The reaction of electrophilic terminal phosphinidene complexes with benzophenone and fluorenone: The unexpected formation of six- and eight-membered heterocycles

Article abstract of DOI:10.1016/S0022-328X(96)06839-8

The phenylphosphinidene-pentacarbonyltungsten complex 2, as generated from the appropriate 7-phosphanorbornadiene complex 1, reacts at 60°C with benzophenone to give a benzo-annellated 1-oxa-2-phosphacyclohex-4-ene 2-oxide as a 1:1 mixture of two isomers 3a,b. The same phosphinidene complex 2 reacts at 120°C with fluorenone. A deoxygenation of fluorenone takes place leading to the bifluorenylidene 4 and to an eight-membered 1,2,8-oxadiphosphocane 2,8-dioxide 5. Both compounds 3b and 8 have been fully characterized by X-ray crystal structure analysis. The two reactions are interpreted as resulting from the initial formation of a P ... O Lewis adduct between the phosphinidene and the ketone.