1319720-89-2Relevant academic research and scientific papers
Olefin cyclopropanation catalyzed by iridium(III) porphyrin complexes
Anding, Bernie J.,Ellern, Arkady,Woo, L. Keith
, p. 3628 - 3635 (2012/06/18)
Tetratolylporphyrinato (TTP) iridium complexes were shown to be extremely active and robust catalysts for the cyclopropanation of olefins using diazo compounds as carbene sources. Ir(TTP)CH3 (1) catalyzed the cyclopropanation of styrene with ethyl diazoacetate (EDA) at -78 °C and achieved 4.8 × 105 turnovers in three successive reagent additions with no sign of deactivation. High yields and moderate trans selectivities were attained for electron-rich and sterically unhindered substrates. A Hammett ρ+ value of -0.23 was determined by competition experiments with para-substituted styrenes. Furthermore, competitive cyclopropanation of styrene and styrene-d8 with EDA and 1 demonstrated a moderate inverse secondary isotope effect of 0.86 ± 0.03. These data are consistent with a catalytic cycle that proceeds through a metalloporphyrin carbene intermediate. Carbene transfer to olefin substrates appears to be rate limiting, as indicated by kinetic studies. Hexavalent iridium halogenato tetratolylporphyrinato complexes of the form Ir(TTP)X(L), where X = Cl, Br, I, NCS and L = CO, NMe3 (2-6), and cationic analogues, where X = BF4 and L = CO or vacant site (7, 8), also demonstrated high catalytic cyclopropanation activity.
Base-promoted selective aryl C-Br and C-I bond cleavage by iridium(III) porphyrin: Reduction of IrIII-OH to IrII for metalloradical ipso substitution of aryl-halogen bonds
Cheung, Chi Wai,Chan, Kin Shing
, p. 4269 - 4283 (2011/10/03)
Base-promoted selective aryl carbon-bromine and carbon-iodine bond (Ar-X, X = Br, I) cleavage by iridium(III) porphyrin carbonyl chloride (Ir III(ttp)(CO)Cl) was achieved in the presence of base (K 2CO3, NaOH) to give iridium(III) porphyrin aryls (Ir III(ttp)Ar). Mechanistic studies revealed that the base undergoes ligand substitution with Ir(ttp)(CO)Cl to yield an iridium(III) hydroxo species (IrIII(ttp)OH). The hydroxo ligand most likely reduces the Ir(III) center to give iridium(II) porphyrin dimer ([IrII(ttp)]2) and H2O2. In a competitive pathway, [Ir II(ttp)]2 disproportionates in the presence of base and residual water to give an iridium(III) hydride (IrIII(ttp)H) and Ir(ttp)OH. In a productive process, [Ir(ttp)]2 undergoes Ir II(ttp) metalloradical-mediated ipso substitution of Ar-X via an addition-elimination pathway to form Ir(ttp)Ar and Ir(ttp)X. Ir(ttp)X is recycled by reacting with base to regenerate [Ir(ttp)]2 for subsequent Ar-X cleavage.
