Stable Platinum(IV) Corroles: Synthesis, Molecular Structure, and Room-Temperature Near-IR Phosphorescence

Abstract

A series of stable Pt(IV) corrole complexes with the general formula Pt^IV[TpXPC](<i>m/p</i>-C₆H₄CN)(py), where TpXPC^3– is the trianion of a tris(<i>p</i>-X-phenyl)corrole and X = CF₃, H, and CH₃, has been synthesized, affording key physicochemical data on a rare and elusive class of metallocorroles. Single-crystal X-ray structures of two of the complexes revealed very short equatorial Pt–N distances of 1.94–1.97 Å, an axial Pt–C distance of ∼2.03 Å, and an axial Pt–N distance of ∼2.22 Å. The complexes exhibit Soret maxima at ∼430 nm, which are essentially independent of the meso-aryl para substituents, and strong Q bands with the most intense peak at 595–599 nm. The substituent-independent Soret maxima are consistent with an innocent Pt^IV–corrole^3– description for the complexes. The low reduction potentials (−1.45 ± 0.08 V vs saturated calomel reference electrode) also support a highly stable Pt(IV) ground state as opposed to a noninnocent corrole•2– description. The reductions, however, are irreversible, which suggests that they involve concomitant cleavage of the Pt–aryl bond. Unlike Pt(IV) porphyrins, two of the complexes, Pt^IV[TpXPC](m-C₆H₄CN)(py) (X = CF₃ and CH₃), were found to exhibit room-temperature near-IR phosphorescence with emission maxima at 813 and 826 nm, respectively. The quantum yield of ∼0.3% is comparable to those observed for six-coordinate Ir(III) corroles.