Potassium Follows Calcium in Heterobimetallic 'K-H-Al' Hydrides on a Picolyl-Derived Chemically Non-innocent Triaza Ligand

Abstract

Heterobimetallic hydrides pairing s- and p-block metals on a single ligand are rare but likely promising for synergic chemistry. We report a series of K-H-Al heterobimetallic hydrides on a chemically non-innocent picolyl-based ethylenediamine ligand through a metal-ligand interplaying mechanism of hydride shuttling. The proligands Ar3NH (Ar = Mes, Ph) and AlH3(NMe2Et) give the AlH2 complexes [(Ar3N)AlH2] (Ar = Mes (1), Ph (6)). Both 1 and 6 react with KN(SiMe3)2 (KHMDS) at room temperature to form 1:1 adducts ‘[(Mes3N)Al(HMDS)(H)2K]’ (7) and [(Ph3N)Al(HMDS)(H)2K]2 (8), respectively. Heating 7 and 8 at 70 °C deprotonates a picolyl C-H to give [(Mes3N-H)Al(HMDS)(H)K]4 (9) and [(Ph3N-H)Al(HMDS)(H)K]2 (10), respectively. Monitoring the thermolysis of 7 to 9 at 50 °C reveals an intermediate [(Mes3N2H)Al(HMDS)(H)K]2 (11), where the ligand pyridyl is reduced by a 2-H insertion. DFT analysis suggests the inserted hydride moves onto the potassium before the deprotonation happens. The overall reaction profile follows a similar Ca-H-Al heterobimetallic case on the same ligand framework, except an adduct like 7 or 8 was unseen before. A Li-Al combination on the same framework differs from the K-Al or Ca-Al cases but follows the pattern of Mg-Al.