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 [(Me 3 Si) 2 N] 3 Ln(μ-Cl)Li(THF) 3 with 1 equiv of [(2,5-Me 2 C 4 H 2 N)CH 2 CH 2 ] 2 NH ( 1 ) in toluene afforded the corresponding lanthanide amides with the formula [η 5:η 1 -(2,5-Me 2 C 4 H 2 N)CH 2 CH 2 ] 2 NLn[N(SiMe 3 ) 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-Me 2 C 4 H 2 N)CH 2 CH 2 ] 2 N}NCyLn[N(SiMe 3 ) 2 ] 2 (Ln = La ( 4 ), Nd ( 5 )). Reactions of the lanthanide amides with Me 3 SiCN were also examined. A mixed reaction of [(Me 3 Si) 2 N] 3 La(μ-Cl)Li(THF) 3, [(2,5-Me 2 C 4 H 2 N)CH 2 CH 2 ] 2 NH ( 1 ), and Me 3 SiCN in toluene at room temperature produced the novel cyano bridged dinuclear lanthanum complex η 5:η 1:η 3 -[(2,5- Me 2 C 4 H 2 NCH 2 CH 2 ) 2 N]La[N(SiMe 3 ) 2 ](μ-CN)La[N(SiMe 3 ) 2 ] 3 ( 6 ). The stoichiometric reactions of lanthanide amides 2 or 3 with Me 3 SiCN produced the novel trinuclear lanthanum and neodymium complexes {(η 5:η 1 -[(2,5-Me 2 C 4 H 2 NCH 2 CH 2 ) 2 N]Ln[N(SiMe 3 ) 2 ](μ-CN)} 3 (Ln = La ( 7 ), Nd ( 8 )) through selective σ-bond metathesis reaction of the terminal Ln–N (N(SiMe 3 ) 2 ) bond with the Si–C bond of Me 3 SiCN. On the basis of the stoichiometric reactions of complexes 2, or 3 with Me 3 SiCN, 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 Me 3 SiCN 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 .