Cycloaddition of diazoacetates to C60 fullerene catalysed by Pd complexes

Abstract

An efficient catalytic method of the cycloaddition to C 60 fullerene of the diazoacetates, containing substituents of diverse structures in ester groups, in the presence of a Pd based three component catalyst was developed. An influence of nature and the structure of substi tuent in the ester group on the activity of diazoacetates in the reaction with C 60 was studied. Yields of respective cycloadducts were determined.An interest in carboxy derivatives of methanofullerenes is caused by a possibility of obtaining of promising prepa rations for medicine and agriculture on their base. 1-5 However, a synthesis of these C 60 derivatives containing substituents in the ester group consists in multi stage con version of carboxymethanofullerene which results in low yields of the target products. 1,3,6-9Recently, an efficient catalytic method of cycloaddi tion of diazoacetic ester and α substituted ethyl diazoace tates to the C 60 fullerene using the three component cata lyst Pd(acac) 2 -PPh 3 -Et 3 Al (20 mol.%) was suggest ed. 10,11 As it is noted, by a ratio of the starting components of catalytic system and the nature of the substituent in α position to the diazo group of the initial diazoacetate, it is possible to definitely regulate a direction of the cycload dition and to selectively obtain both methanofullerenes and homofullerenes.In order to develop our earlier elaborated 10,11 method of the catalytic cycloaddition of the diazoacetates to the C 60 fullerene under the action of catalysts on a basis of low valent Pd complexes, as well as to investigate the in fluence of the structure of substituent in the ester group of diazoacetate on the direction and the structural selectivity of the reaction of the latters with the fullerene C 60 , we studied the cycloaddition of diazoacetates with alkyl, cycloalkyl, allyl, and steroid substituents to the fullerene C 60 catalysed by Pd(acac) 2 -PPh 3 -Et 3 Al (1 : 2 : 4) Results and DiscussionIt was earlier shown, 11 that the influence of nature and substituent structure in the α substituted ethyl diazoace tates on the selectivity of formation of homo and methano fullerenes in the reaction with C 60 is most evident when the three component catalyst Pd(acac) 2 -PPh 3 -Et 3 Al (components molar ratio is 1 : 2 : 4, respectively) is used. During the cycloaddition using the components molar ra tio of this catalytic system equal to 1 : 4 : 4, only the meth anofullerenes were formed regardless of the substituent structure in the diazo compound. Therefore, all the fol lowing experiments were carried out using the catalytic system Pd(acac) 2 -PPh 3 -Et 3 Al (1 : 2 : 4) with a purpose of more detailed study of the influence of the structure of initial diazoacetates on the composition of the cyclo adducts formed.In a reaction of isopropyl diazoacetate with the fullerene C 60 (molar ratio 5 : 1) in the presence of 20 mol.% of three component catalyst Pd(acac) 2 -PPh 3 -Et 3 Al (1 : 2 : 4) in 1,2 dichlorobenzene at 80 °C, in 1 h a mixture of [6,6] closed (1) and two stereoisomeric [5,6] open...

Catalytic cycloaddition of diazoalkanes with heterocyclic substituents to fullerene C60

“…The use of metal complex catalysts makes it possible to direct the cycloaddition of diazo compounds to fullerenes toward formation of individual methanofullerenes. Complexes based on palladium and rhodium were reported to successfully catalyze reactions of fullerene C 60 with diazomethanes [3], diazoacetates [4][5][6][7], and diazo ketones [8-10], and the corresponding cyclopropafullerenes were obtained with high selectivity.We recently showed that homofullerenes and spiro homofullerenes can be synthesized with high selectivity by reaction of C 60 with monosubstituted diazomethanes and cyclic diazoalkanes generated in situ by oxidation of the corresponding hydrazones in the presence of Pd(acac) 2 -PPh 3 -Et 3 Al as catalytic system [11][12][13][14][15][16]. We thus obtained pure [5,6]-open cycloadducts in which bulkier substituent was located above the five-membered fragment of C 60 .…”

“…The use of metal complex catalysts makes it possible to direct the cycloaddition of diazo compounds to fullerenes toward formation of individual methanofullerenes. Complexes based on palladium and rhodium were reported to successfully catalyze reactions of fullerene C 60 with diazomethanes [3], diazoacetates [4][5][6][7], and diazo ketones [8][9][10], and the corresponding cyclopropafullerenes were obtained with high selectivity.…”

Sulfur-Containing Homo- and Methanofullerenes: Synthesis and Study of Tribological Properties

“…As a follow-up to the ongoing work in our group [13][14][15][16][17][18][19][20] related to the selective functionalization of C 60 -fullerene with diazo compounds, we studied the catalytic cycloaddition reaction of sulfur-containing diazoalkanes generated in situ by the oxidation of hydrazones of the corresponding ketosulfides with MnO 2 to C 60 . Of the tested catalysts based on salts 2 of 11 and compounds of Cu, Pd, and Rh, the three-component catalyst prepared in situ from Pd(acac) 2 , PPh 3 , and Et 3 Al, taken in a ratio of 1:2:4, respectively, showed the highest activity in the reaction of diazoalkanes and C 60 -fullerene.…”