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

The complexes [Cp*M(κ³N,N',N″-L)][SbF₆] (Cp* = η⁵-C₅Me₅; M = Rh, 1, Ir, 2; HL = pyridinyl-amidine) display M/N transition metal frustrated Lewis pair reactivity toward a range of substrates containing triple bonds. Whereas the rhodium complex 1 reacts with CO yielding compound [Cp*Rh(CO)(κ²C,N-LCO)][SbF₆] (3), which contains a terminal carbonyl and a carbamoyl group, the iridium complex 2 generates compound [Cp*Ir(κ³C,N,N'-LCO)][SbF₆] (4), which only features the carbamoyl group. Compounds 1 and 2 react with stoichiometric amounts of the isocyanides CNR (R = Cyclohexyl, p-C₆H₄(OMe), CH₂SO₂(p-Tolyl)) to give the corresponding 1,1-insertion complexes [Cp*M(κ³C,N,N'-LCNR)][SbF₆] (5-10). Complexes containing inserted and coordinated isocyanide ligands of formula [Cp*M(CNR)(κ²C,N-LCNR)][SbF₆] (11-15) are obtained upon treating 1 and 2 with excess of the corresponding isocyanide. Compound 2 reacts with CN^tBu affording the adduct [Cp*Ir(CN^tBu)(κ²N,N'-L)][SbF₆] (16) which contains a terminal CN^tBu ligand. Complex 16 is protonated by HSbF₆ to give [Cp*Ir(CN^tBu)(κ²N,N'-HL)][SbF₆]₂ (17). The terminal alkynes HC≡CR (R = Ph, CO₂Et) react with 1 and 2 rendering the alkynyl complexes 18-21. Dimethyl acetylenedicarboxylate reacts with complex 2 to give compound 22 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.