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Title: Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts

Supramolecular mixed metal complexes combining the trimetallic chromophore [{(bpy) 2Ru(dpp)} 2Ru(dpp)] 6+ (Ru 3) with [Rh(bpy)Cl 2] + or [RhCl 2] + catalytic fragments to form [{(bpy) 2Ru(dpp)} 2Ru(dpp)RhCl 2(bpy)](PF 6) 7 (Ru 3Rh) or [{(bpy) 2Ru(dpp)} 2Ru(dpp)] 2RhCl 2(PF 6) 13 (Ru 3RhRu 3) (bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) catalyze the photochemical reduction of protons to H 2. This first example of a heptametallic Ru,Rh photocatalyst produces over 300 turnovers of H 2 upon photolysis of a solution of acetonitrile, water, triflic acid, and N,N-dimethylaniline as an electron donor. Conversely, the tetrametallic Ru 3Rh produces only 40 turnovers of H 2 due to differences in the excited state properties and nature of the catalysts upon reduction as ascertained from electrochemical data, transient absorption spectroscopy, and flash-quench experiments. And while the lowest unoccupied molecular orbital of Ru 3Rh is localized on a bridging ligand, it is Rh-centered in Ru 3RhRu 3 facilitating electron collection at Rh in the excited state and reductively quenched state. The Ru → Rh charge separated state of Ru 3RhRu 3 is endergonic with respect to the emissive Ru → dpp 3MLCT excited and cannot be formed by static electron transfer quenching of themore » 3MLCT state. Instead, a mechanism of subnanosecond charge separation from high lying states is proposed. Multiple reductions of Ru 3 and Ru 3Rh using sodium amalgam were carried out to compare UV–vis absorption spectra of reduced species and to evaluate the stability of highly reduced complexes. Furthermore, the Ru 3 and Ru 3Rh can be reduced by 10 and 13 electrons, respectively, to final states with all bridging ligands doubly reduced and all bpy ligands singly reduced.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [2]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division; Virginia Polytechnic Inst. Blacksburg, VA (United States). Dept. of Chemistry
Publication Date:
Report Number(s):
BNL-114001-2017-JA; BNL-114146-2017-JA
Journal ID: ISSN 0002-7863; R&D Project: CO026; KC0304030; TRN: US1702325
Grant/Contract Number:
SC0012704; FG02-05ER15751
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 23; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1366355
Alternate Identifier(s):
OSTI ID: 1376171

Manbeck, Gerald F., Fujita, Etsuko, and Brewer, Karen J.. Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts. United States: N. p., Web. doi:10.1021/jacs.7b02142.
Manbeck, Gerald F., Fujita, Etsuko, & Brewer, Karen J.. Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts. United States. doi:10.1021/jacs.7b02142.
Manbeck, Gerald F., Fujita, Etsuko, and Brewer, Karen J.. 2017. "Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts". United States. doi:10.1021/jacs.7b02142. https://www.osti.gov/servlets/purl/1366355.
@article{osti_1366355,
title = {Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts},
author = {Manbeck, Gerald F. and Fujita, Etsuko and Brewer, Karen J.},
abstractNote = {Supramolecular mixed metal complexes combining the trimetallic chromophore [{(bpy)2Ru(dpp)}2Ru(dpp)]6+ (Ru3) with [Rh(bpy)Cl2]+ or [RhCl2]+ catalytic fragments to form [{(bpy)2Ru(dpp)}2Ru(dpp)RhCl2(bpy)](PF6)7 (Ru3Rh) or [{(bpy)2Ru(dpp)}2Ru(dpp)]2RhCl2(PF6)13 (Ru3RhRu3) (bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) catalyze the photochemical reduction of protons to H2. This first example of a heptametallic Ru,Rh photocatalyst produces over 300 turnovers of H2 upon photolysis of a solution of acetonitrile, water, triflic acid, and N,N-dimethylaniline as an electron donor. Conversely, the tetrametallic Ru3Rh produces only 40 turnovers of H2 due to differences in the excited state properties and nature of the catalysts upon reduction as ascertained from electrochemical data, transient absorption spectroscopy, and flash-quench experiments. And while the lowest unoccupied molecular orbital of Ru3Rh is localized on a bridging ligand, it is Rh-centered in Ru3RhRu3 facilitating electron collection at Rh in the excited state and reductively quenched state. The Ru → Rh charge separated state of Ru3RhRu3 is endergonic with respect to the emissive Ru → dpp 3MLCT excited and cannot be formed by static electron transfer quenching of the 3MLCT state. Instead, a mechanism of subnanosecond charge separation from high lying states is proposed. Multiple reductions of Ru3 and Ru3Rh using sodium amalgam were carried out to compare UV–vis absorption spectra of reduced species and to evaluate the stability of highly reduced complexes. Furthermore, the Ru3 and Ru3Rh can be reduced by 10 and 13 electrons, respectively, to final states with all bridging ligands doubly reduced and all bpy ligands singly reduced.},
doi = {10.1021/jacs.7b02142},
journal = {Journal of the American Chemical Society},
number = 23,
volume = 139,
place = {United States},
year = {2017},
month = {6}
}