A Comparison of Analogous 4f‐ and 5f‐Element Compounds: Syntheses, X‐ray Crystal Structures and Catalytic Activity of the Homoleptic Amidinate Complexes [M{MeC(NCy) 2 } 3 ] (M = La, Nd or U)

Reaction of UCl 4 with [Li{RC(NCy) 2 }(THF)] 2 (R = Me, 1a ; R = n Bu, 1b ) in THF gave the tris(amidinate) compounds [U{RC(NCy) 2 } 3 Cl] (R = Me, 2a ; R = n Bu, 2b ) which were reduced with lithium powder in THF to the homoleptic complexes [U{RC(NCy) 2 } 3 ] (R = Me, 3a ; R = n Bu, 3b ). Complexes 1a , 1b , 2a and 3a have been crystallographically characterized. Comparison of the crystal structure of 3a with those of the lanthanide analogues [Ln{MeC(NCy) 2 } 3 ] (Ln = La, 4 ; Ln = Nd, 5 ; Ln = Yb, 6 ) shows that the average U−N distance is shorter than expected from a purely ionic bonding model. The uranium complex 3a is much less efficient than its lanthanide counterparts in the catalytic polymerization of ϵ‐caprolactone because of its rapid oxidation into U IV species. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)