This experiment has been modified and expanded from the J. Chem. Ed. article linked below (J. Chem. Ed., 1988, 65, 1020) and includes four syntheses, that of dppm, and then three Mn complexes of dppm. Students must select appropriate characterization methods for their molecule, chosen from a list of available instrumentation including NMR (1H, 13C, 31P), IR, UV-Vis, melting point and optical rotation. Students are graded on yield and purity; there is time during the semester to repeat work for improved yield. Students write a brief abstract/discussion (1/2-1 page) and then a full experimental report including their characterization data, written up as if it were part of a publication.
A student will use liquid ammonia as a solvent
A student will carry out a carbonyl substitution reaction under an inert atmosphere
A student will write up synthetic results in an experimental format
24/40 Gas Inlet Adapter
100 mL Schlenk Flask with 24/40 joint
Syringe filled with grease
Dry Ice Condensor with 24/40 joint
Blast shield (recommended in case of vigorous liquid ammonia boiling during reagent addition; careful work behind hood sash is ok)
My junior level laboratory course is a synthesis and characterization course. Students select 6 syntheses (from a total of 12 in the lab manual) during an 8 week period and carry out their preparation. This laboratory is in 2 parts, synthesis of dppm in liquid ammonia in one week (can be omitted, just use commercial dppm), and synthesis of Mn complexes, done over a 2 week period.
Students write a brief abstract/discussion (~1 page) and then a full experimental report including their characterization data, written up as if it were part of a publication. Students are graded on yield and purity; there is time during the semester to repeat work for improved yield. A grading rubric is attached.
The synthesis of dppm is not particularly challenging but careful addition of the reagents (as specificed in the student notes) is important. Students should obtain a 31P, and 1H NMR spectrum of dppm, as well as melting point. IR and UV-Vis are significantly less informative and can be omitted. For the Mn carbonyl complexes, 1H NMR is complicated, and typically only required for the fac-complex for completeness. However, IR is very informative. For the writeup, I like to see some discussion of analysis of the MO diagram to explain the rearrangement of the complex upon oxidation/reduction. Students have no problems acquiring the IR (and the NMR if they choose to do it) but usually gloss over the MO analysis.
Typical yields: dppm yields are low, less than 40%, and it often must be recrystallized before use. yields of the first two Mn complexes are in the 40-80% range, and for the third, about 20-40%. Yields are generally much higher for the Mn complexes when using commerical dppm.