Photochemical Route to Actinide-Transition Metal Bonds: Synthesis, Characterization and Reactivity of a Series of Thorium and Uranium Heterobimetallic Complexes

A series of actinide–transition metal heterobimetallics has been prepared, featuring thorium, uranium, and cobalt. Complexes incorporating the binucleating ligand N­[ο-(NHCH₂PⁱPr₂)­C₆H₄]₃ with either Th­(IV) (4) or U­(IV) (5) and a carbonyl bridged [Co­(CO)₄]⁻ unit were synthesized from the corresponding actinide chlorides (Th: 2; U: 3) and Na­[Co­(CO)₄]. Irradiation of the resulting isocarbonyls with ultraviolet light resulted in the formation of new species containing actinide–metal bonds in good yields (Th: 6; U: 7); this photolysis method provides a new approach to a relatively unusual class of complexes. Characterization by single-crystal X-ray diffraction revealed that elimination of the bridging carbonyl and formation of the metal–metal bond is accompanied by coordination of a phosphine arm from the N₄P₃ ligand to the cobalt center. Additionally, actinide–cobalt bonds of 3.0771(5) Å and 3.0319(7) Å for the thorium and uranium complexes, respectively, were observed. The solution-state behavior of the thorium complexes was evaluated using ¹H, ¹H–¹H COSY, ³¹P, and variable-temperature NMR spectroscopy. IR, UV–vis/NIR, and variable-temperature magnetic susceptibility measurements are also reported.