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

We introduce the heterocumulene ligand [(Ad)NCC( ^t Bu)] ^- (Ad=1-adamantyl (C ₁₀ H ₁₅ ), ^t Bu=tert-butyl, (C ₄ H ₉ )), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid-base chemistry, which promotes an unprecedented spin-state change of the [V ^III ] ion. These unique scaffolds are prepared via addition of 1-adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡C ^t Bu(OTf)] (A) (BDI ^- =ArNC(CH ₃ )CHC(CH ₃ )NAr), Ar=2,6- ⁱ Pr ₂ C ₆ H ₃ ) and [(dBDI)V≡C ^t Bu(OEt ₂ )] (B) (dBDI ^2- =ArNC(CH ₃ )CHC(CH ₂ )NAr). Complex A reacts with C≡NAd, to generate the high-spin [V ^III ] complex with a κ ¹ -N-ynamide ligand, [(BDI)V{κ ¹ -N-(Ad)NCC( ^t Bu)}(OTf)] (1). Conversely, B reacts with C≡NAd to generate a low-spin [V ^III ] diamagnetic complex having a chelated κ ² -C,N-azaalleneyl ligand, [(dBDI)V{κ ² -N,C-(Ad)NCC( ^t Bu)}] (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.
(© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)