UC Davis

The use of sterically demanding m-terphenyl ligands to kinetically stabilize unusual low coordinate molecular geometries in organometallic complexes of aluminum and lead are described. The influence of attractive intramolecular interligand London dispersion forces on their structures was also studied. In Chapter 2, rare examples of diplumbynes, dilead analogues of alkynes, of the formula RPbPbR with lead-lead multiple bonding were prepared and structurally characterized. Using the m-terphenyl ligands C6H3-2,6-(C6H2-2,4,6-tBu3)2 (ArtBu6) and C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2 (AriPr8) gave multiply bonded structures in the solid state. Calculations in collaboration with Prof. Stefan Grimme, Markus Bursch, Jakob Seibert, and Leonard Maurer showed that dispersion energies also contributed significantly to the stability of these molecules. Chapter 3 describes stable m terphenyl lead(II) hydrides that were isolated in the preparation of the diplumbynes.Chapter 4 describes the metathesis reactions of heavy group 14 element alkyne analogues of Ge, Sn, and Pb with Mo-Mo single and triple bonds. These compounds reversibly dissociate in solution to monomeric radicals. By their direct reaction with (CO)3(η5-C5H5)Mo–Mo(η5-C5H5)(CO)3 and (CO)2(η5-C5H5)Mo≡Mo(η5-C5H5)(CO)2¬¬, the energetically favored group 14 element-Mo bonds are formed. Chapter 5 describes the synthesis of the first isolated species with a one-coordinate aluminum atom. The sterically demanding AriPr8 ligand stabilizes this geometry. Nonetheless, calculations showed that a dimer, the dialuminene AriPr8AlAlAriPr8, is slightly favored. This is supported by the facile reactivity of :AlAriPr8 with H2. In Chapter 6 the reaction of :AlAriPr8 with several organoazides is described. When the m-terphenyl azide ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2 is used, the first compound with an Al-N triple bond AriPr8AlNArMe6 was isolated. The attractive dispersion forces between the two terphenyl substituents on the Al and N atoms contribute a stabilization energy that is on the same order of magnitude as the Al-N π-type bonds in the molecule. Chapter 7 describes a new route to dialuminenes of the formula RAl=AlR. These species are highly reactive towards arene solvents in which they are soluble. By using a terphenyl ligand substituted by the -SiMe3 group, C6H2-2,6-(C6H3-2,6-iPr2)2-4-SiMe3 (AriPr4-4-SiMe3) we anticipated increasing the solubility of the dialuminene in solvents with which it would not react. Direct reduction of the iodide precursors to 4-SiMe3AriPr4Al=AlAriPr4-4-SiMe3 failed, so a new route through the comproportionation of Al(Et2O)I2AriPr4-4-SiMe3 or (AlIAriPr4-4-SiMe3)2 with the dialuminyne salt Na2(AlAriPr4-4-SiMe3)2 was used. In hexanes or ether, this reaction mixture turns deep purple before rapidly decomposing. However, in benzene the dialuminene-benzene [2+4] cycloaddition complex is stoichiometrically obtained from the comproportionation reaction.