Photomechanical Actuation of Ligand Geometry in Enantioselective Catalysis

Abstract

A catalyst that couples a photoswitch to the biaryl backbone of a chiral bis(phosphine) ligand, thus allowing photochemical manipulation of ligand geometry without perturbing the electronic structure is reported. The changes in catalyst activity and selectivity upon switching can be attributed to intramolecular mechanical forces, thus laying the foundation for a new class of catalysts whose selectivity can be varied smoothly and in situ over a useful range by controlling molecular stress experienced by the catalyst during turnover. Forces on the order of 100 pN are generated, thus leading to measurable changes in the enantioselectivities of asymmetric Heck arylations and Trost allylic alkylations. The differential coupling between applied force and competing stereochemical pathways is quantified and found to be more efficient for the Heck arylations.

Mechanochemically Active Soft Robots

“…Covalent polymer mechanochemistry has also been used to trigger crosslinking reactions in response to otherwise destructive forces, 24 and the ability to create self-healing behavior in autonomous soft robots has been noted to be an especially attractive goal, given susceptibility of soft robots to mechanical damage. 9,33,34 While many of these responses might currently be more challenging to realize in PDMS elastomers than spiropyran activation, we note that in at least two cases (perturbed catalysis 35 and retro-cycloaddition 14 ) the requirements for activation appear to be quite similar to those for spiropyran.…”

Quaternary Stereogenic Centers through Enantioselective Heck Arylation of Acyclic Olefins with Aryldiazonium Salts: Application in a Concise Synthesis of (R)‐Verapamil

“…[3] An ew development in this field was the arylation of acyclica lkenyl alcohols recently reported independently by Sigman and Correia using aryldiazonium salts as electrophiles. [4][5][6] Then ewly formed stereogenic centers in the carbopalladation step were preserved owing to the high preference of the palladium hydride species for migration along the carbon chain followed by conversion of the alcohol into an aldehyde group (Scheme 1c).…”

Molecular Mechanochemistry: Engineering and Implications of Inherently Strained Architectures

“…In addition, there are several advantages of the macrocyclic force probe. First, it is compatible with a broad range of functional groups, including cyclobutane [44,106], cyclopropane [103], disulfide [107,108], sulfonate [109], ester [110], and catalytic ligand [111], which allows investigation into various chemical reactions. Second, the restoring force can be adjusted by varying the length and/or conformational flexibility of the linker, up to hundreds of pico-Newtons (Fig.…”