267431-86-7Relevant academic research and scientific papers
Rhodium and iridium β-diiminate complexes - Olefin hydrogenation step by step
Budzelaar, Peter H. M.,Moonen, Nicolle N. P.,De Gelder, Rene?,Smits, Jan M. M.,Gal, Anton W.
, p. 753 - 769 (2007/10/03)
The bulky β-diiminate ligands [(2,6-C6H3X2)NC(Me)CHC(Me)N(2,6- C6H3X2)]- (X = Me, L(Me); X = CL, L(Cl)) have been found to be effective in stabilizing low coordination numbers (CN) in Rh and Ir complexes. The 14-e complex L(Me)Rh(COE) (COE = cyclooctene) has a three-coordinate T-shaped Rh environment and is nonagostic. Coordinative unsaturation is avoided by incorporation of a small ligand (e.g. N2, MeCN, olefins), by the intramolecular coordination of a chlorine atom in L(Cl)Rh(COE), or by an agostic interaction in L(Me)Rh(norbornene). In solution at room temperature, L(Me)Rh(COE) undergoes rapid isomerization according to the allyl hydride mechanism; the corresponding 2,3-dimethylbutene complex actually prefers the allyl hydride structure. Rhodium(I) complexes of L(Me) and L(Cl) catalyze olefin hydrogenation; hydrogenation of 2,3-dimethylbutene has been shown to be preceded by isomerization. The shielding properties of the bulky β- diiminate ligands allow direct observation of a number of reactive intermediates or their iridium analogues, including an olefin-dihydrogen complex (with Rh) and an olefin dihydride (with Ir). These observations, together with calculations on simple model systems, provide us with snapshots of a plausible hydrogenation cycle. Remarkably, hydrogenation according to this cycle appears to follow a 14-e/16-e path, in contrast to the more usual 16-e/18-e paths.
