Bimetallic N‑Heterocyclic Carbene Rh(I) Complexes: Probing the Cooperative Effect for the Catalyzed Hydroelementation of Alkynes

A series of bimetallic N-heterocyclic carbene Rh­(I) complexes (<b>13</b>, <b>14</b>, <b>16</b>, <b>18</b>, <b>19</b>, and <b>21</b>) were prepared, in which two metal fragments are linked to a central organic scaffold. These complexes were investigated as catalysts for the hydroelementation of alkynes, and their efficiency as catalysts was compared to that of a series of monometallic analogues (<b>12</b>, <b>15</b>, <b>17</b>, and <b>20</b>). To determine the catalyst properties that result in a cooperative, bimetallic enhancement of the reaction rate, systematic variation of the intermetallic distance and the ligand donor properties of the bimetallic complexes was explored. Two related catalyzed reactions were investigated: the dihydroalkoxylation and hydrosilylation of alkynes. Nanoparticle formation was observed during the hydrosilylation reaction using complexes <b>17</b>–<b>19</b>.