Vanadium-Lithium Alkoxides : Synthesis , Structure , Spectroscopic Characterisation and Accidental Degradation of Silicone Grease

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 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.


Introduction
The 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. 3However, these syntheses have been hampered by the lack of suitable non-oxo starting materials, as the very stable vanadyl(IV)/(V)-containing precursors which are commercially available have a different reactivity pattern when compared to non-oxo compounds. 4ost vanadium(III)/(IV) alkoxides reported to date are homonuclear compounds with chelating or bulky ligands that help avoiding oligomerization. 5In our work, we have employed less hindered alkyls, such as isopropyl (Pr i ) and (ONep)} 2 ]•C 6 H 14 , product 1, in the presence of the grease, or the desired [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ]•NepOH, thf = tetrahydrofuran, product 2, when the reaction was carried out without grease.Both preparations are readily reproducible.Reactions of lithium-containing compounds or Grignard reagents with silicone grease are not a novelty in the literature; 16,17 however, to our knowledge, this has not been reported before for vanadium systems.The products are promising precursors for mixed metal oxides with vanadium in the +III/+IV oxidation states and, in the case of 1, also for V/Si/Li-containing composites.

Experimental
All reactions were performed under an inert dinitrogen atmosphere with the use of standard Schlenk and glovebox (Nexus System 2000, Vacuum Atmospheres Co.) techniques.Solvents were dried and distilled under N 2 prior to use. 18Commercial 2,2-dimethyl-1-propanol (neopentanol, neopentyl alcohol, Aldrich) was used as purchased.Dow Corning ® high vacuum silicone grease was employed as a lubricant for ground glass joints unless otherwise stated.Lithium neopentoxide, [{Li(μ 3 -ONep)} 8 ], and [VCl 3 (thf) 3 ] were prepared in quantitative yield by published methods. 14lemental (C, H, N) analyses were carried out by Medac Laboratories Ltd. (Surrey, UK).Silicon contents were determined by atomic absorption spectrometry at the Institute of Chemistry, University of Campinas, Brazil, using Analytik Jena Nova 300 equipment.Samples were dissolved in aqueous HNO 3 or HCl (3 mol L -1 ) before analysis, and AccuTrace standard solutions (1000 μg mL -1 ) were employed for instrument calibration.
FTIR spectra were recorded on a BIORAD FTS-3500GX instrument in the 400-4000 cm -1 range, from Nujol mulls spread on KBr plates.Magnetic susceptibility measurements were carried out by a modified Gouy method in the solid state at room temperature, using a MKII magnetic susceptibility balance from Johnson-Matthey.Corrections for the diamagnetism of the ligands were applied by the use of Pascal constants. 19W-EPR experiments were performed at X-band using a Bruker ESP-300E spectrometer equipped with a rectangular TE 102 resonator (Bruker 4102 ST) at both liquid nitrogen (77 K) and room temperatures.Thermal ellipsoids are drawn at the 50% probability level.Vol. 20, No. 4, 2009   package for the Matlab ® platform. 20The best parameter set search was optimized using the simplex algorithm.
NMR experiments were carried out at 295 K in nondeuterated thf containing some toluene-d 8 (lock signal), on a Bruker AVANCE 400 spectrometer operating at 9.4 T and equipped with a 5 mm multinuclear direct detection probe.Because of the low solubility of complex 1, the sample was prepared by heating a saturated solution (with some excess of solid) under ultrasonic treatment; this procedure gave a clear, light brown-pinkish solution that did not precipitate on cooling to room temperature. 29Si{ 1 H} spectra (79.49MHz) were acquired with the inverse gated-decoupling pulse sequence ( 1 H decoupling only during acquisition) and 30 degree excitation pulses.Acquisition parameters were 500 ppm spectral width and 10 s relaxation delay.Processing employed zero-filling to 128 K data points and an exponential multiplication of the FID by a factor of 2 Hz. 29 Si NMR chemical shifts are given in ppm related to the tetramethylsilane signal (tms, 0.0 ppm) as internal reference.

Synthesis of [V 2 (µ-ONep) 2 (ONep) 6 ]
This preparation was based on a report by Haaland et al. 21VCl 3 (thf) 3 ] (4.78 g, 12.8 mmol) was added slowly over 24 h to a boiling white suspension of [{Li(μ 3 -ONep)} 8 ] (5.05 g, 6.72 mmol) in hexane/thf (2.5:1).This produced a dark blue suspension, which received the addition of copper(I) chloride (1.37 g, 12.8 mmol).The redox reaction was immediate, forming a dark green suspension containing a red solid, which was stirred at room temperature for 24 h and then filtered.The green filtrate was concentrated in vacuum and kept at −20 o C for 5 days to give yellowish-green crystals of [V 2 (μ-ONep)  (1)   A blue-greenish solution of [V 2 (μ-ONep) 2 (ONep) 6 ] (0.89 g, 1.11 mmol) in 30 mL of thf was added to a colourless solution of [{Li(μ 3 -ONep)} 8 ] (0.21 g, 0.27 mmol) in 10 mL of thf to give a light green solution, which changed to olive green after stirring at room temperature for 24 h.The solvent was then taken to dryness under vacuum and the dark green slurry was dissolved in 10 mL of hexane and kept at room temperature for 5 days.Olive-brown crystals of 1 (0.

Synthesis of [V(ONep) 3 (µ-ONep) 2 Li(thf) 2 ]⋅NepOH (2)
In this preparation, the contact of solvents or reaction mixtures with silicone grease was carefully avoided.Poly(tetrafluoroethene) (PTFE) sleeves were employed in the place of the grease to protect all ground glass joints.
A blue-greenish solution of [V 2 (μ-ONep) 2 (ONep) 6 ] (1.70 g, 2.13 mmol) in 30 mL of thf was added to a colourless solution of [{Li(μ 3 -ONep)} 8 ] (0.42 g, 0.55 mmol) in 10 mL of thf, giving a dark green solution after stirring at room temperature for 24 h.The reaction mixture was then taken to dryness under vacuum, leaving a light green solid that was redissolved in 10 mL of hexane containing 0.44 g (4.99 mmol) of NepOH.After stirring for 24 h at room temperature, the resulting greenish-yellow solution was cooled down to −20ºC for 2 days.Pale green crystals of 2 were then formed, which were isolated by filtration and dried under vacuum.Yield: and thf/NepOH (2:1).It is also partially soluble in hexane and in a 1:1 hexane/thf mixture.

Crystal structure analyses of products 1 and 2
For each sample, one crystal was mounted under oil on a glass fibre and fixed in the cold nitrogen stream on an Oxford Diffraction Xcalibur-3 CCD diffractometer equipped with Mo-K α radiation (λ = 0.71069 Å) and graphite monochromator.Intensity data were measured by thin-slice ωand ϕ-scans.Data were processed using the CrysAlis-CCD and -RED programs. 22The structures were determined by the direct methods routines in the SHELXS program 23 and refined by full-matrix least-squares methods, on F 2 's, in SHELXL. 23n complex 1 (olive-brown plates), the non-hydrogen atoms (except for the lithium atoms) were refined with anisotropic thermal parameters.Hydrogen atoms were included in idealised positions and their U iso values were set to ride on the U eq values of the parent carbon atoms.At the conclusion of the refinement, 23  ) + (0.0718P) 2 ] -1 with P = (F o 2 + 2F c 2 )/3; for the 'observed' data only, R 1 = 0.063.In the final difference map, the highest peak (ca.0.6 e -Å -3 ) was close to O (14).The unit cell contains one solvent (hexane) molecule per {V 6 Li 10 } aggregate.Crystals of 2 (pale green prisms) contain two independent V-Li complex molecules and two solvent (neopentanol) molecules in the asymmetric unit.One of the complex molecules shows disorder in three of its ligands; these have all been resolved, but in the refinement, the parameters of some atoms, common to more than one ligand orientation, have been tied together.The non-hydrogen atoms, except for a few of low-occupancy components, were refined with anisotropic thermal parameters.Hydrogen atoms were included in idealised positions and their U iso values were set to ride on the U eq values of the parent carbon atoms.At the conclusion of the refinement, 23  )/3; for the 'observed' data only, R 1 = 0.066.In the final difference map, the highest peak (ca.0.35 e -Å -3 ) was close to V(1).
Scattering factors for neutral atoms were taken from reference 24.Computer programs used in these analyses were run through WinGX 25 on a Dell Precision 370 PC; diagrams were drawn with ORTEP3 for Windows. 25Crystal data and refinement results were compiled in Table 1.

Results and Discussion
The 1:2 reaction of [V 2 (μ-ONep) 2 (ONep) 6 ] (Figure 1) with "Li(ONep)" in tetrahydrofuran was carried out according to a synthetic route reported by Hampden-Smith et al. 6 for the preparation of complexes with the general formula "MTi(OPr i ) 5 ", OPr i = isopropoxide; M = Li, Na, K.The procedures employed in the present work gave olive-brown crystals of 1 and pale green crystals of 2 at room temperature; the difference is related to the use of silicone grease in the Schlenk-type glassware during the preparation of 1.
Analytical and spectroscopic data for 1 are consistent with the formulation [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ] •C 6 H 14 , revealed by single crystal X-ray diffraction analysis.The high reactivity of the V IV /Li I alkoxide system, together with its contact with the silicone grease used for sealing the ground glass joints, determined a reaction pathway different from the expected, as revealed by the crystallographic structure of 1 (Figures 2 and 3).The molecular aggregate contains sixteen metal centres and two silanolate units, {OSi(Me 2 )(ONep)} − , the latter provided by the grease.The incorporation of these groups probably followed a nucleophilic attack of neopentoxides on the silicon centres of the (OSiMe 2 ) n polymer.To the best of our knowledge, this is the first report of this type of reaction involving a vanadium (oxo)alkoxide, and one of a few related reports with d-block metal complexes. 17In spite of the accidental nature of this synthesis in the context of the present work, the preparation of 1 is perfectly reproducible in the conditions described in Experimental.
Silicone grease is a linear polymer that consists of chains of alternating dimethylsilylene units and oxygen atoms, (-SiMe 2 -O-) n , terminated in most cases with Si-OH groups.Its partial solubility in tetrahydrofuran facilitates extraction into reaction mixtures containing this solvent.Accidental contact with reactive, highly polar metal-containing species may lead, as in the present case, to unexpected species in solution.Some interesting new compounds have been reported as a result of such combinations, and the subject has drawn the attention of many researchers.These compounds frequently contain large molecular aggregates (sometimes supramolecular assemblies) including polysiloxane grease fragments such as dimethylsilylene and oligosiloxane units. 16roduct 2, in its turn, was prepared and manipulated in the absence of silicone grease.In this case, poly(tetrafluoroethene) (PTFE) sleeves were employed in all synthetic and analytical steps, starting from solvent purification.Differently from those reported for analogous Li I -Ti IV alkoxides (R = Pr i or Nep) 6 and Li I -Nb V neopentoxides, 26 the metal centres in complex 2 do not aggregate to give a tetranuclear {M 2 Li 2 } or a higher nuclearity core (M = transition metal).Instead, binuclear 2 resembles one-half of the vanadium(IV) starting molecule (Figure 1), this time connected to a {Li(thf) 2 } moiety (Figure 4).In fact, the product is simply a V(OR) 4 ⋅(solvated LiOR) adduct, in which the formation of the neopentoxide bridges and the Lewis basicity of thf determine the completion of the metal coordination spheres.The absence of further aggregation is probably related both to the choice of an electron-donating solvent and the fact that non-oxo vanadium(IV) does not commonly reach six-coordination with monodentate, branched alkoxides.To the best of our knowledge, octahedral (homoleptic) alkoxides of non-  oxo V IV are only found with ligands such as methoxide, ethoxide or chelating OR groups, such as those generated from monosaccharides. 27oduct 2 is highly soluble in thf and constitutes a suitable starting material for the preparation of mixed transition metal complexes by salt (LiX) elimination reactions.It has already been employed in our laboratory to produce Li/V oxide films for electrochemical applications, with promising preliminary results.

Solid state structures Complex 1
The solid state structure of compound 1, determined by single crystal X-ray diffraction analysis, consists of [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ]•C 6 H 14 molecules, one in each triclinic (P-1) unit cell (Figures 2 and 3).It illustrates the type of species that may be present in solution after accidental contact of lithium-containing reagents with silicone grease; accordingly, some of the structural features of 1 have been seen in other studies. 14,16On the other hand, this particular structure presents a distinctive condensed system composed of a 24-atom cyclic unit and two distorted heterocubanes, {VLi 3 O 4 }, one on each side of the central, wheel-like aggregate.
The triangle formed by the V(1), V(2) and V(3) centres is connected to the five-coordinate O (15), which is also linked to Li (1) and Li(2).This oxo group, O (15), is a key component of the whole assembly, as it holds five out of the eight metal centres in each half of the aggregate.The square-pyramidal arrangement about O (15) resembles that observed in [Fe 5 (μ 5 -O)(μ-OPr i ) 8 Cl 5 ] 28 and a number of related iron 29 and lanthanide complexes, 30 this time generating a novel pentanuclear {V 3 Li 2 } motif which is, in itself, another relevant structural component of 1.The other oxo ligands, namely the four-coordinate O(13) and the three-coordinate O (14) and O (23), help in stabilizing and shaping the cyclic framework.

Complex 2
There are two independent V-Li complex and two solvent (neopentanol) molecules in the crystal (Figures 4  and S1).One of the complex molecules shows disorder Scheme 1 Reis et al.  in three of its ligands (Figure S1 and additional structure discussion in the Supplementary Information).
The two V-Li molecules have very similar cores, in spite of small differences in bond lengths and angles.Crystallographic data and selected structural parameters are listed in Tables 1, 3 and S2 (2.012(6) Å for bridging and 1.801(6) Å for terminal V-O (Nep) bonds respectively) 15 and [V 2 (μ-OPr i ) 2 (OPr i ) 6 ], 2.012(10) Å and 1.8154(11) Å, 11 in accordance with the very similar coordination spheres of the vanadium in the three complexes.

Spectroscopic and magnetochemical analyses 29 Si{ 1 H} Nuclear magnetic resonance (NMR)
A saturated thf solution of product 1 containing a few drops of toluene-d 8 was analyzed by 29 Si{ 1 H} NMR in order to confirm the presence of silanolate groups; results are summarized in Figure 5.The sample of 1 produced only one, well defined resonance signal at δ = −19.2ppm (Figure 5b).The silicone grease, dissolved in the same solvent mixture, gave a clean signal at −21.9 ppm, which is easily distinguished from that presented by 1 (Figures 5a and 5c).The position of the 29 Si resonance signal of 1 at a higher frequency value as compared to the grease is compatible with the binding of each equivalent {OSi(Me) 2 (ONep)} − group in 1 to three Li sites (Figure 3), which act as electron-withdrawing groups and increase the 29 Si NMR chemical shift.

Electron paramagnetic resonance (EPR) and magnetic moment measurements
The solid state EPR spectrum of powdered 1 at 77 K (Figure 6) exhibits a broad line with partially resolved hyperfine features, centred at ca. 346 mT, that indicates magnetic interaction between the vanadium sites in the solid ( 51 V, I = 7/2).This is in accordance with the total effective magnetic moment of 5.66 β e determined for 1 in the solid state at 300 K, significantly lower than the spin-only value for a system with 4 vanadium(IV) and 2 vanadium(III) independent centres (S = 4, μ eff = 8.94 β e ).These measurements suggest a strong antiferromagnetic interaction among the vanadium centres, possibly by a superexchange mechanism involving the bridging oxo groups O (14), O(15) and O(23) (Figures 2 and 3).The very low solubility of 1 in common organic solvents so far precluded detailed solution studies.
The 77 K powder (solid state) EPR spectrum of 2 (Figure 7) shows a dominant eight-line parallel hyperfine signature of 51 V in the +IV oxidation state, d 1 .The spectrum was simulated using Gaussian lineshapes corrected by small magnetic field and hyperfine strains.Collinear g and A rhombic tensors were used (Table 4).Magnetic moment determinations carried out for solid 2 at 300 K gave an average μ eff value of 1.79 β e , very close to the spin-only figure (1.73 β e ), corroborating the absence of significant orbital contributions to the susceptibility and of magnetic interactions involving the vanadium centres in the solid.
The 77K frozen solution EPR spectrum of 2 (Figure 8) shows the remarkable features of vanadium(IV) (S = ½) along with almost central perpendicular splittings.The simulation parameters are in very good agreement with those of the powder spectrum (Table 4), strongly suggesting that the binuclear aggregation revealed for 2 in the solid state (Figure 4) is kept in thf solution.The small discrepancies between the EPR parameters of the powdered solid and the frozen solution come from line position uncertainties due to molecular strains, as well as from electron dipolar line broadening present in the higher spin concentration solid sample, which leads to larger line widths.In accordance to the above, powdered solid lineshapes tend to best fit to a convolution of Gaussian/Lorentzian (0.75/0.25) lineshapes.Despite at first glance the symmetry at the vanadium site could seem axial (D 3h ), bond lengths about O(13), O (14)  and O(15) are different, leading to the rhombic tensors presented in Table 4.Moreover, the two axial bonds V(1)-O (11) and V(1)-O (12) are not quite colinear, with an angle of 171.34( 14)° (Table 3).
The room temperature solution EPR spectrum (Figure 9) also displays an eight-line pattern.The particular overall shape is due to an interference between the line width lw and the isotropic hyperfine coupling A iso .The ratio lw/A iso can lead from a two-line spectrum, when lw > A iso , to the very well known octet when lw < A iso . 36The linewidth (Lorentzian line shape) observed for 2 is mostly dictated by  a fast motion tumbling regime, with a solution correlation time (τ c ) of 2.29 × 10 -11 s, in agreement with equivalent systems (Table 5). 37The clear correspondence between the simulated A iso and g av parameters presented in Tables 4 and  5 is noteworthy, as far as the 77 K (solid state and frozen solution) and room temperature systems are concerned.This again reinforces the maintenance of the binuclear structure of 2 after dissolution in thf.

Infrared spectroscopy
Figure S2 shows a comparison of the infrared spectra of the vanadium starting material, [V 2 (μ-ONep) 2 (ONep) 6 ], and of the two V/Li compounds described in this work.The FTIR spectra of 1 and 2 present strong absorptions in the 1385-1360 cm -1 range, assignable to skeletal vibrations of the neopentyl group.Strong bands at ca. 1080, 1060 and 1020 cm -1 , and a weak band at ca. 930 cm -1 , may be attributed to C-O stretching frequencies. 14,38The spectra also exhibit absorptions between 650 and 460 cm -1 , which are attributed to V-O stretches. 31,38emical reactivity leading to the formation of products 1 and 2 Intriguingly, complex 1 appears to be a mixed-valence vanadium(III)/vanadium(IV) species, as required by charge balance arguments, considering the presence of ten Li + centres and eight oxo, fourteen neopentoxide and two {OSi(Me) 2 (ONep)} − ligands.This demands four vanadium(IV) and two vanadium(III) centres; any other combination would lead to even lower oxidation state vanadium, which is unlikely in this hard-donor environment.As the vanadium starting material, [V 2 (μ-ONep) 2 (ONep) 6 ], contains only vanadium(IV), this implies the occurrence of a reduction reaction giving vanadium(III), tentatively associated, in 1, with the unique, distorted octahedral V(3) centre (Figures 2 and 3).The five-coordinate V(1) and V(2), in their turn, are supposed to be in the +IV oxidation state.These assignments are based on the inversion symmetry of the molecular assembly and the most common coordination numbers of vanadium(III) and (IV) in O-donor environments. 39The possibility of an oxidation state intermediate between +III and +IV must also be considered, although the different symmetries of the vanadium sites, V(1) ≈ V(2) ≠ V(3), favour more localized valencies. 40On the other hand, the crystal field strengths are similar, the difference in bond lengths about the transition metal centres is small and the bridging oxides lead to short V⋅⋅⋅V distances, so a degree of delocalization, corresponding to Robin and Day's intervalence class II, can be expected.The magnetic properties of 1 also give support to this hypothesis, and further studies are both necessary    and justified in this case, as mixed-valence compounds can show interesting nonlinear optical properties, besides other applications. 41nother relevant structural feature of 1 is the presence of the eight oxo (O 2− ) ligands, which do not appear in 2 or in the starting materials.The origin of these bridging groups could be in the general tendency of ether elimination by high valence transition metal alkoxides, 42 such as the ones formed by vanadium(IV)/(V): and/or in the accidental activation of the silicon grease by the vanadium and lithium precursors, as discussed below.
4][45] Representative reports include (i) αor β-hydride transfer from alkali metal alkoxides or Grignard compounds to organic electrophiles, 44 (ii) ether/ketone elimination 46 and alkyl radical departure from transition metal alkoxides 47 and (iii) metal disproportionation. 45In case (ii), events of transition metal reduction, alkoxide C-O bond homolysis and oxo group formation (both terminal and bridging) are either concomitant or part of further rearrangements in the reaction mixtures.
The mechanism of formation of 1, taking into account both the presence of the oxo groups and vanadium(III), is not yet known.According to Mayer, 43 in general, a ligand C-O or O-H bond should be considered activated for cleavage -leaving metal-bound oxo groups -in all systems where a related metal oxide is accessible.This is surely the case for the reaction mixtures employed in this work.Conditions as those favouring the occurrence of metal reduction are also present.This suggests that vanadium(III) and oxo groups should be formed -not necessarily in the same proportions -in both reaction media described here.However, the distinct and yet reproducible character of the reactions that give 1 and 2 suggest that the involvement of the grease -the main difference between the two procedures -has more significant consequences than the ones tentatively illustrated in Scheme 1.As no trivial redox mechanism involving (poly)alkylsiloxanes as metal reducing agents can be easily envisaged in our reaction conditions, the activation of the silicone chains and the consequent formation of the silanolate groups, {OSi(Me 2 )(ONep)} − , may actually be key thermodynamic factors that determine the stabilization of 1 and drive the equilibrium position in its favour.This apparently prevents the formation of 2 in the presence of the grease.Further studies are needed in order to clarify this.

Conclusions
The attempt to prepare "LiV(OR) 5 "-type compounds from a non-oxo vanadium(IV) starting material and "Li(OR)" (R = neopentyl) gave two products, complexes 1 and 2, with distinctive structural features.While 2 presents a simple binuclear V-Li composition both in thf solution and in the solid state, product 1 is an unexpected mixedvalence vanadium-lithium polynuclear aggregate whose formation follows the accidental solubilization of silicone grease into the reaction media.The reproducibility and high yield of both preparations are promising features to facilitate further investigation of reaction mechanisms and possible synthetic, electrochemical, optical and catalytic applications of the two compounds.Both products are potential precursors for mixed-metal oxides.Complex 1 may also be useful for the preparation of ternary Si-V-Li composites and for the oxo-functionalization of organic substrates, a relevant reaction in academic and industrial research.

Additional notes on the solid state structure of [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ]⋅NepOH (Complex 2)
There are two independent V-Li complex molecules and two solvent (neopentanol) molecules in the crystal.One of the complex molecules shows disorder in three of its ligands, viz the NpO ligands of O (44) and O (45), and the thf ligand of O (46); these have all been resolved.In the thf ligand, one methylene group is disordered over two sites, giving alternative 'flaps' to the envelope conformations of this ligand.There are two distinct arrangements of the ligand of O (44), shown coordinated to V(4) through O(44)  and O(44A); the central carbon atom of each, C(442) and C(44B), is common to both orientations and has been refined with coordinates and thermal parameters tied for the two atoms.The ONp ligand of O( 45) is similar except that three orientations have been resolved for this ligand; the central atoms of all three, C(452), C(45B) and C(45Z), share common coordinates and thermal parameters; the No hydroxyl hydrogen atoms have been located on any of the ONep ligands or discrete solvent molecules/anions.Considering vanadium(IV) and Li + in the complexes, to balance charges, the separate small ONep units must be neopentanol molecules, with hydroxyl H atoms that cannot be seen at the present resolution level.Assuming that the discrete molecules are NepOH, there are suitable acceptor groups for hydrogen bond formation between O(18)-H and O (15), and between O(48)-H and either O(44A) or O (45); the O⋅⋅⋅O distances are 2.844, 2.986 and 3.007 Å respectively, and the corresponding C-O⋅⋅⋅O angles are 104.6,109.2 and 86.0 ° (Figure S1).The oxidation state +IV of the transition metal in 2 is further supported by the EPR studies described in the manuscript.

Figure 1 .
Figure 1.R e p r e s e n t a t i o n o f t h e m o l e c u l a r s t r u c t u r e o f [V 2 (μ-ONep) 2 (ONep) 6 ], Nep = neopentyl, employed as starting material for the synthesis of complexes 1 and 2.15 Thermal ellipsoids are drawn at the 50% probability level.

Figure 3 .
Figure 3.View of one half of the molecular aggregate (1), indicating the atom numbering scheme.Some of the methyl groups and the hydrogen atoms have been omitted for clarity.Thermal ellipsoids are drawn at the 50% probability level.

Figure 4 .
Figure 4.One of the V-Li complex molecules (2) with its NepOH neighbour.Thermal ellipsoids are drawn at the 50% probability level.

Figure 9 .
Figure 9. Experimental (thick line) and simulated solution EPR spectra of 2 in the fast motion regime.Microwave frequency: 9.769 GHz; room temperature; solvent: tetrahydrofuran.

O
atoms, O(45A) and O(45X), of two of the ligands also share sites, and the methyl group carbon atoms C(455) and C(45D), of the ligands of O(45) and O(45A), are shared by the third ligand, of O(45X).

Table 4 .
Gyromagnetic and hyperfine simulated couplings for complex 2 at 77 K (a) A iso = (A x + A y + A z )/3 and (b) g av = (g x + g y + g z )/3.

Table 5 .
Fast motion regime gyromagnetic and hyperfine simulated couplings for complex 2 in thf solution at room temperature