Reactivity of Ir(i)-aminophosphane platforms towards oxidants

Abstract

The iridium(I)-aminophosphane complex [Ir{κ³C,P,P′-(SiNP-H)}(cod)] has been prepared by reaction of [IrCl(cod)(SiNP)] with KCH₃COO. DFT calculations show that this reaction takes place through an unexpected outer sphere mechanism (SiNP = SiMe₂{N(4-C₆H₄Me)PPh₂}₂; SiNP-H = CH₂SiMe{N(4-C₆H₄Me)PPh₂}₂). The reaction of [IrCl(cod)(SiNP)] or [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with diverse oxidants has been explored, yielding a range of iridium(III) derivatives. On one hand, [IrCl(cod)(SiNP)] reacts with allyl chloride rendering the octahedral iridium(III) derivative [IrCl₂(η³-C₃H₅)(SiNP)], which, in turn, reacts with tert-butyl isocyanide yielding the substitution product [IrCl(η³-C₃H₅)(CN^tBu)(SiNP)]Cl via the observed intermediate [IrCl₂(η¹-C₃H₅)(CN^tBu)(SiNP)]. On the other hand, the reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with [FeCp₂]X (X = PF₆, CF₃SO₃), I₂ or CF₃SO₃CH₃ results in the metal-centered two-electron oxidation rendering a varied assortment of iridium(III) compounds. [Ir{κ³C,P,P′-(SiNP-H)}(cod)] reacts with [FeCp₂]⁺ (1 : 2) in acetonitrile affording [Ir{κ³C,P,P′-(SiNP-H)}(CH₃CN)₃]²⁺ isolated as both the triflato and the hexafluorophosphato derivatives. Also, the reaction of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] with I₂ (1 : 1) yields a mixture of iridium(III) derivatives, namely the mononuclear compound [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]I, containing the η²,η³-cycloocta-2,6-dien-1-yl ligand, and two isomers of the dinuclear derivative [Ir₂{κ³C,P,P′-(SiNP-H)}₂(μ-I)₃]I, the first species being isolated in low yield. DFT calculations indicate that [IrI(κ²P,P′-SiNP)(η²,η³-C₈H₁₁)]I forms as the result of a bielectronic oxidation of iridium(I) followed by the deprotonation of the cod ligand by iodide and the protonation of the methylene moiety of the [Ir{κ³C,P,P′-(SiNP-H)}] platform by the newly formed HI. Finally, the oxidation of [Ir{κ³C,P,P′-(SiNP-H)}(cod)] by methyl triflate proceeds via a hydride abstraction from the cod ligand, with the elimination of methane and the formation of the η²,η³-cycloocta-2,6-dien-1-yl ligand with the concomitant two-electron oxidation of the iridium centre. The crystal structures of selected compounds have been determined.