Dynamic Covalent Switching between a 1,1’-Ruthenocene Macrocycle and a Ruthenocenophane through a Transimination Reaction

Abstract

Dynamic covalent chemistry has been employed extensively for connecting amine and aldehyde building blocks to construct organic macrocycles, covalent organic frameworks, and organometallic analogues. However, detailed investigations on covalent dynamic imine chemistry involving metallocenes and diamines are sparse. The synthesis of a 1,1’-ruthenocene-diimine macrocycle (2a) by a condensation reaction of 1,1’-diformylruthenocene (1) and 1,4-diaminobutane is described. The reaction is high-yielding in solution and under mechanochemical conditions. A dynamic equilibrium between dinuclear 2a and a mononuclear ruthenocenophane (2b) was discovered, which allows the synthesis of ruthenocenophanes through dynamic covalent chemistry and further modification. Compounds 2a and 2b can be interconverted in solution by adjusting the temperature or concentration. Reactive 2b can be trapped by reactions at the imine functions, as a diiminium cation through reaction with an acid, and as a trimetallic adduct 3b, through reaction with a palladium N-heterocyclic carbene (NHC) complex. Similarly, a stable hexametallic macrocycle 3a was isolated by reaction of 2a with the palladium NHC complex. The transformation between 2a and 2b proceeds by dynamic transimination. The reactions are likely water-catalysed with several intertwined pathways, and the self-sorting system can be kinetically controlled. A mechanism supported by control experiments and density functional theory calculations is proposed.