Vincent Terrasson

General Access to Aminobenzyl-o-carboranes as a New Class of Carborane Derivatives: Entry to Enantiopure Carborane–Amine Combinations

The convenient synthesis of original aminobenzyl-o-carboranes, which represent a new class of nitrogenated carborane derivatives, is described. These novel compounds have been efficiently prepared starting from commercially available aromatic aldehydes and monosubstituted o-carboranes via carboranyl alcohols and chlorides as intermediates. The key step of this methodology is a selective nucleophilic amination under mild conditions that allows the formation of the expected amines while limiting the partial deboronation of the carborane cluster. This general strategy has been applied to the preparation of a wide variety of aminobenzyl-o-carboranes. The extension of this pathway to the synthesis of enantiopure carborane-amine combinations is also described.

Crystal engineering of o-carboranyl alcohols: syntheses, crystal structures and thermal properties

The syntheses of new o-carboranyl alcohols 1-[R(hydroxy)methyl]-2-methyl-1,2-dicarba-closo-dodecaborane (R = 9-anthracenyl 2, 4-pyridyl 4), 1-[R(hydroxy)methyl]-2-phenyl-1,2-dicarba-closo-dodecaborane (R = 3-phenyl-2-propen-1-ol 6, 2-furanyl 7) are reported. Their crystal structures, along with those for the related 1-[R(hydroxy)methyl]-2-methyl-1,2-dicarba-closo-dodecaborane (R = phenyl 1, 2-pyridyl 3) and 1-[phenyl(hydroxy)methyl]-2-phenyl-1,2-dicarba-closo-dodecaborane (5) derivatives are reported. We provide an analysis of these compounds by means of X-ray crystallography, NMR/IR spectroscopies, thermal analyses and gas phase calculations in the context of crystal engineering. The results show that the crystal packing for these alcohols can be described in terms of three major supramolecular synthons based on hydrogen bonding of OH groups with themselves (O–H⋯O homosynthons: 1, 6 and 7), with the pyridine nitrogen atom (O–H⋯N heterosynthons: 3 and 4) or with aromatic rings (O–H⋯π: 2). The latter shows an unusual combination of O–H⋯π and π–π interactions. The supramolecular heterosynthons are clearly favoured over their respective supramolecular homosynthons. In the absence of a nitrogen atom, the bulkiness around the OH groups seems to play a key role in the formation or not of full O–H⋯O hydrogen bonding. The supramolecular arrays are finally supported by both, weak dihydrogen or hydrophobic interactions, due to the presence of o-carboranyl fragments in these molecules. These compounds display good thermal stabilities, with compound 4 showing an unexpectedly high melting temperature of 256 °C probably arising from an infinite O–H⋯N hydrogen bonding network. Gas phase calculations demonstrate that O–H⋯N hydrogen bonded dimers are 3.5 kcal mol−1 more stable than analogous for O–H⋯O hydrogen bonded ones.