The complex [Ti3(O)(Cl)(ONep)9] and two iron(II)-containing products, [Fe4Cl8(thf)6] and [Fe2Cl3(thf)6][FeCl4], were synthesized by a redox reaction involving [Ti3(OiPr)11][FeCl4] and neopentanol; the structures of compounds [Ti3(O)(Cl)(ONep)9] and [Fe2Cl3(thf)6][FeCl4] have been confirmed by X-ray diffraction methods. Variable-temperature 1H NMR analysis of [Ti3(O)(Cl)(ONep)9] revealed signals for three non-equivalent neopentoxides in the 1:1:1 integration ratio, indicating the maintenance of the trinuclear structure in solution. Alkoxide [Ti3(O)(Cl)(ONep)9] was employed as initiator in both bulk and solution polymerization of ε-caprolactone (ε-CL) at various temperatures, monomer/initiator molar ratios and reaction times. [Ti3(O)(Cl)(ONep)9] produced poly(ε-caprolactone) in high yields, with molecular weights ranging from 7100 to 9800 g mol-1 and PDI (polydispersity index) values between 1.3 to 1.5. The reactivity of [Ti3(O)(Cl)(ONep)9] in the ring-opening polymerization (ROP) of ε-CL was compared to those of [Ti3(OiPr)11][FeCl4] and [Ti(OiPr)4]. The better polymerization reactivity shown by [Ti3(O)(Cl)(ONep)9] seems to be associated with structural features, as well as with the stronger Lewis basicity of -ONep over -OiPr ligands and the maintenance of the trimetallic structure in the reaction media.

The activity of the heterometallic alkoxide [FeCl{Ti2(OiPr)9}] (1) towards polymerization of rac-lactide (rac-LA) and ε-caprolactone (ε-CL) was investigated in toluene solution and in bulk at various temperatures, monomer/heterometallic alkoxide molar ratio and reaction times. The alkoxide 1 was active in solution for ε-CL and in bulk for both monomers. Polymers were obtained in good yields with molecular weights ranging from 3890 to 15000 g moL-1 and polydispersity indexes (PDI) values varying from 1.3 to 2.5. Based on the 1H nuclear magnetic resonance (NMR) end-group analysis of polymers, a coordination-insertion mechanism was suggested for both monomers. The average number of growing chains per molecule of initiator (4 to 5 for rac-LA and 7 to 8 for ε-CL) indicates that both bridging and terminal isopropoxides are active initiating groups. Kinetic studies with ε-CL indicated that the polymerization rate is first order with respect to monomer concentration. The catalytic properties of 1 were compared to those found for other titanium(IV) and iron(II) complexes using ε-CL as a model monomer.

The thermochromic behavior exhibited by vanadium(IV) alkoxides, [V2(μ-OPr i)2(OPr i) 6] and [V2(μ-ONep)2(ONep)6 ], OPr i = isopropoxide and ONep = neopentoxide, was studied by molecular modeling using DFT, TDDFT and INDO/S methods. The vibrational and electronic spectra calculated for [V2(μ-OPr i)2(OPr i) 6] were very similar to the experimental data registered for crystalline samples of the complex and for its solutions at low temperature (< 210 K), while spectra recorded at high temperature (> 315 K) were compatible with those calculated for the monomeric form, [V(OPr i)4]. These results consistently point to a monomer/dimer equilibrium as an explanation for the solution thermochromism of {V(OPr i)4}n. In spite of the structural similarity between [V2(μ-ONep)2(ONep)6 ] and [V2(μ-OPr i)2(OPr i) 6] in the solid state, the thermochromic behavior of the former could not be explained by the same model, and the possibility of tetranuclear aggregation at low temperatures was also investigated.

Dois complexos contendo vanádio e lítio, [V6Li10O8(ONep)14{OSi(Me)2(ONep)2}] (1)e [V(ONep)3(µ-ONep)2Li(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 29Si, 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 2é um simples produto de adição de "V(ONep)4" e "Li(ONep)(thf)2", enquanto 1é um agregado de valência mista com 16 centros metálicos. O oxoalcóxido molecular 1também contém grupos silanolatos, {OSi(Me2)(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, [V6Li10O8(ONep)14{O2Si(Me)2(ONep)}2] (1) and [V(ONep)3(µ-ONep)2Li(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 29Si{¹H} 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 2is a binuclear adduct of "V(ONep)4" and "Li(ONep)(thf)2", while 1is a mixed-valence, 16-metal aggregate. The large molecular oxoalkoxide 1also contains silanolate units, {OSi(Me2)(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.

O alcóxido heterometálico [FeCl{Ti2(OPr i)9}] (1) foi utilizado como um precursor de fonte única para a preparação de óxidos de Fe/Ti sob atmosfera inerte. Três procedimentos sintéticos distintos foram adotados no processamento de 1, com o emprego de soluções aquosas ácidas (HNO3 ou HCl), ou na ausência de ácido mineral. Os produtos foram caracterizados por difratometria de raios X (pó), microscopia eletrônica de varredura combinada com espectroscopia de dispersão de raios X (MEV/EDS) e espectroscopias Raman, de ressonância paramagnética eletrônica (RPE) e Mössbauer. Os óxidos produzidos contêm titânio(IV) e ferro(III) (ou ferro(II)), dependendo das condições de reação e das temperaturas de tratamento térmico. Uma interessante redução de ferro(III) a ferro(II), que levou à obtenção de ilmenita (FeTiO3), foi observada a 1000 ºC no sistema contendo HNO3. Estudos por MEV/EDS revelaram uma distribuição altamente heterogênea dos metais em todos os produtos, possivelmente relacionada com a presença de um conteúdo significativo de carbono e de defeitos estruturais (vacâncias de oxigênio) nos sólidos.

The heterometal alkoxide [FeCl{Ti2(OPr i)9}] (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 ºC in the HNO3-containing system, leading to the detection of ilmenite (FeTiO3). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.

O novo cloroisopropóxido binuclear de titânio(IV), [{TiCl(OPr i)2(HOPr i )}2(mi-OPr i)2] (1), e o primeiro oxo-cloroalcoolato de vanádio(IV) mononuclear, [VCl(O)(HOPr i)4]Cl (2), foram preparados através da reação entre [Ti(OPr i)4], KOPr i e VCl3 em proporção 2:1:1. Os produtos foram caracterizados por análise elementar, espectroscopia na região do infravermelho, RPE, RMN, espectroscopia eletrônica, medidas de susceptibilidade magnética e difratometria de raios-X (monocristal). A estrutura eletrônica de 1 foi analisada através de cálculos mecânico-quânticos em nível semi-empírico. Esses complexos são precursores em potencial de óxidos homo- e heterometálicos.

The novel binuclear titanium(IV) complex [{TiCl(OPr i)2(HOPr i )}2(mu-OPr i)2], 1, and the first mononuclear vanadyl(IV) chloroalcoholate [VCl(O)(HOPr i)4]Cl, 2, have been prepared from 2:1:1 mixtures of [Ti(OPr i)4], KOPr i and VCl3. Products were characterised by elemental analysis, FTIR, EPR, NMR and electronic spectroscopies, magnetic susceptibility measurements and single crystal X-ray diffractometry. A third product was found to be polynuclear and to contain both titanium and vanadium. Semi-empirical quantum-mechanical calculations were carried out for the evaluation of the electronic structure of 1.