Transfer hydrogenation of ketones catalyzed by surface-active ruthenium and rhodium complexes in water

Article abstract of DOI:10.1002/chem.201301679

An improved, high-yield, one-pot synthetic procedure for water-soluble ligands functionalized with trialkyl ammonium side groups H₂N(CH ₂)₂NHSO₂-p-C₆H₄CH ₂[NMe₂(C_nH_2n+1)]⁺ ([HLⁿ]⁺; n=8, 16) was developed. The corresponding new surface-active complexes [(p-cymene)RuCl(Lⁿ)] and [Cp*RhCl(Lⁿ)] (Cp=η⁵-C₅Me ₅) were prepared and characterized. For n=16 micelles are formed in water at concentrations as low as 0.6 mM, as demonstrated by surface-tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C₁₆ tails due to their ability to be adsorbed at the water/substrate interface. The scope of these catalyst systems in aqueous solutions was extended from partially water soluble aryl alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (2-dodecanone). Copyright

Full text of DOI:10.1002/chem.201301679

DOI: 10.1002/chem.201301679
Full Paper
&
Micellar Catalysis
Transfer Hydrogenation of Ketones Catalyzed by Surface-Active
Ruthenium and Rhodium Complexes in Water
Alexander M. Kalsin,*[a, b] Tat’yana A. Peganova,[a] Valentin V. Novikov,[a]
Alexandra I. Zhamoytina,[c] Luca Gonsalvi,*[b] and Maurizio Peruzzini*[b]
Abstract: An improved, high-yield, one-pot synthetic proce-
dure for water-soluble ligands functionalized with trialkyl
ammonium side groups H2N(CH2)2NHSO2-p-C6H4CH2[NMe2-
(CnH2n+1)]+ ([HLn]+; n=8, 16) was developed. The corre-
sponding new surface-active complexes [(p-cymene)RuCl(Ln)]
and [Cp*RhCl(Ln)] (Cp*=h5-C5Me5) were prepared and char-
acterized. For n=16 micelles are formed in water at concen-
trations as low as 0.6 mm, as demonstrated by surface-ten-
sion measurements. The complexes were used for catalytic
transfer hydrogenation of ketones with formate in water.
Highly active catalyst systems were obtained in the case of
complexes bearing C16 tails due to their ability to be ad-
sorbed at the water/substrate interface. The scope of these
catalyst systems in aqueous solutions was extended from
partially water soluble aryl alkyl ketones (acetophenone, bu-
tyrophenone) to hydrophobic dialkyl ketones (2-dodeca-
none).
drogenation in aqueous solution.[10] Different approaches using
water-soluble ligands and catalysts have been investigated; in
particular, aryl-sulfonated[7a,11] and polyethylene-glycol-support-
ed[12] TsDPEN-type ligands functionalized with heterocyclic[13] or
trialkyl ammonium[13c,14] groups have been synthesized. In
some cases polymer-supported[15] or chitosan-anchored[16] cata-
lysts have been used, but the unmodified TsDPEN-based cata-
lysts sometimes performed better.[3,17] Surfactants have been
shown to have generally little effect on the reaction,[7b,18] al-
though in specific cases they improved catalytic performance
significantly.[19] Solid substrates could also be readily hydrogen-
ated with HCOONa in emulsions prepared by sonication in the
presence of a surfactant in water.[20] Only a few examples of
surface-active catalysts that can promote aqueous transfer hy-
drogenation by improving both the catalytic reaction and the
mass transfer between the reagents have been described so
far. Recently two types of 2-aminoethyl(p-tosyl)amide (Ts-EN) li-
gands with NEt3, NMe2Oct and NBu3 substituents were report-
ed.[14] Transfer hydrogenation of benzaldehyde with HCOONa
in water catalyzed by ruthenium and/or iridium complexes pre-
pared in situ from these ligands gave contrasting results de-
pending on the presence and type of substituents, and it was
not clear from these examples whether surface-active ligands
had generally a positive effect on hydrogenation rate.[14] An
amphiphilic-polymer-based iridium catalyst that can assemble
at the interface of emulsion droplets showed remarkable rate
acceleration in transfer hydrogenation of aldehydes in water,[21]
which was attributed to the high surface area of the emulsion
droplets formed during the reaction and the high local con-
centration of reactants around the active sites. Recently,
TsDPEN-based chiral surfactant-type ligands have been used in
micellar rhodium catalysis, with higher ee values in transfer hy-
drogenation of various aryl alkyl and dialkyl ketones than the
Introduction
Over the last 20 years asymmetric transfer hydrogenation
(ATH) of ketones has become a versatile and powerful method
for the synthesis of enantiomerically pure secondary alcohols,
especially with efficient catalysts such as [(h6-arene)RuCl-
(TsDPEN)][1] and [Cp*MCl(TsDPEN)] (M=Rh, Ir;[2] Cp*=h5-C5Me5;
TsDPEN =2-amino-1,2-diphenylethyl(p-tosyl)amide). Aldehydes[3]
and imines[4] were also reduced by this method. The reaction
can tolerate conjugated double[5] and triple[6] bonds or a-halo-
genated substituents,[7] but sometimes hydrogenation of a con-
jugated C=C bond can occur instead of the desired reduction
of a carbonyl group.[8] In 2001 the first case of transfer hydro-
genation of ketones with HCOONa in aqueous solution cata-
lyzed by RuII proline complexes was reported.[9] Since then sev-
eral reviews have been published by Xiao et al. on transfer hy-
[a] Dr. A. M. Kalsin, Dr. T. A. Peganova, Dr. V. V. Novikov
A.N. Nesmeyanov Institute of Organoelement Compounds (INEOS RAS)
Russian Academy of Sciences
28 Vavilova St., Moscow 119991 (Russia)
Fax: (+7)4991350176
E-mail: kalsin@ineos.ac.ru
[b] Dr. A. M. Kalsin, Dr. L. Gonsalvi, Dr. M. Peruzzini
Istituto di Chimica dei Composti OrganoMetallici (ICCOM CNR)
Consiglio Nazionale delle Ricerche
Area di Ricerca di Firenze, via Madonna del Piano 10
50019 Sesto Fiorentino (FI) (Italy)
Fax: (+39)0555225203
E-mail: l.gonsalvi@iccom.cnr.it
maurizio.peruzzini@iccom.cnr.it
[c] A. I. Zhamoytina
Alexandra I. Zhamoytina
Frumkin Institute of Physical Chemistry and Electrochemistry
Russian Academy of Sciences
31 Leninsky Prospect, Moscow 119991 (Russia)
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nonmicellar analogues.[22] Nevertheless, the number of reports
on surface-active catalysts for transfer hydrogenation is very
limited, and many aspects of their interfacial behavior remain
unexplored, also due to the lack of a general and convenient
method of functionalization of Ts-EN ligands with surface-
active groups.
was kept at room temperature for only 2–4 h to ensure com-
plete quaternization of the alkyl dimethyl amine. Longer reac-
tion times should be avoided, as side quaternization of excess
amine with dichloromethane to give ClCH2NMe2(CnH2n+1)+ClÀ
takes place.[23] Before deprotection with concentrated aqueous
HCl, the N-Boc-substituted ligand was quenched with aqueous
KHCO3 and washed with n-hexane or diethyl ether to eliminate
the trialkyl ammonium salt and free amine. After deprotection,
to obtain pure chloride salts and eliminate bromide, which
may still be present as counterion (up to 10%), repeated treat-
ment of the crude product with hydrochloric acid and solvent
evaporation were required. This method was also used to
obtain the known monotosylated diamine ligand bearing a trie-
thylammonium group [HLEt]Cl·HCl. The ligands were isolated
in nearly quantitative yield (93–97%) as hydrochloride salts.
Here we report on the synthesis of surface-active diamine li-
gands with quaternized ammonium groups H2N(CH2)2NHSO2-p-
C6H4CH2[NMe2(CnH2n+1)]+ ([HLn]+, n=8, 16) and with an NEt3
group [HLEt]Cl·HCl by a one-pot procedure that is improved
compared to the literature method[14b] and gives nearly quanti-
tative yields. These ligands were used to obtain the corre-
sponding novel ruthenium [(p-cymene)RuCl(Ln)]Cl and rhodium
[Cp*RhCl(Ln)]Cl complexes MLn (n=8, 16), which were then
tested in aqueous transfer hydrogenation of hydrophilic and
hydrophobic ketones. The effects of the nature of ancillary li-
gands, micelle formation and different absorption at the
water/substrate interface are also discussed.
1
All ligands were characterized by H and 13C{1H} NMR spec-
troscopy and elemental analysis. As expected, the trialkyl am-
monium group imparts water solubility to the ligands, which
were then used to obtain the corresponding water-soluble [(p-
cymene)RuCl(Ln)]Cl (RuLn; n=8, 16) and [Cp*RhCl(Ln)]Cl (RhLn;
n=8, 16) complexes. The complexes were synthesized in a bi-
phasic water/dichloromethane medium from a suitable organ-
ometallic precursor in the presence of potassium bicarbonate
and sodium chloride (Scheme 2). NaCl was required to reduce
Results and Discussion
Synthesis of water-soluble ligands and complexes
Recently, the synthesis of monotosylated diamine ligands
+
having an NR3 group (R=NEt3, NBu3, Me2NOct, Py, 3-methyli-
midazolyl) in the benzylic position of the tosylate group was
reported.[14b] In three steps, N-tert-butoxycarbonylethylenedia-
mine (Boc-En) was converted to the desired hydrochloride salts
of the diamine ligand in 50–65% yield. We modified the
known procedure leading to ligands of general formula
[HLn]Cl·HCl (n=8, 16) using a new one-pot high-yielding
method (Scheme 1). The first two synthetic steps, that is, sulfo-
Scheme 2. Synthesis of RuII and RhIII complexes bearing [HLn]Cl*HCl (n=8,
16).
the solubility of the desired complex in the aqueous phase for
better extractive workup and to ensure full formation of the
chloride derivatives.
Scheme 1. One-pot synthesis of the ligands [HLn]Cl·HCl (n=8, 16). a) N-Boc-
En/Me2NCnH2n+1 (1:1), CH2Cl2, 08C; b) Me2NCnH2n+1 (1.2 equiv), 258C, 4 h;
c) KHCO3/H2O; d) 12m aqueous HCl.
Complexes RuLn and RhLn were characterized by 1H and
13C{1H} NMR spectroscopy, ESI-MS, and elemental analysis. The
1H NMR spectra of RuLn in [D2]dichloromethane confirmed the
formation of the proposed ruthenium arene complexes with
three different coligands. All proton resonances of the ethyle-
nediamine moiety, p-cymene, the diastereotopic protons of the
benzylic CH2 group, N-methyl groups, and methyl groups of
the isopropyl group were non-equivalent, as were the 13C NMR
resonances of methyl groups in NMe2 and p-cymene. The
1H NMR spectrum of RhLn in [D4]MeOH was in agreement with
the expected Cs-symmetric structure (see Experimental Sec-
tion). In [D2]dichloromethane the 1H NMR signals appeared
broadened, most likely due to an exchange process in solution.
The ESI-MS data were in agreement with the proposed struc-
nylation and quaternization, were combined by carrying out
the synthesis in dichloromethane over a short reaction time at
room temperature without the need to isolate the N-Boc-N’-(4-
bromomethyl)benzenesulfonylethylenediamine intermediate.
To suppress side amination of the benzylic position using a pro-
tecting Boc-En group, we found that a mixture of Boc-En and
tertiary amine should be added to a solution of the sulfonyl
chloride, instead of using the reversed order of addition re-
ported in the original procedure.[14b] The corresponding benzyl
bromide was isolated by extraction with diethyl ether in 92%
yield, a significant improvement compared to what was previ-
ously obtained (65% yield).[14b] In step b, the reaction mixture
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tures and showed only two groups of peaks at m/z values cor-
responding to the molecular cations [M+] and [M+ÀHCl]. Due
to the presence of long alkyl chains, it was not possible to
obtain suitable single crystals for collection of X-ray diffraction
data.
case less ordered (bulkier) and less hydrated RhL16 micelles are
likely to form. Similarly, the rH value of RhL8 (0.48 nm) estimat-
ed from DOSY experiments was smaller than that of RuL8
(0.60 nm) due to a lower degree of hydration and more com-
pact folding of RhL8.
The CMCs of ML16 were confirmed by measuring the surface
tension g of solutions of RuL16 and RhL16 as a function of con-
centration (Figure 1). The minimum in g corresponds to the
Micellar properties of MLn
To determine the surface-active properties and aggregation of
complexes ML16, translational diffusion coefficients in aqueous
solutions were measured by diffusion-ordered NMR spectros-
copy (DOSY) at concentrations in the range 0.5–5 mm, the
same as that used in the catalytic tests. The effective size of
the aggregates in solution was estimated[24] by converting the
diffusion coefficients to the corresponding hydrodynamic radii
by using the Stokes–Einstein equation or other models.[25]
While in the case of micelle formation fast exchange between
free monomers and aggregates can lead to underestimation of
micelle size,[18] the concentration dependence of the diffusion
coefficients allows important micelle characteristics, such as
critical micelle concentration (CMC), to be estimated.[26] The dif-
fusion coefficients D and calculated hydrodynamic radii rH for
complexes MLn at different concentrations in water are collect-
ed in Table 1.
Figure 1. Surface tension g versus concentration c for ML16 at 25Æ0.58C.
pre-CMC transition (PCT) of MLn in the chosen medium; the
post-minimum inflection at maximum g values corresponds to
the CMC.[27] The CMCs determined for RuL16 and RhL16 were
1.3 and 0.6 mm, respectively.[28] The CMCs obtained by this
technique are in agreement with those previously estimated
by DOSY NMR experiments.
Interestingly, the CMC of RuL16 (ca. 1.3 mm) compares well
with that of C16H33NMe3+ClÀ (CTAC).[29] In parallel, the rH value
of 2.97 nm approximates well to the size of CTAC micelles
(2.43 nm[30]) plus the size of the [(p-cymene)Ru(Ts-EN)] organo-
metallic moiety. The micellar behavior of RuL16 should thus re-
semble that of CTAC. Unfortunately, it was not possible to
obtain a direct measurement of the CMC of RuL8. However, we
can assume it to be on the order of that of C8H17NMe3+BrÀ
(OTAB, CMC=250 mm[31]), which is much higher than the
range of concentrations used in the corresponding catalytic
tests. In summary, surface tension measurements and calcula-
tions of CMCs prove that RhL16 is less surface active than RuL16
and CTAC,[29] and this confirms the above discussed arguments
based on DOSY measurements on the different organizations
of the micelles.
Table 1. Diffusion coefficients and hydrodynamic radii of MLn in water.[a]
Complex
c [mm]
1011 D [m2 sÀ1
]
rH [nm]
RuL8
0.5
5
0.5
5
5
0.5
1
5
0.5
5
31.3
33.5
41.5
41.4
65.7
14.1
9.9
6.7
6.2
5.9
0.64
0.60
0.48
0.48
0.60
1.41
2.01
2.97
3.21
3.37
RuL8
RhL8
RhL8
RuL16[b]
RuL16
RuL16
RuL16
RhL16
RhL16
[a] For conditions and details, see Experimental Section. [b] In CD3OD.
The complexes with shorter alkyl tails ML8 showed relatively
high diffusion coefficients, with no aggregation in 0.5–5 mm
aqueous solutions. The very small rH values for RuL8 in water,
which are close to those of RuL16 in CD3OD, suggest mono-
mers under these conditions. By increasing the length of the
alkyl tail, a dramatic increase of the rH values for ML16 was ob-
served, which suggests aggregation and formation of micelles.
For complex RuL16 partial aggregation can occur at concentra-
tions as low as 0.5 mm. At 5 mm concentration, the rH value
was calculated to be 3.0 nm, characteristic of micelles with an
aggregation number of about 100 molecules. For RhL16 little
concentration dependence of the D value was observed in
0.5–5 mm aqueous solutions, which again suggests aggrega-
tion and a CMC of about 0.5 mm or lower. The micelle radii es-
timated for RhL16 (3.2–3.4 nm) are slightly larger than those
found for 5 mm RuL16, likely due to the higher hydrophobicity
of the Cp* ligand compared to h6-p-cymene in RuL16. In this
Catalytic transfer hydrogenation of ketones
Complexes MLn (M=Ru, Rh; n=8, 16) were tested as catalysts
for water-phase transfer hydrogenation, and acetophenone (1)
was initially chosen as model substrate. The results of the cata-
lytic tests are listed in Table 2, together with values obtained
with the in-situ-prepared ethyl-tailed analogue [(p-
cymene)RuCl(LEt)]Cl (RuLEt)[14b] for comparison. The experiments
were carried out under nitrogen in Schlenk tubes in degassed
water or degassed water/methanol (1:1) solutions.
From comparison of data in Table 2, the effects of the choice
of metal and the length of the alkyl tail of the ligand and
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Table 2. Transfer hydrogenation of 1 catalyzed by MLn.[a]
Entry
Catalyst
T
[8C]
w(MeOH)
[%]
t
[h]
Conver.
[%]
TOF
[hÀ1
]
[c]
1[b]
2[b]
3
4
5
6
7
8
9
10
11
12
13
14
RuL16
RuL16
RuL16
RuL16
RuL16
RuL16
RuL8
20
20
40
40
60
60
60
60
60
60
20
20
20
20
0
50
0
50
0
50
0
50
0
50
0
50
0
50
7
7
6
6
1
1
1
1
1
1
6
6
6
6
97
40
99
42
98
49
51
45
11
35
88
62
77
55
36
12
330
120
1500
550
350
520
110
470
300
160
35
Figure 2. Transfer hydrogenation conversions of 1 catalyzed by RuL16 and
RhL16 at various water/methanol ratios and temperatures. For conditions,
see Table 2.
RuL8
RuLEt
RuLEt
RhL16
RhL16
RhL8
Increasing the methanol content w(MeOH) in the reaction
mixture decreased the rate of hydrogenation for both RuL16
and RhL16 (Figure 2). This effect is most prominent at
w(MeOH)>30%. Since 1 dissolves completely in H2O/MeOH
mixtures at wꢀ35%, surface-active catalyst molecules may
become assembled at lower MeOH content and be active at
the substrate/water interface. The different behaviors of RuL16
and RhL16 at low methanol content (w=0–20%) must be then
related to their different organization and hydration in mi-
celles, as already discussed. A detailed study of the reaction
profiles in neat water and in water/methanol solutions was
then carried out. The results for RuLn and RhLn are treated sep-
arately in the following.
RhL8
160
[a] Conditions: 1 (0.25m), catalyst (0.25 mm), HCOONa (1.25m), MLn/1/
HCO2Na 1:1000:5000, water/methanol (4 mL total volume). [b] Conditions:
catalyst (1.25 mm), RuL16/1/HCO2Na 1:200:1000. [c] Initial TOF, defined as
(mmol product)(mmol catalyst)À1 hÀ1, measured after 15–30 min.
hence its surface-active properties on the activity can be ap-
preciated at different H2O/MeOH ratios. For RuL16 (Table 2, en-
tries 1–6) the activity in water is about three times higher than
in water/methanol in the temperature range 20–608C. The ac-
tivity of RuL8 is comparable in water and aqueous methanol
(Table 2, entries 7 and 8) and close to that observed for RuL16
in water/methanol (Table 2, entry 6). In aqueous methanol
RuLEt is slightly less active (Table 2, entry 10) than the other
two ruthenium catalysts, while in neat water (Table 2, entry 9)
its activity drops severely and is an order of magnitude lower
than that of RuL16. Interestingly, this finding is in contrast with
earlier reports[14b] that for transfer hydrogenation of benzalde-
hyde with HCOONa in water at 808C, RuLEt was significantly
more active than RuL8.
Transfer hydrogenation of 1 in the presence of RuLn
Figure 3 shows the reaction profile for the conversion of
1 with Ru catalysts bearing different alkyl tails at different sol-
vent compositions. Catalysts RuL8, RuL16, and RuLEt perform
similarly in 50% aqueous methanol, showing initial TOFs in the
Generally the rhodium catalysts RhLn are 5–10 times more
active at 208C (Table 2, entries 11–14) than the corresponding
ruthenium analogues, but the largest effect in catalysis was
caused by the tail length. At higher temperatures, decomposi-
tion of RhLn complexes occurred. This behavior is in line with
that recently reported for transfer hydrogenation of 1 in the
presence of an Rh TsDPEN complex immobilized on a polymer
support.[15c]
Whereas initial turnover frequencies (TOFs) obtained with
MLn catalysts in water/methanol do not differ substantially (see
Table 2, entries 6, 8, and 10 for M=Ru and entries 12 and 14
for M=Rh) and are almost independent of the nature of am-
monium side group, in water a large effect is caused by the
length of the alkyl tail at the ammonium group. The long alkyl
tail may facilitate phase transfer between substrate and for-
mate or may change the structure of the reaction zone favor-
ing micelle formation.
Figure 3. Transfer hydrogenation conversions of 1 catalyzed by RuLn at vari-
ous water/methanol ratios. Conditions: T=608C, H2O/MeOH (4 mL total
volume), HCOONa (1.25m), 1 (0.25m), RuLn (0.25 mm), RuLn/1/HCO2Na
1:1000:5000.
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range 470–550 hÀ1. The rate was observed to decrease steadily
at increasing conversions, in analogy to the common behavior
reported for homogeneously catalyzed transfer hydrogenation
of ketones.
In neat water, complex RuLEt catalyzed the reaction very
slowly (TOF=110 hÀ1) compared to the surface-active RuL16
(TOF=1500 hÀ1), and both reactions became slower with time.
RuL8 gave a sigmoidal profile, which was rather slow in the be-
ginning (TOF=350 hÀ1 at 10% conversion) and significantly ac-
celerated at higher conversions (TOF>800 hÀ1 at 50–70% con-
version). The partial solubility of 1 in water (74 mm at 608C,[32]
lower in the presence of HCO2Na in solution) limits the hydro-
genation rate of 1 catalyzed by RuLEt.
tion rate higher than that of RuLEt. The sigmoidal shape of the
reaction profile and the presence of an induction period for
RuL8 (Figure 3) could be related to increasing formation of the
product (1-phenylethanol) and the byproduct sodium carbon-
ate.[36] At increasing concentrations they may improve the ad-
sorption of RuL8 on the surface of droplets of the ketone. In
fact, binegative counterions are known to be adsorbed strong-
ly on the surface of positively charged micelles and thus de-
crease the CMC of surfactants.[37] Indeed, further rate enhance-
ment was observed on addition of Na2SO4 to the reaction mix-
ture (Figure 5). Alcohols are also known to improve surface-
It was shown above that the C16 alkyl tail allowed RuL16 to
form micelles, with a CMC of about 1.3 mm in neat water. Con-
sidering that the CMC of CTAC in 1m NaCl is about 0.15 mm[33]
and that both ClÀ and carboxylate anions have relatively low
specific adsorption energy towards micelles formed from
+ [34]
CnNMe3
,
we could estimate the CMC of RuL16 in 1.25m
HCOONa electrolyte solution to be about 0.1 mm. The concen-
tration of RuL16 used in transfer hydrogenation (0.25 mm) was
above the estimated CMC under these conditions, so during
the reaction the catalyst will preferably self-assemble to mi-
celles and will be distributed over the surface of the substrate
droplets dispersed in the aqueous phase (Figure 4A). Thus,
rate acceleration in this case originated from the ability of
RuL16 to be adsorbed densely on the surface of the liquid or-
ganic substrate and to form well-dispersed, highly positively
charged droplets with enhanced local concentration of formate
ions. In such a micellar system the concentrations of both cata-
lyst and reductant are much higher at the interface of the sub-
strate droplets compared to the bulk solution. A similar situa-
tion was recently observed for an iridium catalyst grafted to
a linear polymer bearing charged trimethylammonium side-
chain groups.[21]
Conversely, RuL8 aggregates only at high concentrations,
and under the reaction conditions applied here should exist as
monomers, which are adsorbed on the substrate droplets with-
out forming a dense surface layer, similar to what has been re-
ported for the sparse distribution of SDS molecules over the
surface of oil in water.[35] Therefore, RuL8 is distributed be-
tween the bulk aqueous phase and the surface of the sub-
strate droplets (Figure 4B), which gives an overall hydrogena-
Figure 5. Effect of the addition of salt or product on transfer hydrogenation
of 1 catalyzed by RuLn complexes in neat water Conditions: T=608C, H2O
(4 mL), HCOONa (1.25m), 1 (0.25m), RuLn (0.25 mm), RuLn/1/HCO2Na
1:1000:5000. * In the presence of Na2SO4 (0.125m). ** In the presence of 1-
phenylethanol (0.125m).
active properties of surfactants.[38] This effect was confirmed by
adding 1-phenylethanol to the catalytic mixture and observing
that the initial rate (TOF=1300 hÀ1) strongly increased almost
reaching the activity of RuL16 without any induction period
(Figure 5). As expected, no rate enhancement was observed
when 1-phenylethanol was added to the RuLEt-catalyzed reac-
tion, in which the surface-active effect on the aqueous/organic
interface is not present.
Transfer hydrogenation of 1 in
the presence of RhLn
The reaction profiles of transfer
hydrogenation of acetophenone
catalyzed by RhLn complexes
(Figure 6) showed a similar be-
havior to those of RuLn com-
plexes. Again, in 50% aqueous
methanol as reaction medium,
no significant difference in activi-
ty between RhL16 and RhL8 was
observed, with initial TOFs of
Figure 4. Schematic representation of droplets of 1 in water, stabilized with a dense layer of RuL16 (A) and sparse-
ly covered with RuL8 (B).
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the RhL8 monomers in water. When enough 1-phenylethanol
has accumulated in solution, RhL8 is mainly assembled at the
substrate droplets and the major contribution to the reaction
rate comes from the hydrogenation occurring at the droplet
interface.
Transfer hydrogenation of hydrophobic ketones 2 and 3 in
the presence of MLn complexes
We were interested in the applicability of the MLn catalysts in
the transfer hydrogenation of less water soluble or fully hydro-
phobic ketones. Poorly water soluble (2.2 mm) butyrophenone
(2) and hydrophobic dodecanone-2 (3) were then chosen as
model substrates. The reaction profiles obtained with RuLn are
shown in Figure 8.
Figure 6. Transfer hydrogenation conversion of 1 catalyzed by RhLn at vari-
ous water/methanol ratios. Conditions: T=208C, H2O/MeOH (4 mL total
volume), HCOONa (1.25m), 1 (0.25m), RhLn (0.25 mm), RhLn/1/HCO2Na
1:1000:5000.
160 hÀ1. In neat water, surface-active RhL16 performed twice as
well (TOF=300 hÀ1). Addition of 20% methanol caused an in-
crease in TOF to 500 hÀ1, in contrast to the behavior observed
for RuL16 (Figure 3).
In the presence of RhL8 the reaction profile followed a sig-
moidal behavior, with an initial slow rate (TOF=35 hÀ1) that in-
creased at higher conversions to reach TOFꢀ200 hÀ1 at 40–
80% conversion. It can be concluded that the two major differ-
ences between RhLn and RuLn are the need for small quantities
of methanol to gain maximum activity of RhL16, and the great-
er rate enhancement with increasing conversion for RhL8 than
for RuL8.
As already mentioned, we propose that the reason for such
different behavior between Rh and Ru is related to the differ-
ent hydrophobicities of Cp* versus arene coligands. In RhL16
the metal center resides entirely in the hydrophobic phase
(alkyl tails and acetophenone) at the water/substrate interface
(Figure 7), and poor contact with aqueous formate may inhibit
fast regeneration of the active rhodium hydride species,[8,10b]
which is easier in the presence of MeOH. The slow initial rate
found for RhL8 can also be attributed to compact folding of
Figure 8. Transfer hydrogenation conversion of 2 and 3 catalyzed by RuLn in
neat water. Conditions: T=608C, H2O (4 mL), HCOONa (1.25m), substrate
(0.25m), RuLn (0.625 mm), Ru/substrate/HCO2Na 1:400:2000.
For both 2 and 3, a sharp difference in hydrogenation rates
in water between the catalysts RuL8 and RuL16 was observed.
In the case of RuL16, the initial TOFs were 350 and 280 hÀ1 for
2 and 3, respectively, which are only 4–5 times lower than for
1 (TOF=1500 hÀ1). Conversely, the activity of RuL8 in water
dropped severely when hydrophobic ketones 2 (initial TOF=
14 hÀ1) and 3 (initial TOF=0.8 hÀ1) were used instead of 1. At
longer reaction times, however, the same acceleration effect
previously described for 1 was observed. Again, the low sur-
face activity of RuL8, which did not micellize the hydrophobic
ketones efficiently at the beginning of the reaction, is mitigat-
ed by prolonged stirring and accumulation of the alcohol
product with time and allows hydrogenation of hydrophobic
ketones 2 and 3, albeit with low efficiency. When RhLn com-
plexes were tested in neat water under the same conditions
applied for hydrogenation of 1, very low activities in hydroge-
nation of the hydrophobic ketones 2 and 3 were observed,
with TOFꢁ10 and TOF !1 for RhL16 and RhL8, respectively, as
expected for these less surface active catalysts.
Figure 7. Schematic representation of droplets of 1 in water stabilized by
a dense layer of RhL16 bearing a hydrophobic and poorly hydrated Cp*
ligand.
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solved in methanol (30 mL) and treated with an aqueous solution
of KHCO3 (1 g in 10 mL H2O) for 4 h. The suspension was concen-
trated to dryness, washed with diethyl ether (3ꢁ50 mL) and dried.
Finally the solid was quenched with concentrated HCl (15–20 mL
of 12m aqueous solution); after all gas had evolved (ca. 15 min),
the resulting solution was concentrated to dryness. The treatment
with concentrated aqueous HCl was repeated one more time. After
solvent evaporation the glassy solid was dissolved in ethanol
(50 mL), the precipitate was filtered off, and the filtrate was evapo-
rated to dryness to give off-white or pale beige glassy foam.
Conclusion
In our search for efficient micellar catalysts for transfer hydro-
genation of ketones we have developed a novel one-pot syn-
thetic route to Ts-EN ligands modified with trialkyl ammonium
side groups HLn and obtained the surface active Noyori-type
complexes [(p-cymene)RuCl(Ln)] and [Cp*RhCl(Ln)]. The com-
plexes with C16 alkyl tails ML16 form micelles and are densely
adsorbed at the water/substrate interface, where they strongly
enhance the rate of catalytic transfer hydrogenation of ketones
with formate in water compared to complexes with shorter
alkyl chains. Our straightforward approach gives a self-organ-
ized catalyst system directly in the reaction mixture. Such an
approach is applicable also for hydrophobic ketones, for which
the use of the Ru-based micellar catalysts boosts the hydroge-
nation rates by as much as two orders of magnitude compared
to nonmicellar ones. The different abilities of the ligands to
self-assemble and form micelles was rationalized by using
a combination of methods including DOSY NMR and surface-
tension measurements, and correlated to the observed reac-
tion profiles. Ligand modification to give chiral surface-active
catalysts for efficient ATH of hydrophobic ketones in water are
in progress.
[HL8]Cl·HCl: (4-Bromomethyl)benzenesulfonyl chloride (1.35 g,
5.00 mmol), N-Boc-ethylenediamine (800 mL, 5.00 mmol), and N,N-
dimethyloctylamine (2.31 mL, 11.25 mmol) afforded 2.10 g (95%) of
the product. 1H NMR (CD3OD): d=8.02 (d, 3J=8.4 Hz, 2H; C6H4),
7.83 (d, 3J=8.4 Hz, 2H; C6H4), 4.66 (s, 2H; CH2Ar), 3.38 (m, 2H;
Me2NCH2), 3.15 (t, 3J=5.6 Hz, 2H; NCH2CH2N), 3.07 (t, 3J=5.6 Hz,
2H; NCH2CH2N), 3.07 (s, 6H; NMe2), 1.89 (m, 2H; Me2NCH2CH2),
3
1.26–1.44 (m, 10H; 5CH2), 0.90 ppm (t, J=6.8 Hz, 3H; CH3); 13C{1H}
NMR (CD3OD): d=141.9 (i-C(C6H4)), 133.9 (CH(C6H4)), 132.3 (i-
C(C6H4)), 127.5 (CH(C6H4)), 66.2 (Me2NCH2), 65.0 (CH2NMe2), 49.2
(NMe2), 40.2 (NCH2CH2N), 39.3 (NCH2CH2N), 31.5 (CH2), 28.8 (2CH2),
26.0 (CH2), 22.3 (2CH2), 13.0 ppm (CH3); elemental analysis calcd
(%) for C19H37Cl2N3O2S: C 51.57, H 8.43, N 9.50; found: C 51.16, H
8.24, N 9.27.
[HL16]Cl·HCl: (4-Bromomethyl)benzenesulfonyl chloride (1.36 g,
5.05 mmol), N-Boc-ethylenediamine (820 mL, 5.12 mmol), and N,N-
dimethylhexadecylamine (3.84 mL, 11.36 mmol) afforded 2.60 g
1
3
(93%) of the product. H NMR (CD3OD): d=8.04 (d, J=8.4 Hz, 2H;
C6H4), 7.84 (d, 3J=8.4 Hz, 2H; C6H4), 4.66 (s, 2H; CH2Ar), 3.39 (m,
2H; Me2NCH2), 3.16 (t, 3J=5.6 Hz, 2H; NCH2CH2N), 3.09 (t, 3J=
5.6 Hz, 2H; NCH2CH2N), 3.08 (s, 6H; NMe2), 1.91 (m, 2H;
Experimental Section
General procedures
3
All manipulations were carried out by using standard Schlenk tech-
niques under an atmosphere of dry argon or nitrogen. Solvents
were purified by standard methods and distilled prior to use. [{(p-
cymene)RuCl2}2][39] and [{Cp*RhCl2}2][40] were prepared according to
described methods. Other reagents were purchased from commer-
Me2NCH2CH2), 1.26–1.45 (m, 26H; 13CH2), 0.90 ppm (t, J=6.8 Hz,
3H; CH3); 13C{1H} NMR (CD3OD): d=142.5 (i-C(C6H4)), 133.8
(CH(C6H4)), 132.1 (i-C(C6H4)), 127.4 (CH(C6H4)), 66.2 (Me2NCH2), 65.0
(CH2NMe2), 49.2 (NMe2), 43.3 (NCH2CH2N), 40.3 (NCH2CH2N), 31.7
(CH2), 29.4 (6CH2), 29.3 (CH2), 29.2 (CH2), 29.1 (CH2), 28.9 (CH2), 26.1
(CH2), 22.3 (2CH2), 13.1 ppm (CH3); elemental analysis calcd (%) for
C27H53Cl2N3O2S·2H2O: C 54.90, H 9.73, N 7.11; found: C 54.93, H
9.71, N 6.77.
1
cial sources in the highest available purity and used as received. H
and 13C{1H} NMR spectra were recorded at room temperature
(258C) on a Bruker ARX-400 spectrometer operating at frequencies
of 400 and 100 MHz, respectively, and referenced to the residual
proton signals of the deuterated solvent. Elemental analyses were
performed in the Laboratory of Microanalysis at INEOS RAS either
manually (for Ru samples) or on a Carlo Erba 1106 CHN analyzer.
Electrospray mass spectrometry (ESI-MS) was carried out at the
University of Florence, Italy, on a LCQ Orbitrap mass spectrometer
(ThermoFischer, San Jose, CA, USA) equipped with a conventional
ESI source by direct injection of the sample solution and are re-
ported in the form m/z (intensity relative to base=100). GC analy-
ses were performed on a Shimadzu 2010 gas chromatograph
equipped with a flame ionization detector and a VF-WAXms capil-
lary column (30 m, 0.25 mm i.d., 0.25 mm film thickness).
[HLEt]Cl·HCl: (4-Bromomethyl)benzenesulfonyl chloride (2.10 g,
7.80 mmol), N-Boc-ethylenediamine (1250 mL, 7.80 mmol) and trie-
thylamine (2.50 mL, 17.9 mmol) afforded 2.92 g (97%) of the prod-
uct. 1H NMR (CD3OD): d=8.01 (d, 3J=8.4 Hz, 2H; C6H4), 7.81 (d,
3
3J=8.4 Hz, 2H; C6H4), 4.61 (s, 2H; CH2Ar), 3.31 (q, J=7.6 Hz, 6H;
NCH2Me), 3.15 (t, 3J=5.8 Hz, 2H; NCH2CH2N), 3.07 (t, 3J=5.8 Hz,
2H; NCH2CH2N), 1.43 ppm (t, 3J=7.6 Hz, 9H; CH3); 13C{1H} NMR
(CD3OD): d=141.7 (i-C(C6H4)), 133.5 (CH(C6H4)), 132.2 (i-C(C6H4)),
127.6 (CH(C6H4)), 59.0 (Aryl-CH2N), 52.7 (NCH2Me), 40.0 (NCH2CH2N),
39.3 (NCH2CH2N), 6.8 ppm (CH3).
General procedure for synthesis of [(p-cymene)Ru(Ln)Cl]Cl
(RuL8, RuL16) and [Cp*Rh(Ln)Cl]Cl (RhL8, RhL16)
General procedure for synthesis of [HLn]Cl·HCl
A solution of N-Boc-ethylenediamine (1.00 equiv) and trialkyl amine
(1.05 equiv) in dichloromethane (40 mL) was added dropwise to
a solution of (4-bromomethyl)benzenesulfonyl chloride (5.00 mmol,
1.00 equiv) in dichloromethane (50 mL) cooled to 08C with an ice
bath over 0.5 h. The resulting solution was stirred for an additional
0.5 h followed by addition of neat trialkyl amine (1.20 equiv). The
reaction mixture was allowed to warm to room temperature and
stirred for 4 h. The final clear solution was concentrated to dryness;
the residue was washed with diethyl ether (3ꢁ50 mL) to remove
unconverted amine. The insoluble pale beige powder was dis-
A solution of KHCO3 (100 mg, 1.0 mmol) and NaCl (300 mg,
5.1 mmol) in H2O (2 mL) was added to a solution of [{(p-cymene)R-
uCl2}2] or [{Cp*RhCl2}2] (0.15 mmol) and ligand salt [H2Ln]Cl2
(0.31 mmol) in dichloromethane (20 mL); the biphasic mixture was
vigorously stirred overnight. The water/organic layers were allowed
to separate for 2 h. The lightly colored upper aqueous layer was
discarded; the organic layer was dried over Na2SO4 and filtered,
and the solvent was removed in vacuo to afford the product as
a yellow or orange powder.
Chem. Eur. J. 2014, 20, 846 – 854
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RuL8: [{(p-cymene)RuCl2}2] (92 mg, 0.15 mmol) and [H2L8]Cl2
(137 mg, 0.31 mmol) afforded 170 mg (84%) of [(p-cymene)R-
C29H50Cl2N3O2RhS·2H2O: C 48.74, H 7.62, N 5.88; found: C 48.64, H
7.48, N 5.81.
1
u(L8)Cl]Cl as a yellow-orange powder. H NMR (CD2Cl2): d=7.78 (d,
RhL16: [{Cp*RhCl2}2] (92 mg, 0.15 mmol) and [H2L16]Cl2 (172 mg,
3J=8.4 Hz, 2H; C6H4), 7.51 (d, 3J=8.4 Hz, 2H; C6H4), 7.13 (brd, J
ꢀ10 Hz, 1H; NH), 5.90 (d, 3J=6.0 Hz, 1H; C6H4(cymene)), 5.76 (d,
3J=5.6 Hz, 1H; C6H4(cymene)), 5.69 (d, 3J=5.6 Hz, 1H; C6H4-
(cymene)), 5.43 (d, 3J=6.0 Hz, 1H; C6H4(cymene)), 4.83 (d, 2J=
0.31 mmol) afforded 220 mg (93%) of [Cp*Rh(L16)Cl]Cl as an orange
3
powder. 1H NMR (CD3OD): d=7.99 (d, J=8.4 Hz, 2H; C6H4), 7.55 (d,
3J=8.4 Hz, 2H; C6H4), 4.54 (s, 2H; CH2Ar), 3.29 (m, 2H; Me2NCH2),
3
3
3.03 (s, 6H; NMe2), 2.66 (t, J=5.6 Hz, 2H; NCH2CH2N), 2.49 (t, J=
5.6 Hz, 2H; NCH2CH2N), 1.88 (m, 2H; Me2NCH2CH2), 1.76 (s, 15H;
C5Me5), 1.26–1.46 (m, 26H; 13CH2), 0.90 ppm (t, 3J=6.8 Hz, 3H;
CH3); 13C{1H} NMR (CD3OD): d=145.7 (i-C(C6H4)), 132.3 (CH(C6H4)),
2
12.4 Hz, 1H; CHHAr), 4.78 (d, J=12.4 Hz, 1H; CHHAr), 3.40 (m, 2H;
Me2NCH2), 3.11 (s, 3H; NMe2), 3.10 (s, 3H; NMe2), 2.94 (brm, 1H;
NCHHCH2N), 2.93 (sept, 3J=6.8 Hz, 1H; Me2CH(cymene)), 2.65
(brm, 2H; NCH2CH2N), 2.20 (brm, 1H; NCHHCH2N), 2.11 (s, 3H; Me-
(cymene)), 2.02 (brt, Jꢀ10 Hz, 1H; NH), 1.78 (brm, 2H;
Me2NCH2CH2), 1.18–1.40 (m, 10H; 5CH2), 1.24 (d, 3J=6.8 Hz, 3H;
Me2CH(cymene)), 1.23 (d, 3J=6.8 Hz, 3H; Me2CH(cymene)),
2
129.4 (i-C(C6H4)), 128.2 (CH(C6H4)), 94.3 (d, J(Rh,C)=8.5 Hz, C5Me5),
66.8 (Me2NCH2), 64.4 (CH2NMe2), 49.7 (NMe2), 49.1 (NCH2CH2N), 45.6
(NCH2CH2N), 31.7 (CH2), 29.4 (5CH2), 29.3 (CH2), 29.2 (CH2), 29.1
(CH2), 29.0 (CH2), 28.8 (CH2), 26.0 (CH2), 22.3 (2CH2), 13.0 (CH3),
8.2 ppm (C5Me5); ESI-MS (MeOH): m/z (%): 754.37 (95) [M+], 718.39
(5) [M+ÀHCl]; elemental analysis calcd (%) for C37H66Cl2N3O2RhS: C
56.19, H 8.41, N 5.31; found: C 56.39, H 8.45, N 5.19.
3
0.89 ppm (t, J=6.8 Hz, 3H; CH3); 13C{1H} NMR (CD2Cl2): d=145.9 (i-
C(C6H4)), 132.5 (CH(C6H4)), 128.3 (i-C(C6H4)), 127.6 (CH(C6H4)), 101.4
(i-C(cymene)), 97.0 (i-C(cymene)), 82.3 (CH(cymene)), 82.2 (CH-
(cymene)), 80.8 (CH(cymene)), 80.4 (CH(cymene)), 67.1 (Me2NCH2),
64.4 (CH2NMe2), 49.8 (NMe2), 49.7 (NMe2), 48.9 (NCH2CH2N), 47.0
(NCH2CH2N), 31.7 (CH2), 30.4 (Me2CH(cymene)), 29.2 (CH2), 29.1
(CH2), 26.3 (CH2), 23.0 (Me2CH(cymene)), 22.9 (CH2), 22.6 (CH2), 21.6
(Me2CH(cymene)), 18.6 (Me(cymene)), 13.9 ppm (CH3); ESI-MS
(MeOH): m/z (%): 640.23 (55) [M+], 604.25 (45) [M+ÀHCl]; elemen-
tal analysis calcd (%) for C29H49Cl2N3O2RuS: C 51.54, H 7.31; found:
C 51.67, H 7.58.
Transfer hydrogenation tests
The reactions were carried out in Schlenk tubes under an inert at-
mosphere in degassed solvents. Typically the solution of HCO2Na
in water or water/methanol of desired concentration was prepared
directly in the reaction tube. The temperature was set and a fresh
5 mm solution of the precatalyst in degassed water was added to
reach a total volume of 4 mL. Finally the liquid substrate was di-
rectly added by syringe to the reaction mixture under vigorous stir-
ring. An aliquot of the reaction mixture (0.05 mL) was taken by sy-
ringe and diluted with methanol (0.4 mL) or extracted with ethyl
acetate (0.8 mL) before being analyzed by GC. The aliquots in
methanol were usually passed through a plug of silica before injec-
tion to remove traces of metal and salts. Each test was repeated at
least twice to check for reproducibility.
RuL16
:
[{(p-cymene)RuCl2}2] (92 mg, 0.15 mmol) and [H2L16]Cl2
(172 mg, 0.31 mmol) afforded 210 mg (89%) of [(p-cymene)Ru-
(L16)Cl]Cl as a yellow powder. 1H NMR (CD2Cl2): d=7.78 (d, 3J=
8.4 Hz, 2H; C6H4), 7.51 (d, 3J=8.4 Hz, 2H; C6H4), 7.11 (brd, J
ꢀ10 Hz, 1H; NH), 5.89 (d, 3J=6.0 Hz, 1H; C6H4(cymene)), 5.76 (d,
3J=5.6 Hz, 1H; C6H4(cymene)), 5.68 (d, 3J=5.6 Hz, 1H; C6H4-
(cymene)), 5.42 (d, 3J=6.0 Hz, 1H; C6H4(cymene)), 4.82 (d, 2J=
2
12.4 Hz, 1H; CHHAr), 4.77 (d, J=12.4 Hz, 1H; CHHAr), 3.39 (m, 2H;
Me2NCH2), 3.11 (s, 3H; NMe2), 3.10 (s, 3H; NMe2), 2.94 (brm, 1H;
NCHHCH2N), 2.92 (sept, 3J=6.8 Hz, 1H; Me2CH(cymene)), 2.65
(brm, 2H; NCH2CH2N), 2.20 (brm, 1H; NCHHCH2N), 2.10 (s, 3H; Me-
(cymene)), 2.01 (brt, Jꢀ10 Hz, 1H; NH), 1.80 (brm, 2H;
DOSY measurements
DOSY experiments were performed on a Bruker Avance 600 spec-
trometer at 258C by using the DOSY-ONESHOT[41] pulse sequence.
The following experimental parameters of the pulse sequence
were used: diffusion time 0.4 s, gradient pulse duration 2.5 ms, un-
balancing factor alpha 2.0, relaxation delay 5.0 s. Signal attenuation
was achieved by increasing the gradient strength from 5 to 80%
as defined by the pulse sequence in 16 steps with 16 scans each
and maximum gradient strength of 0.27 TmÀ1. The rows of the
pseudo-2D diffusion dataset were phased and baseline-corrected.
The pseudo-2D DOSY spectra were constructed by using standard
fitting procedure of the Bruker Topspin 2.1 software. The true diffu-
sion coefficients were determined by using the T1/T2 analysis
module of the Bruker Topspin 2.1 software. Viscosities of the solu-
tion were obtained by comparing the measured diffusion coeffi-
cients of the residual proton-containing solvents with the known
values (1.902ꢁ10À9 m2 sÀ1 for HDO in D2O[42] and 2.41ꢁ10À9 m2 sÀ1
for MeOH in CD3OD[43]). The hydrodynamic radii and volumes were
calculated from viscosity-corrected diffusion coefficients via the
Stokes–Einstein relation.
3
Me2NCH2CH2), 1.18–1.40 (m, 26H; 13CH2), 1.24 (d, J=6.8 Hz, 3H;
Me2CH(cymene)), 1.23 (d, 3J=6.8 Hz, 3H; Me2CH(cymene)),
3
0.88 ppm (t, J=6.8 Hz, 3H; CH3); 13C{1H} NMR (CD2Cl2): d=145.6 (i-
C(C6H4)), 132.6 (CH(C6H4)), 128.6 (i-C(C6H4)), 127.6 (CH(C6H4)), 101.9
(i-C(cymene)), 96.5 (i-C(cymene)), 82.5 (CH(cymene)), 81.9 (CH-
(cymene)), 81.1 (CH(cymene)), 80.5 (CH(cymene)), 67.2 (Me2NCH2),
64.3 (CH2NMe2), 49.5 (NMe2), 49.3 (NMe2), 49.0 (NCH2CH2N), 47.0
(NCH2CH2N), 31.9 (CH2), 30.4 (Me2CH(cymene)), 29.7 (5CH2), 29.5
(2CH2), 29.4 (2CH2), 26.4 (CH2), 23.2 (Me2CH(cymene)), 23.0 (CH2),
22.7 (2CH2), 21.9 (Me2CH(cymene)), 18.7 (Me(cymene)), 14.1 ppm
(CH3); ESI-MS (MeOH): m/z (%): 752.35 (55) [M+], 716.38 (45) [M+
ÀHCl]; elemental analysis calcd (%) for C37H65Cl2N3O2RuS: C 56.40,
H 8.31; found: C 56.44, H 8.35.
RhL8: [{Cp*RhCl2}2] (92 mg, 0.15 mmol) and [H2L8]Cl2 (137 mg,
0.31 mmol) afforded 180 mg (88%) of [Cp*Rh(L8)Cl]Cl as an orange
3
powder. 1H NMR (CD3OD): d=8.00 (d, J=8.4 Hz, 2H; C6H4), 7.55 (d,
3J=8.4 Hz, 2H; C6H4), 4.54 (s, 2H; CH2Ar), 3.30 (m, 2H; Me2NCH2),
3
3
3.03 (s, 6H; NMe2), 2.65 (t, J=5.2 Hz, 2H; NCH2CH2N), 2.49 (t, J=
5.2 Hz, 2H; NCH2CH2N), 1.88 (m, 2H; Me2NCH2CH2), 1.75 (s, 15H;
C5Me5), 1.28–1.45 (m, 10H; 5CH2), 0.92 ppm (t, 3J=6.8 Hz, 3H;
CH3); 13C{1H} NMR (CD3OD): d=145.7 (i-C(C6H4)), 132.4 (CH(C6H4)),
Determination of CMC
Surface tensions g at the air/solution interface were measured by
the Wilhelmy plate method (KSV Sigma tensiometer, Finland) at
25Æ0.58C. Solutions of RuL16 and RhL16 were prepared in the con-
centration ranges of 0.05–5 mm and 0.05–1.5 mm, respectively, in
deionized water (16 MW resistivity) and were equilibrated at room
temperature for 48 h. The platinum plate was cleaned and heated
2
129.4 (i-C(C6H4)), 128.2 (CH(C6H4)), 94.2 (d, J(Rh,C)=8.5 Hz, C5Me5),
66.8 (Me2NCH2), 64.4 (CH2NMe2), 49.7 (NMe2), 49.1 (NCH2CH2N), 45.6
(NCH2CH2N), 31.5 (CH2), 28.8 (2CH2), 26.0 (CH2), 22.3 (2CH2), 13.0
(CH3), 8.1 ppm (C5Me5); ESI-MS (MeOH): m/z (%): 642.25 (93) [M+],
606.26 (7) [M+ÀHCl]; elemental analysis calcd (%) for
Chem. Eur. J. 2014, 20, 846 – 854
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ments were repeated twice to check for reproducibility, and the
mean values were used for data treatment. The g values were ac-
curate within Æ0.1 mNmÀ1. The results were graphically processed
to determine the CMC.
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Keywords: hydrogenation · micellar catalysis · rhodium ·
ruthenium · water-soluble ligands
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Published online on December 12, 2013
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