Benefit from the strong synergistic electronic effect between Co and CeOx, as well as the strong metalsupport interaction between Co-CeOx and 3D NGH, the as-synthesized Co-(CeOx)0.91/NGH catalyst exhibits excellent catalytic activity toward hydrolysis of ammonia borane, with the turnover frequency (TOF) value of 79.5 min-1. 相似文献
Despite the synthesis and structural characterization of closo-hydroborate dianions, [BnHn]2− (n=6–12) more than 50 years ago, some ambiguity remains about the structure of [B8H8]2−. Although the solid-state structure of [B8H8]2− was established by single-crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of [B8H8]2− by using Cp2MBH3 and structurally characterized two new octaborane analogues, [(Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr ( 1-Zr ) and Hf ( 1-Hf )), so that the dynamics of the B8 skeleton were arrested. The solid-state structures of both 1-Zr and 1-Hf comprise a dodecahedron core protected by {Cp2MBH3} moieties on both sides of the cluster. Spectroscopic characterization (11B NMR) validates the intactness of the B8 dodecahedron core in solution as well. Theoretical calculations establish that the two exo-{Cp2MBH3} fragments provide structural and electronic structural stability to the B8 core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the Bn core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal. 相似文献
A group of α‐ and β‐N, N‐dialkyl amino ketones were reduced enantioselectively by 2 moles of borane‐tetrahydrofuran in the presence of 10 mol% of the in‐situ formed chiral oxazaborolidine, followed by diluted hydrochloric acid. The resulting amino alcohol‐borane complexes were treated with hydrogen chloride‐glycol‐methanol to give the optically active amino alcohol with the ee up to 99%. 相似文献
An efficient synthesis of novelα-aminophosphonates by the reaction of aldehydes and amines with triethyl phosphite in the presence of the easily available,inexpensive,and nontoxic catalyst thiamine hydrochloride(VB1).This method affords theα-aminopho-sphonates under the influence of ultrasound irradiation in aqueous medium,in short reaction times(4-6 min),high yields(85-95%), with improved purity.The process is green,mild,inexpensive and excellent yields are the main compensation of this procedure. 相似文献
The dehydropolymerization of amine–boranes, exemplified as H2RB⋅NR′H2, to produce polyaminoboranes (HRBNR′H)n that are inorganic analogues of polyolefins with alternating main-chain B−N units, is an area with significant potential, stemming from both fundamental (mechanism, catalyst development, main-group hetero-cross-coupling) and technological (new polymeric materials) opportunities. This Concept article outlines recent advances in the field, covering catalyst development and performance, current mechanistic models, and alternative non-catalytic routes for polymer production. The substrate scope, polymer properties and applications of these exciting materials are also outlined. Challenges and opportunities in the field are suggested, as a way of providing focus for future investigations. 相似文献
We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X+ 2E←X 1A1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE0K(NH3BH3, NH3BH2+)= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH3-site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol−1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol−1. 相似文献
The right mix does the trick : Elusive {Ni0(η6‐arene)} moieties can be dramatically stabilized by the N‐heterocyclic silylene ligand 1 , which has a zwitterionic mesomeric structure. The σ, π‐acid–base synergism between nickel and 1 explains the unexpectedly high stability of the new silylene complexes 2 , which enables arene exchange studies at a Ni0 center. Addition of B(C6F5)3 to 2 affords the zwitterionic silylene complex 3 (see scheme, R=2,6‐iPr2C6H3).
The activity of the transition metal complex, such as Ni(2-ethyl hexanoate)2 (1), Co(2-ethyl hexanoate)2 (2), TiCl4 (3), or CpTiCl3 (4) (Cp = cyclopentadiene), in combination with MAO (methylaluminoxane), was investigated in the polymerization of norbornene. The Ni(II) complex 1 with MAO showed moderate activity to give 20.8 kgpolymer/molNi h, while the other three complexes 2-4 with MAO just showed trivial activity. Effects of the Lewis acids on the activation of the catalyst of 1/MAO were examined. The employment of B(C6F5)3 with 1/MAO significantly enhanced the activity to give up to around 133 kgpolymer/molNi h. The use of other borane compounds, such as B(C6H5)3 and BEt3, or the stronger electron acceptor BF3 · OBu2, with 1/MAO in place of B(C6F5)3 clearly showed the main functions of B(C6F5)3. The high Lewis acidity of B(C6F5)3 enabled it to develop matured active complexes, thus enhancing the activity. Several Ni(II) complexes were employed to determine whether their activity was comparable to that of complex 1 in norbornene polymerization. The study of the 1H and 13C NMR spectra of the polynorbornene produced with 1/B(C6F5)3/MAO showed that the initiation of addition polymerization occurred through the insertion of the exo face of the norbornene into the active complex. Effects of the variation in the polymerization variables, such as the levels of B(C6F5)3 and MAO, temperature, and solvent, on the polymerization were discussed. 相似文献
Crystals grown from anhydrous HF solutions of CsAsF6 and Cs2B12F12 or KAsF6 and Cs2B12F12 are shown by Raman spectroscopy and single-crystal X-ray diffraction to be the ternary salts K3(AsF6)(B12F12) or Cs3(AsF6)(B12F12). Both compounds exhibit a modified version of the anti-perovskite structure. They are rare examples of crystals that simultaneously contain octahedral and icosahedral molecular species and are also rare examples of salts containing fluoroanions with different shapes and charges. The crystallographic results show that both compounds are densely packed. 相似文献