Selective synthesis of osmanaphthalene and osmanaphthalyne by intramolecular C-H activation

Full text of DOI:10.1002/anie.200902238

Angewandte
Chemie
DOI: 10.1002/anie.200902238
À
C H Activation
Selective Synthesis of Osmanaphthalene and Osmanaphthalyne by
À
Intramolecular C H Activation**
Bin Liu, Hujun Xie, Huijuan Wang, Liqiong Wu, Qianyi Zhao, Jinxiang Chen, Ting Bin Wen,
Zexing Cao,* and Haiping Xia*
Metallabenzenes[1] and metallabenzynes[2] have attracted
considerable research interest in recent years. However,
their higher homologues are still very rare.[3] In fact, only
two well-characterized examples have been reported. One is
the metallanaphthalene prepared by Paneque et al. in 2003 by
oxidation of a bicyclic iridium complex.[3a] The other is the
metallanaphthalyne synthesized by Jia, Lin, and co-workers
formation of isolated 2 into 3 is also reported. As there is a
metallabenzene unit in 2 and a metallabenzyne unit in 3, the
transformation of 2 into 3 represents the first example of the
conversion from metallabenzene into metallabenzyne.
Heating 1 in DCE (ClCH2CH2Cl) at reflux under a N2
atmosphere gave the (m-Cl)3-bridged bisosmanaphthalene 2,
which was isolated as a green solid in 72% yield (Scheme 1).
The structure of 2 was confirmed by X-ray diffraction. The
asymmetric unit contains two independent molecules (2A
and 2B). A drawing of the cation 2A is shown in Figure 1. In
in 2007 by reduction of an osmium carbyne complex with zinc
[3b]
À
and subsequent C Cl bond activation.
[1a,4]
À
It is known that C H activation
is a very important
method for the synthesis of organic and organometallic
compounds. Recently, we reported the synthesis of osmium
ꢀ À
=
hydride–alkenylcarbyne
complex
[OsH{ C C(PPh3)
CHPh}(PPh3)2Cl2]BF4 (1) and its formal [4+2] cycloaddition
with acetonitrile to give the first late-transition-metal-con-
taining metallapyridine and metallapyridinium compounds.[5]
From our further investigation of the reactivity of 1, we herein
report the selective formation of metallanaphthalene 2 and
metallanaphthalyne 3 from 1 in high yields by intramolecular
À
C H activation of the phenyl ring under a N2 or O2
atmosphere, respectively (Scheme 1). Furthermore, the trans-
Figure 1. X-ray crystal structure of 2A (ellipsoids at the 50% proba-
bility level).[12] Counteranion and phenyl rings in PPh3 groups are
omitted for clarity. Selected bond lengths [ꢀ]: Os1–C11 1.923(8), Os1–
C15 2.039(8), Os1–P1 2.268(2), Os1–Cl1 2.496(2), Os1–Cl2 2.520(2),
Os1–Cl3 2.546(2), Os2–C21 1.914(9), Os2–C25 2.000(8), Os2–P3
2.260(2), Os2–Cl1 2.497(2), Os2–Cl2 2.554(2), Os2–Cl3 2.516(2), P2–
C12 1.786(9), P4–C22 1.779(9), C11–C12 1.395(13), C12–C13
1.375(12), C13–C14 1.421(13), C14–C15 1.420(12), C21–C22 1.396(12),
C22–C23 1.388(12), C23–C24 1.432(12), C24–C25 1.426(12).
2A, two osmanaphthalene metallacycles are connected by
À
three chlorido bridges. The Os Cl bond lengths of the
chlorido bridges are in the range 2.496(2)–2.554(2) ꢀ, which
are similar to those in reported dinuclear osmium complexes
with three chlorido bridges.[6] The mean deviation from the
least-squares plane through the C11, C12, C13, C14, and C15
chain is 0.035 ꢀ, and the value through the C21, C22, C23,
C24, and C25 chain is 0.026 ꢀ. The Os1 atom is out of the
plane of the metallacyclic carbon atoms by 0.736 ꢀ (the
relevant value of Os2 is 0.697 ꢀ), which is similar to the metal
atom displacement in the iridanaphthalene compound
reported by Paneque et al. (0.76 ꢀ).[3a] The dihedral angle
between the plane through C11, C12, C13, C14, and C15 and
the plane constructed by C11, Os1, and C15 is 31.78 (the
relevant dihedral angle in the Os2-containing six-membered
metallacycle is 30.48). These values are comparable with those
found in our previously reported bisruthenabenzene
Scheme 1. Preparation of 2 and 3.
[*] B. Liu, H. Xie, H. Wang, L. Wu, Q. Zhao, J. Chen, Prof. Dr. T. B. Wen,
Prof. Dr. Z. Cao, Prof. Dr. H. Xia
State Key Laboratory of Physical Chemistry of Solid Surfaces
College of Chemistry and Chemical Engineering, Xiamen University
Xiamen 361005 (P.R. China)
Fax: (+86)592-218-6628
E-mail: zxcao@xmu.edu.cn
hpxia@xmu.edu.cn
[**] This work was financially supported by the National Science
Foundation of China (No. 20872123 and No. 20873105).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200902238.
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[{RuK (CHCRCHCRCL H)R}2(m-Cl)3](BF4)3 (R = PPh3) (26.4
(2.110(6) ꢀ) are within the range of those observed for
[2a,9]
and 30.18).[7] The Os1 C11 (1.923(8) ꢀ), Os1 C15
typical Os C bonds (1.69–1.84 ꢀ)
and Os C(aryl) bonds
À
À
ꢀ
À
(2.039(8) ꢀ), Os2 C21 (1.914(9) ꢀ), and Os2 C25
(2.000(8) ꢀ) bond lengths are similar to those observed in
(2.02–2.18 ꢀ),[10] respectively. They are also comparable to
those observed for the osmanaphthalyne reported by Jia and
co-workers (1.732(4) ꢀ and 2.127(3) ꢀ, respectively).[3b] The
À
À
the reported osmabenzenes.[1h,o] All the C C bond lengths of
À
À
the fused benzene rings are comparable to those found in
C C bond lengths of the metallacycle are between those of
iridanaphthalene[3a] and naphthalene.[8] Furthermore, there is
single and double C C bonds, without significant bond length
À
À
no significant C C bond length alternation, thus indicating a
alternation. These data suggest a delocalized structure. The
Os1-C1-C2 bond angle is 151.1(5)8, which is similar to those
found in Jiaꢁs osmanaphthalyne (155.0(3)8)[3b] and osmaben-
zynes (148.3(6)–154.9(9)8).[2a,b]
delocalized structure.
The solid-state structure of 2 is fully supported by solution
NMR spectroscopy. The 1H NMR spectrum shows the signals
of OsCH at d = 21.42 ppm (dd, JP, H = 12.0 and 6.9 Hz) and
OsCHC(PPh3)CH at d = 7.75 ppm (d, JP, H = 18.2 Hz). The
31P{1H} NMR spectrum shows two signals at d = 21.06 (d,
The NMR spectroscopic data of 3 are consistent with its
solid-state structure. The 1H NMR spectrum shows a signal at
ꢀ
d = 8.19 ppm assignable to Os CC(PPh3)CH. The
J
P, P = 3.5 Hz) and À2.20 ppm (d, JP, P = 3.5 Hz) assignable to
31P{1H} NMR spectrum shows two signals at d = 14.33 and
À9.11 ppm assignable to CPPh3 and OsPPh3, respectively.
The 13C{1H} NMR spectrum displays signals for C1 and C5 at
d = 264.9 and 174.2 ppm, respectively.
CPPh3 and OsPPh3, respectively. The 13C{1H} NMR spectrum
displays signals for C11 (C21) at d = 239.2 ppm (d, JP, C
10.9 Hz) and C15 (C25) at 189.0 ppm (d, JP, C = 7.1 Hz).
=
When the transformation of 1 to 2 was carried out in the
presence of a slight amount of air, another product could be
detected from the NMR spectra. When 1 was heated in DCE
at reflux under an O2 atmosphere, this product could be
isolated in high yield and identified as osmanaphthalyne 3.
After optimizing the reaction conditions, 3 could even be
obtained in 84% yield by heating the solid sample of 1 in air at
1208C for 5 h (Scheme 1). This solid-state synthesis is easy to
handle and environmentally benign.
A plausible mechanism for the formation of 2 and 3 is
shown in Scheme 2. The migration of the hydride ligand (H1)
from osmium to the carbyne carbon atom should afford an
The structure of 3 was confirmed by X-ray diffraction. As
shown in Figure 2, 3 has an essentially planar metallacycle.
The sum of angles in the ring constructed by Os1, C1, C2, C3,
C4, and C5 is 719.98, which is almost identical to the ideal
value of 7208. The mean deviation from the least-squares
plane through the six atoms of the Os-containing six-
membered ring is 0.0117 ꢀ, and the value through the 10
atoms of the two fused rings is 0.0421 ꢀ. It is worth noting that
À
À
the Os1 C1 (1.754(7) ꢀ) and Os1 C5 bond lengths
Scheme 2. Proposed mechanism for the formation of 2 and 3.
osmium carbene[5,9a,11] intermediate (A) with an agostic form.
2
À
The ortho C H bond of the phenyl ring of A is further
activated to give intermediate B containing a hydride ligand
(H2). Under a N2 atmosphere, dimerization of B through the
loss of PPh3, HCl, and HBF4 should give 2, whereas in the
presence of O2, B is oxidized to osmanaphthalyne 3 and H2O.
Consistent with the proposed mechanism, when some
weak bases such as NaHCO3 or PhNH2 were purposely added
to the reaction system, the in situ NMR experiment showed
that the formation of 2 was indeed facilitated, even in air. The
reaction was also monitored by 31P and 1H NMR spectroscopy
when 1 was heated at reflux in DCE under an O2 atmosphere.
Both 2 and 3 could be observed in the NMR spectra at the
initial stage (Figure S1 in the Supporting Information). Then,
the signal of 3 increased gradually, accompanied by the
decrease of the signal of 2. Eventually, 3 was obtained as the
main product and isolated in 76% yield. This phenomenon
indicates that 2 could transform into 3 under suitable
conditions. To further confirm the mechanism, the isolated
compound 2 was heated at reflux in DCE under an O2
Figure 2. X-ray crystal structure of 3 (ellipsoids at the 50% probability
level).[12] Anion and hydrogen atoms are omitted for clarity. Selected
bond lengths [ꢀ]: Os1–P1 2.418(1), Os1–P2 2.419(2), Os1–Cl1
2.459(2), Os1–Cl2 2.442(2), Os1–C1 1.754(7), Os1–C5 2.110(6), C1–
C2 1.385(9), C2–C3 1.369(9), C3–C4 1.395(9), C4–C5 1.450(8), C5–C6
1.420(8), C6–C7 1.373(9), C7–C8 1.362(10), C8–C9 1.370(10), C9–C4
1.416(9).
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atmosphere in the presence of HCl (1 equiv), HBF4 (1 equiv),
and excess PPh3 (to balance the equation for the conversion of
2 into 3). As indicated by in situ 31P NMR spectroscopy
(Figure S2 in the Supporting Information), the amount of 3
increased gradually while that of 2 decreased. Although some
unidentified species were observed at the early stages, 35 min
later, 3 became the main product along with excess PPh3. In
sharp contrast, when the reaction was performed under a N2
atmosphere, no appreciable reaction could be observed.
These results strongly support the indispensable role of O2
in the formation of 3.
driven thermodynamically through the reaction of the
intermediate B’ with O2. Such results are consistent with our
present experiments.
Both 2 and 3 have excellent thermal stabilities. Solid
samples of 2 and 3 remain nearly unchanged at 1208C in air
for 5 h. Their remarkable thermal stabilities are related to the
bulky PPh3 substituent or ligands[1f] and their aromaticity.
The transformation of 2 into 3 represents the first example
of the conversion of metallabenzene to metallabenzyne
(path a, Scheme 3). As the transformation of metallabenzyne
into metallabenzene was reported by Jiaꢁs group in 2006
DFT calculations were performed to elucidate the pro-
posed mechanism shown in Scheme 2. Figure 3 shows the
relative energy profiles for the transformation of 1’ into 2’ and
3’ (1’, 2’, and 3’ are the model cations of 1, 2, and 3,
respectively). From the 18-electron reactant 1’ (hydride–
Scheme 3. Interconversion of metallabenzene and matallabenzyne.
(path b, Scheme 3),[2c] the interconversion
between these two kinds of interesting
metallaarenes, namely, metallabenzenes
and metallabenzynes, would now be feasi-
ble.
In summary, we have selectively synthe-
sized bismetallanaphthalene 2 and metal-
lanaphthalyne 3 from 1 in high yields by
À
intramolecular C H activation by control-
ling the atmosphere (either N2 or O2).
Compound 3 can also be obtained by solid-
state synthesis. The formation of metalla-
naphthalyne 3 from metallanaphthalene 2
provides a valuable method for the trans-
formation of metallabenzene into metal-
labenzyne. Investigations into the prepara-
tion of other fused ring metallabenzenoids
Figure 3. Relative energy and free energy (in parentheses) profiles (in kcalmolÀ1) for the
formation of the 2’ and 3’.
employing this convenient method are
ongoing.
alkenylcarbyne), the reaction proceeds to an agostic inter- Experimental Section
2: A green solution of 1 (500 mg, 0.400 mmol) in 1,2-dichloroethane
mediate A’ (alkenylcarbene) via the first transition state (TS1)
with a barrier of 31.5 kcalmolÀ1. Although this barrier is
relatively high, it is feasible when more stable compounds
such as 2 and 3 are formed. Furthermore, the transformation
of an osmium hydride carbyne complex into an osmium
carbene has already been reported.[5,9a,11] Followed by the
(10 mL) was heated at reflux for 8 h under N2. The solvent was
removed in vacuo. Addition of diethyl ether to the resulting residue
led to a brown-green solid, which was washed with a mixture of
methanol and diethyl ether (1:10) and dried in vacuo. Yield: 267 mg,
72%; 1H NMR plus HMQC (300.1 MHz, CDCl3): d = 21.42 (dd,
J(PH) = 12.0 Hz, J(PH) = 6.9 Hz, 2H, OsCH), 7.75 (d, J(PH) =
18.2 Hz, 2H, OsCHC(PPh3)CH), 7.85–6.89 ppm (m, 68H, other
aromatic atoms); 31P{1H} NMR (121.5 MHz, CDCl3): d = 21.06 (d,
J(PP) = 3.5 Hz, CPPh3), À2.20 ppm (d, J(PP) = 3.5 Hz, OsPPh3);
13C{1H} NMR plus DEPT-135 and HMQC (75.5 MHz, CDCl3): d =
À
ortho C H activation of the phenyl ring via the second
transition state (TS2) with a barrier of 17.6 kcalmolÀ1, A’ can
be converted into B’, which contains a hydride ligand. Under
a N2 atmosphere, intermediate B’ can evolve either to 2’
2
=
239.2 (d, J(PC) = 10.9 Hz, Os CH), 189.0 (d, J(PC) = 7.1 Hz, Os-C),
À
through subsequent H Cl bond coupling and HCl removal as
1
2
=
=
153.1 (d, J(PC) = 17.6 Hz, Os CHC(PPh3) CH), 143.3 (d, J(PC) =
À
well as dimerization or to 3’ through H H bond coupling.
We note that the formation of 2’ is more favorable energeti-
cally (by 24.3 kcalmolÀ1) than the generation of 3’ through the
abstraction of dihydrogen. However, under an O2 atmos-
phere, the involvement of O2 in the removal of two H atoms
(H1 and H2 in Figure 3) can facilitate the formation of 3’ with
an overall exothermicity of 40.3 kcalmolÀ1. Presumably,
under an O2 atmosphere, the transformation of 2’ into 3’ is
=
=
=
13.7 Hz, Os CHC(PPh3) CHC), 120.1 (d, J(PC) = 86.7 Hz, Os
CHC(PPh3)), 147.1–121.7 ppm (m, other aromatic carbon atoms).
Anal. calcd (%) for C90H72Cl3P4BF4Os2: C 58.40, H 3.92; found: C
58.44, H 4.08.
3: Method 1: Complex 1 (106 mg, 0.085 mmol) was heated in the
solid state at 1208C in air for 5 h, then washed with a mixture of
methanol and diethyl ether (1:10) and dried in vacuo. Yield: 89 mg,
84%. Method 2: A green solution of 1 (200 mg, 0.16 mmol) in 1,2-
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dichloroethane (10 mL) was heated at reflux for 15 h under an O2
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atmosphere. The solvent was removed in vacuo. Addition of diethyl
ether to the resulting residue led to a green solid, which was washed
with a mixture of dichloromethane and diethyl ether (1:10) and dried
in vacuo. Yield: 152 mg, 76%. Method 3: A green solution of 2
(200 mg, 0.11 mmol) in 1,2-dichloroethane (10 mL) was treated with
HCl (37% in H2O, 9.0 mL, 0.11 mmol), HBF4 (52% in diethyl ether,
18.6 mL, 0.11 mmol), and excess PPh3, then the mixture was heated at
reflux for 2 h under an O2 atmosphere. The solvent was removed
in vacuo. The addition of diethyl ether to the resulting residue led to a
green solid, which was washed with a mixture of dichloromethane and
diethyl ether (1:10) and dried in vacuo. Yield: 237 mg, 88%; 1H NMR
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1
plus HMQC and H{31P} (300.1 MHz, CDCl3): d = 8.19 (d, J(PH) =
13.5 Hz, 1H, OsCC(PPh3)CH), 7.68–5.90 ppm (m, 49H, other aro-
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ꢀ
(100.6 MHz, CD2Cl2): d = 264.9 (br, Os C), 177.9 (d, J(PC) =
ꢀ
8.1 Hz, Os CC(PPh3)CH), 174.2 (br, Os-C), 104.9 (d, J(PC) =
ꢀ
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4.04; found: C 60.18, H 4.26.
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Received: April 27, 2009
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Published online: June 18, 2009
À
Keywords: C H activation · metallacycles · osmium ·
synthesis design
.
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