Abstract
Two novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with tert-butyl(diphenyl)phosphine (PtBuPh2) and (S)-(+)neomenthyldiphenylphosphine [(S)-NMDPP]. The crystal structure of the former was determined by single-crystal X-ray diffraction studies. The two complexes were then used in combination with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene: crystalline highly syndiotactic 1,2 poly(1,3-butadiene)s were obtained, with a 1,2 content and a syndiotactic index (percentage of syndiotactic triads [rr]) up to 95% and 85%, respectively. The results obtained further support and confirm what was already observed in the polymerization of 1,3-butadiene with CoCl2(PRPh2)2−MAO (R = methyl, ethyl, normal-propyl, iso-propyl, and cyclohexyl): the nature of the phosphine ligand strongly affects the polymerization stereoselectivity, the polymer syndiotacticity increasing with increasing phosphine ligand steric hindrance.
Highlights
Cobalt catalysts are well-known in the field of the stereospecific polymerization of 1,3-dienes, and they can perhaps be considered the most versatile catalytic systems among the various transition metal and lanthanide catalysts examined, since, depending on the catalytic formulation, they are able to provide all the possible polybutadiene stereoisomers: cis-1,4 polybutadiene, 1,2 polybutadiene, polybutadiene with a mixed cis-1,4/1,2 structure, and trans-1,4 polybutadiene [1,2,3,4,5,6]
The tacticity of the 1,2 polymers obtained was found to depend on the type of phosphine ligand coordinated to the cobalt atom and on the monomer structure [12,13,14,15,16]: the syndiotacticity increased with increasing steric hindrance of the phosphine ligand, and the same obviously applies to the melting point of the polymers obtained
H-the andpresent the remaining unitsmore are essentially cis-1,4, the trans-1,4 units beingexerts a strong influence on the mutual orientation of the allylic unit of the growing chain and of the new almost negligible; percentage of syndiotactic triads, determined by C-NMR; average molecular incoming monomer that is responsible for the polymerization stereoselectivity
Summary
Cobalt catalysts are well-known in the field of the stereospecific polymerization of 1,3-dienes, and they can perhaps be considered the most versatile catalytic systems among the various transition metal and lanthanide catalysts examined, since, depending on the catalytic formulation, they are able to provide all the possible polybutadiene stereoisomers: cis-1,4 polybutadiene, 1,2 polybutadiene, polybutadiene with a mixed cis-1,4/1,2 structure, and trans-1,4 polybutadiene [1,2,3,4,5,6]. O/CS system [17,18,19,20,21,22], we synthesized two novel cobalt complexes (1 and Molecules 2019, 24, of having a melting point even closer to that of the polymer currently industrially produced by means in Figure 1) by reacting cobalt dichloride with the following highly hindered phosphine ligands: of the Co(acac). 3/AlEt3/H2O/CS2 system [17,18,19,20,21,22], we synthesized two novel cobalt complexes (1 and 2 having a melting point even closer to that of the polymer currently industrially produced[(S)-NMDPP]. 1 was determined by X-ray diffraction, both complexes tert-butyl(diphenyl)phosphine
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