Synthesis of new heteroscorpionate iridium(i) and iridium(iii) complexes

Abstract

The reactivity of different heteroscorpionate ligands based on bis(pyrazol-1-yl)methane, with different iridium-(I) and -(III) precursors is reported. The reaction of the heteroscorpionate lithium salts “Li(bdmpza)”, [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], “Li(bdmpzdta)” [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] and “Li(S)-mbpam” [(S)-mbpam = (S)-(–)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] with 1 equivalent of [IrCl₃(THF)₃] in THF for 18 h affords high yields of neutral and anionic heteroscorpionate chloride iridium complexes [IrCl₂(bdmpza)(THF)] (1), [Li(THF)₄][IrCl₃(bdmpzdta)] (2) and [IrCl₂{(S)-mbpam})(THF)] (3). Solution of complex 3 in acetonitrile at room temperature leads to complex [IrCl₂{(S)-mbpam})(NCCH₃)] (4). Complexes 3 and 4 were isolated as enantiopure compounds. The reaction of the lithium salt “Li(bdmpza)” with [IrCl(η⁴-CH₂C(Me)C(Me)CH₂)]₂ in THF for 18 h gave the Ir(I) complex [Ir(bdmpza)(η⁴-CH₂C(Me)C(Me)CH₂)] (5). The reaction of complex 5 with CO (2 atm) at room temperature leads to a new complex of Ir(III), [Ir(bdmpza)(k²-CH₂C(Me)C(Me)CH₂)(CO)] (6). Treatment of heteroscorpionate ligand precursors “Li(bdmpza)” and “Li(bdmpzdta)” with [IrCp*Cl₂]₂ in THF yielded the iridium(III) complexes [Ir₂Cp*₂Cl₂(bdmpzx)] (x = a 7, x = dta 8). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers were obtained. Complex 7 undergoes a decarboxylation process initiated by the HCl generated in the previous step leading to the known ionic complex [IrClCp*(bdmpm)][IrCl₃Cp*] [bdmpm = bis(3,5-dimethylpyrazol-1-yl)methane] (9). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 4, 6, 8 and 9 were also established.