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 But(6)] are accessible via reaction of the trihydride with [Hg(SR)2](R = Et or But). Products (2)–(6) have been characterised by analytical, 1H and l3C n.m.r. data.