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)­formamidine)
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)2X­(thf)] (2, X = Cl; 3, X = Br; 4, X = I) in good yield. The subsequent metathesis reaction
of [Ln­(DippForm)2X­(thf)] (2, Ln = Sm, X = Cl; Ln = La, X = F) with LiMe and LiCH2SiMe3 generated the samarium alkyl complexes [Sm­(DippForm)2R­(thf)] (5, R = Me; 6, R = CH2SiMe3) and the rare terminal La–Me complex
[La­(DippForm)2Me­(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)­Br2(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 diphenylmercury 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.

分别以叔丁基氯、1,2-二溴乙烷和碘为氧化剂，在室温下对配合物[Sm(DippForm)₂(四氢呋喃₂)]（1；其中DippFormH = N,N'-双(2,6-二异丙基苯基)甲脒）进行氧化反应，以较高收率分离得到浅黄色结晶性三价钐卤化物配合物[Sm(DippForm)₂X(thf)]（2，X=Cl；3，X=Br；4，X=I）。随后，以[Ln(DippForm)₂X(thf)]（2：Ln=Sm，X=Cl；3：Ln=La，X=F）为底物，与甲基锂（LiMe）和三甲基硅基甲基锂（LiCH₂SiMe₃）发生复分解反应，生成钐烷基配合物[Sm(DippForm)₂R(thf)]（5，R=Me；6，R=CH₂SiMe₃）以及罕见的端基La-Me配合物[La(DippForm)₂Me(thf)]（7）。尝试将配合物7与1,2,3,4-四苯基环戊二烯进行配体交换反应时，意外得到了均配型三(甲脒基)镧配合物[La(DippForm)₃]（8），但收率极低。以金属钐、双(2-溴-3,4,5,6-四氟苯基)汞与DippFormH为原料，在四氢呋喃（tetrahydrofuran, thf）中进行氧化转金属化/质子解（redox transmetalation/protolysis, 缩写RTP）反应，得到单(甲脒基)三价钐配合物[Sm(DippForm)Br₂(thf)₃]（9），其与双(甲脒基)配合物3为共存副产物。二价钐配合物[Sm(DippForm)₂(thf)₂]（1）与二苯基汞发生氧化还原反应时，并未得到目标的Sm-Ph配合物，而是生成了乙烯醇根配合物[Sm(DippForm)₂(OCH=CH₂)(thf)]（10），该产物源于路易斯碱四氢呋喃的分解。