Willy Herrmann

The electrochemistry of a dimeric and two monomeric cis-trioxomolybdenum(VI) complexes containing cyclic triamine ligands in protic and aprotic media: model compounds for the active site informate dehydrogenase

Abstract The electrochemistry of two monomeric cis -trioxomolybdenum(VI) complexes containing cyclic triamine ligands N , N ′, N ″-trimethyl-1,4,7-triazacyclononane (L) ( 1 ) or 1,4,7-triazacyclononane (L′)( 2 ) has been studied in protic (CH 3 SO 3 H) and aprotic media (DMF) by cyclic voltammetry at an HMD electrode. 1 and 2 are quasi-reversibly reduced by a 2e − , 4H + step in acidic solutions to give monomeric [LMo(IV)O(OH 2 ) 2 ] 2+ and [L′MoO(OH 2 ) 2 ] 2+ , which in the case of 1 is further reduced to a monomeric Mo(III) species which then undergoes a reversible chemical reaction (dimerizationi?). In contrast, reduced 2 undergoes chemical reactions (dimerization or trimerization of [L′MoO(OH 2 ) 2 ] 2+ or comproportionation reactions) due to the fact that the unmethylated cyclic amine in 2 is sterically less demanding. 1 and 2 are redox-inactive in DMF (+1.0 to −1.7 V vs AgAgCl at a Pt or a glassy-carbon electrode). Dimeric [L 2 Mo 2 O 5 ](PF 6 ) 2 , 3 is reversibly reduced to a Mo(V) 2 dimer (2e − , 2H + process) and, finally, to a Mo(III) 2 dimer(4e − , 4H + ) in 0.1 M CH 3 SO 3 H at an HMD electrode, contrasting with the behavior in aprotic medium (DMF, Pt electrode), where two reversible one-electron transfer processes generating the blue, mixed-valence species Mo(VI)/(V) and an Mo(V) 2 dimer have been observed.

Synthesis, Crystal Structure and Electrochemistry of μ-Acetatodi-μ-hydroxo-bis[(1,4,7-triazacyclononane)ruthenium(III)]-tris-iodide. Characterization of Some Ru(II)—Ru(III) Mixed Valence Species

A series of mononuclear complexes of ruthenium containing the cyclic triamine ligand 1,4,7-triazacyclononane ([9]aneN3 = L; C6H15N3) have been prepared: [RuIIL (dmso)2Cl]Cl (dmso = dimethyl sulfoxide), [RuIIILX3] (X = C1- , Br-), [RuL2](PF6)2, [RuL(C2O4)I]. Hydrolyses of RuLCl3 under a variety of reaction conditions afford dinuclear species: [RuIII2L2(μ-OH)2(μ-CH3CO2)]I3·H2O , [RuIII2L2(μ-OH)2Cl2](PF6)2, and the mixed-valence species [Ru2L2(μ-Cl)3](PF6)2. The complex [Ru2L2(μ-OH)2(μ-CH3CO2)]I3-H2O has been characterized by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic space group P21/c with a = 14.70(1) Å , b = 19.00(1) Å , c = 9.714(7) Å , β = 99.62(7)°, and V = 2674 Å3, dcalcd = 2.37 g cm-3 for Z = 4, and mol wt 952.3. The structure was solved by direct methods using 2519 unique reflections with I > 2σ(I). Final residuals were R1 = 0.0615 and R2 = 0.075. The structure consists of μ-hydroxo- and μ-acetato- bridged dinuclear cations and iodide anions. The observed diamagnetism and a short Ru-Ru bond distance of 2.572(3) Å are indicative of a Ru-Ru single bond. The electrochemical properties of [Ru2L2(μ-OH)2(μ-CH3CO2)]3+ and [Ru2L2(μ-Cl)3]2+ have been investigated by cyclic voltammetry, and by coulometry. Two one-electron redox processes have been identified for both complexes the first of which exhibits a reversible wave, whereas the second wave at more negative potentials is irreversible. The blue mixed valence species [Ru2L2(μ-OH)2(μ-CH3CO2)]2+ has been characterized in solution.