Terminal and bridging parent amido 1,5-cyclooctadiene complexes of rhodium and iridium

摘要

The ready availability of rare parent amido d8 complexes of the type [{M(μ-NH2)(cod)}2] (M=Rh (1), Ir (2); cod=1,5-cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di-olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ-NH2)(CO)2}2] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH2Cl 2 or CHCl3, giving the diiridium(II) products [(Cl)(cod)Ir(μ-NH2)2Ir(cod)(R)] (R=CH2Cl or CHCl2) as a result of a two-center oxidative addition and concomitant metal-metal bond formation. However, reaction with ClCH2CH 2Cl afforded the symmetrical adduct [{Ir(μ-NH2)(Cl) (cod)}2] upon release of ethylene. We found that the rhodium complex 1 exchanged the di-olefines stepwise upon addition of selected phosphanes (PPh3, PMePh2, PMe2Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ-NH2)2Rh(PR3) 2], and finally the isolation of the respective tetraphosphanes [{Rh(μ-NH2)(PR3)2}2]. On the other hand, the iridium complex 2 reacted with PMe2Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH2)(PMePh2)2]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh2)2]. The heterocyclic carbene IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) also split the amido bridges in complexes 1 and 2, allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH 2)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs2CO3, finding that the iridium complex 2 is more active than the rhodium analogue 1.