One-pot atmospheric pressure synthesis of [H3Ru4(CO)12]. Dalton Trans 2021;50:9610-9622. [PMID: 34160508 DOI: 10.1039/d1dt01517f]

Peraurated ruthenium hydride carbonyl clusters: aurophilicity, isolobal analogy, structural isomerism, and fluxionality

The stepwise addition of increasing amounts of Au(PPh3)Cl to [HRu4(CO)12]3- (1) results in the sequential formation of [HRu4(CO)12(AuPPh3)]2- (2), [HRu4(CO)12(AuPPh3)2]- (3), and HRu4(CO)12(AuPPh3)3 (4). Alternatively, 4 can be obtained upon addition of HBF4·Et2O (two mole equivalents) to 3. Further addition of acid to 3 (three mole equivalents) results in the formation of the tetra-aurated cluster Ru4(CO)12(AuPPh3)4 (5). Compounds 2-5 have been characterized by IR, 1H and 31P{1H} NMR spectroscopies. Moreover, the molecular structures of 3-5 have been determined by single crystal X-ray diffraction as [NEt4][3]·2CH2Cl2, 4-b·2CH2Cl2, 4-a, 5·0.5CH2Cl2·solv, and 5·solv crystalline solids. Two different isomers of 4, that is 4-a and 4-b, have been crystallographically characterized and their rapid interconversion in solution was studied by variable temperature 1H and 31P{1H} NMR spectroscopies. Weak aurophilic Au⋯Au contacts have been detected in the solid state structures of 3-5. Computational studies have been performed in order to elucidate bonding and isomerism, as well as to predict the possible structure of the elusive species 2.

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.

Atomically Precise Platinum Carbonyl Nanoclusters: Synthesis, Total Structure, and Electrochemical Investigation of [Pt27(CO)31]4- Displaying a Defective Structure

The molecular Pt nanocluster [Pt₂₇(CO)₃₁]^4– (1^4–) was obtained by thermal decomposition of [Pt₁₅(CO)₃₀]^2– in tetrahydrofuran under a H₂ atmosphere. The reaction of 1^4– with increasing amounts of HBF₄·Et₂O afforded the previously reported [Pt₂₆(CO)₃₂]^2– (3^2–) and [Pt₂₆(CO)₃₂]⁻ (3^–). The new nanocluster 1^4– was characterized by IR and UV–visible spectroscopy, single-crystal X-ray diffraction, direct-current superconducting quantum interference device magnetometry, cyclic voltammetry, IR spectroelectrochemistry (IR SEC), and electrochemical impedance spectroscopy. The cluster displays a cubic-close-packed Pt₂₇ framework generated by the overlapping of four ABCA layers, composed of 3, 7, 11, and 6 atoms, respectively, that encapsulates a fully interstitial Pt₄ tetrahedron. One Pt atom is missing within layer 3, and this defect (vacancy) generates local deformations within layers 2 and 3. These local deformations tend to repair the defect (missing atom) and increase the number of Pt–Pt bonding contacts, minimizing the total energy. The cluster 1^4– is perfectly diamagnetic and displays a rich electrochemical behavior. Indeed, six different oxidation states have been characterized by IR SEC, unraveling the series of 1^n– (n = 3–8) isostructural nanoclusters. Computational studies have been carried out to further support the interpretation of the experimental data.

The synthesis, molecular structure, magnetic properties, computational investigation, electrochemical and IR spectroelectrochemical behavior, and electrochemical impedance spectroscopy investigation of the new multivalent [Pt₂₇(CO)₃₁]⁴⁻ nanocluster are reported.

η6-Coordinated ruthenabenzenes from three-component assembly on a diruthenium μ-allenyl scaffold

The room temperature reactions with internal alkynes, RCCR, of the μ-allenyl acetonitrile complex [Ru₂Cp₂(CO)₂(NCMe){μ-η¹:η²-C¹HC²C³Me₂}]BF₄ (1-NCMe), freshly prepared from the tricarbonyl precursor [Ru₂Cp₂(CO)₃{μ-η¹:η²-C¹HC²C³Me₂}]BF₄, 1, proceeded with alkyne insertion into ruthenium-allenyl bond and allenyl-CO coupling, affording compounds [Ru₂Cp₂(CO)₂{μ-η²:η⁵-C(R)C(R)C¹HC²(C³MeCH₂)C(OH)}]BF₄ (R = Ph, 2; R = CO₂Me, 3; R = CO₂Et, 4) in 83-94% yields. Deprotonation of 2-4 by triethylamine gave [Ru₂Cp₂(CO)₂{μ-η²:η⁵-C(R)C(R)CHC(CMeCH₂)C(O)}] (R = Ph, 5; R = CO₂Me, 6; R = CO₂Et, 7) in 75-88% yields, and 2-4 could be recovered upon HBF₄·Et₂O addition to 5-7. All the products, 2-7, were fully characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structure of 2 was ascertained by single crystal X-ray diffraction and investigated by DFT calculations, revealing a six-membered ruthenacycle with Shannon aromaticity index in line with related compounds. The formation of ruthenium-coordinated ruthenabenzenes from a preexistent diruthenium scaffold is a versatile but underdeveloped approach exploiting cooperative effects typical of a dimetallic core.

Synthesis, molecular structure and fluxional behavior of the elusive [HRu4(CO)12]3- carbonyl anion

The elusive mono-hydride tri-anion [HRu₄(CO)₁₂]^3- (4) has been isolated and fully characterized for the first time. Cluster 4 can be obtained by the deprotonation of [H₃Ru₄(CO)₁₂]^- (2) with NaOH in DMSO. A more convenient synthesis is represented by the reaction of [HRu₃(CO)₁₁]^- (6) with an excess of NaOH in DMSO. The molecular structure of 4 has been determined by single-crystal X-ray diffraction (SC-XRD) as the [NEt₄]₃[4] salt. It displays a tetrahedral structure of pseudo C_3v symmetry with the unique hydride ligand capping a triangular Ru₃ face. Variable temperature (VT) ¹H and ¹³C{¹H} NMR experiments indicate that 4 is fluxional in solution and reveal an equilibrium between the C_3v isomer found in the solid state and a second isomer with C_s symmetry. Protonation-deprotonation reactions inter-converting H₄Ru₄(CO)₁₂ (1), [H₃Ru₄(CO)₁₂]^- (2), [H₂Ru₄(CO)₁₂]^2- (3), [HRu₄(CO)₁₂]^3- (4) and the purported [Ru₄(CO)₁₂]^4- (5) have been monitored by IR and ¹H NMR spectroscopy. Whilst attempting the optimization of the synthesis of 4, crystals of [NEt₄]₂[Ru₃(CO)₉(CO₃)] ([NEt₄]₂[7]) were obtained. Anion 7 contains an unprecedented CO₃^2- ion bonded to a zero-valent Ru₃(CO)₉ fragment. Finally, the reaction of 6 as the [N(PPh₃)₂]⁺ ([PPN]⁺) salt with NaOH in DMSO affords [Ru₃(CO)₉(NPPh₃)]^- (9) instead of 4. Computational DFT studies have been carried out in order to support experimental evidence and the location of the hydride ligands as well as to shed light on possible isomers.

Atomically Precise Ni-Pd Alloy Carbonyl Nanoclusters: Synthesis, Total Structure, Electrochemistry, Spectroelectrochemistry, and Electrochemical Impedance Spectroscopy

The molecular nanocluster [Ni36-xPd5+x(CO)46]6- (x = 0.41) (16-) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37-xPd7+x(CO)48]6- (x = 0.69) (26-) and [HNi37-xPd7+x(CO)48]5- (x = 0.53) (35-) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9-1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35- was extracted in acetone, whereas 26- was soluble in CH3CN. The total structures of 16-, 26-, and 35- were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni-Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16-, 26-, and 35- displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current-potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters.