Electrochemical oxidation of diaquaruthenium(<scp>II</scp>) complexes of quaterpyridines and crystal structure of [RuL¹(PPh₃)₂][ClO₄]₂(L¹= 3″,5,5′,5‴-tetramethyl-2,2′: 6′,2″: 6″,2‴-quaterpyridine)

Abstract

The perchlorate salts of [RuL2(OH2)2]2+1 and [RuL1(OH2)2]2+2(L2= 2,2′:6′,2″:6″,2‴-quaterpyridine, L1= 3″,5,5′,5‴-tetramethyl-2,2′:6′,2″:6″,2‴-quaterpyridine) have been isolated. In acidic solutions both 1 and 2 exhibit reversible RuVI–RuIV and RuIII–RuII couples, though the RuIV–RuIII couples are only quasireversible. The effect of pH on the E½ of these couples has been investigated. At pH 1, the E° values of the [RuL2O2]2+–[RuL2(O)(OH2)]2+ and [RuL1O2]2+–[RuL1(O)(OH2)]2+ couples are 1.12 and 1.05 V vs. saturated calomel electrode respectively. The crystal structure of [RuL1(PPh3)2][ClO4]2·MeCN·H2O has been determined: monoclinic space group P21/n, a= 13.210(4), b= 29.711(7), c= 14.878(3)Å, β= 98.89(2)°, Z= 4. In this complex the quaterpyridine ligand adopts a non-planar conformation with a dihedral angle of 28.3° between the two central pyridyl rings. The two triphenylphosphine ligands are in a trans configuration [P(1)–Ru–P(2) 177.6°]. The complex [RuL2(OH2)2]2+ is an active catalyst for the electrochemical oxidation of propan-2-ol.