Synthesis, Characterization, and Reactivity of Lanthanide Amides Incorporating Neutral Pyrrole Ligand. Isolation and Characterization of Active Catalyst for Cyanosilylation of Ketones

A series of lanthanide amido complexes
incorporating a neutral
pyrrole ligand were synthesized and characterized, and their catalytic
activities were studied. Treatment of [(Me3Si)2N]3­Ln­(μ-Cl)­Li­(THF)3 with
1 equiv of [(2,5-Me2C4H2N)­CH2CH2] 2NH (1) in toluene
afforded the corresponding lanthanide amides with the formula [η5:η1-(2,5-Me2C4H2N)­CH2CH2]2­NLn­[N­(SiMe3)2]2 (Ln = La (2), Nd (3)). Reaction of 2 or 3 with N,N′-dicyclo­hexyl­carbo­diimide
(CyNCNCy) gave the carbodiimide selectively inserted
into the appended Ln–N bond products formulated as CyNC­{[N,N-(2,5-Me2C4H2N)­CH2CH2]2N}­NCyLn­[N­(SiMe3)2]2 (Ln = La (4), Nd (5)). Reactions of the lanthanide amides with Me3SiCN were also examined. A mixed reaction of [(Me3Si)2N]3­La­(μ-Cl)­Li­(THF)3, [(2,5-Me2C4H2N)­CH2CH2]2NH (1), and Me3SiCN in toluene at room temperature produced the novel cyano bridged
dinuclear lanthanum complex η5:η1:η3-[(2,5- Me2C4H2N­CH2CH2)2N]­La­[N­(SiMe3)2]­(μ-CN)­La­[N­(SiMe3)2]3 (6). The stoichiometric
reactions of lanthanide amides 2 or 3 with
Me3SiCN produced the novel trinuclear lanthanum and neodymium
complexes {(η5:η1-[(2,5-Me2C4H2­NCH2CH2)2N]­Ln­[N­(SiMe3)2]­(μ-CN)}3 (Ln = La (7), Nd (8)) through selective
σ-bond metathesis reaction of the terminal Ln–N (N­(SiMe3)2) bond with the Si–C bond of Me3SiCN. On the basis of the stoichiometric reactions of complexes 2, or 3 with Me3SiCN, complexes 2, 3, 4, 5, 7, and 8 as catalysts for cyanosilylation of ketones
were investigated. Results indicated that these complexes displayed
a high catalytic activity on addition of Me3SiCN to ketones,
and the activity of the complexes has the order of 7 ∼ 8 > 2 ∼ 3 ∼ 4 ∼ 5. Thus, complex 7 or 8 was proposed
as the active catalyst in the catalytic reaction for the precatalysts
of 2 and 3.