BIMETALLIC REACTIVITY - CONTROLLED SYNTHESIS OF MONOMETALLIC AND HOMO-BIMETALLIC AND HETEROBIMETALLIC COMPLEXES OF A CHIRAL BINUCLEATING MACROCYCLIC LIGAND BEARING 6- AND 4-COORDINATE SITES

A chiral macrocyclic binucleating ligand, S,S-cypim, bearing four- and six-coordinate binding sites has been prepared. The macrocyclic framework contains the chiral diamine (1S,2S)-trans-1,2-bis(aminomethyl)cyclopentane, which induces one topological chirality about the six-coordinate site. The macrocyclic closure with the chiral diamine is achieved in good yield by Schiff base condensation of metal dialdehyde complexes. In this way the monometallic complexes [M(S,S-cypim)(H+)(2)](2+), M = Zn(II), Cu(II), Ni(II), Co(II), and Mn(II), have been prepared and characterized. These complexes contain a metal in the six-coordinate site and two hydrogen-bonded protons in the four-coordinate site. X-ray crystal structures of the Mn(II) and Zn(II) complexes confirm this formulation. Oxidation of the Co(II) complex gives the stable Co(III) complex [Co(S,S-cypim) (H+)2](3+) from which the heterobimetallic complexes [Co(S,S-cypim)MCl](2+), M Zn(II),Ni(ZI), Co(II), and Mn(II), and [Co(S,S-cypim)Cu](3+) were prepared and isolated. An X-ray crystal structure of the last complex confirms the expected C-2 symmetric geometry. The [M(S,S-cypim) (H+)(2)](2+) complexes are ideal precursors for mild,kinetically controlled synthesis of heterobimetallic complexes containing labile metals. The complexes [M(S,S-cypim)Cu](2+) where M = six-coordinate site metals, Zn(II), Cu(II), Ni(II), Co(II), and Mn(II), were prepared, isolated and characterized. The homobimetallic complexes [Mn(S,S-cypim)MnCl](+) and [Ni(S,S-cypim)NiCl](+) were also isolated, as well as the mixed-valence complex [Mn-II-(S,S-cypim)Mn-II(Cl)(2)](+), which is formed by aerial oxidation of the dimanganese(II) complex. The crystal structures of the complexes [Mn(EtOH)(S,S-cypim)Cu](2+) and [Cu(S,S-cypim)Cu(CH3CN)](2+) are also reported. In the former the Mn(II) atom is seven-coordinate and a highly distorted ligand structure is observed. The dicopper(II) structure is also distorted, but the copper in the potentially six-coordinate site is only five-coordinate. The incorporation of the chiral diamine in the ligand enforces the formation of a single diastereomer of the C-2 symmetric complexes. This is confirmed by the H-1 NMR spectra of the diamagnetic complexes [Zn(S,S-cypim)(H+)(2)](2+), [Co(S,S-cypim)(H+)(2)](3+), and [Co(S,S-cypim)Zn](3+) The topological chirality about the closed-site metals in the [Zn(S,S-cypim)(HC)(2)](2+) and [Co(S,S-cypim)Cu(CH3CN)](3+) complexes was determined to be Delta by crystallographic methods, whereas a Delta absolute configuration was found for the [Mn(S,S-cypim)(H+)(2)](2+) complex. This reversal of diastereoselection is believed to arise from the larger radius of the Mn(II) ions, which causes the ligand to adopt a unique twisted conformation which is considerably different from those observed for [Zn(S,S-cypim) (H+)(2)](2+) and [Co(S,S-cypim)Cu(CH3CN)](3+). Circular dichroism associated with the d-d transitions of the Co(III) complexes indicates that all have the Delta configuration whereas that associated with the azomethine chromophores suggests that all of the C-2 symmetric complexes have the same configuration except the Mn(II) complex.