Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes and their reactions with alkynes and alkenes: An expedient route to silicon-containing polycyclic frameworks

Article abstract of DOI:10.1021/om0607245

A convenient route to polycyclic compounds incorporating a silicon atom at a ring junction has been developed. Benzosilacyclobutenes tethered to alkynes or alkenes undergo intramolecular cycloadditions in the presence of CpCo(CO) ₂. The incorporation of the CpCo(CO) moiety into the benzosilacyclobutene framework occurs regioselectively at the Ar-Si bond of the silacycle to give 1-cobalta-2-silacyclopentenes. On the basis of DFT/B3LYP calculations, a nonadiabatic mechanism involving changes in the spin state is proposed.

Full text of DOI:10.1021/om0607245

Organometallics 2007, 26, 819-830
819
Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes and their
Reactions with Alkynes and Alkenes: An Expedient Route to
Silicon-Containing Polycyclic Frameworks
Nicolas Agenet,‡ Jean-Hugues Mirebeau,‡ Marc Petit,‡ Rene´ Thouvenot,§
Vincent Gandon,*,‡ Max Malacria,*,‡ and Corinne Aubert*,‡
Laboratoire de Chimie Organique (UMR CNRS 7611), Institut de Chimie Mole´culaire (FR 2769),
UniVersite´ Pierre et Marie Curie-Paris 6, Tour 44-54, 4 place Jussieu, F-75252 Paris Cedex 05, France,
and Laboratoire de Chimie Inorganique et Mate´riaux Mole´culaires (UMR CNRS 7071), UniVersite´ Pierre
et Marie Curie-Paris 6, Baˆtiment F, Entre´e 74, 4 place Jussieu, F-75252, Paris Cedex 05, France
ReceiVed August 9, 2006
A convenient route to polycyclic compounds incorporating a silicon atom at a ring junction has been
developed. Benzosilacyclobutenes tethered to alkynes or alkenes undergo intramolecular cycloadditions
in the presence of CpCo(CO)2. The incorporation of the CpCo(CO) moiety into the benzosilacyclobutene
framework occurs regioselectively at the Ar-Si bond of the silacycle to give 1-cobalta-2-silacyclopentenes.
On the basis of DFT/B3LYP calculations, a nonadiabatic mechanism involving changes in the spin state
is proposed.
Introduction
Silacyclobutanes have a rich diversity of chemical applications
due to their ring strain and Lewis acidity. A variety of group
10 transition-metal-catalyzed transformations of silacyclobutanes
has been reported, including ring-opening dimerization and
polymerization (ROP),1 coupling reactions,2 and ring opening
and ring expansion with aldehydes.3 1-Metalla-2-silacyclopen-
tanes have been postulated as likely intermediates in both ROP
and cycloadditions to silacyclobutanes.1,4,5 In analogy with
transition-metal-catalyzed cyclotrimerizations of alkynes,6 or
cocyclizations of alkynes with alkenes,7 which usually proceed
via five-membered metallacycles, one could think of trapping
these intermediates with double or triple C-C bonds (Figure
1). In an intramolecular version, this strategy would provide an
expedient access to (rare8) polycyclic compounds displaying a
silicon atom at the ring junction. This seems particularly relevant
since the incorporation of a silicon atom into the framework of
natural products can have a dramatic influence on the biological
activities.9 Intermolecular cycloadditions of alkynes and allenes
Figure 1. Prototypical metal-mediated intramolecular cycloaddi-
tions of silacyclobutanes to double or triple C-C bonds via C-Si
activation.
to silacyclobutanes have already been successfully achieved
under palladium catalysis.4,10 However, this reaction is not
regioselective and, at least in our hands, not compatible with
alkenes. To address these critical issues, we have explored the
reactivity of silacyclobutanes toward cobalt complexes. The
scope and the limitations of the title reaction, as well as a
mechanistic study based on DFT computations, are reported
herein.
Results and Discussion
* Corresponding
authors.
E-mail:
gandon@ccr.jussieu.fr;
aubert@ccr.jussieu.fr; malacria@ccr.jussieu.fr.
Reactions of Cobalt Complexes with Benzosilacyclobutenes.
We started our investigations using CpCo(C2H4)2,11 which has
been exploited previously as an active source of CpCo in
cooligomerizations of alkynes with alkenes.12 The reaction of
1,1-diphenylbenzosilacyclobutene (1a) with stoichiometric or
catalytic amounts of CpCo(C2H4)2 gave rise to dimerization and
higher oligomerization products (Scheme 1). The structure of
the dimer 2 could be confirmed by its mass spectral character-
istics, including a molecular ion at m/z ) 562 (MNH4+). In the
‡ Laboratoire de Chimie Organique.
§ Laboratoire de Chimie Inorganique et Mate´riaux Mole´culaires.
(1) See inter alia: (a) Weyenberg, D. R.; Nelson, L. E. J. Org. Chem.
1965, 30, 2618-2621. (b) Cundy, C. S.; Eaborn, C.; Lappert, M. F. J.
Organomet. Chem. 1972, 44, 291-297. (c) Brook, M. A. In Silicon in
Organic, Organometallic, and Polymer Chemistry; John Wiley and Sons:
New York, 2000. (d) Ohshita, J.; Matsushige, K.; Kunai, A. Organometallics
2000, 19, 5582-5588. (e) Uenishi, K.; Imae, I.; Shirakawa, E.; Kawakami,
Y. Macromolecules 2002, 35, 2455-2460.
(2) (a) Tanaka, Y.; Yamashita, H.; Tanaka, M. Organometallics 1996,
15, 1524-1526. (b) Bhanu, P. S. C.; Tanaka, Y.; Yamashita, H.; Tanaka,
M. Chem. Commun. 1996, 1207-1208. (c) Tanaka, Y.; Nishigaki, A.;
Kimura, Y.; Yamashita, M. Appl. Organomet. Chem. 2001, 15, 667-670.
(3) Hirano, K.; Yorimitsu, H.; Oshima, K. Org. Lett. 2006, 8, 483-485.
(4) (a) Sakurai, H.; Imai, T. Chem. Lett. 1975, 891-894. (b) Takeyama,
Y.; Nozaki, K.; Matsumo, K.; Oshima, K.; Utimoto, K. Bull. Chem. Soc.
Jpn. 1991, 64, 1461-1466. (c) Kende, A. S.; Mineur, C. M.; Lachicotte,
R. J. Tetrahedron Lett. 1999, 40, 7901-7906.
(6) For general reviews of transition-metal-mediated [2+2+2] cycload-
ditions of alkynes to alkenes, see: (a) Schore, N. E. Chem. ReV. 1988, 88,
1081-1119. (b) Grotjahn, D. B. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L.,
Eds.; Pergamon Press: Oxford, 1995; Vol. 12, pp 741-770. (c) Kotha, S.;
Brahmachary, E.; Lahiri, K. Eur. J. Org. Chem. 2005, 4741-4767. For
reviews of corresponding cobalt-mediated reactions, see: (d) Vollhardt, K.
P. C. Angew. Chem. 1984, 96, 525-541; Angew. Chem., Int. Ed. Engl.
1984, 23, 539-556. See also: (e) Eichberg, M. J.; Dorta, R. L.; Grotjahn,
D. B.; Lamottke, K.; Schmidt, M.; Vollhardt, K. P. C. J. Am. Chem. Soc.
2001, 123, 9324-9337, and pertinent references therein.
(5) Such complexes could be isolated and structurally characterized after
stoichiometric reactions between silacyclobutanes and Pt(PEt3)3 or Me2-
Pd(dmpe): (a) Yamashita, H.; Tanaka, M.; Honda, K. J. Am. Chem. Soc.
1995, 117, 8873-8874. (b) Tanaka, Y.; Yamashita, H.; Shimada, S.; Tanaka,
M. Organometallics 1997, 16, 3246-3248.
10.1021/om0607245 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/20/2007

820 Organometallics, Vol. 26, No. 4, 2007
Agenet et al.
Figure 2. ORTEP of 4 (left) and 9 (right) with hydrogen atoms omitted for clarity (30% thermal ellipsoids).
Scheme 1. Divergent Behaviors of Benzosilacyclobutenes
toward Cobalt Complexes
at room or lower temperatures, CpCo(CO)2 requires light and/
or heat to be active.6 In sharp contrast with CpCo(C2H4)2, the
reactions of 1a-c with CpCo(CO)2 in refluxing hexane under
visible light irradiation gave no ROP products. Instead, 1-co-
balta-2-silacyclobutenes 3a-c were isolated in 88, 48, and 33%
yield, respectively, as deep yellow solids showing unexpected
air stability for CoIII organometallic species. They were purified
by flash chromatography on silica gel without special precau-
tions. The carbonyl functionality was evident from 13C NMR
(3a: δ 203.8 ppm) and IR (3a: ν˜CO ) 1972 cm-1) spectroscopy.
The formation of a Co-Si bond was suggested by the strong
downfield shift of the 29Si nucleus compared to the starting
material (29Si NMR (CDCl3): δ (ppm) ) 48.1 (3a); -4.2 (1a)).
Since 1H and 13C chemical shifts of the CH2 group did not show
any significant alteration compared to the starting material, we
supposed that the Co insertion occurred regioselectively into
the Ar-Si bond.13
Although crystals of 3a were not suitable for single-crystal
X-ray analysis, its structure was unambiguously confirmed after
CO/PPh3 exchange (Figure 2 and Table 1). An equimolar
solution of 3a and PPh3 in CH2Cl2 was allowed to stand at room
temperature for one week, and the slow evaporation produced
X-ray-quality crystals. The diffraction study of complex 4
showed that the insertion of cobalt occurred into the most
electrophilic C-Si bond of the four-membered ring, i.e., the
Csp2-Si one. The metallacycle adopts an envelope conformation
with a fold angle of 136.2° in which the cobalt and the three
carbon atoms are almost coplanar (Co-C7-C2-C1 3.7°). The
Co-P bond length equals those reported for ((cyclopentadi-
enylalkyl)phosphane)cobalt(III) chelate complexes with silyl
ligands (2.17 Å).14 The Co-Si bond is just slightly longer (2.27
vs 2.23-2.25 Å). Interestingly, the quite small Si-Co-C7 angle
of 79.6° is indicative of some strain in the five-membered ring.15
Bimolecular Reactions of the Cobaltasilacyclopentenes
with Alkynes or Alkenes. The site chosen for Co insertion into
benzosilacyclobutenes is the more sterically hindered, but
involves phenyl- rather than benzyl-silicon cleavage. The same
presence of an alkyne such as diphenylacetylene, the [2+2+2]
cocyclization with a cobalt ethene ligand prevailed. To circum-
vent this problem, we decided to carry out a stepwise approach,
acting first on the benzosilacyclobutene. In order to avoid the
dimerization of the substrate, a cobalt complex with less labile
ligands was chosen. Whereas CpCo(C2H4)2 turns over already
(7) For reviews, see: (a) Schore, N. E. In ComprehensiVe Organic
Synthesis; Trost, B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon
Press: Oxford, 1991; Vol. 5, pp 1129-1162. (b) Lautens, M.; Klute, W.;
Tam, W. Chem. ReV. 1996, 96, 49-92. (c) Ojima, I.; Tzamarioudaki, M.;
Li, Z.; Donovan, R. J. Chem. ReV. 1996, 96, 635-662. (d) Saito, S.;
Yamamoto, Y. Chem. ReV. 2000, 100, 2901-2915. (e) Malacria, M.; Aubert,
C.; Renaud, J.-L. In Science of Synthesis: Houben-Weyl Methods of
Molecular Transformations; Lautens, M., Trost, B. M., Eds.; Georg Thieme
Verlag: Stuttgart, 2001; Vol. 1, pp 439-530. (f) Gevorgyan, V.; Radhakrish-
nan, U.; Takeda, A.; Rubina, M.; Rubin, M.; Yamamoto, Y. J. Org. Chem.
2001, 66, 2835-2841. (g) Yamamoto, Y. Curr. Org. Chem. 2005, 9, 1699-
1712.
(8) For examples, see: (a) Matsumoto, K. Miura, K. Oshima, K. Bull.
Chem. Soc. Jpn 1995, 68, 625-634. Maerkl, G.; Hofmeister, P. Angew.
Chem. 1979, 91, 863-864; Angew. Chem., Int. Ed. Engl. 1979, 91, 789-
790. (b) Ando, W.; Tanikawa, H.; Sekiguchi, A. Tetrahedron Lett. 1983,
24, 4245-4248.
(9) (a) Sieburth, S. McN; Chen, C.-A. Eur. J. Org. Chem. 2006, 311-
322. (b) Daiss, J. O.; Burschka, C.; Mills, J. S.; Montana, J. G.; Showell,
G. A.; Warneck, J. B. H.; Tacke, R. Organometallics 2006, 25, 1188-
1198, and pertinent references therein. (c) Pujals, S.; Ferna´ndez-Carneado,
J.; Kogan, M. J.; Martinez, J.; Cavelier, F.; Giralt, E. J. Am. Chem. Soc.
2006, 128, 8479-8483.
(10) For related Pd-catalyzed cycloaddition of alkynes to cyclic silylbo-
ranes, see: Suginome, M.; Noguchi, H.; Hasui, Y.; Murakami, M. Bull.
Chem. Soc. Jpn. 2005, 78, 323-326.
(12) For a recent example, see: Gandon, V.; Lebœuf, D.; Amslinger,
S.; Vollhardt, K. P. C.; Malacria, M.; Aubert, C. Angew. Chem. 2005, 117,
7276-7280; Angew. Chem., Int. Ed. 2005, 44, 7114-7118, and references
therein.
(13) For a related Si-Si bond activation by CpCo(CO)2, see: Jzang,
T.-t.; Liu, C.-s. Organometallics 1988, 7, 1271-1277.
(14) Yong, L.; Hofer, E.; Wartchow, R.; Butenscho¨n, H. Organometallics
2003, 22, 5463-5467.
(15) For a related structure in the rhodium series, see: Mitchell, G. P.;
Tilley, T. D. Organometallics 1998, 17, 2912-2916.
(11) (a) Jonas, K.; Deffense, E.; Habermann, D. Angew. Chem. 1983,
95, 729; Angew. Chem. Suppl. 1983, 1005-1016; Angew. Chem., Int. Ed.
Engl. 1983, 22, 716-717. See also: (b) Cammack, J. K.; Jalisatgi, S.;
Matzger, A. J.; Negron, A.; Vollhardt, K. P. C. J. Org. Chem. 1996, 61,
4798-4800.

Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes
Organometallics, Vol. 26, No. 4, 2007 821
Table 1. Crystal Data and Structure Refinement for
Compounds 4 and 9
Scheme 3. One-Pot Intramolecular Cycloadditions of
Four-Carbon Alkyne-Tethered Benzosilacyclobutenes
4
9
formula
C42H36CoPSi
658.74
monoclinic
P21/n
17.742(5)
18.117(9)
20.848(12)
90
99.46(4)
90
C26H26Si
366.58
triclinic
P1h
M (g‚mol-1
cryst class
)
space group
a (Å)
b (Å)
9.652(4)
10.6303(8)
11.3573(7)
100.878(5)
96.738(5)
113.755(4)
1022.95(9)
2
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
6610(5)
8
0.63
µ (mm-1
T (K)
)
1.22
250
295
diffractometer type
Enraf-Nonius-
Mach3
1, 25
0, 21; 0, 21;
-24, 24
12 435, 11 597, 0.03
KappaCCD-
Enraf-Nonius
2, 30
θ min, max
octants collected
(5), -21.5 (6)).1c Methyl 3-(trimethylsilyl)propiolate gave a 3:1
regioisomeric mixture of compounds 7 and 8 in favor of the
â-disilylated one, as indicated by NOE, DEPT, and 2D-NMR
analyses.
-13, 13; -14, 14;
-15, 15
total and unique no.
of data, Rint
18 799, 5897, 0.032
no. of reflns used
no. of reflns, no.
of params
3791
11 597, 392
3938
5897, 245
Good yields were also obtained from alkenes. For instance,
the reaction of 3a with norbornene gave the polycyclic
compound 9 in 88% yield as a single diastereomer whose
stereochemical arrangement was unambiguously assigned after
single-crystal X-ray analysis (see Table 1 and Supporting
Information). Monosubstituted alkenes such as styrene or
vinyltrimethylsilane gave mixtures of regioisomers in favor of
the less crowded ones in good to excellent yields. Although
not regioselective, the incorporation of ethyl vinyl ether proved
very efficient (99% yield). Compounds 14 and 15 slowly
eliminate ethyl alcohol after prolonged time in CDCl3 to give
silacyclohexene 16. We suspect that this elimination is catalyzed
by adventitious acid.
R, Rw, GOF
0.0832, 0.0795, 1.178
0.037, 0.043, 1.069
Scheme 2. Reactions of Complex 3a with Alkynes and
Alkenes
Intramolecular Version. When applying the conditions
described above to alkyne-tethered benzosilacyclobutenes in-
cluding a 4-methylene spacer, yields and conversion to the
desired products were scarce. For instance, benzosilacyclobutene
17 afforded the linear tricyclic compound 20 in a low 7%
isolated yield (Scheme 3). However, when boiling toluene was
used instead of hexane, the isolated yield was improved to 66%.
The regioselectivity observed during this cyclization rules out
a [4+2] cyclization via a transient ortho(sila)quinodimethane,
as described in the all-carbon series.6d Such a mechanism would
provide only the angular isomer 21, which is not obtained here.
On the other hand, the intermediacy of 1-cobalta-2-silacy-
clobutenes could be confirmed by interrupting the irradiation
after 1 h. In this case, diastereoisomeric complexes 18 and 19
could be isolated from the reaction mixture. Execution of the
previously described palladium-based protocol4 with 17 also led
to cycloaddition products, albeit less efficiently and regiose-
lectively, furnishing the two isomers 20 and 21 (1:1.7), in 33%
combined yield.
Benzosilacyclobutenes 22 and 24 were also rapidly converted
into the corresponding vinyl silanes 23 and 25. The transforma-
tion of the alkynyl-SiMe3 moiety of 24 into a vinylsilane
framework could be evidenced by the downfield shift of the
29Si NMR signals (δ (ppm) -19.4 (24); -8.6 (25)). On the other
hand, the resonance peak of the four-membered ring silicon was
shifted upfield after subsequent vinylation (δ (ppm) 3.6 (24);
-28.4 (25)). Disappointingly, the isolated yields corresponding
to these two transformations were low (20 and 19%, respec-
tively). However, reducing the tether length by one carbon as
in 26 provided the linear 6/6/5 fused heterocycle 27 in an
improved 56% isolated yield (Scheme 4). Intramolecular cy-
regioselectivity was reported with Fe2(CO)9; however the
resulting iron complexes proved unreactive toward alkynes and
alkenes.16 In contrast, under visible light irradiation, complex
3a was actually transformed into benzosilacyclohexene 5 or 6
when mixed with an excess of DMAD or diphenylacetylene in
refluxing hexane (Scheme 2). These products were obtained in
51 and 99% isolated yield, respectively. The incorporation of
π systems into the starting benzosilacyclobutenes resulted in
upfield shifts of the 29Si signals (δ (ppm) ) -4.2 (1a), -18.7
(16) (a) Cundy, C. S.; Lappert, M. F.; Dubac, J.; Mazerolles, P. J. Chem.
Soc., Dalton Trans. 1976, 910-914. (b) Cundy, C. S.; Lappert, M. F. J.
Chem. Soc., Dalton Trans. 1978, 665-673.

822 Organometallics, Vol. 26, No. 4, 2007
Table 2. Electronic Energies, Enthalpies, Free Energies, and Single-Point Energies
Agenet et al.
LACVP(d,p)
G298 (au)b
6-311+G(2d,2p)
E
298 (au)a
H298 (au)b
imaginary frequency (cm-1
)
E298 (au)c
CO
C2H2
-113.304423
-77.302842
-565.199077
-451.814714
-451.860227
-338.483560
-560.919437
-113.301118
-77.299001
-565.189503
-451.807017
-451.851449
-338.477297
-560.911648
-113.323561
-77.321849
-565.233265
-451.846229
-451.895024
-338.512298
-560.950494
-113.351680632
-77.3591391899
-1803.13359318
-1689.69812392
-1689.73800388
-1576.31379994
-561.139267695
-2250.86388551
-2250.90358583
-2137.50656881
-2214.85132367
-2214.87588468
-2214.87042808
-2214.88914073
-2214.88913481
-2214.91325369
-2214.90136677
-2214.96734703
-638.598563997
1[CpCo(CO)2]
1[CpCo(CO)]
3[CpCo(CO)]
3[CpCo]
1[A]
CP1
1[B]
-1012.792175
-899.450007
-1012.776082
-899.435319
-1012.834751
-899.492715
3[C]
CP2
1[D]
-976.758312
-976.754843
-976.776122
-976.741586
-976.739036
-976.759744
-976.800792
-976.795993
-976.819191
TS1
-168
-180
1[E]
CP3
3[E]
-976.801837
-976.794620
-976.861188
-638.324558
-976.785151
-976.778553
-976.845063
-638.315123
-976.846704
-976.838495
-976.906026
-976.906026
TS2
3[F]
1[G]
b
c
a Includes ZPE correction. Includes thermal correction at 298 K. Uncorrected.
Scheme 4. One-Pot Intramolecular Cycloadditions of
Three-Carbon Alkene- and Alkyne-Tethered
Benzosilacyclobutenes
Scheme 5. Computed Pathway for the Formation of
1-Cobalta-2-silacyclopentene B at the DFT/B3LYP Level
(energies in kcal/mol)
No associative pathway between CpCo(CO)2 and benzosilacy-
clobutene A leading to B could be found. Therefore, we
envisaged the dissociation of CpCo(CO)2 into CpCo(CO) and
CO (Scheme 5). It is now well-established that unsaturated d8
CpML species usually exhibit a triplet ground state, whereas
the 18-electron ones (CpMLL′) exhibit a singlet ground state.18
A spin change is therefore required when 1[CpCo(CO)2]
eliminates CO (under irradiation or heat) to give 3[CpCo(CO)].
Reactions that require a spin change are likely to occur if a
minimum energy crossing point (MECP) of the singlet and
triplet energy surfaces can be found close to the reagents (two-
state mechanism).18,19 This was actually the case for the
dissociation of [CpCo(CO)2] into [CpCo(CO)] and CO, as
shown by Harvey and co-workers.18d In order to connect
3[CpCo(CO)] and benzosilacyclobutene A with complex B of
singlet ground state, we sought a nearby MECP. CP1 was
actually located 8.4 kcal/mol above the reactants (Table 2). At
this point, the Co-C and Co-Si bonds are essentially formed
(Figure 3, CP1: Co-C ) 2.04 Å, Co-Si ) 2.37 Å; B: Co-C
cloaddition of C-C double bonds could also be accomplished,
albeit less efficiently. Compounds 29a and 29b were obtained
as single diastereomers in 29 and 26% yield, respectively.
Comparatively, under palladium catalysis, the insertion of the
C-C double bonds did not take place. Contrary to alkyne
insertion, the incorporation of an alkene into the Ar-Si bond
of the benzosilacyclobutene framework resulted in a downfield
shift of the 29Si signals as a result of the partial deconjugation,
the silicon atom bearing two aryl groups in the starting material
and only one in the product (δ (ppm) ) 3.7 (28a); 13.6 (29a)).
Theoretical Calculations. We next attempted to answer some
questions about the mechanism, e.g., (i) does the reaction
between 1-cobalta-2-silacyclobutene and alkynes (alkenes)
proceed associatively or does it require dissociation of CO? (ii)
if CO is lost, does the next step correspond to a [4+2]
cycloaddition between the unsaturated metallacycle and the
alkyne (alkene) or does it correspond to an insertion? (iii) if
insertion prevails, does it occur into the Co-C or the Co-Si
bond of the metallacycle? In order to gain deeper insight, we
studied the mechanism of the reaction of benzosilacyclobutene
A with CpCo(CO)2 and acetylene by means of DFT computa-
tions at the B3LYP/LACVP(d,p) level (Schemes 4 and 5). The
choice of this level of theory was validated by a very good
agreement between the structural parameters of complex 4 and
the computed ones for its parent compound (see Supporting
Information). Energies were then reevaluated at the 6-311+G-
(2d,2p) level for all atoms, as suggested by Poli and Smith.17
1
3
(18) See: (a) Siegbahn, P. E. M. J. Am. Chem. Soc. 1996, 118, 1487-
1496. (b) Su, M.-D.; Chu, S.-Y. Chem.-Eur. J. 1999, 5, 198-207. (c)
Smith, K. M.; Poli, R.; Harvey, J. N. Chem.-Eur. J. 2001, 7, 1679-1690.
(d) Carreo´n-Macedo, J.-L.; Harvey, J. N. J. Am. Chem. Soc. 2004, 126,
5789-5797. (e) Petit, A.; Richard, P.; Cacelli, I.; Poli, R. Chem.-Eur. J.
2006, 12, 813-823. (f) Gandon, V.; Agenet, N.; Vollhardt, K. P. C.;
Malacria, M.; Aubert, C. J. Am. Chem. Soc. 2006, 128, 8509-8520, and
pertinent references therein.
(19) (a) Yarkony, D. R. In Modern Electronic Structure Theory; Yarkony,
D. R., Ed.; World Scientific: Singapore, 1995; p 642. (b) Yarkony, D. R.
J. Phys. Chem. 1996, 100, 18612-18628. (c) Schro¨der, D.; Shaik, S.;
Schwartz, H. Acc. Chem. Res. 2000, 33, 139-145.
(17) Poli, R.; Smith, K. M. Eur. J. Inorg. Chem. 1999, 877-879.

Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes
Organometallics, Vol. 26, No. 4, 2007 823
Figure 3. Structures of various species depicted in Schemes 4 and 5, with selected bond distances (Å).
) 1.97 Å, Co-Si ) 2.29 Å). The distance corresponding to
the breaking Csp2-Si bond is already long (Csp2-Si in A: )
1.87 Å; CP1: 2.29 Å; B: 2.80 Å). The main difference between
CP1 and B is the Co-C-C-C fold angle of the five-membered
ring (CP1: 29.0°; B: 4.2°). This step is appreciably exothermic
by 16.5 kcal/mol.
Again, no favorable associative pathway could be modeled
for the transformation of B into D (Scheme 6). The energy

824 Organometallics, Vol. 26, No. 4, 2007
Agenet et al.
Scheme 6. Computed Pathway for the Formation of Silacyclohexene G at the DFT/B3LYP Level (energies in kcal/mol, relative
to the {3[CpCo(CO)] + A} system)
required for the dissociation of CO was evaluated to be 28.4
kcal/mol. The triplet species C then reacts with acetylene to
give singlet complex D. The crossing point corresponding to
this reaction lies 9.0 kcal/mol above C. The geometry at CP2
is close to that of D except for the distance between Co and the
center of the C-C triple bond (CP2: 2.43 Å; D: 1.90 Å). This
transformation is exothermic by 6.3 kcal/mol. From complex
D, insertion of the complexed alkyne into the Co-Si bond is
found to be kinetically twice as easy as the insertion into the
Co-C bond (3.4 kcal/mol vs 7.5 kcal/mol). The formation of
the resulting 16-electron complex E in the singlet state is
exothermic by 8.4 kcal/mol. The relaxation of this complex to
its triplet ground state (∆ES-T ) 15.3 kcal/mol) is made
straightforward by the existence of CP3, virtually superimposed
with singlet E (∆E < 0.1 kcal/mol, rmsd 0.0007). Finally, a
transition state connecting the two triplet species E and F was
found 7.5 kcal/mol above triplet E. This transformation is
strongly exothermic by 33.9 kcal/mol. The dissociation of F
into the final product G and CpCo requires 34.6 kcal/mol. The
latter fragment has a triplet ground state (∆ESinglet-Triplet ) 38.0
kcal/mol, ∆ESinglet-Quintet ) 29.3 kcal/mol). Manifold effort failed
Experimental Section
General Methods. Reactions were carried out under argon using
standard Schlenk techniques. Dichloromethane was distilled over
calcium hydride. n-Hexane, benzene, and toluene were distilled from
NaK2.8. THF was distilled from sodium benzophenone ketyl. The
reactions were irradiated (visible light) using a quartz (non-UV
block) 300 W ELW AX2275.GY5.3 120V halogen lamp (color
temperature 3350 K) at 50% of its power (using a potentiometer).
Thin-layer chromatography (TLC) was performed on Merck 60 F254
silica gel. Merk Gerudan SI 60 Å silica gel (35-70 µm) was used
for column chromatography. CpCo(CO)2 was purchased from
Aldrich and used as received. CpCo(C2H4)2 was prepared according
to a known procedure.11a 1H, 13C, and 31P NMR spectra were
recorded at 20 °C at 400, 100, and 162 MHz, respectively, on a
Bruker AVANCE400 spectrometer. 29Si spectra were recorded at
20 °C at 60 MHz on a Bruker AVANCE300 spectrometer (SiH
INEPT). Chemical shifts (δ) are given in ppm, referenced to the
residual proton resonance of the solvents (7.26 for CDCl3; 7.16
for C6D6), to the residual carbon resonance of the solvent (77.16
for CDCl3; 128.06 for C6D6), or using a coaxial tube of H3PO4
80% in H2O as a reference for 31P or external reference (TMS) for
29Si. Coupling constants (J) are given in hertz (Hz). The terms m,
s, d, t, q, and quint refer to multiplet, singlet, doublet, triplet, quartet,
and quintet; br means that the signal is broad. When possible, NMR
signals were assigned on the basis of NOE, DEPT, and 2D-NMR
(COSY, HMBC) experiments. Elemental analyses, low-resolution
mass spectra (MS), and high-resolution mass spectra (HRMS) were
performed by the Service Re´gional de Microanalyse de l’Universite´
Pierre et Marie Curie or by the Service de Spectrome´trie de Masse
de l’ICSN-CNRS, Gif-sur-Yvette. Infrared spectra (IR) were
recorded on a Bruker Tensor 27 spectrometer. Melting points were
obtained on a Bu¨chi capillary apparatus and were not corrected.
Copies of the 1H and 13C NMR spectra of all new compounds have
been deposited with the Supporting Information as evidence of their
purity.
3
3
to locate a transition state connecting [CpCo] and A to [C].
This might explain why the reaction requires a stoichiometric
amount of CpCo(CO)2. One way to address this issue could be
the use of an external source of CO to regenerate CpCo(CO).
In conclusion, we have found that the reaction of CpCo(CO)2
with benzosilacyclobutenes gives the corresponding unprec-
edented 1-cobalta-2-silacylobutenes after regioselective insertion
of cobalt into the phenyl-silicon bond of the silacycle. Unlike
their iron counterparts, these complexes are reactive with alkynes
and alkenes (electron-rich or electron-poor) to give benzosila-
cyclohexenes. The one-pot intramolecular version of this
reaction provides access to polycyclic compounds incorporating
a silicon atom at the ring junction. A two-state mechanism is
proposed on the basis of DFT computations. It shows that the
dissociation of CO opens a vacant site for the alkyne, which
inserts preferably into the Co-Si σ-bond. We are now applying
this new reaction to the synthesis of silicon containing bioisos-
ters of natural products.

Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes
Organometallics, Vol. 26, No. 4, 2007 825
(2-Bromobenzyl)dichloro(phenyl)silane.20 The Grignard reagent
of 2-bromobenzyl bromide (25 g, 100 mmol) was prepared at 0 °C
in 100 mL of diethyl ether: the bromide, in 90 mL of diethyl ether,
was added over 2 h on magnesium turnings (2.43 g, 100 mmol)
covered by 10 mL of diethyl ether. Then, the reaction mixture was
allowed to stir for 1 h at rt. The Grignard reagent was transferred
via cannula into a solution of phenyltrichlorosilane (40 mL, 250
mmol) in 80 mL of diethyl ether at 0 °C. The solution was refluxed
for 17 h, the salts were eliminated by filtration, and the solvent
removed in Vacuo. Fraction distillation gave 25.9 g of excess
phenyltrichlorosilane (35 °C, 0.04 mmHg) and 24.7 g (71%) of
(2-bromobenzyl)dichloro(phenyl)silane (110 °C, 0.04 mmHg) as a
colorless oil. 1H NMR (C6D6): δ 7.54-7.52 (m, 2 H), 7.26 (dd, J
) 8.1 Hz, J ) 1.2 Hz, 1 H), 7.10-7.06 (m, 1 H), 7.03-6.99 (m,
2 H), 6.95 (dd, J ) 7.7 Hz, J ) 1.6 Hz, 1 H), 6.80 (td, J ) 7.6 Hz,
J ) 1.3 Hz, 1 H), 6.57 (td, J ) 7.7 Hz, J ) 1.7 Hz, 1 H), 2.89 (s,
2 H). 13C NMR (C6D6): δ 133.7 (Carom), 133.0 (2 CHarom), 132.2
(CHarom), 130.8 (CHarom), 129.9 (CHarom), 127.4 (2 CHarom), 126.6
(CHarom), 126.6 (CHarom), 123.9 (Carom), 29.4 (CH2), one Carom
overlapped with solvent residual peak. 29Si NMR (C6D6): δ 13.4.
Compound 1b: colorless oil. 1H NMR (CDCl3): δ 7.57 (d, J )
7.6 Hz, 4 H), 7.47 (br s, 1 H), 7.38-7.35 (m, 1 H), 7.28-7.26 (m,
overlap with solvent residual peak, 2 H), 3.81 (s, 6 H, H12), 2.56
(d, 2 H, H1). 13C NMR (CDCl3): δ 161.9 (2 C, CIV), 152.2 (CIV),
144.8 (CIV), 137.1 (2 C, CIII), 131.3 (CIII), 128.3 (CIII), 127.5 (CIII),
127.2 (CIII), 125.6 (2 C, CIV), 114.3 (2 C, CIII), 54.5 (2 C, C12),
21.1 (C1). 29Si NMR (CDCl3): δ -4.6. IR (neat): ν˜max 3439, 3023,
2836, 1593, 1503, 1278, 1248, 1208, 1116, 1029 cm-1
.
The following compounds were prepared from 1-chloro- and
1-bromo-1-phenyl-2:3-benzo-1-silacyclobut-2-ene (using the pro-
cedure described in the literature)24 followed by condensation of
the corresponding Grignard or lithium reagent (according to the
procedure reported in the literature).23
1-Chloro- and 1-Bromo-1-phenyl-2:3-benzo-1-silacyclobut-
2-ene.21 (2-Bromobenzyl)dichloro(phenyl)silane (24.7 g, 71 mmol)
and 1,2-dibromoethane (0.6 mL, 7 mmol) in diethyl ether (80 mL)
were added within 6 h, maintaining a gentle reflux, over magnesium
turnings (3.45 g, 142 mmol). The reaction mixture was allowed to
stir for 1 h at rt. The solution was refluxed for 24 h, and then the
salts were removed by filtration and the solvent was removed in
Vacuo. Fraction distillation yielded 13.7 g of 1-chloro- and 1-bromo-
1-phenyl-2:3-benzo-1-silacyclobut-2-ene (65-73 °C, 0.04 mmHg)
Representative Procedure. The Grignard reagent of 1-bromo-
pent-4-ene (1.18 mL, 10 mmol) was prepared at room temperature
in 15 mL of diethyl ether. The bromide was added over 2 h on
magnesium turnings (272 mg, 11.2 mmol), then the reaction mixture
was allowed to stir for 2 h at room temperature. It was then
canulated into a solution of 1-chloro- and 1-bromo-1-phenyl-2:3-
benzo-1-silacyclobut-2-ene (7.5 mmol) in 15 mL of diethyl ether
at -78 °C. The solution was allowed to warm to room temperature
overnight. The reaction was quenched with saturated NH4Cl, and
the organic layer was washed with brine and dried with MgSO4.
The solvent was removed by rotary evaporation. Flash chromatog-
raphy over silica gel using petroleum ether as eluent yields
compound 28a as a transparent oil (1.92 g, 61%).
1
as a 3:1 mixture (colorless oil). H NMR (C6D6): δ 7.63-7.60
(m, 2 H), 7.21-7.19 (m, 1 H), 7.17-6.97 (m, 6 H), 2.60 (d, JAB
)
17.2 Hz, 1 H), 2.48 (d, JAB ) 17.2 Hz, 1 H); Si-Br compound:
2.67 (d, JAB ) 17.2 Hz, 1 H), 2.51 (d, JAB ) 17.2 Hz, 1 H). 13C
NMR (C6D6): δ 150.2 (Carom), 143.2 (Carom), 134.4 (CHarom), 134.3
(CHarom), 133.1 (CHarom), 132.9 (CHarom), 131.4 (CHarom), 130.9
(CHarom), 128.6 (CHarom), 128.0 (CHarom), 127.4 (CHarom), 127.2
(CHarom), 26.4 (CH2, Si-Br), 26.2 (CH2, Si-Cl). 29Si NMR
(C6D6): δ 2.6 (Si-Cl), -1.1 (Si-Br).
Due to 4- and 5-exo-dig autocyclization of the Grignard reagent,25
or the lithium derivative,26 the yields corresponding to compounds
17, 22, 24, and 26 are irremediably low.
Benzosilacyclobutenes. Compounds 1a and 1c were prepared
according to a literature procedure.22
Compound 1b. The Grignard reagent of 4-bromoanisole (1.75
M, 9 mL, 15.7 mmol, prepared as above at gentle reflux instead of
0 °C) was added to a solution of 1,1-dichloro-2:3-benzo-1-
silacyclobut-2-ene23 (1.49 g, 7.9 mmol) in 20 mL of diethyl ether
at -78 °C. The solution was allowed to warm to rt overnight. The
reaction was quenched with saturated NH4Cl, and the organic layer
was washed with brine and dried with MgSO4. The solvent was
removed by rotary evaporation. Flash chromatography over silica
gel using petroleum ether/diethyl ether (9:1) as eluent yielded 1b
as a colorless oil (1.53 g, 58%).
1
Compound 17: colorless oil. H NMR (CDCl3): δ 7.61-7.58
(m, 2 H, H16), 7.42-7.35 (m, 5 H), 7.26-7.20 (m, 2 H), 2.39 (d,
JAB ) 16.7 Hz, 1 H, H8), 2.32 (d, JAB ) 16.7 Hz, 1 H, H8), 2.14-
2.09 (m, 2 H, H4), 1.75 (t, J ) 2.5 Hz, 3 H, H1), 1.60-1.54 (m, 4
H, H5-6), 1.30-1.20 (m, 2 H, H7). 13C NMR (CDCl3): δ 151.7
(C9), 143.7 (C14), 135.7 (C15), 134.2 (2 C, C16), 131.0 (CIII), 130.7
(CIII), 129.8 (CIII), 128.0 (2 C, C17), 126.9 (CIII), 126.5 (CIII), 79.0
(C3), 75.6 (C2), 32.2 (CII), 23.0 (CII), 19.3 (C8), 18.2 (C4), 13.3
(21) Horner, L.; Subramanian, P. V.; Eiben, K. Liebigs Ann. Chem. 1968,
714, 91-111.
(22) Eaborn, C.; Walton, D. R. M.; Chan, M. J. Organomet. Chem. 1967,
9, 251-257.
(23) Kang, K.-T.; Yoon, U. C.; Seo, H. C.; Kim, K. N.; Song, H. Y.;
Lee, J. C. Bull. Korean Chem. Soc. 1991, 12, 57-60.
(24) Gilman, H.; Atwell, W. H. J. Am. Chem. Soc. 1964, 89, 5589-
5593.
(25) Hill, A. E. J. Organomet. Chem. 1975, 91, 123-271.
(26) Bayley, W. F.; Ovaska, T. V. J. Am. Chem. Soc. 1993, 115, 3080-
3090.
(20) (a) Van den Winkel, Y.; Van Baar, B. L. M.; Bastiaans, H. M. M.;
Bickelhaupt, F.; Schenkel, M.; Stegmann, H. B. Tetrahedron 1990, 46,
1009-1024. (b) Oestreich, M.; Schmid, U. K.; Auer, G.; Keller, M.
Synthesis 2003, 2725-2739.

826 Organometallics, Vol. 26, No. 4, 2007
Agenet et al.
(C7), 3.4 (C1). 29Si NMR (CDCl3): δ 3.6. IR (neat): ν˜max 3050, 2918,
2855, 1959, 1584, 1428, 1100, 1041, 780, 734, 697 cm-1. Anal.
Calcd for C21H28Si: C, 82.70; H, 7.63. Found: C, 82.51; H, 7.88.
Compound 28a: colorless oil. 1H NMR (CDCl3): δ 7.59-7.57
(m, 2 H, H14), 7.41-7.34 (m, 5 H), 7.23-7.19 (m, 2 H), 5.76 (ddt,
J ) 17.0 Hz, J ) 10.2 Hz, J ) 6.7 Hz, 1 H, H2), 4.99-4.93 (m,
2 H, H1), 2.38 (d, JAB ) 16.8 Hz, 1 H, H6), 2.31 (d, JAB ) 16.8
Hz, 1 H, H6), 2.17-2.09 (m, 2 H, H3), 1.65-1.53 (m, 2 H, H4),
1.33-1.20 (m, 2 H, H5). 13C NMR (CDCl3): δ 151.7 (C7), 143.7
(C12), 138.5 (C1), 135.7 (C13), 134.1 (2 C, C14), 131.0 (CIII), 130.8
(CIII), 129.8 (CIII), 128.0 (2 C, C15), 126.9 (CIII), 126.6 (CIII), 114.9
(C2), 37.1 (C3), 23.3 (C4), 19.3 (C6), 13.4 (C5). 29Si NMR
(CDCl3): δ 3.7. IR (neat): ν˜max 3052, 2923, 1640, 1585, 1429,
1111 cm-1. Anal. Calcd for C18H20Si: C, 81.76; H, 7.62. Found:
C, 81.33; H, 7.89.
1
Compound 22: colorless oil. H NMR (CDCl3): δ 7.61-7.59
(m, 2 H, H15), 7.42-7.31 (m, 7 H), 7.26-7.19 (m, 5 H), 2.41 (t,
overlap, 2 H, H3), 2..41 (d, overlap, 1 H, H7), 2.33 (d, JAB ) 16.9
Hz, 1 H, H7), 1.70-1.67 (m, 4 H, H4,5), 1.33-1.25 (m, 2 H, H6).
13C NMR (CDCl3): δ 151.7 (C8), 143.6 (C13), 135.6 (C14), 134.2
(2 C, C15), 131.5 (2 C, C19), 131.0 (CIII), 130.8 (CIII), 129.8 (CIII),
128.1 (2 CIII), 128.0 (2 CIII), 127.5 (C21), 126.9 (CIII), 126.6 (CIII),
124.0 (C18), 90.0 (C2), 80.8 (C1), 31.8 (CII), 23.1 (CII), 19.3 (C7),
18.9 (CII), 13.4 (C6). IR (neat): ν˜max 3052, 2929, 2857, 2227, 1598,
1489, 1428, 1110, 1041 cm-1. MS (CI): 388 (M(H2O)NH4+, 100),
370 (MNH4+, 4), 335 (MH+, 2), 279 (10), 230 (8). HRMS(ES+):
calcd for C25H25Si (MH+) 353.1720; found 353.1725.
Compound 28b: colorless oil. 1H NMR (CDCl3): δ 7.60-7.58
(m, 2 H, H15), 7.42-7.34 (m, 5 H), 7.26-7.19 (m, 2 H), 5.78
(ddt, J ) 17.1 Hz, J ) 10.1 Hz, J ) 6.8 Hz, 1 H, H2), 4.99-4.90
(m, 2 H, H1), 2.38 (d, JAB ) 16.7 Hz, 1 H, H7), 2.34 (d, JAB
)
16.7 Hz, 1 H, H7), 2.06-2.01 (m, 2 H, H3), 1.57-1.44 (m, 4 H,
H
4-5), 1.29-1.24 (m, 2 H, H6). 13C NMR (CDCl3): δ 151.7 (C8),
143.8 (C13), 138.8 (C1), 135.8 (C14), 134.1 (2 C, C15), 131.0 (CIII),
130.7 (CIII), 129.8 (CIII), 128.0 (2 C, C16), 126.9 (CIII), 126.5 (CIII),
114.3 (C2), 33.4 (C3), 32.3 (CII), 23.3 (CII), 19.3 (C7), 13.7
(C6). IR (neat): ν˜max 3052, 2922, 1640, 1585, 1428, 1111 cm-1
.
1
Anal. Calcd for C18H20Si: C, 81.95; H, 7.96. Found: C, 81.95; H,
7.96.
Compound 24: colorless oil. H NMR (CDCl3): δ 7.59-7.57
(m, 2 H, H15), 7.42-7.33 (m, 7 H), 7.26-7.19 (m, 2 H), 2.38 (d,
JAB ) 16.7 Hz, 1 H, H7), 2.31 (d, JAB ) 16.7 Hz, 1 H, H7), 2.20
(t, J ) 6.7 Hz, 2 H, H3), 1.60-1.57 (m, 4 H, H4,5), 1.27-1.24 (m,
2 H, H6), 0.11 (s, 9 H, SiMe3). 13C NMR (CDCl3): δ 151.7 (C8),
143.6 (C13), 135.6 (C14), 134.1 (2 C, C15), 131.0 (CIII), 130.8 (CIII),
129.8 (CIII), 128.0 (2 CIII, C16), 126.9 (CIII), 126.6 (CIII), 107.2 (C2),
84.6 (C1), 31.8 (CII), 23.0 (CII), 19.4 (C7), 19.2 (CII), 13.4 (C5),
0.13 (3 C, SiMe3). 29Si NMR (C6D6): δ 3.6, -19.4 (SiMe3), due
to poor spin relaxation, the silicon atom of the silacycle is hardly
Reaction of 1 with CpCo(C2H4)2. CpCo(C2H4)2 (181 mg, 1
mmol or 18 mg, 0.1 mmol) was added at -20 °C to a solution of
benzosilacyclobutene 1 (274 mg, 1 mmol) in n-hexane or THF (10
mL). The solution was allowed to warm to room temperature and
to stir overnight. Silica was added and the solvent was removed
by rotary evaporation. The solid residue was submitted to flash
chromatography over silica gel using a pentane/diethyl ether (9:1)
mixture to afford ∼80 mg (∼30%) of 2.
observed. IR (neat): ν˜max 3053, 2930, 2173, 1429, 1111, 1041 cm-1
.
MS (CI): 384 (M(H2O)NH4+, 100), 367 (M(H2O)H+, 12), 365 (16),
349 (MH+, 9), 324 (23), 307 (15), 230 (7), 90 (18). HRMS(ES+):
calcd for C22H29Si2 (MH+) 349.1802; found 349.1804.
Compound 2: white solid, mp 198-201 °C. 1H NMR (CDCl3):
δ 7.57-7.55 (m, 4 H), 7.42-7.32 (m, 10 H), 7.23-7.12 (m, 4 H),
7.16-7.14 (m, 4 H), 6.98-6.94 (m, 4 H), 6.51-6.49 (m, 2 H),
3.05 (d, JAB ) 13.4 Hz, 2 H, H1), 2.37 (d, JAB ) 13.4 Hz, 2 H,
H1). 13C NMR (CDCl3): δ 145.1 (2 C, CIV), 137.3 (2 C, CIII), 136.4
(4 C, C9), 135.9 (2 C, CIV), 135.3 (4 C, C9), 133.6 (2 C, C8), 133.5
(2 C, C8), 130.3 (2 C, CIII), 129.5 (2 C, CIII), 129.3 (2 C, CIII),
129.2 (2 C, CIII), 127.8 (4 C, C10), 127.5 (4 C, C10), 123.5 (2 C,
CIII), 22.0 (2 C, C1). 29Si NMR (CDCl3): δ -6.2. IR (neat): ν˜max
3048, 1584, 1407, 1197, 1107 cm-1. MS (CI): 562 (MNH4+, 100),
545 (MH+, 98), 467 ((M - Ph)+, 17).
1
Compound 26: colorless oil. H NMR (CDCl3): δ 7.60-7.58
(m, 2 H, H14), 7.41-7.34 (m, 5 H), 7.23-7.19 (m, 2 H), 2.39 (d,
JAB ) 17.8 Hz, 1 H, H6), 2.32 (d, JAB ) 17.8 Hz, 1 H, H6), 2.28
(t, J ) 6.9 Hz, 2 H, H3), 1.77-1.66 (m, 2 H, H4), 1.44-1.32 (m,
2 H, H5), 0.11 (s, 9 H, SiMe3). 13C NMR (CDCl3): δ 151.7 (C7),
143.4 (C12), 135.4 (C13), 134.2 (2 C, C14), 131.0 (CIII), 130.9 (CIII),
129.9 (CIII), 128.0 (2 C, C15), 126.9 (CIII), 126.6 (CIII), 107.1 (C2),
85.0 (C1), 23.3 (C3), 23.1 (C4), 19.3 (C6), 13.3 (C5), 0.2 (3 C,
SiMe3). IR (neat): ν˜max 3053, 2933, 2173, 1428, 1248, 1111, 1041,
841 cm-1. MS (CI): 380 (M(H2O)NH4+, 100), 353 (M(H2O)H+,
20), 335 (MH+, 3). HRMS(ES+): calcd for C21H27Si2 (MH+)
335.1646; found 335.1650.
Preparation of Cobalt Complexes. An n-hexane solution (10
mL) of benzosilacyclobutene 1a (274 mg, 1 mmol) and CpCo-
(CO)2 (140 µL, 1 mmol) was refluxed for 2 h under irradition. The
mixture was concentrated under reduced pressure and purified over
silica gel using a pentane/diethyl ether (95:5) mixture to afford 373
mg (88%) of 3a.
1
Complex 3a: yellow solid, mp 47 °C dec. H NMR (CDCl3):
δ 7.48-7.28 (m, 11 H), 7.20 (d, J ) 7.1 Hz, 1 H), 6.95 (td, J )
7.3 Hz, J’ ) 1.3 Hz, 1 H), 6.86 (td, J ) 7.6 Hz, J’ ) 1.8 Hz, 1 H),

Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes
Organometallics, Vol. 26, No. 4, 2007 827
127.3-127.2 (m, 13 C, CIII), 122.6 (CIII), 122.3 (CIII), 87.6 (5 C,
C16), 28.8 (C7). 31P NMR (CDCl3): δ 56.3.
Bimolecular Insertions of Alkynes or Alkenes. General
procedure: complex 3 (1 mmol) and the desired alkyne or alkene
(5 mmol) were dissolved in n-hexane (10 mL). The mixture was
refluxed under irradiation until completion (ca. 1-2 h). Silica was
added, and the solvent was removed by rotary evaporation. The
solid residue was submitted to flash chromatography over silica
gel using a gradient mixture of pentane and diethyl ether.
4.92 (s, 5 H, Cp), 2.89 (s, 2 H, H7). 13C NMR (CDCl3): δ 203.8
(C12), 152.7 (C6), 144.5 (CIII), 143.6 (CIV), 143.4 (CIV), 140.4 (CIV),
134.6 (2 C, C9), 133.9 (2 C, C9), 128.9 (C11), 128.7 (C11), 127.8 (2
C, C10), 127.7 (2 C, C10), 127.2 (CIII), 124.8 (CIII), 124.2 (CIII),
89.5 (5 C, Cp), 32.2 (C7). IR (neat): ν˜max 3043, 1987 (CO), 1426,
1098, 1006 cm-1 29Si NMR (CDCl3): δ 48.1. MS (CI): 443 (18),
.
442 (MNH4+, 43), 425 (MH+, 6), 399 (12), 398 (45), 397 ((MH
-CO)+, 100), 396 (12), 290 (15). Anal. Calcd for C25H21CoOSi:
C, 70.74; H, 4.99. Found: C, 70.74; H, 5.16.
The same procedure was used to prepare 3b (106 mg, 46%) and
3c (52 mg, 33%) from benzosilacyclobutene 1b (183 mg, 0.55
mmol) and 1c (92 mg, 0.45 mmol) using 63 µL of CpCo(CO)2.
1
Compound 5: white solid, mp 113 °C. H NMR (CDCl3): δ
7.58-7.55 (m, 4 H, H9), 7.41-7.37 (m, 2 H), 7.34-7.31 (m, 4 H),
7.23-7.14 (m, 4 H), 3.93 (s, 3 H, H14), 3.51 (s, 3 H, H12), 2.73 (s,
2 H, H7). 13C NMR (CDCl3): δ 169.6 (C13|15), 169.2 (C13|15), 155.0
(C17), 136.7 (2 C, C8), 135.2 (4 C, C9), 131.9 (CIII), 131.8 (CIV),
131.4 (CIV), 130.3 (CIII), 130.1 (2 C, C11), 129.5 (CIII), 127.9 (4 C,
C10), 127.8 (CIV), 126.3 (CIII), 52.6 (C12|14), 51.7 (C12|14), 19.5 (C7).
29Si NMR (CDCl3): δ -18.7. IR (neat): ν˜max 1734, 1713, 1430,
1236 cm-1. Anal. Calcd for C25H22O4Si: C, 72.44; H, 5.35.
Found: C, 72.10; H, 5.53.
1
Compound 3b: yellow solid, mp 45 °C dec. H NMR (C6D6):
δ 7.53 (d, J ) 7.6 Hz, 1 H), 7.45-7.38 (m, 4 H), 7.23 (d, J ) 7.4
Hz, 1 H), 7.01-6.88 (m, 6 H), 4.95 (s, 5 H, Cp), 3.83 (s, 6 H,
H12), 2.89 (s, 2 H, H7). 13C NMR (C6D6): δ 203.9 (CO), 160.2
(CIV), 160.0 (CIV), 152.7 (CIV), 144.4 (CIII), 143.8 (CIV), 136.0 (CIII),
135.3 (CIII), 134.4 (CIV), 131.6 (CIV), 127.1 (CIII), 124.7 (CIII), 124.1
(CIII), 113.4 (CIII), 113.3 (CIII), 89.5 (5 C, Cp), 55.0 (2 C, C12),
32.9 (C7). 29Si NMR (CDCl3): δ 47.0. IR (neat): ν˜max 2926, 1989,
1591, 1441, 1275, 1245, 1181, 1099, 1030 cm-1. Anal. Calcd for
C27H25CoO3Si: C, 66.93; H, 5.20. Found: C, 66.96; H, 5.57.
Compound 6: yellow solid, mp 58 °C. 1H NMR (C6D6): δ 7.59-
7.57 (m, 4 H, H11), 7.13-6.70 (m, 20 H), 2.81 (s, 2 H, H7). 13C
NMR (CDCl3): δ 153.4 (C9), 142.5 (C14|18), 141.7 (C14|18), 138.7
(CIV), 137.3 (CIV), 135.4 (4 C, C11), 135.3 (CIV), 133.4 (2 C, C10),
131.4 (CIII), 130.6 (2 C, C13), 130.4 (CIII), 129.6 (2 C, C15), 128.6
(2 C, C19), 127.7 (4 C, C12), 127.6 (2 C, C16), 127.5 (CIII), 127.4 (2
C, C20), 126.3 (CIII), 125.4 (CIII), 124.8 (CIII), 20.3 (C7). 29Si NMR
Complex 3c: yellow solid. 1H NMR (C6D6): δ 7.36 (d, J ) 6.6
Hz, 1 H), 7.19-7.16 (m, 1 H), 6.99 (td, J ) 7.3 Hz, J′ ) 1.3 Hz,
(CDCl3): δ -21.5. IR (neat): ν˜max 1427, 1108, 764, 733 cm-1
.
MS (FAB): 469 (38), 468 (MNH4+, 80), 452 (45), 451 (MH+, 100).
HRMS(ES+): calcd for C33H26Si 450.1804; found 450.1795.
1 H), 6.90 (t, J ) 7.6 Hz, 1 H), 4.59 (s, 5 H, Cp), 2.53 (d, JAB
)
16.0 Hz, 1 H, H7), 2.23 (d, JAB ) 16.0 Hz, 1 H, H7), 1.18-1.04
(m, 11 H), 0.78 (d, J ) 7.3 Hz, 3 H, H9). 13C NMR (CDCl3): δ
203.7 (C10), 152.9 (C6), 144.5 (CIII), 127.8 (CIII), 125.0 (CIII), 124.4
(CIII), 87.9 (5 C, Cp), 28.0 (C7), 20.1 (2 C, C9), 19.9 (C8), 19.8
(C8), 19.6 (C9), 19.4 (C9). IR (neat): ν˜max 3054, 2942, 2863, 1972
(CO), 1460 cm-1
.
7:8 mixture: colorless oil. 1H NMR (C6D6): δ 7.57-7.55 (m, 8
H, H11, 7 and 8), 7.35-7.33 (m, 2 H, 7 and 8), 7.10-7.07 (m, 12
H, 7 and 8), 6.94-6.82 (m, 6 H, 7 and 8), 3.49 (s, 3 H, H15, 8),
3.15 (s, 3 H, H15, 7), 2.52 (s, 2 H, H7, 7), 2.41 (s, 2 H, H7, 8), 0.45
(s, 9 H, SiMe3, 7), 0.16 (s, 9 H, SiMe3, 8).
1
Complex 4: red solid. H NMR (CDCl3): δ 8.02-8.00 (m, 1
H), 7.61-7.51 (m, 5 H), 7.31-6.74 (m, 23 H), 4.54 (s, 5 H, H16),
1.86 (d, JAB ) 16.2 Hz, 1 H, H7), 1.16 (d, JAB ) 16.2 Hz, 1 H,
H7). 13C NMR (CDCl3): δ 156.2 (C6), 148.7 (CIV), 147.2 (CIII),
142.8 (CIV), 135.8 (CIV), 135.4 (CIV), 135.3 (CIII), 134.2 (2 C, C9),
134.1 (2 C, C9), 133.5 (CIII), 129.3 (CIII), 128.4 (CIII), 127.7 (CIII),

828 Organometallics, Vol. 26, No. 4, 2007
Agenet et al.
1
Compound 9: white solid, mp 112 °C. H NMR (CDCl3): δ
H9, 14), 1.54 (dd, JAB ) 14.6 Hz, J′ ) 3.5 Hz, 1 H, H9, 14), 1.15
(t, J ) 7.1 Hz, 3 H, H15), 1.06 (t, J ) 7.1 Hz, 3 H, H15).
7.54-7.10 (m, 14 H), 3.36 (d, J ) 9.4 Hz, 1 H, H9), 2.73 (d, JAB
) 15.7 Hz, 1 H, H7), 2.66 (d, J ) 4.0 Hz, 1 H, H17), 2.50 (d, JAB
) 15.7 Hz, 1 H, H7), 2.42 (br s, 1 H, H14), 1.90-1.59 (m, 5 H,
H
15,16,8), 1.46 (br d, JAB ) 9.8 Hz, 1 H, H18), 1.11 (br d, JAB )
10.1 Hz, 1 H, H18).13C NMR (CDCl3): δ 142.6 (CIV), 136.3 (CIV),
135.6 (CIV), 135.4 (2 C, C11), 135.0 (CIV), 134.8 (2 C, C11), 132.6
(C13), 130.2 (C13), 129.5 (CIII), 129.2 (CIII), 127.9 (2 C, C12), 127.8
(2 C, C12), 126.0 (CIII), 125.8 (CIII), 51.4 (C9), 47.2 (C17), 39.1 (C14),
36.2 (C18), 34.1 (C16), 29.6 (C15), 29.0 (C8), 17.9 (C7). 29Si NMR
(CDCl3): δ -13.7. IR (neat): ν˜max 3047, 2943, 2857, 1482, 1425,
1260, 1104, 1025 cm-1. Anal. Calcd for C26H26Si: C, 85.19; H,
7.15. Found: C, 84.95; H, 7.28.
Compound 16: the 14:15 mixture decomposes in CDCl3 to give
16 within 24 h (100% conversion). H NMR (CDCl3): δ 7.66-
6.98 (m, 14 H), 6.33 (d, J ) 14.9 Hz, 1 H, H9), 4.73 (d, J ) 15.1
Hz, 1 H, H8), 2.75 (s, 2 H, H7).
1
Intramolecular Insertion of Alkynes or Alkenes. General
procedure: the benzosilacyclobutene (0.5 mmol) was dissolved in
toluene (5 mL). CpCo(CO)2 (70 µL, 0.5 mmol) was added. The
mixture was refluxed under irradiation until completion (1-2 h).
Silica was added, and the solvent was removed by rotary evapora-
tion. The solid residue was submitted to flash chromatography over
silica gel using a gradient mixture of pentane and diethyl ether.
1
10:11 mixture: colorless oil. H NMR (CDCl3): δ 7.55-6.62
(m, 38 H, 10 and 11), 4.98 (t, J ) 3.6 Hz, 1 H, H9, 11), 3.15-3.10
(m, 2 H, H9, 10), 2.89-2.85 (m, 1 H, H8, 10), 2.83 (d, J ) 3.6 Hz,
2 H, H8, 11), 2.80 (s, 2 H, H7, 11), 2.69 (d, JAB ) 17.4 Hz, 1 H,
H7, 10), 2.52 (d, JAB ) 17.4 Hz, 1 H, H7, 10). The aromatic region
of the spectrum presents too many peaks to be unambiguously
assigned. 13C NMR (CDCl3): δ 37.5 (C8, 11), 34.1 (C9, 11), 31.2
(C8, 10), 29.7 (C9, 10), 23.8 (C7, 11), 20.2 (C7, 10). 29Si NMR
(CDCl3): δ -15,1, -14.6. MS (CI): 394 (MNH4+, 100), 377
(MH+, 19), 316 (5), 302 (8), 290 (70). HRMS(ES+): calcd for
C27H25Si (MH+) 377.1720; found 377.1728.
1
Compound 20: colorless oil. H NMR (CDCl3): δ 7.38-7.35
(m, 1 H), 7.27-7.12 (m, 6 H), 7.06-6.99 (m, 2 H), 3.01 (dt, J )
15.4 Hz, J′ ) 3.8 Hz, 1 H, H13), 2.26 (s, 2 H, H9), 2.20 (d, J ) 1.2
Hz, 3 H, H14), 2.10-2.03 (m, 2 H, H11,13), 1.95-1.92 (m, 1 H,
H12), 1.64-1.56 (m, 1 H, H11), 1.49-1.37 (m, 2 H, H10,12), 0.82
(td, J ) 5.3 Hz, J′ ) 12.9 Hz, 1 H, H10). 13C NMR (CDCl3): δ
141.9 (CIV), 140.3 (CIV), 135.6 (CIV), 134.7 (CIV), 134.6 (CIV), 134.2
(2 C, C16), 131.2 (CIII), 129.2 (CIII), 127.7 (2 C, C17), 126.3 (CIII),
126.1 (CIII), 125.5 (CIII), 32.4 (C13), 29.7 (C12), 23.7 (C11), 20.7
(C9), 16.5 (C14), 12.0 (C10). IR (neat): ν˜max 3066, 3013, 2923, 2851,
2360 (CdC), 2342 (CdC), 1587, 1479, 1427, 1113, 1080 cm-1
.
1
12:13 mixture: colorless oil. H NMR (CDCl3): δ 7.65-7.00
(m, 28 H, 12 and 13), 2.91 (t, J ) 6.7 Hz, 1 H, H9, 13), 2.80 (d,
JAB ) 16.9 Hz, 1 H, H7, 13), 2.58 (s, 2 H, H7, 12), 2.56-2.52 (m
of ABX, 1 H, H8, 12), 2.53 (d, JAB ) 17.2 Hz, 1 H, H7, 13), 1.69
(dd, A of ABX, JAB ) 15.3 Hz, JAX ) 7.6 Hz, 1 H, H9, 12), 1.39
(dd, B of ABX, JAB ) 15.3 Hz, JAX ) 6.8 Hz, 1 H, H9, 12), 1.17
Compound 21 (contaminated by 37% of compound 20): this
compound was obtained under palladium catalysis (colorless oil).4
1H NMR (CDCl3): δ 7.54-7.50 (m, 3 H), 7.30-7.23 (m, 5 H),
7.21-712 (m, 1 H), 3.72 (dd, A of ABX, J ) 20.1 Hz, JAB ) 3.1
Hz, 1 H, H3), 3.44 (d, JAB ) 20.1 Hz, 1 H, H3), 2.88 (dt, J ) 14.6
Hz, J ) 3.5 Hz, 1 H, H13), 2.16-2.05 (m, 2 H, H12,13), 1.94 (s, 3
H, H14), 1.79-1.21 (m, 4 H, H10,11,12), 0.97-0.90 (m, 1 H, H10).
13C NMR (CDCl3): δ 145.9 (CIV), 143.5 (CIV), 137.1 (CIV), 134.5
(2 C, C16), 133.1 (CIII), 133.0 (CIV), 129.2 (CIV), 129.0 (CIII), 128.8
(CIII), 128.1 (CIII), 127.9 (2C, C17), 125.5 (CIII), 42.7(C3), 31.6 (C13),
29.9 (C12), 24.3 (C11), 19.8 (C14), 11.6 (C10).
(dd, JAB ) 15.4 Hz, J’ ) 7.6 Hz, 1 H, H9, 13), 1.01 (dd, JAB
)
15.3 Hz, J’ ) 5.8 Hz, 1 H, H9, 13), 0.13 (s, 9 H, SiMe3, 12), 0.00
(s, 9 H, SiMe3, 13).
1
14:15 mixture: colorless oil. H NMR (CDCl3): δ 7.92-7.00
(m, 28 H, 14 and 15), 4.75 (dd, J ) 6.1 Hz, J′ ) 3.5 Hz, 1 H, H9,
15), 3.93 (t, J ) 7.8 Hz, 1 H), 3.55 (t, J ) 8.5 Hz, 1 H), 3.37-
3.27 (m, 3 H, H8, 14, H14), 3.22-3.18 (m, 1 H, H14), 3.07-3.03
(m, 1 H, H14), 2.94 (d, JAB ) 14.4 Hz, 1 H, H7), 2.75 (d, JAB
)
17.4 Hz, 1 H, H7), 2.56 (d, JAB ) 14.4 Hz, 1 H, H7), 2.50 (d, JAB
) 17.4 Hz, 1 H, H7), 1.96 (dd, JAB ) 14.6 Hz, J′ ) 6.1 Hz, 1 H,

Synthesis of 4:5-Benzo-1-cobalta-2-silacyclopentenes
Organometallics, Vol. 26, No. 4, 2007 829
1
Compound 23: colorless oil. H NMR (CDCl3): δ 7.41-7.37
(CIII), 129.4 (CIII), 129.1 (CIII), 127.9 (2 C, C15), 126.5 (CIII), 125.1
(CIII), 36.4 (C2), 33.7 (C12), 25.8 (C11), 23.0 (C1), 18.2 (C9), 11.7
(C10). 29Si NMR (CDCl3): δ 13.6. IR (neat): ν˜max 3066, 3012, 2920,
2850, 1489, 1453, 1427, 1112, 1065 cm-1. Anal. Calcd for C18H20-
Si: C, 81.76; H, 7.62. Found: C, 81.62; H, 7.82.
(m, 4 H), 7.33-7.23 (m, 4 H), 7.16-7.14 (m, 2 H), 7.09 (d, JAB
)
7.4 Hz, 1 H), 7.00-6.90 (m, 2 H), 6.66 (d, JAB ) 7.6 Hz, 1 H),
2.52-2.44 (m, 2 H, H9,13), 2.38 (d, JAB ) 15.4 Hz, 1 H, H9), 2.13-
2.05 (m, 2 H, H11,13), 1.80-1.77 (m, 1 H, H12), 1.54-1.50 (m, 2
H, H10,11), 1.22-1.15 (m, 1 H, H12), 0.90-0.81 (m, 1 H, H10). 13
C
NMR (CDCl3): δ 149.1 (CIV), 141.4 (CIV), 139.2 (CIV), 135.6 (CIV),
135.3 (CIV), 134.9 (CIV), 134.2 (2 C, C15), 131.4 (CIII), 129.9 (CIII),
129.4 (CIII), 128.1 (2 C, C20), 127.9 (2 C, C16), 126.5 (CIII), 126.3
(CIII), 125.2 (CIII), 34.3 (C13), 30.0 (C12), 23.8 (C11), 20.6 (C9), 12.4
(C10). IR (neat): ν˜max 3013, 2922, 2850, 2246 (CdC), 1949, 1727,
1580, 1441, 1427, 1111, 1028, 906 cm-1
.
Compound 29b: colorless oil. 1H NMR (CDCl3): δ 7.47-7.44
(m, 2 H), 7.34-7.30 (m, 3 H), 7.14-7.07 (m, 4 H), 2.86 (dd, JAB
) 13.7 Hz, J ) 11.0 Hz, 1 H, H2), 2.76 (dd, JAB ) 13.7 Hz, J )
4.5 Hz, 1 H, H2), 2.31 (d, JAB ) 15.4 Hz, 1 H, H9), 2.13 (d, JAB
)
15.4 Hz, 1 H, H9), 1.89-1.77 (m, 2 H), 1.70-1.67 (m, 1 H), 1.52-
1.50 (m, 2 H), 1.44-1.37 (m, 1 H), 1.24-1.18 (m, 2 H), 0.88-
0.81 (m, 1 H, H10), 0.76-0.69 (m, 1 H, H10). 13C NMR (CDCl3):
δ 141.4 (CIV), 137.6 (CIV), 137.1 (CIV), 133.9 (2 C, C15), 130.0
(CIII), 129.2 (CIII), 128.8 (CIII), 127.8 (2 C, C16), 126.4 (CIII), 125.0
(CIII), 37.6 (C2), 31.7 (CII), 25.7 (CII), 23.7 (CII), 20.7 (C1), 19.4
(C9), 10.3 (CII). IR (neat): ν˜max 2915, 1693, 1402, 1113 cm-1. Anal.
Calcd for C18H20Si: C, 81.95; H, 7.96. Found: C, 82.08; H, 8.01.
Crystal Structure Determinations. X-ray intensity data were
recorded on a Enraf-Nonius Mach or Enraf-Nonius KappaCCD
diffractometer with monochromated Mo KR radiation (λ ) 0.71073
Å). Data collection strategies were assigned on the basis of the
apparent Laue symmetry obtained from a preliminary examination
of the unit cell (full sphere for a triclinic setting and an arbitrary
hemisphere for higher symmetries). Data were integrated with the
CRYSTALS software package27 and corrected for Lorentz-
polarization effects, and an empirical absorption correction was
applied within DIFABS.28 The space group for each compound was
assigned on the basis of systematic absences observed within the
data. Structures were solved by direct methods29 and expanded using
Fourier methods and refined routinely.27 Hydrogen atoms were
included in geometrically calculated positions with thermal param-
eters tied to the atom to which they are bonded. A summary of the
crystal and structure refinement data can be found in Table 1. CCDC
600 441 and 600 442 contain the supplementary data for this paper.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
1
Compound 25: colorless oil. H NMR (CDCl3): δ 7.16-6.94
(m, 9 H), 2.52-2.44 (m, 1 H, H13), 2.22-2.14 (m, 4 H, H9,12,13),
2.00-1.96 (m, 1 H, H11), 1.56-1.54 (m, 2 H, H10,12), 1.39-1.35
(m, 1 H, H11), 0.85-0.77 (m, 1 H, H10), 0.3 (s, 9 H, SiMe3). 13C
NMR (CDCl3): δ 157.1 (CIV), 152.2 (CIV), 141.7 (CIV), 134.5 (CIV),
134.3 (2 C, C15), 134.1 (CIV), 130.5 (CIII), 129.3 (CIII), 128.9 (CIII),
127.7 (2 C, C16), 125.4 (CIII), 124.6 (CIII), 37.5 (C13), 30.4 (C12),
24.1 (C11), 21.2 (C9), 12.7 (C10), 2.7 (3 C, SiMe3). 29Si NMR
(C6D6): δ -8.6 (SiMe3), -28.4. IR (neat): ν˜max 3051, 2921, 2852,
+
1711, 1592, 1474, 1404, 1250, 1112 cm-1. MS (CI): 366 (MNH4
,
17), 349 (MH+, 100), 90 (34). HRMS(ES+): calcd for C22H29Si2
(MH+) 349.1802; found 349.1806.
1
Compound 27: colorless oil. H NMR (CDCl3): δ 7.24-7.22
(m, 1 H), 7.17-7.05 (m, 7 H), 6.99-6.95 (m, 1 H), 2.76 (dt, JAB
) 15.5 Hz, J ) 6.2 Hz, 1 H, H12), 2.49 (dt, JAB ) 15.5 Hz, J ) 7.5
Hz, 1 H, H12), 2.31 (d, JAB ) 14.3 Hz, 1 H, H9), 2.23 (d, JAB
)
14.3 Hz, 1 H, H9), 2.11-189 (m, 2 H, H11), 1.22 (dt, JAB ) 14.9
Hz, J ) 7.4 Hz, 1 H, H12), 0.97 (dt, JAB ) 14.9 Hz, J ) 7.3 Hz,
1 H, H12), 0.27 (s, 9 H, SiMe3). 13C NMR (CDCl3): δ 164.5 (CIV),
149.5 (CIV), 143.4 (CIV), 134.5 (CIV), 134.3 (2 C, C14), 133.4 (CIV),
131.4 (CIII), 129.3 (CIII), 128.9 (CIII), 127.7 (2 C, C15), 125.7 (CIII),
125.1 (CIII), 35.1 (C12), 26.8 (C11), 20.5 (C9), 9.8 (3 C, C10), 2.0
(SiMe3). IR (neat): ν˜max 3051, 2925, 2856, 1469, 1447, 1248, 1142
DFT Calculations. All geometries of intermediates and transition
states were optimized fully without symmetry constraints using the
Gaussian 03 program.30 The DFT computations were carried out
using the B3LYP functional as implemented in Gaussian. The
computations were done using the LACVP(d,p) basis set: the cobalt
atom was described by a double-ú basis set with the effective core
potential of Hay and Wadt (LANL2DZ),31 and the 6-31G(d,p) basis
set32 was used for the other elements. Frequency calculations were
performed to confirm the nature of the stationary points and to
obtain zero-point energies (ZPE). The connectivity between station-
ary points was established by intrinsic reaction coordinate calcula-
cm-1
.
(27) CRYSTALS: Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.;
Prout, K.; Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487.
(28) DIFABS: Walker, N.; Stuart, D. Acta Crystallogr. 1983, 39, 158-
166.
(29) SIR-92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi,
A. J. Appl. Crystallogr. 1993, 26, 343.
Compound 29a: colorless oil. 1H NMR (CDCl3): δ 7.38-7.36
(m, 2 H), 7.29-7.23 (m, 3 H), 7.06-6.99 (m, 4 H), 2.89 (dd, JAB
) 13.6 Hz, J ) 5.8 Hz, 1 H, H2), 2.61 (dd, JAB ) 13.4 Hz, J ) 8.4
(30) Frisch et al. Gaussian 03, Revision B.02; Gaussian, Inc.: Walling-
ford, CT, 2004.
(31) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310.
(32) (a) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971,
54, 724-728. (b) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys.
1972, 56, 2257-2261. (c) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta
1973, 28, 213. (d) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27, 209.
(e) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163-168.
Hz, 1 H, H2), 2.29 (d, JAB ) 14.7 Hz, 1 H, H9), 2.19 (d, JAB
)
14.7 Hz, 1 H, H9), 1.82-1.73 (m, 1 H, H12), 1.70-1.63 (m, 1 H,
H11), 1.55-1.44 (m, 2 H, H1,11), 1.40-1.33 (m, 1 H, H12), 0.89-
0.81 (m, 1 H, H10), 0.76-0.69 (m, 1 H, H10). 13C NMR (CDCl3):
δ 140.7 (CIV), 137.2 (CIV), 136.4 (CIV), 134.1 (2 C, C14), 129.7

830 Organometallics, Vol. 26, No. 4, 2007
Agenet et al.
tions (IRC). Single-point calculations were carried out at the
B3LYP/6-311+G(2d,2p) level; the energies given are uncor-
rected. The minimum energy crossing points (MECPs) were
optimized using the code developed by Harvey and co-
workers.33a The vibrational analyses at these points were executed
within the (3N-7)-dimensional hypersurface of the seam of
crossing.33b The Chemcraft program was used to draw the calculated
structures.34
Acknowledgment. This work was supported by CNRS,
MRES, IUF, and DGA. M.P. is thankful to Sanofi-Aventis for
a Ph.D. grant. We used substantial computing facilities from
“CRIHAN, Plan Interre´gional du Bassin Parisien” (project 2006-
013), and the Centre de Calcul Recherche et Enseignement
(CCRE) of the “Universite´ Pierre et Marie Curie- Paris 6”.
Supporting Information Available: NMR spectra of all new
compounds. Coordinates of computed structures. This material is
available free of charge via the Internet at http://pubs.acs.org.
(33) (a) Harvey, J. N.; Aschi, M. Phys. Chem. Chem. Phys. 1999, 1,
5555-5563. (b) Harvey, J. N.; Aschi, M.; Schwarz, H.; Koch, W. Theor.
Chem. Acc. 1998, 99, 95-99.
(34) http://www.chemcraftprog.com.
OM0607245