Two Rhodium(III) Ions Confined in a [18]Porphyrin Frame: 5,10,15,20‐Tetraaryl‐21,23‐Dirhodaporphyrin

Tetraaryl‐21,23‐dirhodaporphyrin and a series of related monorhodaporphyrins have been obtained by tellurium‐to‐rhodium exchange in a reaction of tetraaryl‐21,23‐ditelluraporphyrin with [RhCl(CO)₂]₂. These organometallic metallaporphyrins contain rhodium(III) centers embedded in rhodacyclopentadiene rings, incorporated within the porphyrin frames. The skeletons of 21,23‐dirhodaporphyrin and 21‐rhoda‐23‐telluraporphyrin are strongly deformed in‐plane from the rectangular shape typical for porphyrins, due to rhodium(III) coordination preferences, the large size of the two core atoms, and the porphyrin skeleton constrains. These two metallaporphyrins exhibit fluxional behavior, as studied by ¹H NMR and DFT, involving the in‐plane motion and the switch of the rhodium center(s) between two nitrogen donors. A side product detected in the reaction mixture, 21‐oxa‐23‐rhodaporphyrin, results from tellurium‐to‐oxygen exchange, occurring in parallel to the tellurium‐to‐rhodium exchange. The reaction paths and mechanisms have been analyzed. The title 21,23‐dirhodaporphyrin contains a bridged bimetallic unit, Rh₂Cl₂, in the center of the macrocycle, with two rhodium(III) ions lying approximately in the plane of the porphyrinoid skeleton. The geometry of the implanted Rh₂Cl₂ unit is affected by macrocyclic constrains.

Chemistry inside a Porphyrin Skeleton: Platinacyclopentadiene from Tellurophene

Platinum(II) binds to 21,23-ditelluraporphyrin forming a side-on complex, which can be easily transformed into an aromatic metallaporphyrin, that is, 21-platina-23-telluraporphyrin, with a platinacyclopentadiene unit built in the porphyrin skeleton in place of one pyrrole ring. The central platinum(II) ion with a CCNTe square-planar coordination sphere can be oxidized to platinum(IV) by chlorine, bromine, methyl iodide or allyl chloride to yield octahedral complexes. All platinatelluraporphyrins show dynamic behavior involving the platinum ion coordination sphere fluxionality and the porphyrin skeleton deformation, both in-plane and out-of-plane, as demonstrated by ¹ H NMR spectroscopy.

Expanded Porphyrin Contraction: From [22]Triphyrin(6.6.0) to [22]Triphyrin(6.5.0)

An expanded triphyrin containing a bipyrrole moiety and annulene links, namely tetraphenyl-[22]triphyrin(6.5.0), 2, has been synthesized. The synthesis proceeded by a postsynthetic transformation of tetraphenyl-[22]triphyrin(6.6.0), 1, in a metal-free unexpected and unprecedented ring contraction during column chromatography on alumina. The observed transformation, located at the hydrocarbon chain linking the pyrrole units, formally corresponds to a subtraction of one carbon atom from an annulene circuit. In contrast to the flexible substrate 1, the product 2 is conformationally rigid, and capable of chloride anion binding in its protonated form.

Structural diversity of the complexes of monovalent metal d10 ions with macrocyclic aggregates of iso-tellurazole N-oxides

Iso-tellurazole N-oxides yield a remarkable variety of structures with coinage-metal monocations.