This review provides an overview of the catalytic activity of iron complexes of nitrogen ligands in driving carbene transfers towards CC, C–H and X–H bonds. The reactivity of diazo reagents is discussed as well as the proposed reaction mechanisms.
The cost-effective TPPH 2 /TBACl-catalyzed (TPPH 2 = dianion of tetraphenyl porphyrin; TBACl = tetrabutyl ammonium chloride) carbon dioxide cycloaddition to N-aryl aziridines was successful in synthesizing N-aryl oxazolidin-2-ones. A catalytic tandem reaction was also developed, in which N-aryl aziridines were initially synthesized and then reacted with carbon dioxide without being purified.The procedure occurred with a very high atom economy, molecular nitrogen being the only by-product of the entire tandem process. In addition, the mechanism of catalytic cycle was investigated by DFT calculations.
The direct insertion of carbon dioxide (CO2) into three-membered rings, such as epoxides and aziridines, represents a relevant strategy to obtain cyclic carbonates and oxazolidinones, which are two useful classes of fine chemicals. The synthesis of these compounds can be efficiently catalyzed by a combination of metal porphyrin complexes and various co-catalysts in homogeneous systems. The catalytic efficiency of these systems is discussed herein by taking into account both the characteristics of the metals and the nature of the co-catalysts, either when used as two-component systems or when combined in bifunctional catalysts. Moreover, mechanistic proposals of the CO2 cycloaddition processes are reported to provide a rationale of catalytic cycles in order to pave the way for designing more active and efficient catalytic procedures.
The cycloaddition of CO 2 to N-alkyl aziridines was efficiently promoted by the convenient TPPH 2 /TBACl binary catalytic system. The metal-free procedure was effective for the synthesis of differently substituted N-alkyl oxazolidin-2-ones in yields up to 100 % and excellent regioselectivities (up to 99 %). The mechanism of the reaction was proposed based on a DFT study which indicated the formation of an adduct between TPPH 2 and TBACl as the effective catalytic active species.
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