INVESTIGATION OF LATE TRANSITION METAL BASED CATALYTIC SYSTEMS FOR POLYMERIZATION OF POLAR VINYL MONOMERS

Open Access
Author:
Kang, Myeongsoon
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 11, 2004
Committee Members:
  • Ayusman Sen, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Alan James Benesi, Committee Member
  • Ralph H Colby, Committee Member
Keywords:
  • late transition metal
  • catalysis
  • polymerization
  • polar vinyl monomer
Abstract:
Variable-temperature 1H NMR studies of the reaction of cationic (á-diimine)Pd-alkyl complexes with alkenes are presented. The studies reveal that vinyl bromide coordinates to the Pd(II)-Me complex followed by migratory insertion and â-bromo elimination, to generate free propene. Propene further reacts to give â-agostic Pd(II)-tert-butyl species. From the reactions with vinyl bromide, stable chloro-bridged dicationic Pd complex was isolated and characterized. For a series of alkenes (CH2=CHX), the rate for migratory insertion decreases as follows : X = CO2Me > Br > H > Me. Palladium(1,5-cyclooctadiene)(methyl)(chloride), is a catalyst for the living oligomerization of norbornene. The reaction is attenuated by additives in the following decreasing order, C=C > Cl- > RC(=O)OR. The insertion of norbornene, endo and exo-5-ethylester-2-norbornene, and endo-5-methylacetate-2-norbornene into the palladium-methyl bond of Palladium(1,5-cyclooctadiene)(methyl)(chloride) was examined. Similar rates were found for all the norbornene derivatives, with the product in every case being derived from insertion through the exo face. A series of neutral salicylaldiminato Pd(II) complexes, Pd(Me)(Ph-CH=N-R´)[3-tBu-2-(O)C6H3-CH=N-2,6-di-iPr-C6H3](R=CH3, n-Pr, tert-Bu, Ph, Benzyl) (3a-3e), and Pd(Me)[3-(CH=N-t-Bu)-Py][3-tBu-2-(O)C6H3-CH=N-2,6-di-iPr-C6H3] (4) have been synthesized and characterized. Their structure has been confirmed by an X-ray analysis of complexes 3a, 3c-3e, and 4. Nuclear Magnetic Resonance (NMR) studies utilizing 3c indicate that the complex reacts with CO through a five-coordinate species. The neutral complexes 3a-3e show moderate catalytic activity for the polymerization of methyl acrylate at ambient temperature. In the polymerization reaction, a radical mechanism rather than coordination insertion mechanism is invoked to be operative. The complexes 3a, 3b, 3d, 3e produced poly(norbornene) in low yield. Neutral Pd(II) complexes, [3,5-di-tBu-2-(OH)C6H2N=CH-2-PPh2C6H4]PdMe2 (3) and [3,5-di-tBu-2-(OH)C6H2CH=N-2-PPh2C6H4]PdMe2 (4) have been synthesized and characterized. Their structures have been confirmed by an X-ray analysis of complexes 3 and 4. In the solid state, the structure of the complex 3 significantly deviated from the idealized square planar geometry by virtue of the constraint caused by the large bond length difference between P(1)-C(14) and N(1)-C(8) (1.823(3) and 1.288(3), respectively in the [P,N] six-membered ring. Independently, the title compound did not show catalytic activity for the polymerization or oligomerization of an alkene without an assisting agent. In combination with AlEt3, 3 and 4 have produced PMA, where 4 showed better activity. The complex 4 with Al(C6F5)3 as a cocatalyst polymerized norbornene or n-butylnorbornene in excellent yield, but with B(C6F5)3, it did not produce any polymeric product. Different reaction pathways between complexes 3 or 4 and Al(C6F5)3 or B(C6F5)3 have been proposed based on the results of the polymerization and the NMR experiments. Utilizing methylaluminoxane (MAO) as a co catalyst, 3 and 4 produced poly(norbornene) in good yield with no activity difference between 3 and 4.