Structural and Reactivity Implications of Homo- and Heterobimetallic Co(II) Amides Prepared via Trans(amination) Reactions

Abstract

Cobalt(II) bis(amides)are widely applied in catalysis and material science. Typically, they are prepared via salt metathesis, by reacting a lithium amide with a CoX₂ (X = Cl, Br) salt, requiring, in many cases, the use of low temperatures and other solvents. This work introduces an alternative approach, assessing the reactivity of classical Co(II) amide [Co(HMDS)₂] (1) [HMDS = N(SiMe₃)₂] and heterobimetallic [NaCo(HMDS)₃] (6) as precursors for trans(amination) reactions with DPA(H) (2,2′-dipyridylamine), N-methylaniline, and piperidine. When reacted with the most acidic amine DPA(H), both showed polybasic behavior with excellent stoichiometric control according to the equivalents of DPA(H) employed. Reactions with and piperidine led to an incomplete exchange of the HMDS groups present in 1, even when an excess of the relevant amine is employed. Contrastingly, when assessing the reactivity of sodium cobaltate 6 with these amines, kinetic activation of two (or three) of its HMDS-arms was observed, forming new heterobimetallic species which in all cases proved unstable, undergoing dissociation into their monometallic components or a ligand redistribution process. The catalytic potential of the novel Co(II) complexes was investigated for the hydrosilylation of acetophenone, finding that faster reaction rates and higher chemoselectivities were achieved when using the heterobimetallic Na/Co systems.