Bulky Formamidinate-Supported Lanthanoid Halides and Alkyls, Including a Rare Terminal La-Me Species

The oxidation of [Sm(DippForm)(2)(thf)(2)] (1; DippFormH = N,N'-bis(2,6-diisopropylphenyl)forrnamidine) by tert-butyl chloride, 1,2-dibromoethane, and iodine, respectively, at ambient temperature led to the isolation of the light yellow crystalline samarium(III) halide complexes [Sm(DippForm)(2)X(thf)] (2, X = Cl; 3, X = Br; 4, X = I) in good yield. The subsequent metathesis reaction of [Ln(DippForm)(2)X(thf)] (2, Ln = Sm, X = Cl; Ln = La, X = F) with LiMe and LiCH2SiMe3 generated the samarium alkyl complexes [Sm(DippForm)(2)R(thf)] (5, R = Me; 6, R = CH2SiMe3) and the rare terminal La-Me complex [La-(DippForm)(2)Me(thf)] (7). The attempted ligand exchange reaction of 7 with 1,2,3,4-tetraphenylcyclopentadiene gave, unexpectedly, the homoleptic tris-(formamidinato)lanthanum complex [La(DippForm)(3)] (8) in very low yield. The redox transmetalation/protolysis (RTP) reaction from samarium metal with bis(2-bromo-3,4,5,6-tetrafluorophenyl)mercury and DippFormH in thf yielded the mono(formamidinato)samarium(III) complex [Sm(DippForm)Br-2(thf)(3)] (9) as a coproduct with the bis(formamidinate) 3. Redox reaction of the divalent samarium complex [Sm(DippForm)(2)(thf)(2)] (1) with ciiphenylmercury resulted in the ethenolate complex [Sm(DippForm)(2)(OCH=CH2)(thf)] (10) instead of the target Sm-Ph complex, the product resulting from the decomposition of Lewis base thf molecules.