Structure Function Relationships in Ruthenium Carbon Dioxide Reduction Catalysts with CNC Pincers Containing Donor Groups

Das, Sanjit; Nugegoda, Dinesh; Qu, Fengrui; Boudreaux, Chance M.; Burrow, Phillip E.; Figgins, Matthew T.; Lamb, Robert W.; Webster, Cynthia; Delcamp, Jared H.; Papish, Elizabeth T.

doi:10.1002/ejic.202000444

Cited by 15 publications

(12 citation statements)

References 69 publications

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“…Changes in the current passed under each atmosphere were analyzed as a ratio (i cat /i p ) where the current of the reduction peak under CO 2 is divided by the current of the reduction peak under N 2 . 26 Each cobalt complex studied herein had a reduction peak more positive than fac-Ir(ppy) 3 (−2.61 V vs Fc + /Fc) indicating thermodynamically downhill electron transfer from the reduced photosensitizer to the catalyst (Table 4 and Figure 5). 27 Assuming a pK a value of 18.5 for protonated triethylamine (the strongest acid in the photocatalysis conditions below) in acetonitrile 60,61 and a standard reduction potential of CO 2 in MeCN at −0.12 V vs Fc + /Fc (ferrocenium/ferrocene), 62 then the reduction potential of CO 2 under the photocatalysis conditions is −1.21 V vs Fc + /Fc (Figure 5).…”

Section: ■ Results and Discussionmentioning

confidence: 86%

“…In contrast to L1 complexes, the methoxy derivative with PPh 3 coordinated L2 complex ( 2 PPh3 ) showed significantly less CO production (TON = 26) vs the unsubstituted analogue 1 PPh3 (TON = 199). Thus, the methoxy group is deactivating for these Co(I) complexes which is in contrast to the catalytic trends for these same ligands bound to Ru(II) or with pendatentate Co(II) complexes (e.g., Lit-4 and Lit-3 , respectively, Figure , TON: OMe > H). ,,,, This suggests different ligand design trends may be necessary for optimal low-valent Co(I) catalysts in the PCO 2 RR.…”

Section: Resultsmentioning

confidence: 89%

“…Cyclic voltammetry (CV) experiments with each complex under N 2 , under CO 2 , and CO 2 after a rinse test for homogeneity were conducted (Figures S37–S43). Changes in the current passed under each atmosphere were analyzed as a ratio ( i cat / i p ) where the current of the reduction peak under CO 2 is divided by the current of the reduction peak under N 2 . Each cobalt complex studied herein had a reduction peak more positive than fac -Ir(ppy) 3 (−2.61 V vs Fc + /Fc) indicating thermodynamically downhill electron transfer from the reduced photosensitizer to the catalyst (Table and Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…Proton reduction to form H 2 ( E ° = −0.414 V) is often competitive with these processes. , Thus, product selectivity among these commonly formed products (CO, HCO 2 H, and H 2 ) is an important consideration. − Homogeneous catalysis can often address this selectivity challenge by precise control of the catalyst structure and uniform control of reaction conditions . Targeting CO can lead to a viable solution for fuel production via the well-established Fischer–Tropsch process (FTP) and allows for simple gas phase separation of the CO product from the reduction reaction solution. , …”

Section: Introductionmentioning

confidence: 99%

“…37 Similarly, in Ru(II) CNC pincer complexes methoxy groups led to substantial improvements in PCO 2 RR with catalyst Lit-4 relative to the analogue bearing an H in place of methoxy (TON = 1006 vs 120, respectively). 17,18,26,27 These differences were attributed to more favorable reduction potentials with methoxy groups for electron transfer from the reduced photosensitizer (PS) to the catalyst. 17 The strong donor properties of the NHC rings 38,39 combined with an electronically tunable pyridine ring presents a unique opportunity for catalysis with cobalt.…”

Section: ■ Introductionmentioning

confidence: 99%

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Low-Valent Cobalt(I) CNC Pincer Complexes as Catalysts for Light-Driven Carbon Dioxide Reduction

et al. 2022

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Durable catalysts based on abundant metals are needed for the photocatalytic CO2 reduction reaction (PCO2RR). Thus, we synthesized a series of low-valent cobalt(I) complexes, [(CNC)Co(CO)2]+[Co(CO)4]−, with H (1Co‑ ) or OMe (2Co‑ ) in the 4-position of the pyridyl N donor group (where CNC = L1 and L2 from double deprotonation of the [CNC]2+ preligands L1(HOTf)2 = 1,1′-(pyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium) ditriflate and L2(HOTf)2 = 1,1′-(4-methoxypyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium) ditriflate). Anion exchange for [BArF24]− (tetrakis(3,5-trifluoromethyl)phenyl)borate) produced 1 and 2 and phosphine substitution produced 1PMe3 , 1PPh3 , and 2PPh3 complexes with the structure [(CNC)Co(CO)(PR′3)]+[BArF24]−. In 1DPPP , the DPPP ligand bridges two Co(I) centers (DPPP = 1,3-bis(diphenylphosphino)propane). All complexes were fully characterized, and electrochemical measurements suggest that for most of the phosphine complexes, CO2 binding by the complex occurs prior to reduction due to a vacant coordination site. Intriguingly, the introduction of a phosphine ligand resulted in a geometry change from trigonal bipyramidal to square pyramidal which correlates to preassociation of CO2 to the complex and higher reactivity in the PCO2RR. Complexes 1, 1PMe3 , 1PPh3 , 1DPPP , 2, 2PPh3 , and Na[Co(CO)4] are PCO2RR catalysts with a methoxy substituent deactivating and a phosphine ligand activating. With monodentate phosphines, catalyst 1PPh3 (1 μM) had the highest turnover frequency (TOFM = 3.9 h–1) and turnover number (TON = 199). The dinuclear 1DPPP complex was the most active and robust catalyst with TON = 278 and TOF = 21.1 h–1 at 1 μM loading. Under dilute conditions (1 nM), 1PPh3 produced up to 36,000 TON with TOF = ∼800 h–1 over 6 days, which shows that this is a durable molecular catalyst acting with fast rates in the PCO2RR. Thus, stabilizing low-valent cobalt can offer a unique entry point to highly active PCO2RR catalysts. While cobalt(I) has been proposed as a catalytic species, catalysts that start from Co(I) have not been made previously and the use of phosphine co-ligands has allowed these catalysts to achieve high activity.

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Section: ■ Results and Discussionmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Low-Valent Cobalt(I) CNC Pincer Complexes as Catalysts for Light-Driven Carbon Dioxide Reduction

et al. 2022

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Sensitized and Self‐Sensitized Photocatalytic Carbon Dioxide Reduction Under Visible Light with Ruthenium Catalysts Shows Enhancements with More Conjugated Pincer Ligands

et al. 2022

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A new method to synthesize complexes of the type [(CNC)Ru II -(NN)L] n + has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L = bromide or acetonitrile, and n = 1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studied via cyclic voltammetry under both N 2 and CO 2 atmospheres. Photocatalytic reduction of CO 2 to CO was performed using these complexes both in the presence (sensitized) and absence (self-sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self-sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self-sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self-sensitized photocatalysis requires a diimine ligand for CO 2 reduction with catalyst 2 ACN being the most active catalyst in this series with TON = 85 and TOF = 22 h À 1 with an electron donating 4,4'-dimethyl-2,2'-bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer.

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Design, Synthesis and Evaluation of Photophysical and Biological Properties of Tetrafluoroacridine

Kumar,

Yadav,

Indari

et al. 2024

ChemistrySelect

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Abstract1,4,5,8‐Tetrafluoroacridine was successfully synthesized from 1,4,5,8‐tetrafluoroacridone through transfer hydrogenation using an in‐house ruthenium pincer catalyst followed by in situ dehydration. The synthetic protocol involves the copper‐catalyzed coupling of 2‐amino‐3,6‐difluorobenzoic acid 1 and 1,4‐difluoro‐2‐iodobenzene 2 to obtain 3 followed by cyclization using polyphosphoric acid to get the 1,4,5,8‐tetrafluoroacridone 4. Common synthetic strategies for converting 4 to the 1,4,5,8‐tetrafluoroacridine 5 were unsuccessful and the transfer hydrogenation approach proved to be most fruitful. 1,4,5,8‐Tetrafluoroacridone 4 can be N‐methylated to give 9. The investigation into the photophysical properties of 4, 5, and 9 revealed that the average photoluminescence (PL) lifetime of the acridine derivatives was longer in the aqueous medium than in ethanol and methanol, indicating the influence of the solvent environment on the excited‐state dynamics. To assess their potential therapeutic applications, the cytotoxic activity of these compounds was evaluated against AGS and IMR‐32 cells, and compound 9 showed significant activity. The addition of methyl group to the acridone was found helpful in enhancing the solubility and biological activity.

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Structure Function Relationships in Ruthenium Carbon Dioxide Reduction Catalysts with CNC Pincers Containing Donor Groups

Cited by 15 publications

References 69 publications

Low-Valent Cobalt(I) CNC Pincer Complexes as Catalysts for Light-Driven Carbon Dioxide Reduction

Low-Valent Cobalt(I) CNC Pincer Complexes as Catalysts for Light-Driven Carbon Dioxide Reduction

Sensitized and Self‐Sensitized Photocatalytic Carbon Dioxide Reduction Under Visible Light with Ruthenium Catalysts Shows Enhancements with More Conjugated Pincer Ligands

Design, Synthesis and Evaluation of Photophysical and Biological Properties of Tetrafluoroacridine

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