Organolanthanide-Based Coordination and Insertion Reactivity of the Anion Formed by Deprotonation of ε-Caprolactam

Methods to incorporate the strong ligation capacity of ε-caprolactam into monoanionic ligands suitable for electropositive metals such as yttrium are described. ε-Caprolactam, is deprotonated by (C 5 H 4 Me) 2 Y[N(SiMe 3 ) 2 ] to form the dimeric complex [(C 5 H 4 Me) 2 Y(μ-NC 6 H 10 O)] 2, 1 . Each caprolactamate anion, (NC 6 H 10 O) -, forms one Y−N bond and coordinates to both yttrium centers via a bridging oxygen such that yttrium has a formal coordination number of nine. ε-Caprolactam is also deprotonated by (C 5 Me 5 ) 2 Y(C 3 H 5 )(THF), to form the monomeric, pentamethylcyclopentadienyl analogue (C 5 Me 5 ) 2 Y(NC 6 H 10 O), 2, in which the caprolactamate anion chelates the formally eight-coordinate yttrium. CO 2 inserts into the Ln−N bond in 2 to form [(C 5 Me 5 ) 2 Y(μ-O 2 CNC 6 H 10 O)] 2, 3 . The tridentate monoanionic (O 2 CNC 6 H 10 O) - ligand forms an eight-membered ring via carboxylate oxygen atoms and also coordinates to each yttrium center via the oxygen originating from ε-caprolactam. Phenyl isocyanate inserts into the Y−N bond of 2 to form (C 5 Me 5 ) 2 Y[(μ 2 -OC(NPh)NC 6 H 10 O)], 4, which contains a planar ring and eight-coordinate yttrium. tert -Butyl isocyanide does not undergo insertion chemistry with 2, but instead forms the adduct (C 5 Me 5 ) 2 Y(NC 6 H 10 O)(CNCMe 3 ), 5 .