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

Abstract

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.