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].