Synthesis and reactivity of the imido-bridged metallothiocarboranes CpCo(S2C2B10H10)(NSO2R)

Article abstract of DOI:10.1021/om300735d

The reactions of the 16-electron half-sandwich complex CpCo(S ₂C₂B₁₀H₁₀) (1) (Cp: cyclopentadienyl) with sulfonyl azides (p-toluenesulfonyl azide, TsN ₃; methanesulfonyl azide, MsN₃) in refluxing dichloromethane or at ambient temperature lead to imido-bridged adducts CpCo(S₂C₂B₁₀H₁₀) (NSO₂R) (2a, R = 4-MePh; 2b, R = Me) which can convert to the tetraazadiene cobalt complexes CpCoN₄(SO₂R)₂ (3a, R = 4-MePh; 3b, R = Me) in the presence of excess azide if heated. The reactions of 1 with acyl azides (methyl azidoformate and benzoyl azide) lead to CpCo(S₂C ₂B₁₀H₁₀)(CONR) (4a, R = OMe; 4b, R = Ph) with a newly-generated five-membered metallacyclic ring Co-S-N-C-O. Complexes 2a and 2b show further reactivity toward alkynes to give rise to the insertion products CpCo(S₂C₂B₁₀H₁₀)(R ₁C=CR₂) (NSO₂R) (R₁ = COOMe, R ₂ = H, R = 4-MePh, 5a, R = Me, 5b; R₁ = R₂ = COOMe, R = 4-MePh, 6a, R = Me, 6b; R₁ = COOMe, R₂ = Ph, R = 4-MePh, 8a, R = Me, 8b) formed by alkyne addition to a Co-S bond to generate a Co-C-C-S four-membered ring and CpCo(S₂C₂B ₁₀H₁₀)(R₁C=CR₂NSO₂R) (R₁ = H, R₂ = Ph, R = 4-MePh, 7a, R = Me, 7b; R ₁ = COOMe, R₂ = Ph, R = 4-MePh, 9a, R = Me, 9b) formed by alkyne insertion into a Co-N bond to generate a Co-C-C-N-S five-membered ring. In the case of PhC≡CCO₂Me, the products with insertion into both Co-S and Co-N bonds are isolated. Interestingly, if tert-butylacetylene is used, CpCo(S₂C₂B₁₀H₁₀)(R ₁R₂C - CNSO₂R) (R₁ = tBu, R ₂ = H, R = 4-MePh, 10a, R = Me, 10b) are generated by insertion of terminal carbon into a Co-N bond to form four-membered ring Co-C-N-S. The insertion pathways of these reactions have been discussed on the basis of DFT calculations. All the new complexes were fully characterized, and X-ray structural analyses were performed for 2a, 3a, 3b, 4a, 4b, 5a, 6a, 7a, 7b, 8a, 9a, 9b, and 10b.

Full text of DOI:10.1021/om300735d

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of the Imido-Bridged Metallothiocarboranes
CpCo(S2C2B10H10)(NSO2R)
Wei Zhong,† Qiwu Yang,‡ Yi Shang,† Guifeng Liu,† Haitao Zhao,*,‡ Yizhi Li,† and Hong Yan*,†
†State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing,
Jiangsu 210093, P. R. China
‡Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, P. R. China
S
* Supporting Information
ABSTRACT: The reactions of the 16-electron half-sandwich complex
CpCo(S2C2B10H10) (1) (Cp: cyclopentadienyl) with sulfonyl azides (p-
toluenesulfonyl azide, TsN3; methanesulfonyl azide, MsN3) in refluxing
dichloromethane or at ambient temperature lead to imido-bridged adducts
CpCo(S2C2B10H10) (NSO2R) (2a, R = 4-MePh; 2b, R = Me) which can
convert to the tetraazadiene cobalt complexes CpCoN4(SO2R)2 (3a, R = 4-
MePh; 3b, R = Me) in the presence of excess azide if heated. The reactions of
1 with acyl azides (methyl azidoformate and benzoyl azide) lead to
CpCo(S2C2B10H10)(CONR) (4a, R = OMe; 4b, R = Ph) with a newly-
generated five-membered metallacyclic ring Co−S−N−C−O. Complexes 2a
and 2b show further reactivity toward alkynes to give rise to the insertion
products CpCo(S2C2B10H10)(R1CCR2) (NSO2R) (R1 = COOMe, R2 = H,
R = 4-MePh, 5a, R = Me, 5b; R1 = R2 = COOMe, R = 4-MePh, 6a, R = Me,
6b; R1 = COOMe, R2 = Ph, R = 4-MePh, 8a, R = Me, 8b) formed by alkyne addition to a Co−S bond to generate a Co−C−C−S
four-membered ring and CpCo(S2C2B10H10)(R1CCR2NSO2R) (R1 = H, R2 = Ph, R = 4-MePh, 7a, R = Me, 7b; R1 = COOMe,
R2 = Ph, R = 4-MePh, 9a, R = Me, 9b) formed by alkyne insertion into a Co−N bond to generate a Co−C−C−N−S five-
membered ring. In the case of PhCCCO2Me, the products with insertion into both Co−S and Co−N bonds are isolated.
Interestingly, if tert-butylacetylene is used, CpCo(S2C2B10H10)(R1R2CCNSO2R) (R1 = tBu, R2 = H, R = 4-MePh, 10a, R =
Me, 10b) are generated by insertion of terminal carbon into a Co−N bond to form four-membered ring Co−C−N−S. The
insertion pathways of these reactions have been discussed on the basis of DFT calculations. All the new complexes were fully
characterized, and X-ray structural analyses were performed for 2a, 3a, 3b, 4a, 4b, 5a, 6a, 7a, 7b, 8a, 9a, 9b, and 10b.
precursors for synthesis of mixed-metal clusters to construct
metal−metal bonds.12b−f Meanwhile, the study of addition and
substitution reactions of such complexes with organic substrates
has been widely explored.10,11,13 In particular, systematical
study of the reactivity of [CpCo(E2C2B10H10)] (E = S, Se),
[Cp*M(E2C2B10H10)] (M = Co, Rh, Ir; E = S, Se), and [(p-
cymene)M(S2C2B10H10)] (M = Ru, Os) with alkynes have
been reported.10,11a,b,13 A representative characterization of
these reactions is that the insertion of alkynes into metal−
chalcogen bonds led to B−H bond activation, formation of a
metal−boron bond, and selective functionalization of a
carborane cage in the positions of B(3)/B(6).10,13a−e Recently,
our group reported the reactivity of 16-electron half-sandwich
complex CpCo(S2C2B10H10) with ethyl diazoacetate and gained
a series of unpredictable products with Co−B bond
formation.14 It is clear from these studies that the nature of
the metal center, the chalcogen element, organic substrates, and
reaction conditions strongly influence the reactivity of the
analogous unsaturated 16-electron complexes.
INTRODUCTION
■
Metal dithiolene complexes have been extensively investigated
due to their versatile reaction chemistries,1 specific geo-
metries,1a,2 useful physical properties,3 and important biological
role in enzymes.4 Among a number of dithiolene complexes
which have been developed so far, compounds involving η5-
cyclopentadienyl (Cp) have attracted much attention due to
the diverse chemical reactivities which are derived from
aromatic and unsaturated characters of the five-membered
metallacycle (MS2C2).1a,2 A typical reaction of this type is an
addition reaction occurring between the M−S bond of a
metalladithiolene ring, which has been addressed for many
substrates including diazo compounds,5 alkynes,6 quadricy-
clane,7 and azides.8 In addition, substitution reactions due to
the aromaticity of the metalladithiolene ring have been also
reported.9
Mononuclear 16-electron half-sandwich complexes of Co,
Rh, Ir, Ru, and Os containing a chelating 1,2-dicarba-closo-
dodecaborane-1,2-dichalcogenolate ligand, [E2C2B10H10]2− (E
= S, Se), are analogues of metal dithiolene complexes and have
attracted particular attention due to their rich reaction
chemistry.10−13 For example, these complexes could serve as
Received: August 1, 2012
Published: September 6, 2012
© 2012 American Chemical Society
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Our previous results showed that the reactions of 16-electron
complex Cp*Ir(S2C2B10H10) with substituted aryl azides led to
C(sp3)−H activation and ortho-substituted electron-withdraw-
ing group migration in the final products.15 As part of our
systematic study of the role of metal in the reaction chemistry,
herein we examine the reactivity of CpCo(S2C2B10H10) (1)
toward different kinds of organic azides and the insertion
reactions of the imido-bridged adducts with selected alkynes.
same conditions, only ∼5% complex 4b could be isolated as a
yellow-green solid. An attempt of heating at higher temperature
and prolonging the reaction time did not improve the yield of
4b. In this case, most of complex 1 remains in the mixture since
benzoyl azide readily forms nitrene, then rearranges to form
phenyl isocyanate, which react with each other readily to form
carbamoyl urea (named as N,N′,N″-triphenylbiuret).17 It is
obvious that the formations of 4b and carbamoyl urea are two
competitive reactions and the latter predominates to result in a
lower yield of 4b. Other than the formation of complexes 2a
and 2b via 1,3-dipolar addition, complexes 4a and 4b should be
RESULTS AND DISCUSSION
Reactivity of CpCo(S2C2B10H10) toward Organic
Azides. As outlined in Scheme 1, reactions of CpCo-
■
formed via nitrene, which rearranges to form a conjugated N−
4
3
C−O π system to coordinate to the center metal (see the
Scheme 1. The Reactivity of CpCo(S2C2B10H10) (1) toward
Organic Azides
structural analysis vide infra).
The reaction of complex 1 was extended to other azides, such
as phenyl azide, substituted aryl azides (2,6-Me2C6H3N3 and 2-
Me-6-NO2C6H3N3), and benzyl azide. The results showed that,
no matter which conditions were attempted, e.g., excess azide,
different solvent, prolonging the reaction time, or refluxing in
xylene, the reaction did not work at all with these azides.
This clearly shows that the reactivity of complex 1 is very
different from that of Cp*Ir(S2C2B10H10).15 Moreover,
compared to alkynes and diazo compounds, organic azides
are less reactive to complex 1. Our preliminary study of the
reactivity of complex 1 toward alkynes showed that the cobalt
complex 1 is more reactive than their analogous rhodium and
iridium species,13a−c but for organic azides, the opposite
reactivity of the 16-electron complexes was observed.
Good analytical data were obtained for these complexes,
which were isolated as green (2a, 2b, 4a, and 4b) or yellow
solids (3a and 3b) and are soluble in common organic solvents.
IR and NMR (1H, 11B, 13C) data confirmed the proposed
formulations, which were further supported by X-ray crystal
structure determination with the exception of 2b.
The ORTEP plot and selected bond parameters for 2a are
shown in Figure 1. Similar to the reported alkylidene-
(S2C2B10H10) (1) with excess sulfonyl azides (p-toluenesulfonyl
azide, TsN3, and methanesulfonyl azide, MsN3) in refluxing
dichloromethane afford imido-bridged adducts 2a and 2b in
good yields. The formation of such compounds should be
similar to that of alkylidene-bridging by diazo compounds5a and
result from 1,3-dipolar addition of sulfonyl azides to the Co−S
bond which has been previously reported.8a The reactions also
can be performed in dichloromethane at room temperature. In
such a case, the reaction time proceeds over four days but the
yield is lower. When the reactions are conducted in toluene at
80 °C for 8 h, tetraazadiene cobalt complexes (3a and 3b) are
formed in moderate yields. Interestingly, complex 3a or 3b can
also be obtained via the reaction of 2a or 2b with excess
corresponding sulfonyl azide, and heating at 80 °C in toluene.
This fact suggests that complexes 3a and 3b are formed via
cycloaddition of 2a and 2b to corresponding sulfonyl azide.
Such tetraazadiene derivatives are common products in the
reaction of organic azides with transition metal complexes.16 To
the best of our knowledge, the reactions in this study are the
first examples of tetraazadiene complexes formed from the
reaction of organic azides with transition metal complexes with
dithiolate ligands.
Figure 1. ORTEP plot (30% probability thermal ellipsoids) of 2a with
hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (deg): Co1−N1 = 1.974(2), Co1−S1 = 2.2556(9), Co1−S2 =
2.2000(8), S1−C1 = 1.773(3), S2−C2 = 1.798(3), S2−N1 =
1.695(2); S1−Co1−S2 = 94.48(3), S1−Co1−N1 = 93.57(6), S2−
Co1−N1 = 47.54(6), Co1−S1−C1 = 104.55(9), Co1−S2−N1 =
59.21(7), Co1−S2−C2 = 107.01(8), N1−S2−C2 = 101.99(11),
Co1−N1−S2 = 73.25(8), S1−C1−C2 = 118.49(17), S2−C2−C1 =
115.01(17).
Treatment complex 1 with excess methyl azidoformate in
toluene at 80 °C for 24 h led to a five-membered chelate
metallacycle, 4a, in a yield of 60%. But when the reaction of
complex 1 with excess benzoyl azide was conducted under the
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bridged5a,14 and imido-bridged complexes,8a the generated
three-membered ring (Co1−N1−S2) is almost perpendicular
to the five-membered cobaltadithia-o-carborane ring (Co1−
S1−C1−C2−S2), which almost remained planar (within
0.034°), with the dihedral angle of 93.1° between the two
planes. The Co−S bond lengths (Co1−S2, 2.2000(8) Å, Co1−
S1, 2.2556(9) Å) are slightly longer than those in complex 1
(Co−S, 2.139(8) and 2.129(8) Å),11a but similar to alkylidene-
bridged complexes5a,14 and other imido-bridged complexes.8a
ORTEP representations of 3a and 3b with selected bond
distances and angles are shown in Figure S1 in the Supporting
Information. In 3a, the tetraazabutadiene ligand adopts a syn
conformation, with toluenesulfonyl substituents oriented on the
same sides with respect to the five-membered chelation ring,
which is planar within 0.03°. In contrast, the tetraazabutadiene
ligand in 3b adopts an anti conformation, with methanesulfonyl
substituents oriented on the opposite side with respect to the
five-membered chelation ring, which is planar within 0.01°. A
search of tetraazadiene metal complexes contained in the
Cambridge Structure Database found that all the four similar
tetraazadiene metal complexes adopt an anti conformation.18 In
the tetraaza system of 3a and 3b, the centeral N−N bond is
shorter than the lateral ones by 0.11 Å on average, which is
analogous to reported tetraazadiene metal complexes.18,19 The
average Co−N bond distance is 1.829(7) Å in both
compounds, slightly longer than those found for other
tetraazadiene cobalt complexes.20
1.316(3) Å in 4b) are also shorter than the usual C−N but
longer than the normal CN. This phenomenon indicates that
4
3
N1−C8−O1 is a conjugated π system. The five-membered
metallacyclic rings (Co1−S2−N1−C8−O1) in both com-
pounds are almost planar within 0.04° on average. Different
from the three-membered cobaltathiaziridine ring which is
almost located at a perpendicular position with respect to the
existing five-membered cobaltadithia-o-carborane ring in 2a, the
angles between the two five-membered metallacyclic rings in 4a
and 4b are 99.4° and 100.3°, respectively.
Reactivity of Imido-Bridged Adducts 2a and 2b with
Alkynes. The insertion of unsaturated organic founctional
groups such as alkynes, alkenes, or isocyanides into a metal−
heteroatom bond is a key step of transition-metal-catalyzed
heterofunctionalization of such organic substrates.21 Continu-
ous studies for decades on insertions of organometallic
complexes with unsaturated organic small molecules and their
applications in organic synthesis have experienced extremely
important development and displayed many novel structures of
the intermediate compounds and reactivity patterns.21d,f,22
Compared to the numerous insertion reactions with unsatu-
rated organic small molecules only into metal−carbon bond,23
concerning metal−nitrogen bond24 or metal−sulfur bond,25
there are very few cases of an insertion reaction occurring at
one complex which contains two active metal−heteroatom
bonds.26−28
In our case, imido-bridged adducts 2a and 2b contain both
Co−S and Co−N bonds, which may act as active sites for C
C bond insertion based on some facts as follows. First,
Herberhold’s and our groups have investigated the reactivity of
16-electron half-sandwich complexes Cp″M[E2C2B10H10] (Cp″
= η5-C5Me5, η5-C5H5 or η6-4-isopropyltoluene, E = S, Se, M =
Co, Rh, Ir, Ru or Os) with alkynes systematically and found
that the M−E (E = S, Se) bond in these complexes is very
reactive and it is easy to insert a CC bond.10,13 Second,
Nomura and co-workers8a,29 found that imido-bridged
complexes easily undergo ring-opening and imido group
transfer reactions. Additionally, DFT calculations show that
the contributions of Highest Occupied Molecular Orbital
(HOMO) and Lowest Unoccupied Molecular Orbital
(LUMO) in complexes 2a and 2b are mainly from the S
atom and the Co atom, respetively, which suggest that the S
atom can act as nucleophile while the Co center acts as electron
acceptor for further reaction (Figure 3).
A perspective view of complexes 4a and 4b is present in
Figure 2 and Figure S2 in the Supporting Information,
A terminal alkyne was chosen, methyl propiolate, which acts
as a very reactive alkyne in the reaction with Cp″M-
[E2C2(B10H10)],10a,d,e,13b reacting with 2a and 2b at room
temperature. The color of the mixture changed immediately
from green to brownish black. The reaction was complete
within one hour. After workup with chromatography, brownish
black pastes 5a and 5b were obtained in the yields of 75.2% and
69.0%, respectively. Both 5a and 5b are soluble in common
organic solvents and somewhat thermally unstable, slowly
decomposing at ambient temperature even in the solid state.
Complex 5a was characterized by X-ray crystallography, and
the ORTEP drawing is shown in Figure 4 with selected bond
distances and angles. The structure of 5a shows the expected
four-membered ring formed by insertion of the alkyne into one
Co−S bond followed by the cleavage of the other Co−S bond
to form a distorted Co−S−C−C−S−N six-membered ring. It is
well-known that asymmetric alkyne insertion into a metal−
heteroatom bond shows two possible isomers with regard to
Figure 2. ORTEP plot (30% probability thermal ellipsoids) of 4a with
hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (deg): Co1−S1 = 2.2420(10), Co1−S2 = 2.2129(9), Co1−O1
= 1.951(2), O1−C8 = 1.281(4), N1−C8 = 1.309(4), N1−S2 =
1.662(3); S1−Co1−S2 = 95.95(3), S1−Co1−O1 = 93.64(8), S2−
Co1−O1 = 82.79(7), Co1−S1−C1 = 104.00(13), Co1−S2−C2 =
104.93(11), Co1−S2−N1 = 100.91(10), N1−S2−C2 = 102.98(15),
Co1−O1−C8 = 115.8(2), S2−N1−C8 = 112.3(3), S1−C1−C2 =
117.8(2), S2−C2−C1 = 116.8(2).
respectively. The structure of both compounds shows an
unusual five-membered metallacyclic ring Co−S−N−C−O
which is generated by one azide molecule insertion Co−S
bond with the loss of N2, followed by carbonyl coordination to
the metal. In both compounds, the distances of C8−
O1(1.281(4) Å in 4a, 1.298(3) Å in 4b) are intermediate
between that expected for carbon−oxygen single and double
bonds. The distances of C8−N1(1.309(4) Å in 4a and
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Figure 3. The orbital distribution of complexes 2a (top) and 2b (bottom).
it is an important intermediate for further transformation as
evidenced by dimethyl acetylenedicarboxylate insertion ana-
logues.10d,13c In the present case, the determination of the
structure of 5a provides direct evidence for the key
intermediate and further confirms our mechanistic proposal
on metal-induced B−H activation and B−H functionalization
of the o-carborane cage.10a,d,e 1H NMR spectroscopic
resonances appearing at δ = 6.75 ppm in both compounds
are ascribed to CCH and correspond to 13C NMR signals at
δ = 127.57 and 127.82 ppm, respectively. The 13C data of
carborane (67.11 and 85.04 ppm in 5a and 67.54 and 80.30
ppm in 5b) shift to higher field than the corresponding starting
complexes (87.64 and 90.45 ppm in 2a and 88.35 and 90.31
ppm in 2b). The 11B{1H} NMR spectra of 5a and 5b exhibit
five signals approximately between δ = 2.6 and −10.5 ppm with
an intensity ratio of 1:1:2:4:2.
Similar to methyl propiolate, the reaction of 2a or 2b with
dimethyl acetylenedicarboxylate (DMAD) rapidly gave a color
change of the solution from green to brownish red and was
complete within 2 h to afford 6a or 6b in good yield. The
structure of 6a has been confirmed by X-ray crystallography
and is shown in Figure S3 in the Supporting Information. It
reveals that the alkyne has inserted into the Co−S bond rather
than the Co−N bond to give a four-membered ring, as found in
the same alkyne insertion into Cp*MS2 (M = Rh, Ir), (p-
cymene)MS2 (M = Ru, Os), and CpCoE2 (E = S, Se) half-
sandwich complexes.10a,d,13c Similar to 5a, 6a also contains a
distorted Co−S−C−C−S−N six-membered ring which shares
one Co−S bond of the existing four-membered metallacyclic
Figure 4. Molecular structure of 5a with 30% displacement ellipsoids.
All H atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Co1−S1 = 2.3068(10), Co1−N1 = 1.976(3), Co1−C8 =
1.931(3), N1−S2 = 1.681(3), S1−C9 = 1.761(4), C8−C9 = 1.329(5);
S1−Co1−N1 = 93.29(9), S1−Co1−C8 = 71.05(10), N1−Co1−C8 =
91.91(13), Co1−S1−C1 = 116.76(10), Co1−S1−C9 = 78.20(14),
C1−S1−C9 = 105.27(15), N1−S2−C2 = 102.78(15), Co1−N1−S2 =
113.90(14), Co1−N1−S3 = 122.38(16), S2−N1−S3 = 114.22(17),
S1−C1−C2 = 120.8(2), S2−C2−C1 = 120.1(2), Co1−C8−C9 =
104.3(2), S1−C9−C8 = 106.0(3).
the position of the substituent group compared to the metal
center. In the case of 5a, the structure confirms that only one
regioisomer has formed with the CO2Me group on the carbon
attached to the metal and with the hydrogen next to the
carborane cage. This regioselectivity is also reported in
cyclometalated oxazoline, pyrazole, and imine complexes23a,30
and the reaction of 1 with N-1-naphthylpropargylamide.31a
Compared to the structure of 1, an organic ligand is inserted
into each Co−S bond located at the two sides of the original
Co−S−C−C−S plane.31b,c The Co−C−C−S four-membered
ring is almost planar within 0.04° mean deviation. Very
interestingly, our previous detailed study of the reaction of 1
with methyl propiolate could not obtain a product with one
alkyne inserted into one Co−S bond, although we assumed that
1
ring (Co−S−C−C). The H NMR spectra of 6a and 6b show
the expected signals for Cp and two methoxy signals for the
nonequivalent CO2Me groups of the alkyne. Similar to 5a and
5b, signals of carborane in 13C NMR spectra appear at
approximately 67 and 86 ppm for both compounds which are
10−20 ppm upfield from the corresponding signals of starting
complexes. The same phenomenon was observed in the
addition products of complex 1 and its selenium analogue
with DMAD.13c The chemical shifts of the two olefinic carbon
atoms are similar in both compounds which appear at
approximately 123 and 155 ppm. In contrast to 5a and 5b,
which are unstable both in the solution and in solid form, 6a
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and 6b are stable in solution and solid state for at least several
months.
6b, the structures of 7a and 7b reveal that the alkyne has
inserted into the M−N bond to form a Co−C−C−N−S five-
membered ring. Furthermore, the structures of 7a and 7b show
that the hydrogen atom is located on the carbon attached to the
metal while the phenyl group is next to the original sulfonyl
The reactions of phenylacetylene with 2a and 2b were also
examined and gave yellowish brown solid 7a and 7b with 60%
isolated yield. Suitable crystals of both 7a and 7b were
successfully obtained by slow diffusion of petroleum ether into
a concentrated dichloromethane solution of the complex and
were determined by X-ray crystallography. ORTEP drawings of
7a and 7b and selected bonds and angles are shown in Figure 5
1
group, which is consistent with that H NMR spectroscopic
signal of CCH group at downfield with δ = 7.47 and 7.53
ppm, respectively. Clearly, the different insertion mode of
phenylacetylene is determined by the electronic property of the
phenyl group.
Thus reactions of 2a and 2b with methyl phenylpropiolate
were investigated in order to gain a mixed type of products. As
expected, the reactions gave two types of products 8a, 9a or 8b,
9b respectively. Further detailed studies revealed that the
formation of 8a and 9a or 8b and 9b occurs not by two
competitive processes but by subsequent transformations. This
conclusion is supported by the observations below: (a)
performing the reaction of 2a or 2b with methyl phenyl-
propiolate around half hour gave an incomplete reaction only
affording 8a or 8b; (b) stirring the dichloromethane solution of
8a or 8b at room temperature for 24 h proceeded to generate
9a or 9b in good yield (Scheme 2). These results indicate that
the formation of 8a and 8b takes place by kinetically controlled
processes while 9a and 9b are likely thermodynamic products,
which is further supported by DFT calculations (Figure S8 in
the Supporting Information). It should be noted that attempts
to obtain the analogues of 9a and 9b from 5a and 5b at room
temperature over several days or from 6a and 6b refluxing in
toluene for 24 h just led to decomposition. This anomaly is
possibly attributed to different alkynes in these insertion
reactions undergoing different reaction pathways, which lead to
different kinetic or thermodynamic products (Figures S6−S8 in
the Supporting Information).
Figure 5. Molecular structure of 7a with 30% displacement ellipsoids.
All H atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Co1−S1 = 2.2520(9), Co1−S2 = 2.1442(8), Co1−C8 =
1.927(3), N1−S2 = 1.707(2), N1−C9 = 1.454(3), C8−C9 =
1.331(4); S1−Co1−S2 = 95.26(3), S1−Co1−C8 = 92.23(8), S2−
Co1−C8 = 83.50(8), Co1−S1−C1 = 104.02(9), Co1−S2−N1 =
104.09(7), Co1−S2−C2 = 107.12(8), N1−S2−C2 = 100.23(10), S2−
N1−S3 = 111.45(12), S2−N1−C9 = 111.19(16), S3−N1−C9 =
121.36(17), S1−C1−C2 = 117.62(17), S2−C2−C1 = 115.02(16),
Co1−C8−C9 = 122.4(2), N1−C9−C8 = 117.2(2).
Although 8a, 9a and 8b, 9b are configurational isomers, they
can be readily isolated by chromatography. Furthermore, the
structures of 8a, 9a, and 9b have been determined by X-ray
and Figure S4 in the Supporting Information, respectively.
Differing from the alkyne insertion into the M−S bond in 5a−
a
Scheme 2. The Insertion Reactions of 2a and 2b with Alkynes
a
Conditions: excess alkynes, dichloromethane, room temperature, 1−12 h.
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crystallography and are shown in Figures 6 and 7 and Figure S5
in the Supporting Information. The structure of 8a is analogous
isomers. Signals of carborane appear at approximately 66 and
86 ppm in 8a and 8b but 96 and 103 ppm in 9a and 9b.
Additionally, the chemical shifts of the two olefinic carbon
atoms appear at approximately 135 and 154 ppm in 8a and 8b
but 136 and 144 ppm in 9a and 9b. Similarly, in contrast to all
the signals of 11B NMR spectra in negative values in 9a and 9b,
8a and 8b show two additional positive signals at δ = 2.60 and
0.13 ppm on average. Such difference in NMR data between
the two isomers might be explained by the exogenous ligand
falling in a different chemical environment, where 8a and 8b
possess a Co−C−C−S four-membered ring and 9a and 9b
contain a Co−C−C−N−S five-membered ring.
Surprisingly, the corresponding reaction of 2a and 2b with
tert-butylacetylene affords a new type of product, 10a and 10b,
within 4 h with an isolated yield over 85%. Unlike other
complexes we present in this paper with good solubility in
dichloromethane, chloroform, or tetrahydrofuran, 10a and 10b
are only partially soluble in these solvents. Additionally, 10a
and 10b are not stable in solution or in the solid state, and can
easily decompose in solution within several hours.
Figure 6. Molecular structure of 8a with 30% displacement ellipsoids.
All H atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Co1−S2 = 2.3022(16), Co1−N1 = 1.960(4), Co1−C8 =
1.952(5), N1−S1 = 1.681(4), S2−C9 = 1.802(5), C8−C9 = 1.358(6);
S2−Co1−N1 = 93.67(12), S2−Co1−C8 = 71.24(14), N1−Co1−C8
= 91.28(19), N1−S1−C1 = 104.0(2), Co1−S2−C2 = 116.44(16),
Co1−S2−C9 = 79.61(15), C2−S2−C9 = 107.9(2), Co1−N1−S3 =
125.1(2), S1−N1−S3 = 114.1(3), Co1−N1−S1 = 112.7(2), S1−C1−
C2 = 121.1(3), S2−C2−C1 = 120.2(3), Co1−C8−C9 = 105.3(3),
S2−C9−C8 = 103.3(4).
The structure of 10b has been determined by X-ray
crystallography and is shown in Figure 8 with selected bond
Figure 8. Molecular structure of 10b with 30% displacement ellipsoids.
All H atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Co1−S1 = 2.2417(8), Co1−S2 = 2.1851(7), Co1−C9 =
1.962(2), N1−S2 = 1.673(2), N1−C9 = 1.469(3); S1−Co1−S2 =
96.16(3), S1−Co1−C9 = 92.17(8), S2−Co1−C9 = 74.32(7), Co1−
S1−C1 = 103.88(10), Co1−S2−N1 = 82.42(7), Co1−S2−C2 =
105.38(8), N1−S2−C2 = 104.77(11), S2−N1−S3 = 121.65(13), S2−
N1−C9 = 105.94(15), S3−N1−C9 = 131.41(16), S1−C1−C2 =
118.06(18), S2−C2−C1 = 115.76(16), Co1−C9−N1 = 95.95(14).
Figure 7. Molecular structure of 9a with 30% displacement ellipsoids.
All H atoms are omitted for clarity. Selected bond distances (Å) and
angles (deg): Co1−S1 = 2.2558(10), Co1−S2 = 2.1416(9), Co1−C8
= 1.940(3), N1−S2 = 1.712(2), N1−C9 = 1.458(4), C8−C9 =
1.337(4); S1−Co1−S2 = 95.85(4), S1−Co1−C8 = 91.70(10), S2−
Co1−C8 = 84.79(9), Co1−S1−C1 = 103.07(14), Co1−S2−N1 =
102.80(9), Co1−S2−C2 = 107.11(11), N1−S2−C2 = 101.88(14),
S2−N1−S3 = 111.06(14), S2−N1−C9 = 112.8(2), S3−N1−C9 =
123.0(2), S1−C1−C2 = 118.5(3), S2−C2−C1 = 114.5(2), Co1−C8−
C9 = 121.2(2), N1−C9−C8 = 116.9(3).
lengths and angles. Unlike carbon−carbon triple bond insertion
into metal−heteroatom in the reported literature13c,g,23a,24a and
other compounds in the present text, the structure of 10b
shows that the terminal carbon of tert-butylacetylene inserts
into a Co−N bond to form a Co−C−N−S four-membered ring
accompanied by a 1,2-hydrogen shift to an internal carbon.
Similar proton transfer occurrs commonly in many vinylidene
complexes.32 Here the insertion pattern in 10b is rare and the
nature of the alkyne perhaps plays an important role in the
formation of the final product. 1H NMR spectra of 10a and 10b
show the characteristic resonances for the groups of Ts, Ms,
tBu, and Cp. In particular, the singlet signals at δ = 6.00 and
5.51 ppm are ascribed to CCH in both compounds, which
correspond to 13C NMR signals at δ = 120.41 and 125.85 ppm,
respectively.
to 5a and 6a discussed above, with regioselectivity of the
CO2Me group on the carbon attached to the metal and with the
phenyl group next to the carborane cage. Addtionally, 9a and
9b have the same structure pattern as 7a and 7b except for a
CO2Me group replacing a hydrogen atom on the carbon
1
attached to the metal. The H NMR spectra of 8a and 8b are
similar to those of their isomers 9a and 9b except that the
signal for methoxy is shifted ∼0.5 ppm upfield of the latter. The
13C NMR data have shown some differences between the two
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Scheme 3. Proposed Mechanisms for the Formation of 5a−10b
Mechanistic Considerations. The different behavior of
alkyne insertion into complexes 2a and 2b suggests that the
insertion process may undergo different reaction pathways.
Alkyne insertion into a Co−S or Co−N bond can be
considered as a process of S or N atom nucleophilic addition
to the incoming alkyne. Thus, comparison of the nucleophil-
icity of the S and N atoms in 2a and 2b is very important to
these insertion reactions. As we can see from Figure 3, the
contribution of HOMO orbital is mainly from the S atom,
although partial contribution of the HOMO−1 orbital derives
from the N atom. We can conclude from the orbital
calculations that the S atom has higher nucleophilicity than
the N atom in complexes 2a and 2b, and the S atom
preferentially acts as the nucleophile. The experimental results
show that different kinds of products were obtained where the
S or N atom acts as nucleophile. We speculate that it may be
attributed to the thermodynamically vs kinetically controlled
process, i.e., the S atom has the higher nucleophilicity, whereas
products resulting from N attack are stable under some
conditions. To gain full insight into the mechanism of the
alkyne insertion reactions, related calculations were conducted
and fit the experimental results (Figures S6−S8 in the
Supporting Information).
transition state II yields 5a−6b directly due to the kinetically
preferred processes or 8a, 8b for their considerably kinetical
stability. Complexes 8a and 8b can easily isomerize to 9a and
9b as a result of the thermodynamically preferred processes
(Figure S8 in the Supporting Information). For phenyl-
acetylene, the transition state II may also afford intermediate
III, which is analogous to 5a−6b and 8a, 8b but cannot be
isolated experimentally. In this case, intermediate III readily
rearranges to thermodynamically stable products 7a and 7b.
These subsequent processes are driven by the formation of the
lowest energy product among all the possible products due to
its being a thermodynamically controlled reaction (Figure S7 in
the Supporting Information). Alternatively, for tert-butylacety-
lene, its pathway to form 10a or 10b might be quite different
from the former examples. From alkyne species I, the system
can eventually convert into vinylidene derivatives IV via a
hydride alkynyl or direct 1,2-hydrogen shift of the terminal C−
H of the alkyne, which was proposed or even evidenced in the
formation of many other vinylidene complexes.32,33
A
nucleophilic addition attacked by nitrogen at the terminal
carbon of the alkyne (close to metal center) affords a three-
membered transition state V, which could give rise to 10a or
10b after further rearrangement.
Thus, the experimental results and computational studies
allow us to assume the mechanistic suggestions for the
generation of 5a−10b, which is depicted in Scheme 3. Initial
alkyne coordination to metal center gives species I, which is
well-known as the first step of the interaction between alkyne
and the metal fragment. Alkyne species I has two isomers with
the different direction of the subsitutent groups according the
nature of the alkyne, but only one isomer is preferred to form
thermodynamically stable product (see Figures S6−S8 in the
Supporting Information). From alkyne species I, there are two
reaction pathways to generate final products. One pathway is
that alkyne species I can be easily intramolecular attacked by
one S atom due to its high nucleophilicity to form a four-
membered transition state II, which is similar to alkyne addition
to the 16-electron complexes previously reported.10,13 The
CONCLUSIONS
■
In summary, we have established the reactivity of the 16-
electron half-sandwich complex 1 toward different types of
organic azides, and three different coordination modes of the
products were captured. Compared to previous work which
showed that complex 1 presents a range of reactivities toward
alkynes and diazo compounds,10,13,14 the results presented here
suggest that complex 1 is not a good precursor to react with
organic azides for further functionalization. The insertion
reaction of imido-bridged adducts 2a and 2b with alkynes
under mild conditions was also investigated. These insertion
reactions give three types of products via alkyne addition to
Co−S or Co−N bond according to the nature of alkynes. The
mechanism of such insertion reactions is proposed and
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chromatography using silica gel (dichloromethane/ethyl ether = 10/1,
supported by DFT calculations. The coordination modes of the
insertion products reported in the present study may provide
evidence for the existence of some intermediates in some metal-
induced catalytic cycles involving insertion of carbon−carbon
multiple bonds and be a useful method to construct new
carbon−heteroatom (C−E) bonds of the existing organo-
metallic compounds.
v/v) to give complex 4a or 4b.
1
4a (245.6 mg, 60.7%); green solid. Mp: 268−269 °C. H NMR
(CDCl3, ppm): 5.55 (s, 5H, C5H5), 3.83 (s, 3H, OCH3). 11B{1H}
NMR(CDCl3, ppm): −1.6 (2B), −2.5 (1B), −4.5 (1B), −6.0 (4B),
−7.8 (1B), −8.8 (1B). 13C NMR (CDCl3, ppm): 58.52 (OCH3),
86.08 (Cp), 96.24 (carborane), 103.50 (carborane), 184.23 (CO).
ESI-MS (m/z): 404.17 (77%) [M]+. IR (KBr, cm−1): 2593.5 (νB−H),
1736.6 (νCO). Elemental analysis calcd (%) for C9H18B10NO2S2Co: C
26.80, H 4.50, N 3.47. Found: C 26.46, H 4.61, N 3.29.
EXPERIMENTAL SECTION
■
4b (22.2 mg, 4.9%): yellow-green solid. Mp: 282−284 °C. 1H NMR
(CDCl3, ppm): 8.02 (d, J = 7.5 Hz, 2H, ArH), 7.48 (t, J = 7.5 Hz, 1H,
ArH), 7.37 (t, J = 7.5 Hz, 2H, ArH), 5.57 (s, 5H, C5H5). 11B{1H}
NMR(CDCl3, ppm): −1.2 (2B), −2.3 (1B), −4.4 (1B), −5.9 (4B),
−7.8 (1B), −8.7 (1B). 13C NMR (CDCl3, ppm): 86.50 (Cp), 95.93
(carborane), 104.37 (carborane), 128.13 (CH, Ph), 130.03 (CH, Ph),
131.66 (C, Ph), 131.90 (CH, Ph), 186.50 (CO). ESI-MS (m/z):
449.17 (21%) [M]+, 450.25 (37%) [M + H]+. IR (KBr, cm−1): 2588.2
(νB−H), 1740.2 (νCO). Elemental analysis calcd (%) for
C14H20B10NOS2Co: C 37.41, H 4.48, N 3.12. Found: C 36.99, H
4.66, N 3.27.
General Procedures. nBuLi (2.0 M in hexanes, Aldrich) was used
as supplied. CpCo(CO)I2,34 CpCo(S2C2B10H10),11a and azides35 were
prepared by literature procedures. All reactions were carried out under
argon by using standard Schlenk techniques. All solvents were dried
and deoxygenated prior to use. Diethyl ether, tetrahydrofuran, and
petroleum ether were refluxed and distilled over sodium/benzophe-
none under nitrogen. CH2Cl2 was distilled over CaH2 under nitrogen.
The NMR measurements were performed on a Bruker DRX 500
spectrometer. Chemical shifts were given with respect to CHCl3/
1
CDCl3 (δ H = 7.24 ppm; δ 13C = 77.0 ppm) and external Et2O·BF3
(δ 11B = 0 ppm). The IR spectra were recorded on a Bruker Vector 22
spectrophotometer with KBr pellets in the region of 4000−400 cm−1.
The C, H, and N microanalyses were carried out with an Elementar
Vario EL III elemental analyzer. Mass data were determined with the
LCQ (ESI-MS, Thermo Finnigan) mass spectrometer.
Reactions of 2a or 2b with Alkynes. General Procedures. To
a solution of 2a (75 mg, 0.15 mmol) or 2b (64 mg, 0.15 mmol) in
dichloromethane (15 mL) was added the corresponding alkyne (1.5
mmol). The mixture was stirred at room temperature for 1−12 h. The
solvent was then removed under reduced pressure, and the residue
obtained was dissolved in the minimum amount of dichloromethane
for flash chromatographic separation on silica gel in a gradient eluting
manner (petroleum ether/dichloromethane, 2:1, 1:1, 1:3 and then
dichloromethane/ethyl ether, 10:1) to give the target compounds.
5a (65.7 mg, 75.2%): brownish-black solid. Mp: 86 °C (dec).1H
NMR (CDCl3, ppm): 7.66 (d, J = 8 Hz, 2H, ArH), 7.23 (d, J = 8 Hz,
2H, ArH), 6.75 (s, 1H, CCH), 5.46 (s, 5H, C5H5), 3.96 (s, 3H,
OCH3), 2.39 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): 2.6 (1B),
0.1 (1B), −4.3 (2B), −8.3 (4B), −10.5 (2B). 13C NMR (CDCl3,
ppm): 21.45 (CH3), 52.42 (OCH3), 67.11 (carborane), 85.04
(carborane), 85.35 (Cp), 127.57 (CCH), 128.53 (CH, Ph),
128.89 (CH, Ph), 136.28 (C, Ph), 142.84 (C, Ph), 159.00 (C
CH), 167.46 (CO). ESI-MS (m/z): 584.25 (43%) [M + H]+. IR
(KBr, cm−1): 2586 (νB−H), 1713 (νCO). Elemental analysis calcd (%)
for C18H26B10NO4S3Co: C 37.04, H 4.49, N 2.40. Found: C 37.22, H
4.38, N 2.55.
Reaction of 1 with Sulfonyl Azides. Complex 1 (265 mg, 0.8
mmol) was treated with p-toluenesulfonyl azide (790 mg, 4 mmol) or
methanesulfonyl azide (485 mg, 4 mmol) under reflux in dichloro-
methane (40 mL) under Ar for 18 h. The red-brown mixture turned to
dark-green. The solvent was then removed, and the residue was
chromatographed on silica (dichloromethane/ethyl ether, 20:1) to
give 2a or 2b as a green solid. If the reactions were heated at 80 °C in
toluene for 8 h, 3a or 3b was obtained as a yellow solid.
1
2a (340.5 mg, 85.1%): green solid. Mp: 188−189 °C. H NMR
(CDCl3, ppm): 7.87 (d, J = 7.5 Hz, 2H, ArH), 7.38 (d, J = 7.5 Hz, 2H,
ArH), 5.62 (s, 5H, C5H5), 2.47 (s, 3H, CH3). 11B{1H} NMR (CDCl3,
ppm): −2.1 (2B), −4.0 (1B), −4.9 (2B), −7.2 (4B), −8.9 (1B). 13C
NMR (CDCl3, ppm): 21.76 (CH3), 83.92 (Cp), 87.64 (carborane),
90.45 (carborane), 127.77 (CH, Ph), 129.73 (CH, Ph), 136.41 (C,
Ph), 144.88 (C, Ph). ESI-MS (m/z): 501.17 (100%) [M + H]+. IR
(KBr, cm−1): 2583.5 (νB−H). Elemental analysis calcd (%) for
C14H22B10NO2S3Co: C 33.66, H 4.44, N 2.80. Found: C 33.32, H
4.59, N 2.92.
1
5b (52.5 mg, 69.0%): brownish-black solid. Mp: 78 °C (dec). H
1
NMR (CDCl3, ppm): 6.75 (s, 1H, CCH), 5.51 (s, 5H, C5H5), 3.87
(s, 3H, OCH3), 2.82 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): 2.9
(1B), 0.8 (1B), −4.0 (2B), −8.1 (4B), −10.6 (2B). 13C NMR (CDCl3,
ppm): 38.56 (CH3), 52.46 (OCH3), 67.54 (carborane), 80.30
(carborane), 85.44 (Cp), 127.82 (CCH), 159.00 (CCH),
167.68 (CO). ESI-MS (m/z): 509.33 (100%) [M + H]+. IR
(KBr, cm−1): 2589.1 (νB−H), 1715.2 (νCO). Elemental analysis calcd
(%) for C12H22B10NO4S3Co: C 28.40, H 4.37, N 2.76. Found: C
28.62, H 4.54, N 2.57.
2b (245.2 mg, 72.4%): green solid. Mp: 176−178 °C. H NMR
(CDCl3, ppm): 5.55 (s, 5H, C5H5), 3.29 (s, 3H, CH3). 11B{1H}
NMR(CDCl3, ppm): −1.8 (2B), −4.2 (3B), −6.9 (4B), −8.6 (1B).
13C NMR (CDCl3, ppm): 42.19 (CH3), 84.06 (Cp), 88.35
(carborane), 90.31 (carborane). ESI-MS (m/z): 423.50 (10%) [M]+.
IR (KBr, cm−1): 2588.5 (νB−H). Elemental analysis calcd (%) for
C8H18B10NO2S3Co: C 22.69, H 4.28, N 3.31. Found: C 22.35, H 4.19,
N 3.44.
1
3a (33.5 mg, 45.6%): yellow solid. Mp: 180−182 °C. H NMR
1
6a (84.1 mg, 87.3%): brownish-red solid. Mp: 117−119 °C. H
(CDCl3, ppm): 7.97 (d, J = 8 Hz, 2 × 2H, ArH), 7.29 (d, J = 8 Hz, 2 ×
2H, ArH), 5.94 (s, 5H, C5H5), 2.40 (s, 2 × 3H, CH3). 13C NMR
(CDCl3, ppm): 21.61 (CH3), 81.88 (Cp), 128.94 (CH, Ph), 129.71
(CH, Ph), 135.14 (C, Ph), 144.69 (C, Ph). ESI-MS (m/z): 490.75
(31%) [M + H]+, 512.75 (100%) [M + Na]+ . IR (KBr, cm−1): 1598.5
(νNN). Elemental analysis calcd (%) for C19H19N4O4S2Co: C 46.53,
H 3.90, N 11.42. Found: C 46.28, H 4.09, N 11.23.
NMR (CDCl3, ppm): 7.72 (d, J = 8 Hz, 2H, ArH), 7.23 (d, J = 8 Hz,
2H, ArH), 5.61 (s, 5H, C5H5), 4.03 (s, 3H, OCH3), 3.80 (s, 3H,
OCH3), 2.38 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): 3.1 (1B),
0.3 (1B), −4.9 (2B), −8.4 (4B), −10.7 (2B). 13C NMR (CDCl3,
ppm): 21.52 (CH3), 52.61 (OCH3), 52.87 (OCH3), 67.01
(carborane), 86.35 (carborane), 86.72 (Cp), 123.10 (CC), 128.94
(CH, Ph), 129.12 (CH, Ph), 135.21 (C, Ph), 143.24 (C, Ph), 155.60
(CC), 171.06 (CO), 187.26 (CO). ESI-MS (m/z): 641.33
(6%) [M]+, 665.17 (100%) [M + Na]+. IR (KBr, cm−1): 2583.3
(νB−H), 1714.8 (νCO). Elemental analysis calcd (%) for
C20H28B10NO6S3Co: C 37.44, H 4.40, N 2.18. Found: C 37.53, H
4.56, N 1.97.
1
3b (24.5 mg, 48.2%): yellow solid. Mp: 173−174 °C. H NMR
(CDCl3, ppm): 5.93 (s, 5H, C5H5), 3.46 (s, 2 × 3H, CH3). 13C NMR
(CDCl3, ppm): 40.61 (CH3), 81.89 (Cp). ESI-MS (m/z): 338.08
(34%) [M]+. IR (KBr, cm−1): 1620.6 (νNN). Elemental analysis calcd
(%) for C7H11N4O4S2Co: C 24.86, H 3.28, N 16.56. Found: C 24.62,
H 3.42, N 16.33.
1
6b (59.0 mg, 69.5%): brownish-red solid. Mp: 112−113 °C. H
Reaction of 1 with Methyl Azidoformate or Benzoyl Azide. A
mixture of complex 1 (330 mg, 1 mmol) and methyl azidoformate
(506 mg, 5 mmol) or benzoyl azide (735 mg, 5 mmol) was heated at
80 °C in toluene for 24 h. The red-brown mixture turned to green.
The solvent was removed, and the crude product was purified by flash
NMR (CDCl3, ppm): 5.54 (s, 5H, C5H5), 3.93 (s, 3H, OCH3), 3.82 (s,
3H, OCH3), 2.82 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): 3.3
(1B), 0.6 (1B), −4.6 (2B), −7.9 (4B), −10.3 (1B), −12.3 (1B). 13C
NMR (CDCl3, ppm): 39.15 (CH3), 52.60 (OCH3), 52.98 (OCH3),
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67.33 (carborane), 86.75 (Cp), 86.93 (carborane), 123.12 (CC),
155.52 (CC), 170.84 (CO), 186.63 (CO). ESI-MS (m/z):
567.25 (18%) [M + H]+, 589.17 (100%) [M + Na]+. IR (KBr, cm−1):
2584.7 (νB−H), 1715.9 (νCO). Elemental analysis calcd (%) for
C14H24B10NO6S3Co: C 29.73, H 4.28, N 2.48. Found: C 29.48, H 4.55,
N 2.67.
3H, OCH3), 2.97 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): −1.0
(3B), −4.3 (3B), −7.0 (3B), −9.1 (1B). 13C NMR (CDCl3, ppm):
43.01 (CH3), 51.68 (OCH3), 89.63 (Cp), 96.50 (carborane), 102.52
(carborane), 128.44 (CH, Ph), 129.13 (CH, Ph), 134.65 (C, Ph),
136.56 (CC), 143.51 (CC), 172.96 (CO). ESI-MS (m/z):
585.00 (15%) [M + H]+, 607.08 (100%) [M + Na]+. IR (KBr, cm−1):
2591.1 (νB−H), 1698.1 (νCO). Elemental analysis calcd (%) for
C18H26B10NO4S3Co: C 37.04, H 4.49, N 2.40. Found: C 36.79, H 4.33,
N 2.55.
1
7a (52.8 mg, 58.6%): yellowish-brown solid. Mp: 208−209 °C. H
NMR (CDCl3, ppm): 7.72 (d, J = 8 Hz, 2H, ArH), 7.49 (d, J = 7 Hz,
2H, ArH), 7.47 (s, 1H, CCH), 7.41 (d, J = 8 Hz, 2H, ArH), 7.35 (t,
J = 7 Hz, 2H, ArH), 7.29 (t, J = 7 Hz, 1H, ArH), 4.83 (s, 5H, C5H5),
2.48 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): −0.8 (3B), −3.9
(2B), −5.0 (2B), −6.8 (3B). 13C NMR (CDCl3, ppm): 21.70 (CH3),
88.35 (Cp), 94.97 (carborane), 103.49 (carborane), 126.80 (CH, Ph),
127.80 (CH, Ph), 127.91 (CH, Ph), 128.72 (CH, Ph), 129.73 (CH,
Ph), 133.76 (C, Ph), 136.30 (CCH), 139.70 (CCH), 145.87 (C,
Ph), 146.80 (C, Ph). ESI-MS (m/z): 602.17 (3%) [M]+, 1267.17
(100%) [2M + Na + MeCN]+. IR (KBr, cm−1): 2567.2 (νB−H).
Elemental analysis calcd (%) for C22H28B10NO2S3Co: C 43.91, H 4.69,
N 2.33. Found: C 43.63, H 4.53, N 2.17.
1
10a (75.7 mg, 86.8%): brownish-red solid. Mp: 142−143 °C. H
NMR (CDCl3, ppm): 7.90 (d, J = 8 Hz, 2H, ArH), 7.48 (d, J = 8 Hz,
2H, ArH), 6.00 (s, 1H, CCH), 4.69 (s, 5H, C5H5), 2.54 (s, 3H,
CH3), 1.08 (s, 9H, 3 × CH3). 11B{1H} NMR(CDCl3, ppm): −1.1
(2B), −3.5 (1B), −6.0 (4B), −7.1 (3B). 13C NMR (CDCl3, ppm):
t
t
21.77 (CH3), 31.13 (CH3, Bu), 38.43 (C, Bu), 87.56 (Cp), 98.57
(carborane), 99.69 (carborane), 120.41 (CCH), 128.12 (CH, Ph),
129.77 (CH, Ph), 134.83 (C, Ph), 139.12 (CCH), 145.89 (C, Ph).
ESI-MS (m/z): 583.08 (28%) [M + H]+, 620.92 (100%) [M + K]+. IR
(KBr, cm−1): 2565.3 (νB−H). Elemental analysis calcd (%) for
C20H32B10NO2S3Co: C 41.29, H 5.54, N 2.41. Found: C 41.57, H
5.66, N 2.30.
1
7b (42.0 mg, 53.3%): yellowish-brown solid. Mp: 168−170 °C. H
NMR (CDCl3, ppm): 7.53 (s, 1H, CCH), 7.47 (d, J = 8 Hz, 2H,
ArH), 7.37 (t, J = 7.5 Hz, 2H, ArH), 7.30 (t, J = 7.5 Hz, 1H, ArH),
5.31 (s, 5H, C5H5), 3.12 (s, 3H, OCH3). 11B{1H} NMR(CDCl3,
ppm): −0.8 (3B), −3.9 (1B), −4.7 (2B), −6.8 (3B), −9.3 (1B). 13C
NMR (CDCl3, ppm): 41.87 (CH3), 88.76 (Cp), 95.82 (carborane),
102.58 (carborane), 126.78 (CH, Ph), 128.13 (CH, Ph), 128.35 (CH,
Ph), 135.75 (CCH), 139.80 (CCH), 145.71 (C, Ph). ESI-MS
(m/z): 527.08 (22%) [M + H]+. IR (KBr, cm−1): 2571.0 (νB−H).
Elemental analysis calcd (%) for C16H24B10NO2S3Co: C 36.56, H 4.60,
N 2.66. Found: C 36.33, H 4.85, N 2.49.
1
10b (67.7 mg, 89.3%): brownish-red solid. Mp: 133−134 °C. H
NMR (CDCl3, ppm): 5.51 (s, 1H, CCH), 5.24 (s, 5H, C5H5), 3.24
(s, 3H, CH3), 1.13 (s, 9H, 3 × CH3) . 11B{1H} NMR(CDCl3, ppm):
−1.1 (2B), −3.5 (1B), −5.8 (4B), −7.1 (2B), −8.6 (1B). 13C NMR
(CDCl3, ppm): 31.29 (CH3, tBu), 39.89 38.43 (C, tBu), 41.38 (CH3),
87.97 (Cp), 99.03 (carborane), 99.42 (carborane), 125.85 (CCH),
138.99 (CCH). ESI-MS (m/z): 507.00 (27%) [M + H]+, 544.00
(100%) [M + K]+. IR (KBr, cm−1): 2568.6 (νB−H). Elemental analysis
calcd (%) for C14H28B10NO2S3Co: C 33.26, H 5.58, N 2.77. Found: C
33.53, H 5.39, N 2.91.
1
8a (72 mg, 72.7%): brownish-black solid. Mp: 175−176 °C. H
NMR (CDCl3, ppm): 7.84 (d, J = 8 Hz, 2H, ArH), 7.49 (d, J = 7 Hz,
2H, ArH), 7.37 (m, 3H, ArH), 7.27 (d, J = 8 Hz, 2H, ArH), 5.57 (s,
5H, C5H5), 3.93 (s, 3H, OCH3), 2.41 (s, 3H, CH3). 11B{1H}
NMR(CDCl3, ppm): 2.5 (1B), 0.1 (1B), −3.9 (2B), −8.6 (4B), −10.9
(2B). 13C NMR (CDCl3, ppm): 21.42 (CH3), 52.12 (OCH3), 66.33
(carborane), 85.51 (carborane), 86.28 (Cp), 128.21 (CH, Ph), 128.27
(CH, Ph), 128.46 (CH, Ph), 128.84 (CH, Ph), 129.06 (CH, Ph),
135.39 (CC), 136.68 (C, Ph), 138.54 (C, Ph), 142.76 (C, Ph),
154.06 (CC), 168.74 (CO). ESI-MS (m/z): 659.17 (7%) [M]+,
682.17 (21%) [M + Na]+, 1342.08 (100%) [2M + Na]+. IR (KBr,
cm−1): 2580.7 (νB−H), 1702.4 (νCO). Elemental analysis calcd (%) for
C24H30B10NO4S3Co: C 43.69, H 4.58, N 2.12. Found: C 43.91, H 4.65,
N 2.03.
Transformations of 8a and 8b to 9a and 9b. A solution of 8a
or 8b (0.05 mmol) in CH2Cl2 (10 mL) was stirred for 24 h at room
temperature. After removal of the solvent, the residue was chromato-
graphed on silica, and elution with dichloromethane gave 9a (25.3 mg,
76.7%) or 9b (20.2 mg, 69.2%).
Computational Details. Molecular geometries of model com-
plexes were optimized using the M0636 functional. The M06
functional is a new hybrid meta exchange-correlation functional,
which has been shown to accurately describe transition metal catalyzed
organic transformations in recent reports.37 The 6-31G(d) basis set
was used for C, N, O, and S atoms, and the 6-31G basis set was used
for the B and H atoms. The effective core potentials (ECPs) of Hay
and Wadt with a double-ξ basis set (LanL2DZ)38 were used for Co.
Frequency calculations at the same level of theory have also been
performed to identify all of the stationary points as minima (zero
imaginary frequency) or transition states (one imaginary frequency).
Intrinsic reaction coordinates (IRC)39 were calculated for the
transition states to confirm that such structures indeed connect two
relevant minima. All calculations were performed with the Gaussian
0940 software package.
X-ray Crystal Structure Determinations. Crystals suitable for X-
ray analysis were obtained by the slow evaporation of a solution in
petroleum ether/dichloromethane. Diffraction data were collected on a
Bruker SMART Apex II CCD diffractometer by means of graphite-
monochromated Mo Kα (λ = 0.71073 Å) radiation. During collection
of the intensity data, no significant decay was observed. The intensities
were corrected for Lorentz polarization effects and empirical
absorption by using the SADABS program.41 The structures were
solved by direct methods with the SHELXS-97 program42 and were
refined on F2 with SHELXTL (version 6.14).43 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were included in
calculated positions and were refined using a riding model. A summary
of crystal data, data collection parameters, and structure refinement
details is given in Tables S1 and S2 in the Supporting Information.
CCDC 869405−869417 for the complexes 2a, 3a, 3b, 4a, 4b, 5a, 6a,
7a, 7b, 8a, 9a, 9b, and 10b contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.
uk/data_request/cif.
1
8b (61.5 mg, 70.3%): brownish-black solid. Mp: 161−163 °C. H
NMR (CDCl3, ppm): 7.49 (d, J = 7 Hz, 2H, ArH), 7.38 (m, 3H, ArH),
5.54 (s, 5H, C5H5), 3.87 (s, 3H, OCH3), 2.90 (s, 3H, CH3). 11B{1H}
NMR(CDCl3, ppm): 2.7 (1B), 0.2 (1B), −3.8 (1B), −5.7 (1B), −8.4
(4B), −10.7 (1B), −12.2 (1B). 13C NMR (CDCl3, ppm): 39.67
(CH3), 52.23 (OCH3), 66.64 (carborane), 85.96 (carborane), 86.37
(Cp), 127.82 (CH, Ph), 128.53 (CH, Ph), 129.25 (CH, Ph), 135.20
(CC), 137.30 (C, Ph), 153.84 (CC), 169.20 (CO). ESI-MS
(m/z): 585.17 (20%) [M + H]+, 607.08 (78%) [M + Na]+, 1189.92
(100%) [2M + Na]+. IR (KBr, cm−1): 2583.8 (νB−H), 1703.9 (νCO).
Elemental analysis calcd (%) for C18H26B10NO4S3Co: C 37.04, H 4.49,
N 2.40. Found: C 37.26, H 4.69, N 2.23.
1
9a (15.1 mg, 15.2%): brownish-red solid. Mp: 235−237 °C. H
NMR (CDCl3, ppm): 7.64 (d, J = 8 Hz, 2H, ArH), 7.38 (d, J = 8 Hz,
2H, ArH), 7.32 (m, 5H, ArH), 5.09 (s, 5H, C5H5), 3.36 (s, 3H,
OCH3), 2.48 (s, 3H, CH3). 11B{1H} NMR(CDCl3, ppm): −0.9 (3B),
−4.3 (4B), −6.8 (3B). 13C NMR (CDCl3, ppm): 21.74 (CH3), 51.69
(OCH3), 89.39 (Cp), 95.87 (carborane), 102.98 (carborane), 127.94
(3 × CH, Ph), 128.60 (CH, Ph), 129.91 (CH, Ph), 134.19 (C, Ph),
135.34 (C, Ph), 136.25 (CC), 144.30 (CC), 146.11(C, Ph),
173.51 (CO). ESI-MS (m/z): 661.00 (30%) [M + H]+, 683.08
(100%) [M + Na]+. IR (KBr, cm−1): 2597.9 (νB−H), 1692.6 (νCO).
Elemental analysis calcd (%) for C24H30B10NO4S3Co: C 43.69, H 4.58,
N 2.12. Found: C 43.38, H 4.46, N 1.97.
1
9b (14.5 mg, 16.5%): brownish-red solid. Mp: 216−217 °C. H
NMR (CDCl3, ppm): 7.39 (m, 5H, ArH), 5.47 (s, 5H, C5H5), 3.39 (s,
6666
dx.doi.org/10.1021/om300735d | Organometallics 2012, 31, 6658−6668

Organometallics
Article
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ASSOCIATED CONTENT
* Supporting Information
■
S
The structural views of complexes 3a, 3b, 4b, 6a, 7b, and 9b,
potential energy profiles and corresponding optimized
structures calculated for the insertion reactions, X-ray crystallo-
graphic data and the details of data collection and structural
refinements, and CIF and checkcif files giving X-ray crystallo-
graphic data for the structural determinations of 2a, 3a, 3b, 4a,
4b, 5a, 6a, 7a, 7b, 8a, 9a, 9b, and 10b. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hyan1965@nju.edu.cn; htzhao@tju.edu.cn.
■
(12) (a) Jin, G. X. Coord. Chem. Rev. 2004, 248, 587. (b) Jin, G. X.;
Wang, J. Q.; Zhang, C.; Weng, L. H.; Herberhold, M. Angew. Chem.,
Int. Ed. 2005, 44, 259. (c) Wang, J. Q.; Cai, S. Y.; Jin, G. X.; Weng, L.
H.; Herberhold, M. Chem.Eur. J. 2005, 11, 7342. (d) Cai, S. Y.; Lin,
Y. J.; Jin, G. X. Dalton Trans. 2006, 912. (e) Liu, S.; Han, Y. F.; Jin, G.
X. Chem. Soc. Rev. 2007, 36, 1543. (f) Meng, X.; Wang, F. S.; Jin, G. X.
Coord. Chem. Rev. 2010, 254, 1260.
(13) (a) Xu, B. H.; Wu, D. H.; Li, Y. Z.; Yan, H. Organometallics
2007, 26, 4344. (b) Xu, B. H.; Tao, J. C.; Li, Y. Z.; Li, S. H.; Yan, H.
Organometallics 2008, 27, 334. (c) Xu, B. H.; Peng, X. Q.; Li, Y. Z.;
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (20925104, 21021062, 20872109,
20702037 and 20834002), the National Basic Research
Program of China (2010CB923303), the Natural Science
Foundation of Jiangsu Province (BK2010052), the Ministry of
Education of China (20090091110015), the Scientific Research
Foudation of Graduate School of Nanjing University
(2010CL04) and Innovation Foundation of Tianjin University.
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