Formation of Hydrido–η3‐Allyl Complexes of IrIII by Sequential Olefinic C-H Bond Activation and C-C Coupling of Alkenyl and Olefin Ligands

Abstract

The bis(ethene) complex [Tp^*Ir‐(C₂H₄)₂] (1^*) (Tp^* = tris(3,5‐dimethyl‐1‐pyrazol‐1‐yl)hydroborato) undergoes thermal rearrangement to the hydrido–allyl complex [Tp^*IrH(π³‐C₃H₄Me)] (6^*), through the intermediacy of the hydrido–vinyl complex [Tp^*IrH(C₂H₃)(C₂H₄)] (2^*). The overall conversion of 1^* into 6^* corresponds formally to the dimerisation of ethene by an unprecedented pathway that involves sequential C–H bond activation of a coordinated olefin molecule and C–C bond formation by coupling of the resulting vinyl and ethene moieties. Similar transformations have been observed for monosubstituted olefins like propene and 1‐butene, while the internal alkene cis−2‐butene experiences allylic activation of an sp³ C–H bond, which provides an alternative route to 6^*. The extension of these investigations to the analogous complexes of the unsubstituted tris(pyrazolyl)hydroborato ligand Tp is also reported. Mechanistic studies on the formation of the C–C bond by coupling of the vinyl and the olefin ligands suggest the participation of a vinylidene complex (formed by α‐H abstraction from the vinyl group), which then rearranges to an allene species. Evidence for the involvement of these and other key reaction intermediates is provided.