Answer Happy

3. Answer all parts of the question. Compound A is thermally unstable, decomposing to release nitrogen gas and a mixture of phosphazenes. These are sufficiently stable to allow the trimers (P3N3 ring) and tetramers (PAN4 ning) to be separated by column chromatography. a. Are the trimers and tetramers aromatic? Justify your answer. [3 marks) b. On investigation of a sample of trimers by NMR, it is found that it actually consists of two isomers. i. Draw the two isomers formed. [2 marks] ii. Assuming only 2J coupling, predict the 31P{H} NMR for the two isomers. [5 marks) c. [Rh(PPh:)3Cl] is a precatalyst that can be activated by dissociation of a phosphine ligand to form an active catalyst, B, which is used in the hydrogenation of alkenes. The active catalyst can then undergo oxidative addition in the presence of Hz to form complex C. Propene coordinates to C to form complex D, which then undergoes a 1,2- insertion step to form E. Reductive elimination of propane from E regenerates the active catalyst B. Draw complexes B-E and hence provide a full catalytic cycle, including the activation step, for the hydrogenation of propene [10 marks]