Transition Metal Complexes with Multidentate Phosphorous/nitrogen Ligands. Synthesis, Characterization and Reactivity
Transition Metal Complexes with Multidentate Phosphorous/nitrogen Ligands. Synthesis, Characterization and Reactivity

Author: Sergio Santiago Rozenel

Publisher:

Published: 2011

Total Pages: 256

ISBN-13:

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Abstract Transition metal complexes with multidentate phosphorous/nitrogen ligands. Synthesis, characterization and reactivity. By Sergio Santiago Rozenel Doctor in Philosophy in Chemistry University of California, Berkeley Professor John Arnold, Chair Chapter 1: Chromium complexes supported by the multidentate monoanionic ligand [N2P2] {H[N2P2] = tBuN(H)SiMe2N(CH2CH2PiPr2)2} are presented, and the activity of these complexes towards ethylene oligomerization/polymerization is examined. The complexes [N2P2]CrCl2 (1) and [N2P2]CrCl (2) polymerized ethylene after activation with MAO. Derivatives of 1 and 2 were synthesized in order to gain insights about the active species in the ethylene oligomerization/polymerization processes. The alkyl complexes [N2P2]CrMe (3), [N2P2]CrCH2SiMe3 (4) and [N2P2]Cr(Cl)CH2SiMe3 (5), the cationic species {[N2P2]CrCl}BF4 (7), {[N2P2]CrCl}BPh4 (8) and {[N2P2]CrCH2SiMe3}BF4 (9), and the Cr(II) complex [N2P2]CrOSO2CF3 (11) were not active ethylene oligomerization/polymerization catalysts in absence of an activator. Reaction of 1 with two equivalents of MeLi led to reduction to 3. However, with one equivalent of MeLi the stable mixed alkyl-halide derivative [N2P2]Cr(Cl)Me (6) was obtained. Reaction of 2 with Red-Al® produced the hydride ([N2P2]Cr)2(ì-H)2 (10), which reacted with CO to produce the Cr(I) complex [N2P2]Cr(CO)2 (12). Reduction of 2 with KC8 in the presence of p-tolyl azide produced the dimeric cis μ-imido ([N2P2]Cr)2(ì-NC7H7)2 (13). A similar reduction in the presence of ethylene resulted in the isolation of the Cr(III) metallacyclohexane compound [N2P2]CrC4H8 (14). Chapter 2: A series of Co, Ni and Cu complexes with the ligand HN(CH2CH2PiPr2)2 (HPNP) has been isolated and their electrochemical behavior investigated by cyclic voltammetry. The nickel complexes [(HPNP¬)NiOTf]OTf and [(HPNP)NiNCCH3](BF4)2 display reversible reductions, as does the related amide derivative (NP2)NiBr. Related copper(I) and cobalt(II) derivatives were isolated and characterized. Addition of piperidine to [(HNP2)NiNCCH3](BF4)2 led to the formation of the new species [(HPNP)Ni(N(H)C(CH3)NC5H10)](BF4)2. Nucleophilic addition of piperidine to acetonitrile to produce HN=C(CH3)NC5H10 was catalyzed by [(HPNP)NiNCCH3](BF4)2. Chapter 3: A series of bimetallic ruthenium complexes [HPNPRu(N2)]2(μ-Cl)2](BF4)2 (2), [(HPNPRu(H2)Cl)2(μ-Cl)2](BF4)2 (3), [(HPNPRu)2(μ-H2NNH2)(μ-Cl)2](BF4)2 (4), [(HPNPRu)2(μ-Cl)2(μ-HNNPh)](BF4)2 (5), [HPNPRu(NH3)(ç2-N2H4)](BF4)Cl (6), [(HNP2Ru)2(μ-Cl)2(μ2-OSO2CF3)]OSO2CF3 (7), [HPNPRu]2(μ-Cl)3]BPh4 (8) and [HPNPRu]2(μ-Cl)3]BF4 (9) were isolated and characterized in the course of reactions aimed at studying the reduction of N2 and hydrazine. Complex 4 produces ammonia catalytically from hydrazine, and complex 2 generates ammonia upon reaction with Cp2Co/HLuBF4. DFT calculations support the idea that the diazene complex formed is more stable than the expected Chatt-type intermediate. Chapter 4: The reduction chemistry of cobalt complexes with the PNP ligand was explored. Reaction of (HPNP)CoCl2 (1) with n-BuLi generated the deprotonated Co(II) product (PNP)CoCl (2), and the Co(I) reduced species (HPNP)CoCl (3). The reaction of complex 2 with KC8 was investigated, where it was found that the products obtained depended upon the inert gas used to carry out the reaction: (PNP)CoN2 (4) under N2, bimetallic complex [(PNP)Co]2 (5) under Ar, and (HPNP)Co(H)3 (8) under H2. Complex 5 reacted with H2 to generate the bimetallic complex [(PNP)CoH]2 (6). With H2, H3SiPh and AgBPh4 complex 3 generated the species (HPNP)CoCl(H)2 (9), (HPNP)CoCl(H)SiH2Ph (10) and [(HPNP)CoCl]BPh4 (11) respectively. DFT calculations were performed to gain insights about the transformations observed.

Synthesis and Reactivity of Transition Metal Complexes Bearing the Tridentate Bis(2-mercapto-p-tolyl)amine ([SNS]H 3) Ligand
Synthesis and Reactivity of Transition Metal Complexes Bearing the Tridentate Bis(2-mercapto-p-tolyl)amine ([SNS]H 3) Ligand

Author: Kyle Evan Rosenkoetter

Publisher:

Published: 2017

Total Pages: 196

ISBN-13: 9780355307856

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The work described herein focuses on the synthesis and characterization of new heterobimetallic complexes containing the redox-active W[SNS] 2 metalloligand and investigation into their electronic properties and reactivity. Most recent studies have explored the redox nature of the [SNS]H 3 scaffold through the synthesis and reactivity of a novel set of square-planar nickel complexes.Chapters 2 and 3 describe a modular synthetic approach towards generating a new series of heterobimetallic complexes with the general formula W[SNS]2M(L) ([SNS] = bis(2-mercapto- p-tolyl)amine; M = Ni, Pd, or Pt; and L = dppe, depe, dmpe, dppp, PR'2NRPR'2 (R = phenyl, benzyl; R'=phenyl), DPEphos or dppf). The complexes were prepared by a salt metathesis of Cl2MII(L) with the previously reported W[SNS]2 coordination complex under reducing conditions. X-ray diffraction analysis revealed interesting coordination geometries about the appended Group 10 metal centers moving from Pt and Pd (pseudo-square planar) to the first row Ni (pseudo-tetrahedral) analogue. These complexes demonstrate formal metal--metal bond formation across the series with a tunable first oxidation potential up to 600 mV.Chapter 4 investigates the use of W[SNS]2Ni(dppe) as a catalyst for the electrochemical reduction of protons to hydrogen. This complex was found to catalytically generate hydrogen with an overpotential of 700 mV, a TOF of 14 sec--1, and a Faradaic yield of 80 +/- 3 % using 4-cyanoanilinium tetrafluoroborate in non-aqueous solutions.Chapter 5 demonstrates the effect of exchanging the nickel center of the heterobimetallic complexes discussed in Chapters 2 and 3 with other first row transitions metal ions (i.e. cobalt and copper). Analysis into the observed metal--metal distances reveal stark differences across the series. Additionally, the copper ion containing complexes demonstrate dynamic behavior in solution.Chapter 6 investigates the synthesis and reactivity of a series of monomeric square-planar nickel complexes of the [SNS] scaffold to demonstrate the ligand as redox, proton, and hydrogen atom non-innocent.Appendix A illustrates the electrochemical responses observed for the monoanionic complexes from Chapter 6 in the presence of CO2 and CO. Appendices B and C describe the synthesis and characterization of a five-coordinate cobalt and a heterotrimetallic tungsten-nickel complex, respectively.

Synthesis and Characterization of Transition Metal Complexes with Bulky Tin Ligands for Application in Small Molecule Activation
Synthesis and Characterization of Transition Metal Complexes with Bulky Tin Ligands for Application in Small Molecule Activation

Author: Veeranna Yempally

Publisher:

Published: 2012

Total Pages:

ISBN-13:

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The role of bulky tin ligands in the stabilization of transition metal complexes with electronic unsaturation has been studied to understand the mode of binding of small molecules at an unsaturated metal center. We were able to isolate electronically unsaturated Pt-Sn bimetallic complexes effective in the reversible activation of small molecules including CO, H2, C2H4, and NH3 at room temperature. We have examined the effect of the modification of ligands in Pt-Sn bimetallic complexes for the activation of small molecules and have observed that the Pt(SnBut3)2(CNBut)2 bimetallic complex reversibly activates hydrogen at room temperature both in the solid state and in solution. Similarly, we have also prepared bimetallic Pt-Sn complexes with an NHC carbine ligand which were also shown to activate hydrogen and alkenes reversibly. A bimetallic Fe-Sn cluster complex, Fe2 ([mu]-SnBut2)2(CO)8, was synthesized from the reaction of But3SnH with the Fe2(CO)9 and shown to be selective at activating the benzylic C-H bond of alkylaromatic solvent molecules. The new complexes containing tin have been characterized spectroscopically to gain an insight into the reaction mechanism involved in small molecule activation.

Synthesis, Characterization, and Catalytic and Biological Activities of a Mixed-ligand Cobalt(ii) Bipyridyl/diphenylazodioxide Complex
Synthesis, Characterization, and Catalytic and Biological Activities of a Mixed-ligand Cobalt(ii) Bipyridyl/diphenylazodioxide Complex

Author: Kylin Alice Emhoff

Publisher:

Published: 2021

Total Pages: 160

ISBN-13:

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Transition metal complexes have immense importance in the pharmaceutical industry. These types of complexes can be useful catalysts in the synthesis of medicinal compounds and can act as anticancer drugs. In these pharmaceutical applications, 1st-row transition metal-containing complexes offer certain advantages compared to their 2nd and 3rd-row transition metal counterparts. Our motivation was to investigate pharmaceutical applications of transition metal complexes containing both a 1st-row transition metal and unusual ligands to expand the knowledge of a class of complexes that could potentially be beneficial in the pharmaceutical industry. A class of rare ligands that piqued our interest was that of the diaryl azodioxides, cis-Ar(O)NN(O)Ar, which belong to the wider class of organic derivatives of nitric oxide (NO). Our synthesis and pharmaceutical applications of the azodioxide complex salt [Co(bpy){Ph(O)NN(O)Ph}2](PF6)2 have been able to significantly expand the knowledge of azodioxide complexes by displaying an unusual trigonal prismatic coordination geometry for cobalt(II) with only bidentate ligands, showing evidence of ligand-based redox activity, acting as an active catalyst in allylic amination/C0́2C double-bond transposition reactions, and selectively inducing apoptosis in SK-HEP-1 human liver adenocarcinoma cells. Importantly, catalytic and biological studies of [Co(bpy){Ph(O)NN(O)Ph}2](PF6)2 are ongoing, and focused on its potential for use in the pharmaceutical industry as a drug or catalyst for drug synthesis. Future work will involve comparing the catalytic and biological activities of [Co(bpy){Ph(O)NN(O)Ph}2](PF6)2 with other azodioxide complexes prepared by our group to identify structure-activity relationships and inform the design of more efficient catalysts and anti-cancer, pro-apoptotic agents.