Dötz Benzannulation Reactions: Heteroatom and Substituent Effects in Chromium Fischer Carbene Complexes

Abstract

We have carried out a theoretical investigation of the Dötz reaction between acetylene and a series of chromium Fischer-type carbenes [(CO)(5)Cr=C(X)R] with different representative substituents (R=CH=CH(2), Ph) and heteroatom ligands (X=OH, NH(2), OCH(3), N(CH(3))(2)) by using density functional theory with the B3LYP functional. We have studied the Dötz and chromahexatriene mechanisms of benzannulation and also the reaction mechanism leading to cyclopentannulation. For the benzannulation, it was found that the most likely mechanism in the case of vinylcarbenes is the chromahexatriene route, whereas for phenylcarbenes, the Dötz route via a ketene intermediate is clearly the most favorable. The reactions leading to the cyclopentannulated and benzannulated products are more exothermic with vinylcarbenes than with phenylcarbenes and also more exothermic with alkoxycarbenes than with aminocarbenes. The relative stability of the cyclopentannulated products as compared with the benzannulated products increases for bulkier X substituents and on going from alkoxy- to aminocarbenes. The kinetic data concurs with the experimental product distribution found for vinylcarbenes, by which mainly benzannulated products are obtained, and dimethylaminophenylcarbenes, which lead exclusively to cyclopentannulated adducts.

Synthesis, Structure, and Electrochemistry of Fischer Alkoxy- and Aminocarbene Complexes of Tungsten: The Use of DFT To Predict and Understand Oxidation and Reduction Potentials

“…However, to maintain the classical low oxidation state of Fischer carbenes, the CO ligands should be substituted with neutral ligands. 7,8 Fischer carbenes are known to be electrophilic and are thus susceptible to nucleophilic attack on the carbene carbon. 4,7,9 Alkoxycarbenes are readily altered in this manner, which leads to the formation of amino, thio-and aryl-carbene complexes, respectively (reaction 3, Figure 1).…”

Fischer Carbene Complexes: A Glance at Two Decades of Research on Higher‐Order Cycloaddition Reactions

“…To the best of our knowledge, the current review is the first to focus exclusively on the participation of FCCs in the following higher‐order cycloadditions: [2+2+2+1], [3+2+2], [3+3], [4+2+1], [4+3], [5+2], [5+2+1], [6+2], [6+3], [8+2] and [8+3]. Although the Dötz reaction is regarded a higher‐order cycloaddition, it does not fall within the scope of the present review, [62–65] which focuses on all higher‐order reactions involving more than 6π electrons or over 6 atoms. A great effort was made not to omit any relevant information in the literature.…”

Joint Isotherm Calorimetric Titration–DFT Investigation of the Demethoxy-Amination of Fischer Carbenes

“…Supposedly, the rate and the reversibility of this step-wise reaction is determined by the nucleophilicity (or pK a values) of the amine in question. Intriguingly, although the mechanism of this reaction has been intensively investigated [29,[45][46][47][48] both experimentally and theoretically alongside other structure-reactivity relationship [49][50][51][52][53][54][55][56][57][58][59] evaluations of Fischer carbenes, little has been reported [48] about the actual thermochemistry of any transformation involving Fischer-type carbenes.…”