Convenient route to an electron-deficient Tetraosmium(I) Carboxylate chain

Chor, Bo Yang; Ganguly, Rakesh; Leong, Weng Kee

doi:10.1016/j.jorganchem.2015.12.043

Cited by 4 publications

(2 citation statements)

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“…values for both distances and angles. Os bond length (2.7198 Å ) of any Os 2 sawhorse complex to date (Chor et al, 2016). (Rigaku, 2008) for (3), 7@CH2Cl2; CrysAlis PRO (Rigaku OD, 2015) for (5), (6).…”

Section: Figure 10mentioning

confidence: 99%

Asymmetric diosmium sawhorse complexes

et al. 2019

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Three asymmetric diosmium(I) carbonyl sawhorse complexes have been prepared by microwave heating. One of these complexes is of the type Os2(μ-O2CR)(μ-O2CR′)(CO)4 L 2, with two different bridging carboxylate ligands, while the other two complexes are of the type Os2(μ-O2CR)2(CO)5 L, with one axial CO ligand and one axial phosphane ligand. The mixed carboxylate complex Os2(μ-acetate)(μ-propionate)(CO)4[P(p-tolyl)3]2, (1), was prepared by heating Os3(CO)12 with a mixture of acetic and propionic acids, isolating Os2(μ-acetate)(μ-propionate)(CO)6, and then replacing two CO ligands with two phosphane ligands. This is the first example of an Os2 sawhorse complex with two different carboxylate bridges. The syntheses of Os2(μ-acetate)2(CO)5[P(p-tolyl)3], (3), and Os2(μ-propionate)2(CO)5[P(p-tolyl)3], (6), involved the reaction of Os3(CO)12 with the appropriate carboxylic acid to initially produce Os2(μ-carboxylate)2(CO)6, followed by treatment with refluxing tetrahydrofuran (THF) to form Os2(μ-carboxylate)2(CO)5(THF), and finally addition of tri-p-tolylphosphane to replace the THF ligand with the P(p-tolyl)3 ligand. Neutral complexes of the type Os2(μ-O2CR)2(CO)5 L had not previously been subjected to X-ray crystallographic analysis. The more symmetrical disubstituted complexes, i.e. Os2(μ-formate)2(CO)4[P(p-tolyl)3]2, (8), Os2(μ-acetate)2(CO)4[P(p-tolyl)3]2, (4), and Os2(μ-propionate)2(CO)4[P(p-tolyl)3]2, (7), as well as the previously reported symmetrical unsubstituted complexes Os2(μ-acetate)2(CO)6, (2), and Os2(μ-propionate)2(CO)6, (5), were also prepared in order to examine the influence of axial ligand substitution on the Os—Os bond distance in these sawhorse molecules. Eight crystal structures have been determined and studied, namely μ-acetato-1κO:2κO′-μ-propanoato-1κO:2κO′-bis[tris(4-methylphenyl)phosphane]-1κP,2κP′-bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os2(C2H3O2)(C3H5O2)(C21H21P)2(CO)4]·CH2Cl2, (1), bis(μ-acetato-1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os2(C2H3O2)2(CO)6], (2) (redetermined structure), bis(μ-acetato-1κO:2κO′)pentacarbonyl-1κ2 C,2κ3 C-[tris(4-methylphenyl)phosphane-1κP]diosmium(Os—Os), [Os2(C2H3O2)2(C21H21P)(CO)5], (3), bis(μ-acetato-1κO:2κO′)bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os—Os) p-xylene sesquisolvate, [Os2(C2H3O2)2(C21H21P)2(CO)4]·1.5C8H10, (4), bis(μ-propanoato-1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os2(C3H5O2)2(CO)6], (5), pentacarbonyl-1κ2 C,2κ3 C-bis(μ-propanoato-1κO:2κO′)[tris(4-methylphenyl)phosphane-1κP]diosmium(Os—Os), [Os2(C3H5O2)2(C21H21P)(CO)5], (6), bis(μ-propanoato-1κO:2κO′)bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os2(C3H5O2)2(C21H21P)2(CO)4]·CH2Cl2, (7), and bis(μ-formato-1κO:2κO′)bis[tris(4-methylphenyl)phosphane]-1κP,2κP-bis(dicarbonylosmium)(Os—Os), [Os2(CHO2)2(C21H21P)2(CO)4], (8).

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confidence: 99%

Asymmetric diosmium sawhorse complexes

et al. 2019

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“…Less studied are the analogous diosmium(I) carbonyl sawhorse complexes, Os 2 (μ-O 2 CR) 2 (CO) 6 , which were first reported alongside the diruthenium(I) complexes. 8 More recent investigations have shown that diosmium sawhorse complexes may be used for the chemical vapor deposition of osmium thin films, 9 the production of electron-deficient tetranuclear complexes, 10 and the formation of supramolecular assemblies. 11 These Os 2 2+ complexes have more tightly bound axial CO ligands, which are not as easily lost at room temperature, but can be replaced with other ligands (including solvent molecules) upon heating in common organic solvents such as acetonitrile.…”

Section: Introductionmentioning

confidence: 99%

Kinetic and Computational Analysis of CO Substitution in a Dinuclear Osmium Carbonyl Complex: Intersection between Dissociative and Dissociative-Interchange Mechanisms

et al. 2021

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The mechanism for the CO substitution reaction involving the diosmium carbonyl sawhorse complex Os 2 (μ-O 2 CH) 2 (CO) 6 , which contains an Os−Os single bond, two axial CO ligands, and four equatorial CO ligands, was investigated experimentally and theoretically. Kinetic measurements show 13 CO axial substitution proceeding by a dissociative reaction that is first-order in the complex and zero-order in 13 CO but with an unexpectedly negative entropy of activation. The corresponding electronic structure calculations yield an enthalpy of activation for axial CO dissociation that is much larger than that determined by the kinetic experiments, but in agreement with the complex's stability with respect to CO loss. Additional calculations yield a dissociative interchange transition state whose free energy, enthalpy, and entropy of activation are in good agreement with those obtained from the kinetic measurements for the apparently dissociative substitution. These results point to an exchange reaction mechanism that is surprisingly close to the poorly understood transition from a dissociative mechanism with a CO-loss intermediate to a dissociative interchange mechanism with a transition state involving both the entering and the leaving COs. The key to explain these findings is provided by the vibrational analysis, which shows very low energy wagging motions for the axial COs. Thus, the incoming CO only displaces the outgoing CO when the complex has an outgoing CO near the wag's turning point. This dissociative interchange mechanism predicted by the calculation explains the unexpected combination of kinetics and stability characteristics. Kinetics reveals that the reaction is first-order in the Os dimer with a negative Eyring entropy, while a stability study shows that the Os dimer's decomposition rate is several orders of magnitude slower than CO exchange.

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