Bis(diphenylphosphino) acetylene as bifunctional ligand in dicobalt carbonyl complexes

Article abstract of DOI:10.1021/om0106783

Treatment of bis(diphenylphosphino)acetylene (DPPA) with a bis(diphenylphosphino)-methylene (DPPM)-bridged dicobalt complex, [{μ-P,P-PPh₂CH₂PPh₂}Co₂(CO)₆ ], 3, yielded a DPPA-bridged dicobalt compound

Full text of DOI:10.1021/om0106783

Organometallics 2002, 21, 961-967
961
Bis(d ip h en ylp h osp h in o)a cetylen e a s Bifu n ction a l Liga n d
in Dicoba lt Ca r bon yl Com p lexes
Fung-E Hong,* Yu-Chang Chang, Ruei-E Chang, Shu-Chun Chen, and
Bao-Tsan Ko
Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan
Received J uly 27, 2001
Treatment of bis(diphenylphosphino)acetylene (DPPA) with a bis(diphenylphosphino)-
methylene (DPPM)-bridged dicobalt complex, [{µ-P,P-PPh2CH2PPh2}Co2(CO)6], 3, yielded a
DPPA-bridged dicobalt compound, [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-PPh2CtCPPh2}], 5.
Two oxidized complexes, [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-PPh2CtCP(dO)Ph2}], 6, and [{µ-
P,P-PPh2CH2PPh2}Co2(CO)4{µ-P(dO)Ph2CtCP(dO)Ph2}], 7, were obtained along with 5
during the chromatographic separation process. Further reaction of 5 with selenium powder
in THF at 25 °C produced [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-P(dO)Ph2CtCP(dSe)Ph2}], 8,
a compound with two phosphorus atoms of 5 oxidized by oxygen and selenium, respectively.
The 31P-77Se coupling constant of the Se-P bond is 723 Hz. The reaction of 5 with Mo(CO)6
in toluene at 110 °C yielded [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-P,P-PPh2CtCPPh2}Mo(CO)4],
9. Compounds 5-9 were characterized by spectroscopic means as well as by X-ray diffraction
studies. Crystal structures of 6-8 reveal that the distance between the oxide and the adjacent
methylene proton is within the range of an intramolecular hydrogen bond. The structure of
9 reveals that 5 behaves as a diphosphine chelating ligand toward the Mo(CO)4 fragment.
The fluxional behavior of the DPPM ligands in 5 and 9 were examined by variable-
temperature 1H NMR experiments. The calculated activation energies for the fluxional
processes are 19.2 and 7.1 kcal/mol for 5 and 9, respectively.
Sch em e 1
In tr od u ction
Bidentate phosphine ligands have played an impor-
tant role in transition metal-based homogeneous ca-
talysis.1 Recently, the capacity of bis(diphenylphosphino)-
acetylene (PPh2CtCPPh2) to act as a bifunctional ligand
to transition metals has been examined widely.2
Our previous work described the preparation of one
type of bidentate phosphine ligand, [Co2(CO)6(µ-PPh2Ct
CPPh2)], 1, from the reaction of a bifunctional ligand,
bis(diphenylphosphino)acetylene (DPPA), with 1 equiv
of Co2(CO)8 (Scheme 1).3 Unfortunately, crystallization
* To whom correspondence should be addressed.
(1) (a) Puddephatt, R. J . Coord. Chem. Rev. 1980, 33, 149. (b) Elliot,
D. J .; Holah, D. G.; Hughes, A. N.; Magnuson, V. R.; Moser, I. M.;
Puddephatt, R. J .; Xu, W. Organometallics 1991, 10, 3933. (c) Cornils,
B., Herrmann, W. A., Eds. Applied Homogeneous Catalysis with
Organometallic Compounds; VCH: New York, 1996; Vols. 1, 2. (d)
Noyori, R. Asymmetric Catalysis in Organic Synthesis; J ohn Wiley &
Sons: New York, 1994. (e) Parshall, G. W.; Ittel, S. D. Homogeneous
Catalysis, 2nd ed.; J ohn Wiley & Sons: New York, 1992; Chapter 8.
(f) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1. (g) Kagan, H. B.
Asymmetric Synthesis Using Organometallic Catalysts. In Compre-
hensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel,
E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 8, Chapter 53. (h)
J acobsen, E. N., Pfaltz, A., Yamamoto, H., Eds. Comprehensive
Asymmetric Catalysis; Springer-Verlag: New York, 1999; Vol. I.
(2) (a) Carty, A. J .; Efraty, A.; Ng, T. W.; Birchall, T. Inorg. Chem.
1970, 9, 1263. (b) Nickel, T. M.; Yau, S. Y. W.; Went, M. J ., J . Chem.
Soc., Chem. Commun. 1989, 775. (c) Powell, A. K.; Went, M. J . J . Chem.
Soc., Dalton Trans. 1992, 439. (d) Bennett, M. A.; Castro, J .; Edwards,
A. J .; Kopp, M. R.; Wenger, E.; Willis, A. C. Organometallics 2001, 20,
980. (e) Daran, J .-C.; Cabrera, E.; Bruce, M. I.; Williams, M. L. J .
Organomet. Chem. 1987, 319, 239. (f) Hogarth, G.; Norman, T.
Polyhedron 1996, 15, 2859. (g) Bruce, M. I. Coord. Chem. Rev. 1997,
166, 91.
of 1 was not feasible due to its oily nature.4 Treatment
of 1 with another molar equivalent of Co2(CO)8 yielded
a brown complex, [Co2(CO)4(µ-CO)2{µ-P,P-(µ-PPh2Ct
CPPh2)Co2(CO)6}], 2.
The crystal structure of 2 (Figure 1) shows that the
framework consists of a pseudo-tetrahedral Co2C2 unit
with a bidentate phosphine-bridged Co2 fragment. Both
the -PPh2 substituents are bent away from the DPPA-
bridged dicobalt center and coordinate to another di-
cobalt fragment. The bond angles of P(1)-C(13)-C(14)
and P(2)-C(14)-C(13) are 136.56(19)° and 132.32(18)°,
respectively. The two cobalt atoms Co(1) and Co(2) and
two phosphorus atoms are almost coplanar, with a
dihedral angle of 9.39°. In this respect, it can be
(4) (a) Carty, A. J .; Ng, T. W.; Carter, W.; Palenik, G. J . J . Chem.
Soc., Chem. Commun. 1969, 1101. (b) Carty, A. J .; Ng, T. W. J . Chem.
Soc., Chem. Commun. 1970, 149.
(3) Hong, F.-E.; Huang, Y.-C.; Wang, S.-L.; Liao, F.-L. Inorg. Chem.
Commun. 1999, 2, 450.
10.1021/om0106783 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/07/2002

962 Organometallics, Vol. 21, No. 5, 2002
Hong et al.
Sch em e 2
Sch em e 3
CP(dO)Ph2}], 6, with one phosphorus atom oxidized
and [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-P(dO)Ph2Ct
CP(dO)Ph2}], 7, with two phosphorus atoms oxidized,
along with 5, were obtained. However, compounds 6 and
7 were not present in the crude reaction mixture 1H
NMR. The oxidation must have taken place during the
chromatographic separation process, most likely the
oxide source being from silica gel. This observation is
further supported by the fact that increasing amounts
of 6 and 7 were obtained on prolonging the chromato-
graphic separation process purposely. Since this type
of oxidation was not observed during the purification
process of 1, it is speculated that the addition of the
electron-donating DPPM ligand to the framework of 1
makes the oxidation of the phosphorus atoms more
feasible.7
F igu r e 1. Molecular structure of [Co2(CO)4(µ-CO)2{µ-P,P-
(µ-PPh2CtCPPh2)Co2(CO)6}], 2.
regarded as a modified form of 1,2-bis(diphenylphos-
phino)ethane (DPPE), a very commonly used bidentate
phosphine ligand.5
In this work we explored the bonding capacity of the
bifunctional ligand PPh2CtCPPh2 toward the dicobalt
system. The preparations and reactivities of a series of
compounds related to 1 are presented. To improve the
crystallization of alkyne-bridged dicobalt compounds, a
diphosphine bridging ligand, in this study DPPM, was
used. Here we also report the geometric change of the
bifunctional ligand PPh2CtCPPh2 after coordination to
a dicobalt fragment through its triple bond, which brings
about a significant effect upon chelation toward molyb-
denum carbonyl complex.
Resu lts a n d Discu ssion
Crystallizations of 5, 6, and 7 were successful, which
is contrast to the case of 1, probably due to the addition
of the DPPM ligand, and their crystal structures were
determined by X-ray diffraction studies. The main
frameworks for these three compounds are not much
different (Table 2, Figure 2). All carbonyls are terminal.
The phenyl rings of the bridged DPPA in all three cases
are pointed away from the center of the molecule to
prevent steric hindrance. The oxide points down toward
the adjacent proton of the methylene in the case of 6
and 7. The two cobalt atoms and two phosphorus atoms
of the DPPM are almost coplanar, as in the case of 2.
The dihedral angles are 9.39°, 12.13°, and 7.08° for 5,
6, and 7, respectively. The bond lengths of the bridged
alkynes are 1.344(4), 1.364(5), and 1.359(3) Å for 5, 6,
(A) Syn t h esis of DP P A-Br id ged Dicob a lt Ca r -
bon yl Com p lexes. Treatment of DPPM with 1 equiv
of Co2(CO)8 in THF at 60 °C for 8 h afforded two DPPM-
coordinated dicobalt compounds, [Co2(CO)6(µ-P,P-PPh2-
CH2PPh2)], 3, and [Co2(CO)7(µ-P-PPh2CH2PPh2)], 4
(Scheme 2).6
Further reaction of 3 with DPPA in THF at 45 °C
for 5 h produced a DPPA-bridged dicobalt compound
[{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-PPh2CtCPPh2}], 5
(Scheme 3).
During its chromatographic process, interestingly, two
complexes, [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-PPh2Ct
(5) (a) Collman, P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 3. (b)
Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99.
(7) Patel, H. A.; Carty, A. J .; Hota, N. K. J . Organomet. Chem. 1973,
50, 247.
(6) Lisic, E. C.; Hanson, B. E. Inorg. Chem. 1986, 25, 812.

Bis(diphenylphosphino)acetylene
Organometallics, Vol. 21, No. 5, 2002 963
Ta ble 1. Cr ysta l Da ta of 2, 5, 6, 7, 8, a n d 9
2
5
6
7
8
9
formula
fw
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
38H20Co4O12P2 C57H44Cl4Co2Ã4P4
C55H42Co2Ã5P4 C55H42Co2Ã6P4 C62H42Co2O5P4Se C64H54Cl2Co2MoO9P4
966.20
293(2)
triclinic
P1h
11.2443(7)
11.4188(7)
16.2488(10)
102.9100(10)
90.8810(10)
109.7200(10)
1904.9(2)
2
1176.46
1024.63
293(2)
1040.63
293(2)
1187.66
293(2)
1375.65
293(2)
monoclinic
P2(1)/c
11.8168(8)
12.8713(8)
36.274(2)
293(2)
triclinic
P1h
triclinic
P1h
triclinic
P1h
monoclinic
P2(1)/c
11.7356(7)
23.6043(14)
21.9072(12)
11.9109(10)
12.0575(10)
18.3823(15)
73.746(2)
89.550(2)
74.330(2)
2433.7(3)
2
12.2123(8)
14.3194(9)
15.9432(10)
89.4280(10)
73.5230(10)
66.4200(10)
2433.3(3)
2
12.802(2)
14.786(3)
15.657(3)
106.216(4)
94.134(5)
99.192(4)
2787.9(9)
2
96.2360(10)
90.9150(10)
5484.6(6)
4
1.425
0.71073
0.962
1.68 to 26.02
8577
6067.8(6)
4
Z
Dc (Mg/m3)
λ(Mo KR) (Å)
1.685
0.71073
1.858
1.398
1.420
1.415
1.506
0.71073
0.861
0.71073
0.864
0.71073
1.411
0.71073
0.994
µ (mm-1
)
2θ range (deg)
1.29 to 27.94
2.05to 26.00
6924
1.94 to 26.02
7433
2.25 to 26.10
2792
1.74 to 26.04
9374
no. of obsd reflns 5922
(F>4σ(F))
no. of refined
params
R1a
505
658
595
604
667
747
0.0311
0.0671
0.929
0.0477
0.1465
1.118
0.0580
0.1503
1.226
0.0420
0.1156
0.901
0.0892
0.1875
0.874
0.0353
0.1087
0.885
wR2b
GoFc
R1 ) |∑(|Fo| - |Fc|)/|∑Fo||. wR2 ) {∑[w(Fo - Fc2)2/∑[w(Fo2)2]}1/2; w ) 0.10. c GoF ) [∑w(Fo - Fc2)2/(Nrflns - Nparams)]1/2
.
a
b
2
2
Ta ble 2. Com p a r ison of Selected Str u ctu r a l P a r a m eter s of 5, 6, 7, 8, a n d 9
5
6
7
8
9
Bond Lengths (Å)
Co(1)-Co(2)
C(1)-C(2)
C(1)-Co(1)
C(1)-Co(2)
C(2)-Co(1)
C(2)-Co(2)
C(1)-P(1)
C(2)-P(2)
Co(1)-P(3)
Co(2)-P(4)
C(55)-P(3)
C(55)-P(4)
2.4775(6)
1.344(4)
1.973(3)
1.994(3)
1.973(3)
1.983(3)
1.807(3)
1.802(3)
2.2368(9)
2.2354(9)
1.834(3)
1.829(3)
2.4723(7)
2.4871(5)
1.359(3)
1.972(2)
1.956(3)
1.961(3)
1.956(3)
1.780(2)
1.780(3)
2.2411(7)
2.2415(8)
1.833(3)
1.828(3)
2.466(3)
2.4871(5)
1.365(4)
1.993(3)
2.007(3)
1.980(3)
1.956(3)
1.836(3)
1.802(3)
2.2366(8)
2.2482(8)
1.836(3)
1.831(3)
1.364(5)
1.979(4)
1.972(3)
1.963(4)
1.975(4)
1.779(4)
1.804(4)
2.2342(11)
2.2422(11)
1.828(4)
1.833(4)
1.358(16)
1.997(12)
1.958(13)
1.954(12)
1.882(13)
1.790(14)
1.832(14)
2.264(4)
2.233(4)
1.816(12)
1.811(12)
Bite Distances (Å)
4.201
P(1),P(2)
4.297
4.442
4.191
3.275
Distances (Å)
2.373a
O(1)-H(55a)
2.238a
2.162b
Angles (deg)
P(1)-C(1)-C(2)
P(2)-C(2)-C(1)
Co(1)-C(1)-Co(2)
Co(1)-C(2)-Co(2)
C(1)-Co(1)-C(2)
C(1)-Co(2)-C(2)
P(3)-C(55)-P(4)
Co(1)-P(3)-C(55)
Co(2)-P(4)-C(55)
P(3)-Co(1)-Co(2)
P(4)-Co(2)-Co(1)
148.7(3)
139.0(3)
144.1(3)
139.8(3)
144.1(2)
156.3(2)
77.79(9)
78.81(10)
40.43(10)
40.30(10)
109.14(13)
109.52(9)
108.70(9)
97.22(2)
95.15(2)
146.1(10)
135.9(11)
77.1(5)
80.0(5)
40.2(5)
1179(2)
125.4(2)
76.91(9)
78.38(10)
40.20(11)
40.28(11)
107.91(15)
109.04(10)
107.47(10)
91.14(2)
77.28(11)
77.55(12)
39.84(13)
39.51(13)
109.59(17)
109.19(11)
110.58(11)
99.55(3)
77.48(13)
77.78(13)
40.47(14)
40.43(14)
110.4(2)
111.17(14)
109.80(13)
93.40(3)
41.4(5)
109.0(7)
107.8(4)
109.6(4)
99.20(12)
91.98(12)
92.71(3)
99.37(3)
99.76(2)
a
The positions of methylene protons were located. bThe positions of methylene protons were added.
and 7, respectively, which are all close to the double
bond.8 The bond length values between two cobalt atoms
are very close, i.e., 2.4775(6), 2.4723(7), and 2.4871(5)
Å for 5, 6, and 7, respectively.
In the 31P NMR spectra, three sets of signals, in the
ratio of 2:1:1, were obtained for all three compounds.
The more intense, broad peak was assigned to the two
phosphorus atoms, which are chemically equivalent in
the coordinated DPPM.9 The other two sharp peaks
were assigned to the two nonequivalent phosphorus
atoms of DPPA.
(B) Rea ction of Com p lex 5 w ith Selen iu m . The
reaction of 5 with 2 molar equiv of selenium powder
was carried out in THF at room temperature. Com-
pound 8, [{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-P(dO)Ph2Ct
CP(dSe)Ph2}], with two phosphorus atoms oxidized by
oxygen and selenium separately, was characterized by
spectroscopic means as well as X-ray diffraction studies.
(9) The broad peak is due to the coupling between phosphine and
its attached cobalt (I ) 7/2).
(8) Dickson, R. S. Adv. Organomet. Chem. 1974, 12, 323.

964 Organometallics, Vol. 21, No. 5, 2002
Hong et al.
F igu r e 3. Molecular structures of (a) [{µ-P,P-PPh2CH2-
PPh2}Co2(CO)4{µ-P(dO)Ph2CtCP(dSe)Ph2}], 8, and (b)
[{µ-P,P-PPh2CH2PPh2}Co2(CO)4{µ-P,P-PPh2CtCPPh2}Mo-
(CO)4], 9.
The oxide of compound 8 is believed to originate from
the silica gel during the chromatographic separation
process.
F igu r e 2. Molecular structures of (a) [{µ-P,P-PPh2CH2-
PPh2}Co2(CO)4{µ-PPh2CtCPPh2}], 5, (b) [{µ-P,P-PPh2CH2-
PPh2}Co2(CO)4{µ-PPh2CtCP(dO)Ph2}], 6, and (c) [{µ-P,P-
PPh2CH2PPh2}Co2(CO)4{µ-P(dO)Ph2CtCP(dO)Ph2}], 7.
The crystal structure of 8 reveals that the distance
between the oxide and the adjacent methylene proton,

Bis(diphenylphosphino)acetylene
Organometallics, Vol. 21, No. 5, 2002 965
Sch em e 4
hydrogen bonding. The bite distance between P(1) and
P(2) for 9 is much shorter than the others due to its
binding to a single metal center.
(D) 1H NMR Var iable-Tem per atu r e Exper im en ts.
Unexpectedly, the 1H NMR of 5 does not show the
methylene peaks at room temperature. On the contrary,
the corresponding peaks do appear for 6, 7, and 8. It
was speculated that the thermal motion of the methyl-
2.162 Å, is well within the range of an intramolecular
hydrogen bonding (Table 2, Figure 3).10 The highly
downfield shift of the adjacent methylene proton (6.46
ppm) compared with the remote methylene proton (3.38
ppm) supports this speculation. On the contrary, the
selenide is far away from the methylene protons.11
A
Cs symmetry might be designated for this compound in
solution state. In 31P NMR, three sets of signals in the
ratio of 2:1:1 were obtained. Chemical shifts of all three
sets of signals were within the range 30-35 ppm, which
is consistent with a coordinated or oxidized phosphorus
atom.12 The 31P-77Se coupling constant of the Se-P
bond is 723 Hz, which is consistent with a phosphine
having aromatic substituents.13
(C) Rea ction of Com p lex 5 w ith Mo(CO)6. The
reaction of 5 with 2 molar equiv of Mo(CO)6 in toluene
at 110 °C for 15 h resulted in [(µ-Ph2PCH2PPh2)Co2-
(CO)4][(µ-P,P-Ph2PCtCPPh2)Mo(CO)4], 9, with satisfac-
tory yield (Scheme 4).
Compound 9 was characterized by spectroscopic means
as well as X-ray diffraction studies. The structure of 9
can be regarded as a combination of a Mo(CO)4 fragment
and 5 (Figure 3). In this regard, 5 behaves as an
authentic diphosphine chelating ligand. In contrast with
the previous cases, only two sets of peaks in the ratio
of 2:2 were observed for 9 in the 31P NMR spectrum at
20 °C. They are peaks at 49.7 and 33.9 ppm for DPPA
and DPPM, respectively. The bite angle for P(1)-Mo-
P(2) is 79.6°, which is about 3° smaller than average
DPPE-chelated complexes and 6° larger than average
DPPM-chelated complexes.14 The dicobalt carbonyl frag-
ment bridges to the triple bond of the DPPA in 5 might
indeed narrow the bite angle of the complex.
1
F igu r e 4. Variable-temperature H NMR spectra of 5 in
tolene-d8.
Selected structural parameters of 5-9 are shown in
Table 2 for the purpose of comparison. The atom
numbering of the main structures of all these com-
pounds has been kept the same.
As shown in Table 2, the main frameworks for these
compounds are not much different. Complex 8 has the
shortest distance between O(1) and H(55a) among the
three compounds 6, 7, and 8, with intramolecular
(10) The commonly observed hydrogen bonding ranges from 2.05 to
2.40 Å. Taylor, R.; Kennard, O. J . Am. Chem. Soc. 1982, 104, 5063.
(11) These distances are 6.855 and 7.970 Å.
(12) Normally, a negative value will be obtained for an uncoordi-
nated phosphine in 31P NMR.
(13) Allen, D. W.; Taylor, B. F. J . Chem. Soc., Dalton Trans. 1982,
51.
(14) Dierkes, P.; van Leeuwen, P. W. N. M. J . Chem. Soc., Dalton
Trans. 1999, 1519.
1
F igu r e 5. Variable-temperature H NMR spectra of 9 in
toluene-d8.

966 Organometallics, Vol. 21, No. 5, 2002
Hong et al.
F igu r e 6. Proposed fluxional behavior of DPPM in 9.
ene fragment in the DPPM ligand of 5 caused this
abnormal phenomenon. The variable-temperature 1H
NMR experiment was carried out for 5 in toluene-d8
over the range -90 to 90 °C. Measurements were taken
at intervals of 10 °C (Figure 4). It is clearly seen that
the expected methylene peaks do appear at tempera-
tures below 10 °C. When the temperature was raised
to 90 °C, two sets of peaks merged into one eventually.
1
The variable-temperature H NMR experiments were
carried out for 6 and 8 also in the same manner. The
appearance of two sets of multiplets did not change even
at 90 °C. It was proposed that intramolecular hydrogen
bonding was attributed to these observations. The
distances of oxygen to the adjacent proton of the
methylene are 2.373, 2.238, and 2.162 Å for 6, 7, and 8,
respectively, being within the commonly observed hy-
drogen-bonding range (Table 2, Figures 3-5). It is
believed that in the cases of 6, 7, and 8 the flexibility of
the methylene group, i.e., the up-and-down motions, was
limited by the intramolecular hydrogen bonding be-
tween the oxide and the adjacent proton of the meth-
ylene group, while in the case of 5, the thermal motion
of the methylene group is relatively free and the
corresponding methylene protons disappeared, as the
coalescence temperature for 5 happened to be near room
temperature.15
Only one set of triplet signals in the 1H NMR was
observed at room temperature for the methylene of
DPPM in 9. A variable-temperature experiment was
carried out for 9 similar to the procedures shown above
(Figure 5). Two distinct sets of multiplet signals were
observed at -90 °C. A mechanism is proposed for the
fluxional behavior of DPPM in 9 (Figure 6). It shall work
for 5 as well. The back-and-forth motion of the coordi-
nated ligands on the dicobalt fragment might cause a
change in the positions of the axial carbonyls with
equatorial carbonyls as well as the location of the
DPPM. Two methylene protons are equivalent in the
fast exchange range, while in the slow exchange range
F igu r e 7. Variable-temperature 31P NMR spectra of 9 in
toluene-d8.
the methylene protons are split. The calculated activa-
tion energies from the experiments concerning the
fluxional movements of DPPM in 5 and 9 are 19.2 and
7.1 kcal/mol, respectively, at 293 K. The fact that the
latter value is much less than the former one indicates
that the fluxional motion is much easier in 9. It is
probably because the coordination of the chelating
phosphine ligands lessens the steric hindrance between
phenyl rings from both DPPM and DPPA.
The fluxional behavior of DPPM in 9 is also evidenced
from the variable-temperature 13P NMR (Figure 7). The
splitting pattern of two phosphorus signals from DPPA
is clearly seen as the measured temperature is lowered
to -90 °C.
Su m m a r y
In this work, the bonding capacities of the bifunctional
ligand PPh2CtCPPh2 toward dicobalt carbonyl com-
plexes were explored. The results show that this ligand
could be incorporated into a dicobalt moiety through its
triple bond, forming some new, unconventional mono-
or bidentate phosphine complexes. In contrast to 6, 7,
and 8, the absence of intramolecular hydrogen bonding
accounts for the fluxional behaviors of 5 and 9.
(15) (a) Ebsworth, E. A. V.; Rankin, D. W. H.; Cradock, S. Structural
Methods in Inorganic Chemistry; Blackwell Scientific: Oxford, 1991.
(b) Drago, R. S. Physical Methods for Chemits; Saunders: Philadephia,
1992.
Exp er im en ta l Section
Gen er a l P r oced u r es. All operations were performed in a
nitrogen-flushed glovebox or in a vacuum system. Freshly

Bis(diphenylphosphino)acetylene
Organometallics, Vol. 21, No. 5, 2002 967
distilled solvents were used. All processes of separations of
the products were performed by centrifugal thin-layer chro-
matography (TLC, Chromatotron, Harrison model 8924).
1HNMR spectra were recorded (Varian VXR-300S spectrom-
eter) at 300.00 MHz; chemical shifts are reported in ppm
relative to internal TMS. 31P and 13C NMR spectra were
recorded at 121.44 and 75.46 MHz, respectively. 1H NMR
spectra of variable-temperature experiments were recorded by
the same instrument. Some other routine 1H NMR spectra
were recorded with a Gemini-200 spectrometer at 200.00 MHz
or a Varian-400 spectrometer at 400.00 MHz. IR spectra of
Syn th eses of [{µ-P ,P -P P h 2CH2P P h 2}Co2(CO)4{µ-P (dO)-
P h 2CtCP (dSe)P h 2}], 8. Into a 100 cm3 flask was placed [{µ-
P,P-PPh2CH2PPh2}Co2(CO)4{µ-PPh2CtCPPh2}] (0.880 g, 0.873
mmol) and selenium (0.138 g, 1.746 mmol) in 15 cm3 of THF.
The solution was frozen by liquid N2, then the gas was pumped
out. The solution was warmed to room temperature and then
was stirred for 8 h. The resulting solution was filtered through
a small amount of silica gel. The filtrate was evaporated under
reduced pressure to yield a crude product. Purification with
CTLC was carried out in a 1:1 CH2Cl2/hexane mixed solvent.
The second eluted dark-red-colored product was identified as
8 in a yield of 73.0% (0.7024 g, 0.637 mmol).
Com p lex 8: dark red crystalline solid; 1H NMR (CDCl3,
δ/ppm) 6.90-8.05(m, 40H, arene), 6.46(m, 1H, CH2), 3.38(m,
1H, CH2); 13C NMR (CDCl3, δ/ppm) 25.58(s, 1C), 36.20(t, CH2),
67.95(s, 1C0, 127.80(m, 16C, arene), 129.17(s, 4C, p-arene),
129.75(s, 4C, p-arene), 132.39(m, 16C, arene), 134.29(d, J P-C
) 9.7 Hz, 8C), 200.15(CO), 205.76(CO); 31P NMR (CDCl3,
δ/ppm) 30.31(s, 1P), 33.85(s, 2P), 35.27(d, J Se-P ) 723.7 Hz).
solutions in CH2Cl2 were recorded on
a Hitachi 270-30
spectrometer. Mass spectra were recorded on a J EOL J MS-
SX/SX 102A GC/MS/MS spectrometer. Elemental analyses
were recorded on a Heraeus CHN-O-S-Rapid.
Syn th esis of Co2(CO)4(µ-CO)2(µ-P ,P -(µ-P P h 2CtCP P h 2)-
Co2(CO)6), 2. Into a 100 cm3 flask was placed dicobalt octa-
carbonyl, Co2(CO)8 (1.00 g, 2.924 mmol), and bis(diphenylphos-
phino)acetylene (DPPA) (1.153 g, 2.924 mmol) in 30 cm3 of
THF, and the mixture was stirred for 5 h. The brown product
was recognized as DPPA-bridged dicobalt compound Co2(CO)6-
(µ-PPh2CtCPPh2), 1. Further treatment of 1 (1.2 g, 1.764
mmol) with Co2(CO)8 (0.6 g, 1.755 mmol) in THF at 55 °C for
8 h yielded a brown solution. The solvent was removed, and
the resulting residue was chromatographed by CTLC. 2 (22%)
was obtained from the brown band eluted by CH2Cl2/hexane,
1:1. Crystals were obtained from the CH2Cl2/hexane solution
of 2 at 4 °C.
Anal. Calcd for 6: C 59.85; H, 3.81. Found: C, 59.09; H, 4.38.
+
MS(FAB): m/z 1105(P + 1)
.
Syn th eses of [{µ-P ,P -P P h 2CH2P P h 2}Co2(CO)4{µ-P ,P -
P P h 2CtCP P h 2}Mo(CO)4], 9. Complex 5 (0.83 g, 0.82 mmol)
was placed in a 100 cm3 flask along with 2 molar equiv of
Mo(CO)6 (0.44 g, 1.65 mmol) in 15 cm3 of toluene, and the
mixture was refluxed for 15 h. The residue was filtered
through a small amount of silica gel. Complex 9 was eluted
out during the chromatographic process with a solvent mixture
of 1:1 CH2Cl2/hexane. The yield for 9 was 81.8%.
Com p lex 2: brown crystalline solid; 1H NMR (CDCl3,
δ/ppm) 7.34-7.59(m, 20H, arene); 13C NMR (CDCl3, δ/ppm)
125.00(s, 2C, CtC), 128.17(m, 8C, arene), 130.68(s, 4C, p-
arene), 133.05(m, 8C, arene), 136.37(d, J p-c ) 20.1 Hz, 2C, ipso-
arene), 136.11(d, J p-c ) 20.1 Hz, 2C, ipso-arene), 197.57(m,
COs); 31P NMR (CDCl3, δ/ppm) 53.78; IR(CH2Cl2) ν(CO) 1797(sh),
1984(s), 2013(s), 2044(s), 2066(s), 2097(m) cm-1. Anal. Calcd
for 2: C 47.24; H 2.09. Found: C 46.57; H 2.14. MS: 968(M+
+ 2).
Com p lex 9: dark brownish solid; 1H NMR (CDCl3, δ/ppm)
7.01-7.80(m, 40H, arene), 3.21(t, J P-H ) 11.1 Hz, -CH2 of
dppm); 13C NMR (CDCl3, δ/ppm) 217.57(dd, one CO of Mo),
211.55(dd, one CO of Mo), 203.51(m, two COs of Mo), 127.87-
139.14(m, 48C, arene); 31P NMR (CDCl3, δ/ppm) 33.9(2P of
dppm), 49.7(2P of dppa); IR(CH2Cl2) ν(CO) 2012(s), 1905(vs),
1862(s) cm-1. Anal. Calcd for 5: C, 58.24; H, 3.48. Found: C,
Syn th eses of [{µ-P ,P -P P h 2CH2P P h 2}Co2(CO)4{µ-P P h 2Ct
CP P h 2}], 5, [{µ-P ,P -P P h 2CH2P P h 2}Co2(CO)4{µ-P P h 2Ct
CP (dO)P h 2}], 6, a n d [{µ-P ,P -P P h 2CH2P P h 2}Co2(CO)4{µ-
P (dO)P h 2CtCP (dO)P h 2}], 7. The same procedure described
for 2 was followed. The reaction of Co2(CO)8 with DPPM at 60
°C for 7 h yielded yellow-colored [Co2(CO)6(µ-P,P-PPh2CH2-
PPh2)], 3 (72%), and small amount of green-colored [Co2(CO)7-
(µ-P-PPh2CH2PPh2)], 4. Further reaction of 3 with DPPA at
45 °C for 5 h produced complex 5, from which 6 and 7 were
isolated during the chromatographic process. The yields for
5, 6, and 7 are 53.0%, 17.1%, and 5.7%, respectively.
Com p lex 5: red crystalline solid; 1H NMR (CDCl3, δ/ppm)
7.13-7.40(m, 40H, arene); 13C NMR (CDCl3, δ/ppm) 127.80-
139.03(m, 48C, arene); 31P NMR (CDCl3, δ/ppm) -14.7(1P),
1.2(1P), 31.1(2P); IR (CH2Cl2) ν(CO) 1972(s), 1999(s), 2023(s)
cm-1. Anal. Calcd for 5: C, 65.49; H, 4.20. Found: C, 64.80;
H, 4.11. MS(FAB): m/z 1009(M+).
+
58.41; H, 3.24. MS(FAB): m/z 1217(P + 1)
.
X-r a y Cr ysta llogr a p h ic Stu d ies. Suitable crystals of 2,
5, 6, 7, 8, and 9 were sealed in thin-walled glass capillaries
under a nitrogen atmosphere and mounted on a Bruker AXS
SMART 1000 diffractometer. The crystallographic data were
collected with Mo KR radiation (λ ) 0.71073 Å). Intensity data
were collected in 1350 frames with increasing ω (width of 0.3°
per frame). The absorption correction was based on the
symmetry equivalent reflections using the SADABS program.
The space group determination was based on a check of the
Laue symmetry and systematic absences and was confirmed
using the structure solution. The structure was solved by direct
methods using the SHELXTL package. All non-H atoms were
located from successive Fourier maps, and hydrogen atoms
were refined using a riding model. Anisotropic thermal pa-
rameters were used for all non-H atoms, and fixed isotropic
parameters were used for H atoms. Crystallographic data of
2, 5, 6, 7, 8, and 9 are summarized in Table 1.
Com p lex 6: red crystalline solid; 1H NMR (CDCl3,
δ/ppm): 3.35(q, J H-H ) 12.20 Hz, 1H, CH2), 6.12(q, J H-H
)
13.20 Hz, 1H, CH2), 6.88-7.79(m, 40H, arene); 31P NMR
(CDCl3, δ/ppm) 0.81(1P), 27.01(1P), 35.87(2P); IR (CH2Cl2) ν(CO)
1979(m), 2006(s), 2029(m) cm-1. Anal. Calcd for 6: C, 64.46;
H, 4.13. Found: C, 64.07; H, 6.75. MS(FAB): 1025(M+).
Com p lex 7: orange crystalline solid; 1H NMR (CDCl3,
δ/ppm) 3.32(q, J H-H ) 12.60 Hz, 1H, CH2), 6.10(q, J H-H ) 12.80
Hz, 1H, CH2), 6.86-7.78(m, 40H, arene); 13C NMR (CDCl3,
δ/ppm) 128.04(m, 16C, arene), 129.06(s, 4C, p-arene), 129.65(s,
4C, p-arene), 131.38(m, 16C, arene), 134.63(d, J P-C ) 21.37
Hz, 8C); 31P NMR (CDCl3, δ/ppm) 27.69(1P), 31.48(1P),
Ack n ow led gm en t. We are grateful to the National
Science Council of the R.O.C. (Grant NSC 89-2113-M-
005-026) for financially supporting this research.
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
of 2, 5, 6, 7, 8, and 9, and tables of thermal parameters, bond
lengths and angles, anisotropic thermal parameters, and H
atom coordinates. This material is available free of charge via
the Internet at http://pubs.acs.org.
35.13(2P); IR (CH2Cl2) ν(CO) 1982(w), 2007(w), 2048(w) cm-1
.
Anal. Calcd for 7: C, 63.48; H, 4.07. Found: C, 62.82; H, 4.11.
MS(FAB): 1041(M+).
OM0106783