Unique outcomes have emerged from the redox transmetallation/ protolysis (RTP) reactions of europium metal with [Ag(C6 F5 )(py)] (py=pyridine) and pyrazoles (RR'pzH). In pyridine, a solvent not normally used for RTP reactions, the products were mainly EuII complexes, [Eu(RR'pz)2 (py)4 ] (RR'pz=3,5-diphenylpyrazolate (Ph2 pz) 1; 3-(2-thienyl)-5-trifluoromethylpyrazolate (ttfpz) 2; 3-methyl-5-phenylpyrazolate (PhMepz) 3). However, use of 3,5-di-tert-butylpyrazole (tBu2 pzH) gave trivalent [Eu(tBu2 pz)3 (py)2 ] 4, whereas the bulkier N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) gave divalent [Eu(DFForm)2 (py)3 ] 5. In tetrahydrofuran (thf), the usual solvent for RTP reactions, C-F activation was observed for the first time with [Ag(C6 F5 )(py)] in such reactions. Thus trivalent [{Eu2 (Ph2 pz)4 (py)4 (thf)2 (μ-F)2 }{Eu2 (Ph2 pz)4 (py)2 (thf)4 (μ-F)2 }] (6), [Eu2 (ttfpz)4 (py)2 (dme)2 (μ-F)2 ] (7), [Eu2 (tBu2 pz)4 (dme)2 (μ-F)2 ] (8) were obtained from the appropriate pyrazoles, the last two after crystallization from 1,2-dimethoxyethane (dme). Surprisingly 3,5-dimethylpyrazole (Me2 pzH) gave the divalent cage [Eu6 (Me2 pz)10 (thf)6 (μ-F)2 ] (9). This has a compact ovoid core held together by bridging fluoride, thf, and pyrazolate ligands, the last including the rare μ4 -1η5 (N2 C3 ): 2η2 (N,N'): 3κ(N): 4κ(N') pyrazolate binding mode. With the bulky N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH), which often favours C-F activation in RTP reactions, neither oxidation to EuIII nor C-F activation was observed and [Eu(DippForm)2 (thf)2 ] (10) was isolated. By contrast, Eu reacted with Bi(C6 F5 )3 and Ph2 pzH or tBu2 pzH in thf without C-F activation, to give [Eu(Ph2 pz)2 (thf)4 ] (11) and [Eu(tBu2 pz)3 (thf)2 ] (12) respectively, the oxidation state outcomes corresponding to that for use of [Ag(C6 F5 )(py)] in pyridine.
Keywords: C−F activation; europium; pentafluorophenylsilver; redox transmetallation/protolysis (RTP); trispentafluorophenylbismuth.
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