Guo, Zhifang, Blair, Victoria L., Deacon, Glen B., and Junk, Peter C. (2020) Widely contrasting outcomes from the use of tris(pentafluorophenyl)bismuth or pentafluorophenylsilver as oxidants in the reactions of lanthanoid metals with N,N '-diarylformamidines. Dalton Transactions, 49. pp. 13588-13600.

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Abstract

Reactions of lanthanoid metals with tris(pentafluorophenyl)bismuth or pentafluorophenylsilver and two widely disparate formamidines, N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) and N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH) have been investigated as possible redox transmetallation/protolysis (RTP) syntheses of lanthanoid formamidinates. Thus, (Ln(DFForm)(3)(thf)) (Ln = Lu, 1, Yb, 2, Tm, 3, Er, 4, Ho, 5, Dy, 6; thf = tetrahydrofuran), [Ln(DFForm)(3)(thf)(2)] (Ln = Tb, 7, Gd, 8, Sm, 9, Nd, 10), and (Yb(DippForm)(2)(thf)(2)]center dot 2thf (11) complexes were obtained from an excess of lanthanoid metals, [Bi(C6F5)(3)]center dot 0.5diox (diox = 1,4-dioxane) and the appropriate formamidine. Reaction of neodymium and [Bi(C6F5)(3)]center dot 0.5diox with the bulkier DippFormH in thf resulted in C-F activation and formation of (Nd(DippForm)(2)F(thf)(2)] (12) and o-HC6F4O(CH2)(4)N(Dipp)CH=N(Dipp) (Dipp = 2,6-di-isopropylphenyl). Although the reaction of erbium and [Bi(C6F5)(3)]center dot 0.5diox with DippFormH was not complete after one week (by 19F NMR), use of [Hg(C6F5)(2)] instead of [Bi(C6F5)(3)]center dot 0.5diox resulted in C-F activation and formation of [Er(DippForm)(2)F(thf)) (13) and o-HC6F4O(CH2)(4)N(Dipp)CH=N(Dipp) in two days. Attempted RTP reactions between lanthanoid metals, AgC6F5 and DFFormH in thf gave [Ag-2(DFForm)(2)]center dot 3thf (14), except in the case of ytterbium. All other lanthanoid metals required activation by 12 (2%) before lanthanoid complex formation could be achieved. From these reactions, lanthanoid formamidinates, [Ln(DFForm)(2)(solv)I] (Ln = Lu, 15, Tm, 16, Er, 17, Tb, 18, Gd, 19), (Ln(DFForm)(3)(py)] = Er, 17a, Tb, 18a; py = pyridine), and (Nd(DFForm)(3)(thf)(2)]center dot thf (10) were obtained. Where two types of lanthanoid formamidinates [Ln(DFForm)(3)(pY)] and [Ln(DFForm)(2)(solv)I] were obtained from the Ln metals activated by 12, they could not be separated on preparative scale. From Yb, the peroxide-bridged complex, [Yb-2(DippForm)(2)(O-2)(2)(py)(4)] (20) was surprisingly isolated. Thus [Bi(C6F5)(3)]center dot 0.5diox has potential as an oxidative replacement for diarylmercurials in RTP syntheses of lanthanoid formamidinates but [AgC6F5(py)] does not.

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