Cyclopentadienyl molybdenum(II) N,C-chelating benzothiazole-carbene complexes: Synthesis, structure, and application in cyclooctene epoxidation catalysis

Article abstract of DOI:10.1021/om401128z

A series of new benzothiazolyl-imidazolium salts 1-3 (1-(benzothiazol-2-yl) -3-methylimidazolium chloride (1); 1-(benzothiazol-2-yl)-3-benzylimidazolium chloride (2); 1-(benzothiazol-2-yl)-3-allylimidazolium chloride (3)) have been prepared from nucleophilic substitution of 2-chlorobenzothiazole by imidazoles. They serve as the precursors of hybrid N-heterocyclic carbene (NHC) ligands L1-L3 (L1 = 1-(benzothiazolin-2-yl)-3-methylimidazol-2-ylidene; L2 = 1-(benzothiazolin-2-yl)-3-benzylimidazol-2-ylidene; L3 = 1-(benzothiazolin-2-yl) -3-allylimidazol-2-ylidene). Reactions of 1-3 with Ag₂O result in Ag(I) NHC complexes 4-6 [Ag(L)(μ-Cl)]₂ (L = L1, 4; L = L2, 5) and Ag(L3)Cl (6), in which L1-L3 act as monodentate carbene ligand with a benzothiazolyl pendant. Subsequent transmetalation of 4-6 with CpMo(CO) ₃Br (Cp = cyclopentadienyl) and anion exchange reaction with AgX (X = BF₄, PF₆, or OTf) give complexes [CpMo(CO) ₂(L)]₂[Ag₂Br₄] (L = L1, 7a; L = L2, 8a; L = L3, 9a) and [CpMo(CO)₂(L)][X] (L = L1, X = BF₄, 7b; L = L2, X = BF₄, 8b; X = PF₆, 8c; X = OTf, 8d; L = L3, X = BF₄, 9b), whose structures are reported herein. The ligands L1-L3 show their versatility by switching to be N,C-chelating in these Mo(II) complexes. The chelation of the hybrid NHC ligand results in shorter Mo-C _carbene bonds (2.14-2.16 A) comparing with known Mo(II) NHC complexes in the literature. These complexes are active toward cyclooctene epoxidation with tert-butyl hydroperoxide (TBHP) affording up to 90% yield of epoxide (for 8b) in 3 h at 55 °C.

Full text of DOI:10.1021/om401128z

Article
pubs.acs.org/Organometallics
Cyclopentadienyl Molybdenum(II) N,C-Chelating Benzothiazole-
Carbene Complexes: Synthesis, Structure, and Application in
Cyclooctene Epoxidation Catalysis
Zhe Wang,† Sin Wee Benny Ng,† Lu Jiang,† Wen Jin Leong,† Jin Zhao,*,†,‡ and T. S. Andy Hor*,†,‡
†Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
‡Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602,
Singapore
S
* Supporting Information
ABSTRACT: A series of new benzothiazolyl-imidazolium
salts 1−3 (1-(benzothiazol-2-yl)-3-methylimidazolium chlor-
ide (1); 1-(benzothiazol-2-yl)-3-benzylimidazolium chloride
(2); 1-(benzothiazol-2-yl)-3-allylimidazolium chloride (3))
have been prepared from nucleophilic substitution of 2-
chlorobenzothiazole by imidazoles. They serve as the
precursors of hybrid N-heterocyclic carbene (NHC) ligands
L1−L3 (L1 = 1-(benzothiazolin-2-yl)-3-methylimidazol-2-
ylidene; L2 = 1-(benzothiazolin-2-yl)-3-benzylimidazol-2-
ylidene; L3 = 1-(benzothiazolin-2-yl)-3-allylimidazol-2-yli-
dene). Reactions of 1−3 with Ag2O result in Ag(I) NHC complexes 4−6 [Ag(L)(μ-Cl)]2 (L = L1, 4; L = L2, 5) and
Ag(L3)Cl (6), in which L1−L3 act as monodentate carbene ligand with a benzothiazolyl pendant. Subsequent transmetalation of
4−6 with CpMo(CO)3Br (Cp = cyclopentadienyl) and anion exchange reaction with AgX (X = BF4, PF6, or OTf) give
complexes [CpMo(CO)2(L)]2[Ag2Br4] (L = L1, 7a; L = L2, 8a; L = L3, 9a) and [CpMo(CO)2(L)][X] (L = L1, X = BF4, 7b; L
= L2, X = BF4, 8b; X = PF6, 8c; X = OTf, 8d; L = L3, X = BF4, 9b), whose structures are reported herein. The ligands L1−L3
show their versatility by switching to be N,C-chelating in these Mo(II) complexes. The chelation of the hybrid NHC ligand
results in shorter Mo−Ccarbene bonds (2.14−2.16 Å) comparing with known Mo(II) NHC complexes in the literature. These
complexes are active toward cyclooctene epoxidation with tert-butyl hydroperoxide (TBHP) affording up to 90% yield of epoxide
(for 8b) in 3 h at 55 °C.
catalysis.5,6 This has prompted us to investigate whether similar
type of complexes but supported by hybrid-NHC ligands
INTRODUCTION
■
N-Heterocyclic carbenes (NHCs) have attracted intense
research interest as stable ligand supporting active catalysis.1
possesses higher catalytic performance and whether the
counterion of these ionic NHC complexes has influence on
Recently, many efforts have been dedicated to the design of
hybrid NHC ligands containing other donor function in order
the catalytic activities.
to add coordinative flexibility with metal center. In many
instances, these result in excellent catalytic outcomes.2,3 As part
RESULTS AND DISCUSSION
■
of our continual interest in hybrid NHC ligands,4 we herein
report a series of new benzothiazolyl-imidazolium salts and
Synthesis and Characterization of the NHC Precursors
and the Ag(I)NHC Complexes. Nucleophilic substitution of
their use as NHC precursor in the synthesis of Ag(I)-NHC
2-chlorobenzothiazole with substituted imidazoles under neat
complexes and cyclopentadienyl (Cp) molybdenum(II) NHC
conditions (solvent free) gives new functionalized imidazolium
complexes. We have recently demonstrated catalytic activities
salts 1−3 (1-(benzothiazol-2-yl)-3-methylimidazolium chloride,
of CpMo(II) complex with simple monodentate NHC ligand
1; 1-(benzothiazol-2-yl)-3-benzylimidazolium chloride, 2; 1-
toward cyclooctene epoxidation using tert-butyl hydroperoxide
(benzothiazol-2-yl)-3-allylimidazolium chloride, 3) (Scheme 1)
(TBHP) as oxidant at 55 °C and found that with 1 mol % of
in 60−73% yields. The 1H and 13C NMR spectra of 1, 2, and 3
in DMSO-d6 show downfield resonances of the NCHN protons
at δ 10.54, 10.84, and 10.48 ppm and of the NCHN carbon at δ
137.54, 137.12, and 137.12 ppm, respectively.
catalyst loading the ionic complexes [CpMo(CO)2(IMes)]+
(IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and
[CpMo(CO)2(IBz)]+ (IBz = 1,3-dibenzylimidazol-2-ylidene)
gave epoxide yield of ca. 85% after 4 h reaction time.5,6
Oxidation of these complexes leads to the high-valent dioxo-
Mo(VI)-NHC ionic complexes, which are mechanistically
related with the Mo(II) precursor in the epoxidation
Received: November 21, 2013
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of the Benzothiazolyl-Imidazolium Salts
1−3
The salts 1−3 were refluxed with Ag2O in 1,2-dichloroethane
giving Ag(I)-NHC complexes 4−6 in 67−75% yields. Their
molecular structures are revealed by single-crystal X-ray
diffraction analysis (see below). Complex 4 and 5 are dinuclear
with general formula of [Ag(L)(μ-Cl)]2, (L = L1 = 1-
(benzothiazolin-2-yl)-3-methylimidazol-2-ylidene, 4; L = L2 =
1-(benzothiazolin-2-yl)-3-benzylimidazol-2-ylidene, 5). Com-
plex 6 is a mononuclear complex as Ag(L)Cl, (L = L3 = 1-
(benzothiazolin-2-yl)-3-allylimidazol-2-ylidene). The signals at
δ 180.75 ppm (4), 180.84 ppm (5), and 180.67 ppm (6) in
their 13C NMR spectra (in DMSO-d6) are indicative of the Ag−
Ccarbene bond formation.
Figure 3. ORTEP diagram of 6 (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Ag(1)−C(1) 2.084(3); Ag(1)−Cl(1) 2.3526(8); C(1)−
Ag(1)−Cl(1) 176.50(8).
with different Ag(1)−Cl(1) (2.4089(7) Å in 4, 2.7849(7) Å in
5) and Ag(1)−Cl(1A) (2.7865(7) Å in 4, 2.4005(7) Å in 5)
bond distances. The Ag···Ag distances of 4 (3.789 Å) and 5
(3.650 Å) indicate the absence of interactions. Close proximity
between Ag and S atoms in 4 (3.133 Å) and 5 (2.982 Å) could
suggest weak secondary interactions.7 This is supported by the
inward orientation of the sulfur facing the metal. The Ag−
As shown in the molecular structures of 4−6 (Figures 1−3),
in all three complexes the hybrid NHCs L1−L3 act only as
C
carbene bond lengths (2.098(2) Å in 4 and 2.094(3) Å in 5) are
within the range expected for silver carbene complexes.8
Complex 6 is the mononuclear version of 4 and 5. The
Ccarbene−Ag−Cl is more linear (176.50(8)°) than that of the
Ag(I) benzoxazole-carbene complex (168.5(1)°).9 The Ag−
Ccarbene bond length of 2.084(3) Å in 6 is comparable to those
reported mononuclear Ag(I) NHC complexes.8 A secondary
interaction between Ag and S atoms is also observed in 6 with
Ag(1)···S(1) of 3.135 Å.
Synthesis and Characterization of Cp Mo(II) Carbonyl
NHC Complexes. Transmetalation of CpMo(CO)3Br with
silver complexes 4−6 in toluene under reflux gave [CpMo-
(CO)2(L)]2[Ag2Br4] (L = L1, 7a; L = L2, 8a; L = L3, 9a)
(Scheme 2) in 72−83% yields with the structures elucidated by
Figure 1. ORTEP diagram of 4 (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Ag(1)−C(1) 2.098(2); Ag(1)−Cl(1) 2.4089(7); Ag(1)−
Cl(1A) 2.7865(7); C(1)−Ag(1)−Cl(1) 156.41(7); C(1)−Ag(1)−
Cl(1A) 114.51(7); Cl(1)−Ag(1) −Cl(1A) 86.63(2).
Scheme 2
Figure 2. ORTEP diagram of 5 (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Ag(1)−C(1) 2.094(3); Ag(1)−Cl(1A) 2.4005(7); Ag(1)−
Cl(1) 2.7849(7); C(1)−Ag(1)−Cl(1A) 158.50(7); C(1)−Ag(1)−
Cl(1) 110.59(7); Cl(1A)−Ag(1)−Cl(1) 90.84(2).
single-crystal X-ray diffraction (see below). These complexes
were further treated with AgX (X = BF4, PF6 or OTf) in
acetonitrile at room temperature, affording [CpMo(CO)2(L)]-
[X] (L = L1, X = BF4, 7b; L = L2, X = BF4, 8b; X = PF6, 8c; X
= OTf, 8d; L = L3, X = BF4, 9b) in high yields (Scheme 2). All
the compounds have been characterized by ESI-MS, IR, NMR
spectroscopy (1H, 13C) and elemental analysis, with 7a, 7b, 8a,
monodentate ligand with the benzothiazolyl nitrogen and sulfur
atoms uncoordinated. In 4 and 5, the [Ag2Cl2] core is planar
with the chlorides asymmetrically bound to the silver center
B
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Table 1. CO Stretching Bands in IR Spectroscopy, Mo−Ccarbene Bond Lengths, and Turnover Frequencies (TOFs) for the
Cyclooctene Epoxidation Catalysis of Known Mo(II) NHC Complexes
a
b
entry
complex
[CpMo(CO)2(IMe)Br]
IR: v (CO) (cm−1
)
Mo−Ccarbene (Å)
TOF (h−1
)
ref
1
1955, 1832
1946, 1841
1952, 1874
1953, 1872
1959, 1858
1956, 1860
1953, 1870
1972, 1879
1930, 1858
1943, 1848
1940, 1844
1933, 1834
1935, 1832
1945, 1851
1941, 1860
1919, 1815
1906, 1811
1913, 1829
1950, 1866
−
2.224(3)
2.241(3)
−
1
5
2
[CpMo(CO)2(InPr)Br]
[CpMo(CO)2(IBz)Br]
[CpMo(CO)2(IBz)Cl]
[CpMo(CO)2(IMenPr)Br]
[CpMo(CO)2(IMes)Br]
2
5
3
1
5
4
2.221(3)
2.224(2)
2.244(3)
2.249(3)
2.228(2)
2.187(8)
2.221(4)
2.173(2)
2.207(3)
−
5
5
5
1
5
6
4
5
7
[CpMo(CO)2(IMes)(CH3CN)][BF4]
[CpMo(CO)2(IBz)(CH3CN)][BF4]
[CpMo(CO)2(IMes)H]
21
21
−
9.5
−
−
−
−
5
8
6
9
10
11
12
13
13
13
13
14
15
15
16
16
16
16
16
17
18
18
19
6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
[CpMo(CO)2(Triazolylidene)Cl]
[CpMo(CO)2(Tetrazolylidene)Cl]
[Mo(η5-C5Me4-CH2-CHPh-NHCMe)(CO)2I]
[Mo(η5-C5Me4-CH2-CMePh-NHCMe)(CO)2I]
[Mo(η5-C5H4-CMe2-CHPh-NHCMe)(CO)2I]
[Mo(η5-C5(CH2Ph)4-CHPh-CHPh-NHCMe)(CO)2I]
[Mo(η3-allyl)Cl(CO)2(bis-NHCBz)]
[Mo(η3-allyl)(η2-(NPh2)2CH)(CO)2(IMes)]
[Mo(η3-allyl)(η2-(NPh2)2CH)(CO)2(IiPr)]
[Mo(η3-C4H7)(bipy)(CO)2(IHMe)][OTf]
[Mo(η3-C4H7)(bipy)(CO)2(IHMes)][OTf]
[Mo(η3-C4H7)(bipy)(CO)2(IMeMes)][OTf]
[Mo(η3-C4H7)(bipy)(CO)2(IMeEt)][OTf]
[Mo(η3-C4H7)(bipy)(CO)2(IMeMes)][BAr4]
[Mo(η3-indenyl-NHCMe)(η3-C4H7)(CO)]
[(Cp)2Mo(IiPr)]
−
−
−
c
5.2
d
e
18 /20
2.285(9)
2.276(4)
−
−
−
−
−
−
−
−
−
−
−
−
−
21
2.240(3)
1946, 1865
1947, 1866
−
−
−
2.252(4)
2.189(3)
2.219(7)
2.212(6)
2.152(5), 2.157(5)
2.173(4)
−
1794, 1773
−
−
−
−
[(Cp)2Mo(IMe)]
[Mo(CO)2(IEt)2(OSO2CF3)2]
f
[CpMoO2(IBz)]2[Mo6O19]
f
[CpMoO2(IBz)][BF4]
−
6
a
IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IBz = 1,3-dibenzylimidazol-2-ylidene; IMe = 1,3-dimethylimidazol-2-ylidene; InPr = 1,3-
dipropylimidazol-2-ylidene; IMenPr = 1-methyl-3-propylimidazol-2-ylidene; bis-NHCBz = 1,1′-dibenzyl-3,3′-methylenediimidazoline-2,2′-diylidene;
IiPr = 1,3-diisopropylimidazol-2-ylidene; IEt = 1,3-diethylimidazol-2-ylidene; IHMe = 1-H-3-methylimidazol-2-ylidene; IHMes = 1-H-3-(2,4,6-
trimethylphenyl)imidazol-2-ylidene; IMeMes = 1-methyl-3-(2,4,6-trimethylphenyl)imidazol-2-ylidene; IMeEt = 1-methyl-3-ethylimidazol-2-ylidene.
b
TOFs are calculated on the basis of 4 h yield of cyclooctene oxide for all cases except entry 15. Catalytic reaction conditions: molar ratio of
catalyst:cis-cyclooctene:TBHP = 1:100:200; 55 °C. Catalytic reaction conditions: molar ratio of catalyst:cis-cyclooctene:TBHP = 1:100:300; 55 °C.
TOF is calculated on the basis of 5 h yield of cyclooctene oxide. Catalytic reaction conditions: molar ratio of catalyst:cis-cyclooctene:H2O2 =
1:100:300; 70 °C. Catalytic reaction conditions: molar ratio of catalyst:cis-cyclooctene:TBHP = 1:100:300; 70 °C. For the purpose of comparison,
CpMo(VI)-NHC complexes are also included.
c
d
e
f
8b, and 9b supplemented by single-crystal X-ray diffraction
analysis.
Molecular Structures of 7a, 7b, 8a, 8b, and 9b
Determined by Single-Crystal X-ray Diffraction. The
single crystals of 7a, 7b, 8a, 8b, and 9b were obtained from
slow diffusion method using the solvent pair of acetonitrile and
diethyl ether. X-ray diffraction structural analysis reveals a
common 4-legged piano stool structure of the [CpMo-
(CO)2NHC]+ cation in these compounds (Figures 4−8).
The hybrid ligand coordinates to the Mo(II) center in a
bidentate C,N chelating mode forming a five-member ring. The
N−Mo−Ccarbene chelate angle is between 72.0(3) and
72.66(9)°, whereas Mo−N (benthiazolyl) bond lengths range
between 2.195(5) and 2.217(2) Å. Complexes 7a and 8a
consist of two [CpMo(CO)2NHC]+ cations and one
[Ag2Br4]2− anion, whereas complexes 7b, 8b, and 9b contain
The 1H and 13C NMR spectra of all Mo(II) NHC complexes
were measured in DMSO-d6. The singlet signal of the Cp ring
in 1H NMR spectra appears at δ 5.85−5.98 ppm. In 13C NMR,
the Cp signals are shown at ca. δ 94.7 ppm, and the carbene
signals at δ 198.9−199.9 ppm. The two carbonyls resonate at
ca. δ 247.9−247.5/247.2−246.7 ppm in 13C NMR. The
characteristic 13C NMR signal of triflate anion (−OTf) in 8d
is found at δ 120.65 ppm (q, JC−F = 322 Hz). The
[CpMo(CO)2(L)]+ cation at m/z = 433.8 (for 7a and 7b),
509.8 (for 8a, 8b, 8c, and 8d) and 459.8 (for 9a and 9b) is
verified by ESI-MS spectral analysis (+ve mode). The IR
spectra of these complexes exhibit νsym(CO) between 1963 and
1988 cm−1, and the νasym(CO) between 1864 and 1897 cm−1.
Comparing to the CO stretching bands reported in other
CpMo(II) carbonyl NHC complexes (see Table 1, entries 1−
15),5,6,10−13 the higher carbonyl frequencies in 7−9 clearly
indicate a more electron-deficient Mo center in the [CpMo-
(CO)2(L)]+ cation.
−
only one [CpMo(CO)2NHC]+ cation and one BF4 anion.
Comparing with the Mo−Ccarbene bond lengths observed in
those reported Mo(II) NHC complexes (see Table 1), 7a, 7b,
8a, 8b, and 9b have much shorter Mo−Ccarbene bonds
(2.143(2)−2.166(3) Å) because of the chelation effect of the
hybrid NHC ligand. Complex 9b has the shortest Mo−Ccarbene
bond length (2.143(2) Å) among the crystallographically
C
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Figure 4. ORTEP diagram of one [CpMo(CO)2NHC]+ and
[Ag2Br4]2− of 7a (30% probability ellipsoids). Hydrogen atoms are
omitted. Selective bond lengths (Å) and angles (deg): Mo(1)−C(18)
1.95(1); Mo(1)−C(17) 1.98(1); Mo(1)−C(8) 2.161(9); Mo(1)−
N(1) 2.206(8); C(18)−Mo(1)−C(17) 75.0(5); C(8)−Mo(1)−N(1)
72.0(3).
Figure 7. ORTEP diagram of 8b (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Mo(1)−C(23) 1.988(4); Mo(1)−C(24) 1.944(3); Mo(1)−
C(8) 2.162(3); Mo(1)−N(1) 2.206(2); C(18)−Mo(1)−C(19)
75.2(2); C(8)−Mo(1)−N(1) 72.6(1).
Figure 5. ORTEP diagram of one [CpMo(CO)2NHC]+ and
[Ag2Br4]2− of 8a (30% probability ellipsoids). Hydrogen atoms are
omitted. Selective bond lengths (Å) and angles (deg): Mo(1)−C(24)
1.966(6); Mo(1)−C(23) 1.991(6); Mo(1)−C(8) 2.143(5); Mo(1)−
N(1) 2.195(5); C(24)−Mo(1)−C(23) 75.8(3); C(8)−Mo(1)−N(1)
72.3(2).
Figure 8. ORTEP diagram of 9b (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Mo(1)−C(20) 1.975(2); Mo(1)−C(19) 1.994(2); Mo(1)−
C(8) 2.143(2); Mo(1)−N(1) 2.196(1); C(20)−Mo(1)−C(19)
75.45(7); C(8)−Mo(1)−N(1) 72.58(6).
prototype for studying the effects of hybrid NHC ligand and
counterions on the catalytic activities of CpMo(II) carbonyl
NHC systems toward olefin epoxidation catalysis. In this
context, the catalytic activities of all Mo complexes have been
examined as catalyst for cyclooctene epoxidation with tert-butyl
hydroperoxide (TBHP) as oxidant at 55 °C in the absence of
any cosolvent (see Experimental Section). The time-dependent
epoxide yields catalyzed by 7a, 7b, 8a, 8b, 8c, 8d, 9a, and 9b are
given in Figure 9. No induction period has been observed in the
−
course of the catalysis. The complexes with BF4 as
counteranion, 7b, 8b, and 9b, are most active, giving epoxide
yield of ca. 90% after 4 h of reaction time (TOF of 22.5 h−1,
calculated at 4 h), are comparable to the most active Mo(II)/
(VI) NHC complexes under similar reaction conditions viz.
[CpMo(CO)2(IMes)(CH3CN)][BF4]5 and [CpMo-
(CO)2(IBz)(CH3CN)][BF4]6 (TOF of ca. 21 h−1, calculated
at 4 h; Table 1 entries 7−8) . Complex 8b could reach as high
as 90% yield of epoxide after 3 h. Complexes 7a, 8a, and 9a
with [Ag2Br4]2− anion are significantly inferior with epoxide
yield of 10% after 4 h. Although complexes 8b, 8c, and 8d share
the same cation [CpMo(CO)2(L2)]+, complexes 8c and 8d
Figure 6. ORTEP diagram of 7b (30% probability ellipsoids).
Hydrogen atoms are omitted. Selective bond lengths (Å) and angles
(deg): Mo(1)−C(6) 1.967(3); Mo(1)−C(7) 1.979(3); Mo(1)−C(8)
2.166(3); Mo(1)−N(1) 2.217(2); C(6)−Mo(1)−C(7) 76.7(1);
C(8)−Mo(1)−N(1) 72.66(9).
established Mo NHC complexes in the literature (See Table
1).5,6,10−19 Only [Mo(CO)2(IEt)2(OSO2CF3)2] (IEt = 1,3-
diethylimidazol-2-ylidene) (2.152(5) and 2.157(5) Å) (see
Table 1, entry 27)19 has comparable lengths.
Application of Mo(II) NHC Complexes in Epoxidation
Catalysis. The present ionic Mo complexes provide a
−
−
(with PF6 and OTf anions, respectively) are less active with
ca. 70% epoxide yield after 4 h (TOF of ca. 17.5 h−1). Reaction
D
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1
noted in the time dependent H NMR spectral study of the
oxidation of [CpMo(CO)2(IMes)(CH3CN)][BF4] and
[CpMo(CO)2(IBz)(CH3CN)][BF4] with TBHP to the
oxidation products [CpMoO2(NHC)][BF4] under similar
conditions, in which there are downfield shifts of Cp peaks
from δ 4.94 to 6.26 ppm and δ 5.59 to 6.50 ppm,
respectively.5,6 The emerged new peak at δ 6.58 ppm could
hence be assigned to the Cp signal of [CpMoO2(L2)]+. The
formation of Mo(VI)NHC species from the oxidation of 9b is
also supported by ESI-MS analysis (see Figure 11). The sets of
peaks at 480−490 m/z and 676−686 m/z in the positive mode
spectrum correspond to [CpMoO2 (L2)]+ and
([CpMoO3(L2)] + 2TBHP)+, respectively, in which the
Mo(VI) center coordinates to oxo and/or peroxo ligands.
The fragments related to the NHC ligand L2 are also observed
at 292 m/z and 336 m/z, which correspond to [L2H]+ and [L2
+ COOH]+, respectively. The [L2 + COOH]+ could be
attributed to the reaction between free carbene (L2) and
CO2.5,22 Additionally, the weak peaks observed in the 1H NMR
spectrum at δ 6.53−6.27 ppm and δ 9.45 ppm could be
assigned to the decomposed products of the Cp ligand and the
formation of imidazolium salt, thus revealing the partial
decomposition of 9b during the oxidation process. Although
the molecular structure of [CpMoO2(L2)]+ species is still
unclear, this spectroscopic study indicates the in situ generation
of Mo(VI) NHC species upon the treatment of TBHP during
epoxidation catalysis.
Figure 9. Time-dependent yields of cyclooctene epoxide using
compounds 7a, 7b, 8a, 8b, 8c, 8d, 9a, and 9b as catalysts and using
TBHP as oxidant at 55 °C (catalyst:substrate:oxidant =1:100:200).
temperature has significant influence on the catalytic perform-
ance. For 8b, only 37% (4 h) epoxide yields are obtained at
room temperature. The low catalytic activity at rt is also
observed in other Mo complexes/TBHP catalytic systems.20,21
[Mo(η3-allyl)Cl(CO)2(bis-NHCBz)] was reported to be as
active catalyst for the epoxidation of cis-cyclooctene with either
TBHP or H2O2 as oxidant (TOF of 18 h−1 with H2O2, TOF of
20 h−1 with TBHP, Table 1, entry 16)14 with molar ratio of
catalyst: cis-cyclooctene: TBHP or H2O2 = 1:100:300 at 70 °C.
However, H2O2 is not a suitable oxidant for the Mo(II) NHC
complexes studied in this work. This is illustrated by 9b giving
only 4% epoxide yield in 4 h when H2O2 was employed as
oxidant at 55 °C.
Reactivity of 9b under Oxidative Condition. Complex
9b was treated with 5-fold excess of TBHP (∼5.5 M in decane
over molecular sieves 4 Å) at rt in CD3CN under stirring. The
orange solution was changed to greenish yellow after 5 min
reaction. The time-dependent 1H NMR spectra (see Figure 10)
show that the Cp fingerprint peak of 9b at δ 5.68 ppm can still
be observed after 5 min reaction, as well as emergence of a new
peak at δ 6.58 ppm. After 15 min, the new peak remains while
the Cp peak of 9b disappears. Similar observation has been
CONCLUSION
■
We have demonstrated the transmetalation methodology of
cationic Mo(II) NHC carbene complexes by taking advantage
of the coordinative switch of hybrid carbene-thiazolyl C−N
ligands from Ag(I) to Mo(II). Concomitant generation of a
cationic coordination sphere with a stable chelate that comes
with a shorter Mo−Ccarbene bond has created a new model for
catalytic olefin epoxidation. It is encouraging to observe an
epoxide yield as high as ∼90% under facile conditions (3 h at
55 °C). The anions in these complexes also show significant
influences on catalytic activities in epoxidation. These findings
have prompted us to extend the study to other related stable
cationic carbene catalysts with different counterions, especially
additional chiral features on the hybrid ligand skeleton for
asymmetric epoxidation catalysis.
EXPERIMENTAL SECTION
■
All commercial chemicals were used as purchased. All preparations and
manipulations were performed using standard Schlenk techniques
under a nitrogen atmosphere. Solvents were dried by standard
procedures and distilled under nitrogen and used immediately. TBHP
(tert-butyl hydroperoxide, 5.0−6.0 M in decane), 1-methylimidazole
(99%), 2-chlorobenzothiazole (99%), 1-benzylimidazole (98%) and 1-
allylimidazole (99%) were purchased from commercial sources and
used as received. CpMo(CO)3Br was prepared on the basis of a
literature method.23 Elemental analyses for C, H, N, and S were
performed on a CHNS elemental analyzer and vario MICRO Cube.
1H and 13C NMR were measured at rt with 300 MHz and 500 MHz
FT NMR spectrometers. Electrospray ionization mass spectrometric
(ESI-MS) analysis was performed on a LCQ quadrapole ion trap mass
spectrometer and amaZon X ion trap mass spectrometer. Infrared
spectra were obtained on the FT-IR spectrometer using samples in
KBr disc. Catalytic reactions were monitored by GC methods on a GC
with a DB-5 column.
Synthesis of 1-(Benzothiazol-2-yl)-3-methylimidazolium
Chloride (1). 1-Methylimidazole (1.232 g, 15 mmol) was added to
2-chlorobenzothiazole (2.544 g, 15 mmol) in a 25 mL Schlenk flask,
1
Figure 10. Time-dependent H NMR spectra of the reaction mixture
of 9b and TBHP at rt in CD3CN.
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Figure 11. Positive mode ESI-MS spectrum of the reaction mixture of 9b and TBHP (1:5) after 10 min of reaction time.
materials. The resultant oily product was purified by column
chromatography on silica gel using dichloromethane and methanol
1
as eluents. Yield: 2.499 g, 60%. H NMR (500 MHz, DMSO-d6): δ
(ppm) = 10.48 (s, 1H, NCHN), 8.62 (s, 1H, CHN(benzothiazole)),
8.32 (d, J = 8 Hz, 1H, Hd), 8.12 (s, 1H, CHN(Allyl)), 8.09 (d, J =
8.0 Hz, Ha), 7.66 (dd, J = 8.0, 7.5 Hz, 1H, Hc), 7.60 (t, J = 7.5 Hz, 1H,
Hb), 6.18−6.10 (m, 1H, −CH2CHCH2), 5.47−5.42 (m, 2H, 
CHCH2), 5.04 (s, 2H, CH2CHCH2). 13C NMR (125.77 MHz,
DMSO-d6): δ (ppm) = 154.66 (C7), 148.94 (C5), 137.12 (NCHN),
133.34 (C6), 131.06 (CH2CHCH2), 127.63, 126.68, 123.86,
123.28, 122.94, 120.85 (CHCH2), 51.47 (CH2CHCH2).
Anal. Calcd for C13H12ClN3S: C, 56.21; H, 4.35; N, 15.13; S, 11.54;
Found: C, 56.11; H, 4.05; N, 15.11; S, 11.36. ESI-MS (in MeOH, m/z
(%)): [M − Cl]+ = 242.1 (100).
Synthesis of Silver Carbene Complexes 4, 5, and 6. Ag2O
(0.139 g, 0.6 mmol) was added to the respective imidazolium chloride
salts (1, 0.252 g, 1.0 mmol; 2, 0.328 g, 1.0 mmol; 3, 0.278 g, 1.0 mmol)
in 1,2-dichloroethane (30 mL). After refluxing for overnight with the
exclusion of light, the reaction mixture was filtered through Celite. The
filtrate was dried under a vacuum and washed with deionized water,
hexane, and Et2O. The characterization data for the silver-NHC
complexes 4, 5, and 6 are as follows.
and the mixture was stirred and heated to 100 °C under N2
atmosphere for 16 h. The resultant slurry was washed with CH3CN
(3 × 15 mL) followed by Et2O (20 mL). An off-white solid was
collected and dried in vacuo. Yield: 2.341 g, 62%. 1H NMR(500 MHz,
DMSO-d6): δ (ppm) = 10.54 (s, 1H, NCHN), 8.57 (s, 1H, 
CHN(benzothiazole)), 8.31 (d, J = 8.0 Hz, 1H, Hd), 8.14 (s, 1H, 
CHN(CH3)), 8.05 (d, J = 8.0 Hz, 1H, Ha), 7.64 (dd, J = 8.0, 7.0 Hz,
1H, Hc), 7.58 (dd, J = 8.0, 7.5 Hz, 1H, Hb), 4.04 (s, 3H, N(CH3)).
13C NMR (125.77 MHz, DMSO-d6): δ (ppm) = 154.65 (C7), 148.99
(C5), 137.54 (NCHN), 133.29 (C6), 127.66, 126.70, 125.20 (
CHN(benzothiazole)), 123.32, 122.95, 120.28 (CHN(CH3)), 36.49
(NCH3). Anal. Calcd for C11H10N3SCl: C, 52.48; H, 4.00; N, 16.69; S,
12.74; Found: C, 52.20; H, 3.68; N, 16.52; S, 12.84. ESI-MS (in
MeOH, m/z (%)): [M − Cl]+ = 216.1 (100).
Synthesis of 1-(Benzothiazol-2-yl)-3-benzylimidazolium
Chloride (2). Compound 2 was prepared and purified with a similar
method as described for compound 1. 1-Benzylimidazole (2.373 g, 15
mmol) and 2-chlorobenzothiazole (2.544 g, 15 mmol) were used as
Complex 4. Light brown solid (Yield: 0.267 g, 75%). 1H NMR (300
MHz, CDCl3): δ (ppm) = 8.16 (d, J = 1.8 Hz, 2H, 
CHN(benzothiazole)), 7.95 (dd, J = 7.8, 0.9 Hz, 2H, Hd), 7.88 (dd,
J = 7.8, 0.9 Hz, 2H, Ha), 7.54 (dt, J = 7.5, 1.2 Hz, 2H, Hc), 7.46 (dt, J
= 7.5, 1.2 Hz, 2H, Hb), 7.19 (d, J = 1.8 Hz, 2H, CHN(CH3)), 4.01
(s, 6H, N(CH3)). 13C NMR (125.77 MHz, DMSO-d6): δ (ppm) =
180.75 (NCN), 158.72, 149.20, 131.99, 127.26, 126.13, 125.09, 122.73,
122.43, 120.00, 39.26 (NCH3). ESI-MS (in CH3CN: m/z (%)): [M −
AgCl2]+ = [Ag(L1)2]+ = 539.0 (100), [L1 + H]+ = 216.1 (75). Anal.
Calcd for C22H18N6S2Ag2Cl2: C, 36.84; H, 2.53; N, 11.72; S, 8.94.
Found: C, 37.02; H, 2.84; N, 11.95; S, 8.69.
1
starting materials. Yield: 3.589 g, 73%. H NMR (500 MHz, DMSO-
d6): δ (ppm) = 10.84 (s, 1H, NCHN), 8.61 (s, 1H, CHN-
(benzothiazole)), 8.32 (d, J = 8.0 Hz, 1H, Hd), 8.23 (s, 1H, 
CHN(Bz)), 8.06 (d, J = 8 Hz, 1H, Ha), 7.66−7.57 (m, 4H), 7.46−7.39
(m, 3H), 5.66 (s, 2H, −CH2Ph). 13C NMR (125.77 MHz, DMSO-d6):
δ (ppm) = 154.76 (C7), 148.96 (C5), 137.12 (NCHN), 134.21, 133,37
(C6), 128.87, 128.85, 128.70, 127.64, 126.69, 123.77, 123.30 (
CHN(benzothiazole)), 122.95, 121.14 (CHN(Bz)), 52.44
(−CH2Ph). Anal. Calcd for C17H14ClN3S: C, 62.28; H, 4.30; N,
12.82; S, 9.78; Found: C, 62.47; H, 4.14; N, 12.90; S, 9.39. ESI-MS (in
MeOH, m/z (%)): [M − Cl]+ = 292.1 (100).
1
Complex 5. Brown solid (Yield: 0.282 g, 67%). H NMR (300
MHz, CDCl3): δ (ppm) = 8.16 (d, J = 2.1 Hz, 2H, 
CHN(benzothiazole)), 7.94 (dd, J = 7.8, 0.9 Hz, 2H, Hd), 7.89 (dd,
J = 7.8, 0.9 Hz, 2H, Ha), 7.56−7.32 (m, 14H), 7.13 (d, J = 2.1 Hz, 2H,
CHN(Bz)), 5.44 (s, 4H, −CH2Ph). 13C NMR (125.77 MHz,
DMSO-d6): δ (ppm) = 180.84 (NCN), 158.79, 149.21, 137.14, 136.19,
132.03, 128.91, 127.94, 127.54, 126.21, 124.23, 122.73, 122.49, 120.56,
Synthesis of 1-(Benzothiazol-2-yl)-3-allylimidazolium Chlor-
ide (3). Compound 3 was prepared with a similar method as described
for compound 1. 1-Allylimidazole (1.622 g, 15 mmol) and 2-
chlorobenzothiazole (2.544 g, 15 mmol) were used as starting
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54.28 (PhCH2N). ESI-MS (in CH3CN: m/z): [M − AgCl2]+
=
Synthesis of 7b, 8b, 8c, 8d, and 9b Complexes. AgBF4 (0.0389
g, 0.2 mmol), AgPF6 (0.0506 g, 0.2 mmol) or AgCF3SO3 (0.0514 g,
0.2 mmol) was added to solution of complex 7a (0.14 g, 0.1 mmol), 8a
(0.155 g, 0.1 mmol), or 9a (0.145 g, 0.1 mmol) in dry CH3CN (20
mL). After stirring overnight at rt, the mixture was filtered through
Celite, and the orange filtrate was vacuum dried. The resulting solid
was recrystallized from CH3CN and Et2O twice, yielding orange red
crystals. The characterizations for complexes are as follows.
[Ag(L2)2]+ = 691.0 (100), [L2 + H]+ = 292.1 (15). Anal. Calcd for
C34H26N6S2Ag2Cl2: C, 46.97; H, 3.01; N, 9.67; S, 7.38. Found: C,
46.95; H, 3.26; N, 9.56; S, 7.52.
1
Complex 6. Light brown solid (Yield: 0.269 g, 70.0%). H NMR
(300 MHz, CDCl3): δ (ppm) = 8.18 (d, J = 1.8 Hz, 1H, 
CHN(benzothiazole)), 7.95 (dd, J = 7.8, 0.9 Hz, 1H, Hd), 7.89 (dd, J
= 7.8, 0.9 Hz, 1H, Ha), 7.54 (dt, J = 7.8, 1.5 Hz, 1H, Hc), 7.46 (dt, J =
7.8, 1.5 Hz, 1H, Hb), 7.20 (d, J = 1.8 Hz, 1H, CHN(Allyl)), 6.08−
5.95 (m, 1H, −CH2CHCH2), 5.47−5.35 (m, 2H, −CHCH2),
4.89 (d, J = 6 Hz, 2H, CH2CHCH2). 13C NMR (125.77 MHz,
DMSO-d6): δ (ppm) = 180.67 (NCN), 158.78, 149.19, 133.42, 131.99,
127.28, 126.18, 124.22, 122.72, 122.46, 120.19, 119.24, 54.10 (
CH2CHCH2). ESI-MS (in CH3CN: m/z (%)): [M + L3 − Cl]+ =
[Ag(L3)2]+ = 591.0 (100), [L3 + H]+ = 242.1 (50). Anal. Calcd for
C13H11N3SAgCl: C, 40.59; H, 2.88; N, 10.92; S, 8.34. Found: C, 40.13;
H, 3.34; N, 10.73; S, 8.74.
Synthesis of [CpMo(CO)2(NHC)]2[Ag2Br4] Complexes 7a, 8a,
and 9a. The respective silver-NHC complex (4, 0.179 g, 0.25 mmol;
5, 0.217 g, 0.25 mmol; 6, 0.192 g, 0.5 mmol) and the CpMo(CO)3Br
precursor (0.357 g, 1.1 mmol) were added to dry toluene (30 mL).
The mixture was refluxed for 1 h with the exclusion of light under N2
protection. The precipitate was collected and was washed with toluene,
hexane, and diethyl ether. The characterization data for complexes 7a,
8a, and 9a are as follows.
Complex 7b. Orange red solid (Yield: 0.088 g, 85%). 1H NMR(500
MHz, DMSO-d6): δ (ppm) = 8.78 (d, J = 2.0 Hz, 1H, 
CHN(benzothiazole)), 8.36 (d, J = 8.0 Hz, 1H, Hd), 8.11 (d, J =
8.0 Hz, 1H, Ha), 7.97 (d, J = 2.5 Hz, 1H, CHN(CH3)), 7.75 (dd, J
= 8.5, 7.0 Hz, 1H, Hc), 7.65 (dd, J = 8.0, 7.5 Hz, 1H, Hb), 5.98 (s, 5H,
Cp), 4.05 (s, 3H, N(CH3)). 13C NMR (125.77 MHz, DMSO-d6): δ
(ppm) = 247.76 (Mo-CO), 247.05 (Mo-CO), 198.86 (NCN), 159.04,
148.75, 130.25, 128.55, 128.30, 126.57, 124.61, 121.06, 119.06, 94.63
(Cp), 37.85 (N(CH3)). IR (KBr)/ cm−1: vsym(CO) = 1988, vasym(CO)
= 1884. ESI-MS (in CH3CN: m/z (%)): [M − BF4]+
=
[CpMo(CO)2 (L1)]+
=
433.8 (100). Anal. Calcd for
MoC18H14N3SO2BF4: C, 41.64; H, 2.72; N, 8.09; S, 6.18. Found: C,
41.31; H, 2.70; N, 8.18; S, 6.24.
Complex 8b. Orange red solid (Yield: 0.096 g, 81%). H NMR
1
(500 MHz, DMSO-d6): δ (ppm) = 8.84 (d, J = 2.5 Hz, 1H, 
CHN(benzothiazole)), 8.37 (d, J = 8.5 Hz, 1H, Hd), 8.11 (d, J = 8.0
Hz, 1H, Ha), 7.79 (d, J = 2.5 Hz, 1H, CHN(Bz)), 7.76 (dd, J = 8.5,
7.0 Hz, 1H, Hc), 7.66 (dd, J = 8.0, 7.5 Hz, 1H, Hb), 7.47 (dd, J = 7.5,
7.0 Hz, 2H), 7.40 (dd, J = 7.5, 7.0 Hz, 1H), 7.34 (d, J = 7.0 Hz, 2H),
5.85 (s, 5H, Cp), 5.76−5.56 (m, 2H, −CH2Ph). 13C NMR (125.77
MHz, DMSO): δ (ppm) = 247.47 (Mo-CO), 246.74 (Mo-CO),
199.71 (NCN), 159.25, 148.75, 135.71, 130.28, 128.90, 128.36, 128.22,
127.40, 127.40 (overlap), 126.66, 124.63, 121.04, 119.97, 94.76 (Cp),
53.83 (PhCH2N). IR (KBr)/ cm−1: vsym(CO) = 1984, vasym(CO) =
1891. ESI-MS (in CH3CN: m/z (%)): [M − BF4]+ = [CpMo-
(CO)2(L2)]+ = 509.8 (100). Anal. Calcd for MoC24H18N3SO2BF4: C,
48.43 ; H, 3.05; N, 7.06 ; S, 5.39. Found: C, 48.01 ; H, 3.17 ; N, 7.07;
S, 5.44.
Complex 7a. Yellowish brown solid (Yield: 0.252 g, 72%). 1H
NMR(500 MHz, DMSO-d6): δ (ppm) = 8.78 (d, J = 2.0 Hz, 2H, 
CHN(benzothiazole)), 8.36 (d, J = 8.0 Hz, 2H, Hd), 8.11 (d, J = 8.5
Hz, 2H, Ha), 7.97 (d, J = 2.5 Hz, 2H, CHN(CH3)), 7.75 (dd, J =
8.0, 7.5 Hz, 2H, Hc), 7.65 (dd, J = 8.0, 7.0 Hz, 2H, Hb), 5.98 (s, 10H,
Cp), 4.05 (s, 6H, N(CH3)). 13C NMR (125.77 MHz, DMSO): δ
(ppm) = 247.87 (Mo-CO), 247.16 (Mo-CO), 198.85 (NCN), 159.07,
148.76, 130.28, 128.58, 128.31, 126.57, 124.66, 121.07, 119.10, 94.65
(Cp), 37.88 (N(CH3)). IR (KBr)/ cm−1: vsym(CO) = 1963, vasym(CO)
= 1889. ESI-MS (in CH3CN: m/z (%)): [M − CpMo(CO)2(L1) −
Ag2Br4]+ = [CpMo(CO)2(L1)]+ = 433.8 (100), [L1 + H]+ = 216.2
(10). Anal. Calcd for Mo2C36H28N6S2O4Ag2Br4: C, 30.88; H, 2.02;
N,6.00; S, 4.58. Found: C, 30.66; H, 2.11; N, 6.03; S, 4.62.
Complex 8c. Orange red solid (Yield: 0.103 g, 79%). 1H NMR (500
MHz, DMSO-d6): δ (ppm) = 8.85 (d, J = 2.0 Hz, 1H, 
CHN(benzothiazole)), 8.37 (d, J = 7.5 Hz, 1H, Hd), 8.11 (d, J =
8.0 Hz, 1H, Ha), 7.79 (d, J = 2.5 Hz, 1H, CHN(Bz)), 7.76 (dd, J =
8.5, 7.0 Hz, 1H, Hc), 7.66 (dd, J = 8.0, 7.5 Hz, 1H, Hb), 7.47(dd, J =
7.5, 7.0 Hz, 2H), 7.41 (dd, J = 7.5, 7.0 Hz, 1H), 7.34 (d, J = 7.5 Hz,
2H), 5.86 (s, 5H, Cp), 5.77−5.56 (m, 2H, −CH2Ph). 13C NMR
(125.77 MHz, DMSO): δ (ppm) = 247.60 (Mo-CO), 246.84 (Mo-
CO), 199.78 (NCN), 159.21, 148.74, 135.70, 130.26, 128.87, 128.33,
128.19, 127.39, 127.38, 126.63, 124.62, 121.03, 119.95, 94.69 (Cp),
53.77 (PhCH2N). (KBr)/ cm−1: vsym(CO) = 1987, vasym(CO) = 1881.
ESI-MS (in CH3CN: m/z (%)): [M − PF6]+ = [CpMo(CO)2(L2)]+ =
509.8 (100). Anal. Calcd for MoC24H18N3SO2PF6: C, 44.12; H, 2.78;
N, 6.43 ; S, 4.91. Found: C, 44.02; H, 2.77 ; N, 6.56; S, 5.05.
1
Complex 8a. Orange brown solid (Yield: 0.322 g, 83%). H NMR
(500 MHz, DMSO-d6): δ (ppm) = 8.87 (d, J = 2.0 Hz, 2H, 
CHN(benzothiazole)), 8.38 (d, J = 8.0 Hz, 2H, Hd), 8.11 (d, J = 8.0
Hz, 2H, Ha), 7.80 (d, J = 2.5 Hz, 2H, CHN(Bz)), 7.76 (dd, J = 8.5,
7.0 Hz, 2H, Hc), 7.66 (dd, J = 8.5, 7.0 Hz, 2H, Hb), 7.47 (dd, J = 8.0,
7.0 Hz, 4H), 7.41 (t, J = 7.5 Hz, 2H), 7.34 (d, J = 7.0 Hz, 4H), 5.85 (s,
10H, Cp), 5.76−5.56 (m, 4H, −CH2Ph). 13C NMR (125.77 MHz,
DMSO): δ (ppm) = 247.80 (Mo-CO), 247.03 (Mo-CO), 199.83
(NCN), 159.18, 148.73, 135.71, 130.26, 128.86, 128.32, 128.18,
127.39, 127.35, 126.61, 124.64, 121.03, 119.97, 94.69 (Cp), 53.75
(PhCH2N). IR (KBr)/ cm−1: vsym(CO) = 1973, vasym(CO) = 1897.
ESI-MS (in CH3CN: m/z (%)):[M − CpMo(CO)2(L2) − Ag2Br4]+=
[CpMo(CO)2(L2)]+ = 509.8 (100), [M −CpMo(CO)2(L2) − Ag2Br4
− 2(CO)]+= [CpMo(L)]+ = 454.1 (90), [M − CpMo(CO)2(L2)
−Ag2Br4 − CO]+= [CpMo(CO)(L2)]+ = 481.9 (60). Anal. Calcd for
Mo2C48H36N6S2O4Ag2Br4: C, 37.14; H, 2.34; N, 5.41; S, 4.13. Found:
C, 37.66; H, 2.39; N, 5.56; S, 4.18.
1
Complex 8d. Orange red solid (Yield: 0.108 g, 82%). H NMR
(500 MHz, DMSO-d6): δ (ppm) = 8.87 (d, J = 2.5 Hz, 1H, 
CHN(benzothiazole)), 8.38 (d, J = 8.0 Hz, 1H, Hd), 8.12 (d, J = 8.5
Hz, 1H, Ha), 7.80 (d, J = 2.0 Hz, 1H, CHN(Bz)), 7.78 (dd, J = 8.5,
7.0 Hz, 1H, Hc), 7.66 (dd, J = 8.0, 7.5 Hz, 1H, Hb), 7.47 (dd, J = 8.0,
7.0 Hz, 2H), 7.41 (dd, J = 7.5, 7.0 Hz, 1H), 7.35 (d, J = 7.5 Hz, 2H),
5.87 (s, 5H, Cp), 5.77−5.56 (m, 2H, −CH2Ph). 13C NMR (125.77
MHz, DMSO): δ (ppm) = 247.77 (Mo-CO), 246.99 (Mo-CO),
199.85 (NCN), 159.19, 148.74, 135.72, 130.27, 128.86, 128.32, 128.18,
127.39, 127.36, 126.61, 124.63, 121.04, 120.65 (q, JC−F = 322 Hz,
CF3SO3), 119.96, 94.69 (Cp), 53.75 (PhCH2N). (KBr)/ cm−1:
vsym(CO) = 1988, vasym(CO) = 1864. ESI-MS (in CH3CN: m/z
(%)): [M − CF3SO3]+ = [CpMo(CO)2(L2)]+ = 509.8 (100). Anal.
Calcd for MoC25H18N3S2O5F3: C, 45.67; H, 2.76; N, 6.39 ; S, 9.75.
Found: C, 45.62; H, 2.89; N, 6.49; S, 9.82.
Complex 9a. Reddish brown solid (Yield: 0.272 g, 75%). 1H NMR
(500 MHz, DMSO-d6): δ (ppm) = 8.86 (d, J = 2.0 Hz, 2H, 
CHN(benzothiazole)), 8.37 (d, J = 8.0 Hz, 2H, Hd), 8.11 (d, J = 8.0
Hz, 2H, Ha), 7.94 (d, J = 2.0 Hz, 2H, CHN(Allyl)), 7.75 (dd, J =
8.5, 7.5 Hz, 2H, Hc), 7.65 (dd, J = 8.0, 7.5 Hz, 2H, Hb), 6.23−6.15
(m, 2H), 5.94 (s, 10H, Cp), 5.43−5.31 (m, 4H), 5.08−4.98 (m, 4H).
13C NMR (125.77 MHz, DMSO-d6): δ (ppm) = 247.82 (Mo-CO),
247.09 (Mo-CO), 199.20 (NCN), 159.07, 148.71, 132.89, 130.24,
128.30, 127.04, 126.58, 124.62, 121.02, 119.80, 119.05, 94.68 (Cp),
52.65 (CH2CHCH2). IR (KBr)/ cm−1: vsym(CO) = 1972,
vasym(CO) = 1897. ESI-MS (in CH3CN: m/z (%)):[M − CpMo-
(CO)2(L3) − Ag2Br4]+= [CpMo(CO)2(L3)]+ = 459.8 (100), [L3 +
H]+ = 242.2 (55). Anal. Calcd for Mo2C40H32N6S2O4Ag2Br4: C, 33.08;
H, 2.22; N, 5.79; S, 4.42. Found: C, 33.29; H, 2.26; N, 5.97; S, 4.42.
1
Complex 9b. Orange red solid (Yield: 0.085 g, 78%). H NMR
(500 MHz, DMSO-d6): δ (ppm) = 8.85 (d, J = 2.0 Hz, 1H, 
CHN(benzothiazole)), 8.36 (d, J = 8.0 Hz, 1H), 8.11 (d, J = 8.0 Hz,
1H), 7.93 (d, J = 2.5 Hz, 1H, CHN(Allyl)), 7.77−7.73 (m, 1H),
7.67−7.63 (m, 1H), 6.23−6.15 (m, 1H), 5.94 (s, 5H, Cp), 5.43−5.31
G
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(m, 2H), 5.08−4.98 (m, 2H). 13C NMR (125.77 MHz, DMSO-d6): δ
(ppm) = 247.76 (Mo-CO), 247.05 (Mo-CO), 199.19 (NCN), 159.11,
148.73, 132.90, 130.26, 128.31, 127.05, 126.60, 124.62, 121.04, 119.80,
119.04, 94.70 (Cp), 52.65 (CH2CHCH2). IR (KBr)/ cm−1:
vsym(CO) = 1987, vasym(CO) = 1884. ESI-MS (in CH3CN: m/z (%)):
[M − BF4]+ = [CpMo(CO)2(L3)]+ = 459.8 (100). Anal. Calcd for
MoC20H16N3SO2BF4: C, 44.06; H, 2.96; N, 7.71; S, 5.88. Found: C,
44.04; H, 2.93; N, 7.78; S, 5.87.
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Catalytic Reactions. Cyclooctene (0.4 g, 3.6 mmol), mesitylene
(1 g, internal standard) and catalysts (1 mol %, molybdenum based)
were added to the reaction vessel in air at 55 °C or rt. The reaction
was initiated by the addition of TBHP (5.0−6.0 M in decane) (∼7.2
mmol, 1.36 mL). The course of the reaction was monitored by
quantitative GC analysis. The samples were taken in regular time
intervals, diluted with CH2Cl2, and treated with a small amount of
MgSO4 and MnO2 to remove water and to destroy the excess of
TBHP. The resulting slurry was filtered, and the filtrate was injected
into the GC column. The conversion of cyclooctene and formation of
cyclooctene oxide were calculated from calibration curves (r2 = 0.999).
X-ray Crystallography. Diffraction measurements were con-
ducted at 100(2)−293(2) K on a CCD diffractometer by using Mo
Kα radiation (λ = 0.71073 Å). The data were corrected for Lorentz
and polarization effects with the SMART suite of programs and for
absorption effects with SADABS.24 Structure solutions and refine-
ments were performed by using the programs SHELXS-9725a and
SHELXL-97.25b The structures were solved by direct methods to
locate the heavy atoms, followed by difference maps for the light non-
hydrogen atoms. Anisotropic thermal parameters were refined for the
rest of the non-hydrogen atoms. Hydrogen atoms were placed
geometrically and refined isotropically. Crystal data and experimental
details for the crystals of 4−6, 7a, 7b, 8a, 8b, and 9b are shown in
Table 2.
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ASSOCIATED CONTENT
̈
(11) Schaper, L.-A.; Graser, L.; Wei, X.; Zhong, R.; Ofele, K.; Pothig,
̈
■
A.; Cokoja, M.; Bechlars, B.; Herrmann, W. A.; Kuhn, F. E. Inorg.
̈
S
* Supporting Information
Chem. 2013, 52, 6142−6152.
Crystal data (CIF). CCDC reference numbers: 955019 (4),
955020 (5), 955021 (6), 900510 (7a), 900511 (7b), 955022
(8a), 987063 (8b) and 955024 (9b). This material is available
free of charge via the Internet at http://pubs.acs.org.
̈
(12) Schaper, L.-A.; Wei, X.; Altmann, P. J.; Ofele, K.; Pothig, A.;
Drees, M.; Mink, J.; Herdtweck, E.; Bechlars, B.; Herrmann, W. A.;
̈
Kuhn, F. E. Inorg. Chem. 2013, 52, 7031−7044.
̈
(13) Kandepi, V. V. K. M.; Pontes da Costa, A.; Peris, E.; Royo, B.
Organometallics 2009, 28, 4544−4549.
AUTHOR INFORMATION
(14) Kandepi, V. V. K. M.; Cardoso, J. M. S.; Royo, B. Catal. Lett.
2010, 136, 222−227.
■
Corresponding Authors
(15) Ogata, K.; Yamaguchi, Y.; Kashiwabara, T.; Ito, T. J. Organomet.
Chem. 2005, 690, 5701−5709.
*E-mail: chmzhaoj@nus.edu.sg.
*E-mail: andyhor@nus.edu.sg.
́ ́
(16) Brill, M.; Díaz, J.; Huertos, M. A.; Lopez, R.; Perez, J.; Riera, L.
Chem.Eur. J. 2011, 17, 8584−8595.
Notes
(17) Takaki, D.; Okayama, T.; Shuto, H.; Matsumoto, S.; Yamaguchi,
Y.; Matsumoto, S. Dalton Trans. 2011, 40, 1445−1447.
(18) Yamaguchi, Y.; Oda, R.; Sado, K.; Kobayashi, K.; Minato, M.;
Ito, T. Bull. Chem. Soc. Jpn. 2003, 76, 991−997.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(19) Anderson, D. M.; Bristow, G. S.; Hitchcock, P. B.; Jasim, H. A.;
Lappert, M. F.; Skelton, B. W. J. Chem. Soc., Dalton Trans. 1987,
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We are grateful to the Ministry of Education (R-143-000-361-
112) and A* Star (R143-000-426-305) for funding support. Z.
Wang and L. Jiang acknowledged MOE for graduate scholar-
ship. We thank Dr. L. L. Koh, G. K. Tan and Y. M. Hong for X-
ray diffractometry assistance.
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NOTE ADDED AFTER ASAP PUBLICATION
■
This paper was published on the Web on May 9, 2014, with an
incorrect chemical notation in Table 1, entry 28. The corrected
version was reposted on May 13, 2014.
J
dx.doi.org/10.1021/om401128z | Organometallics XXXX, XXX, XXX−XXX