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(Ph2pz)3(thf)3] (Ph2pz=3,5‐diphenylpyrazolate; Ln=La, 1, Ce, 2, Nd, 3, Tb, 4; thf=tetrahydrofuran), [Ln2(Ph2pz)4(OMe)2(dme)2]⋅2 dme (Ln=Ho, 5, Er, 6, Tm, 7, Lu, 8; dme=1,2‐dimethoxyethane), [Ln(Ph2pz)3(dme)2] (Ln=Dy, 9, Sm, 10), [Ln(tBu2pz)3(thf)2] (tBu2pz=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(C6F5)3]⋅0.5 diox (diox=1, 4‐dioxane) in donor solvents. This is a new and efficient synthetic route in which Bi(C6F5)3 replaces the commonly used Hg(C6F5)2 or HgPh2, and provides proof of concept for the method. [Ln2(Ph2pz)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.

Replacing Mercury: Syntheses of Lanthanoid Pyrazolates from Free Lanthanoid Metals, Pentafluorophenylsilver, and Pyrazoles, Aided by a Facile Synthesis of Polyfluoroarylsilver Compounds

“…However, it is not as reactive as Bi(C 6 F 5 ) 3 or Hg(C 6 F 5 ) 2 , owing to the need for activation of the metal by iodine for Ln = Nd, Tb, Dy, Ho, Er, Lu. On the other hand, crystallization as the pyridine complexes for Ln = Ho, Er, Lu (and Tm), obviated a problem is the reactions with Bi(C 6 F 5 ) 3 as the oxidant where crystallization of the poorly crystalline thf complexes from dme led to C–O activation and formation of [Ln 2 (Ph 2 pz) 4 (µ‐OMe) 2 (dme) 2 ] complexes . Overall use of [AgC 6 F 5 (py)] provides a further reagent to enable the elimination of mercury reagents in RTP reactions with the added advantage that the new synthesis of [AgC 6 F 5 (py)] is simpler than that of Bi(C 6 F 5 ) 3 …”

“…On the other hand, [Nd(Ph 2 pz) 3 (thf) 3 ], previously obtained as a mono(tetrahydrofuran) solvate[31b] has now been obtained as a tris(tetrahydrofuran) solvate, [Nd(Ph 2 pz) 3 (thf) 3 ] · 3thf, a composition previously observed for samarium. [37a] Tris(3,5‐di‐tert‐butylpyrazolato)lanthanoid(III) complexes have been extensively studied both with thf coligands, [31c], [31d] and unsolvated. [34a], [4b] Pyridine complexes [Ln( t Bu 2 pz) 3 (py) 2 ] (Ln = Y, Er) and [Ln( t Bu 2 pz) 3 (L) 2 ] (Ln = Er, Lu; L = 4‐tert‐butylpyridine)[6g] are known with the Er complex valuable as an MOCVD source .…”

“…This enables the more commonly used toxic Hg(C 6 F 5 ) 2 Hg(CCPh) 2 , and HgPh 2 RTP reagents to be avoided. However, with some of the less reactive heavier lanthanoid metals I 2 activation (2 %) was required, a slight drawback compared to diarylmercury reagents and the recently introducedBi(C 6 F 5 ) 3 . In many of the complexes, pyridine from the reactant Ag(C 6 F 5 )(py) is retained, coordinated to the resulting complexes [Ln(R 2 pz) 3 (py) 2 ], despite the use of thf as a donor solvent.…”

“…This enables a comparison with the recent use of tris(pentafluorophenyl)bismuth [eq. (3)], and the earlier use of Hg(C 6 F 5 ) 2 in RTP reactions [eq. (2)] .…”

“…More recently, the less electropositive lanthanoid metals have been shown to react with Bi(C 6 F 5 ) 3 and a range of pyrazoles (RR′pzH) to give an extensive range of lanthanoid pyrazolates [eq. (3)] but the less readily reduced BiPh 3 failed to react . [However, Bi(C 6 F 5 ) 3 was not successful with alkaline earth metals in RTP reactions …”