Theoretical Approach Towards the Understanding of Asymmetric Additions of Dialkylzinc to Enals and Iminals Catalysed by [2.2]Paracyclophane‐Based N,O‐Ligands

Abstract

The 1,2- and 1,4-asymmetric additions of dialkylzinc reagents (ZnMe(2) and ZnEt(2)) to cinnamaldehyde and N-formylbenzylimine catalysed by [2.2]paracyclophane-based N,O-ligands were studied with quantum chemical methods. High level LPNO-CEPA/1 (local pair natural orbital coupled electron pair approximation 1) calculations were performed to obtain reliable reaction barriers and binding energies. The calculations supported the experimentally observed selectivities. In the reaction, the alkyl transfer takes place on a binuclear zinc complex. Regioselectivity can be traced back to changes in π-conjugation. Because the less conjugated N-formylbenzylimine is more flexible, it is better suited for 1,4-additions. Moreover, bulky ligands were shown to be important for stereoselectivity. The reason is that the tricyclic motif present in the transition states is sterically less hindered in the anti conformation. Based on the LPNO-CEPA/1 data, a set of popular theoretical methods are validated. Although it was possible to set up a procedure to obtain the stereoselectivities with computationally less demanding methods, this was not possible for the regioselectivity of the reactions.

The activation strain model and molecular orbital theory

“…Conveniently, there is no special computer code required to perform activation strain analyses: all necessary quantities can be computed using any of the regular quantum‐chemical software packages available. As a result, the activation strain model has been applied by various research groups, on a range of chemical processes, such as nucleophilic substitution, cycloaddition, oxidative addition, isomerization, and many other processes from organic and organometallic chemistry.…”

Roadmap towards N‐Heterocyclic [2.2]Paracyclophanes and Their Application in Asymmetric Catalysis

“…Further investigations, for example, by Noyori and Soai,9,10 showed that catalysis with [2.2]paracyclophane zinc complexes having a nitrogen–oxygen coordination motif is feasible. In recent years, we combined the rigidity of the [2.2]paracyclophane backbone with novel metal coordinating moieties and described the asymmetric conjugate addition (ACA) of diethylzinc to cinnamaldehyde utilizing different [2.2]paracyclophane ligands 11–13. In this publication we present a series of new [2.2]paracyclophane derivatives bearing N‐heterocycles with various substitution patterns.…”

Near-Linear Scaling in DMRG-Based Tailored Coupled Clusters: An Implementation of DLPNO-TCCSD and DLPNO-TCCSD(T)

“…Nowadays, the PNO-based approaches are developed in number of groups including Werner [87][88][89][90] and Hättig [91][92][93] and widely applied to various systems of chemical interest [94][95][96][97][98][99][100][101][102][103] . Apart from single-reference methods, the LPNO and DLPNO methodologies were also successfully applied to multireference CC techniques [104][105][106][107]…”