Synthesis and reactivity of new mono- and dinuclear hydridoirida-β- diketones - The formation and characterization of a dinuclear tris-μ-acyliridium(III) complex

Abstract

The hydridoirida-β-diketone [IrH{[PPh2(o-C 6H4CO)]2H}Cl] (1) reacts with silver salts of potentially coordinating anions such as tosylate (-OTs) or triflate (-OTf) to afford the mononuclear neutral derivatives [IrH{[PPh 2(o-C6H4CO)]2H}(X)] [X = OTs (2), OTf (3)]. In acetone solution the triflate anion in 3 is displaced by the solvent to afford the cationic complex [IrH{[PPh2(o-C 6H4CO)]2H}(acetone)]OTf (4), which is stable only in acetone solution. The reaction of 1 with halide scavengers containing less coordinating anions such as PF6- or BF 4- results in the formation of cationic compounds [{IrH[{PPh2(o-C6H4CO)}2H]} 2(μ-Cl)]A [A = BF4 (5), PF6 (6)] containing a dinuclear species with a single chlorine atom bridging two hydridoirida-β-diketone fragments. Both fragments are magnetically non-equivalent and the acylphosphane groups in each hydridoirida-β-diketone fragment are chemically equivalent. This species undergoes a fluxional process in solution, with ΔH‡ = 7.8 ± 0.4 kcal mol -1 and ΔS‡ = -10.9 ± 0.5 eu. A combination of rotation around the Ir-Cl bonds and variation of the Ir-Cl-Ir angle is suggested to be responsible for the fluxionality. Complex 5 reacts further with AgBF4 to undergo chloride abstraction along with hydrogen loss and deprotonation to give the cationic dinuclear complex [Ir 2H{PPh2(o-C6H4CO)}{μ-PPh 2(o-C6H4CO)}3]BF4 (7), which contains an acylphosphane chelate along with three acylphosphane bridging ligands and a single hydrido ligand. Bubbling of HCl through an MeOH solution of 7 gives 1, thus making the loss of hydride, enolic protons and chloride from complex 1 a reversible process. All the complexes were fully characterized spectroscopically. Single-crystal X-ray diffraction analysis was performed on complexes 5 and 7. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.