Metalation of Tellurophene: Reactivity of 21,23-Ditelluraporphodimethene toward Palladium(II), Platinum(II), and Rhodium(I)

Abstract

Ditelluraporphodimethene, a nonaromatic porphyrinoid containing two tellurophene rings, reacted with palladium(II), platinum(II), and rhodium(I) following two different paths. Palladium(II) formed bonds to two tellurium donors of the macrocycle, yielding a side-on coordination compound, with a square planar (Te 2 Cl 2 ) metal ion environment. An alternative reaction path has been observed for ditelluraporphodimethene with platinum(II) or rhodium(I) in high boiling solvents. These conditions led to the profound transformation, that is, one tellurium atom to a metal atom exchange, resulting in the formation of organometallic species containing metallacyclopentadiene rings, that is, 21-platina-23-telluraporphodimethene and 21-rhoda-23-telluraporphodimethene. The substitution reaction proceeded selectively at the tellurophene ring within the conjugated part of the molecule, that is, the tellurophene ring bound to two sp 2 meso-carbon atoms. In the case of platinum, the exchange was accompanied by one meso-aryl ring fusion with the formed platinacyclopentadiene ring, and the platinum(II) macrocycle underwent reversible oxidation with chlorine. The products are stable and represent first nonaromatic examples of metalloporphyrinoids, with a metallacyclopentadiene ring incorporated into a porphodimethene skeleton.

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

“…The synthesis avoided unlikely four-fold activation of C–H bonds of the formal ligand, 2 , and followed the tellurium-to-metal substitution protocol, employed in our former studies. 15,20–22 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 which served as a starting material for the second substitution with the more reactive rhodium( i ), as shown in Scheme 1.…”

“…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.…”