The Rate-Determining Step in the Rhodium–Xantphos-Catalysed Hydroformylation of 1-Octene

Recent development towards alkene hydroformylation catalysts integrating traditional homo- and heterogeneous catalysis

This mini-review provides the recent progress towards catalysts for the hydroformylation of catalysts that bridge traditional homo- and heterogeneous catalysis, highlighting the future development of heterogeneous catalysts in hydroformylation.

New horizons for catalysis disclosed by supramolecular chemistry

The adoption of a supramolecular approach in catalysis promises to address a number of unmet challenges, ranging from activity (unlocking of novel reaction pathways) to selectivity (alteration of the innate selectivity of a reaction, e.g. selective functionalization of C-H bonds) and regulation (switch ON/OFF, sequential catalysis, etc.). Supramolecular tools such as reversible association and recognition, pre-organization of reactants and stabilization of transition states upon binding offer a unique chance to achieve the above goals disclosing new horizons whose potential is being increasingly recognized and used, sometimes reaching the degree of ripeness for practical use. This review summarizes the main developments that have opened such new frontiers, with the aim of providing a guide to researchers approaching the field. We focus on artificial supramolecular catalysts of defined stoichiometry which, under homogeneous conditions, unlock outcomes that are highly difficult if not impossible to attain otherwise, namely unnatural reactivity or selectivity and catalysis regulation. The different strategies recently explored in supramolecular catalysis are concisely presented, and, for each one, a single or very few examples is/are described (mainly last 10 years, with only milestone older works discussed). The subject is divided into four sections in light of the key design principle: (i) nanoconfinement of reactants, (ii) recognition-driven catalysis, (iii) catalysis regulation by molecular machines and (iv) processive catalysis.

Kinetic evaluation of the hydroformylation of the post-metathesis product 7-tetradecene using a bulky phosphite-modified rhodium catalyst

A mechanism-based rate model was applied for the hydroformylation of the post-metathesis product 7-tetradecene using a bulky phosphite-modified rhodium catalyst.

Rh(DPEPhos)-Catalyzed Alkyne Hydroacylation Using β-Carbonyl-Substituted Aldehydes: Mechanistic Insight Leads to Low Catalyst Loadings that Enables Selective Catalysis on Gram-Scale

The detailed mechanism of the hydroacylation of β-amido-aldehyde, 2,2-dimethyl-3-morpholino-3-oxopropanal, with 1-octyne using [Rh( cis-κ²-_P,P-DPEPhos)(acetone)₂][BAr^F₄]-based catalysts, is described [Ar^F = (CF₃)₂C₆H₃]. A rich mechanistic landscape of competing and interconnected hydroacylation and cyclotrimerization processes is revealed. An acyl-hydride complex, arising from oxidative addition of aldehyde, is the persistent resting state during hydroacylation, and quaternary substitution at the β-amido-aldehyde strongly disfavors decarbonylation. Initial rate, KIE, and labeling studies suggest that the migratory insertion is turnover-limiting as well as selectivity determining for linear/branched products. When the concentration of free aldehyde approaches zero at the later stages of catalysis alkyne cyclotrimerization becomes competitive, to form trisubstituted hexylarenes. At this point, the remaining acyl-hydride turns over in hydroacylation and the free alkyne is now effectively in excess, and the resting state moves to a metallacyclopentadiene and eventually to a dormant α-pyran-bound catalyst complex. Cyclotrimerization thus only becomes competitive when there is no aldehyde present in solution, and as aldehyde binds so strongly to form acyl-hydride when this happens will directly correlate to catalyst loading: with low loadings allowing for free aldehyde to be present for longer, and thus higher selectivites to be obtained. Reducing the catalyst loading from 20 mol % to 0.5 mol % thus leads to a selectivity increase from 96% to ∼100%. An optimized hydroacylation reaction is described that delivers gram scale of product, at essentially quantitative levels, using no excess of either reagent, at very low catalyst loadings, using minimal solvent, with virtually no workup.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Multiphasic aqueous hydroformylation of 1-alkenes with micelle-like polymer particles as phase transfer agents

Micelle-like polymer particles have been applied in aqueous multiphasic hydroformylation reactions of long chain alkenes. These colloids act as phase transfer agents for the nonpolar substrates and as carriers for the catalyst bearing sulfonated ligands by electrostatic attraction. The catalyst performance and the phase separation were optimized with special focus on the conversion, selectivity and catalyst recovery, as those are key points in multiphasic systems to achieve a feasible industrial process. The effect on the catalyst performance of the number of sulfonate groups and electron withdrawing trifluoromethyl groups in the ligand has been studied. The approach was successfully demonstrated for 1-alkenes from 1-hexene to 1-dodecene. For 1-octene, a TOF of more than 3000 h⁻¹ could be achieved at a substrate to catalyst ratio of 80 000, while keeping the rhodium and phosphorous leaching below 1 ppm. In repetitive batch experiments the catalyst was recycled four times, yielding an accumulated TON of more than 100 000 for 1-octene.

Micelle-like polyelectrolyte polymer particles were applied as phase transfer agents and catalyst carriers in the multiphasic hydroformylation of long chain alkenes achieving high turnover frequencies and efficient catalyst recovery.

Computational aspects of hydroformylation

This review is to focus on computational studies on hydroformylation and theoretical coordination chemistry results related to hydroformylation.

Full kinetic analysis of a rhodium-catalyzed hydroformylation: beyond the rate-limiting step picture

A complete dynamic kinetic analysis beyond the steady state approximation of the rhodium-catalyzed hydroformylation with the 6-DPPon ligand is presented. The results show that not one single step but several transition states and intermediates control the selectivity and activity of the catalysis.

Using aqueous ammonia in hydroaminomethylation reactions: ruthenium-catalyzed synthesis of tertiary amines

The direct synthesis of tertiary amines from ammonia and olefins is presented. Using a combination of Ru3 (CO)12 and 2-phosphino-substituted imidazole ligand as catalyst system allows for hydroaminomethylation reactions of bulk aliphatic and functionalized olefins. Tertiary amines are obtained in an atom-efficient domino process in moderate to good isolated yields (45-76%) with excellent regioselectivities (n/iso up to 99:1).

A theoretical study of the activity in Rh-catalysed hydroformylation: the origin of the enhanced activity of the π-acceptor phosphinine ligand

The factors governing the activity in Rh-catalyzed hydroformylation were investigated using DFT and QSAR methods.

Intermolecular hydroacylation: high activity rhodium catalysts containing small-bite-angle diphosphine ligands

Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C(6)H(5)F)(R(2)PCH(2)PR'(2))][BAr(F)(4)] (R, R' = (t)Bu or Cy; Ar(F) = C(6)H(3)-3,5-(CF(3))(2)), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh((t)Bu(2)PCH(2)P(t)Bu(2))H{κ(2)(S,C)-SMe(C(6)H(4)CO)}(L)](+) (L = acetone, MeCN, [NCCH(2)BF(3)](-)) and the decarbonylation product [Rh((t)Bu(2)PCH(2)P(t)Bu(2))(CO)(SMePh)](+) have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio)benzaldehdye. Analogous complexes with the phosphine 2-(diphenylphosphino)benzaldehyde are also reported. Studies indicate that through judicious choice of solvent and catalyst/substrate concentration, both decarbonylation and productive hydroacylation can be tuned to such an extent that very low catalyst loadings (0.1 mol %) and turnover frequencies of greater than 300 h(-1) can be achieved. The mechanism of catalysis has been further probed by KIE and deuterium labeling experiments. Combined with the stoichiometric studies, a mechanism is proposed in which both oxidative addition of the aldehyde to give an acyl hydride and insertion of the hydride into the alkene are reversible, with the latter occurring to give both linear and branched alkyl intermediates, although reductive elimination for the linear isomer is suggested to have a considerably lower barrier.