Novel synthesis of macrocyclic amine-thiophenolate ligands: X-ray crystal structure of a Ni-4 complex of an N8S4 ligand

A novel route to macrocyclic amine-thiophenolate ligands is described. The new, air-stable thiophenolate precursor 1,:2-bis (4-tert-butyl-2, 6-diformy l-phenylsulfanyl) ethane (4) is readily condensed with two equivalents of e thanediamine or 1,3-propanediamine under medium to high dilution conditions to give 2 x 4 condensation products. The smaller 1 x 2 macrocyclic compoun ds are not produced under these conditions. Subsequent reduction with NaBH4 (reduction of imine groups) and Na/NH3 (reductive cleavage of aryl-alkylsu lfides) provides the 36- and 40-membered amine-thiophenolate ligands H(4)6a and H(4)6b. The macrocyclic compounds are versatile ligands for the prepar ation of polynuclear transition metal complexes. With divalent nickel H4(6) a forms the di- and tetranuclear complexes [Ni-2(6a)] (7) and [Ni-4(6a)][Cl O4](4) (8). Reaction of 8 with four equivalents of NH4SCN yields the novel isothiocyanate complex [Ni-4(II)(6a)(NCS)(4)]. 10MeCN (9). The structure co nsists of well-separated molecules of the tetranuclear complex [Ni-4(II)(6a )(NCS)(4)] (C-i symmetry). Two symmetry-related binuclear [N2Ni(mu-SR)(2)Ni N4] fragments composed of thiolate-bridged distorted planar {N2S2Ni}- and d istorted cis-octahedral {(SCN)(2)N2S2Ni} units reside within the cavity of the macrocycle. The intramolecular distance between the two binuclear units is 6.144(1) Angstrom.