Diimine Complexes Research Articles

Synthesis of palladium(II) diimine complexes and their catalytic potential in sonogashira cross coupling reaction

Cross-coupling reactions catalyzed by various transition metal com- plexes are the most powerful synthetic tools for the generation of C = C and C ≡C bonds. Significant effort s have been put into the modification of ligands to increase the catalytic efficiency of the transition metal complexes. In most cases, attention is only paid to highly efficient catalysts and unsuccessful examples are often ig- nored. In this work, four diimine compounds, R-dab, were synthe- sized by condensation reaction and then reacted with the precur- sor [PdCl 2 (MeCN) 2 ] to form a palladium(II) diimine, [PdCl 2 (R-dab)], complex. Our initial hypothesis was that the strong trans -effect from the diimine ligand in [PdCl 2 (R-dab)] would enhance the rate of reductive elimination and subsequently promote the formation of cross coupling product. The catalytic efficiency of [PdCl 2 (R-dab)] complexes in Sonogashira cross coupling reactions were examined at a temperature of 70 °C by reacting methyl-4-bromobenzoate and 2-methylbut-3-yn-2-ol for 5 hours under nitrogen conditions. Un- fortunately, our results showed that the [PdCl 2 (R-dab)] complexes are incapable of inducing the formation of cross coupling product. Despite the fact that these cross-coupling reactions were unsuc- cessful, we set out to explain the reasons for this failure herein

Luminescence Quenching and Enhancement by Adsorbed Metal Ions with Ruthenium Diimine Complexes Immobilized on Silica Polyamine Composites.

Luminescent ruthenium diimine complexes have been covalently bound to the surface of a silica polyamine composite (SPC) using peptide coupling agents. The loading of the complexes using this route is quite low (~0.01-0.04 mmol/g) leaving sufficient surface amines to coordinate added metal ions. When the composite particles containing the Ru complexes are exposed to solutions of Cu2+, Ni2+ or Zn2+, luminescence is quenched with efficiencies that follow concentration dependence and the relative binding affinities of the ions. When heavy metal ions such as mercury or lead are adsorbed onto the same surface, luminescence is enhanced by a factor of ~3.5. When the complexes are exposed to these metals in solution, no quenching or enhancement is observed. Both phenomena were shown to be the result of adsorption of the cations onto the polyamine surface by using the Stern-Volmer relationship. The mechanism of both quenching and enhancement is discussed and the options for further development of this novel metal sensing technique are presented.

Eric N. Jacobsen

Eric N. Jacobsen

Synthesis and characterization of alkynylrhenium(I) tricarbonyl diimine complexes with fused thiophene and cyanoacrylic acid moiety

A series of alkynylrhenium(I) tricarbonyl diimine complexes with fused thiophene and cyanoacrylic acid moiety has been synthesized and characterized. A long-lived charge separated state of these complexes have been found. Preliminary studies to explore the utilization of these complexes as photosensitizers have also been made, which show photoresponse upon light illumination.

Synthesis, characterization and crystal structure of rhenium(I) tricarbonyl diimine complexes coupled with their efficiency in producing hydrogen in a photocatalytic system

Herein, we present the synthesis and characterization of two complexes, namely [ReBr(CO)3amphen] (1) (amphen=1,10-phenanthroline-5-amine) and [ReBr(CO)3pq] (2) (pq=2-(2′pyridyl)quinoxaline); complex 2 is reported for the first time. The X-ray crystal structure of 2 has been determined. Electrochemical and photophysical studies have been performed to study the effect of the variation of the diimine ligand on the redox and optical properties of this class of compounds. Both complexes were used as photosensitizers for hydrogen production in a homogeneous photocatalytic system also carrying [Co(dmgH)2] as a hydrogen reaction catalyst, triethanolamine as an irreversible reductive quencher and AcOH as proton source. Complex 1 produces H2 after only 2h irradiation while complex 2 requires 24h indicating that the differences in the electronic properties influence their photosensitizing ability.

Shape-Memory Platinum(II) Complexes: Intelligent Vapor-History Sensor with ON-OFF Switching Function.

A novel platinum(II)-diimine complex, [Pt(CN)2 (H2 dcphen)] (1; H2 dcphen=4,7-dicarboxy-1,10- phenanthroline), was synthesized and its vapochromic shape-memory behavior was evaluated. The as-synthesized amorphous purple solid, [Pt(CN)2 (H2 dcphen)]⋅2 H2 O (1 P), exhibited vapochromic behavior in the presence of alcoholic vapors through transformation to a red, crystalline, porous, vapor-adsorbed form, 1 R⊃vapor. The obtained 1 R⊃vapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vaporfree, porous 1 R⊃open could detect water or n-hexane vapor, although these vapors could not induce 1 P-to-1 R⊃vapor transformation, and 1 R⊃open could easily be converted to the initial 1 P by manual grinding. These results indicate that 1 is a new shape-memory material that functions through formation and collapse of the porous framework with an emission change upon vapor-adsorption and grinding; this enables it to exhibit vapor history and ON-OFF switching sensing functions.

Influence of a Naphthaldiimide Substituent at the Diimine Ligand on the Photophysics and Reverse Saturable Absorption of PtII Diimine Complexes and Cationic IrIII Complexes

AbstractTwo PtII complexes containing benzothiazolylfluorenyl (BTF) acetylide ligands and different diimine (NN) ligands [NN = 1,10‐phenanthroline (1), 5‐naphthaldiimide–1,10‐phenanthroline (2)] and two heteroleptic cationic IrIII complexes containing the 5‐naphthaldiimide–1,10‐phenanthroline ligand and different phenylpyridine (CN) ligands [CN = 2‐phenylpyridine (3), 2‐{3‐[7‐(benzothiazol‐2‐yl)fluoren‐2‐yl]phenyl}pyridine (4)] were synthesized and characterized. The influence of naphthaldiimide (NDI) attached to the NN ligands and benzothiazolylfluorene attached to the CN ligands on the photophysical properties of these PtII/IrIII complexes has been investigated spectroscopically and theoretically. All complexes exhibit ligand‐localized 1π,π* transitions below 400 nm, and broad and structureless metal‐to‐ligand/ligand‐to‐ligand charge transfer (1MLCT/1LLCT) transitions between 400 and 550 nm. Complexes 1 and 4 show red phosphorescence in toluene solutions at room temperature, where the emitting state is assigned predominantly to the 3π,π* state for complex 1 and 3LLCT/3MLCT states for complex 4. Incorporation of the NDI substituent to the NN ligand completely or partially quenches the emission of complexes 2–4. Complexes 1–4 all possess broad singlet transient absorption from 400 to 800 nm, which is ascribed to 1π,π*/1MLCT/1LLCT states for complex 1, and to 1NDI–· for complexes 2–4. The ns transient absorption study reveals that complex 1 exhibits a broad triplet excited‐state absorption from the 3π,π*/3MLCT states, while complexes 2–4 give moderately strong triplet excited‐state absorption from 3NDI–·. Nonlinear transmission experiments at 532 nm using nanosecond laser pulses demonstrate that these complexes all exhibit strong reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Introduction of the NDI substituent to the NN ligand causes charge transfer to the NDI component, which in turn increases the RSA of the PtII complex 2 in comparison with that of the PtII complex 1; while attaching the BTF component to the CN ligands enhances the RSA of the IrIII complex 4 in comparison with that of complex 3.

Ru(II)-diimine functionalized metalloproteins: From electron transfer studies to light-driven biocatalysis

The unique photochemical properties of Ru(II)-diimine complexes have helped initiate a series of seminal electron transfer studies in metalloenzymes. It has thus been possible to experimentally determine rate constants for long-range electron transfers. These studies have laid the foundation for the investigation of reactive intermediates in heme proteins and for the design of light-activated biocatalysts. Various metalloenzymes such as hydrogenase, carbon monoxide dehydrogenase, nitrogenase, laccase and cytochrome P450 BM3 have been functionalized with Ru(II)-diimine complexes. Upon visible light-excitation, these photosensitized metalloproteins are capable of sustaining photocatalytic activity to reduce small molecules such as protons, acetylene, hydrogen cyanide and carbon monoxide or activate molecular dioxygen to produce hydroxylated products. The Ru(II)-diimine photosensitizers are hence able to deliver multiple electrons to metalloenzymes buried active sites, circumventing the need for the natural redox partners. In this review, we will highlight the key achievements of the light-driven biocatalysts, which stem from the extensive electron transfer investigations. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

Photoinduced cytotoxicity by a platinum diimine complex employing magnetite-silica nanocomposites as delivery vehicles.

Tartaric acid-modified core-shell magnetite-silica nanocomposites were prepared by a sol-gel method, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Then the nanocomposites were employed as carriers of a photoactive platinum diimine complex. Photoinduced cytotoxicity by the photosensitizer-loaded nanocomposites in different human carcinoma cells has been studied by cell viability assay. The results suggest that the as-synthesized nanocomposites have good stability in water, and the cytotoxicity induced by the platinum diimine complex in red light can be significantly enhanced when the photosensitizer is loaded with the magnetic nanocomposites.

Electron Injection from Copper Diimine Sensitizers into TiO2: Structural Effects and Their Implications for Solar Energy Conversion Devices.

Copper(I) diimine complexes have emerged as low cost replacements for ruthenium complexes as light sensitizers and electron donors, but their shorter metal-to-ligand-charge-transfer (MLCT) states lifetimes and lability of transient Cu(II) species impede their intended functions. Two carboxylated Cu(I) bis-2,9-diphenylphenanthroline (dpp) complexes [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(COOH)2)](+) and [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(Φ-COOH)2)](+) (Φ = tolyl) with different linker lengths were synthesized in which the MLCT-state solvent quenching pathways are effectively blocked, the lifetime of the singlet MLCT state is prolonged, and the transient Cu(II) ligands are stabilized. Aiming at understanding the mechanisms of structural influence to the interfacial charge transfer in the dye-sensitized solar cell mimics, electronic and geometric structures as well as dynamics for the MLCT state of these complexes and their hybrid with TiO2 nanoparticles were investigated using optical transient spectroscopy, X-ray transient absorption spectroscopy, time-dependent density functional theory, and quantum dynamics simulations. The combined results show that these complexes exhibit strong absorption throughout the visible spectrum due to the severely flattened ground state, and a long-lived charge-separated Cu(II) has been achieved via ultrafast electron injection (<300 fs) from the (1)MLCT state into TiO2 nanoparticles. The results also indicate that the TiO2-phen distance in these systems does not have significant effect on the efficiency of the interfacial electron-transfer process. The mechanisms for electron transfer in these systems are discussed and used to develop new strategies in optimizing copper(I) diimine complexes in solar energy conversion devices.

Light-driven generation of hydrogen: New chromophore dyads for increased activity based on Bodipy dye and Pt(diimine)(dithiolate) complexes

New dyads consisting of a strongly absorbing Bodipy (dipyrromethene-BF2) dye and a platinum diimine dithiolate (PtN2S2) charge transfer (CT) chromophore have been synthesized and studied in the context of the light-driven generation of H2 from aqueous protons. In these dyads, the Bodipy dye is bonded directly to the benzenedithiolate ligand of the PtN2S2 CT chromophore. Each of the new dyads contains either a bipyridine (bpy) or phenanthroline (phen) diimine with an attached functional group that is used for binding directly to TiO2 nanoparticles, allowing rapid electron photoinjection into the semiconductor. The absorption spectra and cyclic voltammograms of the dyads show that the spectroscopic and electrochemical properties of the dyads are the sum of the individual chromophores (Bodipy and the PtN2S2 moieties), indicating little electronic coupling between them. Connection to TiO2 nanoparticles is carried out by sonication leading to in situ attachment to TiO2 without prior hydrolysis of the ester linking groups to acids. For H2 generation studies, the TiO2 particles are platinized (Pt-TiO2) so that the light absorber (the dyad), the electron conduit (TiO2), and the catalyst (attached colloidal Pt) are fully integrated. It is found that upon 530 nm irradiation in a H2O solution (pH 4) with ascorbic acid as an electron donor, the dyad linked to Pt-TiO2 via a phosphonate or carboxylate attachment shows excellent light-driven H2 production with substantial longevity, in which one particular dyad [4(bpyP)] exhibits the highest activity, generating ∼ 40,000 turnover numbers of H2 over 12 d (with respect to dye).

Electrochemical Reduction of CO2 by M(CO)4(diimine) Complexes (M=Mo, W): Catalytic Activity Improved by 2,2′‐Dipyridylamine

AbstractTetracarbonyl complexes of low‐valent Group VI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO)4(4,6‐diphenyl‐2,2′‐bipyridine) (1), W(CO)4(6‐(2,6‐dimethoxyphenyl)‐4‐phenyl‐2,2′‐bipyridine) (2), Mo(CO)4(2,2′‐dipyridylamine) (3), and W(CO)4(2,2′‐dipyridylamine) (4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO2 in nonaqueous media. Cyclic voltammetry performed under a CO2 atmosphere, revealed that these complexes have significant catalytic activity in acetonitrile, and gas chromatographic measurements together with exhaustive electrolysis showed that CO is the major reduction product. Mechanistic insights were obtained by IR‐spectroelectrochemical measurements. The substantially different electrocatalytic performances obtained for the two classes of catalysts are compared and discussed.

Interaction of rhenium(I) complex carrying long alkyl chain with Calf Thymus DNA: Cytotoxic and cell imaging studies

The interaction of three rhenium(I)-diimine complexes carrying long alkyl chain fac-[Re(CO)3(α-diimine){4-C11py}] CF3SO31a–1c (α-diimine=2,2′-bipyridine (1a), 4,4′-di-tert-butyl-2,2′-bipyridine (1b), 4,4′-dinonyl-2,2′-bipyridine (1c); 4-C11py=(4-undecylpyridine) and fac-[Re(CO)3(α-diimine)(4-Etpy)]CF3SO3 (1d) (α-diimine=2,2′-bipyridine, 4-Etpy=4-Ethylpyridine) with Calf Thymus DNA (CT DNA) is studied by UV–vis absorption, luminescence and CD spectral techniques at pH 7.2. Spectral, viscosity and molecular docking studies unambiguously establish the formation of a groove binding between the Re(I) complex and CT DNA. The binding constant values of 1b and 1c are one order more than that of 1a and 1d indicating the importance of hydrophobic interaction of alkyl groups on bpy and py ligands with DNA. The complexes 1b and 1c exhibit the most pronounced antibacterial activity against four different microorganisms and all Re(I) complexes inhibit the growth of T and B cell lymphoma (Raji and Jurkat) cancer cells. Complex 1c exhibits the moderate cytotoxicity and cellular uptake of cancer cell lines attributed to the lipophilic alkyl chain on bpy and pyridine ligands which facilitate the hydrophobic interaction with DNA and healthy membrane permeability.

Electrophilic C–H activation of benzene with a Shilov-inspired rhodium(III) diimine complex

Four new air and water stable, organometallic rhodium(III) complexes trans-RhIII(α-diimine) (CO)I2Me, 1, [RhIII(α-diimine) (C(O)Me) (H2O)3][BF4]2, 2, [RhIII(α-diimine)Me(H2O)3] [BF4]2, 3, and RhIII(α-diimine) (C(O)Me) (H2O) (OC(O)CF3)2, 4 (α-diimine = 1,4-bis(Ar)-2,3-dimethyl-1,4-diaza-1,3-butadiene, Ar = 3,5-dimethylphenyl) were synthesized and characterized by X-ray crystallography. H/D exchange of C6H6 with TFA-d1 (TFA = trifluoroacetic acid) was observed with 4 mol% loading of 3 at 100 °C with 137 turnovers (98% completion at 91% deuterium incorporation) in 24 h. 3 showed sustained catalytic activity towards H/D exchange of benzene even after three iterations of catalyst recycling.

ChemInform Abstract: Mer and Fac Isomerism in Tris Chelate Diimine Metal Complexes

AbstractReview: 137 refs.

A facile approach for the synthesis of novel 1-oxa- and 1-aza-flavonyl-4-methyl-1H-benzo[d][1,3]oxazin-2(4H)-ones by microwave enhanced Suzuki–Miyaura coupling using bidentate chromen-4-one-based Pd(ii)–diimine complex as catalyst

A facile access to novel 1-oxa- and 1-aza-flavonyl-4-methyl-1H-benzo[d][1,3]oxazin-2(4H)-ones using microwave assisted Suzuki coupling of bromo flavones with boronic acids using a novel catalytic system (C) under aerobic condition is reported.

Luminescent copper(I) halide and pseudohalide phenanthroline complexes revisited: simple structures, complicated excited state behavior.

We have synthesized a series of luminescent trigonal [CuX(dtbphen)] (X = I (), Br (), Cl (), CN (), dtbphen = 2,9-di-tert-butylphenanthroline) and tetrahedral [Cu2(μ-I)2(L)2] (L = phenanthroline (), 2,9-dimethylphenanthroline ()) copper diimine complexes. Bearing in mind the chemical simplicity of this class of long-known Cu(i) phenanthroline compounds, it is surprising that they exhibit non-trivial photophysical properties, which have not been fully recognized. They display broad XMLCT absorption between ca. 450-600 nm, and the broad emission between ca. 550-850 nm in the solid state occurring with lifetimes on the μs timescale indicates phosphorescence, although the energetic overlap between excitation and emission suggests thermally activated delayed fluorescence (TADF) from S1. In line with the latter assumption, low temperature measurements of in the solid state show an energetic separation of emission and excitation. However, a counter-intuitive decrease of emission intensity and simultaneous increase of the emission lifetime at low temperatures are observed for , which indicates two triplet states also being involved. Our DFT and TD-DFT calculations show that emission from the lowest excited triplet state T1 is of (3)LMXCT nature, separated by only ca. 0.16 eV from S1. Low temperature photophysical measurements at 77 K in a glassy matrix of in 2-Me-THF and of in the solid state are in agreement with the theoretical results, revealing in addition that π-interactions in the solid state also greatly influence the photophysical properties, making a clear conclusion towards TADF ambiguous. This study suggests that other related simple and long-known Cu(i) systems may exhibit a similar, more complex excited state behavior than previously appreciated, involving several emitting states and important intermolecular interactions.

Synthesis, characterization and cellular location of cytotoxic constitutional organometallic isomers of rhenium delivered on a cyanocobalmin scaffold.

Constitutional isomers of cyanocobalamin adducts based on a fluorescent rhenium tris-carbonyl diimine complex were prepared, characterized and tested against PC-3 cancer cells. The adducts differ only in the relative binding position of the organometallic species which is either bound at the cyano or the 5'-hydroxo group of vitamin B12. When tested for their cytotoxic potency, the species showed IC50 values in the low μM rage. Upon conjugation to the vitamin an energy transfer process causes an extremely low quantum yield of fluorescence emission, making the conjugates unsuitable for fluorescence imaging. However, by exploiting the vibrational signature of the fac-[Re(CO)3](+) core, their cellular distribution was evaluated via FTIR spectromicroscopy.

Mer and fac isomerism in tris chelate diimine metal complexes.

In this perspective, we highlight the issue of meridional (mer) and facial (fac) orientation of asymmetrical diimines in tris-chelate transition metal complexes. Diimine ligands have long been the workhorse of coordination chemistry, and whilst there are now good strategies to isolate materials where the inherent metal centered chirality is under almost complete control, and systematic methodologies to isolate heteroleptic complexes, the conceptually simple geometrical isomerism has not been widely investigated. In systems where the two donor atoms are significantly different in terms of the σ-donor and π-accepting ability, the fac isomer is likely to be the thermodynamic product. For the diimine complexes with two trigonal planar nitrogen atoms there is much more subtlety to the system, and external factors such as the solvent, lattice packing and the various steric considerations play a delicate role in determining the observed and isolable product. In this article we discuss the possibilities to control the isomeric ratio in labile systems, consider the opportunities to separate inert complexes and discuss the observed differences in their spectroscopic properties. Finally we report on the ligand orientation in supramolecular systems where facial coordination leads to simple regular structures such as helicates and tetrahedra, but the ability of the ligand system to adopt a mer orientation enables self-assembled structures of considerable beauty and complexity.

Strongly phosphorescent neutral rhenium(i) isocyanoborato complexes: synthesis, characterization, and photophysical, electrochemical, and computational studies.

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)3 (N^N)(CNBR3 )], where N^N=bpy, 4,4'-Me2 bpy, phen, 4,7-Me2 phen, 2,9-Me2 phen, 3,4,7,8-Me4 phen; R=C6 F5 , C6 H5 , Cl, 4-ClC6 H4 , 3,5-(CF3 )2 C6 H3 , with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X-ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD-DFT calculations have been performed, which revealed that the lowest-energy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π*(N^N)] and LLCT [π(CNBR3 )→π*(N^N)] transitions.