Cooperative Activation of Isocyanates by Al–N‐Based Active Lewis Pairs and the Generation of a C 5 Chain by Simultaneous Formation of Two C–C Bonds

The active Al/N Lewis pair, (Me 3 C) 2 Al−C(SiMe 3 )=C(H)−N(CHMe‐CH 2 ) 2 CH 2 ( 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−SiMe 3 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 CMe 3 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. Me 3 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 C 1 building block and two C 2 groups gave an unsaturated branched C 5 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.