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[image omitted] Ethyl 2-(N-methylformate-1,4,5,6-tetrahydropyridin-2-yl) acetate with endocyclic double bond was prepared with high regioselectivity and further reduced into (R)-N-protected homopipecolate with a good enantioselectivity using chiral ruthenium catalyst. [ABSTRACT FROM AUTHOR]

The article discusses organic carbonates as alternative or so-called green solvents. It highlights studies on synthesis of organic carbonates and application as a solvent in electrochemical applications of Li batteries, electropolymerizations, analytics, and cleaning processes. Basic properties for the success of organic carbonates are described. It was found that organic carbonates are not magic solvents which can replace every other solvent.

Abstract: Two novel P∗ -stereogenic bisdiamidophosphites derived from (3R,4R)-N-benzyltartarimide as a chiral 1,2-diol have been prepared from readily available starting materials. Palladium and rhodium catalytic systems containing these new P∗ ,P∗ -bidentate ligands afforded 96%, 83% and 65% ee in asymmetric allylic substitution, hydrogenation and addition processes, respectively. These diastereomeric diamidophosphites were found to be complementary stereoselectors. [Copyright &y& Elsevier]

A modular library of readily available phosphite-oxazoline ligands (L1-L16a-f) has been successfully applied for the first time in the Ir-catalyzed asymmetric hydrogenation of a broad range of highly unfunctionalized 1,1,-disubstituted terminal alkenes. Enantioselectivities up to >99% and full conversions were obtained in several 1,1-disubstituted alkenes, including substrate classes that have never been asymmetrically hydrogenated before (i.e., 1,1-heteoraryl-alkyl, 1,1-diaryl, trifluoromethyl, etc.). The results indicated that these catalytic systems have high tolerance to the steric and electronic requirements of the substrate and also to the presence of a neighboring polar group. The asymmetric hydrogenations were also performed using propylene carbonate as solvent, which allowed the Ir catalyst to be reused and maintained the excellent enantioselectivities. [ABSTRACT FROM AUTHOR]

Abstract: The standard molar enthalpies of formation of ethylene carbonate, propylene carbonate, and butylene carbonate were measured using combustion calorimetry. Ab initio calculations of molar enthalpies of formation of alkylene carbonates were performed using the G3MP2 method. The calculated values are in excellent agreement with available experimental data. Ring strain corrections were quantified for the refinement of the group-contribution method for prediction of enthalpies of formation and vaporization of alkylene carbonates. [Copyright &y& Elsevier]

Abstract: The highly enantioselective hydrogenation of methyl 4-tert-butylcarbamoyl-3-oxo-butyrate to the corresponding secondary alcohol, representing an interesting chiral building block, for example, for the synthesis of statins, has been investigated in the presence of homogeneous chiral Rh(I) and Ru(II) complexes bearing phosphine ligands. The highest enantioselectivity (up to 96%) was achieved with a [Ru((R)-BINAP)(p-cymene)Cl]Cl complex (sub./cat. ratio 100:1, 5bar H2, rt, MeOH). [Copyright &y& Elsevier]

Abstract: Molar enthalpies of vaporization of aliphatic alkyl carbonates: dimethyl carbonate [616-38-6], diethyl carbonate [105-58-8], di-n-propyl carbonate [623-96-1], di-n-butyl carbonate [542-52-9], and dibenzyl carbonate [3459-92-5] were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of the primary experimental results on temperature dependences of vapour pressures have been collected from the literature and have been treated uniformly in order to derive vaporization enthalpies of dialkyl carbonates at the reference temperature 298.15K. An internal consistency check was performed on enthalpy of vaporization values for dialkyl carbonates studied in this work. [Copyright &y& Elsevier]

Abstract: A novel readily available P,P-bidentate diamidophosphite ligand with P ∗-stereocentres is prepared from an inexpensive C 2-symmetric 1,4:3,6-dianhydro-d-mannite. By using this efficient ligand, up to 98% ee is achieved in Pd-catalysed asymmetric allylic alkylation, up to 92% ee in Pd-catalysed asymmetric allylic amination and up to 87% ee in Rh-catalysed asymmetric hydrogenation. The influence of the precatalyst, substrate and solvent on the enantioselectivity is discussed. [Copyright &y& Elsevier]

Abstract: Propylene carbonate (PC) may serve as a perfect solvent in the asymmetric rhodium-catalyzed hydrogenations of functionalized olefins like methyl N-acetamido acrylate and methyl α-(Z)-N-acetamido cinnamate using chiral self-assembling catalysts. In several examples superior reaction rates and enantioselectivities were found in comparison to the use of dichloromethane, commonly used as a solvent. The performance of the catalyst is influenced by the bulk of the phosphorus ligands. A 31P NMR spectrum registered in PC showed the same self-assembling architecture as found in other nonprotic solvents. [Copyright &y& Elsevier]

Abstract: A novel chiral phosphite–phosphoramidite ligand based on 2-anilinoethanol and R-BINOL moieties has been synthesized in one-pot. The ligand was evaluated in the rhodium-catalyzed enantioselective hydrogenation of α- and β-dehydroamino acid derivatives and dimethyl itaconate in three different solvents at 25°C, at 1 or 50bar of hydrogen pressure. The solvent and the pressure effect are discussed. [Copyright &y& Elsevier]

Abstract: New chiral phospholanes were prepared by coupling of bromo-substituted heterocycles with the enantiopure, building block (2R,5R)-2,5-dimethyl-1-chlorophospholane. Some of the new phosphine ligands have the potential for self-assembling via hydrogen bondings in a metal complex. By application of these and related ligands in the palladium catalyzed allylic amination reaction, high enantioselectivities (up to 99%) were achieved. The influence of the construction of the cyclic phosphine ligands on the enantioselectivity is analyzed. [Copyright &y& Elsevier]

Abstract: New chiral phospholanes 6 were prepared in both enantiomeric forms starting from l- and d-tartaric acid. The key step in the synthetic sequence is the double hydrophosphination of unsaturated chiral bis(lactone) 9 by NaPhPH(BH3). This method was used for the first time in the formation of chiral phospholanes. The structure of phospholane 6a was confirmed by X-ray crystallography. σ-Donor properties of the phospholanes were estimated by measurement of 1 J(31P–77Se) coupling constants in the corresponding phosphine selenides. The new phospholanes were tested as ligands in the Rh-catalyzed enantioselective hydrogenation of functionalized standard olefins (65–92% ee). [Copyright &y& Elsevier]

Abstract: New electron-rich chiral 1,3-diphosphines of the BDPP type were prepared from 1,3-diphenylpropane-1,3-diol by an economically feasible synthetic approach. The σ-donor properties of the phosphines were determined by measurement of J(31P–77Se) coupling constants in the corresponding phosphine selenides. For comparison related, but electronically different, 1,3-diphosphines were considered. The new diphosphines showed good enantioselectivities as ligands in the Rh-catalyzed enantioselective hydrogenation of benchmark substrates and β-amino acid precursors (up to 98% ee). The electronic effects on the outcome of the enantioselective catalysis have been analyzed. [Copyright &y& Elsevier]

Enantiopure acylphosphites have been prepared based upon chiral nonsubstituted and 3,3′-disubstituted binaphthols in order to elucidate steric and electronic effects on the Rh(I)-catalyzed asymmetric hydrogenation of functionalized olefins. With these new types of ligands, up to 80% ee was obtained. Rate as well as enantioselectivity of the hydrogenation were strongly dependent on the precatalyst preparation and substitution pattern of the ligand. [Copyright &y& Elsevier]

The enantioselective hydrogenation of 1,3-diarylpropane-1,3-diones with chiral Ru(II)-diphosphine catalyst has been studied. In a first approach it was found, that Tol-BINAP together with Ru(COD)methallyl2 formed the most selective catalyst. One of the C2-symmetric enantiopure 1,3-diols obtained in turn was transformed via its 1,3-di-O-mesylate into 1,3-bisdiarylphosphines. One of them, 1,3-diphenyl-1,3-bis(diphenylphosphino)propane, could be advantageously utilized as a ligand for the efficient enantioselective Ru-catalyzed hydrogenation of its own 1,3-diketone precursor. Thus, the condition for a ‘cross self-breeding’ catalytic system is fulfilled. A further reduction of the preparation costs could be achived by application of RuCl3·H2O instead of other more expensive precatalyst precursors without compromosing the enantioselectivity. The ligand was used in the Rh(I)-catalyzed asymmetric hydrogenation of model substrates and β-amino acid precursors where up to 97% ee could be achieved. [Copyright &y& Elsevier]

Enantiopure pyrophosphites have been prepared for the first time based upon two independent synthetic pathways. The new ligands based on binaphthols, which are remarkably stable towards oxidation, were tested in the Rh(I)-catalyzed asymmetric hydrogenation of functionalized olefins, where up to 70% ee could be achieved. [Copyright &y& Elsevier]

The rhodium(I)-catalyzed enantioselective hydrogenation of E- and Z-configured β-acylamido β-alkylacrylates as well as of isomeric mixtures has been investigated. As ligands 1,2-bisphospholanes like DuPHOS, BPE and Me4-BASPHOS have been tested, but also diphosphines forming seven-membered chelates such as DIOP. The effect of additional oxy groups in the diphosphine ligand on rate and enantioselectivity was likewise elucidated. In general, with all catalysts screened the hydrogenation is strongly sensitive to the E/Z-geometry of the substrate. E-Substrates are converted with good or excellent enantioselectivites into the desired β-amino acid derivatives. The hydrogenation of Z-substrates showed the known H2-pressure dependency of the ee. [Copyright &y& Elsevier]

A new diphosphine ligand bearing a hydroxy group in the backbone was synthesized starting from 9-bromocamphor. The rhodium(I) complex based on this ligand was tested in the hydrogenation of α- and β-amino acid precursors. The activity and selectivity of the catalyst were found to be strongly dependent upon the nature of the substrate. Thus, β-acetylamino carboxylates were obtained with up to 97% ee. [Copyright &y& Elsevier]

A facile multigram scale preparation of (1R,3S,4S)-2-azabicyclo[2.2.1]heptane-3-carboxylic acid via stereoselective synthesis of the corresponding α-amino ester hydrochloride is detailed. Hitherto applied protocols for the synthesis of this cyclic proline analogue involving a tedious chromatographic purification step could thus be considerably improved upon. The specific rotation of the α-amino acid reported in the literature has been revised. [Copyright &y& Elsevier]

Abstract: The dynamic kinetic resolution (DKR) of rac-1-tert-butoxypropan-2-ol with isopropenyl acetate in the presence of Novozyme 435 and a ruthenium catalyst produces enantiomerically pure (R)-1-tert-butoxy-2-acetoxy-propane (>99.5 %ee) in a good yield. The product can be easily transformed into (R)-propane-1,2-diol without loss of stereoselectivity. Together with recently published procedures, the herein described DKR offers the possibility to use any lactide source as starting material for the production of (R)-propane-1,2-diol. The chiral diol may serve as the chiral building block for the synthesis of important enantiopure esters, like propylene carbonate, chiral polymers, etc. [Copyright &y& Elsevier]

Abstract: The ruthenium catalyzed inversion of l-lactic acid esters in the presence of Novozym 435 is described which give d-lactates in good yields and with >99% ee. [Copyright &y& Elsevier]

Abstract: The enantioselective hydrogenation of (E)-2-(4-methoxy-3-(3-methoxypropoxy)-benzylidene)-3-methylbutanoic acid (1) to (R)-2-(4-methoxy-3-(3-methoxypropoxy)-benzyl)-3-methylbutanoic acid (2)—a key intermediate in the synthesis of the pharmacologically important renin inhibitor Aliskiren—is described. The stereochemistry of the catalytic transformation has been studied using a number of homogeneous chiral Rh(I) and Ru(II) complexes bearing ferrocene-based phosphine ligands. The highest enantioselectivity for the homogeneous hydrogenation of 1 (up to 95% ee) was achieved with a [Rh(NBD)2]BF4 pre-catalyst (substrate/catalyst ratio 100:1, 10 bar H2, 40°C, in MeOH). To bring the enantioselectivity to perfection an effective method for the isolation of the enantiopure carboxylic acid is suggested likewise. [Copyright &y& Elsevier]

The synthesis of a broad library of new P- chirogenic Xantphos ligands is reported. A special feature is 2,7-di- tert.- butyl substituents in the backbone which requires the modification of the original synthetic approach. In comparison to related ligands reported formerly the substitution has a considerable influence on the results (yield and % e.e.) of metal catalyzed reactions, e.g. asymmetric rhodium catalyzed hydrogenation of isophorone and the palladium catalyzed alkylation, respectively. Image 1 • Synthesis of a broad library of P -chirogenic diphosphines with a rigid xanthene-backbone as Xantphos analogue. • Influence of substitution pattern on selectivity and conversion. • Application as ligands in asymmetric hydrogenation with rhodium-complexes. • Palladium-catalyzed asymmetric allylation of dimethyl malonate. [ABSTRACT FROM AUTHOR]

Multivariate curve resolution methods suffer from the non-uniqueness of the solutions of the nonnegative matrix factorization problem. The solution ambiguity can be considerably reduced by equality constraints in the form of known spectra or concentration profiles. Two measures are suggested that indicate the impact of the equality constraints. The representation of these measures in the area of feasible solutions show strong variations in the restrictiveness of equality constraints. The measures are tested for a three-component model problem and experimental data sets from the hydroformylation process and a catalyst cluster formation. • The strongly varying restrictiveness of the equality constraint in MCR computations is analyzed by two estimators. • The estimator values are visualized in the area of feasible solutions (AFS) by means of an additional color coordinate. • The additional AFS color coordinate improves the information content and can be generalized to other indicator variables. [ABSTRACT FROM AUTHOR]

The crystal-structure determination of the title compound, [RhH(C 46 H 44 O 8 P 2 ) 2 (CO)]·2.25C 7 D 8 , is reported. The bis-phosphite ligand, C 46 H 44 O 8 P 2 , is well known as Biphephos. One specific characteristic of this hydrido rhodium(I) monocarbonyl complex is that one bis-phosphite ligand is coordinated in the expected bidentate mode and the other is coordinated in a monodentate mode. Thus, one phosphite moiety remains non-coordinating. All three coordinating phospho-rus atoms occupy the equatorial positions in the trigonal-bipyramidal environment around the rhodium atom. The crystals of the hydrido rhodium(I) monocarbonyl complex contains deuterated solvent mol-ecules (toluene- d 8 ). Most of them are included in the model, but the contributions of about 0.84 toluene per unit cell were removed from the diffraction data, using the SQUEEZE procedure in PLATON [Spek (2015 ▸). Acta Cryst. C 71 , 9-18]., (© Leidecker et al. 2023.)

The successful rhodium-catalyzed asymmetric hydroformylation and hydroaminomethylation of α-substituted acrylamides is described using 1,3-phosphite-phosphoramidite ligands based on a sugar backbone. A broad scope of chiral aldehydes and amines were afforded in high yields and excellent enantioselectivities (up to 99%). Furthermore, the synthetic potential of this method is demonstrated by the single-step synthesis of the brain imaging molecule RWAY.

Reduction of carbonyl moieties to the corresponding alcohol using simply hydrazine hydrate has been considerably unfeasible until now due to the well-known condensation reaction. However, herein, we report that using an excess of 20-fold equivalents, the reduction proceeds in excellent yields. 1 H NMR study of the reaction and density functional theory (DFT) calculations indicate that the final fate of the hemiaminal intermediate is crucial to obtain the alcohol or the hydrazone.

In the title compound, [RhH(C74H68O8P2)(C18H15P)(CO)]·3C4H10O, the CHP3 coordination set at the Rh(I) ion is arranged in a distorted trigonal-bipyramidal geometry with the P atoms adopting equatorial coordination sites and the C atom of the carbonyl ligand as well as the H atom adopting the axial sites. The asymmetric unit contains two very similar mol-ecules of the rhodium complex, two half-occupied diethyl ether mol-ecules and further diethyl ether solvent mol-ecules which could not be modelled successfully. Therefore contributions of the latter were removed from the diffraction data using the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155].

In the title compound, [Rh(C(74)H(68)O(8)P(2))H(CO)(2)]·C(4)H(10)O, the C(2)HP(2) coordination set at the Rh(I) ion is arranged in a distorted trigonal-planar geometry with one P atom of the diphosphite mol-ecule and the H atom adopting the axial coordination sites.

The reaction of (η(3)-all-yl)[(1,2,5,6-η)-cyclo-octa-1,5-diene]rhodium(I) with tris-(2,4-di-tert-butyl-phen-yl)phosphite in toluene produces the title compound, [Rh(C(42)H(62)O(3)P)(C(8)H(12))]·C(7)H(8), by spontaneous metallation at one of the nonsubstituted phenyl ortho-C atoms of the phosphite mol-ecule. The coordination geometry at the Rh(I) ion is distorted square-planar. The toluene solvent mol-ecule is disordered over two different orientations, with site-occupation factors of 0.810 (2) and 0.190 (2).

Bis-cyclopropanated 1,3,5-tricarbonyl compounds were prepared by a sequence of Claisen condensations and cyclopropanations. The optimization of the conditions proved to be very important to suppress retro-Claisen reactions. The conformation of these molecules was studied by experimental and computational methods. The syn/syn;syn/syn conformation is present for all derivatives. It is exclusively present in the case of the derivative containing a phenyl group located at the terminal carbon atom. In most cases, equilibria with other conformers are found.

O,O'-3,3'-Di-tert-butyl-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diyl phosphonate (1) is the hydrolysis product of several mono- and bis-phosphites used as ligands in industrial hydroformylation and other catalytic reactions. As a result of a tautomeric equilibrium, this pentavalent heteroatom-substituted phosphine oxide (HASPO) can rearrange to the corresponding trivalent phosphorus compound. The latter is able to react with typical rhodium-containing precursors frequently used for the generation of catalysts. The resulting species were characterised by NMR spectroscopy and X-ray structure analysis. Proof is given that a rhodium complex of 1 forms an active hydroformylation catalyst. Moreover, 1 can add to aldehydes, which are generated as products in the hydroformylation. Thus a broad range of subsequent reactions can be associated with the degradation of the original phosphite ligands, which has a strong influence on the overall outcome of the hydroformylation reaction., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

(S)-6-Br-BINOL-derived phosphoramidite, a simple monodentate ligand with a stereogenic center at the phosphorus atom, was synthesized for the first time. This stereoselector generated a high level of enantioselectivity (80-95% ee) in the rhodium-catalyzed hydrogenation of alpha-dehydrocarboxylic acid esters and was also successfully employed in the asymmetric palladium-catalyzed allylic substitution of (E)-1,3-diphenylallyl acetate. The optical yield also showed significant dependence with reaction type: up to 70% ee for allylic amination, up to 75% ee for allylic sulfonylation, and up to 90% ee for allylic alkylation., ((c) 2010 Wiley-Liss, Inc.)

A new robust palladium/phosphine catalyst system for the selective monoarylation of ammonia with different aryl bromides and chlorides has been developed. The active catalyst is formed in situ from [Pd(OAc)(2)] and air- and moisture-stable phosphines as easy-to-handle pre-catalysts. The productivity of the catalyst system is comparable to that of competitive Pd/phosphine systems; full conversion is achieved with most substrates with 1-2 mol % of Pd source and a fourfold excess of ligand (L).

Standard molar enthalpies of formation in the gaseous state of a series of alkyl 3-methylbut-2-enoates have been obtained from combustion calorimetry and results from the temperature dependence of the vapor pressure measured by the transpiration method. To verify the experimental data, we have performed ab initio calculations of all compounds. Enthalpies of formation derived from the G3MP2 method are in excellent agreement with the experimental results. Quantitative analysis of strain effects in alkyl 3-methylbut-2-enoates was discussed in terms of deviations of deltafH degrees m(g) from the group additivity rules. Energetics of the cis-trans isomerization of carboxylic acid derivatives was studied using G3MP2 and DFT methods. Values of strain and cis-trans corrections derived in this work provide further improvement on the group-contribution methodology for prediction of the thermodynamic properties of compounds relevant to biodiesel.

The use of diolefin-containing rhodium precatalysts leads to induction periods in asymmetric hydrogenation of prochiral olefins. Consequently, the reaction rate increases in the beginning. The induction period is caused by the fact that some of the catalyst is blocked by the diolefin and thus not available for hydrogenation of the prochiral olefin. Therefore, the maximum reaction rate cannot be reached initially. Due to the relatively slow hydrogenation of cyclooctadiene (cod) the share of active catalysts increases at first, and this leads to typical induction periods. The aim of this work is to quantify the hydrogenation of the diolefins cyclooctadiene (cod) and norborna-2,5-diene (nbd) for cationic complexes of the type [Rh(ligand)(diolefin)]BF(4) for the ligands Binap (1,1'-binaphthalene-2,2'-diylbis(phenylphosphine)), Me-Duphos (1,2-bis(2,5-dimethylphospholano)benzene, and Catasium in the solvents methanol, THF, and propylene carbonate. Furthermore, an approach is presented to determine the desired rate constant and the resulting respective pre-hydrogenation time from stoichiometric hydrogenations of the diolefin complexes via UV/Vis spectroscopy. This method is especially useful for very slow diolefin hydrogenations (e.g., cod hydrogenation with the ligands Me-Duphos, Et-Duphos (1,2-bis(2,5-diethylphospholano)benzene), and dppe (1,2-bis(diphenylphosphino)ethane).

Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh-catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2-pyridone or 2-alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self-assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH2Cl2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0-99 % ee Complexation studies and DFT calculations were performed to explain these differences.

A set of 16 new and closely related bisphospholane ligands have been prepared by using a highly flexible and convergent approach. Each synthesis can be performed on an industrially relevant scale. The bisphosphines differ in the nature of the bridge connecting both phospholane units. Bridges are formed by three-, four-, five- and six-membered heterocyclic or alicyclic rings. Bisphospholanes and their Rh-precatalysts have been investigated by using results of theoretical calculations (DFT) and analytic measurements ((31)P and (103)Rh NMR spectroscopy, X-ray structure analysis). The studies showed that catalysts based on ligands with maleic anhydride or maleimide bridges give constantly superior enantioselectivities in methanol as the solvent. This may account for optimised steric and electronic effects. However, by changing the solvent catalysts with other backbones can give rise to excellent results. This gives proof that simple correlations between steric and electronic properties and results in the enantioselective hydrogenation frequently claimed in literature are not general.

High-throughput screening considering a library of 96 chiral P-ligands involved in two types of Rh(I) complexes was used for the identification of homogeneous catalysts for the highly enantioselective reductive amination of alpha-keto acids with benzylamine. After optimization of the reaction conditions and scale-up with a cationic Rh-Deguphos catalyst, a range of chiral alpha-amino acids could be produced by this new reaction in good yield and by up to 98% ee.

The highly stereoselective synthesis of a chiral silylphospholane has been described, which can be advantageously used as a building block under base-free conditions for the construction of diphosphines related to DuPHOS. The utility of silylphospholane is shown in the synthesis of a new bisphospholane ligand 1 (MalPHOS), which is characterized by a maleic anhydride backbone. The ligand forms with Rh(I) a complex with a larger bite angle P-Rh-P than the analogue Me-DuPHOS complex. Both complexes have been tested in the asymmetric hydrogenation of unsaturated alpha- and beta-amino acid precursors of pharmaceutical relevance. In several cases, the new catalyst was superior in comparison to the Me-DuPHOS complex, in particular when (Z)-configured beta-acylamido acrylates were used as substrates.

The enantioselective hydrogenation of E- and Z-methyl 3-acetamidobutenoate, key intermediates in the synthesis of a pharmaceutically important chiral beta-amino acid, with RhI catalysts in MeOH as solvent has been investigated in detail. As chiral ligands, Et-DuPHOS, Me4-BASPHOS, DI-PAMP, DIOP, HO-DIOP and Et-Ferro-TANE have been employed. The particular role of oxyfunctionalization in some diphosphine catalysts is addressed in relation to the E/Z geometry of the substrate and the dependency of the ee on the H2 pressure. Kinetic investigations with [Rh(diphosphane)(MeOH)2]-BF4, taking into consideration the special nature of the precatalyst [[Rh-(cod)2]BF4/ligand versus [Rh(cod)ligand)]BF4], NMR spectroscopic measurements and the H2 pressure dependence of the observed enantioselectivity provide evidence that the reaction proceeds via an "unsaturated route" mechanism. This mechanism correlates to catalytic features found in the past for the hydrogenation of related unsaturated alpha-amino acid precursors. The influence of the temperature was similarly investigated. A nonlinear dependency of the enantiomeric ratio as a function of the reciprocal of the temperature has been found. The correlation between temperature and H2 pressure and their effects on the enantioselectivity is discussed. In general, the highest enantioselectivities for the hydrogenation of both isomeric substrates can be achieved at room temperature and below, whereas the fastest conversion takes place at 30-50 degrees C.