Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

Mrinal Bhunia,Gonela Vijaykumar,Shefali Vaidya,Sumeet Ranjan Sahoo,Debashis Adhikari,Bikash Kumar Shaw,Swadhin K Mandal,Anand Pariyar

doi:10.1039/c9sc02057h

Abstract

Storing and transferring electrons for multi-electron reduction processes are considered to be the key steps in various important chemical and biological transformations. In this work, we accomplished multi-electron reduction of a carboxylic acid via a hydrosilylation pathway where a redox-active phenalenyl backbone in Co(PLY-O,O)2(THF)2, stores electrons and plays a preponderant role in the entire process. This reduction proceeds by single electron transfer (SET) from the mono-reduced ligand backbone leading to the cleavage of the Si-H bond. Several important intermediates along the catalytic reduction reaction have been isolated and well characterized to prove that the redox equivalent is stored in the form of a C-H bond in the PLY backbone via a ligand dearomatization process. The ligand's extensive participation in storing a hydride equivalent has been conclusively elucidated via a deuterium labelling experiment. This is a rare example where the ligand orchestrates the multielectron reduction process leaving only the metal to maintain the conformational requirements and fine tunes the electronics of the catalyst.

Highlights

Multi-electron reduction processes are ubiquitous in nature and are involved in extremely important chemical conversions such as nitrogen to ammonia or carbon dioxide to methanol.[1]
The redox active ligand rarely becomes amenable to conducting chemical events like direct bond formation or to function as a key player to handle this challenging problem of multielectron reduction
In the thriving history of PLY based chemistry, for the rst time we uncover that the reducing equivalent can be stored in the PLY backbone in the form of a C–H bond and can be transferred catalytically to the organic substrates in executing the reduction process

Summary

Introduction

Multi-electron reduction processes are ubiquitous in nature and are involved in extremely important chemical conversions such as nitrogen to ammonia or carbon dioxide to methanol.[1]. The redox active ligand rarely becomes amenable to conducting chemical events like direct bond formation or to function as a key player to handle this challenging problem of multielectron reduction. The use of hydrogen in the presence of transition metal complexes may be very atom efficient,[18,19,20,21,22,23] yet the ammability and required high pressure of the gas are the major disadvantages in such reduction. The use of silanes as a reductant may offer ne tuning of their reducibility by the substituents on the silicon atom and will likely be used o en in the future for challenging organic synthesis. It may be worth noting that carboxylic acid derivatives are o en inert toward reduction and except two reports[24,25] which used

Methods

Results

Conclusion