Metathetical Exchange Research Articles

Dielectric response and density functional theory assessment of fluorinated dicationic pyridinium ionic liquids

AbstractThis study represent the synthesis and electrical conductivity of two focused dicationic pyridinium ionic liquids (DiILs) carrying tetrafluoroborate and/or hexafluorophosphate as counter anion. Thus, the synthesis required quaternization of the pyridine nitrogen atoms first, followed by a metathetical exchange reaction to produce the task‐specific ILs bearing tetrafluoroborate and hexafluorophosphate as counter anions. The resulting DiILs were characterized by NMR and MS spectroscopy. The dielectric constant and the conductivity of the targeted DiILs were analyzed in detail, within a frequency‐range of 1 KHz to 0.3 MHz and a temperature range of 25–100°C. Density functional theoretical (DFT) calculations were also carried out at the base site, B3LYP 6–311 g (d,p), for the Syn/E isomers of the investigated ionic liquids (ILs). We found non‐coplanar molecular geometries with a twist angle of the Schiff base, dependent on the type of counter ion present. The energy levels and differences of the frontier molecular orbitals (FMOs) were also predicted using DFT calculations. The results revealed that the ILs incorporating BF4− as counter anions showed high HOMO and LUMO values with a higher energy gap, while low FMOs with a lower energy gap were recorded for the derivative encompassing PF6− counter anions. These findings were used to help explain the dielectric properties of the investigated DiILs.

Toward E-selective Olefin Metathesis: Computational Design and Experimental Realization of Ruthenium Thio-Indolate Catalysts

The selective transformation of 1-alkenes into E-olefins is a long-standing challenge in olefin metathesis. Density functional theory (DFT) calculations predict high E-selectivity for catalysts incorporating a bidentate, dianionic thio-indolate ligand within a RuXX’(NHC)(py)(= CHR) platform (NHC = N-heterocyclic carbene; py = pyridine). Such complexes are predicted to yield E-olefins by favoring anti-disposed substituents in the transition state expected to be rate-determining: specifically, that for cycloreversion of the metallacyclobutane intermediate. Three pyridine-stabilized catalysts Ru21a-c were synthesized, in which the thio-indolate ligand bears a H, Me, or Ph substituent at the C2 position, and the NHC ligand is the unsaturated imidazoline-2-ylidene Me2IMes (which bears N-mesityl groups and methyl groups on the C4,5 backbone). Single-crystal X-ray diffraction analysis of Ru21c confirms the ligand orientation required for E-selective metathesis, with the thio-indolate sulfur atom binding cis to the NHC, and the indolate nitrogen atom trans to the NHC. However, whereas the new complexes mediated metathetic exchange of their 2-thienylmethylidene ligand in the presence of the common metathesis substrates styrene and allylbenzene, no corresponding self-metathesis products were obtained. Only small amounts of 2-butene (73% (Z)-2-butene) were obtained in self-metathesis of propene using Ru21a. Detailed DFT analysis of this process revealed that product release is surprisingly slow, limiting the reaction rate and explaining the low metathesis activity. With the barrier to dissociation of (Z)-2-butene being lower than that of (E)-2-butene, the calculations also account for the observed Z-selectivity of Ru21a. These findings provide guidelines for catalyst redesign in pursuit of the ambitious goal of E-selective 1-alkene metathesis.Graphic abstract

Metathetical Exchange between Metal-Metal Triple Bonds.

The reaction of the molybdenum-molybdenum triple-bonded dimer (CO)2CpMo≡MoCp(CO)2 (Cp = η5-C5H5) with the triple-bonded dimetallynes AriPr4MMAriPr4 or AriPr6MMAriPr6 (AriPr4 = C6H3-2,6-(C6H3-2,6-Pri2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6-Pri3)2; M = Ge, Sn, or Pb) under mild conditions (≤80 °C, 1 bar) afforded AriPr4M≡MoCp(CO)2 or AriPr6M≡MoCp(CO)2 in moderate to excellent yields. The reactions represent the first isolable products from a metathesis of two metal-metal triple bonds. Analogous exchange reactions with the single-bonded (CO)3CpMo-MoCp(CO)3 gave ArM̈-MoCp(CO)3 (Ar = AriPr4 or AriPr6; M = Sn or Pb). The products were characterized by NMR (1H, 13C, 119Sn, or 207Pb), electronic, and IR spectroscopy and by X-ray crystallography.

Carbamato-benzylidene ruthenium chelates – Synthesis, structure and catalytic activity in olefin metathesis

New carbamato-κN-benzylidene ruthenium chelates were synthesized from the first [RuCl2(PCy3)2(=CHPh)] and second [RuCl2(SIMes)(PCy3)(=CHPh)] generation Grubbs catalysts by metathetic exchange of benzylidene ligand for tert-butyl (2-vinylphenyl)carbamates bearing benzylidene ligand substituted in the position para to carbamato functionality with methyl or trifluoromethyl group. In all metathetical transformations tested, i.e. in ROMP of cycloocta-1,5-diene, RCM of diethyl diallylmalonate and diethyl 2-allyl-2-(2-methylallyl)malonate and cross-metathesis of allylbenzene with Z-1,4-diacetoxybut-2-ene, the complexes behave like latent catalysts. Complexes remain completely inactive until they are activated by the addition of ethereal solution of HCl. The presence of the electron-withdrawing group results in a slight increase in the catalytic activity of the activated form of the catalyst relative to a similar form of the unsubstituted complex or the least active complex carrying the electron donating group.

Closing the Loop on Transition-Metal-Mediated Nitrogen Fixation: Chemoselective Production of HN(SiMe3)2 from N2, Me3SiCl, and X-OH (X = R, R3Si, or Silica Gel).

Treatment of the Mo(IV) terminal imido complex, (η5-C5Me5)[N(Et)C(Ph)N(Et)]Mo(NSiMe3) (3), with a 1:2 mixture of iPrOH and Me3SiCl resulted in the rapid formation of the Mo(IV) dichloride, (η5-C5Me5)[N(Et)C(Ph)N(Et)]MoCl2 (1), and the generation of 1 equiv each of HN(SiMe3)2 and iPrOSiMe3. Similarly, a 1:2 mixture of Me3SiOH and Me3SiCl provided 1, HN(SiMe3)2, and O(SiMe3)2. Finally, silica gel, when coupled with excess equivalents of Me3SiCl, was also effectively used as the X-OH reagent for the generation of 1 and HN(SiMe3)2. A proposed mechanism for the 3 → 1 transformation involves formal addition of HCl across the Mo═N imido bond through initial hydrogen-bonding between X-OH and the N-atom of 3 to form the adduct IIIb, followed by chloride delivery from Me3SiCl to the metal center via a six-membered transition state (IV) that leads to the intermediate, (η5-C5Me5)[N(Et)C(Ph)N(Et)]Mo(Cl)(NHSiMe3) (V), and XOSiMe3 as a co-product. Metathetical exchange of the new Mo-N amido bond of V by a second equivalent of Me3SiCl then generates 1 and HN(SiMe3). These results serve to complete a highly efficient chemical cycle for nitrogen fixation that is mediated by a set of well-characterized transition-metal complexes.

Coordination Chemistry of [E(Idipp)]2+Ligands (E = Ge, Sn): Metal Germylidyne [Cp*(CO)2W≡Ge(Idipp)]+and Metallotetrylene [Cp*(CO)3W–E(Idipp)]+Cations

The synthesis and full characterization of the NHC-stabilized tungstenochlorostannylene [Cp*(CO)3W–SnCl(Idipp)] (1Sn), the NHC-stabilized chlorogermylidyne complex [Cp*(CO)2W═GeCl(Idipp)] (2), the tungsten germylidyne complex salt [Cp*(CO)2W≡Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (3), and the cationic metallostannylene [Cp*(CO)3W–Sn(Idipp)][Al(OC(CF3)3)4] (4Sn) are reported (Idipp = 2,3-dihydro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene, Cp* = η5-C5Me5). Metathetical exchange of SnCl2(Idipp) with Li[Cp*W(CO)3] afforded selectively 1Sn. Photolytic decarbonylation of the Ge analogue [Cp*(CO)3W–GeCl(Idipp)] (1Ge) afforded the NHC-stabilized chlorogermylidyne complex (2), featuring a trigonal-planar coordinated germanium center and a W–Ge double bond (W–Ge 2.3496(5) Å). Chloride abstraction from 2 with Na[B(C6H3-3,5-(CF3)2)4] yielded the germylidyne complex salt 3, which contains an almost linear W–Ge–C1 linkage (angle at Ge = 168.7(1)°) and a W–Ge triple bond (2.2813(4) Å). Chloride elimination from 1Ge afforded the tungstenogermylene salt [Cp*(CO)3W–Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (4Ge), which in contrast to 1Ge could not be decarbonylated to form 3 despite the less strongly bound carbonyl ligands. The tin compounds 1Sn and 4Sn did not afford products bearing multiple W–Sn bonds. Treatment of 4Ge with Me2NC≡CNMe2 yielded unexpectedly the neutral germyl complex 5 containing a pendant 1-germabicyclo-[3,2,0]-hepta-2,5-diene ligand instead of the anticipated [2 + 1]-cycloaddition product at the Ge-center.

Chiral (SO)–N–(SO) Sulfoxide Pincer Complexes of Mg, Rh, and Ir: N–H Activation and Selective Sulfoxide Reduction upon Ligand Coordination

Multigram quantities of the optically pure amino–bis-sulfoxide ligand (S,S)-bis(4-tert-butyl-2-(p-tolylsulfinyl)phenyl)amine ((S,S)-3) are accessible by in situ lithiation of bis(2-bromo-4-tert-butylphenyl)amine (1) followed by a nucleophilic displacement reaction with Andersen’s sulfinate 2. Deprotonation of (S,S)-3 with MgPh2 yields the magnesium amido–bis-sulfoxide salt (S,S)-4 quantitatively. Metathetical exchange of (S,S)-4 with [RhCl(COE)2]2 affords the optically pure pseudo-C2-symmetric Rh(I)–amido bis-sulfoxide pincer complex mer-(R,R)-[Rh(bis(4-(tert-butyl)-2-(p-tolylsulfinyl)phenyl)amide)(COE)] (mer-(R,R)-5). This complex reacts with 3 equiv of HCl to give the facial Rh(III) complex fac-(S,R,R)-[Rh(bis(4-(tert-butyl)-2-(p-tolylsulfinyl)phenyl)amine)Cl3] (fac-(S,R,R)-6), in which one of the sulfoxide functions has been reduced to the sulfide and in which the resulting sulfoxide–sulfide–amine ligand is facially coordinated. The same complexes 5 and 6 form in a 1:2 ratio in a disproportionation reaction when [RhCl(COE)2]2 is treated with 2 equiv of neutral ligand 3. N–H activation is directly observed in the reaction of [IrCl(COE)2]2 with 3, affording the amido–hydrido–Ir(III) complex [Ir(bis(4-(tert-butyl)-2-(p-tolylsulfinyl)phenyl)amide)(Cl)(H)(COE)] (8).

Synthesis and reactivity of trans- N, N′-dimethyl- meso-octaalkylporphyrinogen Sm(II), Eu(II) and Yb(II) complexes: Metal-based influences on the reduction of t-butyl-1,4-diazabuta-1,3-diene

Sm(II), Eu(II) and Yb(II) complexes of doubly deprotonated trans- N, N′-dimethyl- meso-octaethylporphyrinogen were synthesised as tetrahydrofuran adducts (Sm and Eu, bis; Yb, mono) by metathetical exchange reactions of the dipotassium macrocyclic precursor complexes with the corresponding metal diiodides in tetrahydrofuran. The Sm and Eu complexes partially desolvate in non-coordinating solvents to give mono-tetrahydrofuran adducts. Subsequent reactions of the initial Eu(II) and Yb(II) complexes with 1,4-di- t-butyl-1,4-diazabuta-1,3-diene failed to yield complexes featuring the 1,4-diazabuta-1,3-diene binding to the lanthanide centres either as neutral Lewis base donors or reduced ligands, which contrasts with previous findings in the case of the analogous Sm(II) reaction. These outcomes are discussed in relation to the variety of Ln(III)–Ln(II) reduction potentials, coordination number and oxidation state dependent ionic radii of the metals and macrocycle–ancillary ligand steric interactions. The complexes were characterised by X-ray crystal structure determination, satisfactory microanalysis and NMR spectroscopy, where possible.

Stable N‐Heterocyclic Carbene Adducts of Arylchlorosilylenes and Their Germanium Homologues

The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me(4)) [Ar=C(6)H(3)-2,6-Mes(2) (Mes=C(6)H(2)-2,4,6-Me(3)), C(6)H(3)-2,6-Trip(2) (Trip=C(6)H(2)-2,4,6-iPr(3))] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl(2) with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me(4)). The analogous arylgermanium(II) chlorides GeArCl(Im-Me(4)) were prepared by metathetical exchange of GeCl(2)(Im-Me(4)) with LiC(6)H(3)-2,6-Mes(2) or addition of Im-Me(4) to GeCl(C(6)H(3)-2,6-Trip(2)). All compounds were fully characterized. Density functional calculations on ECl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)) (Delta(calcd) degrees=28.1 kJ mol(-1)) suggests that the carbene adducts SiArCl(Im-Me(4)) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.

Hirshfeld surface analysis of phosphonium salts

Structurally authenticated phosphonium salts yielded from the treatment of (phosphoniumn+)(Cl− or Br−)n and (imidazoliumn+)(X−)n, n = 1 or 2 have been examined using Hirshfeld surface analysis, revealing the domination of C–H⋯X non-classical hydrogen-bonding between the cations and anions. The crystalline salts of (phosphoniumn+)(X−)n (X− = [SCN]−, [N(CN)2]−, [C(CN)3]−, [PF6]−, [CF3SO3]− or [N(CF3SO2)2]−) were formed by metathetical exchange in the presence of p-sulfonatocalix[4]arene and aquated gadolinium ions.

B(C 6F 5) 3 catalyzed dehydrocarbon polycondensation of PhSiH 3 with (MeO) 4Si as model polyfunctional comonomers in new route to hydrophobic silicone TQ resins

Highly branched methoxy substituted phenylsilsesquioxane-silicate copolymers were obtained by dehydrocarbon polycondensation of phenylsilane (PhSiH 3) with tetramethoxysilane (TMOS) in toluene solution catalyzed by tris(pentafluorophenyl)borane [B(C 6F 5) 3]. This model reaction represents a new non-hydrolytic route to TQ silicone resins, which do not contain reactive and hydrophilic silanol groups and therefore, should be more stable and have better miscibility with some organic polymers. The soluble siloxane copolymers, which do not contain volatile oligomers, were obtained using the PhSiH 3:TMOS molar ratios below 0.9. The dehydrocarbon condensation is accompanied by metathetic exchange of hydrosilyl and methoxysilyl functions, which is responsible for the formation of links between units originating from the same comonomer. Competition between the dehydrocarbon condensation and metathesis is consistent with a mechanism involving the transient formation of a tertiary oxonium ion intermediate. 29Si NMR analysis of the copolymer product proves that extensive cyclization occurs during the polycondensation, most likely leading to a significant proportion of ladder and cage like structures.

Fluoride Ion Uptake by Synthetic Apatites

Fluoride uptake by synthetic apatites from aqueous solutions was studied as a function of fluoride ion concentration. The phosphate minerals synthesized and considered included different varieties of phosphate minerals of the apatite group such as hydroxy-, carbonato- and chloro-apatite, all being precipitated at the boiling point. An ion-selective electrode technique was used for fluoride ion analysis in the adsorption experiments and electrokinetic measurements were utilized to delineate specific adsorption effects. The results suggest that, at low fluoride ion concentrations, a fluoroapatite-type compound may form on the apatite surface via the chemisorption of fluoride ions at calcium sites; at high fluoride ion concentrations, calcium fluoride appears to form at the apatite surface via a surface-precipitation phenomenon. The formation of CaF2 on the surface of fluoride ion-treated apatite was further substantiated by FT-IR spectroscopic measurements, which clearly demonstrated a metathetic exchange w...

Neuartige Silane mit sterisch anspruchsvollen Aryl‐Substituenten

AbstractNovel Silanes with Sterically Demanding Aryl SubstituentsA series of novel m‐terphenylsilanes was synthesized and fully characterized. Halogenation of Si(C6H3‐2,6‐Trip2)H3 (1, Trip = C6H2‐2,4,6‐iPr3) with ICl and BI3 afforded the m‐terphenylmonochlorosilane Si(C6H3‐2,6‐Trip2)H2Cl (2) and the m‐terphenyldiiodosilane Si(C6H3‐2,6‐Trip2)HI2 (3), respectively. The chiral phosphanylmethylsilane Si(C6H3‐2,6‐Trip2)HCl(CH2PMe2) (6) was obtained by metathetical exchange of Si(C6H3‐2,6‐Trip2)HCl2 (4) with the Grignard reagent Me2PCH2MgCl (5). Similarly, metathetical exchange of SiBr4 with 0.5 equiv. of {Li(C6H3‐2,6‐Mes)}2 (7) yielded the m‐terphenyltribromsilane Si(C6H3‐2,6‐Mes2)Br3 (8). A Pd(II) catalyzed reaction of MesSiH3 (10) with 2‐iodopropane afforded the triiodosilane MesSiI3 (11) bearing the sterically less demanding mesityl substituent. The silanes were fully characterized and the molecular structures of compounds 2 and 11 were determined by single‐crystal X‐ray diffraction.

Synthesis of Highly Branched Alkoxysiloxane−Dimethylsiloxane Copolymers by Nonhydrolytic Dehydrocarbon Polycondensation Catalyzed by Tris(pentafluorophenyl)borane

A new approach to the synthesis of highly branched alkoxy functionalized polysiloxanes has been developed. Dehydrocarbon polycondensation of tetraalkoxysilanes with 1,1,3,3-tetramethyldisiloxane (HMMH) catalyzed by tris(pentafluorophenyl)borane [B(C6F5)3] leads to highly branched organopolysiloxanes substituted with alkoxy groups at silicon atoms. These copolymers could be used as silanol-free hydrophobic silicone resins. Polycondensations of HMMH with tetramethoxysilane (TMOS) and with tetraethoxysilane (TEOS), catalyzed by B(C6F5)3, were studied. Use of TMOS or TEOS lead to stable, soluble, branched copolymers containing a great number of reactive alkoxy groups. Dehydrocarbon polycondensation is accompanied by a metathetic exchange of functional groups as well as cleavage of siloxane bonds adjacent to the Si−H group. Both of these reactions, as well as dehydrocarbon polycondensation, occur via the tertiary silyloxonium borate intermediate.

Covalent Functionalization of Carbon Nanotubes Through Organometallic Reduction and Electrophilic Attack

Organometallic reagents such as butyllithium are known to covalently functionalize the sidewalls of carbon nanotubes. The function grafted corresponds to the organic part of the alkali compound, while one negative charge is transferred to the nanotube for each function. Carbon nanotubes reduced by organolithium compounds were used here as nucleophilic reactive species through these transferred and delocalized charges. Various halogenated electrophiles in excess were reacted with them in anhydrous conditions. The grafting of the corresponding chemical function onto the carbon nanotubes through a Lewis metathetic exchange reaction was demonstrated by chemical, thermal, and spectroscopic analyses. This synthetic route applied successfully to both single-walled and multi-walled nanotubes and to a series of electrophiles. The extent of functionalization was found to depend on stoechiometries used, although a direct correlation could not be obtained.

Snapshots of an Alkylidyne for Nitride Triple-Bond Metathesis

The transient titanium alkylidyne complex (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-), [2+2] cycloadds sterically bulky nitriles such as NCR to afford unique examples of kinetically stable azametallacyclobutadienes, (PNP)Ti(NCRCtBu) (R = tBu, 1; Ad, 2). Complexes 1 and 2 can further react with electrophiles such as ClSi(CH3)3 or Al(CH3)3 to extrude the alkyne RC⋮CtBu (R = tBu, 1; R = Ad, 2) and form neutral or zwitterionic titanium imide species, respectively. Imide formation for the latter species results from complete tBuC3- for N3- metathetical exchange. Isotopic labeling studies applying 15N enriched nitrile N⋮CAd clearly reveal the nitrogen atom transfer results from incomplete and complete metathesis of a titanium alkylidyne with a nitrile.

Mono-phosphacyclopentadienyl bis(tetramethylaluminate) lanthanide complexes

Homoleptic complexes Ln(AlMe(4))(3) (Ln = La, Nd) can be straightforwardly utilized in salt metathetic exchange reactions with potassium 2,3,4,5-tetramethylphospholide (KTmp) or 3,4-dimethyl-2,5-bis(trimethylsilyl)phospholide (KDsp) affording monophosphacyclopentadienyl hydrocarbyl complexes (eta(5)-PC(4)Me(4))Ln(AlMe(4))(2) and [eta(5)-PC(4)Me(2)(SiMe(3))(2)]Ln(AlMe(4))(2) (Ln = La, Nd). The solid-state structures reveal distinct metal size effects as evidenced by X-ray diffraction analyses of monomeric neodymium Tmp and Dsp derivatives as well as the dimeric lanthanum Tmp complex. Dimerization is accomplished by intermolecular P --> La donor contacts. Upon activation with [PhMe(2)NH][B(C(6)F(5))(4)] the monophosphacyclopentadienyl complexes initiate the polymerization of isoprene producing 1,4-trans-polyisoprene (tPIP > 87%) with moderate activity (approximately 30 kg(PIP) mol(Ln)(-1) h(-1)).

A Nitridoniobium(V) Reagent That Effects Acid Chloride to Organic Nitrile Conversion: Synthesis via Heterodinuclear (Nb/Mo) Dinitrogen Cleavage, Mechanistic Insights, and Recycling

The transformation of acid chlorides (RC(O)Cl) to organic nitriles (RC[triple bond]N) by the terminal niobium nitride anion [N[triple bond]Nb(N[Np]Ar)3]- ([1a-N]-, where Np = neopentyl and Ar = 3,5-Me2C6H3) via isovalent N for O(Cl) metathetical exchange is presented. Nitrido anion [1a-N]- is obtained in a heterodinuclear N2 scission reaction employing the molybdenum trisamide system, Mo(N[R]Ar)3 (R = t-Bu, 2a; R = Np, 2b), as a reaction partner. Reductive scission of the heterodinuclear bridging N2 complexes, (Ar[R]N)3Mo-(mu-N2)Nb(N[Np]Ar)3 (R = t-Bu, 3b; R = Np, 3c) with sodium amalgam provides 1 equiv each of the salt Na[1a-N] and neutral N[triple bond]Mo(N[R]Ar)3 (R = t-Bu, 2a-N; R = Np, 2b-N). Separation of 2-N from Na[1a-N] is readily achieved. Treatment of salt Na[1a-N] with acid chloride substrates in tetrahydrofuran (THF) furnishes the corresponding organic nitriles concomitant with the formation of NaCl and the oxo niobium complex O[triple bond]Nb(N[Np]Ar)3 (1a-O). Utilization of 15N-labeled 15N2 gas in this chemistry affords a series of 15N-labeled organic nitriles establishing the utility of anion [1a-N]- as a reagent for the 15N-labeling of organic molecules. Synthetic and computational studies on model niobium systems provide evidence for the intermediacy of both a linear acylimido and niobacyclobutene species along the pathway to organic nitrile formation. High-yield recycling of oxo 1a-O to a niobium triflate complex appropriate for heterodinuclear N2 scission has been developed. Specifically, addition of triflic anhydride (Tf2O, where Tf = SO2CF3) to an Et2O solution of 1a-O provides the bistriflate complex, Nb(OTf)2(N[Np]Ar)3 (1a-(OTf)2), in near quantitative yield. One-electron reduction of 1a-(OTf)2 with either cobaltocene (Cp2Co) or Mg(THF)3(anthracene) provided the monotriflato complex, Nb(OTf)(N[Np]Ar)3 (1a-(OTf)), which efficiently regenerates complexes 3b and 3c when treated with the molybdenum dinitrogen anions [N2Mo(N[t-Bu]Ar)3]- ([2a-N2]-) or [N2Mo(N[Np]Ar)3]- ([2b-N2]-), respectively.

Halide Substitution Reactions of the Germylidyne Complexestrans-[X(dppe)2W⋮Ge(η1-Cp*)] (X = Cl, I; dppe = Ph2PCH2CH2PPh2; Cp* = C5Me5)

The first reactions of the germylidyne complexes trans-[X(dppe)2W⋮Ge(η1-Cp*)]·[toluene] (1-Cl·C7H8, X = Cl; 1-I·C7H8, X = I) with nucleophiles and electrophiles are reported. Treatment of 1-I·C7H8 with KBH4 in refluxing THF affords selectively the hydrido−germylidyne complex trans-[H(dppe)2W⋮Ge(η1-Cp*)] (2). Similarly, metathetical exchange of 1-I·C7H8 with an excess of MY (M = Na, K; Y = NCO, N3, NCS, CN) gives the pseudohalide complexes trans-[Y(dppe)2W⋮Ge(η1-Cp*)]·x(toluene) (3a, Y = NCO, x = 0; 3b, Y = N3, x = 0; 3c·C7H8, Y = NCS, x = 1; 3d·0.5C7H8, Y = CN, x = 0.5). Chloride abstraction from 1-Cl·C7H8 with Li[B(C6F5)4]·2.5Et2O yields in the presence of acetonitrile the first cationic germylidyne complex, trans-[(MeCN)(dppe)2W⋮Ge(η1-Cp*)][B(C6F5)4] (4). All new complexes were well characterized. The molecular structures of 2·1.5C6D6, 3a·THF, 3d·0.5C7H8, and 4 were determined by single-crystal X-ray diffraction studies. The germylidyne complexes reveal very short W−Ge distances (dW-Ge = 229.91(9)−231.8...

Synthetic, reactivity, and structural studies on half-sandwich (eta5-C5Me5)Be and related compounds: halide, alkyl, and iminoacyl derivatives.

The half-sandwich compounds [(eta(5)-C(5)Me(5))BeX] (X=Cl, 1 a; Br, 1 b), readily prepared from the reaction of the halides BeX(2) and M[C(5)Me(5)] (M=Na or K), are useful synthons for other (eta(5)-C(5)Me(5))Be organometallic compounds, including the alkyl derivatives [(eta(5)-C(5)Me(5))BeR] (R=Me, 2 a; CMe(3), 2 b; CH(2)CMe(3), 2 c; CH(2)Ph, 2 d). The latter compounds can be obtained by metathetical exchange of the halides 1 with the corresponding lithium reagent and exhibit NMR signals and other properties in accord with the proposed formulation. Attempts to make [(eta(5)-C(5)Me(5))BeH] have proved fruitless, probably due to instability of the hydride toward disproportionation into [Be(C(5)Me(5))(2)] and BeH(2). The half-sandwich iminoacyl [(eta(5)-C(5)Me(5))Be(C(NXyl)Cp')] and [(eta(5)-C(5)Me(4)H)Be(C(NXyl)Cp')]3, 6 where Xyl=C(6)H(3)-2,6-Me(2) and Cp'=C(5)Me(5) or C(5)Me(4)H, are formed when the beryllocenes [Be(C(5)Me(5))(2)], [Be(C(5)Me(4)H)(2)], and [Be(C(5)Me(5))(C(5)Me(4)H)] are allowed to react with CNXyl. Isolation of three different iminoacyl isomers from the reaction of the mixed-ring beryllocene [(eta(5)-C(5)Me(5))Be(eta(1)-C(5)Me(4)H)] and CNXyl, namely compounds 5 a, 5 b, and 6, provides compelling evidence for the existence in solution of different beryllocene isomers, generated in the course of two very facile processes that explain the solution dynamics of these metallocenes, that is the 1,5-sigmatropic shift of the Be(eta(5)-Cp') unit around the periphery of the eta(1)-Cp' ring, and the molecular inversion rearrangement that exchanges the roles of the two rings.