Synthesis Of A Ti(III) Metallocene Using Schlenk Line Technique

Overview

Source: Tamara M. Powers, Department of Chemistry, Texas A&M University

Inorganic chemists often work with highly air- and water-sensitive compounds. The two most common and practical methods for air-free synthesis utilize either Schlenk lines or gloveboxes. This experiment will demonstrate how to perform simple manipulations on a Schlenk line with a focus on solvent preparation and transfer. Through the synthesis of a reactive Ti(III) metallocene complex, we will demonstrate a new, simple method to degas solvent as well as how to transfer solvent by cannula and by syringe on a Schlenk line.

The synthesis of a Ti(III) metallocene compound 3 is shown in Figure 1.¹ Compound 3 is highly reactive with O₂, (see oxidation of compound 3 to Ti(IV) metallocene 4 shown in Figure 1). Therefore, it is important to run the synthesis under anaerobic conditions. The synthesis of target compound 3 can be monitored visually and progresses through one additional color change before arriving at the desired product, which is blue in color. If during the experiment there is an observed color change from blue to yellow (or green = blue + yellow), this is an indication that O₂ entered the flask and that undesired oxidation of compound 3 to the Ti(IV) analog (compound 4) has occurred.

Figure 1. Synthesis of Ti(III) metallocene compound 3 and it's reaction with O₂.

Procedure

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 condense

Results

Upon addition of the acetonitrile in step 4, the solution should change color from orange, to green, to blue (Figure 4). Failure to obtain the blue color indicates a leak in the system. Addition of acetonitrile by syringe in step 6 should result in no color change if anaerobic conditions are maintained. If oxygen is present, the solution will turn from blue, to green, to orange.

Application and Summary

Here, we demonstrated standard Schlenk line technique to synthesize an air-sensitive Ti(III) metallocene complex. The solvent was degassed by bubbling N₂ through the liquid in a Schlenk flask. We also demonstrated how to set up a reaction under anaerobic conditions on the Schlenk line and transfer solvent anaerobically by cannula transfer as well as by syringe.

Inorganic chemists use Schlenk line technique in the synthesis of air- and water-sensitive compounds. The solvent used in t

References

Burgmayer, S. N. Use of a Titanium Metallocene as a Colorimetric Indicator for Learning Inert Atmosphere Techniques. J Chem Educ. 75, 460 (1998).