Adsorption and Oxidation of Phosphine on Activated Carbon

AC (401.4 mg) was placed into an oven-dried Schlenk flask,
dried in vacuo for 30 min at 90 °C, and placed under a dry nitrogen
atmosphere.⁸⁹ In a second oven-dried Schlenk
flask, PⁿBu₃ (1) (29.4 mg, 0.145 mmol, 28% surface coverage) was dissolved in dry
and oxygen-free THF⁹⁰ (10 mL) under a dry
nitrogen atmosphere. The phosphine solution was then transferred to
the AC and stirred for 20 min under a dry nitrogen atmosphere. Subsequently,
THF⁹⁰ was removed in vacuo at 30 °C
until the AC was dry, which took 25 min. Meanwhile, a plastic desiccator
was filled with a mixture of drierite and molecular sieves (3 Å).
Both desiccants had been dried in a drying oven at 250 °C for
3 h and dried at RT in vacuo for an additional h. For the oxidation
of the adsorbed phosphine, a gentle stream of air, monitored by a
bubbler, was blown through the desiccator and into the Schlenk flask
containing 1 adsorbed on AC for 10 min. After the air
flow was stopped, the flask was sealed to allow for an additional
50 min of oxidation time. Then, the AC with adsorbed 1_ox was again placed under a dried nitrogen
atmosphere, 4 mL of dry, degassed THF⁹⁰ was added, and the mixture was stirred for 5 min. A portion of this
suspension was then added to a dried NMR tube under a nitrogen atmosphere,
and a ³¹P NMR spectrum was recorded (Figure S22).