A Comparative Experimental and Computational Study of Heterometallic Fe-M (M = Cu, Ag, Au) Carbonyl Clusters Containing N-Heterocyclic Carbene Ligands

2-D Molecular Alloy Ru-M (M = Cu, Ag, and Au) Carbonyl Clusters: Synthesis, Molecular Structure, Catalysis, and Computational Studies

The reactions of [HRu₃(CO)₁₁]⁻ (1) with M(I) (M = Cu, Ag, and Au) compounds such as [Cu(CH₃CN)₄][BF₄], AgNO₃, and Au(Et₂S)Cl afford the 2-D molecular alloy clusters [CuRu₆(CO)₂₂]⁻ (2), [AgRu₆(CO)₂₂]⁻ (3), and [AuRu₅(CO)₁₉]⁻ (4), respectively. The reactions of 2–4 with PPh₃ result in mixtures of products, among which [Cu₂Ru₈(CO)₂₆]^2– (5), Ru₄(CO)₁₂(CuPPh₃)₄ (6), Ru₄(CO)₁₂(AgPPh₃)₄ (7), Ru(CO)₃(PPh₃)₂ (8), and HRu₃(OH)(CO)₇(PPh₃)₃ (9) have been isolated and characterized. The molecular structures of 2–6 and 9 have been determined by single-crystal X-ray diffraction. The metal–metal bonding within 2–5 has been computationally investigated by density functional theory methods. In addition, the [NEt₄]⁺ salts of 2–4 have been tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone using ⁱPrOH as a solvent and a hydrogen source.

Heterometallic Ru−M (M = Cu, Ag, and Au) carbonyl clusters possessing a 2-D metal core have been investigated by structural and computational methods and tested as catalyst precursors for transfer hydrogenation.

Trinuclear ReFePt clusters with a μ3-phenylvinylidene ligand: synthetic approaches, rearrangement of vinylidene, and redox-induced transformations

A series of trinuclear μ₃-vinylidene ReFePt clusters were synthesized by the application of two approaches: (i) reactions of the binuclear RePt μ-vinylidene complexes with Fe₂(CO)₉; (ii) ligand substitution or exchange reactions at the Pt atom in the synthesized ReFePt clusters. The molecular structures of CpReFePt(μ₃-CCHPh)(CO)₅[P(OEt)₃]L [L = CO; P(OEt)₃] were determined by an X-ray diffraction study. The obtained compounds were studied by IR and ¹H, ¹³C and ³¹P NMR spectroscopy. The spectroscopic study revealed that the clusters CpReFePt(μ₃-CCHPh)(CO)₅[P(OEt)₃]L [L = CO; P(OEt)₃] and CpReFePt(μ₃-CCHPh)(CO)₆[P(OPrⁱ)₃] undergo isomerization upon dissolution, resulting in three isomers with different positions of the μ₃-vinylidene ligand over the ReFePt core. The redox properties of the clusters were studied by electrochemical methods. The relatively stable cation-radicals obtained by chemical oxidation of CpReFePt(μ₃-CCHPh)(CO)₆[P(OPrⁱ)₃] and CpReFePt(μ₃-CCHPh)(CO)₅[P(OEt)₃]₂ with ferrocenium tetrafluoroborate were characterized by EPR spectroscopy.

A Zwitterionic Heterobimetallic Gold-Iron Complex Supported by Bis(N-Heterocyclic Imine)Silyliumylidene

The facile synthesis of the first bis-N-heterocyclic imine-stabilized chlorosilyliumylidene 1 is reported. Remarkably, consecutive reaction of 1 with PPh3 AuCl and K2 Fe(CO)4 gives rise to the unique heterobimetallic complex 1,2-(Mes NHI)2 -C2 H4 -ClSiAuFe(CO)4 (4). The overall neutral complex 4 bears an unusual linear Si-Au-Fe structure and a rare anagostic interaction between the d10 -configured gold atom and a CH bond of the mesityl ligand. According to the computational analysis and 57 Fe Mössbauer spectroscopy, the formal Fe-oxidation state remains at -II. Thus, the electronic structure of 4 is best described as an overall neutral-yet zwitterionic-heterobimetallic "Si(II)+ -Au(I)+ -Fe(-II)2- "-silyliumylidene complex, derived from double anion exchange. The computational analysis indicates strong hyperconjugative back donation from the gold(I) atom to the silyliumylidene ligand.

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.

Polymerization Isomerism in Co-M (M = Cu, Ag, Au) Carbonyl Clusters: Synthesis, Structures and Computational Investigation

The reaction of [Co(CO)4]- (1) with M(I) compounds (M = Cu, Ag, Au) was reinvestigated unraveling an unprecedented case of polymerization isomerism. Thus, as previously reported, the trinuclear clusters [M{Co(CO)4}2]- (M = Cu, 2; Ag, 3; Au, 4) were obtained by reacting 1 with M(I) in a 2:1 molar ratio. Their molecular structures were corroborated by single-crystal X-ray diffraction (SC-XRD) on isomorphous [NEt4][M{Co(CO)4}2] salts. [NEt4](3)represented the first structural characterization of 3. More interestingly, changing the crystallization conditions of solutions of 3, the hexanuclear cluster [Ag2{Co(CO)4}4]2- (5) was obtained in the solid state instead of 3. Its molecular structure was determined by SC-XRD as Na2(5)·C4H6O2, [PPN]2(5)·C5H12 (PPN = N(PPh3)2]+), [NBu4]2(5) and [NMe4]2(5) salts. 5 may be viewed as a dimer of 3 and, thus, it represents a rare case of polymerization isomerism (that is, two compounds having the same elemental composition but different molecular weights) in cluster chemistry. The phenomenon was further studied in solution by IR and ESI-MS measurements and theoretically investigated by computational methods. Both experimental evidence and density functional theory (DFT) calculations clearly pointed out that the dimerization process occurs in the solid state only in the case of Ag, whereas Cu and Au related species exist only as monomers.

Synthesis, Structural Characterization, and DFT Investigations of [MxM'5-xFe4(CO)16]3- (M, M' = Cu, Ag, Au; M ≠ M') 2-D Molecular Alloy Clusters

Miscellaneous 2-D molecular alloy clusters of the type [M_xM'_5-xFe₄(CO)₁₆]^3- (M, M' = Cu, Ag, Au; M ≠ M') have been prepared through the reactions of [Cu₃Fe₃(CO)₁₂]^3-, [Ag₄Fe₄(CO)₁₆]^4- or [M₅Fe₄(CO)₁₆]^3- (M = Cu, Ag) with M'(I) salts (M' = Cu, Ag, Au). Their formation involves a combination of oxidation, condensation, and substitution reactions. The total structures of several [M_xM'_5-xFe₄(CO)₁₆]^3- clusters with different compositions have been determined by means of single crystal X-ray diffraction (SC-XRD) and their nature in solution elucidated by electron spray ionization mass spectrometry (ESI-MS) and IR and UV-visible spectroscopy. Substitutional and compositional disorder is present in the solid state structures, and ESI-MS analyses point out that mixtures of isostructural clusters differing by a few M/M' coinage metals are present. SC-XRD studies indicate some site preferences of the coinage metals within the metal cores of these clusters, with Au preferentially in corner sites and Cu in the central site. DFT studies give theoretical support to the experimental structural evidence. The site preference is mainly dictated by the strength of the Fe-M bonds that decreases in the order Fe-Au > Fe-Ag > Fe-Cu, and the preferred structure is the one that maximizes the number of stronger Fe-M interactions. Overall, the molecular nature of these clusters allows their structures to be fully revealed with atomic precision, resulting in the elucidation of the bonding parameters that determine the distribution of the different metals within their metal cores.