Efficient endo Cycloisomerization of Terminal Alkynols Catalyzed by a New Ruthenium Complex with 8-(Diphenylphosphino)quinoline Ligand and Mechanistic Investigation

Article abstract of DOI:10.1002/chem.201703971

Several new ruthenium complexes supported by the P,N-donor ligand 8-(diphenylphosphino)quinoline (DPPQ) were synthesized, including [RuCl₂(DPPQ)₂] (1), [Ru(μ-Cl)(DPPQ)₂]₂(BPh₄)₂ (2), and [RuCl(DPPQ)₂Py](BF₄) (3). Complex 2, with only 1 mol % loading, was found to be catalytically active for the endo cycloisomerization of various terminal alkynols to endo-cyclic enol ethers in moderate to excellent yields. In particular, the 7- and 8-endo heterocyclization can be achieved efficiently to give the seven-membered 3-benzoxepine and eight-membered 3-benzo[d]oxocine derivatives. The stoichiometric reactions of 2 with various alkynol substrates have been carried out to investigate the mechanism, which led to a series of seven-, six-, and five-membered oxacyclocarbene ruthenium complexes including [RuCl(DPPQ)₂{=CCH₂C₆H₄CH₂CH₂O}](BPh₄) (12) and [RuCl(DPPQ)₂{=CCH₂(CH₂)_nCH₂O}](BPh₄) (n=3, 12′; n=2, 13; n=1, 14). The quantitative transformation of oxacyclocarbene 12 into catalyst 2 and 3-benzoxepine 5 a as well as the efficient catalytic activity of 12 for the endo-cyclization of 2-(2-ethynylphenyl)ethanol (4 a) demonstrated that 12 is a key intermediate involved in the catalytic cycle. Moreover, comparative studies on the modeling reactions and catalytic activity of the series of oxacyclocarbene complexes indicated that the different catalytic activity of 2 for the endo-cycloisomerization of different types of alkynols can be related to the reactivity of the respective ruthenium oxacyclocarbene intermediates.

Full text of DOI:10.1002/chem.201703971

A Journal of
Accepted Article
Title: Efficient Endo Cycloisomerization of Terminal Alkynols Catalyzed
by a New Ruthenium Complex with 8-(Diphenylphosphino)-
quinoline Ligand and Mechanism Investigation
Authors: Tao Cai, Yu Yang, Wei-Wei Li, Wen-Bing Qin, and Ting-Bin
Wen
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10.1002/chem.201703971
Chemistry - A European Journal
Efficient Endo Cycloisomerization of Terminal Alkynols Catalyzed
by a New Ruthenium Complex with 8-(Diphenylphosphino)-
quinoline Ligand and Mechanism Investigation
Tao Cai,[a] Yu Yang,[a] Wei-Wei Li,[a] Wen-Bing Qin,[a] and Ting-Bin Wen*[a]
Abstract: Several new ruthenium complexes supported by the P,N-
donor ligand 8-(diphenylphosphino)quinoline (DPPQ) were
synthesized, including RuCl2(DPPQ)2 (1), [Ru(-Cl)(DPPQ)2]2(BPh4)2
(2) and [RuCl(DPPQ)2Py](BF4) (3). Complex 2, with only 1 mol%
loading, was found to be catalytically active for the endo
cycloisomerization of various terminal alkynols to endo-cyclic enol
ethers in moderate to excellent yields. In particular, the 7- and 8-
endo heterocyclization can be achieved efficiently to give the seven-
membered 3-benzoxepine and eight-membered 3-benzo[d]oxocine
derivatives. The stoichiometric reactions of 2 with various alkynol
substrates have been carried out to investigate the mechanism,
intermediate, while copper, gold, platinum and palladium
systems were proposed to proceed through hydroxyl group
addition to one carbon of
a
η2-alkyne intermediate.
Cycloisomerization of alkynols through metal vinylidene
intermediates can regioselectively lead to endo-cyclic enol
ethers, while those reactions proceed through metal-alkyne π-
complex can lead to either exo- or endo-cyclic enol ethers.
In the past decades, there have been growing efforts in the
endo cycloisomerization of alkynyl alcohols to endo-cyclic enol
ethers through metal vinylidene intermediates. However, it
appears that most of the studies so far mainly focus on the
methodologies for the synthesis of five- and six-membered
oxacycles. Pioneer work in this area using molybdenum and
tungsten carbonyl complexes as the catalysts has been
developed by McDonald and co-workers to successfully
cycloisomerize a range of alkynols into dihydrofuran and
dihydropyran derivants.[5,6a,6b,6d,6f] Other seminal studies were
carried out by Trost later, using catalytic vinylidene species
generated from the cationic ruthenium system (CpRuCl(PAr3)2/n-
Bu4N(PF6)[12a] or rhodium system ([Rh(cod)Cl]2/PAr3)[13a] in the
endo cycloisomerization of homopropargyl and bis-
homopropargyl alcohols. A related rhodium-catalyzed efficient
heterocyclization of 2-ethynyl-anilines or -phenols (aromatic
homopropargylic alcohols) to indoles or benzofurans has been
also described.[15] Shortly after, Saá and Zacuto found that
CpRuCl(PPh3)2 complex accompanied with amines or PPh3
ligand can be also used for the effective endo cycloisomerization
of aromatic homo- and bis-homopropargylic alcohols or amino-
substituted bis-homopropargylic alcohols to afford benzofurans
or dihydropyrans.[12c,12e] By contrast, transition-metal catalyzed
endo cycloisomerization of alkynols into the larger seven- and
eight-membered oxacycles as well as their nine- and ten-
membered counterparts remains a challenging objective, which
is still limited to a few scattering reports on the 7- and 8-endo
cycloisomerization only. In 2010, Jia and coworkers reported the
smooth cycloisomerization of various alkynols with C≡C
attached to aryl or alkyl groups into five- and six-membered
endo-cyclic enol ethers in good to excellent yields catalyzed by
which led to
oxacyclocarbene
[RuCl(DPPQ)2{=CCH2C6H4CH2CH2O}](BPh4)
a series of seven-, six-, and five-membered
ruthenium
complexes
including
and
(12)
[RuCl(DPPQ)2{=CCH2(CH2)nCH2O}](BPh4) (n = 3, 12’; n = 2, 13; n =
1, 14). The quantitative transformation of oxacyclocarbene 12 into
catalyst 2 and 3-benzoxepine 5a as well as the efficient catalytic
activity of 12 for the endo-cyclization of 4a demonstrated that 12 is a
key intermediate involved in the catalytic cycle. Moreover,
comparative studies on the modeling reactions and catalytic activity
of the series of oxacyclocarbene complexes indicated that the
different catalytic activity of 2 for the endo-cycloisomerization of
different types of alknynols can be related to the reactivity of the
respective ruthenium oxacyclocarbene intemediates.
Introduction
The widespread occurrence of oxygen-containing heterocycles
in natural products and biologically active molecules[1] have
stimulated considerable interest in developing efficient
homogeneous catalytic methods for the synthesis of such
heterocyclic compounds.[2,3] The catalytic cycloisomerization of
alkynols represents an atom-economic pathway to afford cyclic
enol ethers, which are very useful synthetic intermediates in the
construction of diverse oxygen-containing heterocycles.[4]
Various transition metals like molybdenum,[5] tungsten,[6]
copper,[7] palladium,[8] platinum,[9] silver,[10] gold,[11] ruthenium,[12]
rhodium,[13] and osmium[14] have been explored as catalysts for
these cycloisomerization reactions. In general, molybdenum,
tungsten, ruthenium, osmium and rhodium systems were
proposed to proceed through intramolecular nucleophilic
addition of the hydroxyl group to a transition metal vinylidene
the new ruthenium complex [Ru(N3P)(OAc)](BPh4) with
tetradentate N3P ligand (N3P = N,N-bis[(pyridin-2-yl)methyl]-[2-
(diphenylphosphino)phenyl]methanamine),[12d]
wherein one
a
example of 7-endo cycloisomerization of the 5-hexyn-1-ol into
the 2,3,4,5-tetrahydrooxepine was also described. Almost at the
same time, Esteruelas et al. developed the 7-endo
cycloisomerization of aromatic alkynols (including one example
of benzylic alkynyl alcohol) to benzoxepine derivatives as well as
one example of 8-endo cyclization of aromatic alkynol by
employing [CpOs(py)3](PF6) complex as the catalysts.[14a] In
addition, heterocyclization of alkynols into seven-membered
oxepines has been also achieved by McDonald in 2004 via
tungsten-vinylidene intermediates, however, the specific
alkynyldiol substrates in the presence of acetonide protecting
[a]
T. Cai, Y. Yang, W.-W. Li, W.-B. Qin and Prof. Dr. T.-B. Wen
Department of Chemistry, College of Chemistry and Chemical
Engineering, Xiamen University, Xiamen, Fujian 361005, P.R. China
E-mail: chwtb@xmu.edu.cn
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201703971
Chemistry - A European Journal
group were required.[6f,6k] Therefore, the development of new
efficient catalysts for the selective synthesis of larger oxygen-
containing heterocyclic compounds are highly desirable,
especially for the seven- and eight-membered candidates in
view of their importance in organic synthesis as well as their
attractive biological significance.[16]
2BPh4
Ph2P
Ru
N
N
NaBPh4
Ph2P
Ph2P
PPh2
DCM, RT, 3 h
N
N
Cl
Cl
PPh2
PPh2
N
P
RuCl2(PPh3)3
Ru
N
Ru
N
DCM
RT, 4 h
Cl
Ph2
Cl
1
Pyridine
RT, 30 min
AgBF4
2
On the other hand, 8-quinolylphosphine ligands possess two
donor groups with different electronic characters, a phosphino
group with a strong π-acidity and a quinoline group as a
moderate σ-donor, and can act as unsymmetrical bidentate
ligands to form a five-membered chelate ring with transition
metals.[17] Such an electronic differentiation of this ligand may
stabilize unusual oxidation states or coordination geometries for
the metal centers, and thus may confer novel structural,
spectroscopic, and photophysical properties as well as intriguing
reactivities to the complexes.[18] Palladium and nickel complexes
with 8-quinolylphosphine ligands have been proved to be
catalytically active for the reductive carbonylation of
BF4
Ph2P
N
N
Ru
P
Cl
Ph2
N
3
Scheme 1. Preparation of complexes 1, 2 and 3
attempt to obtain the mono-DPPQ product RuCl2(DPPQ)(PPh3),
however, the reaction led to an intractable mixture containing the
bis-DPPQ complex 1 and other unknown species, even when a
diluted solution of DPPQ ligand was added dropwise to a
solution of RuCl2(PPh3)3 in either CH2Cl2 or toluene.
Complex 1 has been characterized by NMR spectroscopy,
elemental analysis as well as X-ray single crystal diffraction. A
view of the molecular structure of 1 is shown in Figure 1 with
selected bond lengths and angles. The coordination geometry
around the ruthenium center can be described as a distorted
octahedron with the two chloride ligands in a cis-arrangement
(Cl(1)-Ru(1)-Cl(2), 92.33(3)). The two DPPQ ligands chelate to
Ru nearly perpendicularly to each other with the P atom of one
of the DPPQ ligands trans to one Cl (P(1)-Ru(1)-Cl(1),
171.59(3)), while the N atom trans to the P atom of the other
DPPQ ligand (N(1)-Ru(1)-P(2), 177.78(7)). Consistent with the
solid state structure, the 31P NMR spectrum (in CDCl3) of 1
nitrobenzene[18a]
,
ethylene
polymerization,[18b,18d]
and
methoxycarbonylation of olefins.[18e] For ruthenium, only two
reports have described the syntheses and electrochemical
property studies of
polypyridine complexes
a
series of ruthenium bipyridine or
bearing 8-quinolylphosphine
ligands.[18c,18f] In the search of efficient catalysts for the endo-
cycloisomerization of alkynols, we have now synthesized several
new ruthenium complexes with the heterobidentate P,N-donor
ligand 8-(diphenylphosphino)quinoline
RuCl2(DPPQ)2 (1), [Ru(μ-Cl)(DPPQ)2]2(BPh4)2 (2)
(DPPQ), including
and
[RuCl(DPPQ)2Py](BF4) (3). Complex 2 ，with only 1 mol%
loading, was found to be catalytically active for the endo
cycloisomerization of various alkynols to the corresponding
endo-cyclic enol ethers in moderate to excellent yields. In
particular, the 7-endo and 8-endo heterocyclization of aromatic
alkynols can be achieved efficiently to give seven-membered 3-
benzoxepine
and
eight-membered
3-benzo[d]oxocine
derivatives. The stoichiometric reactions of catalyst 2 with
various alkynol substrates and the comparative studies on the
modeling reactions of the oxacyclocarbene ruthenium
complexes thus obtained have been carried out to investigate
the mechanism for the endo cycloisomerization reaction. Herein,
we reported the details of these studies.
Results and Discussion
Preparation and characterization of DPPQ ruthenium
complexes RuCl2(DPPQ)2 (1), [Ru(-Cl)(DPPQ)2]2(BPh4)2 (2),
and [RuCl(DPPQ)2Py](BF4) (3): The synthetic routes to
complexes 1-3 are outlined in Scheme 1. The ruthenium
complex RuCl2(DPPQ)2 (1) can be readily obtained by treatment
of RuCl2(PPh3)3 with DPPQ in a ratio of 1:2 in CH2Cl2 at room
temperature, which was isolated as a red solid in 96% yield.
Complex 1 is almost insoluble in toluene and only slightly
soluble in CH2Cl2 and CHCl3. We have also performed the
reaction of RuCl2(PPh3)3 with 1.0 equiv of DPPQ ligand in an
Figure 1. Molecular structure of 1 with thermal ellipsoids drawn at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å]
and angles [°]: Ru(1)-N(1) 2.189(2), Ru(1)-N(2) 2.084(2), Ru(1)-P(1) 2.2510(8),
Ru(1)-P(2) 2.2470(8), Ru(1)-Cl(1) 2.4904(7), Ru(1)-Cl(2) 2.4550(7); N(1)-
Ru(1)-P(2) 177.78(7), P(1)-Ru(1)-Cl(1) 171.59(3), N(2)-Ru(1)-Cl(2) 177.63(7),
N(2)-Ru(1)-Cl(1) 85.39(7), N(1)-Ru(1)-Cl(1) 90.82(7), P(2)-Ru(1)-Cl(1)
87.79(3), Cl(2)-Ru(1)-Cl(1) 92.33(3), N(2)-Ru(1)-N(1) 94.75(9), N(2)-Ru(1)-
P(2) 83.42(7), N(2)-Ru(1)-P(1) 91.90(7), N(2)-Ru(1)-P(1) 81.46(7), P(2)-Ru(1)-
P(1) 99.82(3), N(1)-Ru(1)-Cl(2) 84.65(7), P(2)-Ru(1)-Cl(2) 97.13(3), P(1)-
Ru(1)-Cl(2) 90.28(3).
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10.1002/chem.201703971
Chemistry - A European Journal
exhibited two doublet signals at 62.2 and 53.9 (J(PP) = 33.4 Hz)
ppm, indicating the presence of two inequivalent phosphorous
nuclei.
The aromatic alkynol 2-(2-ethynylphenyl)ethanol (4a) was
chosen as the model substrate to test the catalytic activity of
complexes 1-3 (Table 1). Initially, the reactions were
investigated in 1,2-dichloroethane(DCE) at 90 oC under argon
for 13 h with the same loading of ruthenium for complexes 1-3
(2.0 mol% of Ru). Considering that complex 3 may easily
dissociate the coordinated pyridine ligand to initiate the reaction,
Treatment of 1 with sodium tetraphenylborate in CH2Cl2 for 4
h at room temperature gave an orange solution, from which the
dicationic dimeric complex [Ru(-Cl)(DPPQ)2]2(BPh4)2 (2) was
isolated almost quantitatively. Apparently, the cationic
monochloro species [RuCl(DPPQ)2]+ generated via chloride
abstraction dimerized in the solution to give complex 2. In
contrast, when 1 was treated with 1.0 equiv of AgBF4 in pyridine
at room temperature for 30 min, the pyridine coordinated
monocatonic complex [RuCl(DPPQ)2Py](BF4) (3) was isolated as
an orange solid in 98% yield. Both complexes 2 and 3 have
been characterized by multinuclear NMR spectroscopy and
elemental analysis. The structures of 2 and 3 have also been
confirmed by X-ray diffraction studies.
Figure 2 shows the X-ray structure for the cation of complex 2,
which reveals a doubly-chloro-bridged dinuclea structure. The
crystal of 2 belongs to the centrosymetric space group C2/c, and
the structure has a crystallographic C2 symmetry with the 2-fold
axis passing through Cl(1) and Cl(2), and thus the asymmetric
unit contains only half a molecule of 2. The coordination
geometry around each ruthenium center can be described as a
distorted octahedron. The two N atoms of the two chelated
DPPQ ligands are trans to each other, occupying the axial
positions. and the two P atoms are cis-disposed and lie in the
equatorial plane together with the two bridging chlorides.
Consequently, the four DPPQ ligands in complex 2 are
chemically equivalent, as was also reflected by the 31P NMR
spectrum of 2, which displayed a singlet only at 63.5 ppm (in
CD2Cl2).
Figure 2. Molecular structure for the cation of 2 with thermal ellipsoids drawn
at 30% probability. Counter anion and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Ru(1)-N(1) 2.124(4), Ru(1)-N(2)
2.136(4), Ru(1)-P(1) 2.2482(12), Ru(1)-P(2) 2.2604(13), Ru(1)-Cl(1)
2.5077(11), Ru(1)-Cl(2) 2.4982(11); N(1)-Ru(1)-N(2) 175.27(13), P(1)-Ru(1)-
Cl(1) 168.95(4), P(2)-Ru(1)-Cl(2) 170.02(4), N(1)-Ru(1)-P(1) 83.49(10), N(2)-
Ru(1)-P(1) 94.35(10), N(1)-Ru(1)-P(2) 92.28(11), N(2)-Ru(1)-P(2) 83.76(10),
P(1)-Ru(1)-P(2) 96.31(5), N(1)-Ru(1)-Cl(2) 93.94(10), N(2)-Ru(1)-Cl(2)
90.34(10), P(1)-Ru(1)-Cl(2) 92.16(5), N(1)-Ru(1)-Cl(1) 90.53(10), N(2)-Ru(1)-
Cl(1) 92.26(10), P(2)-Ru(1)-Cl(1) 93.20(5), Cl(2)-Ru(1)-Cl(1) 78.95(4), Ru(1)-
Cl(1)-Ru(1A) 100.79(6), Ru(1)-Cl(2)-Ru(1A) 101.31(6). (Symmetry code for A:
–x, y, -z+1/2)
The structure for the cation of 3 is shown in Figure 3, which is
similar to that of 1, with the Cl trans to the P atom in 1 replaced
by a pyridine. Again, as was the case for 1, the 31P NMR
spectrum of 3 exhibited two doublet signals for the two
inequivalent DPPQ ligands at 58.5 and 57.6 (J(PP) = 33.8 Hz)
ppm (in CDCl3).
Endo Cycloisomerization of Alkynols Catalyzed by
Ruthenium DPPQ Complexes: Recently, Esteruelas[14] and co-
workers reported that the osmium complex [CpOs(py)3](PF6) is a
more efficient catalyst for the regioselective 7-endo
heterocyclization
of
aromatic
alkynols
or
o-alkynyl
phenethylamines to give 3-benzoxepines and dopaminergic 3-
benzazepines than the ruthenium catalysts [CpRu(py)3](PF6),
[CpRu(CH3CN)3](PF6) and some tungsten, rhodium catalysts.
Given the rarity of efficient catalysts for the 7-endo
cycloisomerization of alkynyl alcohols reported in the literature
and the success of ruthenium catalysts in the related 5- and 6-
endo cycloisomerization reactions, we were prompted to
investigate the catalytic activity of our DPPQ ruthenium
complexes for such 7-endo reactions. Moreover, from an
economic viewpoint, it is also quite appealing to develop much
cheaper ruthenium catalysts for such reaction compared to
osmium.
Figure 3. Molecular structure for the cation of 3 with thermal ellipsoids drawn
at 30% probability. Counter anion and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Ru(1)-N(1) 2.076(3), Ru(1)-N(3)
2.182(3), Ru(1)-N(2) 2.193(3), Ru(1)-P(1) 2.2556(10), Ru(1)-P(2) 2.2856(10),
Ru(1)-Cl(1) 2.4337(11); N(1)-Ru(1)-N(3) 89.63(11), N(1)-Ru(1)-N(2) 94.60(11),
N(3)-Ru(1)-N(2) 87.87(11),N(1)-Ru(1)-P(1) 83.85(9), N(3)-Ru(1)-P(1):91.46(8),
N(2)-Ru(1)-P(1) 178.32(8), N(1)-Ru(1)-P(2) 92.24(9), N(3)-Ru(1)-P(2)
168.70(8), N(2)-Ru(1)-P(2) 80.88(8), P(1)-Ru(1)-P(2) 99.81(4), N(1)-Ru(1)-
Cl(1) 178.65(8), N(3)-Ru(1)-Cl(1) 89.57(8), N(2)-Ru(1)-Cl(1) 86.45(8), P(1)-
Ru(1)-Cl(1) 95.08(4), P(2)-Ru(1)-Cl(1) 88.75(4).
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10.1002/chem.201703971
Chemistry - A European Journal
the cycloisomerization of 4a with 3 was first examined, which, to
our delight, selectively gave the desired 7-endo cyclization
product 3-benzoxepine 5a in 73% yield (entry 1). More
encouragingly, when the dimeric complex 2 was employed as
the catalyst, the yield of 5a was improved to 81% (entry 2),
indicating that dissociation of the dimeric complex 2 into
catalytically active 16-electron monomeric species could readily
occur in the reaction of 2 with 4a under these conditions. The
dichloride complex 1 could also catalyze the reaction, but with a
much lower yield of product 5a (entry 3) due to the fact as
expected that dissociation of a chloride ligand from 1 to generate
the coordinatively unsaturated species is more difficult than the
dissociation of the dimeric structure in 2 and the pyridine ligand
in 3. Having established complex 2 as the most efficient catalyst,
different solvents were screened for the reactions, suggesting
that DCE is the best choice. The reactions also proceeded well
in tetrahydrofuran (THF) or CHCl3 to give 3-benzoxepine 5a in
64% and 75% yields, respectively (entries 4 and 5). However,
the reactions in 1,4-dioxane, toluene or N,N-dimethylformamide
(DMF) gave only trace amounts of product 5a (entries 6-8),
probably due to the poor solubility of the cationic complex 2 in
the former two solvents and the coordination of DMF with
ruthenium. The reaction temperature was then examined with 2
as the catalyst in DCE solvent. Higher temperature (110 oC) was
found to decrease the yield of 5a (69%, entry 9) due to the
formation of a complex mixture of organic products containing
5a, while lower temperature (60 oC) led to the incomplete
conversion of 4a (about only 50% conversion) and the formation
of a new phosphine-containing complex (the oxacyclocarbene
complex 12, vide infra) (Entry 10). Thereafter, the reaction time
was also carefully checked. When the reaction in DCE was
heated at 90 oC for 2 h, 5 h, 8 h and 11 h, incomplete conversion
of substrate 4a were observed in all case and the yields of
product 5a monitored by GC were 36%, 64%, 72% and 78%,
respectively (entries 11-14). At last, it was found that reducing
the loading of catalyst 2 to 0.5 mol% (1.0% of Ru) resulted in the
incomplete conversion of substrate 4a and a significant drop in
the yield of product 5a (46%, entry 15).
Table 1. Screening of catalysts and optimization of reaction conditions for 7-
endo heterocyclization of 4a.
With the optimized conditions in hand, the substrate scope of
the 7-endo cycloisomerization reactions catalyzed by complex 2
o
(1 mol % loading) was explored in DCE at 90 C. A variety of
aromatic alkynols 4 were converted into their corresponding
seven-membered 3-benzoxepines 5 in moderate to good yields
(Table 2). Besides the parent primary aromatic alkynol 4a,
secondary aromatic alkynols such as 4b-4d were also
exclusively converted to the corresponding 3-benzoxepines 5b-
5d in moderate to excellent yields (entries 2-4). Other secondary
alkynols such as cyclopentanol derivative 4f and cyclohexanol
derivative 4g, and even the sterically hindered tertiary alkynol 4e
all smoothly afforded the corresponding products (entries 5-7) in
high yields. Moreover, both aromatic alkynols with electron-
donating or electron-withdrawing substituents such as Me (4h)
and F (4i) on the aromatic rings were well tolerated to provide
the corresponding 3-benzoxepines in good yields (entries 8 and
Entry
1
Cat. (mol %)
3 (2.0)
2 (1.0)
1 (2.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (1.0)
2 (0.5)
Solvent
DCE
T (oC)
90
t (h)
13
13
13
13
13
13
13
13
13
13
2
Yield[a]
73
2
DCE
90
81 (56[b]
29
)
3
DCE
90
4
THF
90
64
5
CHCl3
1,4-dioxane
toluene
DMF
90
75
6
90
trace
trace
trace
69
7
90
9).
However,
nonterminal
alkynols
(4j)
such
and
as
2-(2-
2-(2-
8
90
(phenylethynyl)phenyl)ethanol
9
DCE
110
60
((trimethylsilyl)ethynyl)phenyl)ethanol (4k) failed to give the
corresponding endo cycloisomerization products (entry 10),
which indirectly indicate that the cyclization occurs via a
vinylidene intermediate.[12d,14a,19] These results are comparable
with those reported for the reactions catalyzed by the osmium
catalyst [CpOs(py)3](PF6) (10 mol% loading, pyridine, 90 oC), [14a]
in that the aromatic alkynols 4a, 4b, 4c and 4g were converted
into the corresponding 3-benzoxepines 5 in 60%, 58%, 65% and
56% yields, respectively, in 0.5-1.5 h.
10
11
12
13
14
15
DCE
50[c]
36
DCE
90
DCE
90
5
64
DCE
90
8
72
DCE
90
11
13
78
In an attempt to extend the 7-endo cycloisomerization
reactions to aliphatic alkynols, the reaction of hex-5-yn-1-ol (4l)
DCE
90
46
in the presence of
2 under the typical conditions was
Typical conditions: [4a] = 0.16
M, oil bath, the reactions were catalyzed by
investigated. Unfortunately, the reaction failed to provide the
corresponding endo cyclized oxepine product 5l (entry 11).
using 0.1 mmol substrate and solvent (0.6 mL) under Ar, unless otherwise
noted. [a] Yield determined by GC methods calculated by using
dibromomethane as internal standard. [b] Isolated yield (the relatively low
isolated yield of 4a is due the low boiling point) [c] Conversion of 4a
determined by 1H NMR, and formation of the oxacyclocarbene complex 12
Instead,
exclusive
formation
of
the
corresponding
oxacyclocarbene complex 12’ (vide infra) was detected by 31P
NMR. Of note, successful endo cycloisomerization of 4l into
oxepine 5l catalyzed by the complex [Ru(N3P)(OAc)](BPh4) has
was detected from 31P NMR. DCE
dimethylformamide.
= 1,2-dichloroethane. DMF = N,N-
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10.1002/chem.201703971
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Isolated
Yield
R
R
R
Table 2. The substrate scope of the cycloisomerization reactions catalyzed
by complex 2.
OH
2
(1 mol %)
6a, 7a
6b, 7b
6c, 7c
H
62%
O
DCE, 100 o
24 h, Ar
C
Me 66%
7
F
6
3-Benzo[d]oxocine
58%
Scheme 2. 8-endo cycloisomerization of aromatic alkynol
benzo[d]oxocine 7 catalyzed by complex 2.
6 to 3-
Entry
Alkynol 4
3-benzoxepine 5
Yield[a]
been reported by Jia and co-workers.[12d] However, the superior
capacity of complex 2 for the catalytic endo heterocyclization
reactions can be demonstrated by the even more challenging
regioselective 8-endo cyclization of aromatic alkynols, although
a longer reaction time (24 h) and a slightly higher temperature
(100 oC) were required (Scheme 2). Again, with 1 mol% loading
of catalyst 2, not only the 2-ethynylphenyl alkynol (6a) but also
other related derivatives with an electron-donating methyl
group (6b) or the electron-withdrawing fluoride (6c) para to the
alkyne on the aromatic ring were all successfully
cycloisomerized to the corresponding endo-cyclic eight-
membered 3-benzo[d]oxocine derivatives 7a-7c, and the product
was isolated in quite good yields of 62%, 66% and 58%,
respectively. Notably, Esteruelas has also reported the 8-endo
cyclization of the parent alkynol 6a catalyzed by [CpOs(py)3](PF6)
in pyridine solvent at 130 oC for 4 h to give 3-benzo[d]oxocine 7a
in 40% yield with 10 mol% loading of catalyst.[14a] In this regard,
complex 2 competes favorable with respect to the osmium
catalyst in terms of the catalytic activity for the 8-endo
cycloisomerizations of aromatic alkynols.
We have also investigated the catalytic activity of 2 for the 6-
and 5-endo cycloisomerization of bis-homopropargylic and
homopropargylic alcohols. It was found that the reactions in
DCE gave poor conversion of the substrates. However, when a
THF solution of the alkynol substrate in the presence of 1 mol%
of complex 2 sealed in a Schlenk tube was heated at 100 oC for
24 h, the 6- and 5-endo cycloisomerization can also be achieved
to provide the endo-cyclic enol ethers in moderate to good yields.
The results are summarized in Table 3. For example, the
aromatic bis-homopropargylic alcohol 8a was smoothly
converted into isochromene 10a in a high 75% yield (entry 1),
while the secondary alkynol 8b gave the corresponding
isochromene 10b in only a moderate 46% yield probably due to
the steric hinderance (entry 2). Cycloisomerization of the
aliphatic bis-homopropargylic pent-4-yn-1-ol (8c) was also
realized to give the 6-endo-cyclic dihydropyran 10c in 51% yield
(entry 3). Under similar conditions, the aliphatic homopropargylic
but-3-yn-1-ol (9a) was transformed to the 5-endo-cyclic
dihydrofuran 11a in 42% yield (entry 4), whereas 5-endo
cyclization of the phenyl substituted secondary alkynol 9b
provided dihydrofuran 11b in a good 64% yield (entry 5). Again,
7-endo cycloisomerization of hex-5-yn-1-ol (4l) cannot be
achieved under this condition. Although the catalytic activity of 2
for the 6-endo and 5-endo cycloisomerization reactions is
relatively lower than those of the reported ruthenium complex
Typical conditions: 1 mol% 2, [4] = 0.16 M, oil bath, 90 oC, 13 h, the
reactions were catalyzed by using 0.1 mmol substrate and solvent (0.6 mL)
under Ar, unless otherwise noted. [a] Isolated yield. [b] Yield determined by
GC methods calculated by using dibromomethane as internal standard. [c]
Exclusive formation of the corresponding oxacyclocarbene complex 12’ was
detected by 31P NMR.
[Ru(N3P)(OAc)](BPh4)[12d]
and
the
CpRuCl(PPh3)2/amine
system,[12c] these results have manifested the versatility of
complex 2 as the catalyst for endo cycloisomerization of alkynols.
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BPh4
BPh4
N
N
Ph2
Ph2
P
Table 3. 6-endo and 5-endo heterocyclization of alkynols catalyzed by
complex 2.
PPh2
P
PPh2
Cl
Ru
Ru
OH
N
OH
N
Cl
4l
O
4a
O
Entry
Alkynol 8 and 9
Product 10 and 11
Yield[a]
DCE
70 oC, 9 h
DCE
70 oC,13 h
12'
12
2
BPh4
OH
BPh4
9a
OH
8c
N
THF/DCM (1:1)
70 oC, 4 h
N
Ph2
P
THF/DCM (1:1)
70 oC, 2 h
Ph2
P
PPh2
Cl
PPh2
Cl
Ru
Ru
N
N
O
O
14
13
Scheme 3. Stoichiometric reactions of 2 with various alkynols.
The structure of complex 12 has been confirmed by X-ray
diffraction. Figure 4 shows the X-ray structure for the cation of
12, from which we can see that the Ru center adopts distorted
octahedral geometry consisting of two DPPQ ligands chelating
to Ru nearly perpendicularly, one chlorine ligand, and one
oxacarbene ligand. The P atom of one of the DPPQ ligands is
trans to the Cl ligand (P(1)-Ru(1)-Cl(1), 167.48(3)), while the N
atom trans to the P atom of the other DPPQ ligand (N(1)-Ru(1)-
P(2), 172.67(7)). The N atom of the other DPPQ ligand is trans
to the oxocarbene ligand (N(2)-Ru(1)-C(1), 168.70(11)). The
Ru=C bond length of 1.937(3) Å is similar to those of other
reported ruthenium oxacyclocarbene complexes.[20,25,27]
Complex 12 was also characterized by multinuclear NMR
spectroscopy and elemental analysis. Consistent with the solid
state structure, the 31P{1H} NMR spectrum (in CD2Cl2) of 12
showed two doublet signals at 58.6 and 49.5 ppm (J(PP) = 31.3
Hz) for the two inequivalent phosphine groups. Due to the
Typical conditions: 1 mol% of 2, [8] or [9] = 0.16 M, oil bath, 100 oC, 24 h,
the reactions were catalyzed by using 0.1 mmol substrate in THF (0.6 mL)
under Ar in a Schlenk tube sealed with a Teflon lined cap, unless otherwise
noted. [a] Isolated yield. [b] In d8-THF, yield determined by 1H NMR
spectroscopic integration with dibromomethane as the internal standard.
Mechanism
study: The mechanism of the endo
cycloisomerization reactions of terminal alkynols catalyzed by
Mo,[5] W,[6] Ru,[12] Rh[13a] and Os[14a] systems were generally
believed to involve the initial formation of
a vinylidene
intermediate that undergoes intramolecular nucleophilic addition
of an OH group to the vinylidene ligand to afford a vinylic
intemediate with an endocyclic enol ether linked to the transition-
metal (or in some cases, interconvertible with the
oxocyclocarbene intermediate[14a,20]), which then followed by
protonation of the metal–carbon bond to give the endocyclized
product. Although experimental evidence for the mechanism is
still rare,[20,21] the mechanism for the Mo and W systems is
supported by DFT studies.[6i,22] In order to isolate some reaction
intermediates from which we could obtain information about the
mechanism of our endo cycloismerization reactions, the
stoichiometric reactions of complex 2 with alkynols were studied.
As mentioned before, during our examining the reaction
temperature for the catalytic cycloisomerization of 2-(2-
ethynylphenyl)ethanol (4a), formation of a new phosphine-
containing complex could be detected by 31P NMR when the
reaction was conducted at a lower temperature (60 oC) (Table 1,
entry 10). Thus the reaction of 2 with 10 equiv of 4a in DCE at
70 oC was carried out. Indeed, the reaction proceeded smoothly
to produce the above-mentioned newly formed complex
quantitatively within 9 h, which was isolated in 95% yield and
identified to be the 3-benzoxepine derivatized seven-membered
ruthenium oxacyclocarbene complex 12 (Scheme 3). Numerous
oxacyclocarbene complexes have been prepared previously
from the reactions of various transition-metal complexes with
terminal -alkynols,[20,23-26] including a number of ruthenium
oxacyclocarbene complexes.[20,25]
Figure 4. Molecular structure for the cation of 12 with thermal ellipsoids drawn
at 30% probability. Counter anion and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Ru(1)-C(1) 1.937(3), Ru(1)-N(1)
2.204(3), Ru(1)-N(2) 2.215(3), Ru(1)-P(2) 2.2798(10), Ru(1)-P(1) 2.2946(11),
Ru(1)-Cl(1) 2.4653(12), O(1)-C(1) 1.323(4), O(1)-C(6) 1.471(4), C(1)-C(2)
1.506(4), C(5)-C(6) 1.491(5); C(1)-Ru(1)-N(1) 93.63(11), C(1)-Ru(1)-N(2)
168.70(11), N(1)-Ru(1)-N(2) 91.21(10), C(1)-Ru(1)-P(2) 93.47(9), N(1)-Ru(1)-
P(2) 172.67(7), N(2)-Ru(1)-P(2) 81.47(8), N(1)-Ru(1)-P(1) 79.84(7), N(2)-
Ru(1)-P(1) 97.74(8), P(2)-Ru(1)-P(1) 101.59(4), N(1)-Ru(1)-Cl(1) 87.66(7),
N(2)-Ru(1)-Cl(1) 81.62(8), P(2)-Ru(1)-Cl(1) 90.71(4), P(1)-Ru(1)-Cl(1)
167.48(3).
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10.1002/chem.201703971
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chirality at the metal center, the two protons of each methylene
group of the oxacyclocarbene ring (Ru=CCH2, Ru=COCH2 and
Ru=COCH2CH2) are diastereotopic, giving rise to complicated 1H
NMR spectrum with three pairs of multiplet signals in the
aliphatic region between 3.05 and 4.85 ppm, similar to what
were reported for other chiral ruthenium oxacyclocarbene
complexes.[20,25f-25j,25l,25m] The 13C{1H} NMR spectrum displayed a
Ru=C signal at 321.6 ppm (2J(PC) = 11.2 Hz), in agreement with
those observed for other ruthenium oxacyclocarbene
complexes.[25,26] The 13C{1H} signals for the Ru=COCH2,
Ru=COCH2CH2 and Ru=CCH2 were observed at 73.0, 55.4, and
32.3 ppm, respectively. Reported examples of seven-membered
oxacyclocarbene complexes are rather limited, specifically
synthesized from the reacions of Ru,[25f,25h,25k] Os,[26b] and Re[26a]
complexes with the aliphatic alkynols. To our knowledge,
complex 12 represents the first example of benzo-
oxacycloheptylidene transition-metal complexes.
then undergoes deprotonation to afford the vinyl complex C.
Finally, protonation of the metal-carbon bond in C would give the
organic compound 5a and regenerate A. The conversion of
metal-carbene to metal-vinyl is present in many catalytic
transformations, and it is particularly favored when the carbene
has a C-H bond.[28,29] In this case, the C-proton of the
oxacyclocarbene intermediate 12 is fairly acidic due to the
cationic nature of the complex. Thus, it should undergo
deprotonation to afford C with the aid of the basic media
presented in the solution (probably could be the trace amounts
of water, the hydroxy group of substrate 4a or the ether
functionality of product 5a).
2+


[Ru( Cl)(DPPQ)2]2
2
+
[RuCl(DPPQ)2]
OH
Moreover, quantitative transformation of complex 12 to give
complex 2 and 3-benzoxepine 5a was observed, as indicated by
A
O
1
the 31P and H NMR spectroscopy, when a solution of 12 was
4a
5a
heated in DCE at 90 oC within 13 h (Scheme 4, Eq 1).
Furthermore, complex 12 is also catalytically active for the 7-
endo cyclization of 4a. Thus, when a DCE slution of 4a in the
presense of 2 mol% 12 was heated at 90 oC, complete
conversion of 4a to 5a was achieved within 13 h, and the
product was isolated in 58% yield (Scheme 4, Eq 2). These
results clearly indicate that oxacyclocarbene complex 12 is
certainly an intermediate involved in the cycloisomerization of 4a
catalyzed by 2.
H+
H
H
C
C
(DPPQ)2ClRu
(DPPQ)2ClRu
O
HO
C
B
H+
H
H
(DPPQ)2ClRu
Key intermediate
12
O
BPh4
Scheme 5. Proposed mechanism of 7-endo cycloisomerization of 2-(2-
ethynylphenyl)ethanol by catalyst 2.
N
Ph2
P
DCE, 90 o
13 h, Ar
C
PPh2
Cl
(1)
Ru
2
+
O
N
O
5a
Despite of the numerous oxacyclocarbene complexes
reported in the literature and the widely accepted idea that they
12
are
relevant
to
transition
metal-catalyzed
endo
OH
12 (2 mol %)
cycloisomerization of terminal alkynols,[5b,12a,14a,20,21a,23] isolation
or even observation of the oxacyclocarbene complexes formed
from the reactions of the catalysts and the substrates has rarely
been achieved. McDonald and co-workers have trapped the
molybdenum oxocyclocarbene intermediate using benzaldehyde
to give the 5-phenyl-3-benzylidene-1-oxacyclopent-2-ylidene
molybdenum complex from the stoichiometric version of the
catalytic reaction of 1-phenylbut-3-yn-1-ol with Et3N:Mo(CO)5.[5b]
In the absence of the Et3N, they also described the reactions of
W(THF)(CO)5 with 4-alkyne-1-ols to result in the tungsten
O
(2)
DCE, 90 oC, 13 h, Ar
(100% Conv.)
5a
4a
Scheme 4. Transformation of complex 12 into complex 2 and 3-benzoxepine
5a and 7-endo cycloisomerization of alkynol 4a to afford 5a catalyzed by 12.
On the basis of these results, a plausible mechanism for the
endo cycloisomerization of alkynols catalyzed by complex 2 is
described in Scheme 5 by using substrate 4a as an example.
Dissociation of the dimeric complex 2 in the solution can
generate the 16-electron monocationic species A, which reacts
with alkynol 4a to form the vinylidene intermediate B tethering
with a hydroxyl chain. Due to the electrophilic and nucleophilic
nature of the C and C atoms of the vinylidene ligand,
respectively, intramolecular addition of the O-H group to the
C=C double bond of the vinylidene ligand could give the seven-
membered ruthenium oxacyclocarbene intermediate 12,[25] which
dihydropyranylidene
complexes,
and
the
subsequent
stoichiometric transformation of them into α-stannyl
dihydropyrans upon treated with tributyltin triflate and
trimethylamine.[21a] In particular, Jia and co-workers[20] have
isolated
the
oxacyclocarbene
ruthenium
complex
{Ru(N3P)[=C(CH2)3O](OAc)}(BPh4) from the reaction of the
catalyst [Ru(N3P)(OAc)](BPh4) with the 3-butyn-1-ol substrate,
but
the
presence
of
extra
base
DIPEA
(N,N-
diisopropylethanamine) was need to facilitate the formation of
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10.1002/chem.201703971
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the oxacyclocarbene. Moreover, they also showed that the
oxocyclocarbene complex can be detected in the catalytic
reaction and the isoltated one is catalytically active for the
cycloisomerization. Our above-mentioned results provided the
most direct evidences for the first time to show the intermediacy
of an oxacyclocarbene complex in the catalytic endo-
cycloisomerization of alkynols.
In this context, it is noted that although complex 2 is not active
for the cycloisomerization of the aliphatic alkynol hex-5-yn-1-ol
(4l), exclusive formation of a new complex with 31P NMR signals
similar to that of complex 12 was detected (Table 2, entry 11).
o
Thus, treatment of of 2 with 10 equiv of 4l in DCE at 70 C
afforded the seven-membered oxacycloheptylidene ruthenium
complex 12’ exclusively, which was isolated in 89% yield. Under
similar reaction conditions, the six- and five-membered
ruthenium oxacyclocarbenes 13 and 14 were also smoothly
obtained in 90% and 92% yields, respectively, from the reactions
of complex 2 with pent-4-yn-1-ol (8c) or but-3-yn-1-ol (9a) in
Figure 5. Molecular structure for the cation of 12’ with thermal ellipsoids
drawn at 30% probability. Counter anion and hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [°]: Ru(1)-C(1) 1.948(3), Ru(1)-
N(1) 2.194(2), Ru(1)-N(2) 2.203(2), Ru(1)-P(2) 2.2764(9), Ru(1)-P(1)
2.2833(14), Ru(1)-Cl(1) 2.4540(13), O(1)-C(1) 1.321(4), O(1)-C(6) 1.466(4),
C(1)-C(2) 1.498(4), C(2)-C(3) 1.538(5), C(3)-C(4) 1.522(6), C(4)-C(5) 1.509(6),
C(5)-C(6) 1.504(6); C(1)-Ru(1)-N(1) 91.16(11), C(1)-Ru(1)-N(2) 170.39(10),
N(1)-Ru(1)-N(2) 92.49(9), C(1)-Ru(1)-P(2) 93.93(9), N(1)-Ru(1)-P(2) 174.78(6),
N(2)-Ru(1)-P(2) 82.30(7), N(1)-Ru(1)-P(1) 80.29(7), N(2)-Ru(1)-P(1) 94.50(7),
P(2)-Ru(1)-P(1) 100.36(4), N(1)-Ru(1)-Cl(1) 89.25(7), N(2)-Ru(1)-Cl(1)
80.99(7), P(2)-Ru(1)-Cl(1) 89.62(4), P(1)-Ru(1)-Cl(1) 168.45(3).
o
DCM/THF (V:V = 1:1) at 70 C for 2 h or 4 h (Scheme 3).
Previous studies have revealed that the intramolecular addition
of the hydroxy group to the C of the vinylidene intermediate is
generally disfavoured with increasing the length of the spacer
between the triple bond and the hydroxyl group in the starting
alkynol due to the higher flexibility of the longer hydroxy alkyl
substituent.[23,25f] Thus, longer reaction time is needed for the
formation of the seven-membered oxacyclocarbene complexes
12 and 12’ than those for the six- and five-membered complexes
13 and 14. It is also noted that reaction of the aromatic alkynol
4a to generate seven-membered oxacyclocarbene 12 took place
faster than that of the aliphatic alkynol 4l (9 h vs 13 h).
Apparently, the presence of the phenyl ring tethering the ortho
terminal alkyne and the hydroxy alkyl substituent in the aromatic
alkynol somehow reduces the flexibility of the hydroxy alkyl
substituent in the vinylidene intermediate, which then favours
intramolecular attack of the hydroxy group to the C.
Complexes 12’, 13 and 14 were characterized by multinuclear
NMR spectroscopy and elemental analysis. Taking 12’ for
example, the 31P{1H} NMR spectrum showed two doublet signals
at 57.6 and 49.1 ppm (J(PP) = 31.7 Hz) in CD2Cl2. The 1H NMR
spectrum displayed characteristic signals for the five pairs of
CH2 proton resonances in the aliphatic region between 4.37 and
0.83 ppm. The 13C{1H} NMR spectrum displayed a Ru=C signal
at 326.5 ppm (2J(CP) = 11.2 Hz), which is similar to that of
complex 12 and those reported for other ruthenium
oxacyclocarbene complexes.[20,25] The 13C{1H} signals for the five
methylene resonances were observed at 77.5, 65.6, 50.1, 28.5
and 19.5 ppm, respectively. The structures of complexes 12’, 13
and 14 have been also confirmed by X-ray diffraction, which are
similar to that of 12. Figures 5-7 showed the X-ray structures for
the cation of complexes 12’, 13 and 14, with the Ru=C bond
lengths being 1.948(3),1.935(5) and 1.930(4) Å, respectively.
Figure 6. Molecular structure for the cation of 13 with thermal ellipsoids drawn
at 30% probability. Counter anion and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Ru(1)-C(1) 1.935(5), Ru(1)-N(1)
2.210(3), Ru(1)-N(2) 2.212(4), Ru(1)-P(2) 2.2844(12), Ru(1)-P(1) 2.2915(15),
Ru(1)-Cl(1) 2.4694(15), O(1)-C(1) 1.292(6), O(1)-C(5) 1.467(7), C(1)-C(2)
1.491(7), C(2)-C(3) 1.413(10), C(3)-C(4) 1.403(12), C(4)-C(5) 1.402(12); C(1)-
Ru(1)-N(1) 93.39(17), C(1)-Ru(1)-N(2) 173.49(17), N(1)-Ru(1)-N(2) 89.16(13),
C(1)-Ru(1)-P(2) 94.89(14), N(1)-Ru(1)-P(2) 171.70(10), N(2)-Ru(1)-P(2)
82.67(10), N(1)-Ru(1)-P(1) 81.57(10), N(2)-Ru(1)-P(1) 95.48(10), P(2)-Ru(1)-
P(1) 97.69(5), N(1)-Ru(1)-Cl(1) 87.06(10), N(2)-Ru(1)-Cl(1) 83.47(10), P(2)-
Ru(1)-Cl(1) 93.45(4), P(1)-Ru(1)-Cl(1) 168.60(4).
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The results obtained above naturally raise the question about
what factors are responsible for the different reactivity of the
oxacyclocarbene intermediates in the catalytic reactions, in
particular the marked difference between 12 and 12’. Initially, we
envisioned that facile tansformation of oxacyclocarbene 12 into
the 3-benzoxepine 5a might be related to the stronger acidity of
the C-protons due to the benzylic character. However, the
control experiments of 12’ in the presence of base have shown
that the acidity issue is very unlikely. At this stage, it appears
likely that the failure for the transformation of oxacyclocarbene
12’ can be rationalized in terms of the conformational flexibility
of the seven-membered aliphatic oxacyclic ring, which
disfavored the deprotonation of the C-protons by baisc media.
Consistent with this assumption, the oxacyclocarbene 12 with a
less flexible benzo-oxacyclic ring can be readily deprotonated
and evolve into catalyst 2 and 3-benzoxepine 5a. In the cases of
aliphatic oxacyclocarbene complexes 13 and 14, deprotonation
of the C-protons could be also achieved under the action of
weak basic THF solvent due to the reduced conformational
flexibility of the smaller oxacycle, albeit not very efficiently as
reflected by the relatively low conversion of substrates 8c and
9a in the catalytic reactions (Table 3 and Scheme 6).
Figure 7. Molecular structure for the cation of 14 with thermal ellipsoids drawn
at 30% probability. Counter anion and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Ru(1)-C(1) 1.930(4), Ru(1)-N(1)
2.187(3), Ru(1)-N(2) 2.215(3), Ru(1)-P(2) 2.2993(10), Ru(1)-P(1) 2.2903(11),
Ru(1)-Cl(1) 2.4480(11), O(1)-C(1) 1.319(5), O(1)-C(4) 1.477(5), C(1)-C(2)
1.512(5), C(2)-C(3) 1.523(6), C(3)-C(4) 1.506(8); C(1)-Ru(1)-N(1) 87.46(14),
C(1)-Ru(1)-N(2) 179.45(14), N(1)-Ru(1)-N(2) 92.93(11), C(1)-Ru(1)-P(2)
98.16(12), N(1)-Ru(1)-P(2) 174.34(8), N(2)-Ru(1)-P(2) 81.45(8), N(1)-Ru(1)-
P(1) 81.17(8), N(2)-Ru(1)-P(1) 88.66(8), P(2)-Ru(1)-P(1) 99.30(4), N(1)-Ru(1)-
Cl(1) 87.85(8), N(2)-Ru(1)-Cl(1) 84.67(8), P(2)-Ru(1)-Cl(1) 90.92(4), P(1)-
Ru(1)-Cl(1) 166.85(4).
Conclusions
In summary, we have prepared several new ruthenium
complexes with the heterobidentate P,N-donor ligand DPPQ,
including RuCl2(DPPQ)2 (1), [Ru(-Cl)(DPPQ)2]2(BPh4)2 (2) and
In agreement with the results of the catalytic reactions, no
reaction occurred when a solution of 12’ was heated in DCE at
90oC or 110 oC for 13 h, and even in the presence of base such
as Et3N and Cs2CO3, which is stark contrast to the facile
tansformation of complex 12 into the 3-benzoxepine 5a. On the
other hand, cycloisomerization of corresponding alkynols
employing complexes 12’, 13 or 14 as catalysts were also
conducted (Scheme 6). Again, no appreciable reaction could be
observed when the reaction of hex-5-yn-1-ol (4l) in the presence
[RuCl(DPPQ)2Py](BF4) (3). Complex
2 was found to be
catalytically active for endo cycloisomerization of a range of
terminal alkynols to form corresponding endo-cyclic enol ethers
in moderate to excellent yields. In particular, with only 1 mol%
loading of 2, the 7-endo and 8-endo heterocyclization of
aromatic alkynols can be achieved efficiently to give the seven-
membered
3-benzoxepine
and
eight-membered
3-
benzo[d]oxocine derivatives. The stoichiometric reactions of
catalyst 2 with various alkynol substrates such as the aromatic
alkynol 4a and the aliphatic alkynols 4l, 8c or 9a have been
carried out to study the mechanism for the endo-
cycloisomerization reactions, which led to the isolation of a
series of seven-, six-, and five-membered oxacyclocarbene
o
of 2.0 mol% complex 12’ in DCE was heated at 90 C for 13 h.
On the contrary, in a d8-THF solution, cycloisomerization of pent-
4-yn-1-ol (8c) or but-3-yn-1-ol (9a) in the presence of 2.0 mol%
13 or 14 could be detected after the reaction solution were
o
heated at 100 C for 24 h, although only partial conversion was
ruthenium
complexes
including
and
achived (50 and 40% for 8c and 9a, respectively).
[RuCl(DPPQ)2{=CCH2C6H4CH2CH2O}](BPh4)
(12)
[RuCl(DPPQ)2{=CCH2(CH2)nCH2O}](BPh4) (n = 3, 12’; n = 2, 13;
n = 1, 14). Complex 12 represents the first example of benzo-
[Cat.]
(2 mol%)
( )n
O
OH
BPh4
oxacycloheptylidene
transition-metal
complexes.
The
Solvent, Ar
( )n
4l
8c
9a
quantitative transformation of complex 12 into catalyst 2 and 3-
benzoxepine 5a as well as the efficient catalytic activity of 12 for
the endo-cyclization of 4a demonstrated that complex 12 is an
intermediate involved in the catalytic cycle, which provided the
most direct evidences for the first time to show the intermediacy
of an oxacyclocarbene complex in the catalytic endo-
cycloisomerization of alkynols. Moreover, comparative studies
on the modeling reactions and catalytic activity of the series of
oxacyclocarbene complexes indicated that the different catalytic
activity of complex 2 for the endo-cycloisomerization of different
(n = 3, ; 2, ; 3,
)
N
Ph2
P
PPh2
Cl
[Cat.]
Temp
Conversion
Time
Solvent
n
3
2
1
Ru
N
DCE 90 oC 13 h
d8-THF 100 oC
24 h
12'
13
0%
O
50%
( )n
12'
[Cat.]
13 14
; 2, ; 1, )
(n = 3,
d8-THF 100 oC
24 h
40%
14
Scheme 6. Endo-cycloisomerization of alkynols catalyzed by oxacyclocarbene
ruthenium complexes.
This article is protected by copyright. All rights reserved.

10.1002/chem.201703971
Chemistry - A European Journal
Preparation of complex 3: A mixture of complex 1 (330 mg, 0.42 mmol)
and AgBF4 (85 mg, 0.42 mmol) in pyridine (10 mL) was stirred at room
temperature for 30 min to give an orange solution and undissolved salt,
which were seperated by filtration on a pad of Celite®. The solution was
removed to about 1 mL, addition of Et2O (15 mL) produced orange-yellow
solid, which was collected by filteration, washed with Et2O (2x10 mL),
and dried under vacuum. Yield: 384 mg (98%). 31P{1H} NMR (202 MHz,
CDCl3) δ 58.5 (d, J (PP)= 33.8 Hz), 57.6 (d, J (PP)= 33.8 Hz); 1H NMR
(500 MHz, CD2Cl2) δ 9.30 (d, J = 5.8 Hz, 1H, quinolyl), 8.63 (dt, J = 8.5,
1.5 Hz, 1H), 8.45 (ddd, J = 8.3, 7.0, 1.3 Hz, 1H), 8.30 – 8.28 (m, 1H),
8.25 (dt (unresolved t), J = 8.5, 1.5 Hz, 1H), 8.21 (dt (unresolved t), J =
8.0, 1.5 Hz, 1H), 8.10 (dt, J = 8.0, 1.8 Hz, 1H), 8.07 – 8.02 (m, 2H), 7.74
– 7.70 (m, 3H), 7.63 – 7.56 (m, 2H), 7.55 – 7.51 (m, 2H), 7.41 (ddd, J =
9.8, 7.1, 1.2 Hz, 1H), 7.37 – 7.32 (m, 3H), 7.20 – 7.13 (m, 3H), 7.09 –
6.98 (m, 8H), 6.77 (dd, J = 8.3, 5.4 Hz, 1H), 6.71 (t, J = 6.6 Hz, 1H), 6.61
(td, J = 8.1, 2.1 Hz, 2H), 6.03 (ddd, J = 10.3, 8.5, 1.7 Hz, 2H); 13C{1H}
NMR (126 MHz, CD2Cl2) δ 156.8, 156.6 (quinolyl), 154.0, 152.7, 152.4 (d,
J = 16.3 Hz, quinolyl), 150.2, 139.1, 139.0, 137.5, 137.2 (d, J = 41.8 Hz,
PPh2), 136.8, 134.5 (d, J = 9.8 Hz, PPh2),, 133.0, 132.9 – 127.6 (m),
125.9, 125.0, 123.5, 122.9; elemental analysis calcd (%) for
C47H37BClF4N3P2Ru•CH2Cl2: C, 56.85; H, 3.88; N, 4.14; found: C, 56.99;
H, 4.10; N, 4.49 (Crystals of 3 grown from CH2Cl2/Hexane were used for
EA analysis and the presence of CH2Cl2 in the sample has been
confirmed by an X-ray diffraction study (See Supporting Information)).
types of alknynols can be related to the reactivity of the
respective ruthenium oxacyclocarbene intemediates.
Experimental Section
General: All manipulations were carried out under an argon atmosphere
by using standard schlenk techniques, unless otherwise noted. Solvents
were distilled from sodium/benzophenone (toluene, tetrahydrofuran,
diethyl ether and n-hexane) or calciumhydride(CH2Cl2,1,4-dioxane,1,2-
dichloroethane) under argon prior to use. All other reagents were used as
received from commercial sources without further purification,unless
otherwise noted. The starting material 8-(diphenylphosphino)quinoline,[30]
[31]
and RuCl2(PPh3)3
were prepared according to literature methods.
NMR spectroscopic experiments were carried out on Bruker AV400 and
Bruker AV500.1H and 13C{1H} NMR chemical shifts are relative to TMS,
and 31P{1H} NMR is relative to 85% H3PO4 as the external standard.
Elemental analyses data were obtained on an Elementar
Analysensysteme GmbH Vario EL III instrument. Mass spectra (HRMS)
were obtained on Bruker En Apex ultra 7.0T FT-MS by the Public
Instrument Platform. Reactions were monitored by using a GC – 9106.
Preparation of complex 1: A mixture of RuCl2(PPh3)3 (1.0 g, 1.04 mmol)
and 8-(diphenylphosphino)quinoline (0.65 g, 2.08 mmol) in
dichloromethane (20 mL) was stirred at room temperature for 3 h to give
a red solution along with a red precipitate. The volume of the reaction
mixture was reduced to ca.10 mL and diethyl ether (20 mL) was added
slowly to the residue with stirring. The mixture was stirred for ca. 5 min.
to complete further precipitation. The solid was collected by filtration,
washed with diethyl ether (3 x 10 mL) and dried under vacuum. Yield: 0.8
g (96%). 31P{1H} NMR (162 MHz, CDCl3) δ 62.2 (d, J (PP) = 33.4 Hz),
53.9 (d, J (PP) = 33.4 Hz); 1H NMR (400 MHz, CDCl3) δ 10.83 (d, J = 4.0
Hz, 1H, quinolyl), 8.43 – 8.34 (m, 4H), 8.05 (d, J = 7.9 Hz, 1H), 7.78 (d, J
= 7.8 Hz, 1H), 7.71 – 7.67 (m, 3H), 7.63 – 7.51 (m, 4H), 7.36 – 7.25 (m,
7H), 7.03 (t, J = 7.7 Hz, 2H), 6.97 (t, J = 7.3 Hz, 1H), 6.84 (t, J = 7.4 Hz,
1H), 6.77 (t, J = 7.5 Hz, 2H), 6.55 (t, J = 7.6 Hz, 2H), 6.36 (dd, J = 7.9,
5.3 Hz, 1H), 6.17 (t, J = 7.2 Hz, 2H). 13C{1H} NMR spectrum was not
collected due to the poor solubility of the compound. elemental analysis
calcd (%) for C42H32Cl2N2P2Ru•2CHCl3: C, 50.94; H, 3.30; N, 2.70; found:
C, 51.04; H, 3.65; N, 2.92 (Crystals of 1 grown from CHCl3/Hexane were
used for EA analysis and the presence of CHCl3 in the sample has been
confirmed by an X-ray diffraction study (See Supporting Information)).
Complex 12: A mixture of complex 2 (210 mg, 0.1 mmol) and 2-(2-
ethynylphenyl)ethanol (146 mg,1.0 mmol) in 1,2-dichloroethane (10 mL)
was stirred at 70 oC for 9 h, then cooled to room temperature. The
solvent was removed to ca. 1 mL under reduced pressure and diethyl
ether (10 mL) was added to the residue to produce a yellow solid, which
was collected by filtration, washed with diethyl ether (2x6 mL),
tetrahydrofuran (6 mL) and dried under vacuum. Yield: 226 mg (95%).
31P NMR (202 MHz, CD2Cl2) δ 58.6 (d, J (PP)= 31.3 Hz), 49.5 (d, J (PP)
= 31.3 Hz); 1H NMR (500 MHz, CD2Cl2) δ 10.73 (s (br), 1H, quinolyl),
8.73 (d, J = 8.2 Hz, 1H, quinolyl), 8.24 (d, J = 8.0 Hz, 1H), 8.19 (d, J = 8.3
Hz, 1H), 8.08 (d, J = 8.0 Hz, 1H), 8.05 – 7.98 (m, 2H), 7.95 – 7.89 (m,
2H), 7.79 (t, J = 7.6 Hz, 1H, PPh2-para), 7.63 (t, J = 7.5 Hz, 1H, PPh2-
para), 7.48 (dt, J = 15.2, 7.8 Hz, 2H), 7.39 – 7.35 (m, 10H, BPh4-ortho
and other aromatic), 7.31 (t, J = 7.2 Hz, 1H), 7.22 (d, J = 3.7 Hz, 1H),
7.18 – 6.99 (m, 18H, BPh4-meta and other aromatic), 6.89 (t, J = 7.2 Hz,
4H, BPh4-para), 6.82 (dd, J = 8.2, 5.0 Hz, 1H), 6.69 (t, J = 7.3 Hz, 1H),
6.65 (dd, J = 7.8, 1.3 Hz, 2H), 6.35 (dd, J = 11.5, 7.7 Hz, 2H), 6.17 (dd, J
= 10.7, 7.8 Hz, 2H), 5.56 (d, J = 7.6 Hz, 1H), 4.85-4.73 (m, 1H,
Ru=COCH2), 4.40 (d, J = 15.0 Hz, 1H, Ru=CCH2), 4.37-4.34 (m, 1H,
Ru=COCH2), 4.23 (d, J = 15.0 Hz, 1H, Ru=CCH2), 3.15-3.05 (m, 2H,
Ru=COCH2CH2); 13C{1H} NMR (126 MHz, CD2Cl2) δ 321.6 (t, J (PC) =
11.2 Hz, Ru=C),164.1 (dd, J = 98.9, 49.1 Hz, quinolyl), 155.6, 152.5,
152.3, 151.7, 151.6, 139.6, 138.5, 137.8, 137.4, 136.5, 136.1 (BPh4-
ortho), 135.8–127.3 (m), 126.6, 125.6 (BPh4-meta), 124.4, 122.1, 121.7
(BPh4-para), 73.0 (Ru=COCH2), 55.4 (Ru=CCH2), 32.3 (Ru=COCH2CH2);
elemental analysis calcd (%) for C76H62BClN2OP2Ru: C, 74.30; H, 5.09;
N, 2.28; found: C, 74.69; H, 5.36; N, 2.50
Preparation of complex 2: A mixture of 1 (0.94 g, 1.17 mmol) and
sodium tetraphenylborate (0.80 g, 2.34 mmol) in dichloromethane (25
mL) was stirred at room temperature for 4 h to give a red solution. The
solvent was removed under reduced pressure. Addition of diethyl ether
(20 mL) to the residue produced an orange-red solid, which was
collected by filtration, washed with THF (2 x 10 mL), MeOH (10 mL),
diethyl ether (10 mL) and dried under vacuum. Yield: 1.26 g (99%).
1
31P{1H} NMR (162 MHz, CD2Cl2) δ 63.5 (s); H NMR (400 MHz, CD2Cl2)
δ 8.82 (d, J = 4.6 Hz, 4H, quinolyl), 8.29-8.26 (m, 8H), 7.90-7.86 (m, 8H),
7.48 (s(br), 16H, BPh4-ortho and other aromatic), 7.38-7.34 (m, 4H),
7.13-7.07 (m, 24H, BPh4-meta and other aromatic), 6.98 – 6.83 (m, 12H,
BPh4-para and other aromatic), 6.74 (s(br), 8H), 6.52 (dd(unresolved), J
= 7.6, 5.5 Hz, 4H), 6.41 (t, J = 7.2 Hz, 8H), 5.59 (s(br), 8H); 13C{1H} NMR
(101 MHz, CD2Cl2) δ 164.1 (dd, J = 98.7, 49.1 Hz, PPh2-ipso), 157.0,
156.6 (t, J = 9.6 Hz, quinolyl), 139.5, 138.1, 136.1 (BPh4-ortho), 133.5,
133.3, 130.5, 130.4, 130.2, 130.7, 129.9, 129.8, 129.7, 129.5, 129.2,
129.0 (br), 128.3 (br), 128.1 (br, BPh4-ipso), 125.7 (br, BPh4-meta), 122.5,
Complex 12’: A mixture of complex 2 (210 mg, 0.1 mmol) and hex-5-yn-
1-ol (115 uL, 1.0 mmol) in 1,2-dichloroethane (10 mL) was stirred at 70
oC for 13 h to give an orange solution, then the solvent was removed to
ca. 1 mL under reduced pressure. Addition of diethyl ether (10 mL) to the
residue produced a yellow solid, which was collected by filtration, washed
with diethyl ether (2x6 mL), tetrahydrofuran (5 mL) and dried under
vacuum at least 3 h. Yield: 204 mg (89%).31P NMR (202 MHz, CD2Cl2) δ
57.6 (d, J = 31.7 Hz), 49.1 (d, J = 31.7 Hz); 1H NMR (500 MHz, CD2Cl2) δ
10.69 (dd (unresolved), J(HH)  5.2 Hz, J(PH)  2.3 Hz, 1H, quinolyl),
8.65 (d, J = 8.3 Hz, 1H, quinolyl), 8.23 (dd, J = 16.8, 8.2 Hz, 2H), 8.09 (d,
J = 8.0 Hz, 1H), 8.02 – 8.00 (m, 3H), 7.93 (dd, J = 8.0, 5.2 Hz, 1H), 7.79
121.9
(BPh4-para);
elemental
analysis
calcd
(%)
for
C132H104B2Cl2N4P4Ru2: C, 73.24; H, 4.84; N, 2.59; found: C, 73.65; H,
5.01; N, 2.38
This article is protected by copyright. All rights reserved.

10.1002/chem.201703971
Chemistry - A European Journal
(t, J = 7.5 Hz, 1H, PPh2-para), 7.74 (t, J = 7.5 Hz, 1H, PPh2-para), 7.49
(dd, J = 13.9, 6.4 Hz, 2H), 7.43 – 7.28 (m, 13H, BPh4-ortho and other
aromatic), 7.26 – 7.19 (m, 3H), 7.12 – 6.97 (m, 12H, BPh4-meta and
other aromatic), 6.90 – 6.87 (m, 5H, BPh4-para and other aromatic), 6.68
(t, J = 6.8 Hz, 2H), 6.59 (dd, J = 10.8, 8.2 Hz, 2H), 6.19 – 6.06 (m, 2H),
4.37 (dd, J = 11.7, 5.9 Hz, 1H), 4.04 (dd, J = 11.0, 9.5 Hz, 1H), 3.05 (dd,
J = 13.7, 9.3 Hz, 1H), 2.35 (t, J = 11.5 Hz, 1H), 1.67 – 1.59 (m, 1H), 1.44
(dd, J = 6.1, 3.9 Hz, 1H), 1.42 – 1.36 (m, 1H), 1.04 – 0.95 (m, 1H), 0.95 –
0.83 (m, 2H); 13C NMR (126 MHz, CD2Cl2) δ 326.5(t, J (PC) =11.2 Hz,
Ru=C), 164.1(dd, J = 98.2, 49.3 Hz, PPh2-ipso), 155.8, 152.4, 152.1,
151.9, 151.8, 139.4, 138.5, 137.9, 135.9 (BPh4-ortho), 135.54, 135.47,
133.4 – 127.3 (m), 125.6 (BPh4-meta), 124.1, 122.2, 121.7 (BPh4-para),
77.5 (RuOCH2), 65.6 (RuOCH2CH2), 50.1 (RuOCH2CH2CH2), 28.5
(RuCH2CH2), 19.5 (RuCH2); elemental analysis calcd (%) for
Hz, 1H), 8.24 (t, J = 9.2 Hz, 2H), 8.13 – 8.09 (m, 2H), 7.93 (dd, J = 8.1,
5.2 Hz, 1H, quinolyl), 7.93 (dd, J = 10.5, 8.0 Hz, 2H), 7.81 (t, J = 7.6 Hz,
1H, PPh2-para), 7.74 (t, J = 7.5 Hz, 1H, PPh2-para), 7.46 (dd, J = 16.0,
8.0 Hz, 2H), 7.42–7.30 (m, 13H, BPh4-ortho and other aromatic), 7.19 (t,
J = 6.6 Hz, 2H), 7.13–7.07 (m, 3H), 7.04 (t, J = 7.3 Hz, 10H, BPh4-meta
and other aromatic), 6.94–6.85 (m, 5H, BPh4-para and other aromatic),
6.73 (t, J = 6.8 Hz, 2H), 6.40 (dd, J = 11.0, 8.1 Hz, 2H), 6.23 (dd, J = 11.0,
7.5 Hz, 2H), 4.48 (dd, J = 16.5, 8.6 Hz, 1H, Ru=C(O-)CH2CH2CH2-), 4.27
(dd, J = 15.4, 8.9 Hz, 1H, Ru=C(O-)CH2CH2CH2-), 3.34 – 3.21 (m, 1H,
Ru=C(O-)CH2), 2.08 (ddd, J = 19.6, 9.3, 5.9 Hz, 1H, Ru=C(O-)CH2),
1.82–1.74 (m, 1H, Ru=C(O-)CH2CH2), 1.39-1.34 (m, 1H, Ru=C(O-
)CH2CH2); 13C{1H} NMR(126 MHz, CD2Cl2) δ 314.14(t, J (PC)= 12.2 Hz,
Ru=C), 164.1 (dd, J = 98.4, 49.5 Hz, PPh2-ipso), 156.1, 152.3, 152.1,
152.0, 151.93, 151.87, 139.5, 138.8, 137.93, 137.87, 135.9 (BPh4-ortho),
135.5, 135.4, 134.2-127.4(m), 125.6 (BPh4-meta), 124.0, 122.3, 121.7
(BPh4-para), 83.1 (Ru=COCH2-), 53.0 (Ru=COCH2CH2CH2-), 20.8
C72H62BClN2OP2Ru•2CH2Cl2: C, 65.82; H, 4.93; N, 2.07; found: C, 66.04;
H, 5.30; N, 2.33 (Crystals of 12’ grown from CH2Cl2/Hexane were used
for EA analysis and the presence of CH2Cl2 in the sample has been
confirmed by an X-ray diffraction study (See Supporting Information)).
(Ru=CCH2-);
70H58BClN2OP2Ru•CH2Cl2: C, 68.91; H, 4.89; N, 2.26; found: C, 69.31;
H, 5.30; N, 2.49
elemental
analysis
calcd
(%)
for
C
Complex 13: A mixture of complex 2 (210 mg, 0.1 mmol) and pent-4-yn-
1-ol (0.1 mL, 0.1 mmol) in dichloromethane/tetrahydrofuran (15 mL, V:V
= 1:1) was stirred at 70 oC for 2 h to give an orange solution. After
cooling down to room temperature, the solvent was removed to ca. 2 mL
under reduced pressure and diethyl ether (10 mL) was added to the
residue to give a yellow solid, which was collected by filtration, washed
with diethyl ether (2 x 6 mL), tetrahydrofuran (6 mL) and dried under
vacuum at least 3 h. Yield: 200 mg (90%). 31P{1H} NMR (162 MHz,
CD2Cl2) δ 58.3 (d, J (PP) = 31.9 Hz), 51.1 (d, J (PP) = 31.9 Hz); 1H NMR
(400 MHz, CD2Cl2) δ 10.74 (d (unresolved), J = 5.2 Hz, 1H, quinolyl),
8.63 (d, J = 8.1 Hz, 1H, quinolyl), 8.23 (d, J = 7.8 Hz, 2H), 8.07 (t, J = 8.0
Hz, 2H), 7.98 (d, J = 7.9 Hz, 2H), 7.93 (dd, J = 8.1, 5.2 Hz, 1H, quinolyl),
7.78 (t, J = 7.9 Hz, 1H, PPh2-para), 7.73 (t, J = 7.8 Hz, 1H, PPh2-para),
7.51 – 7.30 (m, 13H, BPh4-ortho and other aromatic), 7.25 – 7.21 (m, 3H),
7.12 – 6.97 (m, 14H, BPh4-meta and other aromatic), 6.93 – 6.86 (m, 5H,
BPh4-para and other aromatic), 6.73 (dd (unresolved), J  9.0, 6.4 Hz,
2H), 6.46 (t, J = 9.4 Hz, 2H), 6.32 (t, J = 9.0 Hz, 2H), 4.16 – 4.04 (m, 1H,
Typical procedure for the catalytic reactions: Catalyst 2 (0.001 mmol)
was added to a solution of alkynol (0.1 mmol) in DCE or THF. The
resulting solution was stirred at 90 oC or 100 oC and monitored by TLC or
1H NMR spectroscopy. When the conversion of sustrates was complete,
the desired product was isolated by flash column chromatography on
silica gel. For some products of low boiling points, the yields were
determined by GC methods or 1H NMR spectroscopic integration with
CH2Br2 as the internal standards in d8-THF.
Crystallograhic Analysis. Crystals suitable for X-ray diffraction were
grown from a CHCl3 solution (for 1), or CH2Cl2 solution (for 2, 3, 12, 12’,
13, and 14) layered with n-hexane. Data collections were performed on
an Oxford Gemini S Ultra or a Rigaku R-AXIS SPIDER IP CCD area
detector using graphite-monochromated Mo Kα radiation (λ =0.71073 Å).
Multiscan absorption corrections (SADABS) were applied. All of the data
were corrected for absorption effects using the multi-scan technique. The
structures were solved by direct methods, expanded by difference
Fourier syntheses, and refined by full-matrix least-squares on F2 using
the Bruker SHELXTL-97 program and Olex 2. Non-H atoms were refined
anisotropically unless otherwise stated. Hydrogen atoms were introduced
at their geometric positions and refined as riding atoms. The Cell
parameters, data collection, and structure solution and refinement for
complexes 1, 2, 3, 12, 12’, 13 and 14 are given in Tables S1–S3 (See
Supporting Information). CCDC 1469353 (1), 1469355 (2), 1469359 (3),
1469354 (12), 1564337 (12’), 1469356 (13) and 1469357 (14) contain
the crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Ru=C(O-)CH2CH2CH2CH2-),
3.79-3.76
(m,
1H,
Ru=C(O-
)CH2CH2CH2CH2-), 3.67–3.51 (m, 1H, Ru=C(O-)CH2), 2.04–1.89 (m, 1H,
Ru=C(O-)CH2), 1.64-1.58 (m, 1H, Ru=C(O-)CH2CH2), 1.48–1.40 (m, 1H,
Ru=C(O-)CH2CH2), 1.36-1.31 (m, 1H, Ru=CCH2CH2), 1.22–1.12 (m, 1H,
Ru=CCH2CH2); 13C{1H} NMR (101 MHz, CD2Cl2) δ 319.9 (t, J (PC)= 9.9
Hz, Ru=C), 164.1 (dd, J = 98.5, 49.4 Hz, PPh2-ipso), 155.9 (PPh2), 152.1
(PPh2), 151.0 (d, J = 10.0 Hz, quinolyl), 139.4 (quinolyl), 138.7, 137.7,
137.5, 136.8 (d, J = 50.1 Hz, quinolyl), 136.5 (BPh4-ortho), 135.7 (d, J =
9.9 Hz, PPh2), 134.4 (dd, J = 51.2, 40.8 Hz, quinolyl-ipso), 132.5 (t
(unresolved), J  9.1 Hz, BPh4-ipso), 132.2, 132.1, 132.0, 131.7, 131.5,
131.0, 30.6, 130.5, 130.4, 130.3, 130.0, 129.8, 129.5 (d, J = 8.2 Hz,
quinolyl), 128.57, 128.51, 128.47, 128.16, 128.06, 128.02, 127.92, 127.6
(d, J = 9.9 Hz), 127.5 (d, J = 6.2 Hz), 125.6 (BPh4-meta), 124.1, 122.3,
121.7 (BPh4-para), 75.4 (Ru=C(O-)CH2CH2CH2CH2-), 47.5 (Ru=CCH2),
21.3 (Ru=C(O-)CH2CH2),16.6 (Ru=CCH2CH2); elemental analysis calcd
(%) for C71H60BClN2OP2Ru: C, 73.10; H, 5.18; N, 2.40; found: C, 73.44;
H, 5.43; N, 2.62
Acknowledgements
This work was supported by the National Basic Research
Program of China (973 Program 2012CB821600), and Program
for Changjiang Scholars and Innovative Research Team in
University (PCSIRT).
Complex 14: A mixture of complex 2 (210 mg, 0.1 mmol) and but-3-yn-1-
ol (75 uL,1.0 mmol) in dichloromethane/tetrahydrofuran (15 mL, V:V=1:1)
was stirred at 70 oC for 4 h to give an orange solution, and then cooled to
room temperature. The solvent was removed to ca. 2 mL under reduced
pressure and diethyl ether (10 mL) was added to the residue to produce
a yellow solid, which was collected by filtration, washed with diethyl ether
(2x6 mL), tetrahydrofuran (6 mL) and dried under vacuum at least 3 h.
Yield: 210 mg (92%). 31P{1H} NMR (202 MHz, CD2Cl2) δ 57.8 (d, J (PP) =
30.8 Hz), 50.9 (d, J(PP) = 30.8 Hz); 1H NMR (500 MHz, CD2Cl2) δ 10.71
(dd (unresolved), J(PH)  J(HH)  5.2 Hz, 1H, quinolyl), 8.65 (d, J = 8.2
Keywords: alkynes
•
cycloisomerization
•
ruthenium
•
oxacyclocarbene complex • 8-(diphenylphosphino)quinoline
Reference
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Tao Cai, Yu Yang, Wei-Wei Li, Wen-
Bing Qin, and Ting-Bin Wen*
Page No. – Page No.
Efficient Endo Cycloisomerization of
Terminal Alkynols Catalyzed by a
New Ruthenium Complex with 8-
(Diphenylphosphino)quinoline Ligand
and Mechanism Investigation
The new ruthenium complex [Ru(-Cl)(DPPQ)2]2(BPh4)2 (2) (DPPQ = 8-
(diphenylphosphino)quinoline), with only 1 mol% loading, was found to be
catalytically active for the endo-cycloisomerization of various alkynols to endo-cyclic
enol ethers in moderate to excellent yields. In particular, the 7-endo and 8-endo
heterocyclization of aromatic alkynols can be achieved efficiently. The
oxacyclocarbene complex 12 was isolated as the key intermediate.
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