DIMOLYBDENUM(II) CALIXARENE COMPLEXES - SYNTHESIS, STRUCTURE, RAMAN-SPECTROSCOPY, AND BONDING

The preparation of complexes containing metal-metal quadruple bonds supported by calixarene ligands is described. The labile starting materials [Mo-2(OCCH3)(2)(NCCH3)(6)](BF4)(2), a known compound, and [Mo-2(OCCF3)(2)(NCCH3)(6)]-(BF4)(2) (1) were added to solutions of p-tert-butylcalix[4]arene and calix[4]arene that were deprotonated with 2 equiv of KH to give, respectively, [Mo-2(O(2)CR)(2)(H-2-p-tert-butylcalix [4]arene)] (2, 3: R = CH3, CF3) and [Mo-2(O-2-CR)(2)(H-2-calix[4]arene)] (4, 5: R = CH3, CF3). The dimolybdenum calixarene products 2-5 were studied by H-1 NMR, IR, UV-visible, and Raman spectroscopy. X-ray crystallographic analysis revealed the solid state structure of 2(THF). C6H6, which contains a molybdenum-molybdenum quadruple bond (2.1263 (6) Angstrom) spanned by two bridging acetate ligands and a tetradentate, doubly-deprotonated calixarene macrocycle. Each Mo-Mo unit is weakly coordinated by an axial THF solvent molecule which is included in the calixarene basket of the neighboring complex. Crystal data: C58H74O9Mo2, monoclinic, space group P2(1)/c, a = 12.533 (2) Angstrom, b = 23.515 (2) Angstrom, c = = 18.520 (2) Angstrom, beta = 95.66 (2)degrees, V = 5432 (1) Angstrom(3), Z = 4, 6251 unique observed reflections, R = 0.040, R(w) = 0.042, T = -73.8 degrees C. SCF-X alpha calculations revealed the nature of the bonding interactions in this new class of compounds.