Ynamide and Azaalleneyl. Acid-Base Promoted Chelotropic and Spin-State Rearrangements in a Versatile Heterocumulene [(Ad)NCC(tBu)]-

Abstract

We introduce the heterocumulene ligand [(Ad)NCC(Bu-t)](-) (Ad=1-adamantyl (C10H15),Bu- t=tert-butyl, (C4H9)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Bronsted acid-base chemistry, which promotes an unprecedented spin-state change of the [VIII] ion. These unique scaffolds are prepared via addition of 1-adamantyl isonitrile (C equivalent to NAd) across the alkylidyne in complexes [(BDI)V equivalent to(CBu)-Bu-t(OTf)] (A) (BDI-=ArNC(CH3)CHC(CH3)NAr), Ar=2,6-(i)Pr(2)C6H(3)) and [(dBDI)V equivalent to(CBu)-Bu-t(OEt2)] (B) (dBDI(2-)=ArNC(CH3)CHC(CH2)NAr). Complex A reacts with C equivalent to NAd, to generate the high-spin [V-III] complex with a kappa(1)-N-ynamide ligand, [(BDI)V{kappa(1)-N-(Ad)NCC(tBu)}(OTf)] (1). Conversely, B reacts with C equivalent to NAd to generate a low-spin [VIII] diamagnetic complex having a chelated kappa(2)-C,N-azaalleneyl ligand, [(dBDI)V{kappa(2)-N,C-(Ad)NCC(Bu-t)}] (2). Theoretical studies have been applied to better understand the mechanism of formation of 2 and the electronic reconfiguration upon structural rearrangement by the alteration of ligand denticity between 1 and 2.