SYNTHESIS AND REACTIVITY OF RUTHENIUM COMPLEXES BEARING TRIDENTATE PINCER LIGANDS

Nicolas H. Fisher

doi:10.7273/000007853

Metal complexes bearing tridentate bisphosphinoamino pincer ligands have been widely studied for their ability to facilitate many organic transformations. One important aspect of metal complexes bearing these pincer ligands is the ability to perform metal-ligand cooperation (MLC) allowing for the activation and addition of substrates that allows for the generation of reactive complexes with unique reactivity. In this work two different pincer ligands were utilized with ruthenium to form complexes capable of MLC. In Chapters 2 and 3 a pyridine-based pincer ligand 2,6-bis(diisopropylphosphinamine)pyridine (iPrPNHNNHP) was utilized. When bound to ruthenium, this complex was able to add various H-X substrates through 1,3-addition. In Chapter 2 The addition of water, various alcohols and acids led to the respective hydroxide, alkoxide or chloride complexes. While many of these complexes were stable, it was commonly seen that any addition of a ligand with a beta-hydrogen underwent beta-hydride elimination leading to ruthenium hydride. The addition of water to the complex allowed for the transfer of water to a substrate in non-aqueous systems which was demonstrated through the hydration of nitriles. The addition of acids demonstrated the basicity of the backbone nitrogen leading to a cationic complex as well. In Chapter 3 the addition of hydrogen led to the ruthenium hydride complex and the acid-base chemistry of the nitrogen atoms in the backbone was demonstrated via the formation of both an anionic and a cationic hydride complex that were generated via protonation/deprotonation of the backbone N atom. In Chapter 4 a different pincer ligand bis(mesityl-phosphinoethyl)amine (MesPNHP) was used to bind ruthenium. The resultant complex showed the ability to have the ortho-methyl and “tuck-in” methylene protons become deuterated in benzene-d6 under an argon atmosphere. The substrate scope of this H-D exchange was explored, and it was determined that aryl substrates like toluene-d8 and pyridine-d5 were able to perform this deuteration, while aliphatic substrates like tetrahdrofuran-d8 and cyclohexane-d12 were not. The use of this complex to catalyze H-D exchange with aromatic substrates was evaluated through both 1H NMR and GC-MS in order to determine substituent effects on the relative rate of this exchange.

SYNTHESIS AND REACTIVITY OF RUTHENIUM COMPLEXES BEARING TRIDENTATE PINCER LIGANDS

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