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A series of neutral, bulky diazabutadienediyl-substituted beryllacycles Be(DipDAB)(L) (DipDAB = (DipNCH)22–, Dip = 2,6-diisopropylphenyl; L = OEt2, THF, :C(RNCH)2; R = Me (TMC), Pri (IPriMe)) have been prepared and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The preparation of similar complexes bearing the smaller tert-butyl-substituted diazabutadienediyl ligand ((ButNCH)22–, viz. ButDAB) was attempted but gave rise to complex product mixtures, several components of which were isolated in trace yields. This phase of the study did, however, lead to the preparation of the homoleptic beryllium diradical complex Be(ButDAB•)2, which was characterized by X-ray crystallography and EPR spectroscopy. In efforts to access BeI–BeI-bonded dianions, (DipDAB)Be–Be(DipDAB)2–, reductions of Be(DipDAB)(L) were pursued, but these instead afforded largely intractable product mixtures. Treating ethereal solutions of Be(DipDAB)(OEt2) with lithium alkyls afforded highly reactive, heterocyclic beryllate salts, Li(OEt2)2,1Be(DipDAB)R (R = Me, Bun). Subsequent treatment of Li(OEt2)Be(DipDAB)Bun with either N,N,N′,N′-tetramethylethylenediamine (tmeda) or N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (pmdeta) led to the formation of Li(tmeda)2Be(DipDAB)Bun and Li(pmdeta)Be(DipDAB)Bun. Reactions between two of the heterocyclic beryllate salts and BeX2(OEt2)2 (X = Br, I) did not lead to clean salt metathesis reactions but gave mixtures of many products, several of which were isolated in very low yields. While the noninnocent nature of the diazabutadienediyl ligands of Be(DipDAB)(L), and the Be(DipDAB)R− anions, hampered explorations of their further reactivity, these heterocycles hold promise as synthons for beryllium coordination chemistry.
Paparo et al. (Tue,) studied this question.