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

Syntheses and crystal structures of the monomeric bora-amidinate (bam) complexes (NBN)-N-DIPP-Mg center dot(THF)(3) and (NBN)-N-DIPP-Ca center dot(THF)(4) are presented; (NBN)-N-DIPP = HB[N(2,6-iPr(2)-C6H3)](2). The simplicity of their H-1 NMR spectra in THF-d(8) suggest that their monomeric solid state structures are retained in solution. (NBN)-N-DIPP-Mg center dot(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 (NBN)-N-DIPP-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.