Turning the Tables: Ligand-Centered Hydride Shuttling in Organometallic BIP-Al Systems.

Abstract

The reversible storage and release of hydride equivalents remains a central challenge in the design of biomimetic redox systems. Cationic 2,6-bis(imino)pyridine organoaluminum complexes [(4-R-BIP)AlR2]+ (where R = H; R' = Me, 1a; R' = Et, 1b; R = Bn; R' = Me, 1c) and their neutral 2,6-bis(imino)-4-R-dihydropyridinate counterparts [(4-R-HBIP)AlR2] 2a-c are presented as chemically reversible hydride exchangers. Interconversion between these systems is achieved through strong reducing agents such as M+[HBEt3]- (where M = Li; Na) or LiAlH4, while powerful electrophiles like B(C6F5)3 or cationic trityl salts Ph3C+ enable the reverse transformation, with the latter providing complete selectivity. Overall, this reversible hydride exchange mirrors natural NAD(P)H/NADP+ cofactor system. These findings establish a new platform for ligand-centered hydride shuttling, where the metal fragment acts as a passive modulator─inverting the traditional roles assigned to metal and ligand.