A combined experimental and DFT investigation on the structure and CO-releasing properties of mono and binuclear fac-Re^I(CO)₃complexes with 5-pyridin-2-ylmethylene-amino uracils

Abstract

The synthesis, structure and CO-releasing properties of a number of new tricarbonyl rhenium(i) complexes with 5-substituted-6-amino-1,3-dimethyluracils are reported and their structural features discussed on the basis of both spectral and X-ray crystallographic analyses. The 5-substituent library includes -N[double bond, length as m-dash]CH-2py (DAAUPic) and -CH[double bond, length as m-dash]N-N[double bond, length as m-dash]CH-2py (FDUHzPic) as additional metal binding components and chloride, acetonitrile or pyridine acting as ancillary ligands. The compounds have been identified by elemental analysis, NMR, MS and IR spectroscopy. In addition, [ReCl(CO)(DAAUPic)], [Re(CO)(FDUHzPic)py]ClO, [Re(CO)(FDUHzPic)py]PF, [ReCl(CO)(FDUHzPic)] and [ReCl(CO)(FDUHzPicH)(HO)] structures have been solved by X-ray diffraction methods. These studies have clearly shown that the preferred coordination mode to rhenium takes place through the (N1F,N52)-pyridin-2-yl-methyleneamine moiety, the uracil coordinative availability (O4-N51 or N6-N51) being used only to bind the second metal center. The CO-releasing ability of these rhenium compounds has been investigated by the reaction with myoglobin; the corresponding studies have revealed that two of the mononuclear complexes and their related binuclear analogues are able to release CO to a moderate extent. This ability has also been theoretically assessed through a QTAIM analysis. The results, although non-conclusive, may explain somehow possible different preferences in CO releasing power after a comparison between the nature of Re-CO links in mononuclear and binuclear compounds.

Mechanistic insights into the electrochemical reduction of CO2 to CO on Ni(salphen) complexes

“…They are easier for the former and more difficult than for the latter, reflecting the electronic delocalisation of the π system. The frontier orbitals of [1], [2] and [3], obtained from a full geometry optimisation, are in agreement with the proposed ligand-based reduction process (Fig. S2-S4 †).…”

“…Their synthesis and characterisation have been previously reported, as well as their performance in the O 2 reduction reaction. 42,43 The cyclic voltammograms of Ni(II) complexes [1]- [3] in dimethylformamide (DMF) solution using glassy carbon as a working electrode are shown in Fig. 2.…”

“…1,2 One of them is carbon monoxide (CO), considered a silent killer gas, but still employed in several important applications from therapeutics to industry. Indeed, in small amounts, CO has cell protective, anti-inflammatory and vasodilatory properties, 3 and CO-releasing compounds have been developed for this purpose. 4,5 This gas also plays a key role in many relevant chemical reactions such as Fischer-Tropsch 6 or as a C1 source for several carbonylation reactions (e.g.…”

Efficient Direct Nitrosylation of α-Diimine Rhenium Tricarbonyl Complexes to Structurally Nearly Identical Higher Charge Congeners Activable towards Photo-CO Release

“…Spontaneous and light-induced CO release of 16-and 17-electron rhenium complexes [55][56][57], and 18-electron fac-[Re I (CO) 3 (N-N)PR 3 ] + (where PR 3 = phosphine or phosphite) is well known [58][59][60]. In the last five years several examples of diimine complexes bearing either σor π-donating ancillary ligands active towards CO photosubstitution have also been described [61][62][63][64][65]. For PR 3 species, the strong trans-labilizing ability of the phosphorus donor of π-acid ligands is crucial for activating Re tricarbonyl species towards photochemical substitution of CO, and works in conjunction with the internal conversion between the 3 MLCT and thermally accessible higher energy photoexcited 3 LF state that is productive in terms of CO dissociation [66].…”

Efficient direct nitrosylation of a-diimine rhenium tricarbonyl complexes to structurally nearly identical higher charge congeners activable towards photo-CO release

“…[58][59][60] In the last five years several examples of diimine complexes bearing either σor π-donating ancillary ligands active towards CO photosubstitution have also been described. [61][62][63][64][65] For PR 3 species, the strong trans-labilizing ability of the phosphorus donor of π-acid ligands is crucial for activating Re tricarbonyl species towards photochemical substitution of CO, and works in conjunction with the internal conversion between the 3 MLCT and thermally accessible higher energy photoexcited 3 LF state that is productive in terms of CO dissociation. 66 For tricarbonyl rhenium diimine complexes with π-basic ligands, mechanistic studies and picosecond time-resolved IR measurements indicate that only irradiation with higher energy photons can induce photochemical ligand substitution reactions via higher energy vibrational states rather than the lowest-lying 3 MLCT excited or thermally accessible 3 LF states.…”