UC Berkeley

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.