2,3-Benzo-7-phosphanorbornadiene Complexes: Synthesis and Chemistry

The reaction of benzyne with 3,4-dimethylphosphole pentacarbonylmolybdenum complexes affords the corresponding 2,3-benzo-7-phosphanorbornadiene complexes through [4+2] cycloaddition. The condensation takes place on the less hindered side of the phosphole ring corresponding to the phosphorus substituent as shown by the X-ray crystal structure analysis of the phenyl derivative (2). The strain at the bridge of 2 (C−P−C angle ca. 80°) induces a variety of splitting reactions. Upon decomplexation by dppe at 110 °C in toluene, phenylphosphinidene is generated and recovered as phenylphosphine. Upon sulfurization under the same conditions, [PhPS2] is formed and trapped as a [4+2] adduct with 2,3-dimethylbutadiene. Potassium tert-butylate attacks the bridge in THF at −78 °C and, after methylation and hydrolytic workup, yields [Ph(Me)P(OH)Mo(CO)5].