Synthesis and structural characterization of 2,2’-bipyridine zinc formate: Analysis of formate bonding and hydrosilylation of CO2 and carbonyl compounds

Abstract

The zinc formate compound (bipy)Zn(O₂CH)₂ is obtained via the reaction of Zn(O₂CH)₂ with 2,2’-bipyridine (bipy). In addition, (bipy)Zn(O₂CH)₂ may be formed from zinc hydride via addition of bipy followed by addition of (i) HCO₂H and (ii) CO₂. The molecular structure of (bipy)Zn(O₂CH)₂ has been determined by X-ray diffraction, thereby demonstrating that it exists as a monomeric species with a distorted tetrahedral zinc center and κ¹-monodentate formate ligands. As such, the coordination environment of the zinc provides a contrast to the octahedral sites in the isomeric 4,4’-bipyridine counterpart, (bipy^4,4’)Zn(O₂CH)₂, and the aqua derivative, (bipy)Zn(O₂CH)₂(OH₂)·H₂O, both of which feature bridging formate ligands. Analysis of the bonding within the formate ligand indicates that the zinc–formate moiety is not best represented by a Zn–O–C(=O)H resonance structure, but instead possesses a significant ionic component that reduces the C=O bond order and increases the C–O bond order. The formate compound (bipy)Zn(O₂CH)₂ participates in hydrosilylation transformations involving CO₂ and carbonyl compounds, including (i) the reaction of CO₂ with (MeO)₃SiH to afford HCO₂Si(OMe)₃ and (ii) insertion of Ph₂CO, PhC(O)Me, Me₂CO and PhCHO into the Si–H bonds of PhSiH₃ to afford PhSi[OCH(R)R’]₃ via PhSiH₂[OCH(R)R’] and PhSiH[OCH(R)R’]₂.