title: Cooperative Activation of Isocyanates by Al-N-Based Active Lewis Pairs and the Generation of a C5Chain by Simultaneous Formation of Two C-C Bonds.
abstract: The active Al/N Lewis pair, (Me3C)2Al-C(SiMe3)=C(H)-N(CHMe-CH2)2CH2(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-SiMe3an 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 CMe3groups 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. Me3C-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 C1building block and two C2groups gave an unsaturated branched C5moiety 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.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Martinewski
authors.affiliation: Organisch-chemisches Institut and Center for Multiscale Theory and Computation (CMTC), Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149, Münster, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Holtrichter-Rößmann
authors.affiliation: Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Rösener
authors.affiliation: Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Hepp
authors.affiliation: Organisch-chemisches Institut and Center for Multiscale Theory and Computation (CMTC), Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149, Münster, Germany.
authors.forename: Ernst-Ulrich
authors.identifier: http://orcid.org/0000-0003-1327-3721
authors.initials: EU
authors.lastname: Würthwein
authors.affiliation: Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
authors.forename: Werner
authors.identifier: http://orcid.org/0000-0002-7178-5517
authors.initials: W
authors.lastname: Uhl
keywords: C−C bond formation; Lewis pairs; aluminium; bond activation; density functional calculations; isocyanates