Versatility in the mode of coordination {(N), (N,O), (C,N) or (C,N,O)} of [(η-C5H5)Fe{(η-C5H4)-CHN-(C6H4-2OH)}] to palladium(II)

The study of the reactivity of the ferrocenyliminoalcohol [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)}] (1b) with Na₂[PdCl₄] or Pd(OAc)₂ has allowed the isolation and characterization of the heterotrimetallic complexes: trans-[Pd{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)]}₂Cl₂] (2b), [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵-C₅H₅)}{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)]}] (3b) and trans-[Pd{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2O)]}₂] (4b). Ligand 1b acts as a (N) (in 2b) or a (N,O)⁻ (in 4b) ligand; while in 3b the two units of the iminoalcohol exhibit simultaneously different modes of binding {(N) and [C(sp², ferrocene),N,O]²⁻}. The crystal structures of 2b · 3H₂O and 3b · 1/2CHCl₃ are also reported and confirm the mode of binding of the ligand in these compounds. The relative importance of the factors affecting the preferential formation of products (2b-4b) is also discussed. The study of the reactivity of 3b with PPh₃ has enabled the obtention of the cyclopalladated complexes [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵- C₅H₅)}(PPh₃)] (6b) and [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2OH)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (7b), in which 1b behaves as a [C(sp², ferrocene),N,O]²⁻ (in 6b) or [C(sp², ferrocene),N]⁻ (in 7b) ligand. Treatment of 3b with MeO₂C-CC-CO₂Me produces [Pd{[(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵-C₅H₅)}] (8b), that arises from the bis(insertion) of the alkyne into the σ[Pd-C(sp², ferrocene)] bond. The comparison of the results obtained for 1b and [C₆H₅-CHN-(C₆H₄-2OH)] (1a) has allowed to establish the influence of the substituents on the imine carbon on their reactivity in front of palladium(II) as well as on the lability of the Pd-ligands bond. ⁵⁷Fe Mössbauer studies of 2b-4b and 6b provide conclusive evidence of the effect induced by the mode of binding of 1b on the environment of the iron(II).     

Palladacycles bearing pendant benzamidinate ligands as catalysts for the Suzuki and Heck coupling reactions

Three pendant benzamidines [Ph-C(NC₆H₅)-{NH(CH₂)₂NMe₂}] (1), [Ph-C(NC₆H₅)-{NH(CH₂Py)}] (2) and [Ph-C(NC₆H₅)-{NH(o-C₆H₄)(oxazoline)}] (3) are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)₂ in THF give the palladacyclic complexes [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂)₂NMe₂}]Pd(OAc) (4), [Ph-C{-NH(η¹-C₆H₄)}{N (CH₂Py)}]Pd(OAc) (5) and [Ph-C{-NH(η¹-C₆H₄)}{N(o-C₆H₄)(oxazoline)}]Pd(OAc) (6), respectively. Treatment of 4, 5 or 6 with excess of LiCl in chloroform affords [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂)₂NMe₂}]PdCl (7), [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂Py)}]PdCl (8) and [Ph-C{-NH(η¹-C₆H₄)}{N(o-C₆H₄)(oxazoline)}]PdCl (9). The crystal and molecular structures are reported for compounds 1, 3, 5, 6 and 7. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.     

Synthesis of niobocene imido cations: X-ray crystal structure of [Nb(NBu)(η-C5H4SiMe3)2(CNBu)][BPh4]

The reduction of [Nb(NBu^t)(η⁵-C₅H₄SiMe₃)₂Cl] by sodium amalgam followed by oxidation by [Fe(η⁵-C₅H₅)₂][BPh₄] in the presence of CNBu^t gave [Nb(NBu^t)(η⁵-C₅H₄SiMe₃)₂(CNBu^t)][BPh₄] (1). In a similar manner, [Nb(NPh)(η⁵-C₅H₄SiMe₃)₂(CNBu^t)][BPh₄] (2), [Nb(NPh)(η⁵-C₅H₄SiMe₃)₂(CO)][BPh₄] (3) and [Nb(NBu^t){Me₂Si(η⁵-C₅Me₄)(η⁵-C₅H₄)}(CNBu^t)][BPh₄] (4), were prepared. The reduction of [Nb(NBu^t){Me₂Si(η⁵-C₅H₄)₂}Cl] gave, depending on the experimental conditions, either the d¹-d¹ dimer [(Nb{Me₂Si(η⁵-C₅H₄)₂}(μ-NBu^t))₂] (5) or the hydride derivative [Nb(NBu^t){Me₂Si(η⁵-C₅H₄)₂}H] (6). The reaction of 5 with I₂ led to the formation of [Nb(NBu^t){Me₂Si(η⁵-C₅H₄)₂}I] (7). The molecular structure of 1 was determined by single-crystal X-ray diffraction studies.     

McMurry reactions of (η-acetylcyclopentadienyl) cobalt-(η-tetraphenylcyclobutadiene) with benzophenone: ketone couplings and a pinacol/pinacolone rearrangement

The reaction of (η⁴-C₄Ph₄) Co[η⁵-C₅H₄-C(O)Me], 5, with benzophenone under McMurry conditions (TiCl₄/Zn/THF) gives the hetero-coupled product (η⁴-C₄Ph₄)Co[η⁵-C₅H₄-C(Me)CPh₂], 7, together with the dicobalt species: trans-(η⁴-C₄Ph₄)Co[(η⁵-C₅H₄-C(Me)C(Me)-η⁵-C₅H₄₋)] Co(η⁴-C₄Ph₄), 9, and the pinacolone Me[(η⁴-C₄Ph₄)Co(η⁵-C₅H₄)]₂C-C(O)Me, 10. The latter is apparently formed from the pinacol by migration of an (η⁴-C₄Ph₄)Co[(η⁵-C₅H₄) group. Preferential migration of the cobalt sandwich moiety rather than a methyl group is rationalized in terms of a favored transition state involving a metal-stabilized cation. The products 7, 9 and 10, and also the ketone (η⁴-C₄Ph₄)Co[η⁵- C₅H₄-C(O)Et], 6, were all characterized by X-ray crystallography.     

The reactions of some σ-alkynylnickel complexes with 7,7,8,8-tetracyanoquinodimethane

The σ-alkynyl complexes Ni(η⁵-C₅H₅)(PPh₃)-CC-R (1), Ni(η⁵-C₅H₅)(PPh₃)-CC-X-CCH (2) and Ni(η⁵-C₅H₅)(PPh₃)-CC-X-CC-Ni(η⁵-C₅H₅)(PPh₃) (3), reactwith 7,7,8,8-tetracyanoquinodimethane, TCNQ, at 30 °C by insertion of the alkyne CC into a CC(CN)₂ bond to give Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-R (4), from 1, Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-X-CCH (5), from 2, and Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-X-CC-Ni(η⁵-C₅H₅)(PPh₃) (6),and Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}- C{C(CN)₂}-X-C{C(CN)₂}-C{C₆H₄C(CN)₂}-Ni(η⁵-C₅H₅)(PPh₃) (7),from 3 {R = (a) C₆H₅, (b) 4-PhC₆H₄, (c) 4-Me₂NC₆H₄, (d) 1-C₁₀H₇ (1-naphthyl), (e) 2-C₁₀H₇ (2-naphthyl), (f) 9-C₁₄H₉ (9-phenanthryl), (g) 9-C₁₄H₉ (9-anthryl), (h) 3-C₁₆H₉ (3-pyrenyl), (i) 1-C₂₀H₁₁ (1-perylenyl), (j) 2-C₄H₃S (2-thienyl), (k) C₁₀H₉Fe (ferrocenyl = Fc) and (l) H; X = (a) nothing, (b) 1,4-C₆H₄, (c) 1,3-C₆H₄ and (d) 4,4′-C₆H₄-C₆H₄}. The reaction is regiospecificand the other possible insertion product, R-C{C₆H₄C(CN)₂}-C{C(CN)₂}-Ni(η⁵-C₅H₅)(PPh₃) etc., is not formed. Under the same conditions, there is no evidencefor the reaction of TCNQ with the -CCH of 2, PhCCH, 1,4-C₆H₄(CCH)₂ or FcCCH, or for the reaction of more than one CC(CN)₂ of TCNQ with a Ni-alkynyl moiety. Complexes 4-7 are all air-stable, purple solids which have been characterised by elemental analysis and spectroscopy (IR, UV-Vis, ¹H NMR and ¹³C NMR),and by X-ray diffraction for 4a, 4b and 4l. The UV-Vis spectra of 4-7 are very similar. This implies that all contain the same active chromophore which, it is suggested, is Ni-C(5)C₆H₄C(CN)₂ and not R-C(4)C(CN)₂. This isconsistent with the molecular structures of 4a, 4b and 4l which show that the first of these potentially chromophoric fragments is planar or close to it with an in-built potential for delocalisation, whilst in the second the aryl group R is almost orthogonal to the CC(CN)₂ plane. The molecular structures of 4a, 4b and 4l also reveal a short Ni?C(4) separation, indicative of a Ni → C(4) donor-acceptor interaction. The electrochemistry of 4a shows aquasi reversible oxidation at ca. 1 V and complicated reduction processes. It is typical of most 4, but 4l is different in that it shows the same quasi reversible oxidation at ca. 1 V but two reversible reductions at −0.26 and −0.47 V (vs. [Fe(η⁵-C₅Me₅)₂]^+/0 0.0 V).     

SPh functionalized bridging-vinyliminium diiron and diruthenium complexes

The SPh functionalized vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(SPh)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] [R = Xyl, R′ = Me, 2a; R = Me, R′ = Me, 2b; R = 4-C₆H₄OMe, R′ = Me, 2c; R = Xyl, R′ = CH₂OH, 2d; R = Me, R′ = CH₂OH, 2e; Xyl = 2,6-Me₂C₆H₃] are generated in high yields by treatment of the corresponding vinyliminium complexes [Fe₂{μ-η¹:η³-C_γ(R′)C_β(H)C_αN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (1a-e) with NaH in the presence of PhSSPh. Likewise, the diruthenium complex [Ru₂{μ-η¹:η³-C_γ(Me)C_β(SPh)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2f) was obtained from the corresponding vinyliminium complex [Ru₂{μ-η¹:η³-C_γ(Me)C_β(H)C_αN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (1f). The synthesis of 2c is accompanied by the formation, in comparable amounts, of the aminocarbyne complex [Fe₂{μ-CN(Me)(4-C₆H₄OMe)}(SPh)(μ-CO)(CO)(Cp)₂] (3).The molecular structures of 2d, 2e and 3 have been determined by X-ray diffraction studies.     

Study of the reactivity of palladacycles containing [C(sp, ferrocene),N,S] or [C(sp),N,S] terdentate ligands with symmetric alkynes

The study of the reactivity of the cyclopalladated complex [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (1c) with the alkynes R¹-CC-R¹ (with R¹ = CO₂Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO₂C-CC-CO₂Me in refluxing CH₂Cl₂ to give [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (2c), which arises from the monoinsertion of the alkyne into the σ[Pd-C(sp², ferrocene)] bond.However, when the reaction was performed using Ph-CC-Ph or Et-CC-Et no evidence of the insertion of these alkynes into the σ[Pd-C(sp², ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the Tl[BF₄] followed by the removal of the TlCl formed and the subsequent addition of MeO₂C-CC-CO₂Me the reaction gave 2c and [Pd{[(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] (3c); but when the alkyne was R¹-CC-R¹ (with R¹ = Ph or Et), the ionic palladacycles [Pd{[(R¹-CC-R¹)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] · CH₂Cl₂ [with R¹ = Ph (5c) or Et (6c)] were isolated. In compounds 3c, 5c and 6c, the mode of binding of the butadienyl unit is η³. The reactions of 2c, 3c, 5c and 6c with PPh₃ are also reported. The results obtained from these studies reveal that the σ(Pd-S) bond in 2c is more prone to cleave than in 4c-6c. X-ray crystal structures of 2c, 5c and [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (7c), are also described. Compound 7c arises from 2c by cleavage of the Pd-S bond and the incorporation of a PPh₃ in the coordination sphere of the palladium. A parallel study focused on the reactions of [Pd{[2-CH₂-4,6-Me₂-C₆H₂]-CHN-(C₆H₄-2-SMe)}Cl] (1d) (with a [Csp³,N,S]⁻ terdentate group) with the three alkynes reveals that the σPd-C(sp², ferrocene)] bond of 1c is more reactive than the σ[Pd-C(sp³)] bond of 1d.     

Chemistry of vinylidene complexes. XX. Intramolecular carbonylation of vinylidene on the MnFe center: Spectroscopic and structural study. X-ray structure of the new trimethylenemethane type MnFe complex

Reactions of Fe₂(CO)₉ with Cp(CO)₂MnCCHPh (1) and Cp(CO)(PPh₃)MnCCHPh (3) gave the heterometallic trimethylenemethane complexes η⁴-{C[Mn(CO)₂Cp](CO)CHPh}Fe(CO)₃ (2) and η⁴-{C[Mn(CO)(PPh₃)Cp](CO)CHPh}Fe(CO)₃ (4), respectively. The formation of the benzylideneketene [PhHCCCO] fragment included in complexes 2 and 4 occurs via intramolecular coupling of the carbonyl and vinylidene ligands. The structures of 3 and 4 were determined by single crystal XRD methods. The influence of the nature of the L ligands at the Mn atom on the structural and spectroscopic characteristics of η⁴-{C[Mn(CO)(L)Cp](CO)CHPh}Fe(CO)₃ (L = CO (2), PPh₃ (4)) is considered. According to the VT ¹H and ¹³C NMR spectra, complex 2 reversibly transforms in solution into μ-η¹:η¹-vinylidene isomer Cp(CO)₂MnFe(μ-CCHPh)(CO)₄ (2a), whereas complex 4 containing the PPh₃ ligand is not able to a similar transformation.     

Proton reduction catalysis by manganese vinylidene and allenylidene complexes

The present paper reports the unprecedented observation of a catalytic electrochemical proton reduction based on metallocumulene complexes. Manganese phenylvinylidene (η⁵-C₅H₅)(CO)(PPh₃)MnCC(H)Ph (1) and diphenylallenylidene (η⁵-C₅H₅)(CO)₂MnCCCPh₂ (3) are shown to catalyze the reduction of protons from HBF₄ into dihydrogen in CH₂Cl₂ or CH₃CN media at −1.60 and −0.84 V (in CH₃CN) vs. Fc, respectively. The working potential for 3 (−0.84 V vs. Fc in CH₃CN) is the lowest reported to date for protonic acids reduction in non-aqueous media. The similar catalytic cycles disclosed here include the protonation of 1, 3 into the carbyne cations [(η⁵-C₅H₅)(CO)(PPh₃)MnC-CH₂Ph]BF₄ ([2]BF₄), [(η⁵-C₅H₅)(CO)₂MnC-CHCPh₂]BF₄ ([4]BF₄) followed by their reduction to the corresponding 19-electron radicals 2, 4, respectively. Both carbyne radicals undergo a rapid homolytic cleavage of the C_β-H bond generating an H-radical producing molecular hydrogen with concomitant recovery of the neutral metallocumulenes thereby completing a catalytic cycle.     

Further reactions of some bis(vinylidene)diruthenium complexes

Whereas {Ru(dppm)Cp*}₂(μ-CCCC) (2) is the only product formed by deprotonation of [{Ru(dppm)Cp*}₂{μ(CCHCHC)}]⁺ with dbu, a mixture of 2 with Ru{CCCHCH(PPh₂)₂[RuCp*]}(dppm)Cp* (3) and {Cp*Ru(PPh₂CHCCH-)}₂ (4) is obtained with KOBu^t. A similar reaction with [{Ru(dppm)Cp*}₂{μ(CCMeCMeC)}]⁺ (5) gave Ru{CCCMeCH(PPh₂)₂[RuCp*]}(dppm)Cp* (6). X-ray structures of 4, 5 and 6 confirm the presence of the 1-ruthena-2,4-diphosphabicyclo[1.1.1]pentane moiety, which is likely formed by an intramolecular attack of the deprotonated dppm ligand on C(1) of the vinylidene ligand. Protonation of {Ru(dppe)Cp*}₂(μ-CCCC) (8-Ru) regenerates its precursor [{Ru(dppe)Cp*}₂{μ(CCHCHC)}]²⁺ (7-Ru). Ready oxidation of the bis(vinylidene) complex affords the cationic carbonyl [Ru(CO)(dppe)Cp*]PF₆ (9) (X-ray structure).     

Relationships between Fe NMR, Mössbauer parameters, electrochemical properties and the structures of ferrocenylketimines

A comparative study of the electrochemical properties, ⁵⁷Fe NMR and Mössbauer spectroscopic data of compounds [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-C(R¹)N-R²}] {R¹ = H, R² = CH₂-CH₂OH (1a), CH(Me)-CH₂OH (1b), CH₂C₆H₅ (1c), C₆H₄-2Me (1d), C₆H₄-2SMe (1e) or C₆H₄-2OH (1f) and R¹ = C₆H₅, R² = C₆H₄-2Me (2d)} is reported. The X-ray crystal structure of [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-C₆H₄-2OH}] (1f) is also described. Density functional theoretical (DFT) studies of these systems have allowed us to examine the effects induced by the substituents of the “-C(R¹)N-R²” moiety or the aryl rings (in 1d-1f) upon the electronic environment of the iron(II) centre.     

Additions and intramolecular migrations of nucleophiles in cationic diruthenium μ-allenyl complexes

The diruthenium μ-allenyl complex [Ru₂(CO)(NCMe)(μ-CO){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂][BF₄], 3b, reacts with halide anions to yield the neutral derivatives [Ru₂(CO)₂(X){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂] [X = Cl, 4b; X = Br, 4c; X = I, 4d]. Complex 4b undergoes isomerization to the unprecedented bridging vinyl-chlorocarbene species [Ru₂(CO)(μ-CO){μ-η¹:η³- C(Cl)C(H)C(Me)(Ph)}(Cp)₂], 10, upon filtration of a CH₂Cl₂ solution through an alumina column.Complex 3b reacts with an excess of NaBH₄ to give five products: the allene complex [Ru₂(CO)₂{μ-η²:η²- CH₂CC(Me)(Ph)}(Cp)₂], 5; the hydride species trans-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 6, and cis-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 8; the vinyl-alkylidene [Ru₂(CO)(μ-CO){μ-η¹:η³- C(H)C(H)C(Me)(Ph)}(Cp)₂], 9; and the cluster [Ru₃(CO)₃(μ-H)₃(Cp)₃], 7.Studies on the thermal stabilities of 5, 6, 8 and 9 have suggested a plausible mechanism for the formation of these complexes and for the synthesis of 10.     

Factors affecting the lability of the σ(M-X) bond in cycloplatinated and cyclopalladated complexes containing [C(sp, ferrocene),N,X] or [C(sp, phenyl),N,X] (X = S, N) terdentate ligands

The reactions of the cyclometallated complexes [M{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] [with M = Pt (5a) or Pd (5b)] with PPh₃ under different experimental conditions are reported. These studies have allowed the isolation of [M{[(η⁵-C₅H₃)-CHN-C₆H₄-2-SMe]Fe(η⁵-C₅H₅)}(PPh₃)]X [M = Pt and X⁻ = Cl⁻ (6a) or (7a) or M = Pd and X⁻ = Cl⁻ (6b) or (7b)] and the neutral complex [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (8b). In 6-7a,b the ferrocenyl Schiff base behaves as a [C(sp², ferrocene),N,S]⁻ group while in 8b it acts as a [C(sp², ferrocene),N]⁻ ligand. The X-ray crystal structure of 7b confirms the mode of binding of the ferrocenyl ligand. The comparison of the results obtained and those reported for [M{(C₆H₄)-CHN-(CH₂-CH₂-2-SEt)}Cl] and [M{(C₆H₄)-CHN-(C₆H₄-2-SMe)}Cl] {with a [C(sp², phenyl),N,S]⁻ terdentate ligand} or [M{[(η⁵-C₅H₃)-CHN-(CH₂)₃-NMe₂]Fe(η⁵-C₅H₅)}Cl] {in which the ligand acts as a [C(sp², ferrocene),N,N′]⁻ group} have allowed the elucidation of the relative importance of the factors affecting the lability of the M-X (X = S or N′) and M-Cl bonds in cyclometallated compounds with [C,N,S]⁻ and [C(sp², ferrocene),N,X]⁻ ligands.     

From alkenylphosphane aminoallenylidene ruthenium(II) complexes to highly unsaturated ruthenaphosphabicycloheptene complexes

The alkenylaminoallenylidene complex [Ru(η⁵-C₉H₇){CCC(NEt₂)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (2) has been prepared by the reaction of the allenylidene [Ru(η⁵-C₉H₇)(CCCPh₂){κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (1) with the ynamine MeCCNEt₂. The reaction proceeds regio- and stereoselectively, and the insertion of the ynamine takes place exclusively at the C_βC_γ bond of the unsaturated chain. The secondary allenylidene [Ru(η⁵-C₉H₇){CCC(H)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (3) is obtained, in a one-pot synthesis, from the reaction of aminoallenylidene 2 with LiBHEt₃ and subsequent treatment with silica. Moreover, the addition of an excess of NaBH₄ to a solution of the complex 2 in THF at room temperature gives exclusively the alkynyl complex [Ru(η⁵-C₉H₇){CCCH₂[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)] (5). The heating of a solution of allenylidene derivative 3 in THF at reflux gives regio- and diastereoselectively the cyclobutylidene complex [Ru(η⁵-C₉H₇) (PPh₃)][PF₆](4) through an intramolecular cycloaddition of the CC allyl and the C_αC_β bonds in the allenylidene complex 3. The structure of complex 4 has been determined by single crystal X-ray diffraction analysis.     

Dimerisation and reactivity of HCCCCFc at ruthenium centres

In contrast to the simple diynyl complexes formed in reactions between HCCCCFc and MCl(dppe)Cp∗; (M = Fe, Ru), an analogous reaction with RuCl(PPh₃)₂Cp∗; in the presence of KPF₆ and dbu resulted in dimerisation of the diyne at the Ru centre to afford a mixture of [Ru{η¹,η²-C(CCFc)C(L)CHCCCHFc}(PPh₃)Cp∗]PF₆ (L = dbu 1, PPh₃2). Similar reactions with RuCl(PR₃)₂L gave [Ru{η¹,η²-C(CCFc)C(dbu)CHCCCHFc}(PR₃)L]PF₆ (L = Cp, R = Ph 3, m-tol 4; L = η⁵-C₉H₇, R = Ph 5). The reaction between 3 and I₂, followed by crystallization of the paramagnetic product from MeOH, afforded the dicationic [Ru{C(CCFc)C(dbu)CHC(OMe)C(OMe)CHFc}(PPh₃)Cp](I₃)₂6. The molecular structures of 2·2CH₂Cl₂ and 6.S (S = 2CH₂Cl₂, C₆H₆) were determined by single-crystal XRD studies.     

Synthesis and reactivity of η-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η:η-C5Me4CH2CHCH2)Re(CO)2]

The fulvene complexes [(η⁶-C₅Me₄CH₂)Re(CO)₂(R)] (1a, RI; 1b, RC₆F₅) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)]⁻. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)(H)] (2a, RI; 2b, RC₆F₅). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₃] (3) and [Re(CO)₅I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η⁵:η²-C₅Me₄CH₂CHCH₂)Re(CO)₂] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)₅(C₆F₅)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe₃, afforded the phosphine derivative [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(PMe₃)] (5). All the complexes were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η²-coordination of the propenyl side arm of the η⁵-C₅Me₄ ring.     

Assembly and incorporation of a CO2Me group into a bridging vinyliminium ligand in a diiron complex

The diiron complex [Fe₂{μ-к¹(O):η¹(C):η³(C)-C(N(Me)(Xyl))C(H)C(Me)C(O)OMe}(μ-CO)(Cp)₂] (2) has been obtained from the diiron bridging vinyliminium [Fe₂{μ-η¹:η³-C(Me)C(H)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (1; Xyl = 2,5-C₆H₃Me₂) upon treatment with NaH in the presence of CH₂CCMe₂, followed by chromatography on alumina with MeOH as eluent. The reaction consists in the incorporation of a methylcarboxylate unit, assembled from CO and MeO⁻, into the bridging vinyliminium ligand. The resulting complex 2 exhibits a C₄ fragment bridging the two iron centres through the carbonyl oxygen atom and the allylidene moiety.The X-ray molecular structure of 2 has been determined.     

C-C bond formation by cyanide addition to dinuclear vinyliminium complexes

The diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(H)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R=Me, R′ = SiMe₃ (1a); R = Me, R′ = CH₂OH (1b); R = CH₂Ph, R′ = Tol (1c), Tol = 4-MeC₆H₄; R = CH₂Ph, R′ = COOMe (1d); R = CH₂Ph, R′ = SiMe₃ (1e)) undergo regio- and stereo-selective addition by cyanide ion (from ), affording the corresponding bridging cyano-functionalized allylidene compounds [Fe₂{μ-η¹:η³-C(R′)C(H)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (3a-e), in good yields. Similarly, the diiron vinyliminium complexes [Fe₂{μ-η¹:η³-C(R′)C(R′)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = R′ = Me (2a); R = Me, R′ = Ph (2b); R = CH₂Ph, R′ = Me (2c); R = CH₂Ph, R′ = COOMe (2d)) react with cyanide and yield [Fe₂{μ-η¹:η³-C(R′)C(R′)C(CN)N(Me)(R)}(μ-CO)(CO)(Cp)₂] (9a-d). The reactions of the vinyliminium complex [Fe₂{μ-η¹:η³-C(Tol)CHCN(Me)(4-C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (4) with NaBH₄ and afford the allylidene [Fe₂{μ-C(Tol)C(H)C(H)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (5) and the cyanoallylidene [Fe₂{μ-C(Tol)C(H)C(CN)N(Me)(C₆H₄CF₃)}(μ-CO)(CO)(Cp)₂] (6), respectively. Analogously, the diruthenium vinyliminium complex [Ru₂{μ-η¹:η³-C(SiMe₃)CHCN(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (7) reacts with to give [Ru₂{μ-η¹:η³-C(SiMe₃)CHC(CN)N(Me)(CH₂Ph)}(μ-CO)(CO)(Cp)₂] (8).Finally, cyanide addition to [Fe₂{μ-η¹:η³-C(COOMe)C(COOMe)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (2e) (Xyl = 2,6-Me₂C₆H₃), yields the cyano-functionalized bis-alkylidene complex [Fe₂{μ-η¹:η²-C(COOMe)C(COOMe)(CN)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (10). The molecular structures of 3a and 9a have been elucidated by X-ray diffraction.     

Some ruthenium complexes containing cyanocarbon ligands: syntheses, structures and extent of electronic communication in binuclear systems

The preparation of several ruthenium complexes containing cyanocarbon anions is reported. Deprotonation (KOBu^t) of [Ru(NCCH₂CN)(PPh₃)₂Cp]PF₆ (1) gives Ru{NCCH(CN)}(PPh₃)₂Cp (2), which adds a second [Ru(PPh₃)₂Cp]⁺ unit to give [{Ru(PPh₃)₂Cp}₂(μ-NCCHCN)]⁺ (3). Attempted deprotonation of the latter to give the μ-NCCCN complex was unsuccessful. Similar chemistry with tricyanomethanide anion gives Ru{NCC(CN)₂}(PPh₃)₂Cp (4) and [{Ru(PPh₃)₂Cp}₂{μ-NCC(CN)CN}]PF₆ (5), and with pentacyanopropenide, Ru{NCC(CN)C(CN)C(CN)₂}(PPh₃)₂Cp (6) and [{Ru(PPh₃)₂Cp}₂{μ-NCC(CN)C(CN)C(CN)CN}]PF₆ (7). The Ru(dppe)Cp* analogues of 6 and 7 (8 and 9) were also prepared. Thermolysis of 6 (refluxing toluene, 12 h) results in loss of PPh₃ and formation of the binuclear cyclic complex {Ru(PPh₃)Cp[μ-NC{C(CN)C(CN)₂}CN]}₂ (10). The solid-state structures of 2-4 and 8-10 have been determined and the nature of the isomers shown to be present in solutions of the binuclear cations 7 and 9 by NMR studies has been probed using Hartree-Fock and density functional theory.     

Palladium(II)-allyl complexes containing chiral N-donor ferrocenyl ligands

A study of the reactivity of enantiopure ferrocenylimine (S_C)-[FcCHN-CH(Me)(Ph)] {Fc =  (η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-} (1a) with palladium(II)-allyl complexes [Pd(η³-1R¹,3R²-C₃H₃)(μ-Cl)]₂ {R¹ = H and R² = H (2), Ph (3) or R¹ = R² = Ph (4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II):1a = 1} in CH₂Cl₂ at 298 K produced [Pd(η³-3R²-C₃H₄){FcCHN-CH(Me)(Ph)}Cl] {R² = H (5a) or Ph (6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (S_C)-[FcCHN-CH(R³)(CH₂OH)] {R³ = Me (1b) or CHMe₂ (1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl-complex (2-4) or on the ferrocenylimines (1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-(E) conformation and behaves as an N-donor ligand, (b) the chloride is in acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η³-fashion. Solution NMR studies of 5a and 6a and [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(CH₂OH)}Cl] (7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-(E) isomer of Ph-CHCH-CH₂Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (S_C)-H₂N-CH(Me)(Ph) (11) as catalysts in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu⁻) is reported.