Europium is Different: Solvent and Ligand Effects on Oxidation State Outcomes and C‐F Activation in Reactions Between Europium Metal and Pentafluorophenylsilver
- 2 December 2021
- journal article
- research article
- Published by Wiley in Chemistry – A European Journal
- Vol. 28 (3) , e202103865
Abstract
Unique outcomes have emerged from the redox transmetallation/ protolysis (RTP) reactions of europium metal with [Ag(C6F5)(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 (Ph2pz) 1; 3‐(2‐thienyl)‐5‐trifluoromethylpyrazolate (ttfpz) 2; 3‐methyl‐5‐phenylpyrazolate (PhMepz) 3). However, use of 3,5‐di‐tert‐butylpyrazole (tBu2pzH) gave trivalent [Eu(tBu2pz)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(C6F5)(py)] in such reactions. Thus trivalent [{Eu2(Ph2pz)4(py)4(thf)2(μ‐F)2}{Eu2(Ph2pz)4(py)2(thf)4(μ‐F)2}] (6), [Eu2(ttfpz)4(py)2(dme)2(μ‐F)2] (7), [Eu2(tBu2pz)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 (Me2pzH) gave the divalent cage [Eu6(Me2pz)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(N2C3): 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(C6F5)3 and Ph2pzH or tBu2pzH in thf without C−F activation, to give [Eu(Ph2pz)2(thf)4] (11) and [Eu(tBu2pz)3(thf)2] (12) respectively, the oxidation state outcomes corresponding to that for use of [Ag(C6F5)(py)] in pyridine.Keywords
Funding Information
- Australian Research Council (DP190100798)
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