The Nature of seat-ligand fitting in coordination space. V. Steric hindrances and reaction mechanisms — a further discussion on the structure and chemistry of compounds containing three π-bonded cyclopentadienyl groups

Catalytic Organic Transformations Mediated by Actinide Complexes

“…The first step of the mechanism includes the coordination of ε-caprolactone to the thorium center, followed by a displacement of The actinide bis(amidinate) systems ( Figure 8) with functionalized side arms on the amidinate ligand have shown to promote the ROP of ε-caprolactone, furnishing linear polymers with narrow molecular weight distributions [90,91]. A systematic study of a series of bis(amidinate) thorium and uranium complex (21)(22)(23)(24)(25) with a dimethylamine side arms has shown an increase in the catalytic activity in the order 23 > 24 > 25 > 21 > 22 [91]. Hence, the thorium complexes 23-25 are more active than their uranium analogues 21-22, and complexes with a phenyl at the ipso-position (21, 23-24) are more active than the analogous compounds with a pyridyl moiety at the ipso-position (22 and 25).…”

“…The steric hindrance in actinide complexes has been described by the "packing saturation model", which attributes the stability of the respective coordination complex to the sum of the ligands cone angles. Hence, coordinative "over saturated" complexes display lower stabilities [20][21][22]. In addition, de Matos introduced the "steric coordination number" for actinide complexes, which implies a pure ionic bonding model, and is based on the ligands cone angles [23].…”