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      Cooperative Activation of Isocyanates by Al-N-Based Active Lewis Pairs and the Generation of a C5 Chain by Simultaneous Formation of Two C-C Bonds.

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          Abstract

          The active Al/N Lewis pair, (Me3 C)2 Al-C(SiMe3 )=C(H)-N(CHMe-CH2 )2 CH2 (2), reacted with isocyanates to afford a fascinating variety of products. One equivalent of Ph-N=C=O yielded by the release of H-C≡C-SiMe3 an urea-type ligand which coordinated the Al atom in a chelating manner (4). Dipp-N=C=O gave a similar product, but the bulky substituent hindered the approach of the N-aryl group to Al. A situation similar to that of frustrated Lewis pairs resulted in the coordination of the alkyne to the Al and N atoms (6) by C-H bond activation. Dual insertion was observed upon treatment of 2 with two equivalents of isocyanates (8 to 11). The preferred formation of cyclic oligomers is prevented by the specific cooperative properties of the Lewis pair. A metal-free dimeric isocyanate (13) was formed by hydrolysis. Replacement of the CMe3 groups in 2 by less bulky isobutyl groups (7) afforded the insertion of two isocyanate molecules into the Al-vinyl bonds without alkyne elimination. The resulting highly functionalised compound had a chain formed by two isocyanates and the organic backbone of the Lewis pair. Me3 C-N=C=O and 2 afforded a unique compound (14) in which an isocyanate ligand connects two molecules of 2 by the release of dimethylpiperidine. The combination of a C1 building block and two C2 groups gave an unsaturated branched C5 moiety by the simultaneous formation of two C-C bonds. The molecular structure showed an interaction between an Al atom and a C-C π-bond.

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          Author and article information

          Journal
          Chemistry
          Chemistry (Weinheim an der Bergstrasse, Germany)
          Wiley-Blackwell
          1521-3765
          0947-6539
          May 02 2017
          : 23
          : 25
          Affiliations
          [1 ] Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
          [2 ] Organisch-chemisches Institut and Center for Multiscale Theory and Computation (CMTC), Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149, Münster, Germany.
          Article
          10.1002/chem.201604630
          28079943
          6a4e58b6-2856-4a68-a91f-e2f41cd5020e
          History

          C−C bond formation,Lewis pairs,aluminium,bond activation,density functional calculations,isocyanates

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