On the mechanism of olefin polymerisation with titanium β-diketonato complexes.: A model density functional study

被引:2
作者
Bühl, M [1 ]
Mauschick, FT [1 ]
机构
[1] Max Planck Inst Kohlenforsch, D-45470 Mulheim, Germany
关键词
olefin polymerisation; titanium beta-diketonato complex; density functional study;
D O I
10.1016/S0022-328X(01)01448-6
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
According to density functional calculations (BP86/AEI + ZPE level) for a model system with L = HC(O)CHC(O)H, cationic titanium complexes of the type L2TiR+ (R = growing alkyl chain) can be viable intermediates in the homogeneous olefin polymerisation catalysed by titanium beta-diketonato complexes. As with the related cationic metallocenes. olefin insertion in beta- and alpha-agostic intermediates is a facile process. Little activation for chain propagation is computed on the potential energy surface, 2.9 kcal mol(-1) (incl. ZPE), but this value is raised to 15.8 kcal mol(-1) on the free energy surface at 298 K. The main portion of this total barrier stems from the entropic destabilisation of the intermediate olefin pi-complexes. Chain termination via P-H transfer requires significantly higher activation, consistent with the observation of olefin polymerisation, rather than oligomerisation. Electron-withdrawing substituents at the diketonate ligand are predicted to lower the barrier for chain propagation by as much as 4.5 or 5.4 kcal mol(-1) for L = F3CC(O)CHC(O)CF3 (hfac) or NCC(O)CHC(O)CN. respectively. Thus, hfac complexes should produce highly active catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:126 / 133
页数:8
相关论文
共 55 条
[1]  
Bader R. F. W., 1994, ATOMS MOL QUANTUM TH
[2]   A QUANTUM-THEORY OF MOLECULAR-STRUCTURE AND ITS APPLICATIONS [J].
BADER, RFW .
CHEMICAL REVIEWS, 1991, 91 (05) :893-928
[3]   DENSITY-FUNCTIONAL THERMOCHEMISTRY .3. THE ROLE OF EXACT EXCHANGE [J].
BECKE, AD .
JOURNAL OF CHEMICAL PHYSICS, 1993, 98 (07) :5648-5652
[4]   DENSITY-FUNCTIONAL EXCHANGE-ENERGY APPROXIMATION WITH CORRECT ASYMPTOTIC-BEHAVIOR [J].
BECKE, AD .
PHYSICAL REVIEW A, 1988, 38 (06) :3098-3100
[5]   FLUORO-BETA-DIKETONE DERIVATIVES OF TITANIUM [J].
BHARARA, PC ;
GUPTA, VD ;
MEHROTRA, RC .
SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY, 1975, 5 (01) :59-67
[6]   A CORRELATION BETWEEN C-13 AND CO-59 NMR DATA AND THE CATALYTIC ACTIVITY OF ORGANOCOBALT COMPLEXES IN THE SYNTHESIS OF PYRIDINE-DERIVATIVES [J].
BONNEMANN, H ;
BRIJOUX, W ;
BRINKMANN, R ;
MEURERS, W ;
MYNOTT, R ;
VONPHILIPSBORN, W ;
EGOLF, T .
JOURNAL OF ORGANOMETALLIC CHEMISTRY, 1984, 272 (02) :231-249
[7]  
Brintzinger H. H., 1995, ANGEW CHEM, V107, P1255
[8]   Novel olefin polymerization catalysts based on iron and cobalt [J].
Britovsek, GJP ;
Gibson, VC ;
Kimberley, BS ;
Maddox, PJ ;
McTavish, SJ ;
Solan, GA ;
White, AJP ;
Williams, DJ .
CHEMICAL COMMUNICATIONS, 1998, (07) :849-850
[9]  
Britovsek GJP, 1999, ANGEW CHEM INT EDIT, V38, P428, DOI 10.1002/(SICI)1521-3773(19990215)38:4<428::AID-ANIE428>3.0.CO
[10]  
2-3