Formation and reactivity of (tetraarylporphyrinato)rhodium(II) monocarbonyls: bent RhIICO complexes that react like acyl radicals

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

“…large 13 C hyperfine couplings (>300 MHz along all three principal axes). These data indicate the presence of a bent MÀ ÀCO unit with a spin density distribution intermediate between that of a metal and a carbonyl carbon centered radical (134,138,139). The spin density was estimated to be located for > 30% at CO and <60% at Rh (Fig.…”

“…radicals to styrene yielding [Rh III (por)(m-C(O)CH 2 CH(Ph)C(O)À À)Rh III (por)] has also been reported (Fig. 44) (139). The failure of the more hindered complex [Rh II (TMP)] to abstract a hydrogen atom from [Rh III (por)(H)] to produce a formyl complex (in contrast to observations for OEP complexes), was ascribed to the steric bulk of TMP.…”

“…44). The acyl radical contribution to the electronic structure of [Rh II (por)(CO)] species also allows hydrogen radical abstraction reactions from (OEP)RhÀ ÀH bonds (only for the least hindered OEP complexes) (141), and H 2 or HSn(Bu) 3 (with formation of [Sn(Bu) 3 ] 2 ) to form the formyl species [Rh III (por)(C(O)H)] (139). Binuclear coupling of two RhÀ ÀC(O).…”

“…Like [Rh II (OEP)], [Rh II (TMP)] with ethene still rapidly converts to the diamagnetic ethylene bridged species [Rh III (TMP)(m 2 -C 2 H 4 )Rh III (TMP)] involving a bimolecular MÀ ÀC coupling reaction (139). 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.…”

“…(138,139). Similar results were obtained for [Rh II (TXP)] reacting with CO, yielding exclusively [Rh III (TXP) (m 2 -C(O)C(O)À À)Rh III (TXP)].…”