fac-/mer-[RuCl3(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 2 O) 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 ( 31 P{ 1 H}, 15 N{ 1 H} and 1 H), cyclic voltammetry, FTIR, UV–Vis, elemental analysis and X-ray diffraction structure determination. The 31 P{ 1 H} NMR revealed the presence of singlet at 35.6 for ( 1 ) and 28.3 ppm for ( 2 ). The 1 H 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 2 Cl 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 15 NO and both complexes were isolated with 15 N-enriched NO. Upon irradiation, the complex fac- [RuCl 3 (NO)(P–N)] ( 1 ) does not exchange 14 NO by 15 NO, while complex mer,trans- [RuCl 3 (NO)(P–N)] ( 2 ) does. Complex mer,trans- [RuCl 3 ( 15 NO)(P–N)] ( 2 ′) was obtained by direct reaction of mer,trans- [RuCl 3 (NO)(P–N)] ( 2 ) with 15 NO and the complex fac- [RuCl 3 ( 15 NO)(P–N)] ( 1 ′) was obtained by thermal-isomerization of mer,trans- [RuCl 3 ( 15 NO)(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%).