Novel bis(phosphine) pincer complexes of iridium based on ferrocene and ruthenocene have been
synthesized. The reaction of 1,3-bis((di-tert-butylphosphino)methyl)metallocenes [t-BuP,CH,PM] (M =
Fe, 10; M = Ru, 13) with [Ir(COE)2Cl]2 in refluxing toluene leads to the corresponding chloro-hydrido
pincer complexes as a mixture of H-endo- (M = Fe, 11; M = Ru, 14) and H-exo-IrH(Cl)[t-BuP,C,PM] (M
= Fe, 12; M = Ru, 15) isomers. Treatment of compounds 11, 12 and 14, 15 with NaH in hot cyclooctane
generates corresponding dihydrido complexes IrH2[t-BuP,C,PM] (M = Fe, 6; M = Ru, 7). Reactivity of
the chelated iridium atom in hydrido-iridium pincer complexes and oxidation centered at the iron atom
of ferrocene-based pincer complexes were studied. Complexes H-exo-IrH(Cl)(CO)[t-BuP,C,PFe] (20),
Ir(CO)[t-BuP,C,PFe] (21), and Ir(CO)[2,6-(tBu2PO)2C6H3] (30) were characterized by X-ray crystallography.
On the basis of νCO values for carbonyl iridium derivatives, electronic characteristics of the corresponding
fragments {Ir[t-BuP,C,PM]}
n
(n = 0, +1) were elucidated. Complexes 6 and 7 reveal unprecedented catalytic
activity in cyclooctane dehydrogenation in the presence of tert-butylethylene as a hydrogen acceptor:
turnover numbers 3300, 2571, and 1843 were obtained for 6, 7, and the known complex IrH2[2,6-(tBu2PO)2C6H3] (4c), respectively, at 180 °C for 8 h. The high catalytic activity for 6 and 7 and the difference
in the catalytic activity of these “isostructural” complexes are discussed in terms of steric and electronic
effects.
