Oxygenation of ruthenium carbene complexes containing naphthothiophene or naphthofuran: Spectroscopic and DFT studies

Article abstract of DOI:10.1002/asia.201300726

The aryl propargylic alcohol 1-[2-(thiophen-3-yl)phenyl]prop-2-yn-1-ol (1a) is readily prepared from 2-(thiophen-3-yl)benzaldehyde. In the presence of visible light, treatment of 1a with one-half mole equivalent of [Ru]Cl ([Ru]-Cp(dppe)Ru) (dppe=1,2-bis(diphenylphosphino)ethane) and NH ₄PF₆ in O₂ affords the naphtha[2,1-b]thiophene- 4-carbaldehyde (4a) in high yields. The cyclization reaction of 1a proceeds through the formation of the carbene complex 2a that contains the naphtha[2,1-b]thiophene ring, which is isolated in a 1:1 stoichiometric reaction. The C-C bond formation between the inner carbon of the terminal triple bond and the heterocyclic ring is confirmed by structure determination of 2a using single-crystal X-ray diffraction analysis. Facile oxygenation of 2a by O₂ yields the aldehyde product 4a accompanied by the formation of phosphine oxide of dppe. Oxygen is most likely activated by coordination to the ruthenium center when one PPh₂ unit of the dppe ligand dissociates. This dissociated PPh₂ unit then reacts with the coordinated oxygen nearby to generate half-oxidized dppe ligand and an unobserved oxo-carbene intermediate. Coupling of the oxo/carbene ligands followed by demetalation then yields 4a. Presumably the resulting complex with the half-oxidized dppe ligand continuously promotes cyclization/oxygenation of 1a to yield the second aldehyde molecule. In alcohol such as MeOH or EtOH, the oxygenation reaction affords a mixture of 4a and the corresponding esters 5a or 5a'. Four other aryl propargylic alcohols 1b, 1c, 1d, 1e, which contain thiophen-2-yl, isopropenyl, fur-3-yl, and fur-2-yl, respectively, on the aryl ring are also prepared. Analogous aldehydes 4b, 4c, 4d, 4e are similarly prepared from 1b, 1c, 1d, 1e, respectively. For oxygenations of 1b, 1d, and 1e in alcohol, mixtures of aldehyde 4, ester 5, and acetal 8 are obtained. The carbene complex 2b obtained from 1b was also characterized by single-crystal X-ray diffraction analysis. The UV/Vis spectra of 2a and 2b consist of absorption bands with a high extinction coefficient. From DFT calculations on 2a and 2b, the visible light is found to populate the LUMO antibonding orbital of mainly Ru-C bonds, thereby weakening the Ru-C bond and promoting the oxygenation/demetalation reactions of 2. Making light of things: In a one-batch process, cyclization of phenyl propargylic alcohols 1 a with an olefinic group on the ruthenium-1,2-bis(diphenylphosphino) ethane (dppe) complex first afforded the carbene complexes 2 a, then oxygenation of 2 a is promoted by visible light to cause cleavage of the Ru-C bond to generate aldehyde products 4 a (see scheme). Copyright

Full text of DOI:10.1002/asia.201300726

FULL PAPER
DOI: 10.1002/asia.201300726
Oxygenation of Ruthenium Carbene Complexes Containing
Naphthothiophene or Naphthofuran: Spectroscopic and DFT Studies
Fu-Yuan Tsai,[a] Ji-Xian Lo,[a] Hsin-Tzu Hsu,[a] Ying-Chih Lin,*[a] Shou-Ling Huang,[a]
Ju-Chun Wang,*[b] and Yi-Hong Liu[a]
Abstract: The aryl propargylic alcohol
1-[2-(thiophen-3-yl)phenyl]prop-2-yn-1-
ol (1a) is readily prepared from 2-(thi-
ophen-3-yl)benzaldehyde. In the pres-
ence of visible light, treatment of 1a
with one-half mole equivalent of
accompanied by the formation of phos-
phine oxide of dppe. Oxygen is most
likely activated by coordination to the
ruthenium center when one PPh2 unit
of the dppe ligand dissociates. This dis-
sociated PPh2 unit then reacts with the
coordinated oxygen nearby to generate
half-oxidized dppe ligand and an unob-
served oxo–carbene intermediate. Cou-
pling of the oxo/carbene ligands fol-
lowed by demetalation then yields 4a.
Presumably the resulting complex with
the half-oxidized dppe ligand continu-
ously promotes cyclization/oxygenation
of 1a to yield the second aldehyde
molecule. In alcohol such as MeOH or
EtOH, the oxygenation reaction af-
fords a mixture of 4a and the corre-
sponding esters 5a or 5a’. Four other
aryl propargylic alcohols 1b–e, which
contain thiophen-2-yl, isopropenyl, fur-
3-yl, and fur-2-yl, respectively, on the
aryl ring are also prepared. Analogous
aldehydes 4b–e are similarly prepared
from 1b–e, respectively. For oxygena-
tions of 1b, 1d, and 1e in alcohol, mix-
tures of aldehyde 4, ester 5, and acetal
8 are obtained. The carbene complex
2b obtained from 1b was also charac-
terized by single-crystal X-ray diffrac-
tion analysis. The UV/Vis spectra of 2a
and 2b consist of absorption bands
with a high extinction coefficient. From
DFT calculations on 2a and 2b, the
visible light is found to populate the
LUMO antibonding orbital of mainly
Ru=C bonds, thereby weakening the
Ru=C bond and promoting the oxygen-
ation/demetalation reactions of 2.
[Ru]Cl ([Ru]=Cp
1,2-bis(diphenylphosphino)ethane) and
NH4PF6 in O2 affords the naphtha[2,1-
ACHTUNGTRENNUNG(dppe)Ru) (dppe=
AHCTUNGTRENNUNG
b]thiophene-4-carbaldehyde (4a) in
high yields. The cyclization reaction of
1a proceeds through the formation of
the carbene complex 2a that contains
the
naphtha
G
ring,
which is isolated in a 1:1 stoichiometric
ꢀ
reaction. The C C bond formation be-
tween the inner carbon of the terminal
triple bond and the heterocyclic ring is
confirmed by structure determination
of 2a using single-crystal X-ray diffrac-
tion analysis. Facile oxygenation of 2a
by O2 yields the aldehyde product 4a
Keywords: aldehydes · cyclization ·
fused-ring systems · oxygenation ·
ruthenium
Introduction
pounds. The metal-induced cyclization reactions of enyne
with a functionality of propargylic alcohol are known to pro-
ceed first through p coordination of the alkynyl ligand.[2]
This could be followed by a nucleophilic attack of the teth-
ering unsaturated olefinic group to Cb of the alkynyl group
to give a carbene complex with the cyclized moiety,[3,8] or al-
ternatively an allenylidene[4] species formed from the p-al-
kynyl ligand might undergo cyclization to yield an acetylide
complex. For the pathway that leads to carbene, a few stable
metal–carbene complexes after the cyclization reaction
could be isolated.[5] To obtain the cyclized organic product,
subsequent demetalation of these metal–carbene species
generally required the use of oxidant in stoichiometric pro-
portions.[6] In such oxidative reactions, the metal portion
was commonly oxidized and not recovered. For the oxida-
tion of metal–carbenoid intermediates to yield organic car-
bonyl compounds from alkyne precursors in catalytic reac-
tions, only a few examples have been reported.[7] In our pre-
vious investigation, cyclization of aryl propargylic alcohol
that contains a thiophenyl group on the aromatic ring by
Various heterocyclic compounds, especially those that con-
tain O, N, and S in the ring, have attracted a great deal of
attention since these are well-known precursors commonly
used for the synthesis of organic materials, pharmaceuticals,
and agrochemicals.[1] Recent developments in the transition-
metal-induced cyclization reaction of enyne offers an effi-
cient alternative method for the synthesis of such com-
[a] Dr. F.-Y. Tsai, J.-X. Lo, H.-T. Hsu, Prof. Dr. Y.-C. Lin, S.-L. Huang,
Y.-H. Liu
Department of Chemistry, National Taiwan University
Taipei, 106 (Taiwan)
Fax : (+886)233668672
E-mail: yclin@ntu.edu.tw
[b] Prof. Dr. J.-C. Wang
Department of Chemistry, Soochow University
Taipei, 111 (Taiwan)
Fax : (+886)22811053
E-mail: jcwang@scu.edu.tw
[CpACHTNURTGNEUGN(PPh3)2RuCl] (Cp=cyclopentadienyl ligand) was found
to proceed through such a metal–carbene intermediate,
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300726.
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Ying-Chih Lin, Ju-Chun Wang et al.
which then underwent oxygenation to afford aldehyde and/
or ester compounds in good yields in the presence of pro-
moter NEt3.[8] However, two steps are required for this reac-
tion. Formation of the carbene complex is favored only at
low temperature for 7 days. Afterwards, the carbene com-
plex was treated with O2/NEt3 in chloro solvents to give the
affords a mixture of aldehyde and ester in a high total yield.
The yield of ester depends on the steric bulk of alcohol.
Less ester is generated in a bulkier alcohol. Moreover, an
unexpected acetal product is obtained in methanol. Herein
we report our results in the study of the cyclization reaction
of aryl propargyl alcohols, each with an unsaturated substi-
tuted group.
aldehyde product and [CpACHTNUGTRENUNG(PPh3)2RuCl]. Our previous at-
tempt to carry out a one-batch reaction resulted in a low
yield of aldehyde because of the slow formation of aldehyde
at low temperature. Unfortunately, at high temperature, the
reaction yielded a significant amount of the allenylidene
complex, which would not undergo a cyclization reaction. In
this paper, we report the use of complex [Ru]Cl ([Ru]=Cp-
Results and Discussion
Reactions of 1a or 1b
The reaction of 1a with [Ru]Cl in the presence of NH4PF6
in CH2Cl2 for one week affords a mixture of the carbene
complex 2a and the hydroxyvinylidene complex[7] 7a in
a ratio of 1:0.1 (Scheme 1). Complex 7a is easily dehydrated
ACHTUNGTRENNUNG(dppe)Ru), which contains a bidentate 1,2-bis(diphenylphos-
phino)ethane (dppe) ligand in a one-batch process to afford
the aldehyde compound in high yield. Furthermore, the
same reaction in a mixed solvent that contains alcohol also
Abstract in Chinese:
Scheme 1. Reactions of 1a or 1b with [Ru]Cl.
to form the allenylidene complex 3a.[9] Single crystals of
complex 2a are readily obtained in CDCl3 solution. The
structure of 2a was confirmed by a single-crystal X-ray dif-
fraction analysis. An ORTEP drawing of 2a is shown in
ꢀ
Figure 1. The bond length of Ru1 C1 (1.920(3) ꢁ) is be-
tween a single and double metal–carbon bond, most likely
because of the highly conjugated ring structure.[10] The bond
ꢀ
length of the new C2 C13 bond (1.431(4) ꢁ) is also between
ꢀ
a single and double C C bond. The highly conjugated naph-
thothiophene ring is nearly a plane. The bite angle P1-Ru1-
P2 (82.7(3)8) of 2a is significantly smaller than that of the
analogous ruthenium complex (97.93(3)8) with a bidentate
1,1’-bis(diphenylphosphino)ferrocene (dppf) ligand, isolated
previously only as a minor product.[8] This smaller bite angle
of dppe, which makes more space for the approach of the
thiophenyl group to the triple bond in the reaction of 1a
with [Ru]Cl, might favor the formation of 2a as the major
1
product. In the H NMR spectrum of 2a, the triplet reso-
nance of Ca H at d=15.10 ppm with 3JP, H =9.15 Hz is in
ꢀ
a significantly downfield. Complex 2b is also obtained from
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Ying-Chih Lin, Ju-Chun Wang et al.
Formation of aldehyde from 2 is accompanied with oxida-
tion of the dppe ligand; however, addition of free dppe in
solution hinders the oxygenation reaction. This prompts us
to believe that coordination of oxygen is required, and while
coordinating to the metal, O2 might first react with the
nearby dppe ligand to generate partially oxidized phosphine
oxide and a metal-oxo/carbene species for the formation of
aldehyde. The chelating effect of the bidentate ligand makes
dppe a better promoter than PPh3. The half-dissociated
dppe ligand could easily react with the coordinated oxygen
in the vicinity, whereas freely dissociated PPh3 might be far
away from the reactive center and easily oxidized by free
O2. Both PPh2 units of dppe are used and required for oxy-
genation. Therefore, when the amount of [M] is reduced to
less than one-half mole equivalent, incomplete conversion
of 1a to 4a is attributed to the lack of enough phosphine.
To optimize the conversion, several analogous complexes
with bidentate ligand were attempted as catalysts for the
transformation of 1a to 4a in THF; the results are listed in
Figure 1. ORTEP drawing of the cationic complex 2a. For clarity, aryl
groups of the 1,2-bis(diphenylphosphino)ethane ligands on Ru except the
ꢀ
ipso-carbon atoms and PF6 are omitted (thermal ellipsoid is set at the
30% probability level). Selected bond lengths [ꢁ] and angles [8] for 2a:
ꢀ
ꢀ
ꢀ
ꢀ
Ru1 C1 1.920(3), Ru1 P1 2.2989(8), Ru1 P2 2.2865(8), C1 C2 1.454(4);
P1-Ru1-P2 82.7(3).
Table 1. The yield of 4a, obtained by using [CpACHTNUTRGNE(NUG dppm)RuCl]
(dppm=1,1-bis(diphenylphosphino)methane) as a catalyst,
Table 1. Yields of 4a using various complexes.
Figure 2. ORTEP drawing of the cationic complex 2b. For clarity, aryl
groups of the 1,2-bis(diphenylphosphino)ethane ligands on Ru except the
Entry
[M][a]
(PPh3)2RuCl]
(dppp)RuCl]
(dppe)RuCl]
(dppe)RuCl]
(dppm)RuCl]
(dppe)Ru
t [h]
T [8C]
Yield [%][b]
4a/6a[c]
ꢀ
ipso-carbon atoms and PF6 are omitted (thermal ellipsoid is set at the
1
2
3
4
5
[Cp
G
18
18
12
48
12
50
50
50
25
50
50
65
90
80
75
67:33
71:29
91:9
100:0
83:17
30% probability level). Selected bond lengths [ꢁ] and angles [8] for 2b:
G
ACHTUNGTRENNUNG
ꢀ
ꢀ
ꢀ
ꢀ
Ru1 C1 1.919(4), Ru1 P1 2.280(1), Ru1 P2 2.276(1), C1 C2 1.465(6);
P1-Ru1-P2 82.57(4).
AHCTUNGTRENNUNG
A
[CpACHTGNUTRENNUNG
[a] Use of [Cp
U
ACHTUNGTRNEN(UNG NCMe)]PF6 gave only trace amount of 4a, and
1b (see Scheme 1) under the same reaction conditions, and
single crystals were readily grown in CDCl3 by slow diffu-
sion of diethyl ether. An ORTEP drawing of 2b is shown in
Figure 2. All bond lengths and angles are somewhat similar
to that of 2a. The different locations of the S atoms of 2a
and 2b are clearly revealed in the two ORTEP drawings.
Oxygenation reactions of 2a and 2b readily take place in
the presence of visible light and an excess amount of NEt3
to give corresponding aldehyde 4a and 4b in good yield. In-
terestingly, reactions of 1a and 1b, separately, with [Ru]Cl
in the presence of visible light and NH4PF6 with O2 bubbling
through the solution directly affords 4a and 4b, respectively,
in a one-batch process. The reaction requires one-half mole
equivalent of [Ru]Cl to completely convert all the propargyl
substrate to aldehyde. The reaction time decreased from
7 days by using a stepwise procedure to 2 days, and the cycli-
zation and oxygenation are accomplished in one batch.
1a was recovered after purification for RuCl3·nH2O. [b] Yield of 4a after
flash chromatography: silica gel, n-hexane/diethyl ether (9:1). [c] The
ratios of 4a and 6a were determined by H NMR spectra.
1
is less than that using [CpACTHNURGTNE(UNG dppe)RuCl], and the product
mixture contains 4a and 6a, the starting material used for
the preparation of 1a, (Table 1) in a ratio of 83:17. Howev-
er, the side product diminishes when [Cp
used as the catalyst at 258C, and the reaction takes 2 days.
Two other complexes, [Cp(dppe)Ru(NCMe)]PF6 and [Cp-
(dppp)RuCl] (dppp=1,3-bis(diphenylphosphino)propane),
ACHTUNGTREN(NUNG dppe)RuCl] is
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
are less efficient for the production of 4a. The relatively
stronger coordinating MeCN ligand possibly prohibits the
approach of 1a. The activities of these ruthenium complexes
seem to depend on the carbon chain length of the bidentate
ligand Ph2PACHTNUGTRNEG(UN CH2)nPPh2 between two phosphorus atoms. A
faster reaction is observed for complexes with a dppm or
dppe ligand, possibly because of the easy access of the bi-
dentate ligand to the activated O2 to form oxide. Coordina-
tion of the oxygen atom of phosphine oxide back to the
metal center might then reform a stable five- or six-mem-
bered chelating ring. The longer mobile carbon chain of
Catalyst and Solvent
Isolation of phosphine oxide at the end of the reaction and
the fact that the molar ratio of [CpACHTUNTRGNEUNG(dppe)RuCl]/1a should
be at least 0.5:1 reveal many features of the oxygenation.
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Ying-Chih Lin, Ju-Chun Wang et al.
dppp causes less efficient oxygen abstraction, and, even if
the oxide is formed, recoordination of the phosphine oxide
of dppp generates a less stable seven-membered chelating
ring. In the reaction of 1a catalyzed by RuCl3 at 508C, no
4a was formed, and 1a was recovered almost quantitatively
after the reaction.
The solvent effect on this cyclization/oxygenation reaction
is also explored. When a relatively strong coordinating sol-
vent such as MeCN, DMSO, or DMF is used, 4a is not ob-
served, since such molecules might prevent coordination of
1a to the metal center. In H2O, CHCl3, or acetone, the yield
of 4a is very low, and 2a is isolated as a minor product. In
THF, high yield of 4a is obtained with only trace amounts
of other side products. In MeOH, the reaction affords a mix-
ture of 4a and 5a in a ratio of 1:1.3. In EtOH, the reaction
of 1a generates a mixture of 4a and 5a’ (R=Et; see
Table 2) in a ratio of 1:1.1. In a similar reaction using [Cp-
ACHTUNGTRENNUNG(PPh3)2RuCl] in EtOH, the much lower yield of 5a’ relative
Table 2. Yields of 4a in various solvents.
Entry
Solvent[a]
Yield of 4a [%][b]
Yield of 5 [%][b]
1
2
3
4
5
6
THF
toluene
CHCl3
acetone
H2O
MeOH
EtOH
iPrOH
90
8
–
–
–
–
–
15
16
20
36
40
72
Figure 3. The UV/Vis spectra of 2a (top) and 2b (bottom). Experimental
data (CH2Cl2; dashed line) and TD-DFT (CH2Cl2) calculated spectra
(solid line).
45 (5a)
42 (5a’)
9 (5a’’)[d]
7
8[c]
104 Lmolꢀ1 cmꢀ1 for 2a and 2b, respectively. Photophysical
properties of RuII complexes that contain nitrogen donor li-
gands, such as 2,2’-bipyridyl (bpy) or terpyridyl (tpy), used
for dye-sensitized solar cells[11] or organic light-emitting
diodes,[12] have been previously explored. The visible absorp-
tion bands usually fall within a similar range, that is, (450ꢁ
50) nm. In addition, the visible absorption band characteris-
tic of such a molecule is assigned to a charge-transfer band
from the metal d orbital to the ligand p* orbital (MLCT) of
one of the bpy or tpy ligands.[13] Although the UV/Vis spec-
tra of both bpy and tpy complexes and our carbene com-
plexes 2a and 2b show similar absorption bands, an analysis
of UV/Vis spectrum of a ruthenium complex that contains
Cp, phosphine, and a carbene ligand with an aromatic ring is
still lacking. Therefore, DFT and time-dependent (TD)-DFT
calculations were performed on 2a and 2b as representative
examples to gain more insight into the electronic structure
and spectroscopic properties of these ruthenium complexes.
All DFT and TD-DFT calculations on 2a and 2b were
carried out using the Gaussian 09 program package.[14] Start-
ing coordinates for 2a or 2b were obtained from X-ray crys-
tallographic data. The geometry was optimized by the DFT
method with the B3LYP[15] functions using a lanl2dz effec-
tive core potential basis set for ruthenium and 6-31G* for
[a] In CH3CN, DMSO, and DMF, no 4a was isolated. [b] Yields after
flash chromatography: silica gel, n-hexane/diethyl ether (9:1). [c] The re-
action took 2 d to consume 1a. [d] The ester product 5a’’ was confirmed
by EI-MS.
to 5a was previously attributed to the bulkier OEt group.[8]
For reactions that use the dppe complex, yields of 5a and
5a’ are somewhat comparable. This might be due to a rela-
tively smaller steric hindrance of the dppe ligand, thus
making easy access for both OMe and OEt groups to ap-
proach Ca of the oxygenated ligand. However, the steric
effect plays the role in higher alcohol. For example, the re-
action in isopropanol affords a mixture 4a and 5a“ (R=
iPr), identified by the EI-MS spectra, in a ratio of 1:0.13.
Electronic Spectra and Theoretical Calculations
Both complexes 2a and 2b in CH2Cl2 display a yellow color.
Figure 3 shows two UV/Vis absorption spectra of 2a and 2b
in CH2Cl2 with the concentration in the range of 10ꢀ5–10ꢀ6
m
(dashed line). Moderately intense charge-transfer (CT)
bands are observed at lmax =442 nm with emax =1.8ꢂ
104 Lmolꢀ1 cmꢀ1) and at lmax =433 nm with emax =2.3ꢂ
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Ying-Chih Lin, Ju-Chun Wang et al.
Table 4. The relative percentages of atomic contributions for HOMOꢀ3
the remaining atoms. The optimized structures are similar to
their experimental structures. For example, the calculated
(H-3) to LUMO MOs.
Complex MO[a]
Energy [eV] Ru
Ligand[b] dppe Cp
ꢀ
ꢀ
ꢀ
Ru1 P1, Ru1 P2, and Ru1 C1 bond lengths, and the bite
angles of P1-Ru1-P2 are within the range of (2.35ꢁ.01),
(2.35ꢁ.01), and (1.94ꢁ.01) ꢁ and 848 for 2a and 2b, which
are comparable to their experimental values. Detailed opti-
mized coordinates are summarized in the Supporting Infor-
mation. Electronic structure and spectroscopic properties of
many ruthenium polypyridyl complexes[16] have been studied
by using a similar theoretical approach.[17] The coulomb-at-
tenuating method CAM-B3LYP combines the hybrid quali-
ties of B3LYP and long-range correction.[18] Previous studies
demonstrated that these functions provide significant im-
provement on the long-range excitation energies, such as
those of charge-transfer character.[18,19] Therefore, TD-DFT
calculations using CAM-B3LYP//6-31G*/lanl2dz mixed basis
sets[20] in dichloromethane as a solvent by means of the con-
ductor polarizable continuum model (CPCM) were per-
formed on our two representative complexes. Electronic ab-
sorption spectra of 2a and 2b were computed accordingly.
The lowest twenty singlet-to-singlet spin-allowed excitation
states in dichloromethane are taken into account for the cal-
culations of the electronic absorption spectra. Selected exci-
tation energies with transition oscillator strengths (f) larger
than 0.02 are listed in Table 3. The absorption spectra have
2a
LUMO
HOMO
H-1(180)
H-2(179)
H-3(178)
LUMO(182)
HOMO(181)
H-1(180)
H-2(179)
H-3(178)
N
ꢀ3.89
ꢀ9.21
ꢀ9.61
ꢀ9.94
ꢀ10.08
ꢀ3.88
ꢀ9.31
ꢀ9.44
ꢀ9.97
ꢀ10.16
20.01 65.35
8.29
4.95
5.58
21.59 29.63
14.01 13.15
8.09
6.84
2.44
20.80 29.22
18.82 13.17
6.35
4.25
5.01
G
14.28 76.51
9.86 79.55
32.82 15.95
41.41 31.43
19.00 65.37
18.83 68.10
5.95 89.06
37.87 12.11
36.46 31.55
AHCTUNGTRENNUNG
A
AHCTUNGTRENNUNG
2b
7.54
6.22
2.55
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
E
AHCTUNGTRENNUNG
[a] Using the CAM-B3LYP//6-31G*/lanl2dz basis set. [b] The naphtho-
thiophene carbene part.
and HOMOꢀ3 can be assigned to p bonding orbitals
formed by the Ru metal center and the carbene ligand.
Thus the CT bands for both complexes are assigned to
a mix of MLCT (Ru(dp)!ligand(p*)) and ligand-to-ligand
charge transfer (LLCT) (ligand(p)!ligand(p*)). Moreover,
this complicated charge transfer could weaken the Ru=C
bond because the electron is transferred from strong bond-
ing orbitals (H-2 and H-3) of Ru=C to the significantly anti-
bonding orbital of LUMO (see the Supporting Informa-
tion).
In our previous report,[8] car-
bene complexes 2a and 2b
were treated with O2 in the
Table 3. Computed excitation energies [nm] in the visible region of 2a and 2b.
Complex
l [nm]
f[a]
Major transitions [%][b]
presence of NEt3 to give the al-
dehyde compounds 4a and 4b,
respectively, in 2 h in visible
light, whereas in the dark, low
conversion was observed in
12 h. In particular, visible light
is required to promote cleavage
of the Ru=C bond in oxygena-
tion/demetalation steps. This
experimental observation is
now supported by our DFT cal-
culations.
2a
473.45
439.99
402.52
362.36
464.01
430.71
394.36
368.70
0.0993
0.0532
0.3383
0.1074
0.1244
0.0772
0.3986
0.0801
H-3!L[42], H-2!L[19], H!L[22][c]
H-2!L[53], H-1!L[13]
H-3!L[13], H!L[62]
H-1!L[59]
2b
H-4!L[10], H-3!L[25], H-2!L[20], H!L[31]
H-2!L[58], H!L[13]
H-4!L[12], H-3!L[21], H!L[48]
H-1!L[88]
[a] Transitions with f>0.02 are listed. [b] Selection of the major transitions with a percentage contribution of
over 10%. [c] H stands for HOMO, and L for LUMO.
been simulated using GaussSum software on the basis of the
obtained TD-DFT results.[21] The calculated band centered
at lmax =400 nm for 2a, which resulted from multiple elec-
Other Propargylic Alcohols
tronic transitions and consists of HOMO, HOMOꢀ1,
HOMOꢀ2, and HOMOꢀ3 to LUMO, corresponds to the
CT band at lmax =442 nm of the UV/Vis spectrum of 2a. For
2b, the calculated band centered at lmax =397 nm, which re-
sulted from the mixed transitions of HOMO, HOMOꢀ1,
HOMOꢀ2, HOMOꢀ3, and HOMOꢀ4 to LUMO, corre-
sponds to the CT band at lmax =433 nm. These simulated
spectra are in good agreement with CT bands observed in
their UV/Vis spectra as shown in Figure 3.
The compositions of the MOs that are of spectroscopic
importance for CT bands are summarized in Table 4. Both
the frontier molecular orbitals (HOMO, LUMO) of 2a or
2b are dominated by the carbene ligand with significant
contributions from the metal center. HOMOꢀ1 is mainly
composed of orbitals from the carbene ligand; HOMOꢀ2
Other similar propargylic alcohols 1b–e, which are shown in
Table 5, are prepared to react with one-half mole equivalent
of [Ru]Cl under optimized condition; that is, at 508C in wet
THF/NH4PF6 with O2 bubbling through the solution. The
yields of the resulting aldehydes 4b–d obtained in THF all
exceed 80%, as shown in entries 1, 4, and 7 of Table 5.
However, for 1e, a low yield of aldehyde 4e is obtained.
Most of 1e and [Ru]Cl decomposed. The reaction of 1e
with [Ru]Cl might give the corresponding allenylidene com-
plex, which is not stable. We previously reported that the
yield of a similar carbene complex from the cyclization
could be enhanced by running the reaction at lower temper-
ature.[8] In alcohol, these reactions also afford esters in addi-
tion to the aldehyde products. Surprisingly, in the reaction
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Ying-Chih Lin, Ju-Chun Wang et al.
Table 5. Reaction of various propargylic alcohols with [Ru]Cl.
Entry
Substrate
Solvent
Ratio of 4/5/8
Total yields [%][a]
1
2
3
THF
MeOH
EtOH
100:0:0
27:21:52
26:18:56
82
66
60
4
5
6
THF
MeOH
EtOH
100:0:0
91:9:0
100:0:0
80
62
50
7
8
9
THF
MeOH
EtOH
100:0:0
45:36:19
62:25:13
80
58
61
Scheme 2. Proposed mechanism for formation of 4b, 5b, and 8b.
10[b]
11[b]
12[b]
THF
MeOH
EtOH
100:0:0
62:25:13
83:16:1
23[c]
15
15
p-coordinated to the metal center to give 2b. The cycliza-
tion of [D]1b with a deuteration at the terminal alkyne af-
fords [D]2b with complete retention of D at the carbene
ligand, thus indicating the involvement of the p-alkynyl in-
termediate,[8] instead of a vinylidene or an allenylidene in-
termediate. Visible light then promotes cleavage of the Ru=
C bond in the subsequent oxygenation–demetalation reac-
tion. A vacant site created by partial dissociation of the che-
lating dppe ligand is required in the oxygenation process,
because if free phosphine is added, no oxygenation is ob-
served. Coordination of oxygen to the Ru center forms A,[24]
which is probably more reactive than the corresponding spe-
cies with an h2-coordinated O2 ligand. The dissociated PPh2
unit reacts efficiently with the nearby activated O2 to yield
phosphine oxide and a metal–oxo complex.[25] Coupling of
the oxo/carbene ligands, possibly assisted by visible light
and coordination of the OPPh2 portion, gives the intermedi-
ate B,[26] which yields 4b and D in THF. In MeOH, competi-
tive coordination of MeOH to B and then migration of
MeOH to the carbonyl carbon of aldehyde forms C, which
either undergoes b-hydride elimination[27,28] to generate 5b
and ruthenium hydride species or proceeds further to form
the acetal 8b. The latter process probably involves a prior
formation of an oxocarbenium ion.[29] Complete deuteration
at the aldehyde and acetal protons of 4b and 8b, respective-
ly, from [D]1b is consistent with the proposed pathway. To
reuse the metal fragment for the second cyclization process,
coordination of phosphine oxide to Ru after elimination of
4b, 5b, or 8b forms the active intermediate D,[26] in which
the vacant site is used again to promote further cyclization,
oxygenation, and acetalization until both phosphine termi-
nus of dppe are oxidized.
1
[a] Yields were determined by H NMR spectroscopy using benzaldehyde
as an internal standard. [b] The reaction temperature was 258C for 5 d in
entries 10–12. [c] Products include 4e (ꢂ20% yields) and decomposed
species possibly from 1e and other side products.
of 1b with one-half mole equivalent of [Ru]Cl and NH4PF6
at 508C with bubbling O2 in MeOH, formation of acetal 8b
is also observed in addition to 4b and 5b (see Table 5). The
ratio of different products 4b/5b/8b in the mixture is shown
in Table 5, entry 2. We propose that the acetal product 8b
was formed from aldehyde through acetalization. The pro-
tection of a carbonyl compound by reaction with alcohol
and/or with orthoformate generally requires the presence of
a protic or a Lewis acid catalyst.[22] Chemoselective acetali-
zation of aldehydes by using a catalytic amount of rutheni-
um chloride have been examined previously.[23] Therefore,
Ru metal complex may serve as a Lewis acid that promotes
the acetalization of 4b to generate 8b in MeOH or 8b’ in
EtOH. However, for 1a, no acetal compound was produced
under the same reaction conditions, possibly because 4a is
a potential O,S-chelating ligand to the Ru center. The stron-
ger coordinative ability of the S atom than that of the O
atom could decrease the ability of Ru to induce acetaliza-
tion of the carbonyl group. In entries 8 and 9 of Table 5, low
yields of 8d and 8d’ from 1d are due to nearly equal coordi-
native abilities of two O atoms of 4d.
Proposed Mechanism
The proposed mechanism for the cyclization and subsequent
oxygenation/acetalization, using 1b as an example, is shown
in Scheme 2. The carbon–carbon bond formation in the cyc-
lization of 1b takes place, whereas the triple bond of 1b is
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Ying-Chih Lin, Ju-Chun Wang et al.
Synthesis of 1e
Conclusion
Compound 1e (0.92 g, 79% yield) was similarly prepared from ethynyl-
magnesium bromide (0.5m in THF, 29.1 mL, 14.6 mmol) and 2-(furan-2-
yl)benzaldehyde (1.01 g, 5.87 mmol). H NMR (400 Hz, CDCl3): d=6.50–
7.89 (m, 7H; Ph), 5.77 (br, 1H; CH), 2.70 (br, 1H; OH), 2.60 ppm (d,
3JH,H =2.3 Hz, 1H; ꢃCH); 13C NMR (100 Hz, CDCl3): d=152.23, 142.67,
136.67, 129.42, 128.69, 128.42, 128.40, 127.86, 111.64, 109.43 (Ph), 83.37
(Cꢃ), 74.63 (ꢃCH), 62.17 (CH); HRMS (EI): m/z: 198.0681; elemental
analysis calcd (%) for C13H10O2: C 78.77, H 5.09; found: C 78.81, H 5.28.
Cyclizations of five propargylic alcohols 1a–e with either
a thiophenyl, an isopropenyl, or a furyl group in the pres-
ence of oxygen are induced by [Ru]Cl to generate the corre-
sponding polyaromatic aldehyde compounds 4a–e. Cycliza-
tion of the propargylic alcohol first gives the ruthenium car-
bene complex 2. Then the oxygenation of 2 yields aldehyde
with the assistance of visible light. Oxidation of carbene
complex with oxygen possibly proceeds through an oxo/car-
bene intermediate formed by an abstraction of the coordi-
nated oxygen by the dppe ligand, which serves as a promot-
er. The photo process is believed to weaken the metal–car-
bene bond. Two carbene complexes with different thiophen-
yl groups were characterized by single-crystal X-ray diffrac-
tion analysis. On the basis of DFT calculations, the visible
light is believed to populate the M=C antibonding orbital.
In addition to aldehyde, the oxygenation reaction in alcohol
generates the organic ester 5 and, in a few cases, the acetal
compound 8. Various ester compounds 5 that bear slightly
bulkier substituents such as ethoxyl or isopropoxyl groups
are also obtainable. Deuteration studies revealed that ace-
tals 8 are generated through aldehydes 4.
1
Synthesis of 2a
A mixture of [Ru]Cl (0.25 g, 0.42 mmol), 1a (0.10 g, 0.47 mmol), and
NH4PF6 (0.081 g, 0.50 mmol), in CH2Cl2 (20 mL) was stirred at ambient
temperature for one day. The resulting dark brown solution was filtered
through a Celite pad (1ꢂ3 cm), which was eluted with CH2Cl2 until the
eluent was colorless. The filtrate was concentrated to approximately
5 mL, and Et2O (ꢂ60 mL) was added by a syringe to precipitate dark
brown powders, which were collected in a glass frit, washed with diethyl
ether, and dried under vacuum. The collected product was a mixture of
2a and 7a in a ratio of 1:0.1. Recrystallization by slow evaporation of
a concentrated CDCl3 solution gave crystals of 2a (0.26 g, 81%) suitable
for X-ray diffraction analysis. 1H NMR (400 Hz, (CD3)2CO): d=15.24 (t,
3
3JP, H =9.9 Hz, 1H; CaH), 8.37 (d, 3JH,H =8.2 Hz, 1H; Ph), 8.20 (d, JH,H
=
3
8.2 Hz, 1H; Ph), 8.11 (d, JH,H =5.5 Hz, 1H; thiophene), 8.08 (s, 1H; Ph),
3
7.83 (t, 3JH,H =7.5 Hz, 1H; Ph), 7.70–7.65 (m, 4H; Ph), 7.60 (d, JH,H
=
5.5 Hz, 1H; thiophene), 7.62–7.51 (m, 8H; Ph), 7.47–7.42 (m, 4H; Ph),
7.39–7.32 (m, 5H; Ph), 5.67 (s, 5H; Cp), 3.62–3.30 ppm (m, 4H;
CH2CH2); 13C NMR (100 Hz, (CD3)2CO): d=301.21 (m; Ca), 138.48–
123.00 (Ph), 127.78 (Cg), 94.32 (Cp), 29.02–28.56 ppm (m; CH2CH2);
31P NMR (161 Hz, (CD3)2CO): d=83.74 ppm (s; dppe); HRMS (ESI+):
m/z: 761.1134 [M]+; elemental analysis calcd (%) for C44H37F6P3RuS: C
58.34, H 4.12; found: C 58.30, H 4.06.
Experimental Section
General Procedures
Synthesis of 2b
Manipulations were performed under an atmosphere of dry nitrogen by
using vacuum-line and standard Schlenk techniques. Solvents were dried
by standard methods. The ruthenium complex [Ru]Cl ([Ru]=Cp-
Complex 2b (0.089 g, 83% yield) was similarly prepared from 1b
(0.032 g, 0.15 mmol), [Ru]Cl (0.085 g, 0.14 mmol) and NH4PF6 (0.024 g,
0.15 mmol) in CH2Cl2. Recrystallization by slow evaporation of a concen-
trated CDCl3 solution gave single crystals of 2b suitable for X-ray dif-
fraction analysis. 1H NMR (400 Hz, CDCl3): d=15.58 (t, 3JP, H =9.9 Hz,
1H; CaH), 8.15 (d, 3JH,H =8.1 Hz, 1H; Ph), 8.02 (d, 3JH,H =8.1 Hz, 1H;
Ph), 7.90 (s, 1H; Ph), 7.76 (t, 3JH,H =8.2 Hz, 1H; Ph), 7.72–7.35 (m, 22H;
Ph and thiophene), 6.05 (d, 3JH,H =5.3 Hz, 1H; thiophene), 5.63 (s, 5H;
Cp), 3.65–3.23 ppm (m, 4H; CH2CH2); 13C NMR (100 Hz, CDCl3): d=
305.89 (m; Ca), 133.85–124.37 (Ph), 129.06 (Cg), 94.3 (Cp), 30.36–
29.20 ppm (m, CH2CH2); 31P NMR (161 Hz, CDCl3): d=83.51 (s; dppe);
HRMS (ESI+): m/z: 761.1136 [M]+; elemental analysis calcd (%) for
C44H37F6P3RuS: C 58.34, H 4.12; found: C 58.01, H 3.93.
ACHTUNGTRENNUNG
(dppe)Ru)[30] and compounds 1a, 1b, 1c, 4a, and 4b[8] were prepared fol-
lowing the methods reported in the literature. Mass spectra were record-
ed with LCQ Advantage (ESI) and Finnigan MAT 95S (EI) mass spec-
trometers. UV/Vis spectra were measured with a Hitachi U-2900 spectro-
photometer in the wavelength range of 1100–200 nm. NMR spectra were
recorded with Bruker Avance III-400, DMX-500, or Avance III-800 FT-
NMR spectrometers at room temperature (unless stated otherwise). 1H
and 13C NMR spectra were obtained in CDCl3 or (CD3)2CO at ambient
temperature, and chemical shifts (d) are expressed in parts per million.
Proton chemical shifts are referenced to d=7.24 ppm in CDCl3 and d=
2.05 ppm in (CD3)2CO, and carbon chemical shifts are referenced to d=
77.0 ppm in CDCl3 and d=29.5 ppm in (CD3)2CO. 31P NMR (161 MHz)
spectra were measured relative to external 85% phosphoric acid. Both
13C and 31P NMR spectra were proton decoupled. The C and H analyses
and X-ray diffraction studies were carried out at the Regional Center of
Analytical Instrument at the National Taiwan University.
Synthesis of 4d
A mixture of 1d (0.070 g, 0.35 mmol), [Ru]Cl (0.10 g, 0.17 mmol), and
NH4PF6 (0.060 g, 0.35 mmol) in THF (50 mL) was heated to 508C with
bubbling O2 through the mixture for 12 h. THF was removed under
vacuum, and then the residue was further purified by column chromatog-
raphy by using diethyl ether/n-hexane (1:9). The band was dried under
vacuum to give 4d (0.060 g, 87% yield). 1H NMR (400 Hz, CDCl3): d=
10.44 (s, 1H; CHO), 8.24 (s, 1H; Ph), 8.16, 8.14 (2d, 3JH,H =8.2 Hz, 2H;
Synthesis of 1d
Ethynylmagnesium bromide (0.5m in THF, 21.4 mL, 10.7 mmol) was
added under nitrogen to a solution (20 mL) of 2-(furan-3-yl)benzalde-
hyde (0.74 g, 4.30 mmol) in THF. The mixture was stirred at 508C for
24 h. The resulting solution was quenched with a saturated aqueous
NH4Cl solution (30 mL), and ethyl acetate (EA; 3ꢂ10 mL) was used to
extract the crude product. The combined organic layer was dried under
vacuum, and the residue was purified by column chromatography using
EA/n-hexane (1:3) to give 1d (0.71 g, 83% yield). 1H NMR (400 Hz,
CDCl3): d=6.62–7.88 (m, 7H; Ph), 5.57 (d, 3JH,H =1.8 Hz, 1H; CH), 2.65
3
Ph), 8.08 (d, JH,H =2.1 Hz, 1H; Ph), 8.07–7.54 (m, 2H; Ph), 7.30 ppm (d,
3JH,H =2.1 Hz, 1H; Ph); 13C NMR (100 Hz, CDCl3): d=189.30 (CHO),
149.41, 145.68, 131.16, 130.60, 130.52, 125.65, 129.54, 124.65, 123.63,
122.27, 105.32 ppm (Ph); HRMS (EI): m/z: 196.0518; elemental analysis
calcd (%) for C13H8O2: C 79.58, H 4.11; found: C 79.84, H 4.33.
Synthesis of 4e
3
(d, JH,H =1.8 Hz, 1H; ꢃCH), 2.33 ppm (br, 1H; OH); 13C NMR (100 Hz,
A mixture of 1e (0.20 g, 1.00 mmol), [Ru]Cl (0.30 g, 0.50 mmol), and
NH4PF6 (0.33 g, 2.02 mmol) in THF (20 mL) was stirred at room temper-
ature by bubbling O2 through the solution for five days. The solvent was
removed under vacuum, then the residue was further purified by column
chromatography using diethyl ether/n-hexane (1:9) to give 4e (0.040 g,
CDCl3): d=142.96, 140.59, 137.60, 131.76, 129.90, 128.69, 127.87, 127.30,
123.79, 111.80 (Ph), 83.95 (Cꢃ), 74.98 (ꢃCH), 61.70 ppm (CH); HRMS
(EI): m/z: 198.0682; elemental analysis calcd (%) for C13H10O2: C 78.77,
H 5.09; found: C 78.46, H 5.06.
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Ying-Chih Lin, Ju-Chun Wang et al.
20% yield). 1H NMR (400 Hz, CDCl3): d=10.26 (s, 1H; CHO), 8.34,
8.07 (2d, 3JH,H =8.2 Hz, 2H; Ph), 8.18 (s, 1H; Ph), 7.86 (d, 3JH,H =2.0 Hz,
1H; furan), 7.74 (m, 1H; Ph), 7.62 (d, 3JH,H =2.0 Hz, 1H; furan),
7.57 ppm (m, 1H; Ph); 13C NMR (125 Hz, CDCl3): d=192.15 (CHO),
151.23, 145.71, 132.98, 130.28, 129.83, 129.68, 128.70, 126.10, 124.02,
120.38, 119.82, 107.77 ppm (Ph); HRMS (EI): m/z: 196.0520; elemental
analysis calcd (%) for C13H8O2: C 79.58, H 4.11; found: C 79.67, H 4.07.
124.12 (Ph), 52.22 (OCH3), 19.44 ppm (CH3); HRMS (ESI+): m/z:
201.0835.
Synthesis of 5d and 8d
A mixture of 4d, 5d, and 8d in a ratio of 1:0.8:0.4 was similarly obtained
from the reaction of 1d (0.070 g, 0.35 mmol) with [Ru]Cl (0.10 g,
0.17 mmol), O2, and NH4PF6 (0.059 g, 0.36 mmol) in MeOH at 508C for
1
12 h. Total yield obtained on the basis of the H NMR spectroscopic data
Synthesis of 5b and 8b
was 58%. Column chromatography using diethyl ether/n-hexane (1:9)
gave only 8d. Compounds 4d and 5d were not isolated after column
chromatography. Spectroscopic data of 5d from the crude mixture are as
follows: 1H NMR (400 Hz, CDCl3): d=8.47 (s, 1H; Ph), 8.13, 8.03 (2d,
3JH,H =8.2 Hz, 2H; Ph), 7.88 (d, 3JH,H =2.1 Hz, 1H; furan), 7.69–7.51 (m,
2H; Ph), 7.29 (d, 3JH,H =2.1 Hz, 1H; furan), 4.06 ppm (s, 3H; OMe);
13C NMR (100 Hz, CDCl3): d=165.43 (C=O), 149.65, 145.20, 130.05,
129.97, 129.36, 128.67, 125.31, 124.48, 123.36, 115.84, 105.37 (Ph),
52.37 ppm (OMe); HRMS (EI): m/z: 226.0625. Spectroscopic data of 8d
are as follows: H NMR (400 Hz, CDCl3): d=8.11, 7.96 (d, JH,H =8.2 Hz,
2H; Ph), 7.87 (s, 1H; Ph), 7.79 (d, 3JH,H =2.0 Hz, 1H; furan), 7.46–7.60
(m, 2H; Ph), 7.26 (d, 3JH,H =2.0 Hz, 1H; furan), 5.95 (s, 1H; CH),
3.43 ppm (s, 6H; 2OMe); 13C NMR (100 Hz, CDCl3): d=150.05, 144.50,
129.99, 129.19, 127.92, 126.61, 124.75, 123.24, 122.72, 100.16 (Ph), 105.50
(CH), 53.30 ppm (2OCH3); HRMS (EI): m/z: 242.0936; elemental analy-
sis calcd (%) for C15H14O3: C 74.36, H 5.82; found: C 74.60, H 5.59.
A mixture of 1b (0.050 g, 0.23 mmol), [Ru]Cl (0.070 g, 0.12 mmol), and
NH4PF6 (0.040 g, 0.25 mmol) in MeOH (15 mL) was heated to 508C
while O2 was bubbling through the solution for 12 h. A mixture of 4b,
5b, and 8b in a ratio of 1:0.8:1.9 in a total yield of 66% was detected by
1H NMR spectroscopy. Then the solvent was removed under vacuum,
and the residue was further purified by column chromatography by using
diethyl ether/n-hexane (1:9) to give a mixture of 5b and 8b. Spectroscop-
1
ic data of 5b from the mixture are as follows: H NMR (400 Hz, CDCl3):
d=8.54 (s, 1H; Ph), 8.32 (d, 3JH,H =5.4 Hz, 1H; thiophene), 8.12 (d,
1
3
3
3JH,H =8.4 Hz, 1H; Ph), 7.97 (d, 3JH,H =8.1 Hz, 1H; Ph), 7.63 (d, JH,H
=
3
8.1 Hz, 1H; Ph), 7.58 (d, 3JH,H =5.6 Hz, 1H; thiophene), 7.55 (d, JH,H
=
8.2 Hz, 1H; Ph), 4.02 ppm (s, 3H; OCH3); 13C NMR (100 Hz, CDCl3):
d=167.1, 135.2–126.2, 130.55, 130.24, 129.06, 126.94, 125.88, 125.86,
123.48 (Ph) 52.22 ppm (OCH3); HRMS (ESI+): m/z: 243.0463. Spectro-
scopic data of 8b are as follows: 1H NMR (400 Hz, CDCl3): d=8.11 (d,
3JH,H =5.3 Hz, 1H; thiophene), 7.94 (d, 3JH,H =7.7 Hz, 1H; Ph), 7.89 (s,
1H; Ph), 7.75 (d, 3JH,H =5.3 Hz, 1H; thiophene), 7.5–7.53 (m, 3H; Ph),
5.78 (s, 1H; CH), 3.39 ppm (s, 6H; OCH3); 13C NMR (100 Hz, CDCl3):
d=135.21–126.26 (Ph), 129.11–125.01 (3CH), 129.07, 123.93, 123.48,
102.82 (Ph), 53.0 ppm (2OCH3); HRMS (EI): m/z: 258.0713. No attempt
was made to separate the mixture.
Synthesis of 5d’ and 8d’
The reaction of 1d (0.080 g, 0.40 mmol) with [Ru]Cl (0.12 g, 0.20 mmol)
in the presence of NH4PF6 (0.080 g, 0.49 mmol) and O2 in EtOH at 508C
for 12 h afforded a mixture of 4d, 5d’, and 8d’ in a ratio of 1:0.4:0.2.
Total yield on the basis of 1H NMR spectroscopic data was 61%. Purifi-
cation by column chromatography by using diethyl ether/n-hexane (1:9)
gave a mixture of 5d’ and 8d’. Spectroscopic data of 5d’ from the mixture
are as follows: 1H NMR (400 Hz, CDCl3): d=8.46 (s, 1H; Ph), 8.46 (s,
1H; Ph), 8.13, 8.03 (2d, 3JH,H =8.3 Hz, 2H; Ph), 7.88 (d, 3JH,H =2.1 Hz,
1H; furan), 7.50–7.69 (m, 2H; Ph), 7.29 (d, 3JH,H =2.1 Hz, 1H; furan),
4.52 (q, 3JH,H =7.1 Hz, 2H; CH2), 1.48 ppm (t, 3JH,H =7.1 Hz, 3H; CH3);
13C NMR (201 Hz, CDCl3): d=164.93 (C=O), 149.81, 145.23, 130.03,
129.91, 129.17, 128.59, 125.26, 124.47, 123.38, 116.25, 105.32 (Ph), 61.34
(CH2), 14.44 ppm (CH3); HRMS (EI): m/z: 240.0783. Spectroscopic data
Synthesis of 5b’ and 8b’
The reaction of 1b (0.060 g, 0.28 mmol) with [Ru]Cl (0.080 g, 0.13 mmol)
in the presence of NH4PF6 (0.039 g, 0.24 mmol) in EtOH at 508C while
bubbling O2 for 12 h similarly afforded a mixture of 4b, 5b’, and 8b’ in
a ratio of 1.0:0.7:2.1. Total yield obtained on the basis of the 1H NMR
spectroscopic data was 60%. EtOH was removed under vacuum, then
the residue was further purified by column chromatography using diethyl
ether/n-hexane (1:9) to give a mixture of 5b’ and 8b’. Spectroscopic data
of 5b’ from the mixture are as follows: 1H NMR (400 Hz, CDCl3): d=
8.55 (s, 1H; Ph), 8.27 (d, 3JH,H =5.6 Hz, 1H; thiophene), 8.12 (m, 2H;
Ph), 7.69, 7.79, 7.58 (m, 3H; Ph), 4.40 (q, 3JH,H =7.1 Hz, 2H; CH2),
1.37 ppm (t, 3JH,H =7.1 Hz, 3H; CH3); 13C NMR (100 Hz, CDCl3): d=
166.76 (C=O), 139.10, 135.16, 130.94, 130.38, 129.52, 128.96, 126.20,
125.76, 123.74, 123.61, (Ph), 61.16 (CH2), 14.35 ppm (CH3); HRMS (ESI+
1
3
of 8d’ are as follows: H NMR (400 Hz, CDCl3): d=8.09, 7.96 (2d, JH,H
=
8.3 Hz, 2H; Ph), 7.89 (s, 1H; Ph), 7.78 (d, 3JH,H =2.0 Hz, 1H; furan),
7.45–7.58 (m, 2H; Ph), 7.25 (d, 3JH,H =2.1 Hz, 1H; furan), 6.07 (s, 1H;
CH), 3.69 (m, 4H; 2CH2), 1.26 ppm (t, 3JH,H =7.1 Hz, 6H; 2CH3);
13C NMR (201 Hz, CDCl3): d=150.19, 144.39, 130.08, 129.18, 127.84,
126.46, 124.66, 123.82, 123.20, 123.13, 122.85, 98.26 (Ph), 105.47 (CH),
61.71 (2CH2), 15.22 ppm (2CH3); HRMS (EI): m/z: 270.1255.
): m/z: 257.0637. Spectroscopic data of 8b’ are as follows: 1H NMR
3
(400 Hz, [D]acetone): d=8.06 (d, 3JH,H =7.8 Hz, 1H; Ph), 7.95 (d, JH,H
=
3
Computational Methods
7.2 Hz, 1H; Ph), 7.86 (s, 1H; Ph), 7.76 (d, JH,H =5.5 Hz, 1H; thiophene),
7.65 (d, 3JH,H =5.5 Hz, 1H; thiophene), 7.54 (d, 3JH,H =7.5 Hz, 1H; Ph),
7.47 (d, 3JH,H =7.5 Hz, 1H; Ph), 5.81 (s, 1H; CH), 3.55 (m, 4H; CH2),
1.11 ppm (t, 3JH,H =7.1 Hz, 6H; CH3); 13C NMR (100 Hz, [D]acetone):
d=139.66, 137.28, 134.20, 132.13, 130.97, 130.62, 128.79, 127.67, 126.68,
126.29, 125.12, 124.85 (Ph), 102.95 (CH), 62.78 (2CH2), 16.44 ppm
(2CH3); HRMS (EI): m/z: 286.1026.
Density functional calculations were performed by using the Gaussian 09
software package.[14] Geometry optimization and frequency calculations
were performed using the B3LYP[15]//6-31G*/Lanl2dz basis set.[31] The
TD-DFT calculations were performed using the CAM-B3LYP[20]//6-
31G*/Lanl2dz basis set.[31] The conductor polarizable continuum model
(CPCM) was applied to take into account the solvent (dichloromethane)
environment.
Synthesis of 5c
The reaction of 1c (0.070 g, 0.41 mmol) with [Ru]Cl (0.12 g, 0.20 mmol)
and O2 was similarly carried out in the presence of NH4PF6 (0.060 g,
0.37 mmol) in MeOH at 508C for 12 h to afford a mixture of 4c and 5c
in a ratio of 1:0.1. Total yield obtained on the basis of NMR spectroscop-
ic data was 62%. The solvent was removed under vacuum, then the resi-
due was further purified by column chromatography using diethyl ether/
n-hexane (1:9) to give 5c. 1H NMR (400 Hz, CDCl3): d=8.45 (s, 1H;
Ph), 8.00 (d, JH,H =8.5 Hz, 1H; Ph), 7.94 (d, JH,H =7.8 Hz, 1H; Ph), 7.89
(s, 1H; Ph), 7.61 (t, 3JH,H =7.5 Hz, 1H; Ph), 7.52 (t, 3JH,H =7.5 Hz, 1H;
Ph), 3.95 (s, 3H; OCH3), 2.71 ppm (s, 3H; CH3); 13C NMR (100 Hz,
CDCl3): d=167.43, 134.82, 134.82, 130.05, 129.54, 128.12, 126.98, 125.62,
Single-Crystal X-ray Diffraction Analysis
Single crystals of 2a and 2b suitable for X-ray diffraction study were
grown as mentioned above. A single crystal was glued to glass fibers and
mounted on a SMART CCD diffractometer. The diffraction data were
collected by using a 3 kW sealed-tube MoKa radiation source (T=295 K).
Exposure time was 5 s per frame. SADABS[32] absorption correction was
applied, and decay was negligible. Data were processed, and the structure
was solved and refined by using SHELXTL.[33] Hydrogen atoms were
placed geometrically by using a riding model with thermal parameters set
to 1.2 times that for the atoms to which they are attached.
3
3
CCDC 936923 (2a) and -936924 (2b) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
Chem. Asian J. 2013, 8, 2833 – 2842
2840
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Ying-Chih Lin, Ju-Chun Wang et al.
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
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Acknowledgements
We thank the National Science Council, Taiwan, for financial support.
We also thank Professor Yuan-Chung Cheng of National Taiwan Univer-
sity for his assistance with the theoretical calculations.
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Received: May 29, 2013
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