Non‐Planar Structures of Sterically Overcrowded Trialkylamines

Autor: Manuel Heck, Tharallah Shoker, A. Daniel Boese, Andreas Ihle, Michael Wörle, Klaus Banert
Rok vydání: 2020
Předmět:
Zdroj: Chemistry (Weinheim an Der Bergstrasse, Germany)
Chemistry-A European Journal, 27 (11)
ISSN: 1521-3765
0947-6539
DOI: 10.1002/chem.202003933
Popis: Several amines with three bulky alkyl groups at the nitrogen atom, which exceed the steric crowding of triisopropylamine significantly, were synthesized, mainly by treating N‐chlorodialkylamines with Grignard reagents. In six cases, namely tert‐butyldiisopropylamine, 1‐adamantyl‐tert‐butylisopropylamine, di‐1‐adamantylamines with an additional N‐cyclohexyl or N‐exo‐2‐norbonyl substituent, as well as 2,2,6,6‐tetramethylpiperidine derivatives with N‐cyclohexyl or N‐neopentyl groups, appropriate single crystals were generated that enabled X‐ray diffraction studies and analysis of the molecular structures. The four noncyclic amines adopt triskele‐like conformations, and the sum of the three C−N−C angles is always in the range of 351.1° to 352.4°. Consequently, these amines proved to be structurally significantly flatter than trialkylamines without steric congestion, which is also signalized by the smaller heights of the NC3 pyramids (0.241–0.259 Å). There is no clear correlation between the heights of these pyramids and the degree of the steric crowding in the new amines, presumably because steric repulsion is partly compensated by dispersion interaction. In the cases of the two heterocyclic amines, the steric stress is smaller, and the molecular structures include quite different conformations. Quantum chemical calculations led to precise gas‐phase structures of the sterically overcrowded trialkylamines exhibiting heights of the NC3 pyramids and preferred molecular conformers which are similar to those resulting from the X‐ray studies.
Chemistry - A European Journal, 27 (11)
ISSN:0947-6539
ISSN:1521-3765
Databáze: OpenAIRE
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