{2,2′-[Ethane-1,2-diylbis(nitrilomethanylylidene)]diphenolato}(isopropanolato)aluminium dichloromethane hemisolvate

In the title compound, [Al(C16H14N2O2)(C3H7O)]·0.5CH2Cl2, the salen complex is monomeric and the dichlormethane solvent molecule lies on a crystallographic twofold axis. The central Al atom is fivefold coordinated and possesses a square-based pyramidal environment. The Al—OAlk(ipropyl) bond [1.7404 (14) Å] is much shorter than the Al—OAr(salen) bond lengths [1.7974 (15) and 1.8094 (14) Å]. The isopropyloxo group forms an intramolecular C—H⋯N hydrogen bond. In the crystal, the complex molecules are linked by weak C—H⋯O interactions.

This work was partially supported by the RFBR (12-03-00206_a) and a grant from the President of the Russian Federation to support the research of young Russian scientists and doctors (MD-3634.2012.3).

Comment
As a part of our investigation on chemistry of main group elements complexes based on tetradentate ligands (Karlov & Zaitseva, 2001) we obtained and studied the structure of the salen title compound [(salen) AlO-i Pr]. The aluminium complex is monomeric ( Fig. 1) with a fivefold coordinated Al centre. Its coordination geometry is close to square-based pyramidal with the salen ligand occupying the basal plane and the isopropyloxo group in axial position. It was shown, that the closely related methyloxo compound with an unsubstituted salen ligand [(MeO)(salen)Al] 2 is dimeric with two bridging µ 2 -alkyloxo ligands (Gurian et al. (1991)). In contrast, a similar compound with bulky trimethylphenoxo substituent (2,4,6-Me 3 C 6 H 2 O)(salen)Al exhibited monomeric nature (Atwood et al. (1997)). Also all Al compounds with substituted salen ligands, like widely studied complexes of bulky ( t Bu) 4 salen, are monomeric according to CSD data (Allen, 2002), surely due to the steric hindrances. Thus, it may be assumed that the nuclearity of aluminium complexes with an unsubstituted salen ligand depends on the size of the additional alkyloxo group. The isopropyloxo group forms an intramolecular hydrogen bond C1-H1A···N1 with H···N with 2.64 Å and C-H···N 116.0 (1)° that is connected with the mutual ecliptic arrangement of N1-Al1 and O3-C1 bonds.

Experimental
The title compound was obtained from reaction of equimolar amounts of Al(O-iPr) 3 and salen in toluene at reflux as a

Refinement
All hydrogen atoms were placed in calculated positions and refined using a riding model with C-H = 1.00 Å and U iso (H) = 1.2U eq (C) for methyne group; C-H = 0.99 Å and U iso (H) = 1.2U eq (C) for methylene groups; C-H = 0.98 Å and U iso (H) = 1.5U eq (C) for methyl groups; C-H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic H atoms.

Figure 1
The molecular structure of the title compound. Anisotropic displacement ellipsoids are shown at the 50% probability where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.32 e Å −3 Absolute structure: Flack (1983), 1872 Friedel pairs Absolute structure parameter: −0.09 (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.