Electrophilic substitution reactions of metallabenzynes

Article abstract of DOI:10.1021/ja207315h

The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)=C(CH₃)C(R)=CH)Cl₂(PPh₃) ₂ (R = SiMe₃, H) were studied. These metallabenzynes react with electrophilic reagents, including Br₂

Full text of DOI:10.1021/ja207315h

ARTICLE
pubs.acs.org/JACS
Electrophilic Substitution Reactions of Metallabenzynes
Wai Yiu Hung, Bin Liu, Wangge Shou, Ting Bin Wen, Chuan Shi, Herman H.-Y. Sung, Ian D. Williams,
Zhenyang Lin,* and Guochen Jia*
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
S Supporting Information
b
ABSTRACT: The electrophilic substitution reactions of me-
tallabenzynes Os(tCC(R)dC(CH3)C(R)dCH)Cl2(PPh3)2
(R = SiMe3, H) were studied. These metallabenzynes react with
electrophilic reagents, including Br2, NO2BF4, NOBF4, HCl/
H2O2, and AlCl3/H2O2 to afford the corresponding bromina-
tion, nitration, nitrosation, and chlorination products. The
reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes
exhibit aromatic properties.
Scheme 1
’ INTRODUCTION
There has been much interest in the chemistry of transition-
metal-containing metallaaromatics. The chemistry of transition-
metal-containing metallabenzenes,1 in particular, has attracted
considerable recent attention. Previous investigations have led to
the isolation and characterization of an impressive number of
stable metallabenzenes, especially those of osmium,2ꢀ4 iridium,5ꢀ8
platinum,9 ruthenium,10,11 and rhenium.12 The structural para-
meters as well as the NMR (1H and 13C) data associated with the
metallabenzene ring suggest that metallabenzenes have aromatic
character. The fact that metallabenzenes have chemical properties
similar to those of benzene has also been confirmed experimen-
tally through reactivity studies. For example, it has been demon-
strated that metallabenzenes can undergo typical aromatic
electrophilic substitution reactions2b,5d and nucleophilic aromatic
substitution of hydrogens2f and can function as η6 ligands to form
half-sandwich, sandwich,13 and triple-decker14 complexes.
Compounds closely related to metallabenzenes are metalla-
benzynes,15 which can be thought as being formed by replace-
ment of a C atom or a CH group in benzyne with an isolobal
transition-metal fragment. In comparison with that of metalla-
benzenes, the chemistry of metallabenzynes is less developed.
The first such compound was reported in 2001,16 and several
additional stable metallabenzynes have been successfully isolated
more recently.17,18 Unlike benzyne, which is thermally unstable,
metallabenzynes can be isolated as thermally stable solids and can
be conveniently characterized by NMR spectroscopy and X-ray
diffraction. The X-ray diffraction study of known metallaben-
zynes shows that the six-membered metallacycle has a planar
delocalized structure. The delocalized structural feature is similar
to that of aromatic ring systems such as benzene and metalla-
benzenes. In this regard, it would be interesting to find out if
metallabenzynes could also undergo typical reactions of aromatic
compounds or benzynes.
reactions.19 An interesting question is whether metallabenzynes
could also undergo electrophilic aromatic substitution reactions.
In this paper, we report our comprehensive study on the reac-
tions of osmabenzynes Os(tCC(R)dC(CH3)C(R)dCH)Cl2-
(PPh3)2 (R = SiMe3, H) with various electrophiles, including
NO2BF4, NOBF4, HCl/H2O2, AlCl3/H2O2, and Br2. In the
literature, only the reactions of the SiMe3-containing osmaben-
zyne Os(tCC(SiMe3)dC(CH3)C(SiMe3)dCH)Cl2(PPh3)2
with Br2 and HBF4 were briefly communicated by us.17
One of the typical chemical properties of aromatic compounds
is that they can undergo electrophilic aromatic substitution
Received: August 4, 2011
Published: October 13, 2011
r
2011 American Chemical Society
18350
dx.doi.org/10.1021/ja207315h J. Am. Chem. Soc. 2011, 133, 18350–18360
|

Journal of the American Chemical Society
ARTICLE
Table 1. Crystallographic Details
3 2C6H6
4
5 0.5C6H14
6 1.5CH2Cl2
7 0.5C6H14
9 0.75CH2Cl2
3
3
3
3
3
empirical formula
C45H43Cl2NO2
C45H44Cl2NO2
OsP2Si
C
45H43Cl2NOOs
C42H34Cl4OOs
C45H43Cl3OsP2
Si.0.5C6H14
1029.46
C42H35Cl2NO3Os
OsP2Si 2C6H6
P2Si 0.5C6H14
P2 1.5CH2Cl2
P2 0.75CH2Cl2
3
3
3
3
formula wt
temp, K
1137.15
253(2)
981.94
1008.02
100(2)
1076.02
173(2)
988.44
100(2)
100(2)
100(2)
radiation (Mo Kα), Å
cryst syst
0.710 73
monoclinic
P21/c
0.710 73
triclinic
0.710 73
monoclinic
P21/c
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
P21/n
0.710 73
monoclinic
I2
space group
a, Å
P1
10.386(11)
18.76(2)
27.36(3)
90.00
12.0580(10)
12.4671(10)
14.8212(12)
83.779(2)
72.020(2)
75.575(2)
2051.2(3)
2
10.1908(10)
17.7202(18)
24.634
21.2492(10)
10.0490(5)
39.926(2)
90.00
10.0996(7))
18.2847(12)
23.7928(16)
90.00
26.730(5)
10.8726(18)
26.972(5)
90
b, Å
c, Å
α, deg
90
β, deg
99.125(18)
90.00
95.5520(10)ꢀ
90
99.8030(10)
90.00
94.9460(10)
90.00
91.149(5)
90
γ, deg
V, Å3
5265(10)
4
4427.6(8)
4
8401.0(7)
8
4377
7837(2)
8
Z
4
dcalcd, g cmꢀ3
abs coeff, mmꢀ1
F(000)
1.435
1.590
1.512
1.701
1.562
1.676
2.649
3.385
3.137
3.592
3.233
3.617
2296
982
2028
4248
2068
3916
no. of rflns collected
no. of indep rflns
no. of data/restraints/params
goodness of fit on F2
final R (I > 2σ(I))
36 763
11 155
27 899
28 935
33 907
14 803
9155
7827
8602
7245
7584
8029
9155/0/595
0.982
7827/29/505
1.002
8602/8/506
1.019
7245/0/492
1.012
7584/9/500
1.029
8029/16/971
1.036
R1 = 0.0226,
wR2 = 0.0480
0.910 and ꢀ0.365
R1 = 0.0613,
wR2 = 0.0993
1.444 and ꢀ1.420
R1 = 0.0315,
wR2 = 0.0621
0.818 and ꢀ0.436
R1 = 0.0268,
wR2 = 0.0618
0.870 and ꢀ0.861
R1 = 0.0368,
wR2 = 0.0591
0.928 and ꢀ1.087
R1 = 0.0496,
wR2 = 0.1160
2.805 and ꢀ2.718
peak and hole, e Åꢀ3
’ RESULTS AND DISCUSSION
Complex 3 was isolated as a yellow solid. It has been cha-
racterized by elemental analysis and multinuclear NMR spec-
troscopy as well as single-crystal X-ray diffraction analysis. The
crystallographic details are given in Table 1. Selected bond
lengths and angles are given in Table 2.
Reactions of Os(;CC(SiMe3)dC(CH3)C(SiMe3)dCH)Cl2-
(PPh3)2 (1). We have previously reported that reaction of 1 with
excess bromine affords the osmabenzyne Os(tCC(Br)d
C(CH3)C(Br)dCH)Cl2(PPh3)2 (2) asthepredominant product
(Scheme1).17 The reactioncan be regardedasa rareexample of an
electrophilic substitution reaction of a metallabenzyne. The re-
activity is unusual when compared with that of benzynes. The
reactivities of benzynes are usually associated with the CtC triple
bond.20 Thus, benzynes react with bromine to give 1,2-
dibromobenzenes.21 Formation of 2 from the reaction of 1 with
Br2 promoted us to study electrophilic substitution reactions of 1
with other electrophiles. The results are summarized in Scheme 1.
Nitration. Nitration is one of the typical electrophilic substitution
reactions of aromatic organic compounds. Inspired by the success
of the electrophilic substitution reaction of osmabenzene Os-
[C5H4(SMe-1)]I(CO)(PPh3)2 with Cu(NO3)2/(CH3CO)2O,2b
we initially carried out the reaction of 1 with Cu(NO3)2/
(CH3CO)2O. However, the reaction produced a complicated
mixture, which could not be separated and identified. We then
carried out the nitration reaction with the nitronium salt NO2BF4.
Complexes 3 and 4 were isolated from the reaction of 1 with
NO2BF4 (in 1:4.5 molar ratio) in the presence of NaCl in CH2Cl2
at ꢀ16 to ꢀ5 ꢀC (Scheme 1). In the absence of NaCl, a com-
plicated mixture was obtained, probably due to partial displace-
ments of the chloride ligands. The reaction temperature appears
also to be important for the success of the reaction. Higher tem-
perature led to the production of a complicated mixture while the
reaction did not proceed at a lower temperature.
The molecular structure of 3 is shown in Figure 1, which
reveals that it is a metallabenzyne complex formed via replacing
the SiMe3 substituent at C4 in 1 by NO2. The complex contains
an essentially planar six-membered metallacycle, with the sum of
the angles in the six-membered ring of 719.55ꢀ, which is very
close to the ideal value of 720ꢀ. The OsꢀC1 bond length
(1.788(3) Å) is slightly shorter than that of 1 (1.815(4) Å),16
while the OsꢀC5 bond length (2.013(3) Å) is longer than the
corresponding bond of 1 (1.939(5) Å). The bond distances of
the remaining CꢀC bonds within the metallacycle (1.366(4)ꢀ
1.440(4) Å) are within the range of typical aromatic CꢀC bond
lengths. The bond distances of O(1)ꢀN(1) and O(2)ꢀN(1) are
1.215(3) and 1.242(3) Å, respectively, with an O(1)ꢀN(1)ꢀ
O(2) angle of 123.1(3)ꢀ.
The solid-state structure of 3 is supported by multinuclear
NMR spectroscopy and elemental analysis. The 1H NMR
spectrum (in C6D6) showed a downfield singlet signal at 12.88
ppm, which can be assigned to the OsCH proton. The CH3
proton signal was observed at 1.75 ppm. The 13C{1H} NMR
spectrum of 3 (in CDCl3) displayed the signals of the two metal-
bound carbon atoms at 297.5 ppm for the carbyne-like carbon
(OstC) and at 216.4 ppm for the other carbon (OsCH). The
13C signals for the remaining carbon atoms of the metallacycle
(CCH3, OsCHdC(NO2), and OstCC(Si(CH3)3) were ob-
served at 187.3, 171.6, and 116.2 ppm, respectively. The CH3
18351
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Table 2. Selected Bond Lengths and Angles for 3 and 5
3
5
Bond Lengths (Å)
2.425(2)
2.425(2)
2.455(3)
2.474(2)
1.788(3)
2.013(3)
1.375(4)
1.410(4)
1.440(4)
1.366(4)
Os(1)ꢀP(1)
Os(1)ꢀP(2)
Os(1)ꢀCl(1)
Os(1)ꢀCl(2)
Os(1)ꢀC(1)
Os(1)ꢀC(5)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
2.4346(11)
2.4209(7)
2.4502(9)
2.4612(9)
1.770(4)
1.992(3)
1.363(5)
1.405(5)
1.451(5)
1.381(5)
Bond Angles (deg)
78.65(13)
153.7(2)
C(1)ꢀOs(1)ꢀC(5)
C(2)ꢀC(1)ꢀOs(1)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(4)
C(5)ꢀC(4)ꢀC(3)
C(4)ꢀC(5)ꢀOs(1)
79.12(5)
154.7(3)
110.6(3)
120.8(3)
125.0(3)
129.7(3)
Figure 2. Molecular structure of paramagnetic complex 4. The hydro-
gen atoms of PPh3, CH3, and SiMe3 are omitted for clarity.
111.6(3)
119.1(2)
127.4(2)
Table 3. Selected Bond Lengths and Angles for 4
129.1(2)
Bond Distances (Å)
Os(1)ꢀP(1)
Os(1)ꢀCl(1)
Os(1)ꢀC(1)
C(1)ꢀC(2)
C(2)ꢀN(1)
C(3)ꢀC(4)
C(4)ꢀC(5)
N(1)ꢀO(1)
2.398(2)
2.410(2)
1.957(8)
1.395(10)
1.304(9)
1.505(9)
1.369(11)
1.307(10)
Os(1)ꢀP(2)
Os(1)ꢀCl(2)
Os(1)ꢀO(1)
C(1)ꢀC(5)
C(2)ꢀC(3)
C(3)ꢀC(6)
N(1)ꢀO(2)
2.403(2)
2.3233(19)
2.095(5)
1.463(10)
1.502(9)
1.540(9)
1.253(7)
Bond Angles (deg)
C(1)ꢀOs(1)ꢀO(1)
C(2)ꢀC(1)ꢀC(5)
C(2)ꢀC(3)ꢀC(4)
C(5)ꢀC(4)ꢀC(3)
C(2)ꢀC(3)ꢀC(6)
P(1)ꢀOs(1)ꢀP(2)
O(1)ꢀOs(1)ꢀCl(1)
P(2)ꢀOs(1)ꢀCl(1)
76.9(3)
105.5(7)
103.4(8)
106.3(8)
117.7(12)
172.73(8)
C(2)ꢀC(1)ꢀOs(1)
C(1)ꢀC(2)ꢀC(3)
C(4)ꢀC(5)ꢀC(1)
C(5)ꢀC(1)ꢀOs(1)
C(4)ꢀC(3)ꢀC(6)
C(1)ꢀOs(1)ꢀCl(1)
114.6(5)
109.5 (7)
112.5(7)
139.9(6)
118.7(12)
161.4(2)
87.58(7)
92.8(2)
84.57(16) P(1)ꢀOs(1)ꢀCl(1)
86.97(7)
C(1)ꢀOs(1)ꢀCl(2)
O(1)ꢀOs(1)ꢀCl(2) 169.57(17) P(1)ꢀOs(1)ꢀCl(2)
87.58(7)
92.8(2)
P(2)ꢀOs(1)ꢀCl(2)
O(1)ꢀOs(1)ꢀP(1)
O(1)ꢀOs(1)ꢀP(2)
N(1)ꢀC(2)ꢀC(1)
O(2)ꢀN(1)ꢀC(2)
C(2)ꢀN(1)ꢀO(1)
88.94(7)
C(1)ꢀOs(1)ꢀP(1)
94.14(16) C(1)ꢀOs(1)ꢀP(2)
90.14(16) Cl(2)ꢀOs(1)ꢀCl(1) 105.75(7)
118.5(8)
127.0(8)
114.9(7)
93.9(2)
Figure 1. Molecular structure of 3. The hydrogen atoms of PPh3 and
SiMe3 are omitted for clarity.
N(1)ꢀC(2)ꢀC(3)
O(2)ꢀN(1)ꢀO(1)
N(1)ꢀO(1)ꢀOs(1)
131.0(8)
118.1(6)
115.0(4)
signal was observed as a singlet at 23.0 ppm. The 31P{1H} NMR
spectrum (in CDCl3) showed a singlet at ꢀ0.8 ppm.
Complex 4 was isolated as an orange-red solid. The para-
magnetic compound has been characterized by elemental anal-
ysis as well as single-crystal X-ray diffraction analysis. The
molecular geometry is shown in Figure 2. The crystallographic
details are given in Table 1. Selected bond lengths and angles are
given in Table 3.
As shown in Figure 2, the osmium center of 4 is in a five-
membered ring. The OsꢀC1 bond distance (1.957(8) Å) is
within the range of OsꢀC(vinyl) bonds (1.897ꢀ2.195 Å)22,23
and OsꢀC(carbene) bonds (1.837ꢀ2.045 Å for non Fisher Os
carbene).22,24 The C4ꢀC5 bond length of 1.369(11) Å is in the
range of typical CꢀC double bonds, while bond lengths of C(2)ꢀ
C(3) (1.502(8) Å) and C(3)ꢀC(4) (1.505(9) Å) are in the range
of CꢀC single bonds. The bond length of C(1)ꢀC(2)
(1.395(10) Å) is shorter than typical CꢀC single bonds and
longer than typical CꢀC double bonds, probably due to the delo-
calization involving C(1), C(2), and the NO2 group. The C(2)ꢀ
N(1) bond (1.304(9) Å) is appreciably shorter than the CꢀN
bond in complex 3 (1.482(4) Å) and longer than the CdN bond
18352
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Chart 1
Scheme 3
Scheme 2
(Figure 3), suggesting that a biradical can be readily generated
from the intermediate B2 proposed in Scheme 2.
Nitrosation. Electrophilic nitrosation reactions of arenes have
been used previously to prepare nitrosoarenes.27 It is known that
the chemical reactivities of NO+ and NO2 toward aromatic
+
donors are significantly different. The activity of NO+ is esti-
mated to be at least 1014 times lower than that of NO2 . Thus,
+
direct nitration of arenes with nitronium salts generally occurs
immediately upon mixing of reagents even at low temperature,
whereas the corresponding nitrosation with nitrosonium salt is
usually too slow to be detected, except for electron-rich arenes.27
It is then of interest to find out if osmabenzynes can react with the
relatively unreactive electrophile NO+.
Treatment of 1 with NOBF4 (1:4) and NaCl in CH2Cl2 at
ꢀ20 to ꢀ5 ꢀC for 3 h produced a brown solution, from which
complex 5 was isolated as an orange solid in 72% yield
(Scheme 1). As indicated by in situ NMR, the reaction also
produced other minor unidentified products. The structure of 5
has been determined by an X-ray diffraction study. The crystal-
lographic details are listed in Table 1. Selected bond lengths and
angles are given in Table 2. A view of the molecular geometry of 5
is shown in Figure 4. As shown in Figure 4, 5 is a complex formed
through replacing only the SiMe3 group at C4 of 1 by an NO
group. The structural features of the six-membered metallacycle
are nearly identical with those of 3.
(1.283(2) Å) in PhNdC(C6H4-m-NO2).25 The O(1)ꢀN(1)
bond (1.307(10) Å) is appreciably longer than the O(2)ꢀN(1)
bond (1.253(7) Å). The structural parameters suggest that the
metallacycle of 4 has a delocalized structure with contributions
from resonance structures such as 4 and 4A, with 4 being more
important (Chart 1).
A plausible mechanism for the formation of the paramagnetic
species 4 is shown in Scheme 2. Initially electrophilic substitution
+
of NO2 at the C2 position of the metallacycle of 1 would
produce osmabenzyne A, which may undergo reductive elimina-
tion to give intermediate B1 and then B2.26 A biradical B3
generated from B1 could abstract a hydrogen atom from solvent
to give the paramagnetic osmium complex 4.
The solid-state structure of 5 is supported by multinuclear
NMR spectroscopy and elemental analysis. In particular, the
OsCH proton signal was located at 12.11 ppm in the 1H NMR
spectrum (in CDCl3). The CCH3 proton signal was observed at
2.81 ppm. The 13C{1H} NMR spectrum (in CDCl3) displayed
the OstC signal at 297.0 ppm. The signal corresponding to
OsCH appeared at 215.9 ppm. The 13C signals of other carbons
of the metallacycle were observed at 187.0 (CCH3), 171.2
(CNO), and 115.8 (CSi(CH3)3) ppm. The CH3 signal on the
metallacycle appeared at 22.5 ppm. The 31P{1H} NMR spectrum
of 5 (in CDCl3) displayed a singlet at ꢀ0.18 ppm.
One may ask why osmabenzyne A would undergo rearrange-
ment to afford the osmium carbene complex 4 while transforma-
tion of 3 to an osmium carbene complex was not observed.
To gain insight into the difference between A and 3 in this re-
arrangement reaction, we have studied, by DFT calculations, the
reductive elimination reactions of 3-benzyne (a model complex
of 3) and A-benzyne (a model complex of A). Consistent with
the experimental observation, the computational study suggests
that 3-benzyne is thermodynamically more stable than 3-car-
bene, while A-benzyne is thermodynamically less stable than B2-
carbene (Scheme 3). The additional coordination of the NO2
group to the metal center via one of the two NO2 oxygens
apparently stabilizes B2-carbene.
Complex 5 can be regarded as a product resulting from nitro-
sation of 1 at the C4 position of the metallacycle. In the nitration
reaction of 1, we successfully isolated products resulting from
reaction at both C2 and C4. We cannot exclude the possibility
that a product resulting from nitrosation of 1 at the C2 position
of the metallacycle was also produced, although we have failed to
isolate or identify such a species. The fact that complex 5 can be
isolated in 72% yield suggests that nitrosation at the C4 position
is favored. The higher reactivity of C4 compared to that of C2 can
be related to the difference in the π-electron density distribution
Inthe proposed mechanism for the formationof4, weproposed
that a biradical generated from osmabenzyne A is involved. The
calculation indeed confirms that the biradical singletB3-carbene is
more stable than the diamagnetic B2-carbene by 12.3 kcal/mol
18353
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Figure 3. Relative electronic energies of the diamagnetic complex B2-carbene and its biradical singlet species B3-carbene.
Figure 4. Molecular structure of 5. The hydrogen atoms of PPh3, CH3,
and SiMe3 are omitted for clarity.
Figure 5. Molecular structure of complex 6. The hydrogen atoms of
PPh3 and CH3 are omitted for clarity.
in the HOMO of the metallacycle. DFT calculations suggest that
in the HOMO of the complex Os(tCC(SiH3)dC(CH3)C-
(SiH3)dCH)Cl2(PH3)2 (a model of 1), the π-electron popula-
tion on C2 is 0.20e and that on C4 is 0.24e. Thus, C4 is more
nucleophilic and more reactive toward electrophiles. The differ-
ence in the nitration and nitrosation may be related to the
is closely related to the η2-C(S)-containing osmabenzene Os-
2a
(C5H2(S-1))(CO)(PPh3)2 and the iridabenzene [Ir(C5H4-
(S-1))(MeCN)(PPh3)2][CF3SO3].5c As expected, complex 6
also contains a nearly planar six-membered metallacycle. The
OsꢀC1 bond length (1.956(3) Å) is slightly shorter than that of
Os[C5H4(SMe)](Cl)(CO)(PPh3)2 (2.109(3) Å).1c The Osꢀ
C5 bond length (2.041(4) Å) is nearly identical with that of
Os[C5H4(SMe)](Cl)(CO)(PPh3)2 (2.027(3) Å). The distances
of the other CꢀC bonds of the metallacycle are in the range of
1.347(5)ꢀ1.411(6) Å which are between normal CꢀC single-
and double-bond lengths and are close to the distances of the
CꢀC bonds in benzene (1.390 Å).
+
different reactivities of the electrophiles (NO+ and NO2 ). One
might expect that the less reactive electrophile NO+ will react
more selectively, at the more nucleophilic C4 position.
Chlorination. It is known that HCl/H2O2 can be used as a
chlorination reagent for aromatic substrates.28 Consequently, we
investigated the reaction of osmabenzyne 1 with HCl/H2O2.
Treatment of osmabenzyne 1 with excess HCl/H2O2 in dichlor-
omethane at 0 ꢀC produced a mixture of species, from which the
chlorinated product 6 was isolated in 62% yield (Scheme 1).
Complex 6 has been characterized by multinuclear NMR spec-
troscopy and elemental analysis. The solid-state structure has
been confirmed by single-crystal X-ray diffraction.
As shown in Figure 5, complex 6 has two chlorides at the
C2 and C4 positions of the metallacycle. Furthermore, an
oxygen atom is attached at the C1 position and the C1ꢀO unit
is bonded to the osmium center in an η2 fashion. The complex
The solid-state structure of complex 6 is supported by MS,
multinuclear NMR spectroscopy, and elemental analysis. In
particular, the FAB-MS displayed an ion peak at m/z 877.1 for
1
[M ꢀ Cl]+. The H NMR spectrum (in CD2Cl2) showed a
singlet signal at 12.62 ppm which can be assigned to the OsCH
proton. The 13C{1H} NMR spectrum (in CD2Cl2) displayed the
signals of the two metal-bound carbon atoms at 203.6 ppm (OsC-
(O)) and 192.1 ppm (OsCH). The 13C signals of the remaining
18354
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Scheme 4
Table 4. Selected Bond Lengths and Angles for 6, 7, and 9
6
7
9
Bond Lengths (Å)
Os(1)ꢀP(1)
Os(1)ꢀP(2)
Os(1)ꢀCl(1)
Os(1)ꢀCl(2)
Os(1)ꢀC(1)
Os(1)ꢀC(5)
Os(1)ꢀO(1)
O(1)ꢀC(1)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
2.4273(9)
2.4207(9)
2.4437(9)
2.3808(8)
1.956(3)
2.041(4)
2.144(2)
1.234(4)
1.370(5)
1.380(6)
1.411(6)
1.347(5)
2.4155(13)
2.4126(14)
2.4422(12)
2.3894(14)
1.937(6)
2.044(4)
2.131(3)
1.238(6)
1.371(7)
1.390(7)
1.433(7)
1.371(6)
2.424(3)
2.404(3)
2.375(3)
2.424(3)
1.988(13)
2.074(12)
2.145(8)
1.251(15)
1.400 (17)
1.361(18)
1.418(18)
1.370(17)
Figure 6. Molecular structure of complex 7. The hydrogen atoms of
PPh3, CH3, and SiMe3 are omitted for clarity.
Scheme 5
Bond Angles (deg)
C(1)ꢀOs(1)ꢀC(5)
C(1)ꢀOs(1)ꢀO(1)
C(5)ꢀOs(1)ꢀO(1)
O(1)ꢀC(1)ꢀOs(1)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(4)
O(1)ꢀC(1)ꢀC(2)
C(2)ꢀC(1)ꢀOs(1)
C(5)ꢀC(4)ꢀC(3)
C(4)ꢀC(5)ꢀOs(1)
77.79(15
34.64(13)
112.42(13)
81.1(2)
76.2(2)
76.3(5)
35.03(16)
111.20(17)
81.1(4)
35.0(4)
111.2(4)
79.4(7)
121.8(3)
116.7(3)
136.8(3)
142.1(3)
127.2(4)
134.3(3)
119.6(5)
119.2(5)
134.0(6)
144.7(4)
121.5(5)
137.8(4)
120.4(10)
118.1(11)
135.1(12)
145.5(12)
127.8(11)
133.2(9)
carbon atoms of the metallacycle (C-CH3, OsCHdCCl, OsdC-
(O)CCl) were observed at 161.4 (CCH3), 131.1 (OsCHdCCl),
and 125.9 (OsdC(O)CCl) ppm. The CH3 signal on the
metallacycle was observed as a singlet at 22.9 ppm. The 31P{1H}
NMR spectrum (in CD2Cl2) showed a singlet at ꢀ17.7 ppm.
Considering the fact that complex 1 readily undergoes bro-
mination, nitration, and nitrosation reactions at the C2 and C4
positions of the metallacycle, it is likely that complex 6 may be
formed by initial electrophilic substitution of 1 by chlorine
followed by oxidation of C1 of the metallacycle, although the
possibility of initial oxidation of C1 of the metallacycle followed
by electrophilic substitution by chlorine could not be excluded.
Experimentally, we have failed to get evidence for either of
the processes. An example of oxidation of metallabenzenes has
been previously reported. Oxidation of Cα of the iridabenzene
Ir(C5H3Me2)(PMe3)3 with N2O, followed by rearrangement,
affords the iridacyclohexadienone complex IrH(C(O)CMeCH-
CMeCH)(PMe3)3.8c,d
It has been reported that arenes could react with hydrogen
peroxide in the presence of aluminum chloride to give a mixture
of hydroxylated products (phenols) and chlorinated products
(aryl chlorides).29 We have therefore explored the possibility of
hydroxylation of osmabenzyne 1 with hydrogen peroxide/
aluminum chloride. However, the expected hydroxylated osmaben-
zynes could not be obtained from the reaction. The reaction was
found to produce a mixture of species from which the chlorinated
complexes 6 and 7 could be isolated (Scheme 4). The relative
18355
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Nitration. Complex 8 also undergoes a nitration reaction when
treated with NO2BF4. After a mixture of 8 and NO2BF4 (in 1:4
molar ratio) and NaCl in CH2Cl2 was stirred at ꢀ16 to 5 ꢀC for
2 h, a brown solution was obtained, from which the NO2-
containing osmabenzyne complex 9 could be isolated in 30%
yield as an orange solid. The reaction also produced other
unidentified species. Complex 9 is probably formed through a
mononitrated osmabenzyne intermediate analogous to 3, which
+
was oxidized by excess NO2 . The oxygenated product of 3 was
not observed, probably because the SiMe3 group in 3 may help to
prevent it from oxidation.
Complex 9 has been characterized by NMR spectroscopy and
1
elemental analysis. In the H NMR spectrum (in C6D6), the
signals of the two protons of the metallacycle were observed at
13.67 (OsCHd) and 5.53 ppm (OsCHdCH). In the 13C{1H}
NMR spectrum (in CD2Cl2), the signals of the two metal-bound
carbon atoms were observed at 205.2 (OsC(O)) and 203.3
(OsCH) ppm. The 13C signals of the remaining carbon atoms
of the metallacycle (C-CH3, OsCHdCNO2, OsdC(O)CH)
were observed at 161.4, 129.8, and 92.5 ppm. The molecular
structure of 9 has also been unambiguously confirmed by X-ray
diffraction (Figure 7), despite difficulties due to absorption and
desolvation of the crystal. As shown in Table 4, the structural
features associated with the six-membered metallacycle are
similar to those of 6 and 7.
Chlorination. Reaction of 8 with HCl/H2O2 in CH2Cl2 at
room temperature produced a brown solution, from which the
chlorinated product 6 was isolated in about 32% yield. Treatment
of 8 with AlCl3 and H2O2 (in a 1:15:20 molar ratio) in CH2Cl2
at ꢀ15 to 0 ꢀC also afforded 6, which could be isolated in
37% yield.
Figure 7. Molecular structure of 9.
amounts of 6 and 7 can be controlled by the ratio of 1, AlCl3, and
H2O2. Treatment of 1 with AlCl3 and H2O2 (in a 1:21:25 molar
ratio) in CH2Cl2 at ꢀ15 to 0 ꢀCfor2hafforded mainly 6along with
a trace amount of 7. Complex 7 was produced as the major product
when the molar ratio 1:AlCl3:H2O2 is 1:5:10.
’ CONCLUSION
The structure of 7 has been confirmed by single-crystal X-ray
diffraction analysis and multinuclear NMR spectroscopy. The
crystallographic details are given in Table 1, and selected bond
distances and angles are given in Table 4. As shown in Figure 6,
complex 7 is essentially the same as 6, except that 7 has only one
Cl atom at the C2 position of the metallacycle while 6 has two
(one at C2 and the other one at C4). The solid-state structure of
7 is fully consistent with the solution NMR data.
Reactions of Os(;CCHdC(CH3)CHdCH)Cl2(PPh3)2 (8). It is
known that reactions of Ar-SiMe3 with electrophiles usually lead
to the cleavage of the CꢀSiMe3 bond, implying that CꢀSiR3
bonds are more reactive than CꢀH bonds toward electrophiles.
In this respect, it would be interesting to study reactions of
electrophiles with metallabenzynes without a SiMe3 group. For
this reason, we have studied the reaction of Os(tCCHd
C(CH3)CHdCH)Cl2(PPh3)2 (8) with electrophiles such as
Br2, NO2BF4, HCl/H2O2, and AlCl3/H2O2. The results are
summarized in Scheme 5.
Bromination. Treatment of osmabenzyne 8 with excess Br2
produced the brominated product 2 as the major product. The
same complex was produced from the reaction of 1 with Br2.16 As
in the case of reaction involving 1, excess bromine was essential
for obtaining pure osmabenzyne 2. A complicated mixture was
produced, as indicated by the in situ NMR when a lesser amount
of bromine was used, probably due to partial displacement of the
H and Cl groups. For example, when 1 was allowed to react with
1 equiv of Br2, the reaction produced a mixture of at least eight
phosphorus-containing species, including some unreacted 1. It is
difficult to separate or fully separate or identify all these species.
In summary, we have investigated the electrophilic substitu-
tion reactions of two metallabenzynes, including nitration,
nitrosation, chlorination, and bromination. The substitution
reactions occurred at the C2 and C4 positions of the six-
membered metallacycle. The regioselectivity of the electrophilic
substitution reactions can be related to the π electron density
distribution in the HOMO of the metallacycle. The observed
reactivity of the metallabenzynes toward electrophiles demon-
strates that metallabenzynes, like benzene and metallabenzenes,
can undergo electrophilic substitution reactions and exhibit
aromatic properties. Electrophilic substitution reactions of me-
tallabenzynes reported in this work are unusual, especially when
the reactivities of benzynes are considered. The reactivities of
benzynes are usually associated with the CtC triple bond, and
electrophilic substitution reactions of benzynes, to our knowl-
edge, have not been demonstrated. The formation of η2-C(O)-
containing osmabenzenes from the reactions of 1 or 8 with H2O2
or NO2BF4 represents a rare example of oxidation reactions of
osmium carbyne complexes.
’ EXPERIMENTAL SECTION
All manipulations were carried out at room temperature under a
nitrogen atmosphere using standard Schlenk techniques, unless other-
wise stated. Solvents were distilled under nitrogen from sodium benzo-
phenone (hexane, diethyl ether, THF, benzene) or calcium hydride
(dichloromethane, CHCl3). The starting materials Os(tCC(SiMe3)d
C(Me)C(SiMe3)dCH)Cl2(PPh3)2 (1)16 and Os(tCCHdC(Me)-
CHCH) Cl2(PPh3)2 (8)17 were prepared following the procedures
18356
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
described in the literature. Microanalyses were performed at M-H-W
Laboratories (Phoenix, AZ). 1H, 13C{1H}, and 31P{1H} NMR spectra
were collected on a Bruker ARX-300 spectrometer (300 MHz) or a
Bruker ARX-400 spectrometer (400 MHz). 1H and 13C NMR chemical
shifts are relative to tetramethylsilane, and 31P NMR chemical shifts are
relative to 85% H3PO4.
column was eluted with CH2Cl2/n-hexane (1:1) to give an orange
solution, from which Os(C(O)CCldC(CH3)CCldCH)Cl2(PPh3)2
(6) was obtained as an orange solid, after the solvents were removed
completely under vacuum. Yield: 87 mg, 62%.
Method B. To a suspension of 1 (0.280 g, 0.280 mmol) and aluminum
chloride (0.800 g, 6.00 mmol) in CH2Cl2 (15 mL) cooled in an iceꢀsalt
bath was added hydrogen peroxide (0.6 mL, 35% by weight, 6.98 mmol).
The reaction mixture was stirred for 1 h at ꢀ2 to 0 ꢀC to give an orange
solution. The solvent was removed completely under vacuum, and the
resulting orange residue was extracted with benzene (5 mL) and filtered.
The solvent of the extract was removed under vacuum, and the resulting
residue was dissolved in CH2Cl2 (1 mL). Addition of hexane (15 mL) to
the residue gave an orange precipitate which was collected by filtration,
washed with hexane (2 ꢁ 3 mL), and dried under vacuum. The solid was
redissolved in 1 mL of CH2Cl2, and the mixture was loaded on a silica gel
column. The column was eluted with benzene to give an orange solution,
from which Os(C(O)CCldC(CH3)CCldCH)Cl2(PPh3)2 (6) was
obtained as an orange solid, after the solvent was removed completely
under vacuum. Yield: 0.134 g, 50%.
Method C. To a solution of 8 (200 mg, 0.23 mol) in CH2Cl2 (10 mL)
was added HCl (2.3 mL, 1 M in Et2O, 2.3 mmol) and hydrogen peroxide
(220 μL, 35% by weight, 2.2 mmol). The reaction mixture was stirred for
3 h at room temperature to give a brown solution. The solution was
washed with K2CO3 solution (10 mL) and then brine (10 mL ꢁ 2). The
organic layer was dried with anhydrous MgSO4. The solvent was
removed completely under vacuum. The residue was redissolved in
2 mL of CH2Cl2 and loaded on a silica gel column. The column was
eluted with CH2Cl2/n-hexane (1:1) to give an orange solution, from
which Os(C(O)CCldC(CH3)CCldCH)Cl2(PPh3)2 (6) was obtained
as an orange solid, after the solvent was removed completely under
vacuum. Yield: 70 mg, 32%.
Method D. To a suspension of 8 (172 mg, 0.20 mmol) and aluminum
chloride (400 mg, 3 mmol) in CH2Cl2 (15 mL) (cooled to ꢀ15 ꢀC) was
added hydrogen peroxide (0.48 mL, 30% by weight, 4 mmol). The
reaction mixture was stirred for 3 h at ꢀ15 ꢀC. The temperature
was raised to 0 ꢀC naturally to give an orange solution. The solvent
was removed completely under vacuum, and the resulting orange residue
was extracted with benzene (2 ꢁ 8 mL) and then filtered. The filtrate was
evaporated to dryness under vacuum. The resulting residue was dis-
solved in CH2Cl2 (1 mL), which was loaded on a silica gel column. The
column was eluted with benzene to give an orange-red solution, from
which compound 6 was obtained as an orange solid, after the solvent was
removed completely under vacuum. Yield: 69.8 mg, 37%.
Compounds 3 and 4. An ice-cooled solution of 1 (0.300 g, 0.300
mmol) in CH2Cl2 (10 mL) was transferred to a suspension of NO2BF4
(0.178 g, 1.34 mmol) and NaCl (1.000 g, 17.11 mmol) in CH2Cl2
(60 mL) which was kept at ꢀ16 ꢀC. The mixture was stirred for 2 h to
give a brown suspension. The temperature was raised to ꢀ5 ꢀC
naturally. Ice-cooled water (60 mL) was added at ꢀ5 ꢀC with vigorous
stirring. Sodium hydrogen carbonate (0.140 g, 1.67 mmol) in water
(10 mL) was added. After the above mixture was stirred for 2 min, the
top aqueous layer was removed and the organic layer was further washed
with 2 ꢁ 30 mL of water. The solvent of the organic layer was then
removed under vacuum. The residue was dissolved in 3 mL of CH2Cl2
and loaded on a silica gel column. The column was eluted with benzene
to give an orange-red solution, from which the paramagnetic compound
4 was obtained as an orange-red solid, after the solvent was removed
completely under vacuum. Yield: 60 mg, 20%. Anal. Calcd for C45H42-
Cl2NO2P2SiOs: C, 55.04; H, 4.52; N, 1.43. Found: C, 55.18; H, 4.66; N,
1.66. The column was further eluted with benzene to give a yellow
solution, from which the compound Os(tCC(SiMe3)dC(CH3)C-
(NO2)dCH)Cl2(PPh3)2 (3) was obtained as a yellow solid after the
solvent was removed completely under vacuum. Yield: 56 mg, 19%.
1
31P{1H} NMR (121.5 MHz, CDCl3): δ ꢀ0.8 (s). H NMR (300.13
MHz, C6D6): δ 0.00 (s, 9H, Si(CH3)3), 1.75 (s, 3H, CH3), 7.05ꢀ7.46
(m, 30H, PPh3), 12.88 (s, 1H, OsCH). 13C{1H} NMR (75.5 MHz,
CDCl3): δ 297.5 (t, J(PC) = 11.8 Hz, OstC), 216.4 (t, J(PC) = 5.8 Hz,
OsCH), 187.3 (s, CCH3), 171.6 (s, OsCHdC(NO2)), 134.0 (t, J(PC) =
4.9 Hz, m-PPh3), 130.6 (t, J(PC) = 27.8 Hz, ipso-PPh3), 130.3 (s, p-
PPh3), 127.6 (t, J(PC) = 5.2 Hz, o-PPh3), 116.2 (s, OstCC(Si-
(CH3)3)), 23.0 (s, CCH3), 0.4 (s, Si(CH3)3). Anal. Calcd for C45H43-
Cl2NO2P2SiOs 0.5CH2Cl2: C, 52.75: H, 4.06: N, 1.42. Found: C,
3
53.12; H, 4.36; N, 1.38.
Compound 5. An ice-cooled solution of 1 (300 mg, 0.30 mmol) in
CH2Cl2 (10 mL) was transferred to a suspension of NOBF4 (139 mg,
1.19 mmol) and NaCl (600 mg, 10.3 mmol) in CH2Cl2 (20 mL) which
was kept at ꢀ20 ꢀC. The mixture was stirred for 3 h to give a brown
suspension. The temperature was raised to ꢀ5 ꢀC naturally. Ice-cooled
water (20 mL) was added at 0 ꢀC with vigorous stirring. The mixture was
allowed to stand for 5 min. The top aqueous layer was then removed, and
the organic layer was further washed with water (2 ꢁ 20 mL). The
solvent of the organic layer was then removed under vacuum. The
residue was dissolved in 1 mL of CH2Cl2, and diethyl ether (30 mL) was
added slowly with stirring to give an orange precipitate, which was
separated by filtration. The solid was washed with diethyl ether (3 ꢁ
10 mL) and hexane (3 ꢁ 10 mL) and then dried under vacuum. Yield:
287 mg, 72%. 31P{1H} NMR (161.98 MHz, CDCl3): δ ꢀ0.18 (s). 1H
NMR (400.13 MHz, CDCl3): δ 0.33 (s, 9H, Si(CH3)3), 2.81 (s, 3H,
CH3), 7.21ꢀ7.70 (m, 30H, PPh3), 12.11 (s, 1H, OsCH). 13C{1H} NMR
(100.6 MHz, CDCl3): δ 297.0 (s, OstC), 215.9 (s, OsCH), 187.0 (s,
CMe), 171.2 (s, C-NO), 134.5ꢀ127.0 (Ph), 115.8 (s, OstCC(Si-
(CH3)3)), 22.5 (s, CH3), 0.0 (s, Si(CH3)3). Anal. Calcd for C45H43Cl2-
NOP2SiOs: C, 56.01; H, 4.49; N, 1.45. Found: C, 55.80; H, 4.40; N, 1.60.
Compound 6. Method A. To a solution of 1 (150 mg, 0.15 mol) in
CH2Cl2 (10 mL) was added HCl (1.5 mL, 1 M in Et2O, 1.5 mmol) and
hydrogen peroxide (146 μL, 35% by weight, 1.5 mmol). The reaction
mixture was stirred for 0.5 h at 0 ꢀC to give a brown solution. This
solution was washed with a K2CO3 solution (10 mL) and then brine
(10 mL ꢁ 2). The organic layer was dried with anhydrous MgSO4. The
solvent was removed completely under vacuum. The residue was
redissolved in 2 mL of CH2Cl2 and loaded on a silica gel column. The
Characterization data of 6 are as follows. FAB-MS (NBA, m/z): 877.1
1
(M+ ꢀ Cl). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ ꢀ17.7 (s). H
NMR (300.13 MHz, CD2Cl2): δ 1.71 (s, 3H, CH3), 7.27ꢀ7.47 (m,
30H, PPh3), 12.62 (t, J(PH) = 1.4 Hz, 1H, OsCH). 13C{1H} NMR (75.5
MHz, CD2Cl2): δ 203.6 (t, J(PC) = 4.7 Hz, OsdC), 192.1 (t, J(PC) =
6.0 Hz, OsCH), 161.4 (s, CCH3), 134.4 (t, J(PC) = 4.8 Hz, m-PPh3),
131.1 (s, OsCHdCCl), 130.7 (s, p-PPh3), 129.1 (t, J(PC) = 25.7 Hz,
ipso-PPh3), 128.0 (t, J(PC) = 4.9 Hz, o-PPh3), 125.9 (s, OsdC(O)CCl),
22.9 (s, CH3). Anal. Calcd for C42Cl4H34OP2Os: C, 53.76; H, 3.57.
Found: C, 53.59; H, 3.61.
Compound 7. To a suspension of 1 (0.216 g, 0.20 mmol) and
aluminum chloride (0.14 g, 1.0 mmol) in dichloromethane (15 mL)
(cooled to ꢀ15 ꢀC) was added hydrogen peroxide (0.24 mL, 30% by
weight, 2 mmol). The reaction mixture was stirred for 2 h at ꢀ15 ꢀC.
The temperature was raised to 0 ꢀC naturally to give an orange-brown
solution. The solvent was removed completely under vacuum, and the
resulting orange residue was extracted with benzene (10 mL) and filtered.
The filtrate was dried under vacuum. The resulting residue was dissolved
in dichloromethane (1 mL). The mixture was loaded on a silica gel
column. The column was eluted with benzene and then dichloro-
methane to give an orange-yellow solution. The solvent was removed
18357
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
completely under vacuum to give an orange-yellow solid. Yield: 64 mg,
33%. 31P{1H} NMR (121.5 MHz, C6D6): δ ꢀ16.9 (s). 1H NMR
(300.13 MHz, C6D6): δ 0.00 (s, 9H, Si(CH3)3), 1.84 (s, 3H, CH3),
6.91ꢀ7.83 (m, 30H, PPh3), 14.61 (s, br, 1H, OsCH). Anal. Calcd for
As a method of last resort, an empirical correction using the “DIFABS”
procedure of Walker and Stuart was applied.32 The resulting refinement
afforded better discrepancy indices, lower residual peaks and holes near
Os, and more physically sensible refinement of light atom thermal
parameters. The suppression of the absorption peaks also helped reveal
an additional partial CH2Cl2 solvate of crystallization. Despite the
poorer quality of diffraction data, the molecular identity and geometry
of compound 9 were still unambiguously revealed.
Computational Details. Molecular geometries of complexes were
optimized without constraints via DFT calculations using the MPW-
PW91 functional.33 Frequency calculations at the same level of theory
were also performed to identify the stationary points as minima (zero
imaginary frequencies). The 6-31G Pople basis set34 was used for C, O,
N, and H atoms, while the effective core potentials (ECPs) of Hay and
Wadt with a double-ζ valence basis set (Lanl2DZ)35 were used to
describe Os, P, Si, and Cl atoms. The polarization functions were added
for Os (ζ(f) = 0.886), P (ζ(d) = 0.340), Si (ζ(d) = 0.284), and Cl (ζ(d) =
0.514) and C (ζ(d) = 0.600) atoms bonded to the metal center.36
Geometry optimization of the structure of the biradical singlet species
B3-carbene was based on an open-shell singlet state wave function in
which both the α spin density at the metal center and the β spin density
at the methyl-substituted carbon are close to 1. The wave function
obtained for the optimized structure was found to be slightly contami-
nated with triplet state wave functions, and the ÆS2æ values calculated are
close to 1. In order to exclude the triplet state contribution, spin-
projection corrections were applied to re-evaluate the spin-corrected
singlet state total energy Esinglet according to the equation37
C45Cl3H43OP2SiOs 0.5CH2Cl2: C, 52.84; H, 4.34. Found: C, 52.32;
3
H, 4.21.
Compound 2. To a CH2Cl2 solution (1 mL) of 8 (100 mg, 0.100
mmol) in a Schlenk tube was added a solution of Br2 (344 mg,
2.18 mmol) in CH2Cl2 (0.8 mL) with stirring. The reaction mixture
was stirred at room temperature for 1 h to give a brown solution. The
solvent and excess Br2 were removed under vacuum. Addition of hexane
(5 mL) to the residue produced a pale green solid which was collected by
filtration, washed with diethyl ether (2 ꢁ 2 mL), and dried under
vacuum to give a green powder. Yield: 90 mg, 70%. 31P{1H} NMR
(121.5 MHz, CD2Cl2): δ ꢀ4.1 (s). 1H NMR (300.13 MHz, C6D6): δ
1.68 (s, 3H, CH3), 7.23ꢀ7.25 (m, 18 H, PPh3), 7.48ꢀ7.55 (m, 12 H,
PPh3), 12.22 (s, 1H, OsCH). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ
289.0 (t, 2J(PC) = 12.0 Hz, OstC), 199.6 (t, 2J(PC) = 5.7 Hz, OsCH),
167.6 (s, CCH3), 134.8ꢀ128.0 (m, PPh3), 109.9 (s, OsCHdCBr),
107.5 (s, OstCCBr), 27.1 (s, CH3). Anal. Calcd for C42H34Br4OsP2: C,
45.43; H, 3.09. Found: C, 45.53; H, 3.09.
Compound 9. An ice-cooled solution of 1 (300 mg, 0.35 mmol) in
CH2Cl2 (10 mL) was transferred to a suspension of NO2BF4 (185 mg,
1.38 mmol) and NaCl (1.00 g, 17.11 mmol) in CH2Cl2 (60 mL) which
was kept at ꢀ15 ꢀC. The mixture was stirred for 2 h to give a brown
suspension. The temperature was raised to ꢀ5 ꢀC naturally. Ice-cooled
water (20 mL) was added at ꢀ5 ꢀC with vigorous stirring. Sodium
hydrogen carbonate (140 mg, 1.67 mmol) in water (10 mL) was then
added. After the above mixture was stirred for 2 min, the top aqueous
layer was removed and the organic layer was further washed with water
(2 ꢁ 30 mL). The solvent of the organic layer was then removed under
vacuum. The residue was dissolved in 2 mL of CH2Cl2, and the mixture
was loaded on a silica gel column. The column was eluted with benzene
and then with dichloromethane to give an orange-red solution, from
which compound 9 was obtained as an orange-red solid, after the solvent
was removed completely under vacuum. Yield: 95 mg, 30%. 31P{1H}
NMR (161.97 MHz, CD2Cl2): δ ꢀ18.20 (s). 1H NMR (400.13 MHz,
C6D6): δ 1.95 (s, 3H, CH3), 5.53 (s, 1H), 7.50ꢀ7.27 (m, 30H, PPh3),
13.67 (s, 1H, OsCH). 13C{1H} NMR (100.40 MHz, CD2Cl2): δ 205.2
(t, J(PC) = 5.2 Hz, OsC(O)), 203.3 (t, J(PC) = 6.9 Hz, OsCH), 161.4
(s, CCH3), 147.4 (s, p-PPh3), 133.4 4 (t, J(PC) = 4.5 Hz, m-PPh3), 129.8
(s, OsdC(O)C(NO2)), 128.1 1 (t, J(PC) = 25.0 Hz, ipso-PPh3), 127.0
(t, J(PC) = 4.2 Hz, o-PPh3), 92.5 (s, CH), 24.1 (s, CH3). Anal. Calcd for
2EOSS ꢀ EtriplethS2iOSS
Esinglet
¼
2 ꢀ hS2iOSS
where EOSS and Etriplet are the total electronic energies of the open-shell
singlet and triplet states, respectively, obtained from the UMPWPW91
calculations. ÆS2æOSS corresponds to the ÆS2æ value obtained from the
UMPWPW91 calculations of the open-shell singlet state. All the DFT
calculations were performed with the Gaussian 03 package.38
’ ASSOCIATED CONTENT
S
Supporting Information. Text giving the complete ref
b
38, tables giving Cartesian coordinates and electronic energies
for all the calculated structures, and CIF files giving X-ray crystal-
lographic data for 3ꢀ7 and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
C42H35Cl2NO2P2Os 0.2CH2Cl2: C, 54.75; H, 3.85; N, 1.51. Found: C,
3
54.56; H, 4.25; N, 1.42.
Crystallographic Analysis. Crystals suitable for X-ray diffraction
were grown from a benzene solution layered with hexane for 3 and from
CH2Cl2 solutions layered with hexane for 4ꢀ7 and 9, respectively. All
the crystals were mounted on glass fibers. The diffraction intensity data
were collected with a Bruker CCD diffractometer with monochromated
Mo Kα radiation (λ = 0.710 73 Å). Lattice determination and data
collection was carried out using SMART v. 5.625 software. Data
reduction and absorption correction were performed using SAINT v.
6.26 and SADABS v 2.03, respectively. Structure solution and refine-
ment for all four compounds were performed using either SHELXTL v.
6.1030 or OLEX231 software packages. They were solved by direct methods
and refined by full-matrix least squares on F2. All non-hydrogen atoms
were refined anisotropically, and the hydrogen atoms were introduced at
their geometric positions and refined as riding atoms unless specified.
In general the structures refined acceptably well; however, for
compound 9 the data quality was badly impacted by the effect of partial
desolvation and absorption. The structure had large electron density
peaks and difference holes of +4.85/ ꢀ3.88 e/Å3 associated with the two
Os centers of the asymmetric unit, at distances of approximately 0.9 Å.
’ AUTHOR INFORMATION
Corresponding Author
chzlin@ust.hk (Z.L.); chjiag@ust.hk (G.J.).
’ ACKNOWLEDGMENT
This work was supported by the Hong Kong Research Grant
Council (HKUST601007, 602611 and HKU1/CRF/08).
’ REFERENCES
(1) See for example: (a) Bleeke, J. R. Chem. Rev. 2001, 101, 1205.
(b) Landorf, C. W.; Haley, M. M. Angew. Chem., Int. Ed. 2006, 45, 3914.
(c) Wright, L. J. Dalton Trans. 2006, 1821.
(2) (a) Elliott, G. P.; Roper, W. R.; Waters, J. M. J. Chem. Soc., Chem.
Commun. 1982, 811. (b) Rickard, C. E. F.; Roper, W. R.; Woodgate,
S. D.; Wright, L. J. Angew. Chem., Int. Ed. Engl. 2000, 39, 750. (c) Rickard,
C. E. F.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. J. Organomet. Chem.
2001, 623, 109. (d) Clark, G. R.; Johns, P. M.; Roper, W. R.; Wright, L. J.
18358
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
Organometallics 2006, 25, 1771. (e) Johns, P. M.; Roper, W. R.;
Woodgate, S. D.; Wright, L. J. Organometallics 2010, 29, 5358. (f) Clark,
G. R.; Ferguson, L. A.; McIntosh, A. E.; Sohnel, T.; Wright, L. J. J. Am.
Chem. Soc. 2010, 132, 13443.
H. U.; Nietlispach, D.; Salzer, A. Organometallics 1992, 11, 2087. (c) Lin,
W.; Wilson, S. R.; Girolami, G. S. Organometallics 1997, 16, 2356. (d)
Ohki, Y.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 3463. (e) Bertling,
U.; Englert, U.; Salzer, A. Angew. Chem., Int. Ed. Engl. 1994, 33, 1003. (f)
Bleeke, J. R.; Bass, L. A.; Xie, Y. F.; Chiang, M. Y. J. Am. Chem. Soc. 1992,
114, 4213. (g) Kralik, M. S.; Rheingold, A. L.; Hutchinson, J. P.;
Freeman, J. W.; Ernst, R. D. Organometallics 1996, 15, 551.
(14) Liu, S. H.; Ng, W. S.; Chu, H. S.; Wen, T. B.; Xia, H. P.; Zhou,
Z. Y.; Lau, C. P.; Jia, G. Angew. Chem., Int. Ed. 2002, 41, 1589.
(15) (a) Roper, W. R. Angew. Chem., Int. Ed. 2001, 40, 2440. (b) Jia, G.
Acc. Chem. Res. 2004, 37, 479. (c)Jia,G.Coord. Chem. Rev. 2007, 251, 2167.
(16) Wen, T. B.; Zhou, Z. Y.; Jia, G. Angew. Chem., Int. Ed. 2001,
40, 1951.
(17) Wen, T. B.; Ng, S. M.; Hung, W. Y.; Zhou, Z. Y.; Lo, M. F.; Shek,
L. Y.; Williams, I. D.; Lin, Z.; Jia, G. J. Am. Chem. Soc. 2003, 125, 884.
(18) (a) Wen, T. B.; Hung, W. Y.; Sung, H. H. Y.; Williams, I. D.; Jia,
G. J. Am. Chem. Soc. 2005, 127, 2856. (b) Hung, W. Y.; Zhu, J.; Wen,
T. B.; Yu, K. P.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. J. Am.
Chem. Soc. 2006, 128, 13742. (c) He, G.; Zhu, J.; Hung, W. Y.; Wen,
T. B.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. Angew. Chem., Int. Ed.
2007, 46, 9065.
(3) (a) Xia, H.; He, G.; Zhang, H.; Wen, T. B.; Sung, H. H. Y.;
Williams, I. D.; Jia, G. J. Am. Chem. Soc. 2004, 126, 6862. (b) Gong, L.;
Lin, Y.; Wen, T. B.; Zhang, H.; Zeng, B.; Xia, H. Organometallics 2008,
27, 2584. (c) Liu, B.; Xie, H.; Wang, H.; Wu, L.; Zhao, Q.; Chen, J.; Wen,
T. B.; Cao, Z.; Xia, H. Angew. Chem., Int. Ed. 2009, 48, 5461. (d) Gong,
L.; Chen, Z.; Lin, Y.; He, X.; Wen, T. B.; Xu, X.; Xia, H. Chem. Eur. J.
2009, 15, 6258. (e) Zhang, H.; Wu, L.; Wen, T. B.; Xia, H. Chem. Eur. J.
2009, 15, 3546. (f) Wang, T.; Li, S.; Zhang, H.; Lin, R.; Han, F.; Lin, Y.;
Wen, T. B.; Xia, H. Angew. Chem., Int. Ed. 2009, 48, 6453. (g) Huang, J.;
Lin, R.; Wu, L.; Zhao, Q.; Zhu, C.; Wen, T. B.; Xia, H. Organometallics
2010, 29, 2916.
(4) (a) Barrio, P.; Esteruelas, M. A.; Onate, E. J. Am. Chem. Soc. 2004,
126, 1946. (b) Zhao, Q.; Gong, L.; Xu, C.; Zhu, J.; He, X.; Xia, H. Angew.
Chem., Int. Ed. 2011, 50, 1354.
(5) (a) Clark, G. R.; Lu, G.; Roper, W. R.; Wright, L. J. Organome-
tallics 2007, 26, 2167. (b) Clark, G. R.; Johns, P. M.; Roper, W. R.;
Wright, L. J. Organometallics 2008, 27, 451. (c) Dalebrook, A. F.; Wright,
L. J. Organometallics 2009, 28, 5536. (d) Clark, G. R.; Johns, P. M.;
Roper, W. R.; Sohnel, T.; Wright, L. J. Organometallics 2011, 30, 129.
(6) (a) Gilbertson, R. D.; Weakley, T. J. R.; Haley, M. M. J. Am.
Chem. Soc. 1999, 121, 2597. (b) Wu, H. P.; Lanza, S.; Weakley, T. J. R.;
Haley, M. M. Organometallics 2002, 21, 2824. (c) Gilbertson, R. D.; Lau,
T. L. S.; Lanza, S.; Wu, H. P.; Weakley, T. J. R.; Haley, M. M.
Organometallics 2003, 22, 3279. (d) Wu, H. P.; Weakley, T. J. R.; Haley,
M. M. Chem. Eur. J. 2005, 11, 1191. (e) Wu, H. P.; Ess, D. H.; Lanza, S.;
Weakley, T. J. R.; Houk, K. N.; Baldridge, K. K.; Haley, M. M.
Organometallics 2007, 26, 3957.
(19) Olah, G. A. Acc. Chem. Rev. 1971, 4, 240.
(20) (a) Henderson, J. L.; Edwards, A. S.; Greaney, M. F. J. Am.
Chem. Soc. 2006, 128, 7426. (b) Tambar, U. K.; Stoltz, B. M. J. Am. Chem.
Soc. 2005, 127, 5340–5341. (c) Pellissier, H.; Santelli, M. Tetrahedron
2003, 59, 701–730.
(21) Friedman, L.; Logullo, F. M. Angew. Chem., Int. Ed. Engl. 1965,
4, 239.
(22) Based on a search of the Cambridge Structural Database, CSD
version 5.26 (Nov 2009).
(23) For examples, see the following. (a) Os(OTf)(NC5H4CHd
CH)(NC5H4CHdCH2)(PiPr3)]OTf (1.995(2) Å): Esteruelas, M. A.;
Fernandez-Alvarez, F. J.; Olivan, M.; Onate, E. J. Am. Chem. Soc.
2006, 128, 4596. (b) CpOs(CHdCHCOMe)(PiPr3) (1.989(4) Å):
Esteruelas, M. A.; Hernandez, Y. A.; Lopez, A. M.; Olivan, M.; Onate, E.
Organometallics 2005, 24, 5989. (c) Os(SnPh2Cl)(NC5H4CHdCH)-
(H2)(PiPr3)2 (2.068(4) Å): Eguillor, B.; Esteruelas, M. A.; Olivan, M.;
Onate, E. Organometallics 2005, 24, 1428. (d) OsCl(CHdCH(p-tolyl)-
(CO)(PPh3)3 (2.105(7) Å): Xia, H.; Wen, T. B.; Hu, Q. Y.; Wang, X.;
Chen, X.; Shek, L. Y.; Williams, I. D.; Wong, K. S.; Wong, G. K. L.; Jia, G.
Organometallics 2005, 24, 562. (e) OsCl(CHdCHPh)(O)2(PiPr3)2
(1.979(30) Å): Bourgault, M.; Castillo, A.; Esteruelas, M. A.; O~nate,
E.; Ruiz, N. Organometallics 1997, 16, 636. (f) Os(CHdCHPh)-
(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (2.053(3) Å): Bolano, T.; Cas-
tarlenas, R.; Esteruelas, M. A.; Onate, E. J. Am. Chem. Soc. 2006, 128, 3965.
(g) Os(CHdCHCH2NH2)Cl(CO)(nPrNH2)(PiPr3) (2.040(3) Å):
Baya, M.; Esteruelas, M. A.; Onate, E. Organometallics 2010, 29, 6298.
(24) For example, see the following. (a) CpOsCl(dCHPh)-
(PiPr2(C(CH3)dCH2) (1.895(5) Å): Esteruelas, M. A.; Gonzalez,
A. I.; Lopez, A. M.; Onate, E. Organometallics 2004, 23, 4858.
(b) [OsCl(dC(Ph)CH2Ph)(CO)(PiPr3)2][BF4] (1.929(3) Å): Ester-
uelas, M. A.; Lopez, A. M.; Onate, E. Organometallics 2007, 26, 3260.
(c) (η6-C6H3Me3)OsdCR2(O2CCF3)2 (R = p-tolyl) (1.957(7) Å):
Webernd€orfer, B.; Henig, G.; Werner, H. Organometallics 2000, 19, 4687.
(25) Zaheer, M.; Akhter, Z.; Bolte, M.; Siddiqi, H. M. Acta Crystal-
logr., Sect. E 2008, 64, 2381.
(7) (a) Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendꢀon, N.;
Salazar, V.; O~nate, E.; Mereiter, K. J. Am. Chem. Soc. 2003, 125, 9898.
(b) Alvarez, E.; Paneque, M.; Poveda, M. L.; Rendon, N. Angew. Chem.,
Int. Ed. 2006, 45, 474. (c) Ilg, K.; Paneque, M.; Poveda, M. L.; Rendon,
N.; Santos, L. L.; Camona, E.; Mereiter, K. Organometallics 2006,
25, 2230. (d) Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendꢀon,
ꢀ
N.; Santos, L. L.; Alvarez, E.; Salazar, V.; Mereiter, K.; O~nate, E. Organo-
metallics 2007, 26, 3403. (e) Paneque, M.; Poveda, M. L.; Rendꢀon, N.;
ꢀ
Alvarez, E.; Carmona, E. Eur. J. Inorg. Chem. 2007, 2711. (f) Chin, C. S.;
Lee, H. Chem. Eur. J. 2004, 10, 4518. (g) Chin, C. S.; Lee, H.; Eum, M. S.
Organometallics 2005, 24, 4849.
(8) (a) Bleeke, J. R.; Xie, Y. F.; Peng, W. J.; Chiang, M. J. Am. Chem.
Soc. 1989, 111, 4118. (b) Bleeke, J. R.; Xie, Y. F.; Bass, L.; Chiang, M. Y.
J. Am. Chem. Soc. 1991, 113, 4703. (c) Bleeke, J. R.; Behm, R. J. Am.
Chem. Soc. 1997, 119, 8503. (d) Bleeke, J. R.; Behm, R.; Xie, Y. F.;
Chiang, M. Y.; Robinson, K. D.; Beatty, A. M. Organometallics 1997,
16, 606 and references therein.
(9) (a) Jacob, V.; Weakley, T. J. R.; Haley, M. M. Angew. Chem., Int.
Ed. 2002, 41, 3470. (b) Landorf, C. W.; Jacob, V.; Weakley, T. J. R.;
Haley, M. M. Organometallics 2004, 23, 1174. (c) Jacob, V.; Landorf,
C. W.; Zakharov, L. N.; Weakley, T. J. R.; Haley, M. M. Organometallics
2009, 28, 5183.
(10) (a) Zhang, H.; Xia, H.; He, G.; Wen, T. B.; Gong, L.; Jia, G.
Angew. Chem., Int. Ed. 2006, 45, 2920. (b) Zhang, H.; Feng, L.; Gong, L.;
Wu, L.; He, G.; Wen, T. B.; Yang, F.; Xia, H. Organometallics 2007,
26, 2705. (c) Wu, L.; Feng, L.; Zhang, H.; Liu, Q.; He, X.; Yang, F.; Xia,
H. J. Org. Chem. 2008, 73, 2883. (d) Zhang, H.; Lin, R.; Hong, G.; Wang,
T.; Wen, T. B.; Xia, H. Chem. Eur. J. 2010, 16, 6999. (e) Lin, R.; Zhang,
H.; Li, S.; Chen, L.; Zhang, W.; Wen, T. B.; Zhang, H.; Xia, H. Chem. Eur.
J. 2011, 17, 2420. (f) Lin, R.; Zhang, H.; Li, S. H.; Wang, J. I.; Xia, H. P.
Chem. Eur. J. 2011, 17, 4223.
(26) Conversion of metallabenzynes to carbene complexes was
reported recently: Chen, J.; Shi, C.; Sung, H. H. Y.; Williams, I. D.;
Lin, Z.; Jia, G. Angew. Chem., Int. Ed. 2011, 50, 7295.
(27) Bosch, E.; Kochi, J. K. J. Org. Chem. 1994, 59, 5573 and
references therein.
(28) (a) Ben-Daniel, R.; Visser, S. P. d.; Shaik, S.; Neumann, R. J. Am.
Chem. Soc. 2003, 125 (40), 12116. (b) Barhate, N. B.; Gajare, A. S.;
Wakharkar, R. D.; Bedekar, A. V. Tetrahedron Lett. 1998, 39, 6394.
(29) Kurz, M. E.; Johnson, G. J. J. Org. Chem. 1971, 36, 3184.
(30) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(11) Clark, G. R.; O’Neale, T. R.; Roper, W. R.; Tonei, D. M.;
Wright, L. J. Organometallics 2009, 28, 567.
(12) Poon, K. C.; Liu, L.; Guo, T.; Li, J.; Sung, H. H.Y.; Williams,
I. D.; Lin, Z.; Jia, G. Angew. Chem., Int. Ed. 2010, 49, 2759.
(13) See for example: (a) Englert, U.; Podewils, F.; Schiffers, I.;
Salzer, A. Angew. Chem., Int. Ed. 1998, 37, 2134. (b) Bosch, H. W.; Hung,
(31) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
18359
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360

Journal of the American Chemical Society
ARTICLE
(32) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(33) (a) Perdew, J. P.; Burke, K.; Wang, Y. Phys. Rev. B 1996,
54, 16533. (b) Adamo, C.; Barone, V. J. Chem. Phys. 1998, 108, 664.
(34) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971,
54, 724.
(35) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(36) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
A.; Jonas, V.; Kohler, K. F.; Stegmman, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 111.
(37) (a) Yamaguchi, K.; Jensen, F.; Dorigo, A.; Houk, K. N. Chem.
Phys. Lett. 1988, 149, 537. (b) Yamanaka, S.; Kawakami, T.; Nagao, H.;
Yamaguchi, K. Chem. Phys. Lett. 1994, 231, 25. (c) Lim, M. H.;
Worthington, S. E.; Dulles, F. J.; Cramer, C. J. In Chemical Applications
of Density Functional Theory; Laird, B. B., Ross, R. B., Ziegler, T., Eds.;
American Chemical Society: Washington, DC, 1996; Vol. 629, p 402.
(d) Isobe, H.; Takano, Y.; Kitagawa, Y.; Kawakami, T.; Yamanaka, S.;
Yamaguchi, K.; Houk, K. N. Mol. Phys. 2002, 100, 717.
(38) Frisch, M. J. et al. Gaussian 03, revision B05; Gaussian, Inc.,
Pittsburgh, PA, 2003.
18360
dx.doi.org/10.1021/ja207315h |J. Am. Chem. Soc. 2011, 133, 18350–18360