School census autumn 2017 : 16 to 19 reports : user guide

The synthesis of a series of cobalt NHC complexes of the types [Co­(NHC)₂(CO)­(NO)] (NHC = <i>i</i>Pr₂Im (<b>2</b>), <i>n</i>Pr₂Im (<b>3</b>), Cy₂Im (<b>4</b>), Me₂Im (<b>5</b>), <i>i</i>Pr₂ImMe (<b>6</b>), Me₂ImMe (<b>7</b>), Me<i>i</i>PrIm (<b>8</b>), Me<i>t</i>BuIm (<b>9</b>); R₂Im = 1,3-dialkylimidazolin-2-ylidene) and [Co­(NHC)­(CO)₂(NO)] (NHC = <i>i</i>Pr₂Im (<b>13</b>), <i>n</i>Pr₂Im (<b>14</b>), Me₂Im (<b>15</b>), <i>i</i>Pr₂ImMe (<b>16</b>), Me₂ImMe (<b>17</b>), Me<i>i</i>PrIm (<b>18</b>), Me<i>t</i>BuIm (<b>19</b>)) from the reaction of the NHC with [Co­(CO)₃(NO)] (<b>1</b>) is reported. These complexes have been characterized using elemental analysis, IR spectroscopy, multinuclear NMR spectroscopy, and in many cases by X-ray crystallography. Bulky NHCs tend to form the mono-NHC-substituted complexes [Co­(NHC)­(CO)₂(NO)], even from the reaction with an stoichiometric excess of the NHC, as demonstrated by the synthesis of [Co­(Dipp₂Im)­(CO)₂(NO)] (<b>11</b>), [Co­(Mes₂Im)­(CO)₂(NO)] (<b>12</b>), and [Co­(^MecAAC)­(CO)₂(NO)] (<b>20</b>). For <i>t</i>Bu₂Im a preferred coordination via the NHC backbone (“abnormal” coordination at the 4-position) was observed and the complex [Co­(<i>t</i>Bu₂^aIm)­(CO)₂(NO)] (<b>10</b>) was isolated. All of these complexes are volatile, are stable upon sublimation and prolonged storage in the gas phase, and readily decompose at higher temperatures. Furthermore, DTA/TG analyses revealed that the complexes [Co­(NHC)₂(CO)­(NO)] are seemingly more stable toward thermal decomposition in comparison to the complexes [Co­(NHC)­(CO)₂(NO)]. We thus conclude that the cobalt complexes of the type [Co­(NHC)­(CO)₂(NO)] and [Co­(NHC)₂(CO)­(NO)] have potential for application as precursors in the vapor deposition of thin cobalt films

From NHC to Imidazolyl Ligand: Synthesis of Platinum and Palladium Complexes d¹⁰-[M(NHC)₂] (M = Pd, Pt) of the NHC 1,3-Diisopropylimidazolin-2-ylidene

The widely held belief that N-heterocyclic carbenes (NHCs) act only as innocent spectator ligands is not always accurate, even in the context of well-explored reactions. Ligand exchange in the conversion of [Pt­(PPh₃)₂(η²-C₂H₄)] (<b>3</b>) to [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>) depends critically on the particular reaction conditions employed, with slight changes leading to vastly different outcomes. In addition to [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>), complexes [Pt­(<i>i</i>Pr₂Im)­(PPh₃)­(η²-C₂H₄)] (<b>5</b>) and <i>trans</i>-[Pt­(<i>i</i>Pr₂Im)₂(<i>i</i>Pr-Im*)­(H)] (<b>6</b>) were isolated and in the case of <b>6</b> fully characterized. Complex <b>5</b> represents the first mixed-olefin complex in transition metal chemistry containing both an NHC and a phosphine ligand. Chemical degradation of the NHC was shown to yield the new imidazole-2-yl <i>i</i>Pr-Im* in <b>6</b>. Therefore, the synthesis of [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>) via metallic reduction of the ionic precursor [Pt­(<i>i</i>Pr₂Im)₃(Cl)]⁺Cl^– (<b>9</b>) is favorable, a procedure adaptable to analogous palladium compounds. While [Pd­(<i>i</i>Pr₂Im)₃(Cl)]⁺Cl^– (<b>8</b>) is the only product obtained from the reaction of <i>i</i>Pr₂Im and PdCl₂, neutral [Pt­(<i>i</i>Pr₂Im)₂(Cl)₂] (<b>10</b>), formed as a mixture of its two stereoisomers <i><b>cis</b></i><b>-10</b> and <i><b>trans</b></i><b>-10</b>, is available through precise control of the stoichiometry in the reaction of PtCl₂ and exactly 2 equiv of <i>i</i>Pr₂Im