Synthesis of N-heterocyclic carbene rhenium(i) carbonyl complexes

Article abstract of DOI:10.1039/c2dt11974a

Reaction of aminophosphinimine [RHN(CH₂)₂NPPh ₃] (R = H, Et) with Re₂(CO)₁₀ provided the NH-functionalized carbene rhenium complex [Re₂(CNHCH ₂CH₂NR)(CO)₉] (3a, R = H, 3b, R = Et). Treatment of 3 with Br₂ provided the mono nuclear [Re(CNHCH ₂CH₂NR)(CO)₄Br] (1, R = H, 2, R = Et). However, NH-functionalized carbene complexes 1-3 did not undergo N-alkylation with alkyl halides to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)₅Br] with a carbene donor was employed to prepare [Re(IMes₂)(CO)₄Br] (6a, IMes₂ = 1,3-di-mesitylimidazol-2-ylidene; 6b, IMes₂ = 1,3-dimesityl-4,5- dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated NHCs have similar bonding with Re^I metal centers. Reduction of 6a and 6b with LiEt₃BH yielded the corresponding hydrido complexes 7a-b [ReH(CO)₄(IMes₂)], but not 1 and 2. Ligand substitution of 1, 6a and 6b toward 2,2′- bipyridine (bipy) was investigated. Crystal structures of 1, 3a-b, 6a-b and 7b were determined for characterization and comparison. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt11974a

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PAPER
Synthesis of N-heterocyclic carbene rhenium(I) carbonyl complexes†
Chang-Hung Chen, Yi-Hung Liu, Shie-Ming Peng, Jwu-Ting Chen and Shiuh-Tzung Liu*
Received 19th October 2011, Accepted 23rd November 2011
DOI: 10.1039/c2dt11974a
Reaction of aminophosphinimine [RHN(CH2)2NvPPh3] (R = H, Et) with Re2(CO)10 provided the
NH-functionalized carbene rhenium complex [Re2(CNHCH2CH2NR)(CO)9] (3a, R = H, 3b, R = Et).
Treatment of 3 with Br2 provided the mono nuclear [Re(CNHCH2CH2NR)(CO)4Br] (1, R = H, 2, R =
Et). However, NH-functionalized carbene complexes 1–3 did not undergo N-alkylation with alkyl halides
to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)5Br] with a carbene
donor was employed to prepare [Re(IMes2)(CO)4Br] (6a, IMes2 = 1,3-di-mesitylimidazol-2-ylidene; 6b,
IMes2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a
and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated
NHCs have similar bonding with ReI metal centers. Reduction of 6a and 6b with LiEt3BH yielded the
corresponding hydrido complexes 7a–b [ReH(CO)4(IMes2)], but not 1 and 2. Ligand substitution of 1, 6a
and 6b toward 2,2′-bipyridine (bipy) was investigated. Crystal structures of 1, 3a–b, 6a–b and 7b were
determined for characterization and comparison.
ability among these various NHCs toward ReI by means of crys-
tallographic and spectroscopic analyses. In addition, the chemi-
cal properties of these complexes were investigated.
Introduction
The study of transition metal N-heterocyclic carbene (NHC)
complexes has been one of the prominent fields of organometal-
lic chemistry over the past decade.1 Nowadays, NHCs are rela-
tively common donors for various transition metal ions owing to
the ready availability of carbenes or their precursors.1e Among
many studies, the chemistry of rhenium-NHC complexes is less
explored,2–8 despite the fact that the diaminocarbene complex
[Re{CH(NHPh)NHR}(CO)4](PF6) was reported by Fehlhammer
and coworkers in 1986.2 Few known rhenium-NHC complexes
exist on three formal oxidation states (VII, V and I) of the metal
center.2–8 For the high-oxidation-state Re(V/VII) compounds,
NHC ligands are found to stabilize the corresponding oxo and
nitrido complexes efficiently.3 For the low-valent stable ReI-
NHC complexes, the metal centers are generally coordinated
Results and discussion
NH-Functionalized carbene rhenium carbonyl complexes
According to our previously reported method,8a rhenium NHC
complex 1 [Re{C(NHCH2)2}(CO)4Br] could be prepared by a
deoxygenation reaction of [Re(CO)5Br] with H2N(CH2)2-
NvPPh3 to form the corresponding isocyanide complex, which
subsequently underwent intramolecular cyclization to give the
desired complex 1. However, we have developed another
approach leading to this complex (Scheme 1). Treatment of
Re2(CO)10 with H2N(CH2)2NvPPh3 4a readily yielded the di-
rhenium complex 3a in 46% isolated yield. Reaction of 3a with
with
the
carbonyl
ligands
in
the
formula
of
[ReI(CO)m(NHC)nX].4–8
As part of our research on the coordination chemistry of NHC
ligands, we have reported the synthesis of the NH,NH-functiona-
lized carbene complex [Re{C(NHCH2)2}nBr(CO)4−n] I and its
bipyridine derivatives II.8 In this work, we report the preparation
of NH,NH-functionalized, N-substituted-saturated and N-substi-
tuted-unsaturated heterocyclic carbene ReI complexes and their
reactivity. In particular, we make comparison of the donating
Department of Chemistry, National Taiwan University, Taipei, Taiwan
106, Republic of China. E-mail: stliu@ntu.edu.tw; Fax: (8862)
23636359; Tel: (8862)23660352
†Electronic supplementary information (ESI) available: ORTEP plot
and bond distances and angles of 3b. CCDC reference numbers
848936–848941. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt11974a
Scheme 1 Preparation of rhenium NHC complexes.
Dalton Trans., 2012, 41, 2747–2754 | 2747
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Table 1 Selected spectral data for rhenium-NHC complexes
Table 2 Bond lengths and bond angles of 3a
13C NMR shiftsb
Bond distances (Å)
Bond angles (deg)
1H NMR datab
a
Compd. IR (υCO
)
-CHmCHm-
C(carbene) CO
Re(1)–C(1)
Re(1)–C(2)
Re(1)–C(3)
Re(1)–C(4)
Re(2)–C(8)
Re(2)–C(9)
Re(2)–C(10)
Re(2)–C(11)
Re(2)–C(12)
1.972(4)
1.980(5)
1.908(4)
1.986(5)
1.927(5)
1.973(6)
1.992(5)
1.994(6)
1.976(5)
C(1)–Re(1)–C(5)
Re(1)–C(1)–O(1)
C(5)–Re(1)–Re(2)
C(4)–Re(1)–C(5)
C(11)–Re(2)–Re(1)
C(8)–Re(2)–Re(1)
C(2)–Re(1)–C(4)
C(3)–Re(1)–Re(2)
C(9)–Re(2)–C(11)
178.31(17)
177.8(4)
92.40(10)
88.82(17)
86.09(15)
179.0(2)
171.49(19)
177.66(15)
172.3(2)
1
2103, 2005, 1916, 3.72
191.1
185.9,
184.22,
184.18
2
3a
2104, 2010, 1920, 3.65–3.70 (m)
2099, 2027, 1988, 3.65 (s)
1965, 1950, 1900
2097, 2032, 1980, 3.54–3.63 (m)
1972, 1947, 1920
192.8
193.1
185.6, 184.6
200.0, 195.1,
188.2
3b
6a
6b
7a
7b
192.1
177.4
203.9
173.0
201.7
199.3, 194.4,
188.0
184.9, 183.8,
181.7
184.5, 183.6,
181.4
190.5, 189.8,
188.7
2091, 1987, 1927 7.08
2088, 1982, 1923 3.96
2065, 1965, 1924 7.02
2062, 1952, 1920 3.84
C(1) equal to 2.169(4) Å. However, the dihydroimidazolidine
ring is tilted from the coordination plane as evidenced by the tor-
sional angle of N(1)–C(5)–Re(1)–C(4) = 33.2(4)°. Since the
NHC ligand is a strong σ-donor, it would be expected that the
M–CO bond trans to a NHC ligand would be shorter than that
trans to another CO (Table 2). This effect is observed for 3a,
with Re(1)–C(1) trans to NHC (1.972(4) Å) slightly shorter than
the average value of the other Re(2)–CO bonds (1.983 Å).
However, the axial Re–CO bonds (Re(1)–C(3) 1.908(4) and
Re(2)–C(8) 1.927(5) Å) are significantly shorter than the average
Re–CO bonds.9
189.7, 188.5,
188.4
a in KBr, cm−1 b in CDCl3, ppm.
.
Phosphinimine 4b, containing a secondary amine moiety,
underwent deoxygenation smoothly with Re2(CO)10 followed by
the cyclization to yield the mono N-substituted NHC complex
3b. Reaction of 3b with Br2 provided the mono-nuclear species
2 (Scheme 1). The structures of complexes 2 and 3b were
characterized by their IR and NMR spectroscopic analyses
(Table 1).
Comparisons of the infrared carbonyl stretching frequencies
and the 13C NMR shift of the carbene carbon between 1 and 2
can tell the similar structural features of these two species
1
(Table 1). However, the NMR resonances of -CH2- protons of
the NHC ring show a slight difference between these complexes.
The -CH2- protons in the NHC ring of 1 appear at 3.72 ppm as a
singlet, and those of 2 are observed at 3.65–3.70 ppm as a multi-
plet due to their unsymmetrical nature. Similar spectral features
were observed for both complexes 3a and 3b, which supports
the structural formulation of 3b. Nevertheless, the structural
characteristics of 3b were confirmed by the X-ray analysis (see
ESI†). Both crystal structures of 3a and 3b are isomorphous.
We have previously reported a detailed study on the N-alky-
lation of NH,NH-functionalized tungsten carbene complexes
(eqn (1)),8a which generally proceeds via an SN2 type reaction.
In addition, Hahn and coworkers have successfully demonstrated
the intromolecular N-arylation of NH,NH-functionalized carbene
complexes.5 However, rhenium complexes 1–3 did not undergo
N-alkyaltion under various basic conditions. In case of using
strong bases such as LiN(i-Pr)2, tert-BuOK and NaH, the
rhenium complexes decomposed readily leading to a mixture of
unidentified species.
Fig. 1 ORTEP plot of 3a (Drawn with 30% probability ellipsoids).
equal molar amount of Br2 provided the desired complex 1 quan-
titatively. It is noticed that complex 3a did not react with excess
of phosphinimine 4a to generate a dicarbene species. In addition,
carbene complex 1 did not react with excess of Br2, indicating
that Re–C(carbene) bond is stable toward Br2.
The carbene complex 3a is stable in the solid state and sol-
ution. Its infrared spectrum shows a pattern of six peaks in the
carbonyl region (Table 1) which are typical for [Re2(CO)9L]
complexes.9 The 13C NMR spectrum for 3a exhibits a resonance
for the carbene carbon at δ 193.1, which is comparable to that of
191.1 ppm in complex 1.8a Furthermore, the molecular structure
of 3a, determined by single-crystal X-ray diffraction, is depicted
in Fig. 1.
The structure of 3a is similar to that of [Re2(CO)9(CNR)]
having two square-pyramidal rhenium fragments joined by a Re–
Re single bond.10 The equatorial ligands adopt a distorted stag-
gered rotational conformation between the two halves of the
molecule (torsional angles: C(4)–Re(1)–Re(2)–C(11) 39.1(2)°
and C(4)–Re(1)–Re(2)–C(10) 50.8(2)°). The NHC ligand
occupies one of equatorial positions with the bond length Re–
ð1Þ
2748 | Dalton Trans., 2012, 41, 2747–2754
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Scheme 2 Preparation of saturated and unsaturated NHC ReI
complexes.
Fig. 3 ORTEP plot of 6b (Drawn with 30% probability ellipsoids).
Fig. 4 ORTEP plot of 1 (Drawn with 30% probability ellipsoids).
Table 3 Selected bond lengths (Å) and angles (deg) for 6a–b and 1
Fig. 2 ORTEP plot of 6a (Drawn with 30% probability ellipsoids).
Preparation of N-substituted NHC rhenium complexes
Complex
6a
6b
1
Re(1)–C(5)
Re(1)–C(1)
Re(1)–C(2)
Re(1)–C(3)
Re(1)–C(4)
C(1)–O(1)
Re(1)–Br(1)
C(6)–C(7)
Re(1)–C(1)–O(1)
C(5)–Re(1)–C(4)
C(5)–Re(1)–C(2)
N(1)–C(5)–Re(1)–C(2)
2.190(5)
1.937(5)
1.992(6)
1.925(7)
2.010(6)
1.159(6)
2.6243(6)
1.346(9)
179.1(7)
94.6(2)
2.213(4)
1.953(5)
1.999(4)
1.917(5)
1.999(4)
1.137(5)
2.6124(6)
1.517(6)a
178.4(4)
96.2(1)
2.158(5)
1.965(6)
1.999(5)
1.898(5)
1.991(5)
1.130(7)
2.6430(5)b
1.507(7)
178.4(6)
88.4(2)
For the N-substituted NHC complexes, the direct ligand substi-
tution of [Re(CO)5Br] with a carbene donor was employed to
deliver the desired species (Scheme 2).11 Thus, treatment of
1,3-dimesitylimidazolium bromide 5a with tert-BuOK in THF
afforded the corresponding carbene species, which was sub-
sequently reacted with [Re(CO)5Br] to provide the unsaturated
NHC rhenium complex 6a in 75% yield. Similarly, the saturated
NHC rhenium complex 6b was obtained as a white solid in 60%
yield.
95.6(2)
8.2(5)
96.2(1)
0.9(3)
87.5(2)
88.8(5)
The relative chemical shift of the NHC carbon atom differ for
the complexes with saturated and unsaturated NHCs (6a
177.4 ppm and 6b 203.9 ppm), but the chemical shifts of the CO
carbon atoms trans to the bromo ligand or the NHC donor are
nearly the same (Table 1). The presence of three CO bands in
the IR spectra of both 6a and 6b (Table 1) are consistent with
the cis-configurations. However, there is no significant difference
in the carbonyl stretching frequencies for both complexes, indi-
cating that the donating ability of saturated NHCs is similar to
that of unsaturated complex.12 The X-ray crystal structures of the
two compounds confirm their structural details (Fig. 2–3 for 6a
and 6b, respectively). Although complex 1 is a known com-
pound, its crystal structure has never been reported.8a For com-
parison, the crystal structure of 1 was also determined (Fig. 4).
Selected bond lengths and bond angles of 6a–b and 1 are listed
in Table 3.
In all compounds, the rhenium atom is coordinated by the
bromide, four carbonyl ligands and HNC in a slightly distorted
octahedron. As expected from IR spectroscopic data, the
bromide and the carbene donors are seated in a cis-fashion. All
bond lengths and bond angles of both complexes lie within the
typical ranges and compare well to those observed for related
ReI complexes bearing NHC ligands.5,8
a C(6)–C(6A). b Re(1)–H(1).
There is no significant difference between 6a and 6b in the
corresponding bond lengths and angles except the distances of
C(6)–C(7) (double versus single bond), indicating that the intro-
duction of saturated or unsaturated NHC ligand has little effect
on the structural parameters around the metal center. A similar
situation was found between 6b and 1. Thus, all bond distances
and angles in 6b are similar in comparison to equivalent bonds
in 1 except the distance of Re(1)–C(5) and angles of C(5)–
Re(1)–C(4) and (5)–Re(1)–C(2). The distance Re(1)–C(5) in 6b
is longer than that in 1 by 0.06 Å. This observation can be
explained by the steric demand of the mesityl groups, which
leads to the longer Re–C bond in 6b. Such a steric interaction
also causes the angles of C(5)–Re(1)–C(4) and C(5)–Re(1)–C(2)
greater than 90° as compared to those in 1.
NHC-Rhenium hydride complexes
It has been revealed that the rhenium bromide complex can be
converted into the corresponding hydrido species by reduction.13
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Thus we investigated the reduction of [Re(CO)5(NHC)Br] with
LiEt3BH. Both complexes 6a and 6b reacted with LiEt3BH at
ice cold temperature to give the corresponding hydride com-
plexes 7a and 7b, respectively (eqn (2)). However, complexes 1
and 2 did not undergo such a reduction. In the presence of super
hydride, both complexes 1 and 2 readily decomposed, similar to
that of the treatment with strong bases.
ð2Þ
Scheme 3 Preparation of bipyridine NHC ReI complexes.
The hydride ligands resonate in the 1H NMR spectra at δ
−5.08 ppm for 7a and −5.13 ppm for 7b, similar to the hydride
shift for [ReH(CO)4(PPh3)] (−4.45 ppm).13 The 13C NMR
signals due to the carbene carbons for 7a and 7b appear at differ-
ent chemical shifts as a consequence of the unsaturated versus
saturated ring system (173.0 ppm for 7a, 201.7 ppm for 7b, see
Table 1), similar to those for 6a and 6b. The molecular structure
of 7b was unequivocally determined by means of X-ray diffrac-
tion study. The molecular geometry of 7b (Fig. 5) compares well
to that of 6b. All bond lengths and bond angles of 7b lie within
the typical ranges. By judging from the distances of Re(1)–C(1)
[1.943(3) Å] versus Re(1)–C(3) (1.966(4) Å), the donating
nature of the NHC ligand is stronger than that of the hydride
ligand. The calculated bond length of Re(1)–H(1) is 1.68(4) Å,
which is shorter than that of the estimated covalent radius. The
dihedral angle of N(1)–C(5)–Re(1)–C(2) is 9.0(3)°, suggesting
that the plane of the NHC ring is slightly deviated from the
coordination plane.
Both complexes 7a and 7b are air-stable solids. In solution
states such as THF or acetone, these complexes are also stable
toward oxidation with sulfur or oxygen. However, in the pres-
ence of chlorinated solvents such CHCl3, complex 7b was
readily transferred into the chloride species 8 thermally or photo-
chemically (eqn (3)) Although not mechanistically studied, the
reaction pathway leading to 8 possibly involves the formation of
the rhenium radicals that abstract chlorine atoms from the
solvent.14
ð3Þ
Substitution with 2,2′-bipyridine
Reaction of 1 with an equimolar amount of bipyridine in
refluxing acetonitrile provided the substitution product fac-[Re
{C(NHCH2)2}(CO)3(bipy)]Br
9
in 70% isolated yield
(Scheme 3-a), but substitution reactions of 6a–b with bipyridine
did not proceed well under the same conditions with the recov-
ery of most starting materials. Alternatively, the substitution of
6a–b with bipyridine could be achieved by the addition of silver
salt (Scheme 3-b). It appears that the generation of a labile
coordination site on the rhenium centre via the abstraction of
bromide would facilitate substitution reaction. This outcome
suggests that the steric bulkiness of the mesityl groups on the
NHC rings readily hinders the substitution of the incoming
ligands.
Complexes 9 and 10a–b were isolated as light yellow solids
and are stable in both solid states and dichloromethane solutions.
Their infrared spectra show a pattern of three peaks in the carbo-
nyl region (Table 4) which are typical for fac tricarboyl rhenium
complexes. In the 13C NMR spectra, the resonances for the
carbene carbon in 9 and 10a–b appear in the range of
170–200 ppm, which is comparable to those in complexes 1 and
7a–b (Table 1), respectively. It is noticed that there is no signifi-
cant difference among these three complexes in their UV-Vis
absorption spectra.
Summary
In summary, we have reported the synthesis and the full charac-
terization of a series of NHC rhenium complexes. The structures
of complexes 1, 3a–b, 6a–b and 7b were further determined by
X-ray single crystal analyses. This study provides an insight into
NHC ligand effects on ReI metal ions, particularly for the com-
parison of unsaturated, saturated and NH,NH-functionalized
Fig. 5 ORTEP plot of 7b (Drawn with 30% probability ellipsoids).
Re(1)–C(5) 2.188(3) Å; Re(1)–C(1) 1.943(3) Å; Re(1)–C(2) 1.991(3) Å;
Re(1)–C(3) 1.966(4) Å.
2750 | Dalton Trans., 2012, 41, 2747–2754
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Table 4 Spectral data of bipyridine complexes 9 and 10a–b
(-CO), 45.6. Anal. C12H6N2O9Re2: C, 20.75; H, 0.87; N, 4.03.
Found: C, 20.44; H, 0.70; N, 3.64.
13C NMR shiftsb
a
Compound IR (υCO
)
C(carbene) -CO
λmax (ε)c
Preparation of complex 3b
9
2021, 1924,
1894
193.3
173.8
199.7
200.9,
197.4
242 (42.1)
The procedure for preparation of 3b is quite similar to that for
3a. A mixture of [Re2(CO)10] (3.5 g, 5.4 mmol) and EtHNCH2-
CH2NvPPh3, which was prepared in situ by the reaction of
EtHNCH2CH2N3 (0.62 g, 5.4 mmol) with PPh3 (1.4 g,
5.4 mmol) in anhydrous THF (10 mL), was stirred at room temp-
erature for 48 h. The mixture was concentrated and the residue
was chromatographed on silica gel with elution of CH2Cl2/
hexane. Upon concentration, complex 3b was obtained as white
power solids (0.95 g, 23%): IR (KBr, υCO): 2097, 2032, 1980,
316 (21.1)
354 tail to 439
(8.28)
10a
10b
2030, 1917,
1893
197.7,
193.8
239 (45.2)
317 (22.7)
345 tail to 425
(8.11)
2030, 1916,
1893
197.7,
193.8
243 (49.0)
1
1972, 1947, 1920 cm−1; H NMR(CDCl3, 400 MHz): δ 5.77 (s,
317(26.8)
345 tail to 428
(6.80)
1H, -NH-), 3.72 (q, J = 7.2 Hz, 2H, -CH2-), 3.54–3.63 (m, 4H,
-(CH2)2-), 1.27 (t, J = 7.2 Hz, 3H, -CH3); 13C NMR (CDCl3,
100 MHz): δ 199.3 (-CO), 194.4 (-CO), 192.1 (Ccarbene), 188.0
(-CO), 48.0, 46.8, 45.3, 13.6. Anal. Calcd. for C14H10N2O9Re2:
C, 23.27; H, 1.39; N, 3.88. Found: C, 23.01; H, 1.02; N, 3.48.
a KBr, cm−1 b CDCl3, ppm. c in CH2Cl2, nm, ε: 103 M−1cm−1
.
NHCs. Studies on the catalytic reactivity and photophysical
properties of these complexes are ongoing in our laboratory.
Preparation of complex 1 from 3a
To a solution of complex 3a (50 mg, 0.072 mmol) in CH2Cl2
(5 mL) was added Br2 (0.1 mL, 1.9 mmol) at room temperature.
After being stirred for 10 min, the solvent and excess bromine
were removed under reduced pressure to leave a light yellow
solid. The resulting residue was chromatographed on silica gel
with elution of hexane/CH2Cl2. The first fraction collected was
identified as [Re(CO)5Br] (926 mg, 95%), whereas the second
fraction was the desired carbene complex (29 mg, 90%): 1H
NMR (CDCl3, 400 MHz): δ 6.86 (s, 2H, -NH-), 3.72 (s, 4H,
-(CH2)2-); 13C NMR (CDCl3, 100 MHz): δ 191.1 (Ccarbene),
185.9 (-CO), 184.22 (-CO), 184.18 (-CO), 45.5. These spectral
data are essentially identical to the reported ones.8a
Experimental
General information
All reactions and manipulations steps were performed under a
dry nitrogen atmosphere. Tetrahydrofuran was distilled under
nitrogen from sodium benzophenone ketyl. Dichloromethane
and acetonitrile were dried over CaH2 and distilled under nitro-
gen. Other chemicals and solvents were of analytical grade and
were used after degassed process. Preparation of 1,3-dimesityl-
imidazolium bromide 5a and 1,3-dimesityl-4,5-dihydroimidazo-
lium bromide 5b were according to the reported methods.15
Nuclear magnetic resonance spectra were recorded in CDCl3
or acetone-d6 on a Bruker AVANCE 400 spectrometer. Chemical
Preparation of complex 2 from 3b
1
shifts are given in parts per million relative to Me4Si for H and
The procedure is similar to that for 3a. White solid (93% yield):
13C NMR. Infrared spectra were measured on a Varian 640-IR
spectrometer and UV-Vis spectra were recorded on a Shimatzu
PC 2100 spectrometer.
IR (KBr, υCO): 2104, 2010, 1920 cm−1 1H NMR (CDCl3,
;
400 MHz): δ 7.13 (s, 1H, -NH-), 3.65–3.70 (m, 6H, -CH2-),
1.28 (t, J = 7.2 Hz, 3H,-CH3); 13C NMR (CDCl3, 100 MHz): δ
192.8 (Ccarbene), 185.6 (-CO), 184.6 (-CO), 184.5 (-CO) 48.7,
45.9, 45.4, 13.9. Anal. Calcd for C9H10BrN2O4Re: C, 22.70; H,
2.12; N, 5.88. Found: C, 22.86; H, 2.01; N, 5.82.
Preparation of complex 3a
A mixture of [Re2(CO)10] (100 mg, 0.153 mmol) and H2NCH2-
CH2NvPPh3 (167 mg, 0.48 mmol), which was prepared in situ
by the reaction of H2NCH2CH2N3 with an equimolar amount of
PPh3 in anhydrous THF (10 mL), was stirred at room tempera-
ture for 22 h. The mixture was concentrated and the residue was
chromatographed on silica gel with elution of CH2Cl2/hexane. A
yellow band was collected and concentrated to give light yellow
solids as the desired product (50 mg, 46%). Further re-crystalli-
zation from CH2Cl2/hexane provided single crystals suitable for
X-ray structural determination. IR (KBr, υCO): 2099, 2027, 1988,
1965, 1950, 1900 cm−1; 1H NMR (CDCl3, 400 MHz): δ 5.98 (s,
2H, -NH-), 3.65 (s, 4H, -(CH2)2-); 13C NMR (CDCl3,
100 MHz): δ 200.0 (-CO), 195.1 (-CO), 193.1 (Ccarbene), 188.2
Preparation of complex 6a
A mixture of 5a (100 mg, 0.29 mmol) and tert-BuOK (100 mg,
0.89 mmol) in anhydrous THF (10 mL) was stirred at room
temperature for 1 h and then the reaction vessel was connected
to a vacuum system to remove all the solvents. A solution of
[Re(CO)5Br] (200 mg, 0.49 mmol) in pre-dried toluene (20 mL)
was transferred by syringe to the above flask. The resulting
mixture was heated at 50 °C for 10 h. The resulting mixture was
filtered through a silica gel column. The solvent was removed
under reduced pressure to obtain white solids as the desired
complex 6a (140 mg, 75%). Recrystallization of this white
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2747–2754 | 2751

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Reaction of 7b with CHCl3
solids yielded colorless single crystals suitable for X-ray struc-
1
tural determination. IR (KBr,υCO): 2091, 1987, 1927 cm−1; H
To a solution of 7b (5 mg, 8 × 10−3 mmol) in CHCl3 (0.5 mL)
was heated at 70 °C for 20 h. The resulting mixture was filtered
through a silica gel column. The solvent was removed under
reduced pressure to obtain a white solid as the desired complex 8
NMR (CDCl3, 400 MHz): δ 7.08 (s, 2H, -CHvCH-), 7.02 (s,
4H, Ar-H), 2.36 (s, 12H, -Me), 2.18 (s, 6H, -Me); 13C NMR
(CDCl3, 100 MHz): δ 184.9 (Re–CO), 183.8 (Re–CO), 181.7
(Re–CO), 177.4 (Ccarbene), 140.4, 136.8, 136.1, 129.3, 123.2,
21.6, 18.7; Anal. Calcd for C25H24BrN2O4Re: C, 43.99; H,
3.54; N, 4.10. Found: C, 43.85; H, 3.44; N, 3.97.
(5 mg, 95%): IR (KBr, υCO): 2087, 1983, 1922 cm−1; H NMR
1
(CDCl3, 400 MHz): d 6.98 (s, 4H, m-H), 3.96 (s, 4H, -(CH2)2-),
2.39 (s, 12H, Ar-Me), 2.30 (s, 6H, Ar-Me); 13C NMR (CDCl3,
100 MHZ): δ 204.9 (Ccarbene), 185.5 (-CO), 183.9 (-CO), 181.7
(-CO), 139.5, 137.3, 136.7, 129.6, 51.4, 21.6, 19.0. Anal. Calcd.
for C25H26ClN2O4Re: C, 46.91; H, 4.09; N, 4.38. Found: C,
46.71; H, 4.01; N, 4.15.
Preparation of complex 6b
A mixture of 5b (200 mg, 0.52 mmol) and tert-BuOK (174 mg,
1.55 mmol) in anhydrous THF (20 mL) was stirred at room
temperature for 1 h and then the solvent was removed under
nitrogen atmosphere. A solution of [Re(CO)5Br] (200 mg,
0.49 mmol) in pre-dried toluene (40 mL) was transferred to the
above reaction vessel. The resulting mixture was heated at 50 °C
for 20 h. The reaction mixture was chromatographed on silica
gel with the elution of CH2Cl2/hexane. The desired carbene
complex 6b was obtained as crystalline solids (210 mg, 60%).
Preparation of complex 9
To a mixture of 1 (100 mg, 0.22 mmol) and 2,2′-bipyridine
(42 mg, 0.27 mmol) was added CH2Cl2 (10 mL) under nitrogen
atmosphere. The resulting solution was heat to reflux for 20 h.
Ether was added to the reaction mixture and the desired product
precipitated out from the solution as yellow solids (90 mg, 70%):
IR (KBr, υCO): 2088, 1982, 1923 cm−1 1H NMR (CDCl3,
;
IR (KBr, υCO): 2021, 1924, 1894 cm−1 1H NMR (CD3CN,
;
400 MHz): δ 6.98 (s, 4H, Ar-H), 3.96 (s, 4H, -(CH2)2-), 2.40 (s,
12H, -Me), 2.30 (s, 6H, -Me); 13C NMR (CDCl3, 100 MHZ): δ
203.9 (Ccarbene), 184.5 (-CO), 183.6 (-CO), 181.4 (-CO), 139.5,
137.3, 136.7, 129.6, 51.4, 21.5, 18.9. Anal. Calcd for
C25H26BrN2O4Re: C, 43.86; H, 3.83; N, 4.09. Found: C, 43.79;
H, 3.86; N, 3.76.
400 MHz): δ 9.07∼9.08 (m, 2H, bpy), 8.47–8.50 (m, 2H, bpy),
8.22–8.26 (m, 2H, bpy), 7.67–7.70 (m, 2H, bpy), 6.70 (s, 2H,
-NH-), 3.30 (s, 4H, -(CH2)2-); 13C NMR (CD3CN, 100 MHZ): δ
200.9 (Re–CO), 197.4 (Re–CO), 193.3 (Ccarbene), 156.6, 154.6,
141.0, 129.1, 125.4, 45.2. HR-ESI-MS m/z: 497.0618
([M−Cl]+, calcd. for C16H14N4O3Re: 497.0623).
Preparation of complex 7a
Preparation of complex 10a
To a solution of 6a (50 mg, 0.073 mmol) in THF (15 mL) was
slowly added a THF solution of NaEt3BH (1 M, 0.1 mL) at ice-
cooled temperature and the mixture was stirred at that tempera-
ture for 2 h. After reaction was completed, a solution of NaOH
(1 M, 1.5 mL) was added. Upon concentration of the reaction
mixture, the residue was chromatographed on silica gel with the
elution of CH2Cl2/hexane. The desired product was obtained as
a white solid (28 mg, 62%): IR (KBr, υCO): 2065, 1965,
To a solution of 6a (50 mg, 0.073 mmol) in CH2Cl2 (5 mL) was
added AgPF6 (22.2 mg, 0.088 mmol). This mixture was stirred
at room temperature for
1 h. 2,2′-Bipyridine (12 mg,
0.077 mmol) was then added to the above solution. The resulting
mixture was heated to reflux for 36 h. The reaction mixture was
passed through Celite and concentrated. The residue was dis-
solved in a minimum amount of dichloromethane. Addition of
diethyl ether to the solution provided 10a as light yellow precipi-
1924 cm−1 1H NMR (CDCl3, 400 MHz): δ 7.02 (s, 2H,
;
1
tates (51 mg, 79%): IR (KBr, υCO) 2030, 1916, 1893 cm−1; H
-CHvCH-), 7.01 (s, 4H, Ar-H), 2.35 (s, 6H, -Me), 2.05 (s, 12H,
-Me), −5.08 (s, 1H, Re-H); 13C NMR (CDCl3, 100 MHZ): δ
190.5 (-CO), 189.8 (-CO), 188.7 (-CO), 173.0 (Ccarbene), 139.5,
137.7, 135.5, 129.4, 123.2, 21.2, 18.1. Anal. Calcd. for
C25H25N2O4Re: C, 49.74; H, 4.17; N, 4.64. Found: C, 49.50; H,
3.98; N, 4.31.
NMR (CD3CN): d 9.05 ∼9.03 (m, 2H, bipy), 8.42–8.44 (m, 2H,
bipy), 8.23–8.27 (m, 2H, bipy), 7.67–7.70 (m, 2H, bipy), 7.22 (s,
2H, -CHvCH-), 6.96 (s, 4H, Ar-H), 2.41 (s, 6H, Ar-Me), 1.71
(s, 12H, Ar-Me); 13C NMR (CD3CN, 100 MHz): δ 197.7 (-CO),
193.8 (-CO), 183.8 (Ccarbene), 156.9, 155.1, 154.6, 142.1, 140.4,
135.7, 130.7, 130.1, 128.9, 128.8, 125.2, 21.2, 17.5.
HR-ESI-MS m/z: 731.2028 ([M−PF6]+, calcd. for
C34H32N4O3Re: 731.2032).
Preparation of complex 7b
The procedure is similar to that for 7a. White solid (27 mg,
60%): IR (KBr, υCO) 2062, 1952, 1920 cm−1; 1H NMR (CDCl3,
400 MHz): δ 6.97 (s, 4H, Ar-H), 3.84 (s, 4H, -(CH2)2-), 2.30 (s,
6H, -Me), 2.29 (s, 12H, -Me), −5.13 (s, 1H, Re-H); 13C NMR
(CDCl3, 100 MHZ): δ 201.7 (Ccarbene), 189.7 (-CO), 188.5
(-CO), 188.4 (-CO), 138.3, 137.6, 135.9, 129.4, 51.1, 21.5, 18.5.
Anal. Calcd. for C25H27N2O4Re: C, 49.57; H, 4.49; N, 4.62.
Found: C, 49.25; H, 4.24; N, 4.52.
Preparation of complex 10b
The procedure is similar to that for 10a. light yellow solids
(50 mg, 70%): IR (KBr, υCO): 2030, 1917, 1893 cm−1; 1H NMR
(CD3CN): δ 9.05 ∼ 9.03 (m, 2H, bipy), 8.42–8.44 (m, 2H, bipy),
8.23–8.27 (m, 2H, bipy), 7.67–7.70 (m, 2H, bipy), 6.89 (s, 4H,
m-H), 3.86 (s, 4H, -(CH2)2-), 2.37 (s, 6H, Ar-Me), 1.86 (s, 12H,
Ar-Me); 13C NMR (CD3CN, 100 MHz): δ 199.7(Ccarbene), 197.7
2752 | Dalton Trans., 2012, 41, 2747–2754
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Table 5 Crystal data
Complex
1
3a
3b
6a
6b
7b
Formula
Fw
C7H6BrN2O4Re
448.25
C12H6N2O9Re2
694.59
C14H10N2O9Re2
722.64
C25H24BrN2O4Re
682.57
C25H26BrN2O4Re
684.59
C27H33N2O5Re
651.75
Crystal system Monoclinic
Triclinic
P1
Triclinic
P1
Monoclinic
P21/c
17.6499(4)
17.6537(4)
8.6473(2)
90
100.798(2)
90
2646.67(10); 4
1.713
Orthorhombic
Pnma
15.0972(5)
20.2743(7)
8.5553(3)
90
Monoclinic
P21/c
11.0693(2)
10.3030(2)
23.0176(4)
90
90.486(2)
90
2624.99(8); 4
1.649
ˉ
ˉ
Space group
a/Å
b/Å
c/Å
α (°)
P21/c
8.2595(2)
10.7162(3)
13.2087(3)
90
7.9466(2)
8.7775(2)
12.6693(3)
99.095(2)
90.065(2)
101.329(2)
855.11(4); 2
2.698
9.0464(2)
9.3184(2)
12.2154(3)
111.511(2)
91.287(2)
96.573(2)
949.40(4); 2
2.514
β (°)
98.183(3)
90
1157.20(5); 4
2.573
90
90
γ (°)
V/Å3; Z
d (calc.),
Mg m−3
F(0,0,0)
2618.65(16); 4
1.736
816
628
652
1320
1328
1296
Crystal size/mm 0.20 × 0.15 × 0.10 0.20 × 0.15 × 0.10 0.25 × 0.20 × 0.15 0.25 × 0.20 × 0.15
0.25 × 0.20 × 0.15
17083
0.20 × 0.15 × 0.10
30680
Rflns collected 13362
19399
21788
27091
Independent
rflns
2650 [R(int) =
0.0421]
3.13 to 27.50
3933 [R(int) =
0.0290]
3.04 to 27.50
4349 [R(int) =
0.0277]
2.99 to 27.50
5920 [R(int) =
0.0295]
3.09 to 27.50
3096 [R(int) =
0.0358]
2.88 to 27.49
6023 [R(int) =
0.0315]
2.84 to 27.50
θ range, deg
Refined method Full-matrix least-squares on F2
Goodness of fit 1.054
0.995
0.956
0.978
0.922
0.997
on F2
R indices
[I > 2σ(I)]
R indices
(all data)
R1 = 0.0246,
R1 = 0.0237,
wR2 = 0.0608
R1 = 0.0289,
wR2 = 0.0625
R1 = 0.0168,
wR2 = 0.0394
R1 = 0.0240,
wR2 = 0.0407
R1 = 0.0338,
wR2 = 0.1143
R1 = 0.0422,
wR2 = 0.1255
R1 = 0.0245,
wR2 = 0.0574
R1 = 0.0347,
wR2 = 0.0591
R1 = 0.0233,
wR2 = 0.0594
R1 = 0.0285,
wR2 = 0.0632
wR2 = 0.0618
R1 = 0.0306,
wR2 = 0.0675
2 W. P. Fehlhammer, P. Hirschmann and A. Völkl, J. Organomet. Chem.,
1986, 302, 379.
(-CO), 193.8 (-CO), 156.7, 155.1, 154.6, 142.2, 136.0, 135.9,
130.7, 130.1, 130.0, 128.9, 125.1, 51.4, 21.2, 17.5. HR-ESI-MS
m/z: 733.2183 ([M−PF6]+, calcd. for C34H34N4O3Re: 733.2188).
3 (a) H. Bradband, D. Przyrembel and U. Abram, Z. Anorg. Allg. Chem.,
2006, 632, 779–785; (b) H. Braband, T. I. Kueckmann and U. Abram, J.
Organomet. Chem., 2005, 690, 5421; (c) H. Braband, S. Neubacher,
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2007, 633, 830 and references therein.
Crystallography
Crystals suitable for X-ray determination were obtained for 1,
3a–b, 6a–b and 7b by recrystallization at room temperature from
a CH2Cl2/hexane solution: Complex 1: colorless; 3a: light
yellow; 3b: colorless; 6a: colorless; 6b: colorless; 7b: colorless.
Cell parameters were determined either by a Siemens SMART
CCD diffractometer. The structure was solved using the
SHELXS-97 program16 and refined using the SHELXL-97
program17 by full-matrix least-squares on F2 values. All crystal
data are summarized in Table 5. CCDC-848936 (3a); 848937
(3b); 848938 (6b); 848939 (7b); 848940(1); 848941(6a) contain
the supplementary crystallographic data for this paper.†
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Acknowledgements
7 T. A. Martin, C. E. Ellul, M. F. Mahon, M. E. Warren, D. Allan and
M. K. Whittlesey, Organometallics, 2011, 30, 2200.
We thank the National Science Council (Taiwan) for financial
support (NSC100-2113-M-002-001-MY3).
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2754 | Dalton Trans., 2012, 41, 2747–2754
This journal is © The Royal Society of Chemistry 2012