Aromaticity and anti-aromaticity are critical ideas in organic chemistry, which are both exemplified in the molecule biphenylene. Analogues, in which one of the benzene rings has been replaced by a different (4n+2) π-electron system, have only been associated with carbon-rich compounds. This talk will discuss the synthesis and characterization of the first 2-metallabiphenylene compounds. Reduction of (C5Me5)2AnCl2 (An = Th, U) with KC8 in the presence of 1,2-bis(phenylethynyl)benzene affords the thorium and uranium 2-metallabiphenylene complexes, (C5Me5)2An(2,5-Ph2-cyclopentadienyl[3,4]cyclobuta[1,2]benzene) (An = Th, U). Single-crystal X-ray diffraction studies reveal that these complexes have nearly planar, eleven-membered metallatricycles with metrical parameters that compare well to those reported for biphenylene. NMR, FTIR, and UV-visible-NIR spectroscopies, in addition to nuclear independent chemical shift (NICS) calculations, provide evidence that these complexes contain an antiaromatic cyclobutadiene ring and an aromatic benzene ring. Furthermore, spectroscopic evidence, Kohn-Sham MO computations, and natural bond orbital calculations suggest significant covalency and delocalization of the uranium f2 electrons with the carbon-containing ligand.

Thorium and uranium 2-metallabiphenylene complexes

ACS Spring Meeting 2021

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