Cyclopentadienyl Complexes of IrIII for Attempted C−D Bond Activation

The complexes Cp(MeIm)IrI₂ and Cp^Me4(MeIm)IrCl₂ have been prepared and subsequently methylated to form Cp(MeIm)IrMe₂ and Cp^Me4(MeIm)IrMe₂ (Cp=η⁵-C₅H₅, Cp^Me4=η⁵-C₅HMe₄, MeIm=1,3-dimethylimidazol-2-ylidene). We attempted unsuccessfully to use the dimethyl complexes to study C−D bond activation via methyl-group abstraction. Protonation with one equivalent of a weak acid, such as 2,6-dimethylpyridinium chloride, affords methane and Ir^III methyl chloride complexes. ¹H-NMR experiments show addition of pyridinium [BArF₂₀]⁻ (BArF₂₀=[B(C₆F₅)₄]⁻) to the dimethyl species forms [Cp(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ (py=pyridine) or [Cp^Me4(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ respectively, alongside methane, while use of the [BArF₂₀]⁻ salts of more bulky 2,6-dimethylpyridinium and 2,6-di-tert-butylpyridinium gave an intractable mixture. Likewise, the generation of 16 e⁻ species [Cp^Me4(MeIm)IrMe]⁺[BArF₂₀]⁻ or [Cp(MeIm)IrMe]⁺[BarF₂₀]⁻ at low temperature using 2,6-dimethylpyridinium or 2,6-di-tert-butylpyridinium in thawing C₆D₆ or toluene-d₈ formed an intractable mixture and did not lead to C−D bond activation. X-ray structures of several Ir^III complexes show similar sterics as that found for the previously reported Cp* analogue.     

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.     

Low-Valent MxAl3 Cluster Salts with Tetrahedral [SiAl3]+ and Trigonal-Bipyramidal [M2Al3]2+ Cores (M=Si/Ge)

Schnöckel's [(AlCp*)₄] and Jutzi's [SiCp*][B(C₆F₅)₄] (Cp*=C₅Me₅) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]⁺ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)₃][WCA] ([WCA]⁻=[Al(OR^F)₄]⁻ and [F{Al(OR^F)₃}₂]⁻; R^F=C(CF₃)₃). The tetrahedral [SiAl₃]⁺ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low-valent Si−Al clusters in general. For example, an elusive binuclear [Si₂(AlCp*)₅]²⁺ with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge₂(AlCp*)₅]²⁺ dication were also obtained and represent the first mixed Al−Ge cluster.     

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

Homogeneous olefin polymerization catalysts are activated in situ with a co-catalyst ([PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ or [Ph₃C]⁺[B(C₆F₅)₄]⁻) in bulk polymerization media. These co-catalysts are insoluble in hydrocarbon solvents, requiring excess co-catalyst (>3 eq.). Feeding the activated species as a solution in an aliphatic hydrocarbon solvent may be advantageous over the in situ activation method. In this study, highly pure and soluble ammonium tetrakis(pentafluorophenyl)borates ([Me(C₁₈H₃₇)₂N-H]⁺[B(C₆F₅)₄]⁻ and [(C₁₈H₃₇)₂NH₂]⁺[B(C₆F₅)₄]⁻) containing neither water nor Cl⁻ salt impurities were prepared easily via the acid–base reaction of [PhN(Me)₂-H]⁺[B(C₆F₅)₄]⁻ and the corresponding amine. Using the prepared ammonium salts, the activation reactions of commercial-process-relevant metallocene (rac-[ethylenebis(tetrahydroindenyl)]Zr(Me)₂ (1-ZrMe₂), [Ph₂C(Cp)(3,6-^tBu₂Flu)]Hf(Me)₂ (3-HfMe₂), [Ph₂C(Cp)(2,7-^tBu₂Flu)]Hf(Me)₂ (4-HfMe₂)) and half-metallocene complexes ([(η⁵-Me₄C₅)Si(Me)₂(κ-N^tBu)]Ti(Me)₂ (5-TiMe₂), [(η⁵-Me₄C₅)(C₉H₉(κ-N))]Ti(Me)₂ (6-TiMe₂), and [(η⁵-Me₃C₇H₁S)(C₁₀H₁₁(κ-N))]Ti(Me)₂ (7-TiMe₂)) were monitored in C₆D₁₂ with ¹H NMR spectroscopy. Stable [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻ species were cleanly generated from 1-ZrMe₂, 3-HfMe₂, and 4-HfMe₂, while the species types generated from 5-TiMe₂, 6-TiMe₂, and 7-TiMe₂ were unstable for subsequent transformation to other species (presumably, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species). [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species were also prepared from 5-TiCl(Me) and 6-TiCl(Me), which were newly prepared in this study. The prepared [L-M(Me)(NMe(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, [L-Ti(CH₂N(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-, and [L-TiCl(N(H)(C₁₈H₃₇)₂)]⁺[B(C₆F₅)₄]⁻-type species, which are soluble and stable in aliphatic hydrocarbon solvents, were highly active in ethylene/1-octene copolymerization performed in aliphatic hydrocarbon solvents.     

Cationic Functionalisation by Phosphenium Ion Insertion

The reaction of [Cp′′′Ni(η³-P₃)] ( 1 ) with in situ generated phosphenium ions [RR′P]⁺ yields the unprecedented polyphosphorus cations of the type [Cp′′′Ni(η³-P₄R₂)][X] (R=Ph ( 2 a ), Mes ( 2 b ), Cy ( 2 c ), 2,2′-biphen ( 2 d ), Me ( 2 e ); [X]⁻=[OTf]⁻, [SbF₆]⁻, [GaCl₄]⁻, [BAr^F]⁻, [TEF]⁻) and [Cp′′′Ni(η³-P₄RCl)][TEF] (R=Ph ( 2 f ), tBu ( 2 g )). In the reaction of 1 with [Br₂P]⁺, an analogous compound is observed only as an intermediate and the final product is an unexpected dinuclear complex [{Cp′′′Ni}₂(μ,η³:η¹:η¹-P₄Br₃)][TEF] ( 3 a ). A similar product [{Cp′′′Ni}₂(μ,η³:η¹:η¹-P₄(2,2′-biphen)Cl)][GaCl₄] ( 3 b ) is obtained, when 2 d [GaCl₄] is kept in solution for prolonged times. Although the central structural motif of 2 a – g consists of a “butterfly-like” folded P₄ ring attached to a {Cp′′′Ni} fragment, the structures of 3 a and 3 b exhibit a unique asymmetrically substituted and distorted P₄ chain stabilised by two {Cp′′′Ni} fragments. Additional DFT calculations shed light on the reaction pathway for the formation of 2 a – 2 g and the bonding situation in 3 a .     

Preparation and Structural Characterization of [CpRu(1,10-phenanthroline)(CH3CN)][X] and Precursor Complexes (X=PF6, BArF,TRISPHAT-N)

Cationic [Ru(η⁵-C₅H₅)(CH₃CN)₃]⁺ complex, tris(acetonitrile)(cyclopentadienyl)ruthenium(II), gives rise to a very rich organometallic chemistry. Combined with diimine ligands, and 1,10-phenanthroline in particular, this system efficiently catalyzes diazo decomposition processes to generate metal-carbenes which undergo a series of original transformations in the presence of Lewis basic substrates. Herein, syntheses and characterizations of [CpRu(Phen)(L)] complexes with (large) lipophilic non-coordinating (PF₆⁻ and BAr_F⁻) and coordinating TRISPHAT-N⁻ anions are reported. Complex [CpRu(η⁶-naphthalene)][BAr_F] ( [1][BAr_F] ) is readily accessible, in high yield, by direct counterion exchange between [1][PF₆] and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAr_F) salts. Ligand exchange of [1][BAr_F] in acetonitrile generated stable [Ru(η⁵-C₅H₅)(CH₃CN)₃][BAr_F] ( [2][BAr_F] ) complex in high yield. Then, the desired [CpRu(Phen)(CH₃CN)] ( [3] ) complexes were obtained from either the [1] or [2] complex in the presence of the 1,10-phenanthroline as ligand. For characterization and comparison purposes, the anionic hemilabile ligand TRISPHAT−N (TTN) was introduced on the ruthenium center, from the complex [3][PF₆] , to quantitatively generate the desired complex [CpRu(Phen)(TTN)] ( [4] ) by displacement of the remaining acetonitrile ligand and of the PF₆⁻ anion. Solid state structures of complexes [1][BAr_F] , [2][BAr_F] , [3][BAr_F] , [3][PF₆] and [4] were determined by X-ray diffraction studies and are discussed herein.     

A Structural Diversity of Molecular Alkaline-Earth-Metal Polyphosphides: From Supramolecular Wheel to Zintl Ion

A series of molecular group 2 polyphosphides has been synthesized by using air-stable [Cp*Fe(η⁵-P₅)] (Cp*=C₅Me₅) or white phosphorus as polyphosphorus precursors. Different types of group 2 reagents such as organo-magnesium, mono-valent magnesium, and molecular calcium hydride complexes have been investigated to activate these polyphosphorus sources. The organo-magnesium complex [(^DippBDI−Mg(CH₃))₂] (^DippBDI={[2,6-ⁱPr₂C₆H₃NCMe]₂CH}⁻) reacts with [Cp*Fe(η⁵-P₅)] to give an unprecedented Mg/Fe-supramolecular wheel. Kinetically controlled activation of [Cp*Fe(η⁵-P₅)] by different mono-valent magnesium complexes allowed the isolation of Mg-coordinated formally mono- and di-reduced products of [Cp*Fe(η⁵-P₅)]. To obtain the first examples of molecular calcium-polyphosphides, a molecular calcium hydride complex was used to reduce the aromatic cyclo-P₅ ring of [Cp*Fe(η⁵-P₅)]. The Ca-Fe-polyphosphide is also characterized by quantum chemical calculations and compared with the corresponding Mg complex. Moreover, a calcium coordinated Zintl ion (P₇)³⁻ was obtained by molecular calcium hydride mediated P₄ reduction.     

1,3-Diene Polymerization Promoted by Half-Sandwich Rare-Earth-Metal Dimethyl Complexes: Active Species Clustering and Cationization/Deactivation Processes

When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe₂]₃ (Ln=Y, Lu; Cp*=C₅Me₅) promote efficiently the formation of high-cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl. ¹H DOSY). The occurrence of donor-solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe₂]₃ and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*₃Y₃Me₄(CH₂)(thf)₂] and [Cp*₆Y₆Me₄(CH₂)₄], as well as [(Cp*Y)₂Me₂(N(Me)₂(C₆H₄)]_n[B(C₆F₅)₄]_n, implying a multimetallic active species.     

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: N?H and B?H Activation

Treatment of Me₂S ? B(C₆F₅)_nH_3?n (n=1 or 2) with ammonia yields the corresponding adducts. H₃N ? B(C₆F₅)H₂ dimerises in the solid state through N? H???H? B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH₂B(C₆F₅)_nH_3?n]. Reaction of the n=2 reagent with [Cp₂ZrCl₂] leads to disubstitution, but [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] is in equilibrium with the product of β‐hydride elimination [Cp₂Zr(H){NH₂B(C₆F₅)₂H}], which proves to be the major isolated solid. The analogous reaction with [Cp₂HfCl₂] gives a mixture of [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] and the N? H activation product [Cp₂Hf{NHB(C₆F₅)₂H}]. [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] ? PhMe and [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? 4(thf) exhibit β‐B‐agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp₂Hf{NHB(C₆F₅)₂H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond‐length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp₂MMe(μ‐Me)B(C₆F₅)₃] (M=Zr, Hf) with Li[NH₂B(C₆F₅)_nH_3?n] (n=2) results in [Cp₂MMe{NH₂B(C₆F₅)₂H}] complexes, for which the spectroscopic data, particularly ¹J(B,H), again suggest β‐B‐agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp′′₂ZrMe(μ‐Me)B(C₆F₅)₃] precursor (Cp′′=1,3‐C₅H₃(SiMe₃)₂, n=1 or 2) to give [Cp′′₂ZrMe{NH₂B(C₆F₅)_nH_3?n}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp′′₂HfMe₂] and the formation of Li[HB(C₆F₅)₃] through hydride abstraction.     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

Flexidentate Coordination Behavior and Chemical Non-Innocence of a Bis(1,3-Diphosphacyclobutadiene) Sandwich Anion

The homoleptic 1,3-diphosphacyclobutadiene sandwich complex [Co(η⁴-1,3-P₂C₂tBu₂)₂]⁻ behaved as a versatile and highly flexible metalloligand toward Ni²⁺, Ru²⁺, Rh⁺, and Pd²⁺ cations, forming a range of unusual oligonuclear compounds. The reaction of [K(thf)₂{Co(η⁴-1,3-P₂C₂tBu₂)₂}] with [Ni₂Cp₃]BF₄ initially afforded the σ-complex [CpNi{Co(η⁴-1,3-P₂C₂tBu₂)₂}(thf)] ( 2 ), which converted into [Co(η⁴-CpNi{1,3-P₂C₂tBu₂-κP,κC})(η⁴-1,3-P₂C₂tBu₂)] ( 3 ) below room temperature. The structure of 3 contains an unprecedented 1,4-diphospha-2-nickelacyclopentadiene moiety formed by an oxidative addition of a ligand P−C bond onto nickel. At elevated temperatures, 3 isomerized to [Co(η⁴-CpNi{1,4-P₂C₂tBu₂-κ²P,P})(η⁴-1,3-P₂C₂tBu₂)] ( 4 ), which features a 1,3-diphospha-2-nickelacyclopentadiene unit. Transmetalation of [K(thf)₂{Co(η⁴-1,3-P₂C₂tBu₂)₂}] with [Cp*RuCl]₄ (Cp*=C₅Me₅) afforded tetranuclear [(Cp*Ru)₃(μ-Cl)₂{Co(η⁴-1,3-P₂C₂tBu₂)₂}] ( 5 ), in which the [Co(η⁴-1,3-P₂C₂tBu₂]⁻ anion acts as a chelate ligand toward Ru²⁺. The diphosphido complex [(Cp*Ru)₂(μ,η²-P₂)(μ,η²-C₂tBu₂)] ( 6 ) was formed as a byproduct. Pure compound 6 was isolated after prolonged heating of the reaction mixture. The reaction of [K(thf)₂{Co(η⁴-1,3-P₂C₂R₂)₂}] (R=tBu; adamantyl, Ad) with [RhCl(cod)]₂ (cod=1,5-cyclooctadiene) afforded unprecedented π-complexes [Rh(cod){Co(η⁴-1,3-P₂C₂R₂)₂}] ( 7 : R=tBu; 8 : R=Ad), in which one μ:η⁴:η⁴-P₂C₂R₂ ligand bridges two metal atoms. The pentanuclear complex [Pd₃(PPh₃)₂{Co(η⁴-1,3-P₂C₂tBu₂)₂}₂] ( 10 ), featuring a Pd₃ chain and a rare 1,4-diphospha-2-butene ligand, was synthesized by reacting [K(thf)₂{Co(η⁴-1,3-P₂C₂tBu₂)₂}] with cis-PdCl₂(PPh₃)₂. The redox properties of selected compounds were analyzed by cyclic voltammetry, whereas DFT calculations gave additional insight into the electronic structures. The results of this study revealed several remarkable and previously unrecognized properties of the [Co(P₂C₂tBu₂)₂]⁻ anion.     

Simple Synthesis of Ruthenium π Complexes of Aromatic Amino Acids and Small Peptides

The interaction of [Ru(η⁶‐C₁₀H₈)(Cp)]⁺ (Cp=C₅H₅) with aromatic amino acids (L ‐phenylalanine, L ‐tyrosine, L ‐tryptophane, D ‐phenylglycine, and L ‐threo‐3‐phenylserine) under visible‐light irradiation gives the corresponding [Ru(η⁶‐amino acid)(Cp)]⁺ complexes in near‐quantitative yield. The reaction proceeds in air at room temperature in water and tolerates the presence of non‐aromatic amino acids (except those which are sulfur containing), monosaccharides, and nucleotides. The complex [Ru(η⁶‐C₁₀H₈)(Cp)]⁺ was also used for selective labeling of Tyr and Phe residues of small peptides, namely, angiotensin I and II derivatives.     

One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications

Electron-transferable oxidants such as B(C₆F₅)₃/nBuLi, B(C₆F₅)₃/LiB(C₆F₅)₄, B(C₆F₅)₃/LiHBEt₃, Al(C₆F₅)₃/(o-RC₆H₄)AlH₂ (R=N(CMe₂CH₂)₂CH₂), B(C₆F₅)₃/AlEt₃, Al(C₆F₅)₃, Al(C₆F₅)₃/nBuLi, Al(C₆F₅)₃/AlMe₃, (CuC₆F₅)₄, and Ag₂SO₄, respectively were employed for reactions with (L)₂Si₂C₄(SiMe₃)₂(C₂SiMe₃)₂ (L=PhC(NtBu)₂, 1 ). The stable radical cation [ 1 ]^+. was formed and paired with the anions [nBuB(C₆F₅)₃]⁻ (in 2 ), [B(C₆F₅)₄]⁻ (in 3 ), [HB(C₆F₅)₃]⁻ (in 4 ), [EtB(C₆F₅)₃]⁻ (in 5 ), {[(C₆F₅)₃Al]₂(μ-F)]⁻ (in 6 ), [nBuAl(C₆F₅)₃]⁻ (in 7 ), and [Cu(C₆F₅)₂]⁻ (in 8 ), respectively. The stable dication [ 1 ]²⁺ was also generated with the anions [EtB(C₆F₅)₃]⁻ ( 9 ) and [MeAl(C₆F₅)₃]⁻ ( 10 ), respectively. In addition, the neutral compound [(L)₂Si₂C₄(SiMe₃)₂(C₂SiMe₃)₂][μ-O₂S(O)₂] ( 11 ) was obtained. Compounds 2 – 11 are characterized by UV-vis absorption spectroscopy, X-ray crystallography, and elemental analysis. Compounds 2 – 8 are analyzed by EPR spectroscopy and compounds 9 – 11 by NMR spectroscopy. The structure features are discussed on the central Si₂C₄-rings of 1 , [ 1 ]^+., [ 1 ]²⁺, and 11 , respectively.     

Formation of an Azaruthenacyclopentadiene Skeleton via Ammonia Activation by an Electron-Deficient Ru3 Cluster

A dicationic triruthenium complex containing a μ₃-η³-C₃ ring, [(Cp*Ru)₃(μ₃-η³-C₃MeH₂−)(μ₃-CH)(μ-H)]²⁺ ( 1 a , Cp*=η⁵-C₅Me₅), reacted with ammonia to yield a μ-amido complex, [(Cp*Ru)₃(μ₃-η³-CHCMeCH) (μ₃-CH)(μ-NH₂)]²⁺ ( 5 ), via N−H bond scission. Subsequent treatment with base resulted in C−N bond formation to yield a μ₃-η²:η²-1-azabutadien-4-yl complex, [(Cp*Ru)₃(μ₃-CH)(μ₃-η²:η²-NH=CH−CMe=CH−)]⁺ ( 6 a ). The azaruthenacyclopentadiene skeleton was alternatively synthesized by the photolysis of mono-cationic complex [(Cp*Ru)₃(μ₃-η³-C₃RH₂−)(μ₃-CH)]⁺ ( 2 a ; R=Me, 2 b ; R=H) in the presence of ammonia. The C₃ ring skeleton was broken via the electron transfer to the π*(C−C) orbital in the C₃ ring, and a transiently generated unsaturated μ₃-allylic species can take up ammonia, resulting in N−H bond scission followed by C−N bond formation.     

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).     

Aluminum(III) Cations [(NHC) ⋅ AlMes2]+: Synthesis,Characterization, and Application in FLP-Chemistry

The three-coordinate aluminum cations ligated by N-heterocyclic carbenes (NHCs) [(NHC) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ (NHC=IMe^Me 4 , IiPr^Me 5 , IiPr 6 , Mes=2,4,6-trimethylphenyl) were prepared via hydride abstraction of the alanes (NHC) ⋅ AlHMes₂ (NHC=IMe^Me 1 , IiPr^Me 2 , IiPr 3 ) using [Ph₃C]⁺[B(C₆F₅)₄]⁻ in toluene as hydride acceptor. If this reaction was performed in diethyl ether, the corresponding four-coordinate aluminum etherate cations [(NHC) ⋅ AlMes₂(OEt₂)]⁺ [B(C₆F₅)₄]⁻ 7 – 9 (NHC=IMe^Me 7 , IiPr^Me 8 , IiPr 9 ) were isolated. According to a theoretical and experimental assessment of the Lewis-acidity of the [(IMe^Me) ⋅ AlMes₂]⁺ cation is the acidity larger than that of B(C₆F₅)₃ and of similar magnitude as reported for Al(C₆F₅)₃. The reaction of [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ 4 with the sterically less demanding, basic phosphine PMe₃ afforded a mixed NHC/phosphine stabilized cation [(IMe^Me) ⋅ AlMes₂(PMe₃)]⁺[B(C₆F₅)₄]⁻ 10 . Equimolar mixtures of 4 and the sterically more demanding PCy₃ gave a frustrated Lewis-pair (FLP), i.e., [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻/PCy₃ FLP-11 , which reacts with small molecules such as CO₂, ethene, and 2-butyne.     

Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings

New zincocenes [ZnCp′₂] ( 2 – 5 ) with substituted cyclopentadienyl ligands C₅Me₄H, C₅Me₄tBu, C₅Me₄SiMe₂tBu and C₅Me₄SiMe₃, respectively, have been prepared by the reaction of ZnCl₂ with the appropriate Cp′‐transfer reagent. For a comparative structural study, the known [Zn(C₅H₄SiMe₃)₂] ( 1 ), has also been investigated, along with the mixed‐ring zincocenes [Zn(C₅Me₅)(C₅Me₄SiMe₃)] ( 6 ) and [Zn(C₅Me₅)(C₅H₄SiMe₃)] ( 7 ), the last two obtained by conproportionation of [Zn(C₅Me₅)₂] with 5 or 1 , as appropriate. All new compounds were characterised by NMR spectroscopy, and by X‐ray methods, with the exception of 7 , which yields a side‐product ( C ) upon attempted crystallisation. Compounds 5 and 6 were also investigated by ¹³C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped‐sandwich geometries. Compounds 5 and 6 have rigid, η⁵/η¹(σ) structures, in which the monohapto C₅Me₄SiMe₃ ligand is bound to zinc through the silyl‐bearing carbon atom, forming a Zn? C bond of comparable strength to the Zn? Me bond in ZnMe₂. Zincocene 5 has dynamic behaviour in solution, but a rigid η⁵/η¹(σ) structure in the solid state, as revealed by ¹³C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η¹‐Cp′ group (Me and SiMe₃) have permitted observation for the first time of the rigid η⁵/η¹ solution structure. Iminoacyl compounds of composition [Zn(η⁵‐C₅Me₄R)(η¹‐C(NXyl)C₅Me₄R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6‐dimethylphenylisocyanide) have also been obtained and characterised.     

The Arene‐Stabilized η5‐Pentamethylcyclopentadienyl Arsenic Dication [(η5‐Cp*)As(toluene)]2+

Double chloride abstraction of Cp*AsCl₂ gives the dicationic arsenic species [(η⁵‐Cp*)As(tol)][B(C₆F₅)₄]₂ ( 2 ) (tol=toluene). This species is shown to exhibit Lewis super acidity by the Gutmann–Beckett test and by fluoride abstraction from [NBu₄][SbF₆]. Species 2 participates in the FLP activation of THF affording [(η²‐Cp*)AsO(CH₂)₄(THF)][B(C₆F₅)₄]₂ ( 5 ). The reaction of 2 with PMe₃ or dppe generates [(Me₃P)₂As][B(C₆F₅)₄] ( 6 ) and [(σ‐Cp*)PMe₃][B(C₆F₅)₄] ( 7 ), or [(dppe)As][B(C₆F₅)₄] ( 8 ) and [(dppe)(σ‐Cp*)₂][B(C₆F₅)₄]₂ ( 9 ), respectively, through a facile cleavage of C?As bonds, thus showcasing unusual reactivity of this unique As‐containing compound.     

Zur Reaktivität von Titanocenkomplexen [Ti(Cp′)2(η2‐Me3SiC≡CSiMe3)] (Cp′ = Cp,Cp*) gegenüber Benzoldicarbonsäuren

On the Reactivity of Titanocene Complexes [Ti(Cp′)₂(η²‐Me₃SiC≡CSiMe₃)] (Cp′ = Cp, Cp*) towards Benzenedicarboxylic Acids Titanocene complexes [Ti(Cp′)₂(BTMSA)] ( 1a , Cp′ = Cp = η⁵‐C₅H₅; 1b , Cp′ = Cp* = η⁵‐C₅Me₅; BTMSA = Me₃SiC≡CSiMe₃) were found to react with iodine and methyl iodide yielding [Ti(Cp′)₂(μ‐I)₂] ( 2a / b ; a refers to Cp′ = Cp and b to Cp′ = Cp*), [Ti(Cp′)₂I₂] ( 3a / b ) and [Ti(Cp′)₂(Me)I] ( 4a / b ), respectively. In contrast to 2a , complex 2b proved to be highly moisture sensitive yielding with cleavage of HCp* [{Ti(Cp*)I}₂(μ‐O)] ( 7 ). The corresponding reactions of 1a / b with p‐cresol and thiophenol resulted in the formation of [Ti(Cp′)₂{O(p‐Tol)}₂] ( 5a / b ) and [Ti(Cp′)₂(SPh)₂] ( 6a / b ), respectively. Reactions of 1a and 1b with 1,n‐benzenedicarboxylic acids (n = 2–4) resulted in the formation of dinuclear titanium(III) complexes of the type [{Ti(Cp′)₂}₂{μ‐1,n‐(O₂C)₂C₆H₄}] (n = 2, 8a / b ; n = 3, 9a / b ; n = 4, 10a / b ). All complexes were fully characterized analytically and spectroscopically. Furthermore, complexes 7 , 8b , 9a ·THF, 10a / b were also be characterized by single‐crystal X‐ray diffraction analyses.     

Nucleophilic Attack at Pentaarsaferrocene [Cp*Fe(η5-As5)]—The Way to Larger Polyarsenide Ligands

By the reaction of [Cp*Fe(η⁵-As₅)] ( I ) (Cp*=C₅Me₅) with main group nucleophiles, unique functionalized products with η⁴-coordinated polyarsenide (As_n) units (n=5, 6, 20) are obtained. With carbon-based nucleophiles such as MeLi or KBn (Bn=CH₂Ph), the anionic organo-substituted polyarsenide complexes, [Li(2.2.2-cryptand)][Cp*Fe(η⁴-As₅Me)] ( 1 a ) and [K(2.2.2-cryptand)][Cp*Fe{η⁴-As₅(CH₂Ph)}] ( 1 b ), are accessible. The use of KAsPh₂ leads to a selective and controlled extension of the As₅ unit and the formation of the monoanionic compound [K(2.2.2-cryptand][Cp*Fe(η⁴-As₆Ph₂)] ( 2 ). When I is reacted with [M]As(SiMe₃)₂ (M=Li ⋅ THF; K), the formation of the largest known anionic polyarsenide unit in [M′(2.2.2-cryptand)]₂[(Cp*Fe)₄{μ₅-η⁴:η⁴:η³:η³:η¹:η¹-As₂₀}] ( 3 ) occurred (M′=Li ( 3 a ), K ( 3 b )).