Front Cover: Two Rhodium(III) Ions Confined in a [18]Porphyrin Frame: 5,10,15,20‐Tetraaryl‐21,23‐Dirhodaporphyrin (Chem. Eur. J. 46/2022)

Abstract

Dwarfs are shown fixing two rhodium atoms into the skeleton of 21,23‐dirhodaporphyrin, the first [18]porphyrin to incorporate two metal atoms within its macrocyclic frame, in place of two core nitrogen donors. The 18‐π‐electron aromatic circuit is maintained, playing a crucial role in stabilizing the macrocycle, and enforcing the metal centers′ proximity. These small metal sculptures of dwarfs are a tourist attraction scattered around Wrocław, the city in Poland where the dirhodaporphyrin was synthesized. More information can be found in the Research Article by E. Pacholska‐Dudziak and co‐workers (DOI: 10.1002/chem.202201513).

Heterobimetallic 21,23-dimetallaporphyrin: activation of metal–metal interactions within the porphyrinoid macrocycle

“…The synthesis of organometallic aromatic 21,23-dirhodaporphyrin 1 containing two rhodium(III) ions has been reported. 15 The two metal atoms were incorporated into the porphyrin skeleton in place of two NH groups. The bridged Rh 2 Cl 2 unit situated approximately within the macrocyclic plane contains two 18-electron rhodium(III) centres surrounded by octahedral environments.…”

“…The synthesis avoided unlikely four-fold activation of C-H bonds of the formal ligand, 2, and followed the tellurium-tometal substitution protocol, employed in our former studies. 15,[20][21][22] The synthetic path, starting with tetrakis(4-methoxyphenyl)-21, 23-ditelluraporphyrin 3, 16 takes advantage of a significant difference in the reactivity of a tellurophene unit towards platinum(II) and rhodium(I) salts, which determines the order of steps. Thus, a single tellurium-to-metal replacement proceeded with platinum(II), yielding the known 21-platina-23-telluraporphyrin 4, 21 Adducts with [Rh(CO) 2 Cl] fragments attached to one donor atom are known in porphyrinoid chemistry.…”

“…23,24 Generally, it can be considered as a rule, that the tellurium-to-metal substitution in metallaporphyrin synthesis is preceded by the formation of a side-on coordination compound. 15,[20][21][22] The heterobimetallic 5, reacts with chlorine through an oxidative addition at the platinum(II) centre yielding quantitatively the platinum(IV) analogue, 5-Cl 2 . The reaction can be readily reversed with zinc amalgam.…”

“…Such a macrocyclic in-plane deformation has been previously observed for 21-metalla-23-telluraporphyrins 20,21 and for the 21, 23-dirhodaporphyrin 1. 15 Significantly, the metal atoms in 21-platina-23-rhodaporphyrins are accommodated practically within the macrocyclic plane. The deformation of the skeletons of 5 and 5-Cl 2 did not significantly disturb the delocalization within the 18 p-electron conjugation path of the porphyrinoid C 20 N 2 skeleton, shown with the bold line in Scheme 1.…”

“…1), support their 10.08-9.61 ppm; 300 K), similar to those in the known metallaporphyrins. 15,20,21 These resonances are readily distinguished on the basis of heteronuclear couplings with NMRactive nuclei, 103 Rh and 195 Pt. The rhodacyclopentadiene signals were split with small coupling constants by rhodium-103 ( 3 J RhH = 1.5 Hz for 5; 1.2 Hz for 5-Cl 2 ), while the interaction with platinum-195 (37% abundance; 3 J PtH = 51 Hz for 5-Cl 2 ) has been detected as broad satellites present for platinum(IV) species only, while for platinum(II) the severe broadening due to the chemical shift anisotropy relaxation impeded the detection of the lines.…”