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    Pentacoordinated organoaluminum complexes: A computational insight

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    Type
    Article
    Authors
    Milione, Stefano
    Milano, Giuseppe
    Cavallo, Luigi cc
    KAUST Department
    KAUST Catalysis Center (KCC)
    Physical Sciences and Engineering (PSE) Division
    Chemical Science Program
    Date
    2012-12-24
    Permanent link to this record
    http://hdl.handle.net/10754/562464
    
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    Abstract
    The geometry and the electronic structure of a series of organometallic pentacoordinated aluminum complexes bearing tri- or tetradentate N,O-based ligands have been investigated with theoretical methods. The BP86, B3LYP, and M06 functionals reproduce with low accuracy the geometry of the selected complexes. The worst result was obtained for the complex bearing a Schiff base ligand with a pendant donor arm, aeimpAlMe2 (aeimp = N-2-(dimethylamino)ethyl-(3,5-di-tert-butyl)salicylaldimine). In particular, the Al-Namine bond distance was unacceptably overestimated. This failure suggests a reasonably flat potential energy surface with respect to Al-N elongation, indicating a weak interaction with probably a strong component of dispersion forces. MP2 and M06-2X methods led to an acceptable value for the same Al-N distance. Better results were obtained with the addition of the dispersion correction to the hybrid B3LYP functional (B3LYP-D). Natural bond orbital analysis revealed that the contribution of the d orbital to the bonding is very small, in agreement with several previous studies of hypervalent molecules. The donation of electronic charge from the ligand to metal mainly consists in the interactions of the lone pairs on the donor atoms of the ligands with the s and p valence orbitals of the aluminum. The covalent bonding of the Al with the coordinated ligand is weak, and the interactions between Al and the coordinated ligands are largely ionic. To further explore the geometrical and electronic factors affecting the formation of these pentacoordianted aluminum complexes, we considered the tetracoordinated complex impAlMe2 (imp = N-isopropyl-(3,5-di-tert-butyl)salicylaldimine)), analogous to aeimpAlMe 2, and we investigated the potential energy surface around the aluminum atom corresponding to the approach of NMe3 to the metal center. At the MP2/6-31G(d) level of theory, a weak attraction was revealed only when NMe3 heads toward the metal center through the directions trans to the nitrogen atom. The analysis of the binding energies for this adducts revealed that the formation of the pentacoordinated derivative is a result of a subtle balance between the penalty paid to deform the impAlMe2 complex and energy gain resulting from interaction between the two fragments. © 2012 American Chemical Society.
    Publisher
    American Chemical Society (ACS)
    Journal
    Organometallics
    ISSN
    02767333
    DOI
    10.1021/om300689g
    ae974a485f413a2113503eed53cd6c53
    10.1021/om300689g
    Scopus Count
    Collections
    Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC)

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