Abstract
The mechanism of the carbonylation of diazomethane in the presence of iron–carbonyl–phosphine catalysts has been investigated by means of DFT calculations at the M06/def-TZVP//B97D3/def2-TZVP level of theory, in combination with the SMD solvation method. The reaction rate is determined by the formation of the coordinatively unsaturated doublet-state Fe(CO)3(P) precursor followed by the diazoalkane coordination and the N2 extrusion. The free energy of activation is predicted to be 18.5 and 28.2 kcal/mol for the PF3 and PPh3 containing systems, respectively. Thus, in the presence of less basic P-donor ligands with stronger -acceptor properties, a significant increase in the reaction rate can be expected. According to energy decomposition analysis combined with natural orbitals of chemical valence (EDA–NOCV) calculations, diazomethane in the Fe(CO)3(phosphine)(η1-CH2N2) adduct reveals a -donor–-acceptor type of coordination.
Highlights
Ketenes are important and versatile intermediates in synthetic organic chemistry [1,2,3,4,5]
The secondary purpose of this paper is to interpret the electronic structure of reaction intermediates and classify their donor–acceptor character using energy decomposition analysis combined with the natural orbitals of chemical valence (EDA–NOCV) as well as the natural bond orbital (NBO) methodology
The strong acceptor property of the pathway between complex 3F1 and ·Fe(CO)3 (PF3) ligand results in a shorter Fe−P, C=O, and an elongated Fe−C bond in 1F, as compared to those in the complex 1P with PPh3
Summary
Ketenes are important and versatile intermediates in synthetic organic chemistry [1,2,3,4,5]. They can form various carboxylic acid derivatives, such as esters, anhydrides, and amides reacting readily with alcohols, carboxylic acids, or primary amines, respectively [6]. The reactive ethoxycarbonyl ketene can be trapped in situ by various scavengers such as alcohols, amines, and imines affording the corresponding malonic acid derivatives or β-lactams, respectively [9]. In the co-catalyzed domino reaction of ethyl diazoacetate (EDA) with CO, in the presence of ferrocenylimines, the synthesis of unsaturated malonic acid derivatives has been reported [10,11]. No other similar results were published, despite the potential synthetic importance of the diazocarbonylation reaction
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