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 (<b>1</b>) in toluene afforded the corresponding lanthanide amides with the formula [η⁵:η¹-(2,5-Me₂C₄H₂N)­CH₂CH₂]₂­NLn­[N­(SiMe₃)₂]₂ (Ln = La (<b>2</b>), Nd (<b>3</b>)). Reaction of <b>2</b> or <b>3</b> with <i>N</i>,<i>N</i>′-dicyclo­hexyl­carbo­diimide (CyNCNCy) gave the carbodiimide selectively inserted into the appended Ln–N bond products formulated as CyNC­{[<i>N</i>,<i>N</i>-(2,5-Me₂C₄H₂N)­CH₂CH₂]₂N}­NCyLn­[N­(SiMe₃)₂]₂ (Ln = La (<b>4</b>), Nd (<b>5</b>)). 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 (<b>1</b>), 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 (<b>6</b>). The stoichiometric reactions of lanthanide amides <b>2</b> or <b>3</b> 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 (<b>7</b>), Nd (<b>8</b>)) 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 <b>2</b>, or <b>3</b> with Me₃SiCN, complexes <b>2</b>, <b>3</b>, <b>4</b>, <b>5</b>, <b>7</b>, and <b>8</b> 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 <b>7</b> ∼ <b>8</b> > <b>2</b> ∼ <b>3</b> ∼ <b>4 ∼ <b>5</b></b>. Thus, complex <b>7</b> or <b>8</b> was proposed as the active catalyst in the catalytic reaction for the precatalysts of <b>2</b> and <b>3