Unmatched efficiency and selectivity in the epoxidation of olefins with oxo-diperoxomolybdenum(VI) complexes as catalysts and hydrogen peroxide as terminal oxidant

A great variety of olefinic substrates having aromatic, carbocyclic and aliphatic olefins are effectively and selectively oxidized with oxygen-rich molybdenum(VI) complexes, namely [MoO(O₂)₂·2QOH] 1, [MoO(O₂)(QO)₂] 2, [Mo(O)₂(QO)₂] 3, [PPh₄][MoO(O₂)₂(QO)] 4, [PPh₄][Mo(O)₂(O₂)(QO)] 5 and [PPh₄][Mo(O)₃(QO)] 6 (QOH = 8-quinolinol) as catalyst, NaHCO₃ as co-catalyst and H₂O₂ as the terminal oxidant, at room temperature. Catalysts 1 and 4 show unmatched yield, turnover number (TON) and turnover frequency (TOF), and hence shortest reaction time.     

Ion pair symmetrization in metallocenium cations partnered with diborane derived borate counteranions

The thermodynamics of ion pair symmetrization in a series of metallocenium species generated from were studied using a variety of solution dynamic techniques including line broadening, 2D-EXSY, and 1D-DPFGSE-NOE. Ion pairs were generated by methide abstraction using the corresponding trityl salts [1-A] to yield (A = {C₆F₄-1,2-[B(C₆F₅)₂]₂(μ-O(C₆F₅))}⁻, 2-O(C₆F₅); {C₆F₄-1,2-[B(C₆F₅)₂]₂(μ-OPh)}⁻, 2-OPh; {C₆F₄-1,2-[B(C₆F₅)₂]₂(μ-OMe)}⁻, 2-OMe; and [B(C₆F₅)₄]⁻, 2-B(C₆F₅)₄). The observed activation parameters were interpreted on the basis of a solvent-assisted mechanism of ion pair symmetrization.     

Intramolecular nucleophilic substitution in C6F5 moiety. The fluoride-dialkylamino exchange in decafluorodiphenlamino moiety

The reactions of [In(NEt₂)₃]₂ and Sb(NEt₂)₃ with an equimolar amount of decafluorodiphenylamine (DFDPA, LH) lead to the indium or antimony amides [(C₆F₅)₂NIn(NEt₂)₂]₂ (1) and (C₆F₅)₂NSb(NEt₂)₂ (2). Compound 2 rearranged further to give monofluoride Et₂NSb(F)[N(o-Et₂N-C₆F₄)(C₆F₅)] (3) and then difluoride F₂Sb[N(o-Et₂N-C₆F₄)₂] (4). The hydrolysis of 4 gave free ligand HN(o-Et₂N-C₆F₄)₂ (5). Closely related HN(o-Me₂N-C₆F₄)₂ (6) was prepared from the reaction of Bi(NMe₂)₃ with DFDPA. The reactions of LiN(C₆F₅)₂·THF with metal halides gave Sb[N(C₆F₅)₂]₃ (7), Me₃Sb(Br)[N(C₆F₅)₂] (8), Me₃Sb(Cl)[N(C₆F₅)₂] (9), Me₃Sb[N(C₆F₅)₂]₂ (10), [Li(THF)₂][In{N(C₆F₅)₂}₃Cl] (11). The X-ray structural investigations of 2 and 8 are presented.     

Understanding the role of an easy-to-prepare aldimine-alkyne carboamination catalyst, [Ti(NMe2)3(NHMe2)][B(C6F5)4]

A series of reactivity studies of the carboamination pre-catalyst [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] as well as the preparation of other catalysts are reported in this work. Treatment of [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] with the aldimines Ar′NCHtol (Ar′ = 2,6-Me₂C₆H₃, tol = 4-MeC₆H₄), and depending on the reaction conditions, results in isolation of [Me₂NCHR′][B(C₆F₅)₄] (1) or (Me₂N)₂CHtol, as well as the asymmetric titanium dimer [(Me₂N)₂(HNMe₂)Ti(μ₂-N[2,6-Me₂C₆H₃])₂Ti(NHMe₂)(NMe₂)][B(C₆F₅)₄] (2). Protonation of CpTi(NMe₂)₃ and Cp^∗Ti(NMe₂)₃ results in isolation of the salts, [CpTi(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (3) and [Cp^∗Ti(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (4), respectively. Treatment of compounds 3 or 4 with H₂N[2,6-ⁱPr₂C₆H₃] results in formation of the imido salts [CpTi(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (5) (58% yield) or [Cp^∗Ti(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (6). When Ti(NMe₂)₄ is treated with [Et₃Si][B(C₆F₅)₄], the salt [Ti(NMe₂)₃(N[SiEt₃]Me₂)][B(C₆F₅)₄] (7) is obtained, and treatment of the latter with [2,6-ⁱPr₂C₆H₃]NCHtol produces the imine adduct [Ti(NMe₂)₃(κ¹-[2,6-ⁱPr₂C₆H₃]NCHtol)][B(C₆F₅)₄] (8). The carboamination catalytic activity of complexes 2-7 was investigated and compared to [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄]. Likewise, a proposed mechanism to the active carboamination catalyst stemming from [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] is described.     

Preparation of chelate bis(imine)nickel allyl systems by reaction of their corresponding butadiene complexes with electrophiles

The chelate 1,2-bis(imine)nickel(butadiene) complex 4a (chelate ligand derived from condensation of biacetyl with 2,6-diisopropylaniline) adds the strong Lewis acid B(C₆F₅)₃ at the terminal carbon atom of the butadiene ligand to yield the dipolar substituted π-allyl-type betaine complex (lig)Ni[η³-C₃H₄-CH₂B(C₆F₅)₃] (Z-6a). At 90 °C the kinetically formed product equilibrated with its E-6a isomer. Similarly, 4a adds the boron Lewis acid (pyrrolyl)B(C₆F₅)₂ to yield the corresponding neutral dipolar π-allyl betaine complex Z-7a, that slowly equilibrated with E-7a over several hours at ambient temperature. Protonation of the butadiene ligand of complex 4a was achieved by treatment with the neutral Brønsted acid (2H-pyrrol)B(C₆F₅)₃ to yield the [(lig)Ni(η³-crotyl)⁺][(pyrrolyl)B(C₆F₅)₃⁻] salt 9a (Z-/E-9a ratio=90:10 upon preparation). At 298 K this salt rearranged to a 5:95 mixture of Z-9a/E-9a with a Gibbs activation energy of ΔG^‡ (298 K)=22.3±0.2 kcal mol⁻¹. Complex 4a added [Ph₃C⁺] to the butadiene ligand to yield the salt [(lig)Ni(η³-C₃H₄-CH₂CPh₃)⁺][B(C₆F₅)₄⁻] (Z-12a), that proved isomerically stable under the applied reaction conditions. Similar reactions were carried out starting from the acenaphthylene 1,2-dione derived chelate bis(imine)Ni(butadiene) complex 4b. The systems 6, 7, 9 and 12 were found to be active ethene polymerization catalysts in the presence of Al(i-Bu)₃.     

In search for a pentacoordinated monoorgano stannyl cation

Alkylation of Sn(OCH₂CH₂NMe₂)₂ (1) by MeI or MeOTf leads to a mixture of quaternary ammonium salts by alkylation of the NMe₂ moiety. Reaction of Sn(acac)₂ (2) with MeOTf gives unexpected redistribution product Sn(acac)OTf (3), which is a rare example of mono acetylacetonato tin (II) derivatives. Pentacoordinated monoorgano stannyl cation was generated by salt metathesis from PhSn(OCH₂CH₂NMe₂)₂Cl (5) and Ag[Al(OCH(CF₃)₂)₄] or Ag[B(C₆F₅)₄]. This cation was not isolated due to its strong electrophilic nature. It abstracts substituents from aluminate and borate weakly coordinating anions (WCAs) leading to redistribution products [Al[OCH(CF₃)₂]₂OCH₂CH₂NMe₂]₂ (6) and [Ph(C₆F₅)Sn(OCH₂CH₂NMe₂)₂][H₂OB(C₆F₅)₃] (9), respectively. Structures of 3 and 6 were established by single-crystal X-ray diffraction analysis.     

Syntheses of double- and triple-decker clusters of osmium and cobalt metals linked by cyclotetradeca-1,8-diyne ligands

Photoirradiation of Os₃(CO)₁₀(C₁₄H₂₀) (1) in n-hexane produces the double-decker cluster [Os₃(CO)₉(C₂₈H₄₀)] [Os₃(CO)₁₀] (7), which can also be prepared from the reaction of Os₃(CO)₉(C₂₈H₄₀) (2) and Os₃(CO)₁₀(NCMe)₂. Further reaction of 7 with Os₃(CO)₁₀(NCMe)₂ affords the triple-decker cluster [Os₃(CO)₉(C₂₈H₄₀)][Os₃(CO)₁₀]₂ (8). The bis(diyne) complex Os₃(CO)₈(C₁₄H₂₀)₂ (3) reacts with Os₃(CO)₁₀(NCMe)₂ sequentially to yield the double-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Os₃(CO)₁₀] (4) and the triple-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Os₃(CO)₁₀]₂ (5). Treatment of 3 with Co₂(CO)₈ at room temperature leads to the mixed-metal triple-decker cluster [Os₃(CO)₈(C₁₄H₂₀)₂][Co₂(CO)₆]₂ (6), while the reaction of 2 and Co₂(CO)₈ produces [Os₃(CO)₉(C₂₈H₄₀)][Co₂(CO)₆]₂ (9) and [Os₂(CO)₆(C₂₈H₄₀)][Co₂(CO)₆]₂ (10). Compound 10, which involves cluster degradation from Os₃ to Os₂, has been structurally characterized by an X-ray diffraction study.     

Synthesis and characterization of new paramagnetic tetraaryl derivatives of chromium and molybdenum

The low-temperature reaction of [CrCl₃(thf)₃] with LiC₆H₃Cl₂-2,6 yields the organochromium(III) compound [Li(thf)₄][Cr^III(C₆H₃Cl₂-2,6)₄] (1) in 48% yield. The homoleptic, anionic species [Cr^III(C₆H₃Cl₂-2,6)₄]⁻ is electrochemically related to the neutral one [Cr^IV(C₆H₃Cl₂-2,6)₄] (2) through a reversible one-electron exchange process (E_1/2 = 0.16 V, ΔE_p = 0.09 V, i_pa/i_pc = 1.18). Compound 2 was isolated in 74% yield by chemical oxidation of 1 with [N(C₆H₄Br-4)₃][SbCl₆]. Attempts to prepare the salt [NBu₄][Cr^III(C₆Cl₅)₄] (4) by direct arylation of [CrCl₃(thf)₃] with LiC₆Cl₅ in the presence of [NBu₄]Br gave the organochromium(II) salt [NBu₄]₂[Cr^II(C₆Cl₅)₄] (3) instead, as the result of a reduction process. The salt [NBu₄][Cr^III(C₆Cl₅)₄] (4) was cleanly prepared by comproportionation of 3 and [Cr^IV(C₆Cl₅)₄]. The reaction of [MoCl₄(dme)] with LiC₆Cl₅ in Et₂O solution proceeded with oxidation of the metal center to give the paramagnetic (S = 1/2), five-coordinate salt [Li(thf)₄][Mo^VO(C₆Cl₅)₄] (5). The crystal and molecular structures of 1 and 2 have been established by X-ray diffraction methods. The magnetic properties of 1 and 4 (S = 3/2) as well as those of 2 (S = 1) have been established by EPR spectroscopy as well as by ac and dc magnetization measurements.     

Synthesis and characterization of perhalophenyltin derivatives. Study of their reactivity toward phosphine gold(I) chlorides

The (perhalophenyl)tin derivatives [SnR₄] (1-3) and [SnR₃Cl] (4-6) (R = C₆F₅, C₆F₃Cl₂, C₆Cl₅) were prepared from SnCl₄ and LiR or [SnR₄] in the appropriate molar ratio, while the dinuclear complexes [SnR₃]₂ (7-9) were obtained by treatment of [SnR₃Cl] with potassium under toluene reflux. Complexes 2, 6·0.5toluene and 7 were structurally characterized, the latter displaying a Sn-Sn bond of 2.808(7) Å, which indicates a strong tin-tin bond with covalent character in solid state. The hexaaryldistannanes 7-9 undergo transmetallation reactions with gold(I) derivatives, such as [AuCl(PPh₃)] or [(AuCl)₂(μ-dppm)], affording the neutral species [AuR(PPh₃)] (10-12) or [(AuR)₂(μ-dppm)] (13-15) or the ionic product [Au₃Cl₂(μ-dppm)₂][Sn(C₆F₅)₃Cl₂] (16). The crystal structures of 14·CH₂Cl₂, 15 and 16·2CH₂Cl₂ were determined by X-ray diffraction, the latter showing a Au₃ nearly equilateral triangular core in the cation with gold-gold contacts of 3.128(7) and 3.227(12) Å. The main difference between the molecular structures of 14·CH₂Cl₂ and 15 (both of them displaying intramolecular gold-gold contacts of 3.142(6) and 3.160(4) Å, respectively) is the presence of an intermolecular Au?Au interaction of 3.2126(8) Å in the case of the C₆F₃Cl₂ complex that gives rise to a tetranuclear unit.     

Electrophilic reactivity of the zwitterionic titanocene monohalides Cp[η-C5H4B(C6F5)3]TiX (X = Cl, Br): Reactions with water and methanol

The paper reports new data evidencing for a high electrophilicity of the positively charged titanium atom in the previously described zwitterionic titanocene monochloride Cp[η⁵-C₅H₄B(C₆F₅)₃]TiCl (1) and titanocene monobromide Cp[η⁵-C₅H₄B(C₆F₅)₃]TiBr (2), containing a B(C₆F₅)₃ group in one of the C₅ rings. It has been established that on a contact of a toluene solution of these zwitterions with water vapour at 20 °C under Ar, a rapid protolytic cleavage of the otherwise inert B-C₆F₅ bond in the tris(pentafluorophenyl)borane moiety occurs to afford pentafluorobenzene and the corresponding halogenide hydroxide complex of titanocene Cp[η⁵-C₅H₄B(C₆F₅)₂]TiX(μ-OH), where X = Cl (3), Br (4). An X-ray diffraction study of the complexes has shown that the hydroxide group in 3 and 4 is bonded via the oxygen atom both to the titanium and boron atoms. Under similar conditions, the interaction of zwitterion 1 with methanol gives rise to pentafluorobenzene and the chloride methoxide complex of titanocene Cp[η⁵-C₅H₄B(C₆F₅)₂]TiCl(μ-OCH₃). It has been suggested that the driving force of the protolysis of the B-C₆F₅ bond in 1 and 2 is a sharp increase in the acidity of water or methanol molecule as a result of their complexation with the positively charged titanium centre in the starting zwitterion.     

Two-electron reductive reactivity of trivalent uranium tetraphenylborate complexes of (C5Me5) and (C5Me4H)

The reductive reactivity of the (BPh₄)¹⁻ ligand in pentamethylcyclopentadienyl [(C₅Me₅)₂U][(μ-η²:η¹-Ph)₂BPh₂] (1) was compared with that of the tetramethyl analog, [(C₅Me₄H)₂U][(μ-η⁶:η¹-Ph)(μ-η¹:η¹-Ph)BPh₂] (2) using PhSSPh as a probe to determine if the mode of (BPh₄)¹⁻ bonding affected the reduction. Both complexes act as two-electron reductants to form (C₅Me₄R)₂U(SPh)₂ [R = Me, 3; H, 4], but only in the R = H case could the product be crystallographically characterized. An improved synthesis of 1 from [(C₅Me₅)₂UH]₂ (5) and [Et₃NH][BPh₄] is also reported as well as its reaction with MeCN that provides another route to the unusual, parallel-ring, uranium metallocene [(C₅Me₅)₂U(NCMe)₅][BPh₄]₂ (6).     

Coordination properties of N2S (1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane) or N2S2 (1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane or 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene) donor ligands toward Rh(I)

The 1,5-bis(3,5-dimethyl-1-pyrazolyl)-3-thiapentane ligand (bdtp) reacts with [Rh(COD)(THF)₂][BF₄] to give [Rh(COD)(bdtp)][BF₄] ([1][BF₄]), which is fluxional in solution on the NMR time scale. Its further treatment with carbon monoxide leads to a displacement of the 1,5-cyclooctadiene ligand, generating a mixture of two complexes, namely, [Rh(CO)₂(bdtp)][BF₄] ([2][BF₄]) and [Rh(CO)(bdtp-κ³N,N,S)][BF₄] ([3][BF₄]). In solution, [2][BF₄] exists as a mixture of two isomers, [Rh(CO)₂(bdtp-κ²N,N)]⁺ ([2a]⁺) and [Rh(CO)₂(bdtp-κ³N,N,S)]⁺ ([2b]⁺; major isomer) rapidly interconverting on the NMR time scale. At room temperature, [2][BF₄] easily loses one molecule of carbon monoxide to give [3][BF₄]. The latter is prone to react with carbon monoxide to partially regenerate [2][BF₄]. The ligands 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene (bddf) and 1,8-bis(3,5-dimethyl-1-pyrazolyl)-3,6-dithiaoctane (bddo) are seen to react with two equivalents of [Rh(COD)(THF)₂][BF₄] to give the dinuclear complexes [Rh₂(bddf)(COD)₂][BF₄]₂ ([4][BF₄]₂) and [Rh₂(bddo)(COD)₂][BF₄]₂ ([5][BF₄]₂), respectively. In such complexes, the ligand acts as a double pincer holding two rhodium atoms through a chelation involving S and N donor atoms. Bubbling carbon monoxide into a solution of [4][BF₄]₂ results in loss of the COD ligand and carbonylation to give [Rh₂(bddf)(CO)₄][BF₄]₂ ([6][BF₄]₂). The single-crystal X-ray structures of [3][CF₃SO₃], [5][BF₄]₂ and [6][BF₄]₂ are reported.     

Lutetium gets a crown: Synthesis, structure and reaction chemistry of the separated ion pair complex, [Li(12-crown-4)2][(C5Me5)2LuMe2]

Reaction of (C₅Me₅)₂Lu(Me)(μ-Me)Li(THF)₃ (2) with excess 12-crown-4 affords the new separated ion pair complex, [Li(12-crown-4)₂][(C₅Me₅)₂LuMe₂] (3), in excellent yield. This complex reacts with 2,6-diisopropylaniline and phenylacetylene to give the methyl amide complex [Li(12-crown-4)₂][(C₅Me₅)₂Lu(Me)(NH-2,6-ⁱPr₂C₆H₃)] (4) and the bis(acetylide) complex [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5), respectively. Attempts to promote methane loss from complexes 3 and 4 to generate a lutetium methylidene or imido complex, respectively, were unsuccessful. The ability of the bis(acetylide) complex 5 to act as a π-tweezer complex was also explored. Reaction between [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5) and CuSPh gave only intractable lutetium products and the copper(I) species [Li(12-crown-4)₂][Cu(C≡C-Ph)₂] (8). The new lutetium complexes have been characterized by elemental analysis and NMR spectroscopy. Finally, the X-ray crystal structures of (C₅Me₅)₂Lu(Me)(μ-Me)Li(THF)₃ (2), [Li(12-crown-4)₂][(C₅Me₅)₂LuMe₂] (3), [Li(12-crown-4)₂][(C₅Me₅)₂Lu(Me)(NH-2,6-ⁱPr₂C₆H₃)] (4), [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5), and [Li(12-crown-4)₂][Cu(C≡C-Ph)₂] (8) are also reported.     

Chemistry of diphenyltetrafluorophosphazene: Reactions with dilithiated diols

Reaction of gem-diphenyltetrafluorophosphazene, [1,1-(C₆H₅)₂]P₃N₃F₄ (1) with LiO(CH₂)₃OLi resulted in the formation of four products, spiro-{3,3-[O(CH₂)₃O]}[1,1-(C₆H₅)₂]P₃N₃F₂ (2), ansa-{3,5-[O(CH₂)₃O]}[1,1-(C₆H₅)₂P₃N₃F₂] (3), bridged-[1,1-(C₆H₅)₂N₃P₃F₃][O(CH₂)₃O][1,1-(C₆H₅)₂N₃P₃F₃] (4) and dangling-[HO(CH₂)₃O][1,1-(C₆H₅)₂P₃N₃F₃] (5) derivatives of 1, among which compound 5 was found to be the major product. Reaction of 1 with the dilithiated ferrocene derived diol, FcCH₂P(S)(CH₂OLi)₂ resulted in the formation of two isomers of ansa substituted fluorophosphazenes namely endo-[1,1-(C₆H₅)₂]{3,5-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (6) and exo-[1,1-(C₆H₅)₂]{3,5-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (7). These were formed along with the spiro isomer [1,1-(C₆H₅)₂]{3,3-[FcCH₂P(S)(CH₂O)₂]}P₃N₃F₂ (8) the dangling derivative [1,1-(C₆H₅)₂P₃N₃F₃][OCH₂(FcCH₂)P(S)CH₂OH] (9) and the bridged compound [1,1-(C₆H₅)₂P₃N₃F₃][OCH₂(FcCH₂)P(S)CH₂O][1,1-(C₆H₅)₂P₃N₃F₃] (10). All compounds were separated by column chromatography and characterized by ¹H, ³¹P{¹H}, ¹⁹F NMR, mass spectra and elemental analysis. The spirocyclic compound 8 was also characterized by X-ray crystallography.     

Room-temperature long-lived [Nb2F11] salts of radical cations of simple arenes: EPR, UV-Vis and DFT results

The computed structures of the long-lived radical cation salts [Arene][Nb₂F₁₁] [Arene = 1,4-F₂-2,5-(OMe)₂C₆H₂, 2; 1,4-(OMe)₂C₆H₄, 3; 2,5-(OEt)₂(Me)C₆H₃, 4; C₆H₆, 5] and that of the transient [1,3-(OMe)₂C₆H₄][Nb₂F₁₁], 6, obtained for the gas-phase by DFT at the B3LYP/6-31G∗∗ level, are presented. The degree of inertness observed in chloroform solution seems to increase on decreasing the steric demand of the ring substituents, and may be correlated to the calculated distance between the cation-centroid and the niobium atoms. The room-temperature EPR spectra of 2-4, in CHCl₃, are described in detail; the spectrum of 3 is compared to those of analogous 1,4-dimethoxybenzene radical species reported previously. The EPR spectra display a hyperfine structure due to coupling of the unpaired electron with nuclei belonging to both the cation (H and F in the case of 2) and the anion (F and eventually Nb). The UV-Vis spectra of 2-4 exhibit one strong absorption attributed to the cation and one anion-to-cation charge-transfer band (e.g. for 3 at 398 and 589 nm, respectively). Thermodynamic calculations indicate that the low yield formation of the benzene radical salt 5 occurs with Gibbs free energy variation significantly higher than those involved in the synthesis of 2-4 and 6.     

Diastereoselectivity at chiral metal center of half-sandwich-type ruthenium complexes with planar-chiral cyclopentadienyl ligands in multiple ligand transfer reaction

The triple ligand transfer reaction between planar-chiral cyclopentadienyl-ruthenium complexes [Cp′Ru(NCMe)₃][PF₆] (1) (Cp′ = 1-(COOR²)-2-Me-4-R¹C₅H₂; R¹ = Me, Ph, t-Bu) and iron complexes CpFe(CO)(L)X (2) (L = PMe₃, PMe₂Ph, PMePh₂, PPh₃; X = I, Br) resulted in the formation of metal-centered chiral ruthenium complexes Cp′Ru(CO)(L)X (3) in moderate yields with diastereoselectivities of up to 68% de. The configurations of some major diastereomers were determined to be by X-ray crystallography. The diastereoselectivity of 3 was under kinetic control and not affected by the steric effect of the substituents on the Cp′ ring of 1 and the phosphine of 2. Although the double ligand transfer reaction between [Cp′Ru{P(OMe)₃}(NCMe)₂][PF₆] (7) and CpFe(CO)₂X (8) produced Cp′Ru{P(OMe)₃}(CO)X (9), the selectivity at the ruthenium center was low.     

A pyrazolyl-terminated 2,2′:6′,2″-terpyridine ligand: Iron(II), ruthenium(II) and palladium(II) complexes of 4′-(3,5-dimethylpyrazol-1-yl)-2,2′:6′,2″-terpyridine

The preparation of 4′-(3,5-dimethylpyrazol-1-yl)-2,2′:6′,2″-terpyridine (2) under acidic conditions results in the formation of the salts [H₂2][MeOSO₃]₂ and [H₂2][EtOSO₃]₂, treatment of which with base leads to neutral 2. The structure of [H₂2][EtOSO₃]₂ · H₂O has been established by single crystal X-ray diffraction. The complexes [Fe(2)₂][PF₆]₂ and [Ru(2)₂][PF₆]₂ have been prepared and characterized, and the single crystal structure determination of [Ru(2)₂][PF₆]₂ is reported; [Fe(2)₂][PF₆]₂ is isostructural with [Ru(2)₂][PF₆]₂. Treatment of [Fe(2)₂]²⁺ with PdCl₂ produces [Pd(2)Cl]⁺, isolated and structurally characterized as the hexafluoridophosphate salt, illustrating that metal exchange within the tpy-binding domain occurs in preference to palladium(II) coordination by the N-donor atom of the pendant 3,5-dimethylpyrazol-1-yl unit in 2. [Pd(2)Cl]²⁺ can also be prepared from PdCl₂ and [H₂2][MeOSO₃]₂ in refluxing methanol.     

F NMR spectroscopy as useful tool for determining the structure in solution of coordination compounds of MF5 (M = Nb, Ta)

The salts [S(NMe₂)₃][MF₆] (M = Nb, 2a; M = Ta, 2b) and [S(NMe₂)₃][M₂F₁₁] (M = Nb, 2c; M = Ta, 2d) have been prepared by reacting MF₅ (M = Nb, 1a; M = Ta, 1b) with [S(NMe₂)₃][SiMe₃F₂] (TASF reagent) in the appropriate molar ratio. The solid state structure of 2b has been ascertained by X-ray diffraction. The 1:1 molar ratio reactions of 1a with a variety of organic compounds (L) give the neutral adducts NbF₅L [L = Me₂CO, 3a; L = MeCHO, 3b; L = Ph₂CO, 3c; L = tetrahydrofuran (thf), 3d; L = MeOH, 3e; L = EtOH, 3f; L = HOCH₂CH₂OMe, 3g; L = Ph₃PO, 3h; L = NCMe, 3i] in good yields. The complexes MF₅L [M = Nb, L = HCONMe₂, 3j; M = Nb, L = (NMe₂)₂CO, 3k; M = Ta, L = (NMe₂)₂CO, 3l; M = Nb, L = OC(Me)CHCMe₂, 3m] have been detected in solution in admixture with other unidentified products, upon 2:1 molar reaction of 1 with the appropriate reagent L. The ionic complexes [NbF₄(tht)₂][NbF₆], 4a, and [NbF₄(tht)₂][Nb₂F₁₁], 4b, have been obtained by combination of tetrahydrothiophene (tht) and 1a, in 1:1 and 2:3 molar ratios, respectively. The treatment of 1 with a two-fold excess of L leads to the species [MF₄L₄][MF₆] [M = Nb, L = HCONMe₂, 5a; M = Ta, L = HCONMe₂, 5b; M = Nb, L = thf, 5c; M = Ta, L = thf, 5d; M = Nb, L = OEt₂, 5e]. The new complexes have been fully characterised by NMR spectroscopy. Moreover, the revised ¹⁹F NMR features of the known compounds MF₅L [M = Ta, L = Me₂CO, 3n; M = Ta, L = Ph₂CO, 3o; M = Ta, L = MePhCO, 3p; M = Ta, L = thf, 3q; M = Nb, L = CH₃CO₂H, 3r; M = Nb, L = CH₂ClCO₂H, 3s; M = Ta, L = CH₂ClCO₂H, 3t], TaF₄(acac), TaF₄(Me-acac) and [TaF(Me-acac)₃][TaF₆] (Me-acac = methylacetylacetonato anion) are reported.     

An organometallic tetranuclear cluster with phosphine and phosphido ligands in nonclassical bonding modes: X-ray structural characterization

The elimination of the NCMe ligand in [(C₆F₅)₂Pt(μ-PPh₂)₂M(NCCH₃)₂] (M = Pd, Pt) results in the formation of the tetranuclear clusters [Pt₂Pd₂(μ-PPh₂)₃(C₆F₅)₃(PPh₂C₆F₅)] 1 and [Pt₄(μ-PPh₂)₄(C₆F₅)₄] 2. The structure of 1 indicates that one of the palladium centres is connected to the rest of the centres through two M-M bonds and two weaker η²-C₆H₅ and η²-P-C interactions.     

Synthesis of neutral and cationic monocyclopentadienyl alkyl niobium and tantalum complexes

Compound [NbCp′Me₄] (Cp′ = η⁵-C₅H₄SiMe₃, 1) reacted with several ROH compounds (R = tBu, SiiPr₃, 2,6-Me₂C₆H₃) to give the derivatives [NbCp′Me₃(OR)] (R = tBu 2a, SiiPr₃2b, 2,6-Me₂C₆H₃2c). The diaryloxo tantalum compound [TaCp^∗Me₂(OR)₂] (Cp^∗ = η⁵-C₅Me₅, R = 2,6-Me₂C₆H₃3) was obtained by reaction of [TaCp^∗Cl₂Me₂] with 2 equiv of LiOR (R = 2,6-Me₂C₆H₃). Abstraction of one methyl group from these neutral compounds 1-3 with the Lewis acids E(C₆F₅)₃ (E = B, Al) gave the ionic derivatives [NbCp′Me₂X][MeE(C₆F₅)₃] (X = Me 4-E. X = OR; R = SiiPr₃5b-E, 2,6-Me₂C₆H₃5c-E. E = B, Al) and [TaCp^∗Me(OR)₂][MeE(C₆F₅)₃] (R = 2,6-Me₂C₆H₃6-E; E = B, Al). Polymerization of MMA with the aryloxoniobium compound 2c and Al(C₆F₅)₃ gave syndiotactic PMMA in a low yield, whereas the tetramethylniobium compound 1 and the diaryloxotantalum derivative 3 were inactive.