Synthesis and Characterization of Cp*Be‐F‐Al(OR^F)₃

Abstract

The reaction of Ag[Al(OR F ) 4 ] [R F = C(CF 3 ) 3 ] with Cp*Be-Br was investigated. With the less basic CH 2 Cl 2 as solvent, redox chemistry prevailed, elemental silver and the pentamethylcyclopentenyl cation (Cp*H 2 + ) formed. However, upon changing to the more π-basic solvents fluorobenzene and o-difluorobenzene, the silver metathesis reaction went smooth and produced intermediately the [Cp*Be] + cation and AgBr. However, the very strong Lewis acid * Prof. Dr. I. Krossing

Lewis Superacids: Classifications, Candidates, and Applications

“…Ad istinction between neutral and cationic Lewisa cids has to be emphasized. Computed FIAs for beryllium, [56] borenium, [57] carbenium, [58] silylium, [38a, 59] phosphenium, [60] phosphonium, [61] zinc, [62] or other cationic species [63] exceed the threshold to LSA significantly.T he FIA of ac ationic compoundi nt he gas phase is strongly increased by charge neutralization and by electrostatic attraction. However,adamping of the FIA by the enthalpy of solvation (DH solv )i sm uch more pronounced for charged( cationic) than for neutral acids (Figure 4b).…”

Recent Contributions to the Coordination Chemistry of Beryllium

“…Nevertheless, due to the high electrophilicity of the in situ generated [Cp*Be] + + ,t his cation attacks the counterion and abstracts af luoride anion, leadingt ot he cleavage of 2,2-difluoro-3,3-bis(trifluoromethyl)oxirane and to the formation of Al(OC(CF 3 ) 3 ) 3 .S ubsequently,t he Lewis acidic aluminums pecies coordinates to Cp*BeFu nder the formation of adduct 101 (Scheme 13). [87] The related tris(pyrazolylborate) (Tp) beryllium chloride, bromide, and iodide (102 a-c)w erea lso easily synthesized from the correspondingb eryllium halide and KTp in toluene.T hese complexes provedt ob er obuster towards fluorinationa gents than Cp*-beryllium compounds and the halides can be replaced by fluoride, hydride, or azide (Scheme 14). [88] The high stabilityo ft he TpBe moiety is also evidentf rom the fact that iodide is displaced from complex 102 c by THFa ts lightly elevated temperatures to give cationic complex 103.T his compound is stable in solution withouta ny evidence for ring openingo ft he ether,w hich is in distinct contrast to b-diketiminato beryllium iodide 81 (Scheme 10).…”

“…Bromideabstraction of Cp*BeBr leading to the formationo fC p*BeF adduct 101 underd ecomposition of the counterion. [87] Scheme14. The versatile reactivity of tris(pyrazolylborate)beryllium compounds (Tp = [(C 3 H 3 N 2 ) 3 BH] À ;a:X= Cl;b:X= Br;c:X= I).…”

Facile and systematic access to the least-coordinating WCA [(RFO)3Al–F–Al(ORF)3]− and its more Lewis-basic brother [F–Al(ORF)3]− (RF = C(CF3)3)

“…Instead the formal [F–Al(OR F ) 3 ] – anion ([f–al] – ) was obtained, often as part of a neutral compound, like in Me 3 Si–F–Al(OR F ) 3 or Cp*Be–F–Al(OR F ) 3 . 13 , 19 Therefore, both were rationalized as being ion-like compounds that behave intermediate between being covalently bound or separated ions. Nevertheless also compounds, where [f–al] – and the cation are separated, were isolated.…”