Post on 16-May-2020
CMo
P
P P
P
Mo
C
IR (THF): 1945 cm–1,2041 cm–1(nNN)
Mononuclear structurein solution
(equiv/cat.) toluenert, 20 h
cat.(0.010 mmol)
72 equiv/cat. 96 equiv/cat.
N2 + + 2 NH3
1 atm
66 ReductantNH
OTf
Catalytic conversion of dinitrogen to ammonia with molybdenum-PCP[2] complex
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N Dinuclear structure is maintained in solution
Long life due to the strong bondbetween molybdenum and PCP[1] ligand
Highest catalytic activity
Mo–C : 2.153(4) Å∠P–Mo–P : 163.18(8)�∠NHC–N2(terminal) : 43.74(7)�
NN
Remarkable catalytic activity of dinitrogen-bridged dimolybdenum complexes bearing NHC-based PCP-pincer ligands toward nitrogen fixation
NN
NN
1 Department of Systems Innovation and 4 Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan2 School of Liberal Arts and Sciences, Daido University, Takiharu-cho, Minami-ku, Nagoya, 457-8530, Japan3 Institute for Materials Chemistry and Engineering, Kyushu University, Nishi-ku, Fukuoka, 819-0395, Japan
NN
N
N
Aya Eizawa,1 Kazuya Arashiba,1 Hiromasa Tanaka,2 Shogo Kuriyama,1 Yuki Matsuo,3 Kazunari Nakajima,4Kazunari Yoshizawa3 and Yoshiaki Nishibayashi1
This Work
Previous work
Synthesis of dinitrogen-bridged dimolybdenum-dinitrogen complexes bearing PCP ligands
Molybdenum-dinitrogen complexesbearing PCP-type pincer ligands
R = H
R = OMe
23 equiv/cat.[12 equiv/Mo]52 equiv/cat.[26 equiv/Mo]
NMoNNMoN
P
PP
P
N
NN
N
N
NN
N
RR
P = PtBu2
Schrock, R. R. et al.Science 2003, 301, 76.
Nature Chem. 2011, 3, 120.Nature Commun. 2014, 5, 3737.J. Am. Chem. Soc. 2014, 136, 9719.
[ 8 equiv/Mo ]
Mo
N
NNN
iPriPr
iPr
HIPTHIPT
HIPT
NN iPr iPr
iPrcat.
PP
P
ClMo
NPh
+
[ 63 equiv/Mo ]
J. Am. Chem. Soc.2015, 137, 5666.
P = PtBu2
cat. 2 NH3N2 + 6 e− + 6 H+
1 atm Reductant Proton Source rt
More strongly-bindingligand enabled higher catalytic activity.More electron-donating ligand
enabled higher catalytic activity.
cat.
P = PtBu2
2.0�102 equiv/cat. 3.2 equiv/cat.
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
NNN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
NMoNNMoN
P
PP
P
N
NN
N
N
NN
N
cat. 2 NH3N2 + 6 e− + 6 H+
1 atm Reductant Proton Source rt NHCStrong s donorHigh binding ability
NP
NP
Previous work This work
23 equiv/cat.
P = PtBu2
37%
Dinuclear structure is maintained in solution
: 1978 cm–1 (nNN).: 1979 cm–1 (nNN).
IR IR
(KBr)(THF)
: 1936 cm–1 (nNN).: 1944 cm–1 (nNN).
IR IR
(KBr)(THF)
cf) IR (KBr): 1911 cm–1 (nNN).
NMoNNMoN
P
PP
P
N
NN
N
N
NN
N
THFrt, 18 h
N2 (1 atm)Na-Hg
NN MoP
PCl
Cl
Cl NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
53% P = PtBu2
Nature Communications 2017, 8, 14874.
NH3
(equ
iv/ca
t.)
cat.
P = PtBu2
Reductant
(equiv/cat.)
E1/2 (V vs Ag/Ag+) in MeCN −1.15
17.6 11.85.7 −1.35 −1.78
Catalytic conversion of dinitrogen to ammonia with molybdenum-PCP[1] complex
Time (h)10 200
20
40
0
cat. Cr
toluenert, 20 h
cat.(0.0010 mmol)
1440 equiv/cat. 1920 equiv/cat.
N2 + + 2 NH3
1 atm
66NH
OTf
cat. 2 NH3N2 + 6 e− + 6 H+
1 atm 216 equiv/cat. 288 equiv/cat.toluene
rt
2.0�102 equiv/cat. [1.0�102 equiv/Mo]
P = PtBu2
17 h–1
42 h–1
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
Co Cr Co
Reductant
E1/2 (V vs Ag/Ag+) in MeCN −1.15
3.2 2.91.4 −1.35 −1.78
Co Cr Co
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
cat.
P = PtBu2
46 equiv/cat.
23 equiv/cat.
toluenert, 20 h
cat.(0.010 mmol)
72 equiv/cat. 96 equiv/cat.
N2 + + 2 NH3
1 atm
66 ReductantNH
OTf
Mo
P
P
C
46 equiv/cat.
23 equiv/cat. 0 equiv/cat.
23 equiv/cat.
cat. NH3 1st
NN Mo N N Mo
N
N
P
PP
P
NN
N
NN
N
NN
H+
e–
Dinuclear structure is essentialfor the first protonation step.
No protonation to mononuclear dinitrogen complex proceeds.
Mononuclear structure in solution
No catalytic activityProtonation to the dinitrogen ligands is inhibited.
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
NNN Mo N NP
PN
N
N
NTHFrt
+ H+
No reaction
NN Mo N NP
P
NN
NN
e– (216 equiv)H+ (288 equiv)
e– (216 equiv)H+ (288 equiv)
toluenert, 20 h
toluenert, 2 h
N2
cat.+
N2+N2+
NH3 NH3
Mo–C : 2.064(2) Å∠P–Mo–P : 153.95(3)�∠NHC–N2(terminal) : 82.35(5)�
NH3 2nd
Proposed reaction mechanism
PCP[1] ligand PCP[2] ligand
NN
NNNN
P
P
MoC
NN
N
N
Molybdenum-catalyzed reduction of N2into NH3 under ambient reaction conditions
Lifetime of the catalysts
Time profiles
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
NN
N MoP
PCl
Cl
ClTHF
rt, 18 h
N2 (1 atm)Na-Hg
recryst. frombenzene-hexane
NN Mo N NP
PN
N
N
NTHF
rt
PNP complex is deactivatedwithin 20 h.
PCP[1] complex is still active after 20 h of reaction.
NH33 H+, 4 e–
NH3
N2
2 H+, 2 e–
H+N
N Mo N N MoN
N
P
PP
P
NN
N
NN
N
NN
NN Mo N N Mo
N
N
P
PP
P
OTfN
NN
N
NN Mo N N Mo
N
N
P
PP
P
OTfN
NN
N
NN Mo N N Mo
N
N
P
PP
PNH3
NN
N
NN
N
N
NHN
NMoNNMoN
P
PP
P
N
NN
N
N
NN
N
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
cat.
NMoNNMoN
P
PP
P
N
NN
N
N
NN
N
NN Mo N N Mo
N
N
P
PP
PN
N
N
N
N
NN
N
PNP ligand