Preparation and characterization of a cyclic compound consisting of bis(diphenylphosphino)acetylene joined alkyne-bridged dicobalt fragments

Article abstract of DOI:10.1246/cl.2001.1130

A cyclic compound, [Co₂(CO)₄(μ₂-HC≡CSiMe₃)(PPh ₂C≡C-PPh₂)]₂ 2, was identified from the reaction of bis-(diphenylphosphino)acetylene with an alkyne-bridged dicobalt complex, (μ₂-HC≡CSiMe₃)Co₂(CO)₆ 1. Crystal structure of 2 shows that it is a twelve-membered ring complex comprised of two DPPA coordinated pseudo-tetrahedral Co₂C₂ units. Further reaction of 2 with two equivalents of Co₂(CO)₈ resulted in the conversion of 2 into [Co₂(CO)₆{μ-P,P-(μ-PPh₂C≡CPPh₂ )}] [Co₂(CO)₄(μ-HC≡CSiMe₃)]3.

Full text of DOI:10.1246/cl.2001.1130

1130
Chemistry Letters 2001
Preparation and Characterization of a Cyclic Compound Consisting of
Bis(diphenylphosphino)acetylene Joined Alkyne-Bridged Dicobalt Fragments
Fung-E Hong,* Hao Chang, Yu-Chang Chang, and Bao-Tsan Ko
Department of Chemistry, National Chung-Hsing University, Taichung 40227, Taiwan
(Received June 15, 2001; CL-010571)
tive alkyne, were coordinated to Co2C2 units in DPPA.11–15
The twelve-membered ring is not coplanar, rather, it is more
like a Möbius strip. Two bridged alkynes are inside the twelve-
membered ring and point to each other. The distance between
two acetylenic protons is 2.266 Å. Two DPPA ligands almost
remain linear. The bond lengths of two triple bonds are the
same, 1.189 Å. The acetylenic protons exhibit more downfield
A cyclic compound, [Co2(CO)4(µ2-HC≡CSiMe3)(PPh2C≡C-
PPh2)]2 2, was identified from the reaction of bis-
(diphenylphosphino)acetylene with an alkyne-bridged dicobalt
complex, (µ2-HC≡CSiMe3)Co2(CO)6 1. Crystal structure of 2
shows that it is a twelve-membered ring complex comprised of
two DPPA coordinated pseudo-tetrahedral Co2C2 units. Further
reaction of 2 with two equivalents of Co2(CO)8 resulted in the
conversion of 2 into [Co2(CO)6{µ-P,P-(µ-PPh2C≡CPPh2)}]
[Co2(CO)4(µ-HC≡CSiMe3)] 3.
1
shift in H NMR compared with regular alkyne-bridged,
dicobalt-complex. Only one set of triplet acetylenic proton,
caused by two coordinated, equivalent phosphorus atoms, was
observed because of its symmetric conformation. For the same
reason, only one signal was observed for four phosphorus
atoms in 31P NMR.
The phosphine ligands have played an important role ever
since the discovery of the Wilkinson’s catalyst, which probably
is the most studied and well-documented soluble catalyst for
olefin hydrogenation reaction.1–5 Occasionally, some unpre-
dicted marvelous results were reported from the reactions of
multiple-functional phosphine ligands6 such as alkynylphos-
phines RnP(C≡C–R')3–n (n = 0–2), with transition metal com-
pounds.7,8 We report herein the synthesis and a detailed struc-
tural study of an unexpected twelve-membered ring complex
from the reaction of a bi-functional ligand, bis(diphenylphos-
phino)-acetylene (DPPA), with 1.9
Into a 100-cm3 flask was placed dicobalt octacarbonyl,
Co2(CO)8 (0.4 g, 1.17 mmol) and trimethylsilylacetylene (0.16
cm3, 1.17 mmol) with 20 cm3 of THF. The solution was stirred
at room temperature for 3 h. Purification with centrifugal thin-
layer chromatography was carried out from hexane.
Quantitative yield was obtained for the alkyne-bridged dicobalt
octacarbonyl complex, 1. One equivalent of bis(diphenylphos-
phino)acetylene was added into a 100-cm3 flask which contains
1 (0.449 g) with 20 cm3 of THF. The solution was stirred at 50
°C for 24 h. There were three compounds being isolated by the
similar purification procedure as shown above. The first band
was identified as some unreacted 1. The identity of the second
band is unknown. The third band is 2 with the yield of 62%.
Two equivalents of Co2(CO)8 with 2 (0.375 g) were placed
into a 100-cm3 flask with 20 cm3 of THF. The solution was
stirred at 40 °C for 20 h. The reaction product 3 was isolated as
the first band by the similar purification procedure as shown
above. The second band is the unreacted 2 with some unidenti-
fied compounds. The yield of 3 is 18%. The conversion of 2 to
3 might take place through the attack of the triple bond of the
DPPA ligand in 2 by Co2(CO)8. The coordination of dicobalt
fragment to the triple bond of the DPPA ligand will cause the
change of the geometry and the fragmentation follows. The
release of one side of DPPA ligand will coordinate back to
another cobalt center and yield 3.
Compound 2 was characterized by spectroscopic means as
well as crystal structure determination.10 Crystals of 2 were
obtained from the CH2Cl2 solution under 4 °C. The main struc-
ture of 2 is a twelve-membered ring complex comprised of two
DPPA coordinated pseudo-tetrahedral Co2C2 units.
Interestingly, the phosphorous atoms, instead of the more reac-
Crystals of 3 were obtained from the CH2Cl2 solution under
4 °C and the structure was determined.16 The bond lengths of
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1131
bridged alkynes are 1.337 Å and 1.358 Å; they are within the
double bond range. Two sets of Co–Co bond distances are
2.541 Å and 2.459 Å. All carbonyls are terminal. The bulky
group, –SiMe3, points away from the center of molecule. Only
one signal was observed for two equivalent phosphorus atoms
in 31P NMR. There is one set of triplet acetylenic proton,
caused by two coordinated, equivalent phosphorus atoms, was
observed due to its symmetric nature.
6
7
G. Ashkenasy, A. Ivanisevic, R. Cohen, C. E. Felder, D.
Cahen, A. B. Ellis, and A. Shanzer, J. Am. Chem. Soc.,
122, 1116 (2000).
H. Lang and L. Zsolnai, J. Organomet. Chem., 369, 131
(1989).
H. Lang and L. Zsolnai, Chem. Ber., 124, 259 (1991).
F.-E Hong, Y.-C. Huang, S.-L. Wang, and F.-L. Liao,
Inorg. Chem. Commun., 2, 450 (1999).
8
9
10 Crystal data for 2: C71H60Cl2Co4O8P4Si2, Mr = 1527.87, tri-
clinic, space group P2(1)/c, a = 13.1393(13) Å, b =
13.5047(13) Å, c = 23.903(3) Å, α = 95.769(2)°, β =
100.752(2)°, γ = 114.872(2)°, V = 3703.4(6) Å3, Z = 2 , Dc
= 1.370 Mg/m3, R1 = 0.0487. Selected spectroscopic data
for 2: Brown solid; 1H NMR (CDCl3, δ) –0.05 (s, 18H,
–SiMe3), 6.52 (t, JP-H = 6.2Hz, 2H, CH), 7.22–7.84 (m,
40H, arene); 13C NMR (CDCl3, δ): 1.16(s, 6C, –Me);
74.26, 87.33 (s, 2C, C≡C); 110.6 (b, 2C, C≡C); 132.92 (d,
JP-C = 20Hz, 1C, arene); 131.57 (d, JP-C = 13Hz, 1C,
arene); 130.30 (d, JP-C = 9Hz, 1C, arene); 129.61 (s, 1C,
arene); 132.58 (d, JP-C = 24Hz, 1C, arene); 131.20 (d, JP-C
13Hz, 1C, arene); 128.86 (s, 1C, arene); 128.61 (d, JP-C
=
=
9Hz, 1C, arene); 201.783(m, CO); 204.774(m, CO); 31P
NMR (CDCl3, δ): 29.294(s, 4P); Anal. Calcd. for
C71H60Cl2Co4 O8P4Si2: C 58.18, H 4.18. Found C 59.77, H
In this work, an unusual twelve-membered ring compound,
2, which is comprised of two DPPA coordinated pseudo-tetra-
hedral Co2C2 units, was characterized. The fragmentation of 2
occurs and forms 3 while two equivalents of Co2(CO)8 was
added.
4.76; MS(FAB): m/z 1332(M+ – 4CO); IR(CH2Cl2, νCO
,
cm–1) 2057(m), 2020(s), 1993(s), 1965(s).
11 In most cases, alkynes react more rapidly toward Co2(CO)8
than phosphines do; I. Omae, “Applications of
Organometallic Compounds,” John Wiley & Sons, New
York (1998), Chap. 17.
Financial support from National Science Council of the
R.O.C. (Grant NSC-89-2113-M-005-002) is gratefully
acknowledged.
12 C. M. Lukehart, “Fundamental Transition Metal
Organometallic Chemistry,” Brooks/Cole Publishing
Company: Monterey, California, (1985).
13 R. S. Dickson, Adv. Organomet. Chem., 12, 323 (1974).
14 R. S. Dickson and G. R. Tailby, Aust. J. Chem., 23, 229
(1971).
References and Notes
1
2
3
4
J. A. Osborn, F. H. Jardine, J. F. Young, and G. Wilkinson,
J. Chem. Soc. A, 1966, 1711.
R. R. Schrock and J. A. Osborn, J. Am. Chem. Soc., 98,
2134 (1976) and references therein.
R. Noyori, “Asymmetric Catalysis In Organic Synthesis,”
John Wiley & Sons, New York (1994).
R. G. W. Parshall and S. D. Ittel, “Homogeneous
Catalysis,” 2nd ed., John Wiley & Sons, New York (1992),
Chap. 8.
15 U. Kruerke and W. Hubel, Chem. Ber., 94, 2829 (1961).
16 Crystal data for 3: C41H30Co4O10P2Si, Mr = 1008.40, tri-
clinic, space group P1, a =11.7995(8) Å, b = 13..0453(9)
Å, c = 15.5864(11) Å, α = 95.734(2)°, β = 100.2760(10)°,
γ = 111.1890(10)°, V =2165.5(3) Å3, Z = 2 , Dc=1.547
Mg/m3, R1 = 0.0439. Selected spectroscopic data for 3:
Brown solid; 1H NMR (CDCl3, δ) 0.28 (s, 9H, –SiMe3),
5.76 (t, JP-H = 7.8Hz, 1H, CH), 7.32–7.97 (m, 20H, arene);
31P NMR (CDCl3, δ): 56.41 (s, 2P); MS(FAB): m/z
1011(M++1); IR(CH2Cl2, νCO, cm–1) 2056(m), 1991(w),
1958(w).
5
“Applied Homogeneous Catalysis with Organometallic
Compounds,” ed. by B. Cornils, and W. A. Herrmann,
(eds.), VCH, New York (1996), Vols. 1 and 2.