Solid-State End-On to Side-On Isomerization of (NN)^2– in {[(R₂N)₃Nd]₂N₂}^2– (R = SiMe₃) Connects In Situ Ln^III(NR₂)₃/K and Isolated [Ln^II(NR₂)₃]^1– Dinitrogen Reduction

Examination of the reduction chemistry of Nd(NR2)3 (R = SiMe3) under N2 has provided connections between the in situ Ln(III)-based LnIII(NR2)3/K reductions of N2 that form side-on bound neutral (N=N)2– complexes, [(R2N)2(THF)Ln]2[μ-η2:η2-N2], and the Ln(II)-based [LnII(NR2)3]1– reductions by Sc, Gd, and Tb that form end-on bound (N=N)2– complexes, {[(R2N)3Ln]2[μ-η1:η1-N2]}2–, which are dianions. The reduction of Nd(NR2)3 by KC8 under dinitrogen in Et2O in the presence of 18-crown-6 (18-c-6) forms dark yellow solutions of [K2(18-c-6)3]{[(R2N)3Nd]2N2} at low temperatures that become green as they warm up to −35 °C in a glovebox freezer. Green crystals obtained from the solution turn yellow-brown when cooled below −100 °C, and the yellow-brown compound has an end-on Nd2(μ-η1:η1-N2) structure. The yellow-brown crystals isomerize in the solid state on the diffractometer upon warming, and at −25 °C, the crystals are green and have a side-on Nd2(μ-η2:η2-N2) structure. Collection of X-ray diffraction data at 10 °C intervals from −50 to −90 °C revealed that the isomerization occurs at temperatures below −100 °C. In the presence of tetrahydrofuran (THF), the dianionic {[(R2N)3Nd]2N2}2– system can lose an amide ligand to provide the monoanionic [(R2N)3NdIII(μ-η2:η2-N2)NdIII(NR2)2(THF)]1–, characterized by X-ray crystallography. These data suggest a connection between the in situ Ln(III)/K reductions and Ln(II) reductions that depends on solvent, temperature, the presence of a chelate, and the specific rare-earth metal

Synthesis and Characterization of Tris(trimethylsilyl)siloxide Derivatives of Early Transition Metal Alkoxides That Thermally Convert to Varied Ceramic–Silica Architecture Materials

In an effort to generate single-source precursors for the production of metal–siloxide (MSiO_<i>x</i>) materials, the tris­(trimethylsilyl)­silanol (H-SST or H-OSi­(SiMe₃)₃ (<b>1</b>) ligand was reacted with a series of group 4 and 5 metal alkoxides. The group 4 products were crystallographically characterized as [Ti­(SST)₂(OR)₂] (OR = OPr^<i>i</i> (<b>2</b>), OBu^<i>t</i> (<b>3</b>), ONep (<b>4</b>)); [Ti­(SST)₃(OBu^<i>n</i>)] (<b>5</b>); [Zr­(SST)₂­(OBu^<i>t</i>)₂(py)] (<b>6</b>); [Zr­(SST)₃­(OR)] (OR = OBu^<i>t</i> (<b>7</b>), ONep, (<b>8</b>)); [Hf­(SST)₂­(OBu^<i>t</i>)₂] (<b>9</b>); and [Hf­(SST)₂­(ONep)₂(py)_<i>n</i>] (<i>n</i> = 1 (<b>10</b>), <i>n</i> = 2 (<b>10a</b>)) where OPr^<i>i</i> = OCH­(CH₃)₂, OBu^<i>t</i> = OC­(CH₃)₃, OBu^<i>n</i> = O­(CH₂)₃CH₃, ONep = OCH₂C­(CH₃)₃, py = pyridine. The crystal structures revealed varied SST substitutions for: monomeric Ti species that adopted a tetrahedral (<i>T</i>-4) geometry; monomeric Zr compounds with coordination that varied from <i>T</i>-4 to trigonal bipyramidal (<i>TBPY</i>-5); and monomeric Hf complexes isolated in a <i>TBPY</i>-5 geometry. For the group 5 species, the following derivatives were structurally identified as [V­(SST)₃(py)₂] (<b>11</b>), [Nb­(SST)₃­(OEt)₂] (<b>12</b>), [Nb­(O)­(SST)₃(py)] (<b>13</b>), 2­[H]­[(Nb­(μ-O)₂­(SST))₆(μ₆-O)] (<b>14</b>), [Nb₈O₁₀(OEt)₁₈­(SST)₂·1/5Na₂O] (<b>15</b>), [Ta­(SST)­(μ-OEt)­(OEt)₃]₂ (<b>16</b>), and [Ta­(SST)₃­(OEt)₂] (<b>17</b>) where OEt = OCH₂CH₃. The group 5 monomeric complexes were solved in a <i>TBPY</i>-5 arrangement, whereas the Ta of the dinculear <b>16</b> was solved in an octahedral coordination environment. Thermal analyses of these precursors revealed a stepwise loss of ligand, which indicated their potential utility for generating the MSiO_<i>x</i> materials. The complexes were thermally processed (350–1100 °C, 4 h, ambient atmosphere), but instead of the desired MSiO_<i>x</i>, transmission electron microscopy analyses revealed that fractions of the group 4 and group 5 precursors had formed unusual metal oxide silica architectures

Synthesis and Lanthanide Coordination Chemistry of Phosphine Oxide Decorated Dibenzothiophene and Dibenzothiophene Sulfone Platforms

Syntheses for new ligands based upon dibenzothiophene and dibenzothiophene sulfone platforms, decorated with phosphine oxide and methylphosphine oxide donor groups, are described. Coordination chemistry of 4,6-bis­(diphenylphosphinoylmethyl)­dibenzothiophene (<b>8</b>), 4,6-bis­(diphenylphosphinoylmethyl)­dibenzothiophene-5,5-dioxide (<b>9</b>) and 4,6-bis­(diphenylphosphinoyl)­dibenzothiophene-5,5-dioxide (<b>10</b>) with lanthanide nitrates, Ln­(NO₃)₃·(H₂O)_<i>n</i> is outlined, and crystal structure determinations reveal a range of chelation interactions on Ln­(III) ions. The nitric acid dependence of the solvent extraction performance of <b>9</b> and <b>10</b> in 1,2-dichloroethane for Eu­(III) and Am­(III) is described and compared against the extraction behavior of related dibenzofuran ligands (<b>2</b>, <b>3</b>; R = Ph) and <i>n</i>-octyl­(phenyl)-<i>N</i>,<i>N</i>-diisobutylcarbamoylmethyl phosphine oxide (<b>4</b>) measured under identical conditions