Tetrameric thienylcopper and pentanuclear thienylcuprate

Journal article, 2000

The reaction between 2-bromothiophene and magnesium with subsequent addition of copper(I) chloride in tetrahydrofuran followed by dioxane yields thienylcopper, [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 copper(I) complexes are oligomeric and are bridged by the thienyl ligands solely 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 2.453(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 weak (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) Angstrom, indicative of three-centre Cu-C-Cu two-electron bonds, whereas the Cu(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 sulfur in bonding within the [Cu-5(C4H3S)(6)](-) cluster is discussed.