Giuseppe D'Alfonso

Rhenium(V) oxide complexes. Crystal and molecular structures of the compounds trans-ReI2O(OR)(PPh3)2 (R = Et, Me) and of their hydrolysis derivative ReIO2(PPh3)2

Abstract The structure of the complex ReI2O(OEt)(PPh3)2·3/2C6H6 (I) has been investigated: the dark-yellow crystals are monoclinic, space group P21/n, with a = 17.410(8), b = 17.322(6), c = 15.039(5) A, β = 103.49(3)°, Z = 4. Least-squares refinements based on 3636 significant counter data led to a final R value of 0.059. The compound exhibits a slightly distorted octahedral coordination, with the two PPh3 groups trans between themselves (mean ReP 2.523 A), as well as the two iodide ligands (mean ReI 2.789 A). The ethoxo group (ReO 1.880(9) A) and the oxide ligand (ReO 1.715(9) A) occupy the other two coordination sites. Compound I in methanol transforms into ReI2O(OMe)(PPh3)2 (II), which has been characterized by X-ray analysis in crystals containing CHCl3 molecules of solvation. The crystals are triclinic, space group P 1 , a = 12.835(3), b = 13.067(4), c = 13.485(4) A, α = 89.71(2)°, β = 71.61(2)°, γ = 70.19(2)°, Z = 2. The refinements gave a final R value of 0.036, on the basis of 4524 significant counter intensities. The stereochemistry and the bond parameters are similar to those found in compound I. In particular the ReO (methoxo) and ReO (oxide) bond lengths are 1.859(5) and 1.698(5) A respectively. Hydrolysis reactions of both compounds I and II give the violet derivative ReIO2(PPh3)2 (III). The crystal data are: orthorhombic, space group Aba2, a = 19.834(5), b = 16.144(3), c = 10.560(2) A, Z = 4. 1435 significant counter reflections were used in the refinements the final R value being 0.039. The compound is an unusual example of a five coordinate Re(V) complex. It possesses a rigorous C2 crystallographic symmetry and exhibits a distorted trigonal bipyramidal stereochemistry, with the two PPh3 groups in an axial direction (ReP 2.488(3) A) and the two oxide and the iodide ligands in equatorial positions. The ReI and ReO interactions have values of 2.664(2) and 1.742(11) A respectively.

Luminescent conjugates between dinuclear rhenium(I) complexes and peptide nucleic acids (PNA) for cell imaging and DNA targeting

New luminescent dinuclear rhenium(I) tricarbonyl complex-PNA conjugates have been synthesized through a reliable solid-phase synthetic methodology. Their photophysical properties have been measured. The most luminescent Re-PNA conjugate 7 showed interesting two-photon absorption (TPA) properties, that were exploited for imaging experiments, to demonstrate its easy uptake into living cells.

Phosphorescent Organic Light‐Emitting Diodes with Outstanding External Quantum Efficiency using Dinuclear Rhenium Complexes as Dopants

The photophysical and electroluminescence properties of two dinuclear rhenium(I) carbonyl complexes bearing 1,2-diazines are comprehensively investigated. The bromo-bridged complex is successfully used as triplet emitter for the preparation of vacuum-processed OLEDs with outstanding external quantum efficiencies, reaching a value of 10%.

A new class of luminescent tricarbonyl rhenium(I) complexes containing bridging 1,2-diazine ligands: electrochemical, photophysical, and computational characterization.

A novel class of luminescent tricarbonyl rhenium(I) complexes of general formula [Re2(mu-X)2(CO)6(mu-diaz)] (X=halogen and diaz=1,2-diazine) was prepared by reacting [ReX(CO)5] with 0.5 equiv of diazine (seven different ligands were used). The bridging coordination of the diazine in these dinuclear complexes was confirmed by single-crystal X-ray analysis. Cyclic voltammetry in acetonitrile showed for all the complexes (but the phthalazine derivative) a chemically and electrochemically reversible ligand-centered reduction, as well as a reversible metal-centered bielectronic oxidation. With respect to the prototypical luminescent [ReCl(CO)3(bpy)] complex, the oxidation is more difficult and the reduction easier (about +0.3 V), so that a similar highest occupied molecular orbital-lowest unoccupied molecular orbital gap is observed. All of the complexes exhibit photoluminescence at room temperature in solution, with broad unstructured emission from metal-to-ligand charge-transfer states, at lambda in the range 579-620 nm. Lifetimes (tau=20-2200 ns) and quantum yields (Phi up to 0.12) dramatically change upon varying the bridging ligand X and the diazine substituents: in particular, quantum yields decrease in the series Cl, Br, and I and in the presence of substituents at the alpha positions of the pyridazine ring. A combined density functional and time-dependent density functional study of the geometry, relative stability, electronic structure, and photophysical properties of all the pyridazine derivatives was performed. The nature of the excited states involved in the electronic absorption spectra was ascertained, and trends in the energy of the highest occupied and lowest unoccupied molecular orbitals upon changing the pyridazine substituents and the bridging halogen ligands were discussed. The observed emission properties of these complexes were shown to be related to a combination of steric and electronic factors affecting their ground-state geometry and their stability.

A Luminescent Poly(amidoamine)-Iridium Complex as a New Singlet-Oxygen Sensitizer for Photodynamic Therapy

A polymer complex (1P) was synthesized by binding bis(cyclometalated) Ir(ppy)2(+) fragments (ppy = 2-phenylpyridyl) to phenanthroline (phen) pendants of a poly(amidoamine) copolymer (PhenISA, in which the phen pendants involved ∼6% of the repeating units). The corresponding molecular complex [Ir(ppy)2(bap)](+) (1M, bap = 4-(butyl-4-amino)-1,10-phenanthroline) was also prepared for comparison. In water solution 1P gives nanoaggregates with a hydrodynamic diameter of 30 nm in which the lipophilic metal centers are presumed to be segregated within polymer tasks to reduce their interaction with water. Such confinement, combined with the dilution of triplet emitters along the polymer chains, led to 1P having a photoluminescence quantum yield greater than that of 1M (0.061 vs 0.034, respectively, in an aerated water solution) with a longer lifetime of the (3)MLCT excited states and a blue-shifted emission (595 nm vs 604 nm, respectively). NMR data supported segregation of the metal centers. Photoreaction of O2 with 1,5-dihydroxynaphthalene showed that 1P is able to sensitize (1)O2 generation but with half the quantum yield of 1M. Cellular uptake experiments showed that both 1M and 1P are efficient cell staining agents endowed with two-photon excitation (TPE) imaging capability. TPE microscopy at 840 nm indicated that both complexes penetrate the cellular membrane of HeLa cells, localizing in the perinuclear region. Cellular photodynamic therapy tests showed that both 1M and 1P are able to induce cell apoptosis upon exposure to Xe lamp irradiation. The fraction of apoptotic cells for 1M was higher than that for 1P (74 and 38%, respectively) 6 h after being irradiated for 5 min, but cells incubated with 1P showed much lower levels of necrosis as well as lower toxicity in the absence of irradiation. More generally, the results indicate that cell damage induced by 1M was avoided by binding the iridium sensitizers to the poly(amidoamine).

Isolation, reactions and x-ray structure of tetraethylammonium dihydridotetracarbonylrhenate

Abstract The isolation and characterization of the novel hydridic compound [Net 4 ][H 2 Re(CO) 4 ], obtained from the reaction of Re 2 (CO) 10 with methanolic KOH, are described. Its reactions with I 2 , strong acids, and ethanol are reported. The salt gives triclinic crystals, investigated by X-ray analysis, with cell constants a = 14.493(6), b = 7.564(3), c = 7.930(3) A, α = 72.97(4)°, β = 81,73(4)°, γ = 96.63(4)°; space group P 1 . The structure was solved by conventional Patterson and Fourier methods and refined by least-squares up to a final R values of 0.071, for 1586 independent counter data. The anion exhibits a distorted octahedral geometry, with the two hydrido ligands in cis position between themselves. The mean values of the ReC and CO distances are 1.89 and 1.21 A. The carbonyl groups are significantly bent towards the hydrido ligands.

Rhenium(V) oxide complexes. Crystal and molecular structures of ReOI2(PPh3)2(OReO3) and of ReOI2(PPh3)(OPPh3)(OReO3)·0.5C6H6 obtained from the reaction of ReO2I(PPh3)2 with oxygen

The oxygenation reaction of the five-coordinated violet species ReO 2 I(PPh 3 ) 2 leads to isolation of two crystalline compounds, both characterized by X-ray diffraction analysis: the dark-red ReOI 2 (PPh 3 ) 2 (OReO 3 ) (1), which is the main product, and the yellow ReOI 2 (PPh 3 )(OPPh 3 )(OReO 3 )·0.5C 6 H 6 (2). Compound 1 gives monoclinic crystals, space group C 2/ c , with a = 25.033(8), b = 16.944(5), c = 19.495(8) A, β = 116.13(3)°, Z = 8. Compound 2 is monoclinic, space group P 1 / n , with a = 9.498(4), b = 25.048(8), c = 17.148(5) A, β = 92.47(3)°, Z = 4. The structures of 1 and 2 were solved by Patterson and Fourier methods and refined by full-matrix least-squares, on the basis of 4229 ( 1 ) and 2672 ( 2 ) significant counter data ( I > 3σ( I )), respectively. The final values of the conventional agreement indices R and R w were 0.050 and 0.070 ( 1 ) and 0.033 and 0.039 (2), respectively. Both species contain a previously unexpected coordinated perrhenato ligand. The geometry of the two complexes is distorted octahedral: compound 1 contains two trans phosphine ligands (mean ReP= 2.513 A) and two trans iodides (mean ReI 2.730 A), the other two trans coordination sites being occupied by the oxide (ReO = 1.670(7) A) and the perrhenate. Compound 2 shows a similar coordination geometry, with one of the phosphine ligands replaced by a phosphine oxide. The main bond parameters in 2 are: ReP 2.453(4) A, ReI (mean) 2.727 A, ReO(OPPh 3 ) 2.075(9) A, ReO (oxide) 1.639(9) A. The interactions Re(V)-perrhenate are similar in the two complexes, with Re(V)O bonds of 2.031(6) A ( 1 ) and 2.079(9) A ( 2 ). The ReORe angles show some difference: 164.3(4)° ( 1 ) and 153.5(5)° ( 2 ). Within the perrhenates, the ReO bond involving the bridging oxygen atom is somewhat longer than the other ReO bonds.

Pyrolyses of the anion dihydridotetracarbonylrhenate. Crystal and molecular structure of bis(tetraethylammonium) μ-hydrido-dodecacarbonyl-triangulo-trirhenate(2—)

Abstract The pyrolyses of [NEt 4 ][H 2 Re(CO) 4 ] in boiling n-heptane, n-octane and n-nonane are described. Mixtures of polynuclear carbonyl- and hydridocarbonylrhenium species are obtained, the principal products being [Re 4 (CO) 16 ] 2− , [H 2 Re 3 (CO) 12 ], [H 3 Re 3 (CO) 10 ] 2− , [H 3 Re 3 O(CO) 9 ] 2− and [H 6 Re 4 (CO) 12 ] 2− . A red-orange crystalline species was isolated from the reaction in n-heptane and shown by X-ray diffraction to be [Net 4 ] 2 [HRe 3 (CO) 12 ]. It gives orthorhombic crystals, space group Pbca , with cell constants a 16.07(1), b 23.39(2), c 19.49(1) A. The structure was solved by Patterson and Fourier methods and refined by least-squares up to a final R value of 0.061, for 1303 independent counter data. The anion [HRe 3 (CO) 12 ] 2− contains an isosceles metal atom triangle, with two short edges of 3.014(3) and 3.018(3) A and a long hydrogen-bridged edge of 3.125(3) A.

An Intramolecular NH⋅⋅⋅(-H)Re2 Dihydrogen Bond and a Novel 3-2 Coordination Mode of the Pyrazolate Anion on a Triangular Cluster Face

The quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(μ3-H)(μ-H)3(CO)9]− gives the novel unsaturated anion [Re3(μ-H)4(CO)9(Hpz)]− (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solid-state X-ray and IR analyses reveal a rather weak hydrogen-bonding interaction between the NH proton and one of the hydrides bridging the opposite triangular cluster edge (ΔH°=−3.1 kcal mol−1 from the Iogansen equation). Both IR and NMR data indicate that such a proton–hydride interaction is maintained in the major conformer present in CD2Cl2, but also provide evidence of the presence of minor conformers of 1 in which the NH proton is involved in an intermolecular hydrogen bond with the solvent. The μ-H⋅⋅⋅HN bond length evaluated in solution through the T1 minimum value (2.07 A) and that determined in the solid state by X-ray diffraction (2.05 A) are in good agreement. NMR experiments show that, in acetone, intermolecular NH⋅⋅⋅solvent interactions replace the intramolecular dihydrogen bond. At room temperature in CH2Cl2, the pyrazole ligand in 1 is labile and 1 slowly “disproportionates” to [Re3(μ3-H)(μ-H)3(CO)9]− and [Re3(μ-H)3(CO)9(μ-η2-pz)(Hpz)]−, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(μ-H)3(CO)9(pz)]− (5), in which the pyrazolate anion adopts a novel μ3-η2-coordination mode, as revealed by a single-crystal X-ray analysis. The analysis of the bond lengths indicates that the pyrazolate anion in 5 acts as a six-electron donor, with loss of the aromaticity. The formation of 5 from 1 is much faster in solvents with a high dielectric constant, such as acetone or DMF. Anion 5 was also obtained from the reaction of pyrazole with [Re3(μ-H)3(CO)9(μ3-CH3)]− through the intermediate formation of two isomeric addition derivatives and following CH4 evolution.

Tricarbonyl−Rhenium Complexes of a Thiol-Functionalized Amphoteric Poly(amidoamine)

An amphoteric thiol-functionalized poly(amidoamine) nicknamed ISA23SH(10%) was synthesized. Rhenium complexes 1 and 2, containing 0.5 and 0.8 equiv of rhenium, respectively, were easily obtained by reacting ISA23SH(10%) with [Re(CO)(3)(H(2)O)(3)](CF(3)SO(3)) in aqueous solution at pH 5.5. Both ISA23SH(10%), and its rhenium complexes were soluble in water under physiological conditions. The resultant solutions were stable, even in the presence of cysteine. Rhenium chelation occurred through the S and N atoms of the cysteamine moiety, as demonstrated by (1)H, (13)C, and (15)N NMR spectroscopy. The diffusion coefficients and the hydrodynamic radii of ISA23SH(10%) and complex 1 were determined by pulsed gradient spin echo (PGSE) NMR experiments. The radius of the rhenium complexes 1 and 2 was always slightly larger than that of the parent polymer. TEM analysis showed that both complexes form spherical nanoparticles with narrow size distributions. Consistent results were obtained by dynamic light scattering. The observed sizes were in good agreement with those evaluated by PGSE. Preliminary in vitro and in vivo biological studies have been performed on complexes 1 and 2 as well as on the parent ISA23SH(10%). Neither hemolytic activity of the two rhenium complexes and the parent polymer, up to a concentration of 5 mg/mL, nor cytotoxic effects were observed on Hela cell after 48 h at a concentration of 100 ng/mL. In vivo toxicological tests showed that ISA23SH(10%) is highly biocompatible, with a maximum tolerated dose (MTD) of 500 mg/kg. No toxic side effects were apparent after the intravenous injection in mice of the two rhenium complexes in doses up to 20 mg/kg.