Catalytic reduction of dinitrogen to ammonia by use of molybdenum-nitride complexes bearing a tridentate triphosphine as catalysts

Article abstract of DOI:10.1021/jacs.5b02579

Newly designed and prepared molybdenum-nitride complexes bearing a mer-tridentate triphosphine as a ligand have been found to work as the most effective catalysts toward the catalytic reduction of dinitrogen to ammonia under ambient conditions, where up to 63 equiv of ammonia based on the Mo atom of the catalyst were produced.

Full text of DOI:10.1021/jacs.5b02579

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Communication
Catalytic Reduction of Dinitrogen into Ammonia by Use of Molybdenum-
Nitride Complexes Bearing Tridentate Triphosphine as Catalysts
Kazuya Arashiba, Eriko Kinoshita, Shogo Kuriyama, Aya Eizawa, Kazunari
Nakajima, Hiromasa Tanaka, Kazunari Yoshizawa, and Yoshiaki Nishibayashi
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b02579 • Publication Date (Web): 16 Apr 2015
Downloaded from http://pubs.acs.org on April 21, 2015
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Catalytic Reduction of Dinitrogen into Ammonia by Use of
Molybdenum-Nitride Complexes Bearing Tridentate Triphos-
phine as Catalysts
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†
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†
Kazuya Arashiba, Eriko Kinoshita, Shogo Kuriyama, Aya Eizawa, Kazunari Nakajima, Hiromasa
†
‡
‡,§
Tanaka, Kazunari Yoshizawa,* and Yoshiaki Nishibayashi*
†
Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
‡
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8520, Japan
Institute for Materials Chemistry and Engineering and International Research Center for Molecular System, Kyushu Uni-
§
versity, Nishi-ku, Fukuoka 819-0395, Japan
effective catalysts by introducing an electron-donating
group to the pyridine ring of the PNP ligand, where up
to 26 equiv of ammonia were produced based on each
ABSTRACT: Newly designed and prepared molyb-
denum-nitride complexes bearing a mer-tridentate tri-
phosphine as a ligand have been found to work as the
most effective catalysts toward the catalytic reduction of
dinitrogen into ammonia under ambient conditions,
where up to 63 equiv of ammonia were produced based
on the Mo atom of the catalyst.
Mo atom of the catalyst (52 equiv based on the cata-
8
lyst).
More recently, Peters and co-workers have
found the third successful example by using iron-
dinitrogen complexes bearing triphosphineborane and
triphosphinealkyl moieties as ligands, where 7 equiv of
ammonia were produced based on the Fe atom at -78
9-11
°
C.
6
-8
Based on the findings achieved,
we have envis-
The transformation of dinitrogen into ammonia cata-
lyzed by transition metal-dinitrogen complexes under
mild reaction conditions is one of the most realizable
approaches to develop the next-generation nitrogen fixa-
tion system, in place of the Haber-Bosch process for
aged the design of novel [Mo(N ) (PPP)] (µ-N ) (2;
2
2
2
2
PPP
=
bis(di-tert-
12
butylphosphinoethyl)phenylphosphine ) (Scheme 1).
Our motivation for 2 is as follows. The phosphines in
PPP ligand have an advantage of lower Brφnsted basici-
ty and higher stability toward protonation in the catalytic
reaction. In addition, the π-accepting ability of PPP
ligand can stabilize a variety of molybdenum-complexes
bearing a broad range of oxidation states of the Mo cen-
ter during the catalytic reaction. As a result, molyb-
denum complexes bearing PPP ligand have been found
to work as the most effective catalysts, where up to 63
equiv of ammonia were produced based on the Mo atom
of the catalyst. The present catalytic activity is more
1
industrial ammonia production. Although the prepara-
tion of various transition metal-dinitrogen complexes
and their stoichiometric transformation of the coordinat-
ed dinitrogen into ammonia have been thoroughly inves-
2
,3
tigated, only limited examples have been known for
the catalytic conversion of dinitrogen into ammonia by
using transition metal-dinitrogen complexes as catalysts
4
under mild conditions.
In 2003, Schrock and a co-worker reported the first
example of the catalytic reaction of dinitrogen into am-
monia in the presence of molybdenum-dinitrogen com-
plex bearing a tetradentate triamidoamine ligand, where
than five times higher than that of the original complex
6
1
.
The result described in the present paper provides
the first successful example for catalytic nitrogen fixa-
tion by using molybdenum complexes bearing only a
triphosphine as an auxiliary ligand.
8
equiv of ammonia were produced based on the Mo
5
atom. Recently, we have found the second successful
example of the Mo-catalyzed formation of ammonia
At first, we tried to prepare 2 by following the previ-
from dinitrogen by using [Mo(N ) (PNP)] (µ-N ) (1;
2
2
2
2
PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine)
as a catalyst, where up to 12 equiv of ammonia were
Scheme 1. Molybdenum-Catalyzed Reduction of
Dinitrogen into Ammonia under Ambient Conditions.
cat.
6 e–
6 H+
produced based on each Mo atom of the catalyst (23
N2 (1 atm)
2 NH3
rt
6
equiv based on the catalyst).
In this reaction system,
Previous
work
N
N
N
N
N
This work
the dinuclear structure of 1 plays an important role in
P
P
7
P
N
P
N
P
exhibiting the catalytic ability. In addition, some mo-
Ph
P
N
lybdenum-nitride complexes have been found to work as
N
Mo
N
N Mo
N
Mo
N
N
Mo
Ph
7
N
key reactive intermediates.
Based on the elucidation
P
N P
P
N
N
N
N
N
P
of the reaction mechanism, we have developed more
t
t
N
1
, P = P Bu2
2, P = P Bu
2
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6
ous method for 1. However, we could not isolate 2 as
a pure form from reduction of [MoCl (PPP)] (3) with
We carried out the catalytic reduction of dinitrogen
into ammonia using 5 as a catalyst. To a mixture of 5
and 2,6-lutidinium trifluoromethanesulfonate (48 equiv
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
8
3
5
reductants such as Na-Hg, KC , and CoCp* (Cp* = η -
8
2
C Me ) under 1 atm of N in THF at room temperature
for 14 h, although a strong IR-absorption derived from
to 5; [LutH]OTf) as a proton source in toluene was add-
5
5
2
ed a solution of CoCp (36 equiv to 5) as a reductant in
2
the terminal dinitrogen ligands was observed in all cases
toluene via a syringe pump at room temperature over a
period of 1 h, followed by stirring the resulting mixture
1
3,14
(
Scheme 2).
Next, we tried to prepare molyb-
denum-nitride complexes bearing PPP ligand because
molybdenum-nitride complexes bearing PNP ligand
have been found to work as effective catalysts, where
their catalytic activity of the molybdenum-nitride com-
at room temperature for another 19 h under 1 atm of N .
2
After the reaction, the formation of ammonia as well as
dihydrogen was observed, the amounts of which being
1
6
determined by indophenol method and GC, respective-
ly. Typical results are shown in Table 2. The yields of
ammonia and dihydrogen were estimated based on co-
baltocene. In all cases, no formation of other products
such as hydrazine was observed.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7
plexes is almost the same with that of 1.
Scheme 2. Preparation of Molybdenum-Nitride Complexes
Bearing PPP Ligand.
N2 (1atm)
reductant
IR absorbance in THF
1944 cm-1
[
MoCl3(PPP)]
2
THF
rt, 14 h
[1883 cm-1 (15N2;
Table 2. Molybdenum-Catalyzed Reduction of Dinitrogen into
Ammonia under Ambient Conditions.a
3
-1
theoretical 1887 cm )]
reductant: Na-Hg, KC8, CoCp*2
cat.
6 H+
N2
1 atm) (36 equiv)*(48 equiv)*
6 e–
2 NH3
*Based on the Mo
1
2
3
) TMSN3
N
rt
(
atom of the catalyst.
) PPP
P
Ph
) KC8
THF
NH3
H2
run catalyst reductant proton
source
[
MoCl3(thf)3]
P
Mo
Cl
amount
yield
amount
yield
t
(equiv)b (%)c (equiv)b (%)c
P
P = P Bu
2
[
Mo(N)Cl(PPP)] (4) ORTEP drawing of 4.
1
2
3
4
5
5
5
5
5
5
CoCp2 [LutH]OTf
CrCp*2 [LutH]OTf
CoCp*2 [LutH]OTf
CoCp*2 [PicH]OTf
CoCp*2 [ColH]OTf
1.8
2.3
6.1
3.3
9.6
15
19
51
28
80
10.5
8.6
0
0.9
1.1
58
48
0
5
6
N
BArF4
P
[FeCp2]BArF4 Ph
CoCp2]
4
P
Mo
Cl
6
7
4
3
CoCp*2 [ColH]OTf
CoCp*2 [ColH]OTf
11.0
6.4
92
53
0.3
1.7
2
9
[
t
P
P = P Bu2
ORTEP drawing of
cationic part of 5.
Mo(N)Cl(PPP)]BArF4 (5)
aTo a mixture of the catalyst (0.010 mmol) and proton source (48 equiv to the
catalyst) in toluene (1.0 mL) was added a solution of reductant (36 equiv to the
[
Table 1. Electrochemical Data of Molybdenum-Nitride Complexes.
catalyst) in toluene (4.0 mL) at room temperature over a period of 1 h, followed by
stirring at room temperature for another 19 h under 1 atm of N2. bMol equiv based
on the Mo atom of the catalyst. cYield based on reductant.
complex
4
5
[Mo(N)Cl(PNP)]
E1/2a,b
E1/2a,c
-0.99 V
–
-1.25 V
–
-1.02 V
–
E1/2 (V)d
e
reductant
proton source
pKa
a
n
Cyclic voltammetry in 0.1 M [ Bu4N]BF4/THF. Potential value was
referenced to FeCp20/+. bOxidation potential. cReduction potential.
[LutH]OTf
[PicH]OTf
[ColH]OTf
6.77
5.97
7.48
CoCp2
CrCp*2
CoCp*2
-1.25
-1.45
-1.88
7
According to the previous method, we have newly
dElectrochemical data (E1/2 vs FeCp2) of
epKa values of proton
source in H2O.19
prepared neutral and cationic molybdenum-nitride com-
plexes bearing PPP ligand [Mo(N)Cl(PPP)] (4) and
n
18
reductant in MeCN with 0.1 M [ Bu4N]BF4.
In the reaction using 5 as a catalyst, only a stoichio-
metric amount of ammonia was produced based on the
F
F
[
Mo(N)Cl(PPP)]BAr
(5;
bis(trifluoromethyl)phenyl), respectively. Treatment of
[MoCl (thf) ] with Me SiN at 50 ˚C and then addition
Ar
=
3,5-
4
Mo atom of the catalyst (Table 2, run 1).
Use of
3
3
3
3
CrCp* , in place of CoCp , as a reductant slightly in-
2
2
of PPP at 50 ˚C and sequential reduction with KC at
8
creased the amount of ammonia (2.3 equiv based on the
Mo atom) (Table 2, run 2). When the catalytic reaction
room temperature gave 4 in 54% yield (Scheme 2).
F
5
Oxidation of 4 with 1 equiv of [FeCp ]BAr (Cp = η -
2
4
was carried out by using CoCp* of a high reducing
2
C H ) at room temperature for 1 h afforded 5 in 81%
5
5
ability, 6.1 equiv of ammonia were produced based on
the Mo atom (Table 2, run 3). This result indicates that
5 has a catalytic activity toward ammonia formation.
1
4
yield (Scheme 2).
Interestingly, reduction of 5 with 1
equiv of cobaltocene (CoCp ) at room temperature for 1
2
h gave 4 in 42% yield. The molecular structures of 4
and 5 are unambiguously determined by X-ray crystal-
The acidity of the proton sources dramatically affect-
ed the catalytic activity of 5. In fact, a less amount of
ammonia was produced when [PicH]OTf (Pic = 2-
methylpyridine) of a higher acidity than [LutH]OTf was
1
5
lographic analysis (Scheme 2).
Both complexes have
a distorted square pyramidal structure with mer-PPP.
The electrochemical properties of 4 and 5 were estimat-
ed by the cyclic voltammetry (CV). Typical results are
shown in Table 1. The CV of 4 revealed one reversible
oxidation wave assignable to Mo(IV/V) at -0.99 V. The
used as a proton source (Table 2, run 4).
Use of
[
ColH]OTf (Col = 2,4,6-trimethylpyridine) of a lower
acidity than [LutH]OTf substantially increased the
amount of ammonia (9.6 equiv based on the Mo atom)
E
value of 4 is higher than that of [Mo(N)Cl(PNP)].
1
/2
(
Table 2, run 5). Separately, we confirmed the direct
On the other hand, the CV of 5 revealed one reversible
reduction wave assignable to Mo(IV/V) at -1.02 V, the
result being consistent with the redox behavior between
1
5
conversion of dinitrogen into ammonia by using
gas in place of normal N gas.
N
2
1
4
17
The result of the
2
control experiments indicates that the use of both 5 and
4
and 5.
dinitrogen is essential to promote the catalytic reac-
1
7
tion.
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The neutral complex 4 has a similar catalytic activity
lytic activity under the same reaction conditions. This
result indicates that some reactive species such as 2 may
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
with 5 under the present reaction conditions (Table 2,
run 6). It is noteworthy that the formation of ammonia
in 92% yield was observed together with dihydrogen in
only 2%. In sharp contrast to the previous reaction sys-
be generated from the reduction of 3 with CoCp* in the
2
catalytic reaction.
Next, we monitored the time profile of the catalytic
reaction by using 5 as a catalyst. Typical results are
shown in Figure 1 together with the time profile using 1
8
tem catalyzed by 1, the present reaction system by us-
ing 4 and 5 as catalysts can suppress the formation of
dihydrogen as a side-product.
8
as a catalyst. The catalytic formation of ammonia by
Next, we investigated the reaction in the presence of
a catalytic amount of 5 by using larger amounts of
using 5 proceeded more rapidly than that using 1, and
the turnover frequency (TOF) for ammonia, which was
determined by as mols of ammonia (based on the Mo
CoCp* as a reducing reagent and [ColH]OTf as a pro-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
-
1
ton source under similar conditions. Detailed investiga-
tion on the reaction conditions is shown in the Support-
atom) produced in initial 1 h per Mo atom, was 15.3 h
and higher than that using 1 (8.5 h ).
-
1 8
These results
ing Information.
To prevent the direct reaction of
indicate that 5 has the highest performance not only on
the catalytic activity but also on the rate for ammonia
formation.
CoCp* with [ColH]OTf, we carried out the reaction by
2
slow addition of a toluene solution of CoCp* over 10 h,
2
followed by stirring the resulting mixture at room tem-
perature for another 10 h. As a result, 63 equiv of am-
monia were produced based on the Mo atom (35% yield
based on the CoCp* ) from the reaction with CoCp*
To get more information on the reaction pathway, we
have investigated the possibility of the formation of 2 by
the DFT calculations based on the molecular structures
of 4 and 5. An optimized geometry of 2 shown in
Scheme 4 adopts a similar structure with that of 1. For
terminal dinitrogen ligands in 2, the N-N distance (1.140
2
2
(
1.08 mmol; 540 equiv to 5) and [ColH]OTf (1.44
mmol; 720 equiv to 5) in the presence of 5 (0.002 mmol)
as a catalyst in toluene at room temperature for 20 h,
together with dihydrogen (28 equiv based on the Mo
atom; 10% yield) (Scheme 3). This is so far the most
effective catalytic reaction using transition metal-
dinitrogen and its related complexes as catalysts.
20
Å) and the sum of the NPA charge (–0.127) indicate
that the dinitrogen ligands are moderately activated to-
ward protonation in a similar manner as 1 (1.138 Å and
7
–
0.125). The N-N stretching frequency of the terminal
-1
dinitrogen ligands in 2 is calculated to be 1947 cm ,
which is very close to the absorption observed in the IR
spectra (Scheme 2). On the other hand, the bond energy
between the Mo atom and the bridging dinitrogen is 13.6
kcal/mol. This value is substantially smaller than for 1
(24.9 kcal/mol), and thus the isolation of 2 from the re-
action solution is expected to be difficult. As a result,
we consider that the present catalytic reaction by using 4
and 5 as catalysts may proceed via 2 as a key reactive
intermediate.
Scheme 3. Molybdenum-Catalyzed Reduction of Dinitrogen into
Ammonia under Ambient Conditions.
OTf
cat. 5
(0.002 mmol)
N2
6
Co
6
2 NH3
toluene
rt, 20 h
(
1 atm)
N
H
0.125 mmol
(
63 equiv based on
the Mo atom)
35% yield
CoCp*2
[ColH]OTf
(720 equiv)
(540 equiv)
As shown in Table 1, the nature of PPP ligand much
affected the electrochemical property of the molyb-
denum-nitride complexes. These electrochemical prop-
erties indicate that the reduction of molybdenum com-
plexes bearing PPP ligand proceeds more smoothly than
that of molybdenum complexes bearing PNP ligand.
We consider that the higher reactivity of the molyb-
denum complexes bearing PPP ligand toward the reduc-
tion is one of the most important factors to promote the
catalytic reaction more smoothly. This electrochemical
Scheme 4. Optimized Geometry of 2.
N
N
P
N
P
P
Ph
N
P
Mo
N
N
Mo
Ph
N
P
N
N
N
P
t
2, P = P Bu2
Finally, we carried out a stoichiometric reaction of 5
with 5 equiv of CoCp* and 4 equiv of [ColH]OTf in
2
property prompted us to use [MoCl (PPP)] 3 as a pre-
3
toluene at room temperature for 20 h under 1 atm of Ar
to afford 0.77 equiv of ammonia based on 5 in 77%
yield. This result indicates that the nitrogen atom as a
nitride ligand can be converted into ammonia under the
catalytic reaction conditions. Unfortunately, we could
not obtain the imide complexes from the reaction of 4
with 1 equiv of proton sources such as [PyH]OTf (Py =
pyridine), [LutH]OTf, and [ColH]OTf. However, the
formation of the dinitrogen-bridged dimolybdenum core
bearing PPP ligand was detected by mass spectrometry
cursor. As a result, 3 was revealed to have a catalytic
activity, where 6.4 equiv of ammonia were produced
based on the Mo atom (Table 2, run 7). This unex-
pected catalytic reactivity is due to the unique property
of PPP ligand in 3 because [MoCl (PNP)] had no cata-
3
cat.
6 e–
6 H+
N2
2 NH3
rt
1 atm)(108 equiv)*(144 equiv)*
(
*
Based on the Mo atom
2
0
from a reaction mixture of 4 with 4 equiv of CoCp*
1
1
5
2
and 5 equiv of [ColH]OTf in toluene at room tempera-
complex TOF for NH3*
0
5
0
15
ture for 2 h under 1 atm of N .
This result indicates
15.3 h-1
8.5 h-1
15
2
5
1
that some dinitrogen-bridged dimolybdenum complexes
bearing PPP ligand may be generated and work as key
reactive intermediates of the catalytic reaction.
0
5
10
reaction time (h)
20
FIgure 1. Time profiles of the formation of ammonia using
5 (blue) and 1 (red) as catalysts.
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Y.; Yuki, M.; Nakajima, K.; Yoshizawa, K.; Nishibayashi, Y. Angew.
Other researchers, George and co-workers,
and
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Tuczek and co-workers, previously used triphosphines
and tetraphsophines as ligands to prepare highly reactive
molybdenum-dinitrogen complexes. However, the cata-
lytic reaction has never been achieved by using so far
reported molybdenum-dinitrogen complexes bearing
triphosphines and tetraphsophines. In contrast, the pre-
sent molybdenum-nitride complexes bearing PPP ligand
as only an auxiliary ligand have now been found to work
as the most effective catalysts for nitrogen fixation. We
believe that the mer-coordination mode with PPP ligand
to the Mo atom in 4 and 5 provides a suitable environ-
ment to the molybdenum complexes toward the catalytic
22
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(
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reaction.
Further work should be necessary to eluci-
date more detailed reaction pathway.
In summary, we have found that newly designed and
prepared molybdenum-nitride complexes bearing PPP
ligand worked as the most effective catalysts toward the
catalytic reduction of dinitrogen into ammonia under
ambient reaction conditions, where up to 63 equiv of
ammonia were produced based on the Mo atom. This
catalytic activity is more than five times higher than that
(6) (a) Arashiba, K.; Miyake, Y.; Nishibayashi, Y. Nat. Chem.
2011, 3, 120. (b) Kinoshita, E.; Arashiba, K.; Kuriyama, S.; Miyaka,
Y.; Shimazaki, R.; Nakanishi, H.; Nishibayashi, Y. Organometallics
6
of the original reaction system by using 1 as a catalyst.
2
012, 31, 8437.
The result described in this article provides the first suc-
cessful example of catalytic transformation by using
molybdenum complexes bearing only a triphosphine as
an auxiliary ligand. We believe that the present findings
provide useful information to design more effective
catalysts.
(
7) (a) Tanaka, H.; Arashiba, K.; Kuriyama, S.; Sasada, A.;
Nakajima, K.; Yoshizawa, K.; Nishibayashi, Y. Nat. Commun. 2014,
5, 3737. (b) Kinoshita, E.; Arashiba, K.; Kuriyama, S.; Eizawa, A.;
Nakajima, K.; Nishibayashi, Y. Eur. J. Inorg. Chem. 2015, 1789.
(
8) Kuriyama, S.; Arashiba, K.; Nakajima, K.; Tanaka, H.; Kama-
ru, N.; Yoshizawa, K.; Nishibayashi, Y. J. Am. Chem. Soc. 2014, 136,
9719.
(
(10) (a) Rittle, J.; Peters, J. C. Proc. Natl. Acad. Sci. USA. 2013,
10, 15898. (b) Rittle, J.; McCrory, C. C. L.; Peters, J. C. J. Am.
Chem. Soc. 2014, 136, 13853.
(11) Ung, G.; Peters, J. C. Angew. Chem. Int. Ed. 2015, 54, 532.
(
Chem. 2012, 51, 3239.
(13) The absorption at 1883 cm-1 was observed when 15N2 gas was
used under the same reaction conditions. This experimental value
corresponded to the theoretical value (1887cm ). In all cases, no
peaks were observed by NMR, due to their paramagnetic property.
9) Anderson, J. S.; Rittle, J.; Peters, J. C. Nature 2013, 501, 84.
ASSOCIATED CONTENT
1
Supporting Information
Experimental procedures, spectroscopic data, and X-ray
data (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
12) Gilbert-Wilson, R.; Field, L. D.; Bhadbhade, M. M. Inorg.
-
1
AUTHOR INFORMATION
t
14) When PPh groups were used in place of P Bu group in the
2 2
(
Corresponding Author
PPP ligand, we can not prepare the corresponding nitride complexes
under the same reaction conditions.
(
(
(
kazunari@ms.ifoc.kyushu-u.ac.jp
ynishiba@sogo.t.u-tokyo.ac.jp
15) See the Supporting Information in details.
16) Weatherburn, M. W. Anal. Chem. 1967, 39, 971.
17) Separately, we confirmed the direct conversion of molecular
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cat.
6 e–
6 H+
BArF
2 NH3
N2
rt
(
1 atm)
up to 63 equiv based on
the Mo atom of the catalyst
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N
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P
Ph
P
Mo
Cl
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P = P Bu
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[
Mo(N)Cl(PPP)]BArF
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