Synthesis and reactions of ene–hydrazone diphosphine iridium complexes and related species †

Abstract

Treatment of the azine diphosphine Z,Z-PPh₂CH₂C(Bu^t)[double bond, length half m-dash]N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂ I with [IrCl(CO)₂(H₂NC₆H₄Me-4)] in benzene gave the ene–hydrazone diphosphine iridium(III) hydride [IrH(Cl)(CO){PPh₂CH[double bond, length half m-dash]C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}], 1, which isomerised reversibly to the ionic square planar iridium(I) complex [Ir(CO){PPh₂CH₂C(Bu^t)[double bond, length half m-dash]N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}]Cl 2a, containing an azine diphosphine. Treatment of 1 with NEt₃ gave the neutral ene–hydrazone diphosphine iridium(I) complex [Ir(CO){PPh₂CH[double bond, length half m-dash]C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}] 3 which is reactive and undergoes oxidative addition of H₂ to give the iridium(III) dihydride mer,cis-[IrH₂(CO){PPh₂CH[double bond, length half m-dash] C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}] 4 and oxidative addition of MeI to give the methyliridium(III) complex [IrMe(I)(CO){PPh₂CH[double bond, length half m-dash]C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}] 5. It reacted rapidly with olefins or acetylenes (L), i.e.N-methylmaleimide, ethene or dimethyl acetylenedicarboxylate, to give the five-co-ordinate adducts [Ir(CO)L{PPh₂CH[double bond, length half m-dash] C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}], 6a, 6b or 6c, respectively, also with O₂ to give the η²-dioxygen adduct [Ir(CO)(η²-O₂){PPh₂CH[double bond, length half m-dash]C(Bu^t)N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}] 7. Treatment of 3 with 1 mol of picric acid protonated the ene–hydrazone diphosphine backbone to give the azine diphosphine iridium(I) salt [Ir(CO){PPh₂CH₂C(Bu^t)[double bond, length half m-dash]N–N[double bond, length half m-dash] C(Bu^t)CH₂PPh₂}][OC₆H₂(NO₂)₃] 2b. The N-methylmaleimide adduct 6a was similarly protonated to give the corresponding azine diphosphine iridium(I) salt [Ir(CO)(η²-COCH[double bond, length half m-dash]CHCONMe){PPh₂CH₂C(Bu^t)[double bond, length half m-dash]N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}][OC₆H₂(NO₂)₃] 8. Complex 1 was protonated by HCl to give the corresponding azine diphosphine iridium(III) salt [IrH(Cl)(CO){PPh₂CH₂C(Bu^t)[double bond, length half m-dash]N–N[double bond, length half m-dash]C(Bu^t)CH₂PPh₂}]Cl 9a, which is converted into 3 when treated with NEt₃. The ¹H, ¹³C and ³¹P NMR and some IR data are given.

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