1.622(5), P(3)−C(52) 1.747(5), P(4)−C(64) 1.815(5), N(1)−
C(13) 1.340(6), N(2)−C(24) 1.407(6), N(3)−C(48) 1.351(7), N(4)−C(59) 1.400(6), C(13)−C(17) 1.384(6), C(24)−C(29) 1.416(8), C(48)−
C(52) 1.383(7), C(59)−C(64) 1.430(8).
D
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
Table 1. Selected Bond Lengths and ν(N ) Stretching Vibration Frequencies of [Fe(NpNPiPr) ] (μ-N ) and a Comparison with
2
2 2
2
Bond Lengths and ν(N ) Stretching Vibration Frequencies of Formally Monovalent Iron Dinitrogen Compounds Reported
2
Previously
complex
coordination number
Fe−N (Å)
1.816(2)
N−N (Å)
1.151(3)
νNN (cm−1)
ref
a
[
[
[
[
[
[
[
[
{
{
Fe(nacnacMe)(tBupy)] (μ-N )
4
4
4
3
3
4
5
5
8
4
1770
8d
8d
2
2
tBu
Fe(nacnac )(tBupy)] (μ-N )
1.804(2), 1.794(2)
1.800(4), 1.814(4)
1.745(3), 1.775(2)
1.760(6), 1.778(6)
1.811(5), 1.818(5)
1.817(4)
1.161(4)
2
2
iPr
a
Fe(NpNP )] (μ-N )
1.184(6)
1755
this work
2
2
Fe(nacnacMe)] (μ-N )
1.186(7), 1.172(5)
1.182(5)
1810
a
8d
8d
16
9c
17
18
19
2
2
tBu
a
Fe(nacnac )] (μ-N )
1778
2
2
iPr
Fe(PhBP )] (μ-N )
1.138(6)
3
2
2
iPr
b
Fe(SiP )(N )]
1.1065(5)
1.106(3)
2008
3
2
Ph
3
b
Fe(SiP )(N )]
1.819(2)
2041
2
tBu
a
[(ArN) C ]Fe} (μ-N )
1.834(3)
1.124(6)
2005
2
2
2
tBu
a
Fe[N(SiMe N )(C H PiPr )]} (μ-N )
1.8510(15)
1.166(3)
1760
2
2
4
2
2
2
a
b
Measured by resonance Raman spectroscopy. Measured by IR spectroscopy.
N(5) = 1.800(4), and Fe(1)−P(2) = 2.3486(16) Å, while those
around Fe(2) are Fe(2)−N(3) = 1.992(4), Fe(2)−N(4) =
2
2
.125(4), Fe(2)−N(6) = 1.814(4), and Fe(2)−P(4) =
.3466(13) Å. The formally monovalent Fe(I)−dinitrogen
bonds (Fe(1)−N(5) = 1.800(4) and Fe(2)−N(6) = 1.814(4)
Å) are similar to those of [Fe(nacnac )(tBupy)] (μ-N )
Me
2
2
8
b,d
reported previously (Fe−N = 1.800(4) and 1.814(4) Å).
2
The N−N bond length of the bridged N molecule in
2
iPr
[
Fe(NpNP )] (μ-N ) is N(5)−N(6) = 1.184(6) Å, which is
2
2
significantly longer than that of metal-free N (1.098 Å) and
2
slightly elongated compared with those of mononuclear and
dinuclear Fe(I) complexes bound with a dinitrogen molecule
(Table 1).
The activated nature of dinitrogen was also clearly indicated
by vibrational spectroscopy. The resonance Raman spectra of
the dinitrogen complexes as measured with 532 nm excitation
contain a band assignable to the ν(N ) stretching vibration of
2
−
1
iPr
μ-N at 1755 cm for [Fe(NpNP )] (μ-N ) that shifts to
2
2
2
−1
15
14
1
700 cm when N is employed instead of N (Figure 5).
2
2
The isotope shift is within the range of the shift expected for a
coordinated dinitrogen molecule. The observed μ-N is at a
2
lower frequency than the analogous stretching vibrations of
Me
14
15
−1
[
Fe(nacnac )(tBupy)] (μ-N ) ( N 1770/ N 1708 cm )
2 2
tBu
14
−1
and [Fe(nacnac )] (μ-N ) ( N 1778 cm ) reported by
Holland and co-workers
2
2
8
b,d
and has the lowest frequency value
among those reported previously. This indicates that the N2
molecule is moderately activated by a formally monovalent
iPr
Fe(I) complex with an NpNP ligand (Table 1).
iPr
1
iPr
Figure 5. Resonance Raman spectra of [Fe(NpNP )] (μ-N ) in n-
The H NMR spectrum of [Fe(NpNP )] (μ-N ) in C D is
2
2
2
2
6
6
iPr
14
pentane: (a) [Fe(NpNP )] (μ- N ) in n-pentane, (b) [Fe-
NpNP )] (μ- N ) in n-pentane, and (c) n-pentane.
2
2
broad and shifted, consistent with the presence of paramagnetic
iron centers (Figure S6 in the Supporting Information); the
solution-state magnetic moment of μ = 6.91μ (indicating six
iPr
15
(
2 2
eff
B
1
5
unpaired electrons) was measured by the Evans method. In
order to study the oxidation and spin states of the metal center,
N ) is S = 3 with antiferromagnetic coupling between dianionic
2
2−
N2 and diiron(II).
we measured the Mo
̈
ssbauer spectrum of the complex
iPr
DFT Calculations on [Fe(NpNP )] (μ-N ). The molecular
structure optimized for [Fe(NpNP )] (μ-N ) in the S = 3
state was found to be essentially identical to the structure
obtained by X-ray analysis within 0.08 Å, except for the Fe−P
bonds. Such longer bonds are often seen in the structures
optimized under vacuum conditions. The calculated frequency
2
2
iPr
[
Fe(NpNP )] (μ-N ). The spectrum at 78 K showed a
iPr
2
2
2 2
quadrupole doublet with isomer shift (δ) of 0.73 mm/s and a
quadrupole splitting (ΔE ) of 1.83 mm/s (Figure 6), which are
Q
Me
8f
similar to those of [Fe(nacnac )] (μ-N ) reported previously
2
2
(
δ = 0.62 mm/s, ΔE = 1.41 mm/s). This indicates that one
Q
−1
electron from each iron is transferred to an antibonding π*
orbital of the dinitrogen molecule by π back-donation, and the
resultant transferred electron of dinitrogen is antiferromagneti-
of the ν(N ) stretching vibration, 1753 cm , also agrees well
2
with that obtained by Raman measurement. The electronic
structure of the dinitrogen diiron complex was assessed using
density functional theory (DFT) calculation results obtained on
cally coupled with an unpaired electron of high-spin Fe(II) with
four unpaired electrons; the spin state of [Fe(NpNP )] (μ-
iPr
iPr
the basis of the crystal structure of [Fe(NpNP )] (μ-N ).
2
2
2
E
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
metal as well as π back-donation from the metal to the
dinitrogen, which weakens the N−N bond of the dinitrogen
molecule. Interestingly, no differences were observed in the
electron density around the chelating ligand upon coordination
of dinitrogen to the iron sites, as shown in Figure 7a. This
iPr
indicates that the negative charge on the NpNP ligand
functions as a barrier to electron back-flow to assist the π back-
donation from the iron center to the dinitrogen ligand. The
change in the electron distribution at the phosphine ligand is
attributed to a change in electron configuration between the
two dπ orbitals on each iron center that are hyperconjugated
with the P−C σ* orbital. This suggests that some amount of
electron density on the iron center pushed out by σ donation
from the phosphine ligands is moved into the P−C σ* orbital,
iPr
3
16
which might be similar to the case of [Fe(PhBP )] (μ-N ).
2
2
Figure 6. Zero-field 57Fe Mo
2
ssbauer spectrum of [Fe(NpNP )] (μ-
iPr
̈
2
On the basis of the results of natural population analysis for
N ) at 78 K. The dotted line shows the experimental data, and the
solid line is the fitted curve using the parameters δ = 0.73 mm/s and
ΔE = 1.83 mm/s. The line width at half-maximum of the Lorentzian
peaks was estimated to be 0.34 mm/s. The small unfitted areas seen in
the figure are probably due to impurities.
iPr
[Fe(NpNP )] (μ-N ) (Table 2), increases in negative charge
2
2
and β-spin density on the dinitrogen ligand were also observed.
The spin density on the iron center was found to be 3.28 and
the atomic charge of dinitrogen was found to be −0.70,
indicating that the electron density transferred from the high-
spin Fe(I) centers to the dinitrogen ligand is less than 1. For
comparison, we also carried out DFT calculations on the diiron
dinitrogen complexes with β-diketiminato ligands reported
Q
The differential density and spin density maps are shown in
Figure 7a,b, respectively. The density increases in the vicinity of
Me
previously by Holland et al., namely, [Fe(nacnac )] (μ-N ),
2
2
Me
tBu
[
(
Fe(nacnac )(tBupy)] (μ-N ), and [Fe(nacnac )-
2 2
8d
tBupy)] (μ-N ). The atomic charges and spin densities of
2
2
these complexes are listed together in Table 2. The infusion of
electron density into dinitrogen increases in the following
Me
tBu
order: [Fe(nacnac )(tBupy)] (μ-N ) < [Fe(nacnac )-
2
2
iPr
(
(
tBupy)] (μ-N ) < [Fe(NpNP )] (μ-N ) < [Fe-
2 2 2 2
Me
nacnac )] (μ-N ). This appears to be due to the presence
2
2
of a larger negative charge (−1.10, −1.09) on the
iPr
phosphoranimine N atom for [Fe(NpNP )] (μ-N ) than on
2
2
the nacnac N atoms of the reference complexes with the same
Me
coordination number, [Fe(nacnac )] (μ-N ) (−0.69, −0.69),
2
2
Me
[
Fe(nacnac )(tBupy)] (μ-N ) (−0.65, −0.65), and [Fe-
2
2
tBu
(
nacnac )(tBupy)] (μ-N ) (−0.65, −0.69). The larger neg-
2
2
ative charge may have contributed to an increase in π back-
donation from the metal to the dinitrogen. The charges on the
iPr
metal centers in [Fe(NpNP )] (μ-N ) (0.73, 0.72) are less
2
2
Me
than those of the reference complexes, [Fe(nacnac )] (μ-N )
0.93, 0.93), [Fe(nacnac )(tBupy)] (μ-N ) (0.95, 0.95) and
2
2
Me
(
[
2 2
tBu
Fe(nacnac )(tBupy)] (μ-N ) (0.97, 0.97). This suggests that
2 2
the electron density on the iron centers is due to σ donation
from the phosphine ligands, which promotes the π back-
donation from the metal to the dinitrogen.
Orbital Overlap Interactions between the Coordi-
nated Dinitrogen and the Iron Metal Center. To discuss
the contribution of the NpNP ligand to activation of the
iPr
Figure 7. (a) Differential density map with respect to dinitrogen
iPr
complexation in [Fe(NpNP )] (μ-N ). The red and blue regions
coordinated dinitrogen, we focused on the four highest
occupied β orbitals (Figure S7 in the Supporting Information),
which are the most important orbitals when we consider the
bonding nature. Interestingly, these orbitals are all involved in π
back-donation from the iron centers to dinitrogen. The electron
distribution on dinitrogen in the upper two orbitals is at least
two-thirds as large as that on the iron centers (as shown by the
percentage of components of atomic orbitals described in
Figure S7a,b). This observation provides insights into the
formal iron(I) ion, which includes iron(II) ion character.
Additionally, hyperconjugation was identified between the
phosphine σ*(P−C) orbital and the metal dδ orbitals with
the nodal plane along the Fe−P bond. This leads to a modest
2
2
indicate increases and decreases in electron density, respectively, that
iPr
occur upon complexation. (b) Spin density map of [Fe(NpNP )] (μ-
2
N ). The red and blue regions show excess densities of α spin and β
2
spin, respectively.
the Fe−N bond axes and considerably decreases in the N−N σ-
bonding and lone-pair orbitals. The differential density map can
be interpreted using the spin density map (Figure 7b). The
increase in the electron density seen in the vicinity of the
coordinated dinitrogen molecule is induced by β-spin density.
That is, the decrease in the electron density in the N−N
bonding region is due to σ donation from the dinitrogen to the
F
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
Table 2. Population Analysis for Diiron μ-Dinitrogen Complexes
[
Fe(nacnacMe
)
[Fe(nacnactBu
)
iPr
[Fe(nacnacMe)] (μ-N )
a
a
a
[
Fe(NpNP )] (μ-N )
(tBupy)] (μ-N )
(tBupy)] (μ-N )
2
2
2
2
2
2
2
2
bond lengths (Å)
N−N
1.186
1.185
1.746
1.151
1.815
1.167
Fe−N
1.799
337.7
1.812
1.800
349.0
1.799
350.4
b
planarity
337.2
359.1
359.1
345.6
345.6
atomic charges
c
N2
−0.70
−0.77
−0.65
−0.69
Fe
0.73
0.72
0.93
0.93
0.95
0.95
0.97
0.97
d
N(diket)
−0.72
−1.10
−0.73
−1.09
−0.69
−0.69
−0.69
−0.69
−0.69
−0.65
−0.69
−0.65
−0.70
−0.65
−0.65
−0.69
e
N(imino/diket)
atomic spin density
Fe
3.28
3.30
3.37
3.37
c
N2
−0.83
−0.91
−0.79
−0.82
orbital overlap population between Fe and N
f
MO
0.100
0.141
0.099
0.136
0.101
0.146
0.101
0.146
0.092
0.126
0.092
0.126
0.095
0.130
0.095
0.130
g
NO
a
b
The crystal structure was taken from ref 8d. The sum of the three angles around an iron center with respect to the chelate ring and the dinitrogen
c
ligand, as a measure of coplanarity. The value 360° indicates that the dinitrogen ligand is completely coplanar with the chelate ring. The total
charge/spin density of the dinitrogen ligand. The N atoms attached to a phenyl group in our complex, one pair of N atoms in each β-diketiminate
ligand furthest apart in complex [Fe(nacnac )(tBupy)] (μ-N ), and the pair of N atoms furthest apart from the pyridine attached to the other
center in complex [Fe(nacnac )(tBupy)] (μ-N ). The imino N atom in our complex and the other pair of N atoms in each β-diketiminate ligand
in complex [Fe(nacnac )(tBupy)] (μ-N ) and [Fe(nacnac )(tBupy)] (μ-N ). The sum of Q for the four highest occupied Kohn−Sham β
i,Fe−N
orbitals. The sum of Q
d
Me
2
2
tBu
e
2
2
Me
tBu
f
2
2
2
2
g
for the natural orbitals having π bonding and antibonding nature between iron and dinitrogen.
i,Fe−N
lowering of the dδ orbital energy (Figure S7c,d), as described in
Chart 1. Orbital Interactions between the dπ and dδ Orbitals
of Fe and the π* Orbitals of the Coordinated Dinitrogen
Using Virtual Coordination Structures for
Me
Chart 1. On the other hand, in [Fe(nacnac )(tBupy)] (μ-
2
8
d
Me
N2), such hyperconjugation between the nacnac ligand and
the dδ orbitals of the metal ion has not been found (Chart S1 in
the Supporting Information).
iPr
a
[Fe(NpNP )] (μ-N )
2
2
The orbital overlap interactions between metal d orbitals and
dinitrogen orbitals were evaluated by examining the
QFe−N(MO) values (eq 5 in the Experimental Section), which
are listed in Table 2. Interestingly, the QFe−N(MO) values for
iPr
[
[
(
Fe(NpNP )] (μ-N ) (0.100, 0.099) are larger than those of
2 2
Me
Fe(nacnac )(tBupy)] (μ-N ) (0.092, 0.092) and [Fe-
2
2
tBu
nacnac )(tBupy)] (μ-N ) (0.095, 0.095), although their
2
2
Fe−N bond lengths are almost the same within experimental
iPr
error. Also, the values for [Fe(NpNP )] (μ-N ) are similar to
2
2
Me
those for [Fe(nacnac )] (μ-N ) (0.101, 0.101), although the
2
2
Fe−N bonds of the former are longer than those of the latter.
These findings indicate that the infusion of electrons into the
dinitrogen molecule depends on the orbital overlap interaction
rather than the Fe−N bond lengths.
We considered the orbital overlap of the dπ orbitals with the
dinitrogen π* orbitals in the series of diiron dinitrogen nacnac
Me
Me
complexes [Fe(nacnac )] (μ-N ), [Fe(nacnac )(tBupy)] (μ-
2
2
2
tBu
N ), and [Fe(nacnac )(tBupy)] (μ-N ) to compare with that
2
2
2
iPr
Me
in [Fe(NpNP )] (μ-N ). In [Fe(nacnac )] (μ-N ), the
2
2
2
2
effective orbital overlap of the dπ orbitals with the dinitrogen
π* orbitals, which are essentially coplanar with both of the
iron−nacnac planes (359.1°, 359.1°), results in substantial
electron donation from the metal to the dinitrogen. On the
other hand, the orbital overlaps of the dπ orbitals with the
a
(
top, bottom) Hyperconjugation of (top) a dπ orbital and (bottom) a
dδ orbital on each iron center with the σ*(P−C) orbital of the
coordinated phosphine ligand controls the orientations of the dπ
orbitals, leading to a great orbital overlap between the iron dπ orbital
and a π* orbital of the coordinated dinitrogen. The donor−acceptor
interaction energies evaluated with second-order perturbation theory
based on NBO are listed in Table S2 in the Supporting Information.
Stabilization energies arising from the donor−acceptor interaction are
Me
dinitrogen π* orbitals in [Fe(nacnac )(tBupy)] (μ-N ) and
2
2
tBu
[
(
Fe(nacnac )(tBupy)] (μ-N ) are less than that in [Fe-
nacnac )] (μ-N ). This is explained in terms of the fact
2 2
Me
2
2
that the iron−nacnac planes of the former two complexes are
(top) 0.98 to 1.06 and (bottom) 1.46 to 1.61 kcal/mol. (middle)
bent out of the nodal plane of one dinitrogen π* orbital
iPr
Hyperconjugation between Fe and the NpNP ligand is not observed.
Me
(
3
345.6°, 345.6° for [Fe(nacnac )(tBupy)] (μ-N ) and 349.0°,
2 2
tBu
50.4° for [Fe(nacnac )(tBupy)] (μ-N )) in comparison with
2 2
iPr
that of the latter, as shown in Table 2. In [Fe(NpNP )] (μ-
2
G
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
−
N ), the electron infusion into the dinitrogen is as large as that
molecule is N 2 . The effective activation of dinitrogen through
2
2
Me
iPr
in [Fe(nacnac )] (μ-N ) in spite of a large deviation of the π*
π back-donation is induced by the NpNP ligand system,
2
2
orbitals from the enamido−iminophosphorane N−P−N plane
which has negative charges on the enamido N and
phosphoranimine N atoms and the strong electron-donating
ability of the phosphine.
(337.7°, 337.2°). The orbital overlaps of the iron dπ orbitals
with the dinitrogen π* orbitals, as described above, are induced
by hyperconjugation (Chart 1 top and bottom): the σ*(P−
C(isopropyl)) orbital of the coordinated phosphine ligand
overlaps attractively with one of the two dπ orbitals on each
iron center (Chart 1 top), and the σ*(P−C(phenyl)) orbital of
the same phosphine ligand overlaps attractively with the dδ
orbitals (Chart 1 bottom). The orientations of the dπ orbitals
on the iron center are controlled by the hyperconjugation with
the phosphine ligand and by the negative charge on the N
EXPERIMENTAL SECTION
Caution! Because of the sensitivity of the n-BuLi and KC reagents toward
moisture and oxygen, these should be handled with great care.
General Methods. All manipulations were carried out under an
atmosphere of purified argon or dinitrogen gas in an MBRAUN MB
150B-G glovebox or by standard Schlenk techniques. H and P NMR
■
8
1
31
1
spectra were measured on a Varian Mercury 300 spectrometer, and H
and 31P chemical shifts were estimated relative to TMS and H PO as
iPr
atoms of the NpNP ligand; both of these N atoms are just
3
4
internal standards, respectively. Fourier transform infrared (FT-IR)
spectra of solid compounds were measured on KBr pellets using a
JASCO FT/IR-410 spectrophotometer. Elemental analyses were
obtained with a PerkinElmer CHN-900 elemental analyzer. Magnetic
moment measurements (Evans method) in the solid state were
obtained using a Sherwood Scientific Ltd. MSB-MKI magnetic
susceptibility balance. The solution-state magnetic moments were
placed on the nodal planes of a dπ orbital. As structural
evidence, the dihedral angles between the plane defined by the
Fe, P, and dinitrogen N atoms and the plane defined by the Fe,
N(phosphoranimine), and dinitrogen N atoms (86.2° and
8
5.4°, respectively) are close to a right angle. Furthermore, the
P−Fe−N(N ) bond angles are 104.55(13)° and 105.16(13)°,
which are close to a right angle in comparison with the
2
1
15
determined by the Evans method using H NMR spectroscopy.
corresponding angles of N(enamido)−Fe−N(N )
Resonance Raman spectral measurements were carried out using a
JASCO NKS-1000 spectrophotometer. Raman scattering was excited
using the 532 nm emission from an Ar laser (Laser Quantum, Ventus
532) and detected using a CCD detector (Andor, DU420-OE)
attached to a single polychromator (Ritsu Oyo Kogaku, DG-1000).
Spectra were recorded at ambient temperature, and the laser power at
the sample point was 30 mW. The slit width was set to 200 μm. All
measurements were carried out with samples contained in a spinning
cell (3000 rpm) at room temperature. Raman shifts were calibrated
with indene, and the accuracy of the peak positions of the Raman
2
(
122.33(16)°, 122.29(14)°) and N(iminophosphorane)−Fe−
N(N ) (116.23(17)°, 113.38(16)°).
2
iPr
Therefore, the dinitrogen molecule in [Fe(NpNP )] (μ-N )
2
2
iPr
is moderately activated by the supporting functional NpNP
ligand in spite of the bending of the nodal plane of one
dinitrogen π* orbital from the enamido−iminophosphorane
N−P−N plane. This indicates that dinitrogen activation is
promoted by a strong interaction between the phosphine ligand
and the Fe dδ/dπ orbitals. Additionally, as described above, it is
very important that the significant activation of the coordinated
dinitrogen molecule is also induced by the greater negative
charge on the iminophosphorane groups. We can propose that
the combination of the phosphine and iminophosphorane
−1
bands was ±1 cm .
Zero-field 57Fe Mo
ssbauer spectra were recorded on a spectrometer
̈
(
Topologic Systems Inc.) at 78 K in constant-acceleration mode.
Co/Rh was used as the radiation source. MossWinn 4.0Pre software
http://www.mosswinn.com/) was used for quantitative evaluation of
57
(
the spectral parameters (least-squares fitting to Lorentzian peaks).
Isomer shifts were determined relative to α-iron at 298 K.
iPr
groups of the functional NpNP ligand system provide
activation of the dinitrogen molecule.
The τ value is defined in terms of the difference between the sum of
the basal ligand−basal ligand angles and the sum of the basal ligand−
1
3
CONCLUSION
We have succeeded in synthesizing [Fe(NpNP )] (μ-N ), a
novel diiron dinitrogen complex, using our new NpNP ligand,
axial ligand angles:
■
iPr
2
2
∑
(basal−M−basal) − ∑(basal−M−axial)
0°
X-ray Crystallography. All of the single crystals obtained
iPr
τ =
9
(1)
which includes an iminophosphorane backbone with strong σ-
iPr
donating ability. The crystal structure of [Fe(NpNP )] (μ-N )
2
2
iPr
iPr
iPr
iPr
revealed a formally monovalent diiron(I) complex bridged by a
dinitrogen molecule. The two iron sites are twisted around the
dinitrogen molecule with a torsion angle of 92.07°. The N−N
bond length of 1.184(6) Å is very close to the N−N bond
lengths of the previously reported diiron dinitrogen complexes
(HNpNP , Li(NpNP ), FeBr(NpNP ), and [Fe(NpNP )] (μ-
2
N )) were analyzed by X-ray diffraction. Each crystal was mounted on
2
a glass fiber, and diffraction data were collected using a Rigaku/MSC
Mercury CCD with graphite-monochromatized Mo Kα radiation at
−
100 or −150 °C. All crystal data and experimental details are listed in
tBu
Me
Table S1 in the Supporting Information. The crystal structures were
[
Fe(nacnac )] (μ-N ) (1.182(5) Å) and [Fe(nacnac )] (μ-
2
2
2
20
solved by a combination of direct methods (SIR92 ) and Fourier
iPr
N ) (1.186(7) Å). The N−N bond in [Fe(NpNP )] (μ-N )
lies in the longest bond range among those of diiron(I)
dinitrogen complexes reported previously. The ν( N / N )
stretching vibration frequencies, 1755/1700 cm , are the
lowest frequencies observed among the formally monovalent
diiron(I) dinitrogen complexes reported previously (Table 1).
2
2
2
techniques. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were refined by the riding model using the
8d
14
15
2
1
2
2
appropriate HFIX command in SHELXL97. The Sheldrick
−1
weighting scheme was applied for all crystals. Plots of ∑(|F | − |
o
2
F |) versus |F |, reflection order in data collection, sin θ/λ, and various
classes of indices showed no unusual trends. Neutral atomic scattering
factors were taken from Cromer and Waber. Anomalous dispersion
c
0
2
2
̈
The Mossbauer spectrum at 78 K showed a quadrupole doublet
2
3
effects were included in Fcalc
,
and the values for Δf′ and Δf″ were
with δ = 0.73 mm/s and ΔE = 1.83 mm/s. The diiron
Q
24
obtained from Creagh and McAuley. The values for the mass
dinitrogen complex is paramagnetic in benzene solution (S = 3,
25
attenuation coefficients are those of Creagh and Hubbell. All of the
μeff = 6.91μ ) and can be considered to contain two iron(II)
B
calculations were performed using the CrystalStructure crystallo-
graphic software package.
General Procedures. All of the reagents employed were
commercially available. Toluene, THF, and diethyl ether were
purchased in anhydrous form from Wako Ltd. and passed through
6
ions, each in the high-spin d state. The two Fe(II) ions (S = 2
for each) and N2 are antiferromagnetically coupled, similar to
the case of [Fe(nacnac )] (μ-N ). DFT calculations provided
2−
Me
2
2
evidence that the electronic state of the coordinated dinitrogen
H
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
columns containing activated alumina and Ridox catalyst. C D was
For comparison, a similar analysis was carried out for three diiron
6
6
dried by distillation from sodium/benzophenone. Diisopropylamine
dinitrogen complexes with low-coordinate β-diketiminato derivatives
8
d
Me
was dried over CaH and distilled prior to use. n-Butyllithium was
reported previously by Holland et al.: [Fe(nacnac )] (μ-N )
2
2 2
Me
purchased from Aldrich, and the concentration was determined via
(three-coordinate), [Fe(nacnac )(tBupy)] (μ-N ) (two-coordinate),
2 2
and [Fe(nacnac )(tBupy)] (μ-N ) (two-coordinate). The π back-
tBu
direct titration with diphenylcarboxylic acid. KC was prepared
8
2 2
26
according to a literature procedure. All other compounds were
bonding interaction with the σ* orbital along the P−C bond was
purchased from commercial suppliers and used as received. 2,6-
evaluated with second-order perturbation theory analysis of the Fock
3
2
Diisopropyl-N-(2-diisopropylphosphinocyclopentylidene)aniline
matrix in the NBO basis.
iPr
(
HNP ) was synthesized according to the previously published
All of the electronic structure calculations were performed using
1
1
27
33
method. o-Bromophenyl azide was prepared as outlined below.
Gaussian 09, revision D.01, and the isosurfaces of the molecular
34
DFT Calculation Details. The most stable structure of the diiron
dinitrogen complex obtained in the present work was determined by a
full optimization of the structure using a DFT calculation in which the
crystal structure obtained by X-ray analysis was employed as the
starting complex. The DFT calculations for electron and spin density
orbitals were drawn using the MOPLOT and MOVIEW programs
on the Fujitsu CX400 system at the Nagoya University Information
Technology Center.
iPr
iPr
Preparation of LiNpNP and HNpNP . Synthesis of o-
Bromophenyl Azide (2-Br-Ar-N ). The compound was prepared by a
3
2
7
analyses were performed using the crystal structure of [Fe-
modification of a literature procedure. o-Bromoaniline (6.4 g, 37.2
mmol) was added to 5 mL of concentrated hydrochloric acid and 30
mL of water in an ice bath. To the cold solution was slowly added 20
iPr
(
NpNP )] (μ-N ) for the sake of comparison with other compounds.
2 2
28
The calculations were carried out using the B3LYP functional. The
following basis sets were used for the respective atoms: 6-311G(d) for
29e,f
mL of an aqueous solution of NaNO (2.57 g, 37.2 mmol), and the
2
2
9a,b 29c
29d
Fe,
P, N, and olefin C of the chelate ring and 6-31G(d)
resulting mixture was stirred at 0 °C for 0.5 h. This is an exothermic
reaction, and the resulting diazonium salt is unstable at high
temperatures. Stirring vigorously and keeping the temperature low is
important. Excess nitrous acid was removed by addition of urea. NaN3
for other C and H atoms. For drawing electron density maps, 6-311G
was employed for the Fe atom. Two diffuse p functions, which were
developed by Wachters, were added to the basis set of the Fe atom.
29a
These functions were multiplied by 1.5. For the spin state of the Fe
(2.40 g, 37.2 mmol) was then added slowly to the reaction solution,
atom, S = 3, which was obtained from magnetic moment with Evans
and the resulting mixture was stirred for 1 h to obtain a white
precipitate, which was extracted from the solution with 3 × 50 mL of
diethyl ether. The combined extracts were washed with water and
dilute hydrochloric acid (0.1 M) and dried over magnesium sulfate.
The solvent was removed in vacuo, and the oily residue was isolated by
silica gel chromatography with n-hexane as the eluent to yield the
iPr
method, was employed for [Fe(NpNP )] (μ-N ).
2
2
In order to examine the change in electron density accompanying
coordination of a dinitrogen molecule to a pair of the corresponding
monoiron complexes, a differential density function, Δρ(r), was
evaluated according to eq 2:
1
product as a pale-yellow oil (6.49 g, 32.7 mmol, 88% yield). H NMR
Δρ(r) = ρ(r, diiron dinitrogen complex)
(
300 MHz, δ/ppm in CDCl ): 7.01 (t, 1H, Ar−H), 7.17 (d, 1H, Ar−
3
−1
H), 7.35 (t, 1H, Ar−H), 7.55 (d, 1H, Ar−H). FT-IR (ν/cm ): 2131,
2
−
+
{ρ(r, diiron complex without dinitrogen)
ρ(r, dinitrogen)}
037 (azide).
(2)
Synthesis of (E)-N-(2-(((2-Bromophenyl)triazenylidene)-
diisopropylphosphoranyl)cyclopentenyl)-2,6-diisopropylaniline
where ρ(r, X) on the right represents electron density at a point r for
species X with atomic coordinates in the crystal structure of the diiron
dinitrogen complex.
iPr
(
HNpN Br ). Under a dinitrogen atmosphere, o-bromophenyl azide
3
(
16.5 g, 83.4 mmol) was added to a 10 mL solution of 2,6-diisopropyl-
iPr
N-(2-diisopropylphosphinocyclopentylidene)aniline (HNP ) in THF
30.0 g, 83.4 mmol). The resulting mixture was stirred at room
The quantitative changes in natural atomic charges and spin
densities that occur upon coordination of dinitrogen to the metal
(
temperature for 3 h. Volatiles were removed in vacuo. The desired
30
31
complexes were estimated. Mulliken population analysis was
carried out for the four highest occupied Kohn−Sham β orbitals
concerning the π back-donation from iron to dinitrogen, and the
orbital overlap populations (Qi,Fe−N; eq 3) and gross populations (qi,Fe
compound was obtained as a yellow powder (41.5 g, 74.4 mmol, 89%
1
yield). H NMR (300 MHz, δ/ppm in benzene-d ): 1.02−1.09, 1.19−
6
1
.31 (m, 24H, (CH ) CH−Ar and (CH ) CH−P), 1.59 (m, 2H,
CH CH CH ), 2.12 (m, 2H, CH CH CH ), 2.23 (m, 2H,
3
2
3 2
2
2
2
2
2
2
and q ; eq 4) were calculated in order to evaluate the contributions to
i,N
CH CH CH ), 2.25 (m, 2H, (CH ) CH−P), 3.45 (m, 2H,
2
2
2
3 2
the interaction between the iron ions and dinitrogen and their
compositions:
(
CH ) CH−Ar), 6.70−6.75 (m, 2H, Ar−H), 7.08−7.23 (m, over-
3
2
lapped, Ar−H), 7.61 (d, 1H, Ar−H), 7.73 (d, 1H, Ar−H) 10.53 (s,
1
H, NH). 31P NMR (121 MHz, δ/ppm in benzene-d ): 50.18 (s).
6
Q
= ∑ ∑ C C S
i,Fe−N
ai bi ab
Anal. Calcd for C H N P: C, 62.47; H, 7.59; N, 10.05. Found: C,
29
42
4
a∈ Fe b∈ N
(3)
6
2.35; H, 7.92; N, 9.98.
Synthesis of N-(2-Bromophenyl)-P,P-diisopropyl-P-(2-(2,6-
qi,A = ∑ ∑ C C S
ai bi ab
diisopropylphenylamino)cyclopent-1-enyl)phosphoranimine
(HNpNBr ). Under a dinitrogen atmosphere, HNpN Br (25 g, 44.8
(4)
iPr
iPr
a∈ A b∈ all
3
mmol) was dissolved in toluene (100 mL) and heated at 80 °C for 1
day. The solvent was removed in vacuo. The resulting mixture was
redissolved in n-pentane and stored at −35 °C. The desired compound
where A denotes Fe or dinitrogen N, Sab is the overlap integral
between atomic orbitals a and b, and Cμi is the molecular orbital
coefficient for atomic orbital μ in the ith molecular orbital. The sum of
Qi,Fe−N for the four orbitals (QFe−N(MO); eq 5) was estimated as a
measure of π back-donation from the metal dπ orbitals to the
dinitrogen π* orbitals. The sum of Qi,Fe−N weighted by the occupation
1
was obtained as colorless crystals (17.5 g, 33.0 mmol, 74% yield). H
NMR (300 MHz, δ/ppm in benzene-d ): 1.20−1.31 (m, 24H,
6
(
1
2
CH ) CH−Ar and (CH ) CH−P), 1.440 (m, 2H, CH CH CH ),
3
2
3
2
2
2
2
.85 (m, 2H, CH CH CH ), 1.94 (m, 2H, CH CH CH ), 2.32 (m,
2 2 2 2 2 2
number n for the natural orbitals (QFe−N(NO); eq 5) was also
i
H, (CH ) CH−P), 3.61 (m, 2H, (CH ) CH−Ar), 6.54 (m, 1H, Ar−
3
2
3 2
estimated as a measure of the overlap contributed by both the α and β
electrons, where the contributions of π-bonding and π-antibonding
character between iron and dinitrogen predominate in comparison
with the Kohn−Sham orbitals.
H), 7.08−7.14 (m, 3H, Ar−H, Ar−H), 7.21−7.25 (m, 2H, Ar−H, Ar−
31
H), 7.67 (m, 1H, Ar−H) 10.99 (s, 1H, NH). P NMR (121 MHz, δ/
ppm in benzene-d ): 34.98 (s).
6
Synthesis of N-(2-Diisopropylphosphinophenyl)-P,P-diisopropyl-
P-(2-(2,6-diisopropylphenylamido)cyclopent-1-enyl)-
Q
(MO/NO) = ∑ n ∑ ∑ C C S
Fe−N
i
ai bi ab
iPr
phosphoranimine Lithium Salt (LiNpNP ). Under a dinitrogen
i a∈ Fe b∈ N
(5)
atmosphere, to a solution of N-(2-bromophenyl)-P,P-diisopropyl-P-(2-
where n = 1 for occupied Kohn−Sham β orbitals.
(2,6-diisopropylphenylamino)cyclopent-1-enyl)phosphoranimine in
i
I
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
Et O (20 g, 37.7 mmol) was added n-BuLi (1.6 M, 47.2 mL, 75.5
d ). Anal. Calcd for C H Fe N P ·2(C H O): C, 66.00; H, 9.23; N,
2
6
70 110
2
6
4
4
10
mmol) dropwise at −78 °C. The resulting mixture was stirred for 4 h
as it was warmed to 23 °C. The mixture was cooled to −78 °C again,
and 20 mL of a diethyl ether solution of chlorodiisopropylphosphine
5.92. Found: C, 65.69; H, 8.89; N, 5.68.
ASSOCIATED CONTENT
■
(
6 mL, 37.7 mmol) was added dropwise. Thereafter, the reaction
*
S
Supporting Information
mixture was warmed to ambient temperature overnight. Volatiles were
removed in vacuo, and n-pentane was added to the mixture, which was
then filtered through Celite using a glass frit. Excess n-pentane was
removed in vacuo to give a dark-brown oil. The oil was dissolved in n-
pentane again and stored in the freezer at −35 °C. The desired
compound was obtained as a white powder (15.2 g, 26.5 mmol, 70%
1
31
iPr
iPr
H and P NMR spectra of LiNpNP and HNpNP ; crystal
iPr
iPr
iPr
structures of LiNpNP , HNpNP , FeBr(NpNP ), and
iPr
[Fe(NpNP )] (μ-N ) (CIF); detailed information on the X-
2 2
ray crystal analysis; and computational results. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.inorgchem.5b00536.
iPr
yield). Several recrystallizations of LiNpNP from n-pentane gave
1
colorless single crystals suitable for X-ray analysis. H NMR (300
MHz, δ/ppm in benzene-d ): 0.81−1.42 (m, 36H, (CH ) CH−Ar and
6
3 2
AUTHOR INFORMATION
Corresponding Authors
*E-mail: masuda.hideki@nitech.ac.jp.
*E-mail: fryzuk@chem.ubc.ca.
Notes
■
(
CH ) CH−P), 1.78 (m, 7 Hz, 2H, CH CH CH ), 1.89 (m, 2H,
3
2
2
2
2
(
CH ) CH−P), 2.32 (m, 2H, CH CH CH ), 2.49−2.61 (m, 4H,
3
2
2
2
2
CH CH CH and (CH ) CH−P), 3.63 (m, 7 Hz, 2H, (CH ) CH−
2
2
2
3
2
3 2
Ar), 6.74 (t, 1H, Ar−H), 6.92 (m, 1H, Ar−H), 7.09 (m, 1H, Ar−H),
31
7
.15−7.21 (overlapped, Ar−H), 7.27 (d, 2H, Ar−H). P NMR (121
MHz, δ/ppm in benzene-d ): 38.78 (s), −6.68 (s). Anal. Calcd for
C H N P Li: C, 73.40; H, 9.68; N, 4.89. Found: C, 73.17; H, 9.57;
6
The authors declare no competing financial interest.
3
5
55
2 2
N, 4.82.
ACKNOWLEDGMENTS
Synthesis of N-(2-Diisopropylphosphinophenyl)-P,P-diisopropyl-
■
P-(2-(2,6-diisopropylphenylamino)cyclopent-1-enyl)-
We gratefully acknowledge support for this work by a Grant-in-
Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology of Japan and by the
iPr
phosphoranimine (HNpNP ). Under a dinitrogen atmosphere,
Me NHCl (165 mg, 1.75 mmol) was added to 2 mL of a solution
3
iPr
of LiNpNP in THF (1 g, 1.75 mmol). The mixture was stirred at
“
Strategic Young Researcher Overseas Visits Program for
room temperature for 6 h. The reaction mixture was filtered to give a
yellow solution. Volatiles were removed in vacuo, and 2 mL of n-
pentane was added to the mixture, which was then stored in the freezer
Accelerating Brain Circulation” of the Japan Society for the
Promotion of Science. We also thank Toyota Motor
Corporation for financial support and for many helpful
discussions. The NSERC of Canada is also acknowledged for
support in the form of a Discovery Grant to M.D.F. We thank
Prof. Ko Mibu (NIT) for technical assistance.
iPr
at −35 °C. The compound HNpNP was obtained as a white powder
(
545 mg, 55% yield). Several recrystallizations of HNpNPiPr from n-
1
pentane gave colorless single crystals suitable for X-ray analysis. H
NMR (300 MHz, δ/ppm in benzene-d ): 0.97−1.13 (m, 12H,
6
(
CH ) CH−P), 1.12−1.25 (m, 24H, (CH ) CH−P and (CH ) CH−
3
2
3
2
3 2
Ar), 1.55 (m, 2H, CH CH CH ), 2.06 (m, 2H, CH CH CH ), 2.17−
2
(
1
1
2
2
2
2
2
2
REFERENCES
.27 (m, 4H, CH CH CH and (CH ) CH−P), 3.32 (sep, 7 Hz, 2H,
■
2
2
2
3 2
CH ) CH−Ar), 6.81 (t, 1H, Ar−H), 6.88 (m, 1H, Ar−H), 7.07 (d,
(1) Allen, A. D.; Senoff, C. V. Chem. Commun. 1965, 621−622.
(2) (a) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115−1133.
(b) Chirik, P. J. Dalton Trans. 2007, 16−25. (c) Fryzuk, M. D. Chem.
Commun. 2013, 49, 4866−4868. (d) Hidai, M. Coord. Chem. Rev.
1999, 185−186, 99−108. (e) Chatt, J.; Dilworth, J. R.; Richards, R. L.
Chem. Rev. 1978, 78, 589−625.
(3) (a) Einsle, O.; Tezcan, F. A.; Andrade, S. L. A.; Schmid, B.;
Yoshida, M.; Howard, J. B.; Rees, D. C. Science 2002, 297, 1696−1700.
(b) Lancaster, K. M.; Roemelt, M.; Ettenhuber, P.; Hu, Y.; Ribbe, M.
W.; Neese, F.; Bergmann, U.; DeBeer, S. Science 2011, 334, 974−977.
(c) Spatzal, T.; Aksoyoglu, M.; Zhang, L.; Andrade, S. L. A.;
Schleicher, E.; Weber, S.; Rees, D. C.; Einsle, O. Science 2011, 334,
940.
3
2
H, Ar−H), 7.19 (overlapped, Ar−H), 7.21 (m, 2H, Ar−H), 9.00 (s,
H, NH). 31P{ H} NMR (121 MHz, δ/ppm in benzene-d ): 25.09 (s),
1
6
−
4.56 (s). Anal. Calcd for C H N P : C, 74.17; H, 9.96; N, 4.94.
Found: C, 73.17; H, 10.10; N, 4.28.
35 56 2 2
iPr
Preparation of Fe(NpNP )Br. Under a dinitrogen atmosphere,
FeBr (THF) (3.01 g, 8.41 mmol) was added to 40 mL of a solution
2
2
iPr
of LiNpNP in Et O (4.83 g, 8.43 mmol). The mixture was stirred at
room temperature for 3 h. The reaction mixture was filtered through
Celite to give a yellow solution. Volatiles were removed in vacuo, and
2
3
0 mL of n-pentane was added to the mixture, which was then stored
iPr
in the freezer at −35 °C. The compound FeBr(NpNP ) was obtained
as a yellow powder (5.18 g, 7.38 mmol, 87% yield). Several
recrystallizations of FeBr(NpNP ) from n-pentane gave pale-yellow
single crystals suitable for X-ray analysis. H NMR (300 MHz, δ/ppm
iPr
(4) (a) Chatt, J.; Pearman, A. J.; Richards, R. L. Nature 1975, 253,
39−40. (b) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc.,
Dalton Trans. 1977, 1852−1860. (c) Chatt, J.; Dilworth, J. R. Chem.
Commun. 1975, 983−984. (d) George, T. M.; Tisdale, C. J. Am. Chem.
Soc. 1985, 107, 5157−5159. (e) Ogawa, T.; Kajita, Y.; Wasada-Tsutsui,
Y.; Wasada, H.; Masuda, H. Inorg. Chem. 2013, 52, 182−195.
(5) (a) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76−78.
(b) Schrock, R. R. Acc. Chem. Res. 2005, 38, 955−962.
1
in benzene-d ): −146.81, −22.66, −9.90, −8.82, −5.38, −4.44, −2.37,
6
1
4
.12, 3.27, 4.72, 8.13, 12.41, 13.28, 19.16, 24.22, 28.36, 30.25, 33.34,
6.49, 87.88, 106.99. μeff = 5.06μ (Evans method). Anal. Calcd for
B
C H BrFeN P : C, 61.25; H, 7.71; N, 4.46. Found: C, 61.09; H,
3
5
55
2 2
7
.18; N, 4.38.
Preparation of [Fe(NpNPiPr)] (μ-N ). Under a dinitrogen
2
2
atmosphere, KC (100 mg, 0.74 mmol) was added to a slurry of
FeBr(NpNP ) (500 mg, 0.71 mmol) in n-pentane (10 mL). The
(6) Arashiba, K.; Miyake, Y.; Nishibayashi, Y. Nat. Chem. 2011, 3,
120−125.
8
iPr
reaction mixture was stored overnight at −35 °C and then stirred for 1
day at room temperature to yield a dark-red solution. Graphite and
KBr were removed by filtration, and the solvent was reduced in
volume to 1 mL in vacuo. After the solution was stored at −35 °C for a
few days, black needle crystals were obtained (51 mg, 13% yield). The
(7) (a) Russell, S. K.; Darmon, J. M.; Lobkovsky, E.; Chirik, P. J.
Inorg. Chem. 2010, 49, 2782−2792. (b) Trovitch, R. J.; Lobkovsky, E.;
Chirik, P. J. Inorg. Chem. 2006, 45, 7252−7260. (c) Hoyt, J. M.;
Sylvester, K. T.; Semproni, S. P.; Chirik, P. J. J. Am. Chem. Soc. 2013,
135, 4862−4877. (d) Bowman, A. C.; Milsmann, C.; Atienza, C. C. H.;
Lobkovsky, E.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2010, 132,
1676−1684.
(8) (a) Holland, P. L. Dalton Trans. 2010, 39, 5415−5425. (b) Smith,
J. M.; Lachicotte, R. J.; Pittard, K. A.; Cundari, T. R.; Lukat-Rodgers,
G.; Rodgers, K. R.; Holland, P. L. J. Am. Chem. Soc. 2001, 123, 9222−
desired crystals for elemental analysis were also obtained from Et O,
2
and the corresponding crystal structure is shown in Figure S9 in the
1
Supporting Information. H NMR (300 MHz, δ/ppm in benzene-d ):
6
−
37.56, −18.01, 10.53, 0.59, 0.87, 1.22, 17.29, 18.12, 19.77, 23.40,
3
3.73, 39.52, 46.89, 148.29. μeff = 6.92μ (Evans method, in benzene-
B
J
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
9
223. (c) Rodriguez, M. M.; Bill, E.; Brennessel, W. W.; Holland, P. L.
5639−5648. (d) Raghavachari, K.; Binkley, J. S.; Seeger, R.; Pople, J. A.
J. Chem. Phys. 1980, 72, 650−654. (e) Hehre, W. J.; Ditchfield, R.;
Pople, J. A. J. Chem. Phys. 1972, 56, 2257−2261. (f) Hariharan, P. C.;
Pople, J. A. Theor. Chem. Acc. 1973, 28, 213−222.
Science 2011, 334, 780−783. (d) Smith, J. M.; Sadique, A. R.; Cundari,
T. R.; Rodgers, K. R.; Lukat-Rodgers, G.; Lachicotte, R. J.;
Flaschenriem, C. J.; Vela, J.; Holland, P. L. J. Am. Chem. Soc. 2006,
1
28, 756−769. (e) Holland, P. L. Can. J. Chem. 2005, 83, 296−301.
f) Stoian, S. A.; Vela, J.; Smith, J. M.; Sadique, A. R.; Holland, P. L.;
Munck, E.; Bominaar, E. L. J. Am. Chem. Soc. 2006, 128, 10181−
0192. (g) Lee, Y.; Sloane, F. T.; Blondin, G.; Abboud, K. A.; García-
Serres, R.; Murray, L. J. Angew. Chem., Int. Ed. 2015, 54, 1499−1503.
9) (a) Moret, M.-E.; Peters, J. C. J. Am. Chem. Soc. 2011, 133,
(30) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735−746.
(
̈
(31) Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833−1840.
1
(32) (a) Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural
Bond Orbital Donor−Acceptor Perspective; Cambridge University Press:
Cambridge, U.K., 2005. (b) Reed, A. E.; Curtiss, L. A.; Weinhold, F.
Chem. Rev. 1988, 88, 899−926.
(
1
8118−18121. (b) Takaoka, A.; Mankad, N. P.; Peters, J. C. J. Am.
Chem. Soc. 2011, 133, 8440−8443. (c) Whited, M. T.; Mankad, N. P.;
Lee, Y.; Oblad, P. F.; Peters, J. C. Inorg. Chem. 2009, 48, 2507−2517.
(33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
(
(
(
(
4
1
d) Lee, Y.; Mankad, N. P.; Peters, J. C. Nat. Chem. 2010, 2, 558−565.
e) Anderson, J. S.; Rittle, J.; Peters, J. C. Nature 2013, 501, 84−88.
f) Creutz, S. E.; Peters, J. C. J. Am. Chem. Soc. 2014, 136, 1105−1115.
g) Suess, D. L. M.; Peters, J. C. J. Am. Chem. Soc. 2013, 135, 4938−
941. (h) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125,
0782−10783. (i) Hendrich, M. P.; Gunderson, W.; Behan, R. K.;
Green, M. T.; Mehn, M. P.; Betley, T. A.; Lu, C. C.; Peters, J. C. Proc.
Natl. Acad. Sci. U.S.A. 2006, 103, 17107−17112.
(
10) Spencer, L. P.; Altwer, R.; Wei, P.; Gelmini, L.; Gauld, J.;
Stephan, D. W. Organometallics 2003, 22, 3841−3854.
11) (a) Keim, W.; Killat, S.; Nobile, C. F.; Suranna, G. P.; Englert,
U.; Wang, R.; Mecking, S.; Schroder, D. L. J. Organomet. Chem. 2002,
(
̈
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
̈
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.
6
62, 150−171. (b) Zhu, T.; Wambach, T. C.; Fryzuk, M. D. Inorg.
Chem. 2011, 50, 11212−11221. (c) Wambach, T. C.; Ahn, J. M.;
(
34) (a) Wasada, H.; Tsutsui, Y. Bull. Coll. Gen. Educ. 1996, 33, 145−
Patrick, B. O.; Fryzuk, M. D. Organometallics 2013, 32, 4431−4439.
1
58. (b) Takahashi, I.; Wasada, H.; Tsutsui, Y. MOVIEW: Program of
(
12) Ogawa, T.; Suzuki, T.; Hein, N. M.; Pick, F. S.; Fryzuk, M. D.
Nagoya University Information Technology Center Representing Molecular
Dalton Trans. 2015, 44, 54−57.
13) Vela, J.; Cirera, J.; Smith, J. M.; Lachicotte, R. J.; Flaschenriem,
C. J.; Alvarez, S.; Holland, P. L. Inorg. Chem. 2007, 46, 60−71.
14) Weintrob, E. C.; Tofan, D.; Bercaw, J. E. Inorg. Chem. 2009, 48,
808−3813.
15) (a) Schubert, E. M. J. Chem. Educ. 1992, 69, 62. (b) Evans, D. F.
J. Chem. Soc. 1959, 2003−2005.
16) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 6252−
254.
17) Mankad, N. P.; Whited, M. T.; Peters, J. C. Angew. Chem., Int.
Ed. 2007, 46, 5768−5771.
18) Rose, R. P.; Jones, C.; Schulten, C.; Aldridge, S.; Stasch, A.
Chem.Eur. J. 2008, 14, 8477−8480.
19) (a) Chomitz, W. A.; Arnold, J. Chem. Commun. 2007, 4797−
799. (b) Chomitz, W. A.; Arnold, J. Dalton Trans. 2009, 1714−1720.
20) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
35.
21) Sheldrick, G. M. SHELXL97; University of Go
Gottingen, Germany, 1997.
22) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Orbitals and Electron Density Maps by Isosurfaces.
(
(
3
(
(
6
(
(
(
4
(
4
(
̈
ttingen:
̈
(
Crystallography, Vol. IV; Ibers, J. A., Hamilton, W. C., Eds.; Kynoch
Press: Birmingham, U.K., 1974; Table 2.2A.
(
7
(
23) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781−
82.
24) Creagh, D. C.; McAuley, W. J. In International Tables for
Crystallography, Vol. C; Wilson, A. J. C., Ed.; Kluwer: Dordrecht, The
Netherlands, 1992; Table 4.2.6.8, pp 219−222.
(
25) Creagh, D. C.; Hubbell, J. H. In International Tables for
Crystallography, Vol. C; Wilson, A. J. C., Ed.; Kluwer: Dordrecht, The
Netherlands, 1992; Table 4.2.4.3, pp 200−206.
(
26) Bergbreiter, D. W.; Killough, J. M. J. Am. Chem. Soc. 1978, 100,
2
(
126−2134.
27) Al-Benna, S.; Sarsfield, M. J.; Thornton-Pett, M.; Ormsby, D. L.;
Maddox, P. J.; Bres, P.; Bochmann, M. J. Chem. Soc., Dalton Trans.
000, 4247−4257.
̀
2
(
(
28) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
29) (a) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033−1036.
(
1
b) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062−
065. (c) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72,
K
DOI: 10.1021/acs.inorgchem.5b00536
Inorg. Chem. XXXX, XXX, XXX−XXX