Structural Consequences of the Prohibition of Hydrogen Bonding in Copper−Guanidine Systems

The synthesis and structure of copper(I) complexes supported by N-substituted bicyclic guanidines is described. The N-methyl-substituted bicyclic guanidine 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine (hppMe) reacted with copper(I) chloride to afford the ion-pair [Cu(hppMe)2][CuCl2] (1), a rare example of a compound containing an unsupported Cu···Cu interaction. The analogous reaction with CuI, however, afforded the molecular μ,μ-dihalo-bridged dimer [CuI(hppMe)]2 (2). Inclusion of a trimethylsilyl substituent at nitrogen provided a sufficiently sterically encumbered environment to support a two coordinate copper center in CuCl(hppSiMe3) (3). Compounds 1−3 have been fully characterized, including single-crystal X-ray diffraction studies.