PHOTOINDUCED ISOMERIZATION OF THE IRIDIUM(III) COMPLEX TRANS,MER-[IRCL2(CN)(PET2PH)(3)] TO THE FAC AND THE CIS,MER ISOMERS

The chloride ligand trans to PEt2Ph in mer-[IrCl3(PEt2Ph)(3)] has been found to be labile and readily displaced by cyanide ion in methanol t o give trans,mer-[IrCl2(CN)(PEt2Ph)(3)] as the only isomer. The trans, mer isomer may also be synthesized by treating trans,mer-[IrCl2(H2O)(P Et2Ph)(3)][ClO4] with cyanide ions. Irradiation of this isomer in dich loromethane with visible white light led initially to a mixture of the trans,mer isomer with the fac and cis,mer isomers, while extended irr adiation gave almost exclusively the cis,mer isomer with none of the f ac or tuans,mer forms remaining. This contrasts with the visible irrad iation of mer-[IrCl3(PEt2Ph)(3)] which gave exclusively the fac isomer . Reactions were followed by P-31-{H-1} and C-13-{H-1} NMR spectroscop y of (CN)-C-13-enriched samples and by Fourier-transform IR spectrosco py at around 2000 cm(-1). The crystal structures of the trans,mer and cis,mer isomers of [IrCl2(CN)(PEt2Ph)(3)] have been determined. During the photolysis a cyano-bridged species derived from the fac isomer, p robably fac-[(PhEt2P)(3)Cl2Ir(mu-CN)IrCl(CN)(PEt2Ph)(3)]Cl is observed as an intermediate but was not isolated. This salt disappears on exte nded irradiation. Addition of an excess of [N(PPh3)(2)]Cl totally supp ressed the formation of the mu-CN species, consistent with the formula given, while only slightly affecting the rate of conversion of the tr ans,mer into the fac and cis,mer isomers on irradiation.