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Pyrazolate‐Based Dinuclear α‐Diimine‐Type Palladium(II) and Nickel(II) Complexes – a Bimetallic Approach in Olefin Polymerisation
Author(s) -
Noël Gilles,
Röder Jens C.,
Dechert Sebastian,
Pritzkow Hans,
Bolk Lars,
Mecking Stefan,
Meyer Franc
Publication year - 2006
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200505457
Subject(s) - chemistry , diimine , bimetallic strip , palladium , nickel , cationic polymerization , steric effects , imine , polymer chemistry , stereochemistry , metal , aryl , polymerization , olefin fiber , crystallography , medicinal chemistry , photochemistry , catalysis , polymer , organic chemistry , alkyl
A series of compartmental pyrazole/imine dinucleating ligands HL 1 – HL 4 have been prepared with different backbone substitutents and different steric bulk of the appending arylimine groups, and two of them have been structurally characterised. With PdCl 2 all ligands form the anticipated pyrazolate‐bridged bimetallic complexes LPd 2 Cl 3 ( 1a – 4a ) that feature square‐planar metal ions, as is confirmed by the X‐ray crystallographic analyses of L 1 Pd 2 Cl 3 ( 1a ) and L 3 Pd 2 Cl 3 ( 3a ). With NiBr 2 (dme), however, oligonuclear systems [LNi 2 Br 3 ] x ( 1b – 4b ) are formed according to mass spectrometric findings, which is corroborated by the crystallographic structure of [L 3 Ni 2 Br 3 ] 3 . Complexes 1a – 4a can be described as bimetallic versions of Brookhart‐type α‐diimine palladium complexes, where dissociation into mononuclear species is prevented by the dinucleating scaffold and the proximate metal ions are suitably positioned to work in concert during substrate transformation. Upon activation of the complexes with MAO and exposure to ethylene, polyethylene is formed. Whereas the palladium complexes display moderate activities, nickel complexes are very active. From structure/activity correlations it is evident that the presence of backbone substitutents at the pyrazolate scaffold as well as bulky ortho aryl substituents is advantageous for polymerisation. Overall, activities of the Ni complexes and the microstructure of the polymer obtained (total branching, T m and molecular weights) are still rather similar to the data reported previously for mononuclear cationic diimine nickel complexes.