Benchmarking of DFTmethods using experimental free energies and volumes of activation for the cycloaddition of alkynes to cuboidalMo(3)S(4)clusters

Here, the kinetics of the concerted [3 + 2] cycloaddition reaction between the [Mo3(μ3‐S)(μ‐S)3Cl3(dmen)3]+ (dmen = N,N′‐dimethyl‐ethylenediamine) ([1]+) cluster and various alkynes to form dithiolene derivatives is thoroughly studied, with measurements at different temperatures and pressures allowing the determination of the free energies and volumes of activation. These parameters, together with the available single‐crystal X‐ray diffraction structures, are used to test a number of commonly used density functional theory (DFT) methods from Jacob's ladder, as well as the effects associated with the size of the basis sets, the way in which solvent effects are taken into account, or the inclusion of dispersion effects. Overall, a protocol that leads to average deviations between experimental and computed ΔV‡ and ΔG‡ values similar to the uncertainty of the experimental measurements is obtained

Bifunctional W/NH Cuboidal Aminophosphino W3S4 Cluster Hydrides: The Puzzling Behaviour behind the Hydridic-Protonic Interplay

The novel [W3S4H3(edpp)3]+ (edpp=(2-aminoethyl)diphenylphosphine) (1+) cluster hydride with an acidic −NH2 functionality has been synthetized and studied. Its crystal structure shows the characteristic incomplete W3S4 cubane core with the outer positions occupied by the P and N atoms of the edpp ligands. Although no signal due to the hydride ligands is observed in the 1H NMR spectrum, hydride assignment is supported by 1H-15N HSQC techniques, the changes in the 31P{1H} NMR chemical shift, and FT-IR spectra in the W−H region of the deuterated [W3S4D2H(edpp)3]+ (1+-d2) samples. Moreover, all NMR evidences suggest that one of the hydrogen atoms of the NH2 group in 1+ is rapidly exchanging with the hydride. The reaction of 1+ with acids (HCl, HBr and DCl) features complex polyphasic kinetics with zero-order dependence with respect to the acid concentration, being also independent of the solvent nature. This behavior differs from that of their diphosphino analogues, suggesting a different mechanism

Site specific ligand substitution in cubane-type Mo3FeS44+ clusters: Kinetics and mechanism of reaction and isolation of mixed ligand Cl/SPh complexes

The synthesis, crystal structure and solution characterization of the cubane-type [Mo3(FeCl)S4(dmpe)3Cl3] (1) (dmpe = 1,2-bis(dimethylphophane-ethane)) cluster are reported and the ligand substitution processes of chloride by thiophenolate investigated. The kinetics and the intimate mechanism of these substitutions reveal that compound 1 undergoes a number of Fe and Mo site specific ligand substitution reactions in acetonitrile solutions. In particular, PhS− coordination at the tetrahedral Fe site proceeds in a single resolved kinetic step whereas such substitutions at the Mo sites proceed more slowly. The effect of the presence of acids in the reaction media is also investigated and reveals that an acid excess hinders substitution reactions both at the Fe and Mo sites; however, an acid-promoted solvolysis of the Fe–Cl bonds is observed. Electrospray ionization (ESI) and tandem (ESI-MS/MS) mass spectrometry allow the identification of all the reaction intermediates proposed on the basis of stopped-flow measurements. The distinctive site specific reactivity made it possible to isolate two new clusters of the Mo3FeS44+ family featuring mixed chlorine/thiophenolate ligands, namely Mo3S4(FeSPh)(dmpe)3Cl3 (2) and [Mo3S4(FeSPh)(dmpe)3(SPh)3] (3). A detailed computational study has also been carried out to understand the details of the mechanism of substitution at the M–Cl (M = Mo and Fe) bonds as well as the solvolysis at the Fe–Cl sites, with particular emphasis on the role of acids on the substitution process. The results of the calculations are in agreement with the experimental observations, thus justifying the non-existence of an accelerating effect of acids on the thiophenolate substitution reaction, which differs from previous proposals for the Fe4S4 and MoFe3S4 clusters and some related compounds

Cuboidal Mo3S4 Clusters as a Platform for Exploring Catalysis: A Three-Center Sulfur Mechanism for Alkyne Semihydrogenation

We report a trinuclear Mo3S4 diamino cluster that promotes the semihydrogenation of alkynes. Based on experimental and computational results, we propose an unprecedented mechanism in which only the three bridging sulfurs of the cluster act as the active site for this transformation. In the first step, two of these mu-S ligands react with the alkyne to form a dithiolene adduct; this process is formally analogous to the olefin adsorption on MoS2 surfaces. Then, H-2 activation occurs in an unprecedented way that involves the third mu-S center, in cooperation with one of the dithiolene carbon atoms. Notably, this step does not imply any direct interaction between H-2 and the metal centers, and directly results in the formation of an intermediate featuring one (mu-S)-H and one C-H bond. Finally, such half-hydrogenated intermediate can either undergo a reductive elimination step that results in the Z-alkene product, or evolve into an isomerized analogue whose subsequent reductive elimination generates the E-alkene product. Interestingly, the substituents on the alkynes have a major impact on the relative barriers of these two processes, with the semihydrogenation of dimethyl acetylenedicarboxylate (dmad) resulting in the stereoselective formation of dimethyl maleate, whereas that of diphenylacetylene (dpa) leads to mixtures of Z- and E-stilbene. The results herein could have significant implications on the understanding of the catalytic properties of MoS2-based materials