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Extremely Rigid Pincer Ligands in Electropositive Metal Chemistry: From Actinide Organometallic and Redox Chemistry to Alkali Metal‐Alkane Interactions. David Emslie The early actinide elements occupy a unique position in the periodic table where the f‐orbitals have sufficient radial extension to interact with the ligands and can play an important role in bonding. Additionally, uranium is able to gain ready access to a distinctly non‐lanthanide‐like range of oxidation states, from III to VI, and these attributes have the potential to lead to organometallic reactivity inaccessible with transition metal and lanthanide complexes. However, the organometallic chemistry of the actinide elements has been slow to develop relative to that of the transition metals and lanthanides. Furthermore, the organometallic chemistry of non‐carbocyclic ligand supported actinide complexes is much less developed than that of complexes bearing carbocyclic ancillaries, despite the enormous potential for structural and electronic modification of non‐carbocyclic ligands. In this talk the synthesis and structures of thorium and uranium organometallic complexes supported by extremely rigid and sterically encumbered 4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene (XA2) and 4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene (TXA2) ligands will be discussed. The preparation of 4,5‐bis(2,6‐dimesitylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene (XAT), an NON‐
donor pincer ligand with substantially augmented steric bulk, will also be described, and the surprising structures of potassium and lithium derivatives of the XAT ligand will be presented.