Stabilization of Transition-Metal Complexes in High Oxidation States by Macrocyclic Tertiary Amines. Electrochemical Generation and Spectroscopic Properties of Novel Dihalogeno and Pseudohalogeno Tetraamine Complexes of Ruthenium(IV)

1,4,8,12-Tetramethyl-1,4,8,12-tetraazacyclopentadecane (15-TMC) was synthesized by the reaction of 1,4,8,12-tetraazacyclo-pentadecane with formaldehyde. Reactions of K2[RuCl5H2O] with 15-TMC and 16-TMC (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane) in ethanol yielded trans-[RuLCl2]Cl (L = 15-TMC and 16-TMC, respectively) in high yields. The syntheses of trans-[RuLBr2]ClO4[L = (TMEA)2(TMEA = N,N,N',N'-tetramethyl-1,2-ethanediamine), 14-TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and 15-TMC], trans-[Ru(TMEA)2(NCS)2]NCS, and trans-[Ru(14-TMC)(CH3CN)2] [ClO4]2are also described. The electrochemistry of trans-[RuLX2]+[L = (TMEA)2, 14-TMC, 15-TMC, and 16-TMC; X = Cl, Br, and NCO] in acetonitrile were examined. The Ef° values of trans-[RuLCl2]Cl in 2 M HCl have been found to decrease with L in the order 14-TMC > 15-TMC > 16-TMC. Reversible/quasi-reversible Ru(IV)/Ru(III) couples in acetonitrile with Ef° values ranging from 1.05 to 1.27 V vs. the ferrocene couple were observed. Controlled-potential electrolyses of trans-[RuLX2]+at 1.30 V vs. the ferrocene couple generated some novel trans-[RuIVLX2]2+complexes. The ligand-to-metal charge-transfer transitions in the UV-vis spectra of trans-[RuIV(TMEA)2X2]2+have been identified at 410 (X = Cl) and 570 nm (X = Br), which are considerably red-shifted with respect to their Ru(III) counterparts.