- Mechanistic Studies into the Sn/Hg Exchange Reaction of 1,2-Fc(PPh2)(SnMe3) with HgCl2: Competitive Sn-Me over Sn-Fc Cleavage in Noncoordinating Solvents
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Tin-mercury exchange represents one of the most versatile and cleanest routes to arylmercuric halides. We found that reaction of the ferrocenylstannane 1,2-Fc(PPh2)(SnMe3) (1) with HgCl2 in acetone results in the unexpected spontaneous formation of 2·HgCl2, a diferrocenylmercury (Fc2Hg)-supported diphosphine chelate ligand as its HgCl2 complex. Mechanistic investigations into the generation of 2·HgCl2 reveal initial formation of an adduct of 1 with HgCl2, followed by competitive Sn-Me and Sn-Fc bond cleavage with formation of chloromercury and chlorodimethylstannyl-substituted ferrocene species. When the reaction is performed in chloroform as a noncoordinating solvent, formation of 2·HgCl2 is not observed, but instead 1,2-Fc(PPh2)(SnMe2Cl) (5) is generated as the major product. 5 is initially isolated as a complex with MeHgCl (generated as a byproduct), but the latter can be easily released by heating under high vacuum. When 5 is further reacted with 2 equiv of HgCl2 in acetone, the adduct 1,2-Fc(PPh2·HgCl2)(HgCl) (6·HgCl2) forms. An X-ray crystal structure of 6·HgCl2 shows two individual molecules that form Hg···Cl-bridged dimers, which in turn are linked by intermolecular Hg···Cl contacts to give a polymeric structure. In contrast, the equimolar reaction of 5 and HgCl2 results in initial complexation to give 5·HgCl2, which slowly transforms into the diferrocenylmercury species 2·HgCl2. These results confirm that both 1 and the byproduct 5 obtained by Sn-Me bond cleavage are competent intermediates in the formation of complex 2 in acetone. The preferential cleavage of the Sn-Me over the Sn-Fc bond in noncoordinating solvents is attributed to the presence of the diphenylphosphino group in an ortho position. These observations may have broader implications due to the formation of MeHgCl as a highly toxic and volatile byproduct and suggest that noncoordinating solvents are better avoided and extreme caution is necessary when performing Sn/Hg exchange reactions on donor-substituted substrates.
- Tagne Kuate, Alain C.,Lalancette, Roger A.,J?kle, Frieder
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- Asymmetric fluoro-alkynyl mercurials: The synthesis and solid state structures of RHgC=CCF3 (R = Ph, Fc)
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The fluoro-alkynyl mercurials RHgC=CCF3 (R = Ph, Fc) have been prepared, from the respective organomercurihalides and LiC=GCF3, and are the first examples of such materials to be studied crystallographically. These studies have revea
- Brisdon, Alan K.,Crossley, Ian R.,Pritchard, Robin G.
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- Oxidative cleavage reactions of compounds of the type CpRuLL′R (L, L′ = CO, PPh3; R = Me, PhCH2)
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The compounds CpRuLL′R (Cp = η5-C5H5; L, L′ = CO, PPh3; R = Me, PhCH2) have been prepared, some by improved routes. Alkyl cleavage reactions with halogens, hydrogen chloride, mercury(II) halides, and
- Joseph, Michael F.,Page, John A.,Baird, Michael C.
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- Synthesis, characterization, and C-H activation reactions of novel organometallic O-donor ligated Rh(III) complexes
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The synthesis and characterization of the O-donor ligated, air and water stable organometallic complexes trans- (2), and cis-(hfac-O,O) 2Rh(CH3)(py) (3), trans-(hfac-O,O)2Rh(C 6H5)(py) (4), cis-(hfac-O,O)2Rh(C 6H5)(py) (5), and cis-(hfac-O,O)2Rh(Mes)(py) (6) (where hfac-O,O = κ2-O,O-1,1,1,5,5,5- hexafluoroacetylacetonato) are reported. These compounds are analogues to the O-donor iridium complexes that are active catalysts for the hydroarylation and C-H activation reactions as well as the bis-acetylacetonato rhodium complexes, which we recently reported. The trans-complex 2 undergoes a quantitative trans to cis isomerization in cyclohexane to form 3, which activates C-H bonds in both benzene and mesitylene to form compounds 5 and 6, respectively. All of these compounds are air and water stable and do not lead to decomposition products. Complex 5 promotes hydroarylation of styrene by benzene to generate dihydrostilbene.
- Tenn III, William J.,Conley, Brian L.,Bischof, Steven M.,Periana, Roy A.
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p. 551 - 558
(2011/02/28)
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- Evidence for Electron Transfer in Reactions of Thianthrene Cation Radical with Dialkylmercurials
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Reactions of dialkylmercurials (R2Hg) with thianthrene cation radical perchlorate (Th.+ClO4-) in acetonitrile solution have been studied in quantitative detail.Evidence was obtained from reactions of MeHgR (R = Et, i-Pr, tBu) that reaction begins with electron transfer rather than with electrophilic cleavage of an alkyl-mercury bond.That is, each reaction gave MeHg+ and R., diagnostic of the formation and decomposition of MeHgR.+, rather than 5-methylthianthreniumyl perchlorate (1a), which would have been diagnostic of electrophilic displacement of the least hindered group (Me).The radicals R. either were trapped at the sulfur atom of Th.+ to form a 5-alkylthianthreniumyl perchlorate (Et., 1b) and at the ring positions of Th.+ to form 1- and 2-alkylthianthrenes (Et., i-Pr.) or were oxidized to the cations R+ (Et., i-Pr., and t-Bu.).Products of R+ were obtained, after workup with 4 M aqueous LiCl, as alkene, ROH, RNHCOCH3 and RCl.These reactions had the stoichiometric ratio of reactants 2Th.+ClO4-/MeHgR.Reactions of symmetrical R2Hg sometimes followed this stoichiometry (R = Me, Et, Bu) and led to RHg+ and 5-R-thianthreniumyl perchlorates (1a,b,e).Other R2Hg (R = t-Bu, benzyl, allyl) underwent oxidation by 4 equiv of Th.+ClO4-.Di-tert-butyl- and dibenzylmercury gave products derived entirely from the respective cation, R+.Diallylmercury gave some of the sulfonium product, 5-allylthianthreniumyl perchlorate (1g).None of the reactions with R = i-Pr, t-Bu, and benzyl led to the isolation of a thianthreniumyl perchlorate (i.e., 1c,d,f).Oxidations at the 4:1 molar ratio produced Hg(ClO4)2, which formed a partly insoluble complex (2) with thianthrene having the composition Th3Hg(ClO4)2.This product could be isolated if removed before workup treatment with aqueous 4 M LiCl, which, otherwise caused its decomposition into its components.The complex 2 was also prepared directly from reaction of Th with Hg(ClO4)2 in acetonitrile.Oxidation of benzylmercuric chloride by Th.+ClO4- in methylene chloride solution also occurred quantitatively, giving benzyl chloride, 1- and 2-benzylthianthrene, and a mixture of dibenzylthianthrenes.Oxidation of t-BuHgCl in acetonitrile solution led to a quantitative mixture of isobutene, t-BuOH, and t-BuNHAc.Th.+ClO4- also oxidized metallic Hg to either Hg+ or Hg2+, depending on the amount of oxidant used.
- Lochynski, Stanislaw,Shine, Henry J.,Soroka, Miroslaw,Venkatachalam, T. Krishnan
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p. 2702 - 2713
(2007/10/02)
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- Syntheses of monomeric (η5-pentamethylcyclopentadienyl)platinum(IV) methyl and bromo complexes and of [hydrotris(3,5-dimethyl-1-pyrazolyl)borato]trimethylplatinum
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The reaction of Cp*MgCl·THF (Cp* = C5Me5) with 1 equiv of PtMe3I and PtMe2Br2 produces Cp*PtMe3 (1) and Cp*PtMe2Br (2), respectively. Reaction of 2 with Br2 produces Cp*PtMeBr2 (3) in good yield. The structures of 2 and 3 have been determined by X-ray crystallography. Complex 2 crystallizes in the monoclinic space group, P21/m, with a = 7.017 (4) A?, b = 11.573 (4) A?, c = 8.496 (3) A?, β = 98.59 (3)°, Z = 2, V = 682.1 A?3, R = 0.067, and Rw = 0.081. Complex 3 also crystallizes in the monoclinic space group, P21/m, with a = 7.147 (2) A?, b = 12.171 (4) A?, c = 8.617 (2) A?, β = 113.77 (2)°, Z = 2, V = 685.9 A?3, R = 0.036, and Rw = 0.053. The molecules reside on mirror planes and are monomeric pseudotetrahedral Pt(IV) complexes with "piano stool" type geometries and η5-Cp* groups. Both molecules have Br atoms on the mirror. This leads to a disorder of the Me and the second Br positions in complex 3. The average Pt-C(Cp*) bond length is 2.25 (7) A? in 2 and 2.22 (4) A? in 3. The Pt-C(Me) and Pt-Br bond lengths in 2 are 2.07 (2) and 2.498 (2) A?, respectively. The ordered Pt-Br bond length in 3 is 2.496 (2) A?. Treatment of 1 with halogens results in the cleavage of the Pt-Cp* bond. The reaction of PtMe3I with KTp* (Tp* = [HB-(3,5-dimethylpyrazolyl)3]-) in thf gives Tp*PtMe3 (4) in almost quantitative yield. The reaction of 4 with Br2 brominates the 4-position of the pyrazolyl ring only.
- Roth, Steven,Ramamoorthy, Visalakshi,Sharp, Paul R.
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p. 3345 - 3349
(2008/10/08)
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- Electrophilic cleavages in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si, C). 1. Product distribution
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The extent to which Sn-CH2 and/or Sn-CH3 cleavage occurs in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si) in reactions with several electrophiles has been determined. With iodine and with
- Hawker, Darryl W.,Wells, Peter R.
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p. 821 - 825
(2008/10/08)
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- DIRECT TRANSFER OF ALIPHATIC AND AROMATIC SUBSTITUENTS FROM ORGANOSILATRANES TO MERCURY(II) SPECIES
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The relative reaction rates of several silatranes (derivatives of 2,8,9-trioxa-5-aza-1-silatricyclo1,5>undecane) and HgCl2 in acetone-d6 to yield the corresponding organomercury compound are of the order of e.g., 5 * 10-1 1 mol-1 sec-1 or slightly less, a rate that is unexpectedly high compared to the essentially inert parent organotrialkoxysilanes.Thus, the apical Si-C bond of the silatrane is extraordinarily susceptible to direct electrophilic attack by mercury(II).The rates decrease in the order CH2=CH, C6H5, p-ClC6H4 > CH3 > CH3CH2, CH3CH2CH2 > C6H11, ClCH2, Cl2CH, CH3CH2O.The effects of varying the solvent and the counterions are noted, and the probable mechanism is discussed.
- Nies, J. Dirk,Bellama, Jon M.,Ben-Zvi, Nava
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p. 315 - 320
(2007/10/02)
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- REACTIONS OF ORGANOMERCURY FULMINATES WITH ACETYLENE DERIVATIVES
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Organomercury fulminates react with acetylene derivatives to give unstable 3-(organomercurio)isoxazoles, which isomerize to 2-cyanoenolates.These are hydrolyzed with hydrochloric acid to the corresponding enols and are cleaved by water at the double bond.With monosubstituted acetylenes, substitution at the free position by the organomercury residue is predominant.
- Sarlo, Francesco De,Guarna, Antonio,Goti, Andrea,Brandi, Alberto
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p. 115 - 122
(2007/10/02)
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- Selectivity and reactivity in reactions of methylaryltitanium(IV) complexes with electrophiles
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Methyl or phenyl for halogen-exchange reactions occur between [TiMe2(η-C5H5)2] or [TiPh2(η-C5H5)2] with [TiX2(η-C5H5)2], X = halogen, to give [TiXMe(η-C5H5)2] or [TiXPh(η-C5H5)2], respectively. The reactions are complicated by parallel decomposition of the methyl- or phenyltitanium complexes, which is catalyzed by [TiX2(η-C5H5)2] or [TiXR(η-C5H5)2]. In general, there is little difference in the rates of reaction of [TiMe2(η-C5H5)2] and [TiPh2(η-C5H5)2] toward the symmetrization reactions. These reagents also transfer a methyl group or phenyl group to platinum(II) or gold(III), but there are again side reactions. The complex [TiMePh(η-C5H5)2] reacts with electrophiles HCl, HOAc, HgCl2, and MeHgCl to give cleavage of both methyl- and phenyltitanium bonds with little selectivity. In cleavage of [TiMe(C6H4X)(η-C5H5) 2] there is a correlation of the selectivity for cleavage of the aryl group by electrophiles HCl or HgCl2 with the σ+ parameters of substituents X. A mechanism of reaction involving electron transfer from the complex to the electrophile followed by rapid cleavage is tentatively suggested.
- Puddephatt, Richard J.,Stalteri, Maria A.
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p. 1400 - 1405
(2008/10/08)
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- Sterically Hindered Free Radicals, IX. Generation and Structure of Stannyl Radicals R3Sn* with Bulky Groups
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Methylated phenyl groups in hexaaryldistannanes cause reversible thermal dissociation R3Sn-SnR3 (1) 2 R3Sn* (2) only if at least the 2,6-positions are methylated.Further methyl groups enhance this dissociation only when neighbouring these positions and each other, thus causing a buttressing effect .So, DSn-Sn is decreased (51.5 -> 38.5 kcal/mol).ESR data and geometry of 2 are reported, as well as those of stannyl radicals 2, R = PhmMenCCH2 (m + n = 3) generated from the corresponding hydrides.The rotation around C-Sn bonds is hindered with increasing m.A preferred conformation is concluded from ESR data.Numerous compounds 1, R3SnH, and other precursors are prepared for the first time.
- El-Farargy, Ahmed F.,Lehnig, Manfred,Neumann, Wilhelm P.
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p. 2783 - 2794
(2007/10/02)
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- Electron-Transfer Activation in Electrophilic Mechanisms. Cleavage of Alkylmetals by Mercury(II) Complexes
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The disappearance of the transient charge-transfer (CT) absorption bands coincides with the electrophilic (SE2) cleavage of homologous series of alkyltin compounds by various mercury(II) halides, cyanide, and carboxylates.The second-order kinetics for HgCl2 cleavage afford rate constants which vary in a rather unaccountable way with the structure of the alkyltin compound and with the polarity of the solvent.Furthermore, the relative reactivities of these alkyltin compounds in the analogous electrophilic cleavage by I2 or Br2 show poor correlations with HgCl2 cleavages, in different solvents.However, the description of the activation process as an electron transfer in the precursor complex, e.g., -> +HgCl2->, stems from the CT transition energy and leads to a linear free energy relationship in which the activation free energy is equal to the driving force for the formation of the ion pair.The latter is readily dissected by eq 18 into separate changes in electronic, steric and solvation energies.With this mechanistic formulation, the reactivities of various alkyltin compounds follow a remarkably simple linear correlation with the ionization potentials and the solvent effects, in the comparison with I2 and Br2 cleavages.Moreover, the reactivities of the various mercury(II) derivatives relate directly to differences in their electron affinities.
- Fukuzumi, S.,Kochi, J. K.
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p. 7290 - 7297
(2007/10/02)
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