High-valent Transition Metal Research Articles

Synthesis and Characterization of Rhenium(V) Oxo Complexes with a New Thiol-Amide-Thiourea Ligand System. X-ray Crystal Structure of [1-Phenyl-3-[2-((2-thioacetyl)amino)ethyl]thioureato]oxorhenium(V).

General methods for preparing Re(V)O complexes with a novel series of thiol-amide-thiourea (TATU) ligands, a new class of N(2)S(2) chelates, were developed. The TATU ligands, the first multidentate systems designed with a bidentate thiourea moiety, have been used to prepare the first high-valent transition metal complexes with bidentate thiourea coordination. Direct reaction of N-(2-aminoethyl)-2-((triphenylmethyl)thio)acetamide (1) with phenyl, 4-methoxyphenyl, 4-chlorophenyl, and methyl isothiocyanate afforded ready access to the corresponding S-protected TATU ligands in one step. A two-step preparation of the N,N-dimethylthiourea TATU ligand derived from 1 was also developed. Deprotection of thiols in trifluoroacetic acid with triethylsilane followed by a ligand exchange reaction with Re(V)O precursors yielded neutral ReO(TATU) complexes. The structure of [1-phenyl-3-[2-((2-thioacetyl)amino)ethyl]thioureato]oxorhenium(V) (6a) was determined by X-ray diffraction methods. Crystal data for 6a: C(11)H(12)N(3)O(2)ReS(2), fw 468.6, orthorhombic, Pca2(1); a = 22.605(5) Å, b = 13.029(3) Å, c= 9.698(2) Å; V = 2856.3(11) Å(3); Z = 8. The coordination environment of 6a was pseudo-square-pyramidal with a deprotonated thiol S, deprotonated amide N, deprotonated thiourea N, and thiocarbonyl S coordinated in the basal plane and the oxo ligand in the apical position. The thiourea function forms a four-membered chelate ring in the multidentate TATU ligands. The two N-C and the S-C bond distances within the monodeprotonated thiourea moiety were typical of bonds with multiple-bond character. Solution (1)H NMR data for all five complexes were consistent with the solid-state structure of 6a. A broad singlet attributable to the uncoordinated NH group of thiourea was observed for the monosubstituted thiourea complexes but was not present for the N,N-dimethylthiourea derivative. Instead, two singlets of equal intensity were observed for the two methyl groups, indicating that there is restricted rotation around the C-N(CH(3))(2) bond and an extended pi system in the thiourea moiety. The four-membered ring might cause difficulty because the M-S distance would be relatively long in an undistorted ligand. This may be the reason such chelate ligands have not been previously investigated. However, the N-C-S angle narrows to approximately 105 degrees, permitting a Re-S bond with a typical bond length to be formed. We conclude that such a ring represents a versatile new building block to create multidentate ligands.

Theoretical Studies of Organometallic Compounds. 15. Si2H2 and CSiH2 Isomers as Ligands in High-Valent Transition Metal Complexes

Theoretical Studies of Organometallic Compounds. 15. Si2H2 and CSiH2 Isomers as Ligands in High-Valent Transition Metal Complexes

Novel synthesis of 5,10,15,20-tetraarylporphyrins using high-valent transition metal salts

A new synthesis of porphyrins from pyrrole and substituted benzaldehydes, is described, using high-valent transition metal salts [VOCl3, VO(OEt)Cl2, VO(OPri)Cl2, TiCl4 and Mn(OAc)3] as aromatizing agents. This process allows higher working concentrations and larger amounts of reagent to be used, than those previously described.

Oxygen transfer reactions. 2. A comparison of the reactions of ruthenium tetroxide, chromyl chloride, and permanganate with thianthrene 5-oxide

Products obtained from the oxidation of thianthrene 5-oxide, SSO, have been used to compare oxygen transfer mechanisms for three high-valent transition metals. Oxidation of SSO by benzyltriethylammonium permanganate in methylene chloride gives the corresponding sulfone, thianthrene 5,5-dioxide (SSO2), as the exclusive product. Oxidation of SSO by ruthenium tetroxide also gives SSO2 as the predominant product along with minor amounts of the disulfoxide, thianthrene 5,10-dioxide (SOSO). However, the converse is observed when chromyl chloride is used as the oxidant; SOSO is the major product. It is suggested that oxygen transfers from permanganate and ruthenium tetroxide are initiated by complexation between the central metal atom and the oxygen end of the S=O dipole, while oxidation by chromyl chloride is likely initiated by an alternative mechanism, possibly a single electron transfer.

Reduction of manganate(VI) by mandelic acid and its significance for development of a general mechanism of oxidation of organic compounds by high-valent transition metal oxides

Results obtained from a study of the oxidation of mandelic acid and cyclobutanol by manganate(VI) indicate that reaction mechanisms traditionally applied to oxidations of this type (i.e., hydrogen atom or hydride ion transfers) may not be correct. Instead it appears that the reaction may be initiated by a 2+2 addition of the α-C-H bond to a manganese oxo double bond. This interpretation may be useful in the development of a general mechanism for the oxidation of organic compounds by high-valent transition metal oxides including more common oxidants such as permanganate, ruthenium tetroxide, and chromic acid

Kinetics and mechanism of the oxidation of alcohols by ferrate ion

A kinetic study of the reduction of ferrate ion under basic conditions has been completed. The observation that a typical aliphatic ether, tetrahydrofuran, is oxidized at a rate comparable to that of aliphatic alcohols, such as cyclopentanol, indicates that the reaction between ferrate and alcohols is likely initiated by attack of the oxidant at an α-C—H bond, a conclusion that is consistent with the occurrence of primary deuterium kinetic isotope effects (2.8–4.3 at 25 °C) when α-hydrogens are replaced by deuterium. Because only acyclic products are obtained from the oxidation of cyclobutanol by ferrate, it may be concluded that free radical intermediates are involved in the reaction. The insensitivity of the reaction rates to substituent effects during the oxidation of substituted mandelic acids indicates that substantial charges are not built up in the transition state. All of these observations are most readily accommodated by a mechanism in which the reaction is initiated by a 2 + 2 addition of an Fe=O bond to the α-C—H of an alcohol to give an organometallic intermediate that subsequently decomposes by homolytic cleavage of the resulting C—Fe bond. Comparisons are made with the reactions between alcohols and other high-valent transition metal oxides.

High-valent transition metal chemistry. Moessbauer and EPR studies of high-spin (S = 2) iron(IV) and intermediate-spin (S = 3/2) iron(III) complexes with a macrocyclic tetraamido-N ligand

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh-valent transition metal chemistry. Moessbauer and EPR studies of high-spin (S = 2) iron(IV) and intermediate-spin (S = 3/2) iron(III) complexes with a macrocyclic tetraamido-N ligandKimberly L. Kostka, Brian G. Fox, Michael P. Hendrich, Terrence J. Collins, Clifton E. F. Rickard, L. James Wright, and Eckard MunckCite this: J. Am. Chem. Soc. 1993, 115, 15, 6746–6757Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/ja00068a035RIGHTS & PERMISSIONSArticle Views1290Altmetric-Citations148LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Characterisation of chemically prepared ZnO powders in relation to the nonlinear resistors

Abstract ZnO powders prepared from the thermal decomposition of Zn-oxalate, Zn-carbonate and Zn-nitrate have been characterised in relation to the formation of sintered ceramics exhibiting nonlinear resistivity. The particle characteristics such as size, shape, lattice strain, the point defect contents and the nonstoichiometry with respect to δ Zn value in Zn 1+ δ O are found to depend upon the mechanism of reactions of ZnO formation and the effect of back reaction from the evolved gases. The most important characteristic of ZnO powder that considerably influences the nonlinear property of the ceramics is δ Zn . Optimum current-voltage characteristics for the sintered products are obtained when δ Zn in the starting material is in the range 8·5–12 ppma. Because of nonstoichiometry, the native donor states are built in the powder particles. The depletion layers formed at the pre-sintering stage are retained during sintering, as a result of the high valent transition metal ions preferentially present at the grain boundary regions. The energy barriers are stabilised around the grain boundaries by this process.

High valent transition metal chemistry. Synthesis and characterization of an intermediate-spin iron(IV) complex of a strong .pi.-acid ligand

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh valent transition metal chemistry. Synthesis and characterization of an intermediate-spin iron(IV) complex of a strong .pi.-acid ligandTerrence J. Collins, Brian G. Fox, Zheng Guo Hu, Kimberly L. Kostka, Eckard Munck, Clifford E. F. Rickard, and L. James WrightCite this: J. Am. Chem. Soc. 1992, 114, 22, 8724–8725Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ja00048a069RIGHTS & PERMISSIONSArticle Views588Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (284 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Decomposition of chlorinated hydrocarbons using metal oxides supported on carbonaceous adsorbents

A series of catalysts comprised of high-valent transition metal oxides supported in porous, carbonaceous adsorbents oxidize methylene chloride completely to CO, CO2 and HCl at 250 °C and 1 atm; results with CD2Cl2 indicate that C–H bond dissociation is involved in the rate determining step of the reaction.

Kinetics and mechanism of the oxidation of alcohols by ruthenate and perruthenate ions

In addition to being important synthetic reagents, ruthenate and perruthenate are of interest because they are representative of a number of high valent transition metal ions that can be used as oxidants in organic chemistry. In their reactions with alcohols both ions exhibit several striking similarities — concave Hammett plots, primary deuterium isotope effects, small enthalpies of activation, and large negative entropies of activation. The most likely explanation of the concave upward Hammett plots is the involvement of free radical-like transition states that could be formed by the decomposition of organometallic intermediates. Keywords: oxidation, ruthenate, perruthenate, alcohols, mandelic acid.

Oxidation of hydrocarbons. 12. Kinetics and mechanism of the oxidation of trans-cinnamic acid by ruthenate and perruthenate ions

Recent theoretical calculations by Rappé and Goddard have pointed to the importance of spectator oxo groups in stabilizing intermediates produced during the reduction of high-valent transition metal oxides; intermediates which contain triply-bonded metal oxo groups are predicted to be unusually stable. In an attempt to test these conclusions experimentally, the rates of oxidation of cinnamate ion by ruthenate and perruthenate ions have been studied. Since the most likely intermediate formed from perruthenate ion (but not ruthenate ion) would contain a stabilizing, triply-bonded spectator oxo group, it would be expected to react faster if the calculations are correct. In agreement with these predictions, it was found that the activation energy (ΔG‡) for the ruthenate reaction was about 7 kcal/mol higher than for the corresponding perruthenate reaction.