Metal carbonyl clusters of groups 8-10: synthesis and catalysis

In this review article, we discuss advances in the chemistry of metal carbonyl clusters (MCCs) spanning the last three decades, with an emphasis on the more recent reports and those involving groups 8-10 elements. Synthetic methods have advanced and been refined, leading to higher-nuclearity clusters and a wider array of structures and nuclearities. Our understanding of the electronic structure in MCCs has advanced to a point where molecular chemistry tools and other advanced tools can probe their properties at a level of detail that surpasses that possible with other nanomaterials and solid-state materials. MCCs therefore advance our understanding of structure-property-reactivity correlations in other higher-nuclearity materials. With respect to catalysis, this article focuses only on homogeneous applications, but it includes both thermally and electrochemically driven catalysis. Applications in thermally driven catalysis have found success where the reaction conditions stabilise the compounds toward loss of CO. In more recent years, MCCs, which exhibit delocalised bonding and possess many electron-withdrawing CO ligands, have emerged as very stable and effective for reductive electrocatalysis reactions since reduction often strengthens M-C(O) bonds and since room-temperature reaction conditions are sufficient for driving the electrocatalysis.

The First Naked Bismuth-Chalcogen Metal Carbonyl Clusters: Extraordinary Nucleophilicity of the Bi Atom and Semiconducting Characteristics

Mixed bismuth-chalcogen-iron clusters [{EFe₃(CO)₉}Bi]^- [E = Te (1a) or Se (1b)] were produced via the reduction of BiCl₃ with [EFe₃(CO)₉]^2- under mild conditions. X-ray analysis showed that both clusters 1a and 1b had a square-pyramidal geometry, where the naked Bi and chalcogen both adopted a distorted trigonal-pyramidal configuration with a stereoactive lone pair. Complexes 1a and 1b can be further functionalized by methylation and metalation, which permits the nucleophilicity of the 6s/5s and 6s/4s lone pairs to be compared. In the metalation, the 6s pair of the Bi atom in 1a and 1b had an extraordinary nucleophilicity toward the unsaturated Cr(CO)₅ fragment, even in the presence of the more chemically active 5s or 4s pair, whereas in the case of methylation, only the 4s pair of Se could be selectively alkylated. Upon oxidation of 1a and 1b with suitable oxidizing agents, NaBiO₃ or K₂SeO₃, Bi-E bonded tetrahedral complexes [{EFe₂(CO)₆}Bi]^- [E = Te (4a) or Se (4b)] were formed by the elimination of one Fe(CO)₃ vertex. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory (DFT) calculations showed that all of the Bi atoms in these complexes had oxidation states close to +1. Due to the electropositive character of the Bi atom, pronounced induced Bi···E inter- and intramolecular interactions were evident in 1a (1b), 4a (4b), and the metalated 3a (3b), where their linear-like ···Bi···E··· or zigzag-like ···Bi-E··· (E = Te or Se) chain or the Bi···E···E···Bi (E = Te or Se) dimeric chain can further expand into the two-dimensional network via nonclassical C-H···O(carbonyl) interactions, supported by noncovalent interaction index and DFT calculations. These positively charged Bi-induced Bi···E (E = Te or Se) and carbonyl-aided weak interactions can facilitate efficient electron transport within these ternary Bi-E-Fe or quaternary Bi-E-Fe-Cr cluster-based frameworks, resulting in semiconducting behavior with surprising ultranarrow energy gaps of 1.01-1.21 eV.

N-Heterocyclic Carbenes in Materials Chemistry

N-Heterocyclic carbenes (NHCs) have become one of the most widely studied class of ligands in molecular chemistry and have found applications in fields as varied as catalysis, the stabilization of reactive molecular fragments, and biochemistry. More recently, NHCs have found applications in materials chemistry and have allowed for the functionalization of surfaces, polymers, nanoparticles, and discrete, well-defined clusters. In this review, we provide an in-depth look at recent advances in the use of NHCs for the development of functional materials.

Metal carbonyl cluster-based coordination polymers: diverse syntheses, versatile network structures, and special properties

This highlight surveys recent progress in groups 6–10 metal carbonyl cluster-based coordination polymers, focusing on diverse synthetic strategies, versatile structures, structural transformations, and semiconducting as well as magnetic properties.

A comparative study on NHC-functionalized ternary Se/Te–Fe–Cu compounds: synthesis, catalysis, and the effect of chalcogens

A novel family of highly efficient Se–Fe–Cu–NHC catalysts was synthesized, which were suitable models for the study of the chalcogen effect.

Water-soluble superbulky (η6-p-cymene) ruthenium(ii) amine: an active catalyst in the oxidative homocoupling of arylboronic acids and the hydration of organonitriles

Water-soluble superbulky (η⁶-p-cymene) ruthenium(ii) amine complex mediated oxidative homocoupling of arylboronic acids and the hydration of organonitriles are reported.

Semiconducting Coordination Polymers Based on the Predesigned Ternary Te-Fe-Cu Carbonyl Cluster and Conjugation-Interrupted Dipyridyl Linkers

A series of semiconducting cluster-incorporated Cu-based coordination polymers, namely, 1D zigzag polymers [{TeFe₃ (CO)₉ Cu₂ }(L)]_n (L=1,2-bis(4-pyridyl)ethane (bpea), 1; L=1,2-bis(4-pyridyl)ethylene (bpee), 5), 2D honeycomb-like polymers [{TeFe₃ (CO)₉ Cu}Cu(L)_2.5 ]_n (L=bpea, 2; L=bpee, 6), and 2D wave-like cation-anion polymer [{Cu₂ (L)₄ }({TeFe₃ (CO)₉ Cu}₂ (L))]_n (L=1,3-bis(4-pyridyl)propane (bpp), 4), as well as the macrocycle [{TeFe₃ (CO)₉ Cu₂ }₂ (bpp)₂ ] (3) have been quantitatively synthesized via the liquid-assisted grinding from the pre-designed cluster [TeFe₃ (CO)₉ Cu₂ (MeCN)₂ ] with conjugated or conjugation-interrupted dipyridyl linkers. Notably, the most conjugation-interrupted bpp-bridged polymer 4 exhibited extraordinary semiconducting characteristics with an ultra-narrow bandgap of 1.43 eV and a DC conductivity of 1.5×10^-2 Ω^-1  cm^-1 , which violates our knowledge, mainly attributed to the through-space electron transport via non-classical C-H⋅⋅⋅O(carbonyl) hydrogen bonds and aromatic C-H⋅⋅⋅π interactions. The incorporated Te-Fe-CO anions can not only provide numerous possibilities for secondary interactions within these Cu-based polymers but also serve as a redox-active coordination ligand to promote their conductivities. The intriguing structure-property relationships were studied by X-ray and DFT analyses and further demonstrated by significant change in the oxidation state of Cu atoms by XPS and Cu K-edge XANES.

Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid-Base Lewis Adducts and Heteroleptic Clusters

The reactions of anionic platinum carbonyl Chini clusters [Pt_3n(CO)_6n]^2- [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = C₃N₂H₂(C₆H₃ⁱPr₂)₂] afford the neutral acid-base Lewis adducts [Pt₉(CO)₁₈(AgIPr)₂] (4) and [Pt₆(CO)₁₂(AgIPr)₂] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt₃(CO)₄(IPr)₂] (6). Alternatively, 6 can be obtained from the reactions of 1-3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt₄(CO)₄(IPr)₃] (7). The reaction of 6 with free IPr affords the closely related [Pt₃(CO)₃(IPr)₃] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1-3 with Ag(IMes)Cl [IMes = C₃N₂H₂(C₆H₂Me₃)₂] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt₃(CO)₃(IMes)₃(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt₅(CO)₇(IMes)₃] (10) complex. All of the new clusters 4-10 have been spectroscopically characterized and their molecular structures determined by X-ray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)]⁺ moieties. Conversely, 6-9 are based on a Pt₃ triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry.