One-electron activation and coupling of ethene by rhodium(II) porphyrins: observation of an .eta.2-ethene-metalloradical complex

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

“…[60] A similar intermolecular C alkene -C alkene bond formation involving two cot ligands was observed following oxidation of [Rh I (Cp)(cot)]. [61] Neither [60,62] The spin population at rhodium was estimated at about 0.67.…”

“…[60] A similar intermolecular C alkene -C alkene bond formation involving two cot ligands was observed following oxidation of [Rh I (Cp)(cot)]. [61] Neither [60,62] The spin population at rhodium was estimated at about 0.67. 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).…”

“…[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. [60] The reactions of [ [57] On the basis of these arguments (and the above EPR results), the authors argued that [Rh II -(por)(alkene)] complexes are not authentic alkyl radicals and therefore cannot initiate alkene polymerization reactions ( Figure 17). These arguments also imply that formation of "slipped olefin"/ethyl radical species [ 2+ to form an ethylene-bridged species (Figure 18).…”

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

“…Increasing the steric bulk by using the complex [Rh II (TTEPP)], however, prevents direct MÀ ÀC coupling, and bimolecular CÀ ÀC coupling via two rhodium-ethene radicals yields the butylene bridged species [Rh III (TTEPP)(m 2 À ÀCH 2 CH 2 À ÀCH 2 CH 2 À ÀRh III (TTEPP)], (see Fig. 50) (157).…”

A paramagnetic quasi-1D chain comprised of Pt/Rh possessing an unpaired electron

“…Taking into account that the g av value of 4 (g av ¼ 2.032) is much smaller than those of the d z2 -type Pt complexes, it is unlikely that the unpaired electron occupies the d z2 state in 4. It is important to note that the d z2 -type Rh(II) complexes possess relatively large g av value similar to Pt(III) (e.g., g av ¼ 2.176 for (TTiPP)Rh(II) (TTiPP ¼ tetrakis(1,3,5-triisopropylphenyl)porphyrin)) [33]. Considering the small g av value of 4 which is different from both Pt(III) and Rh(II), the singly occupied orbital in 4 is attributed most likely to the Rh(II) d xy orbital, which is raised above d z2 by the p interaction with the amidate ligands (Scheme 2).…”