ToRM-based Catalysts

We have studied a steries of oxazoline-based catalysts for the hydroamination of aminoalkene, using group 2 element-, rare earth element-, and group 4 metal-based catalysts. Monoanionic tris(oxazolinyl)borate ligands, such as ToM and ToT, give catalytically active group 2 catalysts. Through kinetic studies, the magnesium catalyst ToMMgMe provides a key mechanistic insight that two equivalents of aminoalkene for cyclization. Catalytic activity decreases with rare earth element-based ToMY(CH2SiMe3)2THF, and the group 4 complex ToMZr(NMe2)3 does not show catalytic conversion.
{PhB(OxR)2Cp}M-based Catalysts

Substitution of one oxazoline in the tris(oxazolinyl)borate ligands with a C5H4 group gives the dianionic ligand class {PhB(OxR)2Cp}. Catalysts supported by these ligands show a number of interesting features. Zirconium compounds catalyze hydroamination at room temperature and even down to -30 °C. Optically active derivatives, such as {PhB(OxiPr,Me2)2Cp}Zr(NMe2)2 provide five membered and seven membered cyclic amines with high enantioselectivity (up to 99%!) Interestingly, deuterium-substituted aminoalkenes (D2NR) undergo hydroamination with higher enantioselectivity than the unlabeled isotopomers (H2NR). Remarkably, the yttrium-based catalyst {PhB(OxtBu)2Cp}Y(CH2SiMe3)2 gives the mirror image product from the zirconium catalyst {PhB(OxtBu)2Cp}Zr(NMe2)2 supported by the identical ligand!