Water-soluble phenanthroline complexes of rhodium, iridium and ruthenium for the regeneration of NADH in the enzymatic reduction of ketones

Article abstract of DOI:10.1002/ejic.200700505

The nicotinamide coenzyme NADH, consumed in enantioselective reduction of ketones catalysed by alcohol dehydrogenases, needs to be regenerated in order to maintain enzymatic activity. We therefore studied the catalytic potential of the cationic complexes [(η⁵-C₅Me₅) Rh(N∩N)Cl]⁺ (1: N∩N = 1,10-phenanthroline; 2: N∩N = 5-nitro-1,10-phenanthroline; 3: N∩N = 5-amino-1,10-phenanthroline), [(η⁵-C₅Me₅) Ir(N∩N)Cl]⁺ (4: N∩N = 5-nitro-1,10-phenanthroline) and [(η⁶-C ₆Me₆)Ru(N∩N)Cl]⁺ (5: N∩N = 5-nitro-1,10-phenanthroline), isolated as the water-soluble chloride salts, for transfer hydrogenation of NAD⁺ to give NADH in aqueous solution. The best results were obtained with rhodium complex 1, which gave catalytic turnover frequencies up to 2000 h^_1 in aqueous solution at pH 7 and 60°C with sodium formate as the hydrogen source. When this NADH-regenerating catalytic system is combined with NADH-dependent enzymes, it is possible to chemoenzymatically reduce prochiral ketones such as acetophenone or 4-phenylbutan-2-one with high enantioselectivity. Combination of horse liver alcohol dehydrogenase (HLADH) or alcohol dehydrogenase from Rhodococcus sp. (S-ADH) with 1/formate as the NADH-regenerating system resulted in ee values up to 98%, depending on the nature of the substrate and the enzyme. In order to explain the different catalytic activities, the electrochemical behaviour of complexes 1-5 has been studied. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700505

FULL PAPER
DOI: 10.1002/ejic.200700505
Water-Soluble Phenanthroline Complexes of Rhodium, Iridium and Ruthenium
for the Regeneration of NADH in the Enzymatic Reduction of Ketones
[a]
[a]
[b]
ˇ
ˇ
ˇ
Jérôme Canivet, Georg Süss-Fink,* and Petr Stepnicka
Keywords: Cationic complexes / Cofactor regeneration / Chemoenzymatic catalysis / Enantioselective catalysis / Transfer
hydrogenation
The nicotinamide coenzyme NADH, consumed in enantiose-
lective reduction of ketones catalysed by alcohol dehydroge-
formate as the hydrogen source. When this NADH-regener-
ating catalytic system is combined with NADH-dependent
nases, needs to be regenerated in order to maintain enzy- enzymes, it is possible to chemoenzymatically reduce prochi-
matic activity. We therefore studied the catalytic potential of
the cationic complexes [(η5-C5Me5)Rh(NʝN)Cl]+ (1: NʝN =
1,10-phenanthroline; 2: NʝN = 5-nitro-1,10-phenanthroline;
ral ketones such as acetophenone or 4-phenylbutan-2-one
with high enantioselectivity. Combination of horse liver
alcohol dehydrogenase (HLADH) or alcohol dehydrogenase
from Rhodococcus sp. (S-ADH) with 1/formate as the NADH-
regenerating system resulted in ee values up to 98%, de-
pending on the nature of the substrate and the enzyme. In
order to explain the different catalytic activities, the electro-
chemical behaviour of complexes 1–5 has been studied.
3: NʝN
=
5-amino-1,10-phenanthroline), [(η5-C5Me5)
Ir(NʝN)Cl]+ (4: NʝN = 5-nitro-1,10-phenanthroline) and
[(η6-C6Me6)Ru(NʝN)Cl]+ (5: NʝN = 5-nitro-1,10-phenan-
throline), isolated as the water-soluble chloride salts, for
transfer hydrogenation of NAD+ to give NADH in aqueous
solution. The best results were obtained with rhodium com-
plex 1, which gave catalytic turnover frequencies up to
2000 h–1 in aqueous solution at pH 7 and 60 °C with sodium
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
lectivity. More than ten years ago Steckhan et al. intro-
duced the dicationic (aqua)(bipyridine)rhodium complex
[(η5-C5Me5)Rh(bipy)(OH2)]2+ as a catalyst for the regenera-
tion of NADH by using the formate anion as the hydrogen
source in aqueous solution.[30,31] In a pioneering paper,
Fishpp et al. extensively studied kinetic and mechanistic de-
tails of regioselective catalytic reduction by using a variety
of 3-pyridinium NAD+ models in the presence of [(η5-
Introduction
There is an increasing demand for enantiopure biolo-
gically active compounds and their precursors.[1] The transi-
tion-metal-based enantioselective hydrogenation or transfer
hydrogenation of ketones in organic solvents[2–10] as well as
in aqueous solutions[11–21] is one of the most commonly
used synthetic approaches. Biotransformations of organic
substrates by various enzymes have also found widespread
applications, particularly because of their capability to ef-
ficiently perform enantioselective transformations. The use
of redox enzymes for synthetic purposes, however, has been
limited by the need of cofactor regeneration.[22] Therefore,
practical methods for the regeneration of coenzyme 1,4-
NADH, the reduced form of nicotinamide adenine dinucle-
otide (NAD+), are still of significant importance in the field
of biocatalysis.
C5Me5)Rh(bipy)(OH2)]2+ [32–35]
This NADH-regenerating
.
catalytic system was applied to the coupled chemoenzym-
atic enantioselective transfer hydrogenation of ketones in
aqueous solution by combining NADH regeneration by an
organorhodium complex and enantioselective ketone re-
duction performed by an alcohol dehydrogenase (ADH).
Steckhan et al. described the transfer hydrogenation of 4-
phenylbutan-2-one to the corresponding alcohol using
ADH from horse liver with enantiomeric excesses up to
96%.[22] More recently, Schmid et al. reported a system
based on ADH from Thermus sp. coupled with [(η5-C5Me5)
Rh(bipy)(OH2)]2+-promoted regeneration of NADH, which
allowed the reduction of 3-methylcyclohexanone with an
enantiomeric excess up to 97%.[1]
Conversion of NAD+ to NADH by enzymatic,[23–26]
photo- or electrochemical[27–29] methods has been exten-
sively studied in order to increase the rate of cofactor regen-
eration while maintaining the necessary 1,4-dihydro regiose-
In this paper we report a series of water-soluble rhodium,
iridium and ruthenium complexes containing 1,10-phenan-
throline or its 5-substituted analogues as chelating N,N-do-
nor ligands and the catalytic potential of these complexes
for the regeneration of NADH in the chemoenzymatic re-
[a] Institut de Chimie, Université de Neuchâtel,
Case postale 158, 2009 Neuchâtel, Switzerland
E-mail: georg.suess-fink@unine.ch
[b] Department of Inorganic Chemistry, Faculty of Natural Sci-
ence, Charles University in Prague
Hlavova 2030, 12840 Prague, Czech Republic
4736
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 4736–4742

Regeneration of NADH in the Enzymatic Reduction of Ketones
duction of ketones. The electrochemical behaviour of the 1,[36] the new 5-nitro- and 5-amino-1,10-phenanthroline cat-
complexes is also discussed.
ions 2, 3 and 4 are chiral, and compounds [2]Cl, [3]Cl and
[4]Cl are produced as racemic mixtures.
Results and Discussion
Catalytic Reduction of NAD+ to NADH in Aqueous
Solution
Synthesis of Phenanthroline Complexes
Inspired by the pioneering studies of Steckhan[30] and
Complexes [(η5-C5Me5)MCl2]2 (M = Rh, Ir) react at Fish[33] on the use of (η5-cyclopentadienyl)rhodium bipyr-
room temperature in dichloromethane solution with 1,10- idine complexes as catalysts for the regioselective reduction
phenanthroline (phen) or with its 5-nitro or 5-amino deriva- of NAD+ models with the formate anion as the hydrogen
tives to afford quantitatively the cationic complexes [(η5- source in aqueous solution, we studied this reaction cata-
C5Me5)M(NʝN)Cl]+ (1: M = Rh, NʝN = phen; 2: M = lysed by cations 1–4 as well as by the previously described
Rh, NʝN = 5-NO2-phen; 3: M = Rh, NʝN = 5-NH2- complex [(η6-C6Me6)Ru(5-NO2-phen)Cl]+ (5),[37] which is
phen; and 4: M = Ir, NʝN = 5-NO2-phen) [Equation (1)]. known to be active for the reduction of ketones in water
These cations are easily isolated as their chloride salts.
(Scheme 1).
Cations 1–5 were found to promote the reduction of
NAD+ to NADH in aqueous solution with sodium formate
as the hydrogen donor (Table 1). The best results were ob-
tained with rhodium complexes 1–3, which led to TOFs
½[(η5-C5Me5)MCl2]2 + NʝN Ǟ [(η5-C5Me5)Rh(NʝN)Cl]+ + Cl–
(1)
The chloride salts of 1–4 are yellow-orange solids that ranging from 1500 to 2000 h–1 at 60 °C and pH = 7. In
have a high solubility in water, a property that is used to comparison with the analogous bipy complex [(η5-C5Me5)-
remove unreacted starting material after the synthesis. As Rh(bipy)Cl]+ (TOF = 875 h–1), commonly used as a catalyst
there is a risk of slow hydrolysis in water, the aqueous solu- for this reaction, phen analogue 1 is more than twice as
tions are immediately filtered, and the filtrates are concen- active (TOF = 2000 h–1) under the same conditions.
trated to dryness to give the analytically pure salts [1–4]Cl.
Ruthenium complex 5 shows a catalytic activity fifteen
All compounds have been characterised by 1H and 13C times lower than that observed with the related rhodium
NMR spectroscopy, mass spectroscopy and elemental complex 2 (entries 6 and 21). The low activity of the ruthe-
analysis.
nium complex observed in this study is similar to the results
In all cases, the phenanthroline ligand is coordinated in recently published by Sadler et al. describing the use of
the N,N-chelating fashion to the metal centre. In contrast (arene)(ethylenediamine)ruthenium complexes for the re-
to the known, symmetrical 1,10-phenanthroline complex duction of NAD+ to NADH in aqueous solution at 37 °C
Scheme 1. Transfer hydrogenation of NAD+ to NADH in aqueous solution catalysed by cationic chlorido complexes 1 to 5 by using the
formate anion as the hydrogen source.
Eur. J. Inorg. Chem. 2007, 4736–4742
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4737

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J. Canivet, G. Süss-Fink, P. Steˇpnicˇka
FULL PAPER
Table 1. Transfer hydrogenation of NAD+ to NADH in aqueous solution by using the formate anion as the hydrogen source.[a]
[b]
Entry
Catalyst
ns/nc
T[°C]
pH
Conversion [%]
(Time [h])[c]
TOF [h–1][c,d]
1
2
3
4
5
6
7
8
1
2
1000
1000
15
15
50
100
500
1000
1000
15
1000
1000
15
15
50
100
15
15
15
50
100
15
1000
38
60
25
38
38
38
38
38
60
38
38
60
25
38
38
38
38
25
38
38
38
38
60
7
7
7
7
7
7
7
7
100 (2.5)
100 (0.5)
100 (3)
100 (0.25)
100 (0.5)
100 (2.5)
100 (3.5)
100 (4)
100 (0.75)
100 (0.5)
100 (4)
100 (1)
100 (5)
100 (2.5)
100 (4.5)
100 (7)
100 (3)
35 (24)
70 (24)
50 (24)
20 (24)
55 (24)
560
2000
19.5
30
100
150
380
400
1740
29
400
1500
14.4
23
47
58
22.5
1.5
6
8
10
5.4
875
9
7
10
11
12
13
14
15
16
17
18
19
20
21
22
23
4[e]
7
3
4
7
7
7
7
7
4[e]
7
5
7
7
7
4[e]
7
[(η5-C5Me5)Rh(bipy)Cl]+
100 (2)
[a] Conditions: [NAD+] = 8 m, [NaHCO2] = 350 m; reactions carried out in 1 mL of phosphate buffer (pH 7). [b] Mol of substrate
per mol of catalyst. [c] Determined by UV-absorption at 340 nm. [d] Turnover frequencies determined after 30 minutes and expressed in
mol of product/(mol of metal·h). [e] Reactions carried out in phthalate buffer.
strate that the catalytic activity does not show any signifi-
cant pH dependence.
According to the mechanistic scheme proposed by Fish
et al. for the analogous bipy complexes,[33] cationic complex
1 is supposed to react with the formate anion to afford the
corresponding hydrido complex, which can reduce NAD+
to NADH (Scheme 2). The postulated catalytic cycle in-
volves a transition state for hydride transfer from the rho-
dium centre to the pyridinium group, in which the NAD+
and the metal hydride form a kinetically stable six-mem-
bered ring.
Electrochemical Behaviour of the Phenanthroline Complexes
The electrochemical behaviour of complexes 1–4 has
been studied by cyclic voltammetry at a stationary platinum
disc and by voltammetry at a rotating platinum disc elec-
trode (RDE) by using acetonitrile solutions (analyte con-
centration: ca. 5ϫ10–4 ) containing Bu4N[PF6] (0.1 ) as
the supporting electrolyte. Relevant data together with the
parameters for the related Ru complexes[39] are summarised
in Table 2.[40]
The redox response of phenanthroline complex 1 is
shown in Figure 1. The first reduction occurs as a two-elec-
tron irreversible process (up to 500 mVs–1), which is, how-
Scheme 2. Postulated catalytic cycle, based on the work of Fish, for
the reduction of NAD+ to NADH in aqueous solution with 1 as
ever, fast and diffusion controlled (ipa ϰ ν1/2, ilim ϰ ω1/2).
The associated oxidative peak (B) retains the diffusion con-
trol (ip ϰ ν1/2) but shows a peak current lower than that
the catalyst.
and pH = 7.2.[38] Iridium complex 4 is also two times less of the corresponding reduction wave (A). Such behaviour
active than the rhodium analogue 2 under the same condi- parallels that of the related cations [LnMCl(bipy)]+ [LnM =
tions (entries 6 and 16). The results with varied pH demon- (η5-C5Me5)Rh, (η5-C5Me5)Ir and (η6-arene)Ru; bipy =
4738
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 4736–4742

Regeneration of NADH in the Enzymatic Reduction of Ketones
Table 2. Summary of the electrochemical data.[a]
In the case of 2, the metal-centred reduction occurs at
–1.44 V (wave A), while for 5 only a broad wave at around
–1.6 V could be detected. The associated counterwave (if
any) is difficult to detect. This could explain the higher ac-
tivity of rhodium catalyst 2 as compared with that found for
ruthenium catalyst 5 in the reduction of NAD+ to NADH
described above, the more difficult-to-reduce species being
less catalytically active.
Compound
Ep[V]
Reference
this work
[(η5-C5Me5)RhCl(phen)]+ (1)
–1.32 (A), –1.10 (B),
≈ +0.64 (C)
[(η5-C5Me5)RhCl(5-NO2-phen)]+ (2) –1.01/–0.93 (NO2),[b]
–1.43 (A), ≈ +0.64 (C)
this work
this work
this work
[(η5-C5Me5)RhCl(5-NH2-phen)]+ (3) –1.28 (A), –1.16 (B)
[(η5-C5Me5)IrCl(phen)]+ (4)
–0.99 (A), –0.90 (B),
≈ +0.64 (C)
–1.59 (A)
[(η6-C6Me6)RuCl(phen)]+ (5)
[(η6-C6Me6)RuCl(5-NO2-phen)]+
[(η6-C6Me6)RuCl(5-NH2-phen)]+
[39]
[39]
[39]
–0.99 (E°Ј for NO2)
–1.58 (A)
Chemoenzymatic Enantioselective Reduction of Ketones
[a] The potentials are given relative to the ferrocene/ferrocenium
reference (see the Experimental Section for details). Peak potentials
for irreversible processes were obtained at a scan rate of 100 mVs–1.
Definitions: E°Ј = ½(Epa + Epc), ∆Ep = Epa – Epc. [b] Epc/Epa for
the reversible reduction of the nitro group.
In light of the findings by Steckhan[22] and Schmid[1] on
organometallic NADH regeneration for enzymatic ketone
reductions, we studied the chemoenzymatic enantioselective
transfer hydrogenation of 4-phenylbutan-2-one and aceto-
phenone in aqueous solution. We used the NADH-depend-
ent enzymes horse liver alcohol dehydrogenase (HLADH)
or alcohol dehydrogenase from Rhodococcus sp. (S-ADH)
and 1 as the NADH-regenerating catalyst with the formate
anion as the hydrogen source (Scheme 3).
2,2Ј-bipyridine] and [(η5-C5Me5)MCl(bpym)]+ (M = Rh
and Ir; bipym = 2,2Ј-bipyrimidine)[41–43] and can be ex-
plained by reductive removal of the chlorido ligand as
shown in Equation (2).
[(η5-C5Me5)M(phen)Cl]+ + 2e– Ǟ [(η5-C5Me5)M(phen)] + Cl– (2)
Scheme 3. Organometallic NADH regeneration for the stereoselec-
tive reduction of ketones with alcohol dehydrogenase.
The NADH-regenerating catalytic system with 1 as the
catalyst was found to be active in combination with the two
enzymes used (HLADH and S-ADH) for the enantioselec-
tive reduction of the test substrates (Table 3). The reaction
proceeds with good to excellent enantioselectivity, produc-
ing predominantly the S enantiomer.
The results show the enantioselectivities to be similar to
those found without the organometallic NADH regenera-
tion catalyst with ee values up to 92 and 98%. However,
Figure 1. Cyclic voltammogram of 1 as recorded at a platinum disc
electrode in acetonitrile solution at 100 mVs–1 scan rate. The poten-
tials are given relative to the ferrocene/ferrocenium reference.
The neutral electrogenerated species [(η5-C5Me5)- the enzymatic activity with NADH regeneration is some-
M(phen)] is probably rather unstable and becomes oxidised what lower relative to enzymatic ketone reduction with ex-
in a single step, giving rise to wave B. A broad wave (C), cess NADH. This could be explained by a deactivation of
observed in the anodic region, can be attributed to oxi- the organometallic catalyst during the reaction, probably
dation of some decomposition product(s). However, the ex- due to coordination of functional enzyme groups to the
act nature of this redox process remains unclear.
rhodium centre.
The presence of an amino group at the phenanthroline
The mechanistic aspects of the combined organometal-
ligand in 3 has only a minor influence on the electrochemi- lic–enzymatic catalysis are summarised in Scheme 4, which
cal behaviour, manifested mainly by a slight shift of the A is a combination of Scheme 2 and Scheme 3. The organo-
and B waves to higher potentials and also by a diminished metallic intermediates [(η5-C5Me5)Rh(phenanthroline)H]+
A–B separation. On the contrary, substitution with a nitro and [(η5-C5Me5)Rh(phenanthroline)(OH2)]2+ work hand-
group markedly changes the redox response, as the nitro in-hand with the coenzyme intermediates NAD+ and
group is reduced first in a reversible, one-electron process NADH to perform the enantioselective reduction of a
(–NO2 + e– i –NO2–·), the potential of which is indepen- ketone to give the corresponding alcohol, with aqueous so-
dent of the metal (Rh vs. Ir). Such an “inserted” redox step dium formate as hydrogen source and a dehydrogenase en-
naturally influences the following one(s).
zyme as chiral inducer.
Eur. J. Inorg. Chem. 2007, 4736–4742
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4739

ˇ
J. Canivet, G. Süss-Fink, P. Steˇpnicˇka
FULL PAPER
Table 3. Chemoenzymatic enantioselective transfer hydrogenation of ketones with alcohol dehydrogenase and 1 as NADH-regenerating
catalysts in aqueous solution.[a]
Conc. of Rh
[m]
Entry
Ketone
Enzyme
t [h]
Conversion [%][b]
ee [%][b]
1[c]
2[d]
3
4
5
4-phenylbutan-2-one
4-phenylbutan-2-one
4-phenylbutan-2-one
4-phenylbutan-2-one
4-phenylbutan-2-one
4-phenylbutan-2-one
acetophenone
acetophenone
acetophenone
acetophenone
acetophenone
HLADH
none
0
24
24
24
24
24
24
24
24
24
24
24
80
4
62
47
1.2
0.5
2
78
8
58
20
96
n.d.
92
0.5
0.5
0.1
0.01
0.002
0.5
0
0.5
0.5
0.1
HLADH
HLADH
HLADH
HLADH
HLADH
S-ADH
none
88
n.d.
n.d.
n.d.
98
n.d.
74
6
7
8[c]
9[d]
10
11
S-ADH
S-ADH
98
[a] Conditions: [NAD+] = 1 m, [NaHCO2] = 100 m, [ketone] = 33 m, reactions carried out with 1 unit of alcohol dehydrogenase in
1 mL of phosphate buffer (pH 7) at 37 °C. [b] Determined by chiral HPLC analysis. [c] Conditions: [NADH] = 40 m, [NaHCO2] =
100 m, [ketone] = 33 m, reactions carried out with 1 unit of alcohol dehydrogenase in 1 mL of phosphate buffer (pH 7) at 37 °C. [d]
Reaction carried out without HLADH or S-ADH and NAD+.
Scheme 4. Catalytic cycle for the chemoenzymatic enantioselective transfer hydrogenation of ketones with 1 as NADH regenerating
catalyst in aqueous solution.
Conclusions
Experimental Section
General: All manipulations were carried out with freshly distilled
solvents. The 5-amino-1,10-phenanthroline[44] and [(η6-C6Me6)-
Ru(5-NO2-phen)Cl]+ (5)[37] were prepared according to the pub-
lished methods. All other reagents were commercially available and
were used without further purification. NMR spectra were re-
corded with a Bruker 400 MHz spectrometer by using sodium 2,2-
dimethyl-2-silapentane-5-sulfonate in D2O as an internal standard.
Electrospray mass spectra were obtained in the positive-ion mode
with an LCQ Finnigan mass spectrometer. Microanalyses were car-
ried out by the Laboratoire de Chimie Pharmaceutique, Université
de Genève (Switzerland).
In conclusion, we report here a series of five water-solu-
ble rhodium, iridium and ruthenium complexes containing
1,10-phenanthroline and derivatives thereof as chelating li-
gands. All these complexes were found to catalyse the 1,4-
regioselective reduction of NAD+ to NADH in aqueous
solution. TOF values up to 2000 h–1 have been obtained by
using [(η5-C5Me5)Rh(phen)Cl]+ (1) as a catalyst at 60 °C
and pH = 7. Furthermore, rhodium catalyst 1 has been
found to be active as an NADH-regenerating catalyst for
the chemoenzymatic enantioselective transfer hydrogena-
tion of ketones in aqueous solution. Under biological con-
ditions (37 °C, pH = 7), this system, which combines orga-
nometallic NADH regeneration and enzymatic reduction in
aqueous solution, converts ketones into the corresponding
Electrochemical measurements were carried out with a multipur-
pose polarograph PA3 interfaced to a Model 4103 XY recorder
(Laboratorní prˇístroje, Prague) at room temperature by using a
standard three-electrode cell with a rotating platinum disc electrode
chiral alcohols with good activities and enantioselectivities. (RDE; 1 mm diameter) as the working electrode, platinum wire as
4740 Eur. J. Inorg. Chem. 2007, 4736–4742
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Regeneration of NADH in the Enzymatic Reduction of Ketones
the auxiliary electrode and a saturated calomel electrode (SCE) as
the reference electrode. The reference electrode was separated from
the analysed solution by a salt bridge (0.1  Bu4N[PF6] in acetoni-
trile). The samples were dissolved in acetonitrile (Riedel-de Haën,
purissimum p.a.), to give an analyte concentration of 5ϫ10–4 ,
and in 0.1  Bu4N[PF6] (Fluka, purissimum for electrochemistry).
The solutions were purged with argon prior to the measurement
and then kept under an argon blanket. Cyclic voltammograms were
recorded at a stationary platinum disc electrode (scan rates 50–
500 mV/s), while the voltammograms were obtained at a RDE
(1000–2500 rpm, scan rate 20 mV/s). The redox potentials are given
relative to the ferrocene/ferrocenium reference.
m/z = 588 [M]+. C22H22Cl2IrN3O2 (623.55): calcd. C 42.38, H 3.56,
N 6.74; found C 42.24, H 3.67, N 6.54.
Catalytic NADH Regeneration: The reduction of NAD+ (8 m) ca-
talysed by complexes [1–5]Cl with sodium formate (350 m) as the
hydrogen source was carried out in phosphate buffer (1 mL, pH 7)
or in phthalate buffer (1 mL, pH 4). The conversion was deter-
mined by UV absorption at 340 nm. The pH was monitored with
a pH meter (Mettler Toledo InLab® 413). Turnover frequencies
were calculated for all the catalytic reactions from the conversions
observed after 30 min for the hydrogenation reaction of NAD+ to
NADH. The results are summarised in Table 1.
Chemoenzymatic Hydrogenation of Ketones: The enzymatic transfer
hydrogenation reactions of acetophenone or 4-phenylbutan-2-one
(33 m) were carried out in phosphate buffer (1 mL, pH 7) at 37 °C
with 1 unit of alcohol dehydrogenase S-ADH or HLADH respec-
tively, in the presence of NAD+ (1 m) and [1]Cl as NADH-regen-
erating catalyst and NaHCO2 (100 m) as the hydrogen source.
The reactions without rhodium catalyst were performed with
NADH instead of NAD+ (40 m), and the reactions without enzy-
matic reduction were performed without enzyme and NAD+. The
products were extracted with diethyl ether, filtered through silica
and identified (and conversion and enantiomeric excess were deter-
mined) by HPLC on a Chiracel OD-H capillary column (hexane/
2-propanol 9:10, 0.7 mLmin–1, 215 nm). The pH was monitored
with a pH meter (Mettler Toledo InLab® 413).
Preparation of Chlorido Complexes [(η5-C5Me5)M(NʝN)Cl]+ (M =
Rh, Ir and NʝN = phen, 5-NO2-phen, 5-NH2-phen): Two equiva-
lents (0.30 mmol) of the appropriate phenanthroline donor were
added to a suspension of [(η5-C5Me5)MCl2]2 (M = Rh, Ir;
0.15 mmol) in dichloromethane (30 mL). The mixture was stirred
for 3 h at room temperature, while the colour changed from dark
orange to yellow-orange. After concentration to dryness, the resi-
due was dissolved in water. This solution was filtered, and the fil-
trate was concentrated to dryness, which gave the product as a yel-
low powder in good yield.
1
[(η5-C5Me5)Rh(phen)Cl]Cl ([1]Cl): Yield: 74%, 80.8 mg. H NMR
(400 MHz, D2O, 21 °C): δ = 1.70 (s, CH3), 7.99 (s, CH), 8.05–8.12
3
3
3
(dd, JH,H = 5.1 Hz, JH,H = 8.1 Hz, CH), 8.67–8.71 (d, JH,H
=
8.1 Hz, CH), 9.28–9.31 (d, JH,H = 5.1 Hz, CH) ppm. 13C NMR
(200 MHz, D2O, 21 °C): δ = 8.32 [C5(CH3)5], 97.9 [C5(CH3)5],
126.63 (CH), 127.62 (CH), 130.98 (CH), 139.47 (CH), 146.08 (C),
155.62 (C) ppm. MS (ESI): m/z = 453 [M]+. C22H23Cl2N2Rh
(489.24): calcd. C 54.01, H 4.74, N 5.73; found C 53.91, H 4.82, N
5.68.
3
Acknowledgments
This work was financially supported by the Swiss National Science
Foundation and is a part of the long-term research projects sup-
ported by the Ministry of Education, Youth and Sports of the
Czech Republic (project nos. MSM0021620857 and LC06070). The
generous loan of ruthenium(III) chloride hydrate from the Johnson
Matthey Research Centre is gratefully acknowledged.
[(η5-C5Me5)Rh(NO2-phen)Cl]Cl ([2]Cl): Yield: 85%, 85.4 mg. 1H
NMR (400 MHz, D2O, 21 °C): δ = 1.68 (s, CH3), 7.99 (s, CH),
3
3
8.16–8.21 (quint, JH,H = 4.5 Hz, CH), 8.83–8.85 (d, JH,H
=
8.2 Hz, CH), 8.96 (s, CH), 9.19–9.22 (d, 3JH,H = 8.7 Hz, CH), 9.36
(d, JH,H = 4.7 Hz, CH), 9.41 (d, JH,H = 4.8 Hz, CH) ppm. 13C
NMR (200 MHz, D2O, 21 °C): δ = 8.52 [C5(CH3)5], 98.8 [C5(CH3)
5], 123.62 (C), 127.63 (CH), 127.81 (C), 128.38 (CH), 128.41 (CH),
136.51 (CH), 141.71 (CH), 144.31 (C), 145.72 (C), 146.98 (C),
153.44 (CH), 155.14 (CH) ppm. MS (ESI): m/z = 498 [M+].
C22H22Cl2N3O2Rh (534.24): calcd. C 49.46, H 4.15, N 7.87; found
C 49.32, H 4.18, N 7.63.
3
3
[1] F. Holmann, A. Kleeb, K. Otto, A. Schmid, Tetrahedron:
Asymmetry 2005, 16, 3512–3519.
[2] K. Everaere, A. Mortreux, M. Bulliard, J. Brussee, A.
van der Gen, G. Nowogrocki, J. F. Carpentier, Eur. J. Org.
Chem. 2001, 275–291.
[3] J. Diez, M. P. Gamasa, E. Lastra, A. Garcia-Fernandez, M. P.
Tarazona, Eur. J. Inorg. Chem. 2006, 2855–2864.
[4] S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya, R. Noyori, J.
Am. Chem. Soc. 1995, 117, 7562–7563.
[5] N. Dahlin, A. Bogevig, H. Adolfsson, Adv. Synth. Catal. 2004,
346, 1101–1105.
[6] W. He, P. Liu, B. L. Zhang, X. L. Sun, S. Y. Zhang, Appl. Or-
ganomet. Chem. 2006, 20, 328–334.
[7] P. F. Yan, C. H. Nie, G. M. Li, G. F. Hou, W. B. Sun, J. S. Gao,
Appl. Organomet. Chem. 2006, 20, 338–343.
[8] W. He, B. L. Zhang, R. Jiang, P. Liu, X. L. Sun, S. Y. Zhang,
Tetrahedron Lett. 2006, 47, 5367–5370.
[9] B. Z. Li, J. S. Chen, Z. R. Dong, Y. Y. Li, Q. B. Li, J. X. Gao,
J. Mol. Catal. A: Chem. 2006, 258, 113–117.
[10] K. Matsumura, S. Hashiguchi, T. Ikariya, R. Noyori, J. Am.
Chem. Soc. 1997, 119, 8738–8739.
[11] T. Abura, S. Ogo, Y. Watanabe, S. Fukuzumi, J. Am. Chem.
Soc. 2003, 125, 4149–4154.
[12] X. H. Li, J. Blacker, I. Houson, X. F. Wu, J. L. Xiao, Synlett
2006, 1155–1160.
[13] X. G. Li, X. F. Wu, W. P. Chen, F. E. Hancock, F. King, J. L.
Xiao, Org. Lett. 2004, 6, 3321–3324.
[(η5-C5Me5)Rh(NH2-phen)Cl]Cl ([3]Cl): Yield: 80%, 78.7 mg. 1H
NMR (400 MHz, D2O, 21 °C): δ = 1.64 (s, CH3), 6.60 (s, CH),
3
3
7.72–7.79 (dd, JH,H = 5.4 Hz, JH,H = 8.7 Hz, CH), 7.96–8.07 (m,
3JH,H = 8.8 Hz, CH), 8.54–8.58 (d, JH,H = 8.4 Hz, CH), 8.88–8.90
3
3
3
(d, JH,H = 4.4 Hz, CH), 9.22–9.24 (d, JH,H = 4.1 Hz, CH) ppm.
13C NMR (200 MHz, D2O, 21 °C): δ = 8.47 [C5(CH3)5], 97.9
[C5(CH3)5], 107.56 (CH), 126.52 (C), 126.80 (CH), 128.02 (CH),
128.91 (CH), 134.49 (CH), 136.00 (C), 138.41 (C), 145.54 (C),
148.94 (C), 151.81 (CH), 155.71 (CH) ppm. MS (ESI): m/z = 468
[M]+. C22H24Cl2N3Rh (504.26): calcd. C 52.40, H 4.80, N 8.33;
found C 52.18, H 4.92, N 8.16.
[(η5-C5Me5)Ir(NO2-phen)Cl]Cl ([4]Cl): Yield: 84%, 81.2 mg. 1H
NMR (400 MHz, D2O, 21 °C): δ = 1.53 (s, CH3), 8.05–8.09 (dd,
3
3JH,H = 5.3 Hz, JH,H = 8.8 Hz, CH), 8.94 (s, CH), 9.08–9.11 (d,
3
3
3JH,H = 8.7 Hz, CH), 9.22 (d, JH,H = 5.2 Hz, CH), 9.27 (d, JH,H
= 5.4 Hz, CH) ppm. 13C NMR (200 MHz, D2O, 21 °C): δ = 8.14
[C5(CH3)5], 90.72 [C5(CH3)5], 124.02 (C), 127.75 (CH), 128.02 (C),
128.76 (CH), 128.83 (CH), 136.59 (CH), 141.64 (CH), 144.53 (C),
147.14 (C), 148.28 (C), 153.17 (CH), 154.76 (CH) ppm. MS (ESI):
[14] X. F. Wu, X. G. Li, F. King, J. L. Xiao, Angew. Chem. Int. Ed.
2005, 44, 3407–3411.
Eur. J. Inorg. Chem. 2007, 4736–4742
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4741

ˇ
J. Canivet, G. Süss-Fink, P. Steˇpnicˇka
FULL PAPER
[15] J. Canivet, G. Labat, H. Stoeckli-Evans, G. Süss-Fink, Eur. J.
Inorg. Chem. 2005, 4493–4500.
[16] Y. Arakawa, N. Haraguchi, S. Itsuno, Tetrahedron Lett. 2006,
47, 3239–3243.
[17] L. Jiang, T. F. Wu, Y. C. Chen, J. Zhu, J. G. Deng, Org. Biomol.
Chem. 2006, 4, 3319–3324.
[18] H. Y. Rhyoo, H. J. Park, W. H. Suh, Y. K. Chung, Tetrahedron
Lett. 2002, 43, 269–272.
[19] Y. P. Ma, H. Liu, L. Chen, X. Cui, J. Zhu, J. E. Deng, Org.
Lett. 2003, 5, 2103–2106.
[20] F. Wang, H. Liu, L. F. Cun, J. Zhu, J. G. Deng, Y. Z. Jiang, J.
Org. Chem. 2005, 70, 9424–9429.
[21] D. S. Matharu, D. J. Morris, G. J. Clarkson, M. Wills, Chem.
Commun. 2006, 3232–3234.
[22] D. Westerhausen, S. Herrmann, W. Hummel, E. Steckhan, An-
gew. Chem. Int. Ed. Engl. 1992, 31, 1529–1531.
[23] A. Liese in Technology Transfer in Biotechnology: from Lab to
Industry to Production, 2005, 92, 197–224.
[24] H. M. Zhao, W. A. van der Donk, Curr. Opin. Biotechnol. 2003,
14, 583–589.
[31]
[32]
[33]
[34]
[35]
[36]
[37]
R. Ruppert, S. Herrmann, E. Steckhan, J. Chem. Soc. Chem.
Commun. 1988, 1150–1151.
J. Lutz, F. Hollmann, T. V. Ho, A. Schnyder, R. H. Fish, A.
Schmid, J. Organomet. Chem. 2004, 689, 4783–4790.
H. C. Lo, C. Leiva, O. Buriez, J. B. Kerr, M. M. Olmstead,
R. H. Fish, Inorg. Chem. 2001, 40, 6705–6716.
S. Ogo, O. Buriez, J. B. Kerr, R. H. Fish, J. Organomet. Chem.
1999, 589, 66–74.
H. C. Lo, O. Buriez, J. B. Kerr, R. H. Fish, Angew. Chem. Int.
Ed. 1999, 38, 1429–1432.
U. Kolle, M. Grutzel, Angew. Chem. Int. Ed. Engl. 1987, 26,
567–570.
J. Canivet, L. Karmazin-Brelot, G. Süss-Fink, J. Organomet.
Chem. 2005, 690, 3202–3211.
[38] Y. K. Yan, M. Melchart, A. Habtemariam, A. F. A. Peacock,
P. J. Sadler, J. Biol. Inorg. Chem. 2006, 11, 483–488.
[39] P. Stepnicka, J. Ludvik, J. Canivet, G. Süss-Fink, Inorg. Chim.
Acta 2006, 359, 2369–2374.
[40] Epa and Epc are anodic and cathodic peak potentials, respec-
tively. Similarly, ipa and ipc denote the anodic and cathodic peak
currents in cyclic voltammetry; ilim is the limiting current in
voltammetry at Pt-RDE, ν is the scan rate, and ω is the rotation
frequency of the disc electrode.
[25] W. A. van der Donk, H. M. Zhao, Curr. Opin. Biotechnol. 2003,
14, 421–426.
[26] H. Groger, W. Hummel, S. Buchholz, K. Drauz, T.
Van Nguyen, C. Rollmann, H. Husken, K. Abokitse, Org. Lett.
2003, 5, 173–176.
[27] F. Hollmann, A. Schmid, Biocatal. Biotransform. 2004, 22, 63–
88.
[41] M. Ladwig, W. Kaim, J. Organomet. Chem. 1991, 419, 233–
243.
[42] M. Ladwig, W. Kaim, J. Organomet. Chem. 1992, 439, 79–90.
[43] W. Kaim, R. Reinhardt, M. Sieger, Inorg. Chem. 1994, 33,
4453–4459.
[28] K. Vuorilehto, S. Lutz, C. Wandrey, Bioelectrochemistry 2004,
65, 1–7.
[29] R. Ruppert, S. Herrmann, E. Steckhan, Tetrahedron Lett. 1987,
28, 6583–6586.
[30] E. Steckhan, S. Herrmann, R. Ruppert, J. Thommes, C. Wand-
rey, Angew. Chem. Int. Ed. Engl. 1990, 29, 388–390.
[44] D. Garcia-Fresnadillo, G. Orellana, Helv. Chim. Acta 2001, 84,
2708–2730.
Received: May 9, 2007
Published Online: August 13, 2007
4742
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 4736–4742