Electron‐Rich Vaska‐Type Complexes trans ‐[Ir(CO)Cl(2‐Ph 2 PC 6 H 4 COOMe) 2 ] and trans ‐[Ir(CO)Cl(2‐Ph 2 PC 6 H 4 OMe) 2 ]: Synthesis, Characterisation and Reactivity

The underappreciated influence of ancillary halide on metal–ligand proton tautomerism

Syntheses of Vaska-type complexes [IrP₂X(CO)] (P = phosphine, X = halide) with all four common halides (fluoride, chloride, bromide, and iodide) was attempted using a protic and hemilabile imidazolyl di-tert-butyl phosphine ligand. In the solid-state, all four complexes were found to be ionic with the halides in the outer-sphere, and the fourth coordination site of the square plane occupied by the imidazole arm of the ligand. In solution, however, the chloride complex was found to be in equilibrium with an octahedral Ir^III–H species at room temperature. For the bromide and iodide analogs, the corresponding Ir^III–H species were also observed but only after heating the solutions. The neutral Ir^I Vaska's analogs for X = Cl, Br, and I were obtained upon addition of excess halide salt, albeit heating was required for X = Br and I. The Ir^III–H species are proposed to originate from tautomerization of minor amounts of the electron rich neutral Vaska analog (halide inner-sphere and phosphines monodentate) that are in equilibrium with the ionic species. Heating is required for the larger anions of bromide and iodide to overcome a kinetic barrier associated with their movement to an inner-sphere position prior to tautormerization. For the fluoride analog, the Ir^III–H was not observed, attributable to strong hydrogen bonding interactions of the imidazolyl proton with the fluoride anion.

Ligand protonated Ir^I bisphosphine carbonyl complexes isolated as halide salts equilibrate with their neutral Ir^III–H congeners in solution. The equilibrium constant and energy barrier to interconversion are dependent on the identity of the halide.

Hydrogen and oxygen activation by an iridium precursor containing the 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazolate ligand

Complex [Ir(κ²-S,N-(4,5-(P(S)Ph₂)₂Tz))(coe)₂] (coe = cyclooctene) was prepared upon reaction of potassium 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazolate with [Ir(coe)₂(μ-Cl)]₂. Its phosphorus derivatives were susceptible of oxidative addition processes.

Formation and reactivity of an (alkene)peroxoiridium(III) intermediate supported by an amidinato ligand

An Ir(I) complex of an acetamidinato ligand was synthesized by reaction of N,N'-diphenylacetamidine, PhN[double bond, length as m-dash]C(Me)NHPh, with either MeLi and [{Ir(cod)}2(μ-Cl)2] or [{Ir(cod)}2(μ-OMe)2] and was characterized by X-ray crystallography as a mononuclear complex, [Ir{PhNC(Me)NPh}(cod)] (1; where cod = 1,5-cyclooctadiene). Reaction of 1 with CO afforded a dinuclear carbonyl complex, [{Ir(CO)2}2{μ-PhNC(Me)NPh-κN:κN'}2] (2), as indicated by EI mass spectrometry and solution- and solid-state IR spectroscopy [νCO (n-pentane) = 2067, 2034 and 1992 cm(-1)]. Activation of O2 by 1 in solution at 20 °C was irreversible and produced an (alkene)peroxoiridium(iii) intermediate, [Ir{PhNC(Me)NPh}(cod)(O2)] (3), which was characterized by one- and two-dimensional NMR techniques and IR spectroscopy (for 3, νOO = 860 cm(-1); for 3-(18)O2, νOO = 807 cm(-1)). Complex 3 oxidized PPh3 to OPPh3, and its decay in the absence of added substrates followed by reaction with cod yielded 4-cycloocten-1-one and a minor amount of 1. In comparison with the results for the previously reported guanidinato complex [Ir{PhNC(NMe2)NPh}(cod)(O2)] (4), the formation of 3 and its reaction with PPh3 are significantly faster, indicating considerable ligand effects in these reactions.

Evidence for a reactive (alkene)peroxoiridium(III) intermediate in the oxidation of an alkene complex with O2

An (alkene)peroxoiridium(III) complex, [Ir(L)(cod)(O(2))] [where LH = PhN=C(NMe(2))NHPh and cod = 1,5-cyclooctadiene], was identified as an intermediate in the reaction of the Ir(I) precursor [Ir(L)(cod)] with O(2) and characterized by spectroscopic methods. Decay of the intermediate and further reaction with 1,5-cyclooctadiene produced 4-cycloocten-1-one.