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.

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.

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

Reductive carbonylation of RuCl3·3H2O at CO-atmospheric pressure results in the [H3Ru4(CO)12]- (1) polyhydride carbonyl cluster. The one-pot synthesis involves the following steps: heating RuCl3·3H2O at 80 °C in 2-ethoxyethanol for 2 h, addition of three equivalents of KOH, heating at 135 °C for 2 h, addition of a fourth equivalent of KOH and heating at 135 °C for 1 h. The resulting K[1] salt is transformed into [NEt4][1] upon metathesis with [NEt4]Br in H2O. The IR, 1H and 13C{1H} NMR spectroscopic data are in agreement with those reported in the literature. [Ru8(CO)16(X)4(CO3)4]4- (X = Cl, Br, I; 2-X) is formed as a by-product during the synthesis of 1, and the two compounds are separated on the basis of their different solubilities in organic solvents. The nature of the halide of 2-X depends on the [NEt4]X salt used for metathesis. 2-Br is transformed into [Ru10(CO)20(Br)4(CO3)4]2- (3) upon reaction with an excess of HBF4·Et2O. 1 is readily deprotonated by strong bases affording the previously known [H2Ru4(CO)12]2- (4). The reaction of 1 with [Cu(MeCN)4][BF4] affords [H3Ru4(CO)12(CuMeCN)] (7), whereas [H2Ru4(CO)12(CuBr)2]2- (8) is obtained from the reaction of 4 with [Cu(MeCN)4][BF4]/[NEt4]Br. All the compounds have been spectroscopically characterized, their molecular structures determined by single crystal X-ray diffraction (SC-XRD) and investigated using DFT methods in selected cases in order to confirm the hydride positions and to study the relative stability of possible isomers.

Aerobic oxidation of primary benzylic amines to amides and nitriles catalyzed by ruthenium carbonyl clusters carrying N,O-bidentate ligands

Four trinuclear ruthenium carbonyl clusters, (6-BrPyCHRO)₂Ru₃(CO)₈ (R = 4-OCH₃C₆H₄, 1a; R = 4-BrC₆H₄, 1b) and (2-OC₆H₄-HC[double bond, length as m-dash]N-C₆H₄R)₂Ru₃(CO)₈ (R = 4-OCH₃, 2a; R = 4-Br, 2b), were synthesized from the reactions of Ru₃(CO)₁₂ with the corresponding N,O-bidentate ligands (two pyridyl alcohols and two Schiff bases) respectively in a ratio of 1 : 2. Three new complexes 1b, 2a and 2b have been fully characterized by elemental analysis, FT-IR, NMR and X-ray crystallography. The catalytic activity of these ruthenium complexes for the aerobic oxidation of primary benzylic amines to amides and nitriles in the presence of t-BuOK was investigated, of which the Schiff base complex 2a was found to exhibit the highest activity.

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.

Unexpected formation and conversion: role of substituents of 1,3-ynones in the reactivity and product distribution during their reactions with Ru3(CO)12

Electronic and steric effects of the substituents in 1,3-ynones play key roles in the product distribution and molecular structures.

Reaction of FcC[triple bond, length as m-dash]CC(O)R (Fc = ferrocenyl) with Ru3(CO)12 leading to unexpected nitro-group reduced ruthenoles and 1,2-CO-inserted triruthenium clusters

The reaction of Ru3(CO)12 with ferrocene-containing alkynyl ketones FcC[triple bond, length as m-dash]CC(O)R (Fc = ferrocenyl; R = Ph (1); 2-thienyl (2); 4-CH3O-Ph (3); 4-NH2-Ph (4); 4-NO2-Ph (5); ferrocenyl (6)) proceeds in toluene with the formation of triruthenium clusters (1a-6a), ruthenoles (1b-5b, 5c and 1d-5d) and unexpected 1,2-CO-inserted triruthenium clusters (1c-4c). 1a-6a were isolated from the reaction of Ru3(CO)12 with one equivalent of 1-6, respectively. Ruthenoles 1b-5b, 5c and 1d-5d were collected by adding 1-5 to the corresponding 1a-5a in a molar ratio of 1 : 1, respectively. Unexpectedly, the nitro group in one of the two phenyl rings in both 5c and 5d molecules was reduced to an amino group, while their ruthenole skeletons are retained. When 1-4 were added to the corresponding 1a-4a in a molar ratio of 1 : 1, respectively, the unusual triruthenium clusters (1c-4c) were isolated, involving 1,2-insertion of a terminal coordinated carbonyl between two C[triple bond, length as m-dash]C units of the ynone molecules. No reaction between 6a and 6 was observed. And the familiar cyclotrimerization products were not found. All new compounds were characterized by NMR, FT-IR, and MS-ESI and most of them were structurally confirmed by single crystal X-ray diffraction. The results suggested that the ferrocenyl groups in the 1,3-ynones exhibit strong electron and steric effects on the reaction process and product distribution during their reactions with Ru3(CO)12.