Ruthenium Porphyrin Catalyzed Synthesis of Oxazolidin‐2‐ones by Cycloaddition of CO₂ to Aziridines

Abstract

The reaction between N-substituted-2-arylaziridines and CO 2 is efficiently promoted by ruthenium(VI) imidoporphyrin complexes and yields a mixture of 5-aryl (A) and 4-aryl (B) substituted oxazolidin-2-ones with a regioisomeric A/B ratio up to 99:1. Several oxazolidin-2-one molecules were synthe- [a]

Synthesis of cyclic carbonates by ruthenium(VI) bis-imido porphyrin/TBACl-catalyzed reaction of epoxide with CO2

“…All the other starting materials were commercial products and used as received. Analytical data of cyclic carbonates 2, 6-12 [41,42] and oxazolidinone 13 [35] were in accordance with those reported in literature. NMR spectra were recorded at room temperature either on a Bruker Avance 300-DRX, operating at 300 MHz for 1 H and at 75 MHz for 13 C , or on a Bruker Avance 400-DRX spectrometers, operating at 400 MHz for 1 H and at 100 MHz for 13 C. Chemical shifts (ppm) are reported relative to TMS.…”

“…In our previously published paper on the CO 2 cycloaddition to aziridines catalysed by Ru(TPP)(NAr) 2 (1)/TBACl binary system, we reported the formation of the deactivated Ru(TPP)(NAr)(ArNCOO -TBA + ) complex (14) at the end of the catalytic reaction. [35] The formation of this latter complex indicated that the imido axial ligand on the ruthenium atom was able to interact with CO 2 thanks to the high electron density on the nitrogen atom, as already indicated by our previous DFT study. [36] The formation of complex 14 was also detected by ESI-MS at the end of the catalytic reaction forming cyclic carbonate 2.…”

“…[36] The formation of complex 14 was also detected by ESI-MS at the end of the catalytic reaction forming cyclic carbonate 2. Analogously to what was observed in the case of the oxazolidinone synthesis, [35] ruthenium complex 14 was catalytically inactive when used in combination with TBACl for promoting the synthesis of 2, which was formed with the same conversion and selectivity values as achieved in the presence of TBACl alone (see Table 1 Unfortunately, any attempt to detect the adduct A between CO 2 and complex 1 as well as products containing chlorine atoms, which derive from the TBACl decomposition forming 14, have failed up to now. Even if the mechanism showed in Scheme 4 is not fully supported by experimental data, the isolation of compound 14 at the end of the catalytic reaction strongly indicated the reactivity of ruthenium imido nitrogen atoms towards carbon dioxide.…”

“…[18,[32][33][34] Albeit the acidic nature of the catalyst is usually necessary to maximise the reaction performance, we recently reported that the 'non-acidic' bis-imido porphyrin complex Ru(TPP)(NAr) 2 (1) (TPP = dianion of tetraphenyl porphyrin, Ar =3,5-(CF 3 ) 2 C 6 H 3 ), in combination with a tetrabutyl ammonium salt (TBAX), promoted the oxazolidinone synthesis by the cycloaddition of CO 2 to aziridines. [35] Although the reaction mechanism has not been studied in detail, preliminary results showed that the nitrogen atom of the axial imido ligand on the ruthenium centre may activate CO 2 molecule. The metal centre, being coordinatively saturated, doesn't interact with aziridine.…”

“…All the solvents were dried by using standard procedures unless where it is specified. 3,5-Bis(trifluoromethyl)phenyl azide, [37] 3,5-bis(nitro)phenyl azide, [37] Ru(TPP)CO (TPP = dianion of tetraphenyl porphyrin), [38] Ru(TPP)(NAr) 2 (1) (Ar = 3,5-(CF 3 ) 2 C 6 H 3 ), [39] Ru(TPP)(NAr') 2 (3) (Ar' = 3,5-(NO 2 ) 2 C 6 H 3 , [40] Ru(F 20 TPP)(NAr) 2 (4) (F 20 TPP = dianion of tetrapentafluorophenyl porphyrin), [35] and Ru(TMP)(NAr) 2 (5) (TMP = dianion of tetramesityl porphyrin) [35] were synthesised by methods reported in literature or by using minor modifications of them. All the other starting materials were commercial products and used as received.…”