Meridional Isomers Research Articles

Exploring the geometrical and optical properties of neutral rhenium (I) tricarbonyl complex of 1,10-phenanthroline-5,6-diol using relativistic methods

In this contribution, we studied through experimental and relativistic DFT (R-DFT) calculations, the neutral complex fac-[Re(CO)3(1,10-phenanthroline-5,6-diol)Cl] (B1) as a potential precursor compound for designing new fluorophores suitable for confocal microscopy specially in walled cells. This work also describes via DFT calculations the electronic and spectroscopic properties of the facial (fac) and meridional (mer) isomers of this compound. The calculations shows that mer-isomer is 17.5kcal/mol (in vacum) and 21.1kcal/mol (when the solvent is considered) higher in energy with respect to the fac-isomer. The calculated emission spectra of B1, indicates an emission around 620nm in acetonitrile in good agreement with the experimental reports for similar molecules. Finally, the Morokuma–Ziegler energy decomposition analysis shows a major lability for Cl ligand which is ideal for designing new compounds replacing this ligand for another ancillary ligand suitable for biological applications.

Synthesis, characterization and biological activity of gallium(III) complexes with non-symmetrical N2O-donor Schiff bases

Cisplatin and its analogues are some of the most widely used anticancer drugs. However, toxicity and resistance have limited their use, and gallium compounds have emerged as an alternative, due to their remarkable antitumor activity and low toxicity. In this paper, we report on four new mononuclear gallium(III) complexes with the general formula [Ga(bhi-R)2]+, where bhi-R (R=–NO2, –Br, –Cl and –OCH3) is the deprotonated form of imidazole/phenol-containing tridentate Schiff bases. The molecular structures of C1–C4 were solved by single crystal X-ray diffraction revealing mononuclear and isostructural complexes, with the metal center in distorted octahedral geometries. In all cases, the gallium(III) is coordinated to two ligand molecules arranged in meridional fashion, through the imidazole and imino nitrogen atoms, and to the phenolate oxygen. Complexes C1–C4 were also characterized in solution by spectroscopic and spectrometric techniques. DFT calculations were performed to assist the interpretation of experimental results, and also allowed to establish the reasons why only meridional isomers were obtained. The stability of all complexes was evaluated in PBS buffer (1% DMSO) over 24h, and results indicate partial hydrolysis in this period. Finally, the biological activity of C1–C4 was evaluated on human tumor cell lines MCF-7 (breast adenocarcinoma), A-549 (lung adenocarcinoma epithelial) and PC-3 (prostate adenocarcinoma). Complex C1 was the most active, being effective and selective for A-549. The IC50 (94.12±4.62) of C1 is lower than the value (135.10±6.50) obtained for cisplatin, which was tested as a metallodrug reference under the same experimental conditions.

A combined experimental and theoretical study on supramolecular assemblies in octahedral cobalt(III) salicylaldimine complexes having pendant side arms

Two mononuclear cobalt(III) complexes, [Co(L1)(N3)2(deen)] (1) and [Co(L2)(N3)2(DMSO)] (2), where HL1 {2-(2-(diethylamino)ethyliminomethyl)-4-bromophenol} and HL2 {2-(2-(diethylamino)ethyliminomethyl)-6-methoxyphenol} are tridentate and tetradentate Schiff bases, respectively and deen is a bidentate chelating ligand, N,N-diethyl-1,2-diaminoethane, were prepared and characterized by elemental and spectral analysis. X-ray crystal structure determination confirmed their structures. Both complexes are meridional isomers. The solid state structures show the participation of the organic ligands in concurrent conventional and unconventional CH⋯π interactions along with hydrogen bonding. The energetic features of these interactions have also been studied by means of DFT calculations.

A Stable Coordination Complex of Rh(IV) in an N,O-Donor Environment.

We describe facial and meridional isomers of [Rh(III)(pyalk)3], as well as meridional [Rh(IV)(pyalk)3](+) {pyalk =2-(2-pyridyl)-2-propanoate}, the first coordination complex in an N,O-donor environment to show a clean, reversible Rh(III/IV) redox couple and to have a stable Rh(IV) form, which we characterize by EPR and UV-visible spectroscopy as well as X-ray crystallography. The unprecedented stability of the Rh(IV) species is ascribed to the exceptional donor strength of the ligands, their oxidation resistance, and the meridional coordination geometry.

Deep blue phosphorescent organic light-emitting diodes with very high brightness and efficiency.

The combination of both very high brightness and deep blue emission from phosphorescent organic light-emitting diodes (PHOLED) is required for both display and lighting applications, yet so far has not been reported. A source of this difficulty is the absence of electron/exciton blocking layers (EBL) that are compatible with the high triplet energy of the deep blue dopant and the high frontier orbital energies of hosts needed to transport charge. Here, we show that N-heterocyclic carbene (NHC) Ir(III) complexes can serve as both deep blue emitters and efficient hole-conducting EBLs. The NHC EBLs enable very high brightness (>7,800 cd m(-2)) operation, while achieving deep blue emission with colour coordinates of [0.16, 0.09], suitable for most demanding display applications. We find that both the facial and the meridional isomers of the dopant have high efficiencies that arise from the unusual properties of the NHC ligand-that is, the complexes possess a strong metal-ligand bond that destabilizes the non-radiative metal-centred ligand-field states. Our results represent an advance in blue-emitting PHOLED architectures and materials combinations that meet the requirements of many critical illumination applications.

Stable Iridium(IV) Complexes of an Oxidation-Resistant Pyridine-Alkoxide Ligand: Highly Divergent Redox Properties Depending on the Isomeric Form Adopted.

The preparation of the facial and meridional isomers of [Ir(pyalk)3] (pyalk = 2-(2-pyridyl)isopropanoate), as model complexes for a powerful water oxidation catalyst, is reported. The strongly donating N3O3 ligand set is very oxidation-resistant, yet promotes facile metal-centered oxidation to form stable Ir(IV) compounds. The Ir(III/IV) reduction potentials of the two isomers differ by 340 mV despite the identical ligand set. A ligand field rationalization is advanced and supported by DFT calculations.

Synthesis, structure, and spectral and electrochemical properties of chromium(III) tris-(8-hydroxyquinolinate).

The kinetically inert chromium(III) tris-(8-hydroxyquinolinate), Crq3, has been synthesized, crystallized from 90% methanol-water, and characterized by MALDI-TOF mass spectrometry, thermogravimetry, FTIR, NMR spectroscopy, and X-ray powder diffraction. It is formed as a methanol solvate, but the solvent can be removed by heating. Large paramagnetic shifts and spectral broadening in (1)H NMR spectra indicate electron delocalization between the metal and the ligand. DFT calculations show it is present as the meridional isomer, with the HOMO largely based on one of the metal 3d orbitals and the LUMO essentially localized on the ligands. Cyclic voltammetry (CV) in acetonitrile solutions shows four oxidation peaks and two, less intense reduction waves on the first scan. The HOMO energy determined from the first oxidation peak is fairly close to that obtained by DFT, in agreement with this being mainly metal based. Although the number of peaks decreases on subsequent CV scans, the complex shows markedly enhanced electrochemical stability compared with aluminium(III) tris-(8-hydroxyquinolinate). Solution UV/visible absorption and solid diffuse reflectance spectra have a weak, long wavelength band, assigned to the metal based d-d transition, in addition to the normal, ligand based bands seen in metal quinolates. The energy of the lowest energy band is identical to the HOMO-LUMO separation obtained by cyclic voltammetry, in agreement with the above description. The compound is only weakly luminescent, in contrast to many other metal quinolates, due to the lowest energy transition being metal rather than ligand based. The potential of this compound as an electron transporting/hole blocking layer in optoelectronic devices is indicated.

Thermodynamic N-donor trans influence in labile pseudo-octahedral zinc complexes: a delusion?

While the forces responsible for the chelate effect are well-established in coordination chemistry, the origin and implementation of the related thermodynamic trans influence remains debatable. This work illustrates a simple approach for quantifying this effect in labile pseudo-octahedral [Zn(Lk)3](2+) complexes lacking stereochemical preferences (Lk = L1–L4 are unsymmetrical didentate α,α′-diimine ligands). In line with statistics, the triply degenerated meridional isomers mer-[Zn(Lk)3](2+) are stabilized by 0.8 ≤ ΔGexch(mer→fac) ≤ 4.2 kJ/mol over their nondegenerated facial analogues fac-[Zn(Lk)3](2+) and therefore display no apparent trans influence at room temperature. However, the dissection of the free energy terms into opposite enthalpic (favoring the facial isomers) and entropic (favoring the meridional isomers) contributions reveals a trans influence assigned to solvation processes occurring in polar solvents. Altogether, the thermodynamic trans influence operating in [Zn(α,α′-diimine)3](2+) complexes is 1–2 orders of magnitude smaller than the chelate effect. A weak templating effect provided by a noncovalent lanthanide tripod is thus large enough to produce the wanted facial isomer at room temperature.

Electron Transport Materials for Organic Light-Emitting Diodes: Understanding the Crystal and Molecular Stability of the Tris(8-hydroxyquinolines) of Al, Ga, and In

An experimental and theoretical study on the phase and molecular stability of Mq3 (M = Al, Ga, and In; q = 8-hydroxyquinoline) is presented. The results suggest that the energy difference between the meridional and facial isomers of Mq3 shall be significantly lower than previously though and provide an explanation for the reported mer–fac solid–solid transition. The first accurate vapor pressure measurements for Alq3, Gaq3, and Inq3 are presented, which are of great relevance for the manufacturing of thin films by vacuum deposition. Phase transition thermodynamics indicates higher cohesive energies of the mer-isomers and an entropic differentiation that can be associated with the different molecular symmetry of the mer- and fac-isomers.

On the elusive anti-bayerite structure

Abstract Sequential deprotonation of the Cr 3 + hexahydrate in an alkaline environment up to the stage of a charge-neutral active hydroxide was studied via density functional theory. The deprotonation could be characterized as autocatalytic since upon completion of every H-abstraction stage, Cr was found to mediate O–H dissociation in the next stage by pre-conditioning the ligand O atom that contributes the highest 2s density into Cr-4s based molecular orbitals; the latter amounts to a greater Cr–O distance due to increased charge density along the Cr–O axis. A direct effect of such Cr-4s/O-2s mixing is the reduction of electronegativity of the ligand-O atom and a corresponding high Voronoi deformation density (VDD) of the attached ligand-H atoms. Based on bonding energy decomposition, a facial to meridional isomer ratio of between 2:1 and 3:1 was derived as the most probable stereochemical mix of the active hydroxide; the latter forms, by mutual donation and acceptance, six hydrogen bonds with second hydration shell molecules.

Reprint of “Facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with Δ- and Λ-configurations and their enantio-discriminative assembly via imidazole⋯chloride hydrogen bonding and spin cross-over properties”

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2·4H2O and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]Cl·PF6·solvent. Meridional and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]Cl·PF6·1.5H2O (1·PF6·1.5H2O) and fac-[FeII(HLMe-Benz)3]Cl·PF6·EtOH·H2O (2·PF6·EtOH·H2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[FeII(HLMe-Benz)3]Cl·SbF6·H2O (2·SbF6·H2O) and fac-[FeII(HLMe-Benz)3]Cl·ClO4·EtOH·H2O (2·ClO4·EtOH·H2O) are synthesized in ethanol, using the corresponding anions. Each FeII ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring three Cl− ions, and each Cl− ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF6·1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[FeII(HLMe-Benz)3]2+⋯Cl−}3 units with an ΔΔΛ or ΛΛΔ configuration; the PF6− ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[FeII(HLMe-Benz)3]2+⋯Cl−}4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[FeII(HLMe-Benz)3]2+ cations and four Cl− ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S=2) and low-spin (LS, S=0) states.

Room-temperature synthesis of cyclometalated iridium(iii) complexes: kinetic isomers and reactive functionalities

Cyclometalated iridium(III) complexes have been prepared in high yields from base-assisted transmetalation reactions of cis-bis(aquo)iridium(III) complexes with boronated aromatic proligands. Reactions proceed at room temperature. Potassium hydroxide and potassium phosphate are effective supporting bases. Kinetic, meridional isomers are isolated because of the mildness of the new technique. Syntheses are faster with KOH, but the gentler base K3PO4 broadens the reaction's scope. Complexes of chelated ketone, aldehyde, and alcohol complexes are reported that bind iridium through formally neutral oxygen and formally anionic carbon. The new complexes luminesce with microsecond-scale lifetimes at 77 K and nanosecond-scale lifetimes at room temperature; emission quenches in air. Two complexes, an aldehyde and its reduced (alcohol) derivative, are crystallographically characterized. Their bonding is examined with density-functional theory calculations. Time-dependent computations suggest that the Franck–Condon triplet states of these complexes have mixed orbital parentage, arising from one-particle transitions that mingle through configuration interaction.

Green- and blue-emitting tris(8-hydroxyquinoline) aluminum(III) (Alq3) crystalline polymorphs: Preparation and application to organic light-emitting diodes

Tris(8-hydroxyquinoline) aluminum(III) (Alq3) is known to have two isomeric states, namely meridional and facial isomers. Typical Alq3 crystals composed of meridional and facial isomers are α- and δ-form crystals, respectively. First, we investigate the temperature change in the crystalline forms of α-Alq3 and δ-Alq3 in X-ray diffraction experiments in a vacuum. α-Alq3 remains in α-form up to 300°C, immediately before sublimation. In contrast, δ-Alq3 is found to transform into γ-form at ∼180°C, and remain in γ-form immediately before sublimation. Both γ-Alq3 and δ-Alq3 are composed of facial isomers and emit blue luminescence, which is different from the typical green emissions of α-Alq3. Second, we fabricate organic light-emitting diodes (OLEDs) from different crystals as source powders; i.e., from (1) α-Alq3, (2) δ-Alq3, and (3) a mixture of α-, γ-, and δ-Alq3. All the OLEDs exhibit green electroluminescence with almost the same maximum wavelength, suggesting that some facial isomers become meridional while Alq3 is in the gas phase. In contrast, electroluminescence efficiency depends on the Alq3 crystalline polymorph; the OLED fabricated from the mixture of α-, γ-, and δ-Alq3 has up to 1.4 times the efficiency of the OLED fabricated from α-Alq3 for the same device structure.

Electronic structure of tris(2-phenylpyridine)iridium: electronically excited and ionized states

A computational study of tris(2-phenylpyridine)iridium, Ir(ppy)3, is presented. The perspective is that of using organo-transition-metal complexes as phosphorescent species in light-emitting diodes (OLED's). Quantum yields approaching 100% are possible through a triplet harvesting mechanism. Complexes such as Ir(ppy)3 are amenable to exacting experimental and theoretical studies: small enough to accommodate rigor, yet large enough to support bulk phenomena in a range of host materials. The facial and meridional isomers differ by ∼220 meV, with fac-Ir(ppy)3 having the lower energy. Because fac-Ir(ppy)3 dominates in most environments, focus is on this species. Time-dependent density functional theory using long-range-corrected functionals (BNL and ωB97X) is used to calculate excited states of Ir(ppy)3 and a few low energy states of . The calculated T1 – S0 energy gap (2.30 eV) is in reasonable agreement with the experimental value of 2.44 eV. Only a few percent of singlet character in T1 is needed to explain so short a phosphorescence lifetime as 200 ns, because of the large and absorption cross-sections. Equilibrium geometries are calculated for S0, T1, and the lowest cation state (D0), and several ionization energies are obtained: adiabatic (5.86 eV); vertical from the S0 equilibrium geometry (5.88 eV); and vertical ionization of T1 at its equilibrium geometry (5.87 eV). These agree with a calculation by Hay (5.94 eV), and with the conservative experimental upper bound of 6.4 eV. Molecular orbitals provide qualitative explanations. A calculated UV absorption spectrum, in which transitions are vertical from the S0 equilibrium geometry, agrees with the room temperature experimental spectrum. This is consistent with Franck–Condon factors dominated by , as expected given the delocalized nature of the orbitals. Ir(ppy)3 vibrational frequencies were calculated and used to estimate the probability density for 500 K, i.e. the temperature at which the experiments were carried out. In combination with the vibrational energy imparted through photoexcitation, it is seen that a large amount of vibrational energy appears in without causing its fragmentation. Specifically, for = 15,000 cm−1, the probability density for total vibrational energy peaks at ∼31,000 cm−1 with a 7800 cm−1 width.

Unexpected Disproportionation of Tetramethylethylenediamine-Supported Perchlorodisilane Cl3SiSiCl3

The addition compound Cl(3)SiSiCl(3)·TMEDA was formed quantitatively by treatment of Cl(3)SiSiCl(3) with tetramethylethylenediamine (TMEDA) in pentane at room temperature. The crystal structure of Cl(3)SiSiCl(3)·TMEDA displays one tetrahedrally and one octahedrally bonded Si atom (monoclinic, P2(1)/n). (29)Si CP/MAS NMR spectroscopy confirms this structure. Density functional theory (DFT) calculations have shown that the structure of the meridional isomer of Cl(3)SiSiCl(3)·TMEDA is 6.3 kcal lower in energy than that of facial coordinate species. Dissolving of Cl(3)SiSiCl(3)·TMEDA in CH(2)Cl(2) resulted in an immediate reaction by which oligochlorosilanes Si(n)Cl(2n) (n = 4, 6, 8, 10; precipitate) and the Cl(-)-complexed dianions [Si(n)Cl(2n+2)](2-) (n = 6, 8, 10, 12; CH(2)Cl(2) extract) were formed. The constitutions of these compounds were confirmed by MALDI mass spectrometry. Additionally, single crystals of [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(6)Cl(14)] and [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(8)Cl(18)] were obtained from the CH(2)Cl(2) extract. We found that Cl(3)SiSiCl(3)·TMEDA reacts with MeCl, forming MeSiCl(3) and the products that had been formed in the reaction of Cl(3)SiSiCl(3)·TMEDA with CH(2)Cl(2). X-ray structure analysis indicates that the structures of [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(6)Cl(14)] (monoclinic, P2(1)/n) and [Me(3)NCH(2)CH(2)NMe(2)](2)[Si(8)Cl(18)] (monoclinic, P2(1)/n) contain dianions adopting an "inverse sandwich" structure with inverse polarity and [Me(3)NCH(2)CH(2)NMe(2)](+) as countercations. Single crystals of SiCl(4)·TMEDA (monoclinic, Cc) could be isolated by thermolysis reaction of Cl(3)SiSiCl(3)·TMEDA (50 °C) in tetrahydrofuran (THF).

Facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with Δ- and Λ-configurations and their enantio-discriminative assembly via imidazole⋯chloride hydrogen bonding and spin cross-over properties

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2·4H2O and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]Cl·PF6·solvent. Meridional and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]Cl·PF6·1.5H2O (1·PF6·1.5H2O) and fac-[FeII(HLMe-Benz)3]Cl·PF6·EtOH·H2O (2·PF6·EtOH·H2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[FeII(HLMe-Benz)3]Cl·SbF6·H2O (2·SbF6·H2O) and fac-[FeII(HLMe-Benz)3]Cl·ClO4·EtOH·H2O (2·ClO4·EtOH·H2O) are synthesized in ethanol, using the corresponding anions. Each FeII ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring three Cl− ions, and each Cl− ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF6·1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[FeII(HLMe-Benz)3]2+⋯Cl−}3 units with an ΔΔΛ or ΛΛΔ configuration; the PF6− ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[FeII(HLMe-Benz)3]2+⋯Cl−}4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[FeII(HLMe-Benz)3]2+ cations and four Cl− ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S=2) and low-spin (LS, S=0) states.

Synthesis and crystal structure of thiosemicarbazide complexes of nickel(II) and copper(II)

Thiosemicarbazide complexes of nickel(II) (Ni(TSC)2)(HSal)2 ( I) and copper(II) (Cu(TSC) 2 )(HSal) 2 (Ia) (TSC is thiosemicarbazide and HSal is a salycilate anion), as well as complexes (Ni(TSC)2)(SO4) ⋅ 2H2O (II) and (Ni(TSC)3)Cl2 ⋅ H2O (III), are synthesized and characterized by IR spec� troscopy and Xray diffraction. Monoclinic crystals I and Ia are isostructural; space group P21/n, Z = 2. Crys� tals II are monoclinic, space group P21/m, Z = 2. Crystals III are orthorhombic, space group Pbca, Z = 8. In I and Ia, two planar salycilate anions sandwich a planar centrosymmetric (Ni(TSC) 2 ) 2+ cation to form a supermolecule. The cation and anions are additionally bound by hydrogen bonds. Other hydrogen bonds connect supermolecules into planar layers. In structure II, centrosymmetric (Ni(TSC)2) 2+ cations are con� nected by π�stacking interactions into supramolecular ensemb les of a specific type. The ensembles, water molecules, and (SO4) 2- anions are bound in the crystal via hydrogen bonds. In the (Ni(TSC)3) 2+ cation of structure III, ligands coordinate the Ni atom by the bidentate chelate pattern with the formation of five� membered metallocycles. These metallocycles have an envelope conformation unlike those in I and II, which are planar. In III (unlike in analogous complexes), a meridional isomer of the coordination octahedron of the Ni atom is formed. Together with Cl1 - and Cl2 - anions, cations form supermolecules, which are packed into planar layers with a squarecellular structure. The laye rs are linked by hydrogen bonds formed by crystalliza� tion water molecules that are located between the layers.

Synthesis and oxidation of d6 tungsten pincer complexes: a complete series of tungsten(ii) hydridocarbonyl and halocarbonyl pincer complexes

Reaction of the neutral P(H)NP ligand [HN(SiMe(2)CH(2)PPh(2))(2)] with tungsten hexacarbonyl resulted in coordination of P(H)NP through both phosphorus donor atoms to form the tungsten complex [W(P(HN)P)(CO)(4)] (1). Reaction of P(H)NP with tris(acetonitrile)tricarbonyl tungsten gave both facial and meridional tridentate isomers [W(P(H)NP)(CO)(3)] (2-fac and 3-mer). These three d(6) tungsten complexes could be interconverted under appropriate conditions. The thermodynamically favored isomer 3 was protonated to form seven-coordinate [W(P(H)NP)(CO)(3)H][BF(4)] (4). A related series of cationic tungsten(II) halide complexes was synthesized, [W(P(H)NP)(CO)(3)X](+) (6, X = I; 7, X = Br; 8, X = Cl; 9, X = F), by various routes. All of the tungsten(II) complexes underwent deprotonation at the amine site of the P(H)NP ligand when triethylamine was added, resulting in neutral seven-coordinate complexes. Variable temperature (1)H, (31)P{(1)H}, and (13)C{(1)H} NMR spectroscopy showed fluxional behavior for all the seven-coordinate complexes reported here. Analysis of IR and NMR spectroscopic data showed trends through the series of coordinated halides. Crystal structures of tetracarbonyl 1, meridional tricarbonyl 3, and cationic hydride 4 were determined to confirm the coordination mode of the P(H)NP ligand.

“Covalent Hydration” Reactions in Model Monomeric Ru 2,2′-Bipyridine Complexes: Thermodynamic Favorability as a Function of Metal Oxidation and Overall Spin States

Density functional theory (DFT) has been used to investigate the plausibility of water addition to the simple mononuclear ruthenium complexes, [(NH(3))(3)(bpy)Ru═O](2+/3+) and [(NH(3))(3)(bpy)RuOH](3+), in which the OH fragment adds to the 2,2'-bipyridine (bpy) ligand. Activation of bpy toward water addition has frequently been postulated within the literature, although there exists little definitive experimental evidence for this type of "covalent hydration". In this study, we examine the energetic dependence of the reaction upon metal oxidation state, overall spin state of the complex, as well as selectivity for various positions on the bipyridine ring. The thermodynamic favorability is found to be highly dependent upon all three parameters, with free energies of reaction that span favorable and unfavorable regimes. Aqueous addition to [(NH(3))(3)(bpy)Ru═O](3+) was found to be highly favorable for the S = 1/2 state, while reduction of the formal oxidation state on the metal center makes the reaction highly unfavorable. Examination of both facial and meridional isomers reveals that when bipyridine occupies the position trans to the ruthenyl oxo atom, reactivity toward OH addition decreases and the site preferences are altered. The electronic structure and spectroscopic signatures (EPR parameters and simulated spectra) have been determined to aid in recognition of "covalent hydration" in experimental systems. EPR parameters are found to uniquely characterize the position of the OH addition to the bpy as well as the overall spin state of the system.

“Click” Synthesis of Heteroleptic Tris-Cyclometalated Iridium(III) Complexes: Cu(I) Triazolide Intermediates as Transmetalating Reagents

Efficient synthesis of heteroleptic tris-cyclometalated Ir(III) complexes mer-Ir(C(/\)N)(2)(trpy) (trpy = 2-(1H-[1,2,3]triazol-4-yl)pyridine) is achieved by using the Cu(I)-triazolide intermediates formed in "click" reactions as transmetalating reagents. Ligand preparation and cyclometalation of Ir(III) is accomplished in one pot. The robust nature of click chemistry provides opportunities to introduce different functional groups to the cyclometalated system, for example, alkyl, perfluoroalkyl, and aryl moieties. All of the meridional isomers show short-lived phosphorescence at room temperature, both in solution and in the solid state. DFT calculations indicates that the phosphorescence of mer-Ir(C(/\)N)(2)(trpy) is attributed to the (3)MLCT and (3)LC mixed excited states, also supported by the broad spectral shape and hypsochromic shift upon media rigidification. The luminescence efficiency and excited state lifetimes of the cyclometalated complexes can be tuned by varying the substituents on the triazole ring, while the emission color is mainly determined by the phenylpyridine-based ligands. Moreover, the trpy ligand can acquire the N(/\)N chelating mode under selective reaction conditions. mer-Ir(C(/\)N)(2)(trpy) complexes isomerize into cationic [Ir(C(/\)N)(2)(N(/\)N_trpy)](+) species instead of their fac isomers upon heating or UV radiation. This can be explained by the strong trans influence exerted by the phenyl groups. The weakened Ir-C(trpy) bonds are likely to be activated and protonated, leading to the switch of the trpy ligand to a thermodynamically more stable N(/\)N chelating mode.