Synthesis And Properties Of Cyclometalated Ruthenium Nitrosyl Complexes

The formation of the Ru-C?bond in the chemical structure of the cyclometalated ruthenium complex makes its photophysical and chemical properties better than classical polybipyridine ruthenium complex Ru(bpy)₃²⁺(bpy=2,2'-bipyridine).The introduction of carbanion changes the HOMO of the complex,which makes the HOMO originally localized in the metal center move to a mixture of C^N ligand and metal center,accompanied by a large red-shift absorption.Since the metal to ligand charge transfer(MLCT)absorption of this type of complexes is usually above 500 nm and the structure can be modified to achieve functionalization,it has attracted the attention of researchers in the field of photochemistry.On the other hand,the complexes formed by the coordination of ruthenium and nitrosyl have been proven to have the ability to release nitric oxide.Relying on the killing effect of high concentrations of NO on cells,these complexes are also potential anticancer drugs.But so far,reports on cyclometalated ruthenium nitrosyl complexes are rare.Therefore,we tried to react the cyclometalated ruthenium complexes with nitrosyl tetrafluoroborate in one step and successfully prepared six cyclometalated ruthenium nitrosyl complexes.Whether these complexes are capable of release nitric oxide under light conditions has been preliminary explored.The specific content is as follows:1.The cyclometalated ruthenium complexes based on 2-phenylpyridine containing different electron-withdrawing substituents:[Ru(bpy)₂(ppy)]⁺and their analogs(1a-1f,Hppy=2-phenylpyridine,bpy=2,2'-bipyridine)have been synthesized.Their stability under different p H environments were explored,and the chlorine-containing ruthenium nitrosyl complex was successfully prepared by the reaction of acidic sodium nitrite with complex 1a.However,the yield was low and separation and purification were difficult.Then,the nitrosyl ruthenium complex as[Ru(bpy)(C^N)(Me CN)NO]²⁺(2a-2f,,HC^N=2-phenylpyridine and its derivatives)have been obtained by using nitrosyl tetrafluoroborate in CH₃CN which have not been reported.Their structures were characterized by MS,NMR,IR,UV-Vis spectra and X-ray single crystal diffraction,respectively.The results combined with theoretical calculations showed that:1)The coordinated NO ligand is a nitrosyl cation(NO⁺),not a neutral part(NO)or(NO^-);2)The different substituents on the C^N ligands in 1a-1f do not affect the coordination behavior,NO⁺coordinates directly with Ru to form nitrosyl complexes rather than C-nitroso ruthenium complex;3)The EPR experiments showed that these ruthenium nitrosyl complexes are potential photosensitive NO donor molecules.2.The cyclometalated ruthenium complexes containing 2-vinylpyridine and its derivatives were designed and synthesized(3a-3e),which have been characterized by NMR,MS and elemental analysis spectra,respectively.The single crystal structure of3b showed that the carbon in the vinyl group is successfully coordinated with Ru,and the Ru-N bond(2.127(5)A)in the trans position to the Ru-C bond is slightly longer than the general Ru-N bond due to the trans effect of the carbonation.The calculation results and the UV-Vis absorption spectra showed that these complexes all exhibited the characteristic MCLT absorptions that are attributed to the cyclometalated ruthenium complexes.In addition,the dynamic changes of these complexes in acidic solutions were tracked by UV-vis spectra and Maldi-Tof.A possible mechanism for the protonation in the Ru-C bond cleavage process was proposed.