Connecting ruthenium substituted Keggin-type tungstophosphates by oxotungstic bridges: Evidence for the steric effect of {RuL 3 } 2+ (L 3 =η 6 -arene, (DMSO) 3 ) fragments

The intrinsic reactivity of the organoruthenium-grafted tungstophosphates [α-PW11O39{Ru(η6-arene)(H2O)}]5− and [α-PW11O39{Ru(DMSO)3(H2O)}]5− has been studied as a prerequisite for later catalytic studies. Upon reflux in aqueous solution, they partially transform into [{PW11O39Ru(η6-arene)}2{WO2}]8− (when arene=benzene, toluene…) and [α-PW11O39{Ru(DMSO)}]5−, respectively. In the former case, the conversion is markedly increased by deliberate addition of tungstate: through a solution NMR study, we show that [{PW11O39Ru(η6-p-cymene)}2{WO2}]8− is quantitatively obtained by refluxing a 2:1:2 mixture of [α-PW11O39]7−, [Ru(η6-p-cymene)Cl2]2 and [WO4]2− at pH 3. In contrast, a different type of complex, [{PW11O39Ru(DMSO)3}2{(WO2(H2O))2O}]8−, is formed by reaction of [α-PW11O39{Ru(DMSO)3(H2O)}]5− with tungstate; it has been characterized by single crystal X-ray diffraction analysis of an acidic potassium salt, and by 183W solution NMR. The more sterically demanding {Ru(DMSO)3}2+ fragment probably does not allow the formation of [{PW11O39Ru(DMSO)3}2{WO2}]8−, while connection of {PW11O39Ru(DMSO)3}5− subunits is possible through the larger {(WO2(H2O))2O}2+ bridge.