1,2-Azaboratabenzene: A Heterocyclic π-Ligand with an Adjustable Basicity at Nitrogen

1,2-Dihydro-2-phenyl-1,2-azaborine (6a) has
been prepared by a multistep synthesis from the readily
available 2,2-dibutyl-2,5-dihydro-1-trimethylsilyl-1H-1,2-azastannole (7). Deprotonation of 6a affords 1-phenyl-1,2-azaboratabenzene 1a, which on reaction with
[Cp*RuCl]4 gives the sandwich compound 5. 5 has been
shown to function as a nucleophilic catalyst for the
acylation of benzyl alcohol by phenylethylketene.