Monomeric CpAl(i): synthesis, reactivity, and the concept of valence isomerism.

With the isolation of CpAl (), the first monomeric Cp-based Al(i) species could be realized in a pure form a three-step reaction sequence (salt elimination/adduct formation/adduct cleavage) starting from readily available AlBr. Due to its monomeric structure, reactions involving were found to proceed more selectively, faster, and under milder conditions than for tetrameric (Cp*Al). Thus, readily formed simple Lewis acid-base adducts with BuAlCl () and AlBr (), reactions that before have always been interfered with by the presence of aluminum halide bonds. In addition, the 2 : 1 reaction of with AlBr enabled the realization of the very rare trialuminum adduct species . also reacted rapidly with NO and PhN at room temperature to afford AlO and AlN heterocycles and , respectively. With the structural characterization of products and , the reaction of monovalent with CpAlBr () provided the first experimental evidence for the concept of valence isomerism between dialanes and their Al(i)/Al(iii) Lewis adducts.