A simple yet stable molybdenum(0) carbonyl complex for upconver-sion and photoredox catalysis

Abstract

Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with complicated syntheses are oftentimes required to enable photoactivity with non-precious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO)3(tpe) featuring the tripodal ligand tris(pyridyl)ethane (tpe) in two steps with high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer (3MLCT) state as lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of [Ru(bpy)3]2+. Importantly, we found that the title compound is very photostable due to the lack of labilized Mo–CO bonds (as caused by trans-coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet-triplet annihilation mechanism and (2) photoredox catalysis for a green-light driv-en dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to ac-cess stable photoactive complexes of non-precious metals avoiding tedious multi-step syntheses.

Vapor-phase synthesis of low-valent metal-organic frameworks from metal carbonyl synthons

“…Kitzmann et al have recently assigned a reversible couple at E1/2 = −0.20 V (vs Fc + /Fc) to the one-electron oxidation of the structurally related fac-Mo(CO)3(tpe) (tpe = 1,1,1-tris(pyrid-2yl)ethane) complex in DMF. 22 Also shown in Fig. 5 and Fig.…”

“…[7][8][9][10][11][12][13][14][15][16] There is already considerable interest in developing methods to incorporate these functional units into existing MOF scaffolds, [17][18][19][20][21] while very recently they have also proven to be active photoredox catalysts. 22 The applications of MOFs, for example as electrocatalysts 23 or sensors, 24 often require their deposition on various substrates. 25 MOF synthesis and deposition protocols largely rely on solution-phase processes to control homogeneity and crystallization.…”