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

The coordination chemistry of copper(I) and copper(II) ions with novel tripodal peralkylguanidine derivatives of
the tris(2-aminoethyl)amine (tren) backbone TMG3tren (tetramethylguanidino-tren) N{CH2CH2NC(NMe2)2}3
(1) and cyclic DMPG3tren (dimethylpropyleneguanidino-tren) N[CH2CH2NC{NMe(CH2)3NMe}]3 (2) is reported.
These sterically demanding ligands form complexes of constraint trigonal geometry. Their superbasic character
with estimated pKBH+ values 6 orders of magnitude higher than that of the known Me6tren 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 [N4Cu]+ coordination sphere and a sterically protected
open coordination site and of two cationic copper(II) complexes with the characteristic trigonal-bipyramidal
coordination geometry [N4CuCl]+ and [N5Cu]2+ are reported.