Host-guest and supramolecular chemistry of mercuracarborands

Chapter 1. The multidentate Lewis acids B-octamethyl [12]-mercuracarborand-4 (1) and B-hexamethyl [9]-mercuracarborand-3 (2) catalyze the Diels-Alder reaction of a thionoester 4 with cyclopentadiene. The reaction proceeds more rapidly when catalyzed with 1 and 2 than with monodentate bis(closo-9,12-dimethyl-1,2-carboran-1-yl)mercury (3). Mercury-199 NMR studies demonstrated the formation of a 1:1 complex of 1 with 4 in which the thio function of 4 is coordinated to the Hg(II) centers of 1, while the 2•4 and 3•4 complexes are not observed by NMR.; Chapter 2. The “anti-crown” B-hexamethyl 9-mercuracarborand-3 (1) was shown to complex halides ions (I −, Br−, Cl−) in an η 3-sandwich fashion. Symmetry-allowed interactions of the filled iodide p-orbitals and the corresponding empty mercury p-orbitals result in three equivalent P_Hg-P_halide-P_Hg three-center two-electron bonds and a sandwich structure.; Chapter 3. Slow evaporation of an acetone/water solution of trimeric 9-mercuracarborand-3 (1a) yielded single crystals which were examined by X-ray diffraction. Host 1a forms a 1:1 complex with a water molecule and three acetone molecules coordinate to a corresponding mercury center, [1a•(OH₂)•((CH ₃)₂CO)₃] (2). The water molecule lies on the 3-fold axis, located above the Hg₃ plane, and is simultaneously coordinated to all three mercury atoms. Slow evaporation of a benzene/water/methylene chloride solution of B-hexamethyl-9-mercuracarborand-3 (1) yielded single crystals which were examined by X-ray diffraction. The water molecule resides above the Hg₃ plane, similar to complex 2. Hydrogen atoms of water coordinate with the π-electron cloud of benzene leading to sandwich structure, [(1•OH₂) ₂•C₆H₆] (3).; Chapter 4. Modular units of Li₂ [ B-octaiodo-12-Mercuracarborand-4•I₂] (Li₂[(HgC ₂B₁₀H₈I₂)4•I₂]) self-assemble forming infinite one-dimensional chains and microporous channels in the solid state. Self-assembly is directed by an unique B-ILiI-B intermolecular interaction involving electron-rich B-I vertices and electron-deficient lithium cations.; Chapter 5. The synthesis and crystallization of 9,12- bis-(4-fluorophenyl)-1,2-carborane (1) and 9,12- bis-(3,5-difluorophenyl)-1,2-carborane (2) provide the first examples of a supramolecular assemblage directed by C-H_carborane F interactions.