Ambient temperature reactions of the complex (PPri3)2H2Cl2IrIV (1) with ethyl-substituted monodentate phosphine ligands are shown to yield different product types to those obtained both with methyl-substituted analogues and with phosphine itself. With the phosphines PH3 and PMe3-nPhn (n = 0, 1) there is spontaneous reaction to give the complexes mer-trans-(Ppri3)2(PR3)H-trans-Cl2IrIII, whereas with PEt3-nPhn (n = 0-2) the reaction yields mer-cis-(PR3)2(PPri3)H-trans-Cl2IrIII complexes. Under reflux the phosphines PMe3 and PMe2Ph also yield mer-cis-(PR3)2(PPri3)H-trans-Cl2IrIII complexes [PR3 = PMe3 (2), Pme2Ph (3)]. The differing course of the reactions of (1) with PMe3 and with PEt3 has permitted the synthesis of mer-(Pme3)-trans-(PPri3)(PEt3)H-trans-Cl2IrIII, the first example of an octahedral iridium complex containing three different monodentate phosphine ligands. All of the products obtained have been fully characterized by 31P and 1H n.m.r. spectroscopy. Crystal structure analyses of (3) and of its photoisomer mer-cis-(PMe2Ph)2(PPri3)H-cis-Cl2IrIII (4) have been carried out to permit comparison of the metal-ligand bonding in these complexes with that in their previously characterized, sterically less crowded, tris-PMe2Ph analogues. Summary data are as follows: (3), triclinic, Pī, a 13.414(1), b 12.062(1), c 9.077(1) Ǻ, α 79.53(1), β 88.05(1), γ 79.47(1)° [T 158�3 K], Z 2, R 0.022, Rw 0.032 (4822 reflections); (4), monoclinic, P21/n, a 19.694(1), b 15.972(1), c 9.548(1) Ǻ, β 101.45(1)° (T 293�2 K), Z 4, R 0.026, Rw 0.032 (5476 reflections). Both molecules exhibit distorted octahedral coordination of the metal atom and appreciably greater steric strain than in their (Pme2Ph)3HCl2IrIII analogues. Metal-ligand distances to the mutually trans Pme2Ph and PPri3 ligands are 2.322(1) and 2.372(1)Ǻ, respectively, for (3), and 2.359(1) and 2.406(1)Ǻ for (4), and suggest that the thermodynamically favoured cis-dichloro isomer (4) is the more strained. The preparations of the complexes (PCy3)2H2Cl2IrIV (1a) and (PCy3)2H2Br2IrIV (1b) (Cy = cyclohexyl), and their reactions with the same phosphines as used with (1), are also reported.
Chiral-at-metal iridium complex for efficient enantioselective transfer hydrogenation of ketones
