Actinide-Oxygen Multiple Bonds from Air: Synthesis and Characterization of a Thorium Oxo Supported by Redox-Active Ligands.

The first non-uranyl, f-element oxo complex synthesized from dioxygen in dry air is presented in this work. The synthesis was accomplished by treating the redox-active thorium amidophenolate complex, [Th( dipp ap) 3 ][K(15- c -5) 2 ] 2 ( 1-ap crown ), with dioxygen in dry air, forming a rare terminal thorium oxo, [O═Th( dipp isq) 2 ( dipp ap)][K(15- c -5) 2 ] 2 ( 2-oxo ). Compound 1-ap crown was regenerated by treating 2-oxo with potassium graphite. X-ray crystallography of 2-oxo revealed a comparatively longer bond length for the thorium-oxygen double bond when compared to other thorium oxos. As such, several thorium-oxygen single bonds were synthesized for comparison, including Th( dipp isq) 2 (OSiMe 3 ) 2 (THF) ( 4-OSiMe 3 ), Th(OSiMe 3 ) 4 (bipy) 2 ( 5-OSiMe 3 ), and [Th(OH) 2 ( dipp Hap) 4 ][K(15- c -5) 2 ] 2 ( 6-OH ). Full spectroscopic and structural characterization of the complexes was performed via 1 H NMR spectroscopy, X-ray crystallography, EPR spectroscopy, and electronic absorption spectroscopy as well as SQUID magnetometry, which all confirmed the electronic structure of these complexes.