Formation and ethene substrate reactions of iridium(ii) porphyrin metal-centered dπ radicals

The Organometallic Chemistry of Rh‐, Ir‐, Pd‐, and Pt‐Based Radicals: Higher Valent Species

“…5) than in [Rh II (C 6 Cl 5 ) 4 ] 2À . Similar differences in electronic structures of other isostructural Rh and Ir compounds have been observed (33). In the case of [Pt III (C 6 Cl 5 ) 4 ] À and [Pt III (C 6 Cl 4 H-p) 4 ] À (g av ¼ 2.60) larger orbital contributions are found compared to their rhodium analogues, as one can expect from the large spin-orbit coupling constant (l) of the platinum centre (32).…”

“…It seems that mixing of the ground-state SOMO with multiple exited states that are very close in energy to the SOMO results in very fast relaxation processes, thus causing substantial broadening (EPR silence). Fast relaxation processes also cause [Ir II (porphyrin)] species to be EPR silent (33).…”

“…50) (33). Like its rhodium analogue, reaction of [Ir II (TTiPP)] with ethene does not result in MÀ ÀC or CÀ ÀC coupling, and formation of the ethene adduct is witnessed by NMR, UV-Vis (l max 444 and 730 nm), and EPR spectroscopy [< g >¼ 1:987 (290 K); g k ¼ 1:96, g ?…”

Paramagnetic (Alkene)Rh and (Alkene)Ir Complexes: Metal or Ligand Radicals?

“…The equivalence of the two 13 C atoms in the EPR spectrum reveals a symmetrically bound ethene π complex, and the delocalization of the unpaired electron to the ethene fragment ( [63] Reactions of the iridium complexes [Ir II (TMP)] and [Ir II (TTEPP)] with ethene proceed analogously to the above described rhodium analogs ( Figure 16). [64] Like its rhodium analog, reaction of [Ir Selective binding of ethene and butadiene between the two rhodium sites of a tethered bimolecular bis(por)Rh species with steric demands comparable to TMP, results in selective intramolecular coupling (Figure 16). [65] This gives further support to the idea that formation of alkyl-bridged species from alkenes and [M II (por)] requires a concerted action of two metallo-radical sites.…”

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes

“…The intramolecular electron-transfer reaction, from the Ir II centre to the porphyrin ligand, is responsible for the formation of a (P) ·-Ir III (CH 2 =CH 2 ) radical species. [105,106] The formation of such a species during cyclopropanation reactions can explain the low catalytic activity of iridium(II) porphyrins. The SciFinder database contains only an oral communication by Woo et al [107] on the employment of CH 3 -Ir III (TTP) (TTP = dianion of tetratolylporphyrin) and Ir III (TTP)X(CO) (X = Cl, Br and I) as cyclopropanation catalysts.…”