Magic of Alpha: The Chemistry of a Remarkable Bidentate Phosphine, 1,2-Bis(di-tert-butylphosphinomethyl)benzene.

The bidentate phosphine ligand 1,2-bis(di-tert-butylphosphinomethyl)benzene (1,2-DTBPMB) has been reported over the years as being one of, if not the, best ligands for achieving the alkoxycarbonylation of various unsaturated compounds. Bonded to palladium, the ligand provides the basis for the first step in the commercial (Alpha) production of methyl methacrylate as well as very high selectivity to linear esters and acids from terminal or internal double bonds. The present review is an overview covering the literature dealing with the 1,2-DTBPMB ligand: from its first reference, its catalysis, including the alkoxycarbonylation reaction and its mechanism, its isomerization abilities including the highly selective isomerizing methoxycarbonylation, other reactions such as cross-coupling, recycling approaches, and the development of improved, modified ligands, in which some tert-butyl ligands are replaced by 2-pyridyl moieties and which show exceptional rates for carbonylation reactions at low temperatures.

The European Chemical Society (EuChemS).

The European Chemical Society (EuChemS) coordinates the work of almost all the European Chemical Societies. As an organization, it provides an independent and authoritative voice on all matters relating to chemistry, and try to place chemistry at the heart of policy in Europe. Furthermore, EuChemS seeks to develop its members through various activities, workshops and awards. Particularly, EuChemS has fostered growth in its young members through the European Young Chemists' Network. Beyond Europe, EuChemS has collaborated with various organizations in bringing chemistry out of the lab and into society in building a sustainable future for everyone.

Highly versatile catalytic hydrogenation of carboxylic and carbonic acid derivatives using a Ru-triphos complex: molecular control over selectivity and substrate scope.

The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea derivatives. The key control factor for this unique substrate scope results from selective activation to generate either the neutral species [Ru(Triphos)(Solvent)H2] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H2)](+) in the presence of an acid additive. Multinuclear NMR spectroscopic studies demonstrated together with DFT investigations that the neutral species generally provides lower energy pathways for the multistep reduction cascades comprising hydrogen transfer to C═O groups and C-O bond cleavage. Carboxylic esters, lactones, anhydrides, secondary amides, and carboxylic acids were hydrogenated in good to excellent yields under these conditions. The formation of the catalytically inactive complexes [Ru(Triphos)(CO)H2] and [Ru(Triphos)(µ-H)]2 was identified as major deactivation pathways. The former complex results from substrate-dependent decarbonylation and constitutes a major limitation for the substrate scope under the neutral conditions. The deactivation via the carbonyl complex can be suppressed by addition of catalytic amounts of acids comprising non-coordinating anions such as HNTf2 (bis(trifluoromethane)sulfonimide). Although the corresponding cationic cycle shows higher overall barriers of activation, it provides a powerful hydrogenation pathway at elevated temperatures, enabling the selective reduction of primary amides, carbonates, and ureas in high yields. Thus, the complex [Ru(Triphos)(TMM)] provides a unique platform for the rational selection of reaction conditions for the selective hydrogenation of challenging functional groups and opens novel synthetic pathways for the utilization of renewable carbon sources.

On the importance of decarbonylation as a side-reaction in the ruthenium-catalysed dehydrogenation of alcohols: a combined experimental and density functional study.

We report a density functional study (B97-D2 level) of the mechanism(s) operating in the alcohol decarbonylation that occurs as an important side-reaction during dehydrogenation catalysed by [RuH2(H2)(PPh3)3]. By using MeOH as the substrate, three distinct pathways have been fully characterised involving either neutral tris- or bis-phosphines or anionic bis-phosphine complexes after deprotonation. α-Agostic formaldehyde and formyl complexes are key intermediates, and the computed rate-limiting barriers are similar between the various decarbonylation and dehydrogenation paths. The key steps have also been studied for reactions involving EtOH and iPrOH as substrates, rationalising the known resistance of the latter towards decarbonylation. Kinetic isotope effects (KIEs) were predicted computationally for all pathways and studied experimentally for one specific decarbonylation path designed to start from [RuH(OCH3)(PPh3)3]. From the good agreement between computed and experimental KIEs (observed kH/kD =4), the rate-limiting step for methanol decarbonylation has been ascribed to the formation of the first agostic intermediate from a transient formaldehyde complex.

Mechanism of alkyne alkoxycarbonylation at a Pd catalyst with P,N hemilabile ligands: a density functional study.

A detailed mechanism for alkyne alkoxycarbonylation mediated by a palladium catalyst has been characterised at the B3PW91-D3/PCM level of density functional theory (including bulk solvation and dispersion corrections). This transformation, investigated via the methoxycarbonylation of propyne, involves a uniquely dual role for the P,N hemilabile ligand acting co-catalytically as both an in situ base and proton relay coupled with a Pd(0) centre, allowing for surmountable barriers (highest ΔG(≠) of 22.9 kcal mol(-1) for alcoholysis). This proton-shuffle between methanol and coordinated propyne accounts for experimental requirements (high acid concentration) and reproduces observed regioselectivities as a function of ligand structure. A simple ligand modification is proposed, which is predicted to improve catalytic turnover by three orders of magnitude.

Homogeneous catalytic hydrogenation of amides to amines.

Hydrogenation of amides in the presence of [Ru(acac)3] (acacH=2,4-pentanedione), triphos [1,1,1-tris- (diphenylphosphinomethyl)ethane] and methanesulfonic acid (MSA) produces secondary and tertiary amines with selectivities as high as 93% provided that there is at least one aromatic ring on N. The system is also active for the synthesis of primary amines. In an attempt to probe the role of MSA and the mechanism of the reaction, a range of methanesulfonato complexes has been prepared from [Ru(acac)3], triphos and MSA, or from reactions of [RuX(OAc)(triphos)] (X=H or OAc) or [RuH2(CO)(triphos)] with MSA. Crystallographically characterised complexes include: [Ru(OAc-κ(1)O)2(H2O)(triphos)], [Ru(OAc-κ(2)O,O')(CH3SO3-κ(1)O)(triphos)], [Ru(CH3SO3-κ(1)O)2(H2O)(triphos)] and [Ru2(µ-CH3SO3)3(triphos)2][CH3SO3], whereas other complexes, such as [Ru(OAc-κ(1)O)(OAc-κ(2)O,O')(triphos)], [Ru(CH3SO3-κ(1)O)(CH3SO3-κ(2)O,O')(triphos)], H[Ru(CH3SO3-κ(1)O)3(triphos)], [RuH(CH3SO3-κ(1)O)(CO)(triphos)] and [RuH(CH3SO3-κ(2)O,O')(triphos)] have been characterised spectroscopically. The interactions between these various complexes and their relevance to the catalytic reactions are discussed.

Phosphorus containing mixed anhydrides--their preparation, labile behaviour and potential routes to their stabilisation.

Simple mixed anhydrides are known to pose synthetic difficulties relating to their thermal lability and ways to stabilise such mixed anhydride systems by relying on either electronic or steric effects were therefore explored. Thus, a series of acyloxyphosphines and acylphosphites derived from either propanoic acid or phenylacetic acid were prepared and their in solution stability assessed. These compounds were, where stability allowed, fully characterised using standard analytical techniques. NMR studies, in particular, unearthed interesting coupling behaviour for a number of the acyloxyphosphines and acylphosphites as well as their rearrangement products which could be linked to their chiral nature. Furthermore, the crystal structures for three of the prepared mixed anhydrides were determined using X-ray crystallography and are reported herein.

Diazaphospholidine terminated polyhedral oligomeric silsesquioxanes in the hydroformylation of vinyl acetate.

The poorly active, monodentate SemiEsphos phosphine has been turned into an active ligand for rhodium catalysed vinyl acetate hydroformylation by attachment to the periphery of a polyhedral oligomeric silsesquioxane.

Synthesis and characterization of photoluminescent vinylbiphenyl decorated polyhedral oligomeric silsesquioxanes.

Grubbs cross-metathesis has been used to functionalize octavinylsilsesquioxane with fluorescent vinylbiphenyl-modified chromophores to design new hybrid organic-inorganic nanomaterials. Those macromolecules have been characterized by NMR, microanalyses, MALDI-TOF mass spectrometry and photoluminescence. This last method was shown to be an interesting tool in the analysis of the purity of the cube derivatives.

Carbon dioxide induced phase switching for homogeneous-catalyst recycling.

SwitchPhos: Rhodium complexes formed from PPh(3) ligands functionalized with weakly basic amidine groups are highly active catalysts for the hydroformylation of alkenes. On bubbling with CO(2) in the presence of water, the yellow rhodium complexes move into the water phase, whereas bubbling with N(2) at 60 degrees C causes them to switch back into the organic phase. The catalysts can be used for reactions in water or an organic phase.

Synthesis of functional cubes from octavinylsilsesquioxane (OVS).

Octavinylsilsesquioxane, (CH(2)CH)(8)Si(8)O(12), a cubic molecule with vinyl groups at each vertex, has been elaborated to give a series of potential starting materials for nanohybrid synthesis. Terminal bromophenyl groups were introduced onto the surface of octavinylsilsesquioxane either by cross-metathesis or hydrosilylation to give fully bromide substituted POSS A, POSS B and POSS C; the last two were further capped with trimethylsilylacetylene by Sonogashira coupling to produce POSS D and POSS E, showing interesting potential for more useful end group functionalisation. Heck coupling with iodobenzene was used to make the simple phenyl terminated dendrimer POSS F. Cross-metathesis of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styrene with octavinylsilsesquioxane afforded POSS G with eight aryl borate groups on its periphery, suitable for use as a starting material in Suzuki coupling. Finally, POSS H has been functionalized with 8 benzyl chloride groups via Grubbs coupling, allowing further substitutions by nucleophiles.

Insight into the mechanism of decarbonylation of methanol by ruthenium complexes; a deuterium labelling study.

In the reaction of [RuHClP3] (P = PPh3) with NaOMe in methanol, the product is [RuH2(CO)P3]. Short reaction times show that the final product is formed through [RuH4P3] as the major intermediate. Using NaOCD3 in CD3OD, the first formed product is [RuH4P'3] (P' is PPh3 partially deuterated in the ortho positions of the aromatic rings). Further reaction leads to a mixture of [RuHnD2-n(CO)P3] (n = 0, 22%; n = 1, 2 isomers each 28%; n = 2, 22%). Mechanistic aspects of both steps of the reaction are explored and, together with previously published calculations, they provide definitive mechanisms for both dehydrogenation and decarbonylation in these interesting systems.

The synthesis of amines by the homogeneous hydrogenation of secondary and primary amides.

Amides can be hydrogenated to amines using a catalyst prepared in situ from [Ru(acac)(3)] and 1,1,1-tris(diphenylphosphinomethyl)ethane; water is required to stabilize the catalyst and primary amines can only be formed (selectivity up to 85%) if ammonia is also present.

Aqueous-biphasic hydroformylation of higher alkenes promoted by alkylimidazolium salts.

Aqueous-biphasic hydroformylation of higher alkenes (>C5) can be greatly accelerated by addition of 1-octyl-3-methylimidazolium bromide without affecting the phase separation and with good catalyst retention in the aqueous phase.

A computational study of the methanolysis of palladium-acyl bonds.

Density functional calculations suggest that intermolecular attack of methanol may be important in the methanolysis of simple Pd-acyl systems and that the energetics of this process are strongly dependent on the metal coordination environment.

Supported ionic liquid phase catalysis with supercritical flow.

Rapid hydroformylation of 1-octene (rates up to 800 h(-1)) with the catalyst remaining stable for at least 40 h and with very low rhodium leaching levels (0.5 ppm) is demonstrated when using a system involving flowing the substrate, reacting gases and products dissolved in supercritical CO(2) (scCO(2)) over a fixed bed supported ionic liquid phase catalyst.

A new route to N-aromatic heterocycles from the hydrogenation of diesters in the presence of anilines.

The hydrogenation of dicarboxylic acids and their esters in the presence of anilines provides a new synthesis of heterocycles. [Ru(acac)3] and 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) gave good to excellent yields of the cyclic amines at 220 °C. When aqueous ammonia was used with dimethyl 1,6-hexadienoic acid, ε-caprolactam was obtained in good yield. A side reaction involving alkylation of the amine by methanol was suppressed by using diesters derived from longer chain and branched alcohols. Hydrogenation of optically pure diesters (dimethyl (R)-2-methylbutanedioate and dimethyl (S)-2-methylbutanedioate) with aniline afforded racemic 3-methyl-1-phenylpyrrolidine in 78% yield.

Halide-free ethylation of phenol by multifunctional catalysis using phosphinite ligands.

The ortho-alkylation of phenols or aniline by catalytic C-H activation and multifunctional catalysis is described.