Catalytic Hydroboration of Esters by Versatile Thorium and Uranium Amide Complexes

Abstract

The challenging hydroboration of esters is achieved using simple uranium and thorium amides, U­[N­(SiMe3)2]3 and [(Me3Si)2N]2An­[κ2-(N,C)-CH2Si­(CH3)2N­(SiMe3)] (An = Th or U) acting as precatalysts in the reaction with pinacolborane (HBpin). All three complexes showed impressive catalytic activities, reaching excellent yields. A large scope of esters was investigated including aliphatic, aromatic, and heterocyclic esters that were transformed cleanly to the corresponding hydroborated alcohols, which readily hydrolyzed to the free alcohols. Moreover, the actinide catalysts demonstrated unexpected high functional tolerance toward nitro, halide, cyano, and heteroaromatic functional groups. The reaction exhibited excellent selectivity toward the ester when additional double and triple unsaturated C–C bonds were present. Lactones and poly caprolactone have been successfully cleaved to the monomeric units, showing a great promise toward polymer degradation and recycling. Detailed kinetic studies are provided in order to determine the rate dependence on the concentration of catalyst, HBpin, and ester. A plausible mechanism is proposed based on stoichiometric reactions, DFT calculations, thermodynamic measurements, and deuterium-labeling studies.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

“…Examples of catalytic reactions mediated by uranium complexes have appeared in recent decades. [68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] For example, Meyer and coworkers reported an example of uranium-mediated electrocatalytic production of H 2 from H 2 O. 76,77 Recently, Arnold and coworkers demonstrated that a dinuclear uranium complex could bind N 2 , mediating its reduction and functionalization to NH 3 .…”

Achieving High Photo/Thermocatalytic Product Selectivity and Conversion via Thorium Clusters with Switchable Functional Ligands

“…As relatively abundant actinides on earth, thorium and its derivatives have manifested critical applications in nuclear energy, medical, and industrial fields because of their radiation resistance, high temperature resistance, and high thermal conductivity. − However, the relatively low structural variability of these materials restricts their development to some extent in more potential applications. − The development of thorium-based coordination compounds provides more possibilities to overcome these restrictions, because more structural variations and functional modulations can be readily implemented through the diverse coordination numbers and intriguing coordination modes of thorium as well as coordination of different functional ligands . Particularly, thorium-based metal–organic frameworks (Th-MOFs) have been tuned for applications in gas adsorption, ion exchange, and radiation resistance through coordination modification with different organic ligands. − Nevertheless, the application of thorium-based functionalized materials (including thorium-based complexes) in the field of catalysis is still largely unexplored. − To date, a mere handful of Th-MOFs have been reported to be applied as heterogeneous catalysts for CO 2 cycloaddition and photocatalytic oxidation of 2-chloroethyl ethyl sulfide. − …”

tBuOLi-Promoted Hydroboration of Esters and Epoxides

“…Findlater found that the efficient hydroboration of esters could be realized using polynuclear lanthanide–diketonato clusters . Recently, Eisen reported an efficient hydroboration of esters promoted by the thorium and uranium amide complexes U­[N­(SiMe 3 ) 2 ] 3 and [(Me 3 Si) 2 N] 2 An­[κ 2 -(N,C)-CH 2 Si­(CH 3 ) 2 N­(SiMe 3 )] (An = Th or U) . Owing to the complex nature of the reported ester hydroboration catalysts, these protocols have much room for improvement, particularly in terms of easily achieved simple catalysts and workup procedure.…”