Exploring the chemistry of backbone amino(chloro)phosphanyl-substituted imidazole-2-thiones.

Backbone (R'2N)2P-substituted imidazole-2-thiones 2a-c [(R'2N)2P-IMSR,R; IMSR,R = 1,3-dialkylimidazole-2-thione-4-yl, a: R = iPr, R' = Et; b: R = Mes, R' = Et, c: R = Me, R' = iPr] were treated with PCl3 to synthesize R'2N(Cl)P-substituted imidazole-2-thiones 3a-c [R'2N(Cl)P-IMSR,R]. The P-chloro compounds 3a,b were used to explore the chemistry further, i.e. nucleophilic substitution at phosphorus using Ph2CHLi or fluorenyl lithium afforded compounds 4a-c [R'2N(R'')P-IMSR,R; a: R = iPr, R' = Et, R'' = PH2CH; b: R = Mes, R' = Et, R'' = Flu c: R = iPr, R' = Et, R'' = Flu]. Compound 4c was used to access the P-borane adduct 5 [R'2N(R'')(BH3)P-IMSR,R; R = iPr, R' = Et, R'' = Flu] and phosphinoyl-substituted imidazolium hydrogensulfate 6 [[R'2N(R'')(O)P-IMHR,R]HSO4; IMHR,R = 1,3-dialkylimidazolium-4-yl, R = iPr, R' = Et, R'' = Flu]. Compounds 4a,b were transformed into the P-Cl compounds 7a,b [R''(Cl)P-IMSR,R; a: R = iPr, R'' = Ph2CH; b: R = Mes, R'' = Flu] which represent potential starting materials for backbone phosphaalkenyl substituted imidazole-2-thiones. Compound 7a yielded the NHC-stabilized phosphenium salt 8 [[R''(IMe4)P-IMSR,R]Cl; R = iPr, R' = Et, R'' = Ph2CH, IMe4 = 1,3,4,5-tetramethylimidazole-2-ylidene] in reaction with 1,3,4,5-tetramethylimidazole-2-ylidene (IMe4). Attempts to deprotonate 7a,b using nBuLi revealed that nucleophilic substitution of P-Cl to give the P-nBu product occurred preferentially, and dehydrochlorination to the phosphaalkene was not observed.