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 (ΦPL) up to 0.95, whereas the 5-anthracenyl derivatives 9 and 10 have green-bluish fluorescence and a ΦPL 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.

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.

Luminescent Di- and Trinuclear Boron Complexes Based on Aromatic Iminopyrrolyl Spacer Ligands: Synthesis, Characterization, and Application in OLEDs.

New bis- and tris(iminopyrrole)-functionalized linear (1,2-(HNC4 H3 -C(H)N)2 -C6 H4 (2), 1,3-(HNC4 H3 -C(H)N)2 -C6 H4 (3), 1,4-(HNC4 H3 -C(H)N)2 -C6 H4 (4), 4,4'-(HNC4 H3 -C(H)N)2 -(C6 H4 -C6 H4 ) (5), 1,5-(HNC4 H3 C-(H)N)2 -C10 H6 (6), 2,6-(HNC4 H3 C-(H)N)2 -C10 H6 (7), 2,6-(HNC4 H3 C-(H)N)2 -C14 H8 (8)) and star-shaped (1,3,5-(HNC4 H3 -C(H)N-1,4-C6 H4 )3 -C6 H3 (9)) π-conjugated molecules were synthesized by the condensation reactions of 2-formylpyrrole (1) with several aromatic di- and triamines. The corresponding linear diboron chelate complexes (Ph2 B[1,3-bis(iminopyrrolyl)-phenyl]BPh2 (10), Ph2 B[1,4-bis(iminopyrrolyl)-phenyl]BPh2 (11), Ph2 B[4,4'-bis(iminopyrrolyl)-biphenyl]BPh2 (12), Ph2 B[1,5-bis(iminopyrrolyl)-naphthyl]BPh2 (13), Ph2 B[2,6-bis(iminopyrrolyl)-naphthyl]BPh2 (14), Ph2 B[2,6-bis(iminopyrrolyl)-anthracenyl]BPh2 (15)) and the star-shaped triboron complex ([4',4'',4'''-tris(iminopyrrolyl)-1,3,5-triphenylbenzene](BPh2 )3 (16)) were obtained in moderate to good yields, by the treatment of 3-9 with B(C6 H5 )3 . The ligand precursors are non-emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the π-conjugation length. The photophysical properties of the luminescent polyboron compounds were measured, showing good solution fluorescence quantum yields ranging from 0.15 to 0.69. DFT and time-dependent DFT calculations confirmed that molecules 10 and 16 are blue emitters, because only one of the iminopyrrolyl groups becomes planar in the singlet excited state, whereas the second (and third) keeps the same geometry. Compound 13, in which planarity is not achieved in any of the groups, is poorly emissive. In the other examples (11, 12, 14, and 15), the LUMO is stabilized, narrowing the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), and the two iminopyrrolyl groups become planar, extending the size of the π-system, to afford green to yellow emissions. Organic light-emitting diodes (OLEDs) were fabricated by using the new polyboron complexes and their luminance was found to be in the order of 2400 cd m(-2) , for single layer devices, increasing to 4400 cd m(-2) when a hole-transporting layer is used.

Tunable fluorophores based on 2-(N-arylimino)pyrrolyl chelates of diphenylboron: synthesis, structure, photophysical characterization, and application in OLEDs.

Reactions of 2-(N-arylimino)pyrroles (HNC4H3C(H)=N-Ar) with triphenylboron (BPh3) in boiling toluene afford the respective highly emissive N,N'-boron chelate complexes, [BPh2 {κ(2)N,N'-NC4H3C(H)=N-Ar}] (Ar=C6H5 (12), 2,6-Me2-C6H3 (13), 2,6-iPr2-C6H3 (14), 4-OMe-C6H4 (15), 3,4-Me2-C6 H3 (16), 4-F-C6H4 (17), 4-NO2-C6H4 (18), 4-CN-C6H4 (19), 3,4,5-F3-C6H2 (20), and C6F5 (21)) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N-arylimino moieties. The complexes bearing electron-withdrawing aniline substituents 17-20 show more intense (e.g., ϕf =0.71 for Ar=4-CN-C6H4 (19) in THF), higher-energy (blue) fluorescent emission compared to those bearing electron-donating substituents, for which the emission is redshifted at the expense of lower quantum yields (ϕf=0.13 and 0.14 for Ar=4-OMe-C6H4 (15) and 3,4-Me2-C6H3 (16), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6-positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region (λmax =410-465 nm) and a significant decrease in quantum yield (ϕf=0.005, 0.023, and 0.20 for Ar=2,6-Me2-C6H3 (13), 2,6-iPr2-C6H3 (14), and C6F5 (21), respectively, in THF), even when electron-withdrawing groups are also present. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance (ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light-emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m(-2) being achieved for a green-emitting device.

Synthesis and structural characterisation of (aryl-BIAN)copper(I) complexes and their application as catalysts for the cycloaddition of azides and alkynes.

A series of Ar-BIAN-based copper(I) complexes (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine) were synthesised and characterised by (1)H and (13)C NMR spectroscopies, FT-IR spectroscopy, MALDI-TOF-MS spectrometry, cyclic voltammetry and single crystal X-ray diffraction. The bis-chelated complexes of general formula [Cu(Ar-BIAN)(2)]BF(4) (where Ar = C(6)H(5) (1), 4-iPrC(6)H(4) (3), 2-iPrC(6)H(4) (4)) were prepared by reaction of [Cu(NCMe)(4)]BF(4) with two equivalents of the corresponding Ar-BIAN ligands, in dichloromethane, while the mono-chelated complexes of the type [Cu(Ar-BIAN)L(2)]BF(4) (where Ar = 2,6-iPr(2)C(6)H(3), L = PhCN (6); Ar = 4-iPrC(6)H(4), L = PPh(3) (7)) were readily accessible by treatment of [Cu(NCR)(4)]BF(4) (R = Me, Ph) with one equivalent of the corresponding Ar-BIAN ligands in the absence or presence of two equivalents of PPh(3), in the same solvent. The structures of complexes 3, 4, 6 and 7 were obtained by single crystal X-ray diffraction, showing distorted tetrahedral geometries around the copper centres in all cases. The electrochemical studies of these complexes and of the already reported [Cu(2,4,6-Me(3)C(6)H(2)-BIAN)(2)]BF(4) (2) and [Cu(2,6-iPr(2)C(6)H(3)-BIAN)(NCMe)(2)] (5), demonstrated that the bis-chelated complexes 1-4 undergo a reversible one-electron reduction or oxidation processes on copper, while the mono-chelated complexes 5-7 show a partially reversible oxidation and an irreversible reduction feature. Both kinds of (Ar-BIAN)copper(I) complexes are active catalysts for the copper(I)-catalysed azide-alkyne cycloaddition reaction (CuAAC). Complex 7, bearing PPh(3) ligands, exhibits the highest catalytic activity, which is comparable with that of the typical CuSO(4)-sodium ascorbate catalyst system.

Iminopyrrole derivatives containing electron-withdrawing substituents: the formation of dimers and supramolecular arrangements.

The crystal structures of two p-substituted phenylformiminopyrrole derivatives, namely 2-[(4-fluorophenyl)iminomethyl]pyrrole, C(11)H(9)FN(2), (1), and 2-[(1H-pyrrol-2-ylmethylidene)amino]benzonitrile, C(12)H(9)N(3), (2), bear F and C[triple-bond]N electron-withdrawing groups, respectively. Both structures feature two independent molecules in the asymmetric unit forming dimers via N-H...N hydrogen bonds. In the case of (1), each dimer interacts with two other dimers via C-H...F contacts, thus forming one-dimensional chains in the b direction, whereas in the case of (2), a weak C-H...N interaction connects the dimers in one-dimensional chains in the (110) direction.

trans-Chlorido(phenyl)bis(triphenylphosphine)nickel(II) and its 1:1 cocrystal with chloridobis(triphenylphosphine)nickel(I).

Two conformational polymorphs of trans-chlorido(phenyl)bis(triphenylphosphine)nickel(II), [Ni(C(6)H(5))Cl(C(18)H(15)P)(2)], (1), viz. orange needle-shaped crystals (form I) and brown prism-shaped crystals (form II), were obtained under different crystallization conditions from a mixture of toluene and n-hexane, and characterized by single-crystal X-ray diffraction at low temperature. These two forms were compared with that published previously [Zeller, Herdtweck & Strassner (2003). Eur. J. Inorg. Chem. pp. 1802-1806], characterized at room temperature. Additionally, blue-green prisms of a 1:1 cocrystal of complex (1) with chloridobis(triphenylphosphine)nickel(I), (2), viz. trans-chlorido(phenyl)bis(triphenylphosphine)nickel(II)-chloridobis(triphenylphosphine)nickel(I) (1/1), [Ni(C(6)H(5))Cl(C(18)H(15)P)(2)].[NiCl(C(18)H(15)P)(2)], (3), were obtained concomitantly with form I. In forms I and II, as well as in the cocrystal, the overall crystal packings are determined by an energetic interplay between intramolecular torsions and weak intermolecular C-H...pi and C-H...Cl interactions.

5-phenyl-3,4-dihydro-2H-pyrrole: the first example of a planar monosubstituted 1-pyrroline.

In the title compound, C10H11N, the molecules assemble as pseudo-dimers through pi-pi interactions, each dimer being rotated by about 90 degrees with respect to its neighbours. The relative positioning of the dimers and C-H...pi interactions give, when seen along a, a supramolecular zigzag arrangement. The compound contains a planar pyrroline ring and, as a whole, its molecular conformation is also planar, which represents the first example of a totally planar 2-substituted 1-pyrroline and the simplest ever reported by X-ray diffraction.