A series of symmetric divalent Sn(II) hydrides of the general form [(4-X-Ar')Sn(mu-H)]2 (4-X-Ar' = C6H2-4-X-2,6-(C6H3-2,6-iPr2)2; X = H, MeO, tBu, and SiMe3; 2, 6, 10, and 14), along with the more hindered asymmetric tin hydride (3,5-iPr2-Ar*)SnSn(H)2(3,5-iPr2-Ar*) (16) (3,5-iPr2-Ar* = 3,5-iPr2-C6H-2,6-(C6H2-2,4,6-iPr3)2), have been isolated and characterized. They were prepared either by direct reduction of the corresponding aryltin(II) chloride precursors, ArSnCl, with LiBH4 or iBu2AlH (DIBAL), or via a transmetallation reaction between an aryltin(II) amide, ArSnNMe2, and BH3.THF. Compounds 2, 6, 10, and 14 were obtained as orange solids and have centrosymmetric dimeric structures in the solid state with long Sn...Sn separations of 3.05 to 3.13 A. The more hindered tin(II) hydride 16 crystallized as a deep-blue solid with an unusual, formally mixed-valent structure wherein a long Sn-Sn bond is present [Sn-Sn = 2.9157(10) A] and two hydrogen atoms are bound to one of the tin atoms. The Sn-H hydrogen atoms in 16 could not be located by X-ray crystallography, but complementary Mössbauer studies established the presence of divalent and tetravalent tin centers in 16. Spectroscopic studies (IR, UV-vis, and NMR) show that, in solution, compounds 2, 6, 10, and 14 are predominantly dimeric with Sn-H-Sn bridges. In contrast, the more hindered hydrides 16 and previously reported (Ar*SnH)2 (17) (Ar* = C6H3-2,6-(C6H2-2,4,6-iPr3)2) adopt primarily the unsymmetric structure ArSnSn(H)2Ar in solution. Detailed theoretical calculations have been performed which include calculated UV-vis and IR spectra of various possible isomers of the reported hydrides and relevant model species. These showed that increased steric hindrance favors the asymmetric form ArSnSn(H)2Ar relative to the centrosymmetric isomer [ArSn(mu-H)]2 as a result of the widening of the interligand angles at tin, which lowers steric repulsion between the terphenyl ligands.

The synthesis and structural characterization of the first homologous, molecular M-M bonded series for the group 12 metals are reported. The compounds Ar'MMAr' (M = Zn, Cd, or Hg; Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) were synthesized by reduction of the corresponding arylmetal halides by alkali metal/graphite (Zn or Hg) or sodium hydride (Cd). These compounds possess almost linear C-M-M-C core structures with two-coordinate metals. The observed M-M bonds distances were 2.3591(9), 2.6257(5), and 2.5738(3) A for the zinc, cadmium, and mercury species, respectively. The shorter Hg-Hg bond in comparison to that of Cd-Cd is consistent with DFT calculations which show that the strength of the Hg-Hg bond is greater. The arylmetal halides precursors (Ar'MI)(1 or 2), and the highly reactive hydrides (Ar'MH)(1 or 2), were also synthesized and fully characterized by X-ray crystallography (Zn and Cd) and multinuclear NMR spectroscopy. The arylzinc and arylcadmium iodides have iodide-bridged dimeric structures, whereas the arylmercury iodide, Ar'HgI, is monomeric. The arylzinc and arylcadmium hydrides have symmetric (Zn) or unsymmetric (Cd) mu-H-bridged structures. The Ar'HgH species was synthesized and characterized by spectroscopy, but a satisfactory refinement of the structure was precluded by the contamination of monomeric Ar'HgH by Ar'H. It was also shown that the decomposition of Ar'Cd(mu-H)(2)CdAr' at room temperature leads to the M-M bonded Ar'CdCdAr', thereby supporting the view that the reduction of the iodide proceeds via the hydride intermediate.

The synthesis and characterization of a series of digermynes and distannynes stabilized by terphenyl ligands are described. The ligands are based on the Ar 0 (Ar 0 ¼ C 6 H 3 -2,6(C 6 H 3 -2,6-i Pr 2 ) 2 ) or Ar* (Ar* ¼ C 6 H 3 -2,6(C 6 H 2 -2,4,6-i Pr 3 ) 2 ) platforms which were modified at the meta or para positions of their central aryl rings to yield 4-X-Ar 0 (4-X-Ar 0 ¼ 4-X-C 6 H 2 -2,6(C 6 H 3 -2,6-i Pr 2 ) 2 , X ¼ H, F, Cl, OMe, t Bu, SiMe 3 , GeMe 3 ) and 3,5-i Pr 2 -Ar 0 or Ar* and 3,5-i Pr 2 -Ar*. The compounds were synthesized by reduction of the terphenyl germanium(II) or tin(II) halide precursors with a variety of reducing agents. The precursors were obtained by the reaction of one equivalent of the lithium terphenyl with GeCl 2 dioxane or SnCl 2 . For germanium, their X-ray crystal structures showed them to be either Ge-Ge bonded dimers with trans-pyramidal geometries or V-shaped monomers. In contrast, the terphenyl tin halides had no tin-tin bonding but existed either as halide bridged dimers or V-shaped monomers. Reduction with a variety of reducing agents afforded the digermynes ArGeGeAr (Ar ¼ 4-Cl-Ar 0 , 4-SiMe 3 -Ar 0 or 3,5-i Pr 2 -Ar*) or the distannynes ArSnSnAr (Ar ¼ 4-F-Ar 0 , 4-Cl-Ar 0 , 4-MeO-Ar 0 , 4-t Bu-Ar 0 , 4-SiMe 3 -Ar 0 , 4-GeMe 3 -Ar 0 , 3,5-i Pr 2 -Ar 0 , 3,5-i Pr 2 -Ar*), which were characterized structurally and spectroscopically. The digermynes display planar trans-bent core geometries with Ge-Ge distances near 2.26A and bending angles near 128 consistent with Ge-Ge multiple bonding. In contrast, the distannynes had either multiple bonded geometries with Sn-Sn distances that averaged 2.65A and an average bending angle near 123.8 , or single bonded geometries with a Sn-Sn bond length near 3.06 A and a bending angle near 98 . The 3,5-i Pr 2 -Ar*SnSnAr*-3,5-i Pr 2 species had an intermediate structure with a longer multiple bond near 2.73A and a variable torsion angle (14-28 ) between the tin coordination planes. M€ ossbauer data for the multiple and single bonded species displayed similar isomer shifts but had different quadrupole splittings.Scheme 1 Single bonded or multiple bonded trans-bent geometry of RMMR (M ¼ Si, Ge, Sn, Pb; R ¼ terphenyl or silyl substituents)

The monomeric iron(II) amido derivatives Fe{N(H)Ar*}2 (1), Ar* = C6H3-2,6-(C6H2-2,4,6-Pri3)2, and Fe{N(H)Ar#}2 (2), Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2, were synthesized and studied in order to determine the effects of geometric changes on their unusual magnetic properties. The compounds, which are the first stable homoleptic primary amides of iron(II), were obtained by the transamination of Fe{N(SiMe3)2}2, with HN(SiMe3)2 elimination, by the primary amines H2NAr* or H2NAr#. X-ray crystallography shows that they have either strictly linear (1) or bent (2, N–Fe–N = 140.9(2)°) iron coordination. Variable temperature magnetization and applied magnetic field Mössbauer spectroscopy studies reveal a very large dependence of the magnetic properties on the metal coordination geometry. At ambient temperature, the linear 1 displayed an effective magnetic moment in the range 7.0 to 7.50 μB, consistent with essentially free ion magnetism. There is a very high internal orbital field component, HL ≈ 170 T which is only exceeded by a HL ≈ 203 T of Fe{C(SiMe3)3}2. In contrast, the strongly bent 2 displays a significantly lower μeff value in the range 5.25 to 5.80 μB at ambient temperature and a much lower orbital field HL value of 116 T. The data for the two amido complexes demonstrate a very large quenching of the orbital magnetic moment upon bending the linear geometry. In addition, a strong correlation of HL with overall formal symmetry is confirmed. ESR spectroscopy supports the existence of large orbital magnetic moments in 1 and 2, and DFT calculations provide good agreement with the physical data.