Multi-active Site Dynamics on a Molecular Cr/Co/Se Cluster Catalyst

Exploring Charge Redistribution at the Cu/Co6Se8 Interface

This study investigates the electronic interactions and charge redistribution at the dopant-support interface using a Cu/Co6Se8 cluster construct. Specifically, the redox cluster series [Cu3Co6Se8L6]n ([1-Cu3]n; n = 0, -1, -2, -3; L = Ph2PNTol-, Ph = phenyl, Tol = p-tolyl) spanning four distinct oxidation states is synthesized and characterized using a multitude of techniques, including multinuclear NMR, UV-vis, XANES, and X-ray crystallography. Structural investigations indicate that the clusters are isostructural and chiral, adopting a pseudo-D3 symmetry. Paramagnetic 31P NMR spectroscopy and solution-phase magnetic measurements together with DFT calculations are employed to interrogate the electronic structure and spin-state changes across the [1-Cu3]3- to 1-Cu3 redox series, revealing that the copper edge sites retain a +1 oxidation state while the Co/Se core becomes increasingly oxidized, yielding a highly zwitterionic cluster.

Polarized metal-metal multiple bonding and reactivity of phosphinoamide-bridged heterobimetallic group IV/cobalt compounds

Heterobimetallic complexes are studied for their ability to mimic biological systems as well as active sites in heterogeneous catalysts. While specific interest in early/late heterobimetallic systems has fluctuated, they serve as important models to fundamentally understand metal-metal bonding. Specifically, the polarized metal-metal multiple bonds formed in highly reduced early/late heterobimetallic complexes exemplify how each metal modulates the electronic environment and reactivity of the complex as a whole. In this Perspective, we chronicle the development of phosphinoamide-supported group IV/cobalt heterobimetallic complexes. This combination of metals allows access to a low valent Co-I center, which performs a rich variety of bond activation reactions when coupled with the pendent Lewis acidic metal center. Conversely, the low valent late transition metal is also observed to act as an electron reservoir, allowing for redox processes to occur at the d0 group IV metal site. Most of the bond activation reactions carried out by phosphinoamide-bridged M/Co-I (M = Ti, Zr, Hf) complexes are facilitated by cleavage of metal-metal multiple bonds, which serve as readily accessible electron reservoirs. Comparative studies in which both the number of buttressing ligands as well as the identity of the early metal were varied to give a library of heterobimetallic complexes are summarized, providing a thorough understanding of the reactivity of M/Co-I heterobimetallic systems.

Caught in the Act of Substitution: Interadsorbate Effects on an Atomically Precise Fe/Co/Se Nanocluster

Directing groups guide substitution patterns in organic synthetic schemes, but little is known about pathways to control reactivity patterns, such as regioselectivity, in complex inorganic systems such as bioinorganic cofactors or extended surfaces. Interadsorbate effects are known to encode surface reactivity patterns in inorganic materials, modulating the location and binding strength of ligands. However, owing to limited experimental resolution into complex inorganic structures, there is little opportunity to resolve these effects on the atomic scale. Here, we utilize an atomically precise Fe/Co/Se nanocluster platform, [Fe3(L)2Co6Se8L'6]+ ([1(L)2]+; L = CN t Bu, THF; L' = Ph2PN(-)Tol), in which allosteric interadsorbate effects give rise to pronounced site-differentiation. Using a combination of spectroscopic techniques and single-crystal X-ray diffractometry, we discover that coordination of THF at the ligand-free Fe site in [1(CN t Bu)2]+ sets off a domino effect wherein allosteric through-cluster interactions promote the regioselective dissociation of CN t Bu at a neighboring Fe site. Computational analysis reveals that this active site correlation is a result of delocalized Fe···Se···Co···Se covalent interactions that intertwine edge sites on the same cluster face. This study provides an unprecedented atom-scale glimpse into how interfacial metal-support interactions mediate a collective and regiospecific path for substrate exchange across multiple active sites.

Accessing Ta/Cu Architectures via Metal-Metal Salt Metatheses: Heterobimetallic C-H Bond Activation Affords μ-Hydrides

We employ a metal-metal salt metathesis strategy to access low-valent tantalum-copper heterometallic architectures (Ta-μ2 -H2 -Cu and Ta-μ3 -H2 -Cu3 ) that emulate structural elements proposed for surface alloyed nanomaterials. Whereas cluster assembly with carbonylmetalates is well precedented, the use of the corresponding polyarene transition metal anions is underexplored, despite recognition of these highly reactive fragments as storable sources of atomic Mn- . Our application of this strategy provides structurally unique early-late bimetallic species. These complexes incorporate bridging hydride ligands during their syntheses, the origin of which is elucidated via detailed isotopic labelling studies. Modification of ancillary ligand sterics and electronics alters the mechanism of bimetallic assembly; a trinuclear complex resulting from dinuclear C-H activation is demonstrated as an intermediate en route to formation of the bimetallic. Further validating the promise of this rational, bottom-up approach, a unique tetranuclear species was synthesized, featuring a Ta centre bearing three Ta-Cu interactions.

Clustering-Evolved Frontier Orbital for Low-Temperature CO2 Dissociation

In this study, single Ni2 clusters (two Ni atoms bridged by a lattice oxygen) are successfully synthesized on monolayered CuO. They exhibit a remarkable activity toward low-temperature CO2 thermal dissociation, in contrast to cationic Ni atoms that nondissociatively adsorb CO2 and metallic Ni ones that are chemically inert for CO2 adsorption. Density functional theory calculations reveal that the Ni2 clusters can significantly alter the spatial symmetry of their unoccupied frontier orbitals to match the occupied counterpart of the CO2 molecule and enable its low-temperature dissociation. This study may help advance single-cluster catalysis and exploit the unexcavated mechanism for low-temperature CO2 activation.

A general method for metallocluster site-differentiation

The deployment of metalloclusters in applications such as catalysis and materials synthesis requires robust methods for site-differentiation: the conversion of clusters with symmetric ligand spheres to those with unsymmetrical ligand spheres. However, imparting precise patterns of site-differentiation is challenging because, compared with mononuclear complexes, the ligands bound to clusters exert limited spatial and electronic influence on one another. Here, we report a method that employs sterically encumbering ligands to bind to only a subset of a cluster's coordination sites. Specifically, we show that homoleptic, phosphine-ligated Fe-S clusters undergo ligand substitution with N-heterocyclic carbenes (NHCs) to give heteroleptic clusters in which the resultant clusters' site-differentiation patterns are encoded by the steric profile of the incoming NHC. This method affords access to every site-differentiation pattern for cuboidal [Fe4S4] clusters and can be extended to other cluster types, particularly in the stereoselective synthesis of site-differentiated Chevrel-type [Fe6S8] clusters.

Size Effects of Atomically Precise Gold Nanoclusters in Catalysis

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.

Metal-Support Interactions in Molecular Single-Site Cluster Catalysts

This study provides atomistic insights into the interface between a single-site catalyst and a transition metal chalcogenide support and reveals that peak catalytic activity occurs when edge/support redox cooperativity is maximized. A molecular platform MCo₆Se₈(PEt₃)₄(L)₂ (1-M, M = Cr, Mn, Fe, Co, Cu, and Zn) was designed in which the active site (M)/support (Co₆Se₈) interactions are interrogated by systematically probing the electronic and structural changes that occur as the identity of the metal varies. All 3d transition metal 1-M clusters display remarkable catalytic activity for coupling tosyl azide and tert-butyl isocyanide, with Mn and Co derivatives showing the fastest turnover in the series. Structural, electronic, and magnetic characterization of the clusters was performed using single crystal X-ray diffraction, ¹H and ³¹P nuclear magnetic resonance spectroscopy, electronic absorption spectroscopy, cyclic voltammetry, and computational methods. Distinct metal/support redox regimes can be accessed in 1-M based on the energy of the edge metal's frontier orbitals with respect to those of the cluster support. As the degree of electronic interaction between the edge and the support increases, a cooperative regime is reached wherein the support can deliver electrons to the catalytic site, increasing the reactivity of key metal-nitrenoid intermediates.