Oleg V. Gusev

Electrochemical generation of 19- and 20-electron rhodocenium complexes and their properties

Abstract The electrochemical reduction of the rhodocenium salts [Rh(η 5 -C 5 Me 5 )(η 5 -L)] + PF 6 − ( 2 + , L  C 5 H 5 ; 3 + L  C 5 Me 5 ; 4 + L  C 9 H 7 ) has been studied by cyclic voltammetry. All three complexes ( 2 + - 4 + ) are reduced in two one-electron processes, first to the 19-electron radicals ( 2 - 4 ) and then to the 20-electron anions ( 2 − - 4 − ). When complex 2 + was reduced in bulk (NaHg in THF) the dinuclear complex, [(η 5 -C 5 H 5 )Rh(μ-η 4 : η 4 -C 5 Me 5 -C 5 H 5 )Rh(η 5 -C 5 Me 5 )] ( 6a ), obtained by dimerization of 2 , was isolated as sole product. Analogous reduction of 3 + gave the η 4 -pentamethylcyclopentadiene complex, [Rh(η 5 -C 5 Me 5 )(η 4 -C 5 Me 5 H)] ( 7 ). Reduction of 4 + leads to formation of a stable radical 4 .

Cp*Ru(II) and Cp*Ru(IV)-catalyzed reactions of CHX with vinyl C–H bonds: competition between double bond homologation and olefin cyclopropanation by alkyl diazoacetate

When diazoesters are used as carbene precursors, new Ru(II) and Ru(IV) complexes bearing various substitutents tethered ligands mediate the formal carbene insertion into C–H vinyl bonds of (substituted) styrenes to yield mostly E- and Z-styrylacetic esters (e.g. 4-phenylbut-3-enoates with styrene). This rarely observed reaction competes with the cyclopropanation of the double bond. The influence of steric and electronic factors on the two competitive reactions is reported. The observation that the most efficient C–H insertion catalysts also promote the ROMP of norbornene lend support to the formation of ruthenacyclobutanes as reaction intermediates.

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.

Synthesis of cationic allyl- and dienecarbonyl complexes of group VI-VIII metals in the presence of strong protonic acid

Abstract Cationic allylcarbonyl complexes of Cr, Mo, W, Mn, Re, Fe, Co, Rh and Ir are synthesized by reaction of a carbonyl-containing compound with allyl alcohol or conjugated diene in the presence of strong protonic acid. This reaction is promoted by an increase in basicity of the initial complex and an increae in acidity of the medium; the nature of the organic substrate is also important for synthesis of this type of carbonyl complex. Cationic diene complexes have been formed by the action of dienes and acid on compounds with a metal-metal bond or on neutral allyl complexes.

Synthesis of η5-1,2,3,4,5-pentamethylcyclopentadienyl-platinum complexes☆

Reaction of K2PtCl4 with pentamethylcyclopentadiene gave the exo-H isomer (1b, 25%) as well as the endo-H isomer (1a, 75%) of [Pt(η4-C5Me5H)Cl2]. The mixture reacted with AgBF4 in acetone at −78°C to give the mixed endo-H, exo-H isomeric dication solvate complexes [Pt(η4-C5Me5H)(acetone)x]2+(BF4−)2 (2a,b), which decompose at room temperature to give [Pt(η4-C5Me5H)(η5-C5Me5)]+BF4− (3). The same reaction of 1a,b in the presence of dienes (pentamethylcyclopentadiene, cyclopentadiene, 1,3-cyclohexadiene, and 1,5-cyclooctadiene) occurs with spontaneous deprotonation to give the monocationic complexes, 3, [Pt(η4-C5Me5H)(η5-C5Me5)]+BF4− (4a,b), [Pt(η4-C6H8)(η5-C5Me 5)]+BF4− (5), and [Pt(η4-C8H12)(η5-C5Me5)]+BF4− (6 ), respectively, in high yield. The products from the reaction depend on the ability of the coordinated diene to undergo deprotonation in an intermediate, in the order, η4-1,3-cyclohexadiene ∼η4-1,5-cyclooctadiene < η4-endo-pentamethylcyclopentadiene < η4-exo-pentamethylcy- clopentadiene < η4-cyclopentadiene. The solvent complexes [M(η5-C5Me5)(acetone)3]2+(BF4−)2 (M  Rh, Ir) react with C5Me5H to give decamethyl-rhodocenium and -iridocenium salts.

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+.

Reduction of iridocenium salts [Ir(η5-C5Me5)(η5-L)]+ (L = C5H5, C5Me5, C9H7); ligand-to-ligand dimerisation induced by electron transfer

Redox properties of iridium complexes [Ir(η5-C5Me5)(η5-L)]+ (1+, L = C5H5; 2+, L = C5Me5; 3+, L = C9H7) were studied by cyclic voltammetry (CV). All three complexes can be reduced to 19-electron radicals 1–3. The stability and reactivity of these radicals depend on the electronic and steric properties of the ligands. The mixture of dimers [(η5-C5Me5)Ir(μ-η4:η4-C5H5C5Me5)Ir(η5-C5H5)] (4a) and [(η5-C5H5)Ir(μ-η4:η4-C5Me5C5Me5)Ir(η5-C5H5)] (4b) was formed as a result of reduction of 1+ with NaHg in THF. Both chemical and electrochemical reduction of 2+ gave the dimer [(η5-C5Me5)Ir(μ-η4:η4-C5Me5C5Me5)Ir(η5-C5Me5)] (5) in low yield. Reduction of 3+ gave the tetranuclear complex [(η5-C5Me5)Ir(μ-η4:η5-C9H7) Ir(μ-η4:η4-C5Me5C5Me5) Ir(μ-η5:η4-C9H7)Ir(η5-C5Me5)] (6).

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 ).

Investigation of the stereochemistry of transition metal allyl cationic complexes

Abstract Stereochemistry of transition metal-allyl cationic complexes synthesized by reaction of the corresponding metal carbonyls with allyl alcohol or a conjugated diene in the presence of a strong protonic acid has been investigated by means of NMR and IR spectroscopy. The number of isomers, as well as the position of substituents in the allyl ligands of complexes of the group 6 and 7 metals and iron, is determined by the formation of η2-diene complexes in the transoid conformation in which the diene is coordinated via a substituted or non-substituted double bond. The protonation products formed in the initial stage of the reactions of CpM(CO)2 (where M = Co, Rh, Ir) with acids lead to the mixtures of syn- and anti-crotyl isomers in their subsequent reactions with butadiene, the anti-isomers being transformed into syn-complexes on heating. The study of conformational isomerism of the half-sandwich allyl complexes has shown that the Cr, Mo, W, Mn and Re compounds of [LM(CO)2(allyl)]+ BF4− (where L = arene, cyclopentadienyl) exist in the form of equilibrium mixtures of exo- and endo-conformers, the endo-conformer prevailing in the case of Mo, W and Re; for [CpM(CO)(allyl)]+ BF4− (where M = Co, Rh, Ir), disappearance of the endo-isomer on heating has been observed.

Synthesis and reduction of trifluoromethyl-substituted arenecyclopentadienylruthenium sandwiches [Ru(η5-C5Me4CF3)(η6-C6R6)]+ (R=H, Me) and [Ru(η5-C5Me5)(η6-C6H5CF3)]+

Abstract Dimer [Ru 2 ( η 5 -C 5 Me 4 CF 3 ) 2 Cl 2 ( μ -Cl) 2 ] ( 1 ) has been prepared by reaction of RuCl 3 ·(H 2 O) 3 with 1,2,3,4-tetramethyl-5-(trifluoromethyl)cyclopentadiene in ethanol under reflux. Cationic arenecyclopentadienyl complexes [Ru( η 5 -C 5 Me 4 CF 3 )( η 6 -arene)] + PF 6 − ( 2 + , arene=C 6 H 6 ; 3 + , arene=C 6 Me 6 ) and [Ru( η 5 -C 5 Me 5 )( η 6 -C 6 H 5 CF 3 )] + BF 4 − ( 4 + ) were obtained by refluxing [Ru 2 ( η 5 -C 5 Me 4 CF 3 ) 2 Cl 2 ( μ -Cl) 2 ] ( 1 ) or [Ru 2 ( η 5 -C 5 Me 5 ) 2 Cl 2 ( μ -Cl) 2 ] with corresponding arenes in alcohol. The redox properties of 2 + – 4 + were studied by cyclic voltammetry (CV). All three complexes 2 + – 4 + are reduced irreversibly in one-electron process. The values of reduction peak potentials for 2 + – 3 + are less negative than those found for η 5 -C 5 Me 5 analogues. The reduction of 2 + and 3 + with sodium amalgam in tetrahydrofuran led to the formation of dimers [Ru 2 ( η 5 -C 5 Me 4 CF 3 ) 2 ( μ – η 5 : η 5 -C 6 H 6 C 6 H 6 )] ( 5 ) and [Ru 2 ( η 5 -C 5 Me 4 CF 3 ) 2 ( μ – η 5 : η 5 -C 6 Me 6 C 6 Me 6 )] ( 6 ) respectively. The reduction of 4 + gave a non-identifiable mixture of neutral products.