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

A series of stable Pt­(IV) corrole
complexes with the general formula
PtIV[TpXPC]­(m/p-C6H4CN)­(py), where TpXPC3– is the trianion of a tris­(p-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 PtIV–corrole3– 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,
PtIV[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.