Air‐Stable Blue Phosphorescent Tetradentate Platinum(II) Complexes as Strong Photo‐Reductant

Abstract

Strong photo-reductants have applications in photo-redox organic synthesis involving reductive activation of C-X(halide) and C=O bonds. We report herein air-stable Pt complexes supported by tetradentate bis(phenolate-NHC) ligands having peripheral electron-donating N-carbazolyl groups. Photo-physical, electrochemical, and computational studies reveal that the presence of N-carbazolyl groups enhances the light absorption and redox reversibility because of its involvement into the frontier MOs in both ground and excited states, making the complexes robust strong photo-reductant with E([Pt] *) over -2.6 V vs. Cp Fe . The one-electron reduced [Pt] species are stronger reductants with E ([Pt] ) up to -3.1 V vs. Cp Fe . By virtue of the strong reducing nature of these species generated upon light excitation, they can be used in light-driven reductive coupling of carbonyl compounds and reductive debromination of a wide range of unactivated aryl bromides.

Air‐Stable Blue Phosphorescent Tetradentate Platinum(II) Complexes as Strong Photo‐Reductant

“…[11] In both crystal structures,t he peripheral carbazolyl groups are significantly twisted with respect to the phenolate plane.The crystal structure of 2 shows aroughly planar molecular backbone with aP t···Pt and p-p contact of approximately 3.5 in each pair of molecules ( Figure 2). Complexes 1-3 were prepared in 58-89 %y ields by ac onvenient reaction of [Pt(DMSO) 2 Cl 2 ]w ith bis(imidazolium) salts (synthesized from commercially available inexpensive materials).…”

Aryl dechlorination and defluorination with an organic super-photoreductant

“…2). [3][4][5][6][7][8][9][10][11][12][13][14][15][16]78,79 Furthermore, the reducing power of photoexcited TDAE is close to that achievable via electrochemical generation of organic radical anions and their subsequent photo-excitation (green arrows in Fig. 2).…”

“…With these optimized conditions, we began to explore the scope of the reaction, always focusing on fluorinated substrates to permit quantitative analysis by 19 F-NMR spectroscopy in presence of 1-fluoropentane as internal standard ( Table 2). The photodriven hydrodechlorination of aryl chlorides was studied on four substrates with different types of substituents ranging from electron withdrawing (1, 2) to electron donating (4). Nearly all of these reactions proceed well and give product yields about 70%.…”

“…−3.4 V vs. SCE can be estimated for the singlet excited state, which is an exceptionally high value in comparison to most known photoreductants. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, acetone is reduced at a potential of −2.84 V vs. SCE, 73 whereas benzene reduction necessitates a potential of −3.42 V vs. SCE, 74 hence photoexcited TDAE is readily able to reduce acetone, whereas benzene reduction should be much more challenging. Indeed, the fluorescence of TDAE in cyclohexane is quenched by acetone with essentially diffusion-limited kinetics (Fig.…”

“…Photochemistry has become remarkably popular, and numerous classes of chemical reactions can now be driven by visible light. 1,2 Recently, there has been significant interest in developing photosensitizers that are able to provide very high reducing power, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] in order to perform ever more thermodynamically challenging reactions. [17][18][19] At the same time, new multi-photon excitation concepts that rely on the pooling of two visible photons to access highly reducing intermediates have been developed.…”