Abstract
Deprotonation of [U(TrenTIPS)(NH2)] (1) [TrenTIPS = N(CH2CH2NSiPri3)3] with organoalkali metal reagents MR (M = Li, R = But; M = Na–Cs, R = CH2C6H5) afforded the imido-bridged dimers [{U(TrenTIPS)(μ-N[H]M)}2] [M = Li–Cs (2a–e)]. Treatment of 2c (M = K) with 2 equiv of 15-crown-5 ether (15C5) afforded the uranium terminal parent imido complex [U(TrenTIPS)(NH)][K(15C5)2] (3c), which can also be viewed as a masked uranium(IV) nitride. The uranium–imido linkage was found to be essentially linear, and theoretical calculations suggested σ2π4 polarized U–N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U(TrenTIPS)(NH)] (4) resulted in spontaneous disproportionation to give 1 and the uranium–nitride complex [U(TrenTIPS)(N)] (5); this reaction is a new way to prepare the terminal uranium–nitride linkage and was calculated to be exothermic by −3.25 kcal mol–1.
Highlights
Multiple bonds, there is yet to be any report of a metal terminal parent imido linkage in the f block, presumably because large R groups are usually needed to afford kinetic stabilization at large felement centers
We recently reported the inadvertent formation of the uranium amide [U(TrenTIPS)(NH2)] (1) [TrenTIPS = N(CH2CH2NSiPri3)3].6b We have prepared 1 deliberately in high yield, making it an attractive precursor from which to target U−N multiple bonds
Complex 1 was previously isolated from the reaction of [U(TrenTIPS)] with [N3][NBun4] in low yield (29%).6b We have found that 1 can be routinely prepared from [U(TrenTIPS)(Cl)]6a and NaNH2 and isolated in >90% yield,[9] which renders 1 an attractive precursor to U−N multiple bonds
Summary
Multiple bonds, there is yet to be any report of a metal terminal parent imido linkage in the f block, presumably because large R groups are usually needed to afford kinetic stabilization at large felement centers. We describe attempts to oxidize this complex that resulted in disproportionation to give 1 and a uranium(VI) nitride.
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