En route to phosphonato iridium(i) complexes: the decisive effect of an intramolecular hydrogen bond

Abstract

Pentacoordinated iridium(I) complexes of formula IrCl(SiNP)(tfbb) (1) and IrCl(HNP)₂(tfbb) (2) (SiNP = SiMe₂{N(4-C₆H₄CH₃)PPh₂}₂; HNP = NH(4-C₆H₄CH₃)PPh₂) have been prepared and fully characterised. Both feature a distorted square pyramidal coordination polyhedron at the metal centre in the solid state and are fluxional in solution. Their reaction with trimethyl phosphite yields the derivatives [Ir(SiNP){P(OMe)₃}(tfbb)]Cl ([3]Cl) and Ir{PO(OMe)₂}(HNP)₂(tfbb) (4). The course of the reaction between IrCl(HNP)₂(tfbb) (2) and trimethyl phosphite was elucidated by NMR spectroscopy and DFT calculations, showing that the intermediate [Ir(HNP)₂{P(OMe)₃}(tfbb)]⁺ (5⁺) forms and further reacts with the chloride anion yielding the phosphonato derivative 4 and methyl chloride. The decisive role of the N–H group in the formation of the phosphonato ligand has been established by IR and NMR spectroscopic measurements and by DFT calculations.