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Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their coordination chemistry has been characterized using pH-potentiometry and spectroscopic methods [UV-vis, electron paramagnetic resonance (EPR), and electron-electron double resonance (ELDOR)-detected NMR (EDNMR)] in aqueous solution. Several bridging moieties between the two salicylamine functions were introduced, e.g., ethyl (HSS), propyl (PrHSS), butyl (BuHSS), cyclohexyl (cis-CyHSS, trans-CyHSS), and diphenyl (dPhHSS). All of the investigated ligands feature excellent copper(II) binding ability via the formation of a (O-,N,N,O-) chelate system. The results indicated that the cyclohexyl moiety significantly enhances the stability of the copper(II) complexes. EPR studies revealed that the arrangement of the coordinated donor atoms is more symmetrical around the copper(II) center and similar for HSS, BuHSS, CyHSS, and dPhHSS, respectively, and a higher rhombicity of the g tensor was detected for PrHSS. The copper(II) complexes of the sulfosalan ligands were isolated in solid form also and showed moderate catalytic activity in the Henry (nitroaldol) reaction of aldehydes and nitromethane. The best yield for nitroaldol production was obtained for copper(II) complexes of PrHSS and BuHSS, although their metal binding ability is moderate compared to that of the cyclohexyl counterparts. However, these complexes possess larger spin density on the nitrogen nuclei than that for the other cases, which alters their catalytic activity.

In aqueous HBr solution (58% w/w), 1,3,5-triaza-7-phosphaadamantane (PTA) yielded the hitherto unknown triprotonated PTA, as single crystals. In addition, the same reaction mixture deposited crystals of [O = P(CH2NH3)3]Br3 (2), formed presumably by ring opening of [PTA-H3]Br3 (3) and oxidation of the resulting [P(CH2NH3)3]Br3 (1). The solid state structure of 2 and 3 were determined by X-ray diffraction. In water/methanol mixtures, reaction of 1 and [{(η6-C10H14)RuBr2}2] yielded the half-sandwich [(η6-C10H14)RuBr2{P(CH2NH3)3}]Br3 (4) which –in aqueous solution– spontaneously afforded the dinuclear [(η6-C10H14)RuBr2{μ4-P(CH2NH2)3}Ru(η6-C10H14)]Br2 (5).

Four new dinuclear iridium(I) complexes were synthesized from the di(N-heterocyclic carbene) ligand precursors 1,1′-methylene-bis(3-benzyl-imidazolium)dichloride and 1,1′-methylene-bis(3-(2,4,6-trimethylbenzyl)imidazolium)dichloride. The complexes were fully characterized by spectroscopic methods, HR-MS (ESI) spectrometry, furthermore, the structure of complexes 1 and 2 were determined by single-crystal X-ray diffraction. Complexes 3a and 3b which have sulfonated triphenylphosphine ligands, were successfully used under mild conditions as catalysts in reduction reaction of ketones via hydrogen transfer from aqueous 2-propanol, and for hydrogenation of alkynes in aqueous-organic biphasic systems.

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The effect of the mobile interconversion of [RuHCl(CO)(mtppms-Na)3] 1, and [RuH(H2O)(CO)(mtppms-Na)3]+ 2, was studied in hydrogenation of phenylacetylene and cinnamaldehyde in aqueous–organic biphasic systems, as a function of the chloride concentration and the pH of the aqueous phase. Catalytic activity of the two complexes was also determined in homogeneous organic solvents without any additives. In the biphasic system, the rate of selective hydrogenation of phenylacetylene to styrene was strongly increased upon addition of NaCl, while the reaction of cinnamaldehyde slowed, with no change in product distribution. Both reactions responded with a rate decrease upon increasing the pH of the aqueous phase. It was concluded that hydrogenation of phenylacetylene was catalyzed by 1 with no chloride dissociation, while in the reduction of cinnamaldehyde, the aquo-complex 2 was the active catalytic species. Catalytic cycles were suggested to rationalize these findings.

Hydrogen gas generation with an effective response to changing application demands was achieved with the use of a hydrogen storage battery based on aqueous cesium bicarbonate hydrogenation/formate dehydrogenation, homogeneously catalyzed by an Ir(I) N-heterocyclic carbene complex. In this device, the storage solution was circulated through a small volume tubular reactor heated to the required high temperature to allow fast hydrogen evolution while the high volume reservoir was kept at ambient temperature at which no H2 was generated. Merely by the control of the reactor temperature, it was possible to regulate the rate of hydrogen evolution as required. The results also demonstrate the feasibility of homogeneous catalysis for the purpose of hydrogen generation in flow systems.

The adduct of acetylenedicarboxylic acid and the water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA, 1) in 1:2 molar ratio, was synthesized both in aqueous solution and under anhydrous conditions in a planetary ball mill (pbm). The resulting double phosphabetaine (2) was characterized by 1H-, 13C-, and 31P-NMR spectroscopy, ESI-mass spectroscopy, and elemental analysis, furthermore, its solid-state structure was determined by single crystal X-ray diffraction. SXRD also revealed that in aqueous solution 2 reacted with AgSO3CF3 to yield a 2 D polymer.

We have described earlier that in aqueous solutions, the reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with maleic acid yielded a phosphonium-alkanoate zwitterion. The same reaction with 2-methylmaleic acid (citraconic acid) proceeded much slower. It is reported here, that in the case of glutaconic and itaconic acids (constitutional isomers of citraconic acid), formation of the corresponding phosphabetaines requires significantly shorter reaction times. The new phosphabetaines were isolated and characterized by elemental analysis, multinuclear NMR spectroscopy and ESI-MS spectrometry. Furthermore, their molecular structures in the solid state were determined by single crystal X-ray diffraction (SC-XRD). Synthesis of the phosphabetaines from PTA and unsaturated dicarboxylic acids was also carried out mechanochemically with the use of a planetary ball mill, and the characteristics of the syntheses in solvent and under solvent-free conditions were compared. In aqueous solutions, the reaction of the new phosphabetaines with Ag(CF3SO3) yielded Ag(I)-based coordination polymers. According to the SC-XRD results, in these polymers the Ag(I)-ion coordinates to the N and O donor atoms of the ligands, however, Ag(I)-Ag(I) interactions were also identified. The Ag(I)-based coordination polymer (CP1.2) formed with the glutaconyl derivative of PTA (1) showed considerable antimicrobial activity against both Gram-negative and Gram-positive bacteria and yeast strains

Water-soluble salan ligands were synthesized by hydrogenation and subsequent sulfonation of salens (N,N&rsquo, bis(slicylidene)ethylenediamine and analogues) with various bridging units (linkers) connecting the nitrogen atoms. Pd (II) complexes were obtained in reactions of sulfosalans and [PdCl4]2&minus, Characterization of the ligands and complexes included extensive X-ray diffraction studies, too. The Pd (II) complexes proved highly active catalysts of the Suzuki&ndash, Miyaura reaction of aryl halides and arylboronic acid derivatives at 80 &deg, C in water and air. A comparative study of the Pd (II)&ndash, sulfosalan catalysts showed that the catalytic activity largely increased with increasing linker length and with increasing steric congestion around the N donor atoms of the ligands, the highest specific activity was 40,000 (mol substrate) (mol catalyst &times, h)&minus, 1. The substrate scope was explored with the use of the two most active catalysts, containing 1,4-butylene and 1,2-diphenylethylene linkers, respectively.

A water-soluble Pd(II)-salan complex Na2[Pd(HSS)] (HSS = sulfonated tetrahydrosalen or sulfosalan) was examined as a hydrolytically stable catalyst for hydrogenation of various aldehydes. Na2[Pd(HSS)] was found to be a highly selective catalyst towards hydrogenation of C=C over C=O bonds in cinnamaldehyde and crotonaldehyde (used as representative α,β-unsaturated aldehydes). Kinetic measurements revealed an important role of protonation/deprotonation of one of the phenolate oxygens of the N2O2 coordination framework in the reaction mechanism. Na2[Pd(HSS)] was also found an efficient catalyst for transfer hydrogenation of aldehydes from isopropanol in the presence of various bases. The results show, for the first time, the usefulness of easily accessible, hydrolytically stable Pd(II)-salan type catalysts in aqueous catalytic organometallic hydrogenations.

The highly selective formation of cinnamalcohol in hydrogenation of trans-cinnamaldehyde with [{RuCl2(mtppms)2}2] + mtppms as catalyst (mtppms = monosulfonated triphenylphosphine) in aqueous solution was substantially accelerated by NaHCO3 (in 20–50 mol% quantities relative to cinnamaldehyde). More than double conversion compared to bicarbonate-free systems was observed at n(NaHCO3)/n(Ru) = 20. Prehydrogenation of the reaction mixture before the addition of cinnamaldehyde resulted in further rate increase (45.3% conversion vs. 13.1% in water). 1H , 13C and 31P NMR studies revealed that formate produced in hydrogenation of bicarbonate facilitated formation of trans-[Ru(H)2(H2O)(mtppms)3], a better catalyst than cis-fac-[Ru(H)2(H2O)(mtppms)3] which is the product of the reaction of [{RuCl2(mtppms)2}2] + mtppms with H2 in the absence of formate (or bicarbonate). Accordingly, NaHCO2 produced even higher rate increase than the same amount of NaHCO3.

Five new complexes of the type [RuCl2(NHC)(η6-arene)] (4, 5, and 6) and [RuCl(NHC)(η6-arene)(PR3)]Cl (7 and 8) (NHC N-heterocyclic carbene = bmim, emim; arene = benzene, p-cymene; PR3 = PPh3 or pta = 1,3,5-triaza-7-phosphaadamantane) were synthetized and applied as catalysts (together with the known [RuCl2(bmim)(η6-p-cymene)] (3) with and without added PPh3) in racemization of optically active secondary alcohols in toluene. The highest catalytic activity, TOF = 9.3 h−1 (ee as low as 1.3% in 4 h at 95 °C) was observed in racemization of (S)-1-phenylethanol with a catalyst (4 mol%) prepared in situ from 3 and 1 equivalent of PPh3. It is of practical significance that formation of acetophenone byproduct was suppressed to 3.5% by 17% v/v isopropanol in toluene. DFT calculations revealed that the rate determining step in the suggested reaction mechanism was the agostic coordination of hydrogen on the chiral carbon atom of the alcohol substrate.

The newly synthesized mer-trans-[RuCl2(OH2)(PTA)3] (1) is the first compound isolated in solid state containing the Ru(PTA)3-fragment (PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane). Dissolution of 1 in aqueous HCl leads to mer-[RuCl3(HPTA)3]Cl2 (2) which is stable in the dark but is transformed into fac-[RuCl3(HPTA)3]Cl2 (3) under visible light. Irradiation with visible light of an aqueous solution of 1 at room temperature or refluxing of the same solution in the dark leads to the formation of [{Ru(PTA)3}2(μ-Cl)3]Cl (4). The dinuclear complex 4 was also formed upon irradiation of solutions of PTA and various Ru(II)-complexes ([RuCl2(DMSO)4], [{RuCl2(η6-p-cymene)}2]) or cis-cis-trans-[RuCl2(DMSO)2(PTA)2]). All complexes were characterized by elemental analysis and NMR spectroscopy, furthermore solid state structures of 2·1.25H2O, 3·HCl·2H2O and 4·9H2O were also determined by single crystal X-ray diffraction. We have investigated the influence of the above photochemical processes on reduction of benzaldehyde and cinnamaldehyde with trans-[RuCl2(PTA)4] and cis-cis-trans-[RuCl2(DMSO)2L2] (L = PTA, (PTA-Me)CF3SO3, (PTA-Bn)Cl; Me = methyl, Bn = benzyl) complexes as catalysts. The effect of visible light on benzonitrile hydration with various Ru(II)-PTA catalysts is also reported.

In this work we have found, that the water-soluble cis,mer-[IrH2Cl(mtppms)3] (mtppms = monosulfonated triphenylphosphine Na-salt) was an excellent catalyst for reduction of terminal alkynes by hydrogen transfer from aqueous HCOOH/HCOONa mixtures. The conversions strongly depended on the pH of the reaction mixtures, and the highest rate of phenylacetylene transfer hydrogenation was observed at pH 3. The same dihydrido-Ir(III) complex actively catalyzed also the hydrogenation of terminal alkynes under mild conditions (T = 50 °C; P(H2) = 2–10 bar). Importantly, both the hydrogenation and hydrogen transfer reductions afforded exclusively the corresponding alkenes as products. Phenylacetylene and its substituted derivatives reacted smoothly, while benzylic and aliphatic alkynes were less reactive or did not react at all. It was also found, that an excess of the mtppms ligand inhibited the reaction. This was rationalized by formation of cisz-[IrH2(mtppms)4]+ which was also confirmed with multinuclear NMR spectroscopy. On the basis of the experimental results, a joint mechanism was suggested for both the hydrogenation and transfer hydrogenation pathways. The mechanism of hydrogenation and transfer hydrogenation of phenylacetylene was also studied by DFT calculations, which revealed several possibilities for protonation of a vinyl intermediate as the crucial step in formation of the styrene product.

1,3,5-Triaza-7-phosphaadamantane (pta, phosphaurotropine) played a special role in the development of aqueous organometallic chemistry and catalysis. The main reason is in its easy synthesis, oxidation stability, versatile possibilities of functionalization, and high solubility not only in water but also in several common organic solvents. Such favourable solubility behaviour allowed straightforward synthesis of pta-containing transition metal complexes from simple, inexpensive, often commercial starting materials. A further advantage of pta and its complexes is in their pronounced tendency to crystallize which allowed determination of solid-state structures of a great number of such compounds. This review covers synthetic procedures of ruthenium(II)-complexes with pta, and N-alkyl-pta derivatives as ligands, as well as their most important reactions in aqueous systems. Ru(II)-pta complexes were employed as catalysts in several important aqueous-phase processes such as selective hydrogenation and transfer hydrogenation of aldehydes, hydration of nitriles, and redox isomerization of allylic alcohols. Hydrogenation of carbon dioxide/bicarbonate and dehydrogenation of formic acid/aqueous formate were also studied with various Ru(II)-complexes of phosphaurotropines. Altogether the results described in this review made a significant positive impact on the development of green chemical processes.

A new, solvent-free method has been developed for the synthesis of 7-(2-carboxy-ethyl)-1,3,5-triaza-7-(phosphoniatricyclo)[3.3.1.13,7]decane (L). It is disclosed here that 1,3,5-triaza-7-phosphaadamantane (PTA) reacted cleanly with acrylic acid in a planetary ball mill resulting in 88% yield of the corresponding P-carboxy-ethyl derivative, in striking contrast to the complete failure of the synthesis of the same product from the same reactants in solution. The resulting phosphabetaine, L gave crystalline 1D coordination polymers with Ag+-salts bearing PF 6 - , p-toluenesulfonate (tos) and trifluoromethanesulfonate (OTf) anions. According to single-crystal X-ray diffraction studies, the solid state structures of these coordination polymers were decisively influenced by the anion of the Ag+-salt used for synthesis. In addition to single-crystal X-ray diffraction, the new Ag-based coordination polymers, namely [Ag(μ3-L-κ3N:O:O’)]n(PF6)n, (1), [Ag(tos)(μ3-L-κ3N:N:O)]n·nH2O, (2), and [Ag(OTf)(μ3-L-κ3N:O:O’)]n, (3) were characterized also by elemental analysis, 1H-, 13C-, and 31P NMR, as well as IR spectroscopies and with ESI mass spectrometry. Determination of the hydrodynamic diameter of the phosphabetaine ligand and its Ag+-complexes by diffusion NMR measurements revealed, that upon dissolution in water these compounds did not retain their polymeric nature.

The water-soluble [RuCl2(pta)(η6-p-cymene)] (pta = 1,3,5-triaza-7-phosphaadamantane) was applied as catalyst in the transposition of allylic alcohols, such as oct-1-en-3-ol in aqueous media. The isomerisation of oct-1-en-3-ol to octan-3-one took place only at pH > 10 buffer solutions or in the presence of alkali metal carbonates. The aqueous solution of “in situ” catalyst ([RuCl2(pta)(η6-p-cymene)] + 2 eq Na2CO3) could be reused in the biphasic isomerization of oct-1-en-3-ol for at least five times without a significant loss of the catalytic activity. It was demonstrated that carbonate is not only a base in this reaction but leads to formation of a highly active catalyst, [Ru(η2-O2CO)(pta)(η6-p-cymene)]. This compound was isolated as crystalline solid and characterized in detail (including X-ray diffraction).

The formation of hydride derivatives of sulfonated palladium(II) salan (hydrogenated salen) complexes was studied with DFT methods. The non-hydrolytic property, chirality, and flexibility lead to a significant difference compared to salen derivatives. We made a detailed computational study to understand the relevance of the flexibility in contrast to the rigid salen complex. Two main pathways were investigated: one of them was a direct monohydride formation where the oxygen of the phenolate group was substituted by a hydrogen molecule followed by a proton transfer. Another was an indirect monohydride formation involving the substitution of phenolate arm by a solvent water molecule in the first step and subsequent reaction with H2 in the second. We focused on weak interactions among the Pd-complex and water molecules. Trigonal, square, and diamond motifs of H-bond networks were found around the oxygen atom of the phenolate arm which is crucial during the proton transfer step, however, substitution steps prefer chain type motifs.

The recently synthesized water-soluble Na2[Pd(HSS)] (Na2HSS = hydrogenated sulfonated salen) was shown to be a non-toxic, active catalyst for modification of model and biomembranes by homogeneous catalytic hydrogenation. Hydrogenation of the unsaturated fatty acyl residues in soy-bean lecithin liposomes and in biomembranes of intact Pseudomonas putida F1 cells was accompanied by substantial cis-trans isomerization around the C C double bonds. The hydrogenations could be run in aqueous media under mild conditions (25 °C, 1 bar H2). Partial saturation (up to 10% conversion) of the membrane lipids of P. putida F1 did not damage the cells.

An environment-friendly, convenient, fast and solvent-free mechanochemical approach have been accomplished for the synthesis of several diimidazolium salts and the bridging dinuclear rhodium(I)–N-heterocyclic carbene complexes of the type [{RhCl(cod)}2(μ-di-NHC)] derived from them. The compounds were synthesized also by the classical solvent method and the results of the two approaches were compared. A systematic study of both the mechanochemical and the solvent syntheses has also been carried out to determine the effects of various factors influencing the reactions. This is the first report on the mechanochemical synthesis of poly-NHC metal complexes as well as NHC–Rh complexes in ball mill.

With use of a Pd(II)-sulfosalan complex as a water-soluble catalyst, we have developed an efficient synthesis of biaryls via Suzuki–Miyaura cross-coupling in water under aerobic conditions. The water-insoluble target molecules were isolated by simple filtration in analytical purity after washing with 0.01 M aqueous HCl (20 examples). In most cases, palladium contamination was below 5 ppm considered acceptable for active pharmaceutical ingredients. The established method is scalable, reproducible, and provides biaryl products in isolated yields up to 91%.

A novel iridium based, water-soluble phosphine-NHC (N-heterocyclic carbene) complex, Na2[Ir( emim)(η4-COD)( mtppts)] was previously developed in our research group. It was shown that it is a very effective catalyst for the reversible storage of hydrogen based on the formate-bicarbonate equilibrium. In this paper, we present a DFT investigation on the noninnocent behavior of the NHC ligand toward C-H activation of the N-ethyl side chain and its possible role in the hydrogen storage mechanism. After preliminary investigations, using both computations and NMR measurements, we conclude that the COD ligand leaves the precatalyst irreversibly and the C-H activation takes place on a monophosphine complex. Two main pathways are considered in which the active Ir(III) complexes are generated differently: One is the cyclometalation path involving the ethyl side chain, the other is the oxidative addition step of a water molecule which has a higher barrier but provide a more stable starting state. We find that though the latter, a catalytic cycle where a hydride is abstracted from formate and gets protonated by solvent molecules gives the lowest calculated energy barrier, +25.8 kcal mol-1. That is, avoiding further redox processes is preferred. There are other pathways involving thermodynamically accessible C-H activated iridacycles but those involve slightly higher overall activation barriers due to the required Ir(I)/Ir(III) transitions. The cycle which involves only iridacycle intermediates offer the lowest energy span (energy difference calculated between only the highest and lowest energy points inside the cycle), however. Together with the experimental results, this implies that C-H activation of the N-ethyl side chain happens off-cycle or the starting solvent addition step of the dominant pathway is blocked kinetically. We also discuss the hydrogen uptake reaction catalyzed by cyclometalated species where the reduction of CO2 is preferred over reversing the first main cycle.

The catalytic activity of [RuClCp(HdmoPTA)(PPh3)](OSO2CF3) (1) and the dimeric complexes [RuClCp(PPh3)-μ-dmoPTA-1κP:2κ2N,N'-MCl2] (M = Ni (2), Co (3), Zn (4)) for the isomerization in water under Ar and ambient atmosphere of 1-octen-3-ol, 1-hepten-3-ol and 1-hexen-3-ol was investigated. A detailed study was devoted to the catalytic activity under Ar of 1 for the isomerization of 1-octen-3-ol.

Unsaturated aldehydes were efficiently reduced by transfer hydrogenation from sodium formate in water–2-propanol mixtures using a water-soluble Ru(II)-tertiary phosphine catalyst. The reaction yielded unsaturated alcohols with complete selectivity and without hydrogenation or isomerization of C C bonds of the substrates. Very high reaction rate was observed in the transfer hydrogenation of cinnamaldehyde already at 30 °C with turnover frequency of 160 h−1 and this increased to 3800 h−1 at 70 °C. Consequently, the method is applicable to the synthesis of unsaturated alcohols in case of heat sensitive or highly volatile aldehydes, too. Based on multinuclear NMR investigations, trans-[RuH2(H2O)(mtppms)3] is suggested as the key catalytic species.

One of the most frequently used high-resolution glycan analysis methods in the biopharmaceutical and biomedical fields is capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection. Glycans are usually labeled by reductive amination with a charged fluorophore containing a primary amine, which reacts with the aldehyde group at the reducing end of the glycan structures. In this reaction, first a Schiff base is formed that is reduced to form a stable conjugate by a hydrogenation reagent, such as sodium cyanoborohydride. In large scale biopharmaceutical applications, such as clone selection for glycoprotein therapeutics, hundreds of reactions are accomplished simultaneously, so the HCN generated in the process poses a safety concern. To alleviate this issue, here we propose catalytic hydrogen transfer from formic acid catalyzed by water-soluble iridium(III)- and ruthenium(II)-phosphine complexes as a novel alternative to hydrogenation. The easily synthesized water-soluble iridium(III) and the ruthenium(II) hydrido complexes showed high catalytic activity in carbohydrate labeling. This procedure is environmentally friendly and reduces the health risks for the industry. Using carbohydrate standards, oligosaccharides released from glycoproteins with highly sialylated (fetuin), high mannose (ribonuclease B) and mixed sialo and neutral (human plasma) N-glycans, we demonstrated similar labeling efficiencies for iridium(III) dihydride to that of the conventionally used sodium cyanoborohydride based reaction. The derivatization reaction time was less than 20 min with no bias towards the above mentioned specific glycan structures.

1,3,5-triaza-7-phosphaadamantane was alkylated under solvent-free conditions with CH3I, CH3-(CH2)3-Br, Br-(CH2)4-Br, OH-CH2-CH2Br, and CH3CH2OOCCH2Br in a planetary ball mill with yields over 90%. Due to spontaneous resolution, both 1-(2-ethoxy-2-oxoethyl)-3,5-diaza-1-azonia-3,5-diaza-7-phosphaadamantane bromide (4) and (4-bromobutyl)-1-azonia-3,5-diaza-7-phosphaadamantane bromide (5) were obtained in the solid state as conglomerates of enantiomorphic crystals.

With the aim of identifying new types of water-soluble catalyst precursors for modification of biological membranes by homogeneous hydrogenation in aqueous solution and under mild conditions, we have performed detailed equilibrium and spectroscopic characterization of complex formation between nickel(II) or palladium(II) and salan-type ligands sulfonated in their aromatic rings (N,N′-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminoethane (HSS), N,N′-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminopropane (PrHSS) and N,N′-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminobutane (BuHSS)) in the slightly acidic–alkaline pH range. The stability constants of the metal complexes were determined using pH-potentiometry. The catalytic activities of the [Ni(HSS)] and [Pd(HSS)] complexes in hydrogenation and redox isomerization of oct-1-en-3-ol were also studied. The results indicate, that all of the investigated ligands exhibit excellent nickel(II) and palladium(II) binding ability via the formation of (O−,N,N,O−) linked chelate system. Both [Ni(HSS)] and [Pd(HSS)] catalyze the hydrogenation and redox isomerization of oct-1-en-3-ol. [Pd(HSS)] shows excellent activity and the reaction was highly selective to the formation of octan-3-ol. [Ni(HSS)] is also an active and selective catalyst for this hydrogenation reaction and to the best of our knowledge, [Ni(HSS)] is the first nickel(II)-based, hydrolytically stable, water-soluble catalyst bearing sulfonated salan moiety.

Seven new [Ir(NHC)(η4-cod)(L)] complexes (4–9, 11) with NHC = bmim, emim, L = Cl–, H2O, or the water-soluble phosphines mtppms-Na, mtppts-Na3, and pta were synthesized and characterized. Na2[Ir(bmi...

Ground state optimizations and excited state calculations were performed to analyze the possible anionic forms of Alizarin Red S(ulphonated) and its ML2 type metal complexes formed with palladium(II). Six functionals have been tested (B3LYP, M06-2X, M06, BH&HLYP, PBE0, LC-wPBE, and CAM-B3LYP) with two basis sets (6-311+g(d,p) and TZVP). The relative errors of these functionals in reproducing the experimental UV-Vis absorption wavelengths are reported for the energetically lowest lying isomers. It was found that the degree of deprotonation affects several functionals in a systematic way. M06 and CAM-B3LYP xc-functionals gave the best estimates according to the average relative errors. These two functionals were then used to explore the coordination mode (hydroxy-keto or catechol) of the palladium(II) complexes and the effect of (de)protonation. © 2014 Elsevier B.V.

New sulfonated tetrahydrosalen-type ligands and their water-soluble palladium(II) complexes have been synthesized. The palladium(II) complexes catalyze the Sonogashira coupling (23 examples) of various aryl halides (including chloroarenes) with terminal alkynes, with good to excellent conversions under mild conditions (80°C, air, no Cu(I) cocatalyst) in aqueous-organic mixtures and turnover frequencies of up to 2790 h(-1) . Under optimized reaction conditions to minimize environmental contamination, diphenylacetylenes can be isolated in 76-98% yield. The aqueous catalyst solution can be recycled four times with decreasing activity; however, yields between 93 and 98% can still be achieved with extended reaction times. Several water-insoluble products can be isolated in excellent yield by simple filtration and purification by washing with water; this method is used, for the first time, for this type of C-C coupling procedure.

The discovery and development of N-heterocyclic carbenes is no doubt one of the biggest success stories in the era of modern chemistry. In the last three decades, poly-N-heterocyclic carbenes have received increasing attention and a large number of reports have been published on the use of poly-NHC complexes in water. This paper is aimed to provide an overall review on poly-N-heterocyclic carbene complexes that are either water-soluble or have applications in aqueous media or both. The first two sections of the review are related to the types and general structural properties of poly-NHCs. The next part deals with the general advantages of using water and the last two sections are about poly-NHC complexes in aqueous media and their applications in various fields including catalysis, photophysics and medicine.

Molecular hydrogen, obtained by water electrolysis or photocatalytic water splitting, can be used to store energy obtained from intermittent sources such as wind and solar power. The storage and safe transportation of H2 , however, is an open and central question in such a hydrogen economy. Easy-to-synthesize, water-soluble iridium-N-heterocyclic carbene-phosphine (Ir(I) -NHC-phosphine) catalysts show unprecedented high catalytic activity in dehydrogenation of aqueous sodium formate. Fast reversible generation and storage of hydrogen can be achieved with these catalysts by a simple decrease or increase in the hydrogen pressure, respectively.

For applications in aqueous media, sulfonated tetrahydrosalen (sulfosalan, HSS) was synthesized by sulfonation of tetrahydrosalen in fuming sulfuric acid. The Pd(II) complex of this ligand, [Pd(HSS)], showed outstanding activity in hydrogenation and redox isomerization of allylic alcohols in homogeneous aqueous solutions or in aqueous–organic biphasic systems (for oct-1-en-3-ol TOF(hydrogenation) = 1580 h–1, TOF(redox isomerization) = 400 h–1). DFT calculations revealed that H2 is activated heterolytically, resulting in a Pd(II)–hydride complex, [Pd(H)(HSS-Hphen)], in which one of the phenolate oxygens is protonated. Both hydrogenation and redox isomerization take place via concerted transfer of a proton and a hydride from the hydrogenated catalyst to the allylic alcohol.

Hydrogenation of the water-soluble [{RuCl(2)(mtppms)(2)}(2)] (mtppms = monosulfonated triphenylphosphine) was studied in aqueous solutions in the presence of excess mtppms both with H(2) and with aqueous HCOONa. Depending on the reductant, the pH and H(2) pressure altogether nine hydride species were identified. In acidic solutions at 1 bar H(2) pressure the known [RuHCl(mtppms)(3)] (1) and [{RuHCl(mtppms)(2)}(2)] (3) were formed, however, elevated pressure led to the formation of trans-[RuH(2)(mtppms)(4)] (11). In basic solutions at atmospheric pressure cis-fac-[RuH(2)(H(2)O)(mtppms)(3)] (12) was observed which was readily replaced by [RuH(2)(η(2)-H(2))(mtppms)(3)] (13) at higher H(2) pressures. 13 is the first water-soluble and stable η(2)-H(2) Ru(II)-complex stabilized only by monodentate phosphine ligands. [RuHBr(mtppms)(3)] (9) and [RuHI(mtppms)(3)] (10) were obtained analogously to 1. In concentrated aqueous HCOONa solutions (often used in H-transfer hydrogenations) the major species was trans-[RuH(2)(HCOO)(mtppms)](-) (14) while in dilute solutions trans-[RuH(2)(H(2)O)(mtppms)(3)] (15) could be observed. Formation of these various hydride species offers an explanation for the earlier observed pH and pressure dependence of the rates and selectivities in hydrogenation of unsaturated aldehydes catalyzed by [{RuCl(2)(mtppms)(2)}(2)] + mtppms.

The new water-soluble cis-mer-[IrH2Cl(mtppms)3] (mtppms = monosulfonated triphenylphosphine) was employed as a catalyst for selective decomposition of formic acid to H2 + CO2 in aqueous solution at T = 30-100 °C. The easily synthesized compound showed high catalytic activity (TOF up to 298 000 h(-1)) and could be reused several times with no loss of activity (total TON = 67 650). A sharp maximum in the reaction rate was observed at pH = 3.75; its coincidence with the pKa of formic acid shows that both H(+) or HCOOH and HCOO(-) play important roles in the reaction mechanism.

The water-soluble carbene ligand precursors sIMesH + Cl − and sSIMesH + Cl − were synthesized in high yields by direct sulfonation of IMesH + Cl − (1,3-bis(2,4,6-trimethylphenyl) imidazolium chloride) and SIMesH + Cl − (1,3-bis(2,4,6-trimethylphenyl)imidazolinium chloride). Gold(I)-N-heterocyclic carbene complexes [AuCl(sIMes)] and [AuCl(sSIMes)] were prepared by carbene transfer from the zwitterionic [Ag(sIMes) 2 ] and [Ag(sSIMes) 2 ] to [AuCl(tht)] (tht = tetrahydrothiophene). In methanol–water mixtures or in neat water, the new gold(I)–NHC complexes showed high catalytic activity in Markovnikov type hydration of terminal alkynes (up to a turnover frequency 1990 h −1 ; ethynyltoluene, 0.1 mol% catalyst) but were markedly less active in case of internal alkynes (TOF = 3.6 h −1 ; diphenylethyne, 1 mol% catalyst). These new Au(I)-NHC catalysts do not require acid co-catalysts or activation by Ag(I)-additives.

A simple and efficient synthesis of amides by selective hydration of aromatic and aliphatic nitriles is described. The catalysts are prepared in situ from easily available Ru-precursors and ligands using water as the solvent. The most active catalyst, is obtained from [RuCl 2 (dmso) 4 ] and benzylated 1,3,5-triaza-7-phosphaadamantane. Of the 16 substrates examined, 92–99% conversions of 14 nitriles were achieved in one hour at reflux temperature.

In aqueous solutions at 80 °C, [RuClCp(mPTA)2](OSO2CF3)2 (1) and [RuCp(mPTA)2(OH2-κO)](OSO2CF3)3·(H2O)(C4H10O)0.5 (3) (mPTA: N-methyl-PTA) were found effective catalysts of the redox isomerization of alk-1-en-3-ols to the corresponding ketones, characterized by initial turnover frequencies (TOF) of 162 h−1 (3) and 9.6 h−1 (1) in 1-octen-3-ol isomerization. A sharp maximum of the reaction rate as a function of pH was observed with 1 in phosphate buffer solutions. Kinetic and 31P NMR measurements revealed for the first time in aqueous organometallic catalysis that component(s) of phosphate buffer (most probably HPO42−) strongly interact(s) with the catalyst complexes and this interaction leads to a dramatic loss of the catalytic activity.

A series of novel water-soluble AuI complexes using sulfonated N-heterocyclic imidazolylidene carbenes as ligands was prepared by transmetalation from the corresponding bis-carbene AgI complexes. Monocarbene AuI complexes were employed as catalysts in the hydration of terminal alkynes in aqueous media. Hydrations proceeded selectively according to Markovnikov’s rule with high rates and turnover numbers (up to TON 935). The highest activity was achieved in hydration of p-ethynylanisole (TOF = 400.2 h−1). Effects of additives (H2SO4, AgOTs, AgBF4, NaOH) were examined. Corresponding bis-carbene AuI complexes were also isolated and characterized. However, these exhibit no catalytic activity in the explored systems.