The Tris[(+-)-l,2-propanediamine]cobalt(III) System.

Harnung, Sven E.; Kallesoe, Solveig; Sargeson, Alan M.; Schäffer, Claus Erik; Bjørseth, Alf; Powell, D. L.

doi:10.3891/acta.chem.scand.28a-0385

Cited by 30 publications

(15 citation statements)

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“…Furthermore, no racemization occurs in aqueous solution during (a) 3 months at room temperature, (b) 75 min at 85 °C in the presence of 100 equiv of NaNO 2 , or (c) 15 h at reflux in the presence of HCl . However, when activated charcoal is added, racemization takes place within 2 min at 90 °C . The charcoal (or trace impurities therein) is believed to function as a redox catalyst, generating small amounts of substitution-labile cobalt(II).…”

Section: Introductionmentioning

confidence: 99%

Launching Werner Complexes into the Modern Era of Catalytic Enantioselective Organic Synthesis

2020

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Metrics & MoreArticle Recommendations CONSPECTUS: Reactions catalyzed by transition metal complexes almost always entail binding of one or more reactants to the metal center, and nearly every corner of the "chiral pool" has been picked over in efforts to develop enantioselective catalysts. As reported by Alfred Werner in 1911−1912, salts of the formally D 3symmetric [Co(en) 3 ] 3+ trication (en = ethylenediamine) were among the first chiral inorganic compounds to be resolved into enantiomers. These air-and water-stable complexes are substitution-inert, so for 100 years they languished without application in organic synthesis. We then showed that when they are rendered soluble in organic media by lipophilic anions such as fluorinated tetraarylborates BAr f − , they become potent catalysts for a variety of carbon−carbon and carbon−heteroatom bond forming reactions. These involve substrate activation by hydrogen bonding to the coordinated NH 2 units (pK a ca. 15), a "second coordination sphere" mechanism. Only modest enantioselectivities are obtained with [Co(en) 3 ] 3+ 3BAr f − or related chromium, rhodium, iridium, and platinum salts. However, high enantioselectivities are achieved when the three en ligands are replaced by the 1,2-diphenyl analogues (S,S)-or (R,R)-H 2 NCHPhCHPhNH 2 . Here only one BAr f − anion is required to solubilize the trication, so a number of mixed-salt catalysts (2X − BAr f − ) have been evaluated. Alternatively, a dimethylamino group can be tethered to the backbone of one en ligand, providing bifunctional catalysts that obviate any need for an external base. Interestingly, the counteranions modulate the enantioselectivities somewhat. However, catalysts with chiral anions do not significantly outperform benchmark catalysts with achiral anions. Cagelike chiral hexaaminecobalt(III) complexes known as sepulchrates and sarcophagines, which feature secondary NH donor atoms, can also serve as catalysts, but the enantioselectivities are very low. In a spinoff application, certain salts are found to be superb "chiral solvating agents", leading to distinct sets of NMR signals for enantiomers of chiral analytes with Lewis basic functional groups. Loadings of 10−25 mol % generally suffice, providing the best way of assaying the enantiomeric purities of a host of compounds. Also, mixtures of several chiral compounds can be simultaneously analyzed. It is not surprising that complexes that perform well in chiral recognition phenomena also excel as enantioselective catalysts. In this Account, the stereochemical properties of the preceding complexes are treated, as well as arcana generally known only to specialists in the field. These include the use of charcoal for equilibrating configurations of the cobalt stereocenter and Sephadex for separating enantiomers and diastereomers. Other types of metal-containing hydrogen-bond-donor catalysts are briefly surveyed (noncoordinating NH units can also be effective), including several developed by other groups. However, the mechanisms of enantioselection in all o...

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Section: Introductionmentioning

confidence: 99%

Launching Werner Complexes into the Modern Era of Catalytic Enantioselective Organic Synthesis

2020

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“…The different stability of the isomers can be rationalized in terms of the mutual interactions between the ligands by means of the ring-pair relationship model. 5 In this model the obs and leb complexes are characterized by containing three ob-ob and three lel-lel relationships, respectively. Similarly, the obzlel and the lebob complexes have two lel-ob relationships Inorganic Chemistry, Vol.…”

Section: Discussionmentioning

confidence: 99%

The tris[(.+-.)-trans-1,2-cyclohexanediamine]cobalt(III) system

Harnung¹,

Soerensen²,

Creaser³

et al. 1976

Inorg. Chem.

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“…Study of the Energetics. To assess the ability of Molmec, Momec91(H), Momec91(C), and Xnviron to predict the relative stabilities of isomers, five molecules were chosen in which the experimental isomer distributions were measured using equilibration methods: [Co(trap) 2 ] 3+ , [Co(dien) 3 ] 3+ , , [ Co(chxn) 3 ] 3+ , [Co(±bn) 3 ] 3+ , , and [Co(pn) 3 ] 3+ . , A further five molecules were chosen where it is not possible to isolate the isomers because of conformational flexibility but where the conformation is known in the solid state and can be evaluated in solution: [Co(en) 3 ] 3+ , [Co(tmen) 3 ] 3+ , − [Co(sar)] 3+ , [Co((NH 3 ) 2 -sar)] 5+ , and [Co((NMe 3 ) 2 -sar)] 5+ . Minimization of each isomer was carried out using the method described above.…”

Section: Computational Detailsmentioning

confidence: 99%

Critical Evaluation of Metal Complex Molecular Mechanics. Part 1. Cobalt(III) Hexaamines

Bygott

Sargeson

1998

Inorg. Chem.

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The ability of available molecular mechanics programs to calculate structures and relative energies of metal complexes is examined via a comparative study of five different force fields: Molmec, Momec91(H), Momec91(C), Xnviron, and Spartan. The method used for assessing the validity of the force fields showed that four of the force fields were able to reproduce successfully the structures of various Co(III) hexaamine cations determined by X-ray analysis, even when these structures were considerably distorted. In certain cases, the calculated relative steric energies were not reliable. Small variations in force fields parameters sometimes led to large changes in the calculated steric energies, and in some instances, in the order of steric strain for different isomers. The most notable changes occurred when metal-dependent parameters were altered.

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The Tris[(+-)-l,2-propanediamine]cobalt(III) System.

Cited by 30 publications

References 0 publications

Launching Werner Complexes into the Modern Era of Catalytic Enantioselective Organic Synthesis

Launching Werner Complexes into the Modern Era of Catalytic Enantioselective Organic Synthesis

The tris[(.+-.)-trans-1,2-cyclohexanediamine]cobalt(III) system

Critical Evaluation of Metal Complex Molecular Mechanics. Part 1. Cobalt(III) Hexaamines

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