FORMATION OF HYDRIDO-ETA(3)-ALLYL COMPLEXES OF IR-III BY SEQUENTIAL OLEFINIC C-H BOND ACTIVATION AND C-C COUPLING OF ALKENYL AND OLEFIN LIGANDS

The bis(ethene) complex [TpIr-(C2H4)(2)] (Ik) (1p* = tris(3,5-dimethy l-1-pyrazol-1-yl)hydroborato) undergoes thermal rearrangement to the h ydridoallyl complex [TpIrH(eta(3)-C3H4Me)] (6*), through the intermed iacy of the hydridovinyl complex [TpIrH(C2H3)(C2H4)] (2*). The overal l 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 transform ations have been observed for monosubstituted olefins like propene and 1-butene, while the internal alkene cis-2-butene experiences allylic activation of an sp(3) C-H bond, which provides an alternative route t o 6. The extension of these investigations to the analogous complexes of the unsubstituted tris(pyrazolyl)hydroborato ligand Tp is also rep orted. Mechanistic studies on the formation of the C-C bond lay coupli ng of the vinyl and the olefin ligands suggest the participation of a vinylidene complex (Formed by alpha-H abstraction from the vinyl group ), which then rearranges to an allene species. Evidence for the involv ement of these and other key reaction intermediates is provided.