Photochemistry of the metal-metal-bonded complexes . Crystal structure of the photoproduct 2(CN)-iPr-PyCa)Ru(Me)(CO)2>

Article abstract of DOI:10.1016/0022-328X(94)05300-Z

Photochemical reactions are reported for the metal-metal-bonded complexes <(CO)5Mn-Ru(Me)(CO)2(α-diimine)> <α-diimine = pyridine-2-carbaldehyde-N-isopropylimine (ⁱPr-PyCa), N,N'-diisopropyl-1,4-diaza-1,3-butadiene (ⁱPr-DAB) upon irradiation into their lowest-energy absorption band.The radicals ^radical and ^radical are formed by homolytic splitting of the Mn-Ru bond; the latter radicals have been characterized by ESR spectroscopy.In THF, the iPr-DAB)>^radical radicals dimerize to give iPr-DAB)>2, and the corresponding radicals from the ⁱPr-PyCa complex gave an unidentified product.Irradiation of a solution of the complexes in CH2Cl2 or CHCl3 afforded and but in apolar solvents such as hexane, completely different photoproducts, viz. <(CO)3Mn-μ-(?(N),?(N'),η²(CN),η²(C'N')-ⁱPr-DAB)Ru(Me)(CO)2> and <(CO)4Mn-μ-(?(N),?(N'),η²(CN)-ⁱPr-PyCa)Ru(Me)(CO)2> were obtained.The crystal structure of the last complex was determined.The photochemical quantum yield for the disappearance of the ⁱPr-DAB complex was ca. 0.30, but only 0.05 for the ⁱPr-PyCa complex.Low-temperature measurements and flash photolysis data showed that this difference in behaviour is due to the thermal instability of the dimer iPr-PyCa)>2, which leads to partial regeneration of the parent complex at room temperature.At temperatures below 163 K, the photodecomposition into radicals was followed by electron transfer, leading to formation of the ions <(CO)5Mn>^- and ⁺ in 2-MeTHF and the contact ion-pair <(CO)5Mn^-...Ru(Me)(CO)2(α-diimine)⁺> in 2-chlorobutane.Similar photodisproportionation products were formed upon irradiation of the complexes at room temperature in the presence of N- and P-donor ligands.Keywords: Manganese; Ruthenium; Metal-metal bonding; Photochemistry; Diimines; ESR spectroscopy