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The reactivity of the hexa(N-methylideneimine)CoIII complex [Co-hmi-(taci)2]3+ (taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol) towards the nucleophiles ammonia, aniline and cyanide was investigated and the main products were identified by spectroscopic methods and by a crystal structure analysis. The relative energies of the complexes formed and those of possible stereo isomers were analysed by means of molecular mechanics calculations. In the reaction with NH3, two condensation products, [Co(La)]3+ and [Co(Lb)]3+, were identified with the two taci moieties linked by one or two N=CH–N(H)-CH2–NH bridges, respectively. The reaction with aniline yielded the complex [Co(Lc)(Ld)]3+ (where Lc is a mono-N-methylated and Ld a phenylformamidine-substituted taci), whereas the reaction with cyanide resulted in the formation of [Co(Le)]3+ having an NH–CH2–C(NH2)=N bridge between the two taci subunits. A mechanism that accounts for the different types of products can be suggested as follows: In [Co(La)]3+, [Co(Lb)]3+ and [Co(Lc)(Ld)]3+, N-methylation was observed and this can be interpreted in terms of an intramolecular Cannizzaro type hydride shift. For [Co(La)]3+ and [Co(Lb)]3+ two subsequent addition steps of the nucleophile to adjacent imino groups must take place prior to the hydride shift, whereas for [Co(Lc)(Ld)]3+ the hydride shift appears to have already occurred after the first addition step of aniline to an imino group. Formation of [Co(Le)]3+ can be explained in terms of a nucleophilic attack of CN– to an imino group and a subsequent attack of a deprotonated amino group (which must have previously been formed by hydrolysis of a methylideneimino group) to the nitrile C-atom. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

cis-3,4-Diaminopyrrolidine (cis-dap), trans-3,4-diaminopyrrolidine (trans-dap), cis-1,2-cyclopentanediamine (cis-cptn), and trans-1,2-cyclopentanediamine (trans-cptn) have been prepared in multigram quantities. The complexation of these ligands and of 3-aminopyrrolidine (ampy) with Ni^II, Cu^II, Zn^II, and Cd^II has been studied in solution by means of potentiometric and spectrophotometric titrations. The complexes of the triamines cis-dap and trans-dap show a pronounced tendency to form protonated species such as [M^II(HL)]³⁺, [M^II(HL)2]⁴⁺, and [M^II(HL)L]³⁺, indicative of a bidentate coordination mode of the ligand L. The UV/Vis spectra of the corresponding Cu^II complexes further confirmed bidentate coordination with trans-CuN4 geometry. The overall stabilities of the bis complexes [ML2]²⁺ decrease in the order cis-cptn > cis-dap > trans-cptn > ampy > trans-dap. The considerably lower stabilities of the ampy complexes as compared to the corresponding cis-dap complexes indicate metal binding to the two primary amino groups of the latter ligand. This was supported by molecular mechanics calculations (Cu^II and Co^III complexes) and confirmed by single-crystal X-ray diffraction studies of [Pt(Hcis-dap)Cl4]Cl·H2O, [Pd(Hcis-dap)2](ClO4)4·2H2O, and [Cu(Hcis-dap)2(OH2)2](SO4)2·3.5H2O − 2x H⁺ + x Cu²⁺ with 0.01  x  0.11. For the diamine ligands, coordination through the two exocyclic amino groups or through one exocyclic and one endocyclic amino group was established from the X-ray structure analyses of [Ni(cis-cptn)2](ClO4)2 and [Cu(3R-ampy)(3S-ampy)](ClO4)2, respectively. The crystal structure determination of [Co(cis-dap)(tach)][ZnCl4]Cl·C2H5OH (tach = cis-1,3,5-cyclohexanetriamine) revealed tridentate, facial coordination of cis-dap in this particular complex. However, the structural parameters of the [Co(cis-dap)(tach)]³⁺ moiety indicate significant strain for this coordination mode. The coordinating properties of the ligand cis-dap are compared with those of other aliphatic and alicyclic triamines.

Complex formation of the two tetraamine ligands (2S,3S)‐1,2,3,4‐tetraaminobutane (threo‐tetraaminobutane, ttab) and (2R,3S)‐1,2,3,4‐tetraaminobutane (erythro‐tetraaminobutane, etab) with CoIII, NiII, CuII, and PdIIwas investigated in aqueous solution and in the solid state. For NiIIand CuII, the pH‐dependent formation of a variety of species [MIIxLyHz](2x+z)+was established by potentiometric titrations and UV/Vis spectroscopy. In sufficiently acidic solutions the divalent cations formed a mononuclear complex with the doubly protonated ligand of composition [M(H2L)]4+. An example of such a complex was characterized in the crystal structure of [Pd(H2ttab)Cl2]Cl2⋅H2O. If the metal cation was present in excess, increase of pH resulted in the formation of dinuclear complexes [M2L]4+. Such a species was found in the crystal structure of [Cu2(ttab)Br4]⋅H2O. Excess ligand, on the other hand, lead to the formation of a series of mononuclear bis‐complexes [Mq(HxL)(HyL)](q+x+y)+. The crystal structure of [Co(Hetab)2][ZnCl4]2Cl⋅H2O with the inert, trivalent CoIIIcenter served as a model to illustrate the structural features of this class of complexes. By using an approximately equimolar ratio of the ligand and the metal cation, a variety of polymeric aggregates both in dilute aqueous solution and in the solid state were observed. The crystal structure of Cu2(ttab)3Br4, which exhibits a two‐dimensional, infinite network, and that of [Ni8(ttab)12]Br16⋅17.5 H2O, which contains discrete chiral [Ni8(ttab)12]16+cubes with approximate Tsymmetry, are representative examples of such polymers. The energy of different diastereomeric forms of such complexes with the two tetraamine ligands were analyzed by means of molecular mechanics calculations, and the implications of these calculations for the different structures are discussed.