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

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.