Catalytic and asymmetric cyclopropanation of alkenes catalysed by rhenium(I) bipyridine and terpyridine tricarbonyl complexes

Article abstract of DOI:10.1039/b712995e

Re(i) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)₃(MeCN)]OTf complex (L = chiral C₂-symmetric terpyridine ligand). The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b712995e

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Catalytic and asymmetric cyclopropanation of alkenes catalysed by
rhenium(I) bipyridine and terpyridine tricarbonyl complexes†
Chi-Tung Yeung,a Pang-Fei Teng,a Ho-Lun Yeung,a Wing-Tak Wongb and Hoi-Lun Kwong*a
Received 23rd August 2007, Accepted 4th October 2007
First published as an Advance Article on the web 19th October 2007
DOI: 10.1039/b712995e
Re(I) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of
alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and
trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)3(MeCN)]OTf complex
(L = chiral C2-symmetric terpyridine ligand).
Introduction
Since the first isolation of a rhenium carbene complex in 1968,1
their chemistry has been of great interest. Numerous examples,
largely based on cyclopentadienyl (Cp),2–5 imido,6 phosphine,7 and
oxo8 ligands, have been synthesised. A heterocyclic carbene com-
plex with a bipyridine (bpy) ligand was also developed.9 Although
metal–carbenes are generally believed to be an active intermediate
in catalytic cyclopropanation,10 the study of rhenium carbene
transfer has mainly focused on olefin metathesis11 and aldehyde
olefination,12 and only rarely on olefin cyclopropanation.13 One
catalytic study with methyltrioxorhenium was reported but the
active intermediate was not proposed to be a carbene.14 We and
others are interested in the development of metal–pyridyl catalysts
for cyclopropanation.15 Herein we report the use of rhenium(I)
bpy, phenanthroline (phen) and terpyridine (tpy) complexes as
Scheme 1
catalysts for cyclopropanation. With chiral bpy and tpy, we have
achieved asymmetric cyclopropanation with rhenium, previously
unreported.
for [Re(4a)(CO)3Br] and [Re(5b)(CO)3Br], revealing them to be
the first chiral rhenium bipyridine and terpyridine structures. As
shown in Fig. 1 and 2, both show a distorted octahedral geometry
around the central Re atom, with three facial carbonyl ligands
and a bromide. Completing the sphere, the Re is coordinated
to two nitrogen atoms of the chelating ligand to form a five-
membered ring with small bite angles (75.16(37)◦ and 75.42(16)◦,
respectively). In [Re(5b)(CO)3Br], the –Re(1)–N(1)–C(12)–C(13)–
N(2)– ring is not flat, being tilted from the plane by about 20◦.
Also, the trans angles at the site of Re(1) are within the range
Results and discussion
The [Re(L)(CO)3Br] and [Re(L)(MeCN)(CO)3]OTf complexes
used in this work were prepared by modified standard
procedures.16,17 Refluxing an equivalent amount of pyridyl ligand
and [BrRe(CO)5] in degassed heptane for 3 h gave [Re(L)(CO)3Br]
in high yield (Scheme 1). Reaction with AgOTf in acetonitrile gave
[Re(L)(MeCN)(CO)3]OTf which should have a more labile coordi-
nation site. Both bromide and triflate complexes are air stable and
were characterised by conventional spectroscopic methods. In the
1H NMR spectrum, [Re(5a)(CO)3Br], [Re(5a)(MeCN)(CO)3]OTf
and [Re(5b)(MeCN)(CO)3]OTf each appeared as two species in a
1 : 1 ratio. The pair of complexes were assigned to be stereoisomers
coming from the 1,4-metallotropic shifts of the r2-terpyridine
ligands.18 For the structural characterisation, recrystallisation
from CH2Cl2 gave crystals suitable for X-ray crystal analysis
aDepartment of Biology and Chemistry, City University of Hong Kong,
Tat Chee Avenue, Kowloon, Hong Kong SAR, China. E-mail: bhhoik@
cityu.edu.hk; Fax: +852 2788 4706; Tel: +852 2788 7304
Fig. 1 An ORTEP drawing of [Re(4a)(CO)3Br]. Selected bond lengths
(A) and angles ( ): Re(1)–N(1) 2.264(1), Re(1)–N(2) 2.228(1), Re(1)–Br(1)
◦
˚
bDepartment of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong SAR, China
˚
2.626(3), Re(1)–C(1) 1.869(1), Re(1)–C(2) 1.917(8), Re(1)–C(3) 1.940(8) A,
N(2)–Re(1)–C(1) 175.4(5), N(1)–Re(1)–C(3) 170.5(4), Br(1)–Re(1)–C(2)
178.0(3), N(1)–C(15)–C(16)–N(2) 6.8(2)◦.
† CCDC reference numbers 651262 and 651263. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b712995e
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all these can be attributed to the different electronic effect of the
ligands.
Both rhenium bromide and triflate complexes used in this
study are catalysts for cyclopropanation of alkenes with ethyl
diazoacetate (EDA). By using [Re(1a)(CO)3Br] as catalyst in
CH2Cl2 (50 ◦C) and at a catalyst : EDA : styrene ratio of 1 :
50 : 250, the yield of cyclopropanes was low (28%). Yield was
greatly improved (81%) when [Re(1a)(MeCN)(CO)3]OTf was used
as catalyst and benzene (50 ◦C) as solvent (Scheme 2). As they
are generally more reactive, only the results of triflate complexes
are discussed further. The catalytic activities of complexes with
different pyridyl ligands are compared, as shown in Table 1.
Overall, yields of cyclopropanes and coupling products were good.
The chemoselectivities (cyclopropanes : coupling products) of
the bidentate ligands 1a and 2a (entries 1 and 6) were better
than the more bulky 3 (entry 8). The electronic effect of the
substituent seems to be a very important factor; as can be observed
with both bpy (entries 1–5) and phen (entries 6–7) ligands, the
Fig.
2
An ORTEP drawing of [Re(5b)(CO)3Br]. Selected bond
lengths (A) and angles (◦): Re(1)–N(1) 2.234(4), Re(1)–N(2)
2.216(4), Re(1)–Br(1) 2.622(1), Re(1)–C(1) 1.893(6), Re(1)–C(2) 1.872(6),
˚
˚
Re(1)–C(3) 1.920(6) A, N(1)–Re(1)–C(3) 171.1(2), N(2)–Re(1)–C(1)
173.3(2), Br(1)–Re(1)–C(2) 176.5(2), N(1)–C(12)–C(13)–N(2) 7.56(8),
N(2)–C(17)–C(18)–N(3) 137.96(6)◦.
of 171.1–176.5◦. Similar deviations from an ideal octahedral ar-
rangement were also observed in [Re(4a)(CO)3Br] (170.5–178.0◦);
Scheme 2
Table 1 Catalytic cyclopropanation of different alkenes with EDA using rhenium complexes as catalysta
Entry
1
L
Alkene
Yield (%)b
89
Chemoselectivityc
9.6
cis : transd
1a
33 : 67
2
3
4
5
6
7
8
9
1b
1c
1d
1e
2a
2b
3
85
84
83
81
76
82
78
91
5.0
4.9
5.1
3.1
7.9
3.9
4.1
9.6
33 : 67
36 : 64
35 : 65
33 : 67
34 : 66
33 : 67
34 : 66
47 : 53
1b
10
11
12
81
75
97
3.6
2.4
34
24 : 76
28 : 72
—
13
14
68
81
4.6
3.7
30 : 70
—
a Reaction conditions: catalyst : EDA : styrene = 1 : 50 : 250, benzene, 50 ◦C, 4 h addition of EDA and then stirring for additional 16 h (entries 1–8).
Catalyst : EDA : alkene = 1 : 17 : 170, benzene, 70 ◦C, 10 h addition of EDA and then stirring for additional 14 h (entries 9–14). b Isolated yield of
cyclopropanes and coupling products. c Cyclopropanes : coupling products. d Determined by GC-FID.
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chemoselectivities decreased with both electron-donating and -
withdrawing substituents. In all cases, the cis : trans ratios were
not dependent on the chelating effect or electronic properties of
the ligands in the Re catalysts.
(CO)3]OTf. The reaction rate was enhanced by electron-donating
substituents (4-CH3O and 4-CH3) but retarded with electron-
withdrawing groups (4-Cl and 3-NO2) and this indicated that
the intermediate is electrophilic in nature (q+ = −0.57 corre-
lated to r+). When monitored with 1H NMR, the reactions
of EDA with Re complexes of 1c or 5b gave new singlets at
11.68 and 12.03 ppm respectively. These intermediates can be
tentatively assigned to carbene complexes.20 Further evidence
In order to optimise the yield of cyclopropanes, the reaction
between cyclohexene, the poorest substrate, and EDA with the cat-
alyst [Re(1a)(MeCN)(CO)3]OTf was investigated. After increasing
the temperature to 70 ◦C and adding the EDA over a longer time (6
h), no EDA remained and the chemoselectivity was improved (0.8).
The cyclopropane : coupling ratio was further improved to 3.7
when a catalyst : EDA : alkene ratio of 1 : 17 : 170 was used and 10 h
addition of EDA was employed. With this method, the catalytic
results for other alkenes were obtained (entries 9–13). Complex
[Re(1a)(MeCN)(CO)3]OTf catalysed the cyclopropanation of a-
substituted styrenes very efficiently. Very high cyclopropane selec-
tivity was found for 1,1-diphenylethylene. b-Substituted styrenes
and aliphatic alkenes were poorer substrates. For the straight chain
alkenes (1-octene and trans-5-decene), no cyclopropane could be
detected.
from ESI-MS analyses of the mixtures showed new species
+
=
corresponding to [(Re CHCOOEt)(1c)(CO)3] (m/z = 625.2) and
+
=
[(Re CHCOOEt)(5b)(CO)3] (m/z = 806.8), respectively.
Conclusion
In summary, the present works show that chiral or achiral Re(I)
carbene complexes can be generated and serve as good catalysts for
asymmetric cyclopropanation. Further experiments are underway
to characterise the intermediates and to develop more efficient and
selective catalysts for asymmetric cyclopropanation.
The catalytic asymmetric cyclopropanations catalysed by chiral
Re catalysts were investigated in CH2Cl2, as higher enantioselec-
tivities than benzene were usually obtained by this solvent. At
a catalyst : EDA : styrene ratio of 1 : 50 : 250, different chiral
catalysts and diazoacetate were screened and the results are shown
in Table 2. The absolute configuration of the products from the
reaction between styrene and EDA was determined by comparison
with known compounds.19
With [Re(5b)(MeCN)(CO)3]OTf as catalyst, the highest enan-
tioselectivities of the cis- and trans-products, ee = 73 and 62%,
respectively, were obtained; high chemoselectivities were also
observed. When compared with 4b (entry 1), the uncoordinated
pyridine ring in tpy was found to be crucial in obtaining
higher enantioselectivies and better cyclopropane selectivity. As
in the case of 1a and 3, both the cis : trans ratios were
found to be independent of the ligand used. For the sterically
bulkier diazoacetates, no coupling product was observed and the
yield of the cyclopropanes from t-butyl diazoacetate was very
high.
Experimental
General experimental
Unless otherwise stated, all manipulations were carried out under
nitrogen using standard Schlenk line technique. Benzene was
distilled from sodium. Dichloromethane and MeCN were dried
over CaH2 and distilled prior to use. tert-Butyl diazoacetate
(TDA), EDA, alkenes, [Re(CO)5Br], AgOTf and all achiral
ligands are commercially available and were used as received.
(+)- and (−)-menthyl diazoacetate,21a 4a,21b 4b,21b 5a21c and 5b15a
were prepared according to literature procedures. Complexes
[Re(L)(CO)3Br] (L = 1a,16a 1b,16b 1c,16c 1d,16d 1e,16e 2a,16f 2b,16g
3
16h) and [Re(L)(MeCN)(CO)3]OTf (L = 1a,17a 1b,17b 1c,17c 1d,17d
2a,17e 2b,17f ) were synthesised using literature procedures. The
cyclopropanation and competition reactions were monitored by
gas chromatography using a 5% PH ME siloxane column. 1H and
13C NMR spectra were recorded on a Varian 300 MHz Mercury
NMR spectrometer. Positive ion mass spectra were taken on a
PE SCIEX API 365 electrospray mass spectrometer. Elemental
analyses were performed on a Vario EL III elemental analyser.
The reactive intermediate of the cyclopropanation has also been
studied. A linear relationship is observed in competition exper-
iments of substituted styrenes vs styrene with [Re(5b)(MeCN)-
Table 2 Rhenium catalysed cyclopropanation of styrene and diazoacetate with different chiral ligandsa
Ee (%)e
Entry
L
R
Yield (%)b
Chemoselectivityc
cis : transd
cis (1R,2S)
trans (1R,2R)
1
2
3
4
5
6
4b
5a
5b
5b
5b
5b
Ethyl
Ethyl
Ethyl
t-Butyl
(+)-Menthyl
(−)-Menthyl
97
96
91
99
73
89
6.9
7.8
10.8
—
—
—
32 : 68
22 : 78
32 : 68
32 : 68
24 : 76
17 : 83
13
29
73
50
1
24
38
62
57
45
48
54
a Reaction conditions: catalyst : EDA : styrene = 1 : 50 : 250, CH2Cl2, 50 ◦C, 4 h addition of EDA and then stirring for 16 h. b Isolated yield of
cyclopropanes based on expected product. c Cyclopropanes : coupling products. For entries 4–6, no coupling products were observed. d Determined by
GC-FID. e Determined by chiral HPLC or chiral GC.
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Procedure for preparation of [Re(L)(CO)3Br]
Procedure for preparation of [Re(L)(MeCN)(CO)3]OTf
Degassed heptane (3 mL) was added to a 25 mL pear-shaped
flask containing [BrRe(CO)5] (1 mmol) and polypyridine ligand
(1 mmol) under nitrogen. The mixture was refluxed for 3 h, cooled
to room temperature, and concentrated under vacuum. Hexane
was then added and the solution was cooled in an ice bath.
Yellow solid was precipated and filtered. It was then recrystallised
in dichloromethane. The recrystallised solids were collected and
dried under vacuum. The complexes obtained were characterised
with 1H NMR, IR, elemental analyses and ESI-MS.
In a 25 mL pear-shaped flask charged with [Re(L)(CO)3Br]
(0.5 mmol) and MeCN (5 mL), AgOTf (0.6 mmol) was added
under nitrogen. The mixture was stirred in the dark for 3 h. It was
R
then filtered through Celiteꢀ and reduced to dryness. The crude
product, dissolved in minimal amount of MeCN, was agitated
gently and the dark solid formed was removed by filtration.
Hexane or Et2O was then added dropwise to the solution until
a precipite formed. The solid was then collected and dried under
1
vacuum. The complexes were characterised with H NMR, IR,
elemental analyses and ESI-MS.
1
[Re(1e)(MeCN)(CO)3]OTf. Yield: 0.35 g (91%). 1H NMR
(300 MHz, CDCl3): d 1.50 (t, J = 7.0 Hz, 6H), 2.28 (s, 3H),
4.56 (q, J = 7.0 Hz, 4H), 8.21 (dd, J = 5.6, 1.5 Hz, 2H), 9.02–9.20
(m, 2H), 9.12 (dd, J = 5.6, 0.6 Hz, 2H); m (KBr)/cm−1: 2309 w
(CN), 2041 s (CO), 1945 s (CO), 1938 s (CO), 1158 m (SO3), 1029
m (SO3); anal. calcd. for C22H19F3N3O10ReS·(Et2O)0.6: C, 36.41; H,
3.11; N, 5.22, found: C, 37.82; H, 3.09; N, 5.18%; ESI-MS: m/z =
612.2 [M − CF3SO3]+.
[Re(3)(MeCN)(CO)3]OTf. Yield: 0.30 g (86%). 1H NMR
(300 MHz, CD3CN): d 1.97 (s, 3H), 7.62 (t, J = 6.5 Hz, 1H), 7.72–
7.78 (m, 2H), 7.88 (d, J = 7.6 Hz, 1H), 8.04 (t, J = 7.6 Hz, 1H), 8.33
(t, J = 8.2 Hz, 1H), 8.40 (t, J = 7.9 Hz, 1H), 8.61 (t, J = 8.8 Hz, 2H),
8.79 (d, J = 4.4 Hz, 1H), 9.07 (d, J = 5.3 Hz, 1H); m (KBr)/cm−1:
2289 w (CN), 2035 s (CO), 1919 br (CO), 1166 m (SO3), 1032 m
(SO3); anal. calcd. for C21H14F3N4O6ReS·(CH2Cl2)1.25: C, 33.41; H,
2.06; N, 7.01, found: C, 33.24; H, 2.07; N, 6.95%; ESI-MS: m/z =
545.4 [M − CF3SO3]+.
[Re(4a)(MeCN)(CO)3]OTf. Yield: 0.36 g (89%). 1H NMR
(300 MHz, CDCl3): d 0.65 (s, 3H), 0.75 (s, 3H), 1.26 (d, J =
9.9 Hz, 1H), 1.46 (s, 3H), 1.48 (s, 3H), 1.49 (d, J = 3.8 Hz, 1H),
2.33 (s, 3H), 2.55–2.58 (m, 2H), 2.74–2.82 (m, 2H), 2.96–3.01 (m,
2H), 3.40 (dd, J = 17.6, 2.9 Hz, 2H), 3.60 (ddd, J = 17.6, 7.6,
2.9 Hz, 2H), 7.72 (d, J = 3.6 Hz, 1H), 7.75 (d, J = 3.2 Hz, 1H),
8.27 (d, J = 7.9 Hz, 1H), 8.32 (d, J = 7.9 Hz, 1H); m (KBr)/cm−1:
2294 w (CN), 2034 s (CO), 1919 br (CO), 1159 m (SO3), 1030
m (SO3); anal. calcd. for C30H31F3N3O6ReS·CH2Cl2: C, 41.84; H,
3.71; N, 4.72, found: C, 41.17; H, 3.64; N, 4.79%; ESI-MS: m/z =
656.6 [M − CF3SO3]+.
[Re(4b)(MeCN)(CO)3]OTf. Yield: 0.35 g (85%). 1H NMR
(300 MHz, CDCl3): d 0.77 (s, 3H), 0.78 (s, 3H), 1.40 (d, J =
10.3 Hz, 2H), 1.50 (d, J = 6.7 Hz, 3H), 1.51 (s, 6H), 1.56 (d,
J = 7.0 Hz, 3H), 2.25 (s, 3H), 2.32–2.37 (m, 2H), 2.58–2.67
(m, 2H), 2.96–3.04 (m, 2H), 3.83–3.90 (m, 2H), 7.68 (d, J =
7.9 Hz, 1H), 7.79 (d, J = 3.5 Hz, 1H), 7.81 (d, J = 3.5 Hz,
1H), 8.05 (d, J = 7.9 Hz, 1H); m (KBr)/cm−1: 2289 w (CN), 2035 s
(CO), 1922 s (CO), 1157 w (SO3), 1031 w (SO3); anal. calcd. for
C32H35F3N3O6ReS·(CH3CN)0.5·(CHCl3)0.8: C, 42.78; H, 3.93; N,
5.17, found: C, 43.68; H, 3.83; N, 5.06%; ESI-MS: m/z = 683.8
[M − CF3SO3]+.
[Re(4a)(CO)3Br]. Yield: 0.66 g (95%). H NMR (300 MHz,
CDCl3): d 0.72 (s, 3H), 0.75 (s, 3H), 1.32 (d, J = 9.4 Hz, 1H), 1.37
(d, J = 10.6 Hz, 1H), 1.44 (s, 3H), 1.45 (s, 3H), 2.50–2.60 (m, 2H),
2.69–2.77 (m, 2H), 2.90 (t, J = 5.9 Hz, 2H), 3.53 (dd, J = 17.0,
11.7 Hz, 2H), 3.79 (dd, J = 17.6, 5.9 Hz, 2H), 7.48 (d, J = 8.2 Hz,
2H), 7.83 (d, J = 8.2 Hz, 2H); m (KBr)/cm−1: 2018 s (CO), 1896
br (CO); anal. calcd. for C27H28BrN2O3Re: C, 46.69; H, 4.03; N,
4.03, found: C, 45.57; H, 3.93; N, 3.94%; ESI-MS: m/z 616 [M −
Br]+.
1
[Re(4b)(CO)3Br]. Yield: 0.54 g (75%). H NMR (300 MHz,
CDCl3): d 0.80 (s, 3H), 0.94 (s, 3H), 1.35 (d, J = 10.0 Hz, 1H), 1.47
(s, 3H), 1.50 (s, 3H), 1.51 (d, J = 10.6 Hz, 1H), 1.62 (d, J = 6.7 Hz,
3H), 1.71 (d, J = 6.7 Hz, 3H), 2.28–2.37 (m, 2H), 2.53–2.66 (m,
2H), 2.91 (t, J = 5.9 Hz, 2H), 3.96–4.03 (m, 2H), 7.49 (d, J =
8.2 Hz, 1H), 7.50 (d, J = 7.9 Hz, 1H), 7.56 (d, J = 8.2 Hz, 1H),
7.62 (d, J = 7.6 Hz, 1H); m (KBr)/cm−1: 2020 s (CO), 1888 br
(CO); anal. calcd. for C29H32BrN2O3Re: C, 48.20; H, 4.43; N, 3.88,
found: C, 48.32; H, 4.43; N, 3.95%; ESI-MS: m/z 643 [M − Br]+.
1
[Re(5a)(CO)3Br]. Yield: 0.69 g (89%). H NMR (300 MHz,
CDCl3): d 0.66 (s, 3H), 0.72 (s, 3H), 0.77 (s, 3H), 0.84 (s, 3H),
1.30 (d, J = 9.7 Hz, 2H), 1.41 (d, J = 9.7 Hz, 2H), 1.42–1.79
(m, 12H), 2.39–2.44 (m, 2H), 2.53–2.58 (m, 2H), 2.71–2.77 (m,
4H), 2.87–2.96 (m, 4H), 3.09–3.19 (m, 2H), 3.33–3.40 (m, 2H),
3.44–3.52 (m, 2H), 3.73 (dd, J = 17.9, 2.6 Hz, 2H), 7.42 (dd,
J = 7.6, 5.3 Hz, 2H), 7.53 (dd, J = 7.9, 1.8 Hz, 2H), 7.58 (dd,
J = 7.6, 1.8 Hz, 2H), 7.66–7.73 (m, 2H), 7.92 (t, J = 7.0 Hz,
2H), 8.04 (td, J = 7.9, 2.1 Hz, 2H), 8.13 (dd, J = 8.2, 1.2 Hz,
2H); m (KBr)/cm−1: 2019 s (CO), 1915 s (CO), 1885 s (CO); anal.
calcd. for C32H31BrN3O3Re·(CH3CN)0.5·(Et2O): C, 51.30; H, 4.94;
N, 5.66, found: C, 52.98; H, 4.89; N, 5.51%; ESI-MS: m/z 692
[M − Br]+.
1
[Re(5b)(CO)3Br]. Yield: 0.74 g (92%). H NMR (300 MHz,
CDCl3): d 0.74 (s, 3H), 0.84 (s, 3H), 1.40 (d, J = 8.8 Hz, 2H), 1.45
(s, 3H), 1.46 (s, 3H), 1.50 (d, J = 7.0 Hz, 3H), 1.64 (d, J = 7.0 Hz,
3H), 2.20 (td, J = 6.2, 3.2 Hz, 1H), 2.31 (td, J = 9.4, 3.2 Hz,
1H), 2.62 (q, J = 5.9 Hz, 2H), 2.88 (t, J = 5.6 Hz, 1H), 2.93 (t,
J = 6.2 Hz, 1H), 3.30–3.32 (m, 1H), 3.94–3.97 (m, 1H), 7.36–7.39
(m, 2H), 7.54 (d, J = 7.9 Hz, 1H), 7.62–7.65 (m, 1H), 7.95 (d,
J = 7.9 Hz, 1H), 8.03 (t, J = 7.9 Hz, 1H), 8.11 (d, J = 7.9 Hz,
1H); m (KBr)/cm−1: 2020 s (CO), 1916 s (CO), 1891 s (CO); anal.
calcd. for C34H35BrN3O3Re·(CH3CN)0.5·(CH2Cl2)0.5: C, 49.42; H,
4.38; N, 5.68, found: C, 50.07; H, 4.36; N, 5.70%; ESI-MS: m/z =
800 [M + H]+, 720 [M − Br]+.
[Re(5a)(MeCN)(CO)3]OTf. Yield: 0.39 g (89%). 1H NMR
(300 MHz, CD3CN): d 0.68 (s, 3H), 0.72 (s, 3H), 0.73 (s, 3H), 0.78
(s, 3H), 1.22 (d, J = 9.7 Hz, 1H), 1.28 (d, J = 9.7 Hz, 1H), 1.34 (d,
J = 10.0 Hz, 1H), 1.42 (d, J = 10.0 Hz, 1H), 1.450 (s, 3H), 1.454
(s, 3H), 1.46 (s, 3H), 1.47 (s, 3H), 1.96 (s, 3H), 1.97 (s, 3H), 2.40–
2.43 (m, 2H), 2.52–2.58 (m, 2H), 2.80 (q, J = 5.3 Hz, 4H), 2.95
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(t, J = 5.6 Hz, 2H), 3.05–3.14 (m, 4H), 3.26 (dt, J = 18.2, 3.2 Hz,
2H), 3.45 (td, J = 18.0, 2.9 Hz, 2H), 3.57 (td, J = 17.6, 2.8 Hz,
2H), 7.53–7.54 (m, 4H), 7.84 (dd, J = 7.0, 0.9 Hz, 2H), 7.87 (ddd,
J = 7.6, 3.5, 1.2 Hz, 2H), 8.27 (dd, J = 8.2, 4.1 Hz, 2H), 8.33 (t,
J = 7.6 Hz, 2H), 8.48 (dt, J = 8.2, 1.2 Hz, 2H); m (KBr)/cm−1: 2301
w (CN), 2031 s (CO), 1921 br (CO), 1165 m (SO3), 1031 m (SO3);
anal. calcd. for C35H34F3N4O6ReS·(H2O)·(CH2Cl2)2.5: C, 40.50; H,
3.69; N, 5.03, found: C, 41.63; H, 3.73; N, 4.97%; ESI-MS: m/z =
733.6 [M − CF3SO3]+.
[Re(5b)(MeCN)(CO)3]OTf. Yield: 0.39 g (86%). 1H NMR
(300 MHz, CD3CN): d 0.69 (s, 3H), 0.72–0.78 (m, 9H), 1.30 (d,
J = 10.0 Hz, 4H), 1.42 (d, J = 7.0 Hz, 3H), 1.44–1.55 (m, 18H),
1.58 (d, J = 6.7 Hz, 3H), 1.96 (s, 3H), 1.97 (s, 3H), 2.18–2.28 (m,
2H), 2.32–2.37 (m, 2H), 2.64–2.69 (m, 4H), 2.94–2.96 (m, 2H),
3.04–3.09 (m, 2H), 3.24–3.30 (m, 2H), 3.79–3.84 (m, 2H), 7.35
(d, J = 7.3 Hz, 1H), 7.48 (d, J = 7.6 Hz, 2H), 7.74–7.87 (m,
4H), 8.11 (d, J = 7.3 Hz, 2H), 8.26–8.34 (m, 4H), 8.44 (d, J =
8.2 Hz, 1H); m (KBr)/cm−1: 2291 w (CN), 2036 s (CO), 1937 s
(CO), 1921 s (CO), 1162 m (SO3), 1031 m (SO3); anal. calcd. for
C37H38F3N4O6ReS·(CH2Cl2): C, 45.88; H, 4.02; N, 5.63, found: C,
45.14; H, 3.96; N, 5.72%; ESI-MS: m/z = 762 [M − CF3SO3]+.
F000 = 1576, l (Mo-Ka) = 50.85 cm−1. Crystal dimensions 0.45 ×
0.25 × 0.12 mm, 75842 reflections measured, 7435 unique (Rint
=
0.035), R = 0.029 [I > 2.00r(I)] and wR2 = 0.029 [I > 2.00r(I)].
Flack parameter = −0.019(8). CCDC 651263.†
Acknowledgements
Financial support for this research project from the Hong Kong
research grants council CERG grant (CityU 101203) and the City
University of Hong Kong SRG grant (7001792) are gratefully
acknowledged.
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˚
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3864 | Org. Biomol. Chem., 2007, 5, 3859–3864
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The Royal Society of Chemistry 2007
©