Asymmetric catalysis, where a metal catalyst is used to transform a substrate into a single enantiomer of product, has become a popular synthetic technique in both academic and industrial settings. The chirality of compounds leads to applications important in the pharmaceutical and agrochemical industries. Commonly, a metal complex’s ability to create a product of a certain enantiomer relies on a chiral ligand being attached to the metal. Often, the syntheses of these chiral ligands is arduous and expensive. The synthetic methodology incorporates achiral bisphosphine ligands with metals to create complexes containing a stereogenic metal center, considered a “chiral-at-metal,” complex. This type of complex would allow for the usage of achiral phosphines, which are cheaper and easier to synthesize than chiral phosphines.<br/>For this research project, secondary phosphine oxides (SPOs) were used as starting materials for synthesizing bisphosphine oxides, as they are inexpensive and air-stable precursors. The prepared bisphosphine oxides were then reduced to bisphosphines. Three reduction methods were investigated: a one-pot method using (COCl)2; AlH3; and DIBAL. After reduction, the phosphines were used as ligands for preparing chiral-at-metal complexes. The catalytic ability of these complexes was analyzed using transfer hydrogenation of acetophenone. Future work will focus on more economically-friendly and abundant metals.

Synthesis of unsymmetrical bisphosphines for use in chiral-at-metal complexes

ACS Spring 2022

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