Visible Light‐Gated Organocatalysis Using a Ru^II‐Photocage

Abstract

The light‐gated organocatalysis via the release of 4‐N,N‐dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]2+ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre‐catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455 nm. The photochemical process was characterized by steady‐state irradiation and ultrafast transient absorption spectroscopy. The latter enabled the observation of the 3MLCT state and the spectral features of the penta‐coordinated intermediate [Ru(bpy)2(DMAP)]2+. The released DMAP catalyzes the acetylation of a wide range of benzyl alcohols with chemical yields of up to 99 %. Control experiments revealed unequivocally that it is the released DMAP which takes the role of the catalyst.

Metal-Mediated Organocatalysis in Water: Serendipitous Discovery of Aldol Reaction Catalyzed by the [Ru(bpy)2(nornicotine)2]2+ Complex

“…The [Ru­(bpy) 2 (Nor) 2 ] 2+ complex ( 1 ) was prepared from Ru­(bpy) 2 Cl 2 as the precursor and stepwise ligand exchange according to procedures that are reported in the literature. , The analytical characterization ( 1 H NMR, 1 H– 1 H COSY, 13 C NMR DEPT-135, 13 C NMR DEPTQ-135, 1 H– 13 C HSQC, high-resolution mass spectrometry, and FT-IR) revealed the identity and purity of the compound; see Figures S1–S7 in the Supporting Information.…”

“…In the quest for photoactivatable organocatalytic systems, , we have recently focused on the use of Ru­(II)-pyridyl complexes, which are known to release pyridine ligands on irradiation with visible light . However, when exploring the complex [Ru­(bpy) 2 (Nor) 2 ] 2+ ( 1 ; Nor = nornicotine; see structure in Scheme ) with the purpose of photoreleasing nornicotine and initiating a catalyzed aldol reaction between acetone and 4-nitrobenzaldehyde, we noted a significantly accelerated reaction without applying light irradiation.…”

Visible‐Light‐Initiated Palladium‐Catalyzed Cross‐coupling by PPh3 Uncaging from an Azobenzene Ruthenium–Arene Complex

“…[3] Such approach has also been successfully exploited for the generation of a vacant site at a metal center through ligand photo-dissociation in various catalytic transformations such as alkene isomerization, [4] and metathesis, [5] [2 + 2 + 2] cycloadditions, [6] allyl carbamate cleavage, [7] or azide-thioalkyne cycloaddition [8] (Figure 1 a). The strategy in which an organocatalyst is released from a photoactive "cage" substrate has been also explored, though only few examples involving hexylamine (thiol-Michael addition), [9] proline (aldol, Michael and Mannich reaction), [10] thiourea and squaramide (Michael addition), [11] DMAP (acetylation of alcohols) [12] and PPh 3 (aza-Morita À Baylis À Hillman reaction; [13] Figure 1 b). [14] To the best of our knowledge, the complementary approach involving photo-release of a ligand that could in turn generate an active catalytic species from an appropriate precatalyst has not been reported to date (Figure 1 c).…”

A multifunctional nanoplatform delivering carbon monoxide and a cysteine protease inhibitor to mitochondria under NIR light shows enhanced synergistic anticancer efficacy

“…6 The short in vivo retention time and rapid renal clearance of these small molecule inhibitors make them metabolically unfavorable; 7 furthermore, systemic administration of protease inhibitors may lead to a decrease in proteolytic activity in normal tissues, thereby inducing adverse effects. 8 However, this limitation can be circumvented by photocaging that uses Ru(II) polypyridyl complexes as photocages to hold bioactive compounds such as nitriles or aromatic heterocycles for controlled release upon UV, 9 visible, [10][11][12][13][14][15][16] red [17][18][19] or nearinfrared (NIR) 20,21 light irradiation, eventually realizing photoactivated chemotherapy. A photo-activatable Ru complex has been recently reported to release enzyme inhibitors for protease activity regulation under NIR light.…”