Redox Multifunctionality in a Series of PtII Dithiolene Complexes of a Tetrathiafulvalene‐Based Diphosphine Ligand

The redox‐active and chelating diphosphine, 3,4‐dimethyl‐3′,4′‐bis(diphenylphosphino)‐tetrathiafulvalene, denoted as P2 , is engaged in a series of platinum complexes, [(P2)Pt(dithiolene)], with different dithiolate ligands, such as 1,2‐benzenedithiolate (bdt), 1,3‐dithiole‐2‐thione‐4,5‐dithiolate (dmit), and 5,6‐dihydro‐1,4‐dithiin‐2,3‐dithiolate (dddt). The complexes are structurally characterized by X‐ray diffraction, together with a model compound derived from bis(diphenylphosphino)ethane, namely, [(dppe)Pt(dddt)] . Four successive reversible electron‐transfer processes are found for the [(P2)Pt(dddt)] complex, associated with the two covalently linked but electronically uncoupled electrophores, that is, the TTF core and the platinum dithiolene moiety. The assignments of the different redox processes to either one or the other electrophore is made thanks to the electrochemical properties of the model compound [(dppe)Pt(dddt)] lacking the TTF redox core, and with the help of theoretical calculations (DFT) to understand the nature and energy of the frontier orbitals of the [(P2)Pt(dithiolene)] complexes in their different oxidation states. The first oxidation of the highly electron‐rich [(P2)Pt(dddt)] complex can be unambiguously assigned to the redox process affecting the Pt(dddt) moiety rather than the TTF core, a rare example in the coordination chemistry of tetrathiafulvalenes acting as ligands.     

Metal-metal electronic coupling in syn and anti stereoisomers of mixed-valent (FeCp)2-, (RhL2)2-, and (FeCp)(RhL2)-as-indacenediide ions

The extent of metal-metal electronic coupling was quantified for a series of syn and anti stereoisomers of (FeCp)(2)-, (RhL(2))(2)- and (FeCp)(RhL(2))- (L(2)=1,5-cyclooctadiene (cod), L=CO) as-indacenediide mixed-valent ions by spectroelectrochemical and DFT studies. The effect of the syn/anti orientation of the metal units with respect to the planar aromatic ligand indicates that electron transfer occurs through the bridge rather than through space. The nature of the metal was found to be crucial: while homobimetallic diiron species are localised valence-trapped ions (Class II), the dirhodium analogues are almost delocalised mixed-valent ions (borderline and Class III). Finally, despite their redox asymmetry, even in the heterobimetallic iron-rhodium as-indacenediide complexes, strong metal-metal coupling is present. In fact, oxidation of the iron centre is accompanied by electron transfer from rhodium to iron and formation of a reactive 17-electron rhodium site. syn and anti Fe-Rh as-indacenediide complexes are rare examples of heterobimetallic systems which can be classified as borderline Class II/Class III species.     

Stable Mixed‐Valent Radicals from Platinum(II) Complexes of a Bis(dioxolene) Ligand

Three diplatinum(II) complexes [{PtL}₂(μ‐thea)] (H₄thea=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene) have been prepared, with diphosphine or bipyridyl “L” co‐ligands. One‐electron oxidation of these complexes gave radical cations containing a mixed‐valent [thea]^3? ligand with discrete catecholate and semiquinonate centers separated by quaternary methylene spacers. The electronic character of these radicals is near the Robin–Day class II/III border determined by UV/Vis/NIR and EPR spectroscopies. Crystal‐structure determinations and a DFT calculation imply that oxidation of the thea^4? ligand may lead to an increased through‐space interaction between the dioxolene π systems.     

A new family of dinuclear rhodium complexes containing tertiary phosphanes in a semibridging or doubly bridging bonding mode

The reactions of [Rh(2)Cl(kappa(2)-acac)(mu-CPh(2))(2)(mu-SbiPr(3))] (3) and [Rh(2)(kappa(2)-acac)(2)(mu-CPh(2))(2)(mu-SbiPr(3))] (4) with PMe(3) lead to exchange of the bridging ligand and afford the novel PMe(3)-bridged counterparts 5 and 6, in which the phosphane occupies a semibridging (5) or a doubly bridging (6) position. In both cases, the bonding mode was confirmed crystallographically. Treatment of 6 with CO causes a shift of PMe(3) from a bridging to a terminal position and gives the unsymmetrical complex [(kappa(2)-acac)Rh(mu-CPh(2))(2)(mu-CO)Rh(PMe(3))(kappa(2)-acac)] (7). Similarly to 5 and 6, the related compounds 10 and 11 with one or two acac-f(3) ligands were prepared. While both PEt(3) and PnBu(3) react with 3 by exchange of the bridging stibane for phosphane to give compounds 12 and 13, the reactions of 4 with PMePh(2) and PnBu(3) afford the mixed-valent Rh(0)Rh(II) complexes [(PR(3))Rh(mu-CPh(2))(2)Rh(kappa(2)-acac)(2)] (17, 18) in high yields. In contrast, treatment of 4 with PEt(3) and PMe(2)Ph generates the phosphane-bridged compounds [Rh(2)(kappa(2)-acac)(2)(mu-CPh(2))(2)(mu-PR(3))] (14, 15) exclusively. Stirring a solution of 14 (R=Et) in benzene for 15 h at room temperature leads to complete conversion to the mixed-valent isomer 16. The reaction of 6 with an equimolar amount of CR(3)CO(2)H (R=F, H) or phenol in the molar ratio of 1:10 results in substitution of one acac by one trifluoracetate, acetate, or phenolate ligand without disturbing the [Rh(2)(mu-CPh(2))(2)(mu-PR(3))] core. From 6 and an excess of CR(3)CO(2)H, the symmetrical bis(trifluoracetato) and bis(acetate) derivatives [Rh(2)(kappa(2)-O(2)CCR(3))(2)(mu-CPh(2))(2)(mu-PMe(3))] (21, 22) were obtained.     

Chirality Control of Quadruple Helixes of Metal Strings by Peripheral Chiral Ligands

Chirality control of helixes with the Δ (P) or Λ (M) form is interesting in various fields such as extended metal atom chains (EMACs), in which the metal backbones are helically wrapped by four ligands. Herein, we report two EMACs, Δ‐[Ni₅((?)camnpda)₄] and Λ‐[Ni₅((+)camnpda)₄], whose chiralities are controlled by chiral ligands with naphthyridine and camphorsulfonyl groups. There is a large energy difference (108 kcal mol^?1) between the two helical structures with one chiral ligand. Furthermore, the electron communication between [Ni₂]³⁺ units is more pronounced than in [Ni₅(bna)₄Cl₂]²⁺ (bna=binaphthyridylamido). The results demonstrate control of small‐scale helical structure and set the stage for future development of chiral controlled base and nanoelectronic devices.     

Probing the transition between the localised (class II) and localised-to-delocalised (class II-III) regimes by using intervalence charge-transfer solvatochromism in a series of mixed-valence dinuclear ruthenium complexes

Intervalence charge-transfer (IVCT) solvatochromism studies on the diastereoisomeric forms of [{Ru(bpy)(2)}(2)(mu-BL)](5+) (bpy=2,2'-bipyridine; BL=a series of di-bidentate polypyridyl bridging ligands) reveal that the solvent dependencies of the IVCT transitions decrease as the "tail" of the bridging ligand is extended, and the extent of delocalisation increases. Utilising a classical theoretical approach for the analysis of the intervalence charge-transfer (IVCT) solvatochromism data, the subtle and systematic variation in the electronic properties of the bridging ligands can be correlated with the shift between the localised (class II) and localised-to-delocalised (class II-III) regimes. The investigation of the diastereoisomeric forms of two series of complexes incorporating analogous structurally rigid (fused) and nonrigid (unfused) bridging ligands demonstrates that the differences in the IVCT characteristics of the diastereoisomers of a given complex are accentuated in the latter case, due to a stereochemically induced redox asymmetry contribution. The marked dependence of the IVCT transitions on the stereochemical identity of the complexes provides a quantitative measure of the fundamental contributions of the reorganisational energy and redox asymmetry to the intramolecular electron-transfer barrier at the molecular level.     

Deep blue mixed-valent PtIIIPtIIIPtII complex [Pt3Br2(mu-pz)6] (pz=pyrazolate) showing valence-detrapping behavior in solution

The oxidation of the pyrazolate bridged cyclic PtII trimer, [Pt3(mu-pz)6] (1), in the presence of bromide ion gave a deep blue mixed-valent Pt(II,III,III) complex, [Pt3Br2(mu-pz)6] (2). The structural analysis of 2 disclosed that the complex has localized Pt--Pt bond. Our theoretical calculations revealed that the HOMO and LUMO of Pt3 (II,III,III) species mainly consists of (dsigma-dsigma) and (dsigma-dsigma)* orbitals, respectively, and the origin of deep blue color of the bromo complex, 2, arises from the (dsigma-dsigma)-->(dsigma-dsigma)* transition. Unique fluxional behavior was observed due to valence-detrapping of 2 in solution. The activation parameters of the valence-detrapping of 2 obtained by Eyring analyses were DeltaH(not equal)=37(2) kJ mol(-1) and DeltaS(not equal)=-67(7) J mol(-1) K(-1).     

CO oxidation over a Pt-Rh system. 1. Reaction on individual metals

The reaction of CO oxidation over thin films of rhodium and platinum prepared by vacuum evaporation of the metals on an inert support has been investigated at low pressures (P < 2×10^-5 mbar). Rhodium has been found to be more active than platinum in this reaction. The reasons of the higher activity of Rh are discussed.     

Heterometallic Mixed‐Valence Copper(I,II) Cyanides that were Tuned by Using the Chelate Effect: Discovery of Famous Cairo Pentagonal Tiling and Unprecedented (3,4)‐Connected {83}2{86} Topological 3D Net

By using environmentally friendly [Ni(CN)₄]^2? as a cyanide source, three new heterometallic cyano‐bridged mixed‐valence Cu^I/Cu^II coordination polymers with three different electronic configurations (d⁸–d¹⁰), that is, [Cu₂Ni(CN)₅(H₂O)₃] ( 1 ), [Cu₂Ni(CN)₅(pn)H₂O] ( 2 ), and [Cu₃Ni(CN)₆(pn)₂] ( 3 , pn=1,2‐propane diamine) have been synthesized by gradually increasing the amount of pn. Compound 1 , which was hydrothermally synthesized in the absence of pn ligand, exhibits the famous 2D Cairo pentagonal tiling, in which the Cu^I, Cu^II, and Ni^II atoms act as trigonal, T‐shaped, and square‐planar nodes, respectively. Notably, there are three water molecules located at the meridianal positions of the octahedrally coordinated Cu^II atom in compound 1 . A similar reaction, except for the addition of a small amount of pn, generated a similar Cairo pentagonal tiling layer in which two of the water molecules that were located at the meridianal positions of the octahedrally coordinated Cu^II atom were replaced by a chelating pn group. Another similar hydrothermal reaction, with the addition of a larger amount of pn, yielded compound 3 , which showed a related two‐fold‐interpenetrated (3,4)‐connected 3D framework with an unprecedented {8³}₂{8⁶} topology in which the Cu^II atom was chelated by two pn groups. These structural changes between compounds 1 , 2 , 3 can be explained by the chelating effect of the pn group. The replacement of two meridianally coordinated water molecules on the octahedral Cu^II atom in compound 1 by a pn group gives compound 2 , which shows similar Cairo tiling, and a further increase in the amount of pn results in the formation of the [Cu(NC)₂(pn)₂] unit and the two‐fold‐interpenetrated 3D framework of compound 3 . The mixed‐valence properties of compounds 1 , 2 , and 3 were confirmed by variable‐temperature magnetic‐susceptibility measurements.