Synthesis and X-ray crystal structure of polymeric and dimeric copper(I) cyanide complexes incorporating a bicyclic guanidine ligand

1,3,4,6,7,8-Hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) reacts with coppe r(I) cyanide to afford the polymeric chain [(hppH)CuCN]. (1), consisting of distorted trigonal planar copper atoms linked by cyanide bridges. Attempts to isolate molecular species by repeating the reaction in the presence of triphenylphosphine gave a dimeric complex of the general formula [Cu-2(CN)( 2)(PPh3)(4)(hppH)] (2). The solid-state structure of 2 is consistent with a zwitterionic complex, comprising of [Cu(+)-(PPh3)(2)(hppH)] and [Cu(-)(CN) (2)(PPh3)(2)] metal centres, linked by a cyanide bridge. Variable temperatu re NMR studies suggest that the formation of higher oligomers may occur in solution at low temperature. (C) 2001 Published by Elsevier Science Ltd.