Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

Abstract

The unique environment within the core of carbaporphyrinoid systems provides a platform to explore unusual organometallic chemistry. The ability of these structures to form stable organometallic derivatives was first demonstrated for N-confused porphyrins but many other carbaporphyrin-type systems were subsequently shown to exhibit similar or complementary properties. Metalation commonly occurs with catalytically active transition metal cations and the resulting derivatives exhibit widely different physical, chemical and spectroscopic properties and range from strongly aromatic to nonaromatic and antiaromatic species. Metalation may trigger unusual, highly selective, oxidation reactions. Alkyl group migration has been observed within the cavity of metalated carbaporphyrins, and in some cases ring contraction of the carbocyclic subunit takes place. Over the past thirty years, studies in this area have led to multiple synthetic routes to carbaporphyrinoid ligands and remarkable organometallic chemistry has been reported. An overview of this important area is presented.

Linear Extension of Carbaporphyrin Chromophores: Synthesis, Protonation, and Metalation of Anthro[2,3-b]carbaporphyrins: Evidence for 30π-Electron Aromatic Circuits in a Palladium(II) Complex

“…22 Altering the macrocyclic core to CNNN decreases reactivity toward metal cations, but carbaporphyrinoid systems still form stable organometallic derivatives. 2,3 Benzocarbaporphyrins behave as trianionic ligands and it has previously been reported that benzo-5 and naphthocarbaporphyrins 17 generate silver(III) complexes when reacted with silver(I) acetate at room temperature. In order to investigate the coordination chemistry of the anthrocarbaporphyrin system, 8 was reacted with silver(I) acetate in an attempt to prepare 17 (Scheme 4).…”

“…Carbaporphyrins have unique reactivity and readily form organometallic derivatives with late transition metal cations. 2,3 Much of the work in this area has been conducted on benzo-fused carbaporphyrins 1 (Scheme 1) due in part to ease of synthesis. 4 In principle, ring fusion extends conjugation within these porphyrinoid systems, but in practice, 1 still favors an 18π electron delocalization pathway.…”

“…True carbaporphyrins, which possess cyclopentadiene units or related annulated derivatives such as indene in place of the usual pyrrolic moieties within the porphyrin framework, have fully aromatic properties and give electronic absorption spectra that closely resemble regular porphyrins. Carbaporphyrins have unique reactivity and readily form organometallic derivatives with late transition metal cations. , Much of the work in this area has been conducted on benzo-fused carbaporphyrins 1 (Scheme ) due in part to ease of synthesis . In principle, ring fusion extends conjugation within these porphyrinoid systems, but in practice, 1 still favors an 18π electron delocalization pathway.…”

Aromatic Character and Relative Stability of Pyrazoloporphyrin Tautomers and Related Protonated Species: Insights into How Pyrazole Changes the Properties of Carbaporphyrinoid Systems

“…Carbaporphyrinoid systems, porphyrin-like molecules with one or more carbon atoms within the macrocyclic core, exhibit diverse and unusual reactivity and may exist as aromatic, nonaromatic or antiaromatic species [ 1 , 17 , 18 ]. In addition, carbaporphyrin-type systems react with many late transition metal cations to generate stable organometallic derivatives under mild conditions [ 19 , 20 , 21 , 22 ]. N -Confused porphyrins have been particularly well studied with regard to their metalation properties [ 22 ], but complementary organometallic chemistry has also been described for related systems [ 19 , 20 ].…”

“…In addition, carbaporphyrin-type systems react with many late transition metal cations to generate stable organometallic derivatives under mild conditions [ 19 , 20 , 21 , 22 ]. N -Confused porphyrins have been particularly well studied with regard to their metalation properties [ 22 ], but complementary organometallic chemistry has also been described for related systems [ 19 , 20 ]. N -Confused porphyrins have two major tautomeric forms, 1a and 1b , that have dramatically different spectroscopic properties.…”