Nickel(II)−Methyl Complexes with Water-Soluble Ligands L [(salicylaldiminato-κ2 N,O)NiMe(L)] and Their Catalytic Properties in Disperse Aqueous Systems

Neutral (salicylaldiminato)nickel(II) methyl complexes [{6-C(H)NAr-2,4-I2C6H2O-κ2 N,O}NiMe(L)] (Ar = 2,6-{3,5-(F3C)2C6H3}2C6H3) with different water-soluble ligands L (2a, L = 1,3,5-triaza-7-phosphaadamantane; 2b, L = hexamethylenetetramine (urotropine); 2c, L = tetraethylammonium pyridine-3-sulfonate; 2d, L = amino-terminated poly(ethylene glycol) monomethoxy ether) were prepared. 2a−d are potentially water-soluble catalyst precursors for ethylene polymerization, which form a water-insoluble active site [{κ2-N,O}NiR(ethylene)] (R = growing chain). Only complex 2d was found to be water-soluble (>2 mmol L-1); 2c is soluble in water/2-propanol mixtures. In toluene as a reaction medium, only the relatively weakly coordinated tertiary amine complex 2b is polymerization active (1.7 × 104 TO). In aqueous systems 2c,d are also active due to compartmentalization of the active site in the polymer particles and of L in the aqueous phase. Polyethylene particle sizes vary from 18 nm (dispersions formed with 2d) to over 0.5 μm (2c) to suspensions (2b) depending on the initial state of the reaction mixture, correlated with catalyst solubility.