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

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.