Synthesis of β-diketiminato calcium silylamides and their reactions with triethylaluminium

Reaction of the beta-diketiminato calcium amide [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)(2)}(OEt2)] (Ar = 2,6-di-iso-propylphenyl) with triethylaluminium yields a novel calcium aluminate complex, [kappa(3)-{ArNC(Me)C(AlEt3)HC(Me)NAr}Ca{Et4Al}], in which coordination at calcium is provided by not only bridging interactions with the ethyl groups of the aluminate anion but also a tripodal kappa(3)-N,N,C-coordinated ligand derived from further reaction of the 'spectator' beta-diketiminate ligand with triethylaluminium. In the solid state, this compound exists as a 1 : 1 mixture of coordination isomers in which the Et4Al anion binds to calcium via either mu(2)- or mu(3)-coordination modes. Although persistent, and rapidly interconverting, at room temperature in solution, variable temperature NMR studies suggest that these two isomers undergo dissociative loss of triethylaluminium from the diketiminate ligand at low temperature.