Chemistry of Iridium(I) Cyclooctadiene Compounds with Thiapentadienyl, Sulfinylpentadienyl, and Butadienesulfonyl Ligands

The metathesis reaction of [(η⁴-COD)­Ir­(μ-Cl)]₂ (<b>4</b>) with two equivalents of the sodium thiapentadienide (<b>1Na</b>) or potassium sulfinylpentadienide salt (<b>2K</b>) led to the formation of the corresponding dimers [(η⁴-COD)­Ir­(μ₂-1-2,5-η-CH₂CHCHCHS)]₂ (<b>5</b>) and [(η⁴-COD)­Ir­(μ₂-1-2,5-η-CH₂CHCHCHSO)]₂ (<b>9</b>). The single-crystal analysis of <b>5</b> and <b>9</b> reveals the presence of the thiapentadienyl or sulfinylpentadienyl ligands bridging through the sulfur atoms and the terminal double bonds to both iridium centers. Treatment of <b>5</b> with two equivalents of PMe₃ produces [(η⁴-COD)­Ir­(1-2,5-η-CH₂CHCHCHS)­PMe₃] (<b>6</b>), while compound Ir­(1-2,5-η-CH₂CHCHCHS)­(CO)­(PPh₃)₂ (<b>8</b>) is obtained from reaction of Ir­(CO)­(Cl)­(PPh₃)₂ (<b>7</b>) with potassium thiapentadienide (<b>1K</b>). The ¹H and ¹³C NMR support the preferred U conformation and the same η^2,1-bonding mode of the thiapentadienyl ligand in each case. The reaction of <b>4</b> with butadienesulfinate salts M­[CH₂CHCHCHSO₂] (<b>3M</b>) (M = Li, K) affords the ion-pair complexes [(η⁴-COD)­IrCl­(1-2,5-η-CH₂CHCHCHS­(O₂^–M⁺)] (M = Li, <b>10</b>; M = K, <b>11</b>). Compound (η⁴-COD)­Ir­(μ-Cl)­(1-2-η-S,O-μ-OSOCHCHCHCH₂)­Ir­(η⁴-COD) (<b>12</b>) can be isolated if the reaction of <b>4</b> with <b>3K</b> is carried out at low temperature and after a short period of time in solution. The crystal structure of <b>12</b> shows a dinuclear compound where the butadienesulfonyl is bridging through the S and one of the O atoms to the iridium center. In solution, <b>12</b> dissociates in the presence of coordinating solvents, such as DMSO-<i>d</i>₆ or THF-<i>d</i>₈, while the dinuclear asymmetric structure of <b>12</b> remains in CDCl₃. The series of pentacoordinated Ir­(I) complexes of general formula [(η⁴-COD)­Ir­(1-2,5-η-CH₂CHCHCHSO₂)­L] (L = PMe₃, <b>14</b>; PMe₂Ph, <b>15</b>; PMePh₂, <b>16</b>; PPh₃, <b>17</b>; DMSO, <b>18</b>; and CO, <b>19</b>) can be obtained, under mild conditions, from <b>11</b> and the corresponding ligand L, which shows different σ or π donor–acceptor properties. The disubstituted phosphine derivative [(η⁴-COD)­Ir­(5-η-CH₂CHCHCHSO₂)­(PMe₃)₂] (<b>20</b>) can be prepared directly from <b>14</b> and an excess of PMe₃. A comparative study of these derivatives was carried out through the analysis of the IR, mass spectrometry, and ¹H, ¹³C, and ³¹P NMR spectroscopy, as well as through the crystalline structures of <b>12</b>, <b>14</b>, <b>15</b>, and <b>17</b>–<b>20</b>, and allowed establishing trends among them. The presence of the butadienesulfonyl ligand in complexes <b>14</b>–<b>19</b> induces a total asymmetry that is reflected through the ¹H and ¹³C NMR. The preferred coordination mode (1-2,5-η-) in the butadienesulfonyl ligand for complexes <b>14</b>–<b>19</b> was confirmed. A better synthetic procedure for <b>14</b> is described if [(η⁴-COD)­IrClPMe₃] (<b>21</b>) reacts with <b>3K</b>. In contrast, no synthetic advantage was found in the formation of <b>17</b> or <b>20</b> when [(η⁴-COD)­IrClPPh₃] (<b>22</b>) or [(η⁴-COD)­IrCl­(PMe₃)₂] (<b>23</b>) is used as a precursor. Monitoring reactions through ¹H and ³¹P NMR of <b>11</b>, <b>12</b>, and <b>14</b> in the presence of PMe₃ and <b>23</b> with <b>3K</b> afforded mixtures of compounds, from which an equilibrium in the reaction mixture is proposed