The mechanism of the intramolecular hydrocarbyl metathesis within a planar triruthenium cluster - combining core flexibility with hydride mobility.

The transition metal catalysed formation and cleavage of C-C bonds is of utmost importance in synthetic chemistry. While most of the existing homogeneous catalysts are mononuclear, knowledge of the behaviour of polynuclear species is much more limited. By using computational methods, here we shed light into the mechanistic details of the thermally-induced isomerization of Cp*Ru-3(3)(mu-H)(2)(mu(3)-eta(2)-pentyne)(mu(3)-pentylidyne) (2) into Cp*Ru-3(3)(mu-H)(2)(mu(3)-eta(2)-octyne)(mu(3)-ethylidyne) (3), a process that involves the migration of a C(3)fragment between the hydrocarbyl ligands and across the plane formed by the three Ru centres. Our results show this to be a complex transformation that comprises of five individual rearrangements in anA -> B -> A -> B -> Aorder. Each so-called rearrangementAconsists of the CH migration from the mu(3)-eta(2)-alkyne into the mu(3)-alkylidine ligand in the other side of the Ru(3)plane. This process is facilitated by the cluster's ability to adopt open-core structures in which one Ru-Ru bond is broken and a new C-C bond is formed. In contrast, rearrangementsBdo not involve the formation or cleavage of C-C bonds, nor do they require the opening of the cluster core. Instead, they consist of the isomerization of the mu(3)-eta(2)-alkyne and mu(3)-alkylidyne ligands on each side of the triruthenium plane into mu(3)-alkylidyne and mu(3)-eta(2)-alkyne, respectively. Such transformation implies the migration of three H atoms within the hydrocarbyl ligands, and in this case, it is aided by the cluster's ability to behave as a H reservoir. All in all, this study highlights the plasticity of these Ru(3)clusters, whereby Ru-Ru, Ru-C, Ru-H, C-C, and C-H bonds are formed and broken with surprising ease.