Diversifying Metal–Ligand Cooperative Catalysis in Semi‐Synthetic [Mn]‐Hydrogenases

Abstract

The reconstitution of [Mn]-hydrogenases using as eries of Mn I complexes is described. These complexes are designed to have an internal base or pro-base that may participate in metal-ligand cooperative catalysis or have no internal base or pro-base.Only Mn I complexes with an internal base or pro-base are active for H 2 activation;o nly [Mn]hydrogenases incorporating such complexes are active for hydrogenase reactions.These results confirm the essential role of metal-ligand cooperation for H 2 activation by the Mn I complexes alone and by [Mn]-hydrogenases.O wing to the nature and position of the internal base or pro-base,the mode of metal-ligand cooperation in two active [Mn]-hydrogenases is different from that of the native [Fe]-hydrogenase.O ne [Mn]-hydrogenase has the highest specific activity of semisynthetic [Mn]-and [Fe]-hydrogenases.T his work demonstrates reconstitution of active artificial hydrogenases using synthetic complexes differing greatly from the native active site.

A Protic Mn(I) Complex Based on a Naphthyridine-N-oxide Scaffold: Protonation/Deprotonation Studies and Catalytic Applications for Alkylation of Ketones

“…In addition, two doublets for pyridyl N-oxide ring protons appear at δ 7. 64 Deprotonation of 1 with one equivalent of KOH in the presence of 18-crown-6 ether (18-C-6) in tetrahydrofuran (THF) at room temperature for 4 h afforded [18-C-6-K•2] in 80% yield (Scheme 3).…”

“…For examples, Shvo’s catalyst exhibits metal–ligand cooperativity (MLC) through the interconversion between hydroxycyclopentadienyl (η 5 -anionic) and cyclopentadienone (η 4 -neutral) units to facilitate hydrogen transfer reactions. − Fujita and Yamaguchi introduced a range of half-sandwich complexes bearing the hydroxy functionality on 2,2′-bipyridine and 2-phenylpyridine unit to examine their catalytic efficacy toward alcohol oxidation and CO 2 hydrogenation. − Himeda and co-workers exploited bipyrimidine and azole-pyridine/pyrimidine scaffolds for dehydrogenation/hydrogenation reactions. ,− A switchable hydrogenation catalyst bearing uracil-mesoionic carbene (MIC) moiety capable of exhibiting lactam–lactim interconversion was developed by Choudhury’s group . The diversity of the molecular platforms, which includes NNN-, NPN-, PNN-pincer, and nonannulated/annulated NHC-pyridine units, featuring a PRU is widely evident in the literature. ,− While significant progress has been made on designing hydroxy-functionalized protic catalysts with late transition metals, earth-abundant 3d metal-based compounds are relatively less explored. − Some representative examples are collected in Scheme . A Cp*Co­(III) complex with hydroxy functionality on bipyridine moiety, developed by Himeda and Fujita, has been used for hydrogenation of carbon dioxide in aqueous media .…”

Diversifying Metal–Ligand Cooperative Catalysis in Semi‐Synthetic [Mn]‐Hydrogenases

“…X-ray crystallography confirms 1b-e and 3(18-crown-6) as Mn I tetra(carbonyl) complexes ligated by ab identate N-C ligand derived from pyridine (Figure 2B). [8] Thecoordination geometry of Mn ions is best described as pseudo-octahedral. TheN -C ligand forms an on-planar five-membered metallocycle with the Mn ion.…”

Current State of [Fe]‐Hydrogenase and Its Biomimetic Models

“…31 with a weak tertial amide internal base (pKa 1.6–3.6) gave low activity while activity of 29 with a stronger 2‐O − (pKa 8.8±0.1) group was obviously higher. When a proper strong base (KO t Bu) was used, deprotonated form of 30 containing an enolate basic site (pKa 13.7±0.1) showed significantly higher activity (1:2.2, Figure 12b) [23t] …”

“… Mn model complexes reported by Hu and coworkers: (a) H 2 /D 2 exchange reaction and hydrogenation reaction by complex 28 [23s] . (b) Mn‐based complexes 29 – 32 and their corresponding HD/H 2 ratios [23t] . (c) Complex 33 and some selected hydrogenation products [61] .…”