Isolation and structure of a homoleptic yttrium trimethylsilylmethyl complex

Synthesis, Characterization, and Reactivity Studies of New Cyclam-Based Y(III) Complexes

[(Bn2Cyclam)Y(N(SiMe3)2)] was prepared by reaction of H2Bn2Cyclam with Y[N(SiMe3)2]3. The protonation of the macrocycle ligand in [(Bn2Cyclam)Y(N(SiMe3)2)] is observed upon reaction with [HNMe3][BPh4] leading to the formation of [(HBn2Cyclam)Y(N(SiMe3)2)][BPh4]. DFT analysis of [(Bn2Cyclam)Y(N(SiMe3)2)] showed that the HOMO is located on the anionic nitrogen atoms of the cyclam ring indicating that protonation follows orbital control. Addition of H2Bn2Cyclam and H2(3,5-tBu2Bn)2Cyclam to a 1:3 mixture of YCl3 and LiCH2SiMe3 in THF resulted in the formation of [((C6H4CH2)BnCyclam)Y(THF)(µ-Cl)Li(THF)2] and [Y{(η3-3,5-tBu2Bn)2Cyclam}Li(THF)], respectively. The reaction of H23,5-tBu2Bn2Cyclam with Y(CH2SiMe3)3(THF)2 was studied and monitored by a temperature variation NMR experiment revealing the formation of [(3,5-tBu2Bn2Cyclam)Y(CH2SiMe3)]. Preliminary catalytic assays have shown that [Y{(η3-3,5-tBu2Bn)2Cyclam}Li(THF)] is a very efficient catalyst for the intramolecular hydroamination of 2,2-diphenyl-pent-4-enylamine.

Scandium bis(trimethylsilyl)methyl complexes revisited: extending the 45Sc NMR chemical shift range and a new structural motif of Li[CH(SiMe3)2]

Depending on the molar ratio employed, the reaction of ScCl₃(thf)₃ with Li[CH(SiMe₃)₂] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Cl)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Cl)Li(thf)₃, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Me)Li(thf)₃. Aiming at homoleptic {Sc[CH(SiMe₃)₂]₃} both of the mixed [CH(SiMe₃)₂]/Me complexes were treated with AlMe₃. Although LiAlMe₄ separation occurred, aluminium complex Al[CH(SiMe₃)₂]Me₂(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and [Sc(CH₂SiMe₃)₄][Li(thf)₄] revealed the maximum downfield ⁴⁵Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe₃)₂]₃} was also attempted via the aryloxide route applying complexes Sc(OC₆H₂tBu₂-2,6-Me-4)₃ and [Sc(OC₆H₃iPr₂-2,6)₃]₂ along with Li[CH(SiMe₃)₂] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe₃)₂] in the solid state.

Synthesis and structural diversity of trivalent rare-earth metal diisopropylamide complexes

A series of rare-earth metal diisopropylamide complexes has been obtained via salt metathesis employing LnCl3(THF)x and lithium (LDA) or sodium diisopropylamide (NDA) in n-hexane. Reactions with AM : Ln ratios ≥3 gave ate complexes (AM)Ln(NiPr2)4(THF)n (n = 1, 2; Ln = Sc, Y, La, Lu; AM = Li, Na) in good yields. For smaller rare-earth metal centres such as scandium and lutetium, a Li : Ln ratio = 2.5 accomplished ate-free tris(amido) complexes Ln(NiPr2)3(THF). The chloro-bridged dimeric derivatives [Ln(NiPr2)2(μ-Cl)(THF)]2 (Ln = Sc, Y, La, Lu) could be obtained in high yields for Li : Ln = 1.6-2. The product resulting from the Li : La = 1 : 1.6 reaction revealed a crystal structure containing two different molecules in the crystal lattice, [La(NiPr2)2(THF)(μ-Cl)]2·La(NiPr2)3(THF)2. Recrystallization of the chloro-bridged dimers led to the formation of the monomeric species Ln(NiPr2)2Cl(THF)2 (Ln = Sc, Lu) and La(NiPr2)3(THF)2. The reaction of YCl3 and LDA with Li : Y = 2 in the absence of THF gave a bimetallic ate complex LiY(NiPr2)4 with a chain-like structure. For scandium, the equimolar reactions with LDA or NDA yielded crystals of tetrametallic mono(amido) species, {[Sc(NiPr2)Cl2(THF)]2(LiCl)}2 and [Sc(NiPr2)Cl2(THF)]4, respectively. Depending on the Ln(iii) size, AM, and presence of a donor solvent, ate complexes (AM)Ln(NiPr2)4(THF)n show distinct dynamic behaviour as revealed by variable temperature NMR spectroscopy. The presence of weak LnCH(iPr) β-agostic interactions, as indicated by Ln-N-C angles <105°, is corroborated by DFT calculations and NBO analysis.

Reactions of Hypersilyl Potassium with Rare-Earth Metal Bis(Trimethylsilylamides): Addition versus Peripheral Deprotonation

The scope of hypersilyl potassium, KHyp [Hyp = Si(SiMe3)3], as a silylation or deprotonation agent for some rare-earth bis(trimethylsilyl)amides has been explored. Thus, the reaction with Yb{N(SiMe3)2}2 affords the addition product [K][YbHyp{N(SiMe3)2}2] (2) in high yield, which contains a three-coordinate ytterbium atom, therefore representing the first example of a lanthanide silyl with a coordination number lower than 6. In contrast, deprotonation on the periphery is observed with the tris(amides) Ln{N(SiMe3)2}3 (Ln = Y, Yb) and compounds of the type [K][CH2Si(Me)2N(SiMe3)Ln{N(SiMe3)2}2] (Ln = Y (3), Yb (4)) are isolated. Crystallization of 3 from a mixture of benzene and heptane afforded the bis(benzene) solvate [(C6H6)2K][CH2Si(Me)2N(SiMe3)Y{N(SiMe3)2}2] (3a). The reaction between the strong bases nBuLi/tetramethylenediamine (TMEDA) or tBuLi with Y{N(SiMe3)2}3 or Yb{N(SiMe3)2}3 yielded the deprotonation product [(tmeda)Li][CH2Si(Me)2N(SiMe3)Y{N(SiMe3)2}2] (6) and the reduction product [LiYb{N(SiMe3)2}3] (7), respectively. Instead of the expected bimetallic product, the reaction between YbI(2) and 2 equiv of 3 gave the neutral complex [Y{CH2Si(Me)2N(SiMe3)}{N(SiMe3)2}(thf)] (8) in good yield. The compounds have been characterized by melting point, elemental analysis, IR spectroscopy, and X-ray crystallography and for selected species by 1H, 13C, 29Si, and 171Yb NMR spectroscopy. For 3a and 4, the nature of the bonding between the carbanionic centers and the lanthanide and potassium cations was studied by density functional theory calculations.