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)(2)Cp, C[=W(CO)(5)]OLi(THF)(3), CPh2OH, PPh2, P(O)Ph-2). 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 P-31 NMR signals after complexation of the low-coordinated phosphorus atom by W(CO)(5) attest that the ligands are stronger acceptors than donors.