Functionalized cyclopentadienyl rhodium(iii) bipyridine complexes: Synthesis, characterization, and catalytic application in hydrogenation of ketones

Article abstract of DOI:10.1039/c3dt50445j

A series of highly functionalized cyclopentadienyl rhodium(iii) complexes, [Cp′Rh(bpy)Br](ClO₄) (Cp′ = substituted cyclopentadienyl), was synthesized from various multi-substituted cyclopentadienes (Cp′H). [Rh(cod)Cl]₂ and Cp′H were

Full text of DOI:10.1039/c3dt50445j

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Functionalized cyclopentadienyl rhodium(III) bipyridine
complexes: synthesis, characterization, and catalytic
application in hydrogenation of ketones†
Cite this: Dalton Trans., 2013, 42, 9628
Wan-Hui Wang,a,b Yuki Suna,a Yuichiro Himeda,*a,b James T. Muckermanc and
Etsuko Fujitac
A series of highly functionalized cyclopentadienyl rhodium(III) complexes, [Cp’Rh(bpy)Br](ClO4) (Cp’ =
substituted cyclopentadienyl), was synthesized from various multi-substituted cyclopentadienes (Cp’H).
[Rh(cod)Cl]2 and Cp’H were firstly converted to [Cp’Rh(cod)] complexes, which were then treated with Br2 to
give the rhodium(III) dibromides [Cp’RhBr2]2. The novel complexes [Cp’Rh(bpy)Br](ClO4) were obtained readily
by the reaction of 2,2’-bipyridine with [Cp’RhBr2]2. These rhodium complexes [Cp’Rh(bpy)Br](ClO4) were fully
characterized and utilized in the hydrogenation of cyclohexanone and acetophenone with generally high
yields, but they did not exhibit the same reactivity trends for the two substrate ketones. The different activity
of these complexes for the different substrates may be due to the influence of the substituents on the Cp’ rings.
Received 17th February 2013,
Accepted 14th April 2013
DOI: 10.1039/c3dt50445j
www.rsc.org/dalton
annulation under mild conditions.30–32 This convenient
method has been employed by Takahashi and Onitsuka et al.
Introduction
Half-sandwich complexes, [Cp*M(L)X]+ (Cp* = η5-pentamethyl- to construct various chiral Cp′–Fe(II), –Rh(I), and –Ru(II) com-
cyclopentadienyl; M = Rh(III), Ir(III)), have recently attracted plexes which have been demonstrated to be effective catalysts
increasing attention due to their favourable thermal stability for a series of enantioselective reactions.11–14
and water solubility, excellent catalytic activity in various trans-
We have been interested in improving the catalytic activity
formations, and promising anticancer activity.1–4 A large of [Cp*M(L)Cl]+ (M = Rh(III), Ir(III)) for a number of reactions
number of [Cp*M(L)X]+ have been studied using different such as the transfer hydrogenation of unsaturated organic sub-
kinds of ligands (L), such as bpy (2,2′-bipyridine), phen (1,10- strates,33 deuterogenation,34,35 hydrogenation of carbon
phenanthroline), cod (1,5-cyclooctadiene), diamines, NHC (N- dioxide,36–38 and dehydrogenation of formic acid.39,40 By intro-
heterocyclic carbenes), etc.5–7 In contrast, functionalized com- ducing electron-donating groups (OH, OMe, Me) into the bpy
plexes based on cyclopentadienes bearing multiple functional ligands, significantly improved activity was achieved. The multi-
groups have been less investigated.8–14 To a great extent, this is substituted cyclopentadienyl ligands have advantages to modu-
due to the inaccessibility of multi-substituted cyclopenta- late their steric and electronic properties by varying the substitu-
dienes (Cp′H). Functionalized cyclopentadienes are generally ents on the ligand. Consequently, the physical properties and
limited to monosubstituted analogs15–20 and/or confined func- catalytic activity of the corresponding functionalized cyclopenta-
tional groups.8,9 Moreover, feasible and practical synthesis of dienyl complex can be readily fine-tuned.10,19 Accordingly, we
multi-substituted cyclopentadienes is quite limited due to the sought to develop complexes based on highly functionalized
use of complex substrates and/or expensive transition cyclopentadienyl ligands, which are accessible using our pre-
metals.10,21–29 We have reported one-step synthesis of multi- viously reported method, and to investigate the substituent
substituted cyclopentadienes from 3-alkoxycarbonylallylidene- effects thereof. Herein, we report a facile preparation of multi-
phosphorane and α-halocarbonyl compounds via [3 + 2] substituted cyclopentadienyl rhodium complexes [Cp′RhBr(bpy)]-
(ClO4) and their application in the hydrogenation of ketones.
aNational Institute of Advanced Industrial Science and Technology, Tsukuba Central
5-2, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan. E-mail: himeda.y@aist.go.jp;
Tel: +81-298-61-9344
Results and discussion
1. Synthesis of functionalized cyclopentadienes 1a–e
bJST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
cChemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA
†Electronic supplementary information (ESI) available: HHCOSY, NOESY, HMBC
spectra, cyclic voltammograms. CCDC 921223 (6e). For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c3dt50445j
The substituted cyclopentadienes 1a–e were synthesized from
3-alkoxycarbonylallylidenephosphoranes and α-bromocarbonyl
9628 | Dalton Trans., 2013, 42, 9628–9636
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Scheme 1 Synthesis of multi-substituted cyclopentadienes 1a–e (Cp’H). Reac-
tion conditions: (1) for 1a–b: aq. NaHCO3, CH2Cl2, rt, 12 h, (2) for 1c–e: 0.6 eq.
Cs2CO3, CH2Cl2, 30 °C, 48–72 h.
compounds in one step with good to high yields (47–96%)
according to our previously reported method (Scheme 1).30–32
2. Synthesis of the bipyridine complex (3) from 1a and
rhodium chloride
In the same manner as the preparation of the pentamethyl-
cyclopentadienyl analogue [Cp*RhCl2]2,41,42 the cyclopenta-
diene 1a reacted with RhCl3·3H2O in ethanol at reflux for 5 h
to give a dark red solid 2 (Scheme 2). The 1H NMR spectrum of
2 showed the two broad peaks (5.75 and 5.20 ppm) due to the
vinyl protons of the substituted cyclopentadienyl (Cp′) ring,
suggesting the formation of the oligomer [Cp′RhCl2]n 2. Sub-
sequently, addition of 2,2′-bipyridine to the ethanol suspen-
sion of 2 gave the bipyridine complex 3 as a yellow solid with a
yield of 60%. The structure of 3 was fully confirmed by H–H
COSY, NOESY, and HMBC (see ESI, Fig. S1–S3†). Fig. 1 shows
partial 1H and 13C NMR spectra of 3 in CD3CN. The 6,6′-
protons on the bpy were observed at 9.23 and 9.09 ppm which
are markedly downfield shifted compared with those (8.66 ppm)
of [Cp*Rh(bpy)Cl]+ (Table 2).
The NOESY spectrum of complex 3 showed the cross peaks
of 6′-H on the bpy with 2-Me on Cp1, conversely, 6-H on the
bpy with 3,5-H and 4-Me on Cp′. The 13C NMR spectrum
shows that the corresponding pairs of carbons on the bpy are
magnetically nonequivalent (Table 2). It appears that these
observations are attributable to the anisotropy of the unsym-
metrical Cp′ ligand. In addition, 3 was racemic due to the
planar chirality of the unsymmetrical Cp′ ligand,13 but this
subject will not be considered in this paper.
Fig. 1 Partial 1H and 13C NMR spectra of complex 3 in CD3CN.
unsuccessful. Therefore, we employed another route to prepare
the rhodium complexes [Cp′RhX(bpy)]+.
3. Synthesis of the bipyridine complexes (6a–e) from 1 and
[Rh(cod)Cl]2
An alternative procedure for the preparation of rhodium di-
halides was performed by way of [Cp′Rh(diene)] (Scheme 3).43
The cod complexes [Cp′Rh(cod)] 4 were prepared by the reac-
tion of [Rh(cod)Cl]2 with the corresponding cyclopentadienyl
Unfortunately, all attempts to prepare the other substituted
cyclopentadienyl complexes by the above method were
Scheme 3 Synthesis of complexes 6 from cyclopentadienes 1. Reaction con-
ditions: (i) [Rh(cod)Cl]2, Na2CO3/MeOH or n-BuLi/THF; (ii) Br2, Et2O; (iii) bpy then
LiClO4, MeOH.
Scheme 2 Synthesis of complex 3 from cyclopentadiene 1a. Reaction con-
ditions: (i) RhCl3·3H2O, EtOH, reflux, 5 h; (ii) bpy then LiClO4, EtOH, rt.
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Table 1 Synthesis of rhodium complexes 4, 5, and 6 from cyclopentadiene 1
Table 2 Comparison of 1H NMR data for 6,6’-H of bpy and 13C NMR data for
the Cp’ ring in the complexes
Cp′H
Yield of 4a/%
Yield of 5/%
Yield of 6/%
13C NMR/δ
1H NMR/δ
1a
1b
1c
1d
1e
92 (A)
98 (A)
87 (B)
92 (B)
70 (B)
88
90
94
89
85
92
89
81
67
80
Complex
6,6′-H of bpy 1-C
2-C
3-C
4-C
5-C
[Cp*Rh(bpy)Cl]+ 8.66
98.14
—
—
—
—
3
9.23, 9.09
76.45 115.73 82.27 107.97 87.44
76.80 115.47 83.13 107.44 88.30
76.12 115.86 81.57 103.82 86.31
61.45 147.04 83.53 101.78 64.08
60.36 144.73 74.73 114.25 61.77
59.49 152.56 59.54 103.88 99.22
6a
6b
6c
6d
6e
9.20, 9.06
9.05, 8.53
9.20, 8.96
9.15, 9.06
9.26, 8.96
a In parentheses are the reaction methods. Method A: using Na2CO3 in
MeOH. Method B: using n-BuLi in THF.
anions, which were prepared by the treatment of 2-methyl-
cyclopentadienes 1a, b with Na2CO3 or 2-ethoxylcyclopenta-
dienes 1c–e with n-BuLi (Scheme 3). The addition of ca. 2
equivalent of Br2 to a solution of 4 in diethyl ether in an ice
bath gave rhodium dimers 5 as dark red powders in high
yields (85–94%, Table 1). The FAB-MS spectra of 5 showed the
parent peaks corresponding to the loss of one bromine
from the dibromide dimer [Cp′RhBr2]2, which may be con-
sidered as a mixture of diastereoisomers.13 Finally, the reac-
tion of 5 with bpy in methanol, followed by addition of LiClO4,
gave complexes 6, [Cp′Rh(bpy)Br](ClO4), in good to high yields
(67–92%, Table 1).
All the products and intermediates were fully characterized
with NMR, IR, ESI-MS and elemental analysis (see Experi-
mental section). The structure of complex 6e has been con-
firmed by X-ray crystallography (Fig. 2). The average Rh–C
distance (2.181 Å) and the distance between Rh and the centroid
of the Cp ring (1.811 Å) are longer than those (2.151 and 1.776 Å,
respectively) of [Cp*Rh(bpy)Cl]+.44 The two pyridine rings in
[Cp*Rh(bpy)Cl]+ are almost coplanar (dihedral angle: 0.38°). In
contrast, the two pyridine rings of 6e show a relatively larger
dihedral angle of 8.07°. Apparently, the bulky substituents
exhibited a remarkable influence on the molecular structure of
the complex.
The characteristic spectral data of 6 are summarized in
Tables 2 and 3. The NMR spectrum of 6a is in good agreement
with that of 3. It is interesting that an upfield shift of 6-H of
the bpy in 6b was observed, which may be due to the shielding
effect of the phenyl group on the Cp′. In the 13C NMR spec-
trum, the chemical shifts of the carbons of the Cp′ ring were
found to be affected by the substituents (Table 2). To evaluate
the electronic effect of the substituent on the rhodium center,
we performed cyclic voltammetry (CV) measurements and the
results are listed in Table 3. As shown in Fig. S4,† the cyclic vol-
tammogram of [Cp*Rh(bpy)Cl]+ showed a quasi-reversible
reduction peak at −0.78 V. The peaks observed in complex
6a–e were positively shifted by 140–340 mV. When the poten-
tial was swept to −3.0 V vs. Ag/Ag+, complex 6a–e showed
another quasi-reversible peak and irreversible peak which were
observed at more positive potential than the second reduction
peak of [Cp*Rh(bpy)Cl]+. The first reduction peaks correspond
to the two-electron reduction of the metal, in which RhIII is
reduced to RhI with the release of a halide ligand (eqn (1)).
And the following peaks correspond to reduction of the bipyri-
dine ligand (eqn (2) and (3)).45,46 The electron-withdrawing
substituent (COOEt) introduced on the cyclopentadienyl
increases the electron-accepting character of the ligand and
stabilizes the low oxidation state of the metal, resulting in the
positive shift of the reduction processes in complexes 6a–e.
0
½Cp′RhIIIðbpyÞXꢀþ þ 2eꢁ ! ½Cp′RhIðbpyÞꢀ þ X–
ð1Þ
ð2Þ
ð3Þ
½Cp′RhIðbpyÞꢀ þ eꢁ ! ½Cp′RhIðbpy˙ꢁÞꢀꢁ
0
½Cp′RhIðbpy˙ꢁÞꢀꢁ þ eꢁ ! ½Cp′RhIðbpy2ꢁÞꢀ
2ꢁ
Fig. 2 ORTEP view of complex 6e. The thermal ellipsoids are shown at 30%
probability level. The perchlorate anion and all hydrogen atoms are omitted for
clarity. Selected distances (Å): Rh–Br 2.534(6), Rh–N18 2.060(3), Rh–N21 2.081(3),
Rh–C2 2.164(4), Rh–C3 2.165(5), Rh–C6 2.268(4), Rh–C30 2.150(4), Rh–C31
2.159(4), Rh–P3 1.809; selected angles (°): N–Rh–N 78.0(1), N21–Rh–Br 87.74(9),
N18–Rh–Br 84.52(9), P1–P2 8.07, P2–P3 65.59, P1–P3 87.87 (P1: plane of first
pyridine ring, P2: plane of second pyridine ring, P3: plane of Cp’ ring).
The electrochemical behavior and UV/Vis absorption
spectra of all these complexes are similar to that of [Cp*Rh-
(bpy)Cl]+.47,48 The [Cp′Rh(bpy)Br]+ complexes (6a–e) have distinctive
absorption bands around 400 and 305 nm in the UV/Vis spectra
which may be attributed to a LMCT [π(Cp′) → d(RhIII)] and MLCT
(metal to bipyridine), respectively.49
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Table 3 Electrochemical propertiesa and UV/Vis absorption data of the rhodium complexes
RhIII/I
bpy0/˙−
E1/2 b/V
bpy˙−/2−
Epc/V
UV/Vis
(λmax/nm)
Complex
E1/2 b/V
ΔEp/V
ΔEp/V
[Cp*Rh(bpy)Cl]+
−0.78
−0.51
−0.45
−0.56
−0.52
−0.64
0.11
0.08
0.07
0.08
0.09
0.08
−2.23
−1.95
−1.89
−1.95
−1.88
−1.97
0.18
0.10
0.10
0.11
0.11
0.10
—
380, 309, 301
399, 313, 305
409, 313, 305
393, 313, 305
410, 304
6a
6b
6c
6d
6e
−2.40
−2.39
−2.39
−2.35
−2.42
393, 313, 306
b
a The data were obtained from CV experiments in 0.1 M TBAPF6/CH3CN at a scan rate of 100 mV s−1. All potentials are reported vs. SCE. E1/2
=
(Epa + Epc)/2 where Epa and Epc are the anodic and cathodic peak potentials, respectively.
4. Hydrogenation of ketones with complexes 6a–e
under the same conditions. For the hydrogenation of aceto-
phenone (reaction B), all the complexes 6 gave good to high
yields (77–95%). The different activity of complexes 6a–e for
the different substrates may be due to the influence of the sub-
stituents on the Cp′ rings. In other words, the bulky substitu-
ents on the Cp ring may affect the accessibility of the aryl and
alkyl ketones to the metal center and thus influence the cataly-
tic process.
With these complexes in hand, we examined their catalytic
activity in the hydrogenation of ketones with H2 in MeOH in
the presence of KOH. The yields were strongly affected by the
amount of base. The best results were obtained using 0.2
equiv. of KOH. The results of the reaction under the optimized
conditions are summarized in Table 4. Both of the reactions
gave no product without catalyst (entry 1). [Cp*Rh(bpy)Cl]ClO4
showed high activity for both cyclohexanone and acetophe-
none (entry 2). It is noteworthy that chloro Rh complex 3
showed similar activity with the bromo analog 6a for reaction
A, but better performance than 6a for reaction B (entry 3 vs.
entry 4). These results suggest that the halogen ligand might
play a role in its activity to different substrate. For the hydro-
genation of cyclohexanone (reaction A), all the complexes 6
showed high yields (86–99%) except 6c (64%). Interestingly,
when acetophenone was used, 6c gave a high yield of 89%
Conclusions
The present work provides a method for convenient and
efficient syntheses of multi-substituted cyclopentadienyl
rhodium dibromides, [Cp′RhBr2]2, which can be used as useful
starting materials for various functionalized half-sandwich
rhodium complexes. Using the complexes [Cp′RhBr2]2, we syn-
thesized a series of highly functionalized complexes [Cp′Rh-
(bpy)X]+ which were fully characterized by NMR, ESI-MS and
elemental analysis. These novel complexes can catalyze the
hydrogenation of alkyl and aryl ketones with good to high
yields. All the experimental data from spectroscopy (NMR, UV/
Vis), electrochemistry, structure and catalytic activity demon-
strated a significant substituent effect. Further studies on
related catalytic reaction with these new complexes are now in
progress.
Table 4 Hydrogenation of cyclohexanone in MeOH catalyzed by [Cp*Rh(bpy)
Cl]Cl, 3 and 6a–ea
Experimental section
General
All manipulations were carried out under an atmosphere of
argon. All melting points were measured on a Mettler FP62
and are uncorrected. UV spectra were recorded on a JASCO
V-550 spectrometer. IR spectra were recorded on a JASCO FT/
IR-5300 spectrometer. 1H NMR spectra were measured on a
Varian Gemini 300BB spectrometer, using TMS as the internal
standard. 13C NMR were recorded on the spectrometer using
solvent peak (CDCl3: δ 77.0) as a reference. Mass spectra were
collected on a Hitachi M-80B spectrometer. Fast atom bom-
bardment mass spectra (FAB) were recorded on a JEOL
JMS-DX303. Elemental analyses were carried out on an Eager
200 instrument. Preparative chromatography columns were
Yield of
reaction A/%
Yield of
reaction B/%
Entry
Complex
1
2
3
4
5
6
7
8
—
0
99
90
91
93
64
86
99
0
97
95
81
95
89
77
92
[Cp*Rh(bpy)Cl]+
3
6a
6b
6c
6d
6e
a The reaction was carried out with catalyst (2.5 μmol), cyclohexanone
(0.25 mmol) and 1 M KOH (50 μl) in MeOH (2 ml) under 3 MPa of H2
at 60 °C for 6 h.
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packed with aluminum oxide (activated, neutral, Brockmann I, Preparation of complexes 4a–e
ca. 150 mesh). CV was carried out on a BAS Inc., Electrochemi-
cal Analyzer, ALS Model 624D using a Ag/Ag+ reference elec- (1,5-Cyclooctadiene)(η5-1-ethoxycarbonyl-2,4-dimethylcyclopenta-
trode (the electrolyte consists of 0.01 M AgNO3, 0.1 M dienyl)rhodium (4a): to a solution of 1a (138 mg, 0.84 mmol)
tetrabutylammonium perchlorate (TBAP) dissolved in aceto- in MeOH (15 ml) was added [Rh(cod)Cl]2 (187 mg, 0.38 mmol)
nitrile), glassy carbon working electrode and platinum wire and Na2CO3 (190 mg). After the mixture was stirred at room
auxiliary electrode in anhydrous acetonitrile containing 0.1 M temperature for 5 h, the solvent was removed under reduced
tetrabutylammonium hexafluorophosphate (TBAPF6) as a sup- pressure. Diethyl ether (10 ml) was added to the residue. After
porting electrolyte, and the CH3CN solutions were degassed filtration, the solvent of the filtrate was removed in vacuo. The
with argon for approximately 10 min before data collection. All residue was purified by short column chromatography on
voltammograms were obtained with a scan rate of 100 mV s−1 alumina using diethyl ether as an eluent to give 4a (262 mg,
at room temperature. Ferrocene was employed as an internal 92%) as a yellow oil. IR (neat) 1701, 1412 cm−1 1H NMR
;
standard, and its Fe(II/III) half-wave potential (E1/2) was taken to (300 MHz, CDCl3) δ 5.31 (s, 1H, H of Cp′), 5.25 (d, J = 2.2 Hz,
be +0.40 V vs. SCE. GC analysis was performed on a 1H, H of Cp′), 4.35–4.18 (m, 2H, OCH2CH3), 3.92–3.78 (m, 2H,
SHIMADZU gas chromatograph GC2014 using an external HCvC of cod), 3.41–3.32 (m, 2H, HCvC of cod), 2.23–2.15 (m,
standard method. THF was distilled from sodium benzophe- 4H, CH2 of cod), 1.98–1.88 (m, 4H, CH2 of cod), 1.87 (s, 3H,
none ketyl. Aqueous solutions were degassed prior to use. Me of Cp′), 1.86 (s, 3H, Me of Cp′), 1.34 (t, J = 7.1 Hz, 3H,
RhCl3·3H2O and [Rh(cod)Cl]2 were commercially available OCH2CH3); 13C NMR (75 MHz, CDCl3) δ 166.10 (CvO), 103.06
from Kanto Chemical Co. and were used without further (d, JRh–C = 3.4 Hz, C of Cp′), 100.89 (d, JRh–C = 3.4 Hz, C of Cp′),
purification.
94.42 (d, JRh–C = 4.0 Hz, C of Cp′), 89.62 (C of Cp′), 88.56 (d,
Warning! All the perchlorate compounds used in this JRh–C = 4.0 Hz, C of Cp′), 72.40 (d, JRh–C = 13.7 Hz, CH of cod),
study are potentially explosive and must be handled with 67.27 (d, JRh–C = 13.7 Hz, CH of cod), 59.26 (CH2CH3), 32.23,
great care.
32.12 (CH2 of COD), 14.52, 12.76, 11.94; HRMS Calcd for
C18H25O2Rh (M+) 376.0908, found 376.0996; Anal. Calcd for
C18H25O2Rh: H, 6.70; C, 57.45. Found: H, 6.74; C, 57.60.
(1,5-Cyclooctadiene)(η5-1-ethoxycarbonyl-2-methyl-4-phenyl-
cyclopentadienyl)rhodium (4b): in the same manner as
Preparation of [(η5-1-ethoxycarbonyl-2,4-dimethylcyclopenta-
dienyl)(2,2′-bipyridine)chlororhodium]-perchlorate (3)
A mixture of RhCl3·3H2O (186 mg, 0.71 mmol) and cyclopenta- described for the preparation of complex 4a, 1b (139 mg,
diene 1a (130 mg, 0.78 mmol) in EtOH (10 ml) was refluxed 0.57 mmol) was reacted with [Rh(cod)Cl]2 (130 mg,
under Ar for 5 h to give a precipitate as a dark red solid. After 0.26 mmol) and Na2CO3 (130 mg) in MeOH (15 ml) to give 4b
cooling, to the suspension was added 2,2′-bipyridine (110 mg, (226 mg, 98%) as a yellow needle crystal; mp 98.8–99.4 °C
0.71 mg) to give a clear yellow solution. After stirring at room (recrystallization from petroleum ether); IR (KBr) 1686, 1601,
temperature for 3 h, the solution was filtered to remove the 1410 cm−1 1H NMR (400 MHz, CDCl3) δ 7.38 (tt, J = 7.3,
;
insoluble materials. Addition of excess LiClO4 (85 mg, 1.4 Hz, 2H, Ph), 7.30 (dt, J = 7.3, 1.4 Hz, 2H, Ph), 7.19 (tt, J =
80 mmol) to the filtrate gave a yellow solid. The resultant solid 7.3, 1.4 Hz, 1H, Ph), 5.77 (d, J = 2.1 Hz, 1H, 3-H of Cp′), 5.76
was recrystallized by dissolving in acetonitrile (3 ml) and then (d, J = 2.1 Hz, 1H, 5-H of Cp′), 4.40–4.24 (m, 2H, OCH2CH3),
adding diethyl ether to give complex 3 (233 mg, 60%) as a 3.98–3.90 (m, 2H, HCvC of cod), 3.29–3.20 (m, 2H, HCvC of
yellow solid. mp >200 °C (dec.); IR (KBr) 1724, 1606, cod), 2.22–2.03 (m, 4H, CH2 of cod), 2.00 (s, 3H, Me of Cp′),
1448 cm−1
0.7 Hz, 1H, 6-H of bpy), 9.09 (dt, J = 5.8, 0.7 Hz, 1H, 6′-H of OCH2CH3); 13C NMR (100 MHz, CDCl3) δ 165.87 (CvO),
bpy), 8.40 (bd, J = 8.2 Hz, 2H, 3,3′-H of bpy), 8.26 (dt, J = 1.1, 134.00, 128.56, 126.63, 125.39 (C of Ph), 106.28 (d, JRh–C
;
1H NMR (400 MHz, CD3CN) δ 9.23 (dt, J = 5.8, 1.98–1.82 (m, 4H, CH2 of cod), 1.38 (t, J = 7.1 Hz, 3H,
=
8.0 Hz, 2H, 4,4′-H of bpy), 7.80 (dt, J = 1.3, 5.8 Hz, 1H, 5′-H of 3.0 Hz, C of Cp′), 102.49 (d, JRh–C = 3.8 Hz, C of Cp′), 91.61 (d,
bpy), 7.78 (dt, J = 1.3, 5.8 Hz, 1H, 5-H of bpy), 6.13 (d, J = JRh–C = 4.6 Hz, C of Cp′), 91.00 (d, JRh–C = 3.8 Hz, C of Cp′),
1.3 Hz, 1H, 5-H of Cp′), 5.61 (d, J = 1.3 Hz, 1H, 3-H of Cp′), 84.79 (d, JRh–C = 3.8 Hz, C of Cp′), 74.16 (d, JRh–C = 13.7 Hz, CH
4.25 (q, J = 7.1 Hz, 2H, CH2CH3), 2.14 (s, 3H, 2-Me of Cp′), 1.86 of cod), 68.12 (d, JRh–C = 13.7 Hz, CH of cod), 59.58 (CH2CH3),
(s, 3H, 4-Me of Cp′), 1.23 (t, J = 7.1 Hz, 3H, CH2CH3); 13C NMR 32.16, 31.94 (CH2 of cod), 14.68 (CH2CH3), 12.43 (2-Me of Cp′);
(100 MHz, CD3CN) δ 163.05 (CvO), 154.13 (6-C of bpy), 153.96 HRMS Calcd for C23H27O2Rh (M+) 438.1065, found 438.1057;
(2′-C of bpy), 153.56 (2-C of bpy), 152.72 (6′-C of bpy), 139.95, Anal. Calcd for C23H27O2Rh: H, 6.21; C, 63.02. Found: H, 6.20;
139.92 (4,4′-C of bpy), 127.58, 127.55 (5,5′-C of bpy), 123.47, C, 63.06.
123.40 (3,3′-C of bpy), 115.73 (d, JRh–C = 6.1 Hz, 2-C of Cp′),
(1,5-Cyclooctadiene)(η5-2-ethoxy-1-ethoxycarbonyl-4-methyl-
107.97 (d, JRh–C = 6.9 Hz, 4-C of Cp′), 87.44 (d, JRh–C = 7.6 Hz, cyclopentadienyl)rhodium (4c): to a solution of 1c (150 mg,
5-C of Cp′), 82.27 (d, JRh–C = 6.8 Hz, 3-C of Cp′), 76.45 (d, 0.76 mmol) in 10 ml of THF at −78 °C was added n-BuLi
JRh–C = 9.1 Hz, 1-C of Cp′), 61.60 (CH2CH3), 12.44 (CH2CH3), (0.48 ml, 1.6 M in hexane, 0.76 mmol) dropwise via a syringe.
11.26 (2-Me of Cp′), 10.64 (4-Me of Cp′); FAB-MS: m/z 459 After stirring for 20 min, a solution of [Rh(cod)Cl]2 (172 mg,
[M − ClO4]+; Anal. Calcd for C20H21Cl2N2O6Rh: H, 3.79; C, 0.35 mmol) in THF (10 ml) was added to the reaction mixture.
42.96; N, 5.01. Found: H, 3.63; C, 43.34; N, 4.99.
After 24 h of stirring at room temperature, the solvent was
9632 | Dalton Trans., 2013, 42, 9628–9636
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removed under reduced pressure and the residue was purified Hz, CH of cod), 66.14 (OCH2CH3), 59.04 (CO2CH2CH3), 32.89,
by short column chromatography on alumina using diethyl 31.53 (CH2 of cod), 23.25, 23.10, 22.97, 22.79, 22.65 (CH2),
ether as an eluent to give 4c (268 mg, 87%) as a yellow oil: IR 14.70, 14.57, 13.89; HRMS Calcd for
C
22H31O3Rh (M+)
1
(neat) 1707, 1449 cm−1; H NMR (300 MHz, CDCl3) δ 5.27 (d, 446.1327, found 446.1283.
J = 2.0 Hz, 1H, H of Cp′), 5.06 (d, J = 2.0 Hz, 1H, H of Cp′),
4.38–4.18 (m, 2H, CO2CH2CH3), 4.00–3.92 (m, 2H, HCvC of
Typical procedure for preparation of complexes 5a–e
cod), 3.92–3.82 (m, 1H, OCH2CH3), 3.70–3.58 (m, 1H, A solution of complex 4 (0.50 mmol) in diethyl ether (10 ml)
OCH2CH3), 3.56–3.46 (m, 2H, HCvC of cod), 2.30–2.12 (m, 4H, was cooled in an ice bath. After addition of bromine (0.5 ml),
CH2 of cod), 2.08–1.84 (m, 4H, CH2 of cod), 1.84 (s, 3H, 4-Me), the ice bath was removed and the mixture was stirred at room
1.33 (t, J = 7.1 Hz, 3H, CO2CH2CH3), 1.32 (t, J = 7.1 Hz, 3H, temperature for 10 min. The solvent was then removed under
OCH2CH3); 13C NMR (75 MHz, CDCl3) δ 164.78 (CvO), 135.61, reduced pressure. The residue was washed with hexane and
96.75 (d, JRh–C = 4.0 Hz, C of Cp′), 81.97 (d, JRh–C = 4.6 Hz, C of dried in vacuo to give the rhodium dimer 5 as a dark red
Cp′), 79.27 (d, JRh–C = 4.5 Hz, C of Cp′), 77.28 (d, JRh–C = 2.9 Hz, powder. An analytical sample was recrystallized by dissolving
C of Cp′), 72.02 (d, JRh–C = 14.2 Hz, CH of cod), 67.32 (d, JRh–C
=
in acetonitrile (3 ml) and then adding diethyl ether.
13.7 Hz, CH of cod), 66.345 (OCH2CH3), 59.32 (CO2CH2CH3),
Dibromo(η5-1-ethoxycarbonyl-2,4-dimethylcyclopentadienyl)-
32.44, 31.93 (CH2 of cod), 14.68 (OCH2CH3), 14.54 rhodium dimer (5a): IR (KBr) 1730, 1425 cm−1 1H NMR
;
(CO2CH2CH3), 13.06 (4-Me of Cp′); HRMS Calcd for (300 MHz, CD3CN) δ 5.81 (s, 1H, H of Cp′), 5.31 (s, 1H, H of
C19H27O3Rh (M+) 406.1014, found 406.1001.
Cp′), 4.40–4.21 (m, 2H, OCH2CH3), 2.18 (s, 3H, Me of Cp′), 1.99
(1,5-Cyclooctadiene)(η5-2-ethoxy-1-ethoxycarbonyl-4-ethylthio- (s, 3H, Me of Cp′), 1.34 (t, J = 7.1 Hz, 3H, OCH2CH3); FAB-MS:
cyclopentadienyl)rhodium (4d): in the same manner as m/z 775 [M − Br]+; Anal. Calcd for C20H26Br4O4Rh2: H, 3.06; C,
described for the preparation of complex 4c, 1d (125 mg, 28.07; Br, 37.34. Found: H, 2.99; C, 28.10; Br, 37.44.
0.52 mmol) was reacted with [Rh(cod)Cl]2 (116 mg,
0.23 mmol) and n-BuLi (0.32 ml, 1.6 M in hexane, 0.52 mmol) dienyl)rhodium dimer (5b): IR (neat) 1725, 1468 cm−1
to give 4d (195 mg, 92%) as a yellow oil; IR (neat) 1711, NMR (300 MHz, CD3CN) δ 7.81–7.74 (bd, J = 6.8 Hz, 2H, Ph),
1446 cm−1 1H NMR (300 MHz, CDCl3) δ 5.30 (d, J = 2.0 Hz, 7.58–7.45 (m, 3H, Ph), 6.56 (bs, 1H, H of Cp′), 6.05 (bs, 1H, H
Dibromo(η5-1-ethoxycarbonyl-2-methyl-4-phenylcyclopenta-
1H
;
;
1H, H of Cp′), 5.17 (d, J = 2.0 Hz, 1H, H of Cp′), 4.41–4.19 (m, of Cp′), 4.41–4.28 (m, 2H, OCH2CH3), 2.30 (s, 3H, Me of Cp′),
2H, CO2CH2CH3), 4.16–4.07 (m, 2H, HCvC of cod), 3.94–3.83 1.37 (t, J = 7.1 Hz, 3H, OCH2CH3); FAB-MS: m/z 900 [M − Br]+;
(m, 1H, OCH2CH3), 3.75–3.66 (m, 2H, HCvC of cod), 3.66–3.56 Anal. Calcd for C30H30Br4O4Rh2: H, 3.09; C, 36.77. Found: H,
(m, 1H, OCH2CH3), 2.73 (q, J = 7.4 Hz, 2H, SCH2CH3), 3.01; C, 36.85.
2.30–2.12 (m, 4H, CH2 of cod), 2.06–1.85 (m, 4H, CH2 of cod),
Dibromo(η5-2-ethoxy-1-ethoxycarbonyl-4-methylcyclopenta-
1.34 (t, J = 7.1 Hz, 3H, CO2CH2CH3), 1.33 (t, J = 7.1 Hz, 3H, dienyl)rhodium dimer (5c): IR (neat) 1718, 1514 cm−1; H NMR
OCH2CH3), 1.28 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (300 MHz, CD3CN) δ 5.70 (bd, J = 1.6 Hz, 1H, H of Cp′), 5.18 (bs,
(75 MHz, CDCl3) δ 164.00 (CvO), 136.70 (C of Cp′), 92.50 (d, 1H, H of Cp′), 4.36–4.16 (m, 4H, OCH2CH3), 1.99 (s, 3H, Me of
JRh–C = 4.6 Hz, C of Cp′), 85.51 (d, JRh–C = 4.6 Hz, C of Cp′), Cp′), 1.41 (t, J = 7.1 Hz, 3H, CO2CH2CH3), 1.32 (t, J = 7.1 Hz, 3H,
81.48 (C of Cp′), 80.17 (d, JRh–C = 2.9 Hz, C of Cp′), 72.64 (d, OCH2CH3); FAB-MS: m/z 834 [M − Br]+; Anal. Calcd for
JRh–C = 14.2 Hz, CH of cod), 68.75 (d, JRh–C = 13.5 Hz, CH of C22H30Br2O6Rh2: H, 3.30; C, 28.85. Found: H, 3.27; C, 29.09.
1
cod), 66.63 (OCH2CH3), 59.54 (CO2CH2CH3), 32.11, 32.01 (CH2
Dibromo(η5-2-ethoxy-1-ethoxycarbonyl-4-ethylthiocyclopenta-
of cod), 31.50, 31.37 (SCH2CH3), 14.83 (OCH2CH3), 14.61 dienyl)rhodium dimer (5d): IR (neat) 1726, 1512 cm−1; 1H NMR
(CO2CH2CH3), 14.50 (SCH2CH3); HRMS Calcd for (300 MHz, CD3CN) δ 5.70 (bs, 1H, H of Cp′), 5.50 (bs, 1H, H of
C20H29O3RhS (M+) 452.0891, found 452.0821; Anal. Calcd for Cp′), 4.46–4.10 (m, 4H, OCH2CH3), 3.18–2.97 (m, 2H, SCH2CH3),
C20H29O3RhS: H, 6.46; C, 53.10. Found: H, 6.50; C, 53.09.
1.42 (t, J = 7.1 Hz, 3H, CO2CH2CH3), 1.39 (t, J = 7.4 Hz, 3H,
(1,5-Cyclooctadiene)(η5-2-ethoxy-1-ethoxycarbonyltetrahydroin- SCH2CH3), 1.32 (t, J = 7.1 Hz, 3H, OCH2CH3); FAB-MS: m/z 1006
denyl)rhodium (4e): in the same manner as described for the [M]+, 928 [M − Br]+; Anal. Calcd for C24H34Br4O6Rh2S2: H, 3.40;
preparation of complex 4c, 1e (150 mg, 0.64 mmol) was C, 28.59; Br, 31.70. Found: H, 3.30; C, 28.41; Br. 31.87.
reacted with [Rh(cod)Cl]2 (157 mg, 0.32 mmol) and n-BuLi
(0.45 ml, 1.6 M in hexane, 0.72 mmol) to give 4e (197 mg, rhodium dimer (5e): IR (neat) 1723, 1512 cm−1
70%) as a yellow oil; IR (neat) 1690, 1439 cm−1 1H NMR (300 MHz, CD3CN) δ 5.11 (bs, 1H, H of Cp′), 4.27 (q, J = 7.1 Hz,
Dibromo(η5-2-ethoxy-1-ethoxycarbonyltetrahydroindenyl)-
1H NMR
;
;
(300 MHz, CDCl3) δ 5.22 (bs, 1H, H of Cp′), 4.31 (q, J = 7.1 Hz, 2H, CO2CH2CH3), 4.30–4.18 (m, 1H, OCH2CH3), 4.16–4.05 (m,
2H, CO2CH2CH3), 3.86–3.74 (m, 1H, OCH2CH3), 3.70–3.62 (m, 1H, OCH2CH3), 2.85–1.60 (m, 8H), 1.40 (t, J = 7.1 Hz, 3H,
2H, HCvC of cod), 3.64–3.52 (m, 1H, OCH2CH3), 3.52–3.42 (m, CO2CH2CH3), 1.31 (t, J = 7.1 Hz, 3H, OCH2CH3); FAB-MS: m/z
2H, HCvC of cod), 2.68–0.80 (m, 16H), 1.35 (t, J = 7.1 Hz, 3H, 915 [M − Br]+; Anal. Calcd for C28H38Br4O6Rh2: H, 3.85; C,
CO2CH2CH3), 1.28 (t, J = 7.1 Hz, 3H, OCH2CH3); 13C NMR 33.76. Found: H, 3.78; C, 33.47.
(75 MHz, CDCl3) δ 165.58 (CvO), 133.58 (d, JRh–C = 3.4 Hz, C
of Cp′), 128.06 (C of Cp′), 99.11 (d, JRh–C = 4.6 Hz, C of Cp′),
Typical procedure for preparation of complexes 6a–e
98.43 (d, JRh–C = 4.6 Hz, C of Cp′), 73.37 (d, JRh–C = 13.7 Hz, CH To a suspension of complex 5 (0.2 mmol) in MeOH (10 ml)
of cod), 73.67 (d, JRh–C = 3.4 Hz, C of Cp′), 70.26 (d, JRh–C = 13.7 was added 2,2′-bipyridine (0.42 mmol). After stirring at room
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Dalton Transactions
temperature for
3
h,
a
solution of lithium perchlorate 3.93–3.80 (m, 1H, OCH2CH3), 1.88 (s, 3H, 4-Me of Cp′), 1.35 (t,
(0.42 mmol) in MeOH (10 ml) was added to the reaction J = 7.1 Hz, 3H, CO2CH2CH3), 1.33 (t, J = 6.9 Hz, 3H, OCH2CH3);
mixture. Precipitated solid was collected by filtration and dried 13C NMR (100 MHz, CD3CN) δ 162.52 (CvO), 154.11 (2′-C of
under vacuum to give the rhodium complexes 6 as a yellow bpy), 153.62 (2-C of bpy), 152.35 (6-C of bpy), 152.21 (6′-C of
solid. An analytical sample was recrystallized by dissolving in bpy), 147.04 (d, JRh–C = 3.8 Hz, 2-C of Cp′), 139.77, 139.71 (4,4′-
acetonitrile (3 ml) and then adding diethyl ether.
C of bpy), 127.43 (5-C of bpy), 127.01 (5′-C of bpy), 123.38 (3′-C
[(η5-1-Ethoxycarbonyl-2,4-dimethylcyclopentadienyl)(2,2′- of bpy), 122.96 (3-C of bpy), 101.78 (d, JRh–C = 7.6 Hz, 4-C of
bipyridine)bromorhodium]perchlorate (6a): IR (neat) 1725, Cp′), 83.53 (d, JRh–C = 7.6 Hz, 3-C of Cp′), 70.22 (OCH2CH3),
1448 cm−1 1H NMR (400 MHz, CD3CN) δ 9.20 (td, J = 0.7, 64.08 (d, JRh–C = 6.9 Hz, 5-C of Cp′), 61.45 (d, JRh–C = 8.4 Hz,
;
5.6 Hz, 1H, 6-H of bpy), 9.06 (td, J = 0.7, 5.6 Hz, 1H, 6′-H of 1-C of Cp′), 61.33 (CO2CH2CH3), 12.77 (CO2CH2CH3), 12.38
bpy), 8.40 (bd, J = 7.7 Hz, 2H, 3,3′-H of bpy), 8.25 (dt, J = 1.3, (OCH2CH3), 10.77 (4-Me of Cp′); UV λmax (MeCN) 393 (2400),
7.7 Hz, 2H, 4,4′-H of bpy), 7.78 (dt, J = 1.3, 5.6 Hz, 1H, 5′-H of 313 (20 200), 304 nm (sh); ES-MS: m/z 533.75 [M − ClO4]+;
bpy), 7.77 (dt, J = 1.3, 5.6 Hz, 1H, 5-H of bpy), 6.13 (d, J = Anal. Calcd for C21H23BrClN2O7Rh: H, 3.66; C, 39.80; N, 4.42.
1.3 Hz, 1H, 5-H of Cp′), 5.58 (d, J = 1.3 Hz, 1H, 3-H of Cp′), Found: H, 3.61; C, 39.93; N, 4.37.
4.26 (dq, J = 1.5, 7.1 Hz, 2H, CH2CH3), 2.23 (s, 3H, 2-Me of
[(η5-2-Ethoxy-1-ethoxycarbonyl-4-ethylthiocyclopentadienyl)-
Cp′), 1.94 (s, 3H, 4-Me of Cp′), 1.24 (t, J = 7.1 Hz, 3H, CH2CH3); (2,2′-bipyridine)bromorhodium]perchlorate (6d): IR (neat)
1
13C NMR (100 MHz, CD3CN) δ 163.00 (CvO), 154.52 (6-C of 1726, 1451 cm−1; H NMR (400 MHz, CD3CN) δ 9.15 (dd, J =
bpy), 153.94 (2′-C of bpy), 153.53 (2-C of bpy), 153.17 (6′-C of 0.7, 5.5 Hz, 1H, 6-H of bpy), 9.06 (bd, J = 5.0 Hz, 1H, 6′-H of
bpy), 139.90 (4,4′-C of bpy), 127.52, 127.47 (5,5′-C of bpy), bpy), 8.43 (dd, J = 4.0, 8.0 Hz, 2H, 3,3′-H of bpy), 8.27 (tt, J =
123.52, 123.50 (3,3′-C of bpy), 115.47 (d, JRh–C = 6.1 Hz, 2-C of 0.7, 7.7 Hz, 1H, 4,4′-H of bpy), 7.92–7.82 (dd, J = 5.5, 7.1 Hz,
Cp′), 107.44 (d, JRh–C = 6.9 Hz, 4-C of Cp′), 88.30 (d, JRh–C
=
2H, 5,5′-H of bpy), 6.03 (d, J = 2.0 Hz, 1H, 3-H of Cp′), 5.63 (d,
6.9 Hz, 5-C of Cp′), 83.13 (d, JRh–C = 6.9 Hz, 3-C of Cp′), 76.80 J = 2.0 Hz, 1H, 5-H of Cp′), 4.39 (q, J = 7.1 Hz, 2H,
(d, JRh–C = 9.0 Hz, 1-C of Cp′), 61.53 (CH2CH3), 12.52 (CH2CH3), CO2CH2CH3), 4.14–3.98 (m, 1H, OCH2CH3), 3.68–3.56 (m, 1H,
11.79 (2-Me of Cp′), 11.09 (4-Me of Cp′); ES-MS: m/z 503.74 OCH2CH3), 2.90–2.72 (m, 2H, SCH2CH3), 1.37 (t, J = 7.1 Hz,
[M − ClO4]+; UV λmax (MeCN) 399 (2 300), 313 (18 300), 305 nm 3H, CO2CH2CH3), 1.28 (t, J = 7.1 Hz, 3H, OCH2CH3), 1.27 (t, J =
(sh); Anal. Calcd for C20H21BrClN2O6Rh: H, 3.51; C, 39.79; N, 7.4 Hz, 3H, SCH2CH3); 13C NMR (100 MHz, CD3CN) δ 162.43
4.64. Found: H, 3.40; C, 39.92; N, 4.50.
(CvO), 154.26, 153.23 (2,2′-C of bpy), 151.27, 149.37 (6,6′-C of
[(η5-1-Ethoxycarbonyl-2-methyl-4-phenylcyclopentadienyl)- bpy), 144.73 (d, JRh–C = 5.0 Hz, 2-C of Cp′), 139.97, 139.83
(2,2′-bipyridine)bromorhodium]perchlorate (6b): IR (neat) (4,4′-C of bpy), 127.42, 126.87 (5,5′-C of bpy), 123.21, 122.65
1719, 1449 cm−1 1H NMR (300 MHz, CD3CN) δ 9.05 (bd, J = (3,3′-C of bpy), 114.25 (d, JRh–C = 6.8 Hz, 4-C of Cp′), 74.73(d,
;
5.5 Hz, 1H, 6-H of bpy), 8.53 (bd, J = 5.7 Hz, 1H, 6′-H of bpy), JRh–C = 8.3 Hz, 3-C of Cp′), 70.15 (OCH2CH3), 61.77 (d, JRh–C
=
8.34 (bd, J = 7.6 Hz, 1H, 3-H of bpy), 8.28 (bd, J = 7.5 Hz, 1H, 7.6 Hz, 5-C of Cp′), 61.37 (CO2CH2CH3), 60.36 (d, JRh–C = 9.1
3′-H of bpy), 8.23–8.12 (m, 2H, 4,4′-H of bpy), 7.70–7.35 (m, Hz, 1-C of Cp′), 25.37 (SCH2CH3), 12.84 (CO2CH2CH3), 12.27,
7H, 5,5′-H of bpy, Ph), 6.87 (d, J = 1.9 Hz, 1H, H of Cp′), 6.27 11.89 (CH2CH3); UV λmax (MeCN) 410 (sh), 304 nm (19 000);
(d, J = 1.9 Hz, 1H, H of Cp′), 4.45 (q, J = 7.1 Hz, 2H, OCH2CH3), ES-MS: m/z 579.63 [M
−
ClO4]+; Anal. Calcd for
2.36 (s, 3H, Me of Cp′), 1.41 (t, J = 7.1 Hz, 3H, OCH2CH3); 13C C22H25BrClN2O7RhS: H, 3.71; C, 38.87; N, 4.12; S, 4.72. Found:
NMR (75 MHz, CD3CN) δ 163.39 (CvO), 154.08 (2′-C of bpy), H, 3.65; C, 38.59; N, 4.19; S, 4.51.
153.72 (6-C of bpy), 153.31 (2-C of bpy), 152.40 (6-C of bpy),
[(η5-2-Ethoxy-1-ethoxycarbonyltetrahydroindenyl)(2,2′-bipyri-
140.10 (4,4′-C of bpy), 130.86, 128.94 (C of Ph), 127.68 (5′-C of dine)bromorhodium]perchlorate (6e): IR (neat) 1723,
1
bpy), 127.42 (C of Ph), 127.11 (5-C of bpy), 125.07, 123.62 (C of 1451 cm−1; H NMR (400 MHz, CD3CN) δ 9.26 (bd, J = 5.5 Hz,
Ph), 123.17 (3,3′-C of bpy), 115.86 (d, JRh–C = 5.6 Hz, 2-C of 1H, 6-H of bpy), 8.96 (bd, J = 5.5 Hz, 1H, 6′-H of bpy), 8.40 (bd,
Cp′), 103.82, (4-C of Cp′) 86.31 (d, JRh–C = 6.8 Hz, 5-C of Cp′), J = 8.2 Hz, 2H, 3,3′-H of bpy), 8.30–8.23 (m, 2H, 4,4′-H of bpy),
81.57 (d, JRh–C = 6.8 Hz, 3-C of Cp′), 76.15 (1-C of Cp′) 61.81 7.83 (bt, J = 6.7 Hz, 2H, 5,5′-H of bpy), 5.43 (s, 1H, 3-H of Cp′),
(OCH2CH3), 12.74 (OCH2CH3), 11.96 (2-Me of Cp′); UV λmax 4.41 (q, J = 7.1 Hz, 2H, CO2CH2CH3), 4.20–4.06 (m, 1H,
(MeCN) 409 (3300), 313 (18 000), 305 nm (16 400); FAB-MS: m/z OCH2CH3), 3.98–3.82 (m, 1H, OCH2CH3), 2.61–2.35 (m, 2H),
567 [M − ClO4]+; Anal. Calcd for C25H23BrClN2O6Rh: H, 3.48; 2.22–1.90 (m, 2H), 1.72–1.60 (m, 2H), 1.52–1.30 (m, 2H), 1.38
C, 45.11; N, 4.21. Found: H, 3.54; C, 45.40; N, 4.04.
(t, J = 7.1 Hz, 3H, CO2CH2CH3), 1.32 (t, J = 7.1 Hz, 3H,
[(η5-2-Ethoxy-1-ethoxycarbonyl-4-methylcyclopentadienyl)- OCH2CH3); 13C NMR (100 MHz, CD3CN) δ 163.42 (CvO),
(2,2′-bipyridine)bromorhodium]perchlorate (6c): IR (neat) 153.91, 153.43 (2,2′-C of bpy), 152.56 (2-C of Cp′), 151.32 (6,6′-C
1713, 1451 cm−1 1H NMR (400 MHz, CD3CN) δ 9.20 (bd, J = of bpy), 139.57 (4,4′-C of bpy), 127.72, 127.62 (5,5′-C of bpy),
;
5.5 Hz, 1H, 6-H of bpy), 8.96 (bd, J = 5.5 Hz, 1H, 6′-H of bpy), 123.10, 122.88 (3,3′-C of bpy), 103.88 (d, JRh–C = 7.7 Hz, 4-C of
8.42 (bd, J = 8.2 Hz, 2H, 3,3′-H of bpy), 8.31–8.21 (m, 2H, 4,4′- Cp′), 99.22 (d, JRh–C = 8.1 Hz, 5-C of Cp′), 69.88 (OCH2CH3),
H of bpy), 7.84 (ddd, J = 7.7, 5.5, 1.3 Hz, 1H, 5-H of bpy), 7.76 61.23 (CO2CH2CH3), 59.54 (d, JRh–C = 7.7 Hz, 3-C of Cp′), 59.49
(ddd, J = 7.7, 5.5, 1.3 Hz, 1H, 5′-H of bpy), 6.04 (d, J = 1.6 Hz, (d, JRh–C = 8.1 Hz, 1-C of Cp′), 20.76, 19.76, 19.50, 19.48 (CH2),
1H, 3-H of Cp′), 5.52 (d, J = 1.6 Hz, 1H, 5-H of Cp′), 4.38 (q, J = 12.69 (CO2CH2CH3), 12.36 (OCH2CH3); UV λmax (MeCN) 393
7.1 Hz, 2H, CO2CH2CH3), 4.18–4.07 (m, 1H, OCH2CH3), (2000), 313 (17 000), 306 nm (sh); ES-MS: m/z 574.9 [M −
9634 | Dalton Trans., 2013, 42, 9628–9636
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ClO4]+; Anal. Calcd for C24H27BrClN2O7Rh: H, 4.04; C, 42.78; 16 M. Ito, N. Tejima, M. Yamamura, Y. Endo and T. Ikariya,
N, 4.16. Found: H, 3.98; C, 42.76; N, 4.17.
Organometallics, 2010, 29, 1886–1889.
17 A. P. da Costa, R. Lopes, J. o. M. S. Cardoso, J. A. Mata,
E. Peris and B. Royo, Organometallics, 2011, 30, 4437–4442.
18 S. K. S. Tse, T. Guo, H. H.-Y. Sung, I. D. Williams, Z. Lin
and G. Jia, Organometallics, 2009, 28, 5529–5535.
19 A. C. Esqueda, S. Conejero, C. Maya and E. Carmona, Orga-
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20 B. L. Conley, M. K. Pennington-Boggio, E. Boz and
T. J. Williams, Chem. Rev., 2010, 110, 2294–2312.
21 X.-L. Zheng and Y.-M. Zhang, Chin. J. Chem., 2003, 21,
1203–1205.
Typical procedure for the hydrogenation of ketones by
rhodium complexes
A degassed MeOH solution (2 ml) of the complex (2.5 μmol),
ketone (0.25 mmol), and 50 μl of 1 M KOH solution (50 μmol)
was added into a glass reactor and stirred vigorously under
3 MPa of H2 at 60 °C for 6 h. The reaction solution was ana-
lyzed by GC after the reaction to determine the yield.
22 H. Funami, H. Kusama and N. Iwasawa, Angew. Chem., Int.
Ed., 2007, 46, 909–911.
Acknowledgements
23 Z. Wang, H. Fang and Z. Xi, Tetrahedron, 2006, 62, 6967–
6972.
24 C. Wang, G.-L. Mao, Z.-H. Wang and Z.-F. Xi, Eur. J. Org.
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Y.H. and W.-H.W. acknowledge JST, ACT-C for financial
support. J.T.M. and E.F. thank the U.S. Department of Energy
and its Division of Chemical Sciences, Geosciences, and Bio-
sciences, Office of Basic Energy Sciences for funding under
contract DE-AC02-98CH10886 with Brookhaven National Lab-
oratory. We thank Dr Midori Goto and Dr Hide Kambayashi
for X-ray crystallography.
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