The development of atomically precise nanoclusters (APNCs) protected by organometallic ligands, such as acetylides and hydrides, is an emerging area of nanoscience. In principle, these organometallic APNCs should not require harsh pretreatment for activation toward catalysis, such as calcination, which can lead to sintering. Herein, we report the synthesis of the mixed-valent organometallic copper APNC, [Cu(CCPh)(OAc))] (1), via reduction of Cu(OAc) with PhSiH in the presence of phenylacetylene. This cluster is a rare example of a two-electron copper superatom, and the first to feature a tetrahedral [Cu] core, which is a unique "kernel" for a Cu-only superatom. Complex 1 can be readily immobilized on dry, partially dehydroxylated silica, a process that cleanly results in release of 1 equiv of phenylacetylene per Cu cluster. Cu K-edge EXAFS confirms that the immobilized cluster 2 is structurally similar to 1. In addition, both 1 and 2 are effective catalysts for [3+2] cycloaddition reactions between alkynes and azides (i.e., "Click" reactions) at room temperature. Significantly, neither cluster requires any pretreatment for activation toward catalysis. Moreover, EXAFS analysis of 2 after catalysis demonstrates that the cluster undergoes no major structural or nuclearity changes during the reaction, consistent with our observation that supported cluster 2 is more stable than unsupported cluster 1 under "Click" reaction conditions.

Atomically Precise Nanoclusters (APNCs) are an emerging area of nanoscience. Their mono-dispersity and well-defined arrangement of capping ligands facilitates the interrogation of their fundamental physical properties, allowing for the development of structurefunction relationships, as well as their optimization for a variety of applications, including quantum computing, solid-state memory, catalysis, sensing, and imaging. However, AP-NCs present several unique synthetic and characterization challenges. For example, nanocluster syntheses are infamously low yielding and often generate complicated mixtures. This combination of factors makes nanocluster purification and characterization more difficult than that of typical inorganic or organometallic complexes. Yet, while this fact is undoubtedly true, the past lessons learned from the characterization of inorganic complexes are still useful today. In this Account, we discuss six case studies taken from the recent literature in an attempt to identify common challenges and pitfalls encountered in APNC synthesis and characterization. For example, we show that several reducing agents employed in APNC synthesis, including the commonly used reagent NaBH4, do not always behave as anticipated. Indeed, we highlight one case where NaBH4 reduces the ligand and not the metal center, and other cases where NaBH4 acts as a Brønstead base instead of a reducing agent. In addition, we have identified several instances where the use of phase transfer agents, which were added to mediate APNC formation, played no role in the nanocluster synthesis, and likely made the isolation of pure material more difficult. We have also identified several cases of cluster misidentification driven by spurious or ambiguous characterization data, most commonly collected by mass spectrometry. To address these challenges, we propose that the nanocluster community adopt a standard protocol of characterization, similar to those used by the organometallic and coordination chemistry communities. This protocol requires that many complementary techniques be used in concert to confirm formulation, structure, and analytical purity of APNC samples. Two techniques that are under-utilized in this regard are combustion analysis and NMR spectroscopy. NMR spectroscopy, in particular, can provide information on purity and formulation that are difficult to collect with any other technique. X-ray absorption spectroscopy is another powerful method of nanocluster characterization, especially in cases where single crystals for X-ray diffraction are not forthcoming. Chromatographic techniques can also be extremely valuable for assessing purity, but are rarely used during APNC characterization. Our goal with this Account is to begin a discussion with respect to the best protocols for nanocluster synthesis and characterization. We believe that embracing a standard characterization protocol would make APNC synthesis more reliable, thereby accelerating their integration into a variety of technologies.

Self-ordering of covalent electron donor–acceptor building blocks in thin films upon solvent vapor annealing results in a 104 increase in photo-generated charge carrier lifetime.

The tetrametallic Fe ketimide cluster, [Fe4(NCPh2)6], exhibits a thermally persistent S = 7 ground-state along with single molecule magnet behavior.

ABSTRACT:The group 11 hydride clusters [Ag 6 H 4 (dppm) 4 (OAc) 2 ](1) and(2) (dppm = 1,1-bis(diphenylphosphino)methane) were synthesized in moderate yields from the reaction of M(OAc) (M = Ag, Cu) with Ph 2 SiH 2 , in the presence of dppm. Complex 1 is the first structurally characterized homometallic polyhydrido silver cluster to be isolated. Both 1 and 2 catalyze the hydrosilylation of (,-unsaturated) ketones. Notably, this represents the first example of hydrosilylation with an authentic silver hydride complex.

The implementation of a sustainable energy economy based on renewable but intermittent energy sources necessitates the efficient electrogeneration of chemical fuels and the efficient utilization of chemical fuels in a fuel cell. Alcohols, in particular methanol, are attractive targets for the fuel in such a scheme, but the selective, complete oxidation of methanol to carbon dioxide is a challenging multielectron, multiproton process that still requires the development of efficient and selective catalysts. Here, we discuss three case studies that represent the current state of the research field for molecular electrocatalysts capable of alcohol oxidation. These case studies illuminate the key advances critical to effective catalysis and also help to clarify the main challenges with methanol as a substrate. The properties and reactivity of these systems provide a basis for catalyst design principles and future studies in this field, toward the design of electrochemical systems capable of methanol oxidation to carbon dioxide.

We report a critical re-evaluation of the synthesis and characterization of Cu(MPP). This product was reportedly formed by the reaction of Cu(NO) with 2-mercapto-5-n-propylpyrimidine (HMPP) and NaBH, in ethanol, in the presence of [N(CH)][Br]. In our hands, we found no experimental evidence to support the existence of Cu(MPP) in the reaction mixture. Instead, we demonstrate that the material isolated from this reaction is a complex mixture containing [N(CH)], Br, NO, and 2-mercapto-5-n-propyl-1,6-dihydropyrimidine (HMPP*), along with the Cu(I) coordination polymer, [Cu(MPP)]. To support our conclusions, we have independently synthesized HMPP* and [Cu(MPP)], as well as the related Cu(I) coordination complexes, [Cu(HMPP*)] and [Cu(MPP*)]. All new materials were characterized by NMR spectroscopy and mass spectrometry, while HMPP*, [Cu(HMPP*)] (n = 4), and [Cu(MPP)] (n = 6) were also characterized by X-ray crystallography.

Herein, we report the synthesis and characterization of the mixed-valent, ketimide-stabilized Pd7 nanosheet, [Pd7(N=C t Bu2)6] (1), via reaction of PdCl2(PhCN)2 and Li(N=C t Bu2). Also formed in the reaction is t BuCN, isobutylene, and isobutane. The presence of these products suggests that Li(N=C t Bu2) acts as a reducing agent in the transformation, converting the Pd(II) starting material into the mixed-valent Pd(I)/Pd (0) product. Complex 1 features a hexagonal planar [Pd7] 6+ core stabilized by six ketimide ligands, which surround the [Pd7] 6+ center in an alternating up/down fashion. In situ NMR spectroscopic studies, as well as DFT calculations, suggest that 1 is formed via the intermediacy of bimetallic Pd(II) ketimide complex, [( t Bu2C=N)Pd(µ-N,C-(2). DFT calculations also reveal that 1 is a rare example of an all-metal aromatic nanocluster with hexagonal symmetry, sustaining a net diatropic ring-current of 10.6 nA/T, which is similar to that of benzene (11.8 nA/T) or other well-established transition metal aromatic systems. Finally, we have found that 1 reacts with Ph3P, cleanly forming the trisligated 16-electron Pd(0) phosphine complex, Pd(PPh3)3 (3), suggesting that 1 could be a useful pre-catalyst for a variety of cross-coupling reactions.