Co-polymerization of propylene oxide and CO2 using early transition metal (groups IV and V) metallocalix[n]arenes (n = 4, 6, 8) |
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| Authors: | Tian Xing Zhong-Yu Wang Yong-Chang Sun Zhen-Hong He Kuan Wang Zhao-Tie Liu Mark R J Elsegood Elizabeth V Bedwell Carl Redshaw |
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| Affiliation: | 1. Plastics Collaboratory, Department of Chemistry, University of Hull, Hull, UK;2. College of Chemistry and Chemical Engineering, Shaanxi University of Science & Technology, Xi'an, China;3. Chemistry Department, Loughborough University, Loughborough, UK |
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| Abstract: | A number of metallocalixn]arenes, where n = 4, 6, or 8, of titanium and vanadium have been screened for their ability to act as catalysts for the co-polymerization of propylene oxide and CO2 to form cyclic/polycarbonates. The vanadium-containing catalysts, namely VO(L1Me)] (1), (VO2)L2H6] (2), Na(NCMe)6]2(NaVO]4L2)(Na(NCMe))3]2 (3), VO(μ-OH)L3/H2]2?6CH2Cl2 (4), {VO]2(μ-O)L4Na(NCMe)2]2} (5), {V(Np-tolyl)]2L4} (6) and V(Np-RC6H4)Cl3] (R = Cl (7), OMe (8), CF3 (9)), where L1H3 = methylether-p-tert-butylcalix4]areneH3, L2H8 = p-tert-butylcalix8]areneH8, L3H4 = p-tert-butylthiacalix4]areneH4, L4H6 = p-tert-butyltetrahomodioxacalix6]areneH6, performed poorly, affording, in the majority of cases, TONs less than 1 at 90°C over 6 h and low molecular weight oligomeric products (Mn ≤ 1665). In the case of the titanocalix8]arenes, {(TiX)2TiX(NCMe)]2(μ3-O)2(L2)} (X = Cl (10), Br (11), I (12)), which all adopt a similar, ladder-type structure, the activity under the same conditions is somewhat higher (TONs >6) and follows the trend Cl > Br > I; by comparison the non-calixarene species TiCl4(THF)2] was virtually inactive. In the case of 10, it was observed that the use of PPNCl (bistriphenylphosphine]iminium chloride) as co-catalyst significantly improved both the polymer yield and molecular weight (Mn 3515). The molecular structures of the complexes HNEt3]2VO(μ-O)L3H2]2?3CH2Cl2 (4?3CH2Cl2), VO(μ-OH)L3/H2]2?6CH2Cl2 (4/) (where L3/H2 is a partially oxidized form of L3H4) and {(TiCl)2TiCl(NCMe)]2(μ3-O)2(L2)}·6.5MeCN (10·6.5MeCN) are reported. |
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| Keywords: | catalysts non-polymeric materials and composites x-ray |
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