Homogeneous olefin polymerization with organovanadium complexes, and, Synthesis and characterization of III-V single-source precursor molecules for MOCVD.

摘要

Chapter 1 describes the synthesis, characterization and reactivity as olefin polymerization catalysts of vanadium(III) complexes bearing the (2,6-Me 2Ph)2nacnac ligand. The dichloride and a series of dialkyl vanadium complexes, (2,6-Me2Ph)2 nacnacVR2 (R = Cl (1), Me (2), Et (3), CH 2SiMe3 (4), Bn (5) and Ph ( 6)) have been prepared. Upon activation with cocatalysts, e.g. MAO or B(C6F5)3, they became potent catalysts for ethylene polymerization. Attempts to isolate an alkyl vanadium(III) cation revealed that the tetraarylborate counteranion coordinated to the vanadium via eta6-Ph group and induced the homolytic cleavage of V(III)-carbon bonds. In contrast, the reaction of 2 with [NHMe2Ph] [B(C6F5)4] gave a monomethyl vanadium(III) cation, [(2,6-Me2Ph)2nacnacV(Me)(eta6-PhNMe 2)][B(C6F5)4] (16). It, however, showed little activity with ethylene. Finally, the monoalkyl vanadium(III) cations, [(2,6-Me2Ph)2nacnacV(R)(Et2O)] [BARF] R = Me (17), CH2SiMe3 (18), have been isolated. They are active catalysts for the polymerization of ethylene without an activator. 18 is also capable of polymerizing propylene and 1-hexene.Chapter 2 describes the stability and hydrogenolysis of the dialkyl vanadium(III) complexes as well as the chemistry of a vanadium oxo compound. Only 3, which possesses beta-hydrogen atoms, was unstable and decomposed via beta-hydrogen elimination. In the presence of benzene, the decomposition product, [(2,6-Me2Ph)2 nacnacV]2(mu 2-eta6:eta6-C6H6) (19) was isolated. Similarly, the hydrogenolysis of 5 gave the toluene-bridged complex, [(2,6-Me2Ph)2nacnacV] 2(mu2-eta6:eta6-C 7H8) (23). Both complexes exhibit Curie-Weiss paramagnetism with intramolecular ferromagnetic coupling of the V(I) (S = 1) centers. In an attempt to synthesize a vanadium(III) hydride species, a reaction of 1 with LiHBEt3 was carried out. The product was a dinitrogen-bridged complex, namely [(2,6-Me2Ph)2nacnacV({mu-H} 2BEt2)]2(mu-N2) (21). Reaction of VOCl3 with (2,6-Me2Ph)2nacnacLi yielded the chloride-bridged vanadium(IV) oxo complex, [(2,6-Me2Ph) 2nacnacVO]2(mu-Cl)2 (25). Subsequent reaction of 25 with AlMe3 resulted in reduction to the vanadium(III) species, (2,6-Me2Ph)2V(Cl)(Me) ( 7).Chapter 3 details the synthesis and characterization of group 13 metal complexes coordinated by the (iPr)2nacnac ligand. (iPr)2nacnacM(N3)2 (M = Al (29), Ga (30)) have been prepared from ( iPr)2nacnacMCl2 and NaN3 in THF. By using 30 as a single-source precursor for growing a GaN film with a modest NH3 flow rate, polycrystalline to single crystalline GaN with low levels of C and O impurities has been grown at temperatures between 515--725°C.