Formation of ammonia in the reactions of a tungsten dinitrogen with ruthenium dihydrogen complexes under mild reaction conditions

Article abstract of DOI:10.1021/ic000799f

Treatment of cis-[W(N₂)₂(PMe₂Ph)₄] (5) with an equilibrium mixture of trans-[RuCl(η²-H₂)(dppp)₂]X (3) with pK_a = 4.4 and [RuCl(dppp)₂]X (4) [X = PF₆, BF₄, or OTf; dppp = 1,3-bis(diphenylphosphino)propane] containing 10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55°C for 24 h under 1 atm of H₂ gave NH₃ in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)₂] (6). Free NH₃ in 9-16% yields was observed in the reaction mixture, and further NH₃ in 36-45% yields was released after base distillation. Detailed studies on the reaction of 5 with numerous Ru(η²-H₂) complexes showed that the yield of NH₃ produced critically depended upon the pK_a value of the employed Ru(η²-H₂) complexes. When 5 was treated with 10 equiv of trans-[RuCl(η²-H₂)(dppe)₂]X (8) with pK_a = 6.0 [X = PF₆, BF₄, or OTf; dppe = 1,2-bis(diphenylphosphino)ethane] under 1 atm of H₂, NH₃ was formed in higher yields (up to 79% total yield) compared with the reaction with an equilibrium mixture of 3 and 4. If the pK_a value of a Ru(η²-H₂) complex was increased up to about 10, the yield of NH₃ was remarkably decreased. In these reactions, heterolyfic cleavage of H₂ seems to occur at the Ru center via nucleophilic attack of the coordinated N₂ on the coordinated H₂ where a proton (H⁺) is used for the protonation of the coordinated N₂ and a hydride (H-) remains at the Ru atom. Treatment of 5, trans-[W(N₂)₂(PMePh₂)4] (14), or trans-[M(N₂)₂(dppe)₂] [M = Mo (1), W (2)] with Ru(η²-H₂)complexes at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH₂)(PMe₂Ph)₄]OTf (19), trans-[W(OTf)(NNH₂)(PMePh₂)₄]OTf (20), and trans-[WX(NNH₂)(dppe)₂]⁺ [X = O[Tf (15), F (16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of . hydrazido(2-) intermediates such as 19 with H₂ at 55 °C was considered to result in the formation of NH₃, concurrent with the generation of W(VI)species. All of the electrons required for the reduction of N₂ are provided by the zerovalent tungsten.

Full text of DOI:10.1021/ic000799f

5946
Inorg. Chem. 2000, 39, 5946-5957
Formation of Ammonia in the Reactions of a Tungsten Dinitrogen with Ruthenium
Dihydrogen Complexes under Mild Reaction Conditions1
Yoshiaki Nishibayashi,† Shin Takemoto, Shotaro Iwai, and Masanobu Hidai*
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo,
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
ReceiVed July 17, 2000
Treatment of cis-[W(N2)2(PMe2Ph)4] (5) with an equilibrium mixture of trans-[RuCl(η2-H2)(dppp)2]X (3) with
pKa ) 4.4 and [RuCl(dppp)2]X (4) [X ) PF6, BF4, or OTf; dppp ) 1,3-bis(diphenylphosphino)propane] containing
10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55 °C for 24 h under 1 atm of H2 gave
NH3 in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)2] (6). Free
NH3 in 9-16% yields was observed in the reaction mixture, and further NH3 in 36-45% yields was released
after base distillation. Detailed studies on the reaction of 5 with numerous Ru(η2-H2) complexes showed that the
yield of NH3 produced critically depended upon the pKa value of the employed Ru(η2-H2) complexes. When 5
was treated with 10 equiv of trans-[RuCl(η2-H2)(dppe)2]X (8) with pKa ) 6.0 [X ) PF6, BF4, or OTf; dppe )
1,2-bis(diphenylphosphino)ethane] under 1 atm of H2, NH3 was formed in higher yields (up to 79% total yield)
compared with the reaction with an equilibrium mixture of 3 and 4. If the pKa value of a Ru(η2-H2) complex was
increased up to about 10, the yield of NH3 was remarkably decreased. In these reactions, heterolytic cleavage of
H2 seems to occur at the Ru center via nucleophilic attack of the coordinated N2 on the coordinated H2 where a
proton (H+) is used for the protonation of the coordinated N2 and a hydride (H-) remains at the Ru atom. Treatment
of 5, trans-[W(N2)2(PMePh2)4] (14), or trans-[M(N2)2(dppe)2] [M ) Mo (1), W (2)] with Ru(η2-H2) complexes
at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH2)(PMe2-
Ph)4]OTf (19), trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20), and trans-[WX(NNH2)(dppe)2]+ [X ) OTf (15), F
(16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of
hydrazido(2-) intermediates such as 19 with H2 at 55 °C was considered to result in the formation of NH3,
concurrent with the generation of W(VI) species. All of the electrons required for the reduction of N2 are provided
by the zerovalent tungsten.
Introduction
Extensive studies have long been continued to investigate the
reactivities of coordinated N2 in numerous N2 complexes of
transition metals.7-10 Among them, molybdenum and tungsten
N2 complexes of the type [M(N2)2(L)4] (M ) Mo, W; L )
tertiary phosphine)7,10 have been most intensively studied since
Industrial ammonia (NH3) production from dinitrogen (N2)
and dihydrogen (H2) has successfully been carried out for more
than 80 years by the use of Fe-based heterogeneous catalysts,
but the reaction conditions are extremely drastic.2,3 In contrast,
biological nitrogen fixation is well-known to occur at ambient
temperature and pressure.3-6 The mechanism remains unclear
although the X-ray structural model has recently been reported
for the FeMo-cofactor, the site for conversion of N2 to NH3, of
FeMo nitrogenase.4 However, it is generally believed that N2
is coordinated at the multimetallic site and converted to
NH3 by a sequential process of protonation followed by
reduction.5,6
(4) (a) Kim, J.; Rees, D. C. Science 1992, 257, 1677. (b) Kim, J.; Rees,
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* To whom correspondence should be addressed. Present address:
Department of Materials Science and Technology, Faculty of Industrial
Science and Technology, Science University of Tokyo, Noda, Chiba 278-
8510, Japan.
† Present address: Department of Energy and Hydrocarbon Chemistry,
Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-
8501, Japan.
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10.1021/ic000799f CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/29/2000

Formation of Ammonia under Mild Reaction Conditions
Inorganic Chemistry, Vol. 39, No. 26, 2000 5947
the first preparation11 of trans-[Mo(N2)2(dppe)2] [dppe ) 1,2-
bis(diphenylphosphino)ethane] (1) in this laboratory because of,
at least in part, their possible relevance to the active site of
nitrogenase and the unexpected rich chemistry of the coordinated
N2. The ligating N2 can be transformed into NH3 and/or
hydrazine (NH2NH2) by treatment with inorganic acids such as
NH2 has been proposed on the basis of the reactivities of isolable
intermediate complexes such as hydrazido(2-) complexes.12,13
However, the N-H bond formation was not achieved by
treatment of those N2 complexes with H2 because H2 replaced
the ligating N2 to form hydride complexes [MH4(L)4].14
Alternatively, acidic metal carbonyl hydrides such as [HCo-
(CO)4] formally prepared from [Co2(CO)8] and H2 could be
employed for the N-H bond formation of the coordinated N2
on tungsten.15,16 Recently Morris and co-workers employed an
acidic Ru(η2-H2) complex [CpRu(η2-H2)(dtfpe)]BF4 {dtfpe)1,2-
bis[bis(p-trifluoromethylphenyl)phosphino]ethane} with the
pseudo-aqueous pKa ) 4.3 in order to protonate the ligating N2
in trans-[W(N2)2(dppe)2] (2).17 Interestingly, the protonation
occurred to form a hydrazido(2-) complex, although the Ru-
(η2-H2) complex was not available directly from H2.17 The
pseudo-aqueous pKa values are evaluated by acid-base reactions
in organic solvents. We shall simply use the term pKa values
hereafter. Quite recently, Fryzuk and co-workers observed the
N-H bond formation when a dinuclear zirconium complex with
a side-on bridging N2 ligand was treated with H2.18 However,
the reaction stopped at the stage of N2H, and no NH3 was
formed.18
12
H2SO4 and HCl.13 A detailed mechanism for the protonation
of the ligating N2 leading to the formation of NH3 and/or NH2-
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5948 Inorganic Chemistry, Vol. 39, No. 26, 2000
Nishibayashi et al.
Scheme 1
Table 1. Reaction of cis-[W(N2)2(PMe2Ph)4] (5) with an
[RuCl(η2-H2)(dppp)2]PF6 [dppp ) 1,3-bis(diphenylphosphino)-
propane] (3a), has intrigued us because the Ru(η2-H2) complex
is directly prepared from H2 and [RuCl(dppp)2]PF6 (4a),22 and
the pKa value of 3a (pKa ) 4.4)22 is almost the same as that of
Equilibrium Mixture of trans-[RuCl(η2-H2)(dppp)2]X (3) and
[RuCl(dppp)2]X (4) Derived from 10 Equiv of 4a
yield of NH3 (%)b
freec
basicd
[CpRu(η2-H2)(dtfpe)]BF4 employed by Morris for the proto-
17
run
Ru complex
total
nation of coordinated N2. This led to our recent findings of the
formation of NH3 from the reaction of cis-[W(N2)2(PMe2Ph)4]
(5) and complex 3a under 1 atm of H2. The presumed
stoichiometry for the formation of NH3 is shown in Scheme 1,
indicating that the tungsten provides the six electrons for the
reduction of N2. Preliminary results have already been reported
in a previous communication.23 Here we will describe the
detailed results of the reactions between tungsten N2 and acidic
ruthenium H2 complexes, including the mechanism for the
ruthenium-assisted protonation of coordinated N2 on tungsten
with H2.
1
[RuCl(dppp)2]PF6 (4a)
[RuCl(dppp)2]PF6 (4a)
[RuCl(dppp)2]PF6 (4a)
[RuCl(dppp)2]PF6 (4a)
10
4
3
0
0
16
9
45
18
23
0
0
38
36
55e
22
26
0
2f
3g
4h
5i
6
0
[RuCl(dppp)2]BF4 (4b)
[RuCl(dppp)2]OTf (4c)
54e
45e
7
a All of the reactions were carried out in benzene-dichloroethane
under 1 atm of H2 at 55 °C for 24 h after 0.10 mmol of 5 was added
to an equilibrium mixture of 3 and 4 derived from 10 equiv of 4 unless
otherwise stated. b Yield of NH3 was based on the W atom. c Free yield
was before base distillation of the reaction mixture. d Basic yield was
after base distillation to fully liberate NH3. e Variation (3% between
experiments. f The reaction was carried out without pretreatment of 4a
under 1 atm of H2 (see text). g THF was used as solvent in place of
benzene-dichloroethane. h The reaction was carried out under 1 atm
of N2. i The reaction was carried out in the absence of the Ru complex.
Results and Discussion
Formation of NH3 from the Reactions of cis-[W(N2)2-
(PMe2Ph)4] (5) with 10 Equiv of Acidic Ru(η2-H2) Com-
plexes. As reported by Mezzetti and co-workers,22 an equilib-
rium mixture of 4a and 3a in a ratio of about 9:1 was obtained
when a solution of 4a in benzene-dichloroethane was stirred
under 1 atm of H2 at room temperature for 12 h. When 5 was
added to the equilibrium solution containing 10 equiv of the
Ru atom based on tungsten and the mixture was stirred under
1 atm of H2 at 55 °C for 24 h, NH3 was produced in 55% total
yield based on tungsten, where free NH3 in 10% yield was found
in the reaction mixture, and further NH3 in 45% yield was
released after base distillation (Table 1; run 1). The 1H and 31P-
{1H} NMR spectra of the reaction mixture showed the complete
consumption of 5 and the formation of trans-[RuHCl(dppp)2]22,24
(6) in 150% yield, concurrent with small amounts of PMe2Ph
and [PMe2PhH]+. Complex 6 has actually been isolated and
characterized by spectroscopy. On the other hand, when complex
5 was directly treated with 10 equiv of 4a under 1 atm of H2 at
55 °C for 24 h, NH3 was formed in 22% total yield (Table 1;
run 2). This result indicates that the pretreatment of 4a under 1
atm of H2 and the subsequent addition of complex 5 to the
solution is preferred to increase the yield of NH3. The yield of
NH3 was lower when tetrahydrofuran (THF) was used as solvent
(Table 1; run 3). The formation of NH3 was not observed at 25
°C. Both the Ru complex 4a and H2 are essential to the
formation of NH3. This was unequivocally demonstrated by the
experiments without complex 4a or H2 (Table 1; runs 4 and 5).
Two analogous H2 complexes trans-[RuCl(η2-H2)(dppp)2]BF4
(3b) and trans-[RuCl(η2-H2)(dppp)2]OTf (3c) were also prepared
in a similar way from [RuCl(dppp)2]BF4 (4b) and [RuCl(dppp)2]-
OTf (4c) under 1 atm of H2, respectively. The efficiency for
the formation of NH3 did not significantly change when 4b and
4c were employed in place of 4a (Table 1; runs 6 and 7). In all
cases, a trace amount of NH2NH2 was observed. It is noteworthy
that free NH3 was observed in low but substantial yields in all
cases using 4a-4c. This provides clear-cut evidence that NH3
is produced from the coordinated N2 and H2 under mild reaction
conditions.
Reactions of complex 5 with a series of acidic Ru(η2-H2)
complexes were then investigated to elucidate the relationship
between N-H bond formation and the acidity constant pKa of
a η2-H2 ligand. Typical results are shown in Table 2. In sharp
contrast to complex 4a, Ru complexes [RuCl(dppe)2]X (X )
PF6, 7a;25a BF4, 7b;25b OTf, 7c; BAr4, 7d) [Ar ) 3,5-
(CF3)2C6H3] were quantitatively converted under 1 atm of H2
(22) Rocchini, E.; Mezzetti, A.; Ru¨egger, H.; Burckhardt, U.; Gramlich,
V.; Zotto, A. D.; Martinuzzi, P.; Rigo, P. Inorg. Chem. 1997, 36, 711.
(23) Preliminary communication: Nishibayashi, Y.; Iwai, S.; Hidai, M.
Science 1998, 279, 540. A commentary of this work, see: Leigh, G.
J. Science 1998, 279, 506.
(25) (a) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278. (b) Polam, J. R.; Porter,
L. C. J. Coord. Chem. 1993, 29, 109.
(24) James, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1976, 19, L17.

Formation of Ammonia under Mild Reaction Conditions
Inorganic Chemistry, Vol. 39, No. 26, 2000 5949
Table 2. Reaction of cis-[W(N2)2(PMe2Ph)4] (5) with Ru(η2-H2)
(pKa ) 6.0)25 than complex 3a, the ligating N2 in 5 is expected
to be protonated by the coordinated H2 in 8a because the ligating
N2 is protonated by a large excess of MeOH (pKa ) 15)20b to
form NH3 under some conditions.12b,27 Actually, NH3 was
produced in 55% total yield at 55 °C (Table 2; run 1). Treatment
of 5 with 10 equiv of 8b under the same conditions produced
NH3 in 71% total yield (Table 2; run 2). When the reaction
mixture of 5 and 10 equiv of 8b under the same reaction
conditions was extracted with an excess of water instead of base
Complexesa
yield of NH3 (%)b
run
Ru(η2-H2) complex
pKa freec basicd total
1
2
3
4
5
6
7
8
9
trans-[RuCl(η2-H2)(dppe)2]PF6 (8a)
trans-[RuCl(η2-H2)(dppe)2]BF4 (8b)
trans-[RuCl(η2-H2)(dppe)2]BF4 (8b)
trans-[RuCl(η2-H2)(dppe)2]OTf (8c)
trans-[RuCl(η2-H2)(dppe)2]BAr4 h (8d)
[CpRu(η2-H2)(dppm)]OTf (10)
6.0
3
0
52
71
55e
71f
79g
74g
3
0
3
0
0
0
0
3
31
0
6
0
(7.5)i
34j
0
+
distillation, the amount of NH4 in the water extract reached
trans-[RuH(η2-H2)(dppe)2]BF4 (11b)
trans-[RuH(η2-H2)(dppe)2]OTf (11c)
trans-[RuH(η2-H2)(dppe)2]BF4 (12b)
(10.2)k
79% yield based on tungsten (Table 2; run 3). The similar yield
of NH3 was obtained by using 8c (Table 2; run 4). Furthermore,
plausible hydrazido(2-) intermediate complexes, which might
provide NH3 by base treatment,12c were not detected by the
NMR and IR spectra of the reaction mixture (vide infra). These
results indicate that protonation of the coordinated N2 did not
stop at the stage of the hydrazido(2-) form, but proceeded
further to form NH4+. Thus, the reaction mixture was treated
with KOH aqueous solution to fully liberate NH3 (base
distillation). It is to be noted that no formation of NH3 was
observed when the above reactions were performed at ambient
temperature.
6
0
0
15.0
10 trans-[RuH(η2-H2)(dppe)2]OTf4 (12c)
0
a All of the reactions were carried out in benzene-dichloroethane
using 0.10 mmol of 5 and 1.00 mmol of Ru(η2-H2) complex under 1
atm of H2 at 55 °C for 24 h unless otherwise stated. b Yield of NH3
was based on the W atom. c Free yield was before base distillation of
the reaction mixture. d Basic yield was after base distillation to fully
f
liberate NH3. e Variation (10% between experiments. Variation (3%
between experiments. g This yield of NH3 was observed in the water
extract of the reaction mixture (see text). h Ar ) 3,5-(CF3)2C6H3. i The
pKa value of [CpRu(η2-H2)(dppm)]BF4 was reported to be 7.5 (see ref
31). j Variation (4% between experiments. k The pKa value of trans-
[RuH(η2-H2)(dppp)2]PF6 (11a) was reported to be 10.2 (see ref 32).
Employment of [RuCl(dppe)2]BPh4 (7e) did not give NH3
under the same conditions. This might be due to the degrada-
tion28,29 of the initially formed H2 complex trans-[RuCl(η2-H2)-
Table 3. 1H and 31P{1H} NMR Data of
trans-[RuCl(η2-H2)(dppe)2]X (8)a
-
(dppe)2]BPh4 (8e) via nucleophilic attack of the BPh4 anion
X
chemical shift of (η2-H2)b chemical shift of 31P{1H) NMRb
on the η2-H2 ligand. In fact, reaction of 7e with 1 atm of H2 at
room temperature for 24 h gave 9 together with BPh3 and
benzene (eq 2). The formation of BPh3 and benzene was
PF6
-11.8
-11.9
-11.6
-12.5
51.8
51.5
52.2
49.4
BF4
OTf
BAr4
a All of the samples were measured in CDCl3 at 18 °C under 1 atm
of H2. b In ppm.
into the corresponding Ru(η2-H2) complexes trans-[RuCl(η2-
H2)(dppe)2]X (X ) PF6, 8a;25a BF4, 8b;25a OTf, 8c; BAr4, 8d)
within several minutes at ambient temperature, respectively (eq
1).25 The typical 1H and 31P{1H} NMR data of 8 are shown in
confirmed by GLC and GC-MS. On the other hand, Ru(η2-
-
H2) complex 8d with BAr4 anion30 could be prepared in a
similar way to complexes 8a-8c; however, the yield of NH3
from the reaction of 5 with 8d was quite low (Table 2; run 5).
The Ru(η2-H2) complex [CpRu(η2-H2)(dppm)]OTf 31 [dppm
) bis(diphenylphosphino)methane] (10) with relatively lower
acidity31 was less effective for the protonation of the coordinated
N2 in complex 5, and the yield of NH3 was moderate (Table 2;
Table 3. The existence of the η2-H2 moiety in a new complex
8c was confirmed by variable-temperature T1 measurement and
the observation of a large JHD for the corresponding isoto-
pomer.20,21 A minimum T1 value of 24 ms (400 MHz in CD2-
Cl2) at 250 K was obtained for the broad signal at -11.6 ppm
assignable to the η2-H2. The deuterio derivative trans-[RuCl-
(η2-HD)(dppe)2]OTf (8c-d1) was prepared by the reaction of
trans-[RuHCl(dppe)2]25,26 (9) with a stoichiometric amount of
trifluoromethanesulfonic acid-d1 (DOTf) in CD2Cl2 at room
temperature. The complex (8c-d1) has a JHD coupling constant
of 25.6 Hz in CD2Cl2 at 20 °C. These values of minimum T1
and JHD are in good agreement with those of a known complex
8a.25 These results show that the counteranion of complex 8
does not essentially affect the Ru(η2-H2) bonding except for
BPh4- anion (vide infra). Although complex 8a has lower acidity
(27) (a) Hidai, M.; Yokotake, I.; Takahashi, T.; Uchida, Y. Chem. Lett.
1982, 453. (b) Wakatabe, A.; Takahashi, T.; Jin, D.-M.; Yokotake, I.;
Uchida, Y.; Hidai, M. J. Organomet. Chem. 1983, 254, 75.
(28) (a) Bianchini, C.; Farnetti, E.; Graziani, M.; Kaspar, J.; Vizza, F. J.
Am. Chem. Soc. 1993, 115, 1753. (b) Bianchini, C.; Meli, A.; Peruzzini,
M.; Vizza, F.; Frediani, P.; Herrera, V.; Sanchez-Delgado, R. A. J.
Am. Chem. Soc. 1993, 115, 7505. (c) Bianchini, C.; Moneti, S.;
Peruzzini, M.; Vizza, F. Inorg. Chem. 1997, 36, 5818.
(29) Cooper, J. N.; Powell, R. E. J. Am. Chem. Soc. 1963, 85, 1590.
-
(30) (a) The BPh4 anion is susceptible to protonolysis by H2SO4. The
presence of the electron-withdrawing CF3 substituent in the Ar group
-
rendered the BAr4 anion virtually inert toward degradation by H2-
SO4. (b) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.;
Kobayashi, H. Bull. Chem. Soc. Jpn. 1984, 57, 2600. (c) Brookhart,
M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992, 11, 3920.
(31) (a) Jia, G.; Morris, R. H. J. Am. Chem. Soc. 1991, 113, 875. (b) The
pKa value of [CpRu(η2-H2)(dppm)]BF4 was estimated to be 7.5.31a
(26) Chatt, J.; Hayter, R. G. J. Chem. Soc. 1961, 2605.

5950 Inorganic Chemistry, Vol. 39, No. 26, 2000
Nishibayashi et al.
Table 4. Reactions of N2 Complexes of Mo and W with
trans-[RuCl(η2-H2)(dppe)2]OTf (8c),a H2SO4,b,c or HOTfa
runs 4 and 10). In sharp contrast to these findings, the
protonation of 14 with 8c at 55 °C afforded NH3 in only 5%
yield (Table 4; run 7), although the corresponding reaction of
5 with 8c gave NH3 in 74% yield (Table 4; run 1). If the
protonation of the coordinated N2 in either 5 or 14 with 8c
proceeded with a trace of protonic acid HOTf released from
8c, NH3 should have been formed even at ambient temperature
and in almost the same yields in both cases. However, the
reaction at ambient temperature did not give NH3, and the yield
of NH3 by the reaction of 5 with 8c at 55 °C was apparently
higher than that of 14 with 8c (vide supra). Therefore, we are
inclined to the view that the N-H bond formation proceeds
through the direct nucleophilic attack of the coordinated N2 on
W upon the coordinated H2 on Ru, as shown in eq 3. This is
yield of NH3 (%)d
source freee basicf total
proton
run
N2 complex
1
2
3
4
5
6
7
8
9
cis-[W(N2)2(PMe2Ph)4] (5)
cis-[W(N2)2(PMe2Ph)4] (5)
cis-[W(N2)2(PMe2Ph)4] (5)
cis-[W(N2)2(PMe2Ph)4] (5)
cis-[Mo(N2)2(PMe2Ph)4] (13)
cis-[Mo(N2)2(PMe2Ph)4] (13)
8c
74g
198c
H2SO4
HOTf
HOTfi
8c
0
0
0
122 122h
102 102j
0
0
68c
5k
H2SO4
trans- [W(N2)2(PMePh2)4] (14) 8c
trans-[W(N2)2(PMePh2)4] (14) H2SO4
trans-[W(N2)2(PMePh2)4] (14) HOTf
3
2
190c
0
0
0
109 109l
10 trans-[W(N2)2(PMePh2)4] (14) HOTfi
102 102h
11 trans-[W(N2)2(dppe)2] (2)
8c
0
0
a The reactions with 8c or HOTf were carried out in benzene-
dichloroethane using 0.10 mmol of N2 complex and 1.00 mmol of 8c
under 1 atm of H2 or 1.00 mmol of HOTf under 1 atm of N2 at 55 °C
for 24 h. b The reactions with H2SO4 were carried out in methanol using
ca. 15 equiv of H2SO4 at room temperature for 20 h. c See ref 12. d Yield
of NH3 was based on the W atom. e Free yield was before base
distillation of the reaction mixture. f Basic yield was after base
distillation to fully liberate NH3. g This yield of NH3 was observed in
the water extract of the reaction mixture (see text). h Variation (5%
between experiments. i The reactions were carried out at room tem-
perature for 24 h. j Variation (8% between experiments. k Variation
(2% between experiments. l Variation (3% between experiments.
essentially the same as the intermolecular heterolytic cleavage
of η2-H2 ligands by base.20,21 Recently, various complexes
containing intramolecular35,36 or intermolecular35,37 hydrogen
bonds between a metal hydride and a hydrogen bond donor such
as an O-H or an N-H group have been reported which
represent plausible intermediates for the heterolytic cleavage
of coordinated H2.35-37
On the other hand, treatment of trans-[W(N2)2(dppe)2] (2)
with 10 equiv of 8c in benzene-dichloroethane at 55 °C for 24
h under 1 atm of H2 did not give any NH3 (Table 4; run 11),
however, the protonation of the coordinated N2 proceeded to
run 6). Employment of Ru(η2-H2) complexes such as trans-
[RuH(η2-H2)(dppp)2]X22,32 (X ) BF4, 11b; OTf, 11c) and trans-
[RuH(η2-H2)(dppe)2]X33 (X ) BF4, 12b;33 OTf, 12c) with much
lower acidity32,33 resulted in the formation of NH3 in 0-6%
total yields (Table 2; runs 7-10). Conventional hydrogenation
catalysts such as [RuCl2(PPh3)3], [RuH2(PPh3)4], [RhCl(PPh3)3],
and Pd/C (10%) as well as trans-[Mo(CO)(η2-H2)(dppe)2]20a,34
afforded only trace amounts of NH3.
(35) For recent reviews, see: (a) Crabtree, R. H.; Siegbahn, P. E. M.;
Eisenstein, O.; Rheingold, A. L.; Koetzle, T. Acc. Chem. Res. 1996,
29, 348. (b) Shubina, E. S.; Belkova, N. V.; Epstein, L. M. J.
Organomet. Chem. 1997, 536-537, 17. (c) Crabtree, R. H. Science
1998, 282, 2000. (d) Crabtree, R. H.; Eisenstein, O.; Sini, G.; Peris,
E. J. J. Organomet. Chem. 1998, 567, 7. (e) Crabtree, R. H. J.
Organomet. Chem. 1998, 577, 111.
In conclusion, when the acidity constant pKa of a Ru(η2-H2)
complex was increased up to about 10, the yield of NH3 was
remarkably decreased.
(36) O-H: (a) Lee, J. C., Jr.; Rheingold, A. L.; Muller, B.; Pregosin, P.
S.; Crabtree, R. H. J. Chem. Soc., Chem. Commun. 1994, 1021. (b)
Lee, J. C., Jr.; Peris, E.; Rheingold, A. L.; Crabtree, R. H. J. Am.
Chem. Soc. 1994, 116, 11014. (c) Yuo, W.; Crabtree, R. H. Inorg.
Chem. 1996, 35, 3007. N-H: (d) Park, S.; Ramachandran, R.; Lough,
A. J.; Morris, R. H. J. Chem. Soc., Chem. Commun. 1994, 2201. (e)
Lough, A. J.; Park, S.; Ramachandran, R.; Morris, R. H. J. Am. Chem.
Soc. 1994, 116, 8356. (f) Peris, E.; Lee, J. C., Jr.; Rambo, J. R.;
Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 1995, 117, 3485.
(g) Xu, W.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 1549.
(h) Park, S.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 3001.
(i) Lee, D.-H.; Patel, B. P.; Clot, E.; Eisenstein, O.; Crabtree, R. H.
Chem. Commun. 1999, 297. S-H: (j) Schlaf, M.; Morris, R. H. J.
Chem. Soc., Chem. Commun. 1995, 625. (k) Schlaf, M.; Lough, A.
J.; Morris, R. H. Organometallics 1996, 15, 4423.
(37) O-H: (a) Peris, E.; Wessel, J.; Patel, B. P.; Crabtree, R. H. J. Chem.
Soc., Chem. Commun. 1995, 2175. (b) Shubina, E. S.; Belkova, N.
V.; Krylov, A. N.; Vorontsov, E. V.; Epstein, L. M.; Gusev, D. G.;
Niedermann, M.; Berke, H. J. Am. Chem. Soc. 1996, 118, 1105. (c)
Belkova, N. V.; Shubina, E. S.; Ionidis, A. V.; Epstein, L. M.;
Jacobsen, H.; Messmer, A.; Berke, H. Inorg. Chem. 1997, 36, 1522.
(d) Ayllon, J. A.; Gervaux, C.; Sabo-Etienne, S.; Chaudret, B.
Organometallics 1997, 16, 2000. (e) Guari, Y.; Ayllon, J. A.; Sabo-
Etienne, S.; Chaudret, B.; Hessen, B. Inorg. Chem. 1998, 37, 640. (f)
Gru¨ndemann, S.; Ulrich, S.; Limbach, H.-H.; Golubev, N. S.; Denisov,
G. S.; Epstein, L. M.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem.
1999, 38, 2550. N-H: (g) Wessel, J.; Lee, J. C. L., Jr.; Peris, E.;
Yap, G. P. A.; Fortin, J. B.; Ricci, J. S.; Sini, G.; Albinati, A.; Koetzle,
T. F.; Eisenstein, O.; Rheingold, A. L.; Crabtree, R. H. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2507. (h) Patel, B.; Yao, W.; Yap, G. P. A.;
Rheingold, A. L.; Crabtree, R. H. Chem. Commun. 1996, 991. (i)
Abdur-Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.; Morris,
R. H. J. Am. Chem. Soc. 1998, 120, 11826. (j) Gusev, D. G.; Lough,
A. J.; Morris, R. H. J. Am. Chem. Soc. 1998, 120, 13138. (k) Abdur-
Rashid, K.; Gusev, D. G.; Lough, A. J.; Morris, R. H. Organometallics
2000, 19, 834.
Reactions of Other N2 Complexes of Mo and W with
Acidic Ru(η2-H2) Complexes. Reactions of several N2 com-
plexes of Mo and W with an excess amount of Ru(η2-H2)
complex 8c were investigated. Typical results are shown in
Table 4. No NH3 was formed when cis-[Mo(N2)2(PMe2Ph)4]
(13) was used in place of 5, although the protonation with H2-
SO4 gives NH3 in 68% yield12 (Table 4; runs 5 and 6).
Previously, Chatt and co-workers reported that when 5 and
trans-[W(N2)2(PMePh2)4] (14) are treated with H2SO4 at ambient
temperature, NH3 is formed in 198% and 190% yields,
respectively (Table 4; runs 2 and 8).12 We have now found that
treatment of 5 and 14 with 10 equiv of trifluoromethanesulfonic
acid (HOTf) in benzene-dichloroethane under 1 atm of N2 at
55 °C for 24 h gives NH3 in 122% and 109% total yields,
respectively (Table 4; runs 3 and 9). Even at room temperature,
both of the reactions produced NH3 in 102% yield (Table 4;
(32) The pKa value of trans-[RuH(η2-H2)(dppp)2]PF6 (11a) was estimated
to be 10.2.22
(33) (a) Saburi, M.; Aoyagi, K.; Takahashi, T.; Uchida, Y. Chem. Lett.
1990, 601. (b) Bautista, M. T.; Cappellani, E. P.; Drouin, S. D.; Morris,
R. H.; Schweitzer, C. T.; Sella, A.; Zubkowski, J. J. Am. Chem. Soc.
1991, 113, 4876. (c) Cappellani, E. P.; Drouin, S. D.; Jia, G.; Maltby,
P. A.; Morris, R. H.; Schweitzer, C. T. J. Am. Chem. Soc. 1994, 116,
3375. (d) The pKa value of trans-[RuH(η2-H2)(dppe)2]BF4 (12b) was
estimated to be 15.0.33c
(34) (a) Kubas, G. J.; Ryan, R. R.; Unkefer, C. J. J. Am. Chem. Soc. 1987,
109, 8113. (b) Kubas, G. J.; Burns, C. J.; Eckert, J.; Johnson, S. W.;
Larson, A. C.; Vergamini, P. J.; Unkefer, C. J.; Khalsa, G. R. K.;
Jackson, S. A.; Eisenstein, O. J. Am. Chem. Soc. 1993, 115, 569.

Formation of Ammonia under Mild Reaction Conditions
Table 5. Reactions of trans-[Mo(N2)2(dppe)2] (1) or trans-[W(N2)2(dppe)2] (2) with Ru(η2-H2) Complexesa
yield (%)
hydrazido(2-) complexb
Inorganic Chemistry, Vol. 39, No. 26, 2000 5951
run
N2 complex
Ru(η2-H2) complex
pKa
Ru-H complexb,c
1d
2
3
2
2
2
1
2
2
2
[RuCl(η2-H2)(dppp)2]BF4 (3b)e
[RuCl(η2-H2)(dppe)2]BF4 (8b)
[RuCl(η2-H2)(dppe)2]OTf (8c)
[RuCl(η2-H2)(dppe)2]PF6 (8a)
[CpRu(η2-H2)(dppm)]OTf (10)
[RuH(η2-H2)(dppp)2]OTf (11c)
[RuH(η2-H2)(dppe)2]OTf (12c)
(4.4)f
[WF(NNH2)(dppe)2]BF4 (16b), 63%
[WF(NNH2)(dppe)2]BF4 (16b), 99%
[W(OTf)(NNH2)(dppe)2]OTf (15), 75%
[MoF(NNH2)(dppe)2]PF6 (18), 50%
[W(OTf)(NNH2)(dppe)2]OTf (15), 99%
0%k
146% (6)
199% (9)
199% (9)
117% (9)
160%h
4
6.0
5
(7.5)g
(10.2)j
(15.0)l
6i
7i
0%m
a All of the reactions were carried out in benzene-dichloroethane using N2 complex (1 or 2) and 2 equiv of Ru(η2-H2) complex under 1 atm of
H2 at room temperature for 24 h unless otherwise stated. b Yields of hydrazido(2-) and Ru-H complexes were estimated by 31P{1H} NMR (see
text). c Yield of Ru-H complex was based on the W atom. d At 55 °C. e A mixture of 4b and 3b derived from treatment of 2 equiv of 4b with 1
atm of H2 was used for the protonation of coordinated N2. f The pKa value of trans-[RuCl(η2-H2)(dppp)2]PF6 (3a) was reported to be 4.4 (see ref
22). g The pKa value of [CpRu(η2-H2)(dppm)]BF4 was reported to be 7.5 (see ref 31). h [CpRuH(dppm)] and [CpRuCl(dppm)] were obtained in
100% and 60% NMR yields, respectively. In addition, unknown compounds were observed. It was confirmed that [CpRuH(dppm)] partly reacted
with dichloroethane to give [CpRuCl(dppm)] under the same reaction conditions. Thus, the yield of Ru-H complex was estimated to be 160%.
i THF was used as solvent. j The pKa value of trans-[RuH(η2-H2)(dppp)2]PF6 (11a) was reported to be 10.2 (see ref 32). k [WH4(dppe)2] was obtained.
In addition, unknown compounds were observed. l The pKa value of trans-[RuH(η2-H2)(dppe)2]BF4 (12b) was reported to be 15.0 (see ref 33).
m [WH4(dppe)2] was obtained in >95% NMR yield.
showing a doublet band with 183W satellites at 35.0 ppm (JPF
) 39 Hz, JPW ) 290 Hz). With regard to Ru complexes, Ru-H
complex 9, in 199% NMR yield, exhibiting a singlet at 61.9
ppm was a major product, although weak resonances assigned
Figure 1. 31P{1H} NMR spectrum of the reaction mixture of trans-
[W(N2)2(dppe)2] (2) and 2 equiv of trans-[RuCl(η2-H2)(dppe)2]BF4 (8b)
in benzene-dichloroethane at room temperature for 24 h under 1 atm
of H2.
to Ru complexes 8b, 7b, and 12b were also found in the reaction
mixture. These results corroborate the view that the heterolytic
cleavage of H2 occurs at the Ru center where one H atom is
used for the protonation of coordinated N2 on the W atom and
the other H atom remains at the Ru atom as a hydride. The
direct transfer of a proton from the η2-H2 ligand in 8c to the
coordinated N2 in 2 is also strongly supported by the experiment
under 1 atm of D2. 31P{1H} and 2H NMR spectra of the reaction
mixture of 2 and 2 equiv of trans-[RuCl(η2-D2)(dppe)2]OTf (8c-
d2) in benzene-dichloroethane at room temperature for 0.5 h
under 1 atm of D2 showed that the deuterated hydrazido(2-)
complex trans-[W(OTf)(NND2)(dppe)2]OTf (15′) was formed
in ca. 70% NMR yield.
afford the hydrazido(2-) complex trans-[W(OTf)(NNH2)-
(dppe)2]OTf (15) in high yield. The latter complex 15 was
previously prepared by the protonation of 2 with HOTf.38 The
ruthenium-assisted protonation of coordinated N2 affording the
hydrazido(2-) complex occurred even at ambient temperature.
Typical results of the reactions between trans-[M(N2)2(dppe)2]
[M ) Mo (1), W (2)] and Ru(η2-H2) complexes at ambient
temperature are shown in Table 5. The NMR yields of the metal
products were determined by integration of the gated-{1H}-
decoupled 31P resonances against PPh3 added as an internal
reference. Figure 1 shows the 31P{1H} NMR spectrum (in
CDCl3) of the crude reaction mixture of 2 and 2 equiv of 8b in
benzene-dichloroethane at room temperature for 24 h under 1
atm of H2 (eq 4) (Table 5; run 2). This demonstrates that N2
complex 2 was transformed into the hydrazido(2-) complex
Employment of Ru(η2-H2) complexes 11 and 12 with a pKa
value of above 10 did not cause the protonation of coordinated
N2 in complex 2; instead the tetrahydrido tungsten complex
[WH4(dppe)2]14d was obtained as a major product (Table 5; runs
6 and 7). It is to be noted that the tetrahydrido tungsten complex
was produced in a much lower yield in the absence of 11 or 12
under the same conditions. Thus, treatment of 2 with 2 equiv
of 12c in THF at room temperature for 12 h under 1 atm of H2
afforded [WH4(dppe)2] in 75% NMR yield. On the other hand,
the formation of [WH4(dppe)2] in 30% NMR yield was observed
in the absence of 12c under the same reaction conditions. In
both cases, unreacted 2 was recovered; however, no other W
39
trans-[WF(NNH2)(dppe)2]BF4 (16b), in 99% NMR yield,
(38) Field, L. D.; Jones, N. G.; Turner, P. Organometallics 1998, 17, 2394.
(39) (a) Chatt, J.; Heath G. A.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1974, 2074. (b) Chatt, J. C.; Pearman, A. J.; Richards, R. L. J. Chem.
Soc., Dalton Trans. 1976, 1520.

5952 Inorganic Chemistry, Vol. 39, No. 26, 2000
Nishibayashi et al.
complex was formed. Interestingly, the hydrazido(2-) complex
15 was deprotonated by the dihydride complex cis-[RuH2-
(dppe)2]40 (17) at room temperature for 2 h in THF under 1
atm of N2 to give N2 complex 2 and Ru(η2-H2) complex 12c in
60% and 199% NMR yields, respectively (eq 5). This is not
Figure 2. ORTEP drawing for trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf‚
(THF)0.5 [(19)‚(THF)0.5]. Hydrogen atoms except for those attached to
N(2), THF, and OTf anion are omitted for clarity.
surprising because the NH proton in 15 is deprotonated by base
like KOtBu or Et3N.38
Table 6. Selected Bond Lengths and Angles in
trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf‚(THF)0.5 [19‚(THF)0.5
]
The protonation of the coordinated N2 in 1 with 8a also
proceeded smoothly at ambient temperature. The hydrazido-
Bond Lengths (Å)
W(1)-P(1)
W(1)-P(2)
W(1)-P(3)
W(1)-P(4)
2.529(3)
2.555(2)
2.535(3)
2.564(2)
W(1)-O(1)
W(1)-N(1)
S(1)-O(1)
N(1)-N(2)
2.218(5)
1.722(6)
1.479(5)
1.320(9)
41
(2-) complex trans-[MoF(NNH2)(dppe)2]PF6 (18) was ob-
tained in ca. 50% NMR yield, concurrent with the formation
of 9 in 117% NMR yield (Table 5; run 4).
Isolation of Hydrazido(2-) Complexes trans-[W(OTf)-
(NNH2)(L)4]OTf (L ) PMe2Ph, 19; PMePh2, 20) and trans-
[Mo(OTf)(NNH2)(PMe2Ph)4]OTf (21). When the reaction of
5 and 2 equiv of 8c was carried out at room temperature for 20
h in benzene-dichloroethane, the hydrazido(2-) complex trans-
[W(OTf)(NNH2)(PMe2Ph)4]OTf (19) was obtained in 63%
NMR yield together with 9 in 199% NMR yield (eq 6).
Bond Angles (deg)
P(1)-W(1)-P(2)
P(1)-W(1)-P(3)
P(1)-W(1)-P(4)
P(1)-W(1)-O(1)
P(1)-W(1)-N(1)
P(2)-W(1)-P(3)
P(2)-W(1)-P(4)
P(2)-W(1)-O(1)
90.31(7)
175.28(7)
89.37(7)
87.1(1)
P(2)-W(1)-N(1)
P(3)-W(1)-P(4)
P(3)-W(1)-O(1)
P(3)-W(1)-N(1)
P(4)-W(1)-O(1)
P(4)-W(1)-N(1)
W(1)-N(1)-N(2)
W(1)-O(1)-S(1)
94.6(2)
88.58(7)
96.9(1)
86.9(2)
83.2(1)
98.3(2)
178.6(6)
151.0(4)
89.2(2)
92.62(7)
167.16(7)
84.0(1)
spectrum at -18.7 ppm with 183W satellites (JPW ) 282 Hz),
indicating the chemical equivalence of the four phosphorus
atoms. The IR spectrum of 19 shows the νNH band at 3270 cm-1
.
The molecular structure of 19 was unambiguously confirmed
by X-ray analysis. An ORTEP drawing of 19‚(THF)0.5 is shown
in Figure 2. Selected bond lengths and angles are shown in Table
6. The complex adopts a slightly distorted octahedral geometry
around the W center. The four phosphorus atoms occupy the
equatorial coordination sites around the W center, and the W-P
bond distances are almost equal. The hydrazido(2-) and OTf
ligands occupy the remaining axial coordination sites. The
W(1)-N(1)-N(2) linkage is essentially linear and typical of
hydrazido(2-) complexes.38,43 The W(1)-N(1) bond length of
1.722(6) Å indicates a metal-nitrogen triple bond.38,43
Treatment of hydrazido(2-) complex 19 with 10 equiv of
8c in benzene-dichloroethane under 1 atm of H2 at 55 °C for
24 h gave NH3 in 50% total yield. This result indicates that the
formation of NH3 from 5 and 8c proceeds through the
protonation of hydrazido(2-) complex 19.
The hydrazido(2-) complex trans-[W(OTf)(NNH2)(PMePh2)4]-
OTf (20) was prepared in 55% NMR yield by the reaction of
14 and 2 equiv of 8c at room temperature for 1 h in benzene-
dichloroethane (eq 6). Complex 20 was also isolated from the
reaction of 14 and 2 equiv of HOTf in THF in 44% yield.
Analogous hydrazido(2-) complexes trans-[WX(NNH2)(PMe2-
Ph)4]X [X ) Cl, Br, and I] were previously prepared by the
reaction of 5 with anhydrous HX (X ) Cl, Br, and I) in
dichloromethane.39,42 Complex 19 was also isolated from the
reaction of 5 and 2 equiv of HOTf in toluene in 76% yield.
Complex 19 exhibits a single peak in the 31P{1H} NMR
(40) Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H. Organometallics 1997,
16, 5569.
(41) Hidai, M.; Kodama, T.; Sato, M.; Harakawa, M.; Uchida, Y. Inorg.
Chem. 1976, 15, 2694.
(42) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1978, 1766.
(43) For an example, see: Nugent, W. A.; Haymore, B. L. Coord. Chem.
ReV. 1980, 31, 123.

Formation of Ammonia under Mild Reaction Conditions
Inorganic Chemistry, Vol. 39, No. 26, 2000 5953
Figure 3. 31P{1H} NMR spectra of the reaction mixture of cis-[W(N2)2(PMe2Ph)4] (5) and 10 equiv of trans-[RuCl(η2-H2)(dppe)2]OTf (8c) in
benzene-d6-dichloroethane under 1 atm of H2: (a) the reaction mixture after 5 min at room temperature, (b) after 15 min as the reaction temperature
was raised to 55 °C, (c) after 30 min as the reaction temperature was raised to 55 °C, (d) after 45 min as the reaction temperature was raised to 55
°C, (e) after 100 min as the reaction temperature was raised to 55 °C, and (f) after 150 min as the reaction temperature was raised to 55 °C.
Complex 20 exhibits a single peak in the 31P{1H} NMR
spectrum at 19.5 ppm with 183W satellites (JPW ) 170 Hz),
indicating the chemical equivalence of the four phosphorus
19. Previously it was reported that the hydrazido(2-) complex
[WHCl3(NNH2)(PMePh2)2] was produced by the reaction of 14
with anhydrous HCl in dichloromethane.44
atoms. The IR spectrum exhibits the νNH band at 3220 cm-1
.
(44) Chatt, J.; Fakley, M. E.; Hitchcock, P. B.; Richards, R. L.; Luong-
These results show that the structure of 20 is similar to that of
Thi, N. T. J. Chem. Soc., Dalton Trans. 1982, 345.

5954 Inorganic Chemistry, Vol. 39, No. 26, 2000
Nishibayashi et al.
Scheme 2
The hydrazido(2-) complex trans-[Mo(OTf)(NNH2)(PMe2-
Ph)4]OTf (21) was prepared in 30% isolated yield by the reaction
of Mo-N2 complex 13 and 2 equiv of HOTf at room
temperature for 5 min in toluene. Complex 21 exhibits a single
peak in the 31P{1H} NMR spectrum at -1.80 ppm, indicating
the chemical equivalence of the four phosphorus atoms. The
IR spectrum exhibits the νNH band at 3249 cm-1. It is to be
noted that complex 21 was not obtained by treatment of 13 with
2 equiv of 8c at room temperature under H2, although the
formation of hydride 9 was observed. This is compatible with
the finding that no NH3 was formed from the reaction of 13
with excess 8c under H2 (vide supra).
with 9 to afford trans-[WCl(NNH2)(PMe2Ph)4]OTf and 12c.
Actually, the reaction of 19 with 9 at 55 °C for 24 h in THF/
C6D6 (2/1) under 1 atm of H2 afforded trans-[WCl(NNH2)(PMe2-
Ph)4]OTf and 12c in 71% and 44% NMR yields, respectively
(eq 7). Subsequent protonation of hydrazido(2-) complexes 19
NMR Study on the Reaction of cis-[W(N2)2(PMe2Ph)4] (5)
with 10 Equiv of trans-[RuCl(η2-H2)(dppe)2]OTf (8c). To
elucidate the mechanism for the formation of NH3, the reaction
of 5 and 10 equiv of 8c in C6D6/ClCH2CH2Cl (1/3) at room
temperature and 55 °C under 1 atm of H2 was monitored by
31P{1H} NMR. The NMR spectra are shown in Figure 3, where
PPh3 was used as an internal reference because PPh3 was
confirmed not to react with 8c. When 5 was added to the
solution of 8c at room temperature, 5 seemed to be almost
completely consumed within 5 min and the hydrazido(2-)
complex 19 with a resonance at -18.8 ppm was produced in
82% NMR yield, concurrent with the formation of hydride 9
(62.2 ppm) in 214% NMR yield based on tungsten. In addition,
the formation of the hydrido-dihydrogen complex 12c (68.0
ppm) in 31% NMR yield was observed, which was accompanied
by the formation of a small amount of cis- and trans-[RuCl2-
(dppe)2], while a large amount of complex 8c (50.2 ppm)
remained in the mixture. In a separate run, the reaction of 8c
and hydride 9 was performed at room temperature for 1 h in
C6D6/ClCH2CH2Cl (1/2) under H2. The NMR analysis of the
mixture showed the formation of 12c and cis- and trans-[RuCl2-
(dppe)2] in 8% yields, respectively. Thus, this type of reaction
explains the formation of 12c at the early stage of the reaction.
We were not able to observe any intermediates such as diazenido
(N2H) complexes because the transformation of 5 to 19
proceeded quite rapidly even at room temperature. As the
reaction temperature was raised to 55 °C, 8c was gradually
consumed, accompanied by the increase of hydride 9, and the
hydrazido(2-) complex 19 was slowly transformed into another
hydrazido(2-) complex trans-[WCl(NNH2)(PMe2Ph)4]OTf which
finally disappeared after 150 min. It is supposed that 19 reacts
and trans-[WCl(NNH2)(PMe2Ph)4]OTf with H2 complex 8c at
55 °C results in the formation of NH3, concurrent with the
formation of [PMe2PhH]+. After 24 h at 55 °C, hydrides 9 and
12c were formed in 260% and 330% NMR yields based on
tungsten, respectively. It may be concluded that H2 complex
8c is consumed not only for the formation of NH3 but also for
the protonation of NH3 produced and PMe2Ph ligands released
from the tungsten. All of the electrons required for the reduction
of N2 are supplied from the zerovalent tungsten in 5. The
presumed reaction pathway for the formation of NH3 is
summarized in Scheme 2.
It is noteworthy that the protonation of N2 complexes 5 and
14 with 10 equiv of H2 complex 8c occurred rapidly even at
room temperature to form the corresponding hydrazido(2-)
intermediates, respectively; however, they remain unchanged
at that temperature. When the reaction temperature was raised
to 55 °C, subsequent protonation of the hydrazido(2-) inter-
mediates with 8c proceeded to eventually afford NH3. The
significant difference in the yield of NH3 between N2 complexes
5 and 14 in this protonation (vide supra) may arise from the
different reactivity of the corresponding hydrazido(2-) inter-

Formation of Ammonia under Mild Reaction Conditions
Inorganic Chemistry, Vol. 39, No. 26, 2000 5955
Preparation of [RuCl(dppp)2]X (4b and 4c‚CH2Cl2). The follow-
ing procedure for preparation of the complex [RuCl(dppp)2]OTf‚CH2-
Cl2 (4c‚CH2Cl2) is representative.22 A suspension of [RuCl2(PPh3)3]
(11.78 g, 12.3 mmol), dppp (10.0 g, 24.3 mmol), and NaOTf (6.35 g,
36.9 mmol) in EtOH (500 mL) was stirred at reflux temperature for 4
h under 1 atm of N2. After evaporation of the solvent, the residue was
extracted with CH2Cl2 (20 mL). Addition of i-PrOH to the concentrated
CH2Cl2 solution gave 4c‚CH2Cl2 (5.93 g, 4.96 mmol) in 40% yield as
dark red crystals. 1H NMR (CDCl3): δ 0.75 (br t, 2H), 1.62 (br s, 2H),
2.19 (br s, 3H), 2.61 (br s, 2H), 2.86 (br s, 3H), 6.82-7.81 (m, 40H).
31P{1H} NMR (CDCl3): δ -4.32 (t, J ) 33 Hz) and 43.5 (t, J ) 33
Hz). Anal. Calcd for C55H52ClF3O3P4SRu‚CH2Cl2: C, 56.27; H, 4.55.
Found: C, 56.53; H, 4.48.
mediates toward 8c. We presume that hydrazido(2-) complex
19 with PMe2Ph ligands reacts much more readily with H2
complex 8c to afford NH3 than hydrazido(2-) complex 20 with
PMePh2 ligands, because PMe2Ph is a stronger σ-donor than
PMePh2.
Conclusion
We have found a novel synthesis of NH3 from the reactions
of tungsten dinitrogen complex 5 with an excess of acidic
ruthenium dihydrogen complexes (∼10 equiv) under mild
conditions. In these reactions, heterolytic cleavage of H2
proceeds at the Ru center through nucleophilic attack of the
coordinated N2 on the coordinated H2 where a proton (H+) is
used for the protonation of the coordinated N2 and a hydride
(H-) remains at the Ru atom. The protonation initially trans-
forms the coordinated N2 into the NNH2 ligand. Hydrazido-
(2-) complexes have actually been isolated in some cases. We
presume that further protonation of hydrazido(2-) intermediates
at 55 °C results in the formation of NH3 along with W(VI)
species. The yield of NH3 is up to 79% yield based on tungsten
when H2 complex 8b is employed. However, in these reactions,
only one proton formed by the heterolytic cleavage of H2 is
used for the N-H bond formation and all of the electrons
required for the formation of NH3 are supplied from the
zerovalent tungsten. Thus, the remaining hydride is not used
for either the N-H bond formation or reduction of the high-
valent W species to regenerate the starting N2 complex 5. Our
studies are now in progress toward development of bimetallic
systems where both the hydrogen atoms of activated H2 are
effectively used for the catalytic nitrogen fixation.
Similarly, 4b was prepared by using NH4BF4. The physical,
spectroscopic, and analytical data are as follows.
1
[RuCl(dppp)2]BF4 (4b). Yield: 83%. Dark red crystals. H NMR
(CDCl3): δ 0.86 (br t, 2H), 1.68 (br s, 2H), 2.25 (br s, 3H), 2.63 (br
s, 2H), 2.90 (br s, 3H), 6.95-7.82 (m, 40H). 31P{1H} NMR (CDCl3):
δ -4.09 (t, J ) 33 Hz) and 43.1 (t, J ) 33 Hz). Anal. Calcd for C54H52-
BClF4P4Ru: C, 61.88; H, 5.00. Found: C, 61.96; H, 5.04.
Preparation of [RuCl(dppe)2]X (X ) OTf, BAr4) [7c‚(CH2Cl2)0.5
and 7d‚CH2Cl2]. The following procedure for preparation of the
complex [RuCl(dppe)2]OTf‚(CH2Cl2)0.5 [7c‚(CH2Cl2)0.5] is representa-
tive.25 A solution of NaOTf (2.13 g, 12.4 mmol) and cis-[RuCl2(dppe)2]
(10.0 g, 10.3 mmol) in THF (100 mL) and EtOH (50 mL) was stirred
at room temperature for 12 h under 1 atm of Ar. After evaporation of
the solvents, the residue was extracted with CH2Cl2 (100 mL). The
CH2Cl2 solution was washed with H2O and dried over anhydrous
MgSO4. Addition of hexane to the concentrated CH2Cl2 solution gave
7c‚(CH2Cl2)0.5 (8.96 g, 7.97 mmol) in 77% yield as dark red crystals.
1H NMR (CDCl3): δ 1.65 (br s, 4H), 2.56 (br s, 2H), 2.65 (br s, 2H),
6.78-7.76 (m, 40H). 31P{1H} NMR (CDCl3): δ 55.6 (br t, J ) 12
Hz) and 83.7 (br t, J ) 12 Hz). Anal. Calcd for C53H48ClF3O3P4SRu‚
(CH2Cl2)0.5: C, 57.12; H, 4.39. Found: C, 57.13; H, 4.57.
Experimental Section
Similarly, 7d‚CH2Cl2 was prepared by using NaBAr4. The physical,
spectroscopic, and analytical data are as follows. Yield: 67%. Dark
red crystals. 1H NMR (CDCl3): δ 1.66 (br s, 3H), 2.29 (m, 3H), 2.63
(br s, 2H), 6.60-7.80 (m, 52H). 31P{1H} NMR (CDCl3): δ 56.0 (br t,
J ) 12 Hz) and 82.6 (br t, J ) 12 Hz). Anal. Calcd for C84H60BClF24P4-
Ru‚CH2Cl2: C, 54.26; H, 3.32. Found: C, 54.07; H, 3.34.
Preparation of [RuCl(dppe)2]BPh4‚(CH2Cl2)1.5 [7e‚(CH2Cl2)1.5].
A mixture of cis-[RuCl2(dppe)2] (969 mg, 1.00 mmol) and NaBPh4
(1.20 g, 3.50 mmol) in dry EtOH (30 mL) was stirred at reflux
temperature for 1 h under 1 atm of Ar. The resulting red solid was
collected, washed with EtOH, and dried under reduced pressure. The
residue was extracted with CH2Cl2 (15 mL). Addition of methanol to
the CH2Cl2 solution gave 7e‚(CH2Cl2)1.5 (888 mg, 0.64 mmol) in 64%
yield as red crystals. 1H NMR (CDCl3): δ 1.51 (br s, 2H), 2.15 (br s,
4H), 2.33 (br s, 2H), 6.60-7.80 (m, 60H). 31P{1H} NMR (CDCl3): δ
55.8 (br t, J ) 12 Hz) and 82.7 (br t, J ) 12 Hz). Anal. Calcd for
General Procedure. Preparation of complexes was performed under
1 atm of N2 or Ar dried by passage through silica gel and P2O5.
Reactions of N2 complexes with Ru(η2-H2) complexes were carried
out under 1 atm of H2 dried by passage through silica gel and P2O5. D2
(99.9%) was obtained from Takachiho Chemical Industrial Co. LTD.
(Japan). Benzene, hexane, diethyl ether (Et2O), and THF were freshly
distilled over sodium benzophenone ketyl just before use. Dichlo-
romethane and dichloroethane were distilled over P2O5. Unless
otherwise noted, all manipulations were done by use of Schlenk
techniques.
NMR spectra were recorded on a JEOL JNM-LA-400 or a JEOL
JNM-EX-270 spectrometer. IR spectra were recorded on a Shimadzu
FTIR-8100M spectrometer. Quantitative GLC analyses of organic
compounds were performed on a Shimadzu GC-14A instrument
equipped with a flame ionization detector using a 25 m × 0.25 mm
CBP10 fused silica capillary column. GC-MS analyses were carried
out on a Shimadzu GC-MS QP-5000 spectrometer. Elemental analyses
were performed on a Perkin-Elmer 2400 series II CHN analyzer.
Amounts of the solvent molecules in the crystals of new complexes
were determined by both elemental analyses and 1H NMR spectroscopy.
Absorption spectra were recorded on a Shimadzu UV-2400PC.
Dinitrogen complexes12,45,46 such as 1, 2, 5, 13, and 14, hydrazido-
(2-) complexes such as 15,38 16,39 18,41 and trans-[WCl(NNH2)(PMe2-
Ph)4]Cl,42 and other complexes including [RuCl2(PPh3)3],47 [RuH2-
(PPh3)4],48 [RhCl(PPh3)3],49 4a,22 7a,b,25 11b,40 12b,33 trans-[Mo(CO)(η2-
H2)(dppe)2],34 17,40 and cis-[RuCl2(dppe)2]33b were prepared according
to literature procedures.
C
77.5H71BCl4P4Ru: C, 67.45; H, 5.19. Found: C, 67.72; H, 5.13.
Conversion of [RuCl(dppe)2]OTf (7c) into trans-[RuCl(η2-H2)-
(dppe)2]OTf (8c). In a Schlenk tube was placed 7c‚(CH2Cl2)0.5 (15.0
mg, 0.013 mmol) under 1 atm of N2. Dry CD2Cl2 (0.75 mL) was then
added under 1 atm of N2. The reaction mixture was stirred at room
temperature for 5 min under 1 atm of H2. 1H and 31P{1H} NMR spectra
of the reaction mixture showed the complete conversion of 7c into 8c.
1H NMR (CD2Cl2): δ -11.6 (br, 2H), 2.33 (br, 4H), 2.87 (br, 4H),
6.92-7.39 (m, 40H); a minimum T1 value of 24 ms (400 HMz) at 250
K was obtained for the broad signal at -11.6 ppm, assignable to the
η2-H2. 31P{1H} NMR (CD2Cl2): δ 52.2 (s).
Preparation of trans-[RuCl(η2-HD)(dppe)2]OTf (8c-d1). The Ru-
(η2-HD) complex (8c-d1) was prepared in situ by the following
procedure. To a solution of 925,26 (19 mg, 0.02 mmol) in CD2Cl2 (0.75
mL) was added a mixture (15 mg) of HOTf and D2O (1/1, w%) at
room temperature under 1 atm of N2. 1H NMR spectra of the reaction
mixture showed the formation of 8c-d1. 1H NMR (CD2Cl2): δ -12.29
(tq, JPH ) 7.3 Hz, JHD ) 25.6 Hz).
(45) Hussain, W.; Leigh, G. J.; Ali, H. M.; Pickett, C. J.; Rankin, D. A. J.
Chem. Soc., Dalton Trans. 1984, 1703.
(46) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1977, 2139.
(47) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970,
12, 237.
(48) Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 75.
(49) Osborn, J. A.; Wilkinson, G. Inorg. Synth. 1967, 10, 67.
Preparation of [CpRu(η2-H2)(dppm)]OTf (10). To a solution of

5956 Inorganic Chemistry, Vol. 39, No. 26, 2000
Nishibayashi et al.
[CpRuH(dppm)]50 (257 mg, 0.466 mmol) in THF (10 mL) under 1
atm of N2 was added HOTf (69.9 mg, 0.47 mmol), and the mixture
was stirred for 10 min. After evaporation of the solvent, the residue
was extracted with CH2Cl2. Addition of Et2O to the CH2Cl2 solution
afforded 10 (179 mg, 0.26 mmol) in 55% yield as colorless crystals.
1H NMR (CDCl3): δ -7.03 (br s, 2H, η2-H2), 5.13 (s, 5H, Cp), 4.28
(dt, 1H, JHH ) 16 Hz, JPH ) 11 Hz), 5.51 (dt, 1H, JHH ) 16 Hz, JPH
) 11 Hz), 7.4-7.7 (m, 20H). 31P{1H} NMR (CDCl3): δ 4.0 (s). Anal.
Calcd for C31H29F3O3P2SRu: C, 53.07; H, 4.17. Found: C, 52.83; H,
4.13.
JPF ) 39 Hz, JPW ) 290 Hz). 9: 31P{1H} NMR (CDCl3) δ 61.9 (s). 8b:
31P{1H} NMR (CDCl3) δ 51.3 (s).
Reaction of trans-[W(N2)2(dppe)2] (2) with trans-[RuCl(η2-D2)-
(dppe)2]OTf (8c-d2) under 1 atm of D2. In a 50 mL flask was placed
7c‚(CH2Cl2)0.5 (112 mg, 0.10 mmol) under 1 atm of N2. Dry dichlo-
roethane (5 mL) was added, and then the mixture was magnetically
stirred at room temperature for 5 min. After the N2 atmosphere was
replaced by 1 atm of D2 to transform 7c into 8c-d2, a solution of 2 (52
mg, 0.05 mmol) in benzene (5 mL) was added by syringe. The reaction
mixture was stirred at room temperature for 0.5 h under 1 atm of D2.
The solvent was then removed under vacuum, and the residue was
dissolved in CDCl3 to measure the 31P{1H} NMR spectrum. PPh3 (52
mg, 0.20 mmol) was added into the CDCl3 solution as an internal
reference. The NMR yields of the produced complexes were determined
by integration of the gated-{1H}-decoupled 31P resonances against the
standard PPh3. Then the solvent was again evaporated under vacuum,
and the residue was dissolved in CH2Cl2 to measure the 2H NMR
spectrum. C6D6 was added into the CH2Cl2 solution as an internal
reference. The amount of the deuterated species 15′ was determined
Preparation of trans-[RuH(η2-H2)(dppp)2]OTf‚CH2Cl2 (11c‚
CH2Cl2). To a solution of cis-[RuH2(dppp)2]40 (432 mg, 0.47 mmol)
in THF (10 mL) under 1 atm of argon was added HOTf (69.9 mg,
0.47 mmol), and the mixture was stirred for 10 min. After evaporation
of the solvent, the residue was extracted with CH2Cl2. Addition of Et2O
to the CH2Cl2 solution afforded 11c‚CH2Cl2 (417 mg, 0.36 mmol) in
1
77% yield as orange crystals. H NMR (CD2Cl2): δ -8.08 (br s, 1H,
RuH), -3.13 (br s, 2H, η2-H2), 1.31 (br s, 4H), 2.13 (br d, 8H), 6.9-
7.6 (m, 40H). 31P{1H} NMR (CD2Cl2): δ 24.0 (br s). Anal. Calcd for
C56H57Cl2F3O3P4SRu: C, 57.83; H, 4.94. Found: C, 57.62; H, 4.90.
2
by integration of the H signal against the standard C6D6. 15′: 31P-
{1H} NMR (CDCl3) δ 37.5 (s with 183W satellites, JPW ) 321 Hz); 2H
NMR (CH2Cl2) δ 4.60 (br s; WNND2); ca. 70% NMR yield. 9′: 31P-
{1H} NMR (CDCl3) δ 62.4 (s); 2H NMR (CH2Cl2) δ -19.5 (br s; RuD);
ca. 200% NMR yield.
Preparation of trans-[RuH(η2-H2)(dppe)2]OTf‚CH2Cl2 (12c‚
CH2Cl2). To a solution of cis-[RuH2(dppe)2]40 (3.00 g, 3.33 mmol) in
THF (50 mL) under 1 atm of argon was added HOTf (500 mg, 3.33
mmol), and the mixture was stirred overnight. After evaporation of
the solvent, the residue was extracted with CH2Cl2. Addition of hexane
to the CH2Cl2 solution afforded 12c‚CH2Cl2 (3.45 g, 3.04 mmol) in
91% yield as colorless crystals. 1H NMR (CD2Cl2): δ -10.17 (quint,
1H, JPH ) 18 Hz), -4.79 (br s, 2H, η2-H2), 2.15 (br d, 8H), 7.1-7.4
(m, 40H). 31P{1H} NMR (CD2Cl2): δ 68.3 (s). Anal. Calcd for C54H53-
Cl2F3O3P4SRu: C, 57.15; H, 4.71. Found: C, 56.89; H, 4.78.
Reaction of trans-[W(OTf)(NNH2)(dppe)2]OTf (15) with 2 equiv
of cis-[RuH2(dppe)2] (17) under 1 atm of N2. In a 20 mL flask were
placed 15 (26 mg, 0.02 mmol) and 17 (36 mg, 0.04 mmol) under 1
atm of N2. Dry THF (1 mL) was added, and then the mixture was
magnetically stirred at room temperature for 2 h. After evaporation of
the solvent under vacuum, the residue was dissolved in C6D6/ClCH2-
CH2Cl (1/3) to measure the 31P{1H} NMR spectrum. PPh3 (21 mg,
0.08 mmol) was added into the solution as an internal reference. The
NMR yields of the produced complexes were determined by integration
of the gated-{1H}-decoupled 31P resonances against the standard PPh3.
2: 31P{1H} NMR δ 45.5 (s with 183W satellites, JPW ) 320 Hz); 60%
NMR yield. 12c: 31P{1H} NMR δ 68.5 (s); 199% NMR yield. 17: 31P-
{1H} NMR δ 64.9 (t, J ) 15 Hz), 78.9 (t, J ) 15 Hz); <5% NMR
yield. In addition, unknown compounds were observed.
Preparation of trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19). To a
solution of 5 (387 mg, 0.49 mmol) in toluene (7 mL) was added HOTf
(147 mg, 0.98 mmol) under 1 atm of N2. The reaction mixture was
stirred at room temperature for 30 min. Then, Et2O (10 mL) was slowly
added to the reaction mixture to give 19 (393 mg, 0.37 mmol) in 76%
isolated yield as pale brown needles. 1H NMR (CDCl3): δ 1.67 (br s,
24H, PMe2Ph), 7.13 (s, 2H, NNH2), 7.16-7.21 (m, 20H, PMe2Ph).
31P{1H} NMR (CDCl3): δ -18.7 (s with 183W satellites, JPW ) 282
Hz). IR (KBr, cm-1): 3270 (N-H). Anal. Calcd for C34H46-
F6N2O6P4S2W: C, 38.36; H, 4.36; N, 2.63. Found: C, 38.00; H, 4.32;
N, 2.62.
Complex 19 was also prepared from the reaction of 5 with 2 equiv
of 8c under 1 atm of H2. In a 50 mL flask was placed 7c‚(CH2Cl2)0.5
(112 mg, 0.10 mmol) under 1 atm of N2. Dry dichloroethane (3 mL)
and benzene (3 mL) were added, and then the mixture was magnetically
stirred at room temperature for 5 min. After the N2 atmosphere was
replaced by 1 atm of H2 to transform 7c into 8c, 5 (40 mg, 0.05 mmol)
was added portionwise. The reaction mixture was stirred at room
temperature for 20 h under 1 atm of H2. The solvent was then removed
under vacuum, and the residue was dissolved in CDCl3 to measure the
31P{1H} NMR spectrum. PPh3 (52 mg, 0.20 mmol) was added into the
CDCl3 solution as an internal reference. The NMR yields of the
produced complexes were determined by integration of the gated-{1H}-
decoupled 31P resonances against the standard PPh3. Complexes 19 and
9 were formed in 63% and 199% NMR yields, respectively.
Preparation of trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20). To a
solution of 14 (50 mg, 0.048 mmol) in THF (5 mL) was added HOTf
(15 mg, 0.10 mmol) under 1 atm of N2. The reaction mixture was stirred
at room temperature for 30 min. Then, Et2O (15 mL) was slowly added
to the reaction mixture to give 20 (28 mg, 0.021 mmol) in 44% isolated
yield as a brown solid. 1H NMR (CDCl3): δ 2.36 (br s, 12H, PMePh2),
5.26 (br s, 2H, NNH2), 7.23-7.70 (m, 40H, PMePh2). 31P{1H} NMR
(CDCl3): δ 19.5 (s with 183W satellites, JPW ) 170 Hz). IR (KBr, cm-1):
Formation of NH3 in the Reactions of cis-[W(N2)2(PMe2Ph)4] (5)
with Ru(η2-H2) Complexes under 1 atm of H2. A typical procedure
for the reaction of 5 with 10 equiv of 8c under 1 atm of H2 is as follows.
In a 500 mL flask was placed 7c‚(CH2Cl2)0.5 (1.1 g, 1.00 mmol) under
1 atm of N2. Dry dichloroethane (15 mL) and benzene (5 mL) were
added, and then the mixture was magnetically stirred at 55 °C for 15
min. After the N2 atmosphere was replaced by 1 atm of H2 to convert
7c into 8c, 5 (80 mg, 0.10 mmol) was added portionwise. The reaction
mixture was stirred at 55 °C for 24 h under 1 atm of H2. The reaction
mixture was evaporated under reduced pressure, and the distillate was
trapped in dilute H2SO4 solution (1 N; 10 mL). Potassium hydroxide
aqueous solution (40 wt %; 20 mL) was added to the residue, and the
mixture was distilled into another dilute H2SO4 solution (1 N; 10 mL).
NH3 and NH2NH2 present in each of the H2SO4 solutions were
quantitatively analyzed by using indophenol and p-(dimethylamino)-
benzaldehyde reagents, respectively.13c,51
Alternatively, the reaction mixture was diluted with CH2Cl2 (50 mL),
and the solution was extracted with H2O (100 mL × 3). The combined
aqueous extract was treated with activated charcoal and filtered through
Celite. The amount of NH4+ ion in the aqueous solution was determined
by the indophenol reagent.13c,51
Reaction of trans-[W(N2)2(dppe)2] (2) with Ru(η2-H2) Complexes.
A typical experimental procedure for the reaction of 2 with 8b is as
follows. In a 50 mL flask was placed 7b (102 mg, 0.10 mmol) under
1 atm of N2. Dry dichloroethane (3 mL) and benzene (3 mL) were
added, and then the mixture was magnetically stirred at room
temperature for 5 min. After the N2 atmosphere was replaced by 1 atm
of H2 to transform 7b into 8b, 2 (52 mg, 0.05 mmol) was added
portionwise. The reaction mixture was stirred at room temperature for
24 h under 1 atm of H2. The solvent was then removed under vacuum,
and the residue was dissolved in CDCl3 to measure the 31P{1H} NMR
spectrum. PPh3 (52 mg, 0.20 mmol) was added into the CDCl3 solution
as an internal reference because PPh3 was confirmed not to react with
8b. The NMR yields of the produced complexes were determined by
integration of the gated-{1H}-decoupled 31P resonances against the PPh3
standard. 16b: 31P{1H} NMR (CDCl3): δ 35.0 (d with 183W satellites,
(50) Bruce, M. I.; Humphrey, M. G.; Swincer, A. G.; Wallis, R. C. Aust.
J. Chem. 1984, 37, 1747.
(51) Weatherburn, M. W. Anal. Chem. 1967, 39, 971.

Formation of Ammonia under Mild Reaction Conditions
Inorganic Chemistry, Vol. 39, No. 26, 2000 5957
Table 7. Crystallographic Data for
3220 (N-H). Anal. Calcd for C54H54F6N2O6P4S2W: C, 49.40; H, 4.15;
N, 2.13. Found: C, 49.78; H, 4.39; N, 2.39.
trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf‚(THF)0.5 [19‚(THF)0.5
]
Complex 20 was also prepared from the reaction of 14 with 2 equiv
of 8c under 1 atm of H2. In a 50 mL flask was placed 7c‚(CH2Cl2)0.5
(59 mg, 0.052 mmol) under 1 atm of N2. Dry dichloroethane (3 mL)
and benzene (3 mL) were added, and then the mixture was magnetically
stirred at room temperature for 5 min. After the N2 atmosphere was
replaced by 1 atm of H2 to transform 7c into 8c, 14 (30 mg, 0.029
mmol) was added portionwise. The reaction mixture was stirred at room
temperature for 1 h under 1 atm of H2. The solvent was then evaporated
under vacuum, and the residue was dissolved in CDCl3 to measure the
31P{1H} NMR spectrum. PPh3 (5 mg, 0.02 mmol) was added into the
CDCl3 solution as an internal reference. The NMR yields of the
produced complexes were determined by integration of the gated-{1H}-
decoupled 31P resonances against the standard PPh3. Complexes 20 and
9 were formed in 55% and 199% NMR yields, respectively.
formula
fw
C36H50N2F6O6.50S2P4W
1100.66
0.80 × 0.40 × 0.10
monoclinic
P21/n (No. 14)
brown
11.818(5)
33.978(6)
12.163(4)
109.24(2)
4611(2)
4
1.585
2208.00
28.05
8097
5395
cryst size (mm3)
cryst syst
space group
cryst color
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
d
calc (g cm-1
)
F (000)
µ
calc (cm-1
)
Preparation of trans-[Mo(OTf)(NNH2)(PMe2Ph)4]OTf (21). To
a solution of 13 (71 mg, 0.10 mmol) in toluene (4 mL) was added
HOTf (30 mg, 0.20 mmol) under 1 atm of N2. The reaction mixture
was stirred at room temperature for 5 min. Then, Et2O (8 mL) was
slowly added to the reaction mixture to give 21 (29 mg, 0.030 mmol)
no. of unique data
no. of data used (I > 3σ(I))
no. of params refined
Ra
504
0.039
0.033
1.68
b
Rw
1
goodness of fit indicator
in 30% isolated yield as orange crystals. H NMR (CD2Cl2): δ 1.60
max residuals (e Å-3
)
0.96
(br s, 24H, PMe2Ph), 7.30-7.45 (m, 20H, PMe2Ph), 8.37 (s, 2H, NNH2).
31P{1H} NMR (CD2Cl2): δ -1.80 (s). IR (KBr, cm-1): 3249 (N-H).
Anal. Calcd for C34H46F6MoN2O6P4S2: C, 41.81; H, 4.75; N, 2.87.
Found: C, 41.62; H, 4.90; N, 2.92.
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2
.
2
X-ray Crystallographic Studies. Brown crystals of [19‚(THF)0.5
]
31P{1H} NMR Monitoring of the Reaction of cis-[W(N2)2-
(PMe2Ph)4] (5) with 10 Equiv of trans-[RuCl(η2-H2)(dppe)2]OTf (8c)
under 1 atm of H2. A typical experimental procedure for the reaction
described in Figure 3 is as follows. In a 20 mL flask were placed 7c‚
(CH2Cl2)0.5 (110 mg, 0.10 mmol) and PPh3 (10 mg, 0.04 mmol) as an
internal reference under 1 atm of N2. Dry dichloroethane (1.5 mL) and
C6D6 (0.5 mL) were added, and then the mixture was magnetically
stirred at room temperature. After the N2 atmosphere was replaced by
1 atm of H2 to transform 7c into 8c, 5 (8 mg, 0.01 mmol) was added
portionwise. A part of this homogeneous solution (0.5 mL) was
transferred at room temperature into an NMR tube by syringe. The
31P{1H} NMR spectrum of the reaction mixture after 5 min at room
temperature is shown in Figure 3a. The NMR sample was then kept at
55 °C for 150 min under 1 atm of H2. The time dependence of the
31P{1H} NMR spectrum of the reaction mixture is shown in Figure
3b-f. The NMR yields of the produced complexes were determined
by integration of the gated-{1H}-decoupled 31P resonances against the
standard PPh3.
Reaction of trans-[RuCl(η2-H2)(dppe)2]OTf (8c) with 1 Equiv of
trans-[RuHCl(dppe)2] (9) under 1 atm of H2. In a 50 mL flask was
placed 7c‚(CH2Cl2)0.5 (28 mg, 0.025 mmol) under 1 atm of N2. Dry
dichloroethane (1 mL) and C6D6 (0.5 mL) were added, and then the
mixture was magnetically stirred at room temperature for 5 min. After
the N2 atmosphere was replaced by 1 atm of H2 to transform 7c into
8c, 9 (23 mg, 0.025 mmol) was added portionwise. The reaction mixture
was stirred at room temperature for 1 h under 1 atm of H2. PPh3 (26
mg, 0.10 mmol) was added into the solution as an internal reference.
A part of this homogeneous solution (0.5 mL) was transferred at room
temperature into an NMR tube by syringe. The NMR yields of the
produced complexes were determined by integration of the gated-{1H}-
decoupled 31P resonances against the standard PPh3. 12c: 8% NMR
yield. cis- and trans-[RuCl2(dppe)2]: 8% NMR yield.
Reaction of trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19) with 1
Equiv of trans-[RuHCl(dppe)2] (9) under 1 atm of H2. In a 20 mL
flask were placed 19 (21 mg, 0.02 mmol) and 9 (19 mg, 0.02 mmol)
under 1 atm of H2. Dry THF (1 mL) and C6D6 (0.5 mL) were added,
and then the mixture was magnetically stirred at 55 °C for 24 h. PPh3
(21 mg, 0.08 mmol) was added into the solution as an internal reference.
The NMR yields of the produced complexes were determined by
integration of the gated-{1H}-decoupled 31P resonances against the
standard PPh3. trans-[WCl(NNH2)(PMe2Ph)4]OTf: 31P{1H} NMR δ
-23.4 (s with 183W satellites, JPW ) 277 Hz); 71% NMR yield. 12c:
31P{1H} NMR δ 68.5 (s); 44% NMR yield. 9: 31P{1H} NMR δ 62.5
(s); 25% NMR yield. In addition, unknown Ru compounds were
observed.
suitable for X-ray analysis were obtained by recrystallization from
THF-hexane. The single crystal was sealed in a Pyrex glass capillary
under Ar atmosphere and used for data collection. Diffraction data were
collected on a Rigaku AFC-7R four-circle automated diffractometer at
20 °C. Orientation matrixes and unit cell parameters were determined
by least-squares treatment of 25 reflections with 38.9° < 2θ < 40.0°.
No significant decay was observed for three standard reflections
monitored every 150 reflections during the data collection. Intensity
data were corrected for Lorentz-polarization effects and for absorption
(scans). Details of crystal and data collection parameters are summarized
in Table 7. Structures solution and refinements were carried out by
using the teXsan program package.52 The positions of heavy atoms
were determined by Patterson methods and subsequent Fourier syntheses
(DIRDIF PATTY).53 All non-hydrogen atoms except for those in the
solvating THF molecule were refined anisotropically by full-matrix
least-squares techniques (based on F). The C atoms in the solvating
THF molecule were found at two disordered positions. These C atoms
were refined as rigid groups with occupancies of 50%, respectively.
The hydrogen atoms attached to the N(2) atom were found in the final
difference Fourier map, while other hydrogen atoms were placed at
the calculated positions; these hydrogen atoms were included in the
final stage of refinement with fixed parameters. The atomic scattering
factors were taken from ref 54, and anomalous dispersion effects were
included; the values for ∆f ′ and ∆f ′′ were taken from ref 55.
Acknowledgment. This work was supported by a Grant-
in-Aid for Specially Promoted Research (09102004) from the
Ministry of Education, Science, Sports, and Culture of Japan.
We thank Dr. Dai Masui for assistance with 2H NMR analysis.
Supporting Information Available: An X-ray crystallographic file
in CIF format for the structure determination of 19‚(THF)0.5. This
material is available free of charge via the Internet at http://pubs.acs.org.
IC000799F
(52) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corp.: The Woodlands, TX, 1985 and 1992.
(53) Patty: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W.
P.; Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C.
The DIRDIF Program System; Technical Report of the Crystallography
Laboratory, University of Nijmegen: Nijimegen, The Netherlands,
1992.
(54) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(55) International Tables for X-ray Crystallography; Kluwer Academic
Publishers: Boston, MA, 1992; Vol. C.