Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

Visible-light activation of the bimetallic chromophore-catalyst dyad: analysis of transient intermediates and reactivity toward organic sulfides

In order to develop a new photocatalytic system, we designed a new redox-active module (5) to hold both a photosensitizer part, [Ru(II)(terpy)(bpy)X](n+) (where terpy = 2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine), and a popular Jacobsen catalytic part, salen-Mn(III), covalently linked through a pyridine-based electron-relay moiety. On the basis of nanosecond laser flash photolysis studies, an intramolecular electron transfer mechanism from salen-Mn(III) to photooxidized Ru(III) chromophore yielding the catalytically active high-valent salen-Mn(IV) species was proposed. To examine the reactivity of such photogenerated salen-Mn(IV), we employed organic sulfide as substrate. Detection of the formation of a Mn(III)-phenoxyl radical and a sulfur radical cation during the course of reaction using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. This is the first report for the electron transfer reaction of organic sulfide with the photochemically generated salen-Mn(IV) catalytic center.

Binuclear ruthenium η6-arene complexes with tetradentate N,S-ligands containing the ortho-aminothiophenol motif

A series of cationic binuclear (η(6)-cymene-Ru)2 complexes with N2S2-ligands were synthesized in 64% to 85% yield by reaction of [Ru(η(6)-cymene)Cl2]2 with bis-S,S'-(ortho-aminothiophenol)-xylenes as BF4(-) and PF6(-) salts. The compounds were studied using NMR, HRMS, UV-vis and IR spectroscopy, EA and inductively coupled plasma (ICP) MS. It was determined that the hinged binuclear Ru complexes were anti and syn diastereomers obtained in 2 : 1 ratio for ortho- and meta-xylylene bridged ligands and in a 1 : 1 ratio for the para-xylylene bridged ligand. An anion effect was found for the presence of NaBF4 with the meta-xylylene bridged system yielding the targeted binuclear Ru complex and a mononuclear Ru complex. This mononuclear S,S'-coordinated η(6)-cymene Ru chloride structure lacked amine-metal coordination and was obtained in a 1 : 3 ratio of anti : syn diastereomers which were insoluble in CH2Cl2 and soluble in DMSO and DMF. X-ray crystallographic analysis was obtained for the N2S2 ligand, 1,2-bis{(2-aminophenyl)thiomethyl}benzene, showing a CS symmetry with amine groups facing outwards with a tilt of 28.95° from the ortho-aminothiophenol pendant ring. The interatomic sulfur-sulfur distance (S-S') is 4.6405 Å within the crystal structure while accommodating a potential metal bite angle from 1.0 Å to 5.9 Å when allowing rotation of the methylene phenyl bond.