Conner M. Farley

Bio: Conner M. Farley is an academic researcher from Purdue University. The author has contributed to research in topics: Organometallic chemistry & Ligand. The author has an hindex of 4, co-authored 5 publications receiving 60 citations. Previous affiliations of Conner M. Farley include University of Idaho.

Organic Reactions Enabled by Catalytically Active Metal–Metal Bonds

Abstract: Molecular transition-metal catalysts are predominantly Werner-type coordination complexes, wherein a single metal ion surrounded by ligands functions as the sole locus of reactivity. A major focus of organometallic chemistry has been to understand how supporting ligands can be rationally modified in order to access more active and selective catalysts. Since the 1960s, however, it has been recognized that metals can also form direct metal-to-metal bonds, giving rise to an extraordinary diversity of multinuclear assemblies. If metal–metal bonding could be harnessed productively in catalysis, it would provide access to a large parameter space that is not available through ligand modification. This review highlights recent examples of organic transformations that were discovered using catalysts containing metal–metal bonds.

Dinickel Active Sites Supported by Redox-Active Ligands.

Abstract: Redox reactions that take place in enzymes and on the surfaces of heterogeneous catalysts often require active sites that contain multiple metals. By contrast, there are very few homogeneous catalysts with multinuclear active sites, and the field of organometallic chemistry continues to be dominated by the study of single metal systems. Multinuclear catalysts have the potential to display unique properties owing to their ability to cooperatively engage substrates. Furthermore, direct metal-to-metal covalent bonding can give rise to new electronic configurations that dramatically impact substrate binding and reactivity. In order to effectively capitalize on these features, it is necessary to consider strategies to avoid the dissociation of fragile metal-metal bonds in the course of a catalytic cycle. This Account describes one approach to accomplishing this goal using binucleating redox-active ligands.In 2006, Chirik showed that pyridine-diimines (PDI) have sufficiently low-lying π* levels that they can be redox-noninnocent in low-valent iron complexes. Extending this concept, we investigated a series of dinickel complexes supported by naphthyridine-diimine (NDI) ligands. These complexes can promote a broad range of two-electron redox processes in which the NDI ligand manages electron equivalents while the metals remain in a Ni(I)-Ni(I) state.Using (NDI)Ni2 catalysts, we have uncovered cases where having two metals in the active site addresses a problem in catalysis that had not been adequately solved using single-metal systems. For example, mononickel complexes are capable of stoichiometrically dimerizing aryl azides to form azoarenes but do not turn over due to strong product inhibition. By contrast, dinickel complexes are effective catalysts for this reaction and avoid this thermodynamic sink by binding to azoarenes in their higher-energy cis form.Dinickel complexes can also activate strong bonds through the cooperative action of both metals. Norbornadiene has a ring-strain energy that is similar to that of cyclopropane but is not prone to undergoing C-C oxidative addition with monometallic complexes. Using an (NDI)Ni2 complex, norbornadiene undergoes rapid ring opening by the oxidative addition of the vinyl and bridgehead carbons. An inspection of the resulting metallacycle reveals that it is stabilized through a network of secondary Ni-π interactions. This reactivity enabled the development of a catalytic carbonylative rearrangement to form fused bicyclic dienones.These vignettes and others described in this Account highlight some of the implications of metal-metal bonding in promoting a challenging step in a catalytic cycle or adjusting the thermodynamic landscape of key intermediates. Given that our studies have focused nearly exclusively on the (NDI)Ni2 system, we anticipate that many more such cases are left to be discovered as other transition-metal combinations and ligand classes are explored.

Catalytic [5 + 1]-Cycloadditions of Vinylcyclopropanes and Vinylidenes.

Abstract: Polysubstituted cyclohexenes bearing 1,3 (meta) substitution patterns are challenging to access using the Diels-Alder reaction (the ortho-para rule). Here, we report a cobalt-catalyzed reductive [5 + 1]-cycloaddition between a vinylcyclopropane and a vinylidene to provide methylenecyclohexenes bearing all-meta relationships. Vinylidene equivalents are generated from 1,1-dichloroalkenes using Zn as a stoichiometric reductant. Experimental observations are consistent with a mechanism involving a cobaltacyclobutane formed from a [2 + 2]-cycloaddition between a cobalt vinylidene and a vinylcyclopropane.

Catalytic Cyclooligomerization of Enones with Three Methylene Equivalents

Abstract: Cyclic structures are highly represented in organic molecules, motivating a wealth of catalytic methods targeting their synthesis. Among the various ring-forming processes, cyclooligomerization reactions possess several attractive features but require addressing a unique challenge associated with controlling ring-size selectivity. Here we describe the catalytic reductive cocyclooligomerization of an enone and three carbene equivalents to generate a cyclopentane, a process that constitutes a formal [2 + 1 + 1 + 1]-cycloaddition. The reaction is promoted by a (quinox)Ni catalyst and uses CH2Cl2/Zn as the C1 component. Mechanistic studies are consistent with a metallacycle-based pathway, featuring sequential migratory insertions of multiple carbene equivalents to yield cycloalkanes larger than cyclopropanes.

Evolution of Isolated Atoms and Clusters in Catalysis

Abstract: Structural transformation and evolution of active metal sites can occur in metal-catalyzed reactions in both homogeneous and heterogeneous systems. Such structural changes have an important impact on the catalytic behavior, including activity, selectivity, and stability. Aiming to establish a link between homogeneous and heterogeneous catalytic systems, this review begins with a discussion on dynamic structural transformations of metal catalysts in homogeneous reactions and the corresponding implications. We then discuss the evolution of isolated metal atoms and clusters in heterogeneous catalysts during catalyst activation and under reaction conditions. Finally, strategies for stabilizing subnanometric metal species on solid supports are presented for potential industrial applications.

Bimetallic cooperation across the periodic table

Abstract: Organometallic chemistry and its applications in homogeneous catalysis have been dominated by mononuclear transition-metal complexes. The catalytic performance and physico-chemical properties of these mononuclear complexes can be rationally tuned by ligand modification, which has also led to the discovery of new reactions. There is a growing body of evidence implicating the participation of two metals in catalytic processes originally believed to follow monometallic mechanisms. Moreover, the deliberate preparation of bimetallic structures has proven popular because these preorganized structures have many tunable features, such as metal–metal bond order and polarity. These structures can exhibit metal–metal complementarity and allow for multisite activation — reactivity unattainable with truly mononuclear species. This Perspective summarizes the features that are exclusive to bimetallic systems and their roles in substrate activation. Bimetallic complexes are fertile territory for investigating metal–metal cooperativity. This Perspective highlights how complexes with two proximal metals have tunable features of relevance to bond activation, catalysis and unprecedented reactivity.

Metal-metal interactions in correlated single-atom catalysts

Abstract: Single-atom catalysts (SACs) include a promising family of electrocatalysts with unique geometric structures. Beyond conventional ones with fully isolated metal sites, an emerging class of catalysts with the adjacent metal single atoms exhibiting intersite metal-metal interactions appear in recent years and can be denoted as correlated SACs (C-SACs). This type of catalysts provides more opportunities to achieve substantial structural modification and performance enhancement toward a wider range of electrocatalytic applications. On the basis of a clear identification of metal-metal interactions, this review critically examines the recent research progress in C-SACs. It shows that the control of metal-metal interactions enables regulation of atomic structure, local coordination, and electronic properties of metal single atoms, which facilitate the modulation of electrocatalytic behavior of C-SACs. Last, we outline directions for future work in the design and development of C-SACs, which is indispensable for creating high-performing new SAC architectures.