Nickel(II)−Methyl Complexes with Water-Soluble Ligands L [(salicylaldiminato-κ2N,O)NiMe(L)] and Their Catalytic Properties in Disperse Aqueous Systems

Neutral (salicylaldiminato)nickel(II) methyl complexes [{6-C(H) NAr-2,4-I 2 C 6 H 2 O-κ 2 N, O }NiMe(L)] (Ar = 2,6-{3,5-(F 3 C) 2 C 6 H 3 } 2 C 6 H 3 ) 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 [{κ 2 - 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 × 10 4 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.