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The heterolytic cleavage of H2into H+and H−, and the subsequent transfer of these hydrogen species to polarized CX groups, is a useful strategy to obtain high selectivities in catalytic hydrogenation reactions, which are one of the most important chemical processes. In the homogeneous field, this transformation is catalyzed by a wide variety of metal–ligand complexes, leading to the selective reduction of ketones, aldehydes, and imines, to name a few. In many cases, a ligand–metal cooperative mechanism promotes the activation of the hydrogen molecule; that is, a Lewis basic site of the ligand binds the proton, and simultaneously, a coordinated metal atom acts as a Lewis acid and takes the hydride. Similar to homogeneous catalysts based on organometallic complexes, in the field of metal nanoparticle catalysis the use of supports, ligands and additives can promote heterolytic H2splitting by a cooperative mechanism with the metal, and thus produce the selective reduction of thermodynamically more stable unsaturated groups. This successful approach has allowed very high selectivities to be obtained, with both supported and non-supported metal nanoparticles (MNPs). This Perspective aims to carry out a critical review of recent examples on heterolytic cleavage of dihydrogen mediated by MNPs, making a selection of the most representative works in search for general features and new steps to be followed. As will be shown, promising advances have been made through the use of supported MNPs functionalized by organic ligands, which combine the advantages of homogeneous and heterogeneous catalysts (activity, selectivity, stability and recyclability), and thus represent a new research area with tremendous industrial interest.

The main challenge in the hydrogenation of alkynes into (E)- or (Z)-alkenes is to control the selective formation of the alkene, avoiding the over-reduction to the corresponding alkane. In addition, the preparation of recoverable and reusable catalysts is of high interest. In this work, we report novel nickel nanoparticles (Ni NPs) stabilized by three different imidazolium-amidinate ligands (ICy·(Ar)NCN; L1: Ar = p-tol, L2: Ar = p-anisyl and L3: Ar = p-ClC6H4). The as-prepared Ni NPs were fully characterized by (HR)-TEM, XRD, WASX, XPS and VSM. The nanocatalysts are active in the hydrogenation of various substrates. They present a remarkable selectivity in the hydrogenation of alkynes towards (Z)-alkenes, particularly in the hydrogenation of 3-hexyne into (Z)-3-hexene under mild reaction conditions (room temperature, 3% mol Ni and 1 bar H2). The catalytic behaviour of Ni NPs was influenced by the electron donor/acceptor groups (–Me, –OMe, –Cl) in the N-aryl substituents of the amidinate moiety of the ligands. Due to the magnetic character of the Ni NPs, recycling experiments were successfully performed after decantation in the presence of an external magnet, which allowed us to recover and reuse these catalysts at least 3 times preserving both activity and chemoselectivity.

Air-stable nanoparticles stabilized with secondary phosphine oxides (SPOs) can have a remarkable role as catalysts. Since size and activity depend both on the cluster-ligand interaction and the nature of the employed ligand, the present work provides a fresh perspective on the prospects of bonding analysis, rationalizing for the first time the physical nature of interactions between silver nanoclusters (SNCs) and secondary phosphine oxides (SPOs) in the light of energy decomposition (EDA-NOCV) and noncovalent interaction (NCI) analyses, using the silver core of the X-ray structure for a highly symmetric, ligand-decorated Ag44cluster available in the literature. Our findings reveal that phosphines containing aliphatic substituents are more stabilized when interacting with Ag cluster, in contrast to aromatic groups, and that SPOs containing aromatic moieties become aligned to the silver surface upon adsorption. This alignment of aromatic substituents substantially contribute to dispersion interactions, which is observed by both EDA-NOCV and NCI analyses, showing ligand to metal donations and fragment polarizations, as well as metal to ligand backdonations in some cases. Adsorption conformations bearing hydrogen bonds to the surface were found to be the most favorable ones, and models for SPO-cluster hydrogen transfer are in line with previous experimental findings on gold nanoparticles. The present contribution will help pave the way for the rational development of new SPO-protected nanoparticles and nanoclusters, which may become cheaper and more efficient catalysts in the future.

The catalytic activity of a series of Ru-PNP pincer ligand complexes was studied in the direct amination of alcohols with ammonia. It turned out that all complexes of PNP ligands bearing a secondary amine showed no activity in this hydrogen-shuttling reaction sequence, while all complexes of homologous ligands bearing a tertiary amine gave active catalysts. Further comparative studies on catalysts bearing an acridine-based PNP pincer ligand and a PNP ligand of the Xantphos family provided valuable mechanistic insight that led to the design of a highly active catalyst. It appears that in the group of ligands studied here only ligands that do not form stable Ru-amido complexes are active alcohol amination catalysts.

A secondary phosphine oxide (SPO) ligand (tert-butyl(phenyl)phosphine oxide) was employed to generate an Ir–SPO complex which shows a particular ability to activate dihydrogen under mild conditions without the help of an external base or additive. Such an iridium(i) complex serves as a precursor for homogeneous catalysis since under H2it is converted to a mixture of several iridium(iii) hydride species that are the active catalysts. This system was found to be a highly active catalyst for the hydrogenation of substituted aldehydes, giving very high conversions and chemoselectivities for a wide range of substrates. The SPO ligand presumably plays a key role in the catalytic process through heterolytic cleavage of H2by metal–ligand cooperation. In addition, an exhaustive characterization of the different iridium hydride species was performed by 1D and 2D NMR spectroscopy. The oxidative addition of H2to the Ir(i)–SPO complex is highly stereoselective, as all generated Ir(iii) hydrides are homochiral. Finally, the crystal structure, as determined by X-ray diffraction, of a dinuclear iridium(iii) hydride complex is described.

This review highlights the use of a bisphosphine ligand group in homogeneous catalysis. This ligand group is known as the Xantphos-like ligands, which are based on the generic formula of 2,2′-bis(phosphino)diaryl ether. The synthesis of the main members is summarized and emphasis is given to ligands that can be easily synthesized, also on large scale. The catalytic applications are not comprehensively presented, but instead, about 20% of the examples from literature have been extracted, aiming at the demonstration of diversity, peculiar examples, historical development, design vs.trial and error, and new reactions. Metals ranging from group 7 to 11 have been used in a wide variety of reactions: hydroformylation, alkoxycarbonylation, hydrocyanation, cross-coupling reactions for many C–C and C–X bond forming reactions, carbonylative coupling reactions, phosphinations, etc.

Chiral iridium nanoparticles (IrNPs) were synthesized by H2reduction of (1,5-cyclooctadiene)(methoxy)iridium(i) dimer ([Ir(OMe)(COD)]2) in the presence of an asymmetric secondary phosphine oxide (4,5-dihydro-3H-dinaphtho[2,1-c:1′,2′-e] phosphepine-4-oxide, L). This highly reproducible and simple procedure furnished small, well dispersed and soluble nanoparticles of 1.4 (0.2) nm, which were found to be active catalysts for the enantioselective hydrogenation of prochiral ketones. This study represents the first example of asymmetric hydrogenation catalyzed by SPO-ligated metal nanoparticles and also the first example of asymmetric hydrogenation catalyzed by non-supported chiral IrNPs. The IrNPs were characterized by the use of a wide variety of techniques, such as TEM, HRTEM, EDX, XPS, ATR FT-IR, ECD, and MAS-NMR spectroscopy with and without 1H–13C cross-polarization (CP).

Platinum complexes modified with a chiral non-racemizing SPO preligand 1have been applied in the hydration of aromatic nitriles. [Pt(1)3Cl]Cl formed readily from Pt(COD)Cl2. The chiral secondary phosphine oxide complex showed moderate activity in the hydration of para- and meta-substituted benzonitriles, but failed in converting the ortho-substituted derivatives. The hydride complex PtH(PR2OH)(PR2O–HOR2P) (PR2OH = 1) formed from Pt(PPh3)4and 1, and the cationic complex derived from [Pt(1)3Cl]Cl viadirect chloride abstraction with AgNO3were proven to be considerably more active, allowing us to extend the scope to the hydration of ortho-substituted aromatic nitriles, including axially chiral [1,1′-binaphthalene]-2,2′-dicarbonitrile. In the hydration of the racemic dinitrile, successful kinetic resolution has been achieved. The catalysts derived from non-racemizing 1are the first chiral transition metal–SPO complexes that provide kinetic resolution in the hydration of a racemic chiral nitrile.

The synthesis of ruthenium nanoparticles (RuNPs) using secondary phosphine oxides (SPOs) as ligands is reported. These easily accessible ligands allow the formation of small nanoparticles in the size range of 1–2 nm which display a high efficiency for hydrogenation of aromatics with TOFs up to 2700 mol h−1.

A series of new monodentate phosphane ligands 2have been evaluated in the Mizoroki–Heck arylation reaction of iodobenzene and styrene and compared with our previously reported ligands, 1, 3and 4. The concept of rational ligand design is discussed, and we describe how the performance of this new ligand family could be predicted. Employing our best ligand, 3,3′‐di‐tert‐butyl‐5,5′‐dimethoxybiphenyl‐2,2′‐diyl diisopropylphosphoramidite (3b), we explored the scope of the reaction with regards to solvent and the substrate. We also investigated the electronic dependence of the reaction by analysing the relationship between the rate and Hammett constant. Sufficient steric bulk is required to enforce the catalytic reaction to proceed through the mono‐coordinated palladium species, thereby increasing its reactivity. The electronic properties determine the concentration of the active species from the monomer dimer equilibrium and their intrinsic reactivity. The cyclic phosphoramidite 3bprovides an optimum in both properties within the systems studied, resulting in a rate limiting migratory insertion step.

The application of ruthenium nanoparticles (RuNPs) stabilized by the N-heterocyclic carbenes (NHC) N,N′-di(tert-butyl)imidazol-2-ylidene (ItBu) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene IPr as catalysts in the hydrogenation of several substrates is reported under various reaction conditions (solvent, substrate concentration, substrate/metal ratio, temperature). The RuNHC nanoparticles are active catalysts in the hydrogenation of aromatics and show an interesting ligand effect, RuIPr NPs being generally more active than RuItBu.

The coordination geometry around a platinum atom can be controlled by a diphosphane capsule composed of a tetracationic xantphos‐type ligand and a tetraanionic calix[4]arene. Reaction of the diphosphane capsule with the platinum precursor [PtCl2(MeCN)2] yields the bisligated biscalix[4]arene trans‐platinum capsule, whereas the same diphosphane in the absence of calix[4]arene prefers the formation of the monoligated cis‐platinum complex, as indicated by 31P{1H} NMR and ESI‐MS. The two calix[4]arenes stabilize the kinetic product (trans‐Pt), and slow the formation of the thermodynamic product (cis‐Pt).

Self‐assembly and characterization of heterodimeric diphosphine capsules formed by multiple ionic interactions are described. The first type of capsules is composed of one novel tetrasulfonato‐xantphos ligand and one complementary tetraammonium calix[4]arene. Encapsulation of a transition metal is achieved by self‐assembly of a rhodium complex containing the tetraanionic diphosphine ligand and a tetracationic calix[4]arene. The second type of capsules is composed of two oppositely charged diphosphine ligands: one tetrasulfonato‐xantphos and one tetraammonium‐diphosphine (of the xantphos‐, DPEphos‐, and 1,2‐bis(diphenylphosphino)ethane (dppe)‐type). Bis(metallo) capsules, that is, simultaneous encapsulation of two different transition metals, are created by self‐assembly of a palladium or platinum complex containing a tetracationic ligand and a rhodium complex containing a tetraanionic ligand. Diphosphine ligands with different flexibilities and shapes assemble into metallocapsules with a proper capsular structure, as is indicated by 1H NMR and 1D‐NOESY spectroscopy, ESIMS, and modeling studies.

Self‐assembly and characterization of novel heterodimeric diphosphine capsules formed by multiple ionic interactions and composed of one tetracationic diphosphine ligand and one complementary tetraanionic calix[4]arene are described. Encapsulation of a palladium atom within a diphosphine capsule is achieved successfully by using the metal complex of the tetracationic diphosphine ligand for the assembly process. In this templated approach to metal encapsulation, the transition‐metal complex is an integrated part of the capsule with the transition metal located inside the capsule and is not involved in the assembly process. We present two approaches for capsule assembly by mixing solutions of the precharged building blocks in methanol and mixing solutions of the neutral building blocks in methanol. The scope of the diphosphine capsules and the metallodiphosphine capsules is easily extended by applying tetracationic diphosphine ligands with different backbones (ethylene, diphenyl ether, and xanthene) and cationic binding motifs (p‐C6H4‐CH2‐ammonium, m‐C6H4‐ammonium, and m‐C6H4‐guanidinium). These tetracationic building blocks with different flexibilities and shapes readily associate into capsules with the proper capsular structure, as is indicated by 1H NMR spectroscopy, 1D NOESY, ESI‐MS, and modeling studies.

Butadiene and methanol were telomerised in the presence of palladium catalysts with ligands containing 8‐diphenylphosphinochromane‐like substituents at phosphorus. MonoXantphos and monoSPANphos afforded the most active, stable and selective catalysts known to date under commercially relevant production conditions for 1‐methoxyocta‐2,7‐diene, the precursor to oct‐1‐ene.

Supramolecular strategies, based on hydrogen bonds and ionic interactions, were investigated as tools for the recovery and recycling of homogeneous transition‐metal catalysts by using reverse‐flow adsorption (RFA) technology. The association (in solution) and adsorption (on support) of new functionalized host materials and phosphine guest ligands, functionalized with the complementary binding motifs, were fine‐tuned for the application of these materials in a RFA reactor. The RFA technology for process‐integrated recycling of homogeneous catalysts using these tailor‐made phosphine ligands and silica‐supported host materials resulted in a stable, semicontinuous catalytic system. Rhodium‐catalyzed asymmetric hydrogenation of methyl acetamidoacrylate and asymmetric hydrosilylation of acetophenone were studied as test reactions. Depending on the catalytic process the metal complex could be recycled several times without significant loss in conversion.

The self-assembly of Secondary Phosphine Oxides (SPOs) into anionic bidentate chelates was used to construct unique systems for metal catalyzed transfer hydrogenation of ketones in isopropanol. Chelating bidentate or tridentate ligands were formed by assembly of secondary phosphine oxides through hydrogen bonding in the presence of rhodium trichloride as demonstrated by means of NMR spectroscopy and X-ray diffraction. When a chiral version of an SPO was used in asymmetric transfer hydrogenation of isopropanol and acetophenone, an enantiomeric excess of 89% was achieved. The presence of at least two ligands in the catalytically active species was confirmed by a positive non-linear effect. DFT calculations were applied to characterize several intermediates for the isopropanol dehydrogenation to produce a rhodium hydride complex and acetone. A transition state for the hydrogen-transfer was fully characterized, which revealed that the process occurs viaa concerted outer-sphere mechanism.

Three phosphanes containing azobenzene groups were synthesized, and the photochemical behaviour of their platinum complexes was studied by using the lightinduced EZ isomerization as a switch to change ligand properties.

Ligands behaving badly:A series of hindered biaryl phosphine compounds are used as ligands in rhodium‐ catalyzed hydroformylation. In situ analysis of the resultant catalysts under operating conditions shows that the ligands are dissociated under high pressures of syngas, thereby creating an unselective rhodium catalyst for the hydroformylation.

The reaction of [CpFeη5C5H4–CH=N–CH2n–C4H3S] Cp = η5C5H5 and n= 1 1b or 2 1c with Na2[PdCl4] and NaAcO·3H2O gave [CpFeμη5Feη1PdC5H3–CH=N–CH2n–C4H3SCl] n= 1 2b or 2 2c with a [Csp2,ferrocene,N,Sthienyl]–ligand. The study of the reactivity of 2bor 2cwith PPh3under different experimental conditions has afforded the isolation of [CpFeμη5Feη1PdC5H3–CH=N–CH2n–C4H3SClPPh3] n= 1 3b or 2 3c and[CpFeμη5Feη1PdC5H3–CH=N–CH2n–C4H3SPPh3][BF4] n= 1 4b or 2 4c where 1bor 1cbehave as a bidentate [Csp2,ferrocene,N]–in 3band 3c or as a terdentate [Csp2,ferrocene,N,Sthienyl]–in 4band 4c ligand. The crystal structures of 3b·12CH2Cl2, 3c·2H2O and 4c·CH2Cl2confirm the mode of binding of the ligands. The results obtained from these studies and the solution behaviour of 4band 4creveal that the σPd–S bond of 2b, 2c, 4band 4cis more labile that in [CpFeμη5Feη1PdC5H3–CH=N–C6H42SMeCl] or [CpFeμη5Feη1PdC5H3–CH=N–C6H42SMePPh3][BF4] with a [Csp2,ferrocene,N,Sthioether]–ligand.

A family of monodentate polystyrenesupported phosphites, phosphoramidites and phosphanes has been prepared and evaluated as ligands in rhodiumcatalysed asymmetric hydrogenation and palladiumcatalysed asymmetric allylic alkylation. The supported ligands yielded active and enantioselective catalysts, which in selected cases match the performance of the nonsupported counterparts. As expected, the performance of the supported ligands in the rhodiumcatalysed hydrogenation depends on the nature of the ligand, the type of polymeric support, as well as on the substrate. Additionally, the supported ligands have been applied in the monodentate ligand combination approach, by combining them with nonsupported monodentate ligands. The partially supported heteroligand combinations possess different catalytic properties than the related nonsupported combinations. The heteroligand species, however, are not formed selectively, and nonsupported homoleptic complexes also contribute to the overall activity. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

A family of new modular, chiral, bidentate, nitrogendonor ligands containing the large spirobichroman backbone 1SPAN has been prepared. Enantiopure diamines containing the nitrogen donors at the 8,8′ positions of spirobichroman 1have been synthesized through the resolution of the 8,8′diamino racemate 3. Accordingly, secondary and tertiary amines [+6–6and +5–5, respectively] and imino derivatives [+7–7] were obtained in both enantiomeric forms. A new SPAN derivative incorporating aldehyde groups at the 8,8′ positions of the spirobichroman unit [+9–9] has been synthesized with the aim to extend the ligand library by means of Schiff base chemistry. The derivatization of the isolated enantiomers of 9obtained by diastereomer resolution gave derivatives containing the nitrogen atoms at the benzylic positions. The syntheses of ligands +10–10, +11and +12illustrate the scope of this methodology. The coordination ability of ligand –3has been tested by the synthesis and characterization of complex [PdOAc2{–3}] [–13]. Some preliminary results related to the oxidative kinetic resolution of 1phenylethanol with this Pd complex are reported.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

We have previously introduced the SUPRAPhos ligand library, which is based on components that are selfassembled through nitrogen–zinc interactions, and report here an extension of this library, which widens the scope for application in asymmetric homogeneous catalysis. For example, we report the synthesis of phosphorus amidite appended porphyrins and building blocks with stereogenic centers at the phosphorus. With the new building blocks described in this paper we can form a 450membered SUPRAPhos library, which is based on 45 building blocks 30 pyridyl phosphorus ligands and 15 complementary porphyrinappended phosphorus ligands. Examples of the use of members of the library in the rhodiumcatalyzed asymmetric hydroformylation of styrene are included. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

The coordination mode in a metal complex is critically dependent on the ligands surrounding the metal, on the precursors used, and on the conditions during synthesis. Our goal was to obtain palladium compounds with pyridinephosphane ligands for catalysis. Therefore, we synthesized ligands 1a–d, which differ in the bulky aryl substituent at the pyridyl moiety. The palladium complexes 6a–dof these ligands are insoluble and have been characterized by various techniques, including solidstate NMR and for 6a, b, and d singlecrystal Xray diffraction, showing that bimetallic complexes are formed in which two ligands span two palladium centers. The configuration around these centers is determined by the steric bulk of the ligand. In complexes 6c,d, with the ligands bearing the largest steric groups, both centers have a transconfiguration of the methyl and chloride anions. With intermediately sized pyridyl substituents, complex 6bis formed, having one cissurrounded and one transsurrounded palladium center in the molecule. This kind of complexation has not been observed before. With the least bulky ligand, complex 6ais formed. Depending on the synthetic conditions employed, the methyl and the chloride in this complex can be in a cisconfiguration at both palladium atoms, or show the unique cistranscoordination.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

Combinatorial chemistry in combination with highthroughput screening technologies is an important way of finding new successful catalyst systems. The design of ligand libraries of bidentate phosphorus ligands and the application of their transitionmetal complexes in homogeneous asymmetric catalysis reactions will be described in this review. Till now three different approaches were developed to arrive at such libraries of bidentate phosphorus ligands: 1 modular synthesis of bidentate ligands 2 the solid support synthesis of bidentate ligands and 3 the selfassembly of ligand building blocks into bidentate ligands. The scope and limitations of these strategies will be discussed on the basis of a limited number of articles that dealt with the synthesis of at least 15 bidentate phosphorus ligands. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

The synthesis and resolution of chiral phenoxaphosphane 3, with the stereogenic center at the phosphorus atom, is described. Compound 3 has been synthesized following a well-known procedure for trapping a phosphorus atom within a six-membered ring. The resolution of the racemic mixture of 3 was achieved through separation of its diastereomeric palladacycle derivatives 7a,b and 9a,b. The absolute configuration of enantiopure phosphanes 3a,b was assigned unequivocally by means of X-ray crystal structure determination for complex 9a and by combination of NOE(1H–1H)/COSY(1H,1H) spectroscopy and DFT calculations for complexes 7a,b, which in both cases led to identical results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The rate‐determining step in the hydroformylation of 1‐octene, catalysed by the rhodium–Xantphos catalyst system, was determined by using a combination of experimentally determined 1H/2H and 12C/13C kinetic isotope effects and a theoretical approach. From the rates of hydroformylation and deuterioformylation, a small 1H/2H isotope effect of 1.2 was determined for the hydride moiety of the rhodium catalyst. 12C/13C isotope effects of 1.012(1) and 1.012(3) for the α‐carbon and β‐carbon atoms of 1‐octene were determined, respectively. Both quantum mechanics/molecular mechanics (QM/MM) and full quantum mechanics calculations were carried out on the key catalytic steps, for “real‐world” ligand systems, to clarify whether alkene coordination or hydride migration is the rate‐determining step. Our calculations (21.4 kcal mol−1) quantitatively reproduce the experimental energy barrier for CO dissociation (20.1 kcal mol−1) starting at the (bisphosphane)RhH(CO)2resting state. The barrier for hydride migration lies 3.8 kcal mol−1higher than the barrier for CO dissociation (experimentally determined trend ∼3 kcal mol−1). The computed 1H/2H and 12C/13C kinetic isotope effects corroborate the results of the energy analysis.

Chiral calixarene-based diphosphite ligands 3a–d have been obtained via lower-rim functionalisation of the p-tert-butylcalix[4]arene core. High enantiomeric excesses (up to 94 %) and good activities were obtained in the rhodium-catalyzed asymmetric hydrogenation of prochiral olefins withTADDOL-containing diphosphites 3c,d. This is the firstexample of chiral calix[4]arene-modified ligands that induce high enantioselectivity in metal-catalysed asymmetric reactions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Coordinative bonds have been used to prepare supramolecular ligands leading to well-defined catalysts formed by assembly. The construction of these ligands is based on selective metal–ligand interactions between nitrogen donor atoms of phosphorus-nitrogen building blocks and various zinc(II) porphyrins. The major advantage of this supramolecular approach of catalyst preparation is the simplification of ligand variation enabling straightforward modification of steric, electronic and chiral properties of the supramolecular ligand. A large number of new ligands becomes accessible by this modular variation of the building blocks. The ligand assembly based on pyridyl phosphites and zinc(II) porphyrin with electron-withdrawing substituents led to a twelve-fold increase in activity and an increase in enantioselectivity from 17 to 50 % in the rhodium-catalyzed hydrogenation of dimethyl itaconate. The first examples of assemblies based on non-chiral ligands and chiral zinc(II) porphyrin template molecules show, as proof of principle, an enantiomeric excess up to 18 % in the asymmetric palladium-catalyzed allylic alkylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

An ionic interaction has been used for the first time to assemble monophosphane ligands. NMR spectroscopy and X‐ray studies show that cationic and anionic triphenylphosphane derivatives form ion pairs and subsequently act as a ligand in various transition‐metal complexes. The position of the ionic functional groups allows both cisand transcoordination of the novel assembly ligand in square‐planar transition‐metal complexes.

The application of phenoxaphosphino‐modified Xantphos‐type ligands (1–9) in the rhodium‐catalyzed hydroaminomethylation of internal olefins to give linear amines is reported. Excellent chemo‐ and regioselectivities have been obtained through the use of 0.1 mol % [Rh(cod)2]BF4/0.4 mol % xantphenoxaphos (1), providing a practical and environmentally attractive synthetic route for the preparation of amines from internal alkenes. For the first time, both functionalized internal olefins and mixtures of internal and terminal olefins have been converted highly selectively into linear amines. Investigations of the effects of the calculated natural bite angles of ligands on hydroaminomethylation shows that the regioselectivity for the linear product follows a similar trend to that seen in the hydroformylation of internal alkenes with the aid of these ligands. Hydroaminomethylation and each of its individual steps were monitored by high‐pressure infrared spectroscopy. The results suggest that hydroaminomethylations take place by a sequential isomerization/hydroformylation/amination/hydrogenation pathway.

A series of cationic palladium complexes of general formula [Pd(Me)(MeCN)(N–N)][PF6] (N–N = (phen) 1 a, 4,7‐dichloro‐1,10‐phenanthroline (4,7‐Cl2‐phen) 2 a, 4,7‐diphenyl‐1,10‐phenanthroline (4,7‐Ph2‐phen) 3 a, 4‐methyl‐1,10‐phenanthroline (4‐Me‐phen) 4 a, 4,7‐dimethyl‐1,10‐phenanthroline (4,7‐Me2‐phen) 5 a, 5,5,6,6‐tetrafluoro‐5,6‐dihydro‐1,10‐phenanthroline (F4‐phen) 6 a, containing different substituted phenanthroline ligands, have been prepared from the corresponding neutral chloro derivatives [Pd(Me)(Cl)(N–N)], (1 b–6 b). The X‐ray crystal structure of [Pd(Cl)2(4,7‐Cl2‐phen)] (2 b′) was determined. DFT calculations show that the electron density on the metal is tuned by the substituents on the ligands. The catalytic behavior of complexes 1 a–6 ain the CO/styrene and CO/p‐Me‐styrene copolymerizations was studied in detail, showing that the generated catalysts are active for at least 90 h, yielding copolymers of high molecular weight. A firm correlation between the electron density on palladium on the one hand and the catalytic activity of the complexes and the molecular weight and the stereochemistry of the polyketones synthesized on the other hand has been established: the catalyst containing the F4‐phen is thus far the most active among those tested, yielding the syndiotactic CO/styrene copolymer with a stereoregularity of 96 % (uutriad) and with an Mwvalue of 1 000 000.

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Interaction between α-cyclodextrin or β-cyclodextrin and the alkyl sulfonated diphosphines DPPETS tetrasulfonated 1,2-bisdiphenylphosphinoethane, DPPPTS tetrasulfonated 1,3-bisdiphenylphosphinopropane and DPPBTS tetrasulfonated 1,4-bisdiphenylphosphinobutane was investigated by NMR and UV-Visible spectroscopy. Contrary to α-cyclodextrin, β-cyclodextrin forms inclusion complexes with each sulfonated diphosphine. Continuous variation plots and titration experiments obtained from 1H and 31P NMR data indicated the formation of 11 inclusion complexes and allowed the calculation of the association constants for each complex. Information on the structures of these complexes were obtained by T-ROESY NMR experiments. The potential of these ligands associated with methylated α- or β-cyclodextrin during the reaction of hydroformylation of 1-decene was studied. In all cases, the presence of cyclodextrins increased the conversion and the chemoselectivity whereas the linear to branched ratio of the aldehyde product decreased. This decrease in regioselectivity was attributed to the formation of low-coordinated phosphine species. In fact, in order to reduce steric hindrance around the metal center, a mono-dissociation of the bidentate ligand seemed to occur when the inclusion complex between the cyclodextrin and 1-decene approached the metal center. In the case of methylated-β-cyclodextrin, the phenomenon is accentuated since one of the two diphenylphosphino groups of the bidentate could be trapped by this cyclodextrin leading to the formation of a second-sphere coordination adduct.

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Several SPANphos ligands based on a spirobichroman backbone, introduced as a putative transligand, form compounds of the type [Rh(nbd)(SPANphos)]BF4(1–6) in which both norbornadiene and SPANphos act as cischelating ligands. The cyclooctadiene rhodium chloride derivatives form bimetallic complexes. Crystal structures for several of these compounds and free ligands are reported. Semiemperical AM1 and DFT calculations show that spirobichroman can assume several conformations, some of which are suitable for the formation of cischelating SPANphos. All calculations on SPANphos complexes of PdCl2, PtCl2and Rh(CO)Cl show that the transcomplex is more stable by 4–10 kcal mol−1. The cisconformation in 1–6is enforced by the cischelating norbornadiene ligand.

A series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd‐catalysed allylic alkylation reaction. Reaction of disodium diethyl 2‐methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature. The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds. Mono‐coordination occurs when these ligands are ligated in [Pd(allyl)(X)] complexes (allyl=C3H5, 1‐CH3C3H4, 1‐C6H5C3H4, 1,3‐(C6H5)2C3H3; X=Cl, OAc). The solid‐state structure determined by X‐ray diffraction of [Pd(C3H5)(1)(Cl)] reveals a non‐symmetric coordination of the allyl moiety, caused by the stronger transinfluence of the phosphoramidite ligand relative to X−. In all of these complexes, the syn,transisomer is the major species present in solution. Because of fast isomerisation and high reactivity of the syn,ciscomplex, the major product formed upon alkylation is the linear product, especially for monosubstituted phenylallyl substrates in the presence of halide counterions. In the case of biphenol‐ and BINOL‐based phosphoramidites, however, a strong memory effect is observed when 1‐phenyl‐2‐propenyl acetate is employed as the substrate. In this case, nucleophilic attack competes effectively with the isomerisation of the transient cinnamylpalladium complexes. The asymmetric allylic alkylation of 1,3‐diphenyl‐2‐propenyl acetate afforded the chiral product in up to 93 % ee. Substrates with smaller substituents gave lower enantioselectivities. The observed stereoselectivity is explained in terms of a preferential rotation mechanism, in which the product is formed by attack on one of the isomers of the intermediate [Pd{1,3‐(C6H5)2C3H3}(L)(OAc)] complex.

The reaction between RhC5H4CO2CH2OHNBD1 and 1,1′-carbonyldiimidazole CDI leads to the new CO2–imidazole functionalized alkoxycarbonylcyclopentadienyl complex RhC5H4CO2CH22O2C–ImNBD2Im imidazole. The latter was treated with five generations of polypropylenimine dendrimers DAB-dendr-NH2nn  4, 8, 16, 32, 64DAB diaminobutane to accomplish the synthesis of the new organometallic dendritic macromolecules DAB-dendr-NHOCOCH2CH2OCOC5H4RhNBDnn  4 4, 8 5, 16 6, 32 7, 64 8 based on flexible polypropylenimine dendrimer cores, built up to the fifth generation. Spectroscopic characterization of all the new compounds will be presented and discussed.

A highly active and regioselective catalyst obtained from a novel dicationic ligand 1 and RhCO2acac for hydroformylation of 1-hexene and 1-octene in ionic liquids is reported. Optimisation studies of various reaction parameters led to an unprecedentedly active TOFs > 6200 mol mol−1h−1, T 100 °C, selective lb ratios > 40 and stable hydroformylation procedure. No catalyst leaching Rh-loss < 0.07 of initial rhodium intake, P-loss < 0.4 of the initial phosphorus intake or losses in performance could be measured during 1-octene hydroformylation recycle experiments in 1-butyl-3-methylimidazolium hexafluorophosphate. At low catalyst loadings activities and regioselectivities competitive with one-phase catalysis in conventional solvents were observed. At high catalyst loadings the system is extremely stable and has a long shelf-life as a result of the formation of stable, if inactive rhodium dimers.

The effects of wide bite angles of bidentate phosphine ligands on three catalytic reactions are reviewed: rhodium catalysed hydroformylation, nickel catalysed hydrocyanation, and palladium catalysed reactions of ethene, carbon monoxide and methanol leading to polyketone or methyl propanoate. The P–M–P bite angle plays a crucial role in determining the selectivity and rate in all three reactions. In this review an attempt is made to separate the mode of action into a steric and an electronic one. The regioselectivity of hydroformylation seems to be governed by steric factors, while the rate of reaction is determined by the electronic influence of the bite angle. The rates in hydrocyanation and polyketone formation were previously thought to be determined by orbital effects, but that should be questioned. Selectivity in the palladium carbonylation reaction is mainly due to steric factors.

Isolation of a series of sulfonated diphosphines via a new highly efficient method is described. The work-up procedure involves the precipitation of the sulfonated ligand prior to neutralization, and subsequent removal of the sulfuric acid by filtration and washing. Great advantages of this procedure are its simplicity and easiness to scale-up while co-production of large amounts of sulfate salts is avoided.

Isolation of a series of sulfonated diphosphines via a new highly efficient method is described. The work-up procedure involves the precipitation of the sulfonated ligand prior to neutralization, and subsequent removal of the sulfuric acid by filtration and washing. Great advantages of this procedure are its simplicity and easiness to scale-up while co-production of large amounts of sulfate salts is avoided.

Isolation of a series of sulfonated diphosphines via a new highly efficient method is described. The work-up procedure involves the precipitation of the sulfonated ligand prior to neutralization, and subsequent removal of the sulfuric acid by filtration and washing. Great advantages of this procedure are its simplicity and easiness to scale-up while co-production of large amounts of sulfate salts is avoided.

Isolation of a series of sulfonated diphosphines via a new highly efficient method is described. The work-up procedure involves the precipitation of the sulfonated ligand prior to neutralization, and subsequent removal of the sulfuric acid by filtration and washing. Great advantages of this procedure are its simplicity and easiness to scale-up while co-production of large amounts of sulfate salts is avoided.

We present a review concerning the mechanism involved in the hydroxycarbonylation of styrene. We discuss the intermediates proposed in the literature, the effect of the acidic medium, the reactivity and kinetics, as well as the results of theoretical calculations on hydroxycarbonylation and related reactions. We have performed an in situ high-pressure NMR study to obtain more insight into the mechanisms that control the regioselectivity and have assessed how this is affected by the phosphorus ligand and the catalyst precursor. We observed palladium hydride and palladium acyl species and we suggest a catalytic cycle involving palladium hydride, palladium alkyl, and palladium acyl intermediates.

The novel bulky diphosphite (P∩P) ligands (3 and 4) based on the 2,7,9,9-tetramethyl-9H-xanthene-4,5-diol (2) backbone were investigated in the Rh-catalyzed hydroformylation of oct-1-ene, styrene, and (E)-oct-2-ene. These diphosphites gave rise to very active and selective catalysts for the hydroformylation of oct-1-ene to nonanal with average rates>10000 (mol aldehyde)(mol Rh)⁻¹h⁻¹ (P(CO/H2)=20 bar, T=80°, [Rh]=1 mM) and maximum selectivities of 79% for the linear product. Relatively high selectivities towards the linear aldehyde (up to 70%, linear/branched up to 2.3) but very high activities (up to 39000 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were observed for the hydroformylation of styrene in the presence of these bidentate ligands (P(CO/H2)=2 – 10 bar, T=120°, [Rh]=0.2 mM). Remarkable activities (up to 980 (mol aldehyde)(mol Rh)⁻¹h⁻¹) were achieved with these diphosphites for the hydroformylation of (E)-oct-2-ene with selectivities for the linear product of 74% (l/b up to 2.8, P(CO/H2)=2 bar, T=120°, [Rh]=1 mM). A detailed study of the solution structure of the catalyst under catalytic conditions was performed by NMR and high-pressure FT-IR. The spectroscopic data revealed that under hydroformylation conditions, the bidentate ligands rapidly formed stable, well-defined catalysts with the structure [RhH(CO)2(P∩P)]. All the ligands showed a preference for an equatorial-apical (ea) coordination mode in the trigonal bipyramidal Rh-complexes, indicating that a bis-equatorial (ee) coordination is not a prerequisite for highly selective catalysts.

New homochiral xantphos‐type diphosphonite ligands with binaphthoxy substituents have been prepared and characterized by NMR spectroscopy. These ligands have been applied in the nickel‐catalyzed hydrocyanation of styrene and other vinylarenes. Enantioselectivities up to 63 % eehave been obtained by using 4‐isobutylstyrene as a substrate. Addition of an excess of ligand strongly inhibits the hydrocyanation reaction since the bis‐chelate nickel complexes formed are highly stable and catalytically inactive.