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Keywords:

  • frustrated Lewis pairs;
  • hydrogen;
  • iridium;
  • pyridylidenes;
  • reactive intermediates

Abstract

The reactivity of a series of iridium[BOND]pyridylidene complexes with the formula [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (1 a1 c) towards a variety of substrates, from small molecules, such as H2, O2, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e unsaturated [TpMe2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H2 is heterolytically split to give hydride[BOND]pyridylidene complexes, whilst CO, CO2, and H2C[DOUBLE BOND]O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five-membered metallacycles with an IrCH2CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four-membered iridacycles with the IrC([DOUBLE BOND]CH2)N moiety. C6H5(C[DOUBLE BOND]O)H and C6H5C[TRIPLE BOND]CH react with formation of Ir[BOND]C6H5 and Ir[BOND]C[TRIPLE BOND]CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a1 c against O2 is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.