A convenient access to (2S,3S)-β-(trifluoromethyl)-α,β-diamino acid is reported by using highly diastereoselective Mannich addition reactions of either chiral or achiral Ni(II) complexes derived from glycine Schiff bases to a chiral sulfinimine, N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimine. Disassembly of the resultant Ni(II) complexes affords the target amino acid which was, for the first time, isolated in enantiomerically pure form and fully characterized.