Activation of CO, Isocyanides, and Alkynes by Frustrated Lewis Pairs Based on Cp*M/N (M = Rh, Ir) Couples

The complexes [Cp*M(κ³<i>N</i>,<i>N</i>',<i>N</i>″-<b>L</b>)][SbF₆] (Cp* = η⁵-C₅Me₅; M = Rh, <b>1</b>, Ir, <b>2</b>; <b>HL</b> = pyridinyl-amidine) display M/N transition metal frustrated Lewis pair reactivity toward a range of substrates containing triple bonds. Whereas the rhodium complex <b>1</b> reacts with CO yielding compound [Cp*Rh(CO)(κ²<i>C</i>,<i>N</i>-<b>LCO</b>)][SbF₆] (<b>3</b>), which contains a terminal carbonyl and a carbamoyl group, the iridium complex <b>2</b> generates compound [Cp*Ir(κ³<i>C</i>,<i>N</i>,<i>N</i>'-<b>LCO</b>)][SbF₆] (<b>4</b>), which only features the carbamoyl group. Compounds <b>1</b> and <b>2</b> react with stoichiometric amounts of the isocyanides CNR (R = Cyclohexyl, <i>p</i>-C₆H₄(OMe), CH₂SO₂(<i>p</i>-Tolyl)) to give the corresponding 1,1-insertion complexes [Cp*M(κ³<i>C</i>,<i>N</i>,<i>N</i>'-<b>LCNR</b>)][SbF₆] (<b>5-10</b>). Complexes containing inserted and coordinated isocyanide ligands of formula [Cp*M(CNR)(κ²<i>C</i>,<i>N</i>-<b>LCNR</b>)][SbF₆] (<b>11-15</b>) are obtained upon treating <b>1</b> and <b>2</b> with excess of the corresponding isocyanide. Compound <b>2</b> reacts with CN^<i>t</i>Bu affording the adduct [Cp*Ir(CN^<i>t</i>Bu)(κ²<i>N</i>,<i>N</i>'-<b>L</b>)][SbF₆] (<b>16</b>) which contains a terminal CN^<i>t</i>Bu ligand. Complex <b>16</b> is protonated by HSbF₆ to give [Cp*Ir(CN^<i>t</i>Bu)(κ²<i>N</i>,<i>N</i>'-<b>HL</b>)][SbF₆]₂ (<b>17</b>). The terminal alkynes HC≡CR (R = Ph, CO₂Et) react with <b>1</b> and <b>2</b> rendering the alkynyl complexes <b>18-21</b>. Dimethyl acetylenedicarboxylate reacts with complex <b>2</b> to give compound <b>22</b> via the formal 1,2-addition of a basic nitrogen atom and the metal across the alkyne triple bond. The new complexes have been characterized by analytical, spectroscopic and X-ray diffraction (XRD) methods.