Application of Group Theory to IR Spectroscopy

1. Setup of the Schlenk Line (for a more detailed procedure, please review the "Schlenk Lines Transfer of Solvent" video in the Essentials of Organic Chemistry series). Schlenk line safety should be reviewed prior to conducting this experiment. Glassware should be inspected for star cracks before use. Care should be taken to ensure that O₂ is not condensed in the Schlenk line trap if using liquid N₂. At liquid N₂ temperature, O₂ condenses and is explosive in the presence of organic solvents. If it is suspected that O₂ has been condensed or a blue liquid is observed in the cold trap, leave the trap cold under dynamic vacuum. Do NOT remove the liquid N₂ trap or turn off the vacuum pump. Over time the liquid O₂ will sublime into the pump; it is only safe to remove the liquid N₂ trap once all of the O₂ has sublimed.

1. Close the pressure release valve.
2. Turn on the N₂ gas and the vacuum pump.
3. As the Schlenk line vacuum reaches its minimum pressure, prepare the cold trap with either liquid N₂ or dry ice/acetone.
4. Assemble the cold trap.

2. Synthesis of Mo(CO)₄[P(OPh)₃]₂ (Figure 4)¹

Note: Use standard Schlenk line techniques for the synthesis of Mo(CO)₄[P(OPh)₃]₂ (see the "Synthesis of a Ti(III) Metallocene Using Schlenk line Technique" video). Metal carbonyl complexes are a source of free CO, which is highly toxic. Carbon monoxide poisoning occurs when CO binds to hemoglobin, resulting in significant reduction of oxygen supply to the body. Therefore, it is extremely important to take appropriate safety measures when handling and working with metal carbonyl complexes. Reactions that generate free CO need to be conducted in a well-ventilated hood to prevent exposure to the toxic gas.

1. Add 1.6 g (4.92 mmol) Mo(CO)₄(nbd) (nbd = 2,5-Norbornadiene) and 1.6 mL (9.84 mmol) triphenyl phosphite (P(OPh)₃) to a 100 mL Schlenk flask and prepare the Schlenk flask for the cannula transfer of solvent.
   Note: Mo(CO)₄(nbd) ((Bicyclo[2.2.1]hepta-2,5-diene)tetracarbonylmolybdenum(0)) can be purchased from Sigma Aldrich or synthesized using literature methods.²
2. Add 20 mL of degassed dichloromethane to the Schlenk flask via cannula transfer.
3. Stir the reaction mixture for 4 h at room temperature under N₂.
4. Remove the volatiles under vacuum and wash the resulting precipitate with cold hexanes (two washes each with 10 mL, −78 °C). 
5. Dry the solid product under vacuum for 15 min.
6. Measure the IR spectrum of the product in a solution of hexanes.

Figure 4. Synthesis of Mo(CO)₄[P(OPh)₃]_2.