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 (L-1) with [(eta(5)-C5Me5)MCl2](2) (M = Rh, Ir) in acetonitrile in the presence of KPF6 and NaOH at room temperature led to mixtures of two products, [(eta(5)-C5Me5)M(N- C)(NCMe)](PF6) (N-C designating a cyclometalated ligand). These products were cyclometalated complexes of pyrrolidine ((R-C,R-C,R-N,R-M)-1 (M = Ir) or (R-C,R-C,R-N,R-M)-2 (M = Rh)) and of pyrroline ((R-C,S-M)-3 (M = Ir) or (R-C,S-M)-4 (M = Rh)), respectively. With M = Ir, when the reaction was performed in open air, the only product observed was the cyclometalated imine derivative (R-C)-3. The genuine pyrroline complexes were prepared as the racemic compounds (+/-)-3, (+/-)-4, (+/-)-4' in good yields by cyclometalating (+/-)-2,5-diphenylpyrroline (L-2) with [(eta(5)-C5Me5)MCl2](2). These latter compounds were fully characterized; the crystal structures of (R-C)-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 (L-3) with [(eta(5)-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 [(eta(5)-C5Me5)M(C6H4-2-CMe=NCHMePh)](+) were identified by electrospray mass spectroscopy. The corresponding iridium complex was obtained pure and fully characterized as (R-C)-5 in good yield via cyclometalation of the imine ligand (R)-PhMeC=NCHMePh (L-4) with [(eta(5)-C5Me5)IrCL2](2) in the presence of 2 equiv of silver triflate per ligand. NMR and X-ray analyses of (R-C)-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.