| The capacity to reasonably describe theβ-dikentiminate aluminum compound system of several computational methods such as: HF/6-31G(d), B3LYP/6-31G(d), ONIOM(B3LYP/6-31G(d):AM1) , ONIOM(HF/6-31G(d): AM1) and semi empirical AM1 methods, has been evaluated. Though the full molecule B3LYP calculation result was proved most precise, the ONIOM(B3LYP/6-31G(d):AM1) method was found to be most efficient to optimize the molecular structures. It requires much less computational intensity than B3LYP method. So the ONIOM(B3LYP/6-31G(d):AM1) method was chosen as the main method of molecular structure optimization and frequency analysis, while the B3LYP/6-31G(d) method was employed to correct single point energy and investigate the electronic structure and the bonding situation.With that computational tactic, insertion reaction of CO into the complex of LAl[η2-(CSiMe3)2] (L=HC[(CMe)(NAr)]2,Ar=2,6-iPr2C6H3, 1) to yield LAl[η2-(CSiMe3)2] (L=HC[(CMe)(NAr)]2, Ar= 2,6-iPr2C6H3, 2), and into LAl[η2-(CPh)2](L=HC[(CMe)-(NAr)]2, Ar= 2,6-iPr2C6H3, 3) to yield LAl[C(O)C2Ph2](L =HC [(CMe) (NAr)]2, Ar = 2,6-iPr2C6H3, 4) were studied. We found the acylation reactions may be easily taken place due to their rather low reaction energy barriers and not great difference between frontier molecular orbitals. Another interesting thing is that, unlike the transition metal elements withσ-πbonding to the C(O), Al atom and carbon atom is linked together in the way of electrovalent, in which Al is with its 3 s orbital and carbon with its sp2 hybridized orbital, and the acylated compounds of Al may be more active than those analogues formed by transition metals.The compound LAl[C(O)C2Ph2](L =HC [(CMe) (NAr)]2, Ar = 2,6-iPr2C6H3, 4) react toward diphenylketone (COPh2) and TMSCN respectively to yield LAl[OC(Ph)2C(O)C2Ph2](L=HC[(CMe)(NAr)]2, Ar= 2,6-iPr2C6H3,5), and LAl[OSiMe3][C3(Ph)2CN](L=HC[(CMe) (NAr)]2, Ar = 2,6-iPr2C6H3, 6) were also studied. The NBO analysis and electronic density topology (AIM) analysis reveal that in compound 4, there is no feed-back bond between central Al atom and the carbonic C atom, as the Al has no d electron to interact with the COπ* orbital, and thus the C=O character is scarcely affected. The Al-C(O) bond can neither be ranked as the classic covalence bond nor the classic ionic bond, through which the electrons are transferred from Al to the carbonyl group while not affect the C=O structure. As a result, the positive charge distribute on the C atom decreased, the negative charge on O atom increased by a considerable extent, and therefore the whole acyl group take on the acyl anion character. The unique electronic structure of the carbonyl group, together with the steric effect ofβ-diketiminato ligand, make the process from the compound 4 to compound 6 actually two pathway equivalent with each other in energy and chiral symmetrical in structure.
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