Systematic Investigation of Thorium(IV)– and Uranium(IV)–Ligand Bonding in Dithiophosphonate, Thioselenophosphinate, and Diselenophosphonate Complexes

Homoleptic soft-donor actinide complexes of the general form An­[E2PROR′]4 were synthesized from salt metathesis between ThCl4(DME)2 or UI4(1,4-dioxane)2 and M­[E2PROR′], M = Na, K, to yield 2 (An = Th, E = S, R = 4-MeOC6H4, R′ = Me), 3 (An = Th, E = S, R = 4-MeOC6H4, R′ = tBu), 4 (An = U, E = S, R = 4-MeOC6H4, R′ = Me), 5 (An = Th, E = Se, R = C6H5, R′ = Me), and 6 (An = U, E = Se, R = C6H5, R′ = Me). In addition thorium and uranium thioselenophosphinate complexes 7 and 8 were produced from the reaction of ThCl4(DME)2 and UI4(1,4-dioxane)2 and Na­[SSePPh2], respectively. All compounds were characterized using elemental analysis, 1H and 31P NMR, and IR spectroscopy, and the U­(IV) compounds were also examined with UV–vis spectroscopy. The 77Se NMR spectrum of 5 reveals the first reported resonance with a Th–Se bond. The solid-state structures of 2, 5, 7, and 8 were determined by X-ray crystallography. The actinide–ligand bonding was examined using density functional theory calculations in conjunction with quantum theory of atoms-in-molecules analysis and shows slightly increased covalency in actinide–selenium bonds than actinide–sulfur.