Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group

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• 作者：Zhengguo Cai ; Zhongliang Shen ; Xiaoyuan Zhou ; Richard F. Jordan
• 刊名：ACS Catalysis
• 出版年：2012
• 出版时间：June 1, 2012
• 年：2012
• 卷：2
• 期：6
• 页码：1187-1195
• 全文大小：486K
• 年卷期：v.2,no.6(June 1, 2012)
• ISSN：2155-5435

文摘

Binding of B(C₆F₅)₃ to a sulfonate oxygen of (ortho-phosphino-arenesulfonate)PdR catalysts results in a 3鈥? fold increase in the rate of chain growth and a larger increase in the rate of chain transfer. The reaction of (PO-Et)PdMe(py) (1a, [PO-Et]鈭?/sup> = ortho-{(2-Et-Ph)₂P}-para-toluenesulfonate) with 1 equiv of B(C₆F₅)₃ yields the base-free dimer {(PO-Et)PdMe}₂ (2a), in which the (PO-Et)PdMe units are linked through an eight-membered [PdSO₂]₂ ring. The reaction of {(PO-3,5-^tBu₂)PdMe}₂(TMEDA) (4b; [PO-3,5-^tBu₂]鈭?/sup> = ortho-{(3,5-^tBu₂-Ph)₂P}-para-toluenesulfonate, TMEDA = N,N,N鈥?N鈥?tetramethylethylenediamine) with BF₃路Et₂O yields the soluble base-free dimer {(PO-3,5-^tBu₂)PdMe}₂ (2b), in which the (PO-3,5-^tBu₂)PdMe units are linked through a four-membered Pd₂O₂ ring. 2b reacts with 2 equiv of B(C₆F₅)₃ to yield {[PO路B(C₆F₅)₃-3,5-^tBu₂]PdMe}₂ (5b, [PO路B(C₆F₅)₃-3,5-^tBu₂]鈭?/sup> = [2-{(3,5-^tBu₂-Ph)₂P}-4-Me-C₆H₃SO₂OB(C₆F₅)₃]鈭?/sup>), which crystallizes from Et₂O as the monomeric complex [PO路B(C₆F₅)₃-3,5-^tBu₂]PdMe(Et₂O) (6b). In both 5b and 6b, the B(C₆F₅)₃ binds to a sulfonate oxygen. In toluene solution at 60 掳C, 2b polymerizes ethylene (80 psi) to linear polyethylene with M_n = 3,000, while the B(C₆F₅)₃ adducts 5b and 6b yield ethylene oligomers (M_n = 160鈥?70). 5b and 6b are 3鈥? times more active than 2b. Similarly, 1a polymerizes ethylene to linear polyethylene with M_n = 29,300 (toluene, 80 掳C, 435 psi), while 1a-4 B(C₆F₅)₃ yields polymer with M_n = 2,520 with a 4 fold increase in activity. 2b reacts with ethylene at 7 掳C to form the ethylene adduct (PO-3,5-^tBu₂)PdMe(CH₂鈺怌H₂) (7b) followed by multiple insertions to generate (PO-3,5-^tBu₂)Pd(CH₂CH₂)_nCH₃ species. In contrast, 5b reacts with ethylene to form [PO路B(C₆F₅)₃-3,5-^tBu₂]PdMe(CH₂鈺怌H₂) (8b) followed by insertion and 尾-H transfer to yield propene with subsequent catalytic formation of 1-butene and higher olefins. The rate of ethylene insertion of 8b is 3 times greater than that of 7b, consistent with the batch polymerization results. The polymer yield and molecular weight data show that binding of B(C₆F₅)₃ to 2b and 1a increases the chain transfer rates by a factor of 80 and 42, respectively.

Keywords:

ethylene polymerization; ethylene oligomerization; (phosphine-sulfonate)Pd catalyst; Lewis acid; remote binding