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

Syntheses and crystal structures of the monomeric bora-amidinate (bam) complexes DIPPNBN-Mg·(THF)3 and DIPPNBN-Ca·(THF)4 are presented; DIPPNBN = HB[N(2,6-iPr2-C6H3)]2. The simplicity of their 1H NMR spectra in THF-d8 suggest that their monomeric solid state structures are retained in solution. DIPPNBN-Mg·(THF)3 in C6D6, 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 DIPPNBN-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.