Crystalline heaviest pnictogen-dipyrromethenes: isolation, characterization, and reactivity

The heaviest pnictogen-dipyrromethenes DPMPnCl₂ (Pn = Sb, 3; Bi 4), which are direct analogues of boron-dipyrromethene (BODIPY), have been readily prepared and isolated as crystalline solids. Both compounds display green photoluminescence with small full widths at half maximum in toluene. Moreover, the reduction of 3 with sodium metal afforded the cyclic dicoordinate stibinidene 5.

Optical and Thermal Investigations of Eutectic Metallomesogen Mixtures Based on Salicylaldiaminates Metal Complexes with a Large Nematic Stability Range

The mesomorphic behavior and the miscibility properties of binary mixtures of a new series of Schiff base metallomesogen (MOM) are evaluated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Nuclear magnetic resonance (NMR), elemental analysis (CHNX), Fourier−transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to certify the molecular structure of the compounds. The results revealed that the studied mixtures are completely miscible throughout the composition field and exhibit a nematic phase which covered the whole composition range. In the mixtures, the stability of the nematic phase varies continuously, and it is possible to highlight the presence of a eutectic composition with a wide mesogenic stability range.

Trimethylscandium

The hitherto unknown homoleptic tetramethylaluminate complex [Sc(AlMe₄)₃] could be obtained by reacting the ate complex [Li₃ScMe₆(thf)_1.2] with AlMe₃ in the cold. It cocrystallizes with AlMe₃ as [Sc(AlMe₄)₃(Al₂Me₆)_0.5] and decomposes at ambient temperature in n-pentane via multiple C-H bond activations to the mixed methyl/methylidene complex [Sc₃(μ₃-CH₂)₂(μ₂-CH₃)₃(AlMe₄)₂(AlMe₃)₂]. Donor-induced methylaluminate cleavage of [Sc(AlMe₄)₃(Al₂Me₆)_0.5] produced [ScMe₃]_n in good yield, which could be derivatized with trimethyltriazacyclononane (Me₃TACN) to form the structurally characterizable [(Me₃TACN)ScMe₃]. Additionally, half-sandwich complex [Cp*Sc(AlMe₄)₂] and sandwich complex [Cp*₂Sc(AlMe₄)] were accessible by salt metathesis reactions from [Sc(AlMe₄)₃(Al₂Me₆)_0.5] and KCp* (Cp* = C₅Me₅). ⁴⁵Sc NMR spectroscopy was applied as a significant probe to evidence the existence of [ScMe₃]_n. Compounds [(Me₃TACN)ScMe₃] (+624.6 ppm) and [ScMe₃(thf)_x] (+601.7 ppm) gave large ⁴⁵Sc NMR shifts, revealing the strong deshielding effect of the σ-bonded alkyl ligands on the scandium nuclei. Ultimately, cationized [Sc(AlMe₄)₃(Al₂Me₆)_0.5] was employed in isoprene polymerization, leading to polymers in high yields (>95%) and with high (>90%) cis-1,4-polyisoprene content.

Unprecedentedly High Activity and/or High Regio-/Stereoselectivity of Fluorenyl-Based CGC Allyl-Type η3:η1-tert-Butyl(dimethylfluorenylsilyl)amido Ligated Rare Earth Metal Monoalkyl Complexes in Olefin Polymerization

A series of fluorenyl-based constrained-geometry-configuration (CGC) allyl-type rare earth metal monoalkyl complexes bearing the divalent anionic η3:η1-tert-butyl(dimethylfluorenylsilyl)amido (η3:η1-FluSiMe2NtBu) ligand (η3:η1-FluSiMe2NtBu)Ln(CH2SiMe3)(THF)2 (1-3) have been synthesized via the alkane elimination reaction between the FluHSiMe2NHtBu ligand and rare earth metal tri(trimethylsilylmethyl) complexes Ln(CH2SiMe3)3(THF)n. Their structures are characterized by means of NMR spectrum, elemental analyses, and X-ray diffraction. These complexes 1-3 are isostructural and isomorphous, and each of them adopts a distorted-trigonal-bipyramidal configuration containing one η3:η1-FluSiMe2NtBu ligand, one CH2SiMe3 ligand, and two THF molecules. Unlike traditional CGC allyl-type rare earth metal complexes showing no or low activity and regio-/stereoselectivity in styrene or MMA polymerization, these complexes 1-3 exhibit high catalytic activities and/or high regio-/stereoselectivities in the cis-1,4-polymerization of isoprene and myrcene or in the syndiotactic polymerization of styrene under the aid of different activators (borate or borane) and AlR3. The in situ 1H NMR spectra suggest that the exchanges of chelating ligands such as alkyl groups and divalent anionic η3:η1-FluSiMe2NtBu ligands between rare earth metal centers and Al centers result in the formation of a heterobimetallic tetraalkylaluminate complex R2Al(μ-R)2Ln(R)(μ-R)2AlR2, which is activated by activators to form a divalent cationic species [Ln(μ-R)2AlR2]2+ as a catalytically active species in the coordination-insertion polymerization of olefins.