2 resultados para benzene

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Although the transition metal chemistry of many dialkylamido ligands has been well studied, the chemistry of the bulky di(tert-butyl)amido ligand has been largely overlooked. The di(tert-butyl)amido ligand is well suited for synthesizing transition metal compounds with low coordination numbers; such compounds may exhibit interesting structural, physical, and chemical properties. Di(tert-butyl)amido complexes of transition metals are expected to exhibit high volatilities and low decomposition temperatures, thus making them well suited for the chemical vapor deposition of metals and metal nitrides. Treatment of MnBr₂(THF)₂, FeI₂, CoBr₂(DME), or NiBr₂(DME) with two equivalents of LiN(t-Bu)2 in benzene affords the two-coordinate complex M[N(t-Bu)₂]₂, where M is Mn, Fe, Co, or Ni. Crystallographic studies show that the M-N distances decrease across the series: 1.9365 (Mn), 1.8790 (Fe), 1.845 (Co), 1.798 Å (Ni). The N-M- N angles are very close to linear for Mn and Fe (179.30 and 179.45°, respectively), but bent for Co and Ni (159.2 and 160.90°, respectively). As expected, the d⁵ Mn complex has a magnetic moment of 5.53 μΒ that is very close to the spin only value. The EPR spectrum is nearly axial with a low E/D ratio of 0.014. The d⁶ Fe compound has a room temperature magnetic moment of 5.55 μΒ indicative of a large orbital angular momentum contribution. It does not exhibit a Jahn-Teller distortion despite the expected doubly degenerate ground state. Applied field Mössbauer spectroscopy shows that the effective internal hyperfine field is unusually large, Hint = 105 T. The magnetic moments of Co[N(t-Bu)₂]₂ and Ni[N(t-Bu)₂]₂ are 5.24 and 3.02 μΒ respectively. Both are EPR silent at 4.2 K. Treatment of TiCl₄ with three equivalents of LiN(t-Bu)2 in pentane affords the briding imido compound Ti₂[μ-N(t-Bu)]₂Cl₂[N(t-Bu)₂]₂ via a dealkylation reaction. Rotation around the bis(tert-butyl)amido groups is hindered, with activation parameters of ΔH‡ = 12.8 ± 0.6 kcal mol-1 and ΔS‡ = -8 ± 2 cal K-1 ·mol-1, as evidenced by variable temperature 1H NMR spectroscopy. Treatment of TiCl₄ with two equivalents of HN(t-Bu)₂ affords Ti₂Cl₆[N(t-Bu)₂]₂. This complex shows a close-contact of 2.634(3) Å between Ti and the carbon atom of one of the CH₃ substituents on the tert-butyl groups. Theoretical considerations and detailed structural comparisons suggest this interaction is not agostic in nature, but rather is a consequence of interligand repulsions. Treatment of NiI₂(PPh3)₂ and PdCl₂(PPh₃)₂ with LiN(t-Bu)₂in benzene affords Ni[N(t-Bu)₂](PPh₃)I and Pd₃(μ₂-NBut₂)2(μ₂-PPh₂)Ph(PPh₃) respectively. The compound Ni[N(t-Bu)₂](PPh₃)I has distorted T-shape in geometry, whereas Pd₃(μ₂-NBut₂)₂(μ₂-PPh₂)Ph(PPh₃) contains a triangular palladium core. Manganese nitride films were grown from Mn[N(t-Bu)₂]₂ in the presence of anhydrous ammonia. The growth rate was several nanometers per minute even at the remarkably low temperature of 80⁰C. As grown, the films are carbon- and oxygen-free, and have a columnar morphology. The spacings between the columns become smaller and the films become smoother as the growth temperature is increased. The composition of the films is consistent with a stoichiometry of Mn₅N₂.

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Metal-organic frameworks (MOFs) have attracted significant attention during the past decade due to their high porosity, tunable structures, and controllable surface functionalities. Therefore many applications have been proposed for MOFs. All of them however are still in their infancy stage and have not yet been brought into the market place. In this thesis, the background of the MOF area is first briefly introduced. The main components and the motifs of designing MOFs are summarized, followed by their synthesis and postsynthetic modification methods. Several promising application areas of MOFs including gas storage and separation, catalysis and sensing are reviewed. The current status of commercialization of MOFs as new chemical products is also summarized. Examples of the design and synthesis of two new MOF structures Eu(4,4′,4′′,4′′′-(porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid))·2H2O∙xDMF and Zn4O(azobenzene-4,4’-dicarboxylic acid)3∙xNMP are described. The first one contains free-base porphyrin centers and the second one has azobenzene components. Although the structures were synthesized as designed, unfortunately they did not possess the expected properties. The research idea to use MOFs as template materials to synthesize porous polymers is introduced. Several methods are discussed to grow PMMA into IRMOF-1 (Zn4O(benzene-1,4-dicarboxylate)3, IR stands for isoreticular) structure. High concentration of the monomers resulted in PMMA shell after MOF digestion while with low concentration of monomers no PMMA was left after digestion due to the small iii molecular weight. During the study of this chapter, Kitagawa and co-workers published several papers on the same topic, so this part of the research was terminated thereafter. Many MOFs are reported to be unstable in air due to the water molecules in air which greatly limited their applications. By incorporating a number of water repelling functional groups such as trifluoromethoxy group and methyl groups in the frameworks, the water stability of MOFs are shown to be significantly enhanced. Several MOFs inculding Banasorb-22 (Zn4O(2-trifluoromethoxybenzene-1,4-dicarboxylate)3), Banasorb-24 (Zn4O(2, 5-dimethylbenzene-1,4-dicarboxylate)3) and Banasorb-30 (Zn4O(2-methylbenzene-1,4-dicarboxylate)3) were synthesized and proved to have isostructures with IRMOF-1. Banasorb-22 was stable in boiling water steam for one week and Banasorb-30’s shelf life was over 10 months under ambient condition. For comparison, IRMOF-1’s structure collapses in air after a few hours to several days. Although MOF is a very popular research area nowadays, only a few studies have been reported on the mechanical properties of MOFs. Many of MOF’s applications involve high pressure conditions, so it is important to understand the behavior of MOFs under elivated pressures. The mechanical properties of IRMOF-1 and a new MOF structure Eu2(C12N2O4H6)3(DEF)0.87(H2O)2.13 were studied using diamond anvil cells at Advanced Photon Source. IRMOF-1 experienced an irriversible phase transtion to a nonporous phase followed by amorphization under high pressure. Eu2(C12N2O4H6)3(DEF)0.87(H2O)2.13 showed reversible compression under pressure up to 9.08GPa.