Bora-amidinate as a cooperative ligand in group 2 metal catalysis.

Syntheses and crystal structures of the monomeric bora-amidinate (bam) complexes NBN-Mg·(THF) and NBN-Ca·(THF) are presented; NBN = HB[N(2,6-iPr-CH)]. The simplicity of their H NMR spectra in THF-d suggest that their monomeric solid state structures are retained in solution. NBN-Mg·(THF) in CD, however, is in equilibrium with a dimeric species. Calculations (B3PW91/6-311++G**) reveal a very high localized negative charge (NPA: -1.103) on the N atoms in NBN-Mg. The strongly basic properties of the bam ligand are in agreement with catalytic activity of these complexes in the intramolecular alkene hydroamination. A mechanism is proposed in which the bam ligand is non-innocent and cooperative, playing an active role in substrate deprotonation and product protonation.