Rational Preparation of Well-Defined Multinuclear Iridium-Aluminum Polyhydride Clusters and Comparative Reactivity.

We report an original alkane elimination approach, entailing the protonolysis of triisobutylaluminum by the acidic hydrides from Cp*IrH 4 . This strategy allows access to a series of well-defined tri- and tetranuclear iridium aluminum polyhydride clusters, depending on the stoichiometry: [Cp*IrH 3 Al( i Bu) 2 ] 2 ( 1 ), [Cp*IrH 2 Al( i Bu)] 2 ( 2 ), [(Cp*IrH 3 ) 2 Al( i Bu)] ( 3 ), and [(Cp*IrH 3 ) 3 Al] ( 4 ). Contrary to most transition-metal aluminohydride complexes, which can be considered as [AlH x +3 ] x- aluminates and LnM + moieties, the situation here is reversed: These complexes have original structures that are best described as [Cp*IrH x ] n - iridate units surrounding cationic Al(III) fragments. This is corroborated by reactivity studies, which show that the hydrides are always retained at the iridium sites and that the [Cp*IrH 3 ] - moieties are labile and can be transmetalated to yield potassium ([KIrCp*H 3 ], 8 ) or silver (([AgIrCp*H 3 ] n , 10 ) derivatives of potential synthetic interest. DFT calculations show that the bonding situation can vary in these systems, from 3-center 2-electron hydride-bridged Lewis adducts of the form Ir-H⇀Al to direct polarized metal-metal interaction from donation of d -electrons of Ir to the Al metal, and both types of interactions take place to some extent in each of these clusters.