Synthesis and Base Hydrolysis of the Pentaammine(dimethyl sulfide)cobalt(III) Ion

Abstract

The synthesis of the trifluoromethanesulfonate salt of the pentaarnmine (dimethy1 sulfide)-cobalt(III) ion, [NH3)5Co-S(CH3)2]3+, is described along with the kinetics of its hydrolysis in basic and acidic solutions. The synthesis proceeds in 44% yield from the reaction of [(NH3)5Co-OSO2CF3] (CF3SO3)2 with CH3SCH3 in tetramethylene sulfone at 80�C. The salt has been characterized by elemental analysis, visible-U.V. spectroscopy, and 1H n.m.r. In basic solution the complex decomposes by Co-S cleavage to yield [(NH3)5CO-OH]2+ and non-coordinated CH3SCH3. The kinetics of this reaction were studied in phosphate buffers ranging from pH 8.50 to 11.67 ( �= 1.0 M); a linear dependence of the reaction rate on [OH-] was observed. At 25�C, kOH = 8.8 � 0.2 dm3 mol-1 s-1. Activation parameters, determined over a temperature range from 15 to 44�C, were ΔH‡ = 152 � 3 kJ mol-1 and Δ S‡ = 286 � 9 J K-1 mol-1. In 0.01 M HClO4 ( � = 1.0 M, 25�C), the cobaltsulfur bond is cleaved at a rate of 1.6×10-6 s-l. Activation parameters, determined over a temperature range from 25 to 60�C, were ΔH‡ = 106 � 5 kJ mol-1 and ΔS‡= -2 � 16 J K-1 mol-1.

Synthesis and Characterisation of [(en)2Co]3+ Complexes Coordinated by Substituted Thiourea Ligands

“…The triflato ion is readily substituted under mild conditions and these preparations are another example of the synthetic versatility of labile trifluoromethanesulfonato complexes. [6,16,[19][20][21][22][23][24] Isolated product yields ranged from 15 to 50 % and are significantly lower than the nearly quantitative yields often reported for similar reactions. The most prevalent side product is cis-[(en) 2 Co(H 2 O) 2 ] 3þ which forms when unreacted cis-[(en) 2 Co (OSO 2 CF 3 ) 2 ] þ is exposed to water before and during chromatography.…”

“…[9] In addition, the coordination chemistry of urea, [10][11][12] thiourea, [13] and substituted urea ligands [14][15][16] has been of general interest over many years. Continuing our interest in the coordination of sulfur-containing ligands to Co III [17][18][19] we examined the coordination of the N,N 0 -substituted thiourea ligands shown in Fig. 1 to the robust [(en) 2 Co] 3þ fragment.…”

Making a Robust Carbon−Cobalt(III) Bond

“…Monodentate thioether compounds of cobalt(III), for example, [Co(NH 3 ) 5 (S(CH 3 ) 2 )] 3+ , undergo hydrolysis in basic solution to yield the corresponding hydroxo entity, that is, [Co(NH 3 ) 5 (OH)] 2+ , with release of the thioether . Coordination compounds with 2-aminoethyl sulfides, H 2 NCH 2 CH 2 −S−R, reacts similarly when R is a simple alkyl group.…”