Crystal structures of [Li7(i-PrO)3(C4H10NO)3]2O and [Na(i-PrOH)2(C8H18NO2)]2

The crystal structures of [Li7(i-PrO)3(C4H10NO)3]2O (1) and [Na(i-PrOH)2(C8H18NO2)]2 (2) were determined at 100 K. In title compound 2, O—H⋯O hydrogen bonding can be observed which builds up the dimeric structure.


Chemical context
The combination of alkali-metal organyls, aminoalkoxides and alcohols is of great interest for understanding the behaviour of alkali-metal organyls in deprotonation or metalation reactions. Alkoxides, and especially aminoalkoxides, are used to increase the reactivity of alkali-metal organyls through deaggregation (Lochmann & Janata, 2014;Caubé re, 1993). As a result of the formation of oligomers, alkali-metal organyls should be deaggregated to get easily accessible metal centers and thus increase the reactivity (Streitwieser et al., 1976;Gessner et al., 2009). This deaggregation can be carried out by solvent molecules or Lewis bases, such as aminoalkoxides. Thus the use of aminoalkoxides leads to a highly reactive species, which has great impact on deprotonation or metalation reactions with alkali-metal organyls in chemical synthesis (Gros et al., 1995;Gros et al., 1997). Previous studies have shown that the reaction of 2-methoxypyridine with a lithium alkyl and a lithium dimethylaminoethoxide leads to a high yield of the metalated product, while the reaction without the aminoalkoxide only leads to a nucleophilic addition (Gros & Fort, 2002). Besides 2-methoxypyridine, the metalation of pyridine and quinoline with a mixture of lithium alkyl and lithium aminoalkoxide can also be observed, which indicates a higher substrate scope and a higher reactivity (Gros & Fort, 2002). This mixture is a so-called monometallic superbase of the second generation, based on the Lochmann-Schlosser superbase (n-butyllithium and potassium-tert-butoxide) (Schlosser, 1967;Lochmann et al., 1966Lochmann et al., , 1970Lochmann et al., , 1972Lochmann & Janata, 2014). In particular, the insertion of the amine function in the alkoxide shows a high stabilization, which is proven by the structure of (LiDMAE) 8 (Andrews et al., 2002). The structural behaviour exhibits a high stabilization and a broader approach to deprotonation possibilities. Therefore, the use of an alkali-metal aminoalkoxide in combination with an alkali-metal organyl is a potential monometallic superbase of the second generation. But, because of the synthesis of the lithium aminoalkoxide with the aminoalcohol (dimethylaminoethanol), which is added in situ to the butyllithium solution, reaction mixtures can still contain the pure aminoalcohol (Gros et al., 1997). In general, alcohols also affect the structural and chemical behaviour of alkali-metal organyls. As well as the synthesis of the aminoalkoxides, they are also used during the synthesis of alkali-metal organyls such as tertbutyllithium. To gain higher yields, it is reported that the addition of small amounts of tert-butyl alcohol improves the yield to 80% instead of 40% (Smith, 1974). Consequently, in metalation and deprotonation reactions containing aminoalkoxides and alkali-metal organyls, small amounts of alcohols can also be available. Usually the alcohol, which is added during the synthesis of the organometal reagents, is metalated. By adding a second alcohol, the aminoalcohol, it is not clear whether the previous alcohol is still metalated. Therefore, the influence of these amounts of alcohol is of great interest for understanding the reactivity and the mechanistic behaviour. The structures obtained here reflect the interaction of the reagents and can provide insights into the influence of alcohols, which occur during the synthesis of the alkoxide or the synthesis of the organometal reagent. In particular, the insertion of an alcohol that is not based on the aminoalkoxide generates high interest, because it can be concluded whether the aminoalcohol is deprotonated to form the alkali-metal alkoxide or the additional alcohol is deprotonated. The combination of alkali-metal organyls, aminoalkoxides and alcohols is therefore of great interest for understanding the synergistic effect.

Structural commentary
The title compounds 1 and 2 crystallize at 193 K in the presence of isopropanol. Both structures contain an alkali metal, an aminoalkoxide and isopropanol. Compound 1 crystallizes in the monoclinic space group C2/c and the asymmetric unit contains half of the compound, which is built up by a twofold rotation axis. Compound 1 consists of lithium triangles, which are capped by the oxygen atom of the isopropoxide and the aminoalkoxide. Dimethylaminoethanoxide, whose nitrogen atom also coordinates a lithium center, is used as an alkoxide. The molecule contains fourteen lithium centers, which are arranged as a distorted facecentered cube around an oxygen center. The oxygen center is located on a special position (4c, 0.75, 0.25, 0.5) and is dianionic. The structure is shown in Fig. 1 and selected bond lengths and angles are given in Table 1. The distances between the oxygen atom of the aminoalkoxide and the next lithium center are 1.901 (2) Å for Li2-O3, 1.893 (2) Å for  (2) Å for Li4-O5. Comparing these to a similar structure in the literature, containing the same aminoalkoxide, the bond length is, at 1.899 (2) Å , nearly in the same range (Andrews et al., 2002). Furthermore, the bond lengths of the oxygen atom and the lithium center, which is coordinated by a nitrogen atom, are slightly elongated with 1.989 (2) Å (Li3-O3), 1.989 (2) Å (Li1-O1) and 1.997 (2) Å (O5-Li5) because of the rigid structure of the aminoalkoxide and the formed internal ring. The bond lengths between the nitrogen atom of the aminoalkoxide and the lithium center vary between 2.141 (3) Å for Li3-N2, 2.157 (2) Å for Li1-N1 and 2.125 (2) Å for Li5-N3, which is slightly shorter than the bond length in the literature for the (LiDMAE) 8 compound [2.189 (2) Å ; Andrews et al., 2002]. Moreover, the bond lengths of the oxygen atom of the isopropoxide and the lithium centers amount to 1.920 (2) Å for Li2-O2, 1.918 (2) Å for Li4-O4 and 1.910 (2) Å for Li6-O6, respectively. Thus, they are slightly shorter compared to bonds in the literature, which vary between 1.953 (8) and 1.962 (7) Å (Crozier et al., 2013). The bond length of the internal oxygen atom O7 exhibits a very long distance to the opposite lithium center Li7, with a bond length of 2.554 (3) Å . The distances to the other lithium centers Li2, Li4 and Li6 are shorter and come to bond lengths of 2.003 (2) Å for O7-Li2, 2.007 (2) Å for O7-Li4, and 1.997 (2) Å for O7-Li6. The bond angles of the lithium centers and the oxygen of the aminoalkoxide, Li2-O3-Li3, Li1-O1-Li6 and Li4-O5-Li5, are 93.81 (10), 94.45 (10) and 93.77 (10) , respectively, and therefore wider than the bond angles in comparable structures [80.55 (9) ; Andrews et al., 2002]. Moreover, the bond angles of the nitrogen atom of the aminoalkoxide, the lithium center and the oxygen atom of the aminoalkoxide are 88.05 (10) for N2-Li3-O3, 88.06 (10) for N1-Li1-O1 and 88.55 (10) for N3-Li5-O5. Compared to a structure in the literature with an angle of 90.25 (10) (Andrews et al., 2002), the angles in the observed compound are compressed. The bond angle of the lithium atoms and the oxygen atom of the isopropoxide are 79.26 (10) (Li1-O2-Li2), 79.25 (10) (Li3-O4-Li4) and 79.35 (10) (Li5-O6-Li6). In contrast, the angles of the oxygen atom of the isopropoxide and the outermost lithium center Li7 are much wider at 116.92 (11) for Li1-O2-Li7, 116.33 (11) for Li7-O4-Li3 and 116.55 (12) for Li5-O6-Li7.
Compound 2 crystallizes in the triclinic space group P1 and the asymmetric unit contains half of the molecule. [Na(i-PrOH) 2 (C 8 H 18 NO 2 )] 2 is a sodium dimer with a deprotonated alcohol that coordinates the sodium atom with its three donor atoms. The deprotonated alcohol N-methyl(2-methoxyethylamino)-2-methyl-2-propanol consists of a central nitrogen atom and two oxygen atoms. Therefore, it has excellent properties as a donating ligand. The structure of the compound is given in Fig. 2 and selected bond lengths and angles are given in Table 2. The asymmetric unit contains a central sodium atom with a trigonal-bipyramidal coordination sphere. The nitrogen atom of the aminoalkoxide builds up the top pyramid site, while one isopropanol builds up the opposite pyramid site. The two oxygen atoms of the aminoalkoxide and another isopropanol are located triangularly around the sodium atom. The distance between the sodium atom Na1 and  Table 1 Selected geometric parameters (Å , ) for 1.
the nitrogen atom N1 is 2.5707 (11) Å , which is an elongated bond length in comparison to a literature structure [2.528 (2) Å ; Marszałek-Harych et al., 2020]. The bond lengths between the sodium atom and the oxygen atom of the aminoalkoxide are 2.3736 (10) Å for Na1-O2 and 2.2970 (10) Å for Na1-O1, which is in accordance with a similar compound in the literature with bond lengths of 2.239 (2) and 2.352 (2) Å (Marszałek-Harych et al., 2020). Moreover, the bond lengths between the sodium atom and the oxygen atoms of the isopropanols are 2.3905 (10) Å (Na1-O4) and 2.2998 (10) Å (Na1-O3). A similar compound in the literature exhibits an Na-O bond length of 2.402 (6) Å and is therefore much longer (Edema et al., 1991). The bond angles N1-Na1-O1 and N1-Na1-O2 are 73.22 (3) and 69.39 (3) , respectively. Compared to a bond angle in the literature of 66.7 (4) (Schü ler et al., 2019), the angles in the title structure are much wider. That might be traced back to the fact that the angles are limited because of the rigid structure of the aminoalkoxide. As the coordination sphere of the sodium atom is arranged like a trigonal bipyramid, the bond angles correspond to this. One isopropanol molecule is arranged in the triangular sphere around the sodium and therefore exhibits an angle of 109.84 (4) for N1-Na1-O3. The other isopropanol is arranged in the opposite pyramid site of the amine function and shows an angle of 160.83 (4) for N1-Na1-O4, respectively. In this dimeric structure, the two sodium centers are bridged by isopropanol molecules. From the hydrogen atoms of the isopropanol, a hydrogen bond to the oxygen atoms of the aminoalkoxide is formed. Details of the hydrogen bonding are given in Table 3. As hydrogen bonds are present in the compound, it can be shown that the aminoalkoxide oxygen is more acidic than the alcohol function of the isopropanol. The graph-set motifs of the hydrogen bonds a and b are R 2 2 (8) and R 2 2 (8), respectively, and are shown in Fig. 3 (Mercury; Macrae et al., 2020). In addition, a Hirshfeld surface analysis has been carried out with a d norm property over a range of À0.7978 to +1.3992 a.u. The characteristic red spots in Fig. 4 Table 3 Hydrogen-bond geometry (Å , ) for 2.

Figure 3
View of the unit cell of 2, Hydrogen bonding is shown and the graph-set motifs are labelled (Mercury; Macrae et al., 2008). Symmetry operation a = 1 À x, 1 À y, 1 À z.
109.84 (4) N1-Na1-O4 160.83 (4) In 1 as well as in 2, the alcohol characterizes the structural motif. In 1, the isopropanol is crucial for the saturation of the coordination sphere of the lithium atoms. In addition, it serves not only as the anionic part, but also as a ligand. In 2, the isopropanol is located opposite the nitrogen of the aminoalkoxide. It serves as a ligand that bridges the dimeric structure by hydrogen bonding. Therefore, alcohols affect the structural motifs and thus interact with the reagents.

Supramolecular features
The title compound [Li 7 (i-PrO) 3 (C 4 H 10 NO) 3 ] 2 O (1) is a dimeric molecule where the asymmetric unit is half of the molecule and the full structure is build up by a twofold rotation axis. It is packed parallel to the ac plane and to the bc plane, as shown in Fig. 5. The second title compound, [Na(i-PrOH) 2 (C 8 H 18 NO 2 )] 2 (2), is also a dimeric molecule, the asymmetric unit being half of an inversion symmetric aggregate. The molecules are packed parallel to the ab plane and the bc plane.

Database survey
Other examples of crystallographically characterized complexes containing an alkali metal center and a directly to the metal center coordinated isopropanol are C 40 H 88 Cr 2 Na 4 O 12 (Edema et al., 1991) (Kroesen et al., 2017). A very rare example is C 32 H 80 Li 8 N 8 O 8 (Andrews et al., 2002), because the crystallographically characterized complex contains the same aminoalkoxide used in 1. Furthermore, crystallographically characterized sodium complexes containing an aminoalkoxide are C 16 H 34 N 2 NaO 6 I (Fronczek et al., 1983) (Hevia et al., 2006) and C 35 H 58 N 4 Na 2 O 4 (Hevia et al., 2006). In addition, a crystallographically characterized complex containing a pentacoordinated sodium atom and amine and oxygen functions as ligands are C 50 H 88 N 2 Na 2 O 6 , C 74 H 104 N 2 Na 2 O 6 and C 48 H 80 N 2 Na 2 O 8 (Marszałek-Harych et al., 2020).

Synthesis and crystallization
Compound 1 [Li 7 (i-PrO) 3 (C 4 H 10 NO) 3 ] 2 O: Dimethylamino ethanol (100 mg, 1.12 mmol, 1.0 eq.) was added to 1.0 mL of diethyl ether and cooled to 195 K. After that, n-butyllithium in hexane (c = 2.5 mol L -1 , 0.9 mL, 2.24 mmol, 2.0 eq.) was added dropwise and 0.5 mL of benzene were added for crystallization. The reaction mixture was left to stand for 15 min, while warming up to 218 K. Then it was stored at 193 K in the coolant isopropanol. Colorless crystals were formed after 45 d. During storage, the coolant isopropanol seems to have diffused into the vessel, leading to the incorporation of isopropanol in the crystal structure of compound 1.
Compound 2 [Na(i-PrOH) 2 (C 8 H 18 NO 2 )] 2 : Sodium-N-methyl(2-methoxyethylamino)-2-methyl-2-propanoxide (49.5 mg, 0.27 mmol, 1.0 eq.) was dissolved in 2.0 mL of diethyl ether and cooled to 195 K. Then n-butyllithium in hexane (c = 2.5 mol L -1 , 0.13 mL, 0.33 mmol, 1.2 eq.) was added and the reaction mixture was left to stand in the cooling bath for 15min. The reaction mixture warmed up to 218 K and was then stored at 193 K in the coolant isopropanol. Colorless crystals were formed after 60 d. During the storage, the coolant isopropanol seems to have diffused into the vessel, leading to the incorporation of isopropanol in the crystal structure of compound 2.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All of the hydrogen atoms were placed in geometrically calculated positions and were each assigned a fixed isotropic displacement parameter based on a riding-model: C-H = 0.98-1.0 Å with U iso (H) = 1.5U eq (Cmethyl) and 1.2U eq (C) for other H atoms. Apart from this, the O-bound hydrogen atoms of compound 2 were located in the difference-Fourier maps and refined independently. In compound 1, benzene appeared as co-crystallate, but was suppressed by solvent masking because of strong disorder. View of the crystal packing of 1 parallel to the ac plane and the bc plane. SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Hexakis[µ 3 -2-(dimethylamino)ethanolato]hexa-µ 2 -isopropanolato-µ 4 -oxido-tetradecalithium(I) (1)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.