Structural and functional evolution of metallacrowns.

The chemistry of binuclear palladium(II) and platinum(II) complexes

Unter den Komplexen der Ubergangsmetalle mit weichen Liganden spielen die Thiolate eine wichtige und aktuelle Rolle. Durch die vielfaltigen elektronischen und sterischen Moglichkeiten einzahniger Liganden RS⊖ und zweizahniger Chelatliganden ⊖SRS⊖ stabilisieren Thiolate ein weites Spektrum einkerniger, oligomerer und polymerer Komplexe mit neuen und bemerkenswerten Strukturen und Eigenschaften. Besondere Impulse hat der Entwicklung die Synthese polynuclearer kafigartiger homo- und heteroleptischer Metall-Schwefel-Geruste gegeben, die in vielen Fallen als molekulare Ausschnitte aus Sulfid-Festkorperstrukturen anzusehen sind. Grose Bedeutung haben Thiolate und Sulfidothiolate von Mo sowie der spaten offen- und geschlossenschaligen 3d-Metalle (Fe, Co, Ni, Cu, Zn) und einiger ihrer Homologen (Au, Cd, Hg) als Modellkomplexe fur biologisch wichtige Metallzentren mit Schwefelkoordination. Sie haben wesentlich zum Verstandnis von Struktur, Bindung und Funktion der Reaktionszentren etwa in Ferredoxinen, Rubredoxinen, Nitrogenasen, blauen Kupferproteinen, Metallothioneinen sowie antiarthritischen Wirkstoffen beigetragen.

Übergangsmetallthiolate ‐ von molekularen Fragmenten sulfidischer Festkörper zu Modellen aktiver Zentren in Biomolekülen

Hydrogenases catalyze the reversible oxidation of H2, which is crucial for the anaerobic metabolism of microorganisms. They attract growing interest in connection with H2-based energy systems. [NiFe] hydrogenase is the most common type among the currently known hydrogenases, and its active site consists of an “organometallic” Fe–Ni complex supported by cysteinyl thiolate ligands. This review presents an overview of the synthesis, properties, and reactions of thiolate-bridged iron–nickel complexes that model the active site of [NiFe] hydrogenase.

Thiolate-Bridged Iron–Nickel Models for the Active Site of [NiFe] Hydrogenase

Two new oligomeric types of toroidal nickel(II) monothiolate ring systems, cyclo-[Ni(SPh)2]11
(1) and cyclo-[Ni(SPh)2]9
(2), containing heretofore unknown 11-membered (n
= 11) and 9-membered (n
= 9) ring-geometries, respectively, are reported. Our initial isolation of 1 was as an unexpected by-product that resulted from unsuccessful attempts to produce crystalline nanostructural gold thiolate clusters from reactions of alkyl/phenyl thiols with the recently prepared nanostructural [Au16Ni24(CO)40]4− cluster. The unique architecture of 1 led to a designed preparation of it by a direct synthetic route involving reactions of PhSNa with Ni(ClO4)2 in THF or DMF. Slow addition of the reactants at low temperature afforded two crystal forms of 1: namely, the previously isolated triclinic crystals (P) as well as solvated monoclinic crystals (C2/c)
(1a). Normal mixing of the reactants at room temperature gave rise to a trigonal crystal form (P12/c) that was determined to be cyclo-[Ni(SPh)2]9
(2). The atomic arrangements and stoichiometries of both 1 and 2 were unequivocally established from low-temperature CCD area-detector X-ray diffractometry studies; particularly noteworthy is that the structures of both crystal forms of 1 possess nearly identical molecular geometries (including the phenyl-ring orientations) along with an encapsulated THF molecule. These new air-stable molecular additions to the cyclo-[Ni(μ2-SR)2]n family (with n
= 4, 5, 6, and 8) are of particular stereochemical interest in that: (1) in sharp contrast to the previously known monodentate thiolate-bridged members which ideally possess regular convex Ni–S toroids, the assembled n-localized edge-fused square-planar [NiS4] subunits found in the triclinic and monoclinic crystal forms of undecanickel 1 and in the trigonal crystal form of nonanickel 2 have irregularly-shaped mixed concave/convex toroidal pseudo-C2v and pseudo-D3h ring geometries, respectively, that are geometrically unique; (2)
1 is the first host member of any known cyclo-[Ni(SR)2]n oligomer to have a co-crystallized solvated guest molecule (viz., THF); and (3) the observed orientations of adjacent phenyl rings attached to the highly pyramidal sulfur atoms in both 1 and 2 suggest the occurrence of weakly attractive pairwise phenyl⋯phenyl dispersion forces that are presumed to stabilize these novel nickel(II) phenylthiolate oligomers. A comparative analysis of the salient solid-state structural features of the idealized Ni–S ring geometries of the resulting entire cyclo-[Ni(SPh)2]n family (n
= 4, 5, 6, 8, 9, and 11) is presented (under the assumed absence of sterically crowded R-substituents and/or abnormal packing effects). The unsymmetrical enlargement of the pseudo-threefold 9-membered ring in 2 by the formal insertion of two adjacent [Ni(SPh)2] units to give an otherwise analogous Ni–S framework of the 11-membered ring in 1 is attributed to the elongated template-geometry of the guest molecule coupled with the maintenance of attractive pairwise phenyl ring interactions.

Cyclo-[Ni(μ2-SPh)2]9 and cyclo-[Ni(μ2-SPh)2]11: new oligomeric types of toroidal nickel(II) thiolates containing geometrically unprecedented 9- and 11-membered ring systems

C. Germain

Papers

Metal complexes of mercaptoamines—III. Different behaviour of β- and γ-(N,N-dimethyl)-mercaptoamines