• 10.1021/ma071696k
  • Macromolecules
  • Volume 40
  • November 2007
  • pp 8162-8167

Innovative approach but low yields

Details


Summary:

This article describes a method for cyclic olefin polymerization employing a non-chelated monodentate benzimidazole Ni(II) complex. The specific reaction catalysed, is the vinyl polymerization of norbornene. The article also describes the methods for synthesis of the ligands and the corresponding Ni(II) complexes along with the procedure and results of their applications as potential catalysts for vinyl polymerization of norbornene. The methods describes are reproducible, but suffer from the problem of producing low yields. I have some suggestions for increasing the overall yields.

The Reactions of Interest:

The article can be divided into two major parts, one dealing with the synthesis of the precatalysts and the other with the catalytic properties. The first part is represented by the Scheme 1 in the experimental section as:

The action of the synthesized Ni(II) complexes (1 – 4) as precatalysts isndescribed in detail, but the authors have not included a general reaction for the process, in the article. A figure is provided in the abstract instead.

Reproducing the results of catalysis has been fairly easy and the choice of structural features for designing the precatalysts is reflected in the effectiveness of the four complexes.

Practical observations:

  • The choice for synthesis of ligands DF-PBI and DF-BPBI can be understood on account of high electronegativity of F, which renders the attempt to prepare these ligands by simple stirring or reflux in alcoholic medium as ineffective. Such attempts did not produce desirable products in any significant yields. The procedure employed by the authors is therefore very good.
  • The situation however, is straightforward in synthesizing MO-BPBI and I found the method employed in this paper to be rather cumbersome and time-wasting. By simply stirring the mixture of 1,2-diaminobenzene and o-anisaldehyde (1:2) in methanolic medium in presence of 0.01 mol% copper nitrate pentahydrate, resulted in yields of 93%. This is much greater than the 75% yield reported by the authors.
  • The complexes 1 – 4 could be reproduced with the described process, but yields were low and the time taken for completion of reactions was in the range of 6 to 8 hours. An alternate method could be employed by directly using acetonitrile solution of the reactants, although I have not tried it myself.
  • The complex 4 along with MAO showed the highest activity for vinyl polymerisation as pointed out by the authors. The results for complexes 1 – 3 were also convincing and conform to the data in Table 1.

Recommendations:

  • The synthesis of ligand MO-BPBI should be done by stirring 1,2-diaminobenzene and o-anisaldehyde (1:2) in methanolic medium in presence of 0.01 mol% copper nitrate pentahydrate. This will result in much better yields in just 15 minutes of reaction time.
  • The synthesis of complexes in acetonitrile medium can be tried.


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