Preparation and reactions of molybdenum and tungsten hydride complexes containing the tetraphosphane ligand meso-o-C6H 4(PPhCH2CH2PPh2)2

Article abstract of DOI:10.1002/ejic.201000855

The reaction of [Mo(κ²-dppe)(κ⁴-P4)] (1a) {dppe = PPh₂CH₂CH₂PPh₂, P4 = meso-o-C₆H₄(PPhCH₂CH₂PPh ₂)₂} with 1 atm of H₂ at room temperature selectively gave [MoH₂(κ²-dppe)(κ³- P4)] (3a). The W analogue of 1a reacted with 1 atm of H₂ at 80 °C to form a mixture of [WH₂(κ²-dppe) (κ³-P4)] and [WH₄(κ⁴-P4)] (5b), the latter of which could be cleanly prepared by the reduction of [WBr ₂(κ⁴-P4)] with NaBH₄ in ethanol at 50 °C. The molecular structure of complex 5b differed from that of the related complex [WH₄(dppe)₂] and showed much higher reactivity. Insertion into the W-H bonds took place in the reaction of 5b with CS ₂ at 50 °C to give the methylenedithiolate complex [W(κ²-S₂CH₂)(κ⁴-P4)] (6) as the sole product, and the hydride ligands in 5b were replaced by isocyanides at 80 °C to form [W(CNR)₂(κ⁴-P4)] {R = tBu (7), 2,6-Me₂C₆H₃ (8)} in moderate yields. The detailed structures were determined by X-ray crystallography for 3a, 5b, 6, and 7, while the fluxional behavior of 3a in solution was clarified by variable-temperature NMR (VT NMR) spectroscopic studies. Reaction of [WBr ₂(κ⁴-P4)] {P4 = meso-o-C₆H ₄(PPhCH₂CH₂PPh₂)₂} with NaBH₄ in ethanol at 50 °C forms [WH₄(κ ⁴-P4)], which is one of the rare examples of a polyhydride complex containing a tetraphosphane co-ligand. Structure determination by single-crystal X-ray analysis and the reactivity of the complex towards CS₂ and RNC are reported. Copyright

Full text of DOI:10.1002/ejic.201000855

FULL PAPER
DOI: 10.1002/ejic.201000855
Preparation and Reactions of Molybdenum and Tungsten Hydride Complexes
Containing the Tetraphosphane Ligand meso-o-C6H4(PPhCH2CH2PPh2)2
Qi Xiu Dai,[a] Hidetake Seino,*[a] and Yasushi Mizobe*[a]
Keywords: Molybdenum / Tungsten / Phosphane ligands / Hydride ligands
The reaction of [Mo(κ2-dppe)(κ4-P4)] (1a) {dppe
=
the W–H bonds took place in the reaction of 5b with CS2 at
50 °C to give the methylenedithiolate complex [W(κ2-
S2CH2)(κ4-P4)] (6) as the sole product, and the hydride li-
gands in 5b were replaced by isocyanides at 80 °C to form
[W(CNR)2(κ4-P4)] {R = tBu (7), 2,6-Me2C6H3 (8)} in moderate
yields. The detailed structures were determined by X-ray
crystallography for 3a, 5b, 6, and 7, while the fluxional be-
havior of 3a in solution was clarified by variable-temperature
NMR (VT NMR) spectroscopic studies.
PPh2CH2CH2PPh2, P4 = meso-o-C6H4(PPhCH2CH2PPh2)2}
with 1 atm of H2 at room temperature selectively gave
[MoH2(κ2-dppe)(κ3-P4)] (3a). The W analogue of 1a reacted
with 1 atm of H2 at 80 °C to form a mixture of [WH2(κ2-dppe)-
(κ3-P4)] and [WH4(κ4-P4)] (5b), the latter of which could be
cleanly prepared by the reduction of [WBr2(κ4-P4)] with
NaBH4 in ethanol at 50 °C. The molecular structure of com-
plex 5b differed from that of the related complex [WH4-
(dppe)2] and showed much higher reactivity. Insertion into
cause it generates highly reactive 16e or 14e species by liber-
ating one or two mol of H2 either thermally or on irradia-
tion.[6,7] The ability to liberate two H2 and, presumably, the
role of the dppe ligand in protecting the coordinatively un-
saturated intermediates from decomposition, enable the di-
verse chemistry. Although it is expected that polydentate
phosphanes bring about higher stabilization or a different
kind of steric effect, molybdenum and tungsten polyhydride
complexes containing polyphosphanes are quite rare. As far
as we know, there are some precedents with tridentate phos-
phanes,[8] but none of the tetrahydride complexes contain-
ing tetradentate phosphanes are known. Only a class of mo-
lybdenum trihydride complexes with the pentadentate li-
gand comprised of a P–P–E–P–P framework (E = Si,
Ge)[9] and the isoelectronic complex [ReH4(meso-
Ph2PCH2CH2PPhCH2CH2PPhCH2CH2PPh2)]+ have been
reported.[10]
Introduction
Transition-metal polyhydride complexes have been at-
tracting much attention because of their intriguing struc-
tures and unusual reactions.[1,2] The reactivity types of the
polyhydride complexes are not limited to those of the com-
mon hydride complexes because of their ability to generate
coordinatively unsaturated intermediates by the reductive
elimination of H2. Polyhydride complexes containing terti-
ary phosphanes as stabilizing ligands have been extensively
studied. Although a large number of polyhydride complexes
of monodentate and bidentate phosphane ligands are
known, examples of polyhydride complexes having a tri- or
tetraphosphane ancillary ligand are still limited. However,
some of the advantages of chelating polyphosphanes have
been discussed. For instance, [WH6(triphos)] {triphos =
PhP(CH2CH2PPh2)2}[3] exhibits catalytic activity for the
dehydrogenation of cyclooctane, which cannot be attained
by the W monophosphane hexahydride complexes such
as [WH6(PMe2Ph)3]. The complexes [ReH6{PhP(CH2CH2-
CH2PcHex2)2}]+ [4] and [ReH6(triphos)]+ [5] are remarkably
resistant to the loss of H2 in sharp contrast to their mono-
phosphane analogues.
We have previously discovered that when the dinitrogen
complexes trans-[M(N2)2(dppe)2] (M = Mo, W) are heated
in the presence of tertiary phosphanes under an argon
atmosphere
the
tetraphosphane
ligand
meso-o-
C6H4(PPhCH2CH2PPh2)2 (P4) is readily formed by the
condensation of two dppe ligands in the coordination
sphere of the low-valent Mo and W complexes.[11] These
reactions with dppe give [M(κ2-dppe)(κ4-P4)] {M = Mo
(1a), W (1b)} in moderate yield. These complexes serve as
good precursors to various P4 complexes of Mo and W.
The P4 ligand in these complexes shows characteristic bind-
ing modes arising from the unique structure of P4. Because
each five-membered chelate ring is strained by the P–M–P
angle, which is much smaller than 90°, κ4-coordination of
P4 accumulatively causes severe deviation from a regular
The chemistry of molybdenum and tungsten polyhydride
complexes containing phosphane ligands has been devel-
oped over four decades. Among these complexes, the tetra-
hydride complex with diphosphane ligands, [MoH4(dppe)2]
(dppe = PPh2CH2CH2PPh2), is a well studied example be-
[a] Institute of Industrial Science, The University of Tokyo,
Komaba, Meguro-ku, Tokyo 153-8505, Japan
Fax: +81-3-5452-6361
E-mail: seino@iis.u-tokyo.ac.jp
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Q. X. Dai, H. Seino, Y. Mizobe
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octahedron. An uncommon trigonal prismatic structure has dissociated from the metal (Figure 1). The geometry around
been found for [MX2(κ4-P4)] {X = Cl, M = Mo; X = Br, the Mo is a distorted pentagonal bipyramid, like that of
M = Mo (2a), W (2b)}, which is in sharp contrast to the the related complex [MoH2(PMe3)5].[14] The axial sites are
octahedral geometry of trans-[MX2(tertiary phos- occupied by one of the internal phosphorus atoms in P4
phane)4].[12] This structural distortion also facilitates disso- and one in the dppe [P(2)–Mo–P(5) is 174.56(8)°], and the
ciation of one or two terminal P atoms of P4 to take a κ3- other coordinated phosphorus atoms P(1), P(3), and P(6)
or κ2-coordination mode, and various donor molecules can comprise three corners of the pentagonal plane. In compari-
be incorporated into the resulting open sites.[13] Therefore, son to the P(1)–Mo–P(6) angle of 89.82(9)°, the P(1)–Mo–
although it is speculated that the electron-donating proper- P(3) angle of 124.00(9)° and the P(3)–Mo–P(6) angle of
ties and the steric bulk of the ligands in the [M(P4)] and 144.66(8)° are considerably larger, and the peaks of electron
the [M(dppe)2] chromophores will be almost similar, the P4 density assigned to the two hydride ligands H(67) and
complexes are expected to present unique structures and H(68) are found almost at the middle of these two sites,
reactivity that are distinct from those of the dppe com- respectively.
plexes. We aimed to prepare Mo and W polyhydride com-
plexes containing P4 as the co-ligand. A synthetic method
for the W tetrahydride complex has been successfully devel-
oped and its reactivity towards some small molecules has
been examined.
Results and Discussion
Reaction of 1a with H2
A stirred suspension of 1a in thf or an aromatic hydro-
carbon solvent under a H2 atmosphere (1 atm) at room tem-
perature gave the dihydride complex [MoH2(κ2-dppe)(κ3-
P4)] (3a) (Scheme 1). Complex 3a was stable up to 80 °C in
solution even under a N2 atmosphere. In contrast, it has
been reported that the κ3-triphosphane complex [MoH2(tri-
phos)(PMe2Ph)2] loses H2 from its solid state at room tem-
perature under 1 atm of N2 to give [Mo(N2)(triphos)-
(PMe2Ph)2].[8a] Complex 3a was converted into [Mo{(η6-
Ph)PPhCH2CH2PPh2}(κ3-P4)] (4a) by heating under reflux
in toluene. Complex 4a was obtained as a mixture of two
diastereomers (5:4 ratio based on 31P NMR spectroscopy)
that arises from the chirality of the Mo center and of the
phosphorus atom bonded to the η6-Ph group. The same
mixture was obtained by heating 1a under reflux in toluene
under a N2 atmosphere.
Figure 1. The molecular structure of 3a showing the thermal ellip-
soids at a 30% probability. The hydrogen atoms are omitted for
clarity except for the hydride ligands.
The fluxional behavior of 3a was revealed by the VT
NMR measurement in the [D8]toluene solution. At 80 °C,
the hydride ligands were observed as one well resolved sig-
nal at δ = –4.83 ppm, which coupled with five 31P nuclei
bound to the molybdenum center. That signal separated
into two broad signals centered at δ = –6.50 and –2.65 ppm
on cooling to –60 °C, corresponding to two nonequivalent
hydrides as found in the solid-state structure. In the
31P{1H} spectra at –60 °C, five signals for the coordinating
P atoms appeared in the region of δ = 69–107 ppm, and
one signal for the noncoordinating P atom was observed at
δ = –17.8 ppm. The two resonance signals in the low field
assigned to the dppe ligand merged into one at 80 °C, while
the signals of the P4 ligands remained separate. These indi-
cate that the site exchanges of both the hydride ligands and
the coordinated phosphorus atoms take place at high tem-
perature. This fluxional motion is attributed to the nonri-
gidity of the seven-coordinate geometry, but the free ter-
minal PPh2 group in P4 does not participate. Such dynamic
behavior is slower than that of [MoH2(PMe3)5] and
[MoH2{P(OMe)3}5],[14,15] which are nonrigid down to
–83 °C or lower. The highly chelated and sterically hindered
structure of 3a presumably restrains the fluxionality.
Scheme 1.
Reaction of 1b with H2
The X-ray diffraction study of 3a confirmed that the tet-
raphosphane P4 coordinated to the molybdenum center in
Although the W complex 1b did not react with H2 at
a κ3-fashion with one of the terminal phosphorus atoms room temperature, the reaction proceeded by heating the
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Molybdenum and Tungsten Hydride Complexes
(1)
complex in toluene at 80 °C under a H2 atmosphere. Com- Reaction of 2b with NaBH4
plex 1b was consumed after 4 h and the resulting red solu-
Treatment of the WII complex 2b with excess NaBH4 in
ethanol at 50 °C for 4 h formed the tetrahydride complex
5b as the sole complex product, which was obtained as red
crystals in 77% yield [Equation (2)].
tion contained two kinds of hydride complexes in a nearly
1:1 ratio and free dppe as shown by NMR spectroscopy
[Equation (1)]. Attempts to isolate any product from this
reaction mixture were not successful. One product was
identified as [WH2(κ2-dppe)(κ3-P4)] (3b) from the NMR
spectra, which resembled those of 3a. The 31P signals of the
coordinating P atoms in 3b were shifted to a higher field
than those in 3a, but the chemical shifts of the hydride sig-
nals were almost comparable to those of 3a. The other W
species was the tetrahydride complex without the dppe li-
gand [WH4(κ4-P4)] (5b), whose characterization was done
by preparing the complex by a different route (vide infra).
It should be noted that the Mo complex analogous to 5b
was not formed by reacting 1a with 1 atm of H2. Because
the ratio of the tungsten complexes formed in this reaction
was almost the same, even after a long reaction time or at
a high temperature, the existence of an equilibrium between
3b, 5b, dppe, and H2 was postulated. This was confirmed
by the reaction of isolated 5b and dppe at 80 °C under a N2
atmosphere for 4 h to form a mixture of 3b and 5b.
Some hydride complexes of Mo and W containing phos-
phane ligands have been synthesized by the reaction of
zero-valent complexes with H2.[16] The dinitrogen complex
trans-[Mo(N2)2(dppe)2] reacts smoothly with 1 atm of H2 at
room temperature to give [MoH4(dppe)2], and the analo-
gous reaction of the tungsten congener takes place at
55 °C.[17] Treatment of the monophosphane complex
[Mo(PMe3)6] with H2 is also a route to synthesize
[MoH4(PMe3)4].[18] The W analogue [WH4(PMe3)4], as well
as [WH2(PMe3)5], have been prepared from [WH(η2-
CH2PMe2)(PMe3)4] in a similar way except that a higher
temperature (60–65 °C) is required for the W complexes
than that required for the Mo complexes (room tempera-
ture).[19] The electron-donating ability of the metal center is
higher for the PMe3 complexes than for the P4 complexes
and for W than for Mo. The tetrahydride complexes with
the P4 ligand are difficult to form, especially for Mo, prob-
ably because the oxidative addition of H2 to electron-donat-
ing complexes is more advantageous. Another general
method for synthesizing the tetrahydride complexes of Mo
and W containing four P-donors is the reduction of the
high-valent metal species with NaBH4 or LiEt3BH in the
presence of the free phosphane ligands.[20] Since the pres-
ence of dppe seemed to interfere with the selective forma-
tion of 5b, reaction of 2b with NaBH4 was examined.
(2)
A single-crystal X-ray diffraction study was carried out
to determine the solid-state structure of 5b (Figure 2,
Table 1). All the hydride atoms were found in difference
Fourier maps and refined isotropically. The eight-coordi-
nate W atom has an approximately dodecahedral geome-
try.[21] All the crystallographically determined complexes of
the type [MH4(tertiary phosphane)4] (M = Mo, W) have
dodecahedral structures in which all four P atoms occupy
the less-hindered B sites (Scheme 2).[20c,22] In 5b two trape-
zoids defining this geometry are formed as P(1)–H(54)–
P(3)–H(53) and P(2)–H(51)–H(52)–P(4), and these planes
intersect almost orthogonally (87°). Although both the P
atoms in the latter plane occupy the B sites, one P atom in
Figure 2. The molecular structure of 5b showing the thermal ellip-
soids at a 50% probability. The hydrogen atoms are omitted for
clarity except for the hydride ligands.
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Q. X. Dai, H. Seino, Y. Mizobe
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the former plane interchanges with one of the H atoms to wide side are equivalently observed in solution, and the site
be located at an A site. This characteristic can be attributed exchange among these is very rapid even at –70 °C in [D8]-
to the steric restriction due to the triply-linked chelate rings. toluene. The hydride ligand at the opposite narrow side is
almost segregated from the other hydrides, as these hydride
Table 1. Selected bond lengths [Å] and angles [°] in 5b.
signals barely broadened at 80 °C. Nonrigidity of the eight-
coordinate geometry is reflected by the symmetric 31P{1H}
Bond lengths
NMR spectroscopic peaks at δ = 89.8 and 60.8 ppm for the
inner and the outer P atoms, respectively. The IR spectrum
gives a broad and weak absorption at 1775 cm–1 corre-
sponding to the W–H bonds.
W–P(1)
W–P(2)
W–P(3)
W–P(4)
2.4463(10)
2.3827(11)
2.4026(11)
2.4179(9)
W–H(51)
W–H(52)
W–H(53)
W–H(54)
1.68(3)
1.44(5)
1.70(4)
1.61(3)
Preparation of the Mo congener [MoH4(κ4-P4)] (5a) by
the reaction of [MoBr2(κ4-P4)] (2a) with NaBH4 was not
successful under a N2 or a H2 atmosphere. A different kind
of product was observed by NMR spectroscopy in the reac-
tion conducted under a H2 atmosphere, but it could not be
isolated.[24]
Bond angles
P(1)–W–H(53)
H(53)–W–P(3)
P(3)–W–H(54)
H(54)–W–P(1)
P(2)–W–P(4)
152.9(14)
72.4(15)
65.1(14)
68.2(14)
148.28(3)
74.1(16)
P(1)–W–P(2)
P(1)–W–P(3)
P(1)–W–P(4)
P(2)–W–P(3)
P(3)–W–P(4)
81.26(3)
132.25(3)
96.70(3)
78.67(3)
79.69(3)
P(4)–W–H(52)
H(52)–W–H(51) 67(2)
H(51)–W–P(2) 70.1(15)
Reaction of 5b with CS2
The reactivity of the Mo and W polyhydride-phosphane
complexes towards CO2 has often been investigated.[1,25]
The typical reaction is the insertion of CO2 into the M–H
–
bond to form the formato ligand (HCO2 ).[14b,26] Dispro-
portionation of CO2 into the carbonato (CO32–) and the
CO ligands,[27] and the cleavage of a C=O bond to give a
CO ligand and a phosphane oxide,[28] have also been
known. These reactions, in which no hydride is involved,
probably proceed in the low-valent complexes generated by
the reductive elimination of H2 from the metal center. Reac-
tion of 3a with 1 atm of CO2 only resulted in the formation
Scheme 2.
of [Mo(CO)(κ3-P4=O)(κ2-dppe)] {P4=O
=
meso-o-
The molecular structure of 5b can also be viewed as four C6H4(PPhCH2CH2PPh2)[PPhCH2CH2P(O)Ph2]},
which
P atoms constituting a pseudoplane that divides the coordi- was previously prepared from 1a and CO2.[29] The reaction
nation sphere asymmetrically. This results in the location of of 5b with CO2 was also examined, but the products were
only one hydride ligand [H(54)] at the narrow side and the complicated and difficult to characterize.
others at the opposite wide region. Similar ligand locations
have been observed in the X-ray structures of [MoH2(κ1- at 50 °C in toluene cleanly formed [W(κ2-S2CH2)(κ4-P4)]
OCOMe)(P-P-Si-P-P)] {P-P-Si-P-P Si(Ph)[Ph2PCH2- (6), which was obtained as green prismatic crystals in 76%
On the other hand, treatment of 5b with 3 equiv. of CS2
=
CH2P(Ph)C6H4-o-]2-P,P,P,P,Si} and [MoH3(P-P-Si)(dppe)] yield [Equation (3)]. GC analysis confirmed the concomi-
(P-P-Si = {Ph2PCH2CH2P(Ph)C6H4-o-}SiPh2-P,P,Si), in tant formation of H2. In the 1H NMR spectrum no hydride
which the equatorial P4-plane separates one acetate or hy- signals were observed and a singlet signal integrated to 2 H
dride ligand from the Si atom and two hydride ligands at appeared at δ = 6.56 ppm, which could be assigned to the
1
the opposite side.[9c,23] The H NMR spectra of 5b in C6D6 CH2S2 moiety. The 31P{1H} NMR spectrum showed two
at 20 °C showed two hydride signals at δ = –3.05 and peaks with 183W satellites at δ = 61.0 and 105.9 ppm corre-
–5.46 ppm, whose intensities were 3 H and 1 H, respectively. sponding to the outer and inner P atoms, which indicated
This clearly indicates that the three hydride ligands at the Cs molecular symmetry. There have been many examples of
(3)
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Molybdenum and Tungsten Hydride Complexes
CS2 insertion into M–H bonds to give dithioformate com- (Figure 4, Table 2). The W center exhibits a highly distorted
plexes,[25,30] but the formation of a methanedithiolate ligand octahedral structure in which the two isocyanide ligands are
from a CS2 molecule and two hydride ligands is still rare.[31] mutually oriented cis. While the isocyanide ligand trans to
The structure of 6 has been determined by single-crystal P(1) has an essentially linear C–N–C linkage, the other iso-
X-ray crystallography (Figure 3). The W center in 6 has a cyanide [trans to P(3)] deviates considerably [40.7(4)°] from
trigonal prismatic geometry in which one of the three side linearity. Such a bending at the N atom has often been ob-
rectangles is capped by the κ4-P4 ligand. The three edges served in low-valent isocyanide complexes,[36] and can be
of the prism are defined by one SCH2S and two PCH2CH2P explained from the accumulation of electron density at the
chelates. The analogous structure has been found previously N atom by the strong back-donation from the metal center.
for the bis(hydrosulfide) complex [Mo(SH)2(κ4-P4)].[32] The The solid-state FTIR spectrum of 7 showed two intense ab-
solid-state structure of [MoCl2(κ4-P4)] has the same coordi- sorptions at 1804 and 2002 cm–1 that can be assigned to
nation geometry, except for the orientation of the P4 ligand, ν(NϵC). These low frequency shifts indicate the presence
in which each base of the prism comprises a Cl, an inner P, of strong π-back donation from the W center. NMR spec-
and an outer P atom.[12]
troscopic measurement in C6D6 confirmed the rigidity of
the molecular structure. The 31P{1H} NMR spectrum exhi-
1
bits four resolved signals, and the two singlets in the H
NMR spectrum correspond to two nonequivalent tBu
groups.
(4)
Figure 3. The molecular structure of 6 showing the thermal ellip-
soids at a 50% probability. The hydrogen atoms are omitted for
clarity except for those in the S2CH2 ligand.
The bonding parameters of the methanedithiolate ligand
in 6 [C–S: 1.81(1)–1.83(1) Å; S–C–S: 103.0(5)°] are compar-
able to those reported for other transition metal complexes
(C–S: 1.81–1.85 Å; S–C–S: 103–105°)[31c,31e,33] and are no-
ticeably different from those of the dithioformate ligand
(C–S: 1.64–1.69 Å; S–C–S: 112–117°).[34]
Reaction of 5b with Isocyanides
Polyhydride complexes often undergo reactions with do-
nor molecules where hydride ligands are replaced as H2.
For instance, the molybdenum hydride complexes with a
polychelate ligand, [MoH3(P-P-Si)(dppe)] and [MoH3(P-P-
Si-P-P)], react with various isocyanides RNC to give
Figure 4. The molecular structure of 7 showing the thermal ellip-
soids at a 50% probability. The hydrogen atoms are omitted for
clarity.
While the reaction of Equation (4) was complete in 7 h,
[MoH(CNR)(P-P-Si)(dppe)] and [MoH(CNR)(P-P-Si-P- a shorter reaction time (1.5 h) allowed observation of the
P)], respectively.[35] Treatment of 5a with 3 equiv. of RNC intermediary species. These were tentatively formulated as
in toluene at 80 °C cleanly formed [W(CNR)2(κ4-P4)] {R = [WH2(CNR)(κ4-P4)] from the NMR spectroscopic data,[37]
tBu (7), Xy (8) where Xy = 2,6-Me2C6H3} after 7 h [Equa- although isolation and full characterization of the com-
tion (4)]. Complex 8 was identified spectroscopically by plexes has not been successful as yet. The analogous Mo
comparison to the previously known Mo analogue complex, [MoCl2(CNXy)(κ4-P4)], has been reported pre-
[Mo(CNXy)2(κ4-P4)],[13] while 7 was obtained as red needle viously.[38] The Mo complex analogous to 8 has been ob-
crystals in 54% yield and crystallographically analyzed tained before from the reaction of 1a with XyNC, but this
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Q. X. Dai, H. Seino, Y. Mizobe
FULL PAPER
performed with a Shimadzu GC-14B gas chromatograph equipped
with a molecular sieves 13X column.
Table 2. Selected bond lengths [Å] and angles [°] in 7.
Bond lengths
Reaction of [Mo(κ2-dppe)(κ4-P4)] with 1 atm of H2: A suspension
of [Mo(κ2-dppe)(κ4-P4)]·C6H6 (0.129 g, 0.100 mmol) in toluene
(6 mL) was stirred under a H2 atmosphere (1 atm) at 25 °C for 5 h.
Concentration of the resulting orange solution to 3 mL followed
by the addition of ether (12 mL) afforded the orange needles of
[MoH2(κ2-dppe)(κ3-P4)] (3a) (0.102 g, 84% yield). 1H NMR
(400 MHz, [D8]toluene, 80 °C): δ = –4.83 (tddd, JHP = 49, 32, 30,
15 Hz, 2 H, Mo-H) ppm. 1H NMR (400 MHz, [D8]toluene,
–60 °C): δ = –6.8 to –6.2 (br., 1 H, Mo-H), –3.0 to –2.3 (br., 1 H,
Mo-H) ppm. For the 31P spectra, the positions of the P atoms
correspond to those indicated in Scheme 1. 31P{1H} NMR ([D8]-
toluene, 80 °C): δ = –11.2 (Pd), 77.0 (Pe and Pf), 86.1 (Pc), 91.4 (Pa),
108.5 (Pb) ppm, Jab = 18 Hz, Jac = 7 Hz, Jae = 3 Hz, Jaf = 3 Hz,
Jbc = 24 Hz, Jbe = 42 Hz, Jbf = 42 Hz, Jcd = 33 Hz, Jce = 16 Hz,
Jcf = 16 Hz. 31P{1H} NMR ([D8]toluene, –60 °C): δ = –17.8 (Pd),
69.8, 76.2 (1P each, Pe and Pf), 82.4 (Pc), 98.0 (Pa), 106.2 (Pb) ppm,
W–P(1)
W–P(2)
W–P(3)
W–P(4)
2.4542(11)
2.3696(8)
2.3943(8)
2.4255(9)
W–C(47)
W–C(52)
C(47)–N(1)
C(52)–N(2)
2.040(4)
2.016(3)
1.172(6)
1.214(5)
Bond angles
P(1)–W–P(2)
P(1)–W–P(3)
P(1)–W–P(4)
P(2)–W–P(3)
P(2)–W–P(4)
P(3)–W–P(4)
W–C(47)–N(1)
W–C(52)–N(2)
78.00(3)
101.48(3)
92.68(3)
79.50(2)
153.05(3)
77.67(2)
172.9(3)
169.2(3)
P(1)–W–C(47) 161.95(10)
P(1)–W–C(52) 92.02(12)
P(2)–W–C(47) 89.14(9)
P(2)–W–C(52) 102.88(10)
P(3)–W–C(47) 88.36(10)
P(3)–W–C(52) 166.48(13)
P(4)–W–C(47) 104.27(10)
P(4)–W–C(52) 102.67(10)
C(47)–W–C(52) 78.43(16)
C(47)–N(1)–C(48) 176.1(3)
C(52)–N(2)–C(53) 139.9(3)
signals were not resolved. IR (KBr): ν = 1868, 1779 [w, ν(Mo–H)]
˜
reaction system is highly complicated and gives multiple
products depending on the stoichiometry and the reaction
conditions.[13]
cm–1. C72H68MoP6 (1215.11): calcd. C 71.17, H 5.64; found C
71.22, H 5.73.
[Mo{(η6-Ph)PPhCH2CH2PPh2}(κ3-P4)] (4a): Complex [MoH2(κ2-
dppe)(κ3-P4)] (0.121 g, 0.099 mmol) was heated under reflux in tol-
uene (5 mL) under a H2 atmosphere (1 atm) for 5 h. NMR mea-
surement of the resulting orange solution revealed that it contained
two diastereomers of [Mo{(η6-Ph)PPhCH2CH2PPh2}(κ3-P4)] in a
5:4 ratio. Concentration of the solution to 2 mL followed by ad-
dition of hexane (15 mL) afforded orange crystals of the major iso-
mer (0.035 g, 29% yield). Although this sample remained intact in
solution at room temperature, a mixture of diastereomers was
formed once again by heating under reflux in toluene. 1H NMR
(400 MHz, C6D6): δ = 3.31 (t, 1 H), 3.4–3.5 (m, 2 H), 3.51 (t, 1 H),
3.82 (q, 1 H) ppm for η6-Ph. 31P{1H} NMR (C6D6): δ = –13.3 (Pf),
Conclusion
The tetrahydride complex of tungsten containing a tetra-
phosphane co-ligand, 5b, was synthesized for the first time
by the reaction of the dibromide complex 2b with NaBH4.
The highly strained structure of the P4 ligand makes com-
plex 5b highly reactive towards CS2 and RNC. It has been
confirmed that the tetrahydride complex with the diphos-
phane ligands, [WH4(dppe)2], is completely inert towards
these molecules under the same or more severe reaction –12.1 (Pd), –11.4 (Pe), 75.8 (Pc), 86.6 (Pa), 115.9 (Pb) ppm, Jab
=
=
7 Hz, Jac = 22 Hz, Jbc = 24 Hz, Jbe = 3 Hz, Jcd = 31 Hz, Jef
conditions. It is worth mentioning that complex 5b has the
potential to open a coordination site not only by the loss
of H2 but also by dissociation of one or two terminal P
atoms, as proposed for the mechanism of catalysis by
[{P(CH2CH2PPh2)3}FeH(H2)]+.[39] Finally, 5b has been
shown to be a versatile precursor to complexes with a κ4-
tetraphosphane ligand, which are still rarely explored for
the Group 6 metals.[40]
34 Hz. C72H66MoP6 (1213.10): calcd. C 71.29, H 5.48; found C
71.51, H 5.63. 31P{1H} NMR (C6D6) of the minor isomer: δ =
–13.0 (Pf), –11.4 (Pd), –11.3 (Pe), 77.1 (Pc), 86.2 (Pa), 114.4 (Pb)
ppm, Jab = 9 Hz, Jac = 23 Hz, Jbc = 24 Hz, Jbe = 4 Hz, Jcd = 32 Hz,
Jef = 32 Hz. See Scheme 1 for notation of the 31P signals.
Reaction of [W(κ2-dppe)(κ4-P4)] with 1 atm of H2: A suspension
of [W(κ2-dppe)(κ4-P4)]·toluene (0.130 g, 0.0934 mmol) in toluene
(6 mL) was stirred under a H2 atmosphere (1 atm) at 80 °C for 4 h.
NMR measurement of the resulting red solution revealed that it
contained two complexes [WH2(κ2-dppe)(κ3-P4)] (3b) and
[WH4(κ4-P4)] (5b) in a ratio of 1:1. The ratio of these two com-
plexes was same after the reaction was continued for further 20 h.
The NMR spectroscopic data of [WH2(κ2-dppe)(κ3-P4)] are as fol-
Experimental Section
General: All preparations were carried out by using the standard
Schlenk technique under a pure H2 or N2 atmosphere. The solvents
were dried by standard methods and distilled under a N2 atmo-
sphere before use. Complexes [M(κ2-dppe)(κ4-P4)][11] and
[MBr2(κ4-P4)][12] were prepared as described previously, and other
reagents were commercially obtained and used without further pu-
rification.
1
lows: H NMR (400 MHz, C6D6): δ = –4.6 to –4.2 (m, 2 H, W-H)
ppm. 31P{1H} NMR (C6D6): δ = –12.9 (Pd), 57.0 (Pe and Pf), 61.8
(Pc), 65.3 (Pa) and 89.2 (Pb) ppm, assignment of the coupling con-
stants was not possible due to the low S/N ratio. The notation for
the P atoms is same as that for the Mo analogue 3a in Scheme 1.
NMR spectra were measured with JEOL alpha-400 or JEOL ECS
400 NMR spectrometers at 20 °C, except for those indicated other-
wise. Chemical shifts were referenced to the isotopic impurities
[WH4(κ4-P4)] (5b): A mixture of [WBr2(κ4-P4)]·0.5C6H6 (0.682 g,
0.619 mmol) and NaBH4 (0.234 g, 6.19 mmol) in ethanol (30 mL)
was stirred under a N2 atmosphere at 50 °C for 4 h and resulted in
an orange-red suspension. After the suspension was concentrated
in vacuo, the residual solid was extracted with toluene (20 mL).
Red crystals of [WH4(κ4-P4)]·0.5toluene (0.459 g, 77% yield) were
obtained by adding ethanol (5 mL) to the extract after concentra-
1
(C6D6 at 7.15 ppm and [D8]toluene at 2.09 ppm) for H or the ex-
ternal 85% H3PO4 (δ = 0 ppm) for 31P. Fo r t h e 1H data, the signals
due to P4 are omitted. IR spectra were recorded with a JASCO
FTIR-420. Elemental analyses were performed with a Perkin–El-
mer 2400 series II CHN analyzer or a Thermol Fisher Scientific
FLASH 2000 organic elemental analyzer. Gas phase analysis was
1
tion to 3 mL. H NMR (400 MHz, C6D6): δ = –5.46 (m, 1 H, W-
H), –3.05 (m, 3 H, W-H) ppm. 31P{1H} NMR (C6D6): δ = 60.8
146
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 141–149

Molybdenum and Tungsten Hydride Complexes
(JPW = 177 Hz, outer P), 89.8 (JPW = 151 Hz, inner P) ppm,
toluene was stirred at 80 °C under a N2 atmosphere for 7 h. Com-
AAЈXXЈ pattern with 183W satellites, JAX + JAXЈ = 8 Hz. IR (KBr): pound [W(XyNC)2(κ4-P4)] was obtained as an orange-red solid by
ν = 1762 [ν(W–H)] cm–1. C49.5H50P4W (952.68): calcd. C 62.41, H crystallization from toluene and hexane at –20 °C (0.076 g, 64%).
˜
5.29; found C 62.94, H 5.37.
1H NMR (400 MHz, C6D6): δ = 1.54 (s, 6 H, CH3), 2.28 (s, 6 H,
CH3) ppm. 31P{1H} NMR (C6D6): δ = 41.4 (JPW = 202 Hz, Pa),
Reaction of [WH4(κ4-P4)] with CS2: Carbon disulfide (18 μL,
0.30 mmol) was added to a solution of [WH4(κ4-P4)]·0.5toluene
(0.091 g, 0.10 mmol) in toluene and the mixture was stirred at 50 °C
under a N2 atmosphere for 18 h. The resulting green solution was
filtered and diethyl ether (18 mL) was added to the concentrated
filtrate (3 mL) to afford green cubic crystals of [W(κ2-S2CH2)(κ4-
P4)] (6) (0.071 g, 76% yield). In order to determine the concomi-
tantly formed H2 another reaction was carried out under vacuum
and the gas phase was analyzed by GC after dilution with pure
49.3 (JPW = 320 Hz, Pd), 79.4 (JPW = 304 Hz, Pb), 85.2 (JPW
215 Hz, Pc) ppm, Jab = 11 Hz, Jac = 13 Hz, Jad = 15 Hz, Jbc
=
=
4 Hz, Jbd = 80 Hz, Jcd = 12 Hz. IR (KBr): ν = 1837 (s), 1943 (s)
˜
[ν(NϵC)] cm–1.
X-ray Crystallography: A single crystal of 3a was sealed in a glass
capillary tube under an Ar atmosphere and measured at 293 K.
Crystals of 5b, 6, and 7 were mounted on loops with oil and cooled
to 113 K. All diffraction studies were performed with a Rigaku
Mercury-CCD diffractometer equipped with a graphite-monochro-
matized Mo-Kα source. Data were processed using the CrystalClear
program package[41] and corrected for absorption. Among several
trials, crystallization from toluene/diethyl ether gave the largest sin-
gle crystals of 3a. However, the crystal volumes were still not
enough to obtain intense data, and only 29% of the reflections in
the range of 2θ Ͻ 50.5° met the criteria of I Ͼ 2σ(I). Since crystals
of 6 showed severe twinning, diffraction data were collected with a
non-merohedral twin crystal and processed using the TwinSolve
program package.[42] The reflections were assigned to two crystal
domains of different orientations, and the intensity data integrated
for each domain were combined together. The resulting data set,
which included 93% of the unique reflections in the range of 2θ Ͻ
50°, was used in the structure solution and refinement. Details are
listed in Table 3.
1
argon gas. H NMR (400 MHz, C6D6): δ = 6.56 (s, 2 H, CH2S2)
ppm. 31P{1H} NMR (C6D6): δ = 61.0 (br s with 183W satellites,
JPW = 218 Hz, outer P), 105.9 (br s with 183W satellites, JPW
=
214 Hz, inner P) ppm. C47H44P4S2W (980.73): calcd. C 57.56, H
4.52; found C 57.35, H 4.52.
Reaction of [WH4(κ4-P4)] with tBuNC: A solution of [WH4(κ4-
P4)]·0.5toluene (0.082 g, 0.086 mmol) and tBuNC (30 μL,
0.27 mmol) in toluene was stirred at 80 °C under a N2 atmosphere
for 7 h. The resulting red solution was filtered, and hexane (18 mL)
was added to the concentrated filtrate (3 mL) to afford red needle
crystals of [W(tBuNC)2(κ4-P4)] (7). The X-ray crystallographic
study revealed that the crystals contained 0.75 equiv. hexane as the
solvate, which was removed by drying under vacuum (0.050 g, 54%
yield). 1H NMR (400 MHz, C6D6): δ = 0.78 [s, 9 H, C(CH3)3], 1.27
[s, 9 H, C(CH3)3] ppm. 31P{1H} NMR (C6D6): δ = 42.4 (JPW
=
222 Hz, Pa), 54.8 (JPW = 328 Hz, Pd), 81.1 (JPW = 307 Hz, Pb), 90.1
(JPW = 216 Hz, Pc) ppm, Jab = 11 Hz, Jac = 9 Hz, Jad = 13 Hz, Jbc
= 5 Hz, Jbd = 79 Hz, Jcd = 14 Hz. See Equation (4) for the notation
The structure solutions and refinements were performed by using
the CrystalStructure program package.[43] The positions of the non-
hydrogen atoms were determined by the Patterson methods
(PATTY[44] for 3a and 5b or SHELXS97[45] for 6 and 7) and subse-
quent Fourier synthesis (DIRDIF99[46]). These were refined with
anisotropic thermal parameters by full-matrix least-squares tech-
niques. The hydride ligands in 3a and 5b were found in the Fourier
maps and refined isotropically (5b) or with fixed thermal param-
of the P atoms. IR (KBr): ν = 1804 (s), 2002 (s) [ν(NϵC)] cm–1.
˜
C56H60N2P4W (1068.85): calcd. C 62.93, H 5.66, N 2.62; found C
62.49, H 5.69, N 2.55.
Reaction of [WH4(κ4-P4)] with XyNC: A solution of [WH4(κ4-P4)]·
0.5toluene (0.096 g, 0.10 mmol) and XyNC (0.040 g, 0.30 mmol) in
Table 3. Crystallographic data.
3a
5b·0.5toluene
6
7·0.75hexane
Formula
C72H68P6Mo
1215.11
P1 (no. 2)
C49.5H50P4W
952.68
P21/c (no. 14)
12.0415(9)
24.746(1)
14.691(1)
90
108.354(1)
90
4154.9(5)
4
1.523
2.972
0.10ϫ0.08ϫ0.04
0.715–0.888
9882 (0.042)
7683
C47H44 P4S2W
980.73
P21/c (no. 14)
17.815(1)
11.7463(9)
19.319(2)
90
96.850(5)
90
4013.9(6)
4
1.623
3.179
0.25ϫ0.10ϫ0.02
0.787–0.939
13148 (0.081)
10379
C60.5H70.5N2P4W
1133.48
C2/c (no. 15)
45.447(9)
10.479(2)
25.852(5)
90
118.236(2)
90
10846(3)
8
1.388
2.290
0.40ϫ0.15ϫ0.03
0.646–0.934
12806 (0.041)
9906
Formula weight
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
¯
10.228(5)
12.307(5)
24.35(1)
84.43 (1)
88.51(1)
88.71(1)
3049(2)
2
1.324
0.415
0.10ϫ0.06ϫ0.02
0.565–0.992
10696 (0.106)
3088
γ [°]
V [Å3]
Z
ρcalcd [gcm–3]
μ [mm–1]
Crystal size [mm3]
Transmission factor
Unique reflections (Rint
Observed reflections[a]
Variables
)
784
0.0697
0.1502
1.015
589
0.0355
0.0712
1.024
485
0.0713
0.1977
1.137
601
0.0364
0.0776
1.114
[b]
R1
[c]
wR2
Gof[d]
2
2
2 2
[a] Fo Ͼ 2σ(Fo2). [b] R1 = Σ||Fo| – |Fc||/Σ|Fo| for Fo Ͼ 2σ(Fo2). [c] wR2 = [Σw(Fo2 – Fc ) /Σw(Fo2)2]1/2 for all unique data, where w =
[σ(Fo2) + aFo2 + b]–1 for 3a and 5b or w = [σ2(Fo2) + (aP)2 + bP]–1 {P = (Fo2 + 2Fc )/3} for 6 and 7. [d] Gof = [Σw(Fo2 – Fc ) /{(number
2
2 2
of reflections observed) – (number of variables)}]1/2
.
Eur. J. Inorg. Chem. 2011, 141–149
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
147

Q. X. Dai, H. Seino, Y. Mizobe
FULL PAPER
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Acknowledgments
We thank Ms. Yukiko Tanzawa and Mr. Chirima Arita for their
experimental assistance. This work was supported by the Ministry
of Education, Culture, Sports, Science and Technology, Japan: i.
Grant-in-Aid for Scientific Research on Priority Areas, grant
number 18065005, “Chemistry of Concerto Catalysis”, to Y. M.),
ii. Grant-in-Aid for Scientific Research (B), grant number
21350033, to H. S.). H. S. gratefully acknowledges the special fund-
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Received: August 9, 2010
Published Online: November 17, 2010
Eur. J. Inorg. Chem. 2011, 141–149
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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