Theoretical and Synthetic Investigations of Carbodiimide Insertions into Al-CH3 and Al-N(CH3)2 Bonds

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DOIResolve DOI: http://doi.org/10.1021/ic048501z
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TypeArticle
Journal titleInorganic Chemistry
ISSN0020-1669
Volume44
Issue6
Pages19831991; # of pages: 9
AbstractCarbodiimides are known to insert into aluminum-carbon bonds to form four-membered bidentate amidinate chelate rings. Insertions into Al-R and Al-NR'2 (R, R' = alkyl) have been reported in the literature. We have devised a mechanism for these insertions and modeled it using density functional theory (DFT) calculations. The calculated barrier heights for competitive insertions show the insertion into Al-N(CH3)2 goes through a lower barrier than the reaction with Al-CH3 for diisopropyl carbodiimide due to the necessity of forming a pentavalent carbon intermediate in the Al-CH3 case. However, insertion into Al-CH3 has the lower barrier for the reaction with di-tert-butyl carbodiimide because of steric effects, which is consistent with the published experimental results. We have synthesized aluminum amidinates containing two and three acetamidinate rings via insertion of 2 and 3 equiv of diisopropylcarbodiimide into trimethylaluminum (TMA). The crystal structure for [CH3C(NiPr)2]2AlCH3 is reported. We have found that, although the first insertion is rapid at room temperature, the second and third insertions require refluxing above 70 C. We have calculated the barrier heights for the first and second insertion and have found that this is due to a higher barrier for the migration of the methyl group in the second insertion. This higher barrier is the result of the lack of an exergic precoordination of the carbodiimide to the metal center, which facilitates the first insertion.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada
Peer reviewedYes
Identifier10007817
NRC number122
NPARC number12339121
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Record identifier84528e31-1db2-4cfc-8af5-b30e07692270
Record created2009-09-11
Record modified2016-05-09
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