Metalated 1,3-Azaphospholes:  Structure and Reactivity of 2-Lithio-1-methyl-1,3-benzazaphosphole, an Isolable −P&dbd;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&dbd;CLi species, although they lack steric congestion. Reactions with organoelement or organometal halides W(CO)<INF>6</INF> as well as with CO<INF>2</INF> or benzophenone allow access to various novel functionally substituted 1,3-benzazaphospholes (2-R = SnMe<INF>3</INF>, Fe(CO)<INF>2</INF>Cp, C[&dbd;W(CO)<INF>5</INF>]OLi(THF)<INF>3</INF>, CPh<INF>2</INF>OH, PPh<INF>2</INF>, P(O)Ph<INF>2</INF>). The crystal structure of the tungsten-carbene derivative is described. Attempts to lithiate and functionalize a 1,3-benzazaphosphole P−W(CO)<INF>5</INF> complex failed, but reactions of 1-methyl-2-stannyl- and 1-methyl-2-phosphino-1,3-benzazaphosphole with W(CO)<INF>5</INF>(THF) furnished examples for a 2-metalated benzazaphosphole P−W(CO)<INF>5</INF> 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)<INF>5</INF> attest that the ligands are stronger acceptors than donors.