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This thesis explores 4,5-diazafluorenyl derivatives as binucleating ligands for the syntheses of heterobimetallic complexes. The 4,5-diazafluorenide (L-) ligand contains two coordination sites: a Cp moiety and two N-donors. L- was used to construct PtII-CuI and PtII-RuII heterobimetallic complexes. Various modifications have been made to the L- framework to alter the regioselectivity. A pendent phosphine was arm attached to the methylene linker to form 9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorenide (Lp-) and provides a P,C-chelate to anchor metals to the C-donor on the L- backbone. Lp- was used to synthesize PtII-CuI complexes and dinuclear RuII complexes. Bulky mesityl groups were installed ortho- to the N-donors to form 3,6-dimesityl-4,5-diazafluorenide (LMes-). The LMes- derivative provides steric protection that prevents bulky metal fragments from binding to the N-donors. LMes- was used to construct a series of RuII-M complexes (M = FeII, CoII, PtII, CuI) where the metals span from group 8 to 11.

Conventional ligand design in transition metal catalysis capitalizes on the ability of phosphorous, nitrogen, carbon, oxygen, and sulfur-based donors to modify the steric and electronic properties of a reactive metal center. Heterobimetallic transition metal complexes that contain a dative metal-metal bond provide a unique approach to ligand design where the reactivity of the metal center can be modified by metal-metal electronic communication. Our laboratory is interested in using the unique properties of heterobimetallic complexes to address significant limitations in current transition metal catalysis. My PhD work has focused on the ability of early/late transition metal heterobimetallic complexes to facilitate catalysis by speeding up reductive processes that occur at the late transition metal center. My initial studies were aimed at understanding the importance of the metal-metal interaction to catalysis in allylic amination reactions catalyzed by Pd–Ti heterobimetallic complexes and the potential of these catalysts to enable reactivity with challenging nitrogen nucleophiles. We also explored the substrate scope of the allylic amination with a variety of hindered amines and allylic chloride substrates under mild conditions. Aminations of this type have previously been shown to require harsh reaction conditions and tend to give low yields. A variety of sterically hindered secondary amine nucleophiles were able to readily undergo allylic substitution. Many of these aminations were complete within ten minutes. A series of allylic electrophiles were also shown to undergo the reaction. We have also looked at the ability of hindered amines to undergo intramolecular cyclizations to produce pyrrolidine and piperidine products. My continuing efforts in the laboratory are focused on developing chiral titanium-phosphinoamide ligands for enantioselective heterobimetallic catalysis. We have synthesized a series of chiral diamine-based phosphinoamide-titanium ligands in order to investigate enantioselective intramolecular aminations. Importantly, each of these new Ti-ligands enables room temperature catalysis in intramolecular aminations with hindered amines, suggesting contributions by the Ti center. Similar reactivity has not been achieved with monometallic chiral Pd catalysts in our lab. Importantly, many of these ligands enable modest enantioselectivity in the allylic aminations.

This thesis explores 4,5-diazafluorenyl derivatives as binucleating ligands for the syntheses of heterobimetallic complexes. The 4,5-diazafluorenide (L-) ligand contains two coordination sites: a Cp moiety and two N-donors. L- was used to construct PtII-CuI and PtII-RuII heterobimetallic complexes. Various modifications have been made to the L- framework to alter the regioselectivity. A pendent phosphine was arm attached to the methylene linker to form 9-(2-(diphenylphosphino)ethyl)-4,5-diazafluorenide (Lp-) and provides a P,C-chelate to anchor metals to the C-donor on the L- backbone. Lp- was used to synthesize PtII-CuI complexes and dinuclear RuII complexes. Bulky mesityl groups were installed ortho- to the N-donors to form 3,6-dimesityl-4,5-diazafluorenide (LMes-). The LMes- derivative provides steric protection that prevents bulky metal fragments from binding to the N-donors. LMes- was used to construct a series of RuII-M complexes (M = FeII, CoII, PtII, CuI) where the metals span from group 8 to 11.

A family of new [PtM(SAc)4(pySMe)] (M = Mn (42), Fe (43), Co (44), Ni (45), Zn (46)) lanterns and an expansion of the [PtM(SAc)4(pyNH2)] family to include M = Mn (47) and Fe (48) lanterns have been synthesized and their detailed structural and magnetic characterization are reported. Compounds 43-45 have been found to contain exceptionally long Pt…Pt metallophilic contacts with antiferromagnetic coupling across the staggered dimers in the solid state. The utility of the [PtVO(SOCR)4] lanterns as monodentate, terminal oxo-bound ligands is proven in the formation of trimetallic lanthanide complexes [Ln(ODtbp)3{PtVO(SOCR)4}] (Ln = Ce, R = Me (49); Ln = Ce, R = Ph (50); Ln = Nd, R = Me (51); Ln = Nd, R = Ph (52)). Structural and magnetic studies are reported of the four, four-coordinate lanthanide complexes. All four complexes were found to exhibit antiferromagnetic coupling between the 3d-4f ions, the strongest of which is observed in 50. Through AC magnetic susceptibility studies, xii SMM behavior was also observed in all four complexes, with the slowest relaxation found in 52. A pair of [PtNi(SAc)4(L)] (L = pyCN (54), HpipCN (55)) and new {S,N} chelated mercaptopyridine lanterns [PtNi(mpyS)4(L)] (L = H2O (56), MeCN (57), pyCN (58)) have been synthesized and a detailed structural comparison of the systems made. The stronger field mercaptopyridine ligand is shown to decrease the Pt (donor) – M (acceptor) character within the lantern, reducing the Pt(II) Lewis acidity and therefore preventing the formation of intermolecular interactions in Ni(II) complexes 56-58. Additionally, the development of an improved air- and water-stable synthesis for the formation of the di-Pt mercaptopyridine para-hydro lantern, [Pt2(pyS)4], is reported along with its previously unknown crystal structure. In an attempt to make a diamagnetic [PtZn(mpyS)4(L)] analog to the previous Ni(II) mercaptopyridine lanterns, a new series of {PtnZn2} HEMACs has been discovered and structurally characterized with n = 1, 2, 3,. The discovery of a trimetallic {Pt(IV)Zn2} (60) para-methyl mercaptopyridine bridged complex with novel {Pt(IV)S6} ligation is discussed. The use of para-H substituted mercaptopyridine led to insoluble tetranuclear {Pt2Zn2} (61) while use of the para-methyl substituted ligand led to the insoluble pentanuclear {Pt3Zn2} (62) through solvothermal syntheses.

Heterobimetallic complexes present a unique approach to catalyzing challenging reactions. By having two metals in close proximity to each other, the metals are able to interact and alter their electronics in a way that simple organic ligands (carbon, nitrogen, sulfur etc.) cannot. Our studies of heterobimetallic complexes focus on a Pd–Ti complex. The complex features a dative interaction between the palladium and the titanium held together by a phosphonamide scaffold. This interaction increases the electrophilicity of the palladium and makes it a very suitable catalyst for allylic amination reactions. We have conducted extensive studies of this catalyst in allylic aminations, the results of which will be discussed. Our first studies with heterobimetallic Pd–Ti complexes focused on their potential to catalyze challenging allylic amination reactions. These studies showed that the Pd–Ti complex was effective at catalyzing allylic aminations with sterically hindered secondary amines, a reaction which had heretofore proved challenging. We then developed a method for synthesizing the catalyst in situ, greatly simplifying the procedure by which the catalyst is used and making it that much more accessible. We also tested the substrate scope and varied the structure of both the amine and chloride substrates. Our results demonstrated the high catalytic activity of heterobimetallic catalysts with most substrates, in spite of steric hindrance of notoriously challenging substrates. Next, investigated the origin of the fast catalysis we had observed with heterobimetallic Pd–Ti complexes. We confirmed the catalytic cycle and determined the activation barrier for the rate-determining step. We computationally investigated the reactivity of various control catalysts in which the Pd–Ti interaction was severed. These results were compared with the reactivity of the heterobimetallic catalyst. We found that the activation barrier for turnover-limiting reductive amine addition was lowered with the bimetallic complex because of an increased electrophilicity at palladium. We further supported our claim by synthesizing a phosphinoamide palladium complex lacking a titanium atom and testing it in the allylic amination reaction. Our findings in the lab corroborated our calculations. We also ensured that the Pd–Ti catalyst was not transformed prior to catalysts by examining various decomposition pathways and determining that they all resulted in higher energy pathways. We discovered that the Pd–Ti interaction is made possible only by the steric interaction provided by N-tert-butyl groups on the amines which sterically reinforce the Pd–Ti interaction. Lastly, we tested the catalytic activity of the complex with allylic acetates and found them to be ineffective due to catalyst decomposition. It is our hope that these findings can serve as guiding principles when designing heterobimetallic complexes for future catalytic applications.

No description available.

abstract: Understanding the mechanisms of metalloproteins at the level necessary to engineer new functionalities is complicated by the need to parse the complex overlapping functions played by each amino acid without negatively impacting the host organism. Artificial or designed metallopeptides offer a convenient and simpler platform to explore metal-ligand interactions in an aqueous, biologically relevant coordination context. In this dissertation, the peptide SODA (ACDLPCG), a synthetic derivative of the nickel-binding pocket of nickel superoxide dismutase, is used as a scaffold to construct a variety of novel metallopeptides and explore their reactivity. In Chapter 2, I show that SODA binds Co(II) and the resulting peptide, CoSODA, reacts with oxygen in an unexpected two step process that models the biosynthesis of Co nitrile hydratase. First, the thiolate sulfur is oxidized and then the metallocenter is oxidized to Co(III). In Chapter 3, I show that both CoSODA and CuSODA form CN- adducts. Spectroscopic investigations of these metallopeptides are compared with data from NiSODA and Ni(CN)SODA to show the remarkable geometric versatility of SODA with respect to interactions with metallocenters. In Chapter 4, exploiting the propensity of sulfur ligands to form bridging structures, NiSODA is used as a metallosynthon to direct synthesis of hetero bi- and tri-metallic peptides as models for [NiFe]-hydrogenases and the A cluster of acetyl-CoA synthase carbon monoxide dehydrogenase. Building on this synthetic strategy, in Chapter 5, I demonstrate synthesis of NiRu complexes including a Ru(bipyridine)2 moiety and characterize their photochemistry. / Dissertation/Thesis / Ph.D. Chemistry 2012

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Lithium bis(amido)cuprates are an important class of bimetallic base, which can chemo- and regioselectively metalate aromatic compounds, via directed ortho cupration (DoCu). This thesis begins with an introduction to aspects of the chemistry of organolithium compounds, group 11 organometallic compounds and their lithium 'ate complexes. Examples of such synergic bases are presented and the introduction is concluded with a discussion of lithium bis(amido)cuprate bases, which along with their silver congeners, are the subject of this dissertation. In general, syntheses involve the addition of a lithium amide to a group 11 salt, resulting in the formation of a lithium bis(amido)cuprate or argentate. Structurally focussed work commences with the use of new amide ligands to develop heteroleptic bis(amido)cuprate systems. The reaction of mixtures of lithium amides with CuBr provides a series of novel Lipshutz-type and Gilman cuprates. Interesting structural features are uncovered, which are rationalised in terms of altered steric demands in the newly introduced amide ligands in these systems. CuSCN and CuOCN are investigated as inexpensive and safer alternatives to CuCN in cuprate formation. In the solid state, a series of Lipshutz-type cuprates (TMP)2Cu(SCN)Li2(L) (L = Et2O, THF, THP) are revealed, whose molecular conformations are infuenced by the identity of the Lewis base. However, in benzene solution, in situ conversion of Lipshutz-type to Gilman cuprate is found to occur. Moving to the synthetic setting, derivatisation of chloropyridines is attempted and gives functionalised halopyridines in 51-71 % yield. CuOCN is found to behave quite differently when reacted in the same way as CuSCN, whereby X-ray crystallography reveals structures in which Cu-Li substitution is apparent. The unique reactivity of CuOCN is interpreted with the aid of multinuclear NMR spectroscopy. A new route to Lipshutz-type cuprates is explored by the synthesis of (TMP)2Cu(OCN)Li2(THF) from Gilman cuprate and LiOCN. This avoids Cu-Li substitution. Meanwhile, reaction of lithium N,N-diisopropylamide with CuOCN also avoids metal disorder, to give a novel lithium cuprate-lithium amide adduct. Further advances in our understanding of group 11 'ate complexes are made by introducing silver as a spectroscopically active nucleus in the lithium argentates (TMP)2AgLi and (TMP)2Ag(CN)Li2(THF). In the solid state, these parallel the structures known for Gilman cuprate (TMP)2CuLi and Lipshutz cuprate (TMP)2Cu(CN)Li2(THF), respectively. In solution, NMR spectroscopy reveals features consistent with retention of these structures. Lastly, the formation of mixed Cu-Li aggregates from combining TMPLi and TMPCu in aromatic solvent are investigated. Surprising reactivity is uncovered, in which the aromatic solvent is metalated and incorporated into mixed-metal aggregates. This thesis concludes with a summary of the findings and suggestions for future work, including how the findings presented herein may be transformed into practical improvements to cuprate systems. In particular, the possibility that Gilman cuprate may be activated towards the metalation of aromatic substrates by the addition of sub-stoichiometric or catalytic amounts of a lithium salt additive is explored.