Tetrameric thienylcopper and pentanuclear thienylcuprate

The reaction between 2-bromothiophene and magnesium with subsequent additio n of copper(I) chloride in tetrahydrofuran followed by dioxane yields thien ylcopper, [Cu-4(C4H3S)(4)] (1). Without the addition of dioxane, magnesium thienylcuprate(I), [Mg(THF)(6)][Cu-5(C4H3S)(6)](2), (2) is formed. Both cop per(I) complexes are oligomeric and are bridged by the thienyl ligands sole ly through carbon donors, thus lacking Cu-S bonds. The former compound, 1, is tetranuclear with a square-planar copper core and Cu-Cu distances of 2.4 53(3) and 2.507(3) Angstrom, and 2.464(2) and 2.489(2) Angstrom within the two crystallographically independent molecules, respectively; there is a we ak (CuS)-S-... interaction of 3.118(5) Angstrom between these two molecules . The anion of 2 is a closo trigonal bipyramidal cluster of copper atoms in which the (ax)-(eq) edges are bridged by the thienyl ligands. Thus the Cu( ax)-Cu(eq) distances bridged by carbon are short, 2.497(5) and 2.503(5) Ang strom, indicative of three-centre Cu-C-Cu two-electron bonds, whereas the C u(eq)Cu-...(eq) and Cu(ax)Cu-...(ax) distances are considerably longer at 3 .135(7) and 3.423(8) Angstrom, respectively. The lack of participation of s ulfur in bonding within the [Cu-5(C4H3S)(6)](-) cluster is discussed. (C) 2 000 Elsevier Science S.A. All rights reserved.