A new method of creating co-ordinative unsaturation: synthesis and reactions of a reactive iridium(<scp>I</scp>) complex [Ir(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF6: crystal structures of [Ir(CO)(η2-L){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF6(L = MeO2CCCCO2Me or COCHCHCONMe)

Treatment of [IrCl(CO)2(H2NC6H4Me-p)] with the azine diphosphine PPh2CH2(But)N–NC(But)CH2PPh21 in benzene gave the co-ordinatively saturated (18e) octahedral iridium(III) hydride [IrH(Cl)(CO)(PPh2CHC(But)–N–NC(But)CH2PPh2}]3 in which the P,N,P-terdentate diphosphine ligand had lost a hydrogen to give an ene–hydrazone backbone. On dissolution in methanol or ethanol, complex 3 immediately dissolved to give the isomeric but co-ordinatively unsaturated (16e) iridium(I) complex [Ir(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]Cl 4a in which the P,N,P-terdentate ligand backbone contained an azine moiety. Complex 4a was readily converted to the corresponding PF6 salt 4b. On dissolution in dichloromethane or benzene 4a rapidly gave back 3. Treatment of 4b with acetylenes or olefins gave adducts [Ir(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}L]PF6 in which L = MeO2CCCCO2Me 5a, HCCCO2Me 5b, MeN(OC)CHCHCO 8a, trans-MeO2CCHCHCO2Me 8b, trans-EtO2CCHCHCO2Et 8c, C2H48d or CH2CCH28e,8f. Proton NMR studies on the ethene adduct showed that the ethene ligand was rotating at ca. 20 &#176;C but at –40 &#176;C rotation had stopped. Allene gives a mixture of two isomeric adducts 8e and 8f. Complex 4b reacted with PhCCH in a different fashion to give the phenylacetylide hydride fac-[IrH(CCPh)(CO){PPh2CH2C(But)N–NC(Bu)t)CH2PPh2}]PF66 which isomerised on heating to mer-[IrH(CCPh)(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF67. Treatment of 4b with EtO2CNNCO2Et gave an adduct [Ir(CO){PPh2CHC(But)–N–NC(But)CH2PPh2}(EtO2CNHNCO2Et)]PF69 in which the diphosphine backbone had been deprotonated and the diethyl azocarboxylate protonated. Treatment of 4b with carbon monoxide gave the dicarbonyliridium complex [Ir(CO)2{PPh2CH2C(But)N–NC(But)CH2PPh2}]PF610. Treatment of 4b with dihydrogen gave a dihydridoiridium(III) adduct 11 in which the terdentate P,N,P diphosphine was in the fac arrangement. In solution 11 slowly isomerised over several hours to give a dihydride in which the terdentate P,N,P diphosphine was in the mer arrangement, i.e. the structure of the dihydride was 12. Complex 4b underwent other types of oxidative-addition reactions, i.e. with formic acid it gave the hydride mer-[IrH(O2CH)(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF613, with methyl iodide the mer-methyliridium(III) adduct 14 and with bromine the mer-iridium(III) dibromide 15. The crystal structures of 5a and 8a were determined.