Nitric Oxide Insertion into a Metalloporphyrin–Carbon Bond

Nitric oxide (NO) insertion into a metalloporphyrin rhodium–carbon bond is observed when crystals of (TPP)Rh(C₆H₄Cl)(CH₂Cl₂)_x (TPP = tetraphenylporphyrinato dianion) are exposed to NO gas over a two week period. The NO-inserted product was identified by X-ray crystallography as (TPP)Rh(ONC₆H₄Cl-o)(CH₂Cl₂)_0.5·(TPP)Rh(C₆H₄Cl-p/m)(CH₂Cl₂)_0.5, in which NO inserted selectively into the ortho-Cl aryl isomer but not into the para-/meta-Cl aryl isomers. Density functional theory calculations predict a higher reactivity for the ortho-Cl isomer and thus provide a rationale for the preferred NO insertion into the potentially more reactive ortho-Cl isomer under our reaction conditions. Whereas NO insertion reactions are well-known for coordination–organometallic compounds, this result represents the first such NO insertion into a metalloporphyrin metal–carbon bond for any metal.