Date of Award

Spring 1989

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

Mixed-valent tetrametallic complexes of the type Mo$\sb2\lbrack$M(CO)$\sb4$(PhPO$\sb2$)$\sb2\rbrack\sb2\sp{4-}$ (M = Cr, Mo, W) were synthesized by the nucleophilic attack of the phosphonito metallo-ligand cis-M(CO)$\sb4$(PhPO$\sb2$)$\sb2\sp{4-}$ on dimolybdenum tetraacetate. These complexes were characterized by elemental analyses and NMR, IR, and UV-Vis spectroscopy. The x-ray crystal structure for the tetra-molybdenum complex indicates a M-M bondlength of 2.186(2). Only weak interactions were found with potential axial ligands such as amines, phosphines and isonitriles. Oxidation with four equivalents of iodine occurred at the Mo(O) sites yielding Mo$\sb2\lbrack$Mo(CO)$\sb3$I$\sb2$(PhPO$\sb2$)$\sb2\rbrack\sb2\sp{4-}$ with new seven-coordinate Mo(II) sites. The phosphorus-31 NMR spectrum of this complex exhibits temperature-dependent behavior indicating rapid geometric isomerization in solution.

Phosphonito metallo-ligands were also used to assemble bimetallic cage complexes of the adamantane type, (CO)$\sb4$M(RPO$\rbrack\sb4$M(CO)$\sb4$. The reactivity of dimolybdenum cages (R = $\rm\sp{i}$Pr$\sb2$N, Ph) towards halogen oxidation is dependent on the nature of the phosphorus substituent. In a competitive iodination experiment, the phenyl cage reacted more slowly than the isopropylamino cage. Both cages yield mixed-valent dihalo and tetrahalo complexes upon oxidation. Structural data suggests that the mixed-valent dihalo complexes of the isopropylamino cage are dimers in the solid state but monomers in solution. The tetrahalo complexes, (CO)$\sb2$X$\sb2$Mo(RPO$\rbrack\sb4$Mo(CO)$\sb2$X$\sb2$, (X = Cl, Br, I) exhibit solubility behavior consistent with halogen-bridged polymeric units in the solid state.

In contrast, halogen oxidations of the phenyl cage yield the less stable, seven-coordinate mixed valent complexes (CO)$\sb4$Mo(RPO$\rbrack\sb4$Mo(CO)$\sb3$X$\sb2$. These readily lose CO to give unidentified products. Limited data available for the tetrahalo phenyl cage complexes suggest that they exist as seven-coordinate monomers, (CO)$\sb3$X$\sb2$Mo(RPO) $\sb4$Mo(CO)$\sb3$X$\sb2$.

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