Copper Complexes of Novel Superbasic Peralkylguanidine Derivatives of Tris(2-aminoethyl)amine as Constraint Geometry Ligands

Abstract

The coordination chemistry of copper(I) and copper(II) ions with novel tripodal peralkylguanidine derivatives of the tris(2-aminoethyl)amine (tren) backbone TMG(3)tren (tetramethylguanidino-tren) N[CH(2)CH(2)N=C(NMe(2))(2)](3) (1) and cyclic DMPG(3)tren (dimethylpropyleneguanidino-tren) N[CH(2)CH(2)N=C[NMe(CH(2))(3)NMe]](3) (2) is reported. These sterically demanding ligands form complexes of constraint trigonal geometry. Their superbasic character with estimated pK(BH)+ values 6 orders of magnitude higher than that of the known Me(6)tren and their softer N-donor character compared to tert-amine ligands stabilize cationic mononuclear Cu(I) and Cu(II) ions by delocalization of charge into the guanidine functionalities. The crystal structures and spectroscopic features of two cationic copper(I) complexes with an uncommon trigonal-pyramidal [N(4)Cu](+) coordination sphere and a sterically protected open coordination site and of two cationic copper(II) complexes with the characteristic trigonal-bipyramidal coordination geometry [N(4)CuCl](+) and [N(5)Cu](2+) are reported.