The chemistry of [beta]-diketiminate-supported boron, aluminum, gallium and phosphorus compounds
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Six synthetic methods have been explored for the preparation of several boron, aluminum, gallium and phosphorus compounds supported by the C6F5-substituted β- diketiminate ligand. The most significant advance was achieved in the synthesis of β- diketiminato boron dihalide complexes (LBX2, L = β-diketiminate ligand, X = halide) because only a handful of compounds with this general formula were known. These syntheses were carried out in virtually quantitative yields by treatment of an Ntrimethylsilyl aminoimine intermediate with the appropriate boron trihalides. The synthesis and characterization of the elusive monomeric oxoborane, a compound with formal double bond between boron and oxygen, was also achieved by employing the C6F5-substituted β-diketiminate ligand. The overall stability of the resulting monomeric oxoborane was enhanced by complexation of the Lewis acid AlCl3 to the oxoborane oxygen atom. Successful synthetic approaches to the boron, aluminum and gallium bistriflate complexes of the general formula LE(OTf)2, where E = B, Al or Ga, were also developed and preliminary studies involving the use of these compounds as catalysts in organic transformations gave promising results. These bistriflate group 13 compounds also proved to be effective reagents for the synthesis of the first examples of boron, aluminum and gallium dications. The boron and aluminum dications were characterized by single-crystal X-ray diffraction. Finally, the use of the pentamethylcyclopentadienyl group as the boron substituent has allowed the synthesis and structural characterization of a new cationic terminal borylene complex. This complex, together with the two previously reported cationic terminal borylene complexes, demonstrate that the boron-metal bond order is sensitive to the electronic properties of the boron substituents and can vary from 1 to 2.