17-electron Radical Cations Research Articles

Synthesis and redox chemistry of cycloheptatrienyl molybdenum carbon-chain complexes featuring diimine support ligands: [Mo{(C[tbnd]C)nC[tbnd]CR}(R′N[dbnd]CH–CH[dbnd]NR′)(η-C7H7)], (n = 0 or 1)

The alkynyl complexes [Mo(CCR)(R′-dab)(η-C7H7)] (dab = diazabutadiene; R′ = tBu, R = Ph, 2a; C6H4–4-Me, 3a; tBu, 4a; R′ = C6H4–4-Me, R = Ph, 2b) have been synthesised by reaction of [MoBr(R′-dab)(η-C7H7)] with LiCCR in thf. Crystallographic characterisation of [Mo(CCC6H4–4-Me)(tBu-dab)(η-C7H7)], 3a determines a Mo-Cα bond distance of 2.154(3) Å. Cyclic voltammetric investigations on the alkynyl complexes 2a, 2b, 3a, 4a and the extended chain butadiynyl derivative [Mo(CCCCSiMe3)(tBu-dab)(η-C7H7)], 5a, reveal that each complex exhibits a chemically and electrochemically reversible one-electron oxidation to give the corresponding 17-electron radical cation. Characterisation of the radicals [2a]+, [2b]+, [3a]+, and [5a]+ by IR and EPR spectroscopic techniques indicates that the redox process is strongly metal centred. Spectroscopic and synthetic investigations establish that 17-electron radicals of the type [Mo{(CC)nCCR)}(R′-dab)(η-C7H7)]+ (n = 0 or 1) have relatively low thermodynamic stability.

Synthesis, Redox Chemistry, and Electronic Structure of the Butadiynyl and Hexatriynyl Complexes [Mo{(C≡C)nC≡CR}(L2)(η-C7H7)]z+ (n = 1, 2; z = 0, 1; R = SiMe3, H; L2 = 2,2′-bipyridine, Ph2PCH2CH2PPh2)

Two series of extended carbon chain butadiynyl and hexatriynyl complexes, [Mo{(C≡C)nC≡CSiMe3}(bpy)(η-C7H7)] (n = 1, 2; bpy = 2,2′-bipyridine) and [Mo{(C≡C)nC≡CR}(dppe)(η-C7H7)] (n = 1, R = H, SiMe3; n = 2, R = SiMe3; dppe = Ph2PCH2CH2PPh2), have been prepared and structurally characterized. The redox chemistry of these complexes has been investigated by cyclic voltammetry, and the 17-electron radical cations resulting from one-electron oxidation have been characterized by spectroelectrochemical IR and UV–visible methods and EPR spectroscopy. DFT calculations on the H-terminated model complexes [Mo{(C≡C)nC≡CH}(L2)(η-C7H7)]z+ (L2 = bpy, dppe) reveal a largely metal-centered HOMO (z = 0) with a modest increase in carbon chain character with increasing chain length. Spin density calculations for the 17-electron radical cations (z = 1) show large coefficients of spin density at the metal center, consistent with the remarkably high stability of the experimental complexes. However, both DFT theoretical and exper...

Synthesis, Redox Chemistry, and Electronic Structure of the Alkynyl Cyclopentadienyl Molybdenum Complexes [Mo(C≡CR)(CO)(L2)Cp′]n+ (n = 0 or 1; R = Ph or C6H4-4-Me, L2 = Ph2PCH2CH2PPh2 or 2PMe3, Cp′ = Cp or Cp*)

Two series of bis-phosphine-substituted cyclopentadienyl molybdenum alkynyl complexes, [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] (R = Ph or C6H4-4-Me, dppe = Ph2PCH2CH2PPh2, Cp′ = Cp or Cp*), have been prepared and structurally characterized. One-electron oxidation to the 17-electron radical cations has been investigated by cyclic voltammetry and, for selected Cp* derivatives, by spectroelectrochemical IR and UV–visible methods. Through a combination of experimental measurements (IR and EPR spectroscopy) and DFT-based calculations some important differences between the two series of complexes [Mo(C≡CR)(CO)(dppe)Cp′] and trans-[Mo(C≡CR)(CO)(PMe3)2Cp′] have been established. In particular, the change in molecular geometry leads to enhanced alkynyl character in the HOMO of [Mo(C≡CR)(CO)(dppe)Cp′] when compared with the largely metal-centered HOMO of trans-[Mo(C≡CR)(CO)(PMe3)2Cp′].

Anodic Reaction of Co(η5-C5H5)(CO)(PPh3): An Oxidatively Induced Ligand Exchange Involving a 17 e−/18 e− Redox Pair

Unlike a number of other monocarbonyl-substituted complexes CoCp(CO)L (Cp = (η5-C5H5)), chemical oxidation of the L = triphenylphosphine derivative CoCp(CO)(PPh3), 1, is known to give, in the absence of added PPh3, the disubstituted phosphine complex [CoCp(PPh3)2]+ rather than the simple 17-electron radical cation 1+. Electrochemistry of 1 in CH2Cl2/[NBu4][B(C6F5)4] (E1/2(1/1+) = −0.38 V vs ferrocene) shows that the favored anodic products depend on the concentration of 1. At low concentrations (e.g., 10−4 M) and on the cyclic voltammetry time scale, the radical cation 1+ dominates, but at higher concentrations and longer reaction times, a quantitative mixture of CoCp(CO)2 and [CoCp(PPh3)2]+ is produced in an overall “half-electron” process. On the basis of cyclic voltammetry, chronoamperometry, bulk electrolysis, and IR spectroelectrochemistry, a “radical−substrate” mechanism is proposed involving the reaction of 1+ with 1 to give transient [Co2Cp2(CO)2(PPh3)2]+. This putative dimer radical cation interm...

Spectroscopic Properties and Electronic Structure of the Cycloheptatrienyl Molybdenum Alkynyl Complexes [Mo(C≡CR)(Ph2PCH2CH2PPh2)(η-C7H7)]n+(n= 0 or 1; R =But, Fc, CO2Me, or C6H4-4-X, X = NH2, OMe, Me, H, CHO, CO2Me)

A series of molybdenum alkynyl complexes [Mo(C≡CR)(dppe)(η-C7H7)] featuring a range of alkynyl substituents R with varying electron-donating and -withdrawing properties have been prepared. Oxidation of representative members of the series to the corresponding 17-electron radical cations has been achieved through both chemical oxidation and in situ spectroelectrochemical methods. The largely metal-centered character of the HOMO in this class of compounds has been established through a combination of experimental measurements (IR, UV−vis−NIR, EPR spectroscopies) and DFT-based calculations and rationalized in terms of the stabilization of the metal dxy, dyz, dxz, and dx2-y2 through π- and δ-interactions with the C7H7 ring and concomitant destablization of the dz2 orbital.

Reactivity of Electrochemically Generated Rhenium (II) Tricarbonyl α-Diimine Complexes: A Reinvestigation of the Oxidation of Luminescent Re(CO)3(α-Diimine)Cl and Related Compounds

The oxidative electrochemistry of luminescent rhenium (I) complexes of the type Re(CO) 3(LL)Cl, 1, and Re(CO) 3(LL)Br, 2, where LL is an alpha-diimine, was re-examined in acetonitrile. These compounds undergo metal-based one-electron oxidations, the products of which undergo rapid chemical reaction. Cyclic voltammetry results imply that the electrogenerated rhenium (II) species 1 ( + ) and 2 ( + ) disproportionate, yielding [Re(CO) 3(LL)(CH 3CN)] (+), 7, and additional products. Double potential step chronocoulometry experiments confirm that 1 ( + ) and 2 ( + ) react via second-order processes and, furthermore, indicate that the rate of disproportionation is influenced by the basicity and steric requirements of the alpha-diimine ligands. The simultaneous generation of rhenium (I) and (III) carbonyl products was detected upon the bulk oxidation of 1 using infrared spectroelectrochemistry. The rhenium (III) products are assigned as [Re(CO) 3(LL)Cl 2] (+), 5; an inner-sphere electron-transfer mechanism of the disproportionation is proposed on the basis of the apparent chloride transfer. Chemically irreversible two-electron reduction of 5 yields 1 and Cl (-). No direct spectroscopic evidence was obtained for the generation of rhenium (III) tricarbonyl bromide disproportionation products, [Re(CO) 3(LL)Br 2] (+), 6; this is attributed to their relatively rapid decomposition to 7 and dibromine. In addition, the 17-electron radical cations, 7 ( + ), were successfully characterized using infrared spectroelectrochemistry.

Reactivity of 17- and 19-electron organometallic complexes.Formation of bent sandwich 19-electron radical cation complexes of osmium and ruthenium

Redox behavior of indenyl sandwich complexes of general formula (η 5-C 9H 7)ML (M = Ru and L = η 5- C 9H 7 (bdI), η 5-C 5H 5 ( II), η 5-C 5Me 5 ( III); M = Os, L = η 5-C 9H 7 ( IV)) has been studied by means of cyclic voltammetry at the Pt-electrode at −85–20°C in THF, MeCN and CH 2 Cl 2. The title complexes have been found to undergo reversible one-electron oxidation to corresponding radical cations, whose stability and reactivity depend on the nature of both a metal and the second aromatic π-ligand L and nucleophilic properties of the solvent. Fast reversible interaction of the electrogenerated 17-electron radical cations with nucleophiles yields bent sandwich 19-electron radical cations, [(η 5-C 9H 7)M(Nu)L] +.(Nu = Cl −, MeCN, THF), the latter undergo one-electron oxidation to corresponding 18-electron [(η 5-C 9H 7)M(Nu)L] 2+ dications.

Reactivity of 17- and 19-electron organometallic complexes. Formation of bent sandwich 19-electron radical cation complexes of ruthenium and osmium

The redox behavior of sandwich indenyl complexes of the general formula (η5-C9H7)ML (M=Ru and L=η5-C9H7 (1), η5-C5H5 (2), η5-C5Me5 (3); M=Os, L=η5-C9H7 (4)) has been studied in THF, MeCN, and CH2Cl2 by cyclic voltammetry and controlled potential electrolysis on a Pt electrode in the −85 to +20 °C temperature range. The title complexes have been found to undergo reversible one-electron oxidation to the corresponding radical cations, whose stabilities and reactivities depend on the nature of both the metal and °-ligands and of the nucleophilic properties of the solvent. The fast interaction of the electrogenerated 17-electron radical cations with nucleophiles yields bent sandwich 19-electron radical cations, [(η5-C9H7)M(L)(Nu)]+ (Nu = Cl−, MeCN, or THF), the latter undergoing one-electron oxidation to the corresponding [(η5-C9H7)M(L)(Nu)]2+ dications. In the case of Nu=THF, the reaction of the electrogenerated 17-electron radical cations with nucleophiles appears to be reversible. Radical cations [(η5-C9H7)2M]+· (M=Ru, Os) have been characterized by ESR spectra.

Characterization of the 17-Electron Radical Cation [CpCo(1,5-COD)]+ by ESR Spectroscopy

Characterization of the 17-Electron Radical Cation [CpCo(1,5-COD)]+ by ESR Spectroscopy

Redox properties of rhodium diene-cyclopentadienyl complexes

The electrochemical behavior of rhodium sandwich complexes containing η4-pentamethylcyclopentadiene or tetramethylfulvene fragments has been studied by cyclic voltammetry. The complexes undergo one-electron oxidation to give unstable 17-electron radical cations which are converted into rhodocenium salts as a result of elimination or uptake of hydrogen or C-C bond cleavage.

Chemical and electrochemical oxidation of CpRe(PAr3)2H2 complexes to give stable 17-electron radical cations. Disproportionation to diamagnetic species via electron-transfer catalysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemical and electrochemical oxidation of CpRe(PAr3)2H2 complexes to give stable 17-electron radical cations. Disproportionation to diamagnetic species via electron-transfer catalysisMichael R. Detty and William D. JonesCite this: J. Am. Chem. Soc. 1987, 109, 19, 5666–5673Publication Date (Print):September 1, 1987Publication History Published online1 May 2002Published inissue 1 September 1987https://doi.org/10.1021/ja00253a017RIGHTS & PERMISSIONSArticle Views255Altmetric-Citations25LEARN 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 (1)»Supporting Information Supporting Information Get e-Alerts

Ligand exchange of metal carbonyls by chain mechanisms. Electrochemical kinetics of electron transfer catalysis

The metal carbonyl derivatives LM(CO) n of manganese, rhenium, molybdenum and tungsten undergo facile ligand substitution by an electrode-mediated process. Phosphine, pyridine and isocyanaide substitutions are shown to be chain reactions by coulometric analysis and by cyclic voltammetry of the metal carbonyl solutions containing the added nucleophiles L . Reversible electrochemical parameters can be obtained for both LM(CO) n and the substitution product L M(CO) n . These allow the digital simulation of the cyclic voltammograms by Feldberg's method, which provides a detailed analysis of the kinetics of the electrocatalytic mechanism for ligand substitution. Generally, the radical cation LM(CO) n + produced initially at the anode undergoes rapid exchange with L to afford the cationic substituted species L M(CO) n +. This step is followed by electron transfer with the reactant LM(CO) n to yield the substitution product L M(CO) n and regenerate the radical cation LM(CO) n +, which completes the chain propagation sequence. Multiple repetition of this cycle is indicated by the high current efficiencies which are obtainable. The second order rate constants for the ligand exchange of the 17-electron radical cations LM(CO) n + with added L are evaluated, and found to be more than 10 6 times larger than that for the neutral, diamagnetic precursor LM(CO) n . The radical cations L M(CO) n + also react readily with phosphine and alkyl isocyanide nucleophiles, leading to a characteristic distortion of the CV waves. Digital simulation of such cyclic voltammograms allows the kinetics of these processes, particularly the redox catalysis in the oxidation of phosphines by LM(CO) n +, to be evaluated quantitatively. The enhanced reactivity of the 17-electron radical cations LM(CO) n + is discussed in relationship to recent reports of the substitution lability in other 17- and 19-electron metal carbonyls.