Cobalt-mediated B-H activation and cyclopentadienyl-participated diels-alder addition in the reaction of a 16e CpCo complex containing an o-carborane-1,2-dithiolato ligand with HC≡C-C(O)Ph

Article abstract of DOI:10.1021/ic901970b

The reaction of the 16e half-sandwich complex CpCo(S₂C ₂B₁₀H₁₀) (1) with HC≡C-C(O)Ph leads to a 17e complex 2 containing a blcyclo[2.2.1]heptene unit at the B3/B6 site of carborane. In the presence of air, water and silica 2 converts to two 16e complexes, 3 and 4, bearing new types of functionalized groups.

Full text of DOI:10.1021/ic901970b

4
Inorg. Chem. 2010, 49, 4–6
DOI: 10.1021/ic901970b
Cobalt-Mediated B-H Activation and Cyclopentadienyl-Participated
Diels-Alder Addition in the Reaction of a 16e CpCo Complex Containing
an o-Carborane-1,2-dithiolato Ligand with HCtC-C(O)Ph
Yuguang Li,† Qibai Jiang,† Yizhi Li,† Hong Yan,*,† and Vladimir I. Bregadze*,‡
†
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing
‡
University, Jiangsu 210093, China and A. N. Nesmeyanov Institute of Organoelement Compounds (INEOS),
Russian Academy of Sciences, Moscow 119991, Russia
Received October 6, 2009
The reaction of the 16e half-sandwich complex CpCo(S2C2B10H10)
(1) with HCtC-C(O)Ph leads to a 17e complex 2 containing a
bicyclo[2.2.1]heptene unit at the B3/B6 site of carborane. In the
presence of air, water and silica 2 converts to two 16e complexes, 3
and 4, bearing new types of functionalized groups.
alkylborane and arylboron compounds,3 which are useful
synthetic intermediates in organic chemistry. In the poly-
hedral borane chemistry, B-H activation has also played a
key role in the synthesis of highly substituted carboranes,
such as polyalkylated carboranes,4 polyhydroxylated icosa-
hedral boranes,5 and highly halogenated carborane anions.6
These substituted products of B-H vertices have received
much attention for applications in metathesis, stabilization of
unusual cations, catalysis, oxidation chemistry, etc.7 In this
chemistry, however, the selective boron substitution or hy-
droboration has proven rather difficult, although some ex-
amples have been reported.8-10 Additionally, it has been
described that cyclopentadienyl (Cp) and indenyl ligands
Transition-metal-induced B-H activation in organic and
organometallic chemistry has been a subject of interest. B-H
activation has led to the formation of transition-metal
borane, boryl, and borylene complexes.1,2 Transition-me-
tal-catalyzed borylation of hydrocarbons could generate
*To whom correspondence should be addressed. E-mail: hyan1965@nju.
edu.cn (H.Y.), bre@ineos.ac.ru (V.I.B.).
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r
pubs.acs.org/IC
Published on Web 12/04/2009
2009 American Chemical Society

Communication
Inorganic Chemistry, Vol. 49, No. 1, 2010 5
Scheme 1.a
Figure 1. Molecular structure of 2. Selected bond lengths (A): Co1-S1
2.1835(14), Co1-S2 2.1699(15), S1-C2 1.801(4), S2-C1 1.795(5),
C1-C2 1.655(6), S1-C13 1.860(4), B3-C8 1.565(7), C8-C9 1.540(6),
C8-C12 1.528(6), C8-C13 1.579(6), C9-C10 1.535(6), C10-C11
1.501(6), C10-C14 1.578(6), C11-C12 1.319(7), C13-C14 1.541(6).
a Steps: (i) ambient temperature, 12 h, CH2Cl2; (ii) air, silica, CH2Cl2;
(iii) air, H2O, silica, CH2Cl2.
could convert coordination from η5-mode to η3- or η1-mode
and take part in further reactions.11,12 We report herein
how the B-H bond and the unusual η1-Cp-participated
Diels-Alder reaction simultaneously play in a cobalt center
to generate novel type functionalized carboranes.
The reaction of the 16e half-sandwich complex CpCo-
(S2C2B10H10) (1) with HCtC-C(O)Ph at ambient tempera-
ture leads to 2 (Scheme 1). Its solid-state structure contains a
substituted bicyclo[2.2.1]heptene unit that is bound to 1
through both a C-S bond and a C-B bond in the B3/B6
position of the carborane cage (Figure 1). The presence of a
S f Co coordinative bond leads to 2 as a 17e species. This is
confirmed by its broad signals in a range from -5 to 12 ppm
in the 1H NMR spectrum.
Figure 2. Molecular structure of 3. Selected bond lengths (A): Co1-S1
2.1281(8), Co1-S2 2.1425(9), S1-C1 1.780(3), S2-C2 1.779(3), C1-C2
1.640(4), B3-C8 1.571(5), C8-C9 1.558(4), C8-C12 1.556(5), C8-C13
1.513(4), C9-C10 1.505(4), C10-C11 1.499(5), C10-C14 1.516(5),
C11-C12 1.302(5), C13-C14 1.308(5).
ligand in the Diels-Alder reaction. The second was to use an
excess of alkyne, which led to boron disubstitution in the B3
and B6 positions of carborane15 rather than 2. This demon-
strates that the generation of 2 requires excessive 1 to supply
the Cp ligand. The proposed mechanistic pathway in the
formation of 2 is outlined in Scheme S1 (Supporting In-
formation). The processes may involve metal-induced B-H
activation at carborane, the conversion of a η5-Cp binding
mode to a η1-Cp type12 as well as a η1-Cp-participated
Diels-Alder reaction with in situ vinyl ketone.16,17
2 is novel; we are unaware of any previous characterization
of compounds containing a norbornenyl unit at o-carborane,
although a substituted norbornene is quite common13 and
selective hydroboration at o-carborane has been reported.10
Obviously, the origin of the norbornenyl unit arises from a
Cp-involved Diels-Alder reaction. To confirm this, two
experiments were designed. The first was to use a penta-
methylcyclopentadienyl (Cp*) ligand to replace Cp; no
similar 17e cobalt complex was observed. Instead, in the
Cp* analogues,14 two alkyne molecules were inserted into
one of the Co-S bonds, emphasizing the necessity of a Cp
As a CoII species, 2 can be readily oxidized by air in the
presence of silica. This leads to 3, where C-S bond cleavage
and then dehydrogenation may take place (Figure 2). The
resultant substituted norbornadienyl unit at the B3/B6 site of
carborane is analogous to the compound bicycl[2.2.1]hepta-
2,5-dien-2-ylphenylmethanone generated directly from the
Diels-Alder addition of cyclopentadiene and phenyl ethynyl
ketone.18 This provides evidence that the Diels-Alder reac-
tion occurs in the generation of 2. If moisture is copresent,
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116, 12115–12116. (b) Ahrendt, K. A.; Borths, C. J.; MacMillan, D. W. C. J. Am.
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G. E. Angew. Chem., Int. Ed. 2002, 41, 1668–1698. (b) Lam, Y.-h.; Cheong,
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(14) Cp*Co(S2C2B10H10)(C9H6O)2 (Cp*=η5-C5Me5), monoclinic, space
group P21/c, a =16.3162(16) A, b =11.1712(10) A, c =19.0888(18) A,
β=107.930(2)°, V=3310.4(5) A3, Z=4, Fcalc=1.326 g cm-3, GOF=1.009,
3
R1=0.0562 [I > 2σ(I)], wR2=0.1342 (all unique reflections). CCDC 738008.
(15) CpCo(S2C2B10H8)(C9H7O)2 (Cp = η5-C5H5), orthorhombic, space
group P212121, a = 7.9575(8) A, b = 15.6813(14) A, c = 22.837(2) A,
(18) (a) Trost, B. M.; Balkovec, J. M.; Angle, S. R. Tetrahedron Lett.
1986, 27, 1445–1448. (b) Bowden, K.; Jones, E. R. H. J. Chem. Soc. 1946, 52–
54.
V=2849.7(5) A3, Z=4, Fcalc=1.377 g cm-3, GOF=0.992, R1=0.0420
3
[I>2σ(I)], wR2=0.0934 (all unique reflections). CCDC 738002.

6
Inorganic Chemistry, Vol. 49, No. 1, 2010
Li et al.
water. They are generated independently. Both are air-stable
16e CoIII complexes containing unprecedented B substitution
at carborane.
This work demonstrates an unexpected reactivity of
complex 1 with HCtC-C(O)Ph that leads to novel sub-
stitution in the B3/B6 position of o-carborane via cobalt-
mediated B-H activation and Cp-participated Diels-Alder
reaction in one step. This finding offers a facile route to
selective B-H functionalization at carborane and novel
compounds. Detailed investigations are continuing to define
the scope of the reaction reported here with respect to other
alkynes.
Figure 3. Molecular structure of 4. Selected bond lengths (A): Co1-S1
2.1341(10), Co1-S2 2.1243(10), S1-C1 1.782(3), S2-C2 1.786(3),
C1-C2 1.620(4), B3-C8 1.546(5), C8-C9 1.537(4), C8-C12 1.522(4),
C8-C13 1.538(4), C9-C10 1.531(4), C10-C11 1.524(4), C10-C14
1.546(5), C11-C12 1.508(4), C12-C13 1.485(4), C13-C14 1.512(4).
Acknowledgment. We thank the National Science Foun-
dation of China (Grants 90713023, 20771055, and 2072-
1002), the Major State Basic Research Development Pro-
gram of China (Grant 2006CB806104), the National Basic
Research Program of China (Grant 2007CB925101), the
Natural Science Foundation of Jiangsu Province (Grant
BK2007131), and NSFC-RFBR (joint Grants 209111-
20057 and 09-03-92216) for financial support of this work.
2 immediately converts to 4 (Figure 3). Here oxidation at the
metal center initiates cleavage of the C-S bond followed by
attack of H2O at the CdC bond. The newly generated
organic tricyclic (one three-membered and two five-mem-
bered rings) unit is of interest, and related structures were
scarcely described.19 3 cannot convert to 4 in the presence of
Supporting Information Available: Crystallographic data in
CIF format, experimental details, and crystallographic data.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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