10.1021/acs.organomet.9b00507.s001 Michael Haas Michael Haas Andreas Knoechl Andreas Knoechl Tanja Wiesner Tanja Wiesner Ana Torvisco Ana Torvisco Roland Fischer Roland Fischer Cameron Jones Cameron Jones Attempted Synthesis of a Homocyclic Bis(silyl)silylene Leads to the Formation of a Tricyclo[3,1,1,1<sup>2,4</sup>]octasilane American Chemical Society 2019 Et 3 SiH endocyclic disilene 1 hexasilanes 10 2.1 equiv formation dianionic compound 13 salt metathesis reaction KO Dianionic species 12 2019-10-07 19:52:03 Journal contribution https://acs.figshare.com/articles/journal_contribution/Attempted_Synthesis_of_a_Homocyclic_Bis_silyl_silylene_Leads_to_the_Formation_of_a_Tricyclo_3_1_1_1_sup_2_4_sup_octasilane/9946997 The reduction of 1,1-dibromo-cyclopentasilane with a mildly reducing magnesium­(I) dimer [{(MesNacnac)­Mg−}<sub>2</sub>] was examined, which gave rise to the formation of endocyclic disilene <b>1</b>. The formation of <b>1</b> was further confirmed by a trapping experiment with MeOH. Additionally, <b>1</b> was found to dimerize slowly to <b>1-dimer</b>. Furthermore, the formation of the homocyclic silylene was demonstrated by performing the reduction in the presence of Et<sub>3</sub>SiH as a trapping agent. To prevent the 1,2-trimethylsilyl shift, which causes a rapid degradation of the silylene, a second synthetic strategy was established. Therefore, two different tetrasilanes <b>4</b> and <b>5</b> were synthesized. Compounds <b>4</b> and <b>5</b> were subsequently reacted with 2.1 equiv of trifluoromethanesulfonic acid to corresponding bis­(trifluoromethanesulfonates) <b>6</b> and <b>7</b>. 1,4-Dihalo-tetrasilanes <b>8a</b>,<b>b</b> and <b>9</b> as well as hexasilanes <b>10</b> and <b>11</b> were obtained by a subsequent nucleophilic substitution of the triflate substituent with X<sup>–</sup> (X = Cl<sup>–</sup>, Br<sup>–</sup>, or R<sub>3</sub>Si<sup>–</sup>). Dianionic species <b>12</b> and <b>13</b> were synthesized by the reaction of corresponding hexasilanes <b>10</b> and <b>11</b> with 2.1 equiv of KO<i>t</i>-Bu. Surprisingly, the salt metathesis reaction of dianionic compound <b>13</b> does not lead to the formation of the expected 1,1-halocyclopentasilanes. Instead the formation of cyclobutasilane <b>14</b> was observed. The reaction of <b>9</b> with lithium led again to the formation of <b>14</b> alongside with the formation of cyclohexasilane <b>15</b>. Interestingly, <b>14</b> underwent a ring-opening formation by the reaction with gaseous HCl in the presence of AlCl<sub>3</sub> and compound <b>16</b> was formed. The reduction of <b>16</b> allowed straightforward access to <b>17</b> as a structurally complex hitherto unknown tricyclic polysilane.