Interligand interaction and three-dimensional structure of coordination compounds. Compounds of the tris(bidentate)M type

Dashevskii, V. G.; Asatryan, Rubik; Baranov, A. P.

doi:10.1007/bf00752829

Cited by 4 publications

(2 citation statements)

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“…It is equal to 11.5 kcal mol –1 for channel D with an agostic bond energy being 6.6 kcal mol –1 . The higher energy isomer, identified by Weitz and co-workers, also contains an agostic bond (Figure ), which is somewhat weaker than the above ones because it connects the metal center to an αH-atom of ethylene, thus creating a larger ring-strain for the bidentate ligation of −C 2 H 5 group and increased interligand repusions . For this reason, it cannot occupy a separate open ligand site and increase the local symmetry of the iron polyhedron, as agostic bonds linked by βH-atoms identified by us do.…”

Section: Results and Discussionmentioning

confidence: 63%

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Asatryan

Ruckenstein

2013

J. Phys. Chem. A

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The hydrogenation of alkenes catalyzed by metal carbonyls is an intricate process involving reactions of various isomers of labile π- and σ-complexes, hydrides, dihydrides, and their radicals. Two general mechanisms have been suggested in the literature regarding the catalytic hydrogenation of simple alkenes by photochemically activated iron pentacarbonyl: a molecular mechanism that involves the sequential replacement of two carbonyl ligands by hydrogen and unsaturated ligands, and a radical mechanism involving the EPR-identified iron carbonyl hydride radicals. Even though significant results were obtained in numerous experiments and few theoretical studies, these mechanisms remain phenomenological, without detailed information regarding the potential energy surfaces (PES) and the elementary processes. Several major issues also remain open. It is still unclear, for instance, whether the ethane can be formed via a monomolecular reaction of ethyl hydride isomer intermediates HFe(CO)3(C2H5) or the only way to produce C2H6 is a bimolecular reaction assisted by a second ethylene. It is also uncertain if a dihydride or a dihydrogen complex is operating in olefin hydrogenation. To gain insight into these processes, a detailed theoretical examination of various PES for gas-phase reactions of ethylene with potential metallocomplex reagents to primary and secondary products (both singlet and triplet electronic states) was performed using DFT and ab initio methods. Calculations have been carried out for a set of reactions of ethylene with all possible isomers of tricarbonyliron hydrogenates, viz., dihydrides of trans-, cis-, and gauche-configurations (isomers with respect to the two hydridic atoms), and two nonclassical singlet and two triplet dihydrogen complexes, some of them being identified for the first time. The hydrogenation pathways (both molecular and radical) are shown to be strongly stereoselective and dependent on the spin configurations of the initial reagents. The combination of various dihydride isomers with C2H4 as separate reaction channels allowed us to explore relevant PES cross sections and to identify corresponding stereoregulated elementary processes. The reaction channels can alternatively start from the association of ethylene with dihydrogen tricarbonyliron complexes and may involve intersystem crossings with triplet pathways, followed by that of the corresponding singlet PES. Various interconversion and isomerization processes involving single-olefin adducts were found to precede the major ethane-elimination reactions (through both monomolecular and second-ethylene-assisted pathways). Monomolecular processes are suggested to occur under appropriate conditions. The stereospecific mechanistic results and thermochemical parameters constitute a basis for developing detailed kinetic models for iron-carbonyl catalysis.

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Section: Results and Discussionmentioning

confidence: 63%

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Asatryan

Ruckenstein

2013

J. Phys. Chem. A

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“…The conformational flexibility of penta-coordinated compounds plays a key role in the stereoselectivity and catalytic activity in metallocomplexes. − Although the interconversions between ideal trigonal bipyramidal (TBP) and ideal square pyramidal (SP) structures of penta-coordinated compounds are usually facile and rapid, alternative nonideal coordination geometries − and their fluxional behavior − ,,− present a challenge for simple intramolecular exchange mechanisms. Over the past decades, several mechanistic proposals for different metal–ligand species have been made. − ,,,,,− ,− Berry pseudorotation (BPR) is the most commonly proposed mechanism to describe the interchange of axial and equatorial substituents of penta-coordinated, TBP species. In addition to BPR, other mechanisms include the following: the tetrahedral jump for quasi-tetrahedral HML 4 and H 2 ML 3 complexes; ,, the turnstile rotation, ,− ,, which involves an internal rotation of a trio , with respect to pair of substituents; and the reverse BPR, …”

Section: Introductionmentioning

confidence: 99%

Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S₂C₂(CF₃)₂)(CO)(PPh₃)₂: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States

et al. 2020

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The stereodynamics of an ultrafast (picosecond) isomerization in a penta-coordinated ruthenium complex, Ru(S2C2(CF3)2)(CO)(PPh3)2, were characterized by density functional theory (DFT). The ruthenium complex crystallizes in two almost-square pyramidal (SP) forms. The violet form has an apical PPh3 ligand, the orange form has an apical CO ligand, and their solution displays three CO stretching frequencies. With 4 possible centers of chirality (1 ruthenium, 2 phosphines, and 1 dithiolate), there are 24 stereoisomers. DFT calculations of these stereoisomers show structures ranging from almost-perfect SP (τ5 ≈ 0) to structures significantly distorted toward trigonal bipyramidal (TBP) (τ5 ≈ 0.6). The stereoisomers fall neatly into three groups, with νCO ≈ 1960 cm–1, 1940 cm–1, and 1980 cm–1. These isomers were found to interconvert over relatively small barriers via Ru–S bond twisting, CF3 rotation, phenyl twisting, PPh3 rotation, and, in some cases, by coupled motions. The composite energy surface for each CO frequency group shows that interconversions among the low-energy structures are possible via both the direct and indirect pathways, while the indirect pathway via isomers in the νCO ≈ 1980 cm–1 group is more favorable, which is a result consistent with recent experimental work. This work provides the first complete mechanistic picture of the ultrafast isomerization of penta-coordinated, distorted SP, d6-transition-metal complexes.

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Effect of “Reducible” Titania Promotion on the Mechanism of H-Migration in Pd/SiO2 Clusters

Asatryan

Ruckenstein

2015

Catal Lett

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Interligand interaction and three-dimensional structure of coordination compounds. Compounds of the tris(bidentate)M type

Cited by 4 publications

References 33 publications

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S₂C₂(CF₃)₂)(CO)(PPh₃)₂: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States

Effect of “Reducible” Titania Promotion on the Mechanism of H-Migration in Pd/SiO2 Clusters

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Interligand interaction and three-dimensional structure of coordination compounds. Compounds of the tris(bidentate)M type

Cited by 4 publications

References 33 publications

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Mechanism of Iron Carbonyl-Catalyzed Hydrogenation of Ethylene. 1. Theoretical Exploration of Molecular Pathways

Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S2C2(CF3)2)(CO)(PPh3)2: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States

Effect of “Reducible” Titania Promotion on the Mechanism of H-Migration in Pd/SiO2 Clusters

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Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S₂C₂(CF₃)₂)(CO)(PPh₃)₂: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States