Theses and Dissertations at Montana State University (MSU)
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Item Ni-catalyzed cross-coupling reactions of phenol-derived electrophiles(Montana State University - Bozeman, College of Letters & Science, 2022) Russell, John Emmet Alam; Chairperson, Graduate Committee: Sharon Neufeldt; This is a manuscript style paper that includes co-authored chapters.Herein we present in three parts our work on a variety of Ni-catalyzed cross-coupling reactions using phenol-derived electrophiles. The first part details an efficient Ni-catalyzed Stille cross-coupling of C-O electrophiles through a combination of computational and experimental methods. These allowed for the investigation of the mechanism and showed the formation of a novel 8-centered transition state involving KF. Chloride inhibits the reaction through forming a low-energy Ni(II)-chloride species during oxidative addition that has a high activation barrier towards transmetalation. This methodology was shown effective for a wide variety of C-O electrophiles and organostannanes including several difficult bond constructions. The second part explores the development of a chemoselective Ni-catalyzed Suzuki cross-coupling that is selective for C-O bonds in the presence of C-Cl bonds. This selectivity is unusual since organohalides typically undergo oxidative addition with Ni(0) and Pd(0) at similar or faster rates to phenol- derived electrophiles. We were able to pair computational and experimental investigations to develop a reliable strategy and understand the likely origin of this unique selectivity. Stoichiometric experiments showed that small phosphines, like PMe 3 and PPhMe 2 , are unique in their ability to facilitate the selective reaction at C-O bonds in the presence of C-Cl bonds. Computational investigations show the electronic and steric properties of these small ligands are crucial for a close interaction between nickel and a sulfonyl oxygen during oxidative addition, the step where selectivity is determined. The third part looked at the use of aryl methyl ethers as an electrophile under Ni-catalyzed Suzuki-Miyaura and Kumada cross-coupling conditions. Three ligands bearing chelating arms were synthesized, two known and one new, to explore the respective scopes and how these ligands compare to more commonly used ligands such as PCy 3 or ICy. We saw no success under Suzuki-Miyaura conditions but found the hydroxyphosphine ligands facilitated the Ni-catalyzed Kumada cross-coupling of Ar-OMe, which had not been reported. Further investigations proved the hydroxyphosphines had no apparent benefit over commercial ligand as far as yield, scope, or mild reaction conditions.Item Effect of aryldimethylphosphine electronics on rate of oxidative addition of aryl electrophiles at Ni 0(Montana State University - Bozeman, College of Letters & Science, 2019) Giroux, Michael James; Chairperson, Graduate Committee: Sharon NeufeldtAn analysis of kinetics related to the selectivity of aryldimethylphosphine-nickel complexes for reaction at carbon--chlorine versus carbon--tosylate bonds is reported. A series of aryldimethylphosphine ligands bearing electronically-varied substituents were investigated. The rate constants for oxidative addition of ligand-nickel complexes to either aryl chloride or aryl tosylate substrates were calculated. These rate constants were used to construct Hammett plots describing the susceptibility of oxidative addition at both types of electrophiles to electronic influence from the ligand. Oxidation of catalyst to aryl tosylates yields a plot with a negative slope, while addition to aryl chlorides produces a positive slope. With this, we see that electron donating groups accelerate the addition of catalyst to aryl tosylates, while electron withdrawing groups may change the rate determining step of addition to aryl chlorides.Item The examination of chiral X-type ligands in Pd(II)-catalyzed enantioselective oxdiatative transformations(Montana State University - Bozeman, College of Letters & Science, 2015) Aebly, Andrew Henry; Chairperson, Graduate Committee: Trevor J. RaineyPalladium catalysis has been utilized extensively in organic chemistry for the synthesis of complex molecules. Despite its abundant use and many successful applications, there remain challenging transformations, specifically with developing new chiral centers. The aim of this research was to explore the underdeveloped, weakly coordinating X-type ligands and their applicability in enantioselective reactions. The electrophilic catalyst, generated by the coordination of sulfonic or phosphoric acid ligands, was utilized to explore underfunctionalized starting materials, such as unactivated alkenes and aryl C-H bonds. Herein we report two Pd II-catalyzed enantioselective transformations: oxidative amination and 1,2-carboamination. The Wacker-type oxidative amination was accomplished with good yields and modest enantioselectivity in the synthesis of chiral indolines and a cyclic carbamate. Substantial loss in enantioselectivity was seen with ortho-substituted anilines. The 1,2-carboamination coupled a mild, directing group facilitated C-H activation on a series of aryl ureas with a subsequent chiral C-N bond formation. Electron-rich, para-substituted aryl ureas provided the highest consistent yields and enantioselectivities. Electron deficient substrates provided little reactivity and substitutions at the ortho- and meta-positions gave inconsistent results. To our knowledge these transformations mark the first enantioselective examples of Pd II-catalyzed oxidative transformations utilizing chiral sulfonic acid ligands.Item Multi-edge X-ray absorption near-edge spectroscopic analysis of palladium complexes in II, III and IV oxidation states(Montana State University - Bozeman, College of Letters & Science, 2013) Barton, Rhonda Lee Hoffert; Chairperson, Graduate Committee: Robert K. SzilagyiPalladium-based complexes have profoundly impact on the synthetic tools of organic chemists due to their importance as catalysts in a myriad of chemical transformations. Palladium in the 0, II, III and IV oxidation states have all been experimentally observed to have catalytic activity in carbon-carbon bond coupling reactions. A common organometallic research aim is to improve catalytic activity of these complexes by designing and optimizing new ligand systems to access more difficult transformations. In order to understand the electronic effects that ligand systems have on reactivity, X-ray absorption spectroscopy is used to characterize the electronic structure of the ligand and metal components of pre-catalysts and palladium model complexes. The multi-edge X-ray absorption near-edge absorption spectroscopic technique (XANES) is an element specific technique that excites core electrons of the 1s (K-edge) and 2p (L-edge) orbitals to frontier unoccupied molecular orbitals, providing a ground state picture of a complex's ligand and metal electronic structure. This thisis will describe a comparative analysis between homoleptic chloropalladium complexes and interesting heteroleptic palladium based complexes of II, III and IV oxidation states to understand the stabilizing effects of a unique ligand environment. Furthermore, it will emphasize the benefits of using multi-edge XANES technique in rationalized catalyst design.Item Synthesis of novel homochiral phosphine ligands(Montana State University - Bozeman, College of Letters & Science, 1994) Jiang, MeiqunItem The asymmetric Rh(I) catalyzed [4+2] cycloisomerization reaction : new homochiral bisphosphine ligands(Montana State University - Bozeman, College of Letters & Science, 1994) McKinstry, LydiaItem New methods for preparing scalemic P-chiral secondary phosphine-boranes and enantiomerically pure phosphine ligand precursors(Montana State University - Bozeman, College of Letters & Science, 2000) Wolfe, Bradley H.Item Kinetics and mechanism of the reactions of Ni(II)-N,N'-Diglycylethylenediamine and Ni(II)-Malonamide-N,N'bis-(2-aminoethyl) with Triethylenetetramine(Montana State University - Bozeman, College of Letters & Science, 1981) Storvick, Jonathan PaulItem Development of the molecular level descripton for nickel(II)-based ligand-exchange thermochromism(Montana State University - Bozeman, College of Letters & Science, 2014) Queen, Matthew Scott; Co-chairpersons, Graduate Committee: Patrick R. Callis and Robert K. Szilagyi; Bradley D. Towey, Kevin A. Murray, Brad S. Veldkamp, Harlan J. Byker and Robert K. Szilagyi were co-authors of the article, 'Electronic structure of [Ni(II)S 4] complexes from S K-edge X-ray absorption spectroscopy' in the journal 'Coordination chemistry reviews' which is contained within this thesis.; Farideh Jalilehvand and Robert K. Szilagyi were co-authors of the article, 'Electronic structure of Ni(II), Co(II), and Zn(II) thiourea complexes from sulfur K-edge X-ray absorption spectroscopy' submitted to the journal 'Canadian journal of chemistry' which is contained within this thesis.Coordination compound-based nickel(II) thermochromic systems rely on a temperature-dependent equilibrium shift between different coordination environments of the central nickel ion. These systems are found in thermochromic "smart windows" that tint reversibly in response to temperature increases in their environment providing the benefit of energy savings in commercial and private buildings. Despite the stoichiometrically simple equilibrium for these ligand exchange systems, there is a complex and delicate network of chemical interactions that determine the color, and thermodynamic performance. Accurate computational modeling of nickel(II) ligand exchange thermochromic systems is an important first step in the direction of understanding the parameter space that determines whether a given metal ligand system is thermochromic, the color of the high and low temperature species, the temperature at which the system will change color. The research presented in this dissertation uses experimental results to evaluate theoretical models. Core and valence electronic spectroscopies probe the ground and excited state electronic structures of high temperature nickel(II) thermochromic chromophores which range from the very covalent nickel tetrathiocyclotetradecane thiocrownether to the highly ionic nickel dibromodi(1-pentylbenzimidazole)nickel(II). The experimental electronic structures of these high temperature species combined with experimental ligand exchange thermodynamics are used to guide the evaluation of computational modeling methods in search of methods that reproduces the experimental observables. It is found that commercially relevant nickel(II) thermochromism takes place on an extremely flat potential energy surface governed by ion pairing, hydrogen bonding and dispersion interactions. The modeling of these surfaces requires the explicit consideration of ion pairing and solvent-solute interactions.