Mechanism of the conversion of [Ru(CO)5] into [Ru3(CO)12]

Abstract
The conversion of [Ru(CO)5] into [Ru3(CO)12] in cyclohexane at 294–308 K has been shown to involve initial carbon monoxide dissociation to give the intermediate [Ru(CO)4]; the latter then combines further with [Ru(CO)5] in a series of fast steps to form ultimately the trimer [Ru3(CO)12]. The mechanism is thus closely related to the dissociative mechanism demonstrated previously for substitution of one CO of [Ru(CO)5] by PPh3, and essentially identical activation parameters are found for both types of reactions [for the ‘trimerization’, ΔH= 109 (± 15) kJ mol–1, ΔS 53 (± 15) J K–1 mol–1]. The equilibrium constant for the reaction 3[Ru(CO)5]⇆[Ru3(CO)12]+ 3CO at 298 K is 3.0 (± 0.5)× 106 mol dm–3.

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