Synthesis and characterization of coordinatively unsaturated alkynyl- and aryl-cobalt complexes with 15 valence electrons, TpiPr2Co-R, bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2)

Article abstract of DOI:10.1021/om020268u

Coordinatively unsaturated 15e alkynyl- (Tp^iPr2Co-C≡C-R) and aryl-cobalt complexes (Tp^iPr2Co-aryl) bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (Tp^iPr2) are prepared by dehydrative condensation of the hydroxo complex [Tp^iPr2Co(μ-OH)₂]₂ with 1-alkyne and arylation of the chloro complex Tp^iPr2Co-Cl with Grignard reagents, respectively. Spectroscopic and crystallographic analyses reveal the apparent C₃-symmetrical tetrahedral structures with high-spin electronic configuration (S = 3/2), which should result from the property of the Tp^iPr2 ligand as a tetrahedral enforcer. The Tp^iPr2Co and hydrocarbyl fragments, are connected dominantly through σ-bonding interaction, and π-interaction including back-donation is not significant as revealed by EHMO calculations. The Co-C bonds are so polarized as to be readily protonated even by moisture to give the corresponding hydrocarbons, but the reactivity toward unsaturated hydrocarbons turns out to be sluggish. Tp^iPr2Co-C≡C-COOMe is found to catalyze a rare example of specific linear trimerization of methyl propiolate to give (E,E)-MeOOC(H)C=CH-CH=C(COOMe)-C≡C-COOMe.

Full text of DOI:10.1021/om020268u

3762
Organometallics 2002, 21, 3762-3773
Syn th esis a n d Ch a r a cter iza tion of Coor d in a tively
Un sa tu r a ted Alk yn yl- a n d Ar yl-Coba lt Com p lexes w ith
15 Va len ce Electr on s, Tp iP r 2Co-R, Bea r in g th e
Hyd r otr is(3,5-d iisop r op ylp yr a zolyl)bor a to Liga n d (Tp iP r 2
)
Shin-ichi Yoshimitsu, Shiro Hikichi,† and Munetaka Akita*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, J apan
Received April 4, 2002
Coordinatively unsaturated 15e alkynyl- (TpiPr2Co-CtC-R) and aryl-cobalt complexes
(TpiPr2Co-aryl) bearing the hydrotris(3,5-diisopropylpyrazolyl)borato ligand (TpiPr2) are
prepared by dehydrative condensation of the hydroxo complex [TpiPr2Co(µ-OH)2]2 with
1-alkyne and arylation of the chloro complex TpiPr2Co-Cl with Grignard reagents, respec-
tively. Spectroscopic and crystallographic analyses reveal the apparent C3-symmetrical
tetrahedral structures with high-spin electronic configuration (S ) 3/2), which should result
from the property of the TpiPr2 ligand as a tetrahedral enforcer. The TpiPr2Co and hydrocarbyl
fragments are connected dominantly through σ-bonding interaction, and π-interaction
including back-donation is not significant as revealed by EHMO calculations. The Co-C
bonds are so polarized as to be readily protonated even by moisture to give the corresponding
hydrocarbons, but the reactivity toward unsaturated hydrocarbons turns out to be sluggish.
TpiPr2Co-CtC-COOMe is found to catalyze a rare example of specific linear trimerization
of methyl propiolate to give (E,E)-MeOOC(H)CdCH-CHdC(COOMe)-CtC-COOMe.
In tr od u ction
structure with a high-spin electronic configuration, as
analyzed by crystallographic and various spectroscopic
methods as well as molecular orbital calculations.
The study on the TpR′M-R-type coordinatively un-
saturated hydrocarbyl complexes3 has been extended
from the alkyl complexes containing the M-C(sp3) bond
to the alkynyl and aryl complexes containing the
M-C(sp) and M-C(sp2) bond, respectively. For the
synthesis of alkyl complexes, it is essential to prevent
â-hydride elimination. Although such a problem is not
viable in the synthesis of alkynyl and aryl complexes
lacking a â-hydrogen atom, oligomerization could be
another problem to be solved (Scheme 1).7 Coupling of
the coordinatively unsaturated metal center and the
electron-rich π-system may lead to the formation of a
Coordinatively unsaturated hydrocarbyl species are
key intermediates of various transformations mediated
by organometallic species, in particular, for the sub-
strate incorporation step.1 Despite such importance little
knowledge concerning their structure and reactivity has
been accumulated mainly because of their thermal
instability. Most of the previously reported examples of
isolable coordinatively unsaturated organometallic spe-
cies are kinetically stabilized by bulky hydrocarbyl or
ancillary ligands such as those bearing trimethylsilyl
and mesityl substituents.2 In previous papers we3 and
other groups4 reported synthesis and characterization
of coordinatively unsaturated 14e and 15e alkyl com-
plexes with κ3-tripodal ligands [L ) hydrotris(pyrazolyl)-
borato (TpR′),5 phenyltris(pyrazolyl)borato, phenyltris-
(alkylthiomethyl)borato], LM-R (M ) Fe, Co; R ) alkyl,
benzyl).6 Despite their coordinatively unsaturated elec-
tronic configuration they turned out to be stable with
respect to â-hydride elimination, and the stability has
been ascribed to the property of the tripodal ligands as
a tetrahedral enforcer, which stabilizes the tetrahedral
(2) Examples of Mn, Co, and Fe complexes: Mn: Howard, C. G.;
Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B.
J . Chem. Soc., Dalton Trans. 1983, 2631. Buttrus, N. H.; Eaborn, C.;
Hitchcock, P. B.; Smith, J . D.; Sullivan, A. C. J . Chem. Soc., Chem.
Commun. 1985, 1380. C: Morris, R. J .; Gilorami, G. S. Organometallics
1989, 8, 1478. Wehmschulte, R.; Power, P. P. Organometallics 1995,
14, 3264. Hursthouse, M. B.; Izod, K. J .; Motevalli, M.; Thornton, P.
Polyhedron 1996, 15, 135. Fe: Chatt, J .; Shaw, B. L. J . Chem. Soc.
1961, 285. Hermes, A. R.; Girolami, G. S. Organometallics 1987, 6,
763. Mu¨ller, H.; Seidel, W.; Go¨rls, H. J . Organomet. Chem. 1992, 445,
133. Mu¨ller, H.; Seidel, W.; Go¨rls, H. Angew. Chem., Int. Ed. Engl.
1995, 34, 325. Klose, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C.; Re, N. J . Am. Chem. Soc. 1994, 116, 9123. Leung, W.-P.; Lee, H.
K.; Weng, L.-H.; Luo, B-S.; Zhou, Z.-Y.; Mak, T. W. C. Organometallics
1996, 15, 1785. Hursthouse, M. B.; Izod, K. J .; Motevalli, M.; Thornton,
P. Polyhedron 1996, 15, 135. Fryzuk, M. D.; Leznoff, D. B.; Ma, E. S.
F.; Rettig, S. J .; Young, V. G. J r. Organometallics 1998, 17, 2313. Co:
Theopold, K. H.; Silvestre, J .; Byrne, E. K.; Richeson, D. S. Organo-
metallics 1989, 8, 2001. Hay-Motherwell, R. S.; Wilkinson, G.; Hussain,
B.; Hursthouse, M. B. Polyhedron 1990, 9, 931. Hursthouse, M. B.;
Izod, K. J .; Motevalli, M.; Thornton, P. Polyhedron 1996, 15, 135.
Fryzuk, M. D.; Leznoff, D. B.; Thompson, R. C.; Rettig, S. J . J . Am.
Chem. Soc. 1998, 120, 10126.
† Present address: Department of Applied Chemistry, School of
Engineering, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656,
J apan.
(1) Yamamoto, A. Organotransition Metal Chemistry; Wiley-Inter-
science: New York, 1986. Collman, J . P.; Hegedus, L. S.; Norton, J .
R.; Finke, R. G. Principles and Applications of Organotransition Metal
Chemistry, 2nd ed.; University Science Books: Mill Valley, 1987.
Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
3rd ed.; Wiley-Interscience: New York, 2001. Cornils, B.; Herrmann,
W. Applied Homogeneous Catalysis with Organometallic Compounds
(2 vols.); VCH: Oxford, 1996. Abel, E. W.; Stone, F. G. A.; Wilkinson,
G. Comprehensive Organometallic Chemistry II; Pergamon: Oxford,
1995.
10.1021/om020268u CCC: $22.00 © 2002 American Chemical Society
Publication on Web 07/31/2002

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3763
Sch em e 1
Sch em e 2
dimeric or oligomeric structure, and many such ex-
amples have been reported so far. This problem could
also be solved by using the TpR′ ligand. Herein details
of the results of the synthetic study of the alkynyl-
(TpiPr2Co-CtC-R 1) and aryl(p-tolyl)-cobalt complexes
(TpiPr2Co-p-tolyl 2) will be described.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Alk yn yl Com -
p lexes, Tp iP r 2Co-CtC-R. (i) Syn th esis. First at-
tempts to prepare the alkynyl complexes by treatment
of the chloro complex, TpiPr2Co-Cl (3), with alkynylating
reagents [(1) R-CtC-Li; (2) R-CtC-MgBr; (3) R-Ct
C-H/Cu(I) cat./amine8] were unsuccessful. Reaction (1)
afforded TpiPr2Li via metal exchange, and the other
reactions resulted in recovery of 3 or TpiPr2Co-X.
Synthetic study of dioxygen complexes has been a
target of our recent research activity,9,10 and we have
developed a new synthetic method for dioxygen com-
plexes (i.e., dehydrative condensation) in addition to the
classical method involving O2-oxidative addition to a
low-valent precursor. The dehydrative condensation
proceeds via water elimination from the hydroxo com-
plex, [TpR′M-OH]n (n ) 2, 1), and hydrogen peroxide.
Because the terminal hydrogen atom of 1-alkynes is
known to be more acidic than other hydrocarbons,
1-alkynes may undergo dehydrative condensation with
the dinuclear µ-hydroxo complex bearing the TpiPr2
ligand, [TpiPr2Co(µ-OH)]2, 4. As we expected, the desired
alkynyl complexes 1 were obtained successfully (Scheme
2). We already reported formation of enolatopalladium
complexes, (TpR′)(py)Pd-CHXY or (TpR′)(py)Pd-XCHY,
via dehydrative condensation between the pyridine-
coordinated monomeric hydroxo complex, (TpiPr2)(py)-
(3) Akita, M.; Shirasawa, N.; Hikichi, S.; Moro-oka, Y. J . Chem. Soc.,
Chem. Commun. 1998, 973. Shirasawa, N.; Akita, M.; Hikichi, S.;
Moro-oka, Y. J . Chem. Soc., Chem. Commun. 1999, 417. Shirasawa,
N.; Nguyet, T. T.; Hikichi, S.; Moro-oka, Y. Akita, M. Organometallics
2001, 20, 3582. See also: Uehara, K.; Hikichi, S.; Akita, M. Organo-
metallics 2001, 20, 5002.
(4) Kisko, J . L.; Hascall, T.; Parkin, G. J . Am. Chem. Soc. 1988, 110,
10561. J ewson, J . D.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold,
A. L.; Theopold, K. H. Organometallics 1999, 18, 300. Schebler, P. J .;
Mandimutsira, B. S.; Riordan, C. G.; Liable-Sands, L. M.; Incarvito,
C. D.; Rheingold, A. L. J . Am. Chem. Soc. 2001, 123, 331.
(5) Trofimenko, S. J . Am. Chem. Soc. 1966, 88, 1842. Trofimenko,
S. Inorg. Synth. 1970, 12, 99. Trofimenko, S. Chem. Rev. 1993, 93,
943. Trofimenko, S. Scorpionates-The Coordination Chemistry of
Polypyrazolylborate Ligands; Imperial College Press: London, 1999.
(6) Abbreviations used in this paper: TpR, hydrotris(pyrazolyl)borato
ligands; TpiPr2, 3,5-diisopropylpyrazolyl derivative; Tp, nonsubstituted
derivative; pzR, pyrazolyl group in TpR. 4-pz-H, the hydrogen atom at
the 4-position of the pyrazolyl ring. Compound numbers with ′ (prime)
are for nickel derivatives.
(7) Copper complexes can be raised as typical examples. Abel, E.
W.; Stone, F. G. A.; Wilkinson, G. Comprehensive Organometallic
Chemistry II; Pergamon: Oxford, 1995; Vol. 3.
(8) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
50, 4467. Bruce, M. I.; Humphery, M. G.; Matisons, J . G.; Roy, S. K.;
Swincer, A. G. Aust. J . Chem. 1984, 37, 1955.
(9) Akita, M.; Hikichi, S. Bull. Chem. Soc. J pn. 2002, 75, in press.
Hikichi, S.; Yoshizawa, M.; Sasakura, Y.; Komatsuzaki, H.; Moro-oka,
Y.; Akita, M. Chem.-A Eur. J . 2001, 7, 5011. See also references sited
in these papers.
(10) For related dioxygen complexes with Tp and tripodal ligands,
see: Reinaud, O. M.; Theopold, K. H. J . Am. Chem. Soc. 1994, 116,
6979. Reinaud, O. M.; Yap, G. P. A.; Rheingold, A. L.; Theopold, K. H.
Angew. Chem., Int. Ed. Engl. 1995, 34, 2051. Theopold, K. H.; Reinaud,
O. M.; Doren, D.; Konecny, R. In Third World Congress on Oxidation
Catalysis; Grasselli, R. K., Oyama, S. T., Gaffney, A. M., Lyons, J . E.,
Eds.; Elsevier: Amsterdam, 1997; pp 1081-1088. Thyagarajan, S.;
Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H. Chem. Commun.
2001, 2198. Mandimutsira, B. S.; Yamarik, J . L.; Brunold, T. C.; Gu,
W.; Cramer, S. P.; Riordan, C. G. J . Am. Chem. Soc. 2001, 123, 9194.
Hu, Z.; George, G. N.; Gorun, S. M. Inorg. Chem. 2001, 40, 4812. Hu,
Z.; Williams, R. D.; Tran, D.; Spiro, T. G.; Gorun, S. M. J . Am. Chem.
Soc. 2000, 122, 3556. Diaconu, D.; Hu, Z.; Gorun, S. M. J . Am. Chem.
Soc. 2002, 124, 1564

3764 Organometallics, Vol. 21, No. 18, 2002
Yoshimitsu et al.
Ta ble 1. Sp ectr oscop ic Da ta for Alk yn yl
Com p lexes 1
Sch em e 3
f,g
IR/cm-1 a
complex νB-H νCtC (∆ν)b νR (∆ν)b
1H NMR/δH
Me
CHMe2 4-pz-H
1a
1b
1c
1d
1e
1g
1h
1i
2581 2102 (24) 1697 (22)c 3.1, 3.7
2574 2094 (24) 1693 (23)c 2.9, 3.8
2547 2075 (21) 1658 (27)c 2.9, 3.8
11.8
11.8
12.0
11.5
11.5
11.0
10.9
10.5
70.0
70.8
70.6
68.0
68.5
68.9
68.5
67.3
2544 2036 (0)
2540 2034 (2)
1.8, 3.9
1.8, 3.9
2.2, 3.8
2.3, 3.8
1.7, 3.8
d
2543
2543
3287e
Pd-OH, and active methylene compounds (CH2XY; X,
Y: COR, COOR, CN).11
d
2541 2091 (14)
Agitation of a hexane solution of the hydroxo complex
4 and 1-alkyne in the presence of 4 Å molecular sieves
afforded the alkynyl complexes 1 as a blue (1a -g,i) or
green solid (1h ) after filtration and crystallization from
hexane except for the reaction of triphenylsilylacetylene
(see below). It is essential to use hydrocarbon (e.g.,
hexane, pentane, and toluene) as a reaction solvent.12
Otherwise the reaction in, for example, THF resulted
in incomplete conversion of 4 to give a mixture contain-
ing 1 and 4. In the case of the reaction in a hydrocarbon
solvent the eliminated water should be separated from
the organic phase due to the extremely low miscibility
of water in hydrocarbons, whereas in the case of the
reaction in THF the eliminated water remains in the
organic phase so as to hydrolyze the product 1 back to
4.
The efficiency of the condensation depends on the
acidity of 1-alkyne. The pKa values of representative
1-alkynes are shown in the table of Scheme 2.13 The
reaction of acidic substrates bearing a >CdO functional
group (a -c) was almost completed upon mixing, but
analytically pure samples of 1g-i derived from the
alkyl- or aryl-substituted 1-alkynes could not be ob-
tained due to the slow and incomplete conversion.
Complexes 1g-i were characterized by comparison of
their spectroscopic data with those of the fully charac-
terized derivatives.
a
b
Observed as KBr pellets. Values in parentheses refer to the
extent of red-shift of the ν values compared with the corresponding
1-alkynes. νCdO
tions. Signals for R part: 1a , 18.6 (3H); 1b, not obsbd; 1c, 18.6
(3H); 1d , 8.9 (9H); 1e, not observed; 1g, 12.6 (1H); 1h , 21.9 (2H),
-11.2 (2H), -13.2 (1H); 1i, 24.4 (9H). The other CH signals could
not be located.
c
d
e
.
Not observed. νtC-H.
f Observed as C6D6 solu-
g
h
-30 °C, was identified by its IR data (νBH 2536, νCtC
2099, νCdO 1700 cm-1), similar to that of 1a (see below),
and an FD-MS spectrum containing the molecular ion
peak (m/z ) 606). In the reactions of other 1-alkynes
the color change from green to pink or red suggested
formation of tetrahedral species, but the mixture further
turned to brown or red-brown during workup and no
characterizable product could be isolated. In this case,
too, the reaction of Ph3Si-CtC-H afforded the triphen-
ylsiloxo complex, TpiPr2Ni-OSiPh3, 5′ (characterized by
X-ray crystallography; Figure S3),14 via Si attack (Scheme
3).
(ii) Ch a r a cter iza tion . The alkynyl complexes 1 are
characterized by spectroscopic and crystallographic
methods. Selected spectroscopic data are summarized
in Table 1. Molecular structures of 1a ,e are shown in
Figure 1, and selected structural parameters are listed
in Table 2.
Formation of the desired structure was first suggested
by the changes of IR spectra [(i) disappearance of the
νOH vibration of 4 and νtCH vibration of 1-alkyne; (ii)
the νBH absorptions indicating κ3-coordination;15 (iii)
shift of the νCtC and νCdO (when appropriate) vibrations
to lower energies]. The IR data will be discussed in
detail later in combination with the result of the
crystallographic structure determination. The simple 1H
NMR pattern reveals an apparently C3-symmetrical
structure of 1. The TpiPr2 signals appear in a similar
region irrespective of the alkynyl substituent (R),16
although one of the two methine signals of the isopropyl
groups in the TpiPr2 ligand could not be located presum-
ably due to overlap with other signals or broadening.
The monomeric structures are supported by the results
of FD-MS data (see Experimental Section). UV spectra
featured by the two intense absorptions around 300 and
650 nm are typical for high-spin, tetrahedral TpRCo(II)
species, as already discussed for the alkyl complexes.3,4
The high-spin electronic configuration is also supported
by the effective magnetic moment (µeff ) 3.4-3.6 µB),
suggesting a quartet electronic configuration containing
three unpaired electrons (S ) 3/2).17
The reaction of triphenylsilylacetylene did not produce
the expected alkynyl complex 1f but the triphenylsiloxo
complex, TpiPr2Co-OSiPh3, 5, which was characterized
by X-ray crystallography (Figure S3).14 In contrast to
the formation of 1, which involves abstraction of the
terminal hydrogen of 1-alkyne (path a; Scheme 3), the
siloxo complex 5 should be formed via nucleophilic
attack of the hydroxo ligand in 4 at the silicon center
(path b). The silicon atom in triphenylsilylacetylene
should be more electrophilic than that in trialkylsilyl
derivatives due to the electron-withdrawing nature of
the phenyl groups, though the former is more sterically
congested than the latter.
We also attempted synthesis of the nickel derivatives,
TpiPr2Ni-CtC-R, via a similar procedure. The ester
derivative, TpiPr2Ni-CtC-COOMe, 1′,6 obtained as
pink powders by reaction at 0 °C followed by workup at
(11) Kujime, M.; Hikichi, S.; Akita, M. Organometallics 2001, 20,
4049.
(12) We also examined synthesis of other TpR′ derivatives such as
3,5-dimethyl and 3-phenyl-5-methyl derivatives. Although dehydrative
condensation proceeded, the low solubility of the hydroxo complexes
in hydrocarbons resulted in incomplete conversion. Therefore synthesis
of alkynyl complexes via dehydrative condensation is applicable only
for [TpR′M(OH)]n complexes soluble in hydrocarbons.
(13) Kresge, A. J .; Pruszynski, P. J . Org. Chem. 1991, 56, 4808.
Tupitsyn, I. F.; Popov, A. S.; Shibaev, A. Yu. Zh. Obsh. Khim. 1992,
62, 2757.
(15) Akita, M.; Ohta, K.; Takahashi, Y.; Hikichi, S.; Moro-oka, Y.
Organometallics 1997, 16, 4121.
(16) The TpiPr2 signals (1H NMR) are also comparable to those of
the alkyl complexes.3
(14) For details, see Supporting Information.

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3765
F igu r e 1. Molecular structures of 1a and 1e (one of two independent molecules; A-series) showing 30% thermal ellipsoids.
Ta ble 2. Selected Str u ctu r a l P a r a m eter s for
cell of 1e contains two independent molecules with
essentially the same geometry. Bond lengths associated
with the TpiPr2Co-CtC parts of 1a ,e are very similar.
The Co-C1 distances in the range 1.935-1.968 Å
(average 1.956 Å) are substantially longer than those
of the nine alkynylcobalt complexes [1.857-1.948 Å
(average 1.887 Å)], which are included in the CSDS
database.18 Because all nine complexes are coordina-
tively saturated 18e species, the difference in the Co-
Ct lengths should be ascribed to that of the electronic
structure (see below). The CtC lengths of ca. 1.2 Å are
comparable to those of alkynes,19 but it has been known
that the CtC length is not so sensitive to the electronic
effect of the substituents. As for the orientation of the
alkynyl ligand, the SiEt3 complex 1e adopts C3-sym-
metrical tetrahedral structures, and orientation of the
Tp iP r 2Co-CtC-R a n d Tp iP r 2Co-p-tolyla
1ec
SiEt3
complexes
1a b
COOMe
R
molecule 1d
molecule 2e
2f
Co-C1
Co-N11
Co-N12
Co-N31
C1-C2
C2-X
1.968(4)
2.020(3)
2.018(3)
2.043(3)
1.190(6)
1.438(6)
1.965(6)
2.037(5)
2.010(5)
2.019(5)
1.199(8)
1.849(6)
1.935(6)
2.034(5)
2.014(3)
1.990(5)
1.233(9)
1.804(8)
2.011(3)
2.037(3)
2.057(2)
2.060(3)
X:
C3
Si1
Si2
Co1-C1-C2
C1-C2-X
169.0(4)
175.1(4)
112.7(1)
121.1(1)
132.9(1)
94.8(1)
93.1(1)
93.5(1)
167.7(1)
179.0(6)
177.9(8)
123.2(3)
124.4(3)
122.7(2)
91.8(2)
93.2(2)
92.7(2)
179.2(2)
178.9(6)
174.4(9)
126.5(3)
121.2(2)
121.5(3)
91.8(2)
92.5(2)
94.9(2)
176.3(3)
N11-Co-C1
N21-Co-C1
N31-Co-C1
N11-Co-N21
N11-Co-N31
N21-Co-N31
B‚‚‚Co-C1
120.0(1)
124.2(1)
126.3(1)
93.5(1)
90.8(1)
92.97(9)
176.1(1)
(17) The effective magnetic moments below the spin-only value (3.8
µB) should be attributed to the fact that diamagnetic corrections were
not applied, as pointed out by one of the reviewers.
(18) (a) Basallote, M. G.; Hughes, D. L.; J imenz-Tenorio, Leigh, G.
J .; Vizcaino, M. C.; J imenz, P. V. J . Chem. Soc., Dalton. Trans. 1993,
1841. (b) Habadie, N.; Dartiguenave, M.; Britten, J . F.; Beauchamp,
A. L. Organometallics 1989, 8, 2564. (c) Kergoat, R.; L. C. Gomes de
Lima, J egat, C.; Berre, N. L.; Kubicki, M. M.; Guerchais, J . E.; Haridon,
P. L. J . Organomet. Chem. 1990, 389, 71. (d) Klein, H. F.; Beck, H.;
Hammerschmitt, B.; Koch, U.; Koppert, S.; Cordier, G. Z. Naturforsch.
Teil B 1991, 46, 147. (e) Giese, B.; Zehnder, M.; Neuburger, M.; Trach,
F. J . Organomet. Chem. 1991, 412, 415. (f) Bianchini, C.; Peruzzini,
M.; Vacca, A.; Zanobini, F. Organometallics 1991, 10, 3697. (g) Stringer,
G.; Taylor, N. J . Marder, T. B. Acta Crystallogr., Sect. C 1996, 52, 80.
(h) Werner, H.; Xiaolan, L.; Peters, K.; von Schnering, H. G. Chem.
Ber. 1997, 130, 565. (i) Klein, H. F.; Xiaoyan, L.; Sun, H.; Lemke, A.
M.; Florke, U.; Haupt, H. J . Inorg. Chim. Acta 2000, 298, 70.
(19) Smith, M. B.; March, J . Advanced Organic Chemistry, 5th ed.;
Wiley-Interscience: New York, 2001.
a
b
Bond lengths in Å and bond angles in deg. O1-C3, 1.181(6);
O2-C3, 1.330(6); O2-C4, 1.435(8) Å; C1-C2-C3, 175.1(4); O1-
C3-O2, 122.0(5); O1-C3-C2, 126.9(5); O2-C3-C2, 111.0(4)°.
c Si-C(Et), 1.86-1.89(1) Å; C(Et)-Si-C(Et), 106.0-111.7(7)°. A-
d
series. e B-series. f C1-C2, 1.428(5); C1-C6, 1.380(5); C2-C3,
1.384(5); C3-C4, 1.415(5); C4-C5, 1.398(6); C4-C7, 1.501(6); C5-
C6, 1.365(5) Å; C-C-C(tolyl), 111.2-126.3(3)°.
These spectroscopic features are consistent with a C3-
symmetrical tetrahedral core structure, which has been
confirmed by X-ray crystallography for the COOMe (1a )
and SiEt3 derivatives (1e) (Figure 1 and Table 2). A unit

3766 Organometallics, Vol. 21, No. 18, 2002
Yoshimitsu et al.
(∆ν 61) cm-1],18a the extent of the lower energy shift of
1a -c is almost half of that of 6, suggesting that
contribution of the back-donation in 1a -c is not as
significant as that in 6. The difference could be at-
tributed to the different electronic configuration of the
alkynyl complexes. Thus the TpiPr2Co complexes 1a -c
are highly electron-deficient species with 15 valence
electrons, where back-donation does not occur effec-
tively, in contrast to the electron-rich coordinatively
saturated 18e species 6. In conclusion, back-donation
is not significant for the electron-deficient TpiPr2Co-Ct
C-R species; back-donation contributes to a small
extent in the case of alkynyl complexes containing an
electron-withdrawing >CdO group (1a -c), while such
contribution is virtually negligible for those containing
silyl and alkyl substituents (1d -i) due to the electron
donation from the substituent, which destabilizes the
zwitterionic cumulenic resonance structure 1A (Scheme
4). This conclusion is also supported by the EHMO
calculations described below. The back-donation is too
weak to freeze free rotation of the Co-Ct bond to show
Sch em e 4
SiEt3 substituent with respect to the TpiPr2Co moiety is
between an eclipsed and staggered conformation, being
closer to the former one. The dihedral angles between
the N11-Co1-C1 and C2-Si1-C3 planes are 34.2°
(molecule 1) and 23.1° (molecule 2).
In contrast to the highly symmetrical structure of 1e,
the structure of the COOMe derivative 1a is distorted
from a C3-symmetrical one, as is evident from the
ORTEP views. The C1-C2 linkage is tilted toward one
of the three pyrazolyl rings, as is evident from the B1‚
‚‚Co-C1 angle [167.7(1)°; cf. 1e: 179.2(2)°, 176.3(3)°].
In addition, the ester plane is arranged closer to a
coplanar conformation with respect to one of the three
pyrazolyl rings of the TpiPr2 ligand (N11,12-C11-13),
and the dihedral angle between the N11-Co1-C1 and
C2-C3-O2 planes is 19.8°. Because (1) the more bulky
methoxy group is directed toward the bulky pyrazolyl
ring and (2) no nonbonded interaction shorter than 2.5
Å is found, the distortion should result from an elec-
tronic interaction between the TpiPr2Co and CtC-
COOMe fragments rather than a steric repulsion and
crystal-packing effects, as analyzed by EHMO calcula-
tions (see below). No significant difference is observed
for the interatomic distances associated with the ester
π-system [C2-C3 1.438(6), O1-C3 1.181(6), O2-C3
1.330(6) Å; cf. normal values: tC-Cd 1.43, >CdO 1.21,
dC-O 1.34 Å].19 This situation is in sharp contrast to
the coordinatively saturated alkynylcobalt complexes
mentioned above [cf. for example, [(Et2PCH2CH2PEt2)2-
(H)Co-COOEt]+ (6): Co-C 1.91(1), CtC 1.19 (2), t
C-Cd 1.39(2), >CdO 1.18(2) Å],18a where back-dona-
tion from the cobalt atom to the alkynyl ligand (Scheme
4)21 occurs, as is evident from the shortened Co-Ct and
tC-Cd bonds. In particular, the shortened Co-Ct
distance of 6 compared to those of 1a ,e is clear evidence
for multiple-bonding interaction (1A), i.e., back-dona-
tion.
1
the apparent C3-symmetrical H NMR features.
(iii) EHMO Ca lcu la tion s. The above-mentioned
spectroscopic and structural characterization of the
alkynylcobalt complexes 1 reveals some intriguing
structural aspects such as (1) stability of the electron-
deficient species with 15e configuration, (2) the bending
of the Co-CtC linkage and the coplanar arrangement
in 1a , and (3) dependence of the extent of back-donation
on the alkynyl substituent. To consider these problems,
EHMO calculations were performed for TpCo-CtC-
SiMe3, A, and TpCo-CtC-COOMe, B.6 An ideal C3v-
symmetrical structure was assumed for the TpCo frag-
ment, and the CtC-SiMe3 and CtC-COOMe frag-
ments were arranged in the idealized eclipsed and
coplanar conformation, respectively, taking into account
the results of X-ray crystallography.
Molecular orbitals of the alkynylcobalt complexes A
and B resulting from the interactions of those of the
TpCo (C) and CtC-R fragments (D, E) are shown in
Figure 2, where the two fragments are arranged in a
linear fashion. The most significant difference in the Ct
C-R orbitals (D, E) is the π* orbital of the CtC moiety.
In the CtC-COOMe fragment (E) π-conjugation of one
of the two CtC π* orbitals with the p orbital of the
adjacent sp2-hybridized ester carbon atom causes sta-
bilization of E17 (∼-8 eV), while the other three CtC
π* orbitals (E18 and D18,19) remain in almost the same
higher energy region (>-6 eV). The HOMOs of the Ct
C-R fragments (D17, E16) corresponding to the lone
pair electrons are of essentially the same energy level
and interact with C43 of σ-symmetry to form molecular
orbitals for the σ-bonding interaction (A47,60, B56,60).
The rather large energy difference between the orbitals
(C43 - D17/E16) renders the M-C σ bond less covalent,
as previously revealed for the alkyl complexes by us.3
As for the π-interaction, orbital E17 is low in energy
enough to interact with C45 (to form B59,62), while
D18,19 and E19 of higher energies are left virtually
unaffected.
Additional information on the electronic structure of
the M-CtC moiety can be obtained from the IR data.
The νCtC and νCdO vibrations of the alkynyl complexes
1 are shifted to lower energies, as mentioned above, and
the extent of the shift is shown in parentheses in Table
1. Substantial shift to lower energies (>20 cm-1) is
observed for those containing a >CdO functional group
1a -c, whereas no significant shift is observed for the
silyl derivatives 1d ,e. The phenyl derivative 1i is
between these two situations. When the IR data are
compared with that of 6 [νCtC 2076 (∆ν 42); νCdO 1658
(20) (a) Owsten, P. G.; Rowe, J . M. J . Chem. Soc. 1963, 3411. (b)
Ellison, J . J .; Power, P. P. J . Organomet. Chem. 1996, 526, 263-267.
(c) Radonovich, L. J .; Klabunde, K. J .; Berens, C. B.; McCollor, D. P.;
Anderson, B. B. Inorg. Chem. 1980, 19, 1221.
(21) Bruce, M. I. Chem. Rev. 1998, 98, 2797. See also references
therein.
High-spin electronic configuration with S ) 3/2 result
from the large (A61,62 - A63,64; B61 - B62) and small
energy separations (A60 - A61,62; B59,60 - B61);22
that is, the orbitals up to A59 and B58 are occupied by

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3767
F igu r e 2. Orbital interactions between the TpCo and CtC-R fragments.
F igu r e 3. Molecular orbitals of the alkynyl complexes and frontier orbitals of the TpCo fragment.
electron pairs and the orbitals A60-62 and B59-61 are
occupied by unpaired electrons. Such electronic configu-
rations are supported by the result of measurements of
magnetic susceptibility.
Thus all frontier orbitals (A58-62, B57-61) are
singly or fully occupied and the lack of a vacant frontier
orbital should be the origin of the stability of the
electron-deficient 15e species, and essentially the same
bonding scheme was already noted for the alkyl com-
plexes.3,4
The singly occupied orbital B59 (Figure 3) corre-
sponds to π-back-donation from the cobalt center to the
CtC-COOMe ligand. The stabilization obtained by the
interaction, however, is not so large that back-donation
is not significant, as is consistent with the results of
the spectroscopic and crystallographic analyses men-
tioned above. It is notable for the SiMe3 derivative that
the alkynyl fragment virtually does not contribute to
A62 (Figure 3), indicating the negligible back-donation.
The bending of the Co-CtC linkage is also explained
in terms of the back-donation. Orbital C45, which is the
metal-based orbital responsible for the back-donation,
is shown in Figure 3. As is evident from the shape of
the orbital, bending of the Co-Ct linkage causes
effective overlap (B59-bent) of the metal-based orbital
C45 and the π* orbital of the CtC-COOMe fragment
(E17), but, at the same time, the σ-bonding interaction
(C43 + E16) becomes less effective. The arrangement
of the CtC-COOMe ligand should be determined by
balance of these two interactions.23 J udging from the
result of the X-ray crystallography the former π-interac-
tion plays a more important role in determining the
arrangement. The increased back-donation should also
(22) Shriver, D. F.; Atkins, P. W. Inorganic Chemistry, 3rd ed.;
Oxford University Press: Oxford, 1999.

3768 Organometallics, Vol. 21, No. 18, 2002
Yoshimitsu et al.
cause the coplanar arrangement of the ester plane, as
can be seen from the arrangement of B59-bent (Figure
3).
Syn th esis a n d Ch a r a cter iza tion of p-Tolyl Com -
p lex Tp iP r 2Co-C6H4-p-Me, 2. Reaction of the chloro
complex 3 with p-tolyl Grignard reagent gave the p-tolyl
complex 2 as moisture-sensitive blue crystals (Scheme
5).24 An IR spectrum containing the B-H and C(sp2)-H
vibrations [2538, 3043 (KBr pellet); 2543, 3027 cm-1
(ether solution)] reveals the presence of a κ3-TpiPr2
1
ligand15 and an aryl group.25 The H NMR signals for
the TpiPr2 moiety are comparable to those of the alkynyl
complexes 1, and the p-tolyl signals can also be assigned
[δH -2.3, 5.4 (9H × 2, CHMe2), 14.8 (3H, CHMe2; the
other CH signal could not be located), 60.3 (3H, 4-pz),
-16.3 (2H, tol), 72.0 (2H, tol), 44.2 (3H, p-Me)]. At-
tempted synthesis of the nickel derivative, TpiPr2Ni-p-
tolyl, resulted in the formation of an unidentified brown
product, although, in this case, too, the color change to
pink or red was observed.
Sch em e 5
The molecular structure of 2 was determined by X-ray
crystallography, and an ORTEP view and selected
structural parameters are shown in Figure 4 and Table
2, respectively. The core structure is of virtual C3-
symmetry and the Co-C distance is slightly longer than
that in the alkynyl complexes 1, and the difference (ca.
0.05 Å) is comparable to half of the difference of the
C(sp2)-C(sp2) (1.48 Å) and C(sp)-C(sp) single bond
length (1.38 Å).19 The aromatic ring is arranged per-
pendicular to the axial pyrazolyl ring plane, and the
orientation could result from release of steric repulsion
between the two rings as well as very weak back-
donation from C44 (Figure 3; see also M58 in Figure
5), which is degenerated with C45. The p-tolyl complex
2 is a member of a rare class of Co(II)-aryl complexes,
and, to our knowledge, only three examples of simple
nonchelate Co(II)-aryl complexes were reported: (Et3P)2-
Co(mesityl)2 [15e, 1.961(12) Å],20a [(µ-Br)(THF)Co-C6H3-
(o,o′-mesityl)2] [15e, 2.053(8) Å],20b [(η6-toluene)Co-
(C6F5)2] [17e, 1.931(5) Å]20c (electron count and the
Co-C length are shown in brackets). It should be noted
that all these examples including 2 are electron-deficient
species with 15 or 17 valence electrons and that the
Co-C length of 2 is comparable to those of the previous
examples.
F igu r e 4. Molecular structure of 2 showing 30% thermal
ellipsoids.
Sch em e 6
Rea ctivity of th e Alk yn yl a n d p-Tolyl Com -
p lexes. The hydrocarbyl complexes obtained by the
(23) The experimental result that the bent structure is more stable
than the linear structure could not be reproduced by the EHMO
calculation. The linear structure (B) is calculated to be more stable
than the bent structure (B-bent) by ca. 6 kcal/mol. But because the
difference is too small when the reliability of the EHMO calculation is
taken into account, a more detailed calculation is needed to obtain a
definitive conclusion. But the present consideration provides a qualita-
tive explanation.
(24) An analytically pure sample of 2 could not be obtained despite
many attempts due to contamination of a small amount of TpiPr2Co-
Br as revealed by 1H NMR.
(25) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectroscopic
Identification of Organic Compounds, 5th ed.; J ohn Wiley & Sons: New
York, 1991.
present study were subjected to reactions with various
substrates (Scheme 6).
(i) Sta bility. Both of the complexes were readily
hydrolyzed by moisture to give the corresponding hy-
drocarbons and the hydroxo complex 4. The protonation
of the Co-C bond in 1 supports the weak back-donation
discussed above, because effective back-donation usually
induces reaction with electrophiles at the â-carbon atom
(Scheme 7).21 The p-tolyl complex 2 decomposed upon
exposure to O2 atmosphere in a manner similar to the

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3769
Sch em e 7
reaction mixture was retained, and color change to
green was an indication of deactivation of the catalytic
species. 1H NMR analysis of the green reaction mixture
revealed formation of the dinuclear µ-carbonato complex
8,27 which should be formed by interaction of the
hydroxo complex 4 (formed via hydrolysis of 1a ) with
adventitious CO2. The catalytic species 1a could be
regenerated via interaction of the hydroxo complex 4
with methyl propiolate present in the mixture but could
not be formed from the µ-carbonato complex 8.
Sch em e 8
A plausible formation mechanism of 7 should involve
double coordination-insertion of the CtC bond in
methyl propiolate into the Co-Ct bond in 1a : 1a f
TpiPr2Co-CHdC(E)-CtC-E F f TpiPr2Co-CEdCH-
CHdC(E)-CtC-E G (E ) COOMe). Hydrolysis of the
Co-Cd bond in G with a third equivalent of methyl
propiolate would furnish the linear trimer 7. The final
intermediate G could be detected by a deuteration
experiment. When a reaction mixture was quenched by
CH3COOD at an early stage of the catalytic reaction (3
h), ca. 40% of 7-d1 was detected by GC-MS analysis,
and analysis after 23 h revealed less than 5% deutera-
tion. The decrease of the extent of deuteration after a
prolonged reaction time is due to catalytic formation of
7 as well as deterioration of the catalytic species
discussed above, i.e., irreversible conversion to 8. No-
table points of this mechanism are (1) the different
orientation of the alkyne substrate in the two insertion
steps and (2) the specific formation of the linear trimer
7 as a sole organic product. As for point (1), although
the second insertion giving G may be explained in terms
of a Michael addition-type mechanism, we have no
explanation for the regiochemistry of the first insertion
giving F . A radical mechanism may be viable, as
suggested by one of the reviewers, because homolysis
of the M-C bond in TpR′M-alkyl-type complexes has
been noted.3,4 But we have no experimental evidence
that supports any mechanism (except for G, see above).
Point (2) could be interpreted in terms of the steric
environment around the Co-C bond. The R-carbon
atoms of the intermediates F and G carry the H and
COOMe group, respectively. Because the Co-C bond in
the latter intermediate G is sterically congested due to
the ester group at the R-carbon atom, interaction with
another molecule of methyl propiolate leading to oligo-
merization should be hindered, and, instead, protonoly-
sis of the polar Co-C bond with the acidic terminal
hydrogen atom of methyl propiolate leads to the forma-
tion of 7, accompanying regeneration of the catalytic
species 1a . The stereochemistry of 7 should be deter-
mined by the cis-stereochemistry of the insertion steps.
Although catalytic oligomerizations of alkynes such as
linear oligomerization giving oligoenyne compounds and
cyclic oligomerization of alkynes giving, for example,
benzene and cyclooctatriene derivatives have many
precedents,28 to our knowledge only two examples of
alkyl complexes, but the decomposition product could
not be identified. The alkynyl complexes 1 were left
unaffected by O2-exposure. In addition, no significant
thermal deterioration was observed for 1 and 2 by
heating to 100 °C under inert atmosphere.
(ii) R ea ct ion w it h Un sa t u r a t ed H yd r oca r b on s
In clu d in g Ca ta lytic Lin ea r Tr im er iza tion of Meth -
yl P r op iola te by 1a . We also examined reaction of
1a,c,d,e and 2 with unsaturated hydrocarbons [1-alkynes
(R-CtC-H; R ) Ph, n-C4H9, COOMe), Ph-CtC-Ph,
1-alkene (R-CHdCH2; R ) Ph, n-C4H9, COOMe)], but
characterizable products were obtained only in the cases
of the reaction of 1a with H-CtC-COOMe and car-
bonylation of 2 described below.26 The sluggish reactiv-
ity of 1 and 2 could be attributed to the lack of a vacant
coordination site (see above), as already discussed for
the alkyl complexes.
When a benzene solution of 1a and methyl propiolate
was refluxed, catalytic linear trimerization proceeded
to give the (E,E)-buta-1,3-dien-5-yne derivative 7 (Scheme
8). The reaction was slow, and, after heating for 20 h,
ca. 14 equiv of methyl propiolate was converted to 7 (ca.
4.5 turnovers). The catalytic reaction was so specific that
neither another stereoisomer nor oligomer was detected
at all. The stereochemistry of the diene moiety was
determined on the basis of the AMX 1H NMR coupling
pattern of the three adjacent olefinic protons on the
diene linkage and the strong IR absorption at 983
cm-1 25
COOMe moiety is assigned on the assumption of cis-
stereochemistry of the insertion process (see below). 13
,
and the configuration of the C(H)-CtC-
C
NMR and GC-MS data consistent with the structure
were also obtained (see Experimental Section). The
reaction proceeded as long as the blue color of the
(26) Reaction of 1h and Ph-CtC-H gave an unidentified product.
Reaction of 1d with Me3Si-CtC-H in refluxing benzene gave the
siloxo complex, TpiPr2Co-OSiMe3, which was also characterized by
X-ray crystallographic (Figure S4)14 and spectroscopic methods. [Data
for TpiPr2Co-OSiMe3: 1H NMR (C6D6): δH 73.8 (3H, 4-pz-H), 12.4 (3H,
CHMe2), 3.1 (9H, SiMe3), 2.8 (3H, CHMe2), 1.8, 1.5 (18H × 2, CHMe2),
-21.5 (1H, BH). IR: νBH 2543 cm-1. UV-vis:
λ )
max/nm (ꢀ/M-1‚cm-1
820 (21), 654 (630), 582 (233), 295 (300). Anal. Calcd for C30H55N6-
OBSiCo: C, 58.72; H, 9.03; N, 13.70. Found: C, 58.35; H, 9.05; N,
13.51.] TpiPr2Co-OSiMe3 should be formed from 4 (formed by hydroly-
sis of 1d ) and Me3Si-CtC-H following the mechanism shown in
Scheme 3 (path b). Although such a reaction does not occur at ambient
temperature (under the conditions for Scheme 2), reaction under forced
conditions for a prolonged period may form the thermodynamically
more stable siloxo complex.
(27) For TpR′M(κ2-carboxylato) complexes, see, for example: Ogihara,
T.; Hikichi, S.; Akita, M.; Uchida, T.; Kitagawa, T.; Moro-oka, Y. Inorg.
Chim. Acta 2000, 297, 162.
(28) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis
with Organometallic Compounds; VCH: Weinheim, 1996. Ohmura, T.;
Yamamoto, Y.; Miyaura, N. J . Am. Chem. Soc. 2000, 122, 4990-4991.
Ohmura, T.; Yorozuya, S; Yamamoto, Y.; Miyaura, N. Organometallics

3770 Organometallics, Vol. 21, No. 18, 2002
Yoshimitsu et al.
versus aryl groups coordinated at the C(sp2) atom, the
former with more p-character being more nucleophilic.34
Con clu sion s. A series of TpR′Co-R-type hydrocarbyl
complexes containing Co-C(spn) bonds (n ) 1-3) are
prepared and characterized successfully, when the
previous results on the alkyl complexes3 are combined
with the present results. Despite their highly electron-
deficient electronic structures, the hydrocarbyl com-
plexes turn out to be thermally stable species. It is
notable that â-hydride elimination (for alkyl complexes)
and oligomerization (for alkynyl and aryl complexes;
Scheme 1), which are viable decomposition processes for
normal hydrocarbyl complexes, do not operate for the
TpR′Co-R complexes. Such an unusual behavior should
be a result of the lack of vacant frontier orbitals, which
originates from the property of the TpR′ ligand as a
tetrahedral enforcer. Tetrahedral structures with fron-
tier orbitals of a small energy separation (Figure 5:
J 45-49, K56-60, L46-50) cause high-spin electronic
configurations,22 where all frontier orbitals accom-
modate an electron pair or an unpaired electron.
σ-Bonding interaction is the dominant character of
the metal-carbon bonding interaction in the TpR′Co-R
complexes (Figure 5). Because, however, (1) no ad-
ditional orbital mixing occurs due to only one of each
σ-type orbital being included in the TpCo and R frag-
ments (C43-M4/N15/O5) and (2) the energy separation
between the two σ-type orbital is substantial, the
covalent character of the Co-C bond is not significant
and, as a result, the Co-C bond is so polarized as to be
readily protonated even by moisture in the air. On the
other hand, π-bonding interaction is virtually negligible
for the alkynyl (L) and aryl complexes (K). A small
contribution of back-donation is observed, only when an
electron-withdrawing substituent such as C(dO)-X
groups is attached to the π-system.
Sch em e 9
linear trimerization appeared, as reported by Klein29
and Furlani.30
(iii) Ca r bon yla tion . The p-tolyl complex 2 was
readily carbonylated upon exposure to CO (1 atm) to
give a brown mixture (Scheme 9), while the alkynyl
complexes 1 remained unreacted even under pressur-
ized conditions (5 atm). A 1H NMR spectrum of the
brown reaction mixture containing a broad signal at δ
1.931 is distinct from that of 2, suggesting formation of
a new species with a different coordination geometry.
Because (1) the IR spectrum of the reaction mixture
contained an intense νCO vibration (2013 cm-1) in
addition to the νBH absorption (2535 cm-1 15
and (2) no
)
νCdO vibration of an acyl-metal functional group was
detected, the product 9 was assigned to the CO-
coordinated species. Despite many attempts 9 could not
be isolated, and purple crystals of 10 that crystallized
out of the solution were characterized by X-ray crystal-
lography (Figure S4)32 to be the κ2-carboxylato complex
10, which was confirmed by comparison with an au-
thentic sample obtained by dehydrative condensation
between 4 and p-toluic acid. Exposure of a brown
mixture containing 9 to O2 caused an immediate color
change to blue (10). A plausible formation mechanism
of 10 shown in Scheme 9 involves successive CO and
O2 insertion into the Co-C bond in 9 to give the acyl
(H) and acylperoxo intermediates (I), and decomposition
of I should produce the carboxylato complex 10. An
acylperoxometal species has been regarded as a key
intermediate of metal-catalyzed oxidation of organic
compounds,33 and its reactivity as an oxidant is now
under further study. The result of carbonylation of the
p-tolyl complex 2 is in contrast to that of the alkyl
complex, TpiPr2Co-R, which afforded the carbonyl-acyl
species TpiPr2Co(CO)-C(dO)-R. The difference could be
ascribed to the nucleophilicity of the hydrocarbyl
groups: alkyl groups coordinated at the C(sp3) atom
Despite the 15-electron configuration of the TpR′Co-R
complexes, which is short of the coordinatively saturated
18-electron configuration, they turn out to be sluggish
toward organic substrates, in particular, unsaturated
hydrocarbons, and the sluggishness could be ascribed
again to the lack of vacant frontier orbitals as mentioned
above. However, as typically exemplified by the regio-
and stereospecific linear trimerization of methyl propi-
olate catalyzed by 1a , interaction of the TpR′Co-R
species with an organic compound may induce pertur-
bation of their electronic structure to provide an op-
portunity to exhibit unprecedented reactivity.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
under an Ar atmosphere using standard Schlenk tube tech-
niques. THF, ether, toluene, pentane, and hexane were dried
over Na-K/benzophenone under Ar and distilled just before
use. 1H NMR spectra were recorded on a Bruker AC200
spectrometer (1H: 200 MHz). Benzene-d6 and toluene-d8 for
NMR measurements containing 0.5% TMS were dried over
molecular sieves and distilled under reduced pressure. IR and
UV spectra were obtained on J ASCO FT/IR 5300 and V-570
spectrometers, respectively. FD-MS spectra were obtained on
a J EOL J MS-700 mass spectrometer. Magnetic susceptibility
was measured on a Sherwood Scientific MSB-AUTO. Organic
products were identified and quantified by a combination of
1999, 18, 365-367. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
Yi, C. S.; Liu, N. Organometallics 1998, 17, 3158-3160. Pavlic, S.;
Gemel, C.; Slugovc, C.; Mereiter, K.; Schmid, R.; Kirchner, K. J .
Organomet. Chem. 2001, 617-618, 301. See also references cited in
these papers.
(29) Klein, H. F.; Marger, M. Organometallics 1992, 11, 3174.
(30) Carusi, P.; Cerichelli, G.; Furlani, A.; Russo, M. V.; Suber, L.
Appl. Organomet. Chem. 1987, 1, 555
(31) Other signals could not be located presumably due to broaden-
ing, but complete conversion of 2 could be verified by the 1H NMR
analysis.
(32) Kitajima, N.; Hikichi, S.; Moro-oka, Y. J . Am. Chem. Soc. 1993,
115, 5496.
(33) Ohzu, Y.; Hikichi, S.; Akita, M. Unpublished result.
(34) Berke, H.; Hoffmann, R. J . Am. Chem. Soc. 1978, 100, 7224.

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3771
F igu r e 5. Comparison of molecular orbitals of TpCo-Me (J ), -Ph (K), and -CtC-H (L).
GLC (Shimadzu GC17A equipped with a PHA0201 capillary
63.34; H, 9.26; N, 12.66. Found: C, 63.36; H, 9.58; N, 12.41.
1g: λmax/nm (ꢀ/M-1‚cm-1; in hexane): 297 (1154), 654 (678),
column and an FID detector) and GC-MS analyses (Shimadzu
QP5000 connected to GC17A equipped with
a
PHA0201
889 (96), 906 (98). FD-MS: m/z 549 (M+). 1h : λmax/nm (ꢀ/M-1
‚
capillary column). EHMO calculations were done using the
CAChe system (ver. 4.0). The chloro (3, 3′) and hydroxo
complexes (4, 4′) were prepared according to literature proce-
dures.32 Other chemicals were used as received without further
purification.
P r ep a r a tion of Alk yn yl Com p lexes (1). As a typical
example, the synthetic procedure for 1a is described below in
detail, and the other derivatives were prepared in essentially
the same method unless otherwise stated. Yield, reaction time,
and spectroscopic data for 1 are shown in Scheme 2 and Table
1.
cm-1; in hexane): 310 (2554), 663 (685). FD-MS: m/z 625 (M+).
1i: λmax/nm (ꢀ/M-1‚cm-1; in hexane): 306 (735), 318 (735), 662
(449), 888 (35). Analytically pure samples of 1g-i could not
be obtained as described in the main text.
Rea ction of 3 w ith P h 3Si-CtC-H: F or m a tion of
Tp iP r 2Co-OSiP h 3 (5). Reaction of 3 (238 mg, 0.220 mmol)
with Ph3Si-CtC-H (188 mg, 0.660 mg) as described for the
synthesis of 1a gave 5 (235 mg, 0.294 mmol, 68% yield) as
blue needles. 5: 1H NMR (C6D6): δH 74.9 (3H, 4-pz-H), 9.7
(6H, Ph), 7.9 (6H, Ph), 7.4 (3H, Ph), 3.2 (18H, CHMe2), 2.7
(3H, CHMe2), 1.7 (18H, CHMe2). IR: νBH 2544 cm-1. UV-vis:
Tp iP r 2Co-CtC-COOMe (1a ). To a 50 mL Schlenk tube
containing a hexane solution (25 mL) of 3 (181 mg, 0.167
mmol) and molecular sieves (ca. 1.0 g) was added methyl
propiolate (34 mg, 0.401 mmol) via a microsyringe. The color
of the solution changed from red (the color of 3) to blue upon
mixing, and the resultant mixture was stirred for 3 h. Then
the molecular sieves were removed by filtration and removal
of the volatiles under reduced pressure gave blue powers,
crystallization of which from hexane at -30 °C gave 1a (152
mg, 0.250 mmol, 75% yield) as blue crystals. 1a : µeff ) 3.4 µB.
λ
max (ꢀ/M-1‚cm-1) 438 (465), 508 (39), 791 (75), 916 (120). Anal.
Calcd for C45H31N6OBSiCo: C, 67.57; H, 7.69; N, 10.51.
Found: C, 67.42; H, 7.46; N, 10.32. The nickel derivative 5′
was prepared in essentially the same method. 5′ (70% yield,
red crystals): 1H NMR (C6D6): δH 79.2 (3H, 4-pz-H), 8.3 (6H,
Ph), 8.0 (6H, Ph), 7.8 (3H, Ph), 3.1 (18H, CHMe2), 1.4 (18H,
CHMe2), 0.85 (3H, CHMe2). IR: νBH 2538 cm-1. UV-vis: λmax
(ꢀ/M-1‚cm-1) 438 (465), 508 (39), 791 (75), 916 (120). Anal.
Calcd for
C45H31N6OBSiNi: C, 67.60; H, 7.69; N, 10.51.
Found: C, 67.68; H, 7.74; N, 10.29.
λ
max/nm (ꢀ/M-1‚cm-1; in hexane): 290 (1521), 646 (888), 888-
Syn th esis of Tp iP r 2Co-p-tol (2). To an ethereal solution
(10 mL) of 4 (136 mg, 0.243 mmol) cooled at -78 °C was added
p-tol-MgBr (0.65 M ethereal solution, 0.37 mL, 0.32 mmol),
and the resultant mixture was gradually warmed to room
temperature. The color of the mixture changed from blue to
green. When the temperature reached room temperature, the
volatiles were removed under reduced pressure and the
products were extracted with pentane and filtered through a
glass filter. Concentration and cooling to -30 °C gave 2 (117
mg, 0.190 mmol, 78% yield) as blue crystals.24 2: UV-vis: λmax
(ꢀ/M-1‚cm-1) 586 (326), 621 (438), 669 (sh, 891), 697 (1304),
951 (46).
(121). FD-MS: m/z 607 (M+). Anal. Calcd for C31H49N6O2BCo:
C, 61.29; H, 8.13; N, 13.83. Found: C, 61.02; H, 8.30; N, 13.76.
1b: µeff ) 3.4 µB. λmax/nm (ꢀ/M-1‚cm-1; in hexane): 290 (1177),
646 (815), 860 (130), 886 (115). FD-MS: m/z 607 (M+). Anal.
Calcd for C31H51N6O2BCo: C, 61.84; H, 8.27; N, 13.52. Found:
C, 61.53; H, 8.34; N, 13.23. 1c: µeff ) 3.6 µB. λmax/nm (ꢀ/M-1
‚
cm-1; in hexane): 290 (1653), 300 (1639), 646 (1080), 866 (128),
892 (153). FD-MS: m/z 591 (M+). Anal. Calcd for C31H49N6-
OBCo: C, 62.95; H, 8.35; N, 14.21. Found: C, 62.51; H, 8.40;
N, 13.93. 1d : µeff ) 3.6 µB. λmax/nm (ꢀ/M-1‚cm-1; in hexane):
299 (1019), 313 (1004), 657 (776). FD-MS: m/z 621 (M+). Anal.
Calcd for C32H55N6BSiCo: C, 61.83; H, 8.92; N, 13.52. Found:
Lin ea r Tr im er iza tion of Meth yl P r op iola te Ca ta lyzed
by 1a : F or m a tion of 7. A benzene solution (10 mL) contain-
ing 1a (32.8 mg, 0.054 mmol) and methyl propiolate (136 mg,
1.62 mmol) was refluxed for 14 h. Removal of the volatiles
C, 61.93; H, 8.99; N, 12.82. 1e: µeff ) 3.5 µB. λmax/nm (ꢀ/M-1
‚
cm-1; in hexane): 297 (820), 313 (918), 658 (800), 887 (73).
FD-MS: m/z 663 (M+). Anal. Calcd for C35H61N6BSiCo: C,

3772 Organometallics, Vol. 21, No. 18, 2002
Ta ble 3. Cr ysta llogr a p h ic Da ta
Yoshimitsu et al.
1a
1e
2
5
formula
fw
C
31H49BN6O2Co
C35H61BN6Si′Co
663.73
C34H53BN6Co
615.56
C45H61BN6OSiCo
799.83
607.50
cryst syst
space group
a/Å
b/Å
c/Å
orthorhombic
P212121
17.9286(7)
21.6998(8)
8.7517(2)
monoclinic
P21
monoclinic
P21/n
monoclinic
P21/c
14.1440(4)
31.3152(8)
9.5739(2)
108.074(1)
4031.3(2)
4
1.094
0.485
180 (2° step)
90
950
9.3235(4)
15.3962(7)
24.3715(8)
93.506(4)
3853.9(6)
4
1.177
0.525
180 (5° step)
36
360
9.476(2)
24.278(3)
19.695(4)
95.902(4)
4507(2)
4
1.179
0.447
180 (4° step)
45
840
â/deg
V/Å3
3404.8(2)
4
1.185
0.539
180 (3° step)
60
400
383
Z
d
calcd/g‚cm-3
µ/mm-1
oscillation range/deg
no. of oscillation images
exposed time/s‚deg-1
no. of variables
R1 for data
823
0.052
392
0.052
496
0.130
0.049
with I > 2σ(I)
wR2
(for 3722 data)
0.129
(for 5869 data)
0.144
(for 4647 data)
0.145
(for 2918 data)
0.312
(for all 4341 data)
(for all 8957 data)
(for all 7514 data)
(for all 9117 data)
5′‚hexane1/2
10
TpiPr2Co-OSiMe3
formula
fw
C48H68BN6OSiNi
842.69
C35H53BN6O2Co
659.57
C30H55BN6OSiCo
613.63
cryst syst
space group
a/Å
b/Å
c/Å
monoclinic
P21/n
monoclinic
P21/n
monoclinic
C2/c
19.377(1)
13.749(1)
20.130(1)
116.475(2)
4800.7(5)
4
9.449(1)
15.7388(9)
25.962(1)
96.615(2)
3475.2(2)
4
35.122(2)
9.5247(3)
24.002(1)
115.634(1)
7238.8(5)
8
â/deg
V/Å3
Z
d
calcd/g‚cm-3
1.166
0.469
1.137
0.481
1.126
0.537
µ/mm-1
oscillation range/deg
no. of oscillation images
exposed time/s
no. of variables
R1 for data
180 (5° step)
36
420
524
0.068
180 (5° step)
36
1200
414
0.125
180 (5° step)
36
720
376
0.063
with I > 2σ(I)
wR2
(for 5689 data)
0.195
(for 1591 data)
0.309
(for 5753 data)
0.172
(for all 10 740 data)
(for all 8197 data)
(for all 8129 data)
under reduced pressure left a brown solid, washing of which
with hexane several times gave 7 as a pale brown solid (16
mg, 337%). 7: 1H NMR (C6D6): δH 7.76 (1H, dd, J ) 11.9 and
15.2 Hz, MeO2CCHdCH-CHd), 7.42 (1H, dd, 0.8 and 11.9
Hz, MeO2CCHdCH-CHd), 5.79 (1H, dd, J ) 0.8 and 15.2 Hz,
MeO2CCHdCH-CHd), 3.284, 3.276, 3.17 (3H × 3, s × 3,
OMe). 13C NMR (C6D6): δC 165.3, 163.3 (dC-COOMe), 153.5
(tC-COOMe), 148.0, 137.5, 131.9, 118.9 (s × 4, CdC), 90.7
(CtC-COOMe), 78.7 (CtC-COOMe), 52.5, 52.3, 51.5 (OMe).
the volatiles under reduced pressure followed by crystallization
from acetonitrile at -30 °C gave 11 (141 mg, 0.215 mmol, 58%
yield).
X-r a y Cr ysta llogr a p h y. Crystallographic data are sum-
marized in Table 3. Single crystals of 1a , 1e, 5, 5′, 10, TpiPr2
-
Co-OSiMe3 (hexane), and 2 (pentane) were obtained by
recrystallization from the solvents shown in the parentheses
and mounted on glass fibers. Details for 5, 5′, 10, and TpiPr2
Co-OSiMe3 are included in the Supporting Information.
-
IR: ν)CH 3080, νCtC 2212, νCdO 1718, νCdC 1631, δCH 983 cm-1
.
Diffraction measurements were made on a Rigaku RAXIS
IV imaging plate area detector with Mo KR radiation (λ )
0.71069 Å) at -60 °C. Indexing was performed from two
oscillation images, which were exposed for 5 min. The crystal-
to-detector distance was 110 mm (2θmax ) 55°). Readout was
performed with the pixel size of 100 µm × 100 µm. Neutral
scattering factors were obtained from the standard source. In
the reduction of data, Lorentz and polarization corrections and
empirical absorption corrections were made.35 Crystallographic
data and results of structure refinements are listed in Table
3.
The structural analysis was performed on an IRIS O2
computer using the teXsan structure solving program system
obtained from the Rigaku Corp., Tokyo, J apan.36 Neutral
scattering factors were obtained from the standard source.37
The structures were solved by a combination of the direct
methods (SHELXS-8638 or SAPI91 or SIR92 or MITHRIL90)39
GC-MS: m/z 252 (M+). Anal. Calcd for C12H12O6: C, 57.14;
H, 4.80. Found: C, 57.57; H, 4.93.
Ca r bon yla tion -Oxygen a tion of 3: F or m a tion of 10.
Exposure of a pentane solution (10 mL) of 3 (117 mg, 0.189
mmol) to CO (from a rubber balloon) caused a color change
from blue to brown. Evacuation for a short period followed by
filling with O2 gas gave a blue solution, from which 10 (51
mg, 0.078 mmol, 41% yield) was isolated as purple crystals
after concentration and cooling at -30 °C. 10: 1H NMR (C6D6)
δH 64.4 (3H, 4-pz), 58.9 (1H, BH), 52.2 (2H, p-tol), 37.2 (3H,
Me in p-tol), 24.6 (2H, p-tol), 16.9 (3H, CHMe2), 13.1 (18H,
CHMe2), -24.6 (18H, CHMe2), -61.7 (3H, CHMe2). IR: νBH
2529, νCdC(Ar) 1685 cm-1. Anal. Calcd for C35H53N6O2BCo: C,
63.73; H, 8.10; N, 12.74. Found: C, 63.46; H, 8.30; N, 12.24.
An authentic sample of 10 was prepared by the reaction of 3
with p-toluic acid. Addition of (55.3 mg, 0.406 mmol) to an
ethereal solution (10 mL) of 3 (200 mg, 0.185 mmol) caused
an immediate color change from orange to purple. Removal of
(35) Higashi, T. Program for Absorption Correction; Rigaku Corp.:
Tokyo, J apan, 1995.

Alkynyl- and Aryl-Cobalt Complexes
Organometallics, Vol. 21, No. 18, 2002 3773
and Fourier synthesis (DIRDIF94).40 Least-squares refine-
ments were carried out using SHELXL-9738 (refined on F2)
linked to teXsan. All the non-hydrogen atoms were refined
anisotropically. Unless otherwise stated, riding refinements
were applied to the methyl hydrogen atoms [B(H) ) B(C)], and
the other hydrogen atoms were fixed at the calculated posi-
tions. Details of the refinements were as follows. 5′: The
hexane solvate was refined isotropically and the disordered
part was refined taking into account two components (C73:
C73A ) 0.5:0.5). Hydrogen atoms attached to it were not
included in the refinement. 10: The boron atom (B1) was
refined isotropically.
Ack n ow led gm en t. We are grateful to the Ministry
of Education, Culture, Sports, Science and Technology
of the J apanese Government for financial support of this
research (Grant-in-Aid for Scientific Research on Prior-
ity Areas: 11228201).
(36) teXsan; Crystal Structure Analysis Package, ver. 1. 11; Rigaku
Corp.: Tokyo, J apan, 2000.
(37) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, 1975; Vol. 4.
(38) (a) Sheldrick, G. M. SHELXS-86: Program for crystal structure
determination; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(b) Sheldrick, G. M. SHELXL-97: Program for crystal structure
refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(39) (a) SAPI91: Fan, H.-F. Structure Analysis Programs with
Intelligent Control; Rigaku Corp.: Tokyo, J apan, 1991. (b) SIR92:
Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo,
C.; Guagliardi, A.; Polidori, G. J . Appl. Crystallogr. 1994, 27, 435. (c)
MITHRIL90: Gilmore, C. J . MITHRIL-an integrated direct methods
computer program; University of Glasgow: Glasgow, UK, 1990.
Su p p or tin g In for m a tion Ava ila ble: Table of positional
parameters and Beq, anisotropic thermal parameters, and
interatomic distances and bond angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM020268U
(40) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system; Technical Report of the Crystallography
Laboratory; University of Nijmegen: Nijmegen, The Netherlands,
1992.