Highly Stereoselective Formation of Cp*IrCl Complexes of N,N-Dimethylamino Acids

N,N-Dimethylamino acids serve as (N, O)-chelating monoanionic ligands to the prochiral fragment Cp*IrCl. A series of four such complexes and one Rh analog all were formed with diastereoselectivity of ≥50:≤1. The structure of the valine complex 5d (C₁₇H₂₉ClIrNO₂) was analyzed at 298 K, from which a cis-arrangement of Cp* and valine side chain (i-Pr) was revealed. Solution NMR studies of 5d, aided by an unusual zero coupling between the two methine protons of the amino acid, showed that the structures in solution and the solid were very similar. The preference for the cis-oriented Cp* and amino acid side chain in 5 is attributed to a maximum number of gauche interactions in the metallacycle and its substituents, especially pronounced for N,N-disubstituted amino acids.