Copper(II) complexes of novel N-alkylated derivatives of cis,cis-1,3,5-triaminocyclohexane. 1. Preparation and structure

Novel N,N',N " -trialkylated derivatives of cis, cis-1,3,5-triaminocyclohex ane (tach), designated tach-R-3, were prepared through alkylation of N-prot ected tach with subsequent acid deprotection, to afford N-methyl, N-ethyl, and N-n-propyl derivatives as their trihydrobromide salts. The tach-neopent yl(3) and tach-furan(3) derivatives were prepared by formation of the imine from tach and pivaldehyde or furan-2-carboxaldehyde, respectively, followe d by reduction of the imine, Complexes [Cu(tach-R-3)Cl-2] (R = Me, Et, n-Pr , CH2-2-thienyl, and CH2-2-furanyl) were prepared from CuCl2 in MeOH or MeO H-Et2O solvent. Crystallographic characterization of [Cu(tach-Et-3)Br0.8Cl1 .2] (Pnma, a = 8.2265(1) Angstrom, b = 12.5313(1) Angstrom, c = 15.3587(3) Angstrom, Z = 4) reveals a square-based pyramidal CuN3X2 coordination spher e in which one nitrogen donor occupies the apical position at a slightly lo nger distance (Cu-N = 2.218(5) Angstrom) than those of the basal nitrogens (Cu-N = 2.053(2) Angstrom). The solution phase (pH 7.4 buffered and methano l) and solid-phase structures of [Cu(tach-R-3)Cl-2] have been studied exten sively by EPR and visible-near-IR spectroscopies. The square-based pyramida l structure is retained in solution, according to correspondence of solutio n and solid-state data. In aqueous solution, halide is replaced by water, a s indicated by the, high-energy UV-vis spectral shifts and bonding paramete rs of [Cu(tach-Et-3)](2+)(aq) derived from EPR data. The proposed aqueous-p hase species, in the pH range 7.4 to 10.1, is [Cu(tach-Et-3)(H2O)(2)](2+). The complex [Cu(tach-Me-3)](2+)-(aq) does not appear to dimerize or form me tal-hydroxo species at pH 7.4, in contrast to other Cu(Il)-triamine complex es, e.g., [Cu(1,4,7-triazacyclononane)](2+) (aq) and [Cu(tach-H-3)](2+)(aq) (the complex of unalkylated tach). This difference is attributed to the st eric effect of the N-alkyl groups in the tach-R-3 series.