Photolytic and Reductive Activations of 2-Arsaethynolate in a Uranium–Triamidoamine Complex: Decarbonylative Arsenic-Group Transfer Reactions and Trapping of a Highly Bent and Reduced Form

Little is known about the chemistry of the 2-arsaethynolate anion, but to date it has exclusively undergone fragmentation reactions when reduced. Herein, we report the synthesis of [U(Tren^TIPS)(OCAs)] ( 2 , Tren^TIPS=N(CH₂CH₂NSiiPr₃)₃), which is the first isolable actinide-2-arsaethynolate linkage. UV-photolysis of 2 results in decarbonylation, but the putative [U(Tren^TIPS)(As)] product was not isolated and instead only [{U(Tren^TIPS)}₂(μ-η²:η²-As₂H₂)] ( 3 ) was formed. In contrast, reduction of 2 with [U(Tren^TIPS)] gave the mixed-valence arsenido [{U(Tren^TIPS)}₂(μ-As)] ( 4 ) in very low yield. Complex 4 is unstable which precluded full characterisation, but these photolytic and reductive reactions testify to the tendency of 2-arsaethynolate to fragment with CO release and As transfer. However, addition of 2 to an electride mixture of potassium-graphite and 2,2,2-cryptand gives [{U(Tren^TIPS)}₂{μ-η²(OAs):η²(CAs)-OCAs}][K(2,2,2-cryptand)] ( 5 ). The coordination mode of the trapped 2-arsaethynolate in 5 is unique, and derives from a new highly reduced and bent form of this ligand with the most acute O-C-As angle in any complex to date (O-C-As ≈128°). The trapping rather than fragmentation of this highly reduced O-C-As unit is unprecedented, and quantum chemical calculations reveal that reduction confers donor–acceptor character to the O-C-As unit.     

Reactions of alkali metal and yttrium alkyls with a sterically demanding bis(aryloxysilyl)methane: Formation of aryloxide complexes by Si-O bond cleavage

Reaction of bis(bromodimethylsilyl)methane (BrSiMe₂)₂CH₂ (1) with two equivalents of 2,6-diisopropylphenol (Ar′OH) in the presence of the auxiliary base NEt₃ affords the bis(aryloxysilyl)methane (Ar′OSiMe₂)₂CH₂ (2) as a colourless oil following work-up. The reaction of 2 with [Li(Buⁿ)] in the presence of [K(OBu^t)] promoted Si-O bond cleavage and the sole isolable product from this reaction was found to be the colourless, crystalline heterobimetallic complex [{Li(OAr′)}₂{K(OAr′)}₂(THF)₄] (3). The in situ reaction of 2 with one equivalent of [Li(Buⁿ)] in the presence of one equivalent of [K(OBu^t)] and subsequent addition to one equivalent of [Y(I)₃(THF)_3.5] afforded colourless, crystalline [Y(OAr′)(I)₂(THF)₃] (4) as the only isolable product. No reaction was observed between [Y(Bn)₃(THF)₃] (Bn = CH₂C₆H₅) and one equivalent of 2 in toluene at room temperature; heating solutions led to decomposition and recovery of 2. In THF, the reaction between 2 and one equivalent of [Y(Bn)₃(THF)₃] resulted in Si-O bond cleavage with concomitant Si-C bond formation to give (BnSiMe₂)₂CH₂ (5) as a colourless oil and the colourless, crystalline compounds [Y(OAr′)₂(Bn)(THF)] (7), and [Y(OAr′)₃(THF)₂] (8) which were separated by fractional crystallisation. In an attempt to prepare 7 by a rational route, [Y(OAr′)₂(I)(THF)₂] (6) was prepared from the reaction of [Y(I)₃(THF)_3.5] with two equivalents of [K(OAr′)]. However, although 6 could be prepared by a rational salt elimination route, attempts to convert it to 7 resulted instead in 8 being recovered as the only isolable product. This is proposed to be the result of Schlenk-type equilibria, which is supported by the observation that dissolution of pure 6 in benzene results in the additional presence of 8 in the ¹H NMR spectrum over 12 h. Compound 7 was prepared rationally from the reaction between [Y(Bn)₃(THF)₃] and two equivalents of HOAr′. However, although crystalline 7 could be isolated in sufficient quantities for analysis, NMR spectra were consistent with the formation of 8 in solution from Schlenk-type equilibria. Compounds 2–8 have been variously characterised by X-ray diffraction, NMR and FTIR spectroscopy, and CHN microanalyses.     

High-spin structure of yrast-band in 78Kr

Lifetime of levels up to 22⁺, have been measured in ⁷⁸Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that ⁷⁸Kr is highly γ-soft nucleus. The experimental Q _t values coupled with theoretical calculations indicate an oblate shape for ⁷⁸Kr at low spins and triaxial shape at higher spins