Synthesis and reactivity of boryl substituted silaimines.

Reactions of two N-heterocyclic silylenes with a boron azide have given the first N-boryl substituted silaimines, (HCNR)Si[double bond, length as m-dash]N{B(DipNCH)} (R = Dip or Bu, Dip = 2,6-diisopropylphenyl) which are either monomeric or dimeric in the solid state. The compounds shows divergent reactivity with CO, in that the bulkier silaimine undergoes a [2+2] cycloaddition with CO to form (HCNDip)Si{OC([double bond, length as m-dash]O)N[B(DipNCH)]} under mild conditions, while the smaller silaimine undergoes a bond metathesis reaction with CO, affording the boron isocyanate, (HCNDip)B(NCO), and a known oxo-bridged silicon(iv) system. Both silaimines add HO across their Si[double bond, length as m-dash]N bonds to give the boryl-aminosilanols, (HCNR)Si(OH)-(H)N{B(DipNCH)}. The larger silaimine does not react with the bulky boron azide (HCNDip)BN, whereas the smaller system undergoes a [3+2] cycloaddition reaction with the azide to give spirocyclic borasilatetrazoline, (HCNBu)Si{[(HCNDip)B]NN}. Overall, the reactivity of the prepared N-boryl substituted silaimines is similar to that reported for other silaimines. However, the steric differences between the two Si[double bond, length as m-dash]N bonded compounds plays a definitive role in the outcomes of their reactions with the small molecule substrates studied.