HALOGENATED DERIVATIVES OF THE DIMOLYBDENUM TETRAPHOSPHOXANE CAGE

Iodination and chlorination of the dimolybdenum tetraphosphoxane cage complex (CO)4Mo[(i)Pr2NPO]4Mo(CO)4 in dichloromethane afforded first the mixed-valent products X2(CO)2Mo[(i)Pr2NPO]4Mo(CO)4 and then the tetrahalo complexes X2(CO)2Mo[(i)Pr2NPO]4Mo(CO)2X2 (X = Cl, I). The tetrabromo complex can be similarly synthesized, but the dibromo complex is not formed by stoichiometric bromination in CH2Cl2. It was indirectly prepared by metathesis from the diiodo product in CH2Cl2/CH3C = N. The integrity of the adamantane-like Mo2P4O4 cage is maintained in all these halogenation products. For the cage-I2 complex, an intermediate species, I2(CO)3Mo[(i)Pr2NPO]4Mo(CO)4, can be observed at low temperature. This readily decarbonylates to give the isolated product. A single-crystal X-ray structural determination of the diiodo complex, I2(CO)2Mo[(i)Pr2NPO]4Mo(CO)4, has been completed. Crystal data: monoclinic, P2(1)/c, a = 18.915 (2) angstrom, b = 11.911 (2) angstrom, c = 21.063 (2) angstrom, beta = 94.88 (1)-degrees, V = 4728.4 (9) angstrom3, Z = 4, D(calc) = 1.610 g/cm3, mu = 19.8 cm-1, F(000) = 1919.51, Mo K-alpha (lambda = 0.709 30 angstrom), R(F) = 0.058, and R(w) = 0.049 for 4029 unique observed [\F\ greater-than-or-equal-to 2.5-sigma(F)] reflections and 468 parameters. A trigonal-prismatic coordination sphere is found around the 16-electron Mo(II) center. NMR spectroscopic data support the retention of this geometry for all the dihalogenated and tetrahalogenated species in solutions of nonpolar solvents. By contrast to these stable products, halogenation of the phenyl-substituted cage complex, (CO)4Mo[PhPO]4Mo(CO)4, afforded X2(CO)3Mo[PhPO]4Mo(CO)4 and X2(CO)3Mo[PhPO]4Mo(CO)3X2. These complexes show low stability, lose CO readily, and are only poorly characterized.