Performance of Enhanced DuBois Type Water Reduction Catalysts (WRC) in Artificial Photosynthesis - Effects of Various Proton Relays during Catalysis $(document).ready(function() { if (!$("html").hasClass("ie8")) { $.ajax({ url: "https://crossmark-cdn.crossref.org/widget/v2.0/widget.js", dataType: "script", cache: true }).done(function() { $(".crossmark-button").addClass("visible"); }); } });

Abstract

Inspired by natural photosynthesis, features like proton relays are integrated into water reduction catalysts (WRC) for fertile production of hydrogen. Especially DuBois et al. showed the crucial influence of these relays, mostly pendant amine functions. In this work catalysts are presented containing innovative diphosphinoamine ligands: [M(II)Cl₂(PNP-C1)], [M(II)(MeCN)₂(PNP-C1)]²⁺, [M(II)(PNP-C1)₂]²⁺ , and [M(II)Cl(PNP-C2)]⁺ (M = Pt²⁺, Pd²⁺, Ni²⁺, Co²⁺; PNP-C1 = N,N-bis{(di(2-methoxyphenyl)phosphanyl)-methyl}-N-alkylamine, PNP-C2 = N,N-bis{(di(2-methoxyphenyl)phosphanyl)ethyl}-N-alkylamine and alkyl = Me, Et, iso-Pr, Bz). Synthetic strategies including ¹H-, ¹³C-, and ³¹P-NMR analysis, mass spectroscopy and single crystal X-ray diffractometry (XRD) are covered as well as catalytic effects of different pendant amines, auxiliary methoxy coordination sites and an enlarged ligand backbone are investigated during irradiation experiments and gas chromatography. Moreover two very different catalytic cycles due to different ligand backbones are proposed based on density functional theory (DFT) calculations based on XRD data in vacuo and solvent environment. PNP-C1 shows a classical proton relay, whereas PNP-C2 allows an additional coordination of nitrogen and acts optionally like a pincer. Subsequently, new insights into efficiency and stability-increasing influences like proton relays in general, their number per metal centre, an enlarged ligand backbone and solvato instead of halogenido complexes are conclusively gained, culminating in the enhancement of DuBois et al. and recently self-made WRCs. The turn-over number (TON) related to the single site of cost-efficient nickel WRCs is increased from 11.4 to 637, whereas a corresponding palladium catalyst produces even 2289.