Alkyl backbone variations in common β-diketiminate ligands and applications to N -heterocyclic silylene chemistry.

We report the extension of the common β-diketimine proligand class, RAr nacnacH (HC(RCNAr) 2 H), where R is an alkyl group such as Et or iPr, plus Ph, and Ar is a sterically demanding aryl substituent such as Dip = 2,6-diispropylphenyl, Dep = 2,6-diethylphenyl, Mes = 2,4,6-trimethylphenyl or mesityl, Xyl = 2,6-dimethylphenyl, via one-pot condensation procedures. When a condensation reaction is carried out using the chemical dehydrating agent PPSE (polyphosphoric acid trimethylsilylester), β-diketiminate phosphorus(V) products such as ( iPrMes nacnac)PO 2 can also be obtained, which can be converted to the respective proligand iPrMes nacnacH via alkaline hydrolysis. The RAr nacnacH proligands can be converted to their alkali metal complexes with common methods and we have found that deprotonation of iPrDip nacnacH is significantly more sluggish than that of related β-diketimines with smaller backbone alkyl groups. The basicity of the RAr nacnac - anions can play a role in the success of their salt metathesis chemistry and we have prepared and structurally characterised the EtDip nacnac-derived silicon(II) compounds ( EtDip nacnac)SiBr and ( EtDip nacnac')Si, where EtDip nacnac' is the deprotonated variant MeCHC(NDip)CHC(NDip)Et.