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Thesis advisor: Jeffery A. Byers / This dissertation discusses the development of an electrochemically switchable system for copolymer synthesis as well as surface modifications. In Chapter one, the usage of electrochemistry to control polymerization reactivities is introduced. In Chapter two, an electrochemically redox switchable polymerization for lactide and cyclohexene oxide will be presented. In Chapter three, a surface modification method based on the electrochemically redox switchable catalysis is discussed. The surface-anchored catalyst responds to applied electrochemical potentials towards two different ring-opening polymerizations to generate binary polymer patterns in one step. The method represents a facile way to generate polymer coatings on surfaces. In Chapter four, a discussion on the detailed kinetic analysis of an iron-catalyzed epoxide polymerization will be presented, the study allows us to unveil the importance of entropy-controlled reactions. In Chapter five, future perspectives on the electrochemically redox switchable catalysis will be discussed. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Yes / We report the synthesis of halido Os(II) p-cymene complexes bearing bidentate chelating phenylazobenzothiazole (AZBTZ) ligands. Unlike the analogous phenylazopyridine (AZPY) complexes, AZBTZ-NMe2 is capable of both N,N-coordination to Os(II) and cyclometalation to form N,C-coordinated species. N,C-Coordination occurs via an azo nitrogen and an ortho carbon on the aniline ring, as identified by 1H NMR and X-ray crystallography of [Os(p-cym)(N,N-AZBTZ-NMe2)Cl]PF6 (1a), [Os(p-cym)(N,N-AZBTZ-NMe2)Br]PF6 (2a), [Os(p-cym)(N,C-AZBTZ-NMe2)Br] (2b), and [Os(p-cym)(N,C-AZBTZ-NMe2)I] (3b). The N,C-coordinated species is more stable and is not readily converted to the N,N-coordinated complex. Analysis of the crystal structures suggests that their formation is influenced by steric interactions between the p-cym and AZBTZ-NMe2 ligands: in particular, larger monodentate halide ligands favor N,C-coordination. The complexes [Os(p-cym)(N,N-Me2-AZBTZ-NH2)Cl]PF6 (4) and [Os(p-cym)(N,N-Me2-AZBTZ-NH2)I]PF6 (5) were synthesized with methyl groups blocking the ortho positions on the aniline ring, forcing an N,N-coordination geometry. 1H NMR NOE experiments confirmed hindered rotation of the arene ligand and steric crowding around the metal center. Complex 2b exhibited unexpected behavior under acidic conditions, involving regiospecific deuteration of the aniline ring at the meta position, as observed by 1H NMR and high-resolution ESI-MS. Deuterium exchange occurs only under acidic conditions, suggesting an associative mechanism. The calculated partial charges on 2b show that the meta carbon is significantly more negatively charged, which may account for the regiospecificity of deuterium exchange. / ERC, EPSRC, The Royal Society

This thesis presented the synthesis and reactivity of metal complexes for the hydrophosphination of alkenes and dehydrocoupling of phosphines. The mechanism of these metal-catalyzed P-H activation reactions was explored. Half-sandwich Cp*Ru complexes (Cp*= 1,2,3,4,5-pentamethylcyclopentadienyl) were developed as catalysts for hydrophosphination, based on the previous work in the Rosenberg group. Cp*Ru phosphido complexes, Ru(h 5 -Cp*)(PR2 )(PR2 H)2 (Ru-1) were found to be the vital intermediates for the hydrophosphination. Preliminary mechanistic studies also indicate that the catalyst resting state is Ru(h5 -Cp*)(PR2 )(PR2 H)(P) (P = hydrophosphination product) and intramolecular P-H bond cleavage is turnover-limiting. These investigations provide sufficient parallels to our established chemistry of the indenyl analogues to imply that conjugate addition of metal phosphido at alkene plays a significant role in these half-sandwich catalytic systems. The increased steric crowding at the Cp*Ru fragment and P-basicity/nucleophilicity of its phosphido complexes lead to a 30-fold increase in the hydrophosphination activity in the Cp* system compared to the indenyl catalysts. A half-sandwich Co catalyst, Co(h 5 -Cp*)I 2 (CO) (Co-1), was also developed for hydrophosphination along the lines of the conjugate addition mechanism. Similar to the Cp*Ru system, the substrate scope for alkene is limited to electron-deficient alkene. However, the Cp*Co catalyst significantly expands the substrate scope for phosphines (PR2 H and PRH 2 , R = alkyl and aryl). A detailed mechanistic study on the Cp*Co system was performed. The results show that the Co-catalyzed hydrophosphination occurs through iv an outer-sphere mechanism and the stoichiometric formation of diphosphine is a critical catalyst activation step. Since the side product diphosphine was formed during the Co-catalyzed hydrophosphination, using complex Co-1 as a catalyst for dehydrocoupling phosphines was investigated. The preliminary studies reveal the role of base and Cp* ligand in the catalysis. Additionally, the study highlights the importance of removing dihydrogen throughout the process. Thus, hydrogen acceptors (HA) were used to facilitate the dehydrocoupling reactions. Last, the novel P-H activation process between Cp*Co complexes [Co(h5 -Cp*)(NCCH 3 ) 3 ][SbF 6 ] 2 (Co-5) and excess PPh2 H was investigated through various analytical techniques. / Graduate / 2023-09-08

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