S. V. Kukharenko

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

Abstract Redox behavior of indenyl sandwich complexes of general formula (η 5 -C 9 H 7 )ML (M = Ru and L = η 5 - C 9 H 7 (bdI), η 5 -C 5 H 5 ( II ), η 5 -C 5 Me 5 ( III ); M = Os, L = η 5 -C 9 H 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 9 H 7 )M(Nu)L] +. (Nu = Cl − , MeCN, THF), the latter undergo one-electron oxidation to corresponding 18-electron [(η 5 -C 9 H 7 )M(Nu)L] 2+ dications.

Redox-induced ?5 ? ?3 haptotropy of the fluorenyl ligand in 9-substituted ?5-fluorenylmanganesetricarbonyl complexes

It has been shown by cyclic voltammetry in THF within the −90 to 40 °C temperature range that fluorenyl (η5-9-R-C13H8)Mn(CO)3 complexes (R=But (3) and Ph (4)) undergo two-electron reduction to form allyl type [(η3-9-R-C13H8)Mn(CO)3]2− dianions as final products. At low temperatures complexes3 and4 are reduced in two one-electron steps according to the EEC-scheme. The first step is reversible and corresponds to the formation of 19ē-radical anions 3−. and 4−.. TheE0 values for redox pairs30/−. and40/−. are −1.88 and −1.73 V, respectively. The further reduction of radical anions3−. and4−. at more negative potentials is accompanied by fast η5 → η3 haptocoordination of the fluorenyl ligand to form 18ē-dianions [(η3-9-R-C13H8)Mn(CO)3]2−. These dianions obtained by the reduction of complexes3 and4 by the radical anion of pyrene are stable at −80 °C and are characterized by their IR spectra. At room temperature the η5 ⇔ η3 hapticity change is a fast and reversible process occurring at the step of 19ē-radical anions3−. and4−. and leading to the electron deficient 17ē-species [(η3-9-R-C13H8)Mn(CO)3]−., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(η3-9-R-C13H8)Mn(CO)3]2− at room temperature in one reversible two-electron step according to the ECE-scheme. Reactivities of 19e−-species of the isomeric η5- and η6-fluorenylmanganesetricarbonyl complexes are compared.

Oxidation of isomeric η6- and η5-fluorenylchromiumtricarbonyl anions

The oxidation of the carbon-centered [(η6-C13H9)Cr(CO)3]− anion (1−) results in formation of (μ-η6:η6-9,9′-bifluorenyl)bis-chromiumtricarbonyl (3) due to coupling of the intermediate carbon-centered radical (1.). The oxidation of the metal-centered anion [(η5-C13H9)Cr(CO)3]− (2−), which is isomeric to the 1− anion, gives an equilibrium mixture of the chromium-centered radical {(η5-C13H9)Cr(CO)3}. (2.) and its dimer [(η5-C13H9)Cr(CO)3]2 (6). Radical2. readily reacts with MeI and the solvent (THF); the resulting derivatives, (η5-C13H9)Cr(CO)3R (R=Me (10); R=H (7)), undergo fast ricochet inter-ring η5→η6 rearrangements into (η6-9R-C13H9)Cr(CO)3 (R=CH3 (9); R=H (4)).

Electron-transfer induced haptotropic isomerization of fluorenylmanganesetricarbonyl complexes: electrocatalytic and chain mechanisms

The electrochemical reduction of (η6-C13H9)Mn(CO)3 (1, where C13H9—fluorenyl) has been studied in THF by cyclic voltammetry and preparative controlled potential electrolysis. One-electron reduction of1 to the corresponding 19-electron radical anion1.− is accompanied by the haptotropic isomerization of the latter to the radical anion (η5-C13H9)Mn(CO)3.− (2.−), which is oxidized at the electrode to neutral complex2. Electron-transfer induced isomerization1 →2 is an electrocatalytic process with current efficiency of 600%, which can be also promoted by catalytic amounts (≤20%) of the chemical reducing agents (benzophenone radical anion or sodium amalgam). If the reaction is chemically induced, the radical anion2.− is oxidized by initial complex1; as a result the electron-transfer induced isomerization1 →2 proceeds by a chain mechanism. The influence of the electronic state (18e−/19e−) of η6- and η5-fluorenyl complexes on the position of the equilibrium of the intra-ring haptotropic isomerization reaction is discussed.

Synthesis of dibenzocymantrene derivatives (eta(5)-9-RC(13)H(8))Mn(CO)(3) (R=Ph and Bu(t)). Crystal structure of (eta(5)-9-PhC(13)H(8))Mn(CO)(3)

Abstractη5-Fluorenyl complexes of manganese (η5-9-RC13H8)Mn(CO)3, where R = Ph (1) and But (2), have been prepared and characterized for the first time. The structure of complex1 has been established by X-ray structural analysis.

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.

Voltammetry of carbocations stabilized by coordination with tetrahedral molybdenum- and tungsten-carbon clusters. [Cp2M2(CO)4-μ-η2:η3-(HCCCR1R2)]+BF4−(M = Mo, W; R1, R2 = H, Me, and Pri) complexes

The electrochemical reduction of the carbocationic complexes [Cp2M2(CO)4-μ-η2:η3(HCCCR1R2)]+BF4−, where M/R1, R2 = Mo/H, H (1+), Mo/H, Me (2+), Mo/Me, Me (3+), Mo/H, Pri (4+), has been studied by polarography and cyclic voltammetry on a Hg-electrode in THF solution. It has been suggested that carbocationic center-directed reversible two-electron reduction of1+−4+ takes place according to an ECE-mechanism and results in the carbanionic complexes [Cp2M2(CO)4-μ-η2:η3-(HCCCR1R2)] (1−−4−) as final productsvia carbon-centered radicals as intermediates. Anions1−-4− are capable of irreversible two-electron reduction at more negative potentials or protonation resulting in their transformation into the corresponding acetylene complexes [Cp2M2(CO)4(HCCCHR1R2)], which are also capable of irreversible two-electron reduction. Anions1−−4− and their protonated forms are reduced with cleavage of the Mo-Mo bond. The reduction pathways of complexes1+,2+, and4+ with C-H bonds at the carbon atom of the carbocationic center are different on a Pt-electrode. It is suggested that this difference is due to the abstraction of a H-atom from the intermediate radical species by platinum.

Inter-ring η6⇌η5 haptotropic rearrangements of 18ē and 19ē (η5-pentamethylcyclopentadienyl)(η6-9-methylfluorenyl)iron complexes

New cationic complexes [(η6-C13H10)Fe(η5-Cp*)]PF6 and [(η6-9-CH3-C13H9)Fe(η5-Cp*)]PF6 were obtained by the reaction of Cp*Fe(CO)2Br with fluorene and 9-methylfluorene, respectively. Deprotonation of these complexes byt-BuOK in THF affords zwitter-ionic compounds (η6-C13H9)Fe(η5-Cp*) and (η6-9-CH3-C13H8)Fe(η5-Cp*) (A). WhenA is heated in nonane at 150 °C it undergoes η6⇌η5 inter-ring rearrangement with the formation of hexamethyldibenzoferrocene (B). The electrochemical behavior ofA andB was studied by cyclic voltammetry. One-electron reduction ofA andB to the corresponding radical anions induces inter-ring haptotropic rearrangementA.−⇌ηB.−. The equilibrium in the 19ē state is shifted to the η6-isomeric radical anionA.−, while in the 18ē precursors, it shifts to the η5-isomerB.

Electron-transfer induced change of direction of interannular haptotropic isomerization of fluorenyltricarbonylchromium anions

It has been shown by cyclic voltammetry in a THF medium in the temperature range from −70 °C to +20 °C that one-electron electrochemical reduction of (η6-C13H10)Cr(CO)3 (1) to the corresponding 19-electron anion radical (1−) is accompanied by splitting off of a H atom to form the 18-electron carbon-centered anion (η6-C13H9)Cr(CO)3 (−2), which at room temperature undergoes intramolecular haptotropic isomerization to the metal-centered (η5-C13H9)Cr(CO)3− (−3) anion. The reversible one-electron reduction of3− to the corresponding 19-electron radical dianion32.− induces η5→ η6 interannular isomerization. In contrast to the equilibrium shift to the η5-isomer in 18-electron complexes 2 and 3, in their 19-electron analogs the equilibrium is shifted to the η6-isomer.

Reduction of acetylene by zinc amalgam catalyzed by molybdenum cyclopentadienylcarbonyl complexes

ConclusionsThe products of the reduction of Cp2Mo2(CO)6, Cp2Mo2(CO)4, and Cp2Mo2(CO)4(C2H2) are mononuclear CpMo(CO)3-xLx anions (x=0-2). These anions catalyze the reduction of acetylene by zinc amalgam with a quantitative yield of ethane and ethylene relative to amalgam consumed