Synthesis and reactivity of trimethylsilyl substituted mono(cyclopentadienyl)titanium alkyl complexes

The preparation of a series of titanium half-sandwich compounds [Ti(η⁵-C₅H_5−x (SiMe₃) _x R₃] (x = 1–3, R = Cl, Me) and their reactivity for propene polymerization is reported. The compounds 1–3 polymerize propene, albeit in a much lower activity than the reported [Ti(η⁵-C₅Me₅Me₃]/B(C₆F₅)₃ catalyst. Unlike the reported [Ti(η⁵-C₅Me₅Me₃]/B(C₆F₅)₃ catalyst, the quasi living polymerization was not observed. Instead, we observe rather unusual temperature effects when the trityl salt [Ph₃C][B(C₆F₅)₄] was used as activator. The activity increases with increasing temperature, whereas when B(C₆F₅)₃ is used a decrease is observed The rather broad (>2) PDI indicates multisite catalysts, and ¹³C-NMR indicates predominantly atactic polypropene. The solid state structure of the hydrolysis product [{Ti(η⁵-C₅H₄(SiMe₃)Cl₂}O] (4) was determined.     

Electrochemical studies with dissolved and surface-confined forms of neo-pentyl-ferrocene-based polyesters utilising [NBu4][B(C6F5)4] and other electrolytes

The voltammetric oxidation at a glassy carbon electrode of a series of ferrocenyl polyesters PmF{X}, (X=T, terephthalate; N, 2,6-naphthalene dicarboxylate; B, 4,4′-biphenyl dicarboxylate) is reported in the weakly donating and low-polarity CH₂Cl₂ solvent containing [NBu₄][PF₆], [NBu₄][B(C₆F₅)₄], or 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([bmpyr][TFSA]) as the supporting electrolyte. The one electron oxidation of the ferrocenyl groups is strongly influenced by the nature of the supporting electrolyte anion. Use of the conventional [PF₆]⁻ anion or the room temperature ionic liquid (RTIL), [bmpyr][TFSA] as the supporting electrolyte, gives rise to significant oxidation product interaction (precipitation and/or adsorption) with the electrode surface. In marked contrast, diffusion-controlled, chemically and electrochemically reversible processes are observed when the weakly coordinating [B(C₆F₅)₄]⁻ is used as the anionic component of the supporting electrolyte. In this case, data obtained via cyclic voltammetry, chronoamperometry and chronocoulometry are consistent with ideal reversible one electron oxidation processes and a soluble cationic product. Diffusion coefficients of the monomers, polymers, ferrocene and decamethyferrocene are reported in the CH₂Cl₂/[NBu₄][B(C₆F₅)₄] system. Importantly, reversible potentials that are easily obtained under these conditions show that the acyl or methyl linkers, through which the ferrocenyl group is attached to the neo-pentylenediol component, tune the redox properties of the polymers. Electrochemical studies with a glassy carbon electrode modified with microcrystals of the PmFT polymer conducted in aqueous (with KCl supporting electrolyte) or neat ionic liquid ([bmpyr][TFSA]) media also are reported. Different mechanisms apply in each of these cases.     

Strukturen von neuen Bis(pentafluorophenyl)halogenomercuraten [{Hg(C6F5)2}3(μ‐X)]— (X = Cl,Br, I)

Structures of New Bis(pentafluorophenyl)halogeno Mercurates [{Hg(C₆F₅)₂}₃(μ‐X)]^— (X = Cl, Br, I) From the reactions of [PNP]Cl or [PPh₄]Y (Y = Br, I) with Hg(C₆F₅)₂ crystals of the composition [Cat][{Hg(C₆F₅)₂}₃X] (Cat = PNP, X = Cl ( 1 ); Cat = PPh₄, X = Br ( 2 ), I ( 3 )) are formed. 1 crystallizes in the triclinic space group P1¯, 2 and 3 crystallize isotypically in the monoclinic space group C2/c. In the crystals the halide anions are surrounded by three Hg(C₆F₅)₂ molecules. The reaction of [PPh₄]Br with Hg(C₆F₅)₂ under slightly changed conditions gives the compound [PPh₄]₂[{Hg(C₆F₅)₂}₃(μ‐Br)][{Hg(C₆F₅)₂}₂(μ‐Br)] ( 4 ).     

Synthesis and structure of [Cp2Zr(OPr)(HOPr)] and its activity in the polymerisation of propene oxide

The reaction of Cp₂Zr(OPrⁱ)₂ with [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] in dichloromethane at room temperature gives [Cp₂Zr(OPrⁱ)(HOPrⁱ)]⁺[H₂N{B(C₆F₅)₃}₂]⁻ · Et₂O in high yield. The crystal structure is reported. The complex contains a short Zr-alkoxide and a longer Zr-alcohol bond; the OH group of the coordinated isopropanol is hydrogen-bonded to a diethyl ether molecule. The complex initiates the polymerisation of propylene oxide, most probably via a cationic mechanism.     

Complexation and Versatile Reactivity of a Highly Lewis Acidic Cationic Mg Complex with Alkynes and Phosphines

[(BDI)Mg⁺][B(C₆F₅)₄⁻] ( 1 ; BDI=CH[C(CH₃)NDipp]₂; Dipp=2,6-diisopropylphenyl) was prepared by reaction of (BDI)MgnPr with [Ph₃C⁺][B(C₆F₅)₄⁻]. Addition of 3-hexyne gave [(BDI)Mg⁺ ⋅ (EtC≡CEt)][B(C₆F₅)₄⁻]. Single-crystal X-ray analysis, NMR investigations, Raman spectra, and DFT calculations indicate a significant Mg-alkyne interaction. Addition of the terminal alkynes PhC≡CH or Me₃SiC≡CH led to alkyne deprotonation by the BDI ligand to give [(BDI-H)Mg⁺(C≡CPh)]₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 2 , 70 %) and [(BDI-H)Mg⁺(C≡CSiMe₃)]₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 3 , 63 %). Addition of internal alkynes PhC≡CPh or PhC≡CMe led to [4+2] cycloadditions with the BDI ligand to give {Mg⁺C(Ph)=C(Ph)C[C(Me)=NDipp]₂}₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 4 , 53 %) and {Mg⁺C(Ph)=C(Me)C[C(Me)=NDipp]₂}₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 5 , 73 %), in which the Mg center is N,N,C-chelated. The (BDI)Mg⁺ cation can be viewed as an intramolecular frustrated Lewis pair (FLP) with a Lewis acidic site (Mg) and a Lewis (or Brønsted) basic site (BDI). Reaction of [(BDI)Mg⁺][B(C₆F₅)₄⁻] ( 1 ) with a range of phosphines varying in bulk and donor strength generated [(BDI)Mg⁺ ⋅ PPh₃][B(C₆F₅)₄⁻] ( 6 ), [(BDI)Mg⁺ ⋅ PCy₃][B(C₆F₅)₄⁻] ( 7 ), and [(BDI)Mg⁺ ⋅ PtBu₃][B(C₆F₅)₄⁻] ( 8 ). The bulkier phosphine PMes₃ (Mes=mesityl) did not show any interaction. Combinations of [(BDI)Mg⁺][B(C₆F₅)₄⁻] and phosphines did not result in addition to the triple bond in 3-hexyne, but during the screening process it was discovered that the cationic magnesium complex catalyzes the hydrophosphination of PhC≡CH with HPPh₂, for which an FLP-type mechanism is tentatively proposed.     

Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions

As the dysprosocenium complex [Dy(Cp^ttt)₂][B(C₆F₅)₄] (Cp^ttt=C₅H₂tBu₃-1,2,4, 1-Dy ) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Ln ) for all the heavier Ln from Gd–Lu; herein, we extend this motif to the early Ln. We find, for the largest Ln^III cations, that contact ion pairs [Ln(Cp^ttt)₂{(C₆F₅-κ¹-F)B(C₆F₅)₃}] ( 1-Ln ; La–Nd) are isolated from reactions of parent [Ln(Cp^ttt)₂(Cl)] ( 2-Ln ) with [H(SiEt₃)₂][B(C₆F₅)₄], where the anion binds weakly to the equatorial sites of [Ln(Cp^ttt)₂]⁺ through a single fluorine atom in the solid state. For smaller Sm^III, [Sm(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Sm ) is isolated, which like heavier 1-Ln does not exhibit equatorial anion interactions, but the Eu^III analogue 1-Eu could not be synthesised due to the facile reduction of Eu^III precursors to Eu^II products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)₂]⁺ series was isolated for the 3d metals.     

Reduction of bis[(2-phosphinoethyl)tetramethyl-cyclopentadienyl]zirconium dichlorides: intramolecular C-H activation <Emphasis Type="Italic">vs.</Emphasis> stabilization of the low-valence metal center

Reduction of the R₂P-functionalized zirconocene dichlorides [C₅Me₄(CH₂)₂PR₂] (C₅Me₅)ZrCl₂ (R = Me (1) and Ph (2)) and [C₅Me₄(CH₂)₂PMe₂][C₅Me₄(CH₂)₂PR₂]ZrCl₂ (R = Me (3) and Ph (4)) with amalgamated magnesium was studied. In the reduction of compounds 1 and 2, intramolecular C-H activation highly selectively afforded the fulvene hydride complexes Zr(H)(η⁵−C₅Me₅)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PR₂] (R = Me (7), Ph (8)); in the case of compound 2, the aryl hydride Zr(H)(η₅:C₅Me₅)[η⁵:η¹(C)−C₅Me₄CH₂CH₂PPh(o−C₆H₄)] (9) was also formed. The reduction of complexes 3 and 4 gave the Zr^II derivatives Zr[η⁵:η¹(P)− C₅Me₄CH₂CH₂PMe₂]₂ (12) and Zr[η⁵:η₁(P)−C₅Me₄CH₂CH₂PMe₂][η⁵:η¹(P)−C₅Me₄CH₂ CH₂PPh₂] (14) stabilized by two phosphine groups. The second product in the reduction of compound 4 was the fulvene hydride complex Zr(H)(η⁵−C₅Me₄CH₂CH₂PPh₂)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PMe₂] (15). The reaction of compound 7 with an excess of MeI resulted selectively in replacement of the hydride ligand by iodide to give the complex ZrI(η⁵−C₅Me₅)[η⁵:η²(C,P)−(CH₂)C₅Me₃CH₂CH₂PMe₂] (10). In contrast, in the reaction of compound 7 with Me₂Si(H)Cl, the Zr-CH₂ bond underwent cleavage to give the chloride hydride complex Zr(H)Cl(η₅−C₅Me₅)[η⁵:η¹(P)−C₅Me₃(CH₂SiMe₂H)CH₂CH₂PMe₂] (11). In the reaction of complex 12 with CO, a phosphine group was replaced by CO to form the complex Zr(CO)(η5−C₅Me₄CH₂CH₂PMe₂)[η⁵:η¹(P)−C₅Me₄CH₂CH₂PMe₂] (13). The results obtained were compared with analogous reduction reactions of MeO-, MeS-, and Me₂N-functionalized zirconocene dichlorides. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 65–74, January, 2008.     

Hydrothermal synthesis and structural characterization of novel α-Keggin unit-supported Cu(II)- and Mn(II)-bipyridine complexes from a <Emphasis Type="Italic">tri</Emphasis>-lacunary precursor

Blue [{Cu(2,2′-bipy)₂}₂{α-SiW₁₂O₄₀}] (bipy = bipyridyl) (1) and pale yellow [Mn(2,2′-bipy)₃]₂[α-SiW₁₂O₄₀] (2) have been synthesized hydrothermally and characterized by IR spectroscopy and single crystal X-ray structure analysis. In 1, the [α-SiW₁₂O₄₀]⁴⁻ ion acts as a bridge between the two [{Cu(2,2′-bipy)₂]²⁺ moieties via coordination through the terminal oxygen atoms, while in 2, the [Mn(2,2′-bipy)₃]²⁺ ion balances the charge on the polyoxo anion without forming any covalent bond. To the best of our knowledge, this is the first example of transition metal-mediated transformation of [α-SiW₉O₃₄]¹⁰⁻ to [α-SiW₁₂O₄₀]⁴⁻. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preparation and crystal structure of bis[(dibenzo-18-crown-6)potassium]bis(μ<Subscript>2</Subscript>-chloro)-tetrachlorodicuprate(II)

A new complex compound bis[(dibenzo-18-crown-6)potassium]bis(μ₂-chloro)-tetrachlorodicuprate( II), {[K(Db18c6)]₂Cu₂Cl₆} (I) was prepared and its crystal structure was investigated by XRD analysis. Complex molecule I consist of anion [Cu₂Cl₆]²⁻ located in a crystallographic center of inversion, and two centrosymmetrical to each other complex cations [K(Db18c6)]⁺ of “guest-host” type: the cation K⁺ is located in the cavity of the crown-ligand Db18c6 and is coordinated by all its six O atoms, and also by one Cl atom of anion [Cu₂Cl₆]²⁻. The coordination of this cation K⁺ is enlarged up to hexagonal-bipyramidal due to the formation of unusual coordination bond K⁺ → π(      

Alkylation of toluene with dichloromethane in the presence of triisobutylaluminum and perfluorophenylborates

¹H NMR method showed that in systems based on triisobutylaluminum (TIBA) and triphenylcyclopropenylium [Ph₃C₃]⁺[B(C₆F₅)₄]–(CPB) or triphenylmethylium [Ph₃C]⁺[B(C₆F₅)₄]–(TB) perfluorophenylborates in a toluene–dichloromethane mixture the Friedel–Crafts process occurs with the formation of ditolylmethane (DTM) accompanied by the complete decomposition of TIBA to form isobutane. ¹⁹F NMR spectroscopy showed that the [B(C₆F₅)₄]–anion decomposes in the systems to form B(C₆F₅)₃ and HC₆F₅. The short-living [AlBu₂ ⁱ]+ cation formed in the reaction of perfluorophenylborates with TIBA is assumed to be the species initiating the process. It has been shown that CPB is less reactive than TB. The addition of a stoichiometric amount of Ph₂CCpFluHfMe₂ exerts no effect on the process with the CPB-containing system but inhibits the reaction in the case of TB.     

Ionic liquids containing the triply negatively charged tricyanomelaminate anion and a B(C6F5)3 adduct anion

Room‐temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C₃N₆(CN)₃]^3? were synthesized. The 1‐methyl‐3‐methylimidazolium (MMIm), 1‐ethyl‐3‐methylimidazolium (EMIm), and 1‐butyl‐3‐methylimidazolium (BMIm) salts of the tricyanomelaminate ion have glass transition temperatures (?6, ?20, and ?30 °C) similar to those found for the analogous monomeric dicyanoamide salts. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Addition of B(C₆F₅)₃ to M₃[tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C₃N₆{CN ? B(C₆F₅)₃}₃]^3? (tcmel_3B). The solid‐state structure of [MMIm]₃[tcmel] shows only long cation ??? anion contacts but in large number, while the solid‐state structure of [Na(THF)₃]₃[tcmel_3B] ? 1.76 THF displays strong interactions of the sodium cation with the amido nitrogen atoms of the anion. Hence this adduct anion cannot be regarded as a weakly coordinating anion. A similar situation is found for the MMIm salt, [MMIm]₃[tcmel_3B] ? 2.66 CH₂Cl₂, in which weak hydrogen bonds with the acidic proton of the MMIm ion are observed. On the basis of computations the energetics, structural trends, and charge transfer of adduct anion formation were studied.     

New Cyclosiloxanolate Cluster Complexes of Transition Metals

New cyclosiloxanolate transition metal cluster complex derivatives were prepared. PhSiO₂K reacted with NiX₂ (X₂ = Cl₂ or acac) to give K₂{[η⁶−(PhSiO₂)₆]₂[μ₃−(OH)]₂Ni₄K₄}, a mixed group 1–group 10 metal complex. PhSiO₂Na reacted with Ni(NH₃)₆I₂ to give Na{[η⁶−(PhSiO₂)₆]₂Ni₆(μ₆−I)} as the first example of “encapsulated” I⁻ ion in siloxanolate complexes. The macrocyclic Na₄{[η¹²−(PhSiO₂)₁₂]Cu₄} complex reacted with η⁶−(1,3,5−C₇H₈)Cr(CO)₃ to give the heterobimetallic adduct Na₄{[η¹²−(PhSiO₂)₁₂]Cu₄}· [Cr(CO)₃]₃ as one of the rare examples of heterobimetallic complexes with different oxidation numbers of the metals. The copper derivative {[η⁶−(PhSiO₂)₆]₂Cu₆(n−BuOH)₅} reacted in MeOH/CHCl₃ (1:6) with Et₄NCN to give the hexanuclear complex {[η⁶−(PhSiO₂)₆]₂Cu₆(η²−C₃H₅N₂O₂)₂}, containing 2-amino-2-oxoetanimidic acid methyl ester monoanion ligands, product of an unexpected C–C coupling reaction. This latter complex was characterized also by X-ray diffraction crystal and molecular structure determination. This paper is dedicated to the 70th birthday of Professor Dr. Gunter Schmid (Essen), pioneer of large cluster chemistry, known to friends as GOLD-Schmid, because of his famous discovery of the Au₅₅ cluster. The Authors are proud to be within his many friends.     

Synthesis and characterization of new sulfide aggregates of the type [{Pt2(μ3-S)2(P-P)2}M(C6F5)2] (M=Ni, Pd, Pt; P-P=2PPh3, 2PMe2Ph, dppf)

The reaction of [Pt₂(μ-S)₂(P-P)₂] (P-P=2PPh₃, 2PMe₂Ph, dppf) [dppf=1,1^′-bis(diphenylphosphino)ferrocene] with cis-[M(C₆F₅)₂(PhCN)₂] (M=Ni, Pd) or cis-[Pt(C₆F₅)₂(THF)₂] (THF=tetrahydrofuran) afforded sulfide aggregates of the type [{Pt₂(μ₃-S)₂(P-P)₂}M(C₆F₅)₂] (M=Ni, Pd, Pt). X-ray crystal analysis revealed that [{Pt₂(μ₃-S)₂(dppf)₂}Pd(C₆F₅)₂], [{Pt₂(μ₃-S)₂(PPh₃)₂}Ni(C₆F₅)₂], [{Pt₂(μ₃-S)₂(PPh₃)₂}Pd(C₆F₅)₂] and [{Pt₂(μ₃-S)₂(PMe₂Ph)₂}Pt(C₆F₅)₂] have triangular M₃S₂ core structures capped on both sides by μ₃-sulfido ligands. The structural features of these polymetallic complexes are described. Some of them display short metal-metal contacts.     

Synthesis and Crystal Structures of Group 10 Metal Bis(dithiolate) Complexes Constructed by 2,3-Naphtho-15-Crown-5 or 2,3-Naphtho-18-Crown-6

Five novel 2,3-naphtho crown ether group 10 metal bis(dithiolate) complexes, [Na(N15C5)₂]₂[Pd(mnt)₂] (1), [Na(N15C5)]₂[Pd(i-mnt)₂] (2) and [K(N18C6)]₂[M(i-mnt)₂] (3 5) (where mnt = 1,2-dicyanoethylene-1,2-dithiolate, i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and M = Ni, Pd, Pt for complexes 3–5, respectively), have been synthesized and characterized by elemental analysis, FT-IR, UV–Visible spectra and single crystal X-ray diffraction. X-ray diffraction analyses reveal that complexes 1 and 2 have different structural features while complexes 3–5 are structurally isomorphous. Complex 1 consists of two [Na(N15C5)₂]⁺ sandwich complex cations and one [Pd(mnt)₂]²⁻ anion, affording a zero-dimensional structure. For 2, the [Na(N15C5)]⁺ mono-capped complex cations act as the bridges linking the [Pd(i-mnt)₂]²⁻ anions into a 1D infinite chain through Na–N interactions and SȮFC and SȮFπ interactions are observed in the resulting chain. Complexes 3–5 all consist of two [K(N18C6)]⁺ complex cations and one [M(i-mnt)₂]²⁻ (M = Ni, Pd or Pt) anion and the complex molecules are linked into␣1D␣chains by the bridging K–O(ether) interactions between the adjacent [K(N18C6)]⁺ units. What’s novel is that the resulting chains are assembled into novel 2D networks through interchain π–π stacking interactions between the neighboring naphthylene moieties of N18C6. The stack model of naphthylene group in complexes 3–5 is discussed.     

Synthesis and crystal structure of [C6H5Hg(H2NSiMe3)][H2N{B(C6F5)3}2], a phenyl-mercury(II) cation stabilised by a non-coordinating counter-anion

The new heteroleptic mercury(II) complex PhHgN(SiMe₃)₂(1) reacts with the strong Brønsted acid [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] with cleavage of a N-Si bond to give [C₆H₅Hg(H₂NSiMe₃)][H₂N{B(C₆F₅)₃}₂] (2), a phenyl-mercury(II) cation stabilised by a primary amine and a non-coordinating counter-anion. Attempts to generate donor-free aryl mercury cations were not successful. The crystal structure of 2 · CH₂Cl₂ shows short π-bonding interactions between the metal and the phenyl ring of a neighbouring cation; the geometry about the mercury(II) atom is nearly linear. The X-ray structures of the new salts [H₂N(SiMe₃)₂ · H₃NSiMe₃][B(C₆F₅)₄]₂ and [Et₃O][H₂N{B(C₆F₅)₃}₂] · CH₂Cl₂ are also presented.     

Synthesis and Structure of the Alkoxido-Titanium Pentamolybdate (nBu4N)3[(iPrO)TiMo5O18]: An Entry into Systematic TiMo5 Reactivity

The alkoxido-titanium pentamolybdate [(ⁱPrO)TiMo₅O₁₈]³⁻ (1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA)₂[Mo₂O₇], (TBA)₄[Mo₈O₂₆] and Ti(OⁱPr)₄ in MeCN and has been characterised by ¹H, ¹³C, ¹⁷O, ⁴⁹Ti and ⁹⁵Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from [Mo₆O₁₉]²⁻ by replacement of {Mo=O}⁴⁺ by {(ⁱPrO)Ti}³⁺ and shows bond alternation in the TiMo₃O₄ rings, with average bond distances of 1.956(8) ? for Ti–O(Mo), 1.832(7) ? for Mo–O(Ti), 1.943(7) ? for Mo_eq–O(Mo_ax) and 1.910(6) ? for Mo_ax–O(Mo_eq), while the increase in charge results in a decrease in ¹⁷O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo₆O₁₉]²⁻ to δ 875 and 857 for 1 and a shift in ν_Mo=O from 951 cm⁻¹ for [Mo₆O₁₉]²⁻ to 930 cm⁻¹ for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA)₃ 1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)₂[(ⁱPrO)TiMo₅O₁₈]}⁻, {(TBA)[(ⁱPrO)TiMo₅O₁₈]}²⁻, {(ⁱPrO)TiMo₂O₈}⁻, {TiMo₅O₁₈}²⁻, {TiMo₄O₁₅}²⁻ and {Mo₃O₁₀}²⁻.     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).     

Accessing Cationic α-Silylated and α-Germylated Phosphorus Ylides

The synthesis and full characterization of α-silylated (α-SiCPs; 1 – 7 ) and α-germylated (α-GeCPs; 11 – 13 ) phosphorus ylides bearing one chloride substituent R₃PC(R¹)E(Cl)R²₂ (R=Ph; R¹=Me, Et, Ph; R²=Me, Et, iPr, Mes; E=Si, Ge) is presented. The molecular structures were determined by X-ray diffraction studies. The title compounds were applied in halide abstraction studies in order to access cationic species. The reaction of Ph₃PC(Me)Si(Cl)Me₂ ( 1 ) with Na[B(C₆F₅)₄] furnished the dimeric phosphonium-like dication [Ph₃PC(Me)SiMe₂]₂[B(C₆F₅)₄]₂ ( 8 ). The highly reactive, mesityl- or iPr-substituted cationic species [Ph₃PC(Me)SiMes₂][B(C₆F₅)₄] ( 9 ) and [Ph₃PC(Et)SiiPr₂][B(C₆F₅)₄] ( 10 ) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr₂O afforded the protonated α-SiCP [Ph₃PCH(Et)Si(Cl)iPr₂][B(C₆F₅)₄] ( 6 dec ) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph₃PC(Et)SiiPr₂][B(C₆F₅)₄] ( 10 ) readily cleaves the F−C bond in fluorobenzene. Thus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph₃PC(Me)GeMes₂][B{3,5-(CF₃)₂C₆H₃}₄] ( 14 ) was obtained by treating 11 with Na[B{3,5-(CF₃)₂C₆H₃}₄] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong C_Ylide−Ge interaction with high double bond character, and consequently the C−E (E=Si, Ge) bonds in 9 , 10 and 14 were analyzed with NBO and AIM methods.     

Stannylium ions, a tin(II) arene complex, and a tin dication stabilized by weakly coordinating anions

The reactivity of aryl‐substituted stannylenes, Ar₂Sn ( 4 ), towards silylarenium borates, [R₃SiArH][B(C₆F₅)₄] ( 3 ), was investigated. The reaction with 2,3,4‐trimethyl‐6‐tert‐butylphenyl (mebp)‐substituted stannylene gave silyl‐substituted stannylium ions 2 a , b , which were characterized by NMR spectroscopy supported by the results of quantum‐mechanical computations of molecular structures and magnetic properties. The tri‐iso‐propylphenyl‐substituted stannylium ions 2 c , d undergo a decomposition reaction in toluene to give the dicationic tin–arene complex [Sn(C₇H₈)₃]²⁺ ( 5 ) in the form of the [B(C₆F₅)₄] salt in high yields. The 5 [B(C₆F₅)₄]₂ salt was identified by single crystal X‐ray diffraction analysis and by Mössbauer spectroscopy. The bonding situation was investigated by using natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) calculations. The substitution of the weakly coordinating borate anion by the carboranate [CB₁₁H₆Br₆]^? results in replacement of the toluene ligands and formation of tin(II) carboranate with only weak Sn²⁺–anion interactions as suggested by the solid‐state structure of the isolated salt.     

Photochemical arene exchange in the ferracarborane complex [1-(η-C6H6)-12-ButNH-1,2,4,12-FeC3B8H10]+

The benzene complex [1-(η-C₆H₆)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀]⁺ (3a) was synthesized by the photochemical reaction of [(η⁵-C₆H₇)Fe(η-C₆H₆)]⁺ (1) with the anion [7-Bu^tNH-7,8,9-C₃B₈H₁₀]⁻ followed by the treatment of ferracarborane 1-(η⁵-C₆H₇)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀ (2) with hydrochloric acid. The benzene ligand in cation 3a is replaced by alkyl-substituted benzenes under visible light irradiation in CH₂Cl₂ to form [1-(η-C₆R₆)-12-Bu^tNH-1,2,4,12-FeC₃B₈H₁₀]⁺ (3b–e; C₆R₆ is toluene (b), mesitylene (c), hexamethylbenzene (d), or anisole (e)). The structure of [3c]PF₆ was established by X-ray diffraction.