Dois complexos contendo vanádio e lítio, [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ] (1) e [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ] (2), Nep = neopentila, Me = metila e thf = tetraidrofurano, foram isolados em alto rendimento e caracterizados por diversas técnicas incluindo espectroscopias de ressonância paramagnética eletrônica (RPE, banda X) e ressonância magnética nuclear (RMN) de 29 Si, medidas de susceptibilidade magnética e difratometria de raios X de monocristal. A despeito das condições similares de preparação, os dois produtos apresentam características estruturais admiravelmente distintivas: o complexo binuclear não-oxo 2 é um simples produto de adição de "V(ONep) 4 " e "Li(ONep)(thf) 2 ", enquanto 1 é um agregado de valência mista com 16 centros metálicos. O oxoalcóxido molecular 1 também contém grupos silanolatos, {OSi(Me 2 )(ONep)} − , produzidos por ataque nucleofílico de neopentóxidos à graxa de silicone dissolvida acidentalmente no meio de reação. Ambos os produtos têm aplicações promissoras em síntese orgânica e inorgânica, incluindo a preparação de óxidos mistos pouco comuns contendo vanádio, lítio e/ou silício.Two complexes containing both vanadium and lithium, [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ] (1) and [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ] (2), Nep = neopentyl, Me = methyl and thf = tetrahydrofuran, have been isolated in high yield and characterised by a number of techniques including X-band electron paramagnetic resonance (EPR) and 29 Si{ 1 H} nuclear magnetic resonance (NMR) spectroscopies, magnetic susceptibility measurements and single crystal X-ray diffractometry. Despite the similar preparation conditions, the two products present remarkably distinctive structural features: complex 2 is a binuclear adduct of "V(ONep) 4 " and "Li(ONep)(thf) 2 ", while 1 is a mixed-valence, 16-metal aggregate. The large molecular oxoalkoxide 1 also contains silanolate units, {OSi(Me 2 )(ONep)} − , produced by nucleophilic attack of neopentoxide groups on Si-O bonds of silicone grease accidentally dissolved in the reaction media. Both products have promising applications in organic and inorganic synthesis, including the preparation of uncommon V-Li and/or Si containing oxides.
Keywords: vanadium(IV), lithium, alkoxide, silicone grease, neopentoxide
IntroductionThe literature on vanadium alkoxide chemistry describes a number of high valence, vanadium(V) compounds prepared from commercially available VOCl 3 , V 2 O 5 , (NH 4 )VO 3 or VO(OR) 3 (R = alkyl). These species have received attention because of their applications as catalysts in polymerization reactions 1 and as precursors of industrially applied homo-and mixed-metal oxides.2 There is also an increasing interest on the preparation of lower oxidation state vanadium alkoxides, such as non-oxo vanadium(III)/ (IV) compounds, to be employed as direct precursors of less common oxides without the use of reducing reaction conditions.3 However, these syntheses have been hampered by the lack of suitable non-oxo starting materials, as the very stable v...