Computational Modeling to Explore Unconventional Reactivity Patterns in C−H Activation and Boron Chemistry

Identifier:  TDX:2806

Handle: https://hdl.handle.net/20.500.11797/TDX2806

Authors:  García López, Diego

Abstract:
Computational chemistry turns out to be indispensable nowadays since it can provide deeper insights to molecular processes. This thesis can be divided in two parts, the first of which deals with the activation of inert C−H bonds by early- and late-transition-metal systems. Regarding the former case, computationally the mechanism of remote C−H activation observed on titanium dinuclear complexes was determined. Such mechanism generates a transient titanium alkylidene capable of enhancing the activation of C(sp3)−H bonds on the adjacent titanium center. Concerning in late-transition-metal systems, the nature of a rare (an)agostic Ni−(C[Ar]−H) bond observed in solid state was characterized by means of the topology of the electronic density. The second part of this work focuses on boron chemistry. Seeking for a predictive model, a quantitative structure-activity relationships (QSAR) for the nucleophilic activity of trivalent boron compounds was developed, covering boryl fragments bonded to alkali and alkaline-earth metals, to transition metals, and to sp3 boron units in diboron reagents. Multivariate regression techniques were carried out for determining a quantitative relationship between ground-state properties and nucleophilic activity. The use of chemically meaningful descriptors allowed identification of the factors governing the boron nucleophilicity. Also, the QSAR model was used to make a priori predictions of experimentally untested compounds. Unconventional boron reactions to unsatured organic molecules were studied as well. In one case, the formation of two geminal C–Bpin and C–Bdan bonds was rationalised based on DFT calculations to occur via a concerted yet asynchronous mechanism, attaining diastereoselctivity for cyclic substrates. On the other hand, theoretical calculations rationalized the observed regio- and stereoselectivity of the anti-3,4-selenoboration to triple bonds using catalytic amounts of phosphine. The computational study discovered a novel mechanism which differs from previous mechanistic proposals for analogous anti-selective carboration, silaboration and diboration.