N-Heterocyclic phosphenium cations: syntheses and cycloaddition reactions.
June 28th, 2008 | by admin |N-Heterocyclic phosphenium cations: syntheses and cycloaddition reactions.
A series of trifluoromethanesulfonate (OTf) salts of N-heterocyclic phospheniums (NHP) bearing phenyl (), para-methoxyphenyl (), 2,6-diisopropylphenyl () and mesityl () substituents is reported. The compounds are made by a modification to a literature procedure that improves the overall yields for and by 15 and 23%, respectively. Two unwanted side-products in the synthesis of , the diammonium salt, [(2,6-iPr-C(6)H(3))N(H)(2)CH(2)CH(2)N(H)(2)(2,6-iPr-C(6)H(3))]Cl(2) () and the bisphosphine (2,6-iPr-C(6)H(3))N(PCl(2))CH(2)CH(2)N(PCl(2))(2,6-iPr-C(6)H(3)) (), are crystallographically characterized, as is the intermediate cyclic chlorophosphine, C1P[upper bond 1 start]N(4-OMe-C(6)H(4))CH(2)CH(2)N[upper bond 1 end](4-OMe-C(6)H(4)) (). The phenyl-substituted NHP is fully characterized, including by X-ray crystallography, for the first time; this compound contains a short P-O contact of 2.1850(14) A. Cycloaddition reactions of with 2,3-dimethyl-1,3-butadiene give the expected spirocyclic phospholeniums, 7,8-dimethyl-1,4-diaryl-1,4-diaza-5-phopshoniaspiro[4.4]non-7-ene, as their OTf salts (), while reactions with N,N\’-dimesityl-1,4-diaza-1,3-butadiene give, except in the case of , which is too bulky to react, the aza analogues, 1,4-dimesityl-6,9-diaryl-1,4,6,9-tetraaza-5-phosphoniaspiro[4.4]non-2-ene (, and ). The sterically congested is in thermal equilibrium with and free diazadiene, and undergoes a substitution reaction with 2,3-dimethyl-1,3-butadiene to give .
Caputo CA, Price JT, Jennings MC, McDonald R, Jones ND.
Department of Chemistry, The University of Western Ontario, London, Ontario, CanadaN6A 5B7.