A new Ru^IIRh^III bimetallic with a single Rh–Cl bond as a supramolecular photocatalyst for proton reduction

Abstract

A new Ru(II)Rh(III) structural motif [(bpy)2Ru(dpp)RhCl(tpy)](4+) with one halide on the Rh(III) center demonstrates light-driven proton reduction ability, establishing that two halide ligands are not mandatory despite all prior systems containing a cis-RhCl2 catalytic site. This new design provides a novel approach to modulate Rh(III) redox behavior and catalytic activity with insight into catalytic intermediates.

Supramolecular Photocatalyst with a Rh(III)-Complex Catalyst Unit for CO2 Reduction

“…Several homogeneous photocatalytic systems have been reported for the selective formation of HCOOH from CO 2 , such as oligo­( p -phenylenes), a mixed system of phenazine and Co-cyclam, a mixed system with [Ru­(bpy) 2 (CO) 2 ] 2+ (bpy = 2,2′-bipyridine) as a catalyst and [Ru­(bpy) 3 ] 2+ as a photosensitizer, and as supramolecular photocatalysts containing Ru-catalyst and Ru-photosensitizer (PS) units . By contrast, Rh complexes have been reported as efficient H 2 evolution catalysts in various photocatalytic systems, − though there is no report regarding a photochemical system using a Rh-complex catalyst for CO 2 reduction. This study reports on the first supramolecular photocatalyst consisting of [Rh­(BL)­(Cp*)­Cl] + as a catalyst with [Ru­(dmb) 2 (BL)] 2+ as a photosensitizer unit ( Ru–Rh : BL = 1,2-bis­(4′-methyl­[2,2′-bipyridin]-4-yl)­ethane, Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, dmb = 4,4′-dimethyl-2,2′-bipyridine) (Figure ) for CO 2 reduction giving HCOOH as the main product, whereas the mixed system using the corresponding mononuclear complexes, such as [Rh­(dmb)­(Cp*)­Cl] + ( Rh ) and [Ru­(dmb) 3 ] 2+ ( Ru ), produces H 2 as the main product.…”

Increased photocatalytic activity in Ru(II),Rh(III) supramolecular bimetallic complexes with terminal ligand substitution

“…The new Rh monometallic complex was synthesized using a similar procedure reported for [Rh(bpy)Cl 3 (DMF)] (DMF = N,Ndimethylformamide) [34]. RhCl 3 ÁxH 2 O (0.20 g, 0.75 mmol) and 4,4 0 -dimethyl-2,2 0 -bipyridine (0.017 g, 0.92 mmol) were heated at 60°C in 2 mL DMF for 2 h with rapid stirring.…”

“…The judicious choice of molecular components throughout the Ru(II),Rh(III) bimetallic architecture dictates photocatalytic activity towards H 2 O reduction through a careful balance of sterics, electronics, light absorption, and ion pairing throughout the photocatalytic cycle [30][31][32][33][34]. The bimetallic complexes [(Ph 2 phen) 2 Ru(dpp)RhX 2 (Ph 2 phen)] 3+ (X = Cl À or Br À ) represent a systematic study undertaken to determine the influence that the r-donating ability and degree of ion pairing imparted by the monodentate halide ligands have on the photocatalytic H 2 O reduction activity [30].…”

Probing the Diphosphine Ligand’s Impact within Heteroleptic, Visible-Light-Absorbing Cu(I) Photosensitizers for Solar Fuels Production

“…Our Cu­(I)/Rh­(III) PS/CAT photosystem is proposed to function via reduction quenching of the [Cu­(Xantphos)­(biq)] +, * ES by intermolecular electron transfer from a sacrificial electron donor (e.g., N,N′ -dimethylaniline, DMA) to produce [Cu­(Xantphos)­(biq – )], which possesses sufficient reducing potential ( E 1/2 (biq 0/– ) = −1.57 V) to undergo GS electron transfer to cis -[Rh­(Me 2 bpy) 2 ­Cl 2 ] + CAT ( E p c (Rh III/II/I ) = −1.46 V). Following photoinduced multielectron reduction to produce Rh­(I) CAT (either by 2Rh­(II) disproportionation − or sequential electron transfer steps , ) and subsequent protonation, catalytic amounts of H 2 were observed which increased linearly up to 1 h . In an effort to extend light absorption further into the visible, the Cu­(I) PS was modified to include electron-withdrawing substituents on the biq diimine ligand, [Cu­(Xantphos)­(dmebiq)] + (dmebiq = 2,2′-biquinoline-4,4′-dimethyl ester), which produced substoichiometric levels of H 2 under the same photolysis conditions (λ irr = 447.5 nm).…”