This study confirms the hypothesis that [MnCl3(OPPh3)2] (1) and acetonitrile-solvated MnCl3 (i.e., [MnCl3(MeCN) x ]) can be used as synthons to prepare Mn­(III) chloride complexes with facially coordinating ligands. This was achieved through the preparation and characterization of six new {MnIIICl} complexes using anionic ligands TpH (tris­(pyrazolyl)­borate) and TpMe (tris­(3,5-dimethylpyrazolyl)­borate). The MnIII–chloride dissociation and association equilibria (K eq) and MnIII/II reduction potentials were quantified in DCM. These two thermochemical parameters (K eq and E 1/2), in addition to the known Cl-atom reduction potential in DCM, enabled the quantification of the Mn–Cl bond dissociation (homolysis) free energy of 21 and 23 ± 7 kcal/mol at room temperature for R = H and Me, respectively. These are in reasonable agreement with the bond dissociation free energy (BDFEM–Cl) of 34 ± 6 kcal/mol calculated using density functional theory. The BDFEM–Cl of 1 was also calculated (25 ± 6 kcal/mol). These energies were used in predictive C–H bond reactivity.

Herein, we report a new tripodal tris‐benzimidazole ligand (Tbim) that structurally mimics the 3‐His coordination environment of certain nonheme mononuclear iron oxygenases. The coordination chemistry of Tbim was explored with iron(II) revealing a diverse set of coordination modes. The aerobic oxidation of biomimetic model substrate diethyl‐2‐phenylmalonate was studied using the Tbim−Fe and Fe(OTf)2.

Metal-ligand cooperativity (MLC) involving reversible aromatization/dearomatization of pyridine-derived pincer ligands is considered important in acceptorless (de)hydrogenation for dihydrogen generation and storage. Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often leads to dearomatized moieties. Thus, we were surprised to find an aromatized kappa-3-NCP binding mode in [{LutP`}Ru(CO)(H)(PPh3)] (2) upon dehydrohalogenation of the lutidine-derived PN/P complex [{LutP}Ru(CO)(Cl)(H)(PPh3)] (1) with KOtBu. The reaction of H2 with 2 results in formation of a cis-dihydride [{LutP}Ru(CO)(H)2(PPh3)] (3) and labeling studies confirm cooperative metal-ligand activation. 3 exhibits reversible photochemistry that we leveraged to demonstrate a unique strategy for unsensitized single-component photocatalytic H2 production via acceptorless alcohol dehydrogenation. Although labeling studies implicate MLC processes during the photocatalytic reaction, they may be off-path intermediates, emphasizing that aromatization/dearomatization may not be necessary for acceptorless transformations.

Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often leads to dearomatized moieties, such as in Milstein’s PNN-Ru­(CO)­(Cl)­(H) (1Py) catalyst. Thus, we were surprised to find an aromatized κ3-N,C,P binding mode in the lutidine-derived bidentate analogue [{LutP′}­Ru­(CO)­(H)­(PPh3)] (2), instead of a dearomatized compound, upon dehydrohalogenation of [{LutP}­Ru­(CO)­(Cl)­(H)­(PPh3)] (1). The reaction of 2 with H2 results in the formation of the cis-dihydride [{LutP}­Ru­(CO)­(H)2(PPh3)] (3), and labeling studies confirm cooperative metal–ligand activation. 3 exhibits reversible photoisomerization, forming another cis-dihydride isomer (4) upon irradiation. The lability of 4 toward ligand substitution was leveraged to demonstrate photoenhanced H2 production via acceptorless alcohol dehydrogenation. Labeling studies implicate metal–ligand cooperative (MLC) processes during the photocatalytic reaction, but they appear to be off-path processes on the basis of our mechanistic study of the system. The latter emphasizes that aromatization/dearomatization may not be necessary for acceptorless transformations, which is generally consistent with several contemporary studies on analogous Ru catalysts.

Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often lead to dearomatized moieties, such as in Milstein's PNN-Ru(CO)(Cl)(H) (1Py) catalyst. Thus, we were surprised to find an aromatized k 3 -N,C,P binding mode in the lutidine-derived bidentate analog [{LutP`}Ru(CO)(H)(PPh3)] (2), instead of a dearomatized compound, upon dehydrohalogenation of [{LutP}Ru(CO)(Cl)(H)(PPh3)] (1). The reaction of 2 with H2 results in formation of a cis-dihydride [{LutP}Ru(CO)(H)2( PPh3)] (3) and labeling studies confirm cooperative metal-ligand activation. 3 exhibits reversible photochemistry, forming another cis-dihydride isomer (4). The lability of 4 toward ligand substitution was leveraged to demonstrate a unique example of photoswitchable H2 production via acceptorless alcohol dehydrogenation. Labeling studies implicate metal-ligand cooperative (MLC) processes during the photocatalytic reaction, but they appear to be off-path processes based on our mechanistic study of the system. The latter emphasizes that aromatization/dearomatization may not be necessary for acceptorless transformations, which is generally consistent with several contemporary studies on analogous Ru catalysts.

No abstract

Metal-ligand cooperativity (MLC) involving reversible aromatization/dearomatization of pyridine-derived pincer ligands is considered important in acceptorless (de)hydrogenation for dihydrogen generation and storage. Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often leads to dearomatized moieties. Thus, we were surprised to find an aromatized kappa-3-NCP binding mode in [{LutP`}Ru(CO)(H)(PPh3)] (2) upon dehydrohalogenation of the lutidine-derived PN/P complex [{LutP}Ru(CO)(Cl)(H)(PPh3)] (1) with KOtBu. The reaction of H2 with 2 results in formation of a cis-dihydride [{LutP}Ru(CO)(H)2(PPh3)] (3) and labeling studies confirm cooperative metal-ligand activation. 3 exhibits reversible photochemistry that we leveraged to demonstrate a unique strategy for unsensitized single-component photocatalytic H2 production via acceptorless alcohol dehydrogenation. Although labeling studies implicate MLC processes during the photocatalytic reaction, they may be off-path intermediates, emphasizing that aromatization/dearomatization may not be necessary for acceptorless transformations.

Dehydrohalogenation of pyridine-derived pincer ruthenium complexes often lead to dearomatized moieties, such as in Mil-stein’s PNN-Ru(CO)(Cl)(H) (1Py) catalyst. Thus, we were surprised to find an aromatized 3-N,C,P binding mode in the lutidine-derived bidentate analog [{LutP`}Ru(CO)(H)(PPh3)] (2), instead of a dearomatized compound, upon dehydrohalo-genation of [{LutP}Ru(CO)(Cl)(H)(PPh3)] (1). The reaction of 2 with H2 results in formation of a cis-dihydride [{LutP}Ru(CO)(H)2(PPh3)] (3) and labeling studies confirm cooperative metal-ligand activation. 3 exhibits reversible photo-chemistry, forming another cis-dihydride isomer (4). The lability of 4 toward ligand substitution was leveraged to demon-strate a unique example of photoswitchable H2 production via acceptorless alcohol dehydrogenation. Labeling studies impli-cate metal-ligand cooperative (MLC) processes during the photocatalytic reaction, but they appear to be off-path processes based on our mechanistic study of the system. The latter emphasizes that aromatization/dearomatization may not be neces-sary for acceptorless transformations, which is generally consistent with several contemporary studies on analogous Ru cata-lysts.