Synthesis of 2-arylpyrroles via catalytic dehydrogenation of 2-aryl-1-pyrrolines in the presence of palladium-supported on alumina

Boron complexes of aromatic 5-substituted iminopyrrolyl ligands: synthesis, structure, and luminescence properties

A group of new mononuclear boron chelate compounds [BPh₂{κ²N,N'-5-R-NC₄H₂-2-C(H)[double bond, length as m-dash]N-Ar}] (R = Ar = C₆H₅7; R = C₆H₅, Ar = 2,6-iPr₂C₆H₃8; R = Anthracen-9-yl (Anthr), Ar = C₆H₅9; R = Anthr, Ar = 2,6-iPr₂C₆H₃10) were synthesized via the reaction of B(C₆H₅)₃ with the corresponding 5-substituted 2-(N-arylformimino)pyrrole ligand precursors 3-6. These complexes were prepared in order to evaluate the luminescence potential derived from the substitution of the position 5 of the pyrrolyl ring with an aromatic group. Compounds 7-10 were photophysically characterized in solution and in the solid state. The 5-phenyl-2-iminopyrrolyl-BPh₂ complexes 7 and 8 are blue emitters and have enhanced photoluminescence quantum yields in the solid state (Φ_PL) up to 0.95, whereas the 5-anthracenyl derivatives 9 and 10 have green-bluish fluorescence and a Φ_PL of 0.49 and 0.24, respectively. DFT and TDDFT studies were performed, considering the effect of solvent and dispersion, in order to show how the geometries of compounds 7-10 changed from the ground to the excited state, to assign electronic transitions, and to rationalize the observed luminescence. These materials were applied in organic light-emitting diodes (OLEDs), with various device structures, the best showing an external quantum efficiency of 2.75% together with a high luminance of 23 530 cd m^-2.

Hydroboration of terminal olefins with pinacolborane catalyzed by new 2-iminopyrrolyl iron(ii) complexes

New Fe(ii) mono(2-iminopyrrolyl) complexes catalyze the hydroboration of terminal olefins with pinacolborane via a borane oxidative addition pathway.

New phenyl-nickel complexes of bulky 2-iminopyrrolyl chelates: synthesis, characterisation and application as aluminium-free catalysts for the production of hyperbranched polyethylene

A family of mono(2-iminopyrrolyl) complexes with the general formula [Ni{κ2N,N'-5-(aryl)-NC4H2-2-C(H)[double bond, length as m-dash]N-2,6-(aryl)}(C6H5)(PPh3)] were obtained from the reaction of the sodium salts of the newly synthesised 5-aryl-2-(N-arylformimino)pyrroles with the square planar complex trans-[Ni(C6H5)(PPh3)2Cl]. These new iminopyrrole ligand precursors, designed with increasing bulkiness and different electronic properties, and their corresponding nickel(ii) complexes were characterised by NMR spectroscopy and elemental analysis, and their structural features were analysed by single crystal X-ray diffraction. The nickel complexes were tested as aluminium-free catalysts for the polymerisation of ethylene, at low to moderate pressures and different temperatures and in the absence or presence of the phosphine scavenger [Ni(COD)2], giving rise to catalytic activities in the range of 3.61-73.12 kgPE molNi-1 h-1 bar-1. The polyethylene products formed in these catalytic reactions were characterised by GPC/SEC and NMR spectroscopy. Generally, low molecular weight (Mn 510-1300 g mol-1) low viscosity oils were obtained, presenting high branching degrees (80-125 branches per 1000 C atoms), which are characteristic of hyperbranched polyethylene products. In particular, polymerisation reactions using catalyst 7 led to higher viscosity oils with molecular weights between 11 000 and 20 000 g mol-1, and branching degrees of 100-120 branches per 1000 C atoms.

Hydroboration of Terminal Olefins with Pinacolborane Catalyzed by New Mono(2-Iminopyrrolyl) Cobalt(II) Complexes

The 5-substituted 2-aryliminopyrrolyl ligand precursors of the type 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]-1 H-pyrrole (R = 2,6-Me₂-C₆H₃ (1a), 2,4,6-ⁱPr₃-C₆H₂ (1b), 2,4,6-Ph₃-C₆H₃ (1c; reported in this work), anthracen-9-yl (1d), CPh₃ (1e; reported in this work)) were treated with K[N(SiMe₃)₂] in toluene to yield the respective 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]pyrrolyl potassium salts 2a-e in high yields. The paramagnetic 15-electron Co(II) complexes of the type [Co{κ² N,N'-5-R-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(Py)Cl] (3a-e; Py = pyridine) were prepared by salt metathesis of CoCl₂(Py)₄ with the respective potassium salts 2a-e in moderate to good yields. When the CoCl₂(THF)_1.5 precursor was combined with the in situ prepared sodium salt of ligand precursor 1b, the trinuclear complex [Co{κ² N, N'-5-(2,4,6-ⁱPr₃-C₆H₂)-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(μ-Cl)]₂[(μ-Cl)₂Co(THF)₂] (4) was obtained in high yields. Complexes 3a-e have high-spin electronic configurations both in solution and in the solid state. X-ray diffraction studies of complexes 3a,e confirmed distorted tetrahedral coordination geometries. Complex 4, on the other hand, is a linear trinuclear Co(II)-Co(II)-Co(II) complex with two terminal distorted tetrahedral four-coordinate sites and a central octahedral six-coordinate site, all in the high-spin state, S = 3/2, as confirmed by the magnetization measurements and DFT calculations. Solid-state magnetic measurements in both complexes 3a and 4 point to paramagnetic behavior with a significant contribution of spin-orbit coupling. Additionally, intramolecular antiferromagnetic coupling of the adjacent cobalt atoms is observed in 4. The Co(II) family 3a-d, on activation with K(HBEt₃), catalyzed the hydroboration of several α-olefins with pinacolborane, in good to high yields (50-80%). This system almost exclusively yielded the anti-Markovnikov (a-Mk) addition product, except when styrene was used, where the selectivity in the Markovnikov (Mk) product increased with increasing steric bulkiness of the 5-R-2-iminopyrrolyl substituent, with the a-Mk:Mk molar ratio varying from 2.33:1 (3a, R = 2,6-Me₂-C₆H₃) to 0.75:1 (3c, R = 2,4,6-Ph₃-C₆H₃). Preliminary mechanistic studies indicate that the activation by K(HBEt₃) gave rise to a Co(I) species, the catalyst system likely following an oxidative addition pathway.

Exploring the influence of steric hindrance and electronic nature of substituents in the supramolecular arrangements of 5-(substituted phenyl)-2-formylpyrroles

The supramolecular arrangements of 5-(substituted phenyl)-2-formylpyrroles display the core formation of dimers, tetramers or polymers, depending on the phenyl substituents.