S-, D-, and F-block organometallic complexes with trimethylsilyl-substituted allyl ligands

Previous work has shown that sterically bulky substituents have been used to stabilize various first row transition metal allyl complexes [eta 3-1,3-(SiMe3)2C3H3] 2M that have no (C3H5)2M counterparts. These include complexes of chromium, iron, cobalt and nickel in which two allyl anions are bound in a pi-fashion. In the case of chromium, the steric bulk may be tuned by varying the number of trimethylsilyl groups present. The monomeric 12-electron species, [eta3-1,3-(SiMe3 )2C3H3]2Cr, is thermally stable at room temperature and work presented in this dissertation has demonstrated that it will polymerize methyl methacrylate. Removing one trimethylsilyl group permits the isolation of a dimeric chromium allyl species that is similar structurally to the parent dimeric species. Attempts to isolate [eta 3-1,3-(SiMe3)2C3H3] 2Mn have not been successful, but have illustrated various features of the Mn-allyl bond. Manganese (II)allyl species have been shown to bind in a sigma fashion with coordinated solvent molecules in a pseudo-tetrahedral environment. This is likely due to the electronic state of high spin manganese(II), which contains five unpaired electrons, and which displays considerable "ionic" character. Comparison to the similarly sized cation, magnesium(II), has supported this argument in that its small ionic radius allows the isolation of a sigma-bound species that is different from a pi-bound calcium allyl complex reported previously. Variations in the solvent and steric bulk have further illustrated the fact that manganese(II) represents a more ionic center than the other first row transition metals.; Several lanthanide species of the form [eta3-1,3-(SiMe 3)2C3H3]3LnI and [eta3-1,3-(SiMe3)2C3H 3]3Ln(thf) have been isolated and studied as single-site polymerization catalysts. Extension to the actinides series has permitted the study of the coordination environment of Th(IV) in [eta3-1,3-(SiMe 3)2C3H3]4Th and [eta 3-1-(SiMe3)C3H4]4Th. Although tetra (allyl)thorium has been reported, it has not been structurally characterized due to its thermal instability. The enhanced stability of allyl complexes provided by the steric bulk of trimethylsilyl substituents has allowed the study of allyl chemistry to expand across the period table. Preliminary reactivity studies have shown the potential applications of sterically stabilized metal allyl complexes as polymerization catalysts.