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.

Sterically (un)encumbered mer-tridentate N-heterocyclic carbene complexes of titanium(iv) for the copolymerization of cyclohexene oxide with CO2

Titanium(iv) complexes bearing an unsubstituted tridentate bis(phenolate) N-heterocyclic carbene (NHC) were synthesized and structurally identified.

Cerium tetrakis(diisopropylamide)--a useful precursor for cerium(IV) chemistry

Homoleptic cerium(IV) diisopropylamide was synthesized via oxidation of ate complex Ce(NiPr2)4Li(thf) with trityl chloride or hexachloroethane. Due to its ready accessibility, and high pKa value of the proligand HNiPr2, Ce(NiPr2)4 features a promising candidate for protonolysis reactions, as shown for the synthesis of dimeric cerium(IV) tetrakis(1,1,3,3-N,N,N',N'-tetramethylguanidinate).

Siloxide Complexes of Chromium(II), Manganese(II), Cobalt(II), and Chromium(III) Incorporating Potassium(I)

Heteroleptic ate complexes of the type K[M{N(SiMe3)2}2{OSi(OtBu)3}] (M = Cr, Mn, Co) were synthesized by adding one equivalent of the potassium salt KOSi(OtBu)3 to the bis(trimethylsilyl)amide precursors [Cr{N(SiMe3)2}2(thf)2], [Mn{N(SiMe3)2}2(thf)] and [Co{N(SiMe3)2}2(thf)], respectively. Surprisingly, the reaction of CrCl3(thf)3 with only two equivalents of KOSi(OtBu)3 yielded the homoleptic ate complex K[Cr{OSi(OtBu)3}4]. The compounds were characterized by elemental analysis and DRIFT spectroscopy as well as X-ray crystallography.

Selective rearrangement of terminal epoxides into methylketones catalysed by a nucleophilic rhodium–NHC–pincer complex

The highly nucleophilic complex 1 isomerises terminal epoxides exclusively to the respective methylketones in very high yield under mild conditions.

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

Although protected from intermolecular deactivation by a picket-fence-type arrangement of bulky amido ligands the CH₂²⁻ moiety is readily converted into oxo species.

Reactivity of halfsandwich rare-earth metal methylaluminates toward potassium (2,4,6-tri-tert-butylphenyl)amide and 1-adamantylamine

Donor functionalities drastically affect salt-metathetical methylaluminato–amido exchange reactions in Cp^RLn(AlMe₄)₂ by triggering methylaluminate cleavage and C–H bond activation of proximal aliphatic groups.

Europium bis(dimethylsilyl)amides including mixed-valent Eu3[N(SiHMe2)2]6[μ-N(SiHMe2)2]2

Trivalent Eu[N(SiHMe2)2]3(THF)2 can easily be synthesized by applying a routine salt metathesis protocol (EuCl3(THF)2 and 3 equiv. of Li[N(SiHMe2)2] in n-hexane) which crystallizes isotypically to its analogues of the rare-earth metal series (space group P21/c). Transsilylamination of Eu[N(SiMe3)2]2(THF)2 with a slight excess of HN(SiHMe2)2 in n-hexane-THF yields the divalent trinuclear compound Eu{[μ-N(SiHMe2)2]2Eu[N(SiHMe2)2](THF)}2, the solid-state structure of which differs significantly from the samarium and ytterbium analogues by showing three unique molecules in the asymmetric unit of which one is related to the two others by an inversion. Using crude Eu[N(SiMe3)2]3 in transsilylamination reactions with HN(SiHMe2)2 in n-hexane afforded n-hexane-insoluble trivalent ate complexes {MEu[N(SiHMe2)2]4}n (M = Na, K) depending on the synthesis conditions of Eu[N(SiMe3)2]3. Performing the transsilylamination of Eu[N(SiMe3)2]3 with a large excess of HN(SiHMe2)2 at elevated temperatures gave reproducibly the donor-free, mixed-valent, trinuclear compound Eu(II){[μ-N(SiHMe2)2]Eu(III)[N(SiHMe2)2]3}2 in good yield.

Theory-assisted development of a robust and Z-selective olefin metathesis catalyst

DFT calculations have predicted a new, highly Z-selective ruthenium-based olefin metathesis catalyst that is considerably more robust than the recently reported (SIMes)(Cl)(RS)RuCH(o-OiPrC6H4) (3a, SIMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene, R = 2,4,6-triphenylbenzene) [J. Am. Chem. Soc., 2013, 135, 3331]. Replacing the chloride of 3a by an isocyanate ligand to give 5a was predicted to increase the stability of the complex considerably, at the same time moderately improving the Z-selectivity. Compound 5a is easily prepared in a two-step synthesis starting from the Hoveyda-Grubbs second-generation catalyst 3. In agreement with the calculations, the isocyanate-substituted 5a appears to be somewhat more Z-selective than the chloride analogue 3a. More importantly, 5a can be used in air, with unpurified and non-degassed substrates and solvents, and in the presence of acids. These are traits that are unprecedented among highly Z-selective olefin metathesis catalysts and also very promising with respect to applications of the new catalyst.

Asymmetric synthesis of chloroisothreonine derivatives via syn-stereoselective Mannich-type additions across N-sulfinyl-α-chloroimines

Mannich-type reactions across N-sulfinyl-α-chloroaldimines resulted in syn-stereoselective synthesis of chloroisothreonine derivatives as excellent building blocks.

Dynamics and thermodynamics of crystalline polymorphs. 2. β-Glycine, analysis of variable-temperature atomic displacement parameters

The molecular dynamics in the crystal and the thermodynamic functions of the β-polymorph of glycine have been determined from a combination of molecular translation-libration frequencies reflecting the temperature dependence of atomic displacement parameters (ADPs), with frequencies derived from ONIOM(DFT:PM3) calculations on a 15-molecule β-glycine cluster. ADPs have been obtained from variable-temperature diffraction data to 0.5 Å resolution collected with X-ray synchrotron (10-300 K) and sealed tube radiation (50-298 K). At the higher temperatures, the ADPs of β-glycine from synchrotron are larger than those from sealed tube probably due to different experimental conditions. The lattice vibration frequencies from normal-mode analysis of ADPs and the internal vibration frequencies from ONIOM(B3LYP/6-311+G(2d,p):PM3) calculations agree with those from spectroscopy. Estimation of thermodynamic functions using the vibrational frequencies, the Einstein and Debye models of heat capacity, and the room-temperature compressibility provides C(p), H(vib), and S(vib) that agree with those from calorimetry. The β-phase with higher H and G is found to be less stable than the α-phase in the temperature range of the experiment.