Rare-earth metal hydrides supported by silicon-bridged boratabenzene fluorenyl ligands: synthesis, structure and reactivity

Abstract

The reactions of rare-earth metal benzyl complexes supported by silicon-bridged boratabenzene fluorenyl ligands with PhSiH₃ in toluene gave the corresponding dinuclear hydrides [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}Ln(μ-H)(THF)]₂ (3-Ln; Ln = La, Nd, Gd), wherein the rare-earth metal ions are linked by both silicon-bridged boratabenzene fluorenyl ligands and hydrido ligands. The reactivity of these hydrides toward unsaturated substrates was studied. Among these, alkynides [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}Ln(μ-CCPh)]₂ (4-Ln; Ln = La, Nd) were obtained via the σ-bond metathesis reaction, when 3-Ln (Ln = La, Nd) was treated with phenylacetylene. While reacting with 3-hexyne, the mono-addition product [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}Ln]₂(μ-H)[μ-C(Et)[double bond, length as m-dash]C(H)Et] (5-Ln; Ln = La, Nd) was formed. Further investigations on the reactivity of 3-La displayed that benzonitrile and tert-butyl isonitrile readily inserted into the La-H bonds, affording an azomethine complex [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}La{μ-N[double bond, length as m-dash]C(H)Ph}]₂ (6-La) and an N-tert-butylformimidoyl complex [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}La{μ,η²-C(H)[double bond, length as m-dash]N^tBu}]₂ (7-La), respectively. The reaction with N,N'-diisopropylcarbodiimide at room temperature or at 75 °C gave a dimeric complex [{μ-[Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]}La]₂(μ-H)[μ-N(ⁱPr)CHN(ⁱPr)] (8-La) or a monomeric complex [Me₂Si(C₁₃H₈)(C₅H₄BNEt₂)]La[N(ⁱPr)CHN(ⁱPr)] (9-La), respectively.