The Reaction of (PPrⁱ₃)₂H₂Cl₂Ir With Phosphines: Crystal and Molecular Structures of mer-cis-(PMe₂Ph)₂(PPrⁱ₃)-cis-Cl₂HIr^III and mer-cis-(PMe₂Ph)₂(PPrⁱ₃)-trans-Cl₂HIr^III

Abstract

Ambient temperature reactions of the complex (PPrⁱ₃)₂H₂Cl₂Ir^IV (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-_nPh_n (n = 0, 1) there is spontaneous reaction to give the complexes mer-trans-(Pprⁱ₃)₂(PR₃)H-trans-Cl₂Ir^III, whereas with PE^t₃-_nPh_n (n = 0-2) the reaction yields mer-cis-(PR₃)₂(PPrⁱ₃)H-trans-Cl₂Ir^III complexes. Under reflux the phosphines PMe₃ and PMe₂Ph also yield mer-cis-(PR₃)₂(PPrⁱ₃)H-trans-Cl₂Ir^III 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-Cl₂Ir^III, 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-Cl₂Ir^III (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)₃HCl₂Ir^III 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)₂H₂Cl₂Ir^IV (1a) and (PCy₃)₂H₂Br₂Ir^IV (1b) (Cy = cyclohexyl), and their reactions with the same phosphines as used with (1), are also reported.