Synthesis and reactivity of 2-iodophosphinines

The synthesis of 2-iodophosphinines 5 (a, parent compound; b, 4,5-dimethyl derivative) and of their pentacarbonyltungsten complexes 7 is described starting from dichloro-(diiodomethyl)phosphine (2), which was prepared via alkylation of phosphorus trichloride with (diiodomethyl)magnesium chloride (1). The halogen-metal exchange reactions of 5a/b and 7a/b are reported: the lithiation reactions of 5a/b with n-BuLi were not successful. In contrast, the complexes 7a/b were converted to the corresponding lithium derivatives 11a/b with n-BuLi in THF at -100 degrees C. Derivatization of 11a/b with triphenyltin chloride furnished 13a/b, respectively. The reaction of 5b with magnesium in THF at room temperature led to the formation of 3,4-dimethylphosphinine (18) (41.5%), 4,4',5,5'-tetramethyl-2,2'-biphosphinine (16) (1.3%), and 2-(iodomagnesio)-4,5-dimethylphosphinine (17) (19.2%); 37% of the starting material had decomposed. In a reaction with zinc, 5b gave the organozinc derivatives 20 or 21 in THF/TMEDA or DMF, respectively. The same zinc insertion procedures were applied to 7b but did not furnish the pentacarbonyltungsten complexes 22 or 24 in a clean fashion. However, 22 could be prepared via complexation of 20 with (acetonitrile)-pentacarbonyltungsten (6).