Unusual η 1 ‐Coordinated Alkyne and Alkene Complexes

Abstract This mechanistic study demonstrates that an unusual η 1 ‐coordinated alkyne complex is critical for the 1‐pentyne 1,1‐diboration reaction. The comparative studies suggest the “pull–push” antagonistic effect arising from Lewis acidity and steric congestion as the reason for the existence of η 1 ‐coordinated alkyne complexes. Analogous η 1 ‐coordinated alkene complexes are also predicted and seem to be promising for their application to the important olefin polymerization reaction.