Mikhail G. Peterleitner

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 .

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+.

Oxidative dehydrodimerization of manganese phenylvinylidene complex (η5-C5H5)(CO)2MnCC(H)Ph. X-ray structure of phenyl(trityl)vinylidene complex (η5-C5H5)(CO)2MnCC(CPh3)Ph

Abstract The oxidatively induced dehydrodimerization of the manganese vinylidene complex (η 5 -C 5 H 5 )(CO) 2 MnCC(H)Ph ( I ) to the bis-vinylidene compound (η 5 -C 5 H 5 )(CO) 2 MnCC(Ph)C(Ph)CMn(CO) 2 (η 5 -C 5 H 5 ) ( II ) proceeds via C β H bond homolysis in the radical cation ( I + ) and is thought to involve the formally 16-electron mononuclear σ-phenylethynyl cation [(η 5 -C 5 H 5 )(CO) 2 MnCCPh] + ( III ) and the bis-carbyne dication [(η 5 -C 5 H 5 )(CO) 2 MnCC(Ph)C(Ph)CMn(CO) 2 (η 5 -C 5 H 5 )] 2+ ( II 2+ ) as the key sequential intermediates. Compound II 2+ was characterized by IR and CV. The reduction of II 2+ with (C 6 H 6 ) 2 Cr gave II in an 80% yield. Compound II can be prepared more conveniently by treating I with (C 5 H 5 ) 2 FeBF 4 in the presence of Et 3 N. The interaction of I with Ph 3 CPF 6 yields the trityl(phenyl)vinylidene complex (η 5 -C 5 H 5 )(CO) 2 MnCC(CPh 3 )Ph ( IV ) as a result of the electrophilic attack of the trityl cation on C β followed by the loss of a proton. The structure of IV was established by an X-ray structural analysis.

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 ).

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.

Electrochemical substitution of a carbonyl group by a phosphorus ligand in arenechromium tricarbonyl complexes

Abstract Electrochemical oxidation of (η-1,3,5-Me3C6H3)Cr(CO)3 in the presence of P(OEt)3 with subsequent electrochemical reduction results in the formation of a (η-1,3,5-Me3C6H3)Cr(CO)2[P(OEt)3] and (η-1,3,5-Me3C6H3)Cr(CO)[P(OEt)3]2 mixture. Under similar conditions (η6-arene)Cr(CO)3, where arene = 3,5-Me2C6H3(CH2)2OPR2 (R = OEt,OPh,F), yields the corresponding arenephosphite chelate complexes.

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

Electrochemical reductive carbon-to-carbon coupling of σ-ethynyl complexes of transition metals

The electrochemical properties of σ-ethynyl complexes of chromium subgroup metals were studied by cyclic voltammetry and preparative-scale electrolysis. The redox cycle of C5H5(CO)3CrC=CPh was shown to give the bis-carbyne complex (η5-C5H5)(CO)2Cr≡C-C(Ph)=C(Ph)-C-Cr(CO)2(η5-C5H5) formedvia the reductive Cβ−Cβ coupling of ethynyl moieties. The influence of the nature of the metal atom and the ligand environment on the course of this reaction was considered.