Breaking and Entering: Diazene Cleavage and Insertion into U(III)–Si Bonds

Treatment of trivalent [K(18-crown-6)][U(I)2{(Si(SiMe3)2SiMe2)2O}] (1-crown) with aryl diazenes generated a series of uranium(IV) species of the form [(THF)U(I)2{N(R/R′)Si(SiMe3)2SiMe2}2O] (R = R′ = Ph (2-Ph), 4-FC6H4 (2-F), 4-MeC6H4 (2-Tol), 4-OMeC6H4 (2-Mes), and R = 4-MeC6H4, R′ = Ph (2-TolPh). Activation of an ortho-substituted diazene, (2,4,6-Me3C6H2N)2 (MesN═NMes), forms 2-Mes, [K(18-crown-6)][U(I)3{N(Mes)Si(SiMe3)2SiMe2}2O] (2-MesKI), and ([K(18-crown-6][U(I)(NMes)(N[Mes]-3,3,5,5-Me42,2,6,6-(SiMe3)4-tetrasil-3-oxane)]) (3-Mes). The increased sterics of this ortho-substituted substrate slowed insertion, facilitating the observation of 3-Mes by in situ NMR spectroscopy. The redox potentials of the aryl diazenes (R–N═N–R′) were studied using cyclic voltammetry to elucidate their electronic contributions toward their reactivity with 1-crown. The reaction of 1-crown and (Z)-11,12-dihydrodibenzo[c,g][1,2]diazocine is also described, forming the [(THF)U(I)2{[N(C7H6)]2Si(SiMe3)2SiMe2}2O] (2-diazonine) and {(THF)2U(I)2[N(C7H6)]2}2 (4) dimers.