We report the design of a bifunctional metal–organic layer (MOL), Hf12‐Ru‐Co, composed of [Ru(DBB)(bpy)2]2+[DBB‐Ru, DBB=4,4′‐di(4‐benzoato)‐2,2′‐bipyridine; bpy=2,2′‐bipyridine] connecting ligand as a photosensitizer and Co(dmgH)2(PPA)Cl (PPA‐Co, dmgH=dimethylglyoxime; PPA=4‐pyridinepropionic acid) on the Hf12secondary building unit (SBU) as a hydrogen‐transfer catalyst. Hf12‐Ru‐Co efficiently catalyzed acceptorless dehydrogenation of indolines and tetrahydroquinolines to afford indoles and quinolones. We extended this strategy to prepare Hf12‐Ru‐Co‐OTf MOL with a [Ru(DBB)(bpy)2]2+photosensitizer and Hf12SBU capped with triflate as strong Lewis acids and PPA‐Co as a hydrogen transfer catalyst. With three synergistic active sites, Hf12‐Ru‐Co‐OTf competently catalyzed dehydrogenative tandem transformations of indolines with alkenes or aldehydes to afford 3‐alkylindoles and bisindolylmethanes with turnover numbers of up to 500 and 460, respectively, illustrating the potential use of MOLs in constructing novel multifunctional heterogeneous catalysts.
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Enantioselective decarboxylative alkylation using synergistic photoenzymatic catalysis
Photoenzymatic catalysts are attractive for stereoselective radical reactions
because the transformation occurs within tunable enzyme active sites. When
using flavoproteins for non-natural photoenzymatic reactions, reductive
mechanisms are often used for radical initiation. Oxidative mechanisms
for radical formation would enable abundant functional groups, such as
amines and carboxylic acids, to serve as radical precursors. However, excited
state flavin is short-lived in many proteins because of rapid quenching by
the protein scaffold. Here we report that adding an exogenous Ru(bpy)3
2+
cofactor to flavin-dependent ‘ene’-reductases enables the redox-neutral
decarboxylative coupling of amino acids with vinylpyridines with high yield
and enantioselectivity. Additionally, stereo-complementary enzymes are
found to provide access to both enantiomers of the product. Mechanistic
studies indicate that Ru(bpy)3 2+ binds to the protein, helping to localize
radical formation to the enzyme’s active site. This work expands the types
of transformation that can be rendered asymmetric using photoenzymatic
catalysis and provides an intriguing mechanism of radical initiation.
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- Award ID(s):
- 2342328
- NSF-PAR ID:
- 10507429
- Publisher / Repository:
- Nature
- Date Published:
- Journal Name:
- Nature Catalysis
- Volume:
- 7
- Issue:
- 1
- ISSN:
- 2520-1158
- Page Range / eLocation ID:
- 35 to 42
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract We report the design of a bifunctional metal–organic layer (MOL), Hf12‐Ru‐Co, composed of [Ru(DBB)(bpy)2]2+[DBB‐Ru, DBB=4,4′‐di(4‐benzoato)‐2,2′‐bipyridine; bpy=2,2′‐bipyridine] connecting ligand as a photosensitizer and Co(dmgH)2(PPA)Cl (PPA‐Co, dmgH=dimethylglyoxime; PPA=4‐pyridinepropionic acid) on the Hf12secondary building unit (SBU) as a hydrogen‐transfer catalyst. Hf12‐Ru‐Co efficiently catalyzed acceptorless dehydrogenation of indolines and tetrahydroquinolines to afford indoles and quinolones. We extended this strategy to prepare Hf12‐Ru‐Co‐OTf MOL with a [Ru(DBB)(bpy)2]2+photosensitizer and Hf12SBU capped with triflate as strong Lewis acids and PPA‐Co as a hydrogen transfer catalyst. With three synergistic active sites, Hf12‐Ru‐Co‐OTf competently catalyzed dehydrogenative tandem transformations of indolines with alkenes or aldehydes to afford 3‐alkylindoles and bisindolylmethanes with turnover numbers of up to 500 and 460, respectively, illustrating the potential use of MOLs in constructing novel multifunctional heterogeneous catalysts.
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null (Ed.)4,5-diazafluorene (daf) and 9,9’-dimethyl-4,5-diazafluorene (Me2daf) are structurally similar to the important ligand 2,2’-bipyridine (bpy), but significantly less is known about the redox and spectroscopic properties of metal complexes containing Me2daf as a ligand than those containing bpy. New complexes Mn(CO)3Br(daf) (2), Mn(CO)3Br(Me2daf) (3), and [Ru(Me2daf)3](PF6)2 (5) have been prepared and fully characterized to understand the influence of the Me2daf framework on their chemical and electrochemical properties. Structural data for 2, 3, and 5 from single-crystal X-ray diffraction analysis reveal a distinctive widening of the daf and Me2daf chelate angles in comparison to the analogous Mn(CO)3(bpy)Br (1) and [Ru(bpy)3]2+ (4) complexes. Electronic absorption data for these complexes confirm the electronic similarity of daf, Me2daf, and bpy, as spectra are dominated in each case by metal-to-ligand charge transfer bands in the visible region. However, the electrochemical properties of 2, 3, and 5 reveal that the redox-active Me2daf framework in 3 and 5 undergoes reduction at a slightly more negative potential than that of bpy in 1 and 4. Taken together, the results indicate that Me2daf could be useful for preparation of a variety of new redox-active compounds, as it retains the useful redox-active nature of bpy but lacks the acidic, benzylic C–H bonds that can induce secondary reactivity in complexes bearing daf.more » « less
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Understanding relationships among multimodal data extracted from a smartphone-based electrochemiluminescence (ECL) sensor is crucial for the development of low-cost point-of-care diagnostic devices. In this work, artificial intelligence (AI) algorithms such as random forest (RF) and feedforward neural network (FNN) are used to quantitatively investigate the relationships between the concentration of Ru ( bpy ) 3 2 + luminophore and its experimentally measured ECL and electrochemical data. A smartphone-based ECL sensor with Ru ( bpy ) 3 2 + /TPrA was developed using disposable screen-printed carbon electrodes. ECL images and amperograms were simultaneously obtained following 1.2-V voltage application. These multimodal data were analyzed by RF and FNN algorithms, which allowed the prediction of Ru ( bpy ) 3 2 + concentration using multiple key features. High correlation (0.99 and 0.96 for RF and FNN, respectively) between actual and predicted values was achieved in the detection range between 0.02 µM and 2.5 µM. The AI approaches using RF and FNN were capable of directly inferring the concentration of Ru ( bpy ) 3 2 + using easily observable key features. The results demonstrate that data-driven AI algorithms are effective in analyzing the multimodal ECL sensor data. Therefore, these AI algorithms can be an essential part of the modeling arsenal with successful application in ECL sensor data modeling.more » « less
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We report the excited-state behavior of a structurally simple bis -sulfoxide complex, cis -S,S-[Ru(bpy) 2 (dmso) 2 ] 2+ , as investigated by femtosecond pump–probe spectroscopy. The results reveal that a single photon prompts phototriggered isomerization of one or both dmso ligands to yield a mixture of cis -S,O-[Ru(bpy) 2 (dmso) 2 ] 2+ and cis -O,O-[Ru(bpy) 2 (dmso) 2 ] 2+ . The quantum yields of isomerization of each product and relative product distribution are dependent upon the excitation wavelength, with longer wavelengths favoring the double isomerization product, cis -O,O-[Ru(bpy) 2 (dmso) 2 ] 2+ . Transient absorption measurements on cis -O,O-[Ru(bpy) 2 (dmso) 2 ] 2+ do not reveal an excited-state isomerization pathway to produce either the S,O or S,S isomers. Femtosecond pulse shaping experiments reveal no change in the product distribution. Pump–repump–probe transient absorption spectroscopy of cis -S,S-[Ru(bpy) 2 (dmso) 2 ] 2+ shows that a pump–repump time delay of 3 ps dramatically alters the S,O : O,O product ratio; pump–repump–probe transient absorption spectroscopy of cis -O,O-[Ru(bpy) 2 (dmso) 2 ] 2+ with a time delay of 3 ps uncovers an excited-state isomerization pathway to produce the S,O isomer. In conjunction with low-temperature steady-state emission spectroscopy, these results are interpreted in the context of an excited-state bifurcating pathway, in which the isomerization product distribution is determined not by thermodynamics, but rather as a dynamics driven reaction.more » « less
