The behavior of pyrrolyl ligands within the rare-earth metal alkyl complexes. Insertion of CN and CO double bonds into Ln–σ-C bonds

Abstract

This paper presents some unusual reactions of lanthanide tris(alkyl)s or lanthanide mono-Cp′ (Cp′ = (C₅Me₄)SiMe₃) bis(alkyl)s with pyrrolyl ligands, and the η⁵- or η¹-coordination mode of the pyrrolyl ring, as well as CN and CO double bonds insertion into Ln–σ-C moities. N,N,O-tridentate ligand HL¹, 2-(2-CH₃OC₆H₃NCH)–C₄H₃NH, was prepared. Treatment of HL¹ with rare-earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, generated centrosymmetric bimetallic (pyrrolylaldiminato)lanthanide mono(alkyl) complexes [{2-(2-CH₃OC₆H₃NC(H)R)–C₄H₃N}LnR]₂ (1a: Ln = Y; 1b: Ln = Lu) (R = CH₂SiMe₃). In this process, HL¹ was deprotonated by the metal alkyl and its imino CN group was deactivated by the intramolecular alkylation, generating dianionic species that bridged the two metal alkyl units in η⁵/η¹:κ¹ modes. When the reaction was carried out in dimethoxyethane (DME), asymmetric complex [2-(2-CH₃OC₆H₃NC(H)R)–C₄H₃N]₂Y₂R₂(DME) (2) was given. Furthermore, the reaction of alkyl complex 1b and benzophenone (Ph₂CO) afforded alkyl-insertion product [{2-(2-CH₃OC₆H₃NC(H)R)–C₄H₃N}LuOC(R)Ph₂]₂ (3). Both the intermolecular alkylation and the pyrrole's behavior as the hetero-cyclopentadienyl ligand were also observed in complexes 2 and 3. HL¹ reacted with (η⁵-Cp′)Y(CH₂SiMe₃)₂(THF) (E) to form a mixed ligands supported alkyl complex [(η⁵-Cp′)(L¹)]Y(CH₂SiMe₃)(THF) (4), whilst complex E was treated with 2-(2,6-iPr₂C₆H₃NCH)–C₄H₃NH (HL²) to yield [(η⁵-Cp′)(L²)]Y(CH₂SiMe₃)(THF) (5). However, reaction of E and 2-(Me₂NCH₂)–C₄H₃NH (HL³) afforded Y[(η⁵-Cp′)(L³)₂] (6), and ligand redistribution was found in this process. The molecular structures of complexes 5 and 6 were confirmed by X-ray diffraction, which indicated that the CN double bond survived and the pyrrolyl ring coordinated to the metal center in η¹-mode.