Diplatinum Complexes Research Articles

Attachment of Luminescent Neutral “Pt(pq)(C≡CtBu)” Units to Di and Tri N-Donor Connecting Ligands: Solution Behavior and Photophysical Properties

Binuclear derivatives [{Pt(pq)(C≡CtBu)}2(μ-L)] (1a–5a), containing a series of dinitrogen linker ligands and the trinuclear [{Pt(pq)(C≡CtBu)}3(μ-L)] (6a) [L = μ-1,3,5-tris(pyridine-4-ylethynyl)benzene], formed by bridge-splitting reactions with [Pt(pq)(μ-κCα:η2-C≡CtBu)]2 (Pt-1), are reported. The complexes are characterized by a combination of 1H NMR spectroscopy, mass spectrometry and X-ray crystallography (2a and 4a). 1H NMR proves the existence of a dynamic equilibrium in solution between the diplatinum complexes (species a), the corresponding mononuclear complex with terminal N-donor ligands (species b), the starting material (Pt-1) and the free ligand (L). The effects of concentration, temperature and solvent properties on the equilibrium have been studied. The optical properties of these systems have been investigated by UV-visible absorption and emission spectroscopies in solid state and in solution, and the nature of the transitions and the excited state analyzed by theoretical calculations on 2a.

Silver(i) and thallium(i) cations as unsupported bridges between two metal bases

Stirring Lewis-basic transition metal complexes with the salts M[BAr(Cl)4] (M = Ag, Tl; Ar(Cl) = 3,5-C6H3Cl2) resulted in the formation of diplatinum complexes [{(Cy3P)2Pt}2(μ-Ag)][BAr(Cl)4] (3) and [{(Cy3P)2Pt}2(μ-Tl)][BAr(Cl)4] (4) and the diiron compound [{(OC)3(Me3P)2Fe}2(μ-Ag)] (5) featuring bridging, unsupported metal cations. Their properties were investigated by multinuclear NMR spectroscopy, as well as X-ray diffraction and infrared measurements.

ChemInform Abstract: Recent Progress in MMX‐Chain Complexes: Unique Electronic States and Characteristics Developed by Introducing Binary Countercations

AbstractReview: [57 refs.

Two types of heterometallic one-dimensional alignment composed of acetamidate-bridged dirhodium and pivalamidate-bridged diplatinum complexes.

Two types of heterometallic one-dimensional chains, [{Rh2(acam)4}{Pt2(piam)2(NH3)4}2]n(CF3SO3)4n·2nMeOH (2, where acam = acetamidate, piam = pivalamidate) and [{Rh2(acam)4}{Pt2(piam)2(NH3)4}]n(CF3CO2)2n·2nEtOH (3), have been synthesized and characterized by single-crystal X-ray analyses. The chain structures in 2 and 3 are composed of two kinds of dinuclear complexes, [Rh2(acam)4] (i.e., [Rh2]) and [Pt2(piam)2(NH3)4] (i.e., [Pt2]), where Rh and Pt atoms are axially linked by metal-metal bonds. In 2 and 3, each complex is one-dimensionally aligned as -{[Rh2]-[Pt2]-[Pt2]}n- or -{[Rh2]-[Pt2]}n-, respectively, in which different alignments are caused by different isomers of [Pt2] that are HH (head-head) and HT (head-tail) orientation of piam ligands and their hydrogen bonding modes. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 2 and 3, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt2(II,II)]-[Pt2(II,II)]}n- and -{[Rh2(II,II)]-[Pt2(II,II)]}n-, which are unchanged from those in the starting compounds. The diffuse reflectance spectra show that LUMOs are M-M σ-type orbitals. The gap between filled and vacant σ-type orbitals in 3 is narrower than that in 2, and is attributed to the relative higher destabilized filled σ-type orbitals caused by lower numbers of linking platinum atoms.

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 thea4− ligand may lead to an increased through-space interaction between the dioxolene π systems.

Comparison of coordination mode of some biphosphine ligands in cyclometalated organoplatinum(II) complexes

The reaction of the cyclometalated complexes [PtR(CˆN)(SMe2)], 1, in which R is Me or 4-MeC6H4, and CˆN is either ppy (deprotonated 2-phenylpyridine) or bhq (deprotonated benzo-h-quinoline), with 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (dfppe), were studied. When 0.5 equiv of dfppe was added, the binuclear cyclometalated Pt(II) complexes [Pt2R2(CˆN)2(μ-dfppe)], 2i–l, were formed, which are the first examples of diplatinum complexes with bridging dfppe ligands. When the ligand dfppe was reacted with complex 1 in the ratio of 1:1, only in the case of R = Me and CˆN = ppy, the complex [Pt(Me)(κ1-ppy)(κ2-dfppe)], 4d, was obtained, in which the ppy ligand is monodentate and dfppe is chelating, and in other cases the dimers 2j–l were formed. The results were compared, using density functional theory (DFT), with other diphosphine ligands, 1,1-bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe) to clarify the electronic and steric effects of diphosphine ligands on their coordination mode ability.

Synthesis and structural characterization of a sterically encumbered ferrocenecarboxamido diphosphine and its platinum(II) complex

{[Bis(2-(diphenylphosphino)ethyl)amino]carbonyl}ferrocene (3), a bulky ferrocenecarboxamido-diphosphine, was prepared in a good yield by the reaction of pentafluorophenyl ferrocenecarboxylate (2) with bis[2-(diphenylphosphino)ethyl]amine. The NMR data (1H VT NMR study in particular) indicated a limited molecular mobility of amide 3 that presumably results from a hindered rotation around the amide C–N bond leading to a non-equivalency of the substituents attached to the amide nitrogen. Compound 3 was further converted to the corresponding diphosphine disulfide 4 and reacted with [PtCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) to give the symmetric, ligand-bridged diplatinum complex [(μ-3)PtCl2]2 (5) having cis square-planar geometry around the Pt(II) centers. The molecular structures of 4 and 5 were determined by single-crystal X-ray diffraction analysis.

Recent Progress in MMX-Chain Complexes: Unique Electronic States and Characteristics Developed by Introducing Binary Countercations

Abstract MMX-Type quasi-one-dimensional iodide-bridged diplatinum complexes (MMX chains) provide various electronic states and attractive physical properties. In this review, we summarize the recent progress in MMX chains consisting of pyrophosphite (pop) ligands. The MMX chains with binary countercations, which have short Pt–I–Pt distance and robust frameworks, form a new electronic state. They show reversible dehydration–rehydration accompanied by the change of electronic states and electrical conductivity. Relatively high electrical conductivity in the MMX chains with binary countercations enables us to investigate the negative differential resistance (NDR) and electrochemical characteristics in the solid state for the first time in MMX chains.

Bis(diphenylphosphino)acetylene as bifunctional ligand in cycloplatinated complexes: Synthesis, characterization, crystal structures and mechanism of MeI oxidative addition

Binuclear cycloplatinated(II) complexes with general formula of [Pt2Me2(CˆN)2(μ-dppac)], (1, CˆN = deprotonated 2-phenylpyridine (ppy); 2, CˆN = deprotonated benzo{h}quinoline (bhq)) in which dppac = 1,1′-bis(diphenylphosphino)acetylene, are synthesized by the reaction of [PtMe(SMe2)(CˆN)] with 0.5 equiv of dppac at room temperature. The complexes are fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and complex 2 is further identified by single crystal X-ray structure determination. Kinetics of the reaction of complexes 1 and 2 with MeI are investigated in CHCl3 and based on the UV–vis and 31P NMR data, a mechanism involving a double MeI oxidative addition is suggested. The classical SN2 mechanism is proposed for both steps and the involved intermediates are suggested. Although MeI in each step was trans oxidatively added to one of the platinum(II) centers, further trans to cis isomerizations of methyl and iodide ligands were also identified. The rates are almost four times slower in the second step as compared to the first step due to the electronic effects transmitted through the dppac ligand. Reaction rates concerning complex 2, having bhq ligand, are almost 1.3 times slower than those involving the related ppy complex 1. This is attributed to the stronger donor ability of the ppy ligand, as compared to that bhq ligand and is in agreement with the values of 1JPtP observed in the 31P NMR spectra of the complexes 1 and 2. The structure of the Pt(IV)–Pt(IV) dimeric complex [Pt2I2Me4(ppy)2(μ-dppac)], 3, produced by oxidative addition of complex 1 to MeI, is also determined using X-ray diffraction which is the first X-ray structural determination of a diplatinum complex containing two Pt(IV) centers bridged by one dppac ligand.

Bridging and Chelating Roles of Bis(2-(diphenylphosphino)ethyl)phenylphosphine in Stabilizing Binuclear Platinum(II) Complexes

The diorganoplatinum(II) complexes [PtR2(triphos-P,P′)] (1; R = Me, p-MeC6H4 and triphos = bis(2-(diphenylphosphino)ethyl)phenylphosphine), containing one free phosphine atom, react with cyclometalated platinum complexes [PtR′(C∧N)(SMe2)] (2; R′ = Me, p-MeC6H4 and C∧N is deprotonated 2-phenylpyridine (ppy) or deprotonated benzo[h]quinoline (bhq)) to give the cyclometalated diplatinum(II) complexes [Pt2R2R′(C∧N)(triphos)] (3). In these binuclear platinum(II) compounds, triphos acts as both a chelating and bridging ligand to stabilize the produced diplatinum complexes. The complexes 3 were readily characterized by multinuclear NMR spectroscopy and elemental microanalysis. The crystal structure of complex 3f (R = Me, R′ = p-MeC6H4, and C∧N = bhq) was further determined by X-ray crystallography, giving the first example of an X-ray structural determination of a diplatinum complex with a triphos ligand acting simultaneously as both a chelating and bridging ligand.

Synthesis and Characterization of Platinum(II) Complexes Containing Spiro System

Platinum complexes [Pt(bpy)Cl2](bpy: 2,2'-bipyridine) and [Pt(PT)Cl2](PT: 1,10-phenantroline) were reacted with 5,5"-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(2,2'-bipyrine), bpy-spiro-bpy, to afford mono and diplatinium complexes: [(bpy)Pt(bpy-spiro-bpy)][PF6]2, [(bpy)Pt(bpy-spiro-bpy)Pt(bpy)])[PF6]4, and [(PT)Pt(bpy-spiro-bpy)])][PF6]2, which were characterized by NMR, UV/VIS, mass spectrum, and PL spectroscopy. They showed very high internal quantum yields (0.35-0.67) and emitted light in the blue region (473-520 nm). Herein, we describe the synthesis, characterization of the mono- and di-platinum complexes in detail.

Formation of Unique Platinum–Silyl Complexes by the Reactions of a Zero-valent Platinum Complex with Various Trisilanes

Abstract Trisilanes bearing hydrogen atoms at two more silicon atoms reacted with a zero-valent platinum complex [Pt(dppe)(η2-C2H4)] to give various types of mononuclear and dinuclear platinum–silyl complexes. Interestingly, in the case of 1,1,2,3,3-pentamethyltrisilane, the Si–Si bond was uniquely activated, resulting in the formation of the diplatinum complex [Pt2(dppe)2(µ-1,4-SiMe(SiMe2)2SiMe)].

Syntheses of Di- and Trinuclear Platinum Complexes with Multibridged Germanium Centers Derived from Unsymmetrical Digermanes

A trigonal-bipyramidal Pt3Ge2 cluster was synthesized by the reaction of the zerovalent platinum complex [Pt(dppe)(η2-C2H4)] (dppe = 1,2-bis(diphenylphosphino)ethane) with the unsymmetrical digermane H3GeGeEt3 at a 3/2 molar ratio. The platinum centers formed a triangular plane bridged by two germylyne ligands, one of which maintained the Ge–Ge bond. To investigate the Pt3Ge2 cluster formation process, the phenyl-substituted digermanes HPh2GeGeMe3 and H2PhGeGeR3 (R = Me, Et), in which two hydrogen atoms and one hydrogen atoms of the reactive GeH3 moiety were replaced by the bulkier phenyl group(s) together with the substitution of the GeEt3 group by a GeMe3 group, respectively, were used to simplify the reaction system. They provided the digermylplatinum hydride [Pt(dppe)(H)(GePh2GeMe3)] (2) and the bis(μ-germylene)diplatinum complexes [Pt2(dppe)2(μ-GeHPh)(μ-Ge(Ph)GeR3)] (3, R = Me; 4, R = Et) in moderate yields, respectively. For 3 and 4, the first-formed digermylplatinum hydride I-1 underwent dissociati...

DFT study of the mechanism of hydroamination of ethylene with ammonia catalyzed by diplatinum(II) complexes: Inner‐ or outer‐sphere?

A detailed analysis of the reaction profiles of the hydroamination reaction between ethylene and ammonia catalyzed by the diplatinum(II) [{Pt(NH(2))(μ-H)(PPh(3))}(2)] complex is presented herein using density functional theory computational techniques. The coordinatively unsaturated 14e T-shaped [Pt(NH(2))(PPh(3))H] species resulted from the dissociation of the diplatinum [{Pt(NH(2))(μ-H)(PPh(3))}(2)] precatalyst are identified as the active catalytic species. All possible reaction pathways that constitute the entire catalytic cycle have exhaustively been investigated. Overall, the rate-determining step of all catalytic cycles constructed was found to be the oxidative addition of ammonia that leads to the regeneration of the catalyst. According to the energy span model, the outer-sphere mechanism for the hydroamination of ethylene with ammonia catalyzed by the diplatinum complexes is favored over the inner-sphere one, whereas TOF values are in favor of the inner-sphere mechanism.

Electron spin resonance observation of dehydration-induced spin excitations in quasi-one-dimensional iodo-bridged diplatinum complexes

Electron spin resonance (ESR) measurements have been performed on a series of quasi-one-dimensional iodo-bridged diplatinum complexes K${}_{2}$[C${}_{3}$H${}_{5}R$(NH${}_{3}$)${}_{2}$][Pt${}_{2}$(pop)${}_{4}$I]$\ifmmode\cdot\else\textperiodcentered\fi{}$4H${}_{2}$O (pop $=$ P${}_{2}$H${}_{2}$O${}_{5}$${}^{2\ensuremath{-}}$; $R$ $=$ H, CH${}_{3}$, or Cl), where dehydration/rehydration of the crystalline water switches the electronic state reversibly with retention of single crystallinity. We have observed a nonmagnetic nature in as-grown samples, whereas in the dehydrated samples, a clear enhancement of the spin susceptibility has been observed above $\ensuremath{\sim}$80 K with the activation energy ranging 50--60 meV. The activated spins originate from isolated Pt${}^{3+}$ state on the chain, as confirmed from the principal $g$ values. Concomitantly, the ESR linewidth exhibits a prominent motional narrowing, suggesting that the activated Pt${}^{3+}$ spins are mobile solitons generated in the doubly degenerate charge-density-wave states of the dehydrated salts.

Diplatinum(ii)-coordinated polyoxotungstate: synthesis, molecular structure, and photocatalytic performance for hydrogen evolution from water under visible-light irradiation

The synthesis and molecular structure of a monomeric diplatinum(II) complex composed of mono-lacunary α-Keggin polyoxometalate is described. The polyoxometalate, Cs(3)[α-PW(11)O(39){cis-Pt(NH(3))(2)}(2)]·8H(2)O (Cs-1), afforded by a stoichiometric reaction of mono-lacunary Keggin polyoxotungstate with cis-diamminedichloroplatinum(ii) in water, followed by crystallization from water, was obtained as analytically pure, homogeneous, yellow crystals. The compound Cs-1 was characterized by elemental analysis, thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR) and UV-visible spectroscopy, solution (1)H and (31)P nuclear magnetic resonance (NMR), and X-ray crystallography. The single-crystal X-ray structure analysis revealed that the two cis-platinum(ii) moieties, [cis-Pt(NH(3))(2)](2+), were coordinated each to two oxygen atoms in a mono-vacant site of [α-PW(11)O(39)](7-) with asymmetric configuration, resulting in an overall C(1) symmetry. Furthermore, hydrogen evolution from an EDTA·2Na (ethylenediamine tetraacetic acid disodium salt) aqueous solution under visible-light irradiation (≥400 nm) was achieved by using polyoxoanion 1 and titanium dioxide.

σ-Donor–σ-acceptor plumbylene ligands: synergic σ-donation between ambiphilic Pt0 and Pbii fragments

Mono- and diplatinum plumbylene complexes are prepared in which the bonding comprises synergic σ donation between the Pt and Pb atoms. The bonding distinguishes the complexes from both the classical Fischer carbene bonding model and M→Pb dative-only bonding. The Pt-Pb bond of the monoplatinum complex is stable, while the diplatinum complex reversibly loses one Pt fragment.

ChemInform Abstract: A Keggin‐Type Polyoxotungstate‐Coordinated Diplatinum(II) Complex: Synthesis, Characterization, and Stability of the cis‐Platinum(II) Moieties in Dimethylsulfoxide and Water.

Abstract(Me4N)3 [PW11O39{cis‐Pt (NH3)2}2]·10H2O is precipitated from an aqueous solution containing K7[PW11O39], cis‐Pt(NH3)2Cl2, and Me4NBr (25 °C, 24 h, 23% yield).

A cyclometalated diplatinum complex containing 1,1′-bis(diphenylphosphino)ferrocene as spacer ligand: Antitumor study

Cyclometalated platinum(II) complex [Pt(C^N)Cl(dmso)], 1, in which C^N = N(1),C(2′)-chelated deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, was reacted with 1 equiv of 1,1′-bis(diphenylphosphino)ferrocene, dppf, to give the cyclometalated diplatinum(II) complex [Pt 2(C^N) 2Cl 2(μ-dppf)], 2, along with 0.5 equiv of unreacted dppf. However, the related reaction with 0.5 equiv of dppf produced complex 2 in pure form. Complex 2 in solution was fully characterized by using multinuclear NMR spectroscopy ( 1H, 13C, 31P, and 195Pt) and a number of 2D NMR experiments. The structure of complex 2 in solid state was determined by X-ray crystallography showing that the bridging dppf ligand is arranged close to “antiperiplanar staggered” conformation. Cytotoxicity of the complex 2 was studied in three human cancer cell lines derived from ovarian carcinoma(CH1), lung carcinoma(A549), and colon carcinoma (SW480) by means of the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide).

One-Dimensionally Extended Paddlewheel Dirhodium Complexes from Metal–Metal Bonds with Diplatinum Complexes

We have succeeded in obtaining unique one-dimensional (1D) chain complexes (1, 2, and 3) comprised of two types of metal species: rhodium and platinum. These compounds are constructed from a dinuclear rhodium complex (i.e., [Rh(2)]) and a pivalamidate-bridged platinum complex (i.e., [Pt(2)]), forming an attractive quasi-1D infinite chain, expressed as -{[Rh(2)]-[Pt(2)]-[Pt(2)]}(n)-. Interestingly, the bridging ligands of [Rh(2)] can be varied with trifluoroacetate, acetate, and acetamidate groups, indicating the possibility of electronic structure modulation in the 1D chain.