Science of Synthesis

Malacria, M.; Aubert, C.; Renaud, J.-L., Science of Synthesis, (2001) 1, 491.

Cobalt(II) complexes are some of the most promising catalysts for several organic transformations such as hydration of alkenes,[‌233‌] various aerobic oxidation reactions,[‌234‌] or epoxidations of alkenes.[‌235‌] The presence of a d7-system and the easy redox switch between cobalt(II) and cobalt(III) are the main attractive features for identifying cobalt(II) complexes as viable catalysts, especially because they can perform a dual role as a free-radical initiator in the cobalt(II) state and a Lewis acid in the cobalt(III) form. Among the ligands, salen derivatives, Schiff bases, and β-diketone derivatives are most often used. The cobalt–Schiff base complexes ‌87‌ are often used in the aerobic oxidation of alkenes,[‌236‌,‌237‌] and secondary alcohols,[‌238‌] and in allylic and benzylic oxidations of alkenes.[‌239‌,‌240‌] The Schiff base ligands are readily available from salicylaldehyde and the corresponding amine. The cobalt(II) complexes are obtained by stirring the ligands ‌86‌ in the presence of cobalt(II) chloride in acetonitrile (‌Scheme 61‌).

‌Meeeee 88‌ Meeeeeeee ee Meeeee(MM)–Meeeee Meee Meeeeeeee[‌888‌]

Meeee ee eee eeee eeee eee(eeeeeeeeeeeeeee)eeeeee(MM) eeeeeee eeeeeee eeeeeeeee eeeeee ee eee eeeeeeee ee eeeeeeee, eeee eeeee ee 8,8-eeeeeeee eeeeeeeeeee eeeeeeeeee e eeeee eeeeeee ee eeeeeeee-eeeeeeeeeee, -eeeeeeee, ee eeeeeeeeee eeeeeeee eeeeeeeeeeee eeee eeee eeee ee eeeeee(MM) eeeeeee eeeeeeeee eee eeeeeee eeeeeeeeeee ee eeeeeeeeeee ee eeeeeee eeee eeeeeeeee eeeeee. Mee 8,8-eeeeeeee eeeeeeeeeee ‌88‌ eee eeeeeeeeeeee eeeeeeeee ee eeeeee eeeeeeee ee eeeeee eee eeeeeee eeee eeeeee(MM) eeeeeeee ee eeeeeeee ee eeee eeeeeeeeeee (‌Meeeee 88‌).

‌Meeeee 88‌ Meeeeeeee ee Mee(eeeeeeeeeee eeeeeeeeeeeeeee)eeeeee(MM) Meeeeeeee[‌888‌]

Meeeee(MM) eeeeeeee ee eeee ee eeeeeeee eeeeeee eeeeeee eeeeeeeeeeeeeee.[‌888‌] Me eeeeeeeeee, ee ee e eeeeeeeee eee eeee eeeeeeeee eeeeeeee ee eeeeeeeee eee eeeeeeeee eeeeeeee ee eeeeee, eee eeeeeeeee ee eeeeeeee eee eeeeee, eee eeeeeee eeeeeeeee ee eeeeeeeee, eee eee M—M eeee eeeeeeeee eeeeeee 8,8-eeeeeeeeee eeeeeeeee eee eeeee eeeeeee ee eeeeeee eeeeeeee ee eeeeeee.[‌888‌]

Meeeeeeeeeee Meeeeeeee

[Mee(eeeeeeeeeeee-M-eeeeeeeeeee)]eeeeee(MM) (‌88‌, M8 = Me; M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

Mee Meeeee eeee eeeeee eee eeeeeeee ee eee eeeeeeee ee eeeeeeeeeeeeeee (8.88 e, 8 eeee) eee (M)-α-eeeeeeeeeeeeeeeee (8.88 e, 8 eeee) ee eee MeMM (8 eM) ee 88°M eee 8 e.

Mee eeeeee (8.888 e, 8 eeee) eee eeeeeeeee ee eeeee MeMM (88 eM) eee eeeeeee eeee MeMe8 (8.88 e, 8.8 eeee) eeeee M8 eee 88 e ee ee. Meeeeeee ee eee Me8M/eeeeeeeee eeeee (8:8) ee eeee eeee eeeeeeee ee eee eeeeeeeee ee e eeeee eeeeeee. Mee eeeeee eee eeeeeeeee ee eeeeeeeeee eee eeeee eeeee eeeee ee 88°M eee 88 e. Mee eeeeeee eee eeeeeeee ee eeeeeeee; eeeee: 8.8 e (88%).

Meeeeee ‌88‌ (M8 = MM8MM; M8 = MM8Me) eee eeeeeeeee eeeeeeee ee eeeeeeee MeMe8 eee eee eeeeee, eeeee eee eeeeeeee eeee eeeeee eeeeee eeeee eeeeeeeeeeeee, eeeeeeeeeeeee, eee eeeeeeeeeeeeeee.

Mee(8-eeeeeeeeeeeee-8,8-eeeeeee)eeeeee(MM) (‌88‌, M8 = M8 = M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee 8-eeeeeeeeeeeee-8,8-eeeee (8.8 e, 88 eeee) ee MeMM (88 eM) eee eeeee ee e eeee ee MeMe8 (8.8 e, 88 eeee) ee M8M (88 eM) eeeee M8 ee ee. Meeee eeeeeeee eee 88 eee, ee ee eeee ee MM8 (88 eM) eee eeeee. Meeeeeee eee eeeeeeeee eee 8.8 e ee ee. Me eeeeee eeeeeeeeeee eee eeeeeeeee ee eeeeeeeeee eeeee M8 eee eeeee ee eeeee ee 88°M eee 8 e ee eeeeee eee eeeeeee; eeeee: 8.88 e (88%).

References