No abstract

The first beryllium(ii) complex with a quinolino[7,8-h]quinoline based proton sponge reveals a complementary size match.

The synthesis of a boronic acid anhydride‐based ligand containing one three‐ and one four‐coordinated boron atom is presented. This ligand was successfully employed as a tridentate κ1N,κ2O‐ligand in the coordination of beryllium chloride and both the ligand and the resulting complex have been structurally characterized. While the boron‐element separations are within the typical range of related homo‐nuclear compounds, the corresponding beryllium‐element distances are rather long, suggesting unexpectedly high electron density at the beryllium center. Incorporation of a beryllium atom in a six‐membered ring causes no more distortion than the corresponding boron atom, suggesting that analogous ligand systems could be used in boron and beryllium coordination chemistry. The generated hetero‐tri‐nuclear complex enables the direct comparison of bond lengths and angles at beryllium and boron atoms in similar coordination environments and can act as a monomolecular model for beryllium borates.

Quinolino[7,quinoline is a superbasic compound, with a pK aH in acetonitrile greater than that of 1,8-bis(dimethylaminonaphthalene) (DMAN), although its synthesis and the synthesis of its derivatives can be problematic. The use of halogen derivatives 4,9-dichloroquinolino[7,8h]quinoline (16) and 4,9-dibromoquinolino[7,8-h]quinoline ( 17) as precursors has granted the formation of a range of substituted quinolinoquinolines. The basicity and other properties of quinolinoquinolines can be modified by the inclusion of suitable functionalities. The experimentally obtained pK aH values of quinolino[7,8-h]quinoline derivatives show that N 4 ,N 4 ,N 9 ,N 9 -tetraethylquinolino[7,8-h]quinoline-4,9-diamine ( 26) is more superbasic than quinolino[7,8-h]quinoline. Computationally derived pK aH values of quinolinoquinolines functionalized with dimethylamino (NMe 2 ), 1,1,3,3-tetramethylguanidino (NC(NMe 2 ) 2 ) or N,N,N′,N′,N″,N″-hexamethylphosphorimidic triamido (NP(NMe 2 ) 3 ) groups are significantly greater than those of quinolino[7,8-h]quinoline. Overall, electron-donating functionalities are observed to increase the basicity of the quinolinoquinoline moiety, while the substitution of electron-withdrawing groups lowers the basicity.