Bis-Guanidinate Scaffold for the Construction of Unique Zr(IV)-Li(I) Heterobimetallic Complexes

Herein, we report the bis-guanidinate-bridged, unique heterobimetallic organometallic compounds containing lithium and zirconium, revealing new dimensions of ligand-induced structural versatility. The lithiated salts of bis-guanidinates, XylLLi and DepLLi (where L = {(ArHN)(ArN)-C=N-C=(NAr)(NHAr)}; Ar = Xyl = 2,6-Me2-C6H3 and Ar = Dep = 2,6-Et2-C6H3), were reacted with Cp₂ZrHCl (Schwartz’s reagent) in benzene to afford heterobimetallic compounds 1 and 2, respectively, via the elimination of H₂ and HCl. In both compounds 1 and 2, the LX-type ligand anion in LLi is transformed into an L₂X₃-type framework. To our knowledge, these are the first examples in which a bis-guanidinate ligand acts as trianionic (tritopic) at one end and neutral (ditopic) at the other, leading to the formation of two four-membered and one six-membered metallacycles. Solid-state structures revealed that compound 1 adopts a dimeric structure, whereas compound 2 forms a zig-zag coordination polymeric chain. Notably, in compound 2, migration of the Cp group from the zirconium to the lithium center was observed, which is attributed to the influence of the Dep group in the bis-guanidinate anion. Furthermore, the initial catalytic activities of compounds 1 and 2 were investigated in the dihydroboration of nitriles. Surprisingly, compound 1 was catalytically inactive, while compound 2 exhibited excellent activity.