Crystalline amidocerium(iv) oxides and a side-on bridging dioxygen complex

Abstract

Complexes [Ce(NR₂)₃] (1) or [Ce(NR″₂)₃] (2) were cerium(III) precursors to the X-ray characterised crystalline oligomeric oxygen-containing amidocerium(IV) compounds [{Ce(NR₂)₂(μ-O)}_n] (3, n = 2; 4, n = 3), [{Ce(NR″₂)₂(μ-O)}₄] (5), [{(R₂N)₃Ce}₂(μ-OMOM)] (6, M = Na; 7, M = K), [{(R₂N)₃CeOCe(NR₂)₂}₂(μ-OKOK)] (8), and [{Ce(NR₂)₃}₂(μ-η²:η²-O₂)]·2C_nH_2n+2 (9, n = 6; 9′, n = 5) [R = SiMe₃, NR″₂ = TMP = NC(Me)₂(CH₂)₃CMe₂]. Each was isolated in low, or for 5 very low, yield. Except for 4, the oxidising agent was O₂ at −27 °C in hexane (3, 6, 7, 8, 9), pentane (9′), or toluene (5), and a co-reagent for the alkali metal bis(trimethylsilyl)amido(oxy)cerate(IV)s was NaNR₂ (8) or KNR₂ (7, 8). From 1 and an equivalent portion of 2,6-^tBu₂-benzoquinone after 5 weeks in pentane there was obtained the bis(amido)cyclotricer(IV)oxane 4. The NMR spectral solution chemical shifts for NR₂ groups of 3, 4, and 6–9 were consistent with each sample being diamagnetic and hence a Ce(IV) species. A transient amidocerium(IV) superoxide Ce(NR₂)₃(η²-O₂) (J), or its TMP analogue, is considered to be the common first-formed intermediate in each case, while 4 is believed to have arisen from the adventitious hydrolysis of [{Ce(NR₂)₃O}₂(^tBu₂C₆H₂-1,4)].