Synthesis of a Trivalent P-Chloro-Dithienophosphole and its Reactivity with Organometallic Reagents

P-chloro-dithieno[3,2-b:2’,3’-d]phosphole was synthesized and isolated from the reaction of an aminophosphole and HCl. Developed to act as a common starting material for P-functionalized phospholes, the compound exhibits a surprising reactivitiy by generating dimeric biphospholes. Despite this apparent sensitivity, when reacting with organolithium and Grignard reagents, a series of differently P-functionalized dithieno[3,2-b:2’,3’-d]phospholes was accessible. Unexpectedly, organolithium reagents showed reduced reactivity with the chlorophosphole, limiting yields of the desired products due to the competing dimerization. Nonetheless, P- functionalized phospholes were isolated from reactions of the title compound with both Grignard and organolithium reagents in yields equivalent to, or higher, than by previous methods. A bithiophene- bridged bisphosphole system was also successfully synthesized without the necessity of generating a bis(dichlorophosphino) reagent. Finally, the isolated P-functionalized phospholes were analyzed for their photophysical properties. In general, these compounds are strong absorbers in the UV/visible range of the optical spectrum. The phospholes’ emissions were consistent with several previously reported, however, typically with low quantum yields.