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 UCl4 with [Li{RC(NCy)(2)}(THF)](2) (R = Me, 1a; R = nBu, 1b) in THF gave the tris(amidinate) compounds [U{RC(NCy)(2)}(3)Cl] (R = Me, 2a; R = nBu, 2b) which were reduced with lithium powder in THF to the homoleptic complexes [U{RC(NCy)(2)}(3)] (R = Me, 3a; R = nBu, 3b). Complexes la, 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 E:caprolactone because of its rapid oxidation into U-IV species. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.