The reaction of Li[Al(OR)4] R = OC(CF3)2Ph, OC(CF3)3 with NO/NO2 giving NO[Al(OR)4], Li[NO3] and N2O. The synthesis of NO[Al(OR)4] from Li[Al(OR)4] and NO[SbF6] in sulfur dioxide solution

Abstract

NO[Al(OC(CF₃)₂Ph)₄] 1 and NO[Al(OC(CF₃)₃)₄] 2 were obtained by the metathesis reaction of NO[SbF₆] and the corresponding Li[Al(OR)₄] salts in liquid sulfur dioxide solution in ca 40% (1) and 85% (2) isolated yield. 1 and 2, as well as Li[NO₃] and N₂O, were also given by the reaction of an excess of mixture of (90 mol%) NO, (10 mol%) NO₂ with Li[Al(OR)₄] followed by extraction with SO₂. The unfavourable disproportionation reaction of 2NO₂(g) to [NO]⁺(g) and [NO₃]⁻(g) [ΔH° = +616.2 kJ mol⁻¹] is more than compensated by the disproportionation energy of 3NO(g) to N₂O(g) and NO₂(g) [ΔH° = −155.4 kJ mol⁻¹] and the lattice energy of Li[NO₃] (s) [U_POT = 862 kJ mol⁻¹]. Evidence is presented that the reaction proceeds via a complex of [Li]⁺ with NO, NO₂ (or their dimers) and N₂O. NO₂ and Li[Al(OC(CF₃)₃)₄] gave {NO₃(NO)₃}[Al(OC(CF₃)₃)₄]₂, NO[Al(OC(CF₃)₃)₄] and (NO₂)[Al(OC(CF₃)₃)₄] products. The aluminium complex {Li[AlF(OC(CF₃)₂Ph)₃]}₂3 was prepared by the thermal decomposition of Li[Al(OC(CF₃)₂Ph)₄]. Compounds 1 and 3 were characterized by single crystal X-ray structural analyses, 1–3 by elemental analyses, NMR, IR, Raman and mass spectra. Solid 1 contains [Al(OC(CF₃)₂Ph)₄]⁻ and [NO]⁺ weakly linked via donor acceptor interactions, while in the SO₂ solution there is an equilibrium between the associated [NO]⁺[Al(OC(CF₃)₂Ph)₄]⁻ and separated solvated ions. Solid 2 contains essentially ionic [NO]⁺ and [Al(OC(CF₃)₃)₄]⁻. Complex 3 consists of two {Li[AlF(OC(CF₃)₂Ph)₃]} units linked via fluorine lithium contacts. Compound 1 is unstable in the SO₂ solution and decomposes to yield [AlF(OC(CF₃)₂Ph)₃]⁻, [(PhC(CF₃)₂O)₃Al(μ-F)Al(OC(CF₃)₂Ph)₃]⁻ anions as well as (NO)C₆H₄C(CF₃)₂OH, while compound 2 is stable in liquid SO₂. The ν(NO⁺) in 1 and [NO]⁺(toluene)[SbCl₆] are similar, implying similar basicities of [Al(OC(CF₃)₂Ph)₄]⁻ and toluene.