Metalated 1,3-Azaphospholes:  Structure and Reactivity of 2-Lithio-1-methyl-1,3-benzazaphosphole, an Isolable −PC(Li)−NR Heterocycle

The preparation, NMR data, a crystal structure, and the reactivity of isolable 2-lithio-1,3-benzazaphospholes are described. The compounds are or belong to the most stable PCLi species, although they lack steric congestion. Reactions with organoelement or organometal halides W(CO)₆ as well as with CO₂ or benzophenone allow access to various novel functionally substituted 1,3-benzazaphospholes (2-R = SnMe₃, Fe(CO)₂Cp, C[W(CO)₅]OLi(THF)₃, CPh₂OH, PPh₂, P(O)Ph₂). The crystal structure of the tungsten-carbene derivative is described. Attempts to lithiate and functionalize a 1,3-benzazaphosphole P−W(CO)₅ complex failed, but reactions of 1-methyl-2-stannyl- and 1-methyl-2-phosphino-1,3-benzazaphosphole with W(CO)₅(THF) furnished examples for a 2-metalated benzazaphosphole P−W(CO)₅ complex and the preferred complexation of the phosphino substituent, respectively. The considerable upfield shifts of the ³¹P NMR signals after complexation of the low-coordinated phosphorus atom by W(CO)₅ attest that the ligands are stronger acceptors than donors.