Neutral Hexacoordinate Tin(IV) Halide Complexes with 4,4'-Dimethy-2,2'-bipyridine

A series of three neutral, hexacoordinate tin(IV) complexes were synthesized by the reaction of 4,4'-dimethyl-2,2'-bipyridine (DMB) with SnX₄, X = Cl, Br, and I, as starting materials. The complexes (DMB)SnX₄ were characterized in solution by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy, and in the solid-state by ¹¹⁹Sn MAS NMR spectroscopy. In addition, single-crystal X-ray diffraction and elemental analysis were used to confirm the molecular structures. In these complexes, the tin atom adopts a distorted octahedral arrangement and the DMB acts as a bidentate N,N'-chelate ligand. Computational DFT methods were also employed to gain more insight into the nature of the bonding in these complexes, including the hypothetical complexes (DMB)SnX₄ (X = F, At). Additionally, the validity and reliability of the ¹¹⁹Sn NMR chemical shifts were examined. The calculated values were compared with the experimental signals and the effects of structure and solvent are discussed. Finally, all of the complexes (DMB)SnX₄ were successfully tested for the ring-opening polymerization (ROP) of bulk ε-caprolactone under non-dried and aerobic conditions as precatalyst.