Fac-/mer-[RuCl 3(NO)(P–N)] (P–N = [ o-( N, N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Abstract

Complex fac-[RuCl 3(NO)(P–N)] ( 1) was synthesized from the reaction of [RuCl 3(H 2O) 2(NO)] and the P–N ligand, o-[( N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl 3(NO)(P–N)] ( 2) was obtained by photochemical isomerization of ( 1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl 3(NO)(P–N)] ( 3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex ( 2) a thermally induced isomerization occurs and complex ( 1) is regenerated. The complexes were characterized by NMR ( 31P{ 1H}, 15N{ 1H} and 1H), cyclic voltammetry, FTIR, UV–Vis, elemental analysis and X-ray diffraction structure determination. The 31P{ 1H} NMR revealed the presence of singlet at 35.6 for ( 1) and 28.3 ppm for ( 2). The 1H NMR spectrum for ( 1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for ( 2) was observed only one singlet at 3.29 ppm. FTIR Ru–NO stretching in KBr pellets or CH 2Cl 2 solution presented 1866 and 1872 cm −1 for ( 1) and 1841 and 1860 cm −1 for ( 2). Electrochemical analysis revealed a irreversible reduction attributed to Ru II–NO + → Ru II–NO 0 at −0.81 V and −0.62 V, for ( 1) and ( 2), respectively; the process Ru II → Ru III, as expected, is only observed around 2.0 V, for both complexes. Studies were conducted using 15NO and both complexes were isolated with 15N-enriched NO. Upon irradiation, the complex fac-[RuCl 3(NO)(P–N)] ( 1) does not exchange 14NO by 15NO, while complex mer,trans-[RuCl 3(NO)(P–N)] ( 2) does. Complex mer,trans-[RuCl 3( 15NO)(P–N)] ( 2′) was obtained by direct reaction of mer,trans-[RuCl 3(NO)(P–N)] ( 2) with 15NO and the complex fac-[RuCl 3( 15NO)(P–N)] ( 1′) was obtained by thermal-isomerization of mer,trans-[RuCl 3( 15NO)(P–N)] ( 2′). DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex ( 1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for ( 2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for ( 1) is based on NO (52.9%) and is less extent on Ru (38.4%), for ( 2) NO (58.2%) and Ru (31.5%).