Compound 3

potassium µ-oxo-bis[tris-tert-butoxysiloxouranium(III)]

From: The role of bridging ligands in dinitrogen reduction and functionalization by uranium multimetallic complexes

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Synonyms:
  • [K2{[U(OSi(OtBu)3)3]2(μ-O)}]

Compound data: 1H NMR

Compound data: 1H NMR

Compound data: Crystallographic data

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

Excess KC8 (48.3 mg, 0.355 mmol, 5 eq) was added to a cold solution (-80°C) of [{U(OSi(OtBu)3)3}2(μ-O)], 2 (148.1 mg, 0.071 mmol, 1 eq) in THF (3 mL). The suspension was stirred at -80°C for 15 minutes. The reaction mixture was then filtered on cooled (-80°C) glassware in order to remove graphite and unreacted KC8. The resulting dark red solution was concentrated to 1 mL and the solution was kept at -80°C for 1h leading to the formation of a red precipitate. The suspension was filtered on cold glassware affording 61.9 mg of [K2{[U(OSi(OtBu)3)3]2(μ-O)}], 3 (40 % yield). X-ray suitable crystals were obtained by leaving standing a THF solution (0.07 M) of 3 at -40 °C overnight. 1H NMR of the solid (400 MHz, THF-d8, 298 K): δ (ppm) = -0.04 (s, CH3 terminal siloxide) 1H NMR of the solid (400 MHz, tol-d8, 298 K): δ (ppm) = 0.10 (s, CH3 terminal siloxide) 13C NMR of the solid (400 MHz, THF-d8, 298 K): δ (ppm) = 69.67 (s, C(CH3)3), 27.77 (s, C(CH3)3) Anal Calcd for 3 C72H162O25Si6K2U2: C, 40.21; H, 7.59; N, 0.00. Found: C, 40.09; H, 7.63; N, 0.00. The isolated yield is quite low (40 %) due to the good solubility of the complex in THF, but the effective yield is higher. Notably, when N2 is directly added to the reaction mixture obtained by reacting 2 with KC8, the resulting dinitrogen complex [K2{[U(OSi(OtBu)3)3]2(μ-O)(μ-N2)}], 4, is isolated in 70% yield, indicating that the yield in complex 3 is at least of 70%. The use of lower amounts of KC8 or of higher reaction temperatures (-40 °C) in the synthesis of 3 results in the presence of larger amounts of unidentified by-products and to significantly lower yields. Complex 3 is not stable at room temperature in THF solution. Decomposition starts immediately after dissolution and is complete after 12 hours.