N-H Bond Formation in a Manganese(V) Nitride Yields Ammonia by Light-Driven Proton-Coupled Electron Transfer

Article abstract of DOI:10.1021/jacs.8b12957

A method for the reduction of a manganese nitride to ammonia is reported, where light-driven proton-coupled electron transfer enables the formation of weak N - H bonds. Photoreduction of (sal^tBu)Mn^VN to ammonia and a Mn(II) complex has been accomplished using 9,10-dihydroacridine and a combination of an appropriately matched photoredox catalyst and weak Br?nsted acid. Acid-reductant pairs with effective bond dissociation free energies between 35 and 46 kcal/mol exhibited high efficiencies. This light-driven method may provide a blueprint for new approaches to catalytic homogeneous ammonia synthesis under ambient conditions.

Full text of DOI:10.1021/jacs.8b12957

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Communication
N–H Bond Formation in a Manganese(V) Nitride Yields
Ammonia by Light-Driven Proton-Coupled Electron Transfer
Dian Wang, Florian Loose, Paul J. Chirik, and Robert R Knowles
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b12957 • Publication Date (Web): 25 Feb 2019
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N–H Bond Formation in a Manganese(V) Nitride Yields Ammonia
by Light-Driven Proton-Coupled Electron Transfer
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Dian Wang, Florian Loose, Paul J. Chirik,* and Robert R. Knowles*
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Supporting Information Placeholder
A)
Formation ofWeak N–H Bonds Required in Nitride Reduction
ABSTRACT: A method for the reduction of a
manganese nitride to ammonia is reported, where light-
driven proton-coupled electron transfer enables the
formation of weak N-H bonds. Photoreduction of
(saltBu)MnVN to ammonia and a Mn(II) complex has
been accomplished using 9,10-dihydroacridine and a
combination of an appropriately matched photoredox
catalyst and weak Brønsted acid. Acid-reductant pairs
with effective bond dissociation free energies between
35–46 kcal/mol exhibited high efficiencies. This light-
driven method may provide a blueprint for new
approaches to catalytic homogenous ammonia synthesis
under ambient conditions.
N–H BDFE (kcal/mol):
+/0
H
H
N
N
Ph
H
PiPr2
PiPr2
H2
P
Ph
N
H2
P
N
iPr2P Fe
E
Ph
Mo
N
Mo
N
P
P
N
H2
H2
F
(E: B/Si)
43
54–65
~23
B)
Light-Driven PCET in the Homolytic Activation of Ketones
H
A
H
acid cat.
redox cat.
O
O
CO2Me
Hantzsch ester
( )3
Ph
O
blue hν
Ph
Mn
photo-
reductant
H
A-
Metal nitrides have a rich history in coordination
O
PCET
1
chemistry,
and have found applications as
CO2Me
( )3
Ph
thermoelectrics,2 nuclear fuels,3 and in nitrogen-atom
Mn+1
transfer reactions.4 As certain transition metal nitrides
can be prepared directly from thermal
O–H BDFE ~ 26 kcal/mol
ThisWork: N–H Bond Formation via Light-Driven PCET
5
and
photochemical 6 N2 cleavage, these complexes also
represent attractive molecular precursors for catalytic
ammonia synthesis.7 However, the marked kinetic and
thermodynamic stability of the M≡N bond renders
reduction chemistry challenging and in many cases
requires the formation of N–H bonds with bond
dissociation free energies (BDFEs) less than 50 kcal/mol
(Figure 1A). 8 Accordingly, nitride activation often
requires the combined use of strong Brønsted acids and
C)
H
A
A-
H
NH3
M
N
N
PCET
Mn
Mn+1
M
M
photo-
reductant
Effective BDFE = 23.06 Eº(Mn/Mn+1) + 2.3 RT pKa(HA) + CG
Figure 1. (A) Free energies (kcal/mol) of N–H bond
formation for select metal nitrides (ref. 8). N–H BDFE =
Gº (nitride) + Gº (H•) – Gº (imide). (B) Catalytic ketone
reduction by light-driven PCET. (C) N–H bond formation
by reductive multi-site PCET and equation for effective
BDFE of a given acid/reductant pair.
one-electron
reductants
in
superstoichiometric
quantities. While effective, this approach is frequently
limited by significant chemical overpotentials, poor
atom economy, and competitive proton reduction to
8a, 9
generate H2.
In seeking to address these issues, we questioned
whether photo-driven proton-coupled electron transfer
(PCET) reactions could mediate the formation of weak
N–H bonds from metal nitrides en route to ammonia
formation.10 This work finds its basis in recent reports of
photo-driven PCET methods for the homolytic
activation of carbonyl π-systems in aryl ketones (Figure
1B).11 These C–C bond forming processes are jointly
catalyzed by an IrIII or RuII-based photoredox catalyst
and
a
phosphoric acid, and are fueled by
dihydropyridine-based stoichiometric reductants under
blue light irradiation. Notably, these reactions proceed
via the formation of neutral ketyl radical intermediates,
which exhibit unusually weak O–H bonds (O–H BDFEs
~ 26 kcal/mol). With respect to nitride reduction, these
results suggest a number of potentially advantageous
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features. First, the thermodynamic range of excited-state
PCET reactions (which is a dual function of the pKa and
potential of the acid/reductant pair)12 is highly modular
and sufficiently broad to allow favorable formation of
even extraordinarily weak N–H bonds. Moreover, the
use of excited-state redox partners provides an
additional source of driving force and may reduce the
Page 2 of 6
chemistry due to their ability to undergo oxidatively
induced N–N coupling.15 The thermodynamics of NH3
formation from the truncated structure of 1 were first
evaluated using density functional theory (DFT) (Figure
2).16 The addition of H• to the Mn(V) nitride produces a
Mn(IV) imido (S = 3/2) with a computed N–H BDFE of
60 kcal/mol. Subsequent H• additions to form the amido
and ammonia complexes are significantly more
favorable, with driving forces of 84 and 85 kcal/mol,
respectively. This trend is consistent with previous
investigations on NH3 formation from a molybdenum
nitride reported by Schrock and coworkers,8a which
highlight the fact that nitride reduction is often the most
1
2
3
4
5
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8
necessity
for
large
reagent-based
chemical
overpotentials. Second, the ketyl example suggests that
excited-state electron donors may be more tolerant of
Brønsted acids than ground state reductants of similar
potential due to their low concentrations and short
excited-state lifetimes, potentially providing a means to
mitigate undesired proton-reduction pathways. Lastly,
the ability of the excited-state PCET catalyst system to
effectively sensitize the formal transfer of H2 between
the substrate and a stable dihydropyridine reductant
could enable milder reaction conditions relative to
current approaches that use independent electron and
proton donors.
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thermodynamically challenging step in the sequence.7a,
8c
From these values, we anticipated that N–H bond
formation with nitride 1 could be achieved by light-
driven PCET with a Brønsted acid and an excited-state
reductant. In our previous work on ketone reduction
(Figure 1B), we observed that the product yield for C–C
coupling correlated strongly with the effective BDFE of
PCET catalysts, and that acid/reductant combinations
with effective BDFEs significantly stronger than the O–
H bond strength of the neutral ketyl radical intermediate
Here we report the successful adaptation of this
approach to light-driven N–H bond formation, and
describe a catalytic, photo-driven PCET system for the
reduction of a Mn(V) nitride to produce ammonia in
nearly quantitative yield with a catalyst pair composed
of an alkylammonium acid and [RuII(bpy)3]2+
Table 1. Formation of NH3 by Multi-Site PCETa
tBu
tBu
N
photocatalyst, along with
a
dihydroacridine-based
5% redox cat.
10% acid cat.
tBu
tBu
+
O
N
O
N
Mn
stoichiometric reductant. The design, optimization, and
[Mn]red acr
+
acrH2
(2 eq)
NH3
+
0.02 M CH2Cl2
blue LED, rt, 22 h
characterization of this process are described herein.
1
H
Effective NH3%b
N
N
+ H
Entry
redox cat.
[Ir(ppy)2(dtbpy)](PF6) NMe3H+BF4
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
acid cat.
O
N
O
N
O
N
O
N
Mn
Mn
BDFE
35
40
41
45
(1 conv.)
50 (100)
57 (100)
52 (100)
55 (100)
50 (50)
ΔGº = –60
-
-
1
2
3
4
5
6
7
8
(ΔGº = –51)
NMe3H+BF4
S = 0
S = 3/2
NEt3H+BF4
-
ꢀS = 1/2)
PhCO2H
ΔGº = –84
+ H
t
[Ir(ppy)2(dtbpy)](PF6) BuC6H4SO2NH2
46
H
H
H
H
H
[Ru(bpy)3](PF6)2
[Ru(bpm)3](PF6)2
[Ru(bpm)3](PF6)2
AcOH
PhCO2H
48
20 (20)
N
N
+ H
55
19 (38)
O
N
O
N
O
N
O
N
Mn
Mn
tBuC6H4SO2NH2
59
24 (31)
ΔGº = –85
Changes to entry 2
no Ru, no acid catalyst
no Ru
S = 2
S = 5/2
9
15 (15)
13 (13)
57 (95)
<1 (14)
<1 (16)
36 (100)
6 (15)
99 (100)
31 (34)
<1 (11)
10
11
12
13
14
15
16
17
18
Figure 2. Free energy change (kcal/mol) in the
sequential reductions of (salen)MnN (B3LYP/Hay-
Wadt/6-311+G**). For each Mn species, the lowest-
energy spin state is shown in black. ΔGº = Gº (H•
addition product) – Gº (H• addition reactant) – Gº (H•).
See Supporting Information for details.
no acid
no acrH2
no light
t = 2 h
t = 2 h, no acid catalyst
after TMEDA treatment of non-volatile
Hantzsch ester instead of acrH2
Our studies began by testing the reactivity of several
known metal nitrides under reductive PCET
conditions.11a We observed that nitrides supported by
monodentate anionic ligand such as MoN(OtBu)313 are
prone to undergo ligand dissociation (i.e., to form
tBuOH) and only produce trace amounts of NH3. To
mitigate this side reaction, we selected (saltBu)MnN (1)
as a model substrate, expecting that the salen-derived
ligand would provide a more stable chelate coordination
environment. 14 In addition, salen-ligated manganese
nitrides have received recent interest in the context of N2
1,4-cyclohexadiene instead of acrH2
aReactions were performed on 0.02 mmol scale with one 34 W
Kessil lamp. Yields were determined by 1H NMR analysis of
NH4Cl (relative to an internal standard) formed after vacuum
transfer of reaction volatiles to HCl (2 M, Et2O). acrH2: 9,10-
dihydroacridine. acr: acridine. Effective BDFE values calculated
from the equation presented in Figure 1 from pKa and E0 data in
MeCN. See Supporting Information for details. bA typical
variation of ±4% was observed for NH3 yield and conversion.
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were ineffective. We anticipated that reductive PCET of
the organic product, acridine, was formed in 92% yield.
This prompted us to probe the fate of remaining nitrogen
mass balance. Based on reports of (salen)MnII-aquo20
and [MnII(NH3)6]21 complexes, we hypothesized that
additional NH3 may remain bound to the reduced Mn
complex. Consistent with this view, treatment of the
non-volatile product residue with excess CO or
1
2
3
4
5
6
7
8
nitride 1 may exhibit a similar correlation if a concerted
mechanism was operative and that the targeted catalyst
effective BDFE should be close to the driving force of
the first H• addition (51–60 kcal/mol, Figure 2). Once
the MnIV=NH intermediate is generated, formation of
the second and third N–H bonds should be facile, (either
by subsequent PCET or by favorable direct reaction with
the acrH2 derivatives, vide infra), thereby transforming 1
into NH3 and a reduced MnII complex.
tetramethylethylenediamine
(TMEDA)
released
additional NH3. The best yield was achieved when 10
equivalents of TMEDA were added to a solution of the
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tBu
tBu
15N
In this context, we were pleased to find that the
catalyst pair comprised of 5 mol% of [Ru(bpy)3](PF6)2
and 10 mol% NMe3•HBF4 resulted in significant NH3
formation upon blue light irradiation of 1 in CH2Cl2.
Dihydroacridine (acrH2) was the optimal stoichiometric
reductant in this process and likely serves to reductively
quench the excited-state *RuII to generate more strongly
reducing RuI(bpy)3. Additional investigation of
acid/reductant pairs revealed that combinations with
BDFEs between 35–46 kcal/mol were catalytically
competent and afforded NH3 in moderate yields (Table
1, entries 1–5) with ≥50% starting material conversion.
In comparison, catalyst pairs with higher effective
BDFEs (≥48 kcal/mol) led to lower NH3 yields and
conversions (entries 6–8), similar to those from
uncatalyzed background processes (entry 9). This
background reaction produces small amounts of NH3,
and may arise from excitation of 1 by the blue light.17
The discrepancy between the threshold effective BDFE
and N–H bond strength of 1 may relate to DFT error
and/or lack of an accurate CG value (Figure 1C) in
CH2Cl2.18 Several other trends are notable. With the
same photoreductant, stronger acids led to a more
productive reaction than weaker acids (entries 2–4 vs.
6). Similarly, with the same Brønsted acid but varying
redox catalysts, more reducing photocatalysts showed
superior activity (entry 4 vs. 7, entry 5 vs. 8). These
results suggest that both acidity and reducing ability of
the catalyst pairs are important for the efficiency of the
5% Ru(bpy)3(PF6)2
tBu
tBu
+ acrH2
-
10% NMe3H+ BF4
O
N
O
N
Mn
[Mn]red acr
15NH3
65%
+
+
CH2Cl2
blue LED, rt, 22 h
1H NMR of HCl-trapped 15NH3:
+
* : 14NH4
*
*
*
Figure 3. Formation of 15NH3 by photoreduction of
(saltBu)Mn15N. Yield was determined by H NMR analysis
1
of 15NH4Cl relative to an internal standard after vacuum
transfer to a solution of HCl in Et2O. See Supporting
Information for details.
tBu
tBu
tBu
tBu
N
PCET, hν
tBu
tBu
O
N
O
N
tBu
tBu
O
N
O
N
Mn
Mn
–NH3
1
C2Cl6
or NCS
tBu
tBu
Cl
UV-Vis of (saltBu)MnIIICl
standard
tBu
tBu
O
N
O
N
Mn
sample
aq. NH3
bleach
400
500
600
700
800
tBu
tBu
O
N
photoreduction reaction, consistent with
a PCET
l (nm)
tBu
tBu
O
N
Mn
mechanism.11a,b Finally, control experiments showed
that visible light, photocatalyst, and acrH2 are all crucial
to efficient NH3 formation (entries 10, 12, 13). The
background reaction in the absence of acid produces
ammonia, but there is a significant induction period, and
little conversion is observed in the first two hours
(entries 14–15). We speculate that this behavior can be
attributed to in situ generation of an acidic species
during the course of the reaction, likely from
N
1
85–92% from starting MnN
Figure 4. Formation of (saltBu)MnIIICl and (saltBu)MnVN by
oxidative transformations of photoreduction product.
Conditions: Chlorination: (i) C2Cl6 (4 eq), CH2Cl2, 40 ºC, 46
h; or (ii) NCS (5 eq), CH2Cl2, rt, 22 h. MnIII oxidation:
aqueous NH3 (30 eq), bleach (40 eq), CH2Cl2/MeOH (4:1),
rt, 16 h.
•+
deprotonation of acrH2 (pKa~6) that is generated upon
reaction residue in CH2Cl2, rendering the combined
yield of NH3 to be nearly quantitative (57% + 42%, eq.
1).
reductive quenching of the Ru(II) excited state (vide
infra).19
CO
NH3 (30%)
The origin of ammonia was determined by isotopic
PCET, hν
1
labeling using (saltBu)Mn15N as the substrate. H NMR
[Mn]red
(1)
1
– NH3 (57%)
spectroscopy revealed the formation of 15NH3 as the
product (Figure 3), unequivocally indicating that the
NH3 produced originates from the nitride group of 1.
TMEDA
NH3 (42%)
We noted that under the highest-yielding condition
(57% NH3, Table 1, entry 2), 1 was fully consumed, and
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Page 4 of 6
Corresponding Authors
Next, we investigated the nature of the Mn product of
1
2
3
4
5
6
7
8
photoreduction. The EPR spectrum of the non-volatile
portion of the reaction mixture exhibits a broad signal at
g = 2.0 (Figure S3), consistent with previously reported
values for high-spin (salen)MnII compounds. 22 The
identity of Mn product was determined further by
oxidation to known compounds. Treating the crude Mn
residue with chlorine atom donors, such as C2Cl6 or N-
chlorosuccinimide (NCS), affords a dark-brown species,
and its UV-Vis spectrum is identical to that of authentic
(saltBu)MnIIICl (Figure 4). The resulting MnIII species
was further treated with aqueous ammonia and bleach,
reforming (saltBu)MnVN. The yield of regenerated 1 after
the three-step reaction sequence is 85–92% (Figure 4).
*pchirik@princeton.edu
*rknowles@princeton.edu
ORCID
Dian Wang 0000-0001-9965-4079
Florian Loose 0000-0003-1643-4607
Paul J. Chirik 0000-0001-8473-2898
Robert R. Knowles 0000-0003-1044-4900
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Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
Financial support was provided by the Andlinger Center
for Energy and the Environment (Princeton University).
F. L. acknowledges support by DFG Research
Fellowship (LO 2377/1-1). P. J. C. acknowledges
support from the U.S. Department of Energy, Office of
Science, Basic Energy Science (DE-SC0006498).
These results provide strong evidence that
a
[(saltBu)MnII] species is formed in high yield as a
product in the photoreduction step.
A number of potential mechanisms for nitride
reduction to NH3 are feasible in this system. However,
based on both the ketyl example and the effective bond
strength correlations in Table 1, we suggest that the
reaction commences with reductive quenching of the
*RuII excited state (E1/2, MeCN = +0.37 V vs. Fc+/Fc)23 by
acrH2 (E1/2, MeCN = +0.49 V vs. Fc+/Fc)24 to generate a
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more reducing RuI(bpy)3 (E1/2
= –1.71 V vs.
+
II/I
, MeCN
Fc+/Fc) species. Despite being modestly endergonic, the
feasibility of this elementary step was confirmed by a
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kcal/mol) to form a MnIV imido complex. The two
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favorable (N–H BDFEs = 84 & 85 kcal/mol), and may
occur by either a similar PCET mechanism, or by direct
hydrogen atom transfer from various acrH2-based
species in solution, such as acrH2, acrH2 radical cation,
and acrH• (BDFE
= 74, 33 and 43 kcal/mol,
respectively).24,25,26
In conclusion, we have developed a high-yielding
PCET-based method for NH3 synthesis from a MnV
nitride driven by visible light. The results provide
further support for the notion that multi-site PCET can
enable challenging homolytic bond activations and
provide access to intermediates with unusually weak
bonds to hydrogen. We anticipate that these results may
serve as the basis for future efforts in this area, helping
the further advance the state-of-the-art in homogenous
ammonia synthesis.
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Molybdenum Complexes Bearing Ferrocenyldiphosphine. Angew.
Chem. Int. Ed. 2014, 53, 11488-11492. (e) Klopsch, I.; Finger, M.;
Würtele, C.; Milde, B.; Werz, D. B.; Schneider, S. Dinitrogen
Splitting and Functionalization in the Coordination Sphere of
Rhenium. J. Am. Chem. Soc. 2014, 136, 6881-6883. (f) Liao, Q.;
Cavaillé, A.; Saffon-Merceron, N.; Mézailles, N. Direct Synthesis of
Silylamine from N2 and a Silane: Mediated by a Tridentate Phosphine
Molybdenum Fragment. Angew. Chem. Int. Ed. 2016, 55, 11212-
11216. (g) Lindley, B. M.; van Alten, R. S.; Finger, M.;
ASSOCIATED CONTENT
Supporting Information
Experimental
details;
characterization
data;
computational and luminescence quenching data
AUTHOR INFORMATION
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Nitrogen Fixation. J. Am. Chem. Soc. 2016, 138, 13379-13389.
(10) For evaluation of non-photocatalytic PCET in N2 reduction, see:
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Challenges in reduction of dinitrogen by proton and electron transfer.
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Rate-Driving Force Relationships in the Multisite-PCET Activation
of Ketones. J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.8b13451. For
reviews, see: (c) Miller, D. C.; Tarantino, K. T.; Knowles R. R.
Proton-Coupled Electron Transfer in Organic Synthesis:
Fundamentals, Applications, and Opportunities. Topics in Current
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Proton-Coupled Electron Transfer in Organic Synthesis: Novel
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MnVI Nitrides. Angew. Chem. Int. Ed. 2018, 57, 14037-14042.
(16) See Supporting Information for details. DFT computation was
performed at the B3LYP level of theory using Hay-Wadt double
ζ basis set for Mn and 6-311+G (d, p) basis set for C, H, O, N.
(17) See Supporting Information for the UV-Vis spectrum of nitride
1 and emission spectrum of the lamp.
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(18) Due to the lack of pKa and CG data in dichloromethane, BDFEs
in Table 1 were calculated using data obtained in MeCN. To
demonstrate the generality of yield-BDFE correlation, the activities of
various acid/reductant combinations were also tested in THF as the
solvent where BDFE is calculated based on pKa in THF, and a similar
trend was observed. See Supporting Information for details.
(19) Similar observation has been made in our previous study: Rono,
L. J.; Yayla, H. G.; Wang, D. Y.; Armstrong, M. F.; Knowles, R. R.,
Enantioselective Photoredox Catalysis Enabled by Proton-Coupled
Electron Transfer: Development of an Asymmetric Aza-Pinacol
Cyclization. J. Am. Chem. Soc. 2013, 135, 17735-17738.
(20) For example, see: Bermejo, M. R.; Garcia-Deibe, A.; Sanmartin,
J.; Sousa, A.; Aurangzeb, N.; Hulme, C. E.; McAuliffe, C. A.;
Pritchard, R. G.; Watkinson, M. Isolation of a remarkably stable
hydrogen
bonded
dimeric
manganese(II)
complex,
[Mn(L)(OH2)]2(Me2SO)2 from the reduction of a manganese(III)
Schiff base complex [L = the dianion of N,N′-bis(3-bromo-5-
nitrosalicylidene)-1,2-diamino-(2-methyl)ethane]. J. Chem. Soc.,
Chem. Comm. 1994, 645-646.
(21) Sacconi, L.; Sabatini, A.; Gans, P. Infrared Spectra from 80 to
2000 Cm-1 of Some Metal-Ammine Complexes. Inorg. Chem. 1964, 3,
1772-1774.
(22) (a) McAuliffe, C. A.; Parish, R. V.; Ashmawy, F. M.; Issa, R. M.;
Amer, S. A. Synthesis and Characterisation of Some New
Manganese(II) and Manganese(III) Complexes of Tetradentate
Schiff-Base Ligands and Their Reaction with Molecular Oxygen. J.
Chem. Soc., Dalton Trans. 1987, 2009-2012. (b) Dailey, G. C.;
Horwitz, C. P.; Lisek, C. A. Synthesis, Spectroscopic
Characterization, and Electrochemical Properties Of Bis[1,2-Bis(5-
Chlorosalicylideneamino)Ethanato(µ-oxo)Manganese(IV)].
Chem. 1992, 31, 5325-5330.
Inorg.
(23) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
Von Zelewsky, A. Ru(II) polypyridine complexes: photophysics,
photochemistry, eletrochemistry, and chemiluminescence. Coord.
Chem. Rev. 1988, 84, 85-277.
(24) Zhu, X. Q.; Li, H. R.; Li, Q.; Ai, T.; Lu, J. Y.; Yang, Y.; Cheng,
J. P. Determination of the C4–H Bond Dissociation Energies of
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NADH Models and Their Radical Cations in Acetonitrile. Chem. Eur.
J. 2003, 9, 871-880.
(25) See Supporting Information for computed BDFE of acrH2 and
acrH•.
•+
( 26 )
A reviewer noted that disproportionation of the imide
intermediate to the corresponding amide and nitride (ΔGº = –24
kcal/mol) is also a potential pathway en route to to NH3 formation.
For similar reactivity with Ir species, see: Scheibel, M. G.; Abbenseth,
J.; Kinauer, M.; Heinemann, F. W.; Würtele, C.; de Bruin, B.;
Schneider, S., Homolytic N–H Activation of Ammonia: Hydrogen
Transfer of Parent Iridium Ammine, Amide, Imide, and Nitride
Species. Inorg. Chem. 2015, 54, 9290-9302.
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Graphical TOC
H
A
A-
NH3
M
H
Photo-
Driven
N
N
Mn
Mn+1
M
M
PCET
• Weak N-H Bond Formation • Yields of NH3 upto 99%
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