Boron-nitrogen complexes properties

Tetracoordinate Boron. A number of tetracoordmate organoboron species that are photo- and electroluminescent, and thus of interest for device applications have been developed. Characteristic of complexes (168-170) is the presence of chelating nitrogen ligands such as 8-hydroxyquinoline in (168). The qumolate complexes (168) were reported to show superior stabihfy over more commonly used aluminum complexes. Moreover, their photophysical properties were shown to be tunable through ligand variation. ... 

The decisive influence of unoccupied 2p-AO of boron on the molecular properties of 3 is well illustrated by its reaction with pyridine. In the unsymmetrical deuteropyridine complex the empty boron 2p-AO interacts strongly with the nitrogen lone pair. This... 

Since the boron trifluoride adduct is the most stable adduct of the boron complexes of methylenetriphenylphosphorane 121>, it might be expected that this Lewis acid would also form a stable nitrogen ylid adduct. Treatment of the ylid with boron trifluoride gave a white crystalline solid whose properties were consistent with the proposed adduct 11 °>. The adduct decomposes to trimethylamine trifluoroborane... 

NMR investigations show that in the molecule of (4) the nitrogen atom acts as a weak Lewis base (complexes with BBr3 and SbClj), whereas acidic properties of the boron atom were not found (compound (4) does not form an adduct with NH3) <85JA590i>. 

The complex formed by treatment of 2-methyl-5-vinylpyridine with 9-BBN (1 1 molar ratio) gets dissociated readily at 25 or 65 °C due to 2-methylsubstitu-ent, and hydroboration proceeds smoothly to place the boron atom predominantly at the (5-carbon [38]. The electron-withdrawing property of pyridine nitrogen here is transmitted weakly as compared with vinylpyridine. The comparable hydroboration with BMS, 9-BBN, Clix BH, and SiajBH for their steric and electronic consideration along with their molar ratio studies are presented in Table 5.10 [38]. 

Four-co-ordinate boron complexes have been used as control synthons in photocyclizations and the preparation and properties of some new nitrogen heterocyclic tetra-arylborates have been published. ... 

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