Metal complexes of new, chiral N2O2 tetradentate ligands

N,N'-Bis(2R-hydroxy-2R-phenylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L1, and N,N'-bis(2S-hydroxy-2S-methylethyl)-N,N'-dimethyl-1R,2R-diaminocyclohexane, H(2)L2, have been synthesized from readily available chiral precursors. They coordinate as neutral tetradentate ligands to Ni(II) and Cu(II) ions, from which the thiocyanates [M(H2L)(NCS)(2)] have been isolated and the structures of the H(2)L1 complexes determined by single-crystal X-ray techniques. In the blue complex [Ni(H(2)L1)(NCS)(2)]. H2O . 2EtOH, 1, and green [Cu(H(2)L1)(NCS)(2)]. 0.5H(2)O, 2, the neutral tetradentate ligands coordinate with the cis-alpha geometry with mutually cis N-bound thiocyanate groups, though the chiral ligands adopt a different stereochemistry in the two complexes. In 2, the absolute configuration about the Cu(II) center is Delta, with the nitrogens possessing the S stereochemistry, whereas for the Ni(II) analogue, coordination gives the Lambda isomer with the R configuration at the stereogenic nitrogens. Addition of H(2)L1 or H(2)L2 to Mn(II) in basic methanol solution results in rapid aerial oxidation. Delta-cis-alpha-[Mn(L1)(OMe)(2)]. MeOH, 3, was isolated as black crystals from the reaction mixture after addition of 2 mol of NaOMe. The analogous complex with (L2)(2-) proved extremely hygroscopic and was not obtained in pure form. Colorless crystals of Lambda-cis-alpha-[MoO2(L1)], 4, were precipitated from a methanolic solution of [MoO2(acac)(2)] and H(2)L1. The analogous reaction with H(2)L2 gave Delta-cis-alpha-[MoO2(L2)], 5. Structures of 3, 4, and 5 are reported. The reactions of H(2)L1 and H(2)L2 with 1 mol equiv of [Ti(OPri)(4)] produced the complexes Delta-cis-alpha-[Ti(L1)(OPri)(2)] (white solid) and Lambda-cis-alpha-[Ti(L2)(OPri)(2)] (colorless oil), structural assignments for which were made possible by analysis of their H-1 NOE difference spectra. Thus the coordination of these tetradentate ligands is stereospecific, but the absolute configuration of the complexes formed (Delta or Lambda) is dependent on the metal ion involved.