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, ^RArnacnacH (HC(RCNAr)₂H), 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 (^iPrMesnacnac)PO₂ can also be obtained, which can be converted to the respective proligand ^iPrMesnacnacH via alkaline hydrolysis. The ^RArnacnacH proligands can be converted to their alkali metal complexes with common methods and we have found that deprotonation of ^iPrDipnacnacH is significantly more sluggish than that of related β-diketimines with smaller backbone alkyl groups. The basicity of the ^RArnacnac^- anions can play a role in the success of their salt metathesis chemistry and we have prepared and structurally characterised the ^EtDipnacnac-derived silicon(II) compounds (^EtDipnacnac)SiBr and (^EtDipnacnac')Si, where ^EtDipnacnac' is the deprotonated variant MeCHC(NDip)CHC(NDip)Et.