Unlocking the potential of metal ligand cooperation for enantioselective transformations

Metal-ligand cooperation, in which both the metal and the ligand of a transition metal complex actively participate in chemical transformations leading to enhanced reactivity or selectivity in chemical reactions, has emerged as a powerful and versatile concept in catalysis. This Viewpoint discusses the development trajectory of transition metal-based complexes as catalysts in (de)hydrogenative processes, in particular those cases where metal-ligand cooperation has been invoked to rationalise the observed high reactivities and excellent selectivities. The historical context, mechanistic aspects and current applications are discussed with the suggestion to explore the potential of the MLC mode of action of such catalysts in enantioselective transformations beyond (de)hydrogenative processes.

Mn(I) phosphine-amino-phosphinites: a highly modular class of pincer complexes for enantioselective transfer hydrogenation of aryl-alkyl ketones

A series of Mn(I) catalysts with readily accessible and more π-accepting phosphine-amino-phosphinite (P'(O)N(H)P) pincer ligands have been explored for the asymmetric transfer hydrogenation of aryl-alkyl ketones which led to good to high enantioselectivities (up to 98%) compared to other reported Mn-based catalysts for such reactions. The easy tunability of the chiral backbone and the phosphine moieties makes P'(O)N(H)P an alternative ligand framework to the well-known PNP-type pincers.

BOM-Phosphinite as an Electrophilic P-Stereogenic Transfer Reagent for the Synthesis of Bulky Phosphines: Synthesis of tert-Butyl(3,5-di-tert-butylphenyl)BisP

BOM-tert-butylmethylphosphinite borane is an efficient electrophilic P-stereogenic transfer reagent for the synthesis of bulky tertiary phosphines. The novel methodology relies on a one-pot deprotection/substitution on the trivalent phosphinite that takes place with very high stereospecificity. The potential of this strategy is demonstrated with the synthesis of a wide scope of tertiary phosphines in excellent enantiomeric excess. The methodology was applied to the synthesis of a bulky P-stereogenic BisP* ligand analogue.

Sterically hindered ortho-substituted phosphatriptycenes as configurationally stable P-chirogenic triarylphosphines

ortho-Substituted and unsymmetrical 9-phospha-triptycenes were synthesized via two synthetic approaches involving densely functionalized ortho-halogenated triarylmethane or phosphine precursors. ortho-Substituents imposed a considerable steric shielding due to the tricyclic cage-shaped structure with the aryl rings p-systems orthogonal to the phosphorus electron pair. A series of Au(i) and Rh(i) complexes were analysed in the solid state to determine Tolman electronic parameters, cone angles and buried volumes of these unprecedented functionalized phosphines. Quantum chemical calculations of electronic and steric descriptors revealed that these cage-shaped phosphines are electron-poor and that single methyl substituent is enough to provide the largest effect on steric shielding reported so far in triarylphosphines. An unsymmetrically substituted 9-phosphatriptycene was resolved by chiral HPLC, opening the avenue towards stable P-chirogenic triarylphosphines with unlimited configurational stability for new catalyst development in asymmetric transition-metal catalysis.

Configurational landscape of chiral iron(ii) bis(phosphane) complexes

An [FeH(η²-H₂){Me-DuPhos}₂]⁺ complex reacts with ethers and halides to give cis- and trans-dihydrogen substituted isomers and [FeX{Me-DuPhos}₂]⁺ (X = Cl, I) complexes.

Synthesis and application in asymmetric catalysis of P-stereogenic pincer–metal complexes

P-stereogenic pincer: synthesis and application in asymmetric catalysis.