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, nacnacH (HC(RCNAr) 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, 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 ( nacnac)PO can also be obtained, which can be converted to the respective proligand nacnacH alkaline hydrolysis. The nacnacH proligands can be converted to their alkali metal complexes with common methods and we have found that deprotonation of nacnacH is significantly more sluggish than that of related β-diketimines with smaller backbone alkyl groups. The basicity of the nacnac anions can play a role in the success of their salt metathesis chemistry and we have prepared and structurally characterised the nacnac-derived silicon(II) compounds ( nacnac)SiBr and ( nacnac')Si, where nacnac' is the deprotonated variant MeCHC(NDip)CHC(NDip)Et.