Thermal and photochemical behavior of trans-ruthenium(II) dichloride tetraphosphite complexes

trans-[RuCl2{P(OR)3}4] complexes were prepared by reaction between RuCl3 and P(OR)3 ligands: R = CH3, C2H5, iC3H7 and nC4H9. The electronic spectra of freshly prepared solution show similar spectral behavior in two selected pH values: two absorptions bands at 250 nm (ɛ = 103 M−1 cm−1) and at 408 nm (ɛ = 102 M−1 cm−1) and a shoulder at 280 nm (ɛ ≅ 102 M−1 cm−1). The complexes exhibit distinct dissociation behavior of ligands as function of the pH (3.0 and 7.0, respectively) with the increase in the size of the alkyl substituent in the phosphorus ligand. The 31P NMR data at the pH 3.0, show only one signal for complexes freshly prepared solutions with δ = 131, 129, 127 and 125 ppm assigned to R = CH3, C2H5, iC3H7 and nC4H9, respectively. After 24 h reaction, the complexes exhibit 31P NMR signals attributed to new ruthenium compounds formed by chloride and phosphite dissociation, at δ = 145, 143, 140 and 137 ppm for ruthenium complexes, respectively, and signals at δ = 11.8, 9.7, 9.4 and 8.5 ppm, respectively, assigned to free dialkylphosphonate molecules in solution. At pH 7.0, only one 31P NMR signal for each complex was observed with δ = 136, 134, 131 and 130 ppm for R = CH3, C2H5, iC3H7 and nC4H9, respectively. The complexes were photolyzed with light of λ = 410 nm centered on the lowest energy of ligand field transition band. Photoaquation generating Cl− species in solution was observed for all complexes with photoreaction quantum yield ϕ in the range of 0.34–0.35 mol/Einstein at pH 3.0 and in the range of 0.36–0.40 mol/Einstein at pH 7.0. In acidic medium, the irradiation at 408 nm leads to photoaquation of ligands with concomitant stereochemical change, while at neutral conditions only the chloride photolabilization was observed.