NOVEL TRIDENTATE DIAMINO ORGANOMANGANESE(II) COMPLEXES AS HOMOGENEOUSCATALYSTS IN MANGANESE(II) COPPER(I) CATALYZED CARBON-CARBON BOND-FORMING REACTIONS/

The new, paramagnetic arylmanganese(II) complex Li[MnCl2(NCN)] (2, NCN [C6H3(CH2NMe2)(2)-2,6](-)) has been obtained in high yield from the r eaction of MnCl2 and [Li(NCN)](2) in a 2:1 molar ratio. In THF solutio n, 2 is likely an ionic species [Li(THF)(n)] [MnCl2(NCN)] (molecular w eight determination and conductivity measurements), while magnetic mea surements indicate that a high spin d(5) manganese(II) center is prese nt. Subsequent reaction of 2 with RLi afforded [MnR(NCN)I (R = Me (3a) , n-Bu (3b)). Complex 2, using CuCl as a co-catalyst, is an effective catalyst system for cross-coupling of Grignard reagents with alkyl bro mides and the 1,4-addition of organomagnesium halides to alpha,beta-un saturated ketones. No further additives or co-solvents are necessary. For both reactions a dramatic decrease in reaction times is observed w hen compared to standard manganese/copper systems. Alkyl bromides with unsaturated or heteroatom functionalities can be cross-coupled. Also, excellent reactivity towards normally unreactive beta,beta-disubstitu ted ketones has been observed in the 1,4-addition reaction. (C) 1998 E lsevier Science S.A. All rights reserved.