Asymmetric Synthesis and Metal Complexes of a C3-Symmetric P-Stereogenic Triphosphine, (R)-MeSi(CH2PMe(t-Bu))3 (MT-Siliphos)

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Enantioselective Synthesis of Phosphine Boranes via Crystallization-Induced Dynamic Resolution of Lithiated Intermediate by Understanding the Underlying Epimerization Process

Described herein is the successful crystallization-induced dynamic resolution (CIDR) of an α-lithiated phosphine borane utilizing the easily accessible and inexpensive ligand (R,R)-TMCDA. Starting from the essential P-prochiral building block dimethyl phenyl phosphine borane we were able to obtain phosphine boranes in yields up to 80 % and e.r. up to 98 : 2 by crystallization of the lithiated intermediate prior to the trapping reaction. NMR-based deuterium labeling experiments indicate that the epimerization in solution is based on the intermolecular proton transfer between nonlithiated phosphine borane and the corresponding lithiated intermediate, rendering the presence of the remaining starting compound in an optimized solvent mixture the main factor for successful enantioselective synthesis. Quantum chemical calculations using different model systems based on solid state structures confirm these experimental results. By gaining insights into the epimerization mechanism, essential principles for CIDR of lithiated phosphine boranes are elucidated that may be expanded to other important P-stereogenic compounds and simple chiral amines.

Cage-Shaped Phosphites Having C3 -Symmetric Chiral Environment: Steric Control of Lewis Basicity and Application as Chiral Ligands in Rhodium-Catalyzed Conjugate Additions

Designing chiral ligands with an axial symmetry higher than C2 -rotational symmetry is one of the most crucial approaches to improving enantioselectivity in asymmetric synthesis. Herein, C3 -symmetric chiral cage-shaped phosphites are reported. Their Lewis basicity and chiral environment are precisely controlled by the tethered group. The cage-shaped phosphites successfully worked as chiral ligands in Rh-catalyzed asymmetric conjugate additions, realizing acceptable yields with excellent enantioselectivity, and were used to synthesize a pharmacologically important molecule.

Catalytic Asymmetric Synthesis of P-Stereogenic Phosphines: Beyond Precious Metals

Metal-catalyzed asymmetric synthesis of P-stereogenic phosphines is a potentially useful approach to a class of chiral ligands with valuable applications in asymmetric catalysis. We introduced this idea with chiral platinum and palladium catalysts, exploiting rapid pyramidal inversion in diastereomeric metal–phosphido complexes (ML*(PRR′)) to control phosphorus stereochemistry. This Account summarizes our attempts to develop related synthetic methods using earth-abundant metals, especially copper, in which weaker metal–ligand bonds and faster substitution processes were expected to result in more active catalysts. Indeed, precious metals were not required. Without any transition metals at all, we exploited related P-epimerization processes to prepare enantiomerically pure phosphiranes and secondary phosphine oxides (SPOs) from commercially available chiral epoxides.

1 Introduction

2 Copper-Catalyzed Phosphine Alkylation

3 Copper-Catalyzed Tandem Phosphine Alkylation/Arylation

4 Nickel-Catalyzed Phosphine Alkylation

5 Proton-Mediated P-Epimerization in Synthesis of Chiral Phosphiranes

6 Diastereoselective Synthesis of P-Stereogenic Secondary Phosphine Oxides (SPOs) from (+)-Limonene Oxide

7 Conclusions

A shape changing tandem Rh(CNC) catalyst: preparation of bicyclo[4.2.0]octa-1,5,7-trienes from terminal aryl alkynes

The preparation of a range of tetraaryl-substituted bicyclo[4.2.0]octa-1,5,7-trienes using a one-pot procedure starting from terminal aryl alkynes and catalysed by a rhodium(i) complex is reported. This synthesis proceeds by a reaction sequence involving head-to-tail homocoupling of the terminal alkyne and zipper annulation of the resulting gem-enyne. The rhodium catalyst employed is notable for the incorporation of a flexible NHC-based pincer ligand, which is suggested to interconvert between mer- and fac-coordination modes to fulfil the orthogonal mechanistic demands of the two transformations. Evidence for this interesting auto-tandem action of the catalyst is provided by reactions of the precatalyst with model substrates, corroborating proposed intermediates in both component cycles, and norbornadiene, which reversibly captures the change in pincer ligand coordination mode, along with a DFT-based computational analysis.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds

This review reports the best stereoselective or asymmetric syntheses, the most efficient P*-building blocks and functionalisation of P-chirogenic compounds, in the light of chiral phosphorus compound applications.

Complexes of the tripodal phosphine ligands PhSi(XPPh2)3(X = CH2, O): synthesis, structure and catalytic activity in the hydroboration of CO2

The coordination chemistry of Fe²⁺, Co²⁺and Cu⁺ions was explored with the ligands PhSi{CH₂PPh₂}₃(1) and PhSi{OPPh₂}₃(2), so as to evaluate the impact of the electronic properties of the tripodal phosphorus ligands on the structure and reactivity of the corresponding complexes.