Reduction of Dinitrogen to Ammonia and Hydrazine on Low-Valent Ruthenium Complexes

Article abstract of DOI:10.1021/acs.inorgchem.8b02850

The ruthenium(0) dinitrogen complexes [Ru(N₂)(PP₃^R)] [PP₃^R = P(CH₂CH₂PR₂)₃; R = ⁱPr or Cy] react with triflic acid and other strong acids to afford mixtures of ammonia and hydrazine. In this reaction, Ru(0) is oxidized to Ru(II), and depending on the solvent, Ru(II) benzene or triflate complexes are isolated and characterized from the reactions with triflic acid as the final metal-containing products from the reaction. The Ru(II) products are isolated and reduced back to Ru(0) dinitrogen complexes providing a cycle for the reduction of coordinated dinitrogen.

Full text of DOI:10.1021/acs.inorgchem.8b02850

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Reduction of Dinitrogen to Ammonia and Hydrazine on Low-Valent
Ruthenium Complexes
,
†
†
†
‡
§
Leslie D. Field,* Hsiu L. Li, P. Manohari Abeysinghe, Mohan Bhadbhade, Scott J. Dalgarno,
and Ruaraidh D. McIntosh§
†
School of Chemistry, UNSW Sydney, Sydney, NSW 2052, Australia
‡
Mark Wainwright Analytical Centre, UNSW Sydney, Sydney, NSW 2052, Australia
§
School of EPS-Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, United Kingdom
*
S Supporting Information
ABSTRACT: The ruthenium(0) dinitrogen complexes [Ru-
R
R
i
(
N )(PP )] [PP = P(CH CH PR ) ; R = Pr or Cy] react
2 3 3 2 2 2 3
with triflic acid and other strong acids to afford mixtures of
ammonia and hydrazine. In this reaction, Ru(0) is oxidized to
Ru(II), and depending on the solvent, Ru(II) benzene or triflate
complexes are isolated and characterized from the reactions with
triflic acid as the final metal-containing products from the
reaction. The Ru(II) products are isolated and reduced back to
Ru(0) dinitrogen complexes providing a cycle for the reduction
of coordinated dinitrogen.
INTRODUCTION
Scheme 1. Ru(PP
Ammonia upon Treatment with TfOH
3
)(N
2
) Complexes Produce Hydrazine and
■
There have been advances in the conversion of dinitrogen to
ammonia or hydrazine in homogeneous solutions containing
1
2
3
4−7
complexes of vanadium, molybdenum, chromium, iron,
8
and cobalt. Only recently has the chemical transformation of
dinitrogen to ammonia been reported for complexes of
9
ruthenium and osmium.
While ruthenium is not found in biological systems, it is a
component of the catalyst in some industrial processes for
ammonia production such as the Kellogg Brown & Root
10
such that the remaining non-PP donor atoms must occupy
adjacent sites in the coordination sphere. Our interest lies in
Advanced Ammonia Process-Plus (KAAP-plus). Advances
3
14
11
have also been reported in heterogeneous nitrogen fixation1 as
2
the ruthenium PP complexes containing dinitrogen as a ligand;
well as in nitrogen reduction by electrochemical means, all
3
little has been reported about the reactivity of the dinitrogen
utilizing ruthenium as the key reactive metal.
In an important set of experiments, Peters et al. have
15−17
9
ligand itself.
For Ru(0) phosphines containing a N ligand, there are often
demonstrated that the Ru(0) and Os(0) complex [M(SiP )-
2
3
−
i
multiple possible competing reaction pathways (such as
N ] [where M = Ru or Os; SiP = (Si(o-P( Pr) )C H ) ] can
2
3
2
6
4 3
relatively facile substitution of N , reactions at the metal center,
reduce coordinated N and the system also behaves catalytically
2
2
and reaction of the coordinated N ). The rationale for testing
to produce ammonia in the presence of acid and Cp* Co as a
2
2
PP -type ligands with bulky substituents on the terminal
reducing agent.
3
phosphorus donors was that this type of ligand partially
encapsulates the metal and provides steric protection to shut
down or slow down alternate reaction pathways at the metal
center and to direct reaction to the coordinated dinitrogen.
We recently reported an investigation of the reaction of
iron(0) dinitrogen complexes containing bidentate phosphine
ligands, [Fe(N )(PP) ] [PP = 1,2-bis(diethylphosphino)ethane
In this paper, we report the chemistry of N bound to Ru(0)
2
complexes containing the bulky tetraphosphine ligands [Ru-
R
R
i
(
N )(PP )] {PP = P(CH CH PR ) [R = Pr (1), Cy (2), or
2 3 3 2 2 2 3
Ph (3)]} and demonstrate that the isopropyl- and cyclohexyl-
substituted complexes produce ammonia and hydrazine upon
treatment with triflic acid, TfOH (Scheme 1), in single-batch
experiments.
2
2
Many of the metal complexes of the PP ligands are known to
3
13
act as catalysts in a range of different organic transformations.
The PP ligands constrain the geometry of octahedral complexes
Received: October 10, 2018
3
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02850
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
depe) or 1,2-bis(dimethylphosphino)ethane (dmpe)], with
Article
(
broad to be conveniently quantified. Tyler and Ashley have used
+
7,20
1
acid. In this study, we observed primarily protonation at the
colorimetric methods to quantify N H ,
while Mock has
2
5
+
3
metal center to afford metal hydride complexes instead of
used a fitting program to quantify N H by H NMR.
2
5
18
reaction at the coordinated dinitrogen ligand. Treatment of
Fe(N )(dmpe) ] with trimethylsilyl triflate (TMSOTf),
Our method of choice for quantification of both NH and
3
[
N H is gas chromatography−mass spectrometry (GC−MS).
2
2
2
4
+
however, did result in reaction at dinitrogen to give NH on
subsequent treatment with acid. Tyler et al. have reported
reaction of a related system, [Fe(N )(DMeOPrPE) ]
NH
3
can be detected directly by GC−MS, and N H was
2 4
4
18
analyzed after derivatization with acetone to form acetone azine
[Me , 2-(1-methylethylidene)hydrazone 2-
CN−NCMe
2
2
2
2
21
{
DMeOPrPE = 1,2-bis[di(methoxypropyl)phosphino]ethane},
propanone]. Table 1 summarizes the reaction of different
with acids such as triflic acid (TfOH), HBF , and HCl to give
4
5
,7
ammonium in yields of ≤17% with respect to Fe. More
Table 1. Yields of Ammonia and Hydrazine from Reactions of
[Ru(N )(PP R)] with Acids
recently, Ashley has reported that treatment of [Fe(N )-
2
2
3
(
dmpe) ] with TfOH affords hydrazine in yields of ≤9.1%
2
%
4
%
5
% N
2
b
while a similar treatment of [Fe(N )(depe) ] afforded ≤24%
+
a
+
a
2
2
compound
acid
TfOH
NH
N H
2
converted
hydrazine and ≤10.5% ammonia. Interestingly, treatment of the
1
2
3
4
5
6
7
8
9
1
1
1
1
1
2
2
1
1
1
1
1
1
1
3
c
d
c
d
c, e
f
g
h
i
c
d
i
3
2
4
<1
7
0
18
18
5
2
17
0
0
0
0
0
20
19
7
2
21
0
dinitrogen-bridged complex [Fe(dmpe) ] (μ-N ) with TfOH
2
2
2
TfOH
TfOH
TfOH
TfOH
LutHOTf
HCl
19
afforded only low yields of hydrazine and ammonia.
Ph
3
Ru(N )(PP ) 3 was synthesized by treatment of the
2
Ph
dichloro complex [RuCl (PP3 )] with KC in toluene under
an atmosphere of nitrogen (Scheme 2).
2
8
0
0
Scheme 2. Synthesis of Ru(N )(PP3Ph) 3
2
HBF4
<1
<1
2
5
0
<1
<1
1
6
0
CF COOH
3
+
0
1
2
H(OEt2)2
H(OEt2)2
TfOH
+
3
0
a
+
+
Yield in moles of NH or N H per mole of metal complex as
4
2
5
b
quantified by GC. Percentage of complexed dinitrogen from the
starting material that ends up as NH or N H (calculated as half %
+
+
4
2
5
+
+
5
c
d
yield NH + % yield of N H ). Pentane solvent. Benzene solvent.
4
2
e
f
g
The ruthenium(0) dinitrogen complex containing the
With 6 equiv of Cp* Co. THF solvent. Pentane or benzene with
2
i
Pr
h
i
isopropyl-substituted PP ligand [Ru(N )(PP )] 1 and the
ether. Pentane with ether. Pentane or benzene solvent.
3
2
3
1
5
15
N -labeled analogue 1- N were synthesized from the chloro
2
2
i
Pr
+
−
15
Ru(0) PP
In the reaction of complex 1 with TfOH in pentane, NH
formed in approximately 3% yield and N was formed in
approximately 18% yield (entry 1, Table 1).
The combined yields of NH and N are best expressed as
% N converted”, which reveals the percentage of complexed
3
complexes containing bound N
2
with a range of acids.
complex [RuCl(PP )] Cl as previously reported.
3
Cy
3
3
was
Ru(N )(PP ) 2 was synthesized by reduction of the chloro
2
Cy
+
−
H
2 4
complex [RuCl(PP3 )] X (X = Cl or BPh ) with KC by a
4
8
1
7
modification of the previously reported method.
RuH (PP )] 4 was always formed as a minor byproduct in
Cy
3
H
2 4
[
2 3
“
2
the reaction, an authentic sample of the dihydrido complex 4
synthesized independently, and the complex fully characterized
dinitrogen from the starting material that is converted to
19
reduced products. We note that this measure of % N2
(
see the Supporting Information).
converted does not take into account the electrons required to
fuel the production of NH and N H products.
I
REACTION OF [RU(N )(PP PR)] 1 WITH TFOH
3
2
4
2
i
3
■
In batch reactions (with no added reducing agents), all of the
required electrons must derive from the low-oxidation state
metals in the starting materials. In the reaction of complex 1 with
Treatment of [Ru(N )(PP Pr)] 1 with triflic acid in pentane
2
3
immediately precipitates an oily maroon-brown solid that on
dissolution in dimethyl sulfoxide-d (DMSO-d ) shows the
TfOH in pentane as the solvent, the % N converted was 20%.
6
6
2
1
15
15
i
distinctive three-line multiplet at 7.0 ppm in the H nuclear
Treatment of the N-labeled analogue [Ru( N )(PP Pr)]
2 3
+
4
15
15
magnetic resonance (NMR) spectrum characteristic of NH .
1- N with triflic acid in pentane afforded N-labeled
ammonium as observed in the H NMR spectrum as a doublet
with a J of 72 Hz at 7.04 ppm. Signals for ammonium and
2
+
1
1
Routine quantification of NH4 by H NMR spectroscopy was
1
carried out using 1,4-dioxane and/or 1,3,5-trimethoxybenzene
NH
+
14
1
as the internal standard. NH4 was also quantified by N{ H}
NMR spectroscopy using tetramethylammonium iodide as an
internal standard.
hydrazinium at δ 358.8 and −328.7, respectively, are observed in
1
5
1
the N{ H} NMR spectrum.
i
The reaction of [Ru(N )(PP Pr)] 1 with TfOH in benzene as
2
3
While NH is relatively easily detected as NH4+ by NMR
the solvent afforded hydrazine (as N H ) as the major nitrogen-
+
3
2
5
spectroscopy, the case for hydrazine is not so straightforward.
containing product (approximately 18% yield) with only a
minor amount of ammonia (approximately 2%) (entry 2, Table
Chemical exchange with H O and residual TfOH as well as
2
1
quadrupolar broadening means that the H NMR signal for
1) and thus a % N converted of 19% similar to that for the
2
+
N H is typically broadened and usually overlaps with the signal
reaction in pentane.
2
5
1
4
for residual H O and TfOH. N NMR spectroscopy is also not
At the end of the reaction, the main Ru-containing product
2
1
4
6
II
6
3
useful for analyzing hydrazine because N is a quadrupolar
was the η -benzene complex [Ru (η -benzene)(κ -
1
4
i
3+
−
nucleus and, in the absence of high symmetry around the
N
PP PrH)] (OTf ) 5. An X-ray crystal structure of complex
3 3
nucleus, quadrupolar relaxation makes the 14N resonance too
5 (Figure 1) was obtained from crystals grown from a solution of
B
DOI: 10.1021/acs.inorgchem.8b02850
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Inorganic Chemistry
Article
i
Figure 1. ORTEP plot of [Ru(η -benzene)(κ -PP PrH)]3+ 5 (50%
6
3
3
ellipsoid probability; three triflate counterions, dichloromethane
solvate, and hydrogen atoms excluded for the sake of clarity). Selected
bond lengths (angstroms) and angles (degrees): Ru−P3, 2.374(2);
Ru−P1, 2.3019(19); Ru−P2, 2.3771(19); Ru−C, 2.282(6)−2.303(6);
C−C, (benzene) 1.366(10)−1.411(10); P3−Ru−P2, 97.29(7); P1−
Ru−P3, 82.02(8); P1−Ru−P2, 81.31(6).
Figure 2. ORTEP plot of [Ru(OTf)(PP3Cy)]+ 6 (50% ellipsoid
probability; triflate counterion, and hydrogen atoms excluded for the
sake of clarity). Selected bond lengths (angstroms) and angles
(
2
degrees): Ru−P1, 2.3867(5); Ru−P2, 2.2749(5); Ru−P3,
.4127(5); Ru−P4, 2.2271(5); Ru−O1a, 2.2572(14); P1−Ru−P3,
53.925(18); P2−Ru−P1, 96.524(18); P2−Ru−P3, 103.466(18);
1
P4−Ru−P1, 82.939(18); P4−Ru−P2, 83.839(18); P4−Ru−P3,
8
2.748(19); P4−Ru−O1a, 173.24(4); O1a−Ru−P1, 99.87(4);
dichloromethane layered with diethyl ether. There are no known
X-ray crystal structures for Ru arene complexes containing three
additional phosphorus ligands; however, there are structures of
O1a−Ru−P2, 101.85(4); O1a−Ru−P3, 92.31(4).
in the 19F NMR spectrum was observed for the triflate anions
even at a low temperature (193 K), indicating rapid exchange
between the coordinated and uncoordinated triflate anions in
solution.
22
Ru benzene complexes containing two phosphorus ligands or
two phosphorus ligands with an additional ligand such as
2
3
24
25
26
hydride, methyl, chloride, acetonitrile, or substituted
2
7
ethylene that are available for comparison.
While we have not been able to isolate and fully characterize
The Ru−P bond lengths in complex 5 range from 2.3020 to
the second product, it is probably a Ru(II) triflate complex
2
.3772 Å, which are within the range of the corresponding bond
3
containing a κ -coordinated PP ligand with a protonated
6
3
lengths in [Ru(η -benzene)(P )X] complexes (2.176−2.402 Å).
2
pendant phosphine with two coordinated triflate anions,
The Ru−C bond lengths for complex 5 range from 2.282 to
.303 Å, which are also within the range of those of the
3
Cy
+
−
31
[
Ru(OTf) (κ -PP H)] (OTf ) 7. The P NMR shifts at δ
2 3
2
1
09.5, 78.0, and 28.5 are consistent with this formulation, and
6
analogous bonds in [Ru(η -benzene)(P )X] complexes
19
2
the single F NMR signal at δ −76.8 for the triflates indicates
rapid anion exchange.
(
2.201−2.353 Å).
In the reaction of [Ru(N )(PP
Cy)] 2 with benzene as the
REACTION OF [RU(N )(PP CY)] 2 WITH TFOH
2 3
2
3
■
solvent, two Ru-containing products were formed at the end of
Cy
The reaction of [Ru(N )(PP )] 2 with TfOH in pentane
2
3
the reaction: the triflate complex 6 and the benzene complex
+
+
afforded small amounts of NH4 (∼4%) and N H5 (∼5%)
entry 3, Table 1), and the total % N2 converted was
approximately 7%. Only trace amounts of NH4 (<1%) and
N H (2%) were obtained when the reaction was carried out in
6
3
Cy
3+
2
[Ru(η -benzene)(κ -PP H)] 8 that is an analogue of
3
(
complex 5.
+
+
2
5
benzene (entry 4, Table 1). The yields of NH and N H were
3
2
4
Cy
consistently lower for [Ru(N )(PP3 )] 2 than those for the
2
analogous complex containing isopropyl substituents {[Ru-
i
(
N )(PP Pr)] 1}, highlighting the fact that even a small change
2
3
in the ligand structure does have a significant impact on the
course of the reaction.
Unlike the reaction in benzene, in the reaction of [Ru(N )-
PP3 )] 2 with TfOH in pentane, which is a noncoordinating
solvent, two Ru-containing products are observed at the end of
2
Cy
(
Crystals of 8 were formed preferentially from a solution of the
mixture in dichloromethane and diethyl ether, and the complex
was characterized by X-ray crystallography (see the Supporting
Information).
the reaction. One product is the Ru(II) triflate complex
Cy
+
[
Ru(OTf)(PP3 )] 6 whose structure was determined by X-
ray crystallographic analysis (Figure 2).
The isolation of Ru(II) complexes 5−8 at the end of reaction
sequence is important because these complexes all indicate that
the oxidation of the Ru(0) starting materials to Ru(II) products
provides the electrons necessary to fuel the reduction of the
coordinated N to N H and NH4+ in batch reactions with no
The geometry about the Ru center is a distorted square
pyramid with the central phosphorus (P4), two terminal
phosphines (P1 and P3), and the triflate ligand as the square
base of the pyramid with the remaining terminal phosphine (P2)
at the apex of the pyramid. The Ru−O bond length of 2.2572 Å
is within the range reported for similar Ru triflate complexes
+
5
2
2
added reductants.
When any one of the Ru(II) complexes (5, 6, or 7) is treated
with excess KC or with Cp* Co (i.e., strong reductants) under
2
8
31
1
(
2.231−2.411 Å). The P{ H} NMR spectrum of triflate
8
2
complex 6 displays a quartet at 144.5 ppm for the central
phosphorus atom and a broad resonance at 64.5 ppm for the
three terminal phosphorus atoms. Only one signal at −77.8 ppm
N , each gives the respective starting Ru(0) dinitrogen complex
2
1 or 2. While the reduction is not quantitative, this reaction does
open up the possibility that a catalytic cycle could be devised in
C
DOI: 10.1021/acs.inorgchem.8b02850
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
+
which Ru(0) is oxidized to Ru(II) that could then be cycled back
to Ru(0) with an appropriate reductant to re-bind more N2
although no N H was detected in any case (entries 8 and 9,
2 5
Table 1).
Significant amounts of NH + and N H were detected only
when TfOH was used as the proton source. The protonation
reaction with oxonium acid [H(OEt ) ][B(C F ) ] in pentane
or benzene afforded NH4 in approximately 2 and 5% yields,
respectively (entries 10 and 11, respectively, Table 1).
Interestingly, no N H was detected in the reaction with
+
5
(Scheme 3).
4
2
Scheme 3. Reaction Cycle for Reduction of Coordinated N2
to Ammonia and Hydrazine
2 2
6 5 4
+
+
5
2
+
5
pentane as the solvent, while N H was formed in a low yield in
2
the reaction with benzene as the solvent.
Treatment of [Ru(N )(PP3Ph)] 3 with TfOH did not produce
2
N H or NH4+ under the reaction conditions (entry 12, Table
+
2
5
1
).
i
There is a slow but complete conversion of [Ru(N )(PP Pr)]
to the dihydrido complex [RuH (PP Pr)] 10 under an
2
3
i
29
1
2 3
atmosphere of hydrogen gas over several days with no formation
of either NH4+ or N H . Hydrogen gas alone is not able to
+
2
5
i
produce ammonia or hydrazine by the reduction of coordinated
dinitrogen in these systems. The slow formation of 10 from 1 is
When the reaction of [Ru(N )(PP3 Pr)] 1 with TfOH in
2
pentane was repeated with an added 6 equiv of decamethylco-
baltocene (Cp* Co) as a potential external electron source, we
observed no significant increases in the yields of ammonia or
hydrazine (entry 5, Table 1). Cp* Co is not an effective external
source of electrons for this reaction at least under the reaction
not surprising because the loss of N from 1 generates an
2
2
i
electron-deficient [Ru (PP Pr)] species and oxidative addition
0
3
of H gives rise to 10.
2
2
conditions we have explored so far, and this probably reflects the
SUMMARY AND CONCLUSIONS
■
fact that Cp* Co reacts rapidly with the strong acid in the
R
2
In this work, we have synthesized a series of [Ru(N )(PP )]
2
3
reaction mixture.
R
i
complexes [PP3 = P(CH CH PR ) ; R = Pr, Cy, or Ph] and
2
2
2 3
I
REACTION OF [RU(N )(PP PR)] WITH OTHER
treatment of the isopropyl- and cyclohexyl-substituted com-
plexes with acid afforded hydrazine and/or ammonia in yields of
2
3
■
ACIDS/ELECTROPHILES
The dinitrogen complex [Ru(N )(PP3 Pr)] 1 has been previously
≤
18 and ≤5%, respectively, with the highest nitrogen
i
i
Pr
2
conversion from [Ru(N )(PP )].
2
3
reported to react preferentially at the metal center to form the
As a high-level generalization, the P Ru(0) core can both bind
i
4
Pr
+
−
Ru(II) hydrido dinitrogen complex [RuH(N )(PP3 )] BF
9
4
and activate dinitrogen, and in the presence of a strong acid such
as TfOH, Ru(0) is a sufficiently strong reducing agent to reduce
the coordinated dinitrogen.
2
upon protonation with mild acids such as 2,6-lutidinium
1
5
tetrafluoroborate. We repeated this protonation reaction
+
4
with lutidinium triflate (LutHOTf) in THF, and no NH or
In this system, because we observe hydrazine and ammonia as
the reduction products, it appears that the reaction involves a
stepwise metal-mediated reduction of a coordinated N2
probably through a diazene, to hydrazine and eventually
ammonia. It is also clear that in batch reactions of this type,
the reaction is limited by the availability of electrons and the
observed distribution of the hydrazine and ammonia products
probably reflects the progress of the reduction as the supply of
electrons is exhausted.
While we examined a range of different acids, triflic acid
provided the highest conversion of coordinated N to reduced
products, Weaker acids afforded no (or negligible amounts of)
hydrazine or ammonia, and a stronger acid is probably required
to protonate a weakly activated coordinated dinitrogen and
trigger electron transfer from the metal to nitrogen.
+
N H was formed (entry 6, Table 1). Similarly when complex 9
2
5
+
+
was treated with triflic acid, neither NH4 nor N H was
2
5
formed, so complex 9 is not itself a species on the reaction path
+
+
from metal-bound N to N H or NH .
2
2
5
4
i
So while we know that [Ru(N )(PP3 Pr)] 1 reacts with weaker
2
acids to protonate on the metal, it is apparent that stronger acids,
such as triflic acid, react preferentially at the coordinated N2
leading eventually to N reduction products (Scheme 4). There
2
are multiple sites, probably competing, for reaction of the Ru(0)
+
dinitrogen complexes with H .
2
i
Pr
Treatment of [Ru(N )(PP3 )] 1 with HCl in either pentane
2
+
+
or benzene produced neither NH4 nor N H5 (entry 7, Table
). Only trace amounts of NH4 (<1%) were formed upon
2
+
1
treatment of 1 with acids such as HBF and trifluoroacetic acid,
4
It is well-known that Ru(0)−N complexes can be protonated
2
+
at the metal center to give [H−Ru(II)−N ] complexes
2
Scheme 4. Competing Reaction Pathways for the Reaction of
i
+
Pr
particularly with weaker acids. We isolated [H−Ru(II)−N ]
2
[
Ru(N )(PP )] 1 with Acids
2
3
+
complexes and demonstrated that they did not produce NH or
4
+
5
N H when treated with strong acids, so while [H−Ru(II)−
2
+
N ] complexes may be formed by the reaction of Ru(0)−N
2
2
complexes with acids, these compounds are not on the pathway
+
4
+
for reduction of coordinated N to NH and N H .
2
2
5
The reduction of dinitrogen coordinated to Ru(0) is fueled by
oxidation of Ru(0) to Ru(II), and in this work, Ru(II)
complexes with coordinated solvent (benzene) and Ru(II)
D
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Inorganic Chemistry
Article
triflate complexes were isolated and characterized as the final
Ru-containing products.
The fact that we have identified stable Ru(II) complexes as
products is important because we have demonstrated that these
complexes can be treated with an appropriate reductant under
A.; Ogawa, T.; Schrock, R. R.; Mu
̈
ller, P. Reduction of Dinitrogen to
Ammonia Catalyzed by Molybdenum Diamido Complexes. J. Am.
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02850.
■
*
S
(
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AUTHOR INFORMATION
Corresponding Author
E-mail: L.Field@unsw.edu.au.
ORCID
Leslie D. Field: 0000-0001-5519-5472
Hsiu L. Li: 0000-0001-9361-3137
Scott J. Dalgarno: 0000-0001-7831-012X
Ruaraidh D. McIntosh: 0000-0002-7563-5655
■
*
Complex. Science 2011, 334, 780−783.
(
5) Lee, Y.; Mankad, N. P.; Peters, J. C. Triggering N Uptake via
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Redox-induced Expulsion of Coordinated NH and N Silylation at
3
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Trigonal Bipyramidal Iron. Nat. Chem. 2010, 2, 558−565.
(6) Balesdent, C. G.; Crossland, J. L.; Regan, D. T.; Lopez, C. T.;
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Tyler, D. R. Characterization of an Intermediate in the Ammonia-
Forming Reaction of Fe(DMeOPrPE) N with Acid (DMeOPrPE =
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1
Notes
(7) Gilbertson, J. D.; Szymczak, N. K.; Tyler, D. R. Reduction of N to
2
The authors declare no competing financial interest.
Ammonia and Hydrazine Utilizing H as the Reductant. J. Am. Chem.
2
Soc. 2005, 127, 10184−10185.
ACKNOWLEDGMENTS
(8) See for example: (a) Del Castillo, T. J.; Thompson, N. B.; Suess, D.
L. M.; Ung, G.; Peters, J. C. Evaluating Molecular Cobalt Complexes for
the Conversion of N to NH . Inorg. Chem. 2015, 54, 9256−9262.
■
The authors gratefully acknowledge UNSW for funding. The
authors also thank Dr. Martin Bucknall (Bioanalytical Mass
Spectrometry Facility, Mark Wainwright Analytical Centre,
University of New South Wales) and Dr. Samantha Furfari
2
3
(b) Kuriyama, S.; Arashiba, K.; Tanaka, H.; Matsuo, Y.; Nakajima, K.;
Yoshizawa, K.; Nishibayashi, Y. Direct Transformation of Molecular
Dinitrogen into Ammonia Catalyzed by Cobalt Dinitrogen Complexes
Bearing Anionic PNP Pincer Ligands. Angew. Chem., Int. Ed. 2016, 55,
(
School of Chemistry, University of New South Wales) for their
assistance with GC−MS analysis. The authors also thank Mr.
Thomas O. Peters for assistance with the synthesis of compound
1
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4291−14295.
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