Zinc(II) Silanethiolates With Piperazine-Based Ligands: Structural Diversity and Catalytic Activity in Allyl Alcohol Oligomerization.

This study focused on the development of non-toxic, stable catalysts for oligomerization processes. We present the synthesis and detailed characterization of four novel zinc(II) silanethiolate complexes incorporating piperazine-derived ligands: [Zn{(tBuO)3SiS}2(ppz)]n (1), [Zn3{SSi(OtBu)3}6(amppz)2] (2), [Zn2{(tBuO)3SiS}4(bappz)] (3), and [Zn{(tBuO)3SiS}2(bappz)]n (4). The complexes display diverse structural motifs, ranging from discrete dinuclear and trinuclear clusters to 1D coordination polymers. Their structures were elucidated with the use of single-crystal X-ray diffraction and supported by DFT calculations (M11-L/def2-SVP). The catalytic application was evaluated in the oligomerization of allyl alcohol activated by Et2AlCl. All complexes exhibited catalytic activity, however the dinuclear complex 3 demonstrated the highest efficiency (109 g·mmol-1·h-1). A detailed structure-activity relationship (SAR) analysis, supported by Non-Covalent Interaction (NCI) indices, reveals that the higher productivity of 3 is attributed to the balance between stability accessibility of the metallic center. Mechanistic DFT studies (NEB method) propose a ligand-assisted activation pathway for 3, which involves the dissociation of a hemilabile aminopropyl arm and a subsequent N2S2 → NOS2 coordination sphere rearrangement, which opens the metal center for substrate binding. MALDI-TOF-MS analysis of the products confirmed the formation of oligomers ranging from dimers to heptadecamers. These findings highlight the potential of zinc silanethiolates as tuneable, environmentally benign precatalysts.