SYNTHESIS AND CHARACTERIZATION OF CATIONIC SQUARE-PLANAR IRIDIUM(I) COMPLEXES CONTAINING CHIRAL DIPHOSPHINES

Cationic square-planar complexes of the type [Ir(diphosphine)(2)]Cl (diphosphine = (R,R)- and rac-cypenphos, (S,S)-chiraphos, (R)- and rac-prophos, (R)-phenphos) have been synthesized starting from [Ir(COE)(2)Cl](2) or [Ir(C2H4)(2)Cl](2). The complexes were fully characterized through H-1- and P-31{H-1}-NMR spectroscopy. With the C-1 diphosphines both cis and trans isomers are formed with low selectivity. Using racemic cypenphos no diastereoselectivity in the formation of the complexes was observed. For the racemic prophos the diastereoselectivity is different for the two geometrical isomers formed. A study of the electrochemical behavior of these complexes in acetonitrile with some attention to the characteristics of the electron transfer process has been carried out. The results are compared with those previously obtained in the reduction of the corresponding dppe derivative and provide a tool for the determination of the relative basicity of the ligands. The reduction was found to proceed by a single two-electron step to a d(10) anion, which is quenched by the protic solvent to give the final metal hydride derivative which in the case of complexes 2 and 3 were observed by NMR spectroscopy.