The Hydration of Chloroacetonitriles Catalyzed by Mono- and Dinuclear RuII- and OsII-Arene Complexes

Arene-Osmium(II) Complexes in Homogeneous Catalysis

Although the application of arene-osmium(II) complexes in homogeneous catalysis has been much less studied than that of their ruthenium analogues, different works have shown that, in some instances, a comparable or even superior effectiveness can be achieved with this particular class of compounds. This review article focuses on the catalytic applications of arene-osmium(II) complexes. Among others, transfer hydrogenation, hydrogenation, oxidation, and nitrile hydration reactions, as well as different C-C bond forming processes, are comprehensively discussed.

Hydration of Aliphatic Nitriles Catalyzed by an Osmium Polyhydride: Evidence for an Alternative Mechanism

The hexahydride OsH₆(PⁱPr₃)₂ competently catalyzes the hydration of aliphatic nitriles to amides. The main metal species under the catalytic conditions are the trihydride osmium(IV) amidate derivatives OsH₃{κ²-N,O-[HNC(O)R]}(PⁱPr₃)₂, which have been isolated and fully characterized for R = ⁱPr and ^tBu. The rate of hydration is proportional to the concentrations of the catalyst precursor, nitrile, and water. When these experimental findings and density functional theory calculations are combined, the mechanism of catalysis has been established. Complexes OsH₃{κ²-N,O-[HNC(O)R]}(PⁱPr₃)₂ dissociate the carbonyl group of the chelate to afford κ¹-N-amidate derivatives, which coordinate the nitrile. The subsequent attack of an external water molecule to both the C(sp) atom of the nitrile and the N atom of the amidate affords the amide and regenerates the κ¹-N-amidate catalysts. The attack is concerted and takes place through a cyclic six-membered transition state, which involves C_nitrile···O–H···N_amidate interactions. Before the attack, the free carbonyl group of the κ¹-N-amidate ligand fixes the water molecule in the vicinity of the C(sp) atom of the nitrile.

The hexahydride complex OsH₆(PⁱPr₃)₂ competently catalyzes the hydration of aliphatic nitriles to amides. Isolation of the main metal species under the catalytic conditions, kinetics of hydration, and density functional theory calculations support an alternative mechanism to those previously reported.

DFT Investigation of the η6 ⇌ η6-Inter-ring Haptotropic Rearrangement of the Group 8 Metals Complexes [(graphene)MCp]+ (M = Fe, Ru, Os)

Metalcyclopentadienyl complexes (MCp)⁺ (M = Fe, Ru, Os) bound to the large polyaromatic hydrogenated hydrocarbon (PAH) C₉₆H₂₄ used as a model for pristine graphene have been studied using a density functional theory (DFT) generalized gradient approximation (PBE functional) to reveal their structural features and dynamic behavior. The inter-ring haptotropic rearrangements (IRHRs) for these complexes were shown to occur via two transition states and one intermediate. The energy barriers of the η⁶ ⇌ η⁶ IRHRs of the (MCp)⁺ unit were found to be 30, 27, and 29 kcal/mol for M = Fe, Ru, and Os, respectively. These values are significantly lower than the values found previously for smaller PAHs. Both polar and nonpolar solvents were found not to affect significantly the energy barrier heights. Investigated transition metal complexes could be used in general as catalysts in the design of novel derivatives or materials with promising properties. Metalcyclopentadienyl complexes (MCp)⁺ of PAHs show catalytic properties mainly due to their structural details as well as their important characteristic of inter-ring haptotropic rearrangement. IRHRs take place usually by intramolecular mechanisms. During IRHRs, the ML_n organometallic groups (OMGs) undergo shifting along the PAH plane and could coordinate additional reagents, which is important for catalysis. Large PAHs such as graphene, fullerenes, and nanotubes possess intrinsic anticancer activity, and numerous arene complexes of Ru and Os have been proven to have anticancer properties as well. We suppose that coordinating Ru or Os to very large PAHs could synergistically increase the anticancer activity of resulting complexes.

5-Hydr-oxy-2-methyl-4H-pyran-4-one

The title compound, C₆H₆O₃, is a member of the pyrone family. The mol­ecules are planar (r.m.s. deviation of the asymmetric unit is 0.0248 Å, whereas that of the dimer is 0.0360 Å) and they are dimerized due to inter­molecular O—H⋯O hydrogen bonds. The dimers are connected to each other through hydrogen bonds involving the CH₃ group and the hydr­oxy O atom. There are π–π inter­actions between the centroids of the pyrone rings at a distance of 3.8552 (13) Å. A C—H⋯π inter­action also exists between the carbonyl group and the centroid CgA of the pyrone ring, with O⋯CgA = 3.65 (1) Å and C⋯CgA = 4.363 (2) Å.