Rhenium carbonyl biradicals.  Formation, recombination, and halogen atom transfer

Lee, Kang Wook; Hanckel, John M.; Brown, Theodore L.

doi:10.1021/ja00269a024

Cited by 24 publications

(6 citation statements)

References 4 publications

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“…The coordination geometry around the two osmium atoms is that of an irregular octahedron. Bimetallic metal carbonyl compounds with bridging dppp ligands have been reported with several metals, including tungsten, molybdenum, 9a, chromium, 9a, and rhenium; however, to the best of our knowledge, 8 is the first example of a bimetallic osmium compound with a bridging diphosphine ligand and is certainly the only example of a bimetallic dimethylosmium compound.…”

Section: Resultsmentioning

confidence: 98%

Reaction Pathways for fac-Os(CO)₃(MeCN)Me₂ with Mono- and Bidentate Ligands

Overett

Moss

2007

Organometallics

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The reactions of fac-Os(CO) 3 (L)Me 2 (1a, L ) MeCN; 1b, L ) THF) with monodentate and bidentate ligands have been studied for the first time. Treatment of 1a or 1b with PPh 3 gives fac-Os(CO) 3 (PPh 3 )-Me 2 (2), which may be further reacted with Me 3 NO in acetonitrile to give the unexpected isomer cis-Os(CO) 2 (PPh 3 )(MeCN)Me 2 (3). Subsequent reaction of 3 with PPh 3 gives cis,trans-Os(CO) 2 (PPh 3 ) 2 Me 2 (4), with a further isomerization accompanying the ligand substitution. Oxidative decarbonylation of 4 with Me 3 NO was found not to be possible. Treatment of 1a or 1b with bidentate ligands gives different reaction products, depending on the choice of ligand, the reaction conditions, and the stoichiometry. Reactions with small-bite-angle bidentate ligands (L-L) gave the compounds cis-Os(CO) 2 (L-L)(COMe)-Me (5a, L-L ) dppm; 5b, L-L ) dppe; 5c, L-L ) 2,2′-bipy). These mixed methyl acetyl complexes are formed by displacement of the labile ligand and subsequent chelation, accompanied by methyl migration onto carbonyl. Reaction of 1a with 1 equiv of dppp, however, resulted in a series of reactions which led to the formation of the decarbonylated product cis-Os(CO) 2 (dppp)Me 2 (7). However, reaction of 1a with 0.5 equiv of dppp gave the bimetallic dppp-bridged complex [fac-Os(CO) 3 Me 2 ] 2 (µ-dppp) (8). In addition to characterization of all the new compounds by analytical and spectroscopic techniques, the molecular structures of 5a and 8 have been determined by X-ray diffraction.

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Section: Resultsmentioning

confidence: 98%

Reaction Pathways for fac-Os(CO)₃(MeCN)Me₂ with Mono- and Bidentate Ligands

Overett

Moss

2007

Organometallics

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“…However, (μ-H) 2 Ru 3 (CO) 8 (μ-P( t -Bu) 2 ) 2 does not react with benzyl bromide or HSnBu 3 , substrates which typically react rapidly with radicals. Furthermore, previous studies of metal-centered biradicals have found negligible CO dissociation, and the biradicals undergo typical radical reactions such as recombination and halogen atom abstraction .…”

Section: Discussionmentioning

confidence: 94%

“…Furthermore, previous studies of metalcentered biradicals have found negligible CO dissociation, and the biradicals undergo typical radical reactions such as recombination and halogen atom abstraction. 41 Many other 17electron metal complexes undergo rapid associative ligand substitution, but lability for dissociative ligand substitution is uncommon. 42 For these reasons we consider the involvement of a biradical unlikely.…”

Section: Note Added In Proofmentioning

confidence: 99%

Kinetics and Mechanism of Reversible Oxidative Addition of Hydrogen across the Metal−Metal Bond of (μ-H)₂Ru₃(CO)₈(μ-P(t-Bu)₂)₂. Steric Promotion of Metal−Metal Bond Cleavage But a CO Dissociative Mechanism

1996

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The kinetics of the reaction (μ-H)2Ru3(CO)8(μ-P(t-Bu)2)2 + H2 ⇄ (μ-H)2Ru3(CO)8(H)2(μ-P(t-Bu)2)2 have been studied. The reaction of (μ-H)2Ru3(CO)8(μ-P(t-Bu)2)2 with H2 has a rate law which is first-order in cluster concentration and in hydrogen pressure and inverse order in CO pressure; on the basis of the rate law, activation parameters, and deuterium kinetic isotope effect, hydrogen addition is proposed to involve rapid, reversible dissociation of a carbonyl ligand, followed by rate-determining oxidative addition of hydrogen through a three-center transition state at a single metal atom. Loss of hydrogen from (μ-H)2Ru3(H)2(CO)8(μ-P(t-Bu)2)2 also involves reversible loss of a carbonyl, followed by rate-determining reductive elimination of molecular hydrogen. The reaction is highly sensitive to the steric bulk of the phosphido substituents, as (μ-H)2Ru3(CO)8(μ-PR2)2, R = cyclohexyl and phenyl, do not react with hydrogen. In addition, the rate of exchange with 13CO is much faster for R = t-Bu than for R = cyclohexyl. Based upon the temperature dependence of the equilibrium constant for hydrogenation, the energy for the unbridged Ru−Ru bond of (μ-H)2Ru3(CO)8(μ-P(t-Bu)2)2 is estimated to be 47−59 kJ/mol, the low value being attributed to steric strain.

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“…Lifetimes for Miscellaneous Biradicals Other solvents given in original reference 147. in the case of oxygen as compared with CH231 (similar effects are well-known in free radical chemistry).121,122…”

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confidence: 98%