HELVETICA CHIMICA ACTA
·
2017
·Vol. 100
·期 12
·e1700162
·
IF 1.071
Jun Wang,Rui Gao,Na Zhang,Xiangkun Tan,Libo Wang,Lili Ma,Weiguang Shi
Three dendritic PNP ligands with ethylenediamine, 1,4-butanediamine, 1,6-diaminohexane as bridged groups are synthesized in good yields, respectively. Three dendritic PNP chromium complexes ( C1 – C3 ) are prepared with the ligands and chromium(III) chloride tetrahydrofuran complex (CrCl 3 (THF) 3 ) as materials. The dendritic PNP ligands and the synthetic chromium complexes are fully characterized by spectroscopic and analytical methods. All chromium complexes activated with methylaluminoxane (MAO) exhibited moderate activities on ethylene oligomerization (7.90 × 10 4 – 2.15 × 10 5 g (mol Cr h) −1 ] and had better selectivity for C 6 and C 8 oligomer, reaching up to 81%. The chromium complex ( C1 ) activated with diethylaluminium chloride (Et 2 AlCl) has higher catalytic activity than the chromium complex C1 activated with MAO, although the chromium complex ( C1 ) activated with Et 2 AlCl had lower selectivity for C 6 and C 8 oligomer. The effects of solvent and reaction parameters on ethylene oligomerization are also studied using the chromium complex C1 as pre - catalyst and MAO as co - catalyst. Under optimized conditions ([complex] = 2 μmol, Al/Cr = 500, 25 °C, 0.9 MPa ethylene, 30 min), the catalytic activity of complex C1 in toluene is 2.15 × 10 5 g (mol Cr h) −1 and the selectivity for C 6 and C 8 oligomer is 36.76%. In addition, the structure of complexes significantly affects both the catalytic activity and the selectivity on ethylene oligomerization.
研究领域:
化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
APPLIED ORGANOMETALLIC CHEMISTRY
·
2020
·Vol. 34
·期 11
·e5904
·
IF 3.14
Cuiqin Li,Dan Li,Fengfeng Wang,Yuxin Gao,Jin Huang,Feng Li
Series of hyperbranched PNP ligands ( L1 – L3 ) were prepared using three low-generation hyperbranched molecules with the same branching chains and functional groups but different alkyl chain length as backbones in a mixed solvent of acetonitrile and dichloromethane. The chromium complexes ( Cr1 – Cr3 ) were obtained by reacting with CrCl 3 (THF) 3 and the corresponding ligands ( L1 – L3 ). Both L1 – L3 and Cr1 – Cr3 were characterized by elemental analysis, Fourier transform infrared and electrospray ionization–mass spectrometry as well as 1 H nuclear magnetic resonance (NMR) and 31 P NMR measurements in the case of the ligands. When activated with different aluminum co-catalysts, all three chromium complexes were able to catalyze the ethylene oligomerization, but the products of the ethylene oligomerization were mainly dependent on ethylene pressure, co-catalyst and ligand backbone. Upon activation with methylaluminoxane, the catalytic activity and the selectivity of C8 olefin increased with increasing of ethylene pressure for Cr1 , the catalytic activity was 13.83 × 10 5 g·(mol Cr·h) −1 and the main product was C8 olefin (50.68%) at the ethylene pressure of 4.0 MPa. When activated with diethylaluminium chloride, ethylaluminium dichloride and ethylaluminum sesquichloride, Cr1 showed the lower catalytic activity and the higher selectivity of C4 olefin in toluene. An increase in the length of alkyl chain in the hyperbranched PNP ligand backbone caused a decrease in the catalytic activity and an increase in the selectivity of C8 + olefin. The PNP chromium complexes exhibited higher selectivity for higher carbon number olefins compared with the dendritic PNP chromium complex ( Cr5 ).
研究领域:
化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
ELECTROCHIMICA ACTA
·
2022
·
IF 7.336
Mookan Natarajan,Xueming Li,Wei Zhong,Wei Wang,Zhiyin Xiao,Xiujuan Jiang,Chunxin Lu,Xiaoming Liu
Three half-sandwiched iron(II) monocarbonyl cationic complexes ( 1 + − 3 + ) containing a azadiphoshine ligand (PNP, L 1 – 3 ) and an iodide as the counter anion, [Fe(II)Cp(CO)( L 1 – 3 )]Ι (Cp = η 5 -cyclopentadienyl; L 1 = Ph 2 PN(cyclohexyl)PPh 2 , 1 + ; L 2 = Ph 2 PN(phenyl)PPh 2 , 2 + ; L 3 = Ph 2 PN(benzyl)PPh 2 , 3 + ) were reported. All the complexes were fully characterized, of which complexes 2 + and 3 + were crystallographically analysed to confirm their “piano stool” geometry. Electrochemically, complexes 1 + − 3 + exhibited two major reduction events at about −1.9 V and −2.3 V, respectively, assigned to Fe(II) → Fe(I) and Fe(I) → Fe(0), respectively. The first reduction produces a 19e-species, [Fe(I)Cp(CO)( L 1 – 3 )] ( 1, 2 , and 3 ) whereas the second event is not assigned to the further reduction of the 19e-species but a 17e-intermediate ([Fe(I)Cp(CO)( m - L 1 – 3 )]; 1′, 2′ and 3′ ) which is chemically generated from the 19e-species by cleaving one of the two Fe−P bonds. However, the 19e-species 3 is considerably more stable than the other two analogues ( 1 and 2 ) due to H − π interaction between the ortho -H atoms from one of the four phenyl rings on the phosphine atom and the phenyl ring of the benzyl group as revealed by theoretic calculations. Therefore, species 3 is stable enough for the reduction of 3 → 3 − to be electrochemically detected right before the second major reduction. To further shed some light on the electrochemical mechanism, both bulk electrolysis and chemical reduction of complexes 1 + − 3 + with cobaltocene as the reducing agent were conducted. Under N 2 atmosphere, the neutral 17e-species, [Fe(I)Cp(CO)( m - L 1 – 3 )] ( 1′ - 3′ ) was spectroscopically detected whereas under CO atmosphere, CO-adducts, [Fe(I)Cp(CO) 2 ( m - L 1 – 3 )], were generated. The formation of CO-adduct explains the loss of reversibility of the first reduction ( 3 + ) under CO atmosphere in its electrochemistry. With acetic acid as the proton source, only the second major reduction of the complexes exhibited significant catalytic activity, of which complex 1 + possessed the best performance. Significant proton-coupled electron transfer (PCET) effect was observed for complex 1 + due to the strong electron-donating capability of the ligand ( L 1 ).
研究领域:
无机化学
·
催化化学
·
电化学
✓ 已验证
DOI
高影响因子
INORGANIC CHEMISTRY
·
2022
·
IF 5.436
Jingjing Zhai,Fen You,Suting Xu,Ao Zhu,Xiaohui Kang,Yat-Ming So,Xiaochao Shi
A PNP-pincer ligand provides a versatile ligation framework, which is highly useful in organometallic chemistry and catalytic chemistry. In this work, by a de novo strategy, a simple and efficient synthetic pathway, has been developed to prepare the new iminodibenzyl-based PNP pincer proligand imin-RPNP(Li or H) (R = isopropyl, phenyl). By employing salt metathesis or direct alkyl elimination, we successfully synthesized a series of iminodibenzyl-PNP rare-earth-metal (Ln = Sc, Y, Dy, Ho, Er, Tm, Lu) complexes and characterized them by NMR and X-ray diffraction analyses. Upon addition of a borate and triisobutylaluminum (TIBA), the rare-earth-metal complexes 2-Y, 2-Dy, 2-Ho, 2-Er, and 2-Tm bearing the imin-PhPNP ligand exhibited unexpectedly high 3,4-selectivity (up to 95%) for the polymerization of 1,3-dienes (isoprene and myrcene); in particular, the chosen yttrium complex 2-Y promoted the 1,3-diene polymerization in a living manner. A computational study suggested that the sterically congested configuration around the metal center imposed by the imin-RPNP ligand might be the main reason for this unusual selectivity.
研究领域:
有机金属化学
·
催化化学
✓ 已验证
DOI
高影响因子
ELECTROCHIMICA ACTA
·
2020
·
IF 6.215
Zhiyin Xiao,Mookan Natarajan,Wei Zhong,Xiaoming Liu
In this work, four complexes of Co(II) and Ni(II), [Co( L 1 ) 2 (CH 3 CN)](ClO 4 ) 2 ( 1 ), [Ni( L 1 ) 2 ](ClO 4 ) 2 ( 2 ), [Co( L 2 ) 2 (CH 3 CN)](ClO 4 ) 2 ( 3 ) and [Ni( L 2 ) 2 ](ClO 4 ) 2 ( 4 ) were synthesized by reacting the perchlorate hydrate of M(II) (M = Co and Ni) with the ligands, Ph 2 PN(cyclohexyl)PPh 2 ( L 1 ) and Ph 2 PN(pyridin-2-ylmethyl)PPh 2 ( L 2 ), respectively. The complexes were fully characterized, and their absolute structures were determined using X-ray single crystallographic analysis. The cobalt complexes ( 1 and 3 ) exhibited two reductions in acetonitrile , one reversible reduction at about −0.65 V and the other at about −2.0 V at which catalytic reduction of proton was observed. The two reductions were assigned to Co(II) → Co(I) and Co(I) → Co(0) processes, respectively. The reduction of Ni(II) → Ni(I) was negatively shifted by about 300 mV compared to the cobalt analogues and the process showed two closely located reversible reductions due to geometric isomerization between the square planar ( Sp ) and tetrahedral ( Td ) geometries, of which the Td isomer was first reduced due to the lower energy level of its frontier orbitals . The second reduction of the Ni(II) complexes ( 2 and 4 ) was invisible in the potential range examined. Upon addition of acetic acid, it shifted positively by over 300 mV and showed catalysis on proton reduction. The shift was attributed to proton-coupled electron transfer (PCET) effect which was further enhanced by the pendant pyridyl group in ligand L 2 . The nickel complexes showed much higher activity than cobalt analogues in the catalysis on proton reduction and the pendant base group could synergistically enhance the activity of the complex ( 4 ).
研究领域:
无机化学
·
电化学
✓ 已验证
产品关联
DOI
高影响因子
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