A new method of creating co-ordinative unsaturation: synthesis and reactions of a reactive iridium(I) complex [Ir(CO){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF6: crystal structures of [Ir(CO)(η2-L){PPh2CH2C(But)N–NC(But)CH2PPh2}]PF6(L = MeO2CCCCO2Me or COCHCHCONMe)

Abstract

Treatment of [IrCl(CO)₂(H₂NC₆H₄Me-p)] with the azine diphosphine PPh₂CH₂(Bu^t)N–NC(Bu^t)CH₂PPh₂1 in benzene gave the co-ordinatively saturated (18e) octahedral iridium(III) hydride [IrH(Cl)(CO)(PPh₂CHC(Bu^t)–N–NC(Bu^t)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(Bu^t)N–NC(Bu^t)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(Bu^t)N–NC(Bu^t)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 °C but at –40 °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(Bu^t)N–NC(Bu)^t)CH₂PPh₂}]PF₆6 which isomerised on heating to mer-[IrH(CCPh)(CO){PPh₂CH₂C(Bu^t)N–NC(Bu^t)CH₂PPh₂}]PF₆7. Treatment of 4b with EtO₂CNNCO₂Et gave an adduct [Ir(CO){PPh₂CHC(Bu^t)–N–NC(Bu^t)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(Bu^t)N–NC(Bu^t)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(Bu^t)N–NC(Bu^t)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.