A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

Abstract

Titanium and zirconium complexes carrying two 2,6-bis(pyrrolyl)pyridine ligands have been synthesized and characterized. The neutral complexes Ti(PDP) and Zr(PDP) (PDP = 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine) show intense ligand-to-metal charge-transfer bands in the visible region and undergo multiple reversible redox events under highly reducing conditions. Zr(PDP) exhibits photoluminescent behavior and its excited state can be quenched by mild reductants to generate a powerful electron transfer reagent with a ground state potential of -2.16 V vs Fc. This reactivity was utilized to facilitate dehalogenation reactions, the reduction of electron-poor olefins, and the reductive coupling of benzyl bromide via photoredox catalysis. In these reactions, the earth-abundant metal complex Zr(PDP) acts as a substitute for the precious metal photosensitizer [Ru(bpy)].

Deuterated Molecular Ruby with Record Luminescence Quantum Yield

“…[1,2] Except for copper(I) complexes, [2] strongly luminescent molecular complexes of earth-abundant-metal ions were essentially unknown until very recently.N ear-IR (NIR) emission with mononuclear copper(I) complexes is still very rare. [4][5][6][7][8] Milsmann and co-workers reported aluminescent zirconium-(IV) complex bearing 2,6-bis(pyrrolyl)pyridine ligands. [3] Ah andful of examples of luminescent complexes based on earth-abundant-metal ions with d n electron configuration (n < 10) only became available in the last three years (Scheme 1).…”

“…[2b] Even with noble metal complexes,strong NIR emission is challenging. [4] A unique low-spin hexacarbene iron(III) complex with LMCT emission has been reported by Wärnmark. They include ligand-to-metal charge transfer (LMCT), metal-to-ligand (MLCT), and spin-flip emitters.…”

“…[4] A unique low-spin hexacarbene iron(III) complex with LMCT emission has been reported by Wärnmark. [4][5][6][7][8] [*] C. Wang displays asharp,unprecedentedly intense spin-flip emission in the NIR with aphotoluminescence quantum yield of F = 0.11 and al uminescence lifetime of t = 898 msi nH 2 Oa tr oom temperature. [6,7] Thec hromium(III) complex [Cr(ddpd) 2 ] 3+ (1 3+ ) [8] with ad 3 electron configuration is based on the tridentate strongfield ligand N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6diamine (ddpd) introduced into coordination chemistry by the Heinze group (Scheme 1).…”

A Strongly Luminescent Chromium(III) Complex Acid

“…[4][5][6] An emissive d 0 zirconium(IV) complexw ith 2,6-bis(pyrrolyl)pyridine ligandsh as been reported by Milsmann andc o-workers. [4] Wärnmark and colleagues introduced the first example of a low-spind 5 iron(III) complex displaying LMCT fluorescence. [5] The closed-shell isocyanide chelate complexes of Wenger and co-workerss how 3 MLCT phosphorescence in solution (Scheme 1).…”

Alkali Blues: Blue‐Emissive Alkali Metal Pyrrolates

“…In the last decades, these ligands have attracted considerable attention in several fields of chemistry. For example, they have been applied in transition metal or lanthanide complexes, which are used as homogenous catalysts, especially for polymerization, and as biomimetic and bioinspired complexes [e.g. Mo( t Bu L) 2 O 2 or [Cu( t Bu L)] 2 ; H t Bu L=4‐ tert ‐butyl phenyl(pyrrol‐2‐ylmethylene)amine; Scheme ] .…”