The isolation and chemistry of tantalum dimethylamides containing resolved 3,3′-disubstituted-1,1′-bi-2,2′-naphthoxide ligands

Abstract

Reaction of the tantalum dimethylamide substrates [Ta(NMe₂)₅] or mer,cis-[Ta(NMe₂)₂Cl₃(HNMe₂)] with one equivalent of the 3,3′-disubstituted-2,2′-dihydroxy-1,1′-binaphthyl [H₂O₂C₂₀H₁₀(R)₂-3,3′] (R = SiMe₃, 1; SiMe₂Ph, 2; SiMePh₂, 3; SiPh₃, 4) leads to the series of amine adducts [Ta(O₂C₂₀H₁₀R₂-3,3′)(NHMe₂)(NMe₂)₃] (R = SiMe₃, 5; SiMe₂Ph, 6; SiMePh₂, 7; SiPh₃, 8) and [Ta(O₂C₂₀H₁₀R₂-3,3′)(NHMe₂)(NMe₂)Cl₂] (R = SiMe₃, 9; SiMe₂Ph, 10; SiMePh₂, 11; SiPh₃, 12). Structural analyses by X-ray diffraction of (S)-5, (R)-7 and (R,S)-8 show a pseudo-octahedral geometry about tantalum with the coordinated dimethylamine ligand located cis to the two naphthoxide oxygen atoms. In the case of (S)-9, (R)-10 and (S)-12, the solid-state structure consists of both chloride ligands being located trans to the two naphthoxide oxygen atoms. Solution NMR spectroscopic properties of 5–12 are consistent with an identical structure being adopted in solution with the amine ligands being strongly bound in all cases. When (S)-5 is heated under vacuum the dimethylamine ligand is lost leading to [Ta(O₂C₂₀H₁₀{SiMe₃}₂-3,3′)(NMe₂)₃] (S)-13. Reaction of (S)-5 with SiCl₄ leads to a mixture of [Ta(O₂C₂₀H₁₀{SiMe₃}₂-3,3′)(NHMe₂)Cl₃] (S)-14 and [Ta(O₂C₂₀H₁₀-{SiMe₃}₂-3,3′)Cl₄][Me₂NH₂] (S)-15. The solid-state structure of (S)-15 was determined. The amine/amide ligands in (S)-12 undergo insertion of CS₂ leading to the dimethyldithiocarbamate, (S)-[Ta(O₂C₂₀H₁₀-3,3′-{SiPh₃}₂)(CS₂NMe₂)₂Cl] (S)-16. The solid state structure of (S)-16 consists of a pentagonal bipyramidal geometry about Ta with an axial oxygen and chloride ligand.