Rational Preparation of Well-Defined Multinuclear Iridium–Aluminum Polyhydride Clusters and Comparative Reactivity
Léon Escomel, Naïme Soulé, Emmanuel Robin, Iker Del Rosal, Laurent Maron, Erwann Jeanneau, Chloé Thieuleux, Clément Camp
Abstract
We report an original alkane elimination approach, entailing the protonolysis of triisobutylaluminum by the acidic hydrides from Cp*IrH4. This strategy allows access to a series of well-defined tri- and tetranuclear iridium aluminum polyhydride clusters, depending on the stoichiometry: [Cp*IrH3Al(iBu)2]2 (1), [Cp*IrH2Al(iBu)]2 (2), [(Cp*IrH3)2Al(iBu)] (3), and [(Cp*IrH3)3Al] (4). Contrary to most transition-metal aluminohydride complexes, which can be considered as [AlHx+3]x– aluminates and LnM+ moieties, the situation here is reversed: These complexes have original structures that are best described as [Cp*IrHx]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*IrH3]− moieties are labile and can be transmetalated to yield potassium ([KIrCp*H3], 8) or silver (([AgIrCp*H3]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.