Condensation of phthalodinitrile and 2-amino-5,6,7,8-tetrahydroquinoline gave the bis(2-pyridylimino)isoindole protioligand 1 (thqbpiH) in high yield. Deprotonation of thqbpiH (1) using LDA in THF at -78 °C yields the corresponding lithium complex [Li(THF)(thqbpi)] (2) in which the lithium atom enforces almost planar arrangement of the tridentate ligand, with an additional molecule of THF coordinated to Li. Reaction of cobalt(II) chloride or iron(II) chloride with one equivalent of the lithium complex 2 in THF led to formation of the metal complexes [CoCl(THF)(thqbpi)] (3a) and [FeCl(THF)(thqbpi)] (3b). The paramagnetic susceptibility of 3a,b in solution was measured by the Evans method (3a: μ(eff) = 4.17 μ(B); 3b: μ(eff) = 5.57 μ(B)). Stirring a solution of 1 and cobalt(II) acetate tetrahydrate in methanol yielded the cobalt(II) complex 4 which was also accessible by treatment of 3a with one equivalent of silver or thallium acetate in DMSO. Whereas 3a,b were found to be mononuclear in the solid state, the acetate complex 4 was found to be dinuclear, the two metal centres being linked by an almost symmetrically bridging acetate. For all transition metal complexes paramagnetic (1)H as well as (13)C NMR spectra were recorded at variable temperatures. The complete assignment of the paramagnetic NMR spectra was achieved by computation of the spin densities within the complexes using DFT. The proton NMR spectra of 3a and 3b displayed dynamic behaviour. This was attributed to the exchange of coordinating solvent molecules by an associative mechanism which was analysed using lineshape analysis (ΔS(≠)= -154 ± 25 J mol(-1) K(-1) for 3a and ΔS(≠) = -168 ± 15 J mol(-1) K(-1) for 3b).
Since the first report in the early 1950s, 1,3‐bis(2‐pyridylimino)isoindolines (BPIs) have found widespread applications in organic, inorganic and materials chemistry. This microreview focuses on recent progress towards chiral BPI derivatives as ligands for enantioselective catalysis as well as developments in the use of BPI complexes in materials science, focusing on luminescent and birefringent materials.
High-spin Fe(II)-alkyl complexes with bis(pyridylimino)isoindolato ligands were synthesized and their paramagnetic (1)H and (13)C NMR spectra were analyzed comprehensively. The experimental (13)C-(1)H coupling values are temperature (T(-1))- as well as magnetic-field (B(2))-dependent and deviate considerably from typical scalar (1)J(CH) couplings constants. This deviation is attributed to residual dipolar couplings (RDCs), which arise from partial alignment of the complexes in the presence of a strong magnetic field. The analysis of the experimental RDCs allows an unambiguous assignment of all (13)C NMR resonances and, additionally, a structural refinement of the conformation of the complexes in solution. Moreover the RDCs can be used for the analysis of the alignment tensor and hence the tensor of the anisotropy of the magnetic susceptibility.
Iron(II) and cobalt(II) alkyl complexes using tridentate bis(pyridylimino)isoindolates as ancillary ligands have been synthesized from the pyridine alkyl precursor complexes [(py) 2 Fe(CH 2 SiMe 3 ) 2 ] and [(py) 2 Co-(CH 2 SiMe 3 ) 2 ]. The extremely air-and moisture-sensitive compounds were structurally characterized in the solid state by X-ray diffraction as well as in solution by paramagnetic NMR spectroscopy. It is demonstrated that the paramagnetic shifts in the 13 C NMR spectra are dominated by strong Fermicontact interactions. All 13 C NMR signals can be assigned by correlation with DFT-calculated spin-density distributions.
In Ziegler–Natta catalysis,
the catalyst particle size has
a strong influence not only on catalyst performance but also on the
morphology and particle size distribution of the final polymer particles.
Fundamental insight into the catalyst particle formation process is
therefore of industrial importance when addressing specific requirements
in the final products. In the present work, we fully characterize
a single-step catalyst preparation process, which comprises a reactive
precipitation of a MgCl2-supported Ziegler–Natta
catalyst, through decomposition of the hetero-bimetallic complex,
Mg(OR)2·Ti(OR)4, by addition of ethyl aluminum
dichloride (EADC). We track the evolution of both of the concentrations
of the metals (Mg, Ti, Al) as well as Cl in the liquid phase and the
size of the formed catalyst particles. It is observed that the liquid-phase
composition is governed by the EADC feed rate under fully Cl-starved
conditions. The process can be divided into two stages: The first
stage is dominated by the precipitation of the Mg-based support, and
the second stage involves complex adsorption–precipitation
of the Ti species. The growth of the catalyst particle size occurs
only in the first stage and is controlled by the aggregation and breakage
events during the MgCl2 precipitation. It follows that
the hydrodynamic stress in the reactor plays the essential role in
controlling the catalyst size. In the second stage, no further particle
growth occurs, not only because of the depletion of Mg in the liquid
phase but also because the adsorbed Ti complex stabilizes the particles
against aggregation. Finally, we have performed polymerization tests
with the prepared catalysts and found that the size distribution of
the polymer particles indeed closely replicates the one of the used
catalyst particles.
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