Janusz Serwatowski

A tautomeric equilibrium between functionalized 2-formylphenylboronic acids and corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles

Functionalized 2-formylphenylboronic acids undergo an unprecedented tautomeric rearrangement in solution to form corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles. X-Ray analyses of selected examples revealed diverse solid-state molecular structures from a planar open form with a hydrogen-bonded carbonyl group (X = 3-F) through a twisted conformer showing a weak carbonyl–boron interaction (X = 3,5-Br2) to a cyclic oxaborole derivative (X = 3-Br). Variable-temperature 1H NMR spectroscopy was used to determine equilibrium constants as well as enthalpies and entropies of tautomerization in a mixed solvent [D6]acetone–D2O (95 : 5). A computational approach to the process by DFT (B3LYP) and MP2 methods has also been performed.

Towards a monomeric structure of phenylboronic acid: The influence of ortho-alkoxy substituents on the crystal structure

The structures of three ortho-alkoxyphenylboronic acids (2-methoxy-, 2-ethoxy-, 2-isobutoxy-), and three diortho-alkoxyphenylboronic acids (2,6-dimethoxy-, 2,6-diethoxy- and 2-isobutoxy-6-methoxy) were determined by single crystal X-ray diffraction. The study was undertaken with the intention of designing a novel boronic acid having a monomeric structure, which to date has been an unavailable building block for crystal engineering. This motif can be enhanced by involving two hydroxyl groups at the boron atom in intramolecular hydrogen bonds. Although monosubstituted systems form typical dimers in the crystal lattice, disubstituted species reveal a much bigger variety of possible interactions. Among the analyzed compounds, 2,6-dimethoxyphenylboronic acid and 2,6-diethoxyphenylboronic acid crystallize in two polymorphic forms each. The unprecedented packing with monomers as the dominant structural motif has been found in the crystal structure of 2-isobutoxy-6-methoxyphenylboronic acid and one of the polymorphs of both 2,6-dimethoxyphenylboronic acid and 2,6-diethoxyphenylboronic acid. This description of the molecular packing is also supported by the analysis of fingerprint 2-D plots based on the Hirshfeld surfaces. The variety of possible types of interactions either within a single moiety or between moieties in dimers were additionally analyzed on the basis of the interaction energies, which have been estimated by ab initio calculations at the MP2/6-31+G* and B3LYP/6-311+G** level of theory.

Synthesis and structure of alkylaluminoxanes

Abstract The structure of the compounds R4Al2O (where R = H or i-Bu) was studied. The occurrence of R groups bridging aluminium atoms (besides the known oxo bridges) is a characteristic feature of these arrangements. The relative stability of H, Me, Et and i-Bu bridges was compared. The influence of steric factors on the aluminoxane association is discussed. A novel technique developing the known hydrolysis method was employed in the preparation of the investigated systems.

Synthesis of some halogenated tetraarylborates

The reactions of 3,4-dichlorophenylmagnesium bromide and 3,5-dichlorophenylmagnesium bromide with B(OEt) 3 and NaBF 4 were studied The corresponding tetraarylborates [(3,4-Cl 2 C 6 H 3 ) 4 B]NH 4 and [(3,5-Cl 2 C 6 H 3 ) 4 B]Na were obtained and characterized. The significant influence of the substituents inductive effect on the reaction course was revealed. NaBF 4 was found to be a valuable boron reagent in the synthesis of tetraarylborates containing highly electronegative substituents. The molecular structure of [(3-CF 3 C 6 H 4 ) 4 B]NH 4 obtained from the reaction of 3-trifluoromethylbromobenzene with NaBF 4 and Mg was determined using X-ray analysis.

Heteroleptic (2-fluoro-3-pyridyl)arylborinic 8-oxyquinolinates for the potential application in organic light-emitting devices.

A one-pot protocol has been developed to obtain a series of luminescent heteroleptic diarylborinic complexes bearing the 2-fluoro-3-pyridyl and another aryl group attached to the boron atom chelated with a simple or functionalized 8-oxyquinolinato ligand. The tetrahedral geometry around the boron atom in all compounds has been established by the (11)B NMR spectroscopy and/or X-ray diffraction technique. In the solution, the obtained complexes have emission maxima ranging from 502 to 525 nm at room temperature. The quantum yield of emission significantly depends on the type and position of the substituents in the 8-oxyquinolinato ligands and aryl rings. An interpretation of the experimental UV-vis absorption and emission spectral data is supported by theoretical calculations of the frontier molecular orbitals. Marcus theory was used to theoretically evaluate charge-transport properties of the obtained complexes.

Competition between hydrogen and halogen bonding in the structures of 5,10-dihydroxy-5,10-dihydroboranthrenes.

X-ray crystallographic and computational studies are reported for a series of boranthrenes, substituted with halogen atoms. The role of competitive hydrogen (O-H...O, O-H...F, C-H...O) and halogen (Cl...Cl, O...Br, F...F) bonding interactions on the molecular arrangement in the crystal structures is discussed. The structural analysis and calculations reveal that the O-H...O hydrogen bond in the unsubstituted derivative 5,10-dihydroxy-5,10-dihydroboranthrene, C12H10B2O2, is of moderate strength (ca -20 kJ mol(-1)), but weaker than that in the related thiophene derivative 4,8-dihydro-4,8-dihydroxy-p-diborino[2,3-b:5,6-b]dithiophene, C8H6B2O2S2 (ca -40 kJ mol(-1)). This is due to shielding of the OH group by the H atoms in the β-position of the boranthrene unit. Structural diversity derived from the flexibility of the O-H...O hydrogen bond facilitates the occurrence of other competitive interactions. For instance, in the 1,6-difluoro derivative, C12H8B2F2O2, the crystal packing results from O-H...F and F...F interactions. In turn, the 1,6-dibromo derivative, C12H8B2Br2O2, is dominated by Br...O halogen-bond interactions. In the most interesting case, the 1,6-dichloro derivative, C12H8B2Cl2O2, molecular disorder leads to the formation of two different supramolecular arrangements co-existing in the crystal lattice, one based on the Cl...Cl and C-H...O bonds, and the other stabilized by O-H...O hydrogen bonds. Calculations performed with density-functional theory (DFT; CRYSTAL09) and PIXEL methodologies show that both lattices are characterized by similar energy values (ca -100 kJ mol(-1)). A mixed arrangement with random or short-range-ordered molecular orientations can also be expected.

3-formylphenylboronic acid.

The molecule of the title compound, C(7)H(7)BO(3), is planar, and the bond lengths and angles are typical. The formyl group is essentially coplanar with the benzene ring but does not influence significantly the distortion of the ring, although the formyl group does have a strong influence on the crystal packing. The geometry of the boronic acid group is typical. In the crystal structure, the molecules are linked by O-H...O hydrogen bonds.

Complexes of tetraalkylaluminoxanes with some nitrogen-containing lewis bases

Tetraalkylaluminoxanes, R4Al2O (where R  Et, i-Bu), were found to form donor—acceptor complexes with some nitrogen containing electron donors (NMe2Ph, PhHCN-n-Bu and PhCN). These complexes are generally monomeric and have a 1/1 molar ratio of the components. A structure, based on low temperature PMR spectral studies, is postulated for each complex with the bridging nitrogen atom bonded to both aluminium atoms in the complexed aluminoxane. Some steric effects during the complex formation are discussed. It is shown that they are considerably responsible for the complexation.

Tetraethylalumoxane—benzonitrile complex

Abstract Tetraethylalumoxane was found to form a complex with benzonitrile in the molar ratio 1 : 1. This complex is a monomer. The structure of the complex is proposed on the basis of molecular weight determinations, IR and PMR investigations, and the alkyl group exchange reaction with tetramethyllead. The acidities of tetraethylalumoxane and triethylaluminium are compared.

Efficient 8-oxyquinolinato emitters based on a 9,10-dihydro-9,10-diboraanthracene scaffold for applications in optoelectronic devices

A detailed experimental characterization and theoretical evaluation of the optical as well as other relevant physicochemical properties of a series of 9,10-dihydro-9,10-diboraanthracene bis(8-oxyquinolinates) and a few other related systems is reported. The obtained compounds exhibit green luminescence with quantum yields of emission of up to 63% in CH2Cl2. Single crystal X-ray diffraction studies indicate that 9,10-dihydro-9,10-diboraanthracene complexes exist either as bent conformers (stabilized by a weak intramolecular CH⋯O interaction bringing two 8-oxyquinolinato ligands closer to each other) or symmetrical ones (bearing two ligands related by a centre of symmetry and separated from each other). Theoretical calculations revealed that the LUMO levels are lower for the bent conformers than for the symmetrical ones. This suggests that the luminescent properties of the studied compounds are affected by their specific structural properties. The obtained compounds were used as emitters for the construction of organic light emitting diodes (OLEDs). The highest luminance of ca. 2000 cd m−2 was recorded for the device containing only 2.0 wt% of the 1,6-difluoro-9,10-dihydro-9,10-diboraanthracene core in the poly(N-vinylcarbazole/2-t-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD) matrix. The fabricated OLEDs exhibit current efficiency in the range from 0.5 to 1.1 cd A−1.