Publication Date:
2017-07-24
Description:
With the synthesis of ortho -phenylene phosphino-tritylium cations as an objective, we generated (2-lithiophenyl)diphenylphosphine and (2-lithiophenyl)di-isopropylphosphine and allowed these organolithium reagents to react with benzophenone. The resulting phosphino-triarylcarbinols were allowed to react with HBF 4 in the presence of trifluoroacetic anhydride in order to generate the corresponding cations. Instead of the targeted ortho -phenylene phosphino-tritylium, the cations formed in these reactions were identified as the four-membered phosphonium species 7,7-bis(phenyl)-8,8-bis(phenyl)-7-phosphoniabicyclo[4.2.0]octa-1,3,5-triene ( 3 + ) and 7,7-bis(phenyl)-8,8-bis(isopropyl)-7-phosphoniabicyclo[4.2.0]octa-1,3,5-triene ( 4 + ), which were both isolated as tetrafluoroborate salts. The structure of these compounds has been confirmed by X-ray analysis. These new cations are thermally unstable and isomerize into the corresponding 5,10-dihydro-5,5-diphenyl-10-phenyl-acridophosphinium ( 5 + ) and 5,10-dihydro-5,5-di(isopropyl)-10-phenyl-acridophosphinium ( 6 + ) as tetrafluoroborate salts. These reactions suggest the involvement of ortho -phenylene phosphino-tritylium cations, which would be obtained by dissociation of the R 3 P + –CAr 3 bonds in 4 + and 5 + . This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.
Print ISSN:
1364-503X
Electronic ISSN:
1471-2962
Topics:
Mathematics
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Physics
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Technology
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