Bis(cyclopentadienyls) with transition metal–mercury bonds. Part 4. Formation of niobium–mercury bonds and X-ray crystal structure of [Nb(η-C5H5)2{HgS2CN(C2H5)2}3]

Abstract

In aromatic solvents (toluene or benzene–toluene) reaction of [Nb(η-C₅H₅)₂H₃], prepared in situ, with a variety of mercury(II) salts at room temperature yields complexes with two or three Nb–Hg bonds. The product of the reaction with [Hg(S₂CNEt₂)₂] is [Nb(η-C₅H₅)₂(HgS₂CNEt₂)₃](1), which has been characterised by single-crystal X-ray diffraction. Complex (1) crystallises in the monoclinic space group P2₁/n with a= 12.302(10), b= 18.385(11), c= 16.077(5)Å, β= 108.18(5)° and Z= 4. The structure has been solved by heavy-atom methods and refined to R 0.072 for 2 876 unique observed diffractometer data [l > 2σ(l)]. The molecule consists of a rhomboidal tetrametal cluster formally derived from [Nb(η-C₅H₅)₂H₃] by replacement of each hydride ligand by an Hg(S₂CNEt₂) moiety. The dithiocarbamate ligands chelate the mercury atoms asymmetrically with the shorter, stronger Hg–S bond trans to the niobium atom and the ligand plane approximately perpendicular to the NbHg₃ plane. The Nb–Hg distances are indicative of single bonds (mean 2.790 Å), whilst the Hg–Hg separations average 2.892 Å.

The reaction of HgX₂(X = Cl, Br, or l) with [Nb(η-C₅H₅)₂H₃] gives [Nb(η-C₅H₅)₂H(HgX)₂]·xHgX₂, (2)–(4)(x= 0.5 for X = Cl, x= 1 for X = Br, and x= 0.66 for X = l). Although these adducts do not undergo direct substitution of X by thiolates, the thiolate analogues [Nb(η-C₅H₅)₂H(HgSR)₂][R = Et (5) or Bu^t(6)] are accessible via reaction of the trihydride with [Hg(SR)₂](R = Et or Bu^t). Products (2)–(6) have been characterised by analytical, ¹H and ^l3C n.m.r. data.