Towards absolute asymmetric synthesis. Synthesis and crystal structure of stereochemically labile MCl2 (M = Co, Ni, Cu, Zn) complexes with diamine ligands

In search for new conglomerates, seven stereochemically labile complexes between MCl2 (M = Co, Cu, Ni, Zn) and bidentate ligands, the commercially available N,N,N′-trimethylethane-1,2-diamine (trimeda) and the somewhat bulkier N-isopropyl-N,N′,N′-trimethylethane-1,2-diamine (itmeda), have been synthesized and characterized using single crystal X-ray diffraction. The trimeda and itmeda ligands exhibit chirogenic nitrogen centers and may form chiral metal complexes that are candidates for total spontaneous resolution. Copper(II) chloride forms the dimeric meso complexes [{CuCl2(trimeda)}2] (1) and [{CuCl2(itmeda)}2] (2), while [CoCl2(trimeda)2] (3) and [NiCl2(trimeda)2] (4) exhibit six-coordinate but chiral (R,R)- and (S,S)-complexes. Three examples of the chiral target complex, comprising four-coordinate stereochemically labile monomers, was successfully prepared, viz. [NiCl2(itmeda)] (5), [ZnCl2(itmeda)] (6), and [CoCl2(itmeda)] (7).