Alkene C−H Activations at Dinuclear Complexes Promoted by Oxidation

Abstract

Several recent discoveries in the chemistry of transition metal di-and polynuclear complexes have disclosed new methods of hydrocarbon activation and functionalization, favored by polynuclear environments. [1,2] In parallel, considerable progress has been made in understanding the reactivity features resulting from multimetallic reaction sites. [1, 3,4] Together, such advances may contribute to the rational design of new catalysts and applications based on this type of compound. However, the proximity of the metal centers is likely to have significant repercussions for the reactivity, which remain to be determined.In our recent studies on ™open-book∫ d 8 diiridium complexes with N-donor bridges, we have observed a remarkable substrate selectivity in the reactions of these compounds towards oxidative addition reactants. Whereas the d 8 diiridium complexes underwent fast S N 2 oxidative additions with substrates such as halocarbons, [4] the additions of less-polar reactants such as dihydrogen were not observed. The oxidation of these d 8 d 8 diiridium compounds, to species of d 6 d 8 or d 7 d 7 electronic configurations, gave dihydrogen-activating compounds. [5] Here we report that such an oxidation strategy also allows the transformation of nonreactive d 8 d 8 compounds into dinuclear CÀH activating species.The treatment of the diamidonaphthalene ((NH 2 )naphth)bridged diiridium (iii) complex [Ir 2 (m-1,8-(NH) 2 naphth)-(m-H)H 3 (NCCH 3 )(PiPr 3 ) 2 ] (1) with two equivalents of an internal alkyne such as 2-butyne or diphenylacetylene afforded diiridium(i) derivatives of the formula [Ir 2 (m-1,8-(NH) 2 naphth)(h 2 -Z-RHCCHR) 2 (PiPr 3 ) 2 ] (R Me (2), Ph (3)) [Eq. (1)]. The solution NMR spectra of both compounds indicate symmetric C 2 structures with a transoid arrangement of nonrotating Z-alkene ligands. These features have been confirmed by the X-ray crystallographic determination of the structure of 2, [6] (Figure 1). reaction see: M. AlajarÌn, C. Conesa, H. S. Rzepa, J. Chem. Soc.