Iridium-Catalyzed Ligand-Controlled Remote para-Selective C-H Activation and Borylation of Twisted Aromatic Amides.

A method of para-selective borylation of aromatic amides is described. The borylation proceeded via an unprecedented substrate-ligand distortion between the twisted aromatic amides and a newly designed ligand framework (defa) that is different from the traditionally used ligand (dtbpy) for the C-H borylation reactions. The designed ligand framework (defa) has led to the development of a new type of catalytic system that shows excellent para selectivity for a range of aromatic amides.

Iridium-Catalyzed Regioselective Borylation through C-H Activation and the Origin of Ligand-Dependent Regioselectivity Switching.

Research efforts in catalytic regioselective borylation using C-H bond activation of arenes have gained considerable recent attention. The ligand-enabled regiocontrol, such as in the borylation of benzaldehyde, the selectivity could be switched from the to position, under identical conditions, by just changing the external ligand () from 8-aminoquinoline () to tetramethylphenanthroline (). The DFT(B3LYP-D3) computations helped us learn that the energetically preferred catalytic pathway includes the formation of an Ir-π-complex between the active catalyst [Ir()(Bpin)] and benzaldimine, a C-H bond oxidative addition (OA) to form an Ir(V)aryl-hydride intermediate, and a reductive elimination to furnish the borylated benzaldehyde as the final product.

Insights into the role of noncovalent interactions in distal functionalization of the aryl C(sp)-H bond.

Burgeoning interest in distal functionalization of aryl C-H bonds led to the development of iridium-catalyzed borylation reactions. The significance and inadequate mechanistic understanding of C(sp)-H borylations motivated us to investigate the key catalytic steps and the origin of a directing-group-free regiocontrol in the reaction between aryl amides and Bpin (bis(pinacolato)diboron). An Ir(iii)(ubpy)tris(boryl) complex, generated from the pre-catalyst [Ir(OMe)(cod)] by the action of a bipyridine-urea ligand (ubpy) and Bpin, is considered as the most likely active catalyst.