Ring Slippage vs Charge Transfer in the Reductive Chemistry of [IndMo(CO)2(α-diimine)]+ Cations
Cláudia C. L. PereiraPaulo J. CostaMaria José CalhordaCristina FreireSandra RodriguesEberhardt HerdtweckCarlos C. Romão
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Thirteen complexes of the type [IndMo(CO)2L2]+ were prepared from IndMo(η3-C3H5)(CO)2 by protonation with HBF4·Et2O followed by addition of α-diimine ligands L, in the presence of 1,2-dimethoxyethane. The complexes are numbered as follows: L = 1,4-bis(p-tolyl)diazabutadiene (p-tolDAB, 1), 1,4-bis(cyclohexyl)diazabutadiene (cyDAB, 2), biquinoline (biq, 3), 5,6-Ph2-3-(2-py)-1,2,4-Tz (tz, 4), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 5), 2,2'-bipyridine (bipy, 6), 4,4'-diphenyl-2,2'-bipyridine (4,4'-Ph2-bpy, 7), 1,10-phenanthroline (1,10-phen, 8), 4,7-diphenyl-1,10-phenanthroline (4,7-Ph2-1,10-phen, 9), 4,7-dimethyl-1,10-phenanthroline (4,7-Me2-1,10-phen, 10), 2-(2-pyridyl)benzimidazole (2-(2-py)-benz, 11), 2,2'-biimidazole (2,2'-Biim, 12), 1,2-phenylenediamine (phendiam, 13). The bonding mode of the ligand in 4 was ascertained by single-crystal X-ray diffraction. None of the complexes undergo NCMe addition to form ring-slipped [(η3-Ind)Mo(CO)2L2(NCMe)]+ species. The reductive electrochemistry was studied in order to search for possible reductively induced ring-slippage rearrangements. In the cases of 1−5 reversible reduction processes were observed. UV−vis spectroscopy combined with DFT calculations provided an interpretation for the structures of the reduced species. The data suggest that the unpaired electron in the formally 19e reduced products [IndMo(CO)2L2]• is localized on the α-diimine ligand with minimal structural changes and no indenyl slippage taking place. However, such slippage is predicted to take place with the second reduction step, but in most cases MoL2 bond breaking leads to irreversible electrochemistry.Keywords:
Diimine
Bipyridine
HOMO/LUMO
Unpaired electron
Phenazine
Phenanthroline
The improved stability of a photocatalytic proton reduction system is accomplished when a heteroleptic bis-cyclometalated diimine iridium(III) photosensitizer ([Ir(ppy)(2)(bpy)](+), ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine) is replaced with a novel iridium complex, [Ir(phbpy)(2)](+) (phbpy = 6-phenyl-2,2'-bipyridine). The decomposition of [Ir(ppy)(2)(bpy)](+) analogs in photocatalytic systems has been previously shown to result from 2,2'-bipyridine dissociation, which will be hindered by the improved architecture. Although desirable for reasons beyond stability, syntheses of bis-tridentate iridium complexes of 6-phenyl-2,2'-bipyridine are uncommon, with no previous examples having an analogous coordination sphere to the well-studied [Ir(C--N)(2)(N--N)](+) architecture (where C--N = cyclometalating ligand and N--N = neutral diimine ligand). Ligand modification has proven a successful strategy in tuning the photophysical properties of [Ir(C--N)(2)(N--N)](+) complexes and can now be employed for the more robust [Ir(C--N--N)(2)](+) framework (where C--N--N = cyclometalating diimine ligand). Characterization of the novel complex reveals similar electrochemical properties and calculated orbital densities to the parent [Ir(ppy)(2)(bpy)](+) species, while there are notable differences between the absorption and photophysical properties of the two complexes.
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Homoleptic
Bipyridine
2,2'-Bipyridine
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The synthesis and structural stabilities of modified oligonucleotide hairpins containing phenanthroline- and bipyridine-modified loops is reported. Phenanthroline (phen) and bipyridine (bipy) building blocks were synthesized, incorporated into DNA-oligonucleotides, and analyzed by thermal denaturation experiments. The so modified oligomers were found to form stable hairpin structures. Tm values were not affected by divalent transition metals.
Phenanthroline
Bipyridine
Divalent
2,2'-Bipyridine
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9,10-Dihydroplatinaanthracenes with aromatic nitrogen ligands were synthesized, derived from 2,2′-bipyridine, 4,4′-dichloro-2,2′-bipyridine, 4,4′-dimethoxy-2,2′-bipyridine, 4,4′-bis(dimethylamino)-2,2′-bipyridine, 4,4′-di-tert-butyl-2,2′-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 2,2′-biquinoline. For comparison purposes, the N,N,N′,N′-tetramethylethylenediamine-derived compound was also obtained. A single-crystal X-ray structure determination was carried out on [H2C(C6H4)2]Pt(2,9-dimethyl-1,10-phenanthroline), revealing a pronounced boat conformation of the metallacyclic ring. The diimine-derived compounds are highly luminescent in the solid state at room temperature, as well as in frozen solution. The luminescent complexes are easily prepared by ligand substitution from the new organometallic platinum precursor {[H2C(C6H4)2]Pt(SEt2)}n (n = 2, 3). Spectroscopic data are provided on absorbance and emission in the UV–visible range. In order to obtain insight into orbital energies and the tunability of the optical properties, electrochemical data, as well as DFT and TD-DFT data, were obtained. The lowest-energy absorbances are due to charge transfer from orbitals located largely on the electron-rich metallacyclic ligand with some coefficient on Pt into π* orbitals of the diimine. Computations suggest that the low-energy bands mostly originate from charge transfer from the HOMO−2, HOMO−1, and HOMO to the LUMO (rarely LUMO+1 and LUMO+2) molecular orbitals. Emission maxima range from 536 to 690 nm.
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HOMO/LUMO
Bipyridine
Phenanthroline
2,2'-Bipyridine
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Bipyridine
Bridging ligand
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Abstract Complexes of the type [Ru(bxbg) 2 (N‐N)] 2+ , where N‐N denotes 2,2′‐bipyridine (bpy) ( 1 ), 1,10‐phenanthroline (phen) ( 2 ), dipyrido[3,2‐ d :2′,3‐ f ] quinoxaline (dpq) ( 3 ), and dipyrido[3,2‐ a :2′,3′‐ c ]phenazine (dppz) ( 4 ), incorporating bis( o ‐xylene)bipyridine‐glycoluril (bxbg) as an ancillary “molecular clip” ligand, have been synthesized and characterized. These ruthenium(II) complexes of bis( o ‐xylene)bipyridine‐glycoluril self‐associate in water through specific molecular recognition processes to form polycationic arrays. These arrays containing electrostatic binders as well as intercalator ligands at micromolar doses rapidly condense free DNA into globular nanoparticles of various sizes. The DNA condensation induced by these complexes has been investigated by electrophoretic mobility assay, dynamic light scattering, and transmission electron microscopy. The cellular uptake of complex–DNA condensates and the low cytotoxicity of these complexes satisfy the requirements of a gene vector.
Phenazine
Quinoxaline
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DNA condensation
Diimine
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A series of luminescent carbonyl hydrido ruthenium(II) complexes with various diimine ligands with diverse electronic properties, including Me 2 bpy (bpy = bipyridine), Me 2 phen (phen = phenanthroline), PhenCOOH, PhenCN, Me 2 Ph 2 phen, Ph 2 phen, and π‐conjugating dipyrido[3,2‐ d :2′,3′‐ f ]quinoxaline (dpq), dipyrido[3,2‐ a :2′,3′‐ c ](6,7,8,9‐tetrahydro)phenazine (dpqc), and dipyridophenazine (dppz) have been synthesized and characterized. Four of these complexes have been structurally characterized by X‐ray crystallography. The photophysical and electrochemical properties of these complexes have been studied. The effects of the electronic features and π‐conjugation of the diimine ligand on the electronic and photophysical properties of these complexes have also been discussed. Our study revealed that the luminescence performance of these complexes could be significantly enhanced by increasing the rigidity and π‐conjugation of the diimine ligand.
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Phenazine
Quinoxaline
Bipyridine
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Phenazine
Diimine
Quinoxaline
Bovine serum albumin
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Phenanthroline
Bipyridine
Cationic polymerization
2,2'-Bipyridine
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Abstract The synthesis of tri‐heteroleptic complex of Ru(II) with diimine ligands is describe. Ten compounds [Ru(R 2 bpy) (biq) (L)][PF 6 ] 2 (R = H, CH 3 ); L = 2,2′‐bipyridine (bpy), 4,4′‐dimethyl‐2,2′‐bipyridine (Me 2 bpy), 2,2′‐bipyrimidine (bpm), 2,2′‐biisoquinoline (biiq), 1,10‐phenanthroline (phen), dipyrido[3,2‐ c :2′,3′‐ e ]pyridazine (taphen), 2,2′‐biquinoline (biq), 6,7‐dihydrodipyrido[2,3‐ b :3,2‐ j ][1,10]‐phenanthroline (dinapy), 2‐(2[pyridyl)quinoline (pq), 1‐(2‐pyrimidyl)pyrazole] (pzpm), 2,2′‐biimidazole (H 2 biim) are characterized by elemental analysis, electronic and 1 H‐NMR spectroscopy. The relative photosustitution rates of biq in MeCN are given at three temperatures.
Diimine
Pyridazine
Quinoline
Bipyridine
Phenanthroline
Pyrazole
Proton NMR
Quinoxaline
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Diimine
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