A new method for the preparation of seven-membered carbocycles via cobalt-mediated [5+2] cycloaddition methodology is presented. We have demonstrated that Cp*Co(5-pentadienyl)+ systems undergo cycloaddition reactions with alkynes in a diastereocontrolled and high-yielding process. When acetylene is employed as the cycloaddition partner, unprecedented Cp*Co(2,3-cycloheptadienyl)+ complexes were isolated as the cycloaddition product under kinetic control. These allyl/olefin species were further transformed to the thermodynamic Cp*Co(5-cycloheptadienyl)+ complexes. Also described are two methods for the preparation of high-valent Co(III) 5-pentadienyl complexes, a compound class that has been under-reported in the literature. This work fills this void and provides a valuable view of the structural properties of 5-pentadienyl complexes as a function of the substitution pattern. The incorporation of tethered pronucleophiles onto the pentadienyl ligand allowed the preparation of fused bicyclic structures of relevance to natural product synthesis. Both conjugated and unconjugated cycloheptadiene species were prepared, made possible via the differing cycloheptadienyl complex hapticity. The oxidative decomplexation of the organic products is also described. Initial steps towards a divergent pronucleophile-bearing pentadienyl synthesis were also undertaken. The mechanism and structure/reactivity relationships for the [5+2] cycloaddition process were studied via density functional theory calculations. These investigations revealed the existence of several convergent reaction pathways on the potential energy surface, and provided a new rationale for the 2,35 isomerization, thereby explaining the low activation barrier for the isomerization of 2-butyne cycloadducts. Of interest is the elucidation of a radical-type pathway, calculated to be of high energy for the Cp* ligand system, yet energetically competitive in the Cp complex reaction manifold. Further, computations on the Cp system demonstrate a potentially viable pathway on the triplet energy surface, suggesting spin-forbidden transitions may play a role in the mechanism. These observations provide an explanation for the differing cycloaddition efficiencies in these two pentadienyl systems. Calculations also suggest that reaction chemoselectivity is determined during the rate-limiting alkyne complexation step; the energetics of this process being dominated by steric interactions between the pentadienyl substituents and the ancillary ligand.

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Submitted by Beatriz Aline Riga null (beatriz_aline16@hotmail.com) on 2017-03-15T18:07:31Z No. of bitstreams: 1 Riga Rocha, B. A._me_sjrp.pdf: 4397938 bytes, checksum: 97cd69af09e5df0e1dcc372a541946c2 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2017-03-21T16:17:50Z (GMT) No. of bitstreams: 1 rocha_bar_me_sjrp.pdf: 4397938 bytes, checksum: 97cd69af09e5df0e1dcc372a541946c2 (MD5) / Made available in DSpace on 2017-03-21T16:17:50Z (GMT). No. of bitstreams: 1 rocha_bar_me_sjrp.pdf: 4397938 bytes, checksum: 97cd69af09e5df0e1dcc372a541946c2 (MD5) Previous issue date: 2017-02-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho objetivou-se a síntese e caracterização de oito complexos de cobalto(II) que fossem aptos a atuarem como agentes controladores na Polimerização Radicalar Mediada por Cobalto do monômero acetato de vinila. Através da modulação da esfera de coordenação destes complexos com a alteração dos efeitos estéricos e eletrônicos promovidos pela coordenação de ligantes α-diiminas, buscou-se estabelecer parâmetros para propor a forma como estes complexos mediam a CMRP do referido monômero. Os complexos foram divididos em dois grupos, objetivando uma avaliação mais eficiente da forma como os efeitos estéricos e eletrônicos interferem na capacidade controladora dos mesmos. Após a variação sistemática das proporções molares entre complexo, iniciador e monômero encontrou-se na proporção [Co]/[AIBN]/[VAc] = 1/3,25/542 os resultados mais satisfatórios deste trabalho. O uso de DMSO fora prejudicial para os complexos 2a-c, porém fez com que os complexos 2d-h apresentassem melhorias, reduzindo seus valores de polidispersidade e aumentando as massas moleculares dos polímeros. O complexo 2b fora escolhido como o melhor controlador do grupo do efeito estérico, por reunir em si as características estérias e eletrônicas que o fizeram apresentar os menores valores de polidispersidade (Đmáx = 1,43). Com relação ao grupo de complexos do efeito eletrônico, fora o complexo 2f que, devido à maior estabilidade estrutural conferida ao complexo por seu substituinte cicloexil, apresentara as menores polidispersidades de seu grupo, entre 1,12 e 1,58. / This work aimed the synthesis and characterization of eight cobalt(II) complexes which could be able to act as controlling agents in vinyl acetate radical polymerization mediated by cobalt. By modulating the coordination sphere of these complexes, modifying the steric and electronic effects offered by the α-diimine ligands, we sought to establish parameters to propose how these complexes mediate the CMRP of vinyl acetate. The complexes were split in two groups in way to assess efficiently how the electronic and steric effects can affect the controlling capacity of the CoII(α-diimine).A systematic variation of the molar ratio such as [Co]/[initiator] and [Co]/[monomer] made it possible to choose [Co]/[initiator]/[monomer] = 1/3.25/542 as the ratio that provided certain level of control. The addition of DMSO was detrimental to the complexes 2a-c, but caused an improvement to the activity of complexes 2dh, reducing their polydispersity values and increasing the molecular weights of the polymers. Complex 2b was chosen as the best controller of the steric effect group, its steric and electronic characteristics made possible to reach the lowest polydispersity of its group (Đmax = 1.43).Regarding to the group of complexes of the electronic effect, it was the complex 2f that had the smallest polydispersity of its group, between 1.12 and 1.58, due to the greater structural stability conferred to the complex by its cyclohexyl substituent.