activation of molecular nitrogen with ...1 barun jana, steven r. neal, aaron sadow, oleg pestovsky,...
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BarunBarun Jana, Steven R. Neal, Aaron Jana, Steven R. Neal, Aaron SadowSadow, , Oleg Oleg PestovskyPestovsky, and , and Andreja Andreja BakacBakac
ACTIVATION OF MOLECULAR NITROGEN ACTIVATION OF MOLECULAR NITROGEN WITH TRANSITION METAL COMPLEXESWITH TRANSITION METAL COMPLEXES
Ammonia ConferenceKansas City, October 12-13, 2009
Iowa State University, Ames, IA
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•Catalytic steam reforming CH4 + H2O → CO + 3H2
•Water gas shift reactionCO + H2O → CO2 + H2
•Catalytic NH3 formationN2 + 3H2 → 2 NH3 ΔHf
0 = - 46.1 kJ/mol300-5500C, up to 250 atmFe or Ru oxide cat
HABER-BOSCH PROCESS
Thermodynamics are favorable, kinetic barriers
•High temperatures lower equilibrium concentrations and yields of ammonia.•125 bar of H2/N2 (3:1 molar ratio),125 °C - yield of ammonia is 91%. •500 °C, yield is 12%. Must increase pressure. •NEED CATALYTIC REACTION TO LOWER KINETIC BARRIER
N N ΔH0 = 944 kJ/mol
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BIOLOGICAL NITROGEN FIXATION
NITROGENASE ENZYMES (Fe, Mo, V)
N2 from air NH3 + H2
Plants:
Enzyme (= catalyst)+ protons + electrons
M. D. Fryzuk, Chem. Rev. 2004, 104, 385;
4M. D. Fryzuk, Chem. Rev. 2004, 104, 385; Acc. Chem. Res. 2009, 42, 127
BINDING IN METAL-N2 COMPLEXES
Function of:MetalOxidation stateLigands
Free N2: PhN NPh NH2 NH2
N-N 1.0975 Å 1.255 1.460νNN 2331 cm-1 1442 1111
(Ta)
M N N M N N
M N N M M N N M
N
NMM
N
NMM
N
NMM
N
NMM
M
NN
M M
NN
M
Weak Activation Strong Activation
End-onMonometallic
End-onBimetallic
Side-onBimetallic
Side-on End-onBimetallic
(unknown)
(unknown)
5
Hanna, Lobkovsky, Chirik Organometallis 2009, 28, 4079
EFFECT OF SUBSTITUENTS ON BINDING MODE OF N2
N
R
Ti N2
R
R
TiN2
R
R
N2
Ti N
R
R
N Ti
R
R = SiMe2Ph R = i-Pr R = H , Me
R
Ti N
R
R
N Ti
R
R = Me
N
N
N
Ti
N
N
Ti
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Mo(NRAr)3
CLEAVAGE OF N2 AT Mo(III)
Laplaza, Cummins Science 1995, 268, 861
MoArRN
NRAr
NRAr
Mo
ArRNNRAr
NRAr
N
N
N2
1 atm, -35 ºC
Mo(NRAr)3
Mo
ArRNNRAr
NRAr
N
N
Mo
ArRNNRAr
NRAr
30 ºC
t1/2 = 35 minMo
ArRNNRAr
NRAr
N
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Yield: 55%(24 hours)
Nishibayashi et al, Science 1998, 279, 540
BIMETALLIC SYSTEM FOR N2 ACTIVATION
W
N
PN
PP
P
N
N
P = PMe2Ph
+ 6 [RuCl(!2-H2)(dppp)2]X
6 [RuCl(dppp)2]X
H2
(1 atm)
X = PF6 , BF4 , OTf , BPh4
55 ºC2 NH3 + 6 [RuHCl(dppp)2]
+ W(VI) (?)
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CATALYTIC REDUCTION OF N2 AT SINGLE Mo CENTER
Yandulov, Schrock Science 2003, 301, 76
4 Catalytic cycles
1, 2, 3, 4, 7, 8,12,13 prepared & structurally characterized
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HYDROGENATION AND CLEAVAGE OF N2
Pool, Lobkovsky, Chirik Nature 2004, 427, 527
Zr
N
N
Zr Zr
N
NZr
H2
25 °C
H
H
H
H
ZrH
H
H2
85 °C
(60 %)
+ NH3
(10-15 %)
Zr
N
NH2
Zr
85 °C- H2
10Curley, Cook, Reece, Muller, Cummins, J. Am. Chem. Soc. 2008, 130, 9394
PHOTOCHEMICAL CLEAVAGE OF NN BOND
Mo N N MoAr[t-Bu]N
Ar[t-Bu]NAr[t-Bu]N
N[t-Bu]Ar
N[t-Bu]ArN[t-Bu]Ar
Mo
Ar[t-Bu]NN[t-Bu]Ar
N[t-Bu]Ar
N
MoAr[t-Bu]N
N[t-Bu]Ar
N[t-Bu]Ar
+ 22
h!
-78 °C
N-N bond cleavage N2 extrusion- N2
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REDUCTION OF N2 TO NH3 AT IRON
Gilbertson, J. D.; Szymczak, N. K.; Tyler, D. R. J. Am. Chem. Soc. 2005, 127, 10184.
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Tyler , Leigh, et al
P
P
1,2-bis(bis-(methoxypropyl) -phosphino)ethane)
=
Gilbertson, J. D.; Szymczak, N. K.; Tyler, D. R. J. Am. Chem. Soc. 2005, 127, 10184.Leigh, G. J.; Jimenez-Tenorio, M. J. Am. Chem. Soc. 1991, 113, 5862.
Orange
Pale yellow
PFeII
P
P
P
Cl
Cl
PFeII
P
P
PH2
H
PFeII
P
P
P
N2
H
PFe0
P
P
PN2
H2/B-
N2/H+
B-
H+
NH4+/N2H5
+H2O
THF/
Et2O
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•Starting (P2)2FeIICl2 not stable in water
(hydrolyzes in 24 hours, H+-catalyzed)
•Protonation of (P2)2Fe0N2 causes hydrolytic destruction of complex
(free protonated ligand observed)
•Every step carried out independently (protonation/deprotonation)
•Need a "single pot" catalytic process
PROBLEMS
14Patrick L. Holland, . Am. Chem. Soc. 2009, 131, 9471
ACTIVATION OF N2 WITH COBALT COMPLEXES
15
Fe(I)-NN-Fe(I) BY NITRIDE COUPLING
Betley & Peters, J. Am. Chem. Soc 2004, 126, 6252
16
Funding: Iowa Energy Center
Oleg PestovskyBarun Jana
Aaron Sadow
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