Recently, we synthesized the first observed d⁰- metal-alkyl-alkene complex by reaction of (Cp*₂YH)₂ with 3,3-dimethyl-1,4- pentadiene. Evidence for alkene coordination is based on differences between the ¹H and ¹³C NMR vinyl resonances of the chelate complex and those of the starting diene and an unchelated THF complex.