Catalytic transesterification reactions of one-dimensional coordination polymers containing paddle-wheel-type units connected by various bridging ligands

Abstract

The paddle-wheel dinuclear unit consists of two Cu-II ions bridged by four benzoate ligands, and these paddle-wheel [Cu-2(O2CPh)(4)] units are connected by various bridging ligands to form one-dimensional chained compounds formulated as [Cu-2(O2CPh)(4)(mu-L)] (L = 2,4-bpe (1), 3,3'-dipicam (3), 2,5-Me(2)pyz (4), pyz (5), 4,4'-bpy (6), and 4-pds (7)). The compound 2, formulated as [[Cu-2(O2CPh)(4)][Cu(O2CPh)(2)](mu-bpp)(2)], consists of alternating units of [Cu-2(O2CPh)(4)] and [Cu(O2CPh)(2)] connected by via bpp. Compounds 1-5 and 7 efficiently catalyzed the transesterification of a variety of esters, while it has been reported that Cu-containing complexes or coordination polymers do not usually show catalytic activities for the transesterification reactions. Among these compounds, 2 was most effective. It has been proposed that in the transesterification reaction, a mononuclear type of Cu complex might be the major species of compound 2 in solution, while for all other compounds, a paddle-wheel unit might be the major reactive species. (C) 2013 Elsevier B.V. All rights reserved.