Cooperative Reactivity and Catalysis using Abundant Metal Clusters.

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Focused efforts towards the design and synthesis of polynuclear transition metal species have intensified in the last decade. In part, these efforts stem from attempts to mimic the difficult multielectron transformations facilitated by polynuclear metalloenzymes. Examples include the Mn-O cofactor in Photosystem II, as well as the carbide bearing [FeMo] cofactor in Nitrogenase. Although a plethora of transition metal clusters have been reported, the majority are highly stable species, due to coordinative saturation and molecular orbital configurations that feature large HOMO/LUMO gaps that arise from commonly used ligands such as CO. Towards the goal of designing transition metal clusters that have a more reactive nature we are investigating clusters of the late 1st row transition metals that are assembled with inexpensive readily-available ligands that are small enough to permit cluster formation, but large enough to ensure coordinative unsaturation. These complexes behave as a unique and understudied class of clusters, with  varied electron counts that deviate from theoretical predictions, low-lying paramagnetic excited states that may allow low barrier reaction pathways, tolerance to a range of functional groups, and a remarkable propensity for cooperative activation of commonly inert C-H, C-C and C-O bonds. The potential of these clusters as unique catalysts for skeletal bond rearrangements is obvious, but as yet insufficient fundamental understanding is a barrier to their application. The short term goals of this project aim to provide a better understanding of the chemistry of the highly reactive late metal clusters like [(iPr3P)Ni]5H6, with long-term goals of extending its capability in cooperative bond activation to catalytic processes.  The design of more robust clusters anchored by interstitial atoms, inspired by the carbide centre [FeMo] cofactor, provides a route to cluster design that is fundamentally different from those based strictly on complex ancillary ligand design.