GENERAL STRATEGY FOR INDUCING C-H BOND FISSION (CYCLOIRIDATION) IN SOME ARYL, HETEROCYCLIC, ALKENYL OR ALKYL-GROUPS IN AZINES DERIVED FROM ALDEHYDES OR METHYL KETONES

The phosphino hydrazone Z-PPh(2)CH(2)C(Bu(t))=NNH2 I has been shown to be a convenient 'reagent' for converting aldehydes or ketones into azines which can then be cycloiridated rapidly with C-H bond fission to give iridium(III) hydrides. Condensation of I with a series of substituted benzaldehydes (RCHO) gave mixed azines of type Z,E-PPh(2)CH(2)C(BUt)=N-N=CHR [R=C6H2(OMe)(3)-3,4,5 IIa, Ph IIb, C(6)H(4)OMe-4 IIc, C6H4NO2-4 IId, C6H4Br-2 IIe, C6H4Cl-2 IIf, C6H4F-2 IIg, C6H4OH-2 IIh or C6H2(OH-2)(OMe)(2)-4,6, IIi]. The Z,E configuration is necessary for the subsequent cyclometallation acid when the azine IIa was treated with [IrCl(CO)(2)(H(2)NC(6)H(4)Me-p)] in benzene at 75 degrees C for 5 min it underwent an aryl C-H bond fission to give the cyclometallated chlorocarbonlyliridium(III) hydride [IrH(Cl)(CO){PPh(2)CH(2)C(Bu(t))=N-N=CH[C6H(OMe)(3)-3,4,5]}] 1a. The crystal structure of 1a showed that (i) oxidative addition of the aryl C-tl bond to iridium was cis with the hydride ligand trans to chloride, and (ii) the cyclometallated azine ligand was in the terdentate mar arrangement. Azines IIb-IIg reacted similarly. Treatment of IIh with [IrCl(CO)(2)(H(2)NC(6)H(4)Me-p)] in dichloromethane at 20 degrees C effected O-H bond fission to give the O-cyclometallated iridium(III) hydride [IrH(Cl)(CO){PPh(2)CH(2)C(Bu(t))=N-N=CH(C6H4O)}] which isomerised in benzene at 75 degrees C to the C-metallated isomer. Similar treatment of IIi also gave an O-cyclometallated iridium(III) hydride. The phosphino hydrazone I condensed with ferrocenecarbaldehyde to give an azine, which with [IrCl(CO)(2)(H(2)NC(6)H(4)Me-p)] gave a cyclometallated iridium (III) hydride. Treatment of I with the 2-carbaldehydes of pyrrole, N-methylpyrrole or thiophene or with indole-3-carbaldehyde gave the corresponding azine phosphines with the required Z,E configuration. When the pyrrole azine was treated with [IrCl(CO)(2)(H(2)NC(6)H(4)Me-p)] the N-cyclometallated chlorocarbonyliridium(III) hydride [IrH(Cl)(CO){PPh(2)CH(2)C(BUt)=N-N=CH(C4H3N)}] was formed via a N-H bond fission. The azine phosphines of N-methylpyrrole, thiophene and indole gave C-cyclometallated chloro carbonyliridium(III) hydrides. Condensation of I with cinnamaldehyde or 3-methylpent-3-en-2-one gave azines which underwent oxidative addition of the olefinic C-H bonds readily to give corresponding C-cyclometallated chlorocarbonyliridium(III) hydrides. Phosphino hydrazone I also condensed with tert-butyl methyl ketone to give an azine which with [IrCl(CO)(2)(H(2)NC(6)H(4)Me-p)] gave the C-cyclometallated chlorocarbonyliridium(III) hydride, i.e. metallation in this case occurred on the single methyl group. Proton, P-31-{H-1} and some C-13-C(H-1) NMR data are given.