Synthesis and structures of tungsten (1-pyridinio)imido complexes and their facile N-N bond cleavage

Article abstract of DOI:10.1021/ic981116n

The tungsten (1-pyridinio)imido complexes [WX₂(NNC₅H₄OMe)(L)(PMe₂Ph) ₂]⁺, [WX₂(NNC₅H₂Me₃)(L)(PMe ₂-Ph)₂]⁺, and [WCl₂{NNC₅H₂(COOEt)₂Ph}(L)(PMe ₂Ph)₂]⁺ (X = Cl, Br; L = CO, C₂H₄, PMe₂Ph) were synthesized by the reaction of the salts of pyrylium cations with the hydrazido complexes [WX₂(NNH₂)(L)(PMe₂Ph)₂], which were derived from the dinitrogen complex cis-[W(N₂)₂(PMe₂Ph)₄]. The complexes obtained were characterized by spectroscopic measurements as well as crystallographic studies of cis,mer-[WBr₂(NNC₅H₄OMe-4)(PMe ₂Ph)₃]-[PF₆], cis,trans-[WCl₂(NNC₅H₄OMe-4)(CO)(PMe ₂Ph)₂][ClO₄], cis,trans-[WCl₂(NNC₅H₂Me ₃-2,4,6)(CO)(PMe₂-Ph)₂][OTf] (OTf = OSO₂CF₃), and cis,trans-[WCl₂(NNC₅H₄OMe-4)(C ₂H₄)(PMe₂Ph)₂][ClO₄], which revealed that the N-N bond distances of these (1-pyridinio)imido complexes are shorter than those of the trialkyl- or unsubstituted hydrazidium complexes so far reported. The (1-pyridinio)imido complexes with a π-acidic ligand (CO or C₂H₄) underwent smooth N-N bond cleavage on reaction with cobaltocene under ambient conditions to liberate the pyridines in moderate to high yields. In some reactions that were conducted in the presence of HNEt₃-Cl, the corresponding imido (NH) complexes were recovered as the metal products. The (1-pyridinio)imido complexes also reacted with KOH in MeOH to give the pyridines and ammonia in high yields. These reactions provide the first examples of N-N bond cleavage of well-defined hydrazidium complexes and accomplish the synthesis of pyridines from molecular nitrogen under mild conditions.

Full text of DOI:10.1021/ic981116n

Inorg. Chem. 1999, 38, 2489-2496
2489
Synthesis and Structures of Tungsten (1-Pyridinio)imido Complexes and Their Facile N-N
Bond Cleavage1
Hiroshige Ishino, Shin’ichi Tokunaga, Hidetake Seino, Youichi Ishii, and Masanobu Hidai*
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo,
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
ReceiVed September 17, 1998
The tungsten (1-pyridinio)imido complexes [WX2(NNC5H4OMe)(L)(PMe2Ph)2]+, [WX2(NNC5H2Me3)(L)(PMe2-
Ph)2]+, and [WCl2{NNC5H2(COOEt)2Ph}(L)(PMe2Ph)2]+ (X ) Cl, Br; L ) CO, C2H4, PMe2Ph) were synthesized
by the reaction of the salts of pyrylium cations with the hydrazido complexes [WX2(NNH2)(L)(PMe2Ph)2], which
were derived from the dinitrogen complex cis-[W(N2)2(PMe2Ph)4]. The complexes obtained were characterized
by spectroscopic measurements as well as crystallographic studies of cis,mer-[WBr2(NNC5H4OMe-4)(PMe2Ph)3]-
[PF6], cis,trans-[WCl2(NNC5H4OMe-4)(CO)(PMe2Ph)2][ClO4], cis,trans-[WCl2(NNC5H2Me3-2,4,6)(CO)(PMe2-
Ph)2][OTf] (OTf ) OSO2CF3), and cis,trans-[WCl2(NNC5H4OMe-4)(C2H4)(PMe2Ph)2][ClO4], which revealed
that the N-N bond distances of these (1-pyridinio)imido complexes are shorter than those of the trialkyl- or
unsubstituted hydrazidium complexes so far reported. The (1-pyridinio)imido complexes with a π-acidic ligand
(CO or C2H4) underwent smooth N-N bond cleavage on reaction with cobaltocene under ambient conditions to
liberate the pyridines in moderate to high yields. In some reactions that were conducted in the presence of HNEt3-
Cl, the corresponding imido (NH) complexes were recovered as the metal products. The (1-pyridinio)imido
complexes also reacted with KOH in MeOH to give the pyridines and ammonia in high yields. These reactions
provide the first examples of N-N bond cleavage of well-defined hydrazidium complexes and accomplish the
synthesis of pyridines from molecular nitrogen under mild conditions.
Introduction
followed by the condensation reaction of the resultant complexes
with organic carbonyl compounds (R1R2CdO). This condensa-
tion reaction provides a versatile method for the CsN bond
formation at the coordinated dinitrogen and enjoys wide
applicability. The diazoalkane ligands thus formed can be
transformed into nitrogenous compounds, such as amines,5b
azines,3a,5b,6 and pyrazoles.5d,e Furthermore, this condensation
method has been extended to the reaction with dialdehydes or
their equivalents to synthesize the complexes with five-
membered heterocyclic ligands, such as (1-pyrrolyl)imido7 and
(phthalimidin-2-yl)imido ligands,8 from which nitrogen hetero-
cycles, including pyrrole, N-aminopyrrole, phthalimidine, and
N-aminophthalimidine, are released in good yields. These results
stimulated us to investigate the construction of a pyridine ring,
another important nitrogen heterocyclic system, by the reaction
Great efforts have been directed toward the activation and
chemical transformation of dinitrogen assisted by transition
metal complexes with the intention not only of understanding
the biological dinitrogen reduction mechanisms but also of
developing a new nitrogen fixation process under mild condi-
tions.2,3 Incorporation of dinitrogen directly into organic sub-
strates by using transition metal dinitrogen complexes is one
of the most fascinating goals in the chemistry of nitrogen
fixation. In this context, we have continuously been investigating
the conversion of ligating dinitrogen into organonitrogen ligands.
Previously, we have shown that facile transformations of
coordinated dinitrogen in molybdenum or tungsten complexes
of the type [M(N2)2(PR3)4] (M ) Mo, W; PR3 ) tertiary
phosphine) into various diazoalkane ligands4 (N2CR1R2) are
realized by the two-step process:5 the protonation of the
dinitrogen complexes leading to the hydrazido(2-) complexes
(4) (a) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. ReV. 1995, 139,
281-311. (b) Hidai, M.; Ishii, Y. Bull. Chem. Soc. Jpn. 1996, 69,
819-831. (c) Sutton, D. Chem. ReV. 1993, 93, 995-1022. (d) Bruce,
M. I.; Goodall, B. L. In The Chemistry of Hydrazido, Azo, and Azoxy
Groups; Patai, S., Ed.; Wiley: London, 1975; Part 1, Chapter 9.
(5) (a) Hidai, M.; Mizobe, Y.; Sato, M.; Kodama, T.; Uchida, Y. J. Am.
Chem. Soc. 1978, 100, 5740-5748. (b) Bevan, P. C.; Chatt, J.; Hidai,
M.; Leigh, G. J. J. Organomet. Chem. 1978, 160, 165-176. (c)
Mizobe, Y.; Uchida, Y.; Hidai, M. Bull. Chem. Soc. Jpn. 1980, 53,
1781-1782. (d) Harada, Y.; Mizobe, Y.; Ishii, Y.; Hidai, M. Bull.
Chem. Soc. Jpn. 1998, 71, 2701-2708. (e) Harada, Y.; Mizobe, Y.;
Hidai, M. J. Organomet. Chem. 1999, 574, 24-31. (f) Harada, Y.;
Mizobe, Y.; Hidai, M. Inorg. Chim. Acta 1999, 285, 336-340.
(6) (a) Watakabe, A.; Takahashi, T.; Jin, D.-M.; Yokotake, I.; Uchida,
Y.; Hidai, M. J. Organomet. Chem. 1983, 254, 75-82. (b) Hidai, M.;
Kurano, M.; Mizobe, Y. Bull. Chem. Soc. Jpn. 1985, 58, 2719-2720.
(7) (a) Seino, H.; Ishii, Y.; Hidai, M. J. Am. Chem. Soc. 1994, 116, 7433-
7434. (b) Seino, H.; Ishii, Y.; Sasagawa, T.; Hidai, M. J. Am. Chem.
Soc. 1995, 117, 12181-12193. (c) Sasagawa, T.; Seino, H.; Ishii, Y.;
Mizobe, Y.; Hidai, M. Bull. Chem. Soc. Jpn. 1999, 72, 425-432.
(8) Seino, H.; Ishii, Y.; Hidai, M. Inorg. Chem. 1997, 36, 161-171.
(1) Preparation and Properties of Molybdenum and Tungsten Dinitrogen
Complexes. 62. Part 61: see ref 7c.
(2) (a) Hidai, M.; Mizobe, Y. Chem. ReV. 1995, 95, 1115-1133. (b)
Gambarotta, S. J. Organomet. Chem. 1995, 500, 117-126. (c)
Bazhenova, T. A.; Shilov, A. E. Coord. Chem. ReV. 1995, 95, 69-
145. (d) Hidai, M.; Mizobe, Y. In Molybdenum Enzymes, Cofactors
and Model Systems; Stiefel, E. I., Coucouvanis, D., Newton, W. E.,
Eds.; American Chemical Society: Washington, DC, 1993; p 346.
(e) Leigh, G. J. Acc. Chem. Res. 1992, 25, 177-181. (f) Hidai, M.;
Mizobe, Y. In Reactions of Coordinated Ligands; Braterman, P. S.,
Ed.; Plenum Press: New York, 1989; Vol. 2, p 53.
(3) For recent examples: (a) Nishibayashi, Y.; Iwai, S.; Hidai, M. Science
1998, 279, 540-542. (b) O’Donoghue, M. B.; Zanetti, N. C.; Davis,
W. M.; Schrock, R. R. J. Am. Chem. Soc. 1997, 119, 2753-2754. (c)
Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science 1997,
275, 1445-1447. (d) Laplaza, C. E.; Johnson, M. J. A.; Peters, J. C.;
Odom, A. L.; Kim, E.; Cummins, C. C.; George, G. N.; Pickering, I.
J. J. Am. Chem. Soc. 1996, 118, 8623-8638.
10.1021/ic981116n CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/29/1999

2490 Inorganic Chemistry, Vol. 38, No. 10, 1999
Ishino et al.
of hydrazido(2-) complexes with the salts of pyrylium cations.
Herein, we describe the synthesis of (1-pyridinio)imido com-
plexes of tungsten from the dinitrogen complex cis-[W(N2)2-
(PMe2Ph)4] (1) by way of the hydrazido(2-) complexes and
the formation of pyridines via the N-N bond cleavage. A part
of this work has been reported as a preliminary communica-
tion.9
respectively, in high yields (eq 2). Addition of the acid was not
essential for this reaction but appreciably improved the yields.
Results and Discussion
Synthesis of Tungsten (1-Pyridinio)imido Complexes from
the Dinitrogen Complex 1. When the hydrazido(2-) complex
cis,mer-[WBr2(NNH2)(PMe2Ph)3] (2),10 which is readily derived
from complex 1 by protonation with hydrobromic acid, was
allowed to react with 4-methoxypyrylium hexafluorophosphate
at room temperature, the corresponding (1-pyridinio)imido
complex cis,mer-[WBr2(NNC5H4OMe-4)(PMe2Ph)3][PF6] (3)
was isolated in moderate yield after recrystallization (eq 1).
However, complex 2 failed to give any isolable product in
reactions with the salts of 2,6-disubstituted pyrylium cations,
and attempts to synthesize the chloro analogue of 3 from cis,-
mer-[WCl2(NNH2)(PMe2Ph)3] (4) were also unsuccessful.
For example, the yield of complex 8b was increased from 54%
to 92% by conducting the reaction in the presence of a catalytic
amount of hydrochloric acid. The hydrazido(2-) complex with
dppe ligands trans-[WF(NNH2)(dppe)2]+ (dppe ) Ph2PCH2CH2-
PPh2) failed to react with all the salts of pyrylium cations
examined. This result is in contrast to our previous observation
that the same complex readily reacts with 2,5-dimethoxytet-
rahydrofuran in the presence of an acid catalyst to give the (1-
pyrrolyl)imido complex.7
In agreement with the formation of (1-pyridinio)imido ligands,
complexes 3, 8, 9, and 10 exhibited strong IR absorptions at
1613-1642 cm-1 characteristic of a pyridinium skeleton. Their
1H NMR and 31P{1H} NMR spectra were also consistent with
1
the formulation. The H NMR spectra of complexes 8b, 8c,
9b, and 9c showed significant temperature dependence, revealing
their dynamic behavior. At 20 °C in CD2Cl2, complex 8b
exhibited a set of singlets at δ 1.98 (6H), 2.36 (3H), and 7.06
(2H) attributable to the 2,6-Me2, 4-Me, and pyridine ring
protons, respectively. Upon cooling to -40 °C or below, the
singlet signal at δ 1.98 split into two singlets (δ 1.83, 1.91).
Similarly, the OCH2 signal of complex 8c and the 2,6-Me2 signal
of 9b were observed as one broad peak at 20 °C (δ 4.56 for 8c
and δ 1.85 for 9b), which started to split at 0 °C into two
quartets (δ 4.51, 4.62) and two singlets (δ 1.64, 1.98),
respectively. Further, the signals due to the 2,6-(COOEt)2 groups
in 9c appeared as two distinct sets of signals (δ 1.41 (br t, 3H),
1.58 (t, 3H), 4.39 (br, 2H), 4.70 (br, 2H)) even at room
temperature. In contrast, the 1H NMR spectrum of complex 9a,
which has a substituent only at the 4-position of the pyridine
ring, did not show pronounced temperature dependence over
the range of 20 to -40 °C. Considering that the complexes with
the larger steric congestion between the substituents on the
pyridine ring and the equatorial ancillary ligands show the higher
Interestingly, the hydrazido(2-) complexes with a sterically
small π-acceptor ligand cis,trans-[WX2(NNH2)(L)(PMe2Ph)2]
(5, X ) Cl, L ) CO; 6, X ) Cl, L ) C2H4; 7, X ) Br, L )
CO),10 which can be prepared by the ligand substitution reaction
of 2 or 4 with L,11 reacted smoothly even with the salts of 2,6-
disubstituted pyrylium cations to form the corresponding (1-
pyridinio)imido complexes. Thus, reactions of 5, 6, and 7 with
various salts of substituted pyrylium cations in the presence of
a small amount of hydrochloric or hydrobromic acid afforded
the corresponding (1-pyridinio)imido complexes 8 (X ) Cl, L
) CO), 9 (X ) Cl, L ) C2H4), and 10 (X ) Br, L ) CO),
(9) Ishii, Y.; Tokunaga, S.; Seino, H.; Hidai, M. Inorg. Chem. 1996, 35,
5118-5119.
(10) In this paper, the complexes formulated as cis,mer-[WX2(NNH2)(PMe2-
Ph)3] and cis,mer-[WX2(NNC5H4OMe-4)(PMe2Ph)3]+ (X ) Cl, Br)
correspond to those containing mutually cis X ligands and three
meridional PMe2Ph ligands. In the same way, the complexes denoted
as cis,trans-[WX2(NNH2)(L)(PMe2Ph)2], cis,trans-[WX2(NNC5H2R12R2)-
(L)(PMe2Ph)2]+, and cis,trans-[WX2(NH)(L)(PMe2Ph)2] (X ) Cl, Br;
L ) CO, C2H4; R1 ) H, Me, COOEt; R2 ) OMe, Me, Ph) correspond
to those in which two X ligands and two PMe2Ph ligands occupy the
cis and trans positions, respectively.
1
coalescence temperatures, it is obvious that these H NMR
behaviors are due to the sterically restricted rotation around the
W-N-N axis.
Crystal Structures of (1-Pyridinio)imido Complexes. The
molecular structures of the (1-pyridinio)imido complexes were
(11) Aoshima, T.; Tamura, T.; Mizobe, Y.; Hidai, M. J. Organomet. Chem.
1992, 435, 85-99.

Tungsten (1-Pyridinio)imido Complexes
Inorganic Chemistry, Vol. 38, No. 10, 1999 2491
Figure 1. ORTEP drawings for the cationic part of 3 (A), 8a′ (B), 8b′ (C), and 9a′‚0.5(CH2Cl2) (D) (hydrogen atoms except for the ethylene
protons of 9a′‚0.5(CH2Cl2) are omitted for clarity).
Table 1. Bond Lengths (Å) and Angles (deg) of 3
Table 2. Bond Lengths (Å) and Angles (deg) of 8a′
W(1)-N(1)
W(1)-P(1)
W(1)-P(2)
W(1)-P(3)
W(1)-Br(1)
W(1)-Br(2)
N(1)-N(2)
1.747(7)
2.539(2)
2.492(2)
2.525(3)
2.565(1)
2.666(1)
1.379(9)
W(1)-N(1)-N(2)
P(1)-W(1)-N(1)
P(2)-W(1)-N(1)
P(3)-W(1)-N(1)
Br(1)-W(1)-N(1)
Br(2)-W(1)-N(1)
170.3(6)
97.8(2)
92.8(2)
93.6(2)
178.8(2)
91.3(2)
W(1)-N(1)
W(1)-P(1)
W(1)-P(2)
W(1)-Cl(1)
W(1)-Cl(2)
W(1)-C(7)
N(1)-N(2)
1.750(4)
2.519(1)
2.516(1)
2.457(1)
2.417(1)
1.987(6)
1.363(4)
W(1)-N(1)-N(2)
P(1)-W(1)-N(1)
P(2)-W(1)-N(1)
Cl(1)-W(1)-N(1)
Cl(2)-W(1)-N(1)
C(7)-W(1)-N(1)
168.8(3)
93.8(1)
98.9(1)
101.0(1)
169.3(1)
89.1(2)
unambiguously determined by X-ray analysis of complexes 3,
cis,trans-[WCl2(NNC5H4OMe)(CO)(PMe2Ph)2][ClO4] (8a′, the
[ClO4]- analogue of 8a), cis,trans-[WCl2(NNC5H2Me3)(CO)-
(PMe2Ph)2][OTf] (8b′, the [OTf]- analogue of 8b; OTf ) OSO2-
CF3), and cis,trans-[WCl2(NNC5H4OMe)(C2H4)(PMe2Ph)2][ClO4]‚
0.5CH2Cl2 (9a′‚0.5CH2Cl2, the [ClO4]- analogue of 9a). Their
ORTEP drawings are shown in Figure 1, and selected bond
distances and angles are listed in Tables 1-4. It is clearly
confirmed that in each case the terminal nitrogen atom in
complex 2, 5, or 6 is incorporated into the respective pyridine
ring with retention of the stereochemistry around the tungsten
center. The W-N-N linkages are essentially linear (168.8(3)-
172.8(6)°), and the N-N bond distances are in the range of
1.363(4)-1.383(8) Å. It should be pointed out that the (1-
pyridinio)imido complexes can be regarded as hydrazidium
complexes (MNNR3+), only a limited number of which have

2492 Inorganic Chemistry, Vol. 38, No. 10, 1999
Table 3. Bond Lengths (Å) and Angles (deg) of 8b′
Ishino et al.
Henderson and co-workers reported that the Mo(II) organohy-
W(1)-N(1)
W(1)-P(1)
W(1)-P(2)
W(1)-Cl(1)
W(1)-Cl(2)
W(1)-C(9)
N(1)-N(2)
1.744(7)
2.532(2)
2.529(2)
2.445(2)
2.451(3)
2.021(9)
1.383(8)
W(1)-N(1)-N(2)
P(1)-W(1)-N(1)
P(2)-W(1)-N(1)
Cl(1)-W(1)-N(1)
Cl(2)-W(1)-N(1)
C(9)-W(1)-N(1)
170.2(5)
91.8(2)
94.8(2)
170.8(2)
102.3(2)
96.2(3)
drazido(2-) complex [Mo{NN(CH2)4CH2}(dppe)2] reacts with
HBr in a nitrile (NCR) solution to give piperidine and the imido
complex trans-[MoBr(NH)(dppe)2]Br and proposed that the
hydrazidium complex trans-[Mo{NNH(CH2)4CH2}(NCR)-
(dppe)2]+ is an intermediate for the N-N bond cleavage on the
basis of kinetic measurements.19 However, none of the isolated
and characterized trialkyl- or unsubstituted hydrazidium com-
plexes has been reported to undergo the N-N bond cleavage.12,13
For example, the N-N bond in [Cp*MoMe3(NNMe3)][OTf]
was not cleaved by reduction with Zn/Hg or cobaltocene.13 It
is hence of great interest to shed light upon the reactivities of
the N-N bond in the (1-pyridinio)imido complexes, a special
type of hydrazidium complexes. Further, fission of the N-N
bond accomplishes the synthesis of pyridines from coordinated
dinitrogen. Therefore, development of a mild and efficient
method for such a N-N bond cleavage is desirable from the
viewpoint of organic synthesis utilizing molecular nitrogen.
The N-N bond cleavage of a hydrazidium complex (MN-
NR3+) to give the corresponding amine (NR3) and a cationic
nitrido complex (MN+) has to formally accompany a two-
electron oxidation of the metal center. Therefore, we envisaged
that reduction of the tungsten(IV) center of complexes 3, 8, 9,
and 10 might cause such reactions. In fact, when complex 8b
was allowed to react with cobaltocene (2.5 equiv) and HNEt3-
Cl (1.5 equiv) in THF at room temperature, a smooth reaction
took place within 1 h to form 2,4,6-trimethylpyridine (11b) in
87% yield, along with a cobaltocenium salt (eq 3). The tungsten
fragment was recovered as the imido complex cis,trans-
[WCl2(NH)(CO)(PMe2Ph)2] (12)10 in 53% yield, which was
characterized crystallographically.
Table 4. Bond Lengths (Å) and Angles (deg) of 9a′‚0.5CH2Cl2
W(1)-N(1)
W(1)-P(1)
W(1)-P(2)
W(1)-Cl(1)
W(1)-Cl(2)
W(1)-C(7)
W(1)-C(8)
N(1)-N(2)
1.738(6)
2.541(2)
2.551(2)
2.436(2)
2.468(3)
2.22(1)
W(1)-N(1)-N(2)
P(1)-W(1)-N(1)
P(2)-W(1)-N(1)
Cl(1)-W(1)-N(1)
Cl(2)-W(1)-N(1)
C(7)-W(1)-C(8)
172.8(6)
93.1(2)
93.9(2)
178.1(2)
94.8(2)
37.5(4)
2.19(1)
1.373(8)
been synthesized so far.12-16 The N-N bond distances found
for the (1-pyridinio)imido complexes 3, 8a′, 8b′, and 9a′ are
shorter than those in crystallographically determined trialkyl-
or unsubstituted hydrazidium complexes, including [WCl-
(NNH3)(PMe3)4]Cl2 (1.396(20) Å),12 [Cp*MoMe3(NNMe3)]-
[OTf] (Cp* ) η5-C5Me5, 1.426(5) Å),13 and [Cp*TaS(StBu)-
t
(NNMe2 Bu)] (1.46(1) Å),14 but are similar to those found in
titanium (1-pyridinio)imido complexes, such as [CpTiCl2-
(NNC5H5)][PF6] (Cp ) η5-C5H5, 1.363(3) Å).16
In the (2,4,6-trimethyl-1-pyridinio)imido complex 8b′, the
pyridine ring takes the conformation coplanar to the Cl(2)-
W(1)-C(9)-O(1) axis, by which steric congestion between the
2,6-disubstituted pyridine ring and the phosphine ligands is
minimized. This conformation is in good agreement with the
dynamic behavior observed in the 1H NMR spectrum of 8b (vide
supra). Interestingly, one of the phenyl groups of the phosphine
ligands in each of 8a′, 8b′, and 9a′ is oriented in almost parallel
with the pyridine ring (dihedral angles 4.6-16.6°), and the
distances between the atoms of these rings are considerably short
(C(1)‚‚‚C(11) in 8a′, 3.382(6) Å; N(2)‚‚‚C(12) in 8b′, 3.45(1)
Å; N(2)‚‚‚C(11) in 9a′, 3.48(1) Å). These features indicate that
the positively charged pyridinium moiety in each complex has
an attractive interaction with the π-electrons of the phenyl group
located nearby.
N-N Bond Cleavage of (1-Pyridinio)imido Complexes:
Reduction with Cobaltocene. Having a series of (1-pyridinio)-
imido complexes in hand, we have investigated their N-N bond
cleavage reactions in detail. In the chemistry of reducing
dinitrogen to ammonia at transition metal centers, the N-N bond
cleavage of NHx-NHy type ligands has been attracting consid-
The molecular structure of complex 12 is depicted in Figure
2, and selected bond distances and angles are listed in Table 5.
The metrical features found for 12 are similar to those reported
for related tungsten imido complexes, such as [WCl2(NCH2-
CHdCH2)(CO)(PPh2Me)2]20 and [WCl2(NPh)(PMe3)3].21 It
should be pointed out that pyridine 11b was also obtained in
high yield by the reduction conducted in the absence of HNEt3-
Cl, but in this case no characterizable tungsten complex except
for a trace amount of 12 was recovered. Therefore, HNEt3Cl is
not essential for the reductive N-N bond cleavage of 8b but
plays a role in protonating the resultant tungsten complex to
give the stable imido complex 12.
erable attention,2,17 and the NNH3 ligand has been proposed
+
as one of the intermediates for such processes.18 Actually,
(12) Galindo, A.; Hills, A.; Hughes, D. L.; Richards, R. L.; Hughes, M.;
Mason, J. J. Chem. Soc., Dalton Trans. 1990, 283-288.
(13) Vale, M. G.; Schrock, R. R. Inorg. Chem. 1993, 32, 2767-2772.
(14) Kawaguchi, H.; Tatsumi, K. Presented at the 1995 International
Chemical Congress of Pacific Basin Societies, Honolulu; INOR-530.
(15) (a) Barclay, J. E.; Hills, A.; Hughes, D. L.; Leigh, G. J.; Macdonald,
C. J.; Bakar, M. A.; Mohd.-Ali, H. J. Chem. Soc., Dalton Trans. 1990,
2503-2507. (b) Glassman, T. E.; Vale, M. G.; Schrock, R. R. J. Am.
Chem. Soc. 1992, 114, 8098-8109. (c) Retbøll, M.; Møller, E. R.;
Hazell, R. G.; Jørgensen, K. A. Acta Chem. Scand. 1995, 49, 278-
290.
(16) Retbøll, M.; Ishii, Y.; Hidai, M. Organometallics 1999, 18, 150-155.
(17) (a) Kuwata, S.; Mizobe, Y.; Hidai, M. Inorg. Chem. 1994, 33, 3619-
3620. (b) Schrock, R. R.; Glassman, T. E.; Vale, M. G.; Kol, M. J.
Am. Chem. Soc. 1993, 115, 1760-1772. (c) Wagenknecht, P. S.;
Norton, J. R. J. Am. Chem. Soc. 1995, 117, 1841-1842. (d) Demadis,
K. D.; Malinak, S. M.; Coucouvanis, D. Inorg. Chem. 1996, 35, 4038-
4046. (e) Malinak, S. M.; Simeonov, A. M.; Mosier, P. E.; McKenna,
C. E.; Coucouvanis, D. J. Am. Chem. Soc. 1997, 119, 1662-1667.
(18) (a) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. ReV. 1978, 78, 8,
589-625. (b) Richards, R. L. Chem. Br. 1988, 24, 133-136.
(19) Henderson, R. A.; Leigh, G. J.; Pickett, C. J. J. Chem. Soc., Dalton
Trans. 1989, 425-430.
(20) Forster, G. D.; Hogarth, G. J. Organomet. Chem. 1994, 471, 161-
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(21) Bradley, D. C.; Hursthouse, M. B.; Malik, K. M. A.; Nielson, A. J.;
Short, R. L. J. Chem. Soc., Dalton Trans. 1983, 2651-2656.

Tungsten (1-Pyridinio)imido Complexes
Inorganic Chemistry, Vol. 38, No. 10, 1999 2493
Table 7. Reaction of (1-Pyridinio)imido Complexes with KOHa
complex
pyridine, yield (%)
yield of NH3 (%)
3
8a′
8b
9a′
9b
10a
10b
11a, 82
11a, 85
11b, 84
11a, 88
11b, 96
11a, 82
11b, 77
92
94
94
100
100
87
85
a Reaction conditions: (1-pyridinio)imido complex, (0.070-0.10
mmol); KOH (10 equiv); MeOH (3 mL); room temperature; 1 h.
N-N bond cleavage of well-characterized hydrazidium com-
plexes. Further, they demonstrate the synthesis of pyridines using
molecular nitrogen as the nitrogen source under ambient
conditions in a well-defined manner. Very recently, we have
also observed that titanium (1-pyridinio)imido complexes, such
as [Cp*TiCl2(NNC5H3Me2-2,6)] and [Cp*Ti(NNC5H3Me2-2,6)-
(terpy)][OTf]2 (terpy ) 2,2′:6′,2′′-terpyridine) undergo the N-N
bond fission on treatment with sodium amalgam and cobal-
tocene, respectively,16 although the (1-pyridinio)imido ligands
in these titanium complexes are not derived from molecular
nitrogen.
Figure 2. An ORTEP drawing for 12 (hydrogen atoms except for the
NH proton are omitted for clarity).
Table 5. Bond Lengths (Å) and Angles (deg) of 12
W(1)-N(1)
W(1)-P(1)
W(1)-P(2)
W(1)-Cl(1)
W(1)-Cl(2)
W(1)-C(1)
1.740(3)
2.509(1)
2.510(1)
2.472(1)
2.509(1)
1.990(5)
P(1)-W(1)-N(1)
P(2)-W(1)-N(1)
Cl(1)-W(1)-N(1)
Cl(2)-W(1)-N(1)
C(1)-W(1)-N(1)
93.9(1)
93.8(1)
105.9(1)
165.8(1)
89.1(2)
As shown in Table 6, complex 3 failed to react with
cobaltocene. To account for the low reactivity of 3, cyclic
voltammograms of some of the (1-pyridinio)imido complexes
were measured. The data obtained are also listed in Table 6.
Complexes 8b, 9b, and 10b, which produced pyridine 11b in
high yield on treatment with cobaltocene, showed irreversible
reduction waves at -0.77, -0.80, and -0.80 V (Ep vs SCE),
respectively. On the other hand, complex 3 had a much more
negative Ep value of -1.10 V. Since the redox potential for the
cobaltocene/cobaltocenium couple is reported to be -0.80 to
-0.98 V vs SCE,22 it is reasonable to conclude that the N-N
bond cleavage of the (1-pyridinio)imido complexes is initiated
by direct electron transfer from cobaltocene, which does not
occur in the case of complex 3. It is still not clear whether the
N-N bond cleavage proceeds on a W(III) or W(II) center. The
reaction of complex 3 with sodium, which is a stronger reducing
agent than cobaltocene, was also investigated, but the formation
of 4-methoxypyridine could not be observed. Complexes 8a and
10a exhibited reduction waves with more negative Ep potentials
(-0.95 to -0.96 V) than those of 8b and 10b. We consider
that both the lower susceptibility to reduction and the higher
coordination ability of 4-methoxypyridine (11a) than those of
11b are responsible for the low yield of 11a from complexes
8a, 9a, and 10a.
Table 6. Reductive N-N Bond Cleavage of (1-Pyridinio)imido
Complexes with Cobaltocenea
complex
pyridine, yield (%)
W product, yield (%)
0
Ep (V)b
3
8a
0c
-1.10
-0.95
-0.77
d
11a, 49
11b, 87
11b, 87
11c, 62
11a, 25
11b, 88
11b, 88
11c, 52
11a, 36
11b, 89
-
12, 53
8b
8be
8c
12, trace
12, 27
nd
nd
-0.80
9af
9bf
9b
-
d
13, 53
13, 25g
13, 23
9cf
10a
10b
nd
-0.96
-0.80
d
-
14, 47
a Reaction conditions: (1-pyridinio)imido complex (0.066-0.11
mmol); Cp2Co (2.5 equiv); HNEt3Cl (1.5 equiv); THF (3 mL); room
temperature; under N2; 1 h. b Peak potentials for irreversible reduction
waves vs SCE in CH2Cl2/0.1 M [Bu4N][BF4]. Scan rate ) 200 mV‚s-1
.
c No reaction. d Uncharacterized solids were obtained. e In the absence
of HNEt3Cl. f Under an ethylene atmosphere. g A small amount of the
imido complex cis,mer-[WCl2(NH)(PMe2Ph)3], which was character-
ized by preliminary crystallographic analysis, was isolated as a by-
product.
Reaction of (1-Pyridinio)imido Complexes with KOH. We
have already revealed that organonitrogen ligands derived from
the coordinated dinitrogen of molybdenum or tungsten com-
plexes can be liberated by treatment with KOH through the
rupture of the M-N (M ) Mo, W) and/or N-N bond.5d,e,6,7b,c,8
Reactions of complexes 3, 8, 9, and 10 with KOH in MeOH
were also found to produce the corresponding pyridine 11
concomitantly with NH3 under ambient conditions (eq 4). The
tungsten species formed could not be characterized. As sum-
marized in Table 7, the yields of pyridines 11 and ammonia
were very high irrespective of the ancillary ligands on the
tungsten center. The selective formation of 11 through the N-N
bond cleavage is in sharp contrast to the reaction of the (1-
pyrrolyl)imido complex [WBr2(NNC4H4)(CO)(PMe2Ph)2] with
KOH in alcohols, where the W-N bond is selectively cleaved.4b
Treatment of 9b with cobaltocene and HNEt3Cl under an
ethylene atmosphere also produced 11b and the imido complex
cis,trans-[WCl2(NH)(C2H4)(PMe2Ph)2] (13)10 in 88% and 53%
yields, respectively. An analogous reaction of 9b under a
nitrogen atmosphere resulted in the formation of 13 in much
lower yield (25%), although the yield of 11b was the same.
Further results for the cobaltocene reduction of (1-pyridinio)-
imido complexes are summarized in Table 6. In the reactions
of (4-methoxy-1-pyridinio)imido complexes 8a, 9a, and 10a,
the tungsten species recovered were paramagnetic and could
not be characterized, while complex 10b underwent partial
halogen exchange on the tungsten center to give [WBrCl(NH)-
(CO)(PMe2Ph)2] (14) as the metal product.
These findings clearly show that the N-N bonds in com-
plexes 8-10 are cleaved under very mild conditions despite
their relatively short N-N bond distances (vide supra), although
the yields of pyridines 11 vary with the substituents on the
pyridine rings. The reactions provide the first examples of the
(22) (a) Gubin, S. P.; Smirnova, S. A.; Denisovich, L. I. J. Organomet.
Chem. 1971, 30, 257-265. (b) Connelly, N. G.; Geiger, W. E. Chem.
ReV. 1996, 96, 877-910.

2494 Inorganic Chemistry, Vol. 38, No. 10, 1999
Ishino et al.
) 370 Hz, P(unique)). IR (KBr) 1634 (s) cm-1. Anal. Calcd for C30H40-
Br2F6N2OP4W: C, 35.11; H, 3.93; N, 2.73. Found: C, 35.03; H, 4.06;
N, 2.81.
Preparation of cis,trans-[WCl2(NNC5H4OMe-4)(CO)(PMe2Ph)2]-
[PF6] (8a). Hydrazido(2-) complex 5 (297.4 mg, 0.50 mmol) and
4-methoxypyrylium hexafluorophosphate (129.0 mg, 0.50 mmol) were
dissolved in THF (5 mL). The mixture was stirred for 8 h at room
temperature, and the resulting solution was evaporated under vacuum
to give a dark green oil. The residual oil was dissolved in CH2Cl2, and
the solution was filtered and diluted with MeOH. Layering the CH2-
Cl2/MeOH solution with ether afforded blue crystals of 8a, which were
collected, washed with ether, and dried in vacuo (216.7 mg, 52% yield).
1H NMR (CD2Cl2) δ 2.05 (t, 6H, J ) 4.5 Hz), 2.25 (t, 6H, J ) 4.3
Hz), 4.01 (s, 3H), 6.65-6.75 (m, 4H), 7.31-7.38 (m, 6H), 7.65-7.70
(m, 4H). 31P{1H} NMR (CD2Cl2) δ -12.9 (s with 183W satellites, JWP
) 271 Hz). IR (KBr) 1966 (s), 1628 (s) cm-1. Anal. Calcd for C23H29-
Cl2F6N2O2P3W: C, 33.40; H, 3.53; N, 3.39. Found: C, 33.31; H, 3.59;
N, 3.16. The corresponding perchlorate salt cis,trans-[WCl2(NNC5H4-
OMe-4)(CO)(PMe2Ph)2][ClO4] (8a′), which was used for the crystal-
lographic study, was obtained similarly from 5 and 4-methoxypyrylium
perchlorate as blue crystals in 60% yield.
Thermal Decomposition of (1-Pyridinio)imido Complexes.
Finally, pyrolysis of the (1-pyridinio)imido complexes was
examined. Complex 3 with three PMe2Ph ligands is of relatively
low thermal stability and decomposed completely on refluxing
in benzene for 2 h to give 11a in 40% yield and an unidentified
tungsten species. In contrast, carbonyl and ethylene complexes
8a, 8b, 9a, 9b, 10a, and 10b are thermally stable and showed
almost no change in refluxing benzene, probably because of
their low tendency to dissociate PMe2Ph ligands. Such difference
in thermal stability provides, in addition to steric reasons, an
explanation why the hydrazido complexes with a π-acceptor
ligand 5, 6, and 7 act as suitable starting materials for the
synthesis of (1-pyridinio)imido complexes in comparison with
complexes 2 and 4.
Preparation of cis,trans-[WCl2(NNC5H2Me3-2,4,6)(CO)(PMe2Ph)2]-
[BF4] (8b). Hydrazido(2-) complex 5 (117.8 mg, 0.20 mmol) and 2,4,6-
trimethylpyrylium tetrafluoroborate (42.1 mg, 0.20 mmol) were dis-
solved in THF (5 mL), and 37% aqueous hydrochloric acid (5 drops)
was added to the solution. The mixture was stirred for 8 h at room
temperature, and then Na[BF4] (110 mg, 1.0 mmol) was added to the
resultant blue solution. The mixture was stirred for further 2 h at room
temperature, and the solvent was evaporated to give a blue oil. The
residual oil was dissolved in CH2Cl2, and the solution was filtered and
diluted with MeOH. Layering the CH2Cl2/MeOH solution with ether
afforded blue crystals of 8b, which were collected, washed with ether,
Experimental Section
General Procedure. All reactions were carried out under a dry
nitrogen atmosphere unless otherwise noted. Solvents were dried by
usual methods and distilled before use. The tungsten hydrazido(2-)
complexes cis,mer-[WX2(NNH2)(PMe2Ph)3] (2, X ) Br; 4, X ) Cl)23
and cis,trans-[WX2(NNH2)(L)(PMe2Ph)2] (5, X ) Cl, L ) CO; 6, X
) Cl, L ) C2H4; 7, X ) Br, L ) CO),11 2,4,6-trimethylpyrylium
tetrafluoroborate,24 2,4,6-trimethylpyrylium triflate,24 2,6-diethoxycar-
bonyl-4-phenylpyrylium tetrafluoroborate,25 4-methoxypyrylium hexaflu-
orophosphate,26 and 4-methoxypyrylium perchlorate26 were prepared
according to the literature methods. Other reagents were commercially
obtained and used without further purification.
1
and dried in vacuo (143.7 mg, 92% yield). H NMR (CD2Cl2) δ 1.98
(s, 6H), 2.01 (t, 6H, J ) 4.3 Hz), 2.16 (t, 6H, J ) 4.3 Hz), 2.36 (s,
3H), 7.06 (br, 2H), 7.15-7.21 (m, 6H), 7.34-7.42 (m, 4H). 31P{1H}
NMR (CD2Cl2) δ -12.8 (s with 183W satellites, JWP ) 271 Hz). IR
(KBr) 1972 (s), 1642 (s) cm-1. Anal. Calcd for C25H33BCl2F4N2-
OP2W: C, 38.44; H, 4.26; N, 3.59. Found: C, 38.37; H, 4.19; N, 3.44.
The corresponding triflate salt cis,trans-[WCl2(NNC5H2Me3-2,4,6)(CO)-
(PMe2Ph)2][OTf] (8b′), which was used for the crystallographic study,
was obtained similarly from 5 and 2,4,6-trimethylpyrylium triflate as
blue crystals in 77% yield.
Caution! Perchlorate salts are potentially explosive and should be
handled in small quantities.
NMR spectra were recorded on a JEOL JNM-EX-270 spectrometer
(1H, 270 MHz; 31P, 109 MHz), and IR spectra were recorded on a
Shimadzu FTIR-8100M spectrophotometer. Amounts of the solvent
molecules in the crystals were determined not only by elemental
analyses but also by 1H NMR spectroscopy. Quantitative GC analyses
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. Electrochemical measurements were made with
Hokuto Denko instrumentation (HA-501 potentiostat and a HB-105
function generator), by using a glassy carbon working electrode;
potentials were measured in CH2Cl2/0.1 M [Bu4N][BF4] vs an SCE.
GC-MS analyses (70 eV) were carried out on a Shimadzu GC-MS
QP-2000 spectrometer. Elemental analyses were performed on a Perkin-
Elmer 2400 series II CHN analyzer.
Preparation of cis,mer-[WBr2(NNC5H4OMe-4)(PMe2Ph)3][PF6]
(3). Hydrazido(2-) complex 2 (114.4 mg, 0.13 mmol) and 4-meth-
oxypyrylium hexafluorophosphate (33.9 mg, 0.13 mmol) were dissolved
in THF (2 mL), and the mixture was stirred for 2 h at room temperature.
The resulting reaction mixture was evaporated under vacuum to give
a dark red oil. Recrystallization from ClCH2CH2Cl/MeOH/ether af-
forded brown crystals of 3, which were collected, washed with ether,
and dried in vacuo (58.6 mg, 43% yield). 1H NMR (CD2Cl2) δ 1.79 (t,
6H, J ) 3.9 Hz), 1.90 (d, 6H, J ) 8.6 Hz), 2.06 (t, 6H, J ) 3.9 Hz),
4.01 (s, 3H), 6.72 (d, 2H, J ) 7.4 Hz), 7.01 (d, 2H, J ) 7.4 Hz),
7.23-7.74 (m, 15H). 31P{1H} NMR (CD2Cl2) δ -31.6 (s with 183W
satellites, JWP ) 284 Hz, P(trans)), -27.3 (s with 183W satellites, JWP
Preparation of cis,trans-[WCl2{NNC5H2(COOEt)2-2,6-Ph-4}-
(CO)(PMe2Ph)2][BF4] (8c). Hydrazido(2-) complex 5 (117.8 mg, 0.20
mmol) and 2,6-diethoxycarbonyl-4-phenylpyrylium tetrafluoroborate
(77.6 mg, 0.20 mmol) were dissolved in THF (5 mL), and 37% aqueous
hydrochloric acid (5 drops) was added to the solution. The mixture
was stirred for 1 h at room temperature, during which period of time
a green solid precipitated. Addition of hexane to the mixture deposited
an additional quantity of the product. The precipitate was filtered,
washed with hexane, and recrystallized from CH2Cl2/ether to afford
green crystals of 8c, which were collected, washed with ether, and dried
in vacuo (115.1 mg, 60% yield). 1H NMR (CD2Cl2) δ 1.48 (t, 6H, J )
7.1 Hz), 2.07 (t, 6H, J ) 4.6 Hz), 2.12 (t, 6H, J ) 4.3 Hz), 4.56 (br,
4H), 7.15-7.30 (m, 6H), 7.51-7.75 (m, 8H), 7.94 (d, 2H, J ) 7.2
Hz), 8.03 (br, 1H). 31P{1H} NMR (CD2Cl2) δ -12.3 (s with 183W
satellites, JWP ) 269 Hz). IR (KBr) 1991 (s), 1744 (s), 1613 (s) cm-1
.
Anal. Calcd for C34H39BCl2F4N2O5P2W: C, 42.57; H, 4.10; N, 2.92.
Found: C, 42.79; H, 4.14; N, 2.86.
Preparation of cis,trans-[WCl2(NNC5H4OMe-4)(C2H4)(PMe2Ph)2]-
[PF6]‚0.5(CH2Cl2) (9a‚0.5(CH2Cl2)). Complex 9a‚0.5(CH2Cl2) was
prepared from complex 6 and 4-methoxypyrylium hexafluorophosphate
by a similar procedure to that described for complex 8a and isolated
1
as orange crystals in 74% yield. H NMR (CDCl3) δ 2.10-2.15 (m,
12H), 2.40-2.45 (m, 2H), 2.85-2.87 (m, 2H), 4.04 (s, 3H), 6.73 (d,
2H, J ) 6.3 Hz), 7.29 (d, 2H, J ) 6.3 Hz), 7.14-7.30 (m, 6H), 7.51-
7.54 (m, 4H). 31P{1H} NMR (CDCl3) δ -11.4 (s with 183W satellites,
JWP ) 219 Hz). IR (KBr) 1632 (s) cm-1. Anal. Calcd for C24.5H34-
Cl3F6N2OP3W: C, 33.84; H, 3.94; N, 3.22. Found: C, 33.75; H, 4.05;
N, 3.01. The corresponding perchlorate salt cis,trans-[WCl2(NNC5H4-
OMe-4)(C2H4)(PMe2Ph)2][ClO4]‚0.5(CH2Cl2) (9a′‚0.5(CH2Cl2)), which
(23) Chatt, J.; Pearman, A. J.; Richards, R. L. J. Organomet. Chem. 1975,
101, C45-C47.
(24) Praill, P. F. G.; Whitear, A. L. J. Chem. Soc. 1961, 3573-3579.
(25) Katritzky, A. R.; Prout, A.; Agha, B. J.; Alajarin-Ceron, M. Synthesis
1981, 959-961.
(26) Hafner, K.; Kaiser, H. Liebigs Ann. Chem. 1958, 618, 140-152.

Tungsten (1-Pyridinio)imido Complexes
Inorganic Chemistry, Vol. 38, No. 10, 1999 2495
was used for the crystallographic study, was obtained similarly from 6
and 4-methoxypyrylium perchlorate as orange crystals in 84% yield.
Preparation of cis,trans-[WCl2(NNC5H2Me3-2,4,6)(C2H4)(PMe2Ph)2]-
[BF4] (9b). Complex 9b was prepared from complex 6 and 2,4,6-
trimethylpyrylium tetrafluoroborate by a similar procedure to that
described for complex 8b and isolated as orange crystals in 93% yield.
1H NMR (CD2Cl2) δ 1.85 (br, 6H), 2.10 (t, 12H, J ) 4.5 Hz), 2.36 (s,
3H), 2.47-2.59 (m, 4H), 6.99 (br, 2H), 7.15-7.26 (m, 6H), 7.30-
7.38 (m, 4H). 31P{1H} NMR (CD2Cl2) δ -10.5 (s with 183W satellites,
JWP ) 219 Hz). IR (KBr) 1640 (s) cm-1. Anal. Calcd for C26H37B-
Cl2F4N2P2W: C, 39.98; H, 4.77; N, 3.59. Found: C, 39.74; H, 4.72;
N, 3.54.
mg, 0.18 mmol), and HNEt3Cl (14.5 mg, 0.11 mmol) were dissolved
in THF (3 mL), and the mixture was stirred for 1 h at room temperature.
Then, the volatile materials formed were collected by means of a cold
trap. Their GC and GC-MS analyses indicated that 2,4,6-trimethyl-
pyridine was formed in 87% yield. The residual solid was recrystallized
from THF/hexane to give cis,trans-[WCl2(NH)(CO)(PMe2Ph)2] (12)
as brown crystals, which were collected, washed with hexane, and dried
in vacuo (21.2 mg, 53% yield). 1H NMR (CD2Cl2) δ 1.93 (t, 6H, J )
4.1 Hz), 1.98 (t, 6H, J ) 4.1 Hz), 7.37-7.46 (m, 6H), 7.62-7.69 (m,
4H). NH signal could not be found. 31P{1H} NMR (CD2Cl2) δ -10.0
(s with 183W satellites, JWP ) 292 Hz). IR (KBr) 3245 (s), 1975 (s)
cm-1. Anal. Calcd for C17H23Cl2NOP2W: C, 35.57; H, 4.04; N, 2.44.
Found: C, 35.97; H, 4.05; N, 2.37.
Preparation of cis,trans-[WCl2{NNC5H2(COOEt)2-2,6-Ph-4}-
(C2H4)(PMe2Ph)2][BF4] (9c). Complex 9c was prepared from complex
6 and 2,6-diethoxycarbonyl-4-phenylpyrylium tetrafluoroborate by a
similar procedure to that described for complex 8c and isolated as green
Reduction of 9b by a similar procedure under an ethylene atmosphere
afforded 2,4,6-trimethylpyridine as a volatile product (88% yield) and
cis,trans-[WCl2(NH)(C2H4)(PMe2Ph)2] (13) as a pale green solid (53%
yield). 13: 1H NMR (CD2Cl2) δ 1.57-1.60 (m, 2H), 1.73-1.74 (m,
2H), 1.96 (t, 6H, J ) 4.5 Hz), 2.05 (t, 6H, J ) 4.3 Hz), 5.53 (s, 1H),
7.36-7.43 (m, 6H), 7.53-7.60 (m, 4H). 31P{1H} NMR (CD2Cl2) δ
1
crystals in 78% yield. H NMR (CD2Cl2) δ 1.41 (br t, 3H, J ) 6.2
Hz), 1.58 (t, 3H, J ) 6.9 Hz), 2.08 (t, 6H, J ) 4.5 Hz), 2.15 (t, 6H, J
) 4.7 Hz), 2.28 (br, 2H), 2.38 (br, 2H), 4.39 (br, 2H), 4.70 (br, 2H),
7.18-7.28 (m, 6H), 7.51-7.94 (m, 11H). 31P{1H} NMR (CD2Cl2) δ
-9.7 (s with 183W satellites, JWP ) 217 Hz). IR (KBr) 1715 (s), 1613
(s) cm-1. Anal. Calcd for C35H43BCl2F4N2O4P2W: C, 43.82; H, 4.52;
N, 2.92. Found: C, 43.76; H, 4.54; N, 2.83.
-7.6 (s with 183W satellites, JWP ) 236 Hz). IR (KBr) 3206 (s) cm-1
.
Anal. Calcd for C18H27Cl2NP2W: C, 37.66; H, 4.74; N, 2.44. Found:
C, 37.79; H, 4.74; N, 2.39.
Reduction of the (1-Pyridinio)imido Complexes 8c and 9c with
Cobaltocene. Complex 8c (89.0 mg, 0.093 mmol), cobaltocene (43.8
mg, 0.23 mmol), and HNEt3Cl (19.0 mg, 0.14 mmol) were dissolved
in THF (3 mL), and the mixture was stirred for 1 h at room temperature.
Then the solvent was removed under reduced pressure, and the residue
was extracted with ether. The ether solution was concentrated under
reduced pressure until white-green powder began to precipitate.
Addition of hexane to the concentrated extract gave 2,6-diethoxycar-
bonyl-4-phenylpyridine as a slightly greenish solid, which was collected
by filtration, washed with hexane, and dried in vacuo (17.3 mg, 62%
yield). The solid insoluble in ether was recrystallized from THF/hexane
to give complex 12 (14.4 mg, 27% yield). A similar reaction of 9c
with cobaltocene under an ethylene atmosphere afforded 2,6-diethoxy-
carbonyl-4-phenylpyridine and complex 13 in 52% and 23% yields,
respectively.
Reduction of the (1-Pyridinio)imido Complexes 10b with Co-
baltocene. Complex 10b (57.3 mg, 0.066 mmol), cobaltocene (30.2
mg, 0.16 mmol), and HNEt3Cl (13.6 mg, 0.099 mmol) were dissolved
in THF (3 mL), and the mixture was stirred for 1 h at room temperature.
Then the volatile materials formed were collected by means of a cold
trap, and their GC and GC-MS analyses indicated that 2,4,6-
trimethylpyridine was formed in 89% yield. The residual solid was
recrystallized from THF/hexane to give [WBrCl(NH)(CO)(PMe2Ph)2]
(14) as brown crystals, which were collected, washed with hexane, and
dried in vacuo (19.2 mg, 47%). 1H NMR (CD2Cl2) δ 2.03 (t, 6H, J )
4.1 Hz), 2.09 (t, 6H, J ) 4.1 Hz), 7.35-7.44 (m, 6H), 7.61-7.70 (m,
4H). NH signal could not be found. 31P{1H} NMR (CD2Cl2) δ -17.4
(s with 183W satellites, JWP ) 290 Hz). IR (KBr) 3250 (s), 1975 (s)
cm-1. Anal. Calcd for C17H23BrClNOP2W: C, 33.01; H, 3.75; N, 2.26.
Found: C, 32.71; H, 3.67; N, 2.31.
Preparation of cis,trans-[WBr2(NNC5H4OMe-4)(CO)(PMe2Ph)2]-
[PF6] (10a). Hydrazido(2-) complex 7 (135.6 mg, 0.20 mmol) and
4-methoxypyrylium hexafluorophosphate (51.6 mg, 0.20 mmol) were
dissolved in THF (2 mL), and 47% aqueous hydrobromic acid (2 drops)
was added to the solution. The mixture was stirred for 21 h at room
temperature. K[PF6] (368 mg, 2.0 mmol) was added to the resultant
blue solution, and the mixture was stirred for 2 h further. The blue oil
obtained by evaporation of the solvent was dissolved in CH2Cl2, and
the solution was filtered. Addition of MeOH and ether to the CH2Cl2
solution afforded blue crystals of 10a, which were collected, washed
1
with ether, and dried in vacuo (84.3 mg, 46% yield). H NMR (CD2-
Cl2) δ 2.14 (t, 6H, J ) 4.6 Hz), 2.31 (t, 6H, J ) 4.3 Hz), 4.00 (s, 3H),
6.69 (d, 2H, J ) 7.6 Hz), 6.77 (d, 2H, J ) 7.6 Hz), 7.26-7.32 (m,
6H), 7.56-7.68 (m, 4H). 31P{1H} NMR (CD2Cl2) δ -20.5 (s with 183
W
satellites, JWP ) 268 Hz). IR (KBr) 1991 (s), 1626 (s) cm-1. Anal.
Calcd for C23H29Br2F6N2O2P3W: C, 30.16; H, 3.19; N, 3.06. Found:
C, 30.17; H, 3.13; N, 2.96.
Preparation of cis,trans-[WBr2(NNC5H2Me3-2,4,6)(CO)(PMe2Ph)2]-
[BF4] (10b). Hydrazido(2-) complex 7 (136.0 mg, 0.20 mmol) and
2,4,6-trimethylpyrylium tetrafluoroborate (41.9 mg, 0.20 mmol) were
dissolved in THF (3 mL) and 47% aqueous hydrobromic acid (2 drops)
was added to the solution. The mixture was stirred for 14 h at room
temperature, and then Na[BF4] (220 mg, 2.0 mmol) was added to the
resultant blue solution. The mixture was stirred for 2 h further at room
temperature, filtered, and evaporated to dryness to give a blue oil. The
residual oil was dissolved in CH2Cl2, and the solution was filtered and
diluted with MeOH. Layering this CH2Cl2/MeOH solution with ether
afforded blue crystals of 10b, which were collected, washed with ether,
1
and dried in vacuo (133.3 mg, 77% yield). H NMR (CD2Cl2) δ 1.98
(s, 6H), 2.14 (t, 6H, J ) 4.6 Hz), 2.28 (t, 6H, J ) 4.3 Hz), 2.34 (s,
3H), 7.20-7.24 (m, 8H), 7.41-7.48 (m, 4H). 31P{1H} NMR (CD2Cl2)
δ -21.0 (s with 183W satellites, JWP ) 268 Hz). IR (KBr) 1977 (s),
1626 (s) cm-1. Anal. Calcd for C25H33BBr2F4N2OP2W: C, 34.52; H,
3.82; N, 3.22. Found: C, 34.41; H, 3.88; N, 3.01.
Reduction of (1-Pyridinio)imido Complexes 8a, 9a, and 10a with
Cobaltocene. The following account is a representative procedure.
Complex 8a (82.2 mg, 0.099 mmol), cobaltocene (47.0 mg, 0.25 mmol),
and HNEt3Cl (20.6 mg, 0.15 mmol) were dissolved in THF (3 mL)
under a nitrogen atmosphere, and the mixture was stirred for 1 h at
room temperature. The volatile products were collected by means of a
cold trap, and their GC and GC-MS analyses indicated that 4-meth-
oxypyridine was formed in 49% yield. The tungsten species was
recovered as an unidentified red solid.
Reaction of the (1-Pyridinio)imido Complexes with KOH. The
following account is a representative procedure. To a suspension of
complex 8b (55.0 mg, 0.070 mmol) in MeOH (3 mL) was added KOH
(10 equiv), and the mixture was stirred for 1 h at room temperature.
Organic volatile products were collected by means of a cold trap, and
their GC-MS and quantitative GC analyses revealed that 2,4,6-
trimethylpyridine was formed in 84% yield. In a separate run, the
reaction mixture was distilled under reduced pressure, and the distillate
was trapped in aqueous H2SO4, which was used for the determination
of ammonia (94% yield, indophenol method).
Pyrolysis of (1-Pyridinio)imido Complexes. In a typical run, a
suspension of complex 3 (28.7 mg, 0.028 mmol) in benzene (2 mL)
was refluxed for 2 h. The initial brown suspension gradually changed
to a pale brown solution. Organic volatile products were collected by
means of a cold trap under vacuum and analyzed by GC and GC-
MS, which indicated that 4-methoxypyridine was formed in 40% yield.
The tungsten species formed could not be characterized. Complexes
8a, 8b, 9a, 9b, 10a, and 10b were recovered unchanged after similar
treatment.
A similar reaction of 9a under an ethylene atmosphere and a reaction
of 10a under a nitrogen atmosphere gave 4-methoxypyridine in 25%
and 36% yields, respectively.
Reduction of the (1-Pyridinio)imido Complexes 8b and 9b with
Cobaltocene. Complex 8b (55.0 mg, 0.070 mmol), cobaltocene (33.5

2496 Inorganic Chemistry, Vol. 38, No. 10, 1999
Ishino et al.
Table 8. Crystallographic Data for 3, 8a′, 8b′, 9a′‚0.5CH2Cl2, and 12
3
8a′
8b′
9a′‚0.5CH2Cl2
12
formula
formula weight
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C30H40Br2F6N2OP4W
1026.20
P21/c
9.593(1)
30.315(4)
13.708(2)
90
108.66(1)
90
3777.0(9)
4
C23H29Cl2N2O6P2W
781.65
P1h
C26H33Cl2F3N2O4P2SW
843.32
P21/n
8.823(4)
34.939(5)
10.729(3)
90
93.58(3)
90
3301(1)
4
1.697
38.75
0.041
0.027
C24.5H34Cl4N2O5P2W
824.16
C2/c
20.266(2)
10.502(1)
30.363(2)
90
96.012(7)
90
6426.9(10)
8
C17H23Cl2NOP2W
574.08
P21/a
13.0529(8)
9.985(2)
18.070(1)
90
110.755(4)
90
2202.2(4)
4
10.068(1)
10.756(1)
14.323(2)
98.640(10)
96.330(9)
96.472(9)
1510.7(3)
2
1.718
42.37
0.032
0.029
Z
d
calc (g cm-3
)
1.805
54.10
0.044
0.035
1.703
40.66
0.044
0.027
1.731
56.43
0.027
0.018
µ
calc (cm-1
)
Ra
b
Rw
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2, w ) 1/σ2(Fo).
2
Crystallography. Crystals of 3, 8a′, 8b′, 9a′‚0.5(CH2Cl2), and 12
suitable for X-ray analyses were sealed in Pyrex glass capillaries under
an argon atmosphere and used for data collection. Diffraction data were
collected on a Rigaku AFC-7R four-circle automated diffractometer
with Mo KR (λ ) 0.710 69 Å) radiation and a graphite monochromator
at 20 ( 1 °C, using the ω scan technique (5 < 2θ < 55) for 3, 8b′,
and 9a′‚0.5(CH2Cl2), and the ω-2θ scan technique (5 < 2θ < 55) for
8a′ and 12. Accurate cell dimensions of each crystal were determined
by least-squares refinement of 25 machine-centered reflections. Empiri-
cal absorption correction based on ψ scans and Lorentz-polarization
correction were applied. For all crystals, no significant decay was
observed for the respective three standard reflections during the data
collection. Details of the X-ray diffraction study are summarized in
Table 8. The structure solution and refinements were performed by
using the TEXSAN program package.27 The structures were solved by
a combination of heavy-atom Patterson methods (DIRDIF PATTY27)
and Fourier techniques. All non-hydrogen atoms were found from the
difference Fourier maps and refined by full-matrix least-squares
techniques with anisotropic thermal parameters. The C2H4 hydrogens
in 9a′‚0.5(CH2Cl2) and the NH hydrogen in 12 were found in the
difference Fourier map, while the other hydrogen atoms were placed
at the calculated positions. All the hydrogen atoms were included in
the refinements with fixed isotropic parameters.
Acknowledgment. This work was supported by a Grant-
in-Aid for Specially Promoted Research (09102004) from the
Ministry of Education, Science, Sports, and Culture, Japan.
Supporting Information Available: X-ray crystallographic files
in CIF format are available for 3, 8a′, 8b′, 9a′‚0.5CH2Cl2, and 12.
Supporting Information is available free of charge via the Internet at
http://pubs.acs.org.
IC981116N
(27) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. 1992. The
DIRDIF program system, Technical Report of the Crystallography
Laboratory, The University of Nijmegen, The Netherlands.