Preparation and protonation of tungsten- and molybdenum-dinitrogen complexes bearing bis(dialkylphosphinobenzene)chromiums as auxiliary ligands

Article abstract of DOI:10.1021/om9006467

Tungsten- and molybdenum-dinitrogen complexes bearing bis(dialkylphosphinobenzene)chromiums have been prepared and characterized by X-ray crystallography. Reactions of these dinitrogen complexes with an excess amount of sulfuric acid in methanol at room t

Full text of DOI:10.1021/om9006467

Organometallics 2009, 28, 5821–5827 5821
DOI: 10.1021/om9006467
Preparation and Protonation of Tungsten- and Molybdenum-Dinitrogen
Complexes Bearing Bis(dialkylphosphinobenzene)chromiums as
Auxiliary Ligands
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
Received July 22, 2009
Tungsten- and molybdenum-dinitrogen complexes bearing bis(dialkylphosphinobenzene)chromiums
have been prepared and characterized by X-ray crystallography. Reactions of these dinitrogen complexes
with an excess amount of sulfuric acid in methanol at room temperature give ammonia in good yields.
Stoichiometric reactions of some dinitrogen complexes with 2 equiv of trifluoromethanesulfonic acid afford
the corresponding hydrazido complexes, which may be considered to be one of the reactive intermediates.
Introduction
previous results that protonolysis of tungsten- and molybde-
num-dinitrogen complexes bearing conventional diphosphines
such as [M(N2)2(dppe)2] and [M(N2)2(depe)2] (M = W or Mo;
dppe=1,2-bis(diphenylphosphino)ethane); depe=1,2-bis-
(diethylphosphino)ethane) does not produce ammonia.4 The
unique behavior of the metallocene moiety in those tungsten-
and molybdenum-dinitrogen complexes prompted us to devel-
op other types of tungsten- and molybdenum-dinitrogen
complexes bearing bis(phosphinobenzene)chromiums as aux-
iliary ligands because bis(phosphinobenzene)chromiums5
have a similar sandwich structure to the ferrocenyl- and
ruthenocenyl-diphosphines. In addition, it is well known that
the redox potential of bis(benzene)chromium is considerably
more negative than those of ferrocene and ruthenocene.6,7
We report herein the preparation of some tungsten- and
molybdenum-dinitrogen complexes bearing bis(dialkylphos-
phinobenzene)chromiums as auxiliary ligands and their che-
mical behavior to sulfuric acid.
Metallocene- and bis(arene)metal-based ligands are widely
used in organometallic chemistry and material sciences due
to their unique electronic and structural properties.1 For
example, 1,10-bis(diphenylphosphino)ferrocene (dppf) is well
known to work as a common diphosphine ligand for a variety
of transitionmetal complexes in organicsynthesisbecause of a
relatively large bite angle, capacity of dative bond formation
with electron-deficient metal centers, and chemical robustness
of the ferrocene skeleton.2 Recently, we have reported the
preparation of tungsten- and molybdenum-dinitrogen com-
plexes bearing ferrocenyl- or ruthenocenyl-diphosphines as
auxiliary ligands [M(N2)2(L)2] (M = W, Mo; L = ferrocenyl-
or ruthenocenyl-diphosphines; depf = 1,10-bis(diethylphos-
phino)ferrocene, depr=1,10-bis(diethylphosphino)ruthenocene,
dmpr = 1,10-bis(dimethylphosphino)ruthenocene).3 Reac-
tions of these dinitrogen complexes with an excess amount
of sulfuric acid afforded ammonia in good yields. Although
the detailed reaction mechanism is not yet clear, we believe
that the metallocene moiety in these complexes plays an
important role in the facile conversion of the coordinated
dinitrogen into ammonia. This result is in sharp contrast to the
(5) (a) Elschenbroich, C.; Stohler, F. J. Organomet. Chem. 1974, 67,
C51. (b) Elschenbroich, C.; Stohler, F. Angew. Chem., Int. Ed. Engl. 1975,
14, 174. (c) Elschenbroich, C.; Heikenfeld, G.; W€unsch, M.; Massa, W.;
Baum, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 414. (d) Elschenbroich,
C.; Metz, B.; Neum€uller, B.; Reijerse, E. Organometallics 1994, 13, 5072.
(e) Elschenbroich, C.; Isenburg, T.; Metz, B.; Behrend, A.; Harms, K.
J. Organomet. Chem. 1994, 481, 153. (f) Elschenbroich, C.; Isenburg, T.;
Metz, B.; Behrend, A.; Frenzen, G.; Harms, K. J. Organomet. Chem. 1995,
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Neum€uller, B.; Harms, K. Organometallics 2005, 24, 5509. (h) Song,
L.-C.; Yu, G.-A.; Hu, Q.-M.; Che, C.-M.; Zhu, N.; Huang, J.-S. J. Organo-
met. Chem. 2006, 691, 787.
*To whom correspondence should be addressed. E-mail: ynishiba@
sogo.t.u-tokyo.ac.jp.
(1) Organometallics; Elschenbroich, C., Ed.; Wiley-VCH: Weinheim,
Germany, 2006.
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terial Science; Togni, A.; Hayashi, T., Eds.; VCH: Weinheim, Germany,
1995. (b) Ferrocenes. Ligands, Materials and Biomolecules; Stepnicka, P.,
Ed.; John Wiley & Sons: Sussex, England, 2008.
(6) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(3) (a) Yuki, M.; Miyake, Y.; Nishibayashi, Y.; Wakiji, I.; Hidai, M.
Organometallics 2008, 27, 3947. (b) Yuki, M.; Midorikawa, T.; Miyake, Y.;
Nishibayashi, Y. Organometallics 2009, 28, 4741.
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r
2009 American Chemical Society
Published on Web 09/15/2009
pubs.acs.org/Organometallics

5822 Organometallics, Vol. 28, No. 19, 2009
Yuki et al.
Results and Discussion
Bis(dialkylphosphinobenzene)chromiums were prepared
by a similar procedure to that for bis(diphenylphosphino-
benzene)chromium.5a Dilithiation of bis(benzene)chromium
with n-butyllithium-TMEDA in cyclohexane at reflux tem-
perature afforded a powder of bis(dilithiobenzene)chromium,
which was treated with Et2PCl to give bis(diethylphosphino-
benzene)chromium (bepc) in 41% yield (Scheme 1). Similarly,
Scheme 1
Figure 1. ORTEP view of 1 with 50% thermal ellipsoids. Se-
˚
lected interatomic distances (A) and bond angles (deg): W-P(1)
2.4607(11), W-P(2) 2.4727(12), W-P(3) 2.4759(11), W-P(4)
2.4754(13), W-N(1) 1.990(4), W-N(3) 2.000(4), N(1)-N(2)
1.138(6), N(3)-N(4) 1.140(6), W Cr(1) 4.7679(7), W Cr(2)
3 3 3
3 3 3
4.7473(7), P(1)-W-P(2) 93.60(4), P(1)-W-P(3) 175.42(4),
P(1)-W-P(4) 87.36(4), P(2)-W-P(3) 85.78(4), P(2)-W-P(4)
177.23(4), P(3)-W-P(4) 93.47(4), N(1)-W-N(3) 178.83(15),
W-N(1)-N(2) 178.7(3), W-N(3)-N(4) 178.8(3).
bis(dimethylphosphinobenzene)chromium5c,5g (bmpc) was
prepared in 58% yield using Me2PCl in place of Et2PCl.
The reaction of trans-[W(N2)2(PPh2Me)4] with 2 equiv of
bmpc at 60 °C for 48 h gave trans-[W(N2)2(bmpc)2] (1) as a
major product (Scheme 2). Recrystallization from THF-
W(0/I) redox couple in 1 was observed at -0.49 V. When we
compared this value with those of the W(0/I) redox couple in
other dinitrogen complexes as shown in Table 1, complex 1 was
revealed to show significant anodic shift of the potential.
The reaction of trans-[W(N2)2(PPh2Me)4] with 1 equiv of
bmpc at 60 °C for a short reaction time such as 2 h gave
trans-[W(N2)2(bmpc)(PPh2Me)2] (2) in 86% isolated yield
(Scheme 2). The IR spectrum of 2 showed one strong νNN
absorption band at 1892 cm-1, indicating a trans conforma-
tion of two dinitrogen ligands. In the 31P{1H} NMR spec-
trum, two doublet signals along with the tungsten-183
satellites were observed at -19.1 and -6.0 ppm, which were
assigned to phsophorous atoms of bmpc and PPh2Me
ligands, respectively. A cyclic voltammogram of 2 showed
two reversible one-electron oxidation waves at -1.16 and
-0.53 V corresponding to Cr(0/I) and W(0/I) redox couples,
respectively. Separately, we confirmed that complex 2 was
easily converted to 1 in 47% yield when a solution of 2 with
bmpc was heated at 60 °C for 48 h.
Scheme 2
hexane afforded orange-red prisms of 1 in 29% yield. The IR
spectra of 1 exhibited one absorption band of νNN at 1885 cm-1
,
On the other hand, the reaction of trans-[W(N2)2-
(PPh2Me4)4] with 2 equiv of bepc proceeded sluggishly. A
mixture of trans-[W(N2)2(bepc)2] (3) and trans-[W(N2)2-
(bepc)(PPh2Me)2] (4) was formed when the reaction was
carried out at 60 °C for 48 h (Scheme 3). Fortunately, both
complexes are isolated in 41% and 17% yields, respectively.
The IR, NMR, and analytical data of 3 and 4 supported the
molecular structures of 3 and 4 (see Experimental Section for
details). The molecular structure of 4 was unequivocally
determined by X-ray crystallography. An ORTEP drawing
and selected bond distances and angles of 4 are shown in
Figure 2. The bite angle of the bepc ligand in 4 is 96.43(4)°.
indicating trans arrangement of two dinitrogen ligands. The IR
spectral data of 1 also displayed the strong electron-donating
property of bmpc. In the 31P{1H} NMR spectrum, the four
phosphorus atoms were observed equivalently at -19.8 ppm
with a tungsten satellite (1JPW = 316 Hz). The molecular struc-
ture of 1 was unequivocally determined by X-ray crystallo-
graphy. An ORTEP drawing and selected bond distances and
angles of 1 are shown in Figure 1. Two dinitrogen ligands are
oriented trans to each other. The bite angles of the bmpc ligand in
1 are 93.60(4)° and 93.47(4)°. The W-Cr distances of 4.7679(7)
˚
and 4.7472(7) A indicate no bonding interaction between chro-
mium and tungsten atoms. A cyclic voltammogram of 1 showed
two reversible one-electron oxidation waves corresponding to
two Cr(0/I) redox couples at -1.19 and -1.12 V, respectively.
This result indicates the presence of a weak electronic interaction
between two chromium centers in 1. An oxidation wave of the
˚
The W-Cr distance of 4.7622(7) A in 4 indicated no bonding
interaction between chromium and tungsten atoms. A cyclic
voltammogram of 4 showed two reversible one-electron
oxidation waves at -1.17 and -0.54 V corresponding to
Scheme 3

Article
Organometallics, Vol. 28, No. 19, 2009 5823
Table 1. IR and Electrochemical Data of Tungsten- and Molybdenum-Dinitrogen Complexes
E1/2/V c
complexa
ν
NN /cm-1 b
Cr(0/I)
W(0/I) or Mo(0/I)
ref
trans-W(N2)2(bmpc)2 (1)
trans-W(N2)2(bmpc)(PPh2Me)2 (2)
trans-W(N2)2(bepc)2 (3)
trans-W(N2)2(bepc)(PPh2Me)2 (4)
trans-W(N2)2(depf)2
trans-W(N2)2(depr)2
trans-W(N2)2(depe)2
trans-W(N2)2(dppe)2
trans-W(N2)2(dchpe)2
trans-W(N2)2(depr)(PPh2Me)2
trans-W(N2)2(dmpr)(PPh2Me)2
trans-W(N2)2(dppe)(PPh2Me)2
trans-W(N2)2(PPhMe2)4
trans-W(N2)2(PPh2Me)4
trans-Mo(N2)2(bmpc)2 (5)
trans-Mo(N2)2(bmpc)(PPh2Me)2 (6)
trans-Mo(N2)2(bepc)2 (7)
trans-Mo(N2)2(bepc)(PPh2Me)2 (8)
trans-Mo(N2)2(depf)2
trans-Mo(N2)2(depe)2
trans-Mo(N2)2(dppe)2
trans-Mo(N2)2(dmpr)(PPh2Me)2
trans-Mo(N2)2(dppe)(PPh2Me)2
trans-Mo(N2)2(PPh2Me)4
bmpc
1885
1892
1880
1895
1883
1879
1895
1943
1880d
1895
1899
1920d
1898
1899
1923
1918
1906
1919
1907
1928
1975
1923
1943d
1922
-1.19, -1.12
-1.16
-0.49
-0.53
this work
this work
this work
this work
3a
e
e
-
-
-1.17
-0.54
-0.95
-0.97
-0.96
-0.68
-1.02
-0.83
-0.80
3b
8a, 8b
8a, 8b
8b
3b
3b
8c
8d
-0.83
-0.71
-0.49
-0.56
3a, 8c
this work
this work
this work
this work
3a
8b, 8e
8b
3b
-1.18, -1.10
-1.17
e
e
-
-
-1.18
-0.57
-0.97
-0.97
-0.70
-0.80
8c
-0.71
8f, 8g
this work
this work
-1.14
-1.12
bepc
a dppe = 1,1’-bis(diphenylphosphino)ethane. depe = 1,1’-bis(diethylphosphino)ethane. dchpe = 1,1’-bis(dicyclohexylphosphino)ethane. b Asym-
metric NN stretching bands in KBr pellet. c Relative to ferrocene-ferrocenium couple in THF. d Nujol mull. e A cyclic voltammogram could not be
carried out due to the low solubility in THF.
Cr(0/I) and W(0/I) redox couples, respectively. The proper-
ties of 4 are almost the same as those of 2. Unfortunately, the
cyclic voltammogram of 3 could not be carried out due to the
low solubility of 3 in THF.
Scheme 4
Analogous molybdenum-dinitrogen complexes were ob-
tained by a similar procedure. The reaction of trans-[Mo(N2)2-
(PPh2Me4)4] with 2 equiv of bmpc at room temperature for
48 h gave trans-[Mo(N2)2(bmpc)2] (5) in 56% isolated yield
(Scheme 4). The IR, NMR, and analytical data supported the
molecular structure of 5 (see Experimental Section for details).
The molecular structure of 5 was unequivocally determined by
X-ray crystallography. An ORTEP drawing and selected bond
distances and angles of 5 are shown in Figure 3. The electro-
chemical behavior of 5 was also quite similar to that of 1. In
fact, a cyclic voltammogram of 5 showed three reversible one-
electron oxidation waves at -1.18, -1.10, and -0.49 V
corresponding to two Cr(0/I) redox couples and one Mo(0/I)
redox couple, respectively (Table 1). When the reaction of
trans- [Mo(N2)2(PPh2Me4)4] with 1 equiv of bmpc was carried
out at room temperature for 6 h, trans-[Mo(N2)2(bmpc)-
(PPh2Me4)2] (6) was isolated in 37% yield (Scheme 4). The
spectroscopic and analytical data were consistent with the
molecular structure of 6 (see Experimental Section for details).
Similarly, trans-[Mo(N2)2(bepc)2] (7) and trans-[Mo(N2)2-
(bepc)(PPh2Me)2] (8) were obtained in 25% and 35% yields,
respectively (Scheme 5). The IR, NMR, and analytical data
supported the molecular structures of 7 and 8 (see Experi-
mental Section for details). The molecular structure of 8 was
unequivocally determined by X-ray crystallography. An
ORTEP drawing and selected bond distances and angles of
8 are shown in Figure 4.
of sulfuric acid in methanol at room temperature for 24 h
produced ammonia in good to high yields. Typical results are
shown in Table 2. The yield of ammonia was based on the
tungsten or molybdenum atom. In any case, no hydrazine
was detected at all as a product. Similar to the previous
results, the protonation of dinitrogen complexes9 bearing
two monodentate phosphines as auxiliary ligands such as 2,
(8) (a) Nordwig, B. L.; Ohlsen, D. J.; Beyer, K. D.; Brummer, J. G.
Inorg. Chem. 2006, 45, 858. (b) Hussain, W.; Leigh, G. J.; Mohd.-Ali, H.;
Pickett, C. J.; Rankin, D. A. J. Chem. Soc., Dalton Trans. 1984, 1703.
(c) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1977, 2139. (d) George, T. A.; DeBord, J. R. D.; Kaul, B. B.; Pickett, C. J.;
Rose, D. J. Inorg. Chem. 1992, 31, 1295. (e) Filippou, A. C.; Schnakenburg,
G.; Philippopoulos, A. I.; Weidemann, N. Angew. Chem., Int. Ed. 2005, 44,
5979. (f) George, T. A.; Noble, M. E. Inorg. Chem. 1978, 17, 1678.
(g) Lazarowych, N. J.; Morris, R. H.; Ressner, J. M. Inorg. Chem. 1986,
25, 3926.
Next, we investigated the reactivity of these tungsten- and
molybdenum-dinitrogen complexes toward protonolysis.
Protonation of dinitrogen complexes with an excess amount

5824 Organometallics, Vol. 28, No. 19, 2009
Yuki et al.
Figure 3. ORTEP view of 5 with 50% thermal ellipsoids. Se-
˚
lected interatomic distances (A) and bond angles (deg): Mo-P-
(1) 2.4782(6), Mo-P(2) 2.4831(6), Mo-N(1) 2.0401(17),
Figure 2. ORTEP view of 4 with 50% thermal ellipsoids. Se-
˚
N(1)-N(2) 1.101(2), Mo Cr 4.7693(2), P(1)-Mo-P(2)
3 3 3
lected interatomic distances (A) and bond angles (deg): W-P(1)
93.892(19), P(1)-Mo-P(1)* 85.80(2), P(1)-Mo-P(2)*
177.895(16), P(2)-Mo-P(2)* 86.49(2), Mo-N(1)-N(2)
179.71(18). Asterisks denote atoms related by the symmetry
operation -x, þy, 1/2-z.
2.5066(13), W-P(2) 2.5171(13), W-P(3) 2.4638(13), W-P(4)
2.4728(13), W-N(1) 2.005(4), W-N(3) 2.009(3), N(1)-N(2)
1.123(5), N(3)-N(4) 1.142(5), W Cr 4.7622(7), P(1)-W-P-
3 3 3
(2) 96.43(4), P(1)-W-P(3) 166.98(4), P(1)-W-P(4) 88.92(4),
P(2)-W-P(3) 91.44(4), P(2)-W-P(4) 168.34(4), P(3)-W-
P(4) 85.30(4), N(1)-W-N(3) 177.84(16), W-N(1)-N(2)
179.6(4), W-N(3)-N(4) 179.4(3).
4, 6, and 8 gave ammonia in good to high yields (Table 2, runs
2, 4, 6, and 8). Interestingly, the protonation of dinitrogen
complexes bearing two bis(dialkylphosphinobenzene)chro-
miums (bmpc and bepc) as auxiliary ligands such as 1, 3, 5,
and 7 gave also ammonia in similar yields (Table 2, runs 1, 3,
5, and 7). This result is in sharp contrast to those from
molybdenum- and tungsten-dinitrogen complexes bearing
chelating diphosphines as auxiliary ligands [M(N2)2L2]
(M = Mo, W; L = dppe, depe), where ammonia was not
produced by protonation and only the formation of the
corresponding hydrazido complexes was observed.4 On the
other hand, the result described in this paper was similar to
those of protonation of tungsten- and molybdenum-dinitro-
gen complexes bearing ferrocenyl- and ruthenocenyl-dipho-
sphines such as trans-[M(N2)2L2] (M = W, Mo; L = depf,
depr) with sulfuric acid, where ammonia was obtained in
good to high yields.3 At present, we have not yet clarified
the exact role of these chelating metallocenes and bis-
(dialkylphosphinobenzene)chromiums in the conversion of
the coordinated dinitrogen into ammonia.
Figure 4. ORTEP view of 8 with 50% thermal ellipsoids. Se-
˚
lected interatomic distances (A) and bond angles (deg): Mo-
P(1) 2.5273(16), Mo-P(2) 2.5397(14), Mo-P(3) 2.4836(17),
Mo-P(4) 2.4911(14), Mo-N(1) 2.010(4), Mo-N(3) 2.012(4),
N(1)-N(2) 1.135(7), N(3)-N(4) 1.125(6), Mo Cr 4.7784(9),
3 3 3
P(1)-Mo-P(2) 96.22(5), P(1)-Mo-P(3) 167.50(5), P(1)-
Mo-P(4) 89.06(5), P(2)-Mo-P(3) 91.31(5), P(2)-Mo-
P(4) 168.63(4), P(3)-Mo-P(4) 85.35(5), N(1)-Mo-N(3)
177.76(16), Mo-N(1)-N(2) 178.1(4), Mo-N(3)-N(4) 179.3(4).
Scheme 5
Scheme 6

Article
Organometallics, Vol. 28, No. 19, 2009 5825
Table 2. Protonation of Tungsten- and Molybdenum-Dinitrogen
Complexes.a
run
[M(N2)2L4]
yield of NH4þ (%)b
1
2
3
4
5
6
7
8
trans-[W(N2)2(bmpc)2] (1)
trans-[W(N2)2(bmpc)(PPh2Me)2] (2)
trans-[W(N2)2(bepc)2] (3)
trans-[W(N2)2(bepc)(PPh2Me)2] (4)
trans-[Mo(N2)2(bmpc)2] (5)
trans-[Mo(N2)2(bmpc)(PPh2Me)2](6)
trans-[Mo(N2)2(bepc)2] (7)
trans-[Mo(N2)2(bepc)(PPh2Me)2](8)
51
124
148
152
64
33
16
41
a All reactions were carried out by treatment of dinitrogen complex
(0.035 mmol) with an excess amount of sulfuric acid (0.05 mL) iþn
methanol (5 mL) at room temperature for 24 h. b The yield of NH4
was determined by the indophenol method (see Experimental Section for
details). The yield of NH4þ was based on the W or Mo atom.
Figure 5. ORTEP view of 9 with 50% thermal ellipsoids.
˚
Selected interatomic distances (A) and bond angles (deg):
W-P(1) 2.5281(15), W-P(2) 2.5598(19), W-P(3) 2.5350(15),
W-P(4) 2.5665(18), W-N(1) 1.736(4), W-O(1) 2.209(3), N-
Hoping to obtain any information on the reaction path-
way for ammonia, we tried to isolate some reactive inter-
mediates. The reaction of 1 with 2 equiv of trifluoro-
methanesulfonic acid at room temperature for 10 min gave
the corresponding tungsten hydrazido complex [W(NNH2)-
(OTf)(bmpc)2]OTf (9) in 41% isolated yield (Scheme 6).
Unfortunately, we could not obtain any detailed information
from 9 by NMR because of its low solubility, but its
molecular structure was unequivocally determined by X-ray
crystallography. An ORTEP drawing and selected bond
distances and angles of 9 are shown in Figure 5. The W-N
(1)-N(2) 1.346(8), N(2)-H(1) 0.98(10), H(1) O(4) 2.06(11),
3 3 3
W
Cr(1) 4.7442(11), W Cr(2) 4.7800(12), Cr(1) Cr(2)
3 3 3
9.5236(16).
3 3 3
3 3 3
Protonation of these complexes with an excess amount of
sulfuric acid in methanol produced ammonia in good to
high yields. This result is in sharp contrast to the previous
finding that protonolysis of tungsten- and molybdenum-
dinitrogen complexes bearing conventional diphosphines
such as 1,2-bis(diphenylphosohino)ethane does not pro-
duce ammonia. We believe that the sandwich structure of
bis(benzene)chromium plays an important role for the
facile conversion of the coordinated dinitrogen into ammo-
nia, although its exact role has not yet been clarified.
Stoichiometric reactions of the dinitrogen complexes with
2 equiv of trifluoromethanesulfonic acid yielded the corre-
sponding hydrazido complexes, which may be considered
to be one of the reactive intermediates.
˚
and N-N bond lengths of 1.737(4) and 1.345(8) A in 9 were
similar to those of the previously reported tungsten hydra-
zido complexes.4,9 The W-Cr distances of 4.7445(12) and
4.7799(13) A indicated no bonding interaction between
˚
chromium and tungsten atoms. A hydrogen bond was
observed between one of the oxygen atoms of the triflate
anion and one of the terminal hydrogen atoms of the
hydrazido ligand. Similarly, the corresponding molybde-
num hydrazido complex [Mo(NNH2)(OTf)(bmpc)2]OTf
(10) was obtained in 44% yield from the reaction of 5 with
2 equiv of trifluoromethanesulfonic acid under the same
reaction conditions (Scheme 6). Separately, we carried out
the protonolysis of the isolated hydrazido complexes (9 and
10) and found the formation of ammonia in 68% and 55%
yields, respectively. These results indicate that the ammonia
formation might proceed via hydrazido complexes as
key intermediates. However, we could not detect any struc-
turally defined complexes after the protonation of dinitro-
gen and hydrazido complexes with an excess amount of
sulfuric acid.
Experimental Section
General Method. 1H NMR (270 MHz), 13C{1H} (67.8 MHz),
and 31P{1H} NMR (109 MHz) spectra were measured on a
JEOL Excalibur 270 spectrometer, 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 trans-
form infrared spectrophotometer. Elemental analyses were
performed on an Exeter Analytical CE-440 elemental analyzer.
Cyclic voltammograms were recorded on an ALS/Chi model
610C electrochemical analyzer with platinum working elec-
trode in THF containing 0.1 M nBu4NBF4 as a supporting
electrolyte. The potentials were quoted relative to the ferro-
cene/ferrocenium couple. All manipulations were performed
under a dry nitrogen atmosphere. Solvents were dried over
appropriate reagents and distilled prior to use. N,N,N0,N0-Tetra-
methylethylenediamine (TMEDA) was distilled from calcium
In summary, we have prepared and characterized tung-
sten- and molybdenum-dinitrogen complexes bearing bis-
(dialkylphosphinobenzene)chromiums as auxiliary ligands.
(9) (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. Nature 1975,
253, 39. (c) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton
Trans. 1977, 1852. (d) Hidai, M.; Mizobe, Y.; Takahashi, T.; Uchida, Y. Chem.
Lett. 1978, 1187. (e) Takahashi, T.;Mizobe, Y.;Sato, M.; Uchida, Y.;Hidai, M.
J. Am. Chem. Soc. 1979, 101, 3405. (f) George, T. A.; Kovar, R. A. Inorg.
Chem. 1981, 20, 285. (g) Anderson, S. N.; Fakley, M. E.; Richards, R. L.;
Chatt, J. J. Chem. Soc., DaltonTrans. 1981, 1973. (h) Bossard, G. E.; George,
T. A.; Lester, R. K. Inorg. Chim. Acta 1982, 64, L227. (i) Anderson, S. N.;
Richards, R. L.; Hughes, D. L. J. Chem. Soc., Dalton Trans. 1986, 245.
hydride. Complexes trans-[W(N2)2(PPh2Me)4] 1.5THF,8c
3
trans-[Mo(N2)2(PPh2Me)4],10 and bmpc5g were prepared by
the literature methods. Chlorodialkylphosphines (R2PCl; R =
Me, Et) were prepared by the reaction of Et2NPCl2 with
(10) Lazarowych, N. J.; Morris, R. H.; Ressner, J. M. Inorg. Chem.
1986, 25, 3926.

5826 Organometallics, Vol. 28, No. 19, 2009
Yuki et al.
alkylmagnesium bromide in ether followed by treatment with 2
equiv of HCl in diethyl ether.11 Other reagents were purchased
and used as received.
(m, 8H), 2.52-2.33 (m, 8H), 1.33-1.18 (m, 24H). 31P{1H}
NMR (C6D6): δ -6.6 (s with 183W satellite, JPW = 310 Hz).
IR (KBr): νNN 1975vw, 1880vs cm-1. Anal. Calcd for
C40H60N4Cr2P4W: C, 47.63; H, 6.00; N, 5.55. Found: C,
47.40; H, 5.80; N, 5.43.
Preparation of bepc. To a mixture of bis(benzene)chromium
(1.00 g, 4.80 mmol) and TMEDA (2.0 mL, 13.3 mmol) in
cyclohexane (30 mL) was added nBuLi (1.58 M in hexane,
8.0 mL, 12.6 mmol). The reaction mixture was heated at reflux
for 2 h. After cooling, the supernatant was removed by decanta-
tion. The residue was washed with n-hexane (20 mL x 2) and
dried in vacuo. The solid was suspended in cold diethyl ether
(30 mL, -30 °C), and Et2PCl (1.41 g, 11.3 mmol) was slowly
added to the suspension. The mixture was stirred at room
temperature overnight. Volatiles were removed under vacuum.
The orange-brown residue was extracted with toluene (20 mL).
The extract was passed through an alumina pad. The eluent was
concentrated to dryness, giving a crude product. Recrystalliza-
tion from n-hexane at -35 °C afforded a dark yellow micro-
crystalline solid of bepc in 41% yield (763 mg). 1H NMR (C6D6):
δ 4.53 (br t, JHH = 5 Hz, 4H), 4.42-4.31 (m, 6H), 1.59 (dq,
Data for 4. 1H NMR (C6D6): δ 7.67 (br t, JHH = 7 Hz, 8H),
7.13-6.98 (m, 12H), 4.68 (t, JHH = 5 Hz, 4H), 4.36 (dt, JHH
=
2 and 5 Hz, 2H), 4.22 (t, JHH = 5 Hz, 4H), 2.23-2.13 (m, 4H),
2.10 (d, JHP = 5 Hz, 6H), 1.65 (br s, 4H), 1.02-0.86 (m, 12H).
31P{1H} NMR (C6D6): δ -3.5 (dt with 183W satellite, JPP = 111
and 3 Hz, JPW = 313 Hz), -19.1 (br d, JPP = 111 Hz). IR (KBr):
ν
NN 1966w, 1895vs cm-1. Anal. Calcd for C48H60CrN4O0.5P4W
(4 0.5THF): C, 54.35; H, 5.70; N, 5.28. Found: C, 54.57; H,
3
5.90; N, 4.95.
Preparation of trans-[Mo(N2)2(bmpc)2] (5). A toluene (20 mL)
solution of trans-[Mo(N2)2(PPh2Me)4] (466 mg, 0.489 mmol)
and bmpc (327 mg, 0.996 mmol) was stirred at room tempera-
ture for 48 h. After concentration of the reaction mixture, the
residue was washed with diethyl ether (15 mL) and extracted
with toluene (15 mL). The toluene extract was dried under
vacuum, and the residue was dissolved in 5 mL of THF and
layered with 10 mL of n-hexane. Standing at -35 °C overnight
afforded an orange-yellow crystalline solid of 5 (220 mg, 56%).
1H NMR (C6D6): δ 4.69 (br d, JHH = 5 Hz, 8H), 4.39-4.25
(m, 12H), 1.75 (br s, 24H). 31P{1H} NMR (C6D6): δ 8.3 (s). IR
(KBr): νNN 1996w, 1923vs cm-1. Anal. Calcd for C32H44-
N4Cr2MoP4: C, 47.54; H, 5.49; N, 6.93. Found: C, 47.54; H,
5.59; N, 6.70.
J
HP = 3 Hz, JHH = 7 Hz, 8H), 1.05 (dt, JHP = 15 Hz, JHH =
7 Hz, 12H). 31P{1H} NMR (C6D6): δ -12.7 (s). Anal. Calcd for
C20H30CrP2: C, 62.49; H, 7.87. Found: C, 62.29; H, 7.73.
Preparation of trans-[W(N2)2(bmpc)2] (1). A toluene (15 mL)
solution of trans-[W(N2)2(PPh2Me)4] 1.5THF (143 mg, 0.137
3
mmol) and bmpc (100 mg, 0.305 mmol) was heated at 60 °C for
48 h. The solution was concentrated under reduced pressure,
giving a dark orange oil. After washing with n-hexane, the solid
residue was crystallized from THF-n-hexane at -35 °C, afford-
1
ing orange-red crystals of 1 (36 mg, 29%). H NMR (C6D6):
Preparation of trans-[Mo(N2)2(bmpc)(PPh2Me)2] (6). A tol-
uene (20 mL) solution of trans-[Mo(N2)2(PPh2Me)4] (191 mg,
0.200 mmol) and bmpc (69 mg, 0.210 mmol) was stirred at
room temperature for 6 h. After concentration of the reaction
mixture, the residue was treated with diethyl ether (10 mL),
affording an orange-red crystalline solid. The solid was
washed with n-hexane (10 mL) and dried under vacuum to give
δ 4.69 (br d, JHH = 5 Hz, 8H), 4.35 (br t, JHH = 5 Hz, 4H), 4.27
(br t, JHH = 5 Hz, 8H), 1.85 (br s, 24H). 31P{1H} NMR (C6D6):
δ -19.8 (s with 183W satellite, JP-W = 316 Hz). IR (KBr): νNN
1968vw, 1885vs cm-1. Anal. Calcd for C32H44N4Cr2P4W: C,
42.87; H, 4.95; N, 6.25. Found: C, 43.18; H, 5.06; N, 6.41.
Preparation of trans-[W(N2)2(bmpc)(PPh2Me)2] (2). A toluene
1
(15 mL) solution of trans-[W(N2)2(PPh2Me)4] 1.5THF (300 mg,
6 0.5Et2O (68 mg, 37%). H NMR (C6D6): δ 7.62 (m, 8H),
3
3
0.261 mmol) and bmpc (100 mg, 0.305 mmol) was heated at
60 °C for 2 h. The solution was concentrated under reduced
pressure, giving a dark orange oil. To the residue was added
diethyl ether (5 mL), and the mixture was cooled at -35 °C
overnight, precipitating an orange-red crystalline solid of
7.10-6.98 (m, 12H), 4.40-4.35 (m, 4H), 4.24-4.18 (m, 6H),
1.89 (br d, JHP = 2 Hz, 6H), 1.33 (br d, JHP = 5 Hz, 12H).
31P{1H} NMR (C6D6): δ 21.9 (d, JPP = 93 Hz), 9.9 (d, JPP = 93
Hz). IR (KBr): νNN 1994w, 1918vs cm-1. Anal. Calcd for
C44H53N4CrMoO0.5P4: C, 57.58; H, 5.82; N, 6.10. Found: C,
57.36; H, 5.85; N, 5.84.
2 Et2O (234 mg, 86%). 1H NMR (C6D6): δ 7.61 (t, JHH
=
3
8 Hz, 8H), 7.13-6.96 (m, 12H), 4.59 (t, JHH = 5 Hz, 4H), 4.26
Preparation of trans-[Mo(N2)2(bepc)2] (7) and trans-[Mo(N2)2-
(bepc)2(PPh2Me)2] (8). A THF (10 mL) solution of trans-
[Mo(N2)2(PPh2Me)4] (192 mg, 0.202 mmol) and bepc (158 mg,
0.411 mmol) was stirred at room temperature for 48 h. As the
reaction proceeded, orange-brown precipitates were formed.
The precipitates were dried in vacuo after decantation and
washing with a small amount of THF to give pure 7 (47 mg,
25%). On the other hand, an orange crystalline solid of
(d, JHH = 5 Hz, 2H), 4.18 (t, JHH = 5 Hz, 4H), 2.03 (d, JHP
=
5 Hz, 6H), 1.36 (d, JHP = 6 Hz, 12H). 31P{1H} NMR (C6D6):
δ -6.0 (d with 183W satellite, JPP = 108 Hz, JPW = 311 Hz),
-19.1 (d with 183W satellite, JPP = 108 Hz, JPW = 322 Hz). IR
(KBr): 1964w, 1892vs cm-1. Anal. Calcd for C46H58N4CrOP4W
(2 Et2O): C, 52.80; H, 5.59; N, 5.13. Found: C, 52.99; H, 5.61;
3
N, 5.37.
Conversion of 2 to 1. A toluene (15 mL) solution of 2 Et2O
3
8 0.5THF was obtained from the supernatant after recrystalliz-
3
(506 mg, 0.485 mmol) and bmpc (199 mg, 0.606 mmol) was
heated at 60 °C for 48 h. The solution was concentrated under
reduced pressure, giving a dark orange oil. After washing with
n-hexane, the solid residue was crystallized from THF-n-hexane
at -35 °C, affording orange-red crystals of 1 (205 mg, 47%).
Preparation of trans-[W(N2)2(bepc)2] (3) and trans-[W(N2)2-
(bepc)2(PPh2Me)2] (4). A THF (15 mL) solution of trans-
ing from THF-n-hexane (66 mg, 34%).
Data for 7. 1H NMR (C6D6): δ 4.73 (d, JHH = 5 Hz, 8H), 4.43
(t, JHH = 5 Hz, 4H), 4.32 (t, JHH = 5 Hz, 8H), 2.57-2.2.43
(m, 8H), 2.38-2.23 (m, 8H), 1.32-1.20 (m, 24H). 31P{1H} NMR
(C6D6): δ 23.5 (s). IR (KBr): νNN 1989w, 1906vs cm-1. Anal.
Calcd for C40H60N4Cr2MoP4: C, 52.18; H, 6.57; N, 6.08. Found:
51.47; H, 6.60; N, 5.55.
Data for 8. 1H NMR (C6D6): δ 7.67 (br t, JHH = 7 Hz, 8H),
[W(N2)2(PPh2Me)4] 1.5THF (345 mg, 0.300 mmol) and bepc
3
(250 mg, 0.650 mmol) was heated at 60 °C for 48 h. As the
reaction proceeded, orange-red precipitates were formed. The
precipitates were dried in vacuo after decantation and washing
with a small amount of THF to give an orange-red powder of 3
7.12-6.96 (m, 12H), 4.69 (t, JHH = 5 Hz, 4H), 4.35 (dt, JHH
=
2 and 5 Hz, 2H), 4.24 (t, J = 5 Hz, 4H), 2.10-1.93 (m, 4H), 1.96
(d, JHP = 5 Hz, 6H), 1.52 (br s, 4H), 1.05-0.92 (m, 12H).
=
31P{1H} NMR (C6D6): δ 24.1 (d, JPP = 91 Hz), 20.1 (d, JPP
91 Hz). IR (KBr): νNN 1994w, 1919vs cm-1. Anal. Calcd for
(125 mg, 41%). Crystals of 4 0.5THF were obtained from the
3
supernatant of the reaction mixture by recrystallizing from
THF-n-hexane (55 mg, 17%).
C48H60CrN4MoO0.5P4 (8 0.5THF): C, 59.26; H, 6.22; N, 5.76.
3
Found: C, 58.39; H, 6.01; N, 5.43.
Data for 3. 1H NMR (C6D6): δ 4.72 (d, JHH = 5 Hz, 8H), 4.43
(t, JHH = 5 Hz, 4H), 4.30 (t, JHH = 5 Hz, 8H), 2.70-2.54
Preparation of [W(NNH2)(OTf)(bmpc)2]OTf (9). To a ben-
zene (4 mL) solution of 1 (89 mg, 99 μmol) was added HOTf
(32 mg, 211 μmol) in benzene (1 mL). The solution was stirred at
room temperature for 10 min to form dark yellow precipitates.
(11) Burg, A. B.; Slota, P. J., Jr. J. Am. Chem. Soc. 1958, 80, 1107.

Article
Organometallics, Vol. 28, No. 19, 2009 5827
Table 3. Summary of Crystallographic Data
4 0.5THF 5 2THF
1
8 0.5THF
3
9 2THF
3
3
3
formula
fw
C32H44N4Cr2P4W C48H60N4CrO0.5P4W C40H60N4Cr2MoO2P4 C48H60N4CrMoO0.5P4 C42H62N2Cr2F6O8P4S2W
1312.81
896.46
1060.77
952.77
972.86
cryst size/mm
color, habit
cryst syst
space group
0.40 ꢀ 0.30 ꢀ 0.20 0.12 ꢀ 0.10 ꢀ 0.08
0.55 ꢀ 0.50 ꢀ 0.05
orange-yellow plate
orthorhombic
Pbcn (No. 60)
14.5417(3)
10.0118(3)
28.9647(6)
90
0.50 ꢀ 0.25 ꢀ 0.10
orange plate
monoclinic
P21/n (No. 14)
11.0795(5)
19.6088(7)
21.2952(9)
97.9919(15)
4581.6(3)
4
1.410
0.690
36 678 (2θ < 50°)
8390 (0.086)
581
0.50 ꢀ 0.20 ꢀ 0.03
dark yellow plate
monoclinic
P21/n (No. 14)
16.7101(9)
10.0276(4)
31.4981(14)
103.4649(19)
5132.8(4)
4
1.699
2.932
44 149 (2θ < 55°)
1116 (0.076)
587
orange-red prism orange prism
monoclinic
P21/n (No. 14)
14.7803(7)
12.6823(6)
18.9408(8)
105.9520(19)
3413.7(3)
4
monoclinic
P21/n (No. 14)
11.0977(3)
19.5256(6)
21.2340(5)
97.8723(7)
4557.8(2)
4
˚
a/A
˚
b/A
˚
c/A
β/deg
3
˚
V/A
4216.91(18)
4
1.501
Z
dc/g cm-3
1.744
4.208
1.546
2.943
μ(Mo KR)/mm-1
no. of data collected
no. of unique data (Rint
no. of params refined
R1a (F2 > 2σ)
wR2b (all data)
0.990
31 096 (2θ < 55°) 42 313 (2θ < 55°)
38 509 (2θ < 55°)
4787 (0.057)
270
0.027
0.064
1.01
þ0.72 to -0.55
)
7839 (0.073)
432
10349 (0.119)
581
0.036
0.050
0.044
0.057
0.050
0.098
1.03
þ1.65 to -1.88
0.049
0.106
1.01
þ2.87 to -1.99
goodness of fit indicatorc
residual electron density/e A
1.01
þ1.79 to -1.76
1.01
þ2.33 to -1.99
-3
˚
P
P
P
P
P
a R1 =
Fo| - |Fc
/
|Fo|. b wR2 = [
w(Fo2 - Fc2)2/
w(Fo)2]1/2
.
[
w(Fo2 - Fc2)2/(Nobs - Nparam)]1/2
.
c
The volatile materials were removed under vacuum. The residue
was extracted with THF (10 mL) and recrystallized from
THF-n-hexane to afford dark yellow rectangular crystals of
X-ray Crystallography. Crystallographic data are summarized
in Table 3. 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-monochrometed Mo KR radiation (λ =
9 2THF. Drying under vacuum resulted in the partial loss of a
3
solvent molecule to give a yellow powder of 9 THF (51 mg,
41%). Detailed information was not obtained by NMR because
3
˚
0.71069 A). Data were corrected for absorption, Lorentz, and
of the low solubility of 9. IR (KBr): νNH 3262 cm-1. Anal. Calcd
for C38H54N2Cr2F6O7P4S2W (9 THF): C, 36.79; H, 4.39; N,
2.26. Found: C, 36.98; H, 4.14; N, 2.23.
polarization effects. Structures were solved by the direct methods
(SIR97)14 and expanded using Fourier techniques.15 Anisotropic
thermal parameters were introduced for non-hydrogen atoms.
A hydrogen atom (H1) of 9 was located from a difference Fourier
map and was refined isotropically. The other hydrogen atoms
3
Preparation of [Mo(NNH2)(OTf)(bmpc)2]OTf (10). To a ben-
zene (4 mL) solution of 5 (42 mg, 52 μmol) was added HOTf
(17 mg, 113 μmol) in benzene (1 mL). The solution was stirred at
room temperature for 10 min to form dark yellow precipitates.
The volatile materials were removed under vacuum. The residue
was extracted with THF (6 mL) and recrystallized by adding
n-hexane (6 mL) to afford a dark yellow crystalline solid. Drying
˚
were generated at calculated positions (dC-H = 0.97 A) and
treatedas riding atoms withisotropicthermal factors. Full-matrix
least-squares refinement on F2 was carried out until maximum
parameter-shift/esd converged to less than 0.001.16 All calcula-
tions were performed using the Crystal Structure software pack-
age.17 Crystallographic data are given in a CIF file.
under vacuum gave a yellow solid of 10 1.5THF (27 mg, 44%).
Detailed information was not obtained by NMR because of the
3
low solubility of 10. IR (KBr): νNH 3243 cm-1. Anal. Calcd for
C40H58N2Cr2F6MoO7.5P4S2 (10 1.5THF): C, 40.41; H, 4.92; N,
2.36. Found: C, 40.16; H, 4.66; N, 2.26.
Acknowledgment. This work was supported by
Grants-in-Aid for Scientific Research for Young Scien-
tists (S) (No. 19675002) and for Scientific Research on
Priority Areas (No. 18066003) from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan. Y.N. thanks the Iwatani Naoji Foundation.
3
Protonation of Dinitrogen Complexes. To a dinitrogen com-
plex (35 μmol) suspended in methanol (5 mL) was added
concentrated sulfuric acid (0.05 mL). The mixture was stirred
at room temperature for 24 h. To the resulting green solution
was added aqueous KOH (30 wt %, 10 mL). After stirring for
10 min, the mixture was distilled under reduced pressure.
Volatiles were passed through aqueous sulfuric acid (0.5 M,
10 mL), where ammonia was trapped as ammonium sulfate. The
collected ammonia was quantified by the indophenol method.12
No hydrazine was detected by p-(dimethylamino)benzaldehyde
reagent.13
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.
(15) 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.
(16) Carruthers, J. R.; Rollett, J. S.; Betteridge, P. W.; Kinna, D.;
Pearce, L.; Larsen, A.; Gabe, E. CRYSTALS Issue 11; Chemical Crystal-
lography Laboratory: Oxford, U.K., 1999.
(12) Chaney, A. L.; Marbach, E. P. Clin. Chem. 1962, 8, 130.
(13) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952, 24, 2006.
(14) 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.
(17) CrystalStructure 38: Crystal Structure Analysis Package; Rigaku
and Rigaku Americas, 2000-2007.