Dinuclear Model Complexes Research Articles

Synthesis and characterization of platinum(II) polymetallaynes functionalized with phenoxazine-based spacer. A comparison with the phenothiazine congener

A new series of soluble, solution-processable metallopolyynes of platinum(II) functionalized with electron-rich phenoxazine–oligothiophene rings and their corresponding dinuclear model complexes were synthesized and characterized. The influence of the inclusion of thienyl rings along the polymer chain on the optical, electronic and photovoltaic properties of these metallopolymers was studied. The evolution of the singlet and triplet excited states in these metal-based materials was elucidated in detail. It is shown that addition of the thiophene rings can elevate the HOMO energy level of the polymers. The absorption edge of the oxygen analogue is more red-shifted than that of the sulfur congener, which is attributed to the stronger electron-donating ability of the phenoxazine unit than that of the phenothiazine group. The down-shifted HOMO level of the phenothiazine-based polymer is found to enhance the photovoltaic performance by increasing the open-circuit voltage of the polymer solar cell relative to the phenoxazine-based congener. At the same donor:acceptor blend ratio of 1:4, the light-harvesting capability and solar cell efficiency notably increase as the thienyl rings are added.

Synthesis and Photovoltaic Properties of New Metalloporphyrin-Containing Polyplatinyne Polymers

Three new solution-processable platinum(II) polyyne polymers containing zinc(II) porphyrinate chromophores P1, P2, and P3 and their corresponding dinuclear model complexes were synthesized via the CuI-catalyzed dehydrohalogenation reaction of the platinum(II) chloride precursor and each of the respective bis(ethynyl)-zinc(porphyrin) metalloligands. The thermal, photophysical (absorption, excitation and emission spectra), electrochemical, and photovoltaic properties of P1–P3 were investigated. These results are also correlated by time-dependent density functional theory (TDDFT) calculations. The computations corroborate the presence of moderate conjugation in the π-systems, somewhat more accentuated for P3 where more favorable dihedral angles between the porphyrin and thiophene rings are noted. Moreover, the computed excited states are predicted to be π–π* in nature with some charge transfer components from the trans-[−C≡CPt(L)2C≡C−]n unit to the porphyrin rings. The optical bandgaps range from 1.93 to 2.0...

Energy Transfer Dynamics in Multichromophoric Arrays Engineered from Phosphorescent PtII/RuII/OsII Centers Linked to a Central Truxene Platform

A rigid star-shaped tetrachromophoric trimetallic complex engineered from a 5,5',10,10',15,15'-hexabutyltruxene platform functionalized in the 2,7,12 positions with three different metal centers, namely, a terpyridine-Pt(II) ethynylene unit and Ru(II) and Os(II) bipyridine centers, was synthesized in a controlled fashion and characterized by (1)H NMR and mass spectrometry. The protocol was devised in such a way that key mono and dinuclear model complexes and two reference truxene ligands could also be prepared. Room temperature (RT) optical absorption and RT and 77 K luminescence studies were performed on the truxene ligands, the trimetallic species, the various mono- and binuclear complexes and precursors lacking the truxene fragment; RT nanosecond transient absorption measurements were also carried out in particular cases. The electronic properties of the Ru and Os subunits in the arrays were found to be unaffected by the presence of the truxene core whereas direct linking of the Pt subunit to the truxene via the σ-alkyne bond markedly influences the spectroscopic behavior of the Pt center. Remarkably the truxene phosphorescence was clearly established in the two ligands (lifetime of 4.3 s for the mono ethynyl-bipy substituted truxene and 17.5 ms for the bis ethynyl-bipy substituted truxene) and also detected in the Pt-containing complexes PtL' (model Pt-truxene) and Pt-Os (Pt-truxene-Os dyad) at low temperature. This is attributed to the closeness in energy of the Pt (3)CT level and the truxene triplet at low temperature and to the spin-orbit coupling induced by the Pt heavy atom. Transient absorbance measurements evidenced the population of the Pt-based triplet in the Pt-truxene mononuclear complex PtL' at room-temperature. For the trimetallic complex, where the various centers exhibit an energy gradient for the local excited levels, and following an approach based on the use of selected excitation of the components, an initial energy transfer was found to occur from the central truxene unit toward the peripheral Pt, Ru, and Os metal-based centers. Subsequent Pt-based and Ru-based excited state depletion contributes to the final sensitization of the low-lying Os triplet excited state; the excited state dynamics for these multicascade processes are examined in detail.

Harvesting solar energy using conjugated metallopolyyne donors containing electron-rich phenothiazine–oligothiophene moieties

A new family of soluble, solution-processable metallopolyynes of platinum(II) functionalized with electron-rich phenothiazine–oligothiophene rings and their corresponding dinuclear model complexes were synthesized and characterized. The organometallic polymers show different degrees of absorption capabilities in the solar spectral region, rendering some of them good electron donors for fabricating bulk heterojunction polymer solar cells by blending with a methanofullerene electron acceptor. The influence of the number of thienyl rings along the polymer chain on the optical and photovoltaic properties of these metallopolymers was studied. At the same donor:acceptor blend ratio of 1:4 or 1:5, the light-harvesting capability and solar cell efficiency notably increase as the number of thienyl rings is doubled. Photoexcitation of the polymer solar cells results in a photoinduced electron transfer from the π-conjugated metallopolyyne to [6,6]-phenyl C 61-butyric acid methyl ester and the best-performing polymer showed a power conversion efficiency (PCE) up to ∼1.3% with a corresponding peak external quantum efficiency of 63% under air mass (AM1.5) simulated solar illumination even at shorter absorption wavelength regime. The power dependencies of the solar cell parameters (including the short-circuit current density, open-circuit voltage, fill-factor and PCE) were also tested in detail.

Synthesis, Optical Properties, and Photoluminescence of Organometallic Acetylide Polymers of Platinum Functionalized with Si and Ge-Bridged Bis(3,6-Diethynyl-9-butylcarbazole)

A series of light-emitting group 14 element-containing organometallic platinum polyynes of the form trans-[–Pt(PBu3)2C≡ CArC≡ C(ER2)C≡ CArC≡ C–] n (Ar = 9-butylcarbazole-3,6-diyl, ER2 = SiMe2, SiPh2, GeMe2, GePh2) were synthesized and spectroscopically characterized. The solution properties and regiochemical structures of this new structural class of organosilicon- and organogermanium-based metallopolyynes were studied by IR and NMR (1H, 13C, 29Si, and 31P) spectroscopies. The optical absorption and photoluminescence spectra of these metallopolymers were examined and compared with their well-defined dinuclear model complexes trans-[Pt(Ph)(PEt3)2C≡ CArC≡ C(ER2)C≡ CArC≡ CPt(Ph)(PEt3)2]. The influence of the heavy platinum atom and the group 14 silyl or germyl structural unit possessing different side group substituents on the thermal and phosphorescence properties were investigated in detail. We have also established the goal for studying the evolution of the lowest singlet and triplet excited states with the nature of ER2 unit in these metallopolymers. The present work indicates that the phosphorescence emission efficiency harnessed through the heavy-atom effect of platinum in the main chain changes significantly with the identity of ER2 in the general orders GeR2 > SiR2 (R = Me, Ph) and EMe2 > EPh2 (E = Si, Ge).

Effect of Acetylenic Chain Length on the Tuning of Functional Properties in Fluorene-Bridged Polymetallaynes and Their Molecular Model Compounds

We describe for the first time thermally stable and high-molecular-weight group 10 platinum(II) and group 12 mercury(II) polyyne polymers consisting of 2,7-bis(buta-1,3-diynyl)-9,9-dihexylfluorene linking units trans-[Pt(PBu3)2(C⋮C)2R(C⋮C)2]n and [Hg(C⋮C)2R(C⋮C)2]n (R = 9,9-dihexylfluorene-2,7-diyl). The optical absorption and photoluminescence spectra of these carbon-rich metallopolymers were examined and compared with their dinuclear model complexes trans-[Pt(Ph)(PEt3)2(C⋮C)2R(C⋮C)2Pt(Ph)(PEt3)2] and [MeHg(C⋮C)2R(C⋮C)2HgMe] as well as the group 11 gold(I) congener [(PPh3)Au(C⋮C)2R(C⋮C)2Au(PPh3)]. The regiochemical structures of the polymers were studied by NMR spectroscopy and ascertained by single-crystal X-ray structural analysis for the model platinum(II) compound. The heavy-atom effects of group 10−12 transition metals in triplet light energy harvesting and the influence of the C⋮C chain length on the spatial extent of singlet and triplet excitons in metalated systems of the form [M(C⋮C)mR(C⋮C)mM]n ...

Synthesis, Characterization and Optoelectronic Properties of Dimeric and Polymeric Metallaynes Derived from 3,6-Bis(buta-1,3-diynyl)-9-butylcarbazole

A thermally stable platinum(II) polyyne polymer incorporating carbazole-based linking units, trans-[–Pt(PBu3)2C≡CC≡CRC≡CC≡C–] n (R = 9-butylcarbazole-3,6-diyl), was prepared by polycondensation polymerization of trans-[PtCl2(PBu3)2] with H–C≡CC≡CRC≡CC≡C–H. We report the optical absorption and photoluminescence spectra of this carbon-rich metallopolymer and compare its photophysics with its molecular dinuclear model complex trans-[Pt(Ph)(PEt3)2C≡CC≡CRC≡CC≡CPt(Ph)(PEt3)2] as well as the group 11 gold(I) congener, [(PPh3)AuC≡CC≡CRC≡CC≡CAu(PPh3)]. Characterization of the polymer and metal complexes was accomplished by FT-IR and NMR spectroscopies and FAB mass spectrometry. Our investigations showed that harvesting of the organic triplet emissions can be achieved by the heavy-atom effect of Pt and Au centers, which enables a very high efficiency of intersystem crossing from the S1 singlet excited state to the T1 triplet excited state. The influence of the metal and the C≡C chain length on the intersystem crossing rate and the spatial extent of singlet and triplet excitons is characterized. The present work indicates that high-energy triplet states intrinsically give more efficient phosphorescence in metal-containing diethynylcarbazole systems than in the corresponding bis(butadiynyl) congeners and can thus enhance the radiative decay pathway.

Mixed-ligand organometallic polymers containing the "Pd(2)(dmb)2(2+)" fragment: properties of the [Pd2(dmb)2(diphos)2+](n) polymers/oligomers in solution and in the solid state.

The 1:1 reaction between the d(9)-d(9) Pd(2)(dmb)(2)Cl(2) complex (dmb = 1,8-diisocyano-p-menthane) and the diphosphine ligands (diphos) bis(diphenylphosphino)butane (5, dppb), bis(diphenylphosphino)pentane (6, dpppen), bis(diphenylphosphino)hexane (7, dpph), and bis(diphenylphosphino)acetylene (8, dpa) in the presence of LiClO(4) leads to the [[Pd(2)(dmb)(2)(diphos)](ClO(4))(2)](n) polymers. These new materials are characterized by NMR ((1)H, (13)C, (31)P), IR, Raman, and UV-vis spectroscopies (466 < lambda(max)(dsigma-dsigma*) < 480 nm), by ATG, XRD, and DSC methods, and by the capacity to make stand-alone films. From the measurements of the intrinsic viscosity in acetonitrile, the M(n) ranges from 16000 to 18400 (12 to 16 units). The dinuclear model complex [Pd(2)(dmb)(2)(PPh(3))(2)](ClO(4))(2) (4) is prepared and investigated as well. The molecular dynamic of the title polymers in acetonitrile solution is investigated by means of (13)C spin-lattice relaxation time (T(1)) and nuclear Overhauser enhancement methods (NOE). The number of units determined by T(1)/NOE methods is 3 to 4 times less than that found from the measurements of intrinsic viscosity, and is due to flexibility in the polymer backbone, even for bridging ligands containing only one (dmb) or two C-C single bonds (dpa). During the course of this study, the starting material Pd(2)(dmb)(2)Cl(2) was reinvestigated after evidence for oligomers in the MALDI-TOF spectrum was noticed. In solution, this d(9)-d(9) species is a binuclear complex (T(1)/NOE). This result suggests that the structure of the title polymers in solution and in the solid state may not be the same either. Finally, these polymers are strongly luminescent in PrCN glasses at 77 K, and the photophysical data (emission lifetimes, 1.50 < tau(e) < 2.75 ns; quantum yields, 0.026 < Phi(e) < 0.17) are presented. X-ray data for [Pd(2)(dppe)(2)(dmb)(2)](PF(6))(4): monoclinic, space group C2/c, a = 24.3735 A, b = 21.8576(13) A, c = 18.0034(9) A, b = 119.775(1) degrees, V = 8325.0(8) A(3), Z = 4.

Heterodinuclear Zinc(II)−Iron(III) Complexes and Dinuclear Zinc Complexes as Models for Zinc-Containing Phosphatases

Five new dinuclear model complexes for zinc-containing phosphatases with dinucleating ligands have been prepared and characterized by single-crystal X-ray crystallography. The heterodinuclear, μ-alkoxo-bridged zinc(II)−iron(III) complexes 1−3 contain the symmetric ligands N,N,N′,N′-tetrakis[2-(5,6-dimethyl)benzimidazolylmethyl]-1,3-diamino-2propanol (Htdmbpo) and N,N,N′,N′-tetrakis{2-[N′′-(2hydroxyethyl)]benzimidazolylmethyl}-1,3-diamino-2-propanol (Hthebpo), and the asymmetric ligand N,N-bis[2-(4,5-dimethyl)benzimidazolylmethyl]-N′,N′-bis(2-pyridylmethyl)-1,3-diamino-2-propanol (Hbdmbbppo), respectively. X-ray crystallography revealed that the zinc center exhibits a trigonal-bipyramidal coordination, while the octahedral coordination sphere of the iron center is completed by a solvent molecule. In contrast, the zinc complexes 4 and 5, which also have (alkoxo)(cacodylato)dimetal cores with the dinucleating ligands used in 1 and 3, exhibit both metal centers in a trigonal-bipyramidal environment. Additionally, the solution speciation of the zinc(II) complexes formed with Htdmbpo and Hbdmbbppo were determined and the activity of the in situ prepared zinc complexes towards the transesterification of the RNA model substrate 2-(hydroxypropyl)-4-nitrophenyl phosphate (hpnp) was investigated. The dinuclear [Zn2LH−1(OH)]2+ complex of both ligands efficiently promotes the transesterification. The kinetic data indicated a higher activity for the complex of the asymmetric ligand Hbdmbbppo, as a result of its stronger substrate binding ability. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Heterodinuclear Zinc(II)−Iron(III) Complexes and Dinuclear Zinc Complexes as Models for Zinc-Containing Phosphatases

Five new dinuclear model complexes for zinc-containing phosphatases with dinucleating ligands have been prepared and characterized by single-crystal X-ray crystallography. The heterodinuclear, μ-alkoxo-bridged zinc(II)−iron(III) complexes 1−3 contain the symmetric ligands N,N,N′,N′-tetrakis[2-(5,6-dimethyl)benzimidazolylmethyl]-1,3-diamino-2propanol (Htdmbpo) and N,N,N′,N′-tetrakis{2-[N′′-(2hydroxyethyl)]benzimidazolylmethyl}-1,3-diamino-2-propanol (Hthebpo), and the asymmetric ligand N,N-bis[2-(4,5-dimethyl)benzimidazolylmethyl]-N′,N′-bis(2-pyridylmethyl)-1,3-diamino-2-propanol (Hbdmbbppo), respectively. X-ray crystallography revealed that the zinc center exhibits a trigonal-bipyramidal coordination, while the octahedral coordination sphere of the iron center is completed by a solvent molecule. In contrast, the zinc complexes 4 and 5, which also have (alkoxo)(cacodylato)dimetal cores with the dinucleating ligands used in 1 and 3, exhibit both metal centers in a trigonal-bipyramidal environment. Additionally, the solution speciation of the zinc(II) complexes formed with Htdmbpo and Hbdmbbppo were determined and the activity of the in situ prepared zinc complexes towards the transesterification of the RNA model substrate 2-(hydroxypropyl)-4-nitrophenyl phosphate (hpnp) was investigated. The dinuclear [Zn2LH−1(OH)]2+ complex of both ligands efficiently promotes the transesterification. The kinetic data indicated a higher activity for the complex of the asymmetric ligand Hbdmbbppo, as a result of its stronger substrate binding ability. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and Magnetic Properties of MnIIIMnIIMnIII Trinuclear Complexes with Hydroxo Bridges. Comparison of Magnetic Properties between Hydroxo- and Alkoxo-Bridged Complexes by Density Functional Calculations

Abstract A hydroxo-bridged MnIIIMnIIMnIII trinuclear complex, [Mn3(L1)2(2,6-dcba)2(OH)2] (1), where H2L1 is N′,N′-bis-(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine and H2,6-dcba is 2,6-dichlorobenzoic acid, was synthesized by the reaction of Mn(ClO4)2·6H2O with H2L1, H2,6-dcba, and a base in acetonitrile. The structure of 1 was determined by X-ray crystallography: 1 crystallizes in the monoclinic space group P21/c with a = 9.616(4) Å, b = 12.537(4) Å, c = 23.099(4) Å, β = 94.73(2)°, V = 2775(1) Å3, and Z = 2. The central MnII and terminal MnIII ions are bridged by phenolato, carboxylato, and hydroxo ligands to form a linear MnIII–MnII–MnIII arrangement. The bridging structure between MnIII and MnII is similar to that of analogous alkoxo-bridged complexes, [Mn3(L)2(carboxylato)2(alkoxo)2], where L is L1 or its derivatives. Most of the alkoxo-bridged complexes [Mn3(L)2(carboxylato)2(alkoxo)2] exhibit a weak ferromagnetic interaction between MnIII and MnII, while the hydroxo-bridged complex 1 exhibits a weak antiferromagnetic interaction. A comparison of the magnetic properties between the hydroxo- and alkoxo-bridged complexes was performed by density functional calculations of MnIIIMnII dinuclear model complexes.

Reactivity of μ-Hydroxodizinc(II) Centers in Enzymatic Catalysis through Model Studies

The stable dinuclear complex [Zn2(BPAM)(mu-OH)(mu-O2PPh2)](ClO4)2, where BPAN = 2,7-bis[2-(2-pyridylethyl)-aminomethyl]-1,8-naphthyridine, was chosen as a model to investigate the reactivity of (mu-hydroxo)dizinc(II) centers in metallohydrolases. Two reactions, the hydrolysis of phosphodiesters and the hydrolysis of beta-lactams, were studied. These two processes are catalyzed in vivo by zinc(II)-containing enzymes: P1 nucleases and beta-lactamases, respectively. The former catalyzes the hydrolysis of single-stranded DNA and RNA. beta-Lactamases, expressed in many types of pathogenic bacteria, are responsible for the hydrolytic degradation of beta-lactam antibiotic drugs. In the first step of phosphodiester hydrolysis promoted by the dinuclear model complex, the substrate replaces the bridging diphenylphosphinate. The bridging hydroxide serves as a general base to deprotonate water, which acts as a nucleophile in the ensuing hydrolysis. The dinuclear model complex is only 1.8 times more reactive in hydrolyzing phosphodiesters than a mononuclear analogue, Zn(bpta)(OTf)2, where bpta = N,N-bis(2-pyridylmethyl)-tert-butylamine. Hydrolysis of nitrocefin, a beta-lactam antibiotic analogue, catalyzed by [Zn2(BPAN)(mu-OH)(mu-O2PPh2)](ClO4)2 involves monodentate coordination of the substrate via its carboxylate group, followed by nucleophilic attack of the zinc(II)-bound terminal hydroxide at the beta-lactam carbonyl carbon atom. Collapse of the tetrahedral intermediate results in product formation. Mononuclear complexes Zn(cyclen)-(NO3)2 and Zn(bpta)(NO3)2, where cyclen = 1,4,7,10-tetraazacyclododecane, are as reactive in the beta-lactam hydrolysis as the dinuclear complex. Kinetic and mechanistic studies of the phosphodiester and beta-lactam hydrolyses indicate that the bridging hydroxide in [Zn2(BPAN)(mu-OH)(mu-O2PPh2)](ClO4)2 is not very reactive, despite its low pKa value. This low reactivity presumably arises from the two factors. First, the briding hydroxide and coordinated substrate in [Zn2(BPAN)(mu-OH)(substrate)]2+ are not aligned properly to favor nucleophilic attack. Second, the nucleophilicity of the bridging hydroxide is diminished because it is simultaneously bound to the two zinc(II) ions.