Comparative Study of Rhodium and Iridium Porphyrin Diaminocarbene and N-Heterocyclic Carbene Complexes

Iridium meso-tetratolylporphyrinato (TTP) mono- and bis-diaminocarbene complexes, [Ir(TTP)[═C(NHBn)(NHR)]2–x(C≡NBn)x]BF4, where R = Bn, n-Bu and x = 1, 0, were synthesized by nucleophilic addition of amines to the bis-isocyanide complex [Ir(TTP)(C≡NBn)2]BF4. Rhodium and iridium porphyrinato N-heterocyclic carbene (NHC) complexes M(TTP)CH3(NHC), where NHC = 1,3-diethylimidazolylidene (deim) or 1-(n-butyl)-3-methylimidazolylidene (bmim), were prepared by the addition of the free NHC to M(TTP)CH3. The NHC complexes displayed two dynamic processes by variable-temperature NMR: meso-aryl–porphyrin C–C bond rotation and NHC exchange. meso-Aryl–porphyrin C–C bond rotation was exhibited by both rhodium and iridium complexes at temperatures ranging between 239 and 325 K. Coalescence data for four different complexes revealed ΔG⧧ROT values of 59 ± 2 to 63 ± 1 kJ·mol–1. These relatively low rotation barriers may result from ruffling distortions in the porphyrin core, which were observed in the molecular structures of...