Evidence for transmetalation of zirconacyclopentadiene to cobalt complex

Article abstract of DOI:10.1246/cl.2002.578

Transmetalation reaction of zirconacyclopentadienes with cobalt(III) complex, CpCo(PPh₃)I₂, proceeded to afford (cyclobutadiene)cobalt(I) complexes, CpCo(C₄R₄). The structure of one of the cobalt complexes was v

Full text of DOI:10.1246/cl.2002.578

578
Chemistry Letters 2002
Evidence for Transmetalation of Zirconacyclopentadiene to Cobalt Complex
Hui Wang, Fu-Yu Tsai, Kiyohiko Nakajima,y and Tamotsu TakahashiÃ
Catalysis Research Center and Graduate School of Pharmaceutical Sciences, Hokkaido University,
and CREST Science and Technology (JST), Sapporo 060-0811
yAichi University of Education, Igaya, Kariya, Aichi 448-8542
(Received February 14, 2002; CL-020148)
Transmetalation reaction of zirconacyclopentadienes with
as monoclinic crystals, whereas the published ones were as
triclinic crystals.12
cobalt(III) complex, CpCo(PPh3)I2, proceeded to afford (cyclo-
butadiene)cobalt(I) complexes, CpCo(C4R4). The structure of
one of the cobalt complexes was verified by X-ray structure
analysis.
Transmetalation of zirconacycles to other metal species is of
increasing importance in organic synthesis. Since we have
reported the first example of transmetalation from zirconacyclo-
pentadienes to Cu,1 Ni,2 Li,3 and Zn,4 both stoichiometric and
catalytic reactions have been rapidly developed illustrating their
growing importance in organic synthesis.5
In order to study the scope of such transmetalation reactions
of zirconacyclopentadienes with respect to other transition metal
salts, we decided to investigate their reactions with cobalt
compounds.
We envisioned that this approach could grant us a new access
to cobaltacyclopentadienes that are useful intermediates in
organic synthesis for the preparation of arenes and heteroarenes
derivatives.6 Herein, we would like to report our results and the
evidence for transmetalation of zirconacyclopentadienes (1) to a
cobalt complex.
We assumed that the reaction of 1 with cobalt complexes
would proceed in a similar manner to previously observed
reactions, e.g. Ni, as shown in eq 1 and will give rise to
cobaltacyclopentadiene (2).
Figure 1. ORTEP drawing of 3a. Benzene molecule was
ꢀ
omitted. Some selected interatomic distances (A) and
angles (deg): Co–C(1) 1.978(3), Co–C(2) 1.972(3), Co–
C(3) 1.978(3), Co–C(4) 1.963(3), C(1)–C(2) 1.463(3),
C(2)–C(3) 1.455(4), C(3)–C(4) 1.458(3), C(1)–C(4)
1.463(4), C(1)–C(2)–C(3) 90.8(2), C(2)–C(3)–C(4)
89.6(2), C(1)–C(4)–C(3) 90.6(2), C(2)–C(1)–C(4) 89.1(2).
Initially, we carried out reactions of tetraarylzircona-
cyclopentadienes. The results are shown in eq 2. A typical
procedure is as follows: to a toluene solution of tetraphenyl-
zirconacyclopentadiene (1a), which was prepared in situ by the
reaction of Cp2ZrCl2 (1.0 mmol) and 2 eq of n-BuLi (Negishi
reagent) with 2 eq of diphenylacetylene (2.0 mmol),7 was added
Complex 3b with tolyl groups was prepared by using the
same strategy and its 13C NMR spectrum in C6D6 showed
characteristic signals at 74.50 and 83.02 ppm of a cyclopentadi-
enyl ligand and a cyclobutadiene moiety, respectively.13
In order to understand the process during the transmetalation
of zirconacyclopentadiene with cobalt(III) complex, the reaction
mixture was monitored by NMR and the change of shifts for
cyclopentadienyl signals of organozirconium compound was
followed. The NMR analysis of aliquots of the reaction mixture
revealed only signals of starting materials and that of product 3a.
Moreover, Cp signals belonging to zirconium species were
observed at 114.63, 115.34 and 115.69 ppm which can be
assignable to Cp2ZrI2, Cp2ZrClI and Cp2ZrCl2. Its presence
indicates a transfer of iodine from cobalt to zirconium and hence
the transmetalation of the Zr-C bond to the Co-C bonds.
8
CpCo(PPh3ÞI2 (1 mmol) at room temperature. The mixture was
stirred at 110 ꢀC for 3 days under nitrogen atmosphere. After
cooling, the solvent was removed under reduced pressure and the
crude product was separated by column chromatography on silica
gel (10/1 hexane/ether). However, instead of 2, (cyclobutadie-
ꢁ
ne)cobalt(I) complex, CpCo(C4Ph4Þ C6H6 (3a) was obtained in
24% yield after recrystallization from a mixture of benzene/
hexane. The 13C NMR spectrum in C6D6 of 3a showed signals
which were consistent with previously reported data.9;10 Further-
more, the structure of 3a was confirmed by X-ray structure
analysis, as shown in Figure 1.11 However, our data were obtained
The formation of cobalt complexes 3 from zirconacyclopen-
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
579
tadienes can be explained as shown in Scheme 1. Zirconacyclo-
pentadiene 1 reacts with CpCo(PPh3)I2 at 110 ꢀC to give 4 with
concomitant formation of Cp2ZrI2. High reaction temperature
induces rapid rearrangement of 4 into 3. Such a type of the
rearrangement has been observed by Yamazaki and Hagihara.14
Due to the presence of 2 eq of LiCl in the reaction mixture,
Cp2ZrCl2 and Cp2ZrClI were formed by halogen exchange
process from Cp2ZrI2. In fact, addition of LiCl to Cp2ZrI2 in
afforded Cp2ZrCl2 and Cp2ZrClI.
Although, the phosphorus signal of the intermediate 4 was
not observed during monitoring of the reaction mixture, 4 is the
most likely intermediate with respect to the above-obtained
results. In addition, the rate-determining step is the transmetala-
tion, which is considerably slower than the metalacyclopenta-
diene-cyclobutadiene complex rearrangement.
Kitamura, B. Shen, and K. Nakajima, J. Am. Chem. Soc., 122,
12876 (2000). For a review on transmetalation of acyclic
organozirconocene, see: d) P. Wipf and H. Jahn, Tetrahedron,
52, 12853 (1996).
6
a) Y. Wakatsuki and H. Yamazaki, J. Chem. Soc., Chem.
Commun., 1973, 280. b) Y. Wakatsuki and H. Yamazaki,
Tetrahedron Lett., 1973, 3383. For reviews, see: c) K. P. C.
Vollhardt, Angew. Chem., Int. Ed. Engl., 23, 539 (1984). d) N.
E. Schore, Chem. Rev., 88, 1081 (1988). e) P. J. Harrington, in
‘‘Transition Metals in Total Synthesis,’’ John Wiley & Sons,
New York (1990), p 200. f) N. E. Schore, in ‘‘Comprehensive
Organic Synthesis,’’ ed. by B. M. Trost and I. Fleming,
Pergamon Press Ltd., Oxford (1991), Vol. 5, p 1129. g) D. B.
Grotjahn, in ‘‘Comprehensive Organometallic Chemistry II,’’
ed. by E. W. Abel, F. G. A. Stone, and G. Wilkinson, Elsevier
Science Ltd., Oxford (1995), Vol. 12. p 741. h) M. Lautens,
W. Klute, and W. Tam, Chem. Rev., 96, 49 (1996).
E. Negishi, F. E. Cederbaum, and T. Takahashi, Tetrahedron
Lett., 27, 2829 (1986).
7
8
9
R. B. King, Inorg. Chem., 5, 82 (1966).
For the first preparation of 3a, see: a) A. Nakamura and N.
Hagihara, Bull. Chem. Soc. Jpn., 34, 452 (1961). b) M. D.
Rausch and R. A. Geneti, J. Am. Chem. Soc., 89, 5502 (1967).
10 R. M. Harrison, T. Brotin, B. C. Noll, and J. Michl,
Organometallics, 16, 3401 (1997).
Scheme 1.
11 Crystal data for 3a: C39H31Co, M ¼ 558:61, monoclinic,
In addition, we also carried out the reaction of tetraethyl-
zirconacyclopentadiene with CpCo(PPh3)I2 in THF at 75 ꢀC. The
reaction mixture was again monitored by NMR, and we observed
disappearance of signals at 110.10 and 86.92 ppm, which account
for signals of Cp rings of tetra-ethylzirconacyclopentadiene and
CpCo(PPh3)I2, respectively, and appearance of new peaks at
85.88 and 81.72 ppm, which should belong to unsaturated
systems attached to Co(I) metal center. Unfortunately, we were
not able to isolate the products to unequivocally characterize
them.
space group P21; a ¼ 11:4741ð9Þ, b ¼ 11:427ð1Þ, c ¼
ꢀ
ꢀ
ꢀ 3
11:503ð1Þ A; ꢀ ¼ 106:580ð3Þ ; V ¼ 1445:4ð2Þ A ; Z ¼ 2;
Dc ¼ 1:283 g cmÀ3; No. of reflections measured ¼ 6153; No.
of reflections with I > 2:0ꢁðIÞ ¼ 5203; R ¼ 0:044, Rw ¼
0:054. A cyclopentadienyl ring was found to be disordered,
and this was resolved into two half-occupancy orientations.
Crystallographic data reported in this paper have been
deposited with Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-183109. Copies of the
data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK (fax: (þ44)1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk). Instruction for
depositing the crystallographic data is available on the Web at
http://www.ccdc.cam.ac.uk/conts/depositing.html.
In conclusion, we demonstrated here the evidence for
transmetalation of zirconacyclopendienes to cobalt complexes.
References and Notes
1
2
3
T. Takahashi, M. Kotora, K. Kasai, and N. Suzuki,
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12 M. D. Rausch, G. F. Westover, E. Mintz, G. M. Reisner, I.
Bernal, A. Clearfield, and J. M. Troup, Inorg. Chem., 18, 2605
(1979).
13 Tetrakis(4-methylphenyl)cyclobutadiene]cyclopentadienyl-
cobalt (3b): 1H NMR (C6D6, Me4Si) ꢂ 2.34(s, 12H), 4.62 (s,
5H), 7.04(d, J ¼ 7:8 Hz, 8H), 7.38 (d, J ¼ 7:9 Hz, 8H); 13
C
4Z. Duan, K. Nakajima, and T. Takahashi, Chem. Commun.,
2000, 1672.
NMR (C6D6, Me4Si) ꢂ 21.38, 74.50, 83.02, 128.57, 128.68,
133.51, 135.60; MS (m/z): 536 (Mþ).
5
For a review, see: a) T. Takahashi, M. Kotora, R. Hara, and Z.
Xi, Bull. Chem. Soc. Jpn., 72, 2591 (1999) and references
therein. See also, b) T. Takahashi, F.-Y. Tsai, and M. Kotora,
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14H. Yamazaki and N. Hagihara, J. Organometal. Chem., 7, 22
(1967).