Agostic interactions in yttrium alkyls are structure dependent. Primary alkyl yttrium complexes have beta-CH2 agostic interactions at low temperature, but a shift toward alpha-agostic interactions occurs on warming. For the more crowded beta-disubstituted yttrium alkyls, an alpha-CH2 agostic interaction is seen. The thermodynamics of alkene binding to the primary alkyl yttrium complex CP*2YCH2CH2CH(CH3)(2) (2) depend strongly on the structure of the alkene. A single allylic substituent on the alkene has a small effect on alkene binding, but a second allylic substituent has a large destabilizing effect. Propene binding to yttrium alkyls is largely independent of the nature of the alkyl ligand. Equilibrium constants for propene binding to n-, gamma-substituted, beta-substituted, and secondary alkyl yttrium complexes are similar. The rate of migration of an alkyl group to a coordinated alkene depends strongly on the structure of the alkyl group: n-alkyl; gamma-substituted much greater than beta-substituted much greater than alpha-substituted. The similar to200-fold slower insertion of propene into Cp*2YCH(2)-CH(CH3)(2) (6) than that into CP*(2)gammaCH(2)CH(2)CH(CH3)(2) (2) is therefore due to kinetically slow migration of the beta-disubstituted alkyl group of 6 and not to differences in the equilibrium binding of propene. Processes related to chain transfer and site epimerization at the metal center are also reported.