Aryldiazenido- and aryldiazene complexes: reaction of ethanol with aryldiazenido-complexes of iridium(III) to form orthometallated derivatives

Abstract

A re-examination ofthe products of the reaction of [IrCl(CO)(PPh₃)₂] with diazonium salts, [RN₂][BF₄], in benzene–ethanol or benzene–propan-2-ol shows them now to include the complexes [IrCl₂(N₂R)(CO)(PPh₃)₂](4) and the orthometallated arylhydrazido-complex [[graphic omitted])(CO)(PPh₃)₂][BF₄](5), in addition to the previously found diaryltetrazenido-complex [Ir(N₄R₂)(CO)(PPh₃)₂][BF₄](1) and orthometallated aryldiazene complex [[graphic omitted])(CO)(PPh₃)₂][BF₄](2; X = Cl). Complex (5) readily oxidizes to (2; X = Cl, F, or BF₄), depending on the availability of the ligand X. These results, taken together with those from reactions of (a)[IrCl(CO)(PPh₃)₂] and [RN₂][BF₄] in acetone, which yield [{IrCl(N₂R)(CO)(PPh₃)₂}₂][BF₄]₂, (b)[IrH(CO)(PPh₃)₃] and [RN₂][BF₄] in acetone, yielding (5), and (c)[{IrCl(N₂R)(CO)(PPh₃)₂}₂][BF₄]₂ with ethanol or propan-2-ol, yielding variously (2), (4), and (5), allow a mechanism for the reactions in benzene–ethanol to be proposed. It envisages that the chlorine-bridged aryldiazenido-complex [{IrCl(N₂R)(CO)(PPh₃)₂}₂][BF₄]₂ is first formed, and subsequently undergoes hydrogen transfer from the alcohol to yield (4) plus the intermediate [Ir(NHNR)(CO)(PPh₃)₂][BF₄]. The latter then (a) orthometallates to give (5), and hence (2), or (b) reacts with further [RN₂][BF₄] to give (1).