An alternative synthesis method for [Os(NN)(CO)2X2] complexes (NN = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine; X = Cl, Br, I). Electrochemical and photochemical properties and behavior

Abstract

A novel synthesis method is introduced for the preparation of [Os(NN)(CO)(2)X(2)] complexes (X = Cl, Br, I, and NN = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmbpy)). In the first step of this two-step synthesis, OsCl(3) is reduced in the presence of a sacrificial metal surface in an alcohol solution. The reduction reaction produces a mixture of trinuclear mixed metal complexes, which after the addition of bpy or dmbpy produce a trans(Cl)-[Os(NN)(CO)(2)Cl(2)] complex with a good 60-70% yield. The halide exchange of [Os(bpy)(CO)(2)Cl(2)] has been performed in a concentrated halidic acid (HI or HBr) solution in an autoclave, producing 30-50% of the corresponding complex. All of the synthesized trans(X)-[Os(bpy)(CO)(2)X(2)] (X = Cl, Br, I) complexes displayed a similar basic electrochemical behavior to that found in the ruthenium analog trans(Cl)-[Ru(bpy)(CO)(2)Cl(2)] studied previously, including the formation of an electroactive polymer [Os(bpy)(CO)(2)](n) during the two-electron electrochemical reduction. The absorption and emission properties of the osmium complexes were also studied. Compared to the ruthenium analogues, these osmium complexes display pronounced photoluminescence properties. The DFT calculations were made in order to determine the HOMO-LUMO gaps and to analyze the contribution of the individual osmium d-orbitals and halogen p-orbitals to the frontier orbitals of the molecules. The electrochemical and photochemical induced substitution reactions of carbonyl with the solvent molecule are also discussed.

Towards New Molecular Photocatalysts for CO2 Reduction: Photo‐Induced Electron Transfer versus CO Dissociation within [Os(NN)(CO)2Cl2] Complexes

“…(1)- (3); NN = dmbpy]. [16] The reduction behaviour of C2, not previously described, has been conducted in MeCN and PrCN electrolytes. Exhaustive reduction of C2 in MeCN leads to the formation of the corresponding electroactive Os-bonded polymer (as for C1) which is partially soluble (20 %).…”

“…The details of the latter reaction have been already published. [16] Photo-induced CO-release reactions in metal carbonyl complexes are generally a consequence of the population of a ligand field (LF) state after excitation in the 1 MLCT band.…”

“…Complexes C1 and C2 were synthesised following procedures already published. [16] Electrochemistry: All electrochemical measurements were run under an argon atmosphere in a dry glovebox at room temperature. Cyclic voltammetry (CV) (E pa , anodic peak potential; E pc , cathodic peak potential; E 1/…”

“…For instance the photo-induced replacement of the carbonyl ligand by a solvent molecule in [OsA C H T U N G T R E N N U N G (bpy)(CO) 2 Cl 2 ] (C1) and [OsA C H T U N G T R E N N U N G (dmbpy)(CO) 2 Cl 2 ] (C2; dmbpy = 4,4'-dimethyl 2,2'-bipyridine) to form the corresponding monocarbonyl (C3) or (C4) relevant complexes (Scheme 1) is markedly slower than for the corresponding ruthenium complexes. Furthermore, in contrast to their ruthenium analogues, complexes C1 and C2 display pronounced photoluminescence properties, in the visible region, with a lifetime of few tens of nanoseconds in MeCN [16] and up to 239 ns in CH 2 Cl 2 for the diiodo [OsA C H T U N G T R E N N U N G (bpy)(CO) 2 I 2 ] derivative. [17] These observations suggest that these Os II complexes may act as the photosensitiser in a photoredox reaction.…”

“…Emission quantum yield f L were determined at 25 8C in deoxygenated acetonitrile solutions with 6 ) 2 used as a standard (f= 0.062) by using a methodology already reported. [16] Emission lifetime measurements were performed after irradiation at l = 400 nm obtained by the second harmonic of a Titanium:Sapphire laser (picosecond Tsunami laser spectra physics 3950M1BB + 3986-03 pulse picker doubler). Fluotime 200 from AMS technologies was used for the decay acquisition.…”