Formation of an α-Diimine from Isocyanide Coupling Using Thorium(IV) and Uranium(IV) Phosphido–Methyl Complexes

Abstract

To probe the reactivity of two potential sites at tetravalent thorium and uranium metal centers, we examined the monophosphido methyl complexes, (C5Me5)2An(CH3)[P(SiMe3)(Mes)], An = Th, U; Mes = 2,4,6-Me3C6H2. Reaction of these mixed ligand complexes with one, two, and three (or excess) equivalents of tBuNC was explored. When (C5Me5)2An(CH3)[P(SiMe3)(Mes)] is treated with one equivalent of tBuNC, the iminoacyl products, (C5Me5)2An[η2-tBuN═CCH3][P(SiMe3)(Mes)], are formed. Using three equivalents (or excess) of tBuNC results in the formation of an α-diimine moiety, (C5Me5)2An[κ2-(N,N)–N(tBu)C═CN(tBu)C═N(tBu)CH2]. When two equivalents of tBuNC are added, only the mono-insertion or α-diimine was observed in a 3:1 ratio. Density functional theory calculations were carried out to determine the lowest energy pathway in the formation of the α-diimine product via the iminoacyl complex.