Electronic Tuning of Dimolybdenum Complexes Through Symmetry Manipulation of Formamidinate Ligands in Their Second Coordination Sphere
Alternative sustainable energy sources are required to decrease our dependence on carbon-based fuels. Small molecule activation is one of the most promising to fulfill global energy demand and maintain a sustainable world. Most of the industrial processes relevant for global energy supply and expenditure involves small molecules and metal catalysts. However, it is still required to gain fundamental insights on how these catalysts achieve such reactions. Dinuclear compounds, namely dimolybdenum complexes, may serve as a good experimental model to understand metal-metal cooperativity and its influence in catalysis. In Chapter 2, three unsymmetric aryl formamidines were synthesized and characterized through 1H NMR, LCMS and SC-XRD. Compound 1 was compared with its symmetric analogs through NMR and was synthesized under equivalent conditions of its symmetric isomers. Syntheses of 2 and 3 required a stepwise approach and column but were accomplished, nonetheless. Bond distances in crystal structures manifested that the N=C bond resided on the most electron donating side on the unsymmetric aryl formamidine. and the proton are situated in the unsymmetric aryl formamidines. Furthermore, σ values were obtained for the synthesized ligands (1 = – 0.075, 2 = – 0.023, 3 = – 0.060). Chapter 3 discusses synthesis, characterization, and electrochemical studies of dimolybdenum complexes. Crystal structures for 5 and 6 were obtained with metal-metal bond distances of 2.0991 Å and 2.1009 Å, respectively. Cyclic voltammetry (CV) upon 5 depicts a one-electron reversible redox event at – 0.240 V. Electrochemical redox potential of 5 was compared to its symmetric analogs and fell between its homologues. Changing the position of one of the substituents in the phenyl ring tuned the redox behavior of the system. Compounds 6 and 7 display a one-electron reversible redox events – 0.283 V and – 0.260 V, respectively. Redox potentials for 6 and 7 have proximate values between them as well as their average Hammett constant, σ. As σ is constructed to be more negative, the redox potential will decrease for dimolybdenum compounds. Studying unsymmetric aryl formamidine ligands in dimolybdenum complexes gives rise to resourceful tool of electronic tuning empowered by a wide variation of possible substituents for ligand design.
Cervantes Martínez, Iván Alonso Cervantes, "Electronic Tuning of Dimolybdenum Complexes Through Symmetry Manipulation of Formamidinate Ligands in Their Second Coordination Sphere" (2019). ETD Collection for University of Texas, El Paso. AAI27671639.