Preparation, structures, and some reactivities of five-coordinate alkyne complexes of mo with tetraphosphine or diphosphine coligand [mo(rc≡cr ){mes0-0-c6h4(pphch2ch2pph 2)2}] and [mo(rc≡cr

Article abstract of DOI:10.1021/om800615a

The five-coordinate alkyne complexes [MO(η²-RC≡CR )(κ⁴-P4)] (3; P4 = meso-o-C₆H₄(PPhCH ₂CH₂PPh₂)₂) were synthesized by treatment of the Mo(0) tetraphosphine complex [M

Full text of DOI:10.1021/om800615a

1112
Organometallics 2009, 28, 1112–1121
Preparation, Structures, and Some Reactivities of Five-Coordinate
Alkyne Complexes of Mo with Tetraphosphine or Diphosphine
Coligand [Mo(RCt CR′){meso-o-C6H4(PPhCH2CH2PPh2)2}] and
[Mo(RCt CR′)(Ph2PCH2CH2PPh2)2]
Fumiya Niikura, Hidetake Seino, and Yasushi Mizobe*
Institute of Industrial Science, The UniVersity of Tokyo, Komaba, Meguro-ku, Tokyo 153-8505, Japan
ReceiVed June 30, 2008
The five-coordinate alkyne complexes [Mo(η2-RCt CR′)(κ4-P4)] (3; P4
) meso-o-C6H4-
(PPhCH2CH2PPh2)2) were synthesized by treatment of the Mo(0) tetraphosphine complex [Mo(κ4-
P4)(dppe)] (1; dppe ) Ph2PCH2CH2PPh2) with internal alkynes RCt CR′. The X-ray analysis of 3a (R
) Me, R′ ) COOMe) and 3b (R ) R′ ) Ph) has disclosed their trigonal-bipyramidal geometry in a
solid state, whereas their fluxional feature in solution has been demonstrated by the VT-NMR study.
New closely relating diphosphine complexes [Mo(η2-RCt CR′)(dppe)2] (4) have also been obtained
analogously from the reactions of trans-[Mo(N2)2(dppe)2] with RCt CR′, and their trigonal-bipyramidal
structures have been confirmed by the X-ray diffraction for 4a (R ) Me, R′ ) COOMe). Complexes 3a,
3b, 4a, and 4b were allowed to react with aqueous HCl in THF to give hydrogenation products from
coordinated alkynes including cis/trans-alkenes and/or alkanes, the yields of which depend upon the
nature of the alkyne complexes and the amounts of acid. From the reactions of 3a with HBF4 · Et2O
under the controlled conditions, two intermediate complexes were isolated, namely, a hydridoalkyne
complex [MoH(η2-MeCt CCOOMe)(κ4-P4)][BF4] and an η3-allyl complex [Mo(η3-CH2CHCHCOOMe-
κO)(κ4-P4)][BF4], and the mechanism for the formations of hydrogenation products of alkynes via these
intermediate stages has been proposed. Reaction of 3a with H2S gas also resulted in the hydrogenation
of the coordinated alkyne to the alkene, which was further converted to the H2S adduct smoothly under
the reaction conditions. Oxidation of 3a by I2 yielding a cationic alkyne complex [MoI(η2-
MeCt CCOOMe)(κ4-P4)]I is also described.
dppe ligands [Mo(η2-RCt CR′)(dppe)2] (4) newly prepared from
2. Protonation of the coordinated alkynes in 3 and 4 to give
hydrogenation products is also reported.
Introduction
Since the isolation of the zerovalent Mo complex containing
a new tetraphosphine coligand [Mo(κ4-P4)(dppe)] (1; P4 )
meso-o-C6H4(PPhCH2CH2PPh2)2, dppe ) Ph2PCH2CH2PPh2)
from the reaction of trans-[Mo(N2)2(dppe)2] (2) with dppe via
the condensation of two dppe ligands to form P4 under forcing
conditions,1 we have been investigating the reactivities of 1
toward a series of small molecules. These studies have disclosed
already the reactivities distinctively displayed by this {Mo(P4)}
site, which include the formations of zerovalent P4 complexes
Results and Discussion
Preparation of 3 from 1. When treated with alkynes
RCt CR′ in toluene at 80 °C, 1 was converted into 3a (R )
Me, R′ ) COOMe) and 3b (R ) R′ ) Ph), which are isolable
as analytically pure crystals in satisfactory yields (eq 1). For
MeCt CPh, the similar product 3c (R ) Me, R′ ) Ph) was
obtained, as was confirmed by the X-ray analysis and spectro-
scopic data, but isolation in a pure form was unsuccessful due
to the contamination by dppe. Although 3 were also produced
for RCt CR′ (R, R′ ) Me or primary alkyl groups), isolations
failed because of their lower stabilities than 3a-3c in addition
to the difficulty in separation from free dppe. The alkynes having
bulky substituents such as ButCt CMe and Me3SiCt CSiMe3
did not react with 1 under these conditions.
having one, two, and/or three CO, nitrile, isocyanide,2 and N2
1b
ligands as well as the cleavages of the CdO bond in CO2, the
CdS bond in RNCS,3 and CsX bonds in PhCH2X (X ) Cl,
Br)4 in the coordination sphere of Mo. Now, we have found
that the reactions of 1 with internal alkynes RCt CR′ afford
the five-coordinate alkyne complexes [Mo(η2-RCt CR′)(κ4-P4)]
(3). In this paper, we wish to describe in detail the characteriza-
tion of 3, together with their analogues consisting of bidentate
* To whom correspondence should be addressed. E-mail: ymizobe@
iis.u-tokyo.ac.jp.
(1) (a) Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Chem. Lett. 1999,
28, 611. (b) Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Bull. Chem. Soc.
Jpn. 2001, 74, 561.
(2) Seino, H.; Arita, C.; Hidai, M.; Mizobe, Y. J. Organomet. Chem.
2002, 658, 106.
(3) Ohnishi, T.; Seino, H.; Hidai, M.; Mizobe, Y. J. Organomet. Chem.
2005, 690, 1140.
(4) Seino, H.; Watanabe, D.; Ohnishi, T.; Arita, C.; Mizobe, Y. Inorg.
Chem. 2007, 46, 4784.
10.1021/om800615a CCC: $40.75
2009 American Chemical Society
Publication on Web 01/26/2009

FiVe-Coordinate Alkyne Complexes of Mo
Organometallics, Vol. 28, No. 4, 2009 1113
Figure 1. An ORTEP drawing for 3a at 30% probability level.
Hydrogen atoms are omitted for clarity.
Figure 2. An ORTEP drawing for 3b at 30% probability level.
Hydrogen atoms are omitted for clarity.
Preparation of 4 from 2. For comparison of the structures
and properties, synthesis of the dppe analogues 4 from 2 was
also attempted, and we have found that the corresponding alkyne
complexes 4a-4c are isolable by treatment of 2 with RCt CR′
in benzene at reflux, as shown in eq 2. Under these conditions,
reactions with the alkynes having But and Me3Si groups did
not occur also for 2. Two complexes of this type, [Mo(η2-
HCt CH)(dppe)2] (4d)5 and [Mo(η2-MeCt CMe)(dppe)2] (4e),6
are precedented, the former of which was obtained in 32% yield
from the reaction of 2 with excess HCt CLi · H2NCH2CH2NH2
and the latter in 2-5% yields from [MoCl4(dppe)], dppe, and
MeCt CMe under reductive conditions. The reactions reported
here demonstrate a convenient and reliable method to prepare
4, although the analogues containing terminal alkynes are not
available by this procedure due to the facile formations of
bis(alkyne) complexes [Mo(η2-RCt CH)2(dppe)2] (R ) Me7 and
Ph8) or the products resulting from the alkynic CsH bond
cleavage.8
Table 1. Selected Bond Distances (Å) and Angles (°) in 3a and 3b
3a
(a) Bond Distance
Mo-P(1)
2.3801(6) Mo-P(2)
2.3627(6) Mo-P(4)
2.075(2) Mo-C(48)
1.312(3)
2.4093(5)
2.4392(5)
2.062(2)
Mo-P(3)
Mo-C(47)
C(47)-C(48)
(b) Bond Angle
P(1)-Mo-P(2)
P(1)-Mo-P(4)
P(2)-Mo-P(4)
C(47)-Mo-C(48)
Mo-C(47)-C(49)
Mo-C(48)-C(47)
77.57(2)
88.80(2)
148.20(2)
36.99(9)
154.2(2)
72.1(1)
P(1)-Mo-P(3)
101.66(2)
P(2)-Mo-P(3)
P(3)-Mo-P(4)
Mo-C(47)-C(48)
77.80(2)
77.04(2)
71.0(1)
C(48)-C(47)-C(49) 134.8(2)
Mo-C(48)-C(50) 149.7(2)
C(47)-C(48)-C(50) 137.2(2)
3b
(a) Bond Distance
2.4016(8) Mo-P(2)
2.3452(7) Mo-P(4)
2.081(2) Mo-C(48)
1.316(3)
Mo-P(1)
2.4202(6)
2.4506(5)
2.069(2)
Mo-P(3)
Mo-C(47)
C(47)-C(48)
(b) Bond Angle
P(1)-Mo-P(2)
77.04(2)
89.38(2)
147.72(2)
36.98(9)
155.1(2)
72.0(1)
P(1)-Mo-P(3)
102.61(2)
P(1)-Mo-P(4)
P(2)-Mo-P(3)
P(3)-Mo-P(4)
Mo-C(47)-C(48)
77.09(2)
77.56(2)
71.0(1)
P(2)-Mo-P(4)
C(47) -Mo-C(48)
Mo-C(47)-C(49)
Mo-C(48)-C(47)
C(48)-C(47)-C(49) 133.1(2)
Mo-C(48)-C(55) 155.4(2)
C(47)-C(48)-C(55) 132.6(2)
Structures of 3 and 4. The single-crystal X-ray analysis has
been undertaken for 3a and 3b to clarify their structures in detail.
Figures 1 and 2 depict the ORTEP drawings for 3a and 3b,
respectively, while Table 1 lists the selected bond distances and
angles therein. The structure of 3c was also confirmed by the
X-ray crystallography, which is included in Supporting Informa-
tion.
The structures of 3a and 3b are essentially identical. Thus,
complexes 3 have a distorted trigonal-bipyramidal structure with
one inner P atom, P(2), and one outer P atom, P(4), in P4 at
the axial positions. The η2-alkynes are ligating to the Mo center
in a manner that the alkynic CsC bond is oriented perpendicu-
larly to the triangular equatorial plane defined by P(1), P(3),
and the midpoint of the alkynic CsC bond. The P(2)-Mo-P(4)
linkages are bent toward the direction opposite to the alkynes,
with the P-Mo-P angles at 148.20(2) and 147.72(2)° for 3a
and 3b, respectively. As for the structures of coordinated
alkynes, the Ct CsC arrays are bent significantly with the
substituents R and R′ directed away from the Mo centers, where
the observed Ct CsC angles of 132.6(2)-137.2(2)° are rather
closer to those of the sp2 C atoms than the sp C atoms.
Consistently, the alkynic CsC bond lengths are elongated to
1.312(3) and 1.316(3) Å for 3a and 3b, which are comparable
to those of the typical CsC double bonds. The distances of
alkynic C atoms from Mo at 2.062(2)-2.081(2) Å fall in the
range of the 4e-donating alkynes (1.93-2.09 Å) and are
(5) Ishino, H.; Kuwata, S.; Ishii, Y.; Hidai, M. Organometallics 2001,
20, 13.
(6) Davies, S. C.; Henderson, R. A.; Hughes, D. L.; Oglieve, K. E. Chem.
Commun. 1996, 2039.
(7) Henderson, R. A.; Oglieve, K. E.; Salisbury, P. J. Chem. Soc., Dalton
Trans. 1995, 2479.
(8) Hills, A.; Hughes, D. L.; Kashef, N.; Lemos, A. N. D. A.; Pombeiro,
A. J. L.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1992, 1775.

1114 Organometallics, Vol. 28, No. 4, 2009
Niikura et al.
Table 2. Selected Bond Distances (Å) and Angles (°) in 4a
Scheme 1
molecule 1
molecule 2
(a) Bond Distances
2.428(1)
Mo(1)-P(1)
Mo(1)-P(2)
Mo(1)-P(3)
Mo(1)-P(4)
Mo(1)-C(53)
Mo(1)-C(54)
C(53)-C(54)
2.418(1)
2.473(1)
2.427(1)
2.449(1)
2.070(3)
2.068(4)
1.318(6)
2.483(1)
2.415(1)
2.449(1)
2.065(3)
2.060(3)
1.314(5)
(b) Bond Angles
78.18(3)
107.09(3)
87.96(3)
86.80(3)
155.80(3)
78.35(3)
37.1(1)
P(1)-Mo(1)-P(2)
78.41(3)
103.84(3)
88.10(3)
87.77(3)
157.90(3)
78.48(3)
37.2(2)
P(1)-Mo(1)-P(3)
P(1)-Mo(1)-P(4)
P(2)-Mo(1)-P(3)
P(2)-Mo(1)-P(4)
P(3)-Mo(1)-P(4)
C(53) sMo(1)-C(54)
Mo(1) sC(53) sC(54)
Mo(1)-C(53) sC(55)
C(54) sC(53)-C(55)
Mo(1)-C(54) sC(53)
Mo(1)-C(54)-C(56)
C(53)-C(54)-C(56)
71.2(2)
71.3(2)
156.4(3)
132.4(3)
71.6(2)
153.5(3)
134.6(3)
155.7(3)
132.9(3)
71.5(2)
147.5(5)a
138.2(5)a
a Data for the COOMe group in the predominant disordered
molecule.
with the alkyne molecule binding in parallel to the axial
P(2)-P(4) vector. It is noteworthy that the P(2)-Mo-P(4)
angles in 4a at 155.80(3) and 157.90(3)° are considerably larger
than that in 3a (148.20(2)°). However, this difference does not
affect the bonding parameters associated with the alkyne, that
is, the Mo-C bond distances (2.060(3)-2.070(3) Å) as well
as the alkynic CsC bond lengths (1.314(5) and 1.318(6) Å)
and bent Ct CsC angles (132.4(3)-138.2(5)°) in 4a are almost
comparable to those in 3a described above. On the other hand,
in the unsubstituted alkyne complex 4d,5 the axial P-Mo-P
angle is wider (161.28(5)°), while the MosC distances at
2.071(5) and 2.061(5) Å are analogous to those in 3a and 4a,
although the alkynic CsC bond length of 1.265(7) Å is slightly
shorter.
Fluxional Feature in Solution. The X-ray analysis of 3a
has disclosed the coordination of the alkyne parallel to the
P(2)-P(4) vector, where the COOMe substituent points to the
direction of the inner P(2) atom exclusively (i in Scheme 1).
However, as for the 1H NMR resonances of the ligated alkyne
in 3a at 20 °C, one somewhat broadened signal was observed
for the COOMe protons, but the resonance due to the CMe
protons was not assignable. On the other hand, the 31P{1H}
NMR spectrum of 3a at 20 °C showed two sets of four broad
multiplets. Since these findings seemed to suggest the fluxional
feature of 3a in solution, the VT-NMR study has been carried
out. As shown in Figure 4, the 31P{1H} NMR spectrum recorded
at -20 °C showed eight multiplets, indicating clearly the
presence of two isomers each consisting of four inequivalent P
Figure 3. An ORTEP drawing for one of the two crystallographi-
cally independent molecules of 4a (30% probability level). All
hydrogen atoms and the solvating benzene are omitted for clarity.
significantly shorter than those of the 2e-donating alkynes
(2.13-2.24 Å),9 which is in good agreement with the fact that
the electron count of the Mo center in 3 becomes 18 by assuming
the donation of 4 electrons from the coordinated alkyne.
To compare the structures in detail, the X-ray analysis has
also been carried out for the diphosphine complex 4a. The single
crystal of 4a contained two crystallographically independent
molecules with essentially identical structures. Selected bond
distances and angles are listed in Table 2, while the ORTEP
drawing is depicted in Figure 3 for only one of the two
molecules. As observed for the previously reported 4d5 and 4e,6
4a has a distorted trigonal-prismatic geometry, analogous to 3a,
(9) (a) Baker, P. K. AdV. Organomet. Chem. 1996, 40, 45. (b) Templeton,
J. L. AdV. Organomet. Chem. 1989, 29, 1.

FiVe-Coordinate Alkyne Complexes of Mo
Organometallics, Vol. 28, No. 4, 2009 1115
Figure 5. An ORTEP drawing for the cation in 5 at 30% probability
level. Hydrogen atoms are omitted for clarity.
Table 3. Selected Bond Distances (Å) and Angles (°) in 5
(a) Bond Distance
Mo-P(1)
Mo-P(3)
Mo-I
2.581(1) Mo-P(2)
2.487(1) Mo-P(4)
2.873(5) Mo-C(47)
2.002(5) C(47)-C(48)
2.478(1)
2.547(1)
1.997(5)
1.328(7)
Mo-C(48)
(b) Bond Angle
P(1)-Mo-P(2)
P(1)-Mo-P(4)
P(2)-Mo-P(3)
P(2)-Mo-I
79.76(4)
113.71(4)
77.52(4)
78.78(3)
78.33(3)
38.8(2)
P(1)-Mo-P(3)
P(1)-Mo-I
150.05(4)
78.32(3)
150.83(4)
79.68(4)
78.98(3)
70.8(3)
P(2)-Mo-P(4)
P(3)-Mo-P(4)
P(4)-Mo-I
Figure 4. VT-NMR spectra of 3a in toluene-d8.
P(3)-Mo-I
atoms. The 1H NMR spectrum at the same temperature exhibited
two sets of two singlets due to COOMe and CMe protons,
showing also the presence of two isomers, the ratio of which
was 0.53:0.47. The 13C{1H} NMR spectum at this temperature
is consistent with these findings, displaying the signals sug-
gesting the presence of two isomers in a ratio of approximately
1:1. As the recording temperatures were raised in a stepwise
manner up to 60 °C, the 31P{1H} NMR signals broadened
gradually and coalesced, while the 1H NMR signals were
converted finally to one singlet for COOMe protons and one
broad peak for CMe protons. The 13C{1H} NMR spectrum at
40 °C also exhibited only one set of broad signals assignable
to the alkynic C atoms. These spectral features may be
interpreted in terms of the presence of two isomers containing
the alkynes with different orientations, which may interconvert
in the NMR time scale as shown in Scheme 1. Thus, upon
starting from the solid-state structure i, rotation of the alkyne
ligand around the Mo-alkyne bonding axis by 90° forms two
isomers ii and iii, where iii corresponds to the enantiomer of i.
This process also exchanges the axial and equatorial P atoms
probably via the Berry mechanism involving a square-pyramidal
intermediate since the orientation of the alkyne ligand parallel
to the equatorial plane is energetically disfavored, as confirmed
previously by the EHMO calculation using the model [Mo(η2-
HCt CH)(PH3)4].5 These reversible interconversions totally give
two enantiomer pairs (i, iii) and (ii, iv) in equilibrium that are
separable as two species from NMR criteria under appropriate
conditions.
C(47)-Mo-C(48)
Mo-C(47)-C(49)
Mo-C(48)-C(47)
Mo-C(47)-C(48)
155.1(4)
70.4(3)
C(48)-C(47)-C(49) 133.5(5)
Mo-C(48)-C(50)
157.2(4)
C(47)-C(48)-C(50) 132.3(5)
4a. Thus, the 1H NMR signals of the alkyne ligand in 4a were
resolved well in the whole temperature range of recording.
However, the site exchange of P atoms exists. The 31P{1H}
NMR spectra of 4a at room temperature showed only one set
of three slightly broadened resonances with the intensity ratio
of 2:1:1 due to four essentially inequivalent P atoms, where
two signals may be accidentally overlapping, which broadened
further upon the increase in the recording temperature and were
finally recorded as one broad signal at +80 °C. This indicates
that the pseudorotation of alkyne is also occurring in 4a. The
observed coalescence temperature is lower for 3a than that for
4a probably because the square-pyramidal intermediate is more
readily accessible for 3a with the tetradentate ligand. Accord-
ingly, from the NMR criteria, all three complexes 3 are highly
fluxional, and their features are almost similar, whereas those
of 4 clearly depend on the nature of the alkyne with the
fluxionality decreasing in the order 4b > 4c > 4a.
Reaction of 3a with Iodine. We have found that the reaction
of 3a with 1 equiv of I2 in toluene at 0 °C affords the
Mo(II)-alkyne complex [MoI(η2-MeCt CCOOMe)(κ4-P4)]I (5)
in moderate yield (eq 3). For comparison with the Mo(0)-alkyne
complexes 3, the structure of 5 has been determined by the X-ray
diffraction as shown in Figure 5. Selected bond distances and
angles are summarized in Table 3. It is worth noting that the
related alkyne complexes [MoCl(η2-RCt CR′)(κ4-P4)]Cl (R )
Ph, R′ ) H; R ) p-tolyl, R′ ) H; R ) Me, R′ ) Ph) were
In contrast to the tetraphosphine complex 3a with inequivalent
axial P atoms, similar isomerization by the orientation of the
alkyne does not occur in the case of the diphosphine complex

1116 Organometallics, Vol. 28, No. 4, 2009
Niikura et al.
isolated recently from the reactions of [MoCl2(κ4-P4)] (6) with
RCt CR′, but their X-ray structures were not available.10
was reported to give the Mo(II) alkyne complex trans-[MoF(η2-
HCt CH)(dppe)2][BF4] and H2.5 Now, we have studied the
reactions of the tetraphosphine complexes 3a and 3b with
aqueous hydrochloric acid, and these results have been compared
with those of the reaction of the diphosphine complexes 4a and
4b conducted under the same conditions.
When the diphenylacetylene complex 3b was treated with 2
equiv of concentrated HCl(aq) in THF at 0 °C for 1 h, trans-
PhCHdCHPh was obtained in 62% yield as the major product
together with PhCH2CH2Ph (10%) and free diphenylacetylene
(12%). Formation of cis-PhCHdCHPh was almost negligible.
Presence of the dichloro complex 6 in the reaction mixture as
the predominant Mo-containing product was confirmed by the
31P{1H} NMR spectroscopy (eq 4).4 An increase in the amount
of hydrochloric acid to 3 equiv afforded essentially the same
results with respect to the yields of the products originating from
the alkyne. On the other hand, similar treatment of 4b with 2
equiv of HCl also resulted in the formation of trans-
PhCHdCHPh as the predominant product, but its yield was
much lower (31%). Concomitant formations of cis-
PhCHdCHPh and PhCH2CH2Ph in 8 and 4% yields, respec-
tively, were observed together with the liberation of 20% of
coordinated diphenylacetylene. It is to be noted that in the case
of 4b, the yields of the hydrogenation products become nearly
comparable to those from 3b by increasing the amount of HCl
Complex 5 consists of a discrete cation of an octahedral
structure with the linear tetraphosphine ligand at the equatorial
four sites. One axial site is occupied by the alkyne π-bonded
in the direction parallel to the Mo-P(1) bond, whereby the two
C and two O atoms in the COOMe group oriented toward the
P(1) atom are almost coplanar and this plane is twisted so that
the π-stacking interaction is available with the phenyl group
attached to P(1). At the trans site of the alkyne, the iodide ligand
is present, and the phenylene group in P4 is directed to this
side of the equatorial plane.
The Mo-P bond lengths in the range of 2.47-2.59 Å for 5
are significantly longer than those in 3a (2.36-2.44 Å), whereas
the MosC distances at 1.997(5) and 2.002(5) Å in the former
are considerably shorter than those in the latter at 2.075(2) and
2.062(2) Å. However, bonding parameters associated with the
CsCt CsC arrays of the coordinated MeCt CCOOMe are
almost comparable between 5 and 3a, being consistent with the
feature of the 4e-donating alkyne.9b
to
3
equiv, namely, trans-PhCHdCHPh, 52%; cis-
PhCHdCHPh, 6%; PhCH2CH2Ph, 6%; and PhCt CPh, 15%.
Presence of [MoH2Cl2(dppe)2]12 or [MoCl2(dppe)2]13 in these
reaction mixtures was demonstrated by their NMR spectra. The
related reactions converting coordinated alkynes into alkenes
by treatment with protic acid have been reported for several
transition-metal complexes of, for example, Mo,14 W,15 V,16
Nb,17 Ti,18 Zr,19 and Pt,20 where preferential formation of
E-isomers observed here was reported only for the Pt system.20
The 31P{1H} NMR spectra of 5 at room temperature showed
two multiplets with the same intensity at δ 41.1 and 88.0 due
1
to the outer and inner P atoms of P4, while the H NMR
spectrum at room temperature exhibited two sharp singlets at δ
1.20 and 3.13 assignable to CMe and OMe protons, respectively.
These findings indicate that the orientation of the binding alkyne
in 5 is not rigid in solution, which results in the equivalent
feature of the two inner P atoms as well as the two outer P
atoms on the NMR time scale.
Reactions of 3 and 4 with Acids. As for the reactivity of
the coordinated alkyne toward acid,11 Davies and co-workers
reported briefly that the reaction of 4e with HCl in THF at 25
°C gave predominantly [MoCl2(dppe)2] with the concomitant
formation of 1-butene (69%) and cis-2-butene (10%) together
with the liberation of 2-butyne (21%) and [MoH2Cl2(dppe)2].6
On the other hand, the reaction of 4d with excess HBF4 · OEt2
Interestingly, as shown in Table 4, the reaction of 3a with 2
equiv of hydrochloric acid under analogous conditions gives a
significant amount of the terminal alkene CH2dCHCH2COOMe
(10%) in addition to the expected inner alkenes trans-
CH3CHdCHCOOMe (36%) and cis-CH3CHdCHCOOMe (4%)
as well as the alkane CH3CH2CH2COOMe (13%), although the
combined yield of these four was 63%. When the amount of
HCl was increased, only the yield of CH2dCHCH2COOMe
increased, and it reached 44% by treatment with 4 equiv of HCl,
where the total yield of these four compounds was 98%. The
results for the reactions of 4a with 2 and 12 equiv of
hydrochloric acid under the analogous conditions are also shown
in Table 4, indicating much lower combined yields of these
four hydrogenated products than those from 3a. From the
reaction mixtures, [MoH2Cl2(dppe)2]12 and [MoCl(η2-
MeCt CCOOMe)(dppe)2]Cl were isolated as the Mo-containing
products. These findings may suggest that 4a is more amenable
to double protonation at the Mo center than 3a and the generated
dihydrido species [MoH2(η2-MeCt CCOOMe)(dppe)2]2+ does
not produce hydrogenated alkynes but releases alkyne or H2 to
give [MoH2Cl2(dppe)2] and [MoCl(η2-MeCt CCOOMe)-
(dppe)2]Cl, respectively. It is also interesting to note that the
reaction of the bis(alkyne) complex trans-[Mo(η2-MeCt
CH)2(dppe)2] with excess HCl gas is known to give no free
(10) Ohnishi, T.; Tsuboi, H.; Seino, H.; Mizobe, Y. J. Organomet. Chem.
2008, 693, 269.
(11) (a) Henderson, R. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 946.
(b) Pombeiro, A. J. L.; Richards, R. L. Coord. Chem. ReV. 1990, 104, 13.
(c) Seino, H.; Mizobe, Y.; Hidai, M. Chem. Rec. 2001, 1, 349.
(12) Chatt, J.; Heath, G. A.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1974, 2074.
(13) Busby, D. C.; George, T. A.; Iske, T. D. A., Jr.; Wagner, S. D.
Inorg. Chem. 1981, 20, 22.
(14) (a) Thomas, J. L. J. Am. Chem. Soc. 1973, 95, 1838. (b) Herberich,
G. E.; Englert, U.; Fassbender, W. J. Organomet. Chem. 1991, 420, 303.
(15) Theopold, K. H.; Holmes, S. J.; Schrock, R. R. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 1010.
(16) Henderson, R. A.; Lowe, D. L.; Salisbury, P. J. Organomet. Chem.
1995, 489, C22.
(17) Labinger, J. A.; Schwartz, J. J. Am. Chem. Soc. 1975, 97, 1596.
(18) Shur, V. B.; Burlakov, V. V.; Vol’pin, M. E. J. Organomet. Chem.
1988, 347, 77.
(19) Takahashi, T.; Swanson, D. R.; Negishi, E. Chem. Lett. 1987, 16,
623.
(20) (a) Barlex, D. M.; Kemmit, R. D. W.; Littlecott, G. W. Chem.
Commun. 1969, 613. (b) Tripathy, P. B.; Roundhill, D. M. J. Am. Chem.
Soc. 1970, 92, 3825.

FiVe-Coordinate Alkyne Complexes of Mo
Organometallics, Vol. 28, No. 4, 2009 1117
Table 4. Yields of Hydrogenation Products from the Reactions of 3a and 4a with Hydrochloric Acid
Table 5. Selected Bond Distances (Å) and Angles (°) in 8
alkenes or alkanes but the vinyl species trans-[MoCl(CH-
CHMe)(dppe)2] together with 1 equiv of free MeCt CH.7
Mechanism for the Hydrogenation of Coordinated
Alkyne. When the reaction of 3a with hydrochloric acid was
monitored by the use of NMR spectroscopy, it was verified that
the reaction mixture at the initial stages contained the species
showing the characteristic hydride resonance at δ -4.13, which
then disappeared with concurrent generation of the signals due
to the alkenes. An analogous species was also detected for the
reaction of 3b with hydrochloric acid, which showed the hydride
resonance at δ -3.80 as a triplet of triplets (JP-H ) 44 and 42
Hz) and two signals at δ 78.5 and 101.1 with the same intensities
(a) Bond Distance
Mo-P(1)
2.4638(5) Mo-P(2)
2.4363(7) Mo-P(4)
2.306(1) Mo-C(48)
2.320(3) Mo-C(50)
1.242(3) C(47)-C(48)
1.409(3) C(49)-C(50)
2.522(2)
2.4226(4)
Mo-P(3)
2.5523(6)
2.329(3)
2.334(2)
1.445(4)
1.373(4)
Mo-O(2)
Mo-C(49)
O(2)-C(47)
C(48)-C(49)
cf. Mo · · · C(47)
(b) Bond Angle
P(1)-Mo-P(2)
P(1)-Mo-P(4)
P(2)-Mo-P(4)
O(1)-C(47)-O(2)
76.69(2)
89.77(2)
144.38(2)
123.2(2)
P(1)-Mo-P(3)
P(2)-Mo-P(3)
P(3)-Mo-P(4)
104.23(2)
75.89(2)
75.84(2)
1
in the H or 31P{1H} NMR spectrum, respectively. Attempts
O(1)-C(47)-C(48) 114.2(2)
O(2)-C(47)-C(48) 122.6(2)
C(47)-C(48)-C(49) 123.8(2)
have been made to characterize these intermediates unambigu-
ously, and it has turned out that careful treatment of 3a with 1
equiv of HBF4 · Et2O results in the isolation of the hydridoalkyne
complex [MoH(η2-MeCt CCOOMe)(κ4-P4)][BF4] (7) as the
possible initial intermediate for the hydrogenation reaction of
the MeCt CCOOMe complex 3a (eq 6). The 31P{1H} NMR
spectrum showing two broad signals with the same intensities
at 20 °C as well as the 1H NMR spectrum exhibiting the hydride
resonance at δ -4.13 as a triplet of triplets is consistent with
this proposed structure that is closely related to the X-ray
analyzed structure of 5.
C(48)-C(49)-C(50) 122.8(2)
for the Mn complex [Mn(PhCH2CHCHCHCONMe2)(CO)3].21
Analogous nonplanar η5-oxapentadienyl ligands observed in
certain Mn22 and Rh23 complexes were also interpreted in terms
of the contribution of this acyl-κO-η3-allyl structure. On the
other hand, planar η5-oxapentadienyl ligands were found in some
Mn,24 Re,25 and Ru26 complexes, in which the π-electrons are
presumed to delocalize over three CsC and one CsO bonds.
As for this Mn complex,24 the bonding parameters associated
with the oxametallacycle can rather be interpreted by the
dienolate structure [Mn{CH2dCHCHdC(Me)O}(CO)3].
Upon standing the solution overnight at room temperature, 7
has proved to be converted into the oxapentadienyl complex
[Mo(η3-CH2CHCHCOOMe-κO)(κ4-P4)][BF4] (8) (eq 6), which
was fully characterized by the X-ray crystallography. An
ORTEP drawing is depicted in Figure 6, while selected bond
distances and angles are listed in Table 5. As shown in Figure
6, 8 has an η3-allyl group with the COOMe substituent at the
anti position, where the carbonyl O atom is also binding to
the Mo center. Four P atoms coordinate to the Mo center from
the other side, comprising a basal plane. Three allyl C atoms
C(48)-C(50) and the acyl O atom O(2) are almost coplanar,
but the acyl C atom C(47) having no bonding interaction with
Mo deviates by 0.26 Å from the least-squares plane defined by
the above four atoms. The acyl-κO-η3-allyl type ligand observed
here was previously demonstrated, to the best of our knowledge,
In consideration of these findings, the mechanism for the
hydrogenation of alkynes might be proposed as follows (Scheme
2). After the migration of the hydride in the hydridoalkyne
complexes (e.g., 7) to the coordinated alkyne, the generated η2-
(21) Abu Bakar, A.; Bryan, C. D.; Cordes, A. W.; Allison, N. T.
Organometallics 1994, 13, 3375.
(22) Masters, A. P.; Richardson, J. F.; Sorensen, T. S. Can. J. Chem.
1990, 68, 2221.
(23) Bleek, J. R.; Donnay, E. Organometallics 2002, 21, 4099.
(24) Cheng, M.-H.; Cheng, C.-Y.; Wang, S.-L.; Peng, S.-M.; Liu, R.-S.
Organometallics 1990, 9, 1853.
(25) Baudry, D.; Daran, J. C.; Dromzee, Y.; Felkin, H.; Jeannin, Y.;
Zekrzewski, J. J. Chem. Soc., Chem. Commun. 1983, 813.

1118 Organometallics, Vol. 28, No. 4, 2009
Niikura et al.
Scheme 2
vinyl species v affords cis- and trans-inner alkenes upon facile
second protonation. On the other hand, in the case of
MeCt CCOOMe, a significant amount of v presumably isomer-
izes to the η3-allyl species vi and 8, which may produce
predominantly the terminal alkene by the following second
protonation. Due to the considerable stability of 8, an excess
amount of acid seems to be required to liberate the alkene from
the Mo site of 8.
Two intermediate stages may be considered further in the
pathways from v (R ) Me, R′ ) COOMe) to 8; one is the
η3-allyl {Mo(η3-CH2CHCH-COOMe)} species vi via the
internal H-shift, which corresponds to the intermediate proposed
previously for the reaction of 4e with HX to give the inner and
terminal alkenes (vide supra).6 Transformations of η2-vinyl
complexes27 to η3-allyl species through H migration have been
observed previously for the other Mo(II)28 and W(II)29 com-
plexes. It might also be possible that the intermediate vi directly
affords the alkene mixture in the presence of an excess amount
of HCl. The other intermediate to 8 is the κ2-C,O-vinyl
{Mo(MeCdCHCOOMe)} species vii, and the complexes of this
type are precedented, which include [MoH2(HCdCH-
COOR)(dppe)2][BF4]30 together with some related Mo com-
plexes.31 Although these complexes were derived through the
different reaction courses, formation of the κ2-C,O-vinyl
{M(HCdCHCOOMe)} complex from the hydrido complex with
HCt CCOOMe was demonstrated for M ) Fe.32
Reactions of 3a and 3b with H2S Gas. When 3a dissolved
in THF was treated with excess H2S gas at room temperature,
formation of MeCH(SH)CH2COOMe in 54% yield was ob-
served in the reaction mixture. This thiol is presumably produced
through the addition of H2S to the hydrogenated product
CH2dCHCH2COOMe. This was confirmed independently by
treating this alkene with H2S gas in THF, although this
conversion into the thiol was considerably slower than its
formation from 3a and H2S gas. On the other hand, the reaction
of MeCHdCHCOOMe with H2S did not proceed under these
conditions. As the Mo-containing product, the expected bis(hy-
(26) Schmidt, T.; Goddard, R. J. Chem. Soc., Chem. Commun. 1991,
1427.
(27) Frohnapfel, D. S.; Templeton, J. L. Coord. Chem. ReV. 2000, 206-
207, 199.
(28) (a) Bottrill, M.; Green, M. J. Am. Chem. Soc. 1977, 99, 5795. (b)
Green, M. J. Organomet. Chem. 1986, 300, 93, and references therein. .
(29) (a) Feng, S. G.; Templeton, J. L. Organometallics 1992, 11, 2168.
(b) Frohnapfel, D. S.; White, P. S.; Templeton, J. L. Organometallics 1997,
16, 3737. (c) Frohnapfel, D. S.; White, P. S.; Templeton, J. L. Organome-
tallics 2000, 19, 1497.
(30) Kashef, N.; Richards, R. L. J. Organomet. Chem. 1989, 365, 309.
(31) (a) Ito, T.; Tosaka, H.; Yoshida, S.; Mita, K.; Yamamoto, A.
Organometallics 1986, 5, 735. (b) Woodworth, B. E.; Frohnapfel, D. S.;
White, P. S.; Templeton, J. L. Organometallics 1998, 17, 1635.
(32) Almeida, S. S. P.; Duarte, M. T.; Ribeiro, L. M. D.; Gormley, F.;
Galvao, A. M.; da Silva, J. J. R. F.; Pombeiro, A. J. L. J. Organomet. Chem.
1996, 524, 63.
Figure 6. An ORTEP drawing for the cation in 8 at 30% probability
level. Hydrogen atoms except for those of the allyl group are
omitted for clarity.

FiVe-Coordinate Alkyne Complexes of Mo
Organometallics, Vol. 28, No. 4, 2009 1119
drosulfido) complex [Mo(SH)2(κ4-P4)] (9), having the trigonal-
prismatic structure analogous to the dichloro complex 6,4 was
isolated in 46% yield (eq 7). It has already been found separately
by us that 9 can be obtained directly from the reaction of 1
with H2S gas, and its structure has been determined in detail
by the X-ray analysis, which will be reported elsewhere.33 From
the reaction of 3b with H2S gas, a mixture of trans- and cis-
PhCHdCHPh (26 and 23% yields, respectively) was produced
in addition to PhCH2CH2Ph (12%) and free PhCt CPh (2%),
which presents a sharp contrast to the reactions of 3b with 2 or
3 equiv of hydrochloric acid described above to give no cis-
stilbene.
1.5 mmol), and a mixture was stirred for 4 h at 80 °C. A resultant
red solution was concentrated, and hexane was added. Title
compound 3a · 0.5C6H5CH3 was obtained as red crystals (416 mg,
1
87% yield). H NMR (C6D6): δ 3.33 (s, 3H, COOMe). The CMe
protons could not be assigned (see text). 31P{1H} NMR (C6D6): δ
103.7 (m), 109.2 (m), 121.0 (m), and 135.2 (m) for the major isomer
and 95.2 (m), 111.0 (m), 125.1 (m), and 133.2 (m) for the minor
isomer. 13C{1H} NMR (THF-d8, 40 °C): δ 19.2 (br, MeC), 26.3,
31.4 (br, PCH2), 50.4 (s, OMe), 125-150 (m, aromatic), 172-178
(vbr, CCO2Me), 180.5 (vbr, CdO), 186-192 (vbr, MeC). 13C{1H}
NMR (THF-d8, -20 °C): δ 18.8 (br d, J ) 5 Hz, MeC), 20.3 (br
d, J ) 7 Hz, MeC), 24-34 (m, PCH2), 50.4, 50.8 (s, OMe),
125-150 (m, aromatic), 173.9 (br d, JCP ) 20 Hz, CCO2Me), 178.3
(br dd, JCP ) 20, 2 Hz, CCO2Me), 179.7 (br d, JCP ) 7 Hz, CdO),
181.6 (br d, JCP ) 4 Hz, CdO), 186.0 (br dd, JCP ) 25, 8 Hz,
MeC), 189.7 (br d, JCP ) 23 Hz, MeC). The ratio of the major and
the minor isomers was about 1:1. IR (KBr): ν(Ct C), 1626;
ν(CdO), 1675 cm-1. Anal. Calcd for C54.5H52MoO2P4: C, 68.27;
H, 5.47. Found: C, 68.34; H, 5.28.
Preparation of 3b. This product was obtained from the
analogous reaction of 1 · C6H6 (648 mg, 0.502 mmol) and PhCt CPh
(267 mg, 1.50 mmol) in toluene (20 mL) at 80 °C for 6 h. The
evaporated reaction mixture residue was extracted with ether, and
after addition of hexane to the concentrated extract, 3b was isolated
as red crystals (418 mg, 84% yield). 31P{1H} NMR (C6D6): δ 101,
108, 125, 133 (br, 1P each). 13C{1H} NMR (THF-d8, 40 °C): δ
26.8 (br t, JCP ) 19 Hz, PCH2), 31.6 (br t, JCP ) 21 Hz, PCH2),
122.9 (s, p-C of CPh), 125.4 (br, o- or m-C of CPh), 149.0 (s,
ipso-C of CPh), 126-154 (m, aromatic), 186-191 (vbr, Ct C).
IR (KBr): ν(Ct C), 1633 cm-1. Anal. Calcd for C60H52MoP4: C,
72.58; H, 5.28. Found: C, 72.74; H, 5.57.
Conclusion
A series of Mo(0) tetraphosphine complexes [Mo(RCt
CR′)(P4)] (3) and their diphosphine analogues [Mo(RCt
CR′)(dppe)2] (4) have been prepared and their trigonal-
bipyramidal structures in a solid state fully characterized. These
demonstrate the new candidates of the still rare five-coordinate
Mo(0) complexes. In 3 and 4, the alkynes occupying one
equatorial site bind to the Mo center parallel to the axial PsP
vector. The VT-NMR study has disclosed that these complexes
are fluxional in solutions, where the rotation of the alkynes takes
place probably via the square-pyramidal intermediates. Reactions
of 3 and 4 with HCl(aq) in THF gave the mixtures of alkenes,
alkanes, and liberated alkynes, the ratio of which sharply
depends upon the nature of the alkynes, phosphines, and the
ratio of HCl to the complex; for example, the P4 comlexes 3
tend to give alkenes in higher yields than the dppe complexes
4. Two new P4 complexes 7 and 8 have been isolated as the
intermediate stages in the hydrogenation reactions of coordinated
alkyne in the MeCt CCOOMe complex 3a, and the mechanism
for this hydrogenation reaction including 7 and 8 has been
proposed.
Preparation of 3c. This product was obtained from the analogous
reaction of 1 · C6H6 (129 mg, 0.100 mmol) and PhCt CMe (38 µL,
0.30 mmol) in toluene (5 mL) at 80 °C for 2 h. The evaporated
reaction mixture residue was extracted with ether, and 3c was
obtained as red crystals after the storage of the concentrated extract
at -20 °C for a week. However, crystals of 3c deposited as a
mixture with dppe and could not be purified despite repeated trials.
1H NMR (THF-d8, 40 °C): δ 2.18 (br s, MeC). 31P{1H} NMR
(C6D6): δ 104, 110, 122, 134 (br, 1P each). 13C{1H} NMR (THF-
d8, 40 °C): δ 19.3 (br s, MeC), 26.3, 31.7 (br, PCH2), 122.5 (s, p-C
of CPh), 124.8 (s, o- or m-C of CPh), 149.9 (s, ipso-C of CPh),
126-153 (m, aromatic), 184.3, 185.8 (br, Ct C). IR (KBr):
ν(Ct C), 1643 cm-1. Satisfactory analytical data were not available.
Preparation of 4a. A solution of 2 (495 mg, 0.522 mmol) and
MeCt CCOOMe (150 µL, 1.5 mmol) in benzene (20 mL) was
refluxed for 3 h with stirring. The resultant dark red solution was
filtered, and hexane was added to the concentrated filtrate to give
4a · 0.5C6H6 as red crystals (428 mg, 80% yield). 1H NMR (C6D6):
δ 2.70 (s, 3H, CMe), 3.18 (s, 3H, COOMe). 31P{1H} NMR (C6D6):
δ 86.1 (m, 1P), 94.6 (m, 1P), 108.1 (m, 2P). 13C{1H} NMR (THF-
d8): δ 21.1 (br d, JCP ) 5 Hz, MeC), 33.5-34.5, 35-36 (m, PCH2),
50.5 (s, OMe), 126-152 (m, Ph), 177.5 (br d, JCP ) 27 Hz,
CCO2Me), 180.5 (s, CdO), 189.9 (br d, JCP ) 33 Hz, MeC). IR
(KBr): ν(Ct C), 1622; ν(CdO), 1683 cm-1. Anal. Calcd for
C60H57MoO2P4: C, 69.97; H, 5.58. Found: C, 69.86; H, 5.55.
Preparation of 4b. A solution of 2 (478 mg, 0.504 mmol) and
PhCt CPh (268 mg, 1.50 mmol) in benzene (25 mL) was refluxed
for 3 h with stirring, and then, the resultant red suspension was
filtered off. The red brown solid of 4b was washed with benzene
and dried in vacuo (318 mg). An additional amount of 4b was
obtained by refluxing the filtrate further for 3 h and concentrating
the resultant mixture (45 mg). The combined yield was 67%.
31P{1H} NMR (THF-d8): δ 90-95, 101-106 (br, 2P each). 13C{1H}
NMR (THF-d8): δ 123.0 (s, p-C of CPh), 126.0, 127.0 (s, o- and
m-C of CPh), 149.7 (s, ipso-C of CPh), 190.6 (m, Ct C); other
signals were not assignable due to severe broadening. IR (KBr):
Experimental Section
General. All manipulations were carried out under N2 using
standard Schlenk techniques. Solvents were dried by common
methods and distilled under N2 before use. Complexes 11 and 234
were prepared according to the literature methods, while other
chemicals were obtained commercially and used as received.
NMR and IR spectra were measured on a JEOL alpha-400 or a
JASCO FT/IR-420 spectrometer. The NMR data described below
were obtained at 20 °C, except for those stated otherwise. For the
1H NMR data, the signals due to phenyl, phenylene, and methylene
groups are omitted. GC-MS analyses used Shimadzu GCMS
QP5050 equipped with a CBP10 capillary column, while quantita-
tive GLC analyses were by Shimadzu GC14B with a CBP1 or
CBP10 capillary column. Elemental analyses were done with a
Perkin-Elmer 2400 series II CHN analyzer.
Preparation of 3a. To a suspension of 1 · C6H6 (645 mg, 0.500
mmol) in toluene (20 mL) was added MeCt CCOOMe (150 µL,
(33) Iwasa, K.; Seino, H.; Niikura, F.; Mizobe, Y. Unpublished results.
(34) (a) Hidai, M.; Tominari, K.; Uchida, Y. J. Am. Chem. Soc. 1972,
94, 110. (b) Dilworth, J. R.; Richards, R. L. Inorg. Synth. 1980, 20, 119.

1120 Organometallics, Vol. 28, No. 4, 2009
Niikura et al.
Table 6. Crystal Data for 3a · 0.5C6H5CH3, 3b, 4a · 0.5C6H6, 5 · 3CH2Cl2, and 8 · 0.75Et2O · 0.25CH2Cl2
3a · 0.5C6H5CH3
3b
4a · 0.5C6H6
5 · 3CH2Cl2
8 · 0.75Et2O · 0.25CH2Cl2
formula
fw
space group
a, Å
b, Å
c, Å
C54.5H52MoO2P4
958.84
P1 (No. 2)
C60H52MoP4
992.91
P1 (No. 2)
C60H57MoO2P4
1029.94
P1 (No. 2)
C54H54Cl6I2MoO2P4
1421.38
P21/n (No. 14)
14.207(2)
26.132(3)
15.818(2)
90
90.2654(5)
90
5873(1)
4
C54.25H57BCl0.5F4MoO2.75P4
1077.41
P1 (No. 2)
j
j
j
j
11.649(1)
13.909(1)
17.279(1)
97.083(6)
105.394(6)
114.742(6)
2361.8(3)
2
12.564(1)
12.9979(3)
17.618(2)
94.064(6)
102.6552(3)
115.018(5)
2499.9(4)
2
13.615(2)
18.151(3)
21.636(4)
94.861(3)
91.653(2)
102.108(3)
5203(2)
4
12.972(2)
14.103(2)
16.393(2)
65.491(4)
73.284(5)
81.146(6)
2611.4(6)
2
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
F
calcd, g cm-3
1.348
1.319
1.315
1.607
1.370
crystal size, mm3
no. of unique reflns
no. of data (I > 2σ(I))
no. of variables
transmn factor
R1a
0.40 × 0.30 × 0.30
0.40 × 0.30 × 0.15
0.40 × 0.40 × 0.30
0.50 × 0.30 × 0.10
0.50 × 0.35 × 0.15
11192
11326
23508
13907
12381
9107
612
0.678-0.873
0.036
0.107
1.005
8822
638
0.719-0.938
0.036
0.108
1.009
16035
1354
0.674-0.882
0.063
0.167
1.020
9081
683
0.547-0.844
0.054
0.151
1.043
9881
755
0.688-0.934
0.038
0.110
1.029
wR2b
GOFc
b
c
a R1 ) Σ|Fo| - |Fc|/Σ|Fo| (I > 2σ(I)). wR2 ) [Σ(w(Fo - Fc2)2)/Σw(Fo )2]1/2 (all data). GOF ) [Σw(|Fo| - |Fc|)2/{(no. observed) - (no.
2
2
variables)}]1/2
.
ν(Ct C), 1607 cm-1. Anal. Calcd for C66H58MoP4: C, 74.02; H,
5.46. Found: C, 73.84; H, 5.41.
COOMe)(dppe)2]Cl as green crystals (17 mg, 16% yield). The
benzene extract was dried up, and the residue was crystallized from
THF-ether, giving [MoH2Cl2(dppe)2] as orange crystals (8 mg, 8%
yield). Although the isolation was unsuccessful, the presence of
trans-[MoCl2(dppe)2] in the reaction mixture was confirmed by its
characteristic, paramagnetically shifted signals in the 1H NMR
Preparation of 4c. This complex was obtained from 2 (474 mg,
0.500 mmol) and PhCt CMe (190 µL, 1.5 mmol) in benzene (25
mL) in 40% yield (204 mg) by the procedure analogous to that for
1
4a. H NMR (C6D6): δ 2.60 (s, 3H, CMe). 31P{1H} NMR (C6D6):
δ 88.3 (br, 1P), 94.6 (br, 1P), 98.8 (br, 1P), 102.8 (br, 1P). 13C{1H}
NMR (THF-d8): δ 21.0 (s, MeC), 33-37 (m, PCH2), 123.0 (s, p-C
of CPh), 125.7, 127.5 (s, o- and m-C of CPh), 150.5 (s, ipso-C of
CPh), 126-152 (m, PPh), 186.2 (br t, JCP ) 13 Hz, C≡C), 187.8
(br t, JCP ) 16 Hz, Ct C). IR (KBr): ν(Ct C), 1608 cm-1. Anal.
Calcd for C61H56MoP4: C, 72.62; H, 5.59. Found: C, 72.78; H, 5.70.
Preparation of 5. Into a stirred solution of 3a · 0.5C6H5CH3 (94
mg, 0.098 mmol) in toluene (2 mL) was added a solution of I2 (25
mg, 0.10 mmol) in toluene (3 mL) through canulei at 0 °C. The
mixture was continuously stirred at 0 °C for 3 h and then filtered
off. Crystallization of the remaining solid from CH2Cl2-ether
afforded 5 · 3CH2Cl2 as green crystals. Several crystals were
collected and sealed immediately in glass capillaries for the X-ray
diffraction study. Other crystals were filtered off and dried
thoroughly under vacuum, which were formulated as 5 · 0.25CH2Cl2
from the 1H NMR spectrum (62 mg, 53% yield). 1H NMR (CDCl3):
δ 1.10 (s, 3H, CMe), 3.13 (s, 3H, COOMe), 5.30 (s, 0.5H, CH2Cl2).
31P{1H} NMR (CDCl3): δ 41.2, 88.0 (2P each); AA′XX′ pattern
with JA-X + JA-X′ ) 93 Hz. 13C{1H} NMR (CD2Cl2): δ 21.7 (s,
MeC), 27.4 (br d, JCP ) 30 Hz, PCH2), 33.9 (dd, JCP ) 31, 13 Hz,
PCH2), 52.5 (s, OMe), 127-150 (m, PPh), 172.8 (br t, JCP ) 5 Hz,
spectrum. Data for [MoCl(MeCt CCOOMe)(dppe)2]Cl: H NMR
1
(CD2Cl2): δ 1.70 (s, 3H, CMe), 2.84 (s, 3H, OMe). 31P{1H} NMR
(CD2Cl2): δ 40-43 (m). IR (KBr): ν(CdO), 1701 cm-1. Satisfactory
analysis data were not available even after repeated crystallization.
Preparation of 7. To a solution of 3a · 0.5C6H5CH3 (95 mg,
0.099 mmol) in THF (3 mL) was added 54% HBF4 · Et2O (14 µL,
0.10 mmol) at 0 °C. After stirring at this temperature for 40 min,
ether (10 mL) was added slowly with stirring, and the mixture was
filtered. The filtrate was dried up in vacuo at 0 °C, and the residual
solid was washed repeatedly with ether. The yield of 7 as a purple
solid was 47 mg (∼47%). Since 7 was thermally unstable and
contained small amounts of impurities even after recrystallization,
satisfactory analysis data were not available. 1H NMR (CD2Cl2): δ
-4.13 (tt, JP-H ) 45 and 41 Hz, 1H, MoH), 2.17 (s, 3H, CMe),
3.25 (s, 3H, COOMe). 31P{1H} NMR (CD2Cl2): δ 81.7 (br, 2P),
99.7 (m, 2P). IR (KBr): ν(CdO), 1698 cm-1
.
Isolation of 8. Complex 7 (40 mg, ∼0.040 mmol) was dissolved
in CH2Cl2 (2 mL), and ether (17 mL) was layered on it. After being
kept at room temperature for 10 days, dark red crystals grown were
collected by filtration. The filtrate was dried up in vacuo, and the
residue was subjected to the same procedure two more times,
affording 8 · 0.75Et2O · 0.25CH2Cl2 in 56% combined yield (24 mg).
From the NMR criteria, existence of two isomers in a ratio of 5:3
in equiribrium was confirmed at 0 °C, and significant broadening
of the signals due to the exchange between these two was observed
at the temperatures higher than 20 °C. 1H NMR (CD2Cl2, 0 °C): δ
2.09 (s, OMe of the major isomer), 2.57 (s, OMe of the minor
isomer), 1.12 (t, 4.5H, Et2O), 3.40 (q, 3H, Et2O), 5.31 (s, 0.5H,
CH2Cl2). The signals due to π-allyl group were not assignable
because of their overlapping with those of PCH2 in the range δ
0.3-3.8. 31P{1H} NMR (CD2Cl2, 0 °C): δ 58.3 (ddd, J ) 26, 25,
14 Hz), 77.6 (ddd, J ) 31, 25, 10 Hz), 110.1 (ddd, J ) 52, 26, 10
Hz), 119.1 (ddd, J ) 52, 31, 14 Hz) for the major isomer and 49.8,
65.7, 120.2, 130.4 (m) for the minor isomer. IR (KBr): ν(CdO),
1549 cm-1. Anal. Calcd for C54.25H57BCl0.5F4MoO2.75P4: C, 60.48;
H, 5.33. Found: C, 60.52; H, 5.38.
CdO), 222.0 (dd, JCP ) 15, 6 Hz, t CCOOMe), 236.7 (dd, JCP
)
13, 9 Hz, MeCt ). IR (KBr): ν(CdO), 1708 cm-1. ν(Ct C), not
assignable. Anal. Calcd for C51.25H48.5Cl0.5I2MoO2P4: C, 51.82; H,
4.12. Found: C, 51.25; H, 4.01.
Reactions of Alkyne Complexes with Aqueous HCl. Typical
procedures are as follows. Aqueous HCl (35%) was added to a
solution of 3 or 4 (0.10 mmol) in THF (4 mL) at 0 °C, and the
mixture was stirred at this temperature for 1 h. Organic compounds
produced were analyzed by GLC and GC-MS methods, where the
yields were determined by the use of naphthalene (for 3a and 4a)
or biphenyl (for 3b and 4b) as the internal standard.
Isolation of [MoCl(MeCt CCOOMe)(dppe)2]Cl. Into a stirred
THF solution (4 mL) of 4a (105 mg, 0.102 mmol) was added
aqueous HCl (35%, 18 µL, 0.21 mmol) at 0 °C. After 1 h at 0 °C,
the mixture was evaporated to dryness under reduced pressure, and
the green residue was washed with ether. The residual solid was
extracted with benzene (10 mL), and the remaining solid was
crystallized from CH2Cl2-ether to afford [MoCl(MeCt C-
Reactions of 3a with H2S Gas. (1) Through a solution of
3a · 0.5C6H5CH3 (96 mg, 0.10 mmol) in THF (3 mL), H2S gas was
bubbled for 10 min at 0 °C, and the mixture was stirred at room

FiVe-Coordinate Alkyne Complexes of Mo
Organometallics, Vol. 28, No. 4, 2009 1121
temperature for 24 h. Complex 9 precipitated as a green solid, which
techniques, while all hydrogens were placed at the calculated
positions, except for those stated otherwise, and included at the
final stages of the refinements.
was filtered off, washed with ether, and dried in vacuo (41 mg,
1
47% yield). Complex 9 was identified by comparing its H and
31P{1H} NMR spectra with those of the authenticated complex.33
In the crystal of 3a · 0.5C6H5Me, the solvating toluene was present
at the center of symmetry, and the Me group was disordered over
two positions with the same occupancies. The crystal of 4a · 0.5C6H6
contained two crystallographically independent molecules, in one
of which the COOMe group was disordered over two positions
with a 6:4 occupancy ratio. In 5 · 3CH2Cl2, one Cl atom in one of
the three solvating CH2Cl2 molecules was disordered over two
positions in a ratio of 3:1. In the crystal of 8 · 0.75Et2O · 0.25CH2Cl2,
the position of solvating molecule was occupied by disordered Et2O
or CH2Cl2 in a ratio of 3:1. Hydrogen atoms in these molecules
were not placed for calculation. Four H atoms in the allyl group
were found from the Fourier map and refined isotropically.
(2) After the analogous treatment of a solution of 3a · 0.5C6H5CH3
(55 mg, 0.057 mmol) in THF-d8 (2 mL), the yield of
MeCH(SH)CH2COOMe35 was determined to be 54% by recording
the 1H NMR spectrum of the liquid phase using triphenylmethane
as an internal standard. δ 1.32 (d, J ) 6.8 Hz, 3H, MeC), 2.12 (d,
J ) 6.8 Hz, 1H, SH), 2.52 (dd, J ) 16.0, 7.7 Hz, 1H, CH2), 2.59
(dd, 1H, J ) 16.0, 6.5 Hz, 1H, CH2), 3.28 (m, 1H, MeCH), 3.62
(s, 3H, OMe). Formations of trace amounts of methyl tetrolate and
its hydrogenation products were also observed.
X-ray Crystallography. Single crystals of 3a · 0.5C6H5CH3, 3b,
4a · 0.5C6H6, 5 · 3CH2Cl2, and 8 · 0.75Et2O · 0.25CH2Cl2 were sealed
in glass capillaries under argon and mounted on a Rigaku mercury-
CCD diffractometer equipped with a graphite-monochromatized Mo
KR source. All diffraction studies were done at 23 °C, whose details
are listed in Table 6. The X-ray analysis was carried out also for
3c, whose data are added in Supporting Information. Data collection
were performed by using the CrystalClear program package.36 All
data were corrected for Lorentz and polarization effects as well as
for absorption.
Acknowledgment. This work was supported by Grant-
in-Aid for Scientific Research on Priority Areas (No.
18065005, “Chemistry of Concerto Catalysis”) from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan, and by CREST of JST (Japan Science and
Technology Agency).
Supporting Information Available: Details of VT-NMR data
for 3 and 4 and crystallographic data of 3a · 0.5C6H5CH3, 3b, 3c,
4a · 0.5C6H6, 5 · 3CH2Cl2, and 8 · 0.75Et2O · 0.25CH2Cl2 in CIF
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
Structure solution and refinements were conducted by using the
CrystalStructure program package.37 The positions of non-hydrogen
atoms were determined by Patterson methods (PATTY)38 and
subsequent Fourier synthesis (DIRDIF99).39 These were refined
with anisotropic thermal parameters by full-matrix least-squares
OM800615A
(35) Kumar, I; Jolly, R. S. Org. Lett. 1999, 1, 207.
(38) PATTY: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykall, C. The
DIRDIF Program System, Technical Report of the Crystallography Labora-
tory; University of Nijmegen: Nijmegen, The Netherlands, 1992.
(39) DIRDIF-99: Beurskens, P. T.; Admiraal, G.; Beurskens, G.;
Bosman, W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99
Program System, Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1999.
(36) (a) CrystalClear 1.3.5; Rigaku Corporation, 1999; CrystalClear
Software User′s Guide; Molecular Structure Corporation, 2000. (b) Pflugrath,
J. W. Acta Crystallogr., Sect. D 1999, 55, 1718.
(37) (a) CrystalStructure 3.8.0, Crystal Structure Analysis Package;
Rigaku and Rigaku/MSC, 2000-2006. (b) Carruthers, J. R.; Rollett, J. S.;
Betteridge, P. W.; Kinna, D.; Pearce, L.; Larsen, A.; Gabe, E. CRYSTALS
Issue 11; Chemical Crystallography Laboratory: Oxford, U.K., 1999.