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Struktur der aktiven Spezies und Erklärung des Wanderungsmechanismus bei der 2,ω‐polymerisation von α‐olefinen
Author(s) -
Schubbe Regine,
Angermund Klaus,
Fink Gerhard,
Goddard Richard
Publication year - 1995
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1995.021960202
Subject(s) - chemistry , nickel , polymer chemistry , polymerization , catalysis , trimethylsilyl , ligand (biochemistry) , double bond , pyridine , medicinal chemistry , organic chemistry , polymer , biochemistry , receptor
Abstract The catalytic system nickel(0) compound and bis(trimethylsilyl)amino‐bis(trimethylsilylimino)‐phosphoran polymerizes α‐olefins via 2,ω‐linkage. Therefore this reaction is called 2,ω‐polymerization. Using tris(ethylene)nickel as the nickel compound in these systems, it is possible to obtain catalytically active species. The X‐ray analysis of these crystals proves that the nickel atom is complexed by one of the imino nitrogen atoms and fixed over a C2 bridge at the phosphorus atom. The unusual 5‐membered ring for complexes of this type gives a view into the mechanism of the 2, ω‐polymerization. The phosphorus ligand shields the nickel atom at which the insertion takes place so effectively that the nickel is practically sitting in a “cave” with a very small entrance. Inside the cave NiC reacts to NiH and CC and also in reverse: this means the enthalpy change is zero and it is a question of statistics (entropy) which C atoms of the double bond will be attacked. Varying the phosphorus compound demonstrates the high sensitivity of the catalytic system with respect to this compound. Substituting the trimethylsilyl groups at the imino nitrogen atoms by the more voluminous dimethyl‐ tert ‐butyl groups, we obtained an absolutely inactive system. In contrast, nickel(II)‐bis(acetylacetonate) can be used in combination with the phosphoran and aluminium triethyl as cocatalyst to obtain a catalytically active system for the 2,ω‐polymerization. The structure of this complex was identified by X‐ray analysis. Because of the higher volume of the ligand, this system is unable to polymerize branched α‐olefins; only linear α‐olefins will be polymerized via 2, ω‐linkage.