Svetlana M. Peregudova

Reduction of ruthenium arenecyclopentadienyl complexes reactions induced by electron transfer

Abstract Ruthenium arenecyclopentadienyl complexes [Ru(η5-C5R5)(η6-arene)]+ (1, R = H, arene = C6H6; 2, R = Me, arene = C6H6; 3, R = H; arene = C6H3Me3; 4, R = Me, arene = C6H3Me3; 5, R = H, arene = C6Me6; 6, R = Me, arene = C6Me6; 7, R = Me, arene = C10H8) and [Ru(η5-C9H7)(η6-C6H6)]+ (8) have been studied by cyclic voltammetry; the complexes are capable of both reduction and oxidation. The reduction peak potential values for 1–6 become more negative by about 31 mV for each Me-group at the arene ring and 61 mV for each Me-group at the cyclopentadienyl ring. Reduction of naphthalene complex 7 proceeds by two one-electron processes; the first one is reversible and the second one is irreversible. Two reversible reduction peaks were observed for indenyl complex 8. The following reactions occur on reduction of benzene complexes 1, 2 and 8 with sodium amalgam in tetrahydrofuran (THF): hydrogen atom addition to and decoordination of benzene ligand as well as dimerization of ligand-to-ligand type. Mesitylene compounds 3 and 4 form dimers [(η5-C5R5)Ru(μ-η5:η5-Me3H3C6C6H3Me3)Ru(η5-C5R5)] (14, R = H; 15, R = Me) in both chemical and electrochemical reduction processes. Reaction of [Ru(η5-C5H5)(η6-C6Me6)]+ (5) with sodium amalgam in THF leads to the dimer [(η5-C5H5)Ru(μ-η5:η5-Me6C6C6Me6)Ru(η5-C5H5)] (16) as the major product; products of H-atom addition to both hexamethylbenzene and cyclopentadienyl ligands, [Ru(η5-C5H5)(η5-C6Me6H)] (17) and [Ru(η4-C5H6)(η6-C6Me6)] (18), are also formed in low yields. In the case of permethylated 6 only H-atom addition to hexamethylbenzene was observed and the mixture of endo-H and exo-H isomers [Ru(η5-C5H5)(η5-C6Me6H)] (19a,b) was isolated. Reduction of 7 gives [Ru(η5-C5Me5)(η5-C10H9)] (20). The modes of reaction of 19-electron radicals formed by reduction of 1–8 depend on electronic and steric properties of ligands.

Redox-induced activation of CH bonds in 1,2,3,4,5-pentamethylcyclopentadiene platinum complexes

The electrochemical behaviour of the platinum complexes [Pt(η4C5Me5H)(η5C5H5)] +BF4− (1+) and [Pt(η4-diene)(η5C5Me5)]+BF4− (diene = C5Me5H (2+) or 1,3-cyclohexadiene; (3+) 1,5-cyclooctadiene(4+)) has been studied by cyclic voltammetry. The complexes 1+−4+ are capable of both oxidation and reduction. The bulk electrolysis of 2+ at the potential of its reduction gives a mixture of twe neutral isomeric complexes 5a and 5b. These are assigned structures with η3-allylic and of σ, π-bonding methylene cyclopentenyl Me3C5H(CH2) ligand. This is the proposed result from methyl CH bond breakage in pentamethylcyclopentadiene ligand of an intermediate 19-electron complex [Pt(η4C5Me5H) (η5C5Me5)]. (2.). The same mixture of isomers 5a and 5b forms in interaction of 2+ and tBuOK in tetrahydrofuran. The preparative electrochemical oxidation of 2+ proceeds with CH bond scission at the pentamethylcyclopentadiene sp3-hydridized carbon in an intermediate 17-electron dication radical [Pt(η4C5Me5H)(η5C5Me5)].2+ (2.2+) to give decamethylplatinacene dication [Pt(η5C5Me5)2]2+(BF4−)2 (72+). The one-electron reduction of 72+ regenerates 2+.

Synthesis of palladium cyclopentadienyl complexes. Decamethylpalladocene dication [Pd(ν5-C5Me5)]2+

Abstract The palladium pentamethylcyclopentadiene complex [Pd( ν 4 -C 5 Me 5 H)Cl 2 ] ( 1 ) reacted with AgBF 4 , in the presence of 1,5-cyclooctadiene or pentamethylcyclopentadiene, to give the cationic compounds [Pd( ν 4 -diene)(C 5 Me 5 )] + BF 4 − (diene = C 8 H 12 ( 2 ) or C 5 Me 5 H( 3 )). The cyclopentadienyl complex [Pd( ν 4 -C 5 Me 5 H 5 )] + BF 4 − ( 4 ) was prepared by the action of a mixture of CpTl and TlBF 4 on 1 in acetone solution. Cyclic voltammetry showed that all three complexes 2–4 can be oxidized and reduced. The oxidation of 3 with (NH 4 ) 2 [Ce(NO 3 ) 6 ] leads to the first palladocene; the decamethylpalladocene dication [Pd( ν 5 )-C 5 Me 5 ) 2 ] 2+ (BF 4 − ) 2 ( 5 ).

Exohedral mono- and bimetallic hydride complexes of rhodium and iridium with C60 and C70: syntheses and electrochemical properties

Abstract Syntheses of mono- and bimetallic hydride complexes of rhodium and iridium with fullerenes C 60 and C 70 are described and the results of their cyclic voltammetry (CV) studies are presented. The metal-containing [HM(CO)(PPh 3 ) 2 ] moiety (M=Rh and Ir) coordinates with high stereo- and regioselectivity to the 1,2 bond of these fullerenes to form the only isomer in both cases. The attachment of the second [HM(CO)(PPh 3 ) 2 ] moiety results in a complex mixture of positional and geometric isomers. Due to a high rate of formation, metallofullerene complexes may be generated in situ in the electrochemical cell. The electrochemical behavior (their redox potentials and stability of the oxidized and reduced forms) of the studied C 60 and C 70 organometallic derivatives with the same metal-containing fragment is identical.

Bis(η5-pentamethylcyclopentadienyl)-and(η5cyclopentadienyl) (η5-pentamethylcyclopentadienyl)-platinium dications: Pt(IV) metallocenes

Abstract Reaction of [Pt2(η5-C5Me5)2(η-Br)3]3+(Br−)3 with C5R5H (R = H,Me) in the presence of AgBF4 gives the first platinocenium dications, [Pt(η5-C5Me5)(η5-C5R5)]2+(BF4− )2. On electrochemical reduction, [pt(η5-C5Me5)2]2+ yields [Pt(η4-C5Me5H)(η2-C5Me5)]+ BF4−. kw]Cyclopentadienyl; Metallocenes; Platinum; Electrochemistry

19-Electron arenecyclopentadienyl complexes of ruthenium

A series of are necyc lope ntadienyl complexes,i. e., [Ru(η5-c5R5)(η6- are ne)]+ (1, R= H, arene = C6H6; 2, R = Me, arme = C6H6; 3, R = H, arctic = C6H3Me3; 4, R = Me, arene = C6H3Me3; 5, R = H, arene = C6Me6; 6, R = Me, arene = C6Me6) was studied by cyclic voltammetry. These compounds are capable of both oxidation and reduction. The reduction potential values depend on the number of methyl groups in the complex. Reduction of benzene complexes I and 2 by sodium amalgam in THF leads to the formation of decomplexation products, the addition of hydrogen to benzene, and dimerization of the benzene ligands. Both chemical and electrochemical reductions of mesitylene complexes3 and4 result in dimeric products [(η5-C5R5)Ru(μ-η5;η5-Me3H3C6H3Me3)Ru(η5-C5R5)] (14, R = H; 15, R = Me). The action of sodium amalgam on compound5 gives products of hydrogen addition to both hexamethylbenzene (17) and cyclopentadienyl (18) ligands along with the major product, the dimer [η5-C5H5)Ru(μ-η5; η5-Me6C6C6Me6)Ru(η5-C5H5)] (16). In contrast to5, its permcthylated analog 6 is only capable of adding hydrogen to the hexamethylbenzene ligand.

Electrochemical synthesis and properties of δ-fluoroacyl and δ-perfluoroalkyl transition metal complexes

The electrochemical synthesis of δ-fluoroacyl complexes [M]-δ-CORf(M=C5H5(CO)3W or (CO)5Mn; Rf=CF3 or C4F9) was performed according to two procedures: (1) the preliminary electrochemical synthesis of [M]− from [M]2 followed by reaction with a fluorine-containing compound and (2) the electrochemical synthesis of [M]− in the presence of a fluorine-containing compound. Trifluoroacetic anhydride was demonstrated to be the best acylating agent in these reactions. The electrochemical properties of the resulting complexes were studied.

Electrochemical oxidation and reduction of rhodium and iridium complexes with fullerenes C60 and C70

The electrochemical behavior of rhodium and iridium complexes with fullerences C60 and C70 was studied by cyclic voltammetry in a THF—toluene mixture. The complexes were found to be capable of oxidation and reduction. It was demonstrated that thein situ generation of metallofullerene complexes in the electrochemical cell by the interaction of C60 and C70 with hydridocarbonylphosphine complexes of rhodium and iridium, HM(CO)(PPh3)3, is possible. The influence of structural factors and the action of CO2 on changes in the redox properties of fullerene complexes was considered.

Electron-transfer induced cleavage and formation of C-H-bonds in 17ē and 19ē platinum complexes

The electrochemical behavior of platinum complexes [Pt(η4-diene)(η5-C5R5)]+BF4− (1+, diene = C5Me5H, R = H;2+, diene = C5Me5H, R = Me;3+, diene = C6H8, R = Me;4+, diene = C8H12, R = Me) was studied by cyclic voltammetry. Complexes1+ and2+ are shown to be capable of both oxidation and reduction. One-electron reduction of2+ gives a mixture of two neutral isomeric complexes5a,b of η3-allylic and σ,π,-olefinic type due to the cleavage of C-H bonds in the methyl groups of the pentamethylcyclopentadiene ligand of 19ē complexes2. The preparative electrochemical oxidation of2+ results in cleavage of the C-H bond at the sp3-hybridized pentamethylcyclopentadiene carbon atom in 17ē dication radical22+ to give the decamethylplatinocene dication [Pt(η5-C5Me5)2]2+(BF4)2 (72+). It is shown that one-electron reduction of72+ and one-electron oxidation of5a,b is accompanied by the formation of C-H bonds to form2+.