Redox Isomerization of Allylic Alcohols Catalyzed by New Water-Soluble Rh(I)- N -Heterocyclic Carbene Complexes

: New water-soluble, N -heterocyclic carbene (NHC) or mixed NHC / tertiary phosphine complexes [RhCl(cod)(sSIMes)], Na 2 [Rh(bmim)(cod)( m tppts)], and [Rh(bmim)(cod)(pta)]BF 4 were synthetized and applied for the ﬁrst time as catalysts in redox isomerization of allylic alcohols in aqueous media. [RhCl(cod)(sSIMes)] (with added sulfonated triphenylphosphine) and [Rh(bmim)(cod)(pta)]BF 4 catalyzed selectively the transformation of allylic alcohols to the corresponding ketones. The highest catalytic activity, TOF = 152 h − 1 (TOF = (mol reacted substrate) × (mol catalyst × time) − 1 ) was observed in redox isomerization of hept-1-en-3-ol ([S] / [cat] = 100). The catalysts were reused in the aqueous phase at least three times, with only modest loss of the catalytic activity and selectivity.


Introduction
Catalytic isomerization of allylic alcohols is a remarkable way to obtain carbonyl compounds without classical oxidation/reduction steps, and is a 100% atom economic process of producing aldehydes and ketones (Scheme 1). The most efficient complexes for isomerization of allylic alcohols have been used in organic solvents [1][2][3]. However, water, as an environmentally friendly solvent for organic reactions, has received increasing attention. In aqueous oraqueous/biphasic systems the catalyst recycling is easier, and the process becomes more economical and environmentally friendly. Aqueous organometallic catalysis led to the development of a huge number of new and greener synthetic methodologies in organic synthesis. Lots of research has been done to develop efficient catalytic systems for the production of carbonyl compounds [4][5][6][7][8].

Results and Discussion
An efficient synthetic strategy of Rh(I)-NHC complexes uses the easily available [RhCl(cod)] 2 , [Rh(cod)(MeO)] 2 or [Rh(OH)(cod)] 2 dinuclear complexes as starting materials. Reaction of these compounds with imidazolium halides or tetrafluoroborates in the presence of bases often leads to clean formation of neutral or cationic mononuclear Rh(I)-NHC complexes [RhX(cod)(NHC)] and [Rh(cod)(NHC)]BF 4 , both in organic and aqueous solvents. Further reaction of these mononuclear complexes with tertiary phosphines results in formation of mixed-ligand NHC/phosphine Rh(I)complexes. We also followed this general strategy and used sulfonated NHC or/and water-soluble phosphine ligands to achieve water-solubility of the resulting complexes. The [RhCl(sSIMes)(cod)] (1) complex was prepared following the literature procedure, previously reported for water-insoluble Rh(I)-N-heterocyclic carbene complexes [45]. The synthesis involved reaction of [RhCl(cod)] 2 and the NHC ligand precursor, [sSIMesH]Cl, in the presence of excess K 2 CO 3 in MeOH at reflux temperature (Scheme 2). The resulting complex is highly soluble in water and methanol, and insoluble in dichloromethane and other non-polar solvents. In the 13 [45], and with the values obtained for water-insoluble analogues [46]. Unfortunately, despite all our attempts, 1 could not be isolated as a pure solid. 1 H and 13 C{ 1 H} NMR spectra showed decomposition during isolation, which is in accord with the reported instability of the [sSIMesH]Cl ligand in basic solvents [47], especially in solutions containing minute amounts of water. Conversely, methanolic solutions of 1, (see Section 2.2) showed consistent catalytic activity, and were studied in aqueous solutions containing 13 % methanol.
Attempts were made to prepare the mixed ligand NHC-phosphine-Rh(I) complex (denoted 2 on Scheme 3) in the reaction of 1 and mtppms-Na. Nevertheless, all our efforts to isolate a uniform product failed. 31 P{ 1 H} NMR of the resulting solution displayed a doublet at δ = 27.14 ppm with a coupling constant 1 J Rh-P = 147.0 Hz, which unambiguously revealed the coordination of mtppms to Rh(I). Nevertheless, the addition of 1-equivalent of mtppms-Na to a solution of 1 largely increased the Catalysts 2020, 10, 1361 4 of 18 catalytic activity of 1 in the redox isomerization of allylic alcohols. Such solutions of 1/mtppms-Na showed reproducible catalytic activity, and were used for the catalytic experiments (see below).
A probable cause of the failure in synthesis of the elusive compound 2 may be in the high steric demand of both the sSIMes and the mtppms ligands. Analogous NHC-phosphine-Ir(I) complexes with non-sulfonated NHC ligands, such as [Ir(bmim)(cod)(mtppms)] [44], and [Ir(cod)(emim)(mtppms)] (emim = 1-ethyl-3-methyl-imidazol-2-ylidene) [48] are known, however, those contain small size NHC ligands, compared to sSIMes. Another difference is that the mentioned Ir(I)-complexes showed only negligible solubility in aqueous solutions, since they were obtained as zwitterionic species, formed with loss of chloride and the sodium ion of the mtppms-Na ligand. In contrast, mixtures of 1 and 1-equivalent mtppms-Na did not yield a less soluble zwitterionic product, most probably due to the two −SO − 3 . substituents in the sSIMes ligand. The [RhCl(sSIMes)(cod)] (1) complex was prepared following the literature procedure, previously reported for water-insoluble Rh(I)-N-heterocyclic carbene complexes [45]. The synthesis involved reaction of [RhCl(cod)]2 and the NHC ligand precursor, [sSIMesH]Cl, in the presence of excess K2CO3 in MeOH at reflux temperature (Scheme 2). The resulting complex is highly soluble in water and methanol, and insoluble in dichloromethane and other non-polar solvents. In the 13 [45], and with the values obtained for water-insoluble analogues [46]. Unfortunately, despite all our attempts, 1 could not be isolated as a pure solid. 1 H and 13 C{ 1 H} NMR spectra showed decomposition during isolation, which is in accord with the reported instability of the [sSIMesH]Cl ligand in basic solvents [47], especially in solutions containing minute amounts of water. Conversely, methanolic solutions of 1, (see Section 2.2) showed consistent catalytic activity, and were studied in aqueous solutions containing 13 % methanol. Attempts were made to prepare the mixed ligand NHC-phosphine-Rh(I) complex (denoted 2 on Scheme 3) in the reaction of 1 and mtppms-Na. Nevertheless, all our efforts to isolate a uniform product failed. 31 P{ 1 H} NMR of the resulting solution displayed a doublet at δ = 27.14 ppm with a coupling constant 1 JRh-P = 147.0 Hz, which unambiguously revealed the coordination of mtppms to Rh(I). Nevertheless, the addition of 1-equivalent of mtppms-Na to a solution of 1 largely increased the catalytic activity of 1 in the redox isomerization of allylic alcohols. Such solutions of 1/mtppms-Na showed reproducible catalytic activity, and were used for the catalytic experiments (see below). A probable cause of the failure in synthesis of the elusive compound 2 may be in the high steric demand of both the sSIMes and the mtppms ligands. Analogous NHC-phosphine-Ir(I) complexes with non-sulfonated NHC ligands, such as [Ir(bmim)(cod)(mtppms)] [44], and [Ir(cod)(emim)(mtppms)] (emim = 1-ethyl-3-methyl-imidazol-2-ylidene) [48] are known, however, those contain small size NHC ligands, compared to sSIMes. Another difference is that the mentioned Ir(I)-complexes showed only negligible solubility in aqueous solutions, since they were obtained as zwitterionic species, formed with loss of chloride and the sodium ion of the mtppms-Na ligand. In contrast, mixtures of 1 and 1-equivalent mtppms-Na did not yield a less soluble zwitterionic product, most probably due to the two −SO 3 substituents in the sSIMes ligand. Complex 3 is very poorly soluble in water, but the chloride on rhodium can be easily replaced by a water-soluble ligand. Due to this, water-soluble, phosphine-containing Rh(I)-NHC complexes were prepared by ligand exchange.  Complex 3 is very poorly soluble in water, but the chloride on rhodium can be easily replaced by a water-soluble ligand. Due to this, water-soluble, phosphine-containing Rh(I)-NHC complexes were prepared by ligand exchange.  Triply-sulfonated triphenylphosphine sodium-salt, mtppts-Na3, is one of the most water-soluble tertiary phosphines (its solubility at room temperature is about 1400 g/L) [50]. It was expected that reaction of mtppts-Na3 and [RhCl(bmim)(cod)] (3) would result in the formation of a highly water-soluble mixed ligand Rh(I)-NHC-phosphine complex, with low solubility in apolar organic solvents. Indeed, the reaction depicted in Scheme 4 yielded 4 as orange powder, highly soluble in water. In MeOD solution, the 31 P{ 1 H} NMR spectrum of 4, a doublet can be seen at δ = 27.31 ppm ( 1 JRh-P = 160.4 Hz) ( Figure S8), while the 13 C{ 1 H} NMR signal of the carbene carbon atom appeared at δ = 174.62 ppm as a doublet of a doublet ( Figure S7), because both carbon-rhodium(I) and carbon-phosphorus coupling occurred ( 1 JRh-C = 49.2 Hz, 2 JC-P = 15.4 Hz).
According  (5), which was isolated as an orange powder.
Method B of the synthesis of 5 was based on chloride removal from 3. [RhCl(bmim)(cod)] was stirred with NaBF 4 in MeOH at room temperature. The resulting NaCl was removed by filtration, then 1-equivalent of pta was added to the solution (Scheme 4). The coordination of the phosphine ligand to rhodium(I) was displayed by 31 P{ 1 H} NMR. The spectrum recorded in MeOD showed a doublet ( Figure S11) at δ = −54.90 ppm ( 1 J Rh-P = 125.6 Hz), while the 13 C{ 1 H} NMR resonance of the carbene carbon appeared as a doublet of a doublet, at δ = 176.71 ppm ( 1 J Rh-C = 48.5 Hz, 3 J C-P = 18.5 Hz). Formation of 5 was unambiguously identified by the appearance of the [Rh(bmim)(cod)(pta)] + (506.1915 Da) molecular ion peak in the ESI-TOF MS spectrum, with an exact match of the experimentally determined and calculated isotope distributions. ( Figure S15).

Redox isomerization of allylic alcohols with water soluble Rh(I)-NHC catalysts
The new water-soluble Rh(I)-NHC and Rh(I)-NHC-phosphine complexes were studied as catalysts for redox isomerization of allylic alcohols in aqueous media (Scheme 5). In most cases, oct-1-en-3-ol was used to optimize the conditions.

Redox isomerization of allylic alcohols with water soluble Rh(I)-NHC catalysts
The new water-soluble Rh(I)-NHC and Rh(I)-NHC-phosphine complexes were studied as catalysts for redox isomerization of allylic alcohols in aqueous media (Scheme 5). In most cases, oct-1-en-3-ol was used to optimize the conditions.

Redox isomerization of allylic alcohols with water soluble Rh(I)-NHC catalysts
The new water-soluble Rh(I)-NHC and Rh(I)-NHC-phosphine complexes were studied as catalysts for redox isomerization of allylic alcohols in aqueous media (Scheme 5). In most cases, oct-1-en-3-ol was used to optimize the conditions. Scheme 5. General scheme of redox isomerization of allylic alcohols. Scheme 5. General scheme of redox isomerization of allylic alcohols.
The isomerization reactions were investigated using [RhCl(cod)(sSIMes)] (1), and the catalyst prepared in situ from 1 and 1-equivalent mtppms-Na. The effects of various added phosphines, mtppms-Na, mtppts-Na 3 , pta, and PPh 3 were also studied. The results are shown in Table 1. With the use of Rh(I)-NHC catalyst (1), the reaction proved selective for the isomerized product, but the conversion was low (entry 1). Running the reaction in an H 2 atmosphere of 1 bar pressure did not increase the total conversion significantly, however, octan-3-ol also appeared among the products (entry 2). Consequently, all further experiments were conducted under an argon atmosphere. Under such conditions, addition of 1-eq. mtppms-Na to 1, increased the activity by about a factor of three (entries 3 vs 1). Concerning the effect of added tertiary phosphines (entries 7-10), the highest conversion was achieved with addition of PPh 3 , while the lowest catalytic activity was observed in the presence of mtppts. An increase of the [PR 3 ]/[Rh] molar ratio above 1 resulted in strong inhibition of redox isomerization of oct-1-en-3-ol (entries 3-5). In the control experiments (entries 11, 12), mtppms did not show any isomerization activity, while the use of [RhCl(cod)] 2 led to a mere 3% conversion, in contrast to the value of 98% achieved with 1/mtppms-Na under identical conditions (entry 6). Under slightly different conditions (aqueous phosphate buffer, 1 bar H 2 , pH 7.0, 80 • C), 4 was found to have a preference for hydrogenation (58% yield in 1 h) over redox isomerization (48% yield), and was not further scrutinized in detail. Figure 2 shows the progress of the redox isomerization of oct-1-en-3-ol with 1/mtppms-Na as the catalyst. The reaction proceeded smoothly according to a saturation curve, was selective to formation of octan-3-one, and led to a conversion of 98% in one hour at 80 • C. a mere 3% conversion, in contrast to the value of 98% achieved with 1/mtppms-Na under identical conditions (entry 6). Under slightly different conditions (aqueous phosphate buffer, 1 bar H2, pH 7.0, 80 °C), 4 was found to have a preference for hydrogenation (58% yield in 1 h) over redox isomerization (48% yield), and was not further scrutinized in detail. Figure 2 shows the progress of the redox isomerization of oct-1-en-3-ol with 1/mtppms-Na as the catalyst. The reaction proceeded smoothly according to a saturation curve, was selective to formation of octan-3-one, and led to a conversion of 98% in one hour at 80 °C. Study of the effect of temperature on the rate of isomerization revealed that the reaction proceeded slowly at low temperatures (below 40 • C, Figure 3). In contrast, above 55 • C an increase of the reaction rate was observed, so much so, that at 80 • C, 99% conversion was achieved in 2 hours. Therefore, further measurements were carried out at 80 • C. As seen on Figure 3, the temperature dependence of the reaction rate did not follow the Arrhenius relation. However, it should be mentioned, that this relation is valid only to the temperature dependence of rate coefficient(s) of known kinetic equations. Data at high conversions are not suitable to represent the reaction rate, furthermore, in aqueous-organic biphasic systems, transport of the substrate to the aqueous phase may have a smaller temperature dependence than the catalytic reaction itself. Altogether, these causes may lead to deviations from the expected exponential rate increase. Study of the effect of temperature on the rate of isomerization revealed that the reaction proceeded slowly at low temperatures (below 40 °C, Figure 3). In contrast, above 55 °C an increase of the reaction rate was observed, so much so, that at 80 °C, 99% conversion was achieved in 2 hours. Therefore, further measurements were carried out at 80 °C. As seen on Figure 3, the temperature dependence of the reaction rate did not follow the Arrhenius relation. However, it should be mentioned, that this relation is valid only to the temperature dependence of rate coefficient(s) of known kinetic equations. Data at high conversions are not suitable to represent the reaction rate, furthermore, in aqueous-organic biphasic systems, transport of the substrate to the aqueous phase may have a smaller temperature dependence than the catalytic reaction itself. Altogether, these causes may lead to deviations from the expected exponential rate increase. From an environmental and economic point of view, the amount of the applied catalyst cannot be neglected. Increasing the amount of the catalyst in the reaction mixture, resulted in a linear increase of the conversion (Figure 4). Beyond practical considerations, this rate dependence suggests a 1 st order kinetics with regard to the catalyst concentration. Nevertheless, it has to be born in mind, that the detailed study of the reaction kinetics was not considered as a part of the present study, and the data shown on Figures 2-4 rather serve the optimization of a synthetic procedure than the scrutiny of the underlying molecular events.
Due to the in situ preparation of the catalyst solution, most of the reaction mixtures contained 13.0% V/V methanol. In such a solution the conversion increased to 60% from 40%, determined in From an environmental and economic point of view, the amount of the applied catalyst cannot be neglected. Increasing the amount of the catalyst in the reaction mixture, resulted in a linear increase of the conversion (Figure 4). Beyond practical considerations, this rate dependence suggests a 1st order kinetics with regard to the catalyst concentration. Nevertheless, it has to be born in mind, that the detailed study of the reaction kinetics was not considered as a part of the present study, and the data shown on Figures 2-4 rather serve the optimization of a synthetic procedure than the scrutiny of the underlying molecular events.
Catalysts 2020, 10, x FOR PEER REVIEW 9 of 18 a very important aspect for the pharmaceutical industry. Complexes containing highly ionic ligands, such as sulfonated water-soluble phosphines and/or N-heterocyclic carbenes, usually have very low solubility in organic solvents and thus do not pollute the product. We checked the recovery and reuse of the catalyst 1/mtppms-Na in redox isomerization of oct-1-en-3-ol (Table 2). After each catalytic cycle, the reaction mixture was cooled to room temperature, and was extracted with hexane. After phase separation, the catalyst-containing aqueous phase was used again to catalyze the reaction of a new batch of oct-1-en-3-ol. In the first recycle, the catalytic activity of complex 2 dropped approximately 20%, however, in the third recycle it did not decrease significantly. Table 2. Recycling of the catalyst (1/mtppms-Na) in redox isomerization of oct-1-en-3-ol. We undertook a study of the isomerization of various allylic alcohols with catalysts 1/mtppms-Na and 5, and the summarized results are presented in Table 3. The water-insoluble (or only slightly soluble) allylic alcohols were isomerized with high turnover frequencies, however the water-soluble substrates like prop-1-en-3-ol and but-1-en-3-ol showed smaller conversions. The obtained TOF values calculated from conversions determined at 30 min reaction times, were between 13-152 h -1 .

Entry Run Octan-3-on (%) a TOF (h
In aqueous organometallic catalysis, one of the most important reaction parameters is the solution pH, especially in cases when the reactions proceed with formation or consumption of H + (a typical example is the heterolytic splitting of H2) [55]. For that reason, we investigated the effect of the pH of the reaction mixture on the isomerization of 2-methylprop-1-en-3-ol, using 5 as the catalyst. As can be seen on Figure 5, the conversion of the substrate allylic alcohol varied according to a maximum curve, with the highest conversions around pH 7.5.  Due to the in situ preparation of the catalyst solution, most of the reaction mixtures contained 13.0% V/V methanol. In such a solution the conversion increased to 60% from 40%, determined in water alone as solvent. The increased conversion was most probably due to the increased solubility of oct-1-en-3-ol in the mixed solvent. Nevertheless, these data show, that an aqueous solution of 2 is suitable as a catalyst for the redox isomerization of oct-1-en-3-ol, as well as in the absence of any co-solvent. In such cases, however, an aqueous-organic biphasic reaction mixture is obtained, in which the organic phase is formed by the substrate itself.
One important reason for application of water-soluble catalysts in organic synthesis is the possible recirculation of the catalyst solution. Provided the catalyst is insoluble in the organic phase made up by appropriate solvents and/or the substrates/products, recovery of the catalyst can be achieved by liquid-liquid phase separation. In favorable cases, not only can the catalyst be recycled, but the product can be collected practically free of catalyst residues (metal contamination), which is a very important aspect for the pharmaceutical industry. Complexes containing highly ionic ligands, such as sulfonated water-soluble phosphines and/or N-heterocyclic carbenes, usually have very low solubility in organic solvents and thus do not pollute the product.
We checked the recovery and reuse of the catalyst 1/mtppms-Na in redox isomerization of oct-1-en-3-ol (Table 2). After each catalytic cycle, the reaction mixture was cooled to room temperature, and was extracted with hexane. After phase separation, the catalyst-containing aqueous phase was used again to catalyze the reaction of a new batch of oct-1-en-3-ol. In the first recycle, the catalytic activity of complex 2 dropped approximately 20%, however, in the third recycle it did not decrease significantly. We undertook a study of the isomerization of various allylic alcohols with catalysts 1/mtppms-Na and 5, and the summarized results are presented in Table 3. The water-insoluble (or only slightly soluble) allylic alcohols were isomerized with high turnover frequencies, however the water-soluble substrates like prop-1-en-3-ol and but-1-en-3-ol showed smaller conversions. The obtained TOF values calculated from conversions determined at 30 min reaction times, were between 13-152 h −1 . In aqueous organometallic catalysis, one of the most important reaction parameters is the solution pH, especially in cases when the reactions proceed with formation or consumption of H + (a typical example is the heterolytic splitting of H 2 ) [55]. For that reason, we investigated the effect of the pH of the reaction mixture on the isomerization of 2-methylprop-1-en-3-ol, using 5 as the catalyst. As can be seen on Figure 5, the conversion of the substrate allylic alcohol varied according to a maximum curve, with the highest conversions around pH 7.5.
As discussed earlier, the rate of the redox isomerization of allylic alcohols was a linear function of the catalyst concentration, and the reaction was inhibited by an excess of mtppms-Na. Furthermore, the catalysts [Rh(bmim)(cod)(pta)]BF 4 (5), and with lesser activity, [RhCl(cod)(sSIMes)] (1) did not need the presence of H 2 gas for catalysis of the reaction. Finally, the rate of redox isomerization of 2-methylprop-1-en-3-ol, catalyzed by 5, showed a sharp maximum as the function of pH. All these findings are consistent with the η 3 -oxo-allyl mechanism of such reactions ( Figure 6).
Catalysts 2020, 10, x FOR PEER REVIEW 11 of 18 Figure 6. The suggested η 3 -oxo-allyl mechanism of the redox isomerization of allylic alcohols in aqueous media catalyzed by the Rh(I)-complexes 1, 1/mtppms-Na, and 5 studied in this work.
According to the suggested mechanism, in the first step of the catalytic cycle, a deprotonated allylic alcohol coordinates to the metal complex, both with its olefinic bond, and the oxygen donor atom. This step is facilitated in more basic solutions but is retarded by an excess of the phosphine ligand, provided that the required free coordination site on Rh(I) is created by phosphine dissociation. Subsequent β-hydride elimination results in formation of a hydrido-metal-enone intermediate which rearranges to a π-oxo-allyl complex. Protonation (from the solvent) of this intermediate leads to formation of the free enol, which then rearranges to the more stable carbonyl product. This last step is more facile in acidic solutions, and the proton production and consumption in the first and lasts steps of the catalytic cycle, respectively, may lead to the observed maximum of the rate as the function of pH. This description of the reaction mechanism agrees with the limited experimental findings, however, for establishing a sound mechanistic suggestion more detailed investigations are required.

General Methods
1 H and 13 C{ 1 H}, 31 P{ 1 H} NMR spectra were recorded on Bruker Avance 360 MHz and Bruker DRX 400 NMR spectrometers (Bruker, Billerica, MA, USA) and were referenced to residual solvent According to the suggested mechanism, in the first step of the catalytic cycle, a deprotonated allylic alcohol coordinates to the metal complex, both with its olefinic bond, and the oxygen donor atom. This step is facilitated in more basic solutions but is retarded by an excess of the phosphine ligand, provided that the required free coordination site on Rh(I) is created by phosphine dissociation. Subsequent β-hydride elimination results in formation of a hydrido-metal-enone intermediate which rearranges to a π-oxo-allyl complex. Protonation (from the solvent) of this intermediate leads to formation of the free enol, which then rearranges to the more stable carbonyl product. This last step is more facile in acidic solutions, and the proton production and consumption in the first and lasts steps of the catalytic cycle, respectively, may lead to the observed maximum of the rate as the function of pH. This description of the reaction mechanism agrees with the limited experimental findings, however, for establishing a sound mechanistic suggestion more detailed investigations are required.

General Methods
1 H and 13 C{ 1 H}, 31 P{ 1 H} NMR spectra were recorded on Bruker Avance 360 MHz and Bruker DRX 400 NMR spectrometers (Bruker, Billerica, MA, USA) and were referenced to residual solvent peaks and to 85% phosphoric acid. A Bruker maXis II MicroTOF-Q type Qq-TOF-MS instrument (Bruker Daltonik, Bremen, Germany) was used to obtain high-resolution electrospray ionization mass spectra (HR ESI-MS) in positive ion mode, and controlled by Compass Data Analysis 4.4 software from Bruker.

Synthesis of [RhCl(bmim)(cod)] (3)
In an argon-filled Schlenk tube in 20 mL distilled CH 2 Cl 2 0.327 g (0.717 mmol) [Rh(OH)(cod)] 2 was dissolved, and then 5 mL CH 2 Cl 2 0.25 g (1.434 mmol) [bmimH]Cl was added. The solution was stirred for 6 h at reflux temperature, and then the solvent was removed under vacuum yielding a dark yellow sticky residue. This residue was cooled in liquid N 2 , and triturated several times with small portions of cold diethyl ether, yielding 3 as a light yellow powder. Yield: 0.413 g (1.08 mmol), 75%. 1

Synthesis of Na 2 [Rh(bmim)(cod)(mtppts)] (4)
In an argon-filled Schlenk tube, 0.200 g (0.520 mmol) [RhCl(bmim)(cod)] (3) was dissolved in 20 mL acetone. To the resulting clear yellow solution 0.323 g (0.520 mmol) mtppts-Na 3 was added followed by 3.5 mL deoxygenated water, upon which the colour of the solution became dark yellow. After 5 min stirring the solvent was evaporated in vacuum, and the resulting sticky residue, cooled in liquid N 2 , was triturated with small portions of cold diethyl ether, yielding 4 as a yellow solid. Yield: 0.212 g (0.210 mmol), 40%. 1 4 were dissolved. The solution was stirred at reflux temperature for 4 h, followed by filtering under argon. A portion of 0.137 g (0.88 mmol) pta was added and stirred for another 2 h at reflux temperature. Then it was filtered again and the solvent was removed by evaporation under vacuum. The sticky residue was cooled in liquid N 2 and triturated with small portions (5 mL) of cold diethyl ether yielding 0.332 g (0.559 mmol), 64%, product.

General Procedure Redox Isomerization of Allylic Alcohols
Catalytic isomerization of allylic alcohols was performed in Schlenk tubes, into which 1× 10 −3 mol allylic alcohol and 1 × 10 −5 mol 1, 3, 4, 5, or 2 × 10 −5 mol 1 together with 2 × 10 −5 mol mtppms-Na (in 450 µL MeOH) were dissolved in 3 mL deoxygenated water or aqueous phosphate buffer. All reactions were carried out under oxygen-free atmosphere using argon or nitrogen gas. The reaction mixtures were heated (80 • C) in a thermostated bath and stirred for the desired reaction time, then cooled to room temperature. In the case of water-insoluble substrates, the product mixtures were extracted twice with 1 mL of chloroform, the extracts were dried over MgSO 4 , and the conversions were determined by gas chromatography or by 1 H NMR (CDCl 3 ). In the case of water-soluble allylic alcohols, the conversions were determined by 1 H NMR (D 2 O). The presented yields are averages of 3-5 measurements, with a reproducibility of ±3%.
In the catalyst recycling experiments, the reaction mixtures was cooled down to room temperature (r.t.). The extraction was done under argon with 2 mL of hexane. Traces of hexane were removed from the aqueous phase by stirring under vacuum for 20 min at r.t., and the resulting aqueous solution of the catalyst was used in the next catalytic cycle.

Conclusions
We have prepared new water-soluble Rh(I)-NHC complexes with a combination of bmim or sulfonated SIMes (sSIMes) as N-hetrocyclic carbene, and mono-or trisulfonated triphenylphosphine (mtppms-Na, mtppts-Na 3 ) or 1,3,5-triaza-7-phosphadamantane (pta) as phosphine ligands. These complexes proved active catalysts for redox isomerization of various alk-1-en-3-ols in aqueous reaction systems. The reactions were selective to the ketone product and proceeded under inert atmosphere with no need of hydrogen. The water-solubility of the catalysts allowed recycling with modest loss of activity. Based on these attributes, the redox isomerization of allylic alcohols catalyzed by the Rh(I)-NHC-phosphine complexes may serve as the basis for useful synthetic procedures.