Synthesis and Characterization of (2,6-<i>ⁱ</i>PrNCN)HfCl₂^- and (3,5-MeNCN)₂Hf^2- (where NCN = 2,6-bis[phenylazanidyl]methylphenyl): New Trianionic Pincer Ligands

The synthesis, isolation, and metalation of the trianionic NCN-pincer ligand [2,6-iPrNCNLi3]2 (2) is described. The terdentate coordination ability of 2 is demonstrated in the synthesis of the hafnium dichloride anion [2,6-iPrNCNHfCl2][Li(DME)3] (3-DME). Complex 3-DME is distorted square pyramidal in the solid state, but NMR evidence indicates the complex is fluxional and trigonal bypyramidal in solution. Straightforward ligand modification provides the additional trianionic pincer ligand [3,5-MeNCNLi2]2[Li2(DME)6] (5). This sterically smaller ligand leads to the hafnium pincerate dianion complex [(3,5-MeNCN)2Hf][Li2(DME)2] (6), which contains two trianionic pincer ligands. The new compounds are characterized by elemental analysis, multinuclear NMR, and X-ray diffraction crystallography.