Synthesis and reactivity of tungsten- and molybdenum-dinitrogen complexes bearing ferrocenyldiphosphines toward protonolysis

Article abstract of DOI:10.1021/om800327j

Novel tungsten- and molybdenum-dinitrogen complexes bearing 1,1′-bis(diethylphosphino)ferrocenes as auxiliary ligands have been prepared and characterized crystallographically. Reactions of these complexes with an excess amount of sulfuric acid in methano

Full text of DOI:10.1021/om800327j

Organometallics 2008, 27, 3947–3953
3947
Synthesis and Reactivity of Tungsten- and
Molybdenum-Dinitrogen Complexes Bearing
Ferrocenyldiphosphines toward Protonolysis
Masahiro Yuki, Yoshihiro Miyake, and Yoshiaki Nishibayashi*
Institute of Engineering InnoVation, School of Engineering, The UniVersity of Tokyo, Yayoi, Bunkyo-ku,
Tokyo 113-8656, Japan
Issei Wakiji and Masanobu Hidai†
Department of Chemistry and Biotechnology, School of Engineering, The UniVersity of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
ReceiVed April 14, 2008
Novel tungsten- and molybdenum-dinitrogen complexes bearing 1,1′-bis(diethylphosphino)ferrocenes
as auxiliary ligands have been prepared and characterized crystallographically. Reactions of these
complexes with an excess amount of sulfuric acid in methanol at room temperature yield ammonia in
good yields. This result is in sharp contrast to the previous result that protonolysis of tungsten- and
molybdenum-dinitrogen complexes bearing conventional diphosphines such as 1,2-bis(diphenylphos-
phino)ethane does not produce ammonia. Reactions of the dinitrogen complexes with 2 equiv of
trifluoromethanesulfonic acid give the corresponding hydrazido complexes as intermediates. Molecular
structures of these hydrazido complexes have been determined by X-ray analysis.
dihydrogen complexes at 55 °C give ammonia in good yields
based on the W atom.6 We believe that this methodology
provides a promising pathway to produce ammonia from
dinitrogen and dihydrogen under mild reaction conditions. More
recently, the use of multimetallic centers to activate molecular
dinitrogen provided a significant advance for the development
of effective transformation of coordinated dinitrogen molecules.7,8
Ferrocene and its derivatives are widely used as structural
units for the construction of unusual compounds and components
in material sciences.9 Moreover, ferrocene-based ligands are of
Introduction
Development of dinitrogen fixation systems under ambient
reaction conditions is one of the most important subjects in
chemistry. Toward this end, the preparation and reactivity of
transition metal dinitrogen complexes have been intensively
investigated for the last several decades.1,2 The first transition
metal-dinitrogen complex, [Ru(N2)(NH3)5]X2 (X ) Br, I, BF4,
PF6), was reported by Allen and Senoff in 1965.3 As to the
group 6 metal-dinitrogen complex, trans-[Mo(N2)2(dppe)2]
(dppe ) 1,1′-bis(diphenylphosphino)ethane) was reported by
Hidai and his co-workers in 1969.4 In 1975 Chatt and his co-
workers found the formation of ammonia by protonolysis of
tungsten- and molybdenum-dinitrogen complexes [M(N2)2-
(PR3)4] (M ) W, Mo).5 We have so far disclosed that reactions
of the tungsten-dinitrogen complexes with ruthenium-
(6) (a) Nishibayashi, Y.; Iwai, S.; Hidai, M. Science 1998, 279, 506.
(b) Nishibayashi, Y.; Takemoto, S.; Iwai, S.; Hidai, M. Inorg. Chem. 2000,
39, 5946.
(7) For recent examples of homometallic complexes, see: (a) Pool, J. A.;
Lobkovsky, E.; Chirik, P. J. Nature 2004, 427, 527. (b) Evans, W. J.; Lee,
D. S.; Ziller, J. W.; Kaltsoyannis, N. J. Am. Chem. Soc. 2006, 128, 14176.
(c) Hirotsu, M.; Fontaine, P. P.; Zavalij, P. Y.; Sita, L. R. J. Am. Chem.
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Toomey, H. E.; Chirik, P. J. J. Am. Chem. Soc. 2008, 130, 4248. (g) Morello,
L.; Ferreira, M. J.; Patrick, B. O.; Fryzuk, M. D. Inorg. Chem. 2008, 47,
1319.
(8) For heterometallic complexes, see: (a) Mizobe, Y.; Yokobayashi,
Y.; Oshita, H.; Takahashi, T.; Hidai, M. Organometallics 1994, 13, 3764.
(b) O’Donoghue, M. B.; Zanetti, N. C.; Davis, W. M.; Schrock, R. R. J. Am.
Chem. Soc. 1997, 119, 2753. (c) Mindiola, D. J.; Meyer, K.; Cherry, J.-
P. F.; Baker, T. A.; Cummins, C. C. Organometallics 2000, 19, 1622. (d)
Ishino, H.; Nagano, T.; Kuwata, S.; Yokobayashi, Y.; Ishii, Y.; Hidai, M.;
Mizobe, Y. Organometallics 2001, 20, 188. (e) Mori, H.; Seino, H.; Hidai,
M.; Mizobe, Y. Angew. Chem., Int. Ed. 2007, 46, 5431.
(9) (a) Hudson, R. D. A. J. Organomet. Chem. 2001, 637-639, 47. (b)
Nishihara, H. AdV. Inorg. Chem. 2002, 53, 41. (c) Nakamura, E. Pure Appl.
Chem. 2003, 75, 427. (d) van Staveren, D. R.; Metzler-Nolte, N. Chem.
ReV. 2004, 104, 5931. (e) Nakamura, E. J. Organomet. Chem. 2004, 689,
4630. (f) J. Inorg. Organomet. Polym. Mater. 2005, 15,No. 1 (the special
issue celebrating the 50th anniversary of polyferrocenes). (g) Fouda,
M. F. R.; Abd-Elzaher, M. M.; Abdelsamaia, R. A.; Labib, A. A. Appl.
Organomet. Chem. 2007, 21, 613. (h) Gao, Y.; Shreeve, J. M. J. Inorg.
Organomet. Polym. Mater. 2007, 17, 19. (i) Seiwert, B.; Karst, U. Anal.
Bioanal. Chem. 2008, 390, 181.
* Corresponding author. E-mail: ynishiba@sogo.t.u-tokyo.ac.jp.
† Present address: Department of Materials Science and Technology,
Faculty of Industrial Science and Technology, Tokyo University of Science,
Noda, Chiba 278-8510, Japan.
(1) For recent reviews, see: (a) Hidai, M.; Mizobe, Y. Chem. ReV. 1995,
95, 1115. (b) Gambarotta, S. J. Organomet. Chem. 1995, 500, 117. (c)
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MacKay, B. A.; Fryzuk, M. D. Chem. ReV. 2004, 104, 385. (e) Gambarotta,
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Y Can. J. Chem. 2005, 83, 358. (g) Himmel, H.-J.; Reiher, M. Angew.
Chem., Int. Ed. 2006, 45, 6264.
(2) For recent examples of mononuclear complexes, see: (a) Yandulov,
D. V.; Schrock, R. R. Science 2003, 301, 76. (b) Curley, J. J.; Sceats, E. L.;
Cummins, C. C. J. Am. Chem. Soc. 2006, 128, 14036. (c) Smythe, N. C.;
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(3) Allen, A. D.; Senoff, C. V. Chem. Commun. 1965, 621.
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10.1021/om800327j CCC: $40.75
2008 American Chemical Society
Publication on Web 07/12/2008

3948 Organometallics, Vol. 27, No. 15, 2008
Yuki et al.
Table 1. IR and Electrochemical Data of Tungsten- and
Scheme 1
Molybdenum-Dinitrogen Complexes
complexa
ν
NN/cm-1
E1/2/Vc
ref
b
cis-W(N2)2(depf)2 (cis-1)
cis-W(N2)2(PMe3)4
cis-W(N2)2(PPhMe2)4
cis-W(N2)2(dppm)2
trans-W(N2)2(depf)2 (trans-1)
trans-W(N2)2(depe)2
trans-W(N2)2(dchpe)2
trans-W(N2)2(PPhMe2)4
trans-W(N2)2(dppe)2
trans-W(N2)2(PPh2Me)4
trans-Mo(N2)2(depf)2 (trans-2)
trans-Mo(N2)2(depe)2
trans-Mo(N2)2(dppe)2
trans-Mo(N2)2(PPh2Me)4
1972, 1906
1980, 1920d
1991, 1913
2000, 1935e
1883
-0.88qr
this work
13a
13b
-0.83qr
13c
-0.95
-0.96
-1.02
-0.83
-0.68
-0.71f
-0.97
-0.97
-0.70
-0.71
this work
13d, 13e
13e
13b
13d, 13e
13f
this work
13e, 13g
13e
1904
1880e
1898
increasing importance for transition-metal-catalyzed organic
syntheses including asymmetric transformations based on the
planar chirality of ferrocene derivatives.10,11 For instance, 1,1′-
bis(diphenylphosphino)ferrocene (dppf) became a commonly
used ligand because of relatively large bite angles, capacity of
dative bond formation with electron-deficient metal centers, and
chemical robustness of the ferrocene skeleton.11 As an extension
of our continuing study,12 we have now envisaged the prepara-
tion of tungsten- and molybdenum-dinitrogen complexes
bearing ferrocenyldiphosphines as auxiliary ligands. Herein, we
report the synthesis and characterization of tungsten- and
molybdenum-dinitrogen complexes bearing 1,1′-bis(dieth-
ylphosphino)ferrocene (depf) such as [M(N2)2(depf)2] together
with their stoichiometric reactivity toward protonolysis.
1943
1910e
1907
1928
1976e
1922
13h, 13i
a dppm)1,1′-bis(diphenylphosphino)methane.depe)1,1′-bis(diethylphos-
phino)ethane. dchpe ) 1,1′-bis(dicyclohexylphosphino)ethane. b KBr pellet.
c Relative to ferrocene-ferrocenium couple in THF. qr ) quasi-reversible.
d n-Hexane solution. e Nujol mull. f This work.
Results and Discussion
Treatment of WCl6 with 2 equiv of depf in the presence of
an excess amount of magnesium in tetrahydrofuran (THF) under
a dinitrogen atmosphere at room temperature for 24 h gave a
mixture of cis- and trans-[W(N2)2(depf)2] (1) in the ratio of 6:
1 (Scheme 1). The major isomer (cis-1) was isolated in 19%
yield by recrystallization. The IR spectrum of cis-1 exhibited
two strong νNN bands at 1972 and 1906 cm-1, consistent with
the cis arrangement of two dinitrogen ligands. These νNN
frequencies of cis-1 are lower than those of cis-[W(N2)2(PR3)4]
complexes as shown in Table 1. This result indicates that the
depf ligand has a highly electron-donating nature as a result of
strong π-back-donation from the tungsten center to the dini-
trogen ligands. In the 31P{1H} NMR spectrum of cis-1, two
triplet peaks were observed at -5.1 and -1.9 ppm correspond-
ing to phosphorus atoms cis and trans to dinitrogen ligands or
vice versa. The molecular structure of cis-1 was unambiguously
clarified by X-ray crystallography, an ORTEP drawing of cis-1
Figure 1. ORTEP view of cis-1 with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
being shown in Figure 1. Selected bond lengths and angles of
cis-1 are listed in Table 2. Around the octahedrally coordinated
tungsten center, two dinitrogen ligands occupied cis positions
each other. The W-N(1) and N(1)-N(2) distances of 1.994(3)
and 1.121(5) Å are not unusual. The bite angle of the
diphosphine ligand (P1-W-P2 89.05(3)°) is smaller than that
observed for [W(CO)4(dppf)]14 (95.24(5)°) and [W(CO)3-
(NCMe)(dppf)]15 (98.05(6)°), but similar to [W(CO)3(η2-
C60)(dppf)]14 (88.63(4)°), suggesting steric congestion around
the tungsten center of cis-1. The W-Fe distance of 4.61 Å
precludes the direct bonding interaction between the tungsten
and iron atoms.16,17 Separately, we confirmed that no intercon-
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Tungsten- and Molybdenum-Dinitrogen Complexes
Organometallics, Vol. 27, No. 15, 2008 3949
Table 2. Selected Interatomic Distances and Bond Angles for cis-1a
Distances (Å)
W-P(1)
W-N(1)
W · · · Fe
2.5129(10)
1.994(3)
4.6101(6)
W-P(2)
N(1)-N(2)
2.4655(10)
1.121(5)
Angles (deg)
P(1)-W-P(2)
P(1)-W-P(2)*
P(1)-W-N(1)
P(2)-W-N(1)
N(1)-W-N(1)*
89.05(3)
98.42(3)
86.73(10)
87.14(10)
83.74(14)
P(1)-W-P(1)*
P(2)-W-P(2)*
P(1)-W-N(1)*
P(2)-W-N(1)*
W-N1-N2
103.45(3)
167.96(3)
168.40(12)
83.90(10)
174.2(4)
a Asterisks denote atoms related by the symmetry operation -x, y,
-z+1/2.
Figure 2. ORTEP view of trans-1 with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
Scheme 2
Table 3. Selected Interatomic Distances and Bond Angles for trans-1
Distances (Å)
W-P(1)
2.4858(6)
2.4789(6)
1.993(2)
1.136(3)
4.5269(4)
W-P(2)
2.4856(9)
2.4667(8)
1.999(2)
1.139(3)
4.4301(4)
W-P(3)
W-P(4)
W-N(1)
N(1)-N(2)
W · · · Fe(1)
W-N(3)
N(3)-N(4)
W · · · Fe(2)
version between cis-1 and trans-1 was observed at room
temperature for several days. Unfortunately, when dppf was used
in place of depf, the formation of the corresponding tungsten-
dinitrogen complex was not observed at all.
Angles (deg)
P(1)-W-P(2)
P(1)-W-P(3)
P(2)-W-P(3)
P(1)-W-N(1)
P(2)-W-N(1)
P(3)-W-N(1)
P(4)-W-N(1)
N(1)-W-N(3)
W-N(3)-N(4)
95.72(2)
169.53(2)
90.32(2)
88.61(6)
82.59(8)
100.67(6)
84.79(8)
169.24(11)
174.0(2)
P(3)-W-P(4)
P(1)-W-P(4)
P(2)-W-P(4)
P(1)-W-N(3)
P(2)-W-N(3)
P(3)-W-N(3)
P(4)-W-N(3)
W-N(1)-N(2)
84.99(2)
91.11(2)
165.48(2)
85.57(6)
88.98(9)
85.99(6)
104.34(9)
174.9(2)
Heating of trans-[W(N2)2(PPh2Me)4]18 with 2 equiv of depf
in THF at reflux temperature for 4 h gave trans-1 in 43%
isolated yield (Scheme 2). No formation of cis-1 was observed
after the reaction. The IR spectrum of trans-1 exhibited a νNN
band at 1883 cm-1, which is one of the most red-shifted values
among the reported tungsten-dinitrogen complexes such as
trans-[W(N2)2(PR3)4], as shown in Table 1. A cyclic voltam-
mogram of trans-1 showed a reversible one-electron oxidation
wave at -0.95 V (versus the ferrocene-ferrocenium redox
couple), corresponding to the W(0/I) redox couple. This value
is similar to those of trans-[W(N2)2(depe)2] (depe ) 1,1′-
bis(diethylphosphino)ethane) and trans-[W(N2)2(dchpe)2] (dchpe
) 1,1′-bis(dicyclohexylphosphino)ethane) (Table 1). These
results indicate that the electron donation from each depf ligand
proved to be as strong as two trialkylphosphine ligands. As a
result, the strong π-back-donation ability of 1 is expected to
make the ligating dinitrogen molecules highly reactive. In the
31P{1H} NMR spectrum of trans-1, a singlet peak was observed
Scheme 3
being 9.9° and 47.3°, respectively.19 The distortion of the
N(1)-W-N(3) angle in trans-1 is probably due to the steric
repulsion of the coordinated ligands. The other bond distances
and angles are almost the same as those of cis-1.
1
at -7.2 ppm (s with 183W satellite, JP-W ) 316 Hz). The
molecular structure of trans-1 was unambiguously clarified by
X-ray crystallography, an ORTEP drawing of trans-1 being
shown in Figure 2. Selected bond lengths and angles of trans-1
are listed in Table 3. Similar to cis-1, there is no bonding
interaction between tungsten and iron centers (W-Fe: 4.43 and
4.52 Å).13,14 The bite angles of two depf ligands in trans-1 differ
significantly (P(1)-W-P(2) 85.11(3)°, P(3)-W-P(4) 95.81(3)°),
which corresponds to a synperiplanar and staggered conforma-
tion of the ferrocene units, the rotation angles of ferrocene units
The
molybdenum-dinitrogen
complex
trans-
[Mo(N2)2(depf)2] (trans-2) was prepared by a similar procedure
to that of cis-1. Treatment of MoCl5 with 2 equiv of depf in
the presence of an excess amount of magnesium in THF under
an atmosphere of dinitrogen at room temperature for 24 h gave
trans-2 in 13% yield (Scheme 3). The IR spectrum of trans-2
exhibited one νNN band at 1907 cm-1 consistent with the trans
conformation. No cis isomer was observed at all probably due
to the so-far-known fast cis-trans isomerization of molybdenum
analogues.20 The molecular structure of trans-2 was unambigu-
ously clarified by X-ray crystallography, an ORTEP drawing
of trans-2 being shown in Figure 3. Selected bond lengths and
angles of trans-2 are listed in Table 4. The crystals of trans-2
were isomorphous to those of trans-1, and the structural
parameters of trans-2 are also the same as those of trans-1.
Next, we examined the reactivity of the tungsten- and
molybdenum-dinitrogen complexes 1 and 2 toward protonolysis
(17) (a) Seyferth, D.; Hames, B. W.; Rucker, T. G. Organometallics
1983, 2, 472. (b) Akabori, S.; Kumagai, T.; Shirahige, T.; Sato, S.; Kawazoe,
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3950 Organometallics, Vol. 27, No. 15, 2008
Yuki et al.
Scheme 5
protonolysis of tungsten- and molybdenum-dinitrogen com-
plexes bearing conventional diphosphines such as 1,2-bis(diphe-
nylphosohino)ethane does not produce ammonia.22
To obtain more information on the reaction pathway for the
formation of ammonia, we investigated reactions of 1 and 2
with 2 equiv of trifluoromethanesulfonic acid (HOTf) in toluene
at room temperature for 1 h. As a result, the corresponding
hydrazido complexes trans-[M(NNH2)(OTf)(depf)2]OTf (3; M
) W, 4; M ) Mo) were obtained in 58% and 41% isolated
yields, respectively (Scheme 5). Molecular structures of 3 and
4 were unambiguously clarified by X-ray crystallography,
ORTEP drawings of 3 and 4 being shown in Figures 4 and 5.
Selected bond lengths and angles of 3 and 4 are listed in Tables
5 and 6. In both cases, a hydrogen bond was observed between
Figure 3. ORTEP view of trans-2 with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
Table 4. Selected Interatomic Distances and Bond Angles for trans-2
Distances (Å)
Mo-P(1)
Mo-P(3)
Mo-N(1)
N(1)-N(2)
Mo · · · Fe(1)
2.4991(4)
2.4945(4)
2.0097(16)
1.124(2)
Mo-P(2)
Mo-P(4)
Mo-N(3)
N(3)-N(4)
Mo · · · Fe(2)
2.4971(6)
2.4801(6)
2.0211(15)
1.122(2)
4.5366(3)
4.4391(2)
Angles (deg)
P(1)-Mo-P(2)
P(1)-Mo-P(3)
P(2)-Mo-P(3)
P(1)-Mo-N(1)
P(2)-Mo-N(1)
P(3)-Mo-N(1)
P(4)-Mo-N(1)
N(1)-Mo-N(3)
Mo-N(3)-N(4)
95.563(18)
169.675(19)
90.417(17)
88.56(4)
82.78(5)
100.56(4)
84.76(5)
P(3)-Mo-P(4)
P(1)-Mo-P(4)
P(2)-Mo-P(4)
P(1)-Mo-N(3)
P(2)-Mo-N(3)
P(3)-Mo-N(3)
P(4)-Mo-N(3)
Mo-N(1)-N(2)
84.883(17)
91.208(17)
165.647(17)
85.82(4)
88.86(6)
85.90(4)
104.28(6)
174.32(16)
169.43(7)
173.8(2)
Scheme 4
because it is well-known that the stoichiometric reactions of
tungsten- and molybdenum-dinitrogen complexes bearing at
least one monodentate phosphine with a Brønsted acid gave
ammonia and/or hydrazine.5,21
Treatment of cis- and trans-1 with an excess amount of
sulfuric acid in methanol at room temperature for 24 h produced
ammonia in 137% and 129% yields based on the W atom,
respectively (Scheme 4). In both cases, no formation of
hydrazine was observed. On the other hand, the reaction of
trans-2 with sulfuric acid under the same reaction conditions
gave ammonia in 48% yield based on the Mo atom. These
results are apparently different from the previous results that
Figure 4. ORTEP view of 3 with 50% thermal ellipsoids. Hydrogen
atoms except for the hydrazido ligand are omitted for clarity.
(21) (a) Chatt, J.; Heath, G. A.; Richards, R. L. J. Chem. Soc., Dalton
Trans. 1974, 2074. (b) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem.
Soc., Dalton Trans. 1977, 1852. (c) Hidai, M.; Mizobe, Y.; Takahashi, T.;
Uchida, Y. Chem. Lett. 1978, 1187. (d) Takahashi, T.; Mizobe, Y.; Sato,
M.; Uchida, Y.; Hidai, M. J. Am. Chem. Soc. 1979, 101, 3405. (e) Anderson,
S. N.; Fakley, M. E.; Richards, R. L.; Chatt, J. J. Chem. Soc., Dalton Trans.
1981, 1973. (f) Anderson, S. N.; Richards, R. L.; Hughes, D. L. J. Chem.
Soc., Dalton Trans. 1986, 245.
(22) (a) Heath, G. A.; Mason, R.; Thomas, K. M. J. Am. Chem. Soc.
1974, 96, 259. (b) Hidai, M.; Kodama, T.; Sato, M.; Hirakawa, M.; Uchida,
Y. Inorg. Chem. 1976, 15, 2694. (c) Chatt, J.; Leigh, G. J.; Neukomm, H.;
Pickett, C. J.; Stanley, D. R. J. Chem. Soc., Dalton Trans. 1980, 121. (d)
Nishihara, H.; Mori, Y.; Nakano, K.; Saito, T.; Sasaki, Y. J. Am. Chem.
Soc. 1982, 104, 4367. (e) Henderson, R. A. J. Chem. Soc., Dalton Trans.
1982, 917. (f) Bakar, M. A.; Hughes, D. L.; Hussain, W.; Leigh, G. J.;
Macdonald, C. J.; Mohd.-Ali, H. J. Chem. Soc., Dalton Trans. 1988, 2545.
(g) Barclay, J. E.; Hills, A.; Hughes, D. L.; Leigh, G. J.; Macdonald, C. J.;
Bakar, M. A.; Mohd.-Ali, H. J. Chem. Soc., Dalton Trans. 1990, 2503.
Figure 5. ORTEP view of 4 · THF · 0.5C6H14 with 50% thermal
ellipsoids. Hydrogen atoms except for the hydrazido ligand and
n-hexane solvate are omitted for clarity.

Tungsten- and Molybdenum-Dinitrogen Complexes
Organometallics, Vol. 27, No. 15, 2008 3951
Table 5. Selected Interatomic Distances and Bond Angles for 3
Scheme 6
Distances (Å)
W-P(1)
2.5459(8)
2.5948(8)
1.748(2)
1.350(3)
0.94(4)
W-P(2)
2.5397(8)
2.5492(8)
2.2195(18)
0.99(4)
1.93(4)
4.3407(4)
W-P(3)
W-P(4)
W-N(1)
W-O(1)
N(1)-N(2)
N(2)-H(2)
W · · · Fe(1)
N(2)-H(1)
O(4) · · · H(1)
W · · · Fe(2)
[M(N2)2(PR3)4] (M ) Mo, W), produce ammonia and/or
hydrazine by treatment with Brønsted acid such as sulfuric acid
in methanol.5,21 Interestingly, no formation of ammonia was
observed when molybdenum- and tungsten-dinitrogen com-
plexes bearing chelating diphosphines as auxiliary ligands,
[M(N2)2L2] (M ) Mo, W, L ) dppe, depe), were employed;
only the formation of the corresponding hydrazido complexes
was observed.22 Our observation is the first example of the
formationofammoniafrommolybdenum-andtungsten-dinitrogen
complexes bearing two chelating diphosphines via the corre-
sponding hydrazido complexes as intermediates. At present, we
have not yet clarified the exact role of depf in these dinitrogen
complexes, but it may be possible that the electron transfer
process from ferrocene units to the tungsten or molybdenum
center assists the reduction of the dinitrogen molecule into
ammonia because George and his co-worker previously indi-
cated the critical role of the ferrocene moiety on the formation
of ammonia and/or hydrazine from other types of molybdenum
monodinitrogen complexes, [Mo(N2){PhP(C2H4PPh2)2}L] (L )
dppf, dppe, dppm, 2 PPh3).26
In summary, we have newly designed and prepared novel
tungsten- and molybdenum-dinitrogen complexes bearing 1,1′-
bis(diethylphosphino)ferrocenes. Protonation of these complexes
with an excess amount of sulfuric acid in methanol produced
ammonia in good yields. This result is in sharp contrast to the
previous findings that protonolysis of tungsten- and moly-
bdenum-dinitrogen complexes bearing conventional diphos-
phines such as 1,2-bis(diphenylphosohino)ethane does not
produce ammonia. Stoichiometric reactions of the dinitrogen
complexes with 2 equiv of trifluoromethanesulfonic acid yielded
the corresponding hydrazido complexes as reactive intermedi-
ates. Molecular structures of newly prepared complexes were
confirmed by X-ray analysis.
4.5709(4)
Angles (deg)
P(1)-W-P(2)
P(1)-W-P(3)
P(2)-W-P(3)
P(1)-W-N(1)
P(2)-W-N(1)
P(3)-W-N(1)
P(4)-W-N(1)
N(1)-W-O(1)
94.24(2)
164.07(2)
88.11(2)
94.26(8)
87.58(8)
101.58(8)
86.71(8)
174.72(10)
P(3)-W-P(4)
P(1)-W-P(4)
P(2)-W-P(4)
P(1)-W-O(1)
P(2)-W-O(1)
P(3)-W-O(1)
P(4)-W-O(1)
W-N(1)-N(2)
86.98(2)
92.35(2)
171.58(2)
82.90(6)
97.05(6)
81.18(6)
88.96(6)
177.1(2)
Table 6. Selected Interatomic Distances and Bond Angles for
4 · THF · 0.5C6H14
Distances (Å)
Mo-P(1)
Mo-P(3)
Mo-N(1)
N(1)-N(2)
N(2)-H(1)
O(4) · · · H(1)
Mo · · · Fe(1)
2.5459(11)
2.5921(11)
1.730(2)
1.345(4)
1.00(4)
Mo-P(2)
Mo-P(4)
Mo-O(1)
2.5664(9)
2.5999(9)
2.237(2)
N(2)-H(2)
O(7) · · · H(2)
Mo · · · Fe(2)
0.94(4)
1.95(4)
4.4150(6)
1.85(3)
4.5929(6)
Angles (deg)
P(1)-Mo-P(2)
P(1)-Mo-P(3)
P(2)-Mo-P(3)
P(1)-Mo-N(1)
P(2)-Mo-N(1)
P(3)-Mo-N(1)
P(4)-Mo-N(1)
N(1)-Mo-O(1)
93.85(3)
163.76(3)
91.75(3)
92.70(12)
84.02(9)
103.05(12)
87.10(9)
174.93(14)
P(3)-Mo-P(4)
P(1)-Mo-P(4)
P(2)-Mo-P(4)
P(1)-Mo-O(1)
P(2)-Mo-O(1)
P(3)-Mo-O(1)
P(4)-Mo-O(1)
Mo-N(1)-N(2)
85.49(3)
91.44(3)
169.86(3)
82.28(8)
97.02(7)
81.91(8)
92.26(7)
171.1(3)
one of the oxygen atoms of the triflate anion and one of the
terminal hydrogen atoms of the hydrazido ligand. There was
no structural evidence for the electronic interaction between the
tungsten or molybdenum and iron atoms in the hydrazido
complexes.
We confirmed the formation of ammonia from reactions of
hydrazido complexes with an excess amount of sulfuric acid in
methanol at room temperature for 24 h (Scheme 6). These results
indicate that the formation of ammonia proceeds via hydrazido
complexes as key intermediates. We could not detect any
structurally defined complexes after the protonation of these
hydrazido complexes with sulfuric acid, only free depf ligand
being observed by 31P{1H} NMR.
Since the first discovery of the formation of ammonia from
the coordinated dinitrogen molecules on molybdenum and
tungsten atoms, many efforts have been made including a
mechanistic study on the reaction pathway.5,18,21–25 As a result,
it is generally known that molybdenum- and tungsten-dinitrogen
complexes bearing monodentate phosphines as auxiliary ligands,
Experimental Section
General Method. 1H NMR (270 MHz) and 31P{1H} NMR (109
MHz) spectra were measured on a JEOL Excalibur 270 spectrom-
eter, and 31P chemical shifts were quoted relative to an external
standard of 85% H3PO4. IR spectra were recorded on a JASCO
FT/IR 4100 Fourier transform infrared spectrophotometer. Elemen-
tal analyses were performed at Microanalytical Center of The
University of Tokyo. Cyclic voltammograms were recorded on an
ALS/Chi model 610C electrochemical analyzer with platinum
working electrode in THF containing 0.1 M nBu4NBF4 as a
supporting electrolyte. The potentials are quoted relative to the
ferrocene/ferrocenium couple. All manipulations were performed
under a dry nitrogen atmosphere. Solvents were dried over
appropriate reagents and distilled prior to use. N,N,N′,N′-Tetram-
ethylethylenediamine (TMEDA) was distilled from calcium hydride.
The complex trans-[W(N2)2(PPh2Me)4] · 1.5THF was prepared by
the literature method18 and recrystallized from THF-iPrOH. Other
reagents were purchased and used as received.
(23) (a) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton
Trans. 1978, 1766. (b) Hidai, M.; Takahashi, T.; Yokotake, I.; Uchida, Y.
Chem. Lett. 1980, 645. (c) Hanson, I. R.; Hughes, D. L. J. Chem. Soc.,
Dalton Trans. 1981, 390. (d) Galindo, A.; Hills, A.; Hughes, D. L.; Richards,
R. L.; Hughes, M.; Mason, J. J. Chem. Soc., Dalton Trans. 1990, 283. (e)
George, T. A.; Kaul, B. B.; Chen, Q.; Zubieta, J. Inorg. Chem. 1993, 32,
1706.
(24) (a) Lehnert, N.; Tuczek, F. Inorg. Chem. 1999, 38, 1671. (b) Horn,
K. H.; Lehnert, N.; Tuczek, F. Inorg. Chem. 2003, 42, 1076.
(25) As a related reaction system, Schrock and his co-workers discovered
the catalytic formation of ammonia by using a molybdenum-dinitrogen
complex: Schrock, R. R. Acc. Chem. Res. 2005, 38, 955, and references
therein.
Preparation of 1,1′-Bis(diethylphosphino)ferrocene (depf). 27
A mixture of ferrocene (9.30 g, 50.0 mmol), TMEDA (15.0 mL,
99.4 mmol), and nBuLi (1.55 M, 80.0 mL, 124 mmol) in n-hexane
(26) George, T. A.; Tisdale, R. C. J. Am. Chem. Soc. 1985, 107, 5157.
(27) Gusev, O. V.; Peganova, T. A.; Kalsin, A. M.; Vologdin, N. V.;
Petrovskii, P. V.; Lyssenko, K. A.; Tsvetkov, A. V.; Beletskaya, I. P.
Organometallics 2006, 25, 2750.

3952 Organometallics, Vol. 27, No. 15, 2008
cis-1 · 2.5THF
Yuki et al.
Table 7. Summary of Crystallographic Data
trans-1
trans-2
3
4 · THF · 0.5C6H14
formula
fw
C46H76N4Fe2O2.5P4W C36H56N4Fe2P4W
1144.57 964.30
C36H56N4Fe2MoP4
876.39
C38H58N2F6Fe2O6P4S2W C45H73N2F6Fe2MoO7P4S2
1236.44
1263.72
cryst size/mm
color, habit
cryst syst
space group
a/Å
0.25 × 0.20 × 0.20 0.30 × 0.30 × 0.25 0.50 × 0.30 × 0.20 0.25 × 0.25 × 0.20
0.50 × 0.50 × 0.07
orange plate
triclinic
orange-yellow block orange-red prism
orange-red prism
orange plate
monoclinic
P21/c (No. 14)
16.9906(5)
14.3654(3)
19.4780(5)
90
monoclinic
C2/c (No. 15)
16.7672(9)
13.9265(6)
21.5321(10)
90
116.4261(9)
90
4502.6(4)
4
triclinic
P1 (No. 2)
triclinic
P1 (No. 2)
j
j
j
P1 (No. 2)
10.3251(5)
12.9548(7)
16.0045(8)
68.5308(15)
75.0976(15)
75.3906(16)
1895.23(17)
2
10.3341(3)
12.9756(4)
16.0505(4)
68.4688(18)
75.0902(17)
75.3883(8)
1904.58(9)
2
10.8177(5)
11.2497(5)
23.4127(9)
77.5875(14)
78.6013(15)
84.5651(16)
2723.69(20)
2
b/Å
c/Å
R/deg
ꢀ/deg
105.0220(6)
90
4591.7(2)
4
γ/deg
V/Å3
Z
dc/g cm-3
µ(Mo KR)/mm-1
no. of data collected
no. of unique data (Rint
no. of params refined
R1a (F2 > 2σ)
wR2b (all data)
1.688
3.374
21 335
5159 (0.056)
286
0.036
0.088
1.03
1.690
3.986
18 639
8599 (0.032)
480
0.024
0.063
1.01
+1.45 to -1.15
1.528
1.274
17 543
8462 (0.024)
480
0.026
0.090
1.02
+0.50 to -0.67
1.788
3.426
42 091
10 471 (0.041)
608
0.025
0.056
1.00
+1.57 to -1.09
1.541
1.014
25 891
12 301 (0.047)
686
0.053
0.162
1.00
+1.46 to -1.13
)
goodness of fit indicatorc
residual electron density/e Å-3 +1.66 to -0.81
2
2 2
2
2 2
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) [∑w(Fo - Fc ) /∑w(Fo2)2]1/2
.
c [∑w(Fo - Fc ) /(Nobs - Nparam)]1/2
.
(80 mL) was stirred at room temperature overnight. The orange
precipitates were separated from the supernatant by decantation and
were washed with n-hexane (50 mL). After removal of the
washings, the precipitates were suspended into hexane (80 mL).
To the suspension was added PEt2Cl (12.8 g, 103 mmol), and the
mixture was stirred at room temperature for 1 day. The reaction
mixture was filtered with a Celite pad, and the filtrate was
concentrated in Vacuo. The orange, oily residue was subjected to
silica gel column chromatography. Elution with n-hexane-benzene
(1:1) afforded depf (12.2 g, 67%) as an orange oil, which solidified
below 0 °C. 1H NMR (C6D6): δ 4.19-4.17 (m, 4H, C5H4),
4.17-4.14 (m, 4H, C5H4), 1.65-1.43 (m, 8H, CH2), 1.05 (dt, 3JPH
) 14 Hz, 3JHH ) 7 Hz, 12H, CH3). 31P{1H} NMR (C6D6): δ -27.1
(s).
(KBr): νNN 1883 cm-1. Anal. Calcd for C36H56N4Fe2P4W: C, 44.84;
H, 5.85; N, 5.81. Found: C, 44.99; H, 5.78; N, 5.80.
Synthesis of trans-[Mo(N2)2(depf)2] (trans-2). To a mixture of
magnesium turnings (159 mg, 6.54 mmol) and depf (213 mg, 0.588
mmol) in THF (8 mL) was added MoCl5 (70 mg, 0.256 mmol).
The mixture was stirred under dinitrogen atmosphere at room
temperature for 24 h. After concentration in vacuo, the residue was
extracted with benzene. Removal of benzene and recrystallization
from n-hexane at -30 °C afforded orange-red prisms of trans-2
(28 mg, 13%). 1H NMR (C6D6): δ 4.48-4.44 (m, 8H, C5H4),
4.13-4.10 (m, 8H, C5H4), 2.39-2.13 (m, 16H, CH2), 1.23-1.10
(m, 24H, CH3). 31P NMR (C6D6): δ 19.6 (s). IR (KBr): νNN 1907
cm-1. Anal. Calcd for C36H56N4Fe2MoP4: C, 49.34; H, 6.44; N,
6.39. Found: C, 49.23; H, 6.33; N, 6.23.
Synthesis of [W(NNH2)(OTf)(depf)2]OTf (3). To a toluene (10
mL) solution of trans-1 (97 mg, 0.10 mmol) was added trifluo-
romethanesulfonic acid (HOTf) (31 mg, 0.20 mmol). The resulting
dark yellow solution was concentrated to dryness. Recrystallization
from THF-ether-n-hexane (10:10:1) afforded pale orange plates
(53.5 mg, 42%). X-ray analysis and elemental analysis indicated
that the crystals were composed of 3 and 3 · THF · 0.5C6H14 in a
ratio of 3:1.28 1H NMR (C6D6): δ 7.94 (br, 2H, NNH2), 4.56 (br,
4H, C5H4), 4.35 (br, 4H, C5H4), 4.30 (br, 4H, C5H4), 4.03 (br, 4H,
C5H4), 2.61-2.40 (m, 4H, CH2), 2.35-2.23 (m, 12H, CH2),
1.06-0.86 (m, 24H, CH3). 31P NMR (C6D6): δ 1.5 (s with 183W
satellite, 1JP-W ) 286 Hz). IR (KBr): νNH 3295 cm-1. Anal. Calcd
Synthesis of cis-[W(N2)2(depf)2] (cis-1). To a mixture of
magnesium turnings (303 mg, 12.5 mmol) and depf (420 mg, 1.16
mmol) in THF (15 mL) was added WCl6 (221 mg, 0.557 mmol).
The suspension was stirred under dinitrogen atmosphere at room
temperature for 24 h. After concentration in vacuo, the residue was
extracted with benzene. Removal of benzene and washing with
n-hexane afforded a yellow powder. Recrystallization from THF-n-
hexane gave dark yellow blocks of cis-1 · 2.5THF (121 mg, 19%).
1H NMR (C6D6): δ 4.35 (br, 2H, C5H4), 4.30 (br, 2H, C5H4), 4.16
(br, 2H, C5H4), 4.13 (br, 2H, C5H4), 4.03 (br, 2H, C5H4), 4.00 (br,
2H, C5H4), 3.93 (br, 4H, C5H4), 3.00-2.75 (m, 4H, CH2),
2.58-2.24 (m, 8H, CH2), 2.15-1.97 (m, 4H, CH2), 1.63-1.39 (m,
12H, CH3), 0.93-0.70 (m, 12H, CH3). 31P{1H} NMR (C6D6): δ
-5.1 (t with 183W satellite, 3JPP ) 9 Hz, 1JPW ) 322 Hz), -1.9 (t
for
C39.75H61.75N2F6Fe2O6.25P4S2W (3:1 mixture of 3 and
3 · THF · 0.5C6H14): C, 37.73; H, 4.92; N, 2.21. Found: C, 37.65;
H, 4.84; N, 2.21.
3
1
with 183W satellite, JPP ) 9 Hz, JPW ) 316 Hz). IR (KBr): νNN
Synthesis of 3 from cis-1. The complex cis-1 (49 mg, 0.046
mmol) was treated with HOTf (14 mg, 0.089 mmol) in THF (5
mL). After 1 h, the solution was concentrated and the residue was
recrystallized from THF--n-hexane to give 3 in 58% yield (34
mg).
Synthesis of [Mo(NNH2)(OTf)(depf)2]OTf (4). trans-2 (86.2
mg, 0.0984 mmol) was treated with HOTf (30.4 mg, 0.0.203 mmol)
in toluene (12 mL). After 1 h, the solution was concentrated and
the residue was washed with n-hexane. Recrystallization from
THF-ether containing a small amount of n-hexane gave orange
platelet crystals of 4 · THF · 0.5C6H14 (51.4 mg, 41%). 1H NMR
1972, 1906 cm-1
.
Anal. Calcd for C46H76N4Fe2O2.5P4W
(1 · 2.5THF): C, 48.27; H, 6.69; N, 4.90. Found: C, 48.29; H, 6.67;
N, 4.86.
Synthesis of trans-[W(N2)2(depf)2] (trans-1). A mixture of trans-
[W(N2)2(PPh2Me)4] · 1.5THF (217 mg, 0.189 mmol) and depf (173
mg, 0.478 mmol) in THF (10 mL) was heated at reflux for 4 h.
The solution was concentrated under reduced pressure. The dark
red oil was extracted with 30 mL of n-hexane. The extract was
concentrated and recrystallized from THF-n-hexane, giving orange-
red prisms of trans-1 (86 mg, 0.089 mmol) in 43% yield. 1H NMR
(C6D6): δ 4.47-4.44 (m, 8H, C5H4), 4.12-4.09 (m, 8H, C5H4),
2.53-2.25 (m, 16H, CH2), 1.24-1.06 (m, 24H, CH3). 31P{1H}
NMR (C6D6): δ -7.2 (s with 183W satellite, 1JP-W ) 316 Hz). IR
(28) Crystal data of 3 · THF · 0.5C6H14 are given in the Supporting
Information.

Tungsten- and Molybdenum-Dinitrogen Complexes
Organometallics, Vol. 27, No. 15, 2008 3953
(C6D6): δ 9.56 (br, 2H, NNH2), 4.63 (br, 4H, C5H4), 4.41 (br, 4H,
C5H4), 4.36 (br, 4H, C5H4), 4.06 (br, 4H, C5H4), 2.53-2.12 (m,
16H, CH2), 1.07-0.89 (m, 24H, CH3). 31P NMR (C6D6): δ 17.7
(s). IR (KBr): νNH 3268 cm-1. Anal. Calcd for C45H73-
N2F6Fe2MoO7P4S2 (4 · THF · 0.5C6H14): C, 42.77; H, 5.82; N, 2.22.
Found: C, 42.68; H, 5.88; N, 2.16.
ligands in complex 3 and 4 were located from a difference Fourier
map and were refined isotropically. All other hydrogen atoms were
generated at calculated positions (dC-H ) 0.97 Å) and treated as
riding atoms with isotropic thermal factors. Full-matrix least-squares
refinement on F2 was carried out until the maximum parameter-
shift/esd converged to less than 0.001.33 All calculations were
performed using the Crystal Structure software package.34 Crystal-
lographic data are given in a CIF file.
Protonolysis of Complexes 1-4. To a methanol (5 mL)
suspension of a complex (ca. 40 µmol) was added H2SO4 (0.05
mL). After 24 h stirring at room temperature, ammonia was base
distilled and quantified by the indophenol method.29 Hydrazine was
also analyzed by p-(dimethylamino)benzaldehyde reagent.30
X-ray Crystallography. Crystallographic data are summarized
in Table 7. The paraffin-coated crystals were placed on a nylon
loop and mounted on a Rigaku RAXIS RAPID imagining plate
system. Data were collected at -100 °C under a cold nitrogen
stream using graphite-monochromated Mo KR radiation (λ )
0.71069 Å). Data were corrected for absorption, Lorentz, and
polarization effects. Structures were solved by the direct methods31
and expanded using Fourier techniques.32 Badly disordered THF
molecules cocrystallizing with cis-1 could not be located success-
fully, but the treatment of the five highest peaks as carbon atoms
gave better results. A disordered methyl group in 3 was refined
isotropically. Anisotropic thermal parameters were introduced for
the other non-hydrogen atoms. Hydrogen atoms of hydrazido
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research for Young Scientists (S) (No.
19675002) and for Scientific Research on Priority Areas (No.
18066003) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan, and Industrial Technology
Research Grant Program in 2005 from New Energy and
Industrial Technology Development Organization (NEDO)
of Japan. We thank Prof. Youichi Ishii and Dr. Yoshiaki
Tanabe (Chuo University) for the measurement of cyclic
voltammograms. We also thank the Tokyo Ohka Foundation
for the Promotion of Science and Technology and Sekisui
Integrated Research.
Supporting Information Available: X-ray crystallographic file
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(29) Chaney, A. L.; Marbach, E. P. Clinical Chem. 1962, 8, 130.
(30) Watt, G. W.; Chrisp, J. D Anal. Chem. 1952, 24, 2006.
(31) SIR97: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. C.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(32) DIRDIF99: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99 program
system; Technical Report of the Crystallography Laboratory; University of
Nijmegen: The Netherlands, 1999.
OM800327J
(33) Carruthers, J. R.; Rollett, J. S.; Betteridge, P. W.; Kinna, D.; Pearce,
L.; Larsen, A.; Gabe, E. CRYSTALS Issue 11; Chemical Crystallography
Laboratory: Oxford, U.K., 1999.
(34) Crystal Structure 3.8, Crystal Structure Analysis Package; Rigaku
and Rigaku Americas, 2000-2007.