Alkynylaluminum Synthesis Catalyzed by a Zwitterionic Neodymium(III) Heterobimetallic Compound

Abstract

The reaction of H{PhB(OxMe2)2C5H5} (OxMe2 = 4,4-dimethyl-2-oxazoline) with Nd(AlMe4)3 (1) provides Me2Al{(OxMe2)2PhBCp}Nd(AlMe4)2 (2) as a heterobimetallic complex containing inequivalent organoaluminum sites. The piano-stool coordination geometry around Nd includes a rare O-bonded oxazoline, while both oxazolines coordinate to AlMe2 as part of a 6-membered, nonplanar BC2N2Al ring. The zwitterionic κ2-Ph(C5H5)B(OxMe2)2AlMe2 (3), formed by the protolytic reaction of H{PhB(OxMe2)2C5H5} and (AlMe3)2, also provides 2 upon reaction with Nd(AlMe4)3. Compounds 1–3 are precatalysts for the selective metalation of terminal alkynes by trialkylaluminums to yield (alkynyl)dialkylalanes of the type R′C≡C–AlR2, which are valuable as alkynyl transfer reagents. This catalytic reaction provides metalation products exclusively, as compared to the mixture of products from uncatalyzed processes. In addition, heteroleptic heterobimetallic 2 is a superior catalyst to 1 and 3.