The coordination chemistry of cis-3,4-diaminopyrrolidine and related polyamines

cis-3,4-Diaminopyrrolidine (cis-dap), trans-3,4-diaminopyrrolidine (trans-d ap), cis-1,2-cyclopentanediamine (cis-cptn), and trans-1,2-cyclopentanediam ine (trans-cptn) have been prepared in multigram quantities. The complexati on 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 s pectrophotometric titrations. The complexes of the triamines cis-dap and tr ans-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 bidentat e coordination mode of the ligand L. The UV/Vis spectra of the correspondin g Cull complexes further confirmed bidentate coordination with trans-CuN4 g eometry, The overall stabilities of the bis complexes [ML2](2+) decrease in the order cis-cptn > cis-dap > trans-cptn > ampy > trans-dap. The consider ably lower stabilities of the ampy complexes as compared to the correspondi ng cis-dap complexes indicate metal binding to the two primary amino groups of the latter ligand. This was supported by molecular mechanics calculatio ns (Cu-II and Co-III complexes) and confirmed by single-crystal X-ray diffr action studies of [Pt(Hcis-dap)Cl-4]Cl .H2O, [Pd(Hcis-dap)(2)](ClO4)(4). 2H (2)O, and [Cu(Hcis-dap)(2)(OH2)(2)]-(SO4)(2).3.5H(2)O - 2x H+ + x Cu2+ with 0.01 less than or equal to x less than or equal to 0.11. For the diamine l igands, coordination through the two exocyclic amino groups or through one exocyclic and one endocyclic amino group was established from the X-ray str ucture analyses of [Ni(cis-cptn)(2)](ClO4)(2) and [Cu(3R-ampy)(3S-ampy)]-(C lO4)2, respectively. The crystal structure determination of [Co(cis-dap)(ta ch)][ZnCl4]Cl .C2H5OH (tach = cis-1,3,5-cyclo-hexanetriamine) revealed trid entate, facial coordination of cis-dap in this particular complex. However, the structural parameters of the [Co(cis-dap)(tach)](3+) moiety indicate s ignificant strain for this coordination mode. The coordinating properties o f the ligand cis-dap are compared with those of other aliphatic and alicycl ic triamines.