Can Bismuth Replace Mercury in Redox Transmetallation/Protolysis Syntheses from Free Lanthanoid Metals?

Abstract

Tris(pentafluorophenyl)bismuth has been examined as a potential replacement for diarylmercurials in redox transmetallation/protolysis (RTP) syntheses of reactive rare earth compounds from free rare earth metals, HgAr₂ , and a proligand HL. Thus, the lanthanoid pyrazolates, [Ln(Ph₂ pz)₃ (thf)₃ ] (Ph₂ pz=3,5-diphenylpyrazolate; Ln=La, 1, Ce, 2, Nd, 3, Tb, 4; thf=tetrahydrofuran), [Ln₂ (Ph₂ pz)₄ (OMe)₂ (dme)₂ ]⋅2 dme (Ln=Ho, 5, Er, 6, Tm, 7, Lu, 8; dme=1,2-dimethoxyethane), [Ln(Ph₂ pz)₃ (dme)₂ ] (Ln=Dy, 9, Sm, 10), [Ln(tBu₂ pz)₃ (thf)₂ ] (tBu₂ pz=3,5-di-tert-butylpyrazolate; Ln=La, 11, Ce, 12, Sm, 13, Gd, 14, Dy, 15, Ho, 16, Tm, 17, Yb, 18, Lu, 19), [Ln(ttfpz)₃ (thf)₃ ] (ttfpz=3-(2'-thienyl)-5-(trifluoromethyl)pyrazolate; Ln=La, 20, Sm, 21), and [Er(PhMepz)₃ (thf)₂ ] 22 (PhMepz=3-phenyl-5-methylpyrazolate) have been prepared in good yields by redox transmetallation/protolysis reactions employing lanthanoid metals and trispentafluorophenylbismuth [Bi(C₆ F₅ )₃ ]⋅0.5 diox (diox=1, 4-dioxane) in donor solvents. This is a new and efficient synthetic route in which Bi(C₆ F₅ )₃ replaces the commonly used Hg(C₆ F₅ )₂ or HgPh₂ , and provides proof of concept for the method. [Ln₂ (Ph₂ pz)₄ (OMe)₂ (dme)₂ ]⋅2 dme (5-8) complexes are derived from C-O bond activation of dme on crystallization of the initial products from this solvent, and are dimeric methoxide-bridged species. Other structures are monomeric with η² -bound pyrazolate ligands and nine-coordinate metal atoms for complexes 1-4, 9-10 and 20-21, and eight-coordinate metal atoms for complexes 11-19 and 22.

Keywords: crystal structures; lanthanoid metals; lanthanoid pyrazolates.; new synthetic method; redox transmetallation/protolysis (RTP) reactions; trispentafluorophenylbismuth (Bi(C6F5)3).