CATALYTIC EPOXIDATION OF UNFUNCTIONALIZED ALKENES BY DINUCLEAR NICKEL(II) COMPLEXES

The synthesis, crystal and molecular structure and catalytic activity in epoxidation reactions of new dinuclear nickel(II)-complexes, octahe dral mu-diacetato-mu-[2,6-bis[N-2-(2'-pyridylethyl) formimidoyl]phenol ato]bisnickel(II). perchlorate . methanol (6) and square planar formim idoyl]phenolato]bisnickel(II)-bisperchlorate (7), are described. For t he preparation of 7 a new 5-step route for homochiral bisamine (S)-ben zyl-2-aminomethyl-pyrrolidine (19) was developed starting from (S)-pro line. Epoxidation of unfunctionalized alkenes with sodium hypochlorite and tert-butyl hydroperoxide as terminal oxidants was effectively cat alyzed with bisnickel(II)-complexes 6 and 7, and a turnover of 165 was reached using trans-beta-methylstyrene (34). The epoxidations probabl y proceed via a radical intermediate (such as OCl .) and no enantiosel ectivity is obtained under phase transfer conditions. In epoxidation r eactions employing tert-butyl hydroperoxide as terminal oxidant a turn over of 43 was obtained with trans-stilbene (30) as substrate. Unexpec tedly in the case of styrene (29) 1,2-bis-(tert-butylperoxy)ethylbenze ne (59) was isolated as the major product.