Mixed-Metal Supramolecular Complexes Coupling Phosphine-Containing Ru(II) Light Absorbers to a Reactive Pt(II) through Polyazine Bridging Ligands

Abstract

Supramolecular bimetallic Ru(II)/Pt(II) complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) and their synthons [(tpy)Ru(L)(BL)](n)()(+) (where L = Cl(-), CH(3)CN, or PEt(2)Ph; tpy = 2,2':6',2''-terpyridine; and BL = 2,2'-bipyrimidine (bpm) or 2,3-bis(2-pyridyl)pyrazine (dpp)) have been synthesized and studied by cyclic voltammetry, electronic absorption spectroscopy, mass spectral analysis, and (31)P NMR. The mixed-metal bimetallic complexes couple phosphine-containing Ru chromophores to a reactive Pt site. These complexes show how substitution of the monodentate ligand on the [(tpy)RuCl(BL)](+) synthons can tune the properties of these light absorbers (LA) and incorporate a (31)P NMR tag by addition of the PEt(2)Ph ligand. The redox potentials for the Ru(III/II) couples occur at values greater than 1.00 V versus the Ag/AgCl reference electrode and can be tuned to more positive potentials on going from Cl(-) to CH(3)CN or PEt(2)Ph (E(1/2) = 1.01, 1.55, and 1.56 V, respectively, for BL = bpm). The BL(0/-) couple at -1.03 (bpm) and -1.05 V (dpp) for [(tpy)Ru(PEt(2)Ph)(BL)](2+) shifts dramatically to more positive potentials upon the addition of the PtCl(2) moiety to -0.34 (bpm) and -0.50 V (dpp) for the [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) bridged complex. The lowest energy electronic absorption for these complexes is assigned as the Ru(d pi) --> BL(pi*) metal-to-ligand charge transfer (MLCT) transition. These MLCT transitions are tuned to higher energy in the monometallic synthons when Cl(-) is replaced by CH(3)CN or PEt(2)Ph (516, 452, and 450 nm, for BL = bpm, respectively) and to lower energy when Pt(II)Cl(2) is coordinated to the bridging ligand (560 and 506 nm for BL = bpm or dpp). This MLCT state displays a broad emission at room temperature for all the dpp systems with the [(tpy)Ru(PEt(2)Ph)(dpp)PtCl(2)](2+) system exhibiting an emission centered at 750 nm with a lifetime of 56 ns. These supramolecular complexes [(tpy)Ru(PEt(2)Ph)(BL)PtCl(2)](2+) represent the covalent linkage of TAG-LA-BL-RM assembly (TAG = NMR active tag, RM = Pt(II) reactive metal).

Activating a Low Overpotential CO2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst

“…Cyclic voltammograms (CVs) of 1 2+ and 2 2+ in Ar-purged CH 3 CN solutions using 0.1m Bu 4 NPF 6 as the supporting electrolyte are shown in Figure 1. On the anodic scan, reversible waves can be detected at 0.77 and 0.83 Vv ersus Fc +/0 for 1 2+ and 2 2+ ,r espectively.I na nalogy to previous reports, [14] this couple can be assigned to am etal-based Ru 3+/2+ oxidation, which is consistent with density function theory (DFT) calculations ( Figure S4). Thelower potential of 1 2+ as compared to 2 2+ reflects the slightly increased electrondonating character of 4,4'-dmbpy as compared to 6-mbpy.The cathodic scans (scan rate v = 200 mV s À1 )s how ar eversible couple at E 1/2 = À1.78 Va nd À1.76 Vf or 1 2+ and 2 2+ , respectively,f ollowed by as econd irreversible reduction (E p,c = À2.09 Va nd À1.98 Vf or 1 2+ and 2 2+ ,r espectively).…”

Catalytic and Surface‐Electrocatalytic Water Oxidation by Redox Mediator–Catalyst Assemblies

“…The assemblies can be synthesized in two steps: 1) Reaction of [Ru II (bpy) 2 Cl 2 ] ⋅ 2 H 2 O with [Ru II (LLL)(bpm)Cl] + 7, 8 in 1:1 EtOH:H 2 O (LLL=tpy or Mebimpy: 2,6‐bis(1‐methylbenzimidazol‐2‐yl)pyridine; structures in Figure 1 a); 2) removal of the chloro ligand and chloride counter ions in the resulting ligand‐bridged assemblies [(bpy) 2 Ru II (bpm)Ru II (LLL)Cl]Cl 3 by reaction with neat HOTf (OTf − =trifluoromethanesulfonate) followed by displacement of OTf − in water to give [(bpy) 2 Ru II (bpm)Ru II (tpy)(OH 2 )] 4+ ( 1 ) or [(bpy) 2 Ru II (bpm)Ru II (Mebimpy)(OH 2 )] 4+ ( 2 ). Purification was achieved by column chromatography (Sephadex LH‐20) by using water as the eluant.…”

Catalytic and Surface‐Electrocatalytic Water Oxidation by Redox Mediator–Catalyst Assemblies

“…[5] We also reported that rates of cerium(IV)-catalyzed water oxidation by the blue dimer are greatly enhanced by added redox mediators, [Ru(bpy) 2 (LL)] 2+ (LL = bpy, bpm, or bpz) and [Ru-(bpm) 3 ] 2+ . [6] Herein, we present stable, robust water oxidation catalysis based on assemblies containing both functions in solution, and notably in methylenephosphonate derivatives on electrode surfaces, for which turnovers of more than 28 000 have been achieved.The assemblies can be synthesized in two steps: 1) Reaction of [Ru II (bpy) 2 Cl 2 ]·2 H 2 O with [Ru II (LLL)(bpm)Cl] + [7,8] in 1:1 EtOH:H 2 O (LLL = tpy or Mebimpy: 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; structures in Figure 1 a); 2) removal of the chloro ligand and chloride counter ions in the resulting ligand-bridged assemblies [(bpy) 2 Ru II -(bpm)Ru II (LLL)Cl]Cl 3 by reaction with neat HOTf (OTf À = trifluoromethanesulfonate) followed by displacement of OTf À in water to give [(bpy) 2 Ru II (bpm)Ru II (tpy)(OH 2 )] 4+ (1) or [(bpy) 2 Ru II (bpm)Ru II (Mebimpy)(OH 2 )] 4+ (2). Purification was achieved by column chromatography (Sephadex LH-20) by using water as the eluant.The corresponding methylenephosphonate ethyl esther derivatives were prepared by similar strategies by replacing [Ru II (bpy) 2 Cl 2 ]·2 H 2 O with [{[4,4'-(EtO) 2 OPCH 2 ] 2 -bpy} 2 Ru II Cl 2 ].…”

“…The assemblies can be synthesized in two steps: 1) Reaction of [Ru II (bpy) 2 Cl 2 ]·2 H 2 O with [Ru II (LLL)(bpm)Cl] + [7,8] in 1:1 EtOH:H 2 O (LLL = tpy or Mebimpy: 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; structures in Figure 1 a); 2) removal of the chloro ligand and chloride counter ions in the resulting ligand-bridged assemblies [(bpy) 2 Ru II -(bpm)Ru II (LLL)Cl]Cl 3 by reaction with neat HOTf (OTf À = trifluoromethanesulfonate) followed by displacement of OTf À in water to give [(bpy) 2 Ru II (bpm)Ru II (tpy)(OH 2 )] 4+ (1) or [(bpy) 2 Ru II (bpm)Ru II (Mebimpy)(OH 2 )] 4+ (2). Purification was achieved by column chromatography (Sephadex LH-20) by using water as the eluant.…”