Rare-earth metal methylidene complexes with Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3 core structure

Abstract

Trinuclear rare-earth metal methylidene complexes with a Ln₃(μ₃-CH₂)(μ₃-Me)(μ₂-Me)₃ structural motif were synthesized by applying three protocols. Polymeric [LuMe₃]_n (1-Lu) reacts with the sterically demanding amine H[NSiMe₃(Ar)] (Ar = C₆H₃iPr₂-2,6) in tetrahydrofuran via methane elimination to afford isolable monomeric [NSiMe₃(Ar)]LuMe₂(thf)₂ (4-Lu). The formation of trinuclear rare-earth metal tetramethyl methylidene complexes [NSiMe₃(Ar)]₃Ln₃(μ₃-CH₂)(μ₃-Me)(μ₂-Me)₃(thf)₃ (7-Ln; Ln = Y, Ho, Lu) via reaction of [LnMe₃]_n (1-Ln; Ln = Y, Ho, Lu) with H[NSiMe₃(Ar)] is proposed to occur via an “intermediate” species of the type [NSiMe₃(Ar)]LnMe₂(thf)_x and subsequent C−H bond activation. Applying Lappert's concept of Lewis base-induced methylaluminate cleavage, compounds [NSiMe₃(Ar)]Ln(AlMe₄)₂ (5-Ln; Ln = Y, La, Nd, Ho) were converted into methylidene complexes 7-Ln (Ln = Y, Nd, Ho) in the presence of tetrahydrofuran. Similarly, tetramethylgallate complex [NSiMe₃(Ar)]Y(GaMe₄)₂ (6-Y) could be employed as a synthesis precursor for 7-Y. The molecular composition of complexes 4-Ln, 5-Ln, 6-Y and 7-Ln was confirmed by elemental analyses, FTIR spectroscopy, ¹H and ¹³C NMR spectroscopy (except for holmium derivatives) and single-crystal X-ray diffraction. The Tebbe-like reactivity of methylidene complex 7-Nd with 9-fluorenone was assessed affording oxo complex [NSiMe₃(Ar)]₃Nd₃(μ₃-O)(μ₂-Me)₄(thf)₃ (8-Nd). The synthesis of 5-Ln yielded [NSiMe₃(Ar)]₂Ln(AlMe₄) (9-Ln; Ln = La, Nd) as minor side-products, which could be obtained in moderate yields when homoleptic Ln(AlMe₄)₃ were treated with two equivalents of K[NSiMe₃(Ar)].