Clara S. B. Gomes

New tetradentate N,N,N,N-chelating α-diimine ligands and their corresponding zinc and nickel complexes: synthesis, characterisation and testing as olefin polymerisation catalysts

A series of zinc complexes of the general formula {[ZnCl(ArN=C(An)-C(An)=NAr)](+)}(2)[Zn(2)Cl(6)](2-) (where Ar = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl 2a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)phenyl 2b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl 2c; An = acenaphthene backbone) were prepared by the condensation of acenaphthenequinone with the corresponding o-triazolyl-substituted anilines (2-(1-benzyl-1H-1,2,3-triazol-4-yl)aniline 1a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)aniline 1b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline 1c) which were formed by the copper(I)-catalyzed Huisgen[3+2] dipolar cycloaddition between 2-ethynylaniline and the corresponding azides in high yields, using anhydrous ZnCl(2) as the metal template, in boiling glacial acetic acid. Zinc complexes of the type [ZnCl(ArN=C(An)-C(An)=NAr)](+)[ZnCl(3)(NCCH(3))](-) (4a-c) were synthesized by crystallisation of the corresponding complexes 2a-c in acetonitrile, at -20 °C. After removal of zinc dichloride from complexes 2a-c by the addition of potassium oxalate, in dichloromethane, the tetradentate N,N,N,N-chelating α-diimine ligands of the type ArN=C(An)-C(An)=NAr (5a-c) were obtained. The new ligand precursors and zinc complexes were characterised by elemental analysis, (1)H and (13)C{(1)H} NMR spectroscopy, two-dimensional NMR spectroscopy, and X-ray diffraction. Reaction of the ligand precursors 5a-c with [NiBr(2)(DME)], in dichloromethane, gave nickel complexes of the type [NiBr(2)(ArN=C(An)-C(An)=NAr)] (6a-c). The results of single crystal X-ray diffraction characterisation and magnetic susceptibility measurements demonstrated that nickel complexes 6a-c possess octahedral geometries around the nickel atoms with variable configurations, the Br atoms of which can be ionized when dissolved in methanol. In preliminary catalytic tests, complexes 6a-c revealed to be active as catalysts for the polymerisation of norbornene and styrene, when activated by cocatalyst MAO. The characterisation of the polymers by (1)H and (13)C{(1)H} NMR spectroscopy, gel permeation chromatography/size-exclusion chromatography (GPC/SEC) revealed that these polymers were formed by a coordination addition mechanism.

2H-Azirines as dipolarophiles

2H-Azirine-3-carboxylates unsubstituted at C-2 act as dipolarophiles in the reaction with diazomethane giving new 4,5-dihydro-3H-pyrazole derivatives. The synthesis of a pyrimidine was also achieved via 1,3-dipolar cycloaddition of methyl 2-bromo-3-phenyl-2H-azirine-2-carboxylate with an azomethine ylide.

Reactions of Nitrosoalkenes with Dipyrromethanes and Pyrroles: Insight into the Mechanistic Pathway

The reactivity of nitrosoalkenes toward dipyrromethanes, pyrrole, and 2,5-dimethylpyrrole is described. 1-(p-Bromophenyl)nitrosoethylene shows a different chemical behavior with these heterocycles than the previously reported reactions of ethyl nitrosoacrylate, which proceeds via a Diels-Alder reaction. 1-(p-Bromophenyl)nitrosoethylene reacts with dipyrromethanes and pyrrole to afford two isomeric oximes via conjugate addition followed by rearomatization of the pyrrole unit. On the other hand, this nitrosoalkene reacts with 2,5-dimethylpyrrole through an initial conjugate addition followed by intramolecular O- and N-nucleophilic addition with the formation of the corresponding bicyclic oxazine and five-membered cyclic nitrone, respectively. Quantum chemical calculations, at the DFT level of theory, indicate that the barriers associated with the Diels-Alder reactions of ethyl nitrosoacrylate are over 30 kJ/mol lower than those that would be required for the cycloadditions of 1-(p-bromophenyl)nitrosoethylene. Thus, calculations predict that the Diels-Alder reaction is privileged in the case of ethyl nitrosoacrylate and point to a different reaction pathway for 1-(p-bromophenyl)nitrosoethylene, corroborating the experimental findings.

Cycloaddition reactions of 3-aryl-5-phenyl-5H, 7H-thiazolo[3,4-c]oxazol-4-ium-1-olates

Intermolecular 1,3-dipolar cycloaddition of (5R)- and (5S)-3,5-diphenyl-5H,7H-thiazolo[3,4-c]oxazol-4-ium-1-olates, (5R)- and (5S)-3-(p-methoxyphenyl)-5-phenyl-5H,7H-thiazolo-[3,4-c]oxazol-4-ium-1-olates with a range of dipolarophiles is described. New chiral 5-aryl-3-phenyl-1H,3H-pyrrolo[1,2-c]thiazoles with R and S configuration were obtained. The structure of methyl (3R)-3-phenyl-5-(p-methoxyphenyl)-1H,3H-pyrrolo[1,2-c]thiazole-6-carboxylate was determined by X-ray crystallography. The synthesis of 7,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazole-6,7-dicarboxylates was also achieved.

Boron complexes of aromatic ring fused iminopyrrolyl ligands: synthesis, structure, and luminescence properties

The condensation reactions of 2-formylindole (1) or 2-formylphenanthro[9,10-c]pyrrole (2) with various aromatic amines afforded the corresponding phenyl or phenanthrene ring fused mono-/bis-iminopyrrole ligand precursors 3-8, which, upon reaction with BPh3 in an appropriate molar ratio, led to the new mono- and diboron chelate compounds Ph2B[NC8H5C(H)[double bond, length as m-dash]N-2,6-Ar] (Ar = 2,6-iPr2C6H39; C6H510), Ph2B[(NC8H5C(H)[double bond, length as m-dash]N)2-1,4-C6H4]BPh211, Ph2B(NC16H9C(H)[double bond, length as m-dash]N-Ar) (Ar = 2,6-iPr2C6H312; C6H513), and Ph2B[(NC16H9C(H)[double bond, length as m-dash]N)2-1,4-C6H4]BPh214, respectively. Boron complexes 12-14, containing a phenanthrene fragment fused to the pyrrolyl C3-C4 bond, are highly fluorescent in solution, with quantum efficiencies of 37%, 61% and 58% (in THF), respectively, their emission colours ranging from blue to orange depending on the extension of π-conjugation. Complexes 9-11, containing a benzene fragment fused to the pyrrolyl C4-C5 bond, are much weaker emitters, exhibiting quantum efficiencies of 10%, 7% and 6%, respectively. DFT and TDDFT calculations showed that 2,6-iPr2C6H3N-substituents or, to a smaller extent, the indolyl group prevent a planar geometry of the ligand in the excited state and reveal the existence of a low energy weak band in all the indolyl complexes, which is responsible for the different optical properties. Non-doped single-layer light-emitting diodes (OLEDs) were fabricated with complexes 9-14, deposited by spin coating, that of complex 13 revealing a maximum luminance of 198 cd m-2.

Synthesis and Characterization of 8-(2-((Trimethylsilyl)ethynyl)phenylamino)-7H-naphtho[1,8-bc]acridin-7-one

Abstract An unexpected heterocyclic cyclization reaction of acenaphthenequinone and 2-(trimethylsilylethynyl)aniline in the presence of p-toluenesulfonic acid is reported. A new heterocyclic aromatic compound, 8-(2-((trimethylsilyl)ethynyl)phenylamino)-7H-naphtho[1,8-bc]acridin-7-one, was synthesized as the sole isolated reaction product and characterized by elemental analysis; NMR, IR, and UV spectroscopies; mass spectrometry, and single-crystal x-ray diffraction.

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

A family of 5-(substituted phenyl)-2-formylpyrrole compounds, exhibiting different electronic and steric features at the phenyl ring, was synthesised through the formylation reaction of the corresponding 2-(substituted phenyl)pyrrole precursors, using Vilsmeier–Haack acylation conditions. The products were obtained in moderate to high yields, being systematically characterised by NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The corresponding crystalline packings were discussed on the basis of three types of arrangements, leading to the formation of dimers, polymers or the newly observed tetramers, all of them essentially governed by strong N–H⋯O hydrogen bonding interactions. Important C–H⋯O, C–H⋯π, π⋯π and, in the case of fluorinated compounds, C–H⋯F interactions also contributed to the growth of the three-dimensional crystalline network. DFT calculations helped to rationalise the relationship between the steric and electronic properties of the molecules and the basic units observed in the corresponding solid state structures.

Synthesis and Characterization of a Cationic Cyclopentadienyl Nickel(II) Complex of Bis(mesityl-imino)acenaphthene and its Evaluation as a New Catalyst Precursor for Ethylene Polymerization

5 -C 5 H 5 )(Mes-BIAN))PF 6 (Mes = mesityl = 2,4,6-Me 3 -C 6 H 2 ; Mes-BIAN = bis(mesityl- imino)acenaphthene), was synthesized via two alternative routes, being obtained in moderate to quantitative yields. Although electronically saturated, this new complex was tested in the polymerization of ethylene and propylene in the presence of the cocatalyst methylaluminoxane (MAO), and found to behave as an efficient catalyst precursor for the polymerization of ethylene under mild reaction conditions (low temperature and pressure), whereas it was inactive towards propylene. The polyethylenes produced show methyl branching and a low content of long branches.

Bilateral renal cell carcinoma in a paediatric patient with tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a genetic neurocutaneous disorder characterised by seizures, mental retardation and hamartoma formation in multiple organs, mainly in the brain, skin, kidney, liver, lung and heart. Renal manifestations occur in about 60–80% of all patients with TSC and their rate increases with age. We report the case of a 17-year-old boy with tuberous sclerosis who presented with abdominal pain associated with kidney failure. Investigation revealed bilateral renal lesions, suggesting angiomyolipomas. On further work-up, malignancy was suspected and the patient underwent bilateral partial nephrectomy with histological diagnosis of bilateral renal cell carcinoma. This is a rare complication of TSC, particularly in a paediatric setting. Adequate surveillance of kidney disorders in patients with TSC is warranted, to guarantee an early diagnosis and treatment.

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.