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

We report the extension of the common beta-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), beta-diketiminate phosphorus(V) products such as ((iPrMes)nacnac)PO2 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 beta-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.