Synthesis, characterization and redox properties of mixed phosphine nitroruthenium(II) complexes. crystal structure of trans-[Ru(NO2)(terpy)-(PMe3)(PPh3)][ClO4]·H2O

Abstract

The mixed phosphine complexes trans-[Ru(NO₂)(terpy)(PMe₃)(PR₃)][ClO₄](terpy = 2,2′ : 6′,2″-terpyridine; R = Et, Pr, Bz or Ph) were synthesized in high yields by a stepwise addition of each phosphine. These syntheses demonstrate the utility of ruthenium(II) in the preparation of mixed phosphine complexes. The stereochemistry of trans-[Ru(NO₂)(terpy)(PMe₃)(PPh₃)][ClO₄]·H₂O was confirmed by a single-crystal X-ray diffraction study. This species crystallizes in the monoclinic space group P2₁/c with a= 11.0199(15), b= 18.3888(28), c= 19.3089(25)Å, β= 112.845(9)° and Z= 4. The two phosphine ligands are mutually trans, with P–Ru–P 177.5(1)°. The relative redox stabilities of the mixed phosphine complexes and a related series of trans-[Ru(NO₂)(terpy)(PR₃)₂][ClO₄](R = Et, Pr, Bz or Ph) complexes were evaluated using cyclic voltammetric peak current ratios (i_pc/i_pa) for the ruthenium(III)–ruthenium(II) couples. The rate constants for nitroruthenium(III) decomposition were calculated from the i_pc/i_pa data and the contributions of electronic (E) and steric (S) factors to its rate of decomposition were determined using the relationship ln k=aE+bS+c. The average ratio of steric to electronic ligand effects on ln k is approximately 30 : 70.