Dihydroperimidine-derived N-heterocyclic pincer carbene complexes via double C-H activation

The reactions of 1,8-diaminonaphthalene with paraformaldehyde and secondary phosphines (HPR₂, R = Ph, Cy) directly afford N,N'- bis(phoshinomethyl)dihydroperimidines H₂C(NCH₂PR ₂)₂C₁₀H₆ (R = Ph (1a), Cy (1b)), the methylene group of which undergoes chelate-assisted double C-H activation with [RhCl(PPh₃)₃] to afford dihydroperimidine-derived N-heterocyclic pincer carbene (per-NHC) complexes [RhCl{=C(NCH ₂PR₂)₂C₁₀H₆}] (R = Ph (2a), Cy (2b)). Insight into the mechanism of these C-H activation processes is provided by the reaction of 1b with [IrCl(CO)(PPh₃)₂] to provide the dihydroperimidinyl-hydrido complex [IrHCl(CO){CH(NCH ₂PR₂)₂C₁₀H₆}] (3b), which in turn reacts with silver salts Ag[Y] to afford, via hydride abstraction and subsequent C-H activation, the per-NHC ligated salts [IrHCl(CO){=C(NCH ₂PR₂)₂C₁₀H₆}] ([4b]Y, Y = PF₆, SbF₆, PO₂F₂).