Reaction of Chiral Secondary Amines with [(η5-C5Me5)MCl2]2 (M = Rh(III), Ir(III)): Cyclometalation with or without Dehydrogenation

The reaction of (2R,5R)-2,5-diphenylpyrrolidine (L1) with [(η5-C5Me5)MCl2]2 (M = Rh, Ir) in acetonitrile in the presence of KPF6 and NaOH at room temperature led to mixtures of two products, [(η5-C5Me5)M(N−C)(NCMe)](PF6) (N−C designating a cyclometalated ligand). These products were cyclometalated complexes of pyrrolidine ((RC,RC,RN,RM)-1 (M = Ir) or (RC,RC,RN,RM)-2 (M = Rh)) and of pyrroline ((RC,SM)-3 (M = Ir) or (RC,SM)-4 (M = Rh)), respectively. With M = Ir, when the reaction was performed in open air, the only product observed was the cyclometalated imine derivative (RC)-3. The genuine pyrroline complexes were prepared as the racemic compounds (±)-3, (±)-4, and (±)-4′ in good yields by cyclometalating (±)-2,5-diphenylpyrroline (L2) with [(η5-C5Me5)MCl2]2. These latter compounds were fully characterized; the crystal structures of (RC)-3 and (±)-4′ were similar and revealed that the CN units were endo to the metallacyclic ring. The reaction in acetonitrile of (R,R)-bis(1-phenylethyl)amine (L3) with [(η5-C5Me5)MCl2]2 (M = Rh, Ir) in the presence of KPF6 and NaOH at room temperature led to mixtures, within which the cyclometalated dehydrogenated imine cations [(η5-C5Me5)M(C6H4-2-CMeNCHMePh)]+ were identified by electrospray mass spectroscopy. The corresponding iridium complex was obtained pure and fully characterized as (RC)-5 in good yield via cyclometalation of the imine ligand (R)-PhMeCNCHMePh (L4) with [(η5-C5Me5)IrCl2]2 in the presence of 2 equiv of silver triflate per ligand. NMR and X-ray analyses of (RC)-5 indicated that the CN moiety was endo as in 3, 4, and 4′; however, two diastereomers in equimolar amounts were identified in solution, in contrast to the case for the pyrroline complexes.