Search

In order to explore the boron mediated C-S bond activation of the thiolate ligand in transition metal thiolate complexes, several bis(phosphinite) (POCOP) pincer ligated palladium complexes bearing a benzylthiolate or mercapto auxiliary ligand, [2,6-(R2PO)2C6H3]PdY (Y = SCH2Ph, R = tBu, 1a, iPr, 1b; Y = SH, R = tBu, 2a, iPr, 2b), were synthesized and fully characterized by multinuclear NMR, FTIR, X-ray crystallography and elemental analysis. The reactions of complexes 1a-b or 2a-b with BH3·THF at room temperature produced exclusively the corresponding tetrahydroborate complexes, [2,6-(R2PO)2C6H3]Pd(η1-HBH3) (R = tBu, 3a; iPr, 3b), through Pd-S bond cleavage. Complexes 3a and 3b are air/moisture sensitive and thermally unstable. X-ray crystallography and FTIR spectra supported a η1-HBH3 monodentate coordination mode for the BH4 ligand in complexes 3a and 3b. The boron mediated C-S bond cleavage was not observed in the reactions of complexes 1a and 1b with BH3·THF perhaps due to the relatively weak Pd-S bond.

A pair of novel optically pure phosphinite ligands were synthesized by ring opening reaction of chiral amines with (R)-styrene oxide or (S)-glycidyl phenyl ether oxide using a straightforward method in high yields and their ruthenium complexes were described in detail. The ruthenium complexes proved to be highly efficient catalysts for the enantioselective hydrogenation of ketones, affording products up to 99% ee. The results showed that the corresponding chiral alcohols could be obtained with high activity and excellent enantioselectivities at the desired temperature. (2S)-1-{benzyl[(1S)-1-(naphthalen-1-yl)ethyl]amino}-3-phenoxypropan-2-yl diphenylphosphinito[dichloro(η6-benzene)ruthenium (II)] acts an excellent catalyst in the reduction of ketones, giving the corresponding alcohol up to 99% ee.

Chiral C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes have been synthesized and used as catalysts in the ruthenium-catalyzed asymmetric transfer hydrogenation of aromatic, methyl alkyl and alkyl/aryl ketones using 2-propanol as both the hydrogen source and solvent in the presence of KOH. Under optimized conditions, all complexes showed high catalytic activity as catalysts in the reduction of various ketones to corresponding chiral secondary alcohols. Products were obtained with high conversions (99%) and moderate to good enantioselectivities (82% ee). Furthermore, C2-symmetric bis(phosphinite) ligands and their binuclear ruthenium(II) complexes were characterized by multinuclear NMR spectroscopy, FT-IR spectroscopy, LC/MS-MS and elemental analysis.

Kinetic resolution of secondary alcohols by benzoylation using a phosphinite derivative of (1S,2R)-1-amino-2-indanol as the catalyst was investigated. The aminophosphinite catalyst is effective for the kinetic resolution of aryl cycloalkyl carbinols with a small number of examples for organocatalytic kinetic resolution to achieve resolution with s = up to 44. Although the benzoylation of phenylalkanols proceeded with a low selectivity, 1-arylalkanols bearing at least one substituent at the ortho position on the benzene ring or a branched alkyl group on the carbinol carbon were resolved with acceptable selectivity.

The success of phosphine-oxazoline ligands (PHOX) inspired the progress in P-oxazoline ligand families by modifying either the ligand backbone, the electronic and/or steric properties of the phosphine group or by exchanging the phosphine to a phosphinite or a phosphite group. In this respect, the structures of chiral P-oxazoline ligands have become more diverse and new families of very efficient ligands have emerged, which have improved catalytic performance in some asymmetric transformations, with an increased versatility, both in the range of reactions and in the range of substrates/reagents. In addition, most of ligands are synthesized from easily accessible chiral amino alcohols, maintaining the short and efficient synthetic route developed for PHOX ligands. New ligands have been developed by replacing the oxazoline functionality with several other N-donor groups, e.g. imidazole, thiazole, oxazole, pyridine, etc., and O- and S-groups. This review offers a critical overview of the utility of these most successful bidentate heterodonor P-N, P-O and P-S ligand families applied in metal-mediated processes. We illustrate how, through proper ligand design, these heterodonor bidentate ligand families can be an excellent source of ligands, with superior catalytic performance in many asymmetric reactions than the best C2-symmetric N,N and P,P-ligands reported so far.

Ferrocene-containing phosphorus derivatives are important as ligands in transition-metal catalysis. We have investigated the synthesis of ferrocene-based phosphanes from corresponding phosphinites via retro-phospha-Brook rearrangement. Ferrocenyl phosphinites isomerize to thermodynamically more stable phosphine oxides. Interestingly, retro-phospha-Brook rearrangement proceeds on the adjacent phenyl ring with the assistance of the ferrocenyl moiety. DFT calculations provided insight into the reaction mechanisms of these transformations. Isomerization probably proceeds intramolecularly with the participation of developing charge stabilization with iron´s d-orbitals. BH3 complexation seems to favor the phosphinite structure as was evidenced by 31P-11B scalar coupling. Retro-phospha-Brook rearrangement also likely proceeds as intramolecular migration of the phosphanyl group from oxygen to carbon, from both BH3 complexes and the uncomplexed starting material.

Hydrogen transfer reduction methods are attracting increasing interest from synthetic chemists in view of their operational simplicity. Thus, interaction of [Rh(μ-Cl)(cod)] 2 and Ir(η 5 -C 5 Me 5 )(μ-Cl)Cl] 2 with phosphinite ligand [(Ph 2 PO)-C 7 H 11 N 2 Cl]Cl, 1 gave new monodendate (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ 4 -1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro ɳ 5 -pentamethylcyclopentadienyl iridium(III))], 3 complexes, which were characterized by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. 1 H-{ 31 P} NMR, 1 H- 13 C HETCOR or 1 H- 1 H COSY correlation experiments were used to confirm the spectral assignments. The novel catalysts were applied to transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with high activity (up to 99%) under mild conditions. Notably, (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ 4 -1,5-cyclooctadiene rhodium(I))], 2 complex is much more active than the other analogous complex, 3 in the transfer hydrogenation. Furthermore, compound, 2 acts as excellent catalysts, giving the corresponding alcohols in 97–99% conversions in 5 min (TOF ≤ 1176 h −1 ).

Half-sandwich mixed phosphine-phosphinite ruthenium complexes [RuCp’Cl(PPh3)L] [Cp’ = Cp (1), Cp* (2)], and [RuCp*ClL2] (3) were prepared by substitution of the triphenylphosphine by the phosphinite ligand PPh2OCH2Ph, L, on the parent complexes [RuCp’Cl(PPh3)2]. Allenylidene compounds [Ru(η5-C5H5){ C C = CPh2}(PPh3)L][PF6] (4) and [Ru(η5-C5Me5){ C C = CPhR}(L)(L’)][BPh4] [L’ = PPh3 (5), L (6); R = Ph (a), R = Me (b)] were obtained by reaction of compounds 1–3 with the appropriate propargylic alcohols 1,1-diphenyl-2-propyn-1-ol, and 2-phenyl-3-butyn-2-ol. Diazoalkane complexes [RuCp(N2CAr1Ar2)(PPh3)L][PF6] [Ar1 = Ar2 = Ph (7a), Ar1Ar2 = C12H8 (7b)] and [RuCp*{N2C(C12H8)}L2][PF6] (8) were obtained by reaction of 1 or 3 with the corresponding diazoalkanes in the presence of NaPF6. Complexes were characterized by IR and NMR spectroscopy and, in the case of compounds 1 and 7a, by X-ray diffraction analysis.

Highly selective isomerization-hydroformylation of 2-butene was achieved with the presence of Rh(acac)(CO)2 and a phosphoramidite bidentate ligand which bearing 2,2′-dihydroxy-1,1′-binaphthyl backbone and N-indolyl substitute. The molar ratio of n- to isovaleraldehyde (217) is distinctly higher than the reported systems. NMR and IR revealed that the five-coordinate HRh(ligand)(CO)2 was an equatorial-equatorial configuration which contributed to the n-selectivity of valeraldehyde. The strong π-acceptor ability of ligand was suggested to play a key role in fast isomerization of 2-butene. Hydrolysis and oxidation experiments demonstrated that the ligand was water- and air-stable. Cyclic voltammetry measurement confirmed that this phosphoramidite ligand is more difficult to be oxidized, compared with the phosphine, phosphinite and phosphite ligands. Inspiringly, recycling experiments showed the catalytic system could work for at least 7 runs with unchanged selectivity.

A series of bis(phosphinite) (POCOP) pincer ligated nickel complexes, [2,6-(tBu2PO)2C6H3]NiX (X = SH, 1; SCH2Ph, 2; SPh, 3; N CS, 4; N3, 5), were used to catalyse the hydrosilylation of aldehydes. It was found that both complexes 1 and 2 are active in catalysing the hydrosilylation of aldehydes with phenylsilane and complex 1 is comparatively more active. The expected alcohols were isolated in good to excellent yields after basic hydrolysis of the resultant hydrosilylation products. However, no reaction was observed when complex 3 or 4 or 5 was used as the catalyst. The results are consistent with complexes 1 and 2 serving as catalyst precursors, which generate the corresponding nickel hydride complex [2,6-(tBu2PO)2C6H3]NiH in situ, and the nickel hydride complex is the active species that catalyses this hydrosilylation process. The in situ generation of the nickel hydride species was supported by both experimental results and DFT calculation.

A quantum-chemical mechanistic investigation using density functional theory (DFT) on ammonia-borane dehydrogenation catalyzed by a series of iron bis(phosphinite) pincer complexes is reported. A metal-ligand cooperation mechanism has been proposed, in which the hydrogen atom of B H moves to metal Fe and proton of N H transfers to pincer ipso carbon simultaneously with the lowest activation barriers. DFT calculations and natural bond orbital (NBO) charge analysis suggest that Fe POCOP complex with an electron-donating MeO group at the para position to the ipso carbon exhibits the highest catalytic activity. A plausible explanation of the observed catalytic activities is also given.

Known Ru(II), Rh(I) and Ir(III) complexes of C2-symmetric ferrocenyl based chiral bis(phoshinite) ligands were catalyzed the asymmetric transfer hydrogenation of alkyl/aryl or alkyl methyl ketones. Corresponding secondary alcohols were obtained with high enantioselectivities up to 98% ee and reactivities using iso-propanol as the hydrogen source.

The asymmetric reduction of prochiral ketones is a pivotal reaction for the preparation of chiral alcohols which form an extremely important class of intermediates for fine chemicals and pharmaceuticals. Especially, iridium-based asymmetric reduction of ketones to enantiomerically enriched alcohols has recently attracted important attention by a number of research groups and interest in this area is growing. Therefore, a series of novel neutral mononuclear iridium(III) ferrocenyl-phosphinite complexes have been prepared and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenation (ATH) of ketones to give corresponding secondary alcohols with outstanding enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 99% ee and 99% conversion). It was seen that the substituents on the backbone of the ligands resulted in a significant effect on both the activity and % enantioselectivity. Furthermore, the structural elucidation of the complexes was carried out by elemental analysis, IR and multi-nuclear NMR spectroscopic data.

Catalytic dehydrogenation of ammonia borane by a series of iron bis(phosphinite) pincer complexes, such as [2,6-(Me2PO)2C6H3]Fe(H)(PMe3)2, [2,6-(Me2PO)2C6H3]Fe(H)(PMe2Ph)2, and [2,6-(Me2PO)2-4-(MeO)C6H2]Fe(H)(PMe2Ph)2, have been examined theoretically. Calculation of the energy diagram for the catalytic reaction steps using these catalysts showed that the rate-determining step is different for each ligand. The calculations also revealed that NH2BH2 is likely to be eliminated before H2 release because of the electrostatic repulsion between bulky ligands. Moreover, the electron-donating groups of the ligands stabilize the intermediate and transition states. The difference between the catalytic activities in this series of complexes can be explained by the above effects caused by changes in the ligands.

Mono-dispersed and small-sized bimetallic copper and palladium nanoparticles were successfully supported on phosphinite functionalized agarose biopolymer. The new material was characterized using various techniques such as solid state UV–vis and FT-IR spectroscopies, SEM, EDX, TGA, HRTEM, SAED, EDX-Map, and nitrogen adsorption–desorption analysis. The heterogeneous and recyclable catalyst has been used in Sonogashira coupling reaction of aryl iodides at room temperature and aryl bromides at 50 °C under low palladium loading conditions (0.05 mol %).

A series of nickel pincer complexes of the type [4-Z-2,6-(R2PO)2C6H2]NiX (R = tBu, iPr, Ph; Z = H, CO2Me; X = N CS, N3) have been synthesized from the reactions of the corresponding nickel chloride complexes [4-Z-2,6-(R2PO)2C6H2]NiCl and potassium thiocyanate or sodium azide. X-ray structure determinations of these complexes have shown that the thiocyanate ion binds to the nickel center through the nitrogen. A comparable Ni–N bond length (approx. 1.87 A for the isothiocyanate complexes and 1.91 A for the azide complexes) and an almost identical Ni–Cipso bond length (approx. 1.89 A) have been observed for these complexes. Metathesis reactivity of [4-Z-2,6-(R2PO)2C6H2]NiCl and ligand exchange reactions between the nickel isothiocyanate and nickel azide complexes have been investigated. The metathesis reactions with thiocyanate/azide complexes are faster with a less electron rich and more sterically accessible nickel center. The thermodynamic stability of these nickel complexes has been rationalized using hard-soft acid-base theory (HSAB theory); a harder ligand prefers a less electron rich nickel center. These experimental results have been supported by quantum chemical analysis of the coordinating nitrogen atoms in SCN– and N 3 − .

The electrochemical behaviour of a series of rhodium(I) complexes of the type [Rh(CH3COCHCOCH3)CO(Ph2POPh-p-R)], where R = H (1), CH3 (2), tBu(3) and Cl(4)] revealed an irreversible oxidation of Rh(I) to Rh(III), an irreversible oxidation of the phosphorus atom followed by the decomposition of the phosphinite ligand. An unexpected reaction occurred between the electrochemical internal standard, free ferrocene, in its ferricinium ion form and the radical cation of the oxidised diphenyl phosphinite, leading to uncharacteristic electrochemical behaviour. Electronic communication between different molecular fragment was confirmed by the linear relationships obtained between the Gordy group electronegativities of the R-groups on the phosphinites (χR) and the Epa of Rh and the phosphorus atoms as well as the binding energy (eV) (measured by XPS) of the Rh 3d and P 2p peak positions. V-shape correlations were found between the Hammett constants of the R-groups on the phosphinites (χR) and the oxidation potentials and binding energies. This shows the difference in stabilisation either resonance or inductive between the electrondonating and electronwithdrawing substituents.

A series of chiral modular C-2-symmetric ferrocenyl phosphinite ligands have been synthesized in good yields by using 1,1'-ferrocenedicarboxyaldehyde and various amino alcohols as starting materials, and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenations of aromatic ketones to give the corresponding secondary alcohols with good enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 98% ee and 99% conversion). The substituents on the backbone of the ligands were found to have a significant effect on both the activity and enantiomeric excess. The structures of these complexes have been clarified by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. (C) 2015 Elsevier Ltd. All rights reserved.

New bromo- and chloro- tricarbonylrhenium(I) complexes [ReX(CO)3)L2] [X = Cl (1); Br(2)] containing the bifunctional phosphinite/ alkene ligand Ph2POCH2CH = CH2(L), have been prepared by reaction of the complexes[ReX(CO)5] (X = Cl, Br) with L, in refluxing toluene. Both mer, trans (a) and fac, cis (b) isomers were obtained and the structures of derivatives 1a, 1b and 2a have been determined by single crystal X-ray diffraction analysis.

New chiral C2-symmetric bis(phosphinite) ligands containing imine group were synthesized from 1-({[(1R,2R)-2-{[(2-hydroxynaphthalen-1-yl)methylidene] amino}cyclohexyl]- imino}methyl)- naphthalen-2-ol and two equivalents of Ph2PCl, (i-Pr)2PCl or (Cy)2PCl, in high yields. Binuclear C2-symmetric half sandwich η6-p-cymene-Ru(II) complexes of the chiral phosphinite ligands were synthesized by treating of [Ru(η6-p-cymene)(μ-Cl)Cl]2 with the phosphinites in 1:1 M ratio in CH2Cl2. Their catalytic activities in asymmetric transfer hydrogenation (ATH) were investigated for the reaction of acetophenone derivatives with isopropyl alcohol. The corresponding optically active secondary alcohols were obtained in excellent levels of conversion (96–99%) and moderate enantioselectivity (up to 60% ee). Among three complexes investigated, complex 4 was the most efficient one.

The known readily available phosphinite, (1R,2S,5R)-menthyloxydiphenylphosphine, was introduced as a chiral derivatizing agent for the enantiomeric purity determination of the optically active CN-palladacycles using 31P NMR spectroscopy. The advantages of the methodology proposed include opportunity of the in situ analysis, without any complications from geometric isomerism or palladacycle dechelation, with a rather high level of the palladacycle enantiomers spectral recognition. In addition, the valuable palladacycle may be recovered after its testing from the phosphinite adduct, and this phosphinite reagent may be also used for the racemic palladacycle optical resolution or for the enantiopurity increasing of the scalemic dimer.

The majority of the known pincer iridium based catalysts for dehydrogenation of alkanes has arene-based backbones. Here, the catalytic activity of aliphatic iridium pincer complexes, viz, the cyclohexane-based phosphine complex (PCyP)IrHCl (4) (PCyP = {cis-1,3-bis-[(di-tert-butylphosphino)methyl]cyclohexane}(-)) and the 2-methylpropane-based phosphinite complex (POCOP)IrHCl (5) (POCOP = 1,3-bis-(di-tert-butyl-phosphinito)-2-methylpropane(-)), in dehydrogenation of cyclooctane and triethylamine was studied. They give TONs that are in the range of 0-200. In addition, improved procedures for synthesis and metallation of the PCyP ligand (3) are presented. (C) 2014 Elsevier Ltd. All rights reserved.

A series of para-substituted phenyl diphenylphosphinites [Ph2POPh-p-R, where R H (1), CH3 (2), tBu (3) and Cl (4)] were prepared in near quantitative yields, by the reaction between the desired para-substituted phenol and chlorodiphenylphosphine, in the presence of triethylamine. The electrochemical data obtained for the phosphinite series, showed a one-electron oxidation of the free electron-pair of the phosphorous atom, as well as either the oxidation or the electrochemical decomposition of this phosphinite radical cation. The oxidation peak potential was found to be dependent on the group-electronegativity of the respective para-R-substituent. An unexpected reaction occurred between the electrochemical internal standard, free ferrocene, in its ferricinium ion form and the radical cation of the oxidized diphenyl phosphinite, leading to uncharacteristic electrochemical behaviour.

Five new functionalized ionic liquids (FILs), tetraethylammonium di(2-ethylhexyl)phosphate ([N 2222 ][DEHP]), tetraethylammonium bis(2,4,4-trimethylpentyl)phosphinite ([N 2222 ][BTMPP]), tetraethylammonium bis(2,4,4-trimethylpentyl)dithiophosphinite ([N 2222 ][BTMPDTP]), tetrahexylammonium di(2-ethylhexyl)phosphate ([N 6666 ][DEHP]), and tetraoctylammonium di(2-ethylhexyl)phosphate ([N 8888 ][DEHP]) were synthesized and characterized. These ILs along with two previously synthesized FILs ([N 4444 ][DEHP] and [N 1888 ][DEHP]) were used as ionic extractants and investigated for rare earth elements (REEs) separation in 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide/bis(perfluoroethanesulfonyl)imide ([C 10 mim][NTf 2 ]/[BETI]). These FILs as ionic extractants were miscible with [C 10 mim][NTf 2 ]/[BETI]. We herein report the applications of these FILs in an IL-based TALSPEAK-like process and the optimization of the process by adjusting the cations and anions of the FILs, concentrations of the FILs as ionic extractants in the IL phase, concentrations of diethylenetriamine pentaacetic acid (DTPA) in the aqueous phase, and acidities of the aqueous phase.

The reactions of coordinated phosphorus-donor ligands have previously been used to prepare bimetallic trans-[cis-Mo(CO)4(PPh2NHCH2CH2NCH(o-C6H4)O)2]M (M = Ni(II), Cu(II)) complexes. Similar bimetallic complexes containing trans-tetracarbonyl-bis(phosphinite)molybdenum(0) centers could be even more interesting because they could serve as molecular gyroscopes. In an attempt to prepare such complexes, the three intermediate compounds trans-Mo(CO)4(PPh2Cl)2 (1), trans-Mo(CO)4(PPh2NHCH2CH2NH2)2 (2), and trans-Mo(CO)4(PPh2NHCH2CH2NCH(o-C6H4)OH)2 (3) were successfully synthesized and fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. However, the reaction of 3 with Ni(OAc)2(H2O)4 yielded a mixture of crude products with the previously reported trans-[cis-Mo(CO)4(PPh2NHCH2CH2NCH(o-C6H4)O)2]Ni being the only product successfully isolated. The cis product was formed due to facile trans–cis isomerization during the coordination of the Ni(II) to 3. To gain more insight into such isomerizations, the trans–cis isomerizations of 2 and 3 have been followed by 31P{1H} NMR spectroscopy. The reactions follow reversible first order kinetics and appear to display intramolecular mechanisms due to the lack of carbonyl substitutions of the phosphinamidite ligands when the isomerizations are performed under CO atmospheres. Eyring analyses performed on the two complexes show that they have nearly identical activation energies (2: ΔH = 10 ± 2 kJ mol−1, ΔS = 39 ± 5 J mol−1 K−1; 3: ΔH = 11 ± 2 kJ mol−1, ΔS = 41 ± 7 J mol−1 K−1).

We report here new examples of enantiomerically pure monodendate phosphinite ligands containing both a ferrocene moiety and NH bridging moiety adjacent to the stereocenter, as well as their ruthenium(II) dichloro complexes. The phosphinites based on ferrocenyl moiety possessing stereogenic center have been screened as ligands for ruthenium(II)-catalyzed transfer hydrogenation of aromatic ketones to give corresponding secondary alcohols using iso -PrOH as the hydrogen source in the presence of NaOH. Up to 99% conversion with 97% ee was obtained in the transfer hydrogenation of acetophenone derivatives. Furthermore, the catalytic properties of these catalysts based on ferrocenyl-phosphinite backbone are also discussed briefly. The structures of these ligand and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis.

A simple and efficient Rh-phosphinite complex catalyst was studied for the selective hydroformylation of various olefins. The influence of various reaction parameters including the effect of temperature, pressure, catalyst loading, time, and solvents was studied. The protocol was also applied for the synthesis of various acetals via tandem hydroformylation–acetalization of olefins in alcohols as solvents. High activity and selectivity for acetal formation was achieved in the absence of co-catalysts with admirable substrate to catalyst mole ratio (TON 2500). The developed protocol works for a wide range of olefins to synthesize corresponding aldehydes and acetals under optimized reaction conditions.

A new and versatile class of unsymmetrical ferrocenyl-phosphinite ligands possessing a stereogenic center has been prepared from commercially available, inexpensive aminoacids such as, d -, l -phenylglycine and d -, l -phenylalanine, through a concise synthetic procedure. These ligands are not very sensitive to air and moisture, and display good enantioselectivities in the ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives, in which up to 91% ee was obtained. A comparison of the catalytic properties of amino alcohols and other analogues based on a ferrocenyl backbone is also discussed briefly. The structures of these ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis.

Asymmetric transfer hydrogenation processes of ketones with chiral molecular catalysts are attracting increasing interest from synthetic chemists due to their operational simplicity. C-2-symmetric catalysts have also received much attention and been used in many reactions. A series of new chiral C-2-symmetric bis(phosphinite) ligands has been prepared from corresponding amino acid derivated amino alcohols or (R)-2-amino-1-butanol through a three- or four-step procedure. Their structures have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. H-1-P-31 NMR, DEPT, H-1-C-13 HETCOR or H-1-H-1 COSY correlation experiments were used to confirm the spectral assignments. In situ prepared ruthenium catalytic systems were successfully applied to ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives by iso-PrOH. Under optimized conditions, these chiral ruthenium catalyst systems serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iso-PrOH and act as good catalysts, giving the corresponding optical secondary alcohols in 99% yield and up to 79% ee. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

A very easy method is described for direct phosphorylation of silica gel to afford silica diphenylphosphinite (SDPP). This new phosphorylated silica contains higher amounts of P(III) moiety compared to the method based on the sol-gel technique. The phosphorylated silica reacts with Pd(II) to produce nano Pd(0)/SDPP which was characterized by different techniques. The obtained nano Pd(0) catalyst exhibited excellent reactivity and stability in the Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions with different aryl iodides and bromides. This heterogeneous catalyst can be easily recovered and reused in several runs.

Silicadiphenyl phosphinite (SDPP) as a new phosphorylated silica and catalytic amounts of Pd(II) generates nano SDPP/Pd(0) catalyst for the efficient aminocarbonylation of aryl halides in the presence of POCl 3 and N , N -dimethylformamide (DMF). Amides are obtained in high yields from aryl iodides and also activated aryl bromides, chlorides.

A new nickel bis(phosphinite) pincer complex [2,6-(R 2 PO) 2 C 6 H 3 ]NiCl (L R NiCl, R = cyclopentyl) has been prepared in one pot from resorcinol, ClP(C 5 H 9 ) 2 , NiCl 2 , and 4-dimethylaminopyridine. The reaction of this pincer compound with LiAlH 4 produces a nickel hydride complex, which is capable of reducing CO 2 rapidly at room temperature to give a nickel formate complex. X-ray structures of two related nickel formate complexes L R NiOCHO (R = cyclopentyl and isopropyl) have shown an “in plane” conformation of the formato group with respect to the coordination plane. The stoichiometric reaction of nickel formate complexes L R NiOCHO (R = cyclopentyl, isopropyl, and tert -butyl) with catecholborane has suggested that the reaction is favored by a bulky R group. L R NiOCHO (R = tert -butyl) does not react with PhSiH 3 at room temperature; however, it reacts with 9-borabicyclo[3.3.1]nonane and pinacolborane to generate a methanol derivative and a boryl formate species, respectively. The catalytic reduction of CO 2 with catecholborane is more effectively catalyzed by a more sterically hindered nickel pincer hydride complex with bulky R groups on the phosphorus donor atoms. The nickel pincer hydride complexes are inactive catalysts for the hydrosilylation of CO 2 with PhSiH 3 .

Reaction of 2 equivalents of 1,3-bis-(di-tert-butylphosphinito)-2-methyl-propane (1a) with [Ir(COD)Cl](2) affords the first aliphatic diphosphinite PCP pincer complex with iridium, Ir(H){(t-Bu2POCH2)(2)C(Me)}Cl (2). The poor yield of 2 is partly explained by the formation of a di-nuclear byproduct [IrCl(COD)](2)(mu(2)-{(t-Bu2POCH2)(2)CH(Me)}) (3). Reaction of 1,3-bis-(di-iso-propylphosphinito)-2-methyl-propane (1b) under the same condition does not give any cyclometallation, and reaction with IrCl3 center dot H2O in DMF leads to complete decomposition of the pincer ligand under the formation of Ir(H)(i-Pr2P(OH))(3)(CO) (4), underpinning the comparatively low thermal stability of aliphatic phosphinite pincer systems. (C) 2011 Elsevier B.V. All rights reserved. (Less)

Novel mono- and bisphosphinite (−)-pinane-based ligands have been synthesized from (−)-α-pinene. Mixed with [(COD)2Rh]+[BF4]−, these ligands displayed moderate up to high catalytic activity in hydrogenation of dimethyl itaconate with dihydrogen. It has been observed that the structure of the ligand, the reaction temperature and solvent are important to define productivity of the phosphinite-based Rh-catalysts. Bisphosphinite ligands in hydrogenation reactions suffered from an Arbuzov rearrangement, leading to fast deactivation of the hydrogenation catalyst. In contrast, monophosphinite-derived Rh-catalysts showed increased productivity as well as thermal stability. An almost quantitative conversion of dimethyl itaconate has been achieved at elevated temperatures in toluene. Alternatively, hydrogenation of dimethyl itaconate with monophosphinite ligands has been carried out in MeOH at room temperature or 40 °C and has led to a nearly quantitative conversion.

Two unsymmetrical PCN pincer Pd(II) complexes 3a–3b which are based on (pyrazolyl)aryl phosphinite ligands and contain two fused six-membered palladacycles have been synthesized from 3-(3,5-dimethylpyrazol-1-ylmethyl)benzyl alcohol (2) by one-pot phosphorylation/palladation reaction via C–H bond activation of the related ligands. The pyrazole-coordinated phosphine-free Pd(II) complex (4) was also isolated in the preparation of pincer complex 3a. The new complexes were characterized by elemental analysis, 1H NMR, 13C NMR, 31P {1H} NMR (for pincer complexes) and IR spectra. And the molecular structures of 3b and 4 have been further determined by X-ray single-crystal diffraction. The pincer Pd complexes 3a and 3b exhibited rather low activity in the allylation of benzaldehyde.

Enantioselective reduction of prochiral ketones to optically active secondary alcohols is an important subject in synthetic organic chemistry because the resulting chiral alcohols are extremely useful, biologically active compounds. The new chiral ligands (2R)-2-[benzyl{(2-((diphenylphosphanyl)oxy)ethyl)}amino]butyldiphenylphosphinite, 1 and (2R)-2-[benzyl{(2-((dicyclohexylphosphanyl)oxy)ethyl)}amino]butyldicyclohexylphosphinite, 2 and the corresponding ruthenium(II) complexes 3 and 4 have been prepared. The structures of these complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. 31P–{1H} NMR, DEPT, 1H–13C HETCOR or 1H–1H COSY correlation experiments were used to confirm the spectral assignments. These ruthenium(II)–phosphinite complexes have been used as catalysts for the asymmetric transfer hydrogenation of acetophenone derivatives. Under optimized conditions, aromatic ketones were reduced in good conversions and in moderate to good enantioselectivities (up to 85% ee).

A novel Schiff base N3,N3′-di-2-hydroxybenzylidene-[2,2′]bipyridinyl-3,3′-diamine, 1 was synthesized from condensation of salicylaldehyde with 3,3′-diamino-2,2′-bipyridine. Reaction of 1 with two equivalents of PPh2Cl in the presence of Et3N proceeds in toluene to give N3,N3′-di-2-(diphenylphosphino)benzylidene-[2,2′]bipyridinyl-3,3′-diamine, 2 in quantitative yield. Ruthenium(II) dimers [Ru(η6-arene)(μ-Cl)Cl]2 readily react with phosphinite ligand [(Ph2PO)2-C24H16N4], 2 in toluene at room temperature, to afford the neutral derivatives [C24H16N4{OPPh2–Ru(η6-arene)Cl2}2] {arene: benzene 3, p-cymene, 4}. All the complexes were fully characterized by analytical and spectroscopic methods. 31P–{1H} NMR, 1H–13C HETCOR or 1H–1H COSY correlation experiments were used to confirm the spectral assignments. Molecular structure of the Schiff base, 1 was also determined by X-ray single crystal diffraction study. The catalytic activity of complexes 3 and 4 in the transfer hydrogenation of acetophenone derivatives was tested. Stable ruthenium(II)–phosphinite complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in excellent conversions up to 99% (up to 530 per hour) in the presence of iso-PrOH/KOH.

A novel palladium catalyst based on modified crosslinked polyacrylamide containing phosphinite ligand was synthesized and characterized. It exhibits excellent activity and stability in Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions with different aryl halides including inactive aryl chlorides. Short reaction times with good to excellent yields of the desired products express the effectiveness of this catalyst in these reactions. Transmission electron microscopy (TEM) shows that palladium particles are well-dispersed and of typical diameter of 18–30 nm. The X-ray powder diffraction (XRD) pattern of the Pd catalyst is consistent with the metallic Pd(0). The turnover number (TON) of this catalyst reaches up to 9.5 × 104 for these C–C bond forming reactions. Elemental analysis of Pd by ICP-OES and hot filtration test shows low leaching of the metal into solution from the supported catalyst which confirms the full heterogeneous character of the catalytically active species. The catalyst can be used many times in repeating cycles without considerable loss in its activity.

Asymmetric transfer hydrogenation of ketones with chiral molecular catalysts is realized to be one of the most magnificent tools to access chiral alcohols in organic synthesis. A new chiral phosphinite compound N,N′ -bis[(1 S )-1-benzyl-2- O -(diphenylphosphinite)ethyl]ethanediamide ( 1 ), has been synthesized by the reaction of chlorodiphenylphosphine with N,N′ -bis[(1 S )-1-benzyl-2-hydroxyethyl]ethanediamide under argon atmosphere. The oxidation of 1 with aqueous hydrogen peroxide, elemental sulfur or grey selenium in toluene gave the corresponding oxide 1a , sulfide 1b and selenide 1c , respectively. Pd, Pt and Ru complexes were obtained by the reaction of 1 with [MCl 2 (cod)] (M: Pd 1d , Pt 1e ) and [Ru( p -cymene)Cl 2 ] 2 1f , respectively. All these new complexes were characterized by using NMR, FT-IR spectroscopies and microanalysis. Additionally, as a demonstration of their catalytic reactivity, the ruthenium complex 1f was tested as catalyst in the asymmetric transfer hydrogenation reactions of acetophenone derivatives with i PrOH was also investigated.

Hydrogen-transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity. The new chiral C 2 -symmetric ligands N,N ′-bis-[(1 S )-1- sec -butyl-2- O- (diphenylphosphinite)ethyl]ethanediamide, 1 and N,N′ -bis-[(1 S )-1-phenyl-2- O -(diphenylphosphinite)ethyl]ethanediamide, 2 and the corresponding ruthenium complexes 3 and 4 have been prepared and their structures have been elucidated by a combination of multi-nuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. 1 H– 31 P NMR, DEPT, 1 H– 13 C HETCOR, or 1 H– 1 H COSY correlation experiments were used to confirm the spectral assignments. The catalytic activity of complexes 3 and 4 in transfer hydrogenation of acetophenone derivatives by iso- PrOH has also been studied. Under optimized conditions, these chiral ruthenium complexes serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iso -PrOH and act as excellent catalysts, giving the corresponding chiral alcohols in 99% yield and up to 75% ee. This transfer hydrogenation is characterized by low reversibility under these conditions.

The use of an imidazolium-based phosphinite ionic liquid (IL-OPPh2) as both solvent and ligand for Pd offers an efficient catalytic system for silylation of aryl iodides, bromides and also chlorides by triethylsilane in the presence of Cs2CO3. In the absence of base, this system is also performed for catalytic dehalogenation of aryl halides. The ionic liquid containing its corresponding Pd(0) complex can be easily recovered and reused in several runs without losing its efficiency.

A new class of amino-phosphinite chiral ligands was prepared and applied in zinc-catalyzed addition of aryl boronic acids to aldehydes; the reaction furnished the diarylmethanols in excellent yields and with a high level of enantioselectivity (up to 93% ee).

Phosphinite POCOP pincer compounds [4-(n-C12H25)-C6H3-1,3-(OPR2)2] R Ph (1), Pri (2) derived from 4-n-dodecylresorcinol and their group 10 derivatives [MCl{3-(n-C12H25)-C6H2-2,6-(OPR2)2}] M(R) = Ni(Ph) (3), Ni(Pri) (6), Pd(Ph) (4), Pd(Pri) (7) and Pt(Ph) (5), Pt(Pri) (8) were synthesized and the catalytic activity of the palladium species explored in the Mizoroki-Heck and Suzuki-Miyaura cross coupling reactions.

Palladium(II), platinum(II), rhodium(I), rhodium(III) and iridium(III) complexes of the tridecafluorohexyl-derivatised diphenylethylphosphinite (PPh 2 OC 2 H 4 R f ), phenyldiethylphosphonite {PPh(OC 2 H 4 R f ) 2 }, triethylphosphite {P(OC 2 H 4 R f ) 3 }, triphenylphosphinite (PPh 2 OC 6 H 4 -4-R f ), triphenylphosphonite {PPh(OC 6 H 4 -4-R f ) 2 }, ethyldiphenylphosphine (PPh 2 C 2 H 4 R f ), diethylphenylphosphine {PPh(C 2 H 4 R f ) 2 } and triethylphosphine {P(C 2 H 4 R f ) 3 } ligands are synthesized by conventional ligand displacement and/or halide-bridge cleaved reactions, and their spectroscopic parameters are compared with those for the related ligands lacking the tridecafluorohexyl ponytails.

The dimeric starting material [Ru(η 6 - p -cymene)(μ-Cl)Cl] 2 reacts with N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine, 1 and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester, 2 ligands to afford bridged dinuclear complexes [C 10 H 6 N 2 {NHPPh 2 -Ru(η 6 - p -cymene)Cl 2 } 2 ], 3 and [C 10 H 6 N 2 {OPPh 2 -Ru(η 6 - p -cymene)Cl 2 } 2 ], 4 in quantitative yields. These bis(aminophosphine) and bis(phosphinite) based Ru(II) complexes serve as active catalyst precursors for the transfer hydrogenation of acetophenone derivatives in 2-propanol and especially 4 acts as a good catalyst, giving the corresponding alcohols in 99% yield in 20 min (TOF ⩽ 280 h −1 ).

Five non-symmetrical PCN pincer palladium(II) complexes [PdCl{C6H3-2-(CH NR)-6-( OPR 2 ′ )}] (R = m-ClC6H4, R′ = Ph (2a); R = Ph, R′ = Ph (2b); R = i-Pr, R′ = Ph (2c); R = m-ClC6H4, R′ = i-Pr (2d); R = (S)-1-phenylethyl, R′ = Ph (2e)) have been easily prepared in only two steps from readily available m-hydroxybenzaldehyde and characterized by HRMS, 1H NMR, 13C NMR, 31P NMR and IR spectra. The molecular structures of 2a and 2b have been further determined by X-ray single-crystal diffraction. The obtained Pd complexes were found to be effective catalysts for the Suzuki and copper-free Sonogashira cross-coupling reactions which could be carried out in the undried solvent under air.

The stoichiometry of the OsO4-catalysed oxidation of phosphinite (R = H) and phenylphosphinite ion

A new proposed methodology for the preparation of phosphapalladacycles in enantiopure form includes the use of the same optically active cyclopalladated CN-reagent for both resolution of a racemic ligand and subsequent direct C–H bond activation of the enantiopure ligand via the cyclopalladated ligand exchange reaction. This protocol was successfully employed for the preparation of the complex, which is both the first PC-palladacycle with a non-metallocenic planar chirality based on the [2.2]paracyclophane framework and the first representative of chiral phosphinite PC-palladacycles.

The use of an imidazolium-based phosphinite ionic liquid (IL-OPPh 2 ) as ligand for Pd offers an efficient reagent system for the selective dehalogenation or homocoupling of aryl halides in the presence of NaOPr i or Et 3 N, respectively. This ionic liquid plays a dual role as both the reaction media and also as the potential complexing agent with Pd via its phosphinite carrying group. The ionic liquid containing its corresponding Pd complex can be easily recovered and reused in several runs.

Two new N -pyrazole, P -phosphinite hybrid ligands 3-(3,5-dimethyl-1 H -pyrazol-1-yl)propyldiphenylphosphinite ( L 3 ) and 2-(3,5-diphenyl-1 H -pyrazol-1-yl)ethyldiphenylphosphinite ( L 4 ) are presented. The reactivity of these ligands and two other ligands reported in the literature (3,5-dimethyl-1 H -pyrazol-1-yl)methyldiphenylphosphinite ( L 1 ) and 2-(3,5-dimethyl-1 H -pyrazol-1-yl)ethyldiphenylphosphinite ( L 2 ) towards [RhCl(CO) 2 ] 2 ( 1 ) have been studied and complexes [RhCl(CO) L ] ( L = L 2 ( 2 ), L 3 ( 3 ) and L 4 ( 4 )) have been obtained. For L 1 only decomposition products have been achieved. All complexes were fully characterised by analytical and spectroscopic methods and the resolution of the crystalline structure of complexes 2 and 3 by single-crystal X-ray diffraction are also presented. In these complexes, the ligands are coordinated via κ 2 (N,P) to Rh(I), forming metallocycles of seven ( 2 and 4 ) or eight ( 3 ) members and finish its coordination with a carbonyl monoxide and a trans -chlorine to phosphorus atom. In both complexes, weak intermolecular interactions are present. NMR studies of complexes 2 – 4 show the chain N–(CH 2 ) x –O becomes rigid and the protons diastereotopic.