Reversible β-hydride elimination of amine ligands forming stable cis-η2-iminium hydride OsII complexes

Orth, Stephen D.; Barrera, Joseph; Rowe, Steven M.; Helberg, Lisa E.; Harman, W. Dean

doi:10.1016/s0020-1693(97)05867-2

Cited by 11 publications

(12 citation statements)

References 27 publications

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“…30,49,50 This aspect of the metal cannot be changed through ligand alterations, as previous studies have shown that substitution of a single ammine ligand renders the metal incapable of η 2 binding of aromatic molecules. 51 In addition, because the {Os(NH 3 ) 5 } 2+ fragment is used stoichiometrically, the cost of osmium is a significant deterrent to its widespread use.…”

Section: Introductionmentioning

confidence: 99%

“…Despite its remarkable ability to promote a number of otherwise inaccessible organic transformations (see Scheme ), the pentaammineosmium(II) system has several inherent limitations. The complex is achiral, and thus the transformations that it facilitates either are limited to racemic reactions or require the use of chiral auxiliary strategies. ,, This aspect of the metal cannot be changed through ligand alterations, as previous studies have shown that substitution of a single ammine ligand renders the metal incapable of η 2 binding of aromatic molecules . In addition, because the {Os(NH 3 ) 5 } 2+ fragment is used stoichiometrically, the cost of osmium is a significant deterrent to its widespread use.…”

Section: Introductionmentioning

confidence: 99%

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A New Generation of π-Basic Dearomatization Agents

2005

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A new generation of dearomatizing π-bases having the general form {TpM(L)(π-acid)} (where Tp ) hydridotris(pyrazolyl)borate, M ) rhenium, molybdenum, tungsten, L ) variable ligand, and π-acid ) CO, NO + ) has been developed. These fragments show reactivity patterns similar to those of their pentaammineosmium(II) predecessor, binding aromatic molecules across two carbons and subsequently activating these ligands toward electrophilic addition and cycloaddition reactions. In many cases, these second-generation dearomatization agents show a greater degree of π-back-bonding than was observed for the analogous pentaammineosmium(II) complexes. A number of unprecedented reaction pathways have been discovered for these second-generation systems, most notably a broad array of cyclization reactions. In addition, these chiral-at-metal dearomatization agents are readily resolved and have been utilized in reaction sequences to give highly enantioenriched polycyclic molecules from common aromatic precursors. Scheme 1. Early Examples of Hydrogenation, Electrophilic Addition, and Cycloaddition of Aromatic Molecules Mediated by the π-Base Pentaammineosmium(II) ([Os] 2+ )

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A New Generation of π-Basic Dearomatization Agents

2005

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“…A significant drawback to the [Os] fragment is the inability to modify the ligand set to modulate the reactivity of the heterocyclic ligand. , In addition, the pentaammineosmium(II) fragment is achiral, and therefore it is not possible to control the absolute stereochemistry of ligand-centered organic transformations. Our group has recently developed a series of electron-rich Re(I) fragments capable of binding a wide variety of aromatic molecules in dihapto fashion .…”

Section: Introductionmentioning

confidence: 99%

Methanol Addition to Dihapto-Coordinated Rhenium Complexes of Furan

2001

J. Am. Chem. Soc.

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The complexes [TpRe(CO)(L)(4,5-eta(2)-furan)], present as diastereomeric mixtures (L = (t)BuNC (1A, 1B), PMe(3) (2A, 2B), pyridine (3A, 3B), or 1-methylimidazole (4A, 4B)), undergo acid-catalyzed methanol addition in CH(2)Cl(2) at -40 degrees C, resulting in the syntheses of dihapto-coordinated 2-methoxy-2,3-dihydrofuran complexes. In all cases, two diastereomers resulted, one in which the oxygen of the dihydrofuran is oriented toward the L ligand (5A, 6A, 7A, and 8A), and one in which the oxygen is oriented away from the L ligand (5B, 6B, 7B, and 8B). In all cases, the methoxy group adds stereoselectively, anti to the metal fragment. In addition, the (t)BuNC complex 1 yields a dihapto-coordinated vinyl ether (5C) that results from ring opening of the protonated furan ligand. In no case does the diastereomeric ratio of products correlate with that of the starting material.

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“…Yet, the use of stoichiometric osmium as a tool in organic synthesis has been largely unrealized owing to the cost of the metal, its toxicity, and the dicationic charge of the complexes which limit the solvent environments and purification techniques available. In addition, the inability to manipulate the ligand set of {Os(NH 3 ) 5 } 2+ without disrupting the binding affinity precludes the use of a chiral derivative of the pentaammineosmium system for use in enantioselective reactions. , Thus, our lab has been targeting the synthesis of π-basic metal systems that mimic the osmium in its ability to dearomatize organic systems, yet overcome the disadvantages mentioned above. Given the paucity of thermally stable η 2 -aromatic complexes, − we have focused our search on complexes that are isoelectronic with {[Os(NH 3 ) 5 ] 2+ } .…”

Section: Introductionmentioning

confidence: 99%

Stereoselective Dihapto-Binding of Prochiral Aromatic Compounds by {TpRe(CO)(PMe₃)}: Synthesis, Characterization, Stability, and Enantiofacial Discrimination (Tp = Hydrido(tris)pyrazolylborate)

2000

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Synthetic access to {TpRe(CO)(PMe 3 )} and the ability of this fragment to bind unsaturated compounds are reported. A variety of complexes of the type TpRe(CO)(PMe 3 )(η 2 -L) (L ) cyclohexene, cyclopentene, naphthalene, phenanthrene, thiophene, 2-methylthiophene, furan, or acetone) have been isolated and characterized, and stereochemical and stability issues of aromatic molecules bound to {TpRe(CO)(PMe 3 )} are discussed in detail. In particular, a solidstate structural study of TpRe(CO)(PMe 3 )(η 2 -cyclohexene) has provided a foundation for a discussion of the stereoelectronic features of the Re(I) fragment, and substitution reactions of an aromatic ligand by acetone provide insight into the stability of these aromatic complexes. In addition, a solid-state X-ray diffraction study of the Re(II) complex TpRe(CO)(PMe 3 )-(OTf) (OTf ) trifluoromethanesulfonate) is presented.

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Reversible β-hydride elimination of amine ligands forming stable cis-η2-iminium hydride OsII complexes

Cited by 11 publications

References 27 publications

A New Generation of π-Basic Dearomatization Agents

A New Generation of π-Basic Dearomatization Agents

Methanol Addition to Dihapto-Coordinated Rhenium Complexes of Furan

Stereoselective Dihapto-Binding of Prochiral Aromatic Compounds by {TpRe(CO)(PMe₃)}: Synthesis, Characterization, Stability, and Enantiofacial Discrimination (Tp = Hydrido(tris)pyrazolylborate)

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Reversible β-hydride elimination of amine ligands forming stable cis-η2-iminium hydride OsII complexes

Cited by 11 publications

References 27 publications

A New Generation of π-Basic Dearomatization Agents

A New Generation of π-Basic Dearomatization Agents

Methanol Addition to Dihapto-Coordinated Rhenium Complexes of Furan

Stereoselective Dihapto-Binding of Prochiral Aromatic Compounds by {TpRe(CO)(PMe3)}: Synthesis, Characterization, Stability, and Enantiofacial Discrimination (Tp = Hydrido(tris)pyrazolylborate)

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Stereoselective Dihapto-Binding of Prochiral Aromatic Compounds by {TpRe(CO)(PMe₃)}: Synthesis, Characterization, Stability, and Enantiofacial Discrimination (Tp = Hydrido(tris)pyrazolylborate)