Yttrium Siloxide Complexes Bearing Terminal Methyl Ligands: Molecular Models for Ln−CH3 Terminated Silica Surfaces

Surface organometallic chemistry (SOMC) on silica materials is a prominent approach for the generation of highly active heterogenized polymerization catalysts. Despite advanced methods of characterization, the elucidation of the catalytically active surface species remains a challenging task. Alkylated rare‐earth metal siloxide complexes can be regarded as molecular models of respective covalently bonded alkylated surface species, primarily used for 1,3‐diene polymerization. Here, we performed both salt metathesis reactions of [Y(MMe₄)₃] (M = Al, Ga) with [K{OSi(OtBu)₃}] and alkylation reactions of [Y{OSi(OtBu)₃}₃]₂ with AlMe₃. The obtained complexes [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂](AlMe₄)]₂, [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂]‐{OSi(OtBu)₃}], [Y{OSi(OtBu)₃}₃(μ‐Me)Y(μ‐Me)₂Y{OSi(OtBu)₃}₂(AlMe₄)], and [Y(CH₃)(GaMe₄){OSi(OtBu)₃}]₂ represent rare examples of organoyttrium species with terminal methyl groups. The formation and purity of the mixed methyl/siloxy yttrium complexes could be enhanced by treating [Y(MMe₄)₃] with [K(MMe₂){OSi(OtBu)₃}₂]_n (M=Al: n=2; M=Ga: n=∞). Complexes [K(MMe₂){OSi(OtBu)₃}₂]_n were obtained by addition of [K{OSi(OtBu)₃}] to [Me₂M{OSi(OtBu)₃}]₂. Deeper insight into the fluxional behavior of the mixed methyl/siloxy yttrium complexes in solution was gained by ¹H and ¹³C NMR spectroscopic studies at variable temperature and ¹H–⁸⁹Y HSQC NMR spectroscopy.     

Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization

Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(O^tBu)₃)₃]₂} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐N^tBu)(μ‐O₂Si(O^tBu)₂)U₂(OSi(O^tBu)₃)₅}. Complex 1 displayed reactivity towards CS₂ and CO₂ at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS₂ yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS₃)[U(OSi(O^tBu)₃)₃]₂} via a putative NCS^?/S^2? intermediate. The reaction of 1 with one equivalent of CO₂ resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(O^tBu)₃)₃]₂}. Addition of excess CO₂ to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC₂O₄)[U(OSi(O^tBu)₃)₃]₂}.     

Synthesen und Reaktionen von Aluminiumalkoxid‐Verbindungen

Syntheses and Reactions of Aluminium Alkoxide Compounds Al(O^cHex)₃ ( 1 ) can be synthesized by the reaction of Al with cyclohexanol under evolving of H₂ in boiling xylene. [Li{Al(OCH₂Ph)₄}] ( 2 ) was obtained by treatment of PhCH₂OH with a 1 M solution of LiAlH₄ in THF. [{(THF)Li}₂{Al(O^tBu)₄}Cl] ( 3 ) is the result of the reaction of four equivalents of LiO^tBu on AlCl₃ in THF. 3 is the educt for the reactions with the Lewis‐acids InCl₃ and FeCl₃ in THF leading to the metalates [{(THF)₂Li}₂{Al(O^tBu)₄}] · [MCl₄] [M = In ( 4 ), Fe ( 5 )]. The attempt to react InCl₃ with four equivalents of LiO^tBu leads to only one isolated and characterized product, the complex [Li₄(O^tBu)₃(THF)₃Cl]₂ · THF ( 6 · THF), which can also be synthesized by the treatment of LiCl with three equivalents of LiO^tBu in THF. 1–6 · THF were characterized by NMR, IR and MS techniques as well as by X‐ray structure determinations. According to them, 1 , which is tetrameric in solution, is the first structurally characterized example of the proposed trimer form of aluminium alkoxides [ROAl{Al(OR)₄}₂] with a central trigonal bipyramidal coordinated Al atom. 2 forms a coordination polymer with a distorted tetrahedral coordination sphere of Li and Al, running along [100]. The trinuclear structure skeleton [{(THF)₂Li}₂{Al(O^tBu)₄}]⁺ is still present in the isotypical metalates 4 and 5 . The counter ions [MCl₄]^– possess nearly T_d symmetry. The remarkable structural motif of 6 · THF are two heterocubanes [Li₄(O^tBu)₃(THF)₃Cl] dimerized by Li–Cl bonds.     

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 3 ) and [K₂{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 4 ) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 2 ) with stoichiometric amounts of KC₈ yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being U^V–(arene^4?)–U^V, KU^IV–(arene^4?)–U^V, and K₂U^IV–(arene^4?)–U^IV for complexes 2 , 3 , and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the U^IV mononuclear complex [U(OSi(OtBu)₃)₃(OTf)(thf)₂] ( 5 ). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.     

Metallat‐Ionen [Al(OR)4]— als Chelatliganden für Übergangsmetall‐Kationen

Metalat Ions [Al(OR)₄]^— as Chelating Ligands for Transition Metal Cations Waterfree CoCl₂ can be reacted with [{Li(Diglyme)}{Al(O^tBu)₄}] in THF to the complex [Li(THF)₄][{CoCl₂}{Al(O^tBu)₄}]. Addition of diglyme to the reaction mixtures gives the blue compound [Li(diglyme)₂][{CoCl₂}{Al(O^tBu)₄}] ( 1 ). According to this procedure the Fe^II complex [Li(Diglyme)₂][{FeCl₂}₂{Al(O^tBu)₄}] ( 2 ) was formed by treatment of FeCl₂ with Li[Al(O^tBu)₄]. [{Li(diglyme)}{Al(O^tBu)₄}] in THF/diglyme can be used as alkoxide transfer reagent on TiCl₄ to give the neutral complex [TiCl₂(O^tBu)₂(diglyme)] ( 3 ). The sky‐blue salt [Li(THF)₄]₂[{CoCl₂}₃{Al(OCH₂Ph)₄}₂] ( 4 ) was obtained by reaction of Li[Al(OCH₂Ph)₄] with CoCl₂ in THF. By treatment of 4 with diglyme ligand redistribution was observed giving the sky‐blue compound [Li(Diglyme)₂]₂[{CoCl₂}₃{Al(OCH₂Ph)₄}₂] ( 5 ) and the violet salt [Li(Diglyme)₂]₂[Co₂Cl₅(OCH₂Ph)] ( 6 ). A similar salt can be synthesized also directly from Li[Al(O^tBu)₄] and CoCl₂ in diglyme to give [Li(Diglyme)₂]₂[Co₂Cl₅(O^tBu)] ( 7 ). 1 — 7 were characterized by IR spectroscopy, partly by mass spectrometry and X‐ray analyses. UV‐VIS spectra were recorded from 1 and 5 . According to the X‐ray analyses the M^II ions as well as the Al^III ions are coordinated distorted tedrahedrally. In 1 , 2 , 4 und 5 the unit [Al(OR)₄]^— acts a chelating ligand as desired.     

Chalcogenide Derivatives of Imidotin Cage Complexes

Reaction of the secocubane [Sn₃(μ₂‐NHtBu)₂(μ₂‐NtBu)(μ₃‐NtBu)] ( 1 ) with dibutylmagnesium produces the heterobimetallic cubane [Sn₃Mg(μ₃‐NtBu)₄] ( 4 ) which forms the monochalcogenide complexes of general formula [ESn₃Mg(μ₃‐NtBu)₄] ( 5 a , E=Se; 5 b , E=Te) upon reaction with elemental chalcogens in THF. By contrast, the reaction of the anionic lithiated cubane [Sn₃Li(μ₃‐NtBu)₄]^? with the appropriate quantity of selenium or tellurium leads to the sequential chalcogenation of each of the three Sn^II centres. Pure samples of the mono‐ or dichalcogenides are, however, best obtained by stoichiometric redistribution reactions of [Sn₃Li(μ₃‐NtBu)₄]^? and the trichalcogenides [E₃Sn₃Li(μ₃‐NtBu)₄]^? (E=Se, Te). These reactions are conveniently monitored by using ¹¹⁹Sn NMR spectroscopy. The anion [Sn₃Li(μ₃‐NtBu)₄]^? also acts as an effective chalcogen‐transfer reagent in reactions of selenium with the neutral cubane [{Snμ₃‐N(dipp)}₄] ( 8 ) (dipp=2,6‐diisopropylphenyl) to give the dimer [(thf)Sn{μ‐N(dipp)}₂Sn(μ‐Se)₂Sn{μ‐N(dipp)}₂Sn(thf)] ( 9 ), a transformation that results in cleavage of the Sn₄N₄ cubane into four‐membered Sn₂N₂ rings. The X‐ray structures of 4 , 5 a , 5 b , [Sn₃Li(thf)(μ₃‐NtBu)₄(μ₃‐Se)(μ₂‐Li)(thf)]₂ ( 6 a ), [TeSn₃Li(μ₃‐NtBu)₄][Li(thf)₄] ( 6 b ), [Te₂Sn₃Li(μ₃‐NtBu)₄][Li([12]crown‐4)₂] ( 7 b′′ ) and 9 are presented. The fluxional behaviour of cubic imidotin chalcogenides and the correlation between NMR coupling constants and tin–chalcogen bond lengths are also discussed.     

Characteristics of the Template Synthesis of Mesoporous Materials Based on Titanosilicon Esters

Titanosilicon mesoporous materials with a high content of titanium (up to Ti/Si 0.36) and high adsorptive characteristics have been obtain from the titanosilicon ester molecular precursors (BuO)₂Ti[OSi(O ^t Bu)₃]₂ and BuOTi[OSi(O ^t Bu)₃]₃ by template synthesis in the presence of micelle forming surfactants. A characteristic of these mesoporous matrices is the considerable size of the walls of the mesopores (2-4 nm) which may results from the use of the bulky titanosilicon building blocks in the template synthesis.     

Reversible Dihydrogen Activation and Hydride Transfer by a Uranium Nitride Complex

Cleavage of dihydrogen is an important step in the industrial and enzymatic transformation of N₂ into ammonia. The reversible cleavage of dihydrogen was achieved under mild conditions (room temperature and 1 atmosphere of H₂) by the molecular uranium nitride complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐N)] 1, leading to a rare hydride–imide bridged diuranium(IV) complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐H)(μ‐NH)], 2 that slowly releases H₂ under vacuum. This complex is highly reactive and quickly transfers hydride to acetonitrile and carbon dioxide at room temperature, affording the ketimide‐ and formate‐bridged U^IV species [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐NH)(μ‐CH₃CHN)], 3 and [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐HCOO)(μ‐NHCOO)], 4 .     

Vanadium(V) Oxo and Imido Calix[8]arene Complexes: Synthesis,Structural Studies,and Ethylene Homo/Copolymerisation Capability

Interaction of p‐tert‐butylcalix[8]areneH₈ (L⁸H₈) with [NaVO(OtBu)₄] (formed in situ from VOCl₃) afforded the complex [Na(NCMe)₅][(VO)₂L⁸H]?4 MeCN ( 1 ?4 MeCN). Increasing [NaVO(OtBu)₄] to 4 equiv led to [Na(NCMe)₆]₂[(Na(VO)₄L⁸)(Na(NCMe))₃]₂?10 MeCN ( 2 ?10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)₃] with L⁸H₈ afforded the alkali‐metal‐free complex [(VO)₄L⁸(μ³‐O)₂] ( 3 ); solvates 3 ?3 MeCN and 3 ?3 CH₂Cl₂ were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert‐butoxide was added to L⁸H₈ and then treated with 2 equiv of VOCl₃; crystallisation afforded [(VO₂)₂Li₆[L⁸](thf)₂(OtBu)₂(Et₂O)₂]?Et₂O ( 4 ?Et₂O). Upon extraction into acetonitrile, [Li(NCMe)₄][(VO)₂L⁸H]?8 MeCN ( 5 ?8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)₃] and [V(Np‐tolyl)(OtBu)₃] and L⁸H₈, afforded [tBuNH₃][{V(p‐tolylN)}₂L⁸H]?3 1/2 MeCN ( 6 ?3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1 , 3 , and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)^?1 were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl₂]. For copolymerisation, incorporation of propylene was 7.1–10.9 mol % (compare 10 mol % for [VO(OEt)Cl₂]), although catalytic activities were lower than [VO(OEt)Cl₂].     

Polyimido Sulfur(VI) Phosphanyl Ligand in Metal Complexation

Herein, new complexes containing the [Ph₂PCH₂S(NtBu)₃]^? anion are presented, supplying three imido nitrogen atoms and a remote phosphorus atom as potential donor sites to main group and transition‐metal cations. The lithiated complex [(tmeda)Li{(NtBu)₃SCH₂PPh₂}] ( 1 ) is an excellent starting material in transmetalation reactions. Herein, the transition‐metal complexes [M{(NtBu)₃SCH₂PPh₂}₂] (M=Mn ( 2 ), Ni ( 3 ), Zn ( 4 )) were synthesized and structurally characterized. Their isotypical molecules show SN₂ chelation and no employment of the adjacent phosphorus atom in coordination. The third pendent imido group is always twisted toward the vacant face of the tetrahedrally coordinated sulfur atom.     

The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines,Carbenes, and Phosphide

Alkylation of spiro[fluorene-9,3’-indazole] at N(1) and N(2) with tBuCl affords the nitrenium cations [C₆H₄N₂(tBu)C(C₁₂H₈)][BF₄], 1 and 2 , respectively. Compound 1 converts to 2 over the temperature range 303–323 K with a free energy barrier of 28±5 kcal mol⁻¹. Reaction of 1 with PMe₃ afforded the N-bound phosphine adduct [C₆H₄N(tBu)N(PMe₃)C(C₁₂H₈)]BF₄] 3 . However, phosphines attack 2 at the para-carbon atom of the aryl group with concurrent cleavage of N(2)−C(1) bond and proton migration to C(1) affording [(R₃P)C₆H₃NN(tBu)CH(C₁₂H₈)][BF₄] (R=Me 4 , nBu 5 ). Analogous reactions of 1 and 2 with the carbene SIMes prompt attack at the para-carbon with concurrent loss of H^. affording the radical cation salts [(SIMes)C₆H₃N(tBu)NC(C₁₂H₈)^.][BF₄] 6 and [(SIMes)C₆H₃NN(tBu)C(C₁₂H₈)^.][BF₄] 7 , whereas reaction of 2 with BAC gives the Lewis acid-base adduct, [C₆H₄N(BAC)N(tBu)C(C₁₂H₈)][BF₄] 8 . Finally, reactions of 1 and 2 with KPPh₂ result in electron transfer affording (PPh₂)₂ and the persistent radicals C₆H₄N(tBu)NC(C₁₂H₈)^. and C₆H₄NN(tBu)C(C₁₂H₈)^.. The detailed reaction mechanisms are also explored by extensive DFT calculations.     

Treatment of a Methylene‐Bridged Dialuminium Compound with Lithium Alkanides and Alkynides ‐ Single vs. Twofold Terminal Coordination

We have investigated the coordination of alkanide and alkynide anions to the coordinatively unsaturated aluminium atoms of the methylene‐bridged dialuminium compound R₂Al‐CH₂‐AlR₂ [ 1 , R = CH(SiMe₃)₂]. Treatment of 1 with the corresponding lithium derivatives in the presence of a small excess of TMEN (TMEN = tetramethylethylenediamine) yielded mono‐adducts [M]⁺[R₂Al‐CH₂‐AlR₂R']^– [ 2a , M = Li(TMEN)₂, R' = Me; 2b , M = Li(TMEN)₂, R' = n‐Bu; 3a , M = Li(TMEN)₂, R' = C≡C‐SiMe₃; 3b , M = Li(TMEN)₂, R' = C≡C‐t‐Bu; 3d , M = Li(DME)₃, R' = C≡C‐Ph; 3e , M = Li(TMEN)₂, R' = C≡C‐PPh₂)] and bis‐adducts [Li(TMEN)₂]⁺[LiCH₂(AlR₂R')₂]^– [ 4a , R' = C≡C‐CH₂‐NEt₂; 4b , R' = C≡C‐t‐Bu]. In the solid state the mono‐adducts have clearly separated coordinatively saturated (coordination number four) and unsaturated aluminium atoms (coordination number three). In solution the groups R' show a fast exchange between both aluminium atoms as evident from the room temperature NMR spectra that showed in most cases equivalent CH(SiMe₃)₂ groups despite different coordination spheres of the metal atoms. Only 2b gave the expected splitting of resonances at ambient temperature, while cooling was required to prevent the dynamic process for 3a . The dialkynide 4a has a unique molecular structure with one of the lithium cations bonded to the α‐carbon atoms of the alkynido ligands and to the carbon atom of the methylene bridge which is five‐coordinate with a distorted trigonal bipyramidal coordination sphere.     

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).     

Bidentate Disilicate Framework for Bis-Grafted Surface Species

Recent advances in surface organometallic chemistry have enabled the detailed characterization of the surface species in single-site heterogeneous catalysts. However, the selective formation of bis-grafted surface species remains challenging because of the heterogeneity of the supporting surface. Herein, we introduce a metal complex bearing bidentate disilicate ligands, −OSi(O^tBu)₂OSi(O^tBu)₂O−, as a molecular precursor, which has a silicate framework adjacent to the metal (Pt) center. The grafting of the precursors on silica supports (MCM-41 and CARiACT Q10) proceeded through a substitution reaction on the silicon atoms of the disilicate ligand, which was verified by the detection of isobutene and ^tBuOH as the elimination products, to selectively yield bis-grafted surface species. The chemical structure of the surface species was characterized by solid-state NMR, and the chemical shift values of the ancillary ligands and ¹⁹⁵Pt nuclei suggested that the bidentate coordination sphere was maintained following grafting.     

Facile synthesis of zwitterionic organoaluminum complexes containing formally dianionic homoscorpionate ligands

A series of zwitterionic aluminum complexes of the type AlX[(2‐O‐3,5‐tBu₂C₆H₂)₃PZ] (AlX [O₃PZ]; X = Cl, Me, Et, and iBu; Z = H, Me) containing C₃‐symmetric, formally dianionic, facially tridentate ligands [O₃PZ]^2? were prepared and structurally characterized. Although serendipitous, these complexes can be readily synthesized by partial protonolysis of AlX₃ with equal molar (2‐HO‐3,5‐tBu₂C₆H₂)₃P (H₃[O₃P]) or [(2‐HO‐3,5‐tBu₂C₆H₂)₃p.m.e](OTf) ({H₃[O₃PMe]}OTf) in THF at 25°C or elevated temperatures. Alcoholysis of AlMe[O₃PMe] ( 2 ) with an excess amount of MeOH in refluxing toluene generates AlOMe[O₃PMe] ( 10 ). Salt metathesis of AlCl[O₃PMe] ( 6 ) with nBuM (M = Li, MgCl) and NaOR (R = tBu, Ph) in ethereal solutions affords AlnBu[O₃PMe] ( 9 ) and AlOR[O₃PMe] (R = tBu ( 11 ), Ph ( 12 )), respectively. Reactivity of 10 , 11 , and 12 with respect to catalytic ring‐opening polymerization of ε‐caprolactone is assessed.     

Creating Iron– and Rhenium–Bismuth Bonds by Reactions with Organometallic Hydrides

While addition of [Cp₂ReH] to [Bi(OtBu)₃] leads to an equilibrium containing [Cp₂Re‐Bi(OtBu)₂], [{Cp₂Re}₂Bi(OtBu)], tBuOH and [CpRe(μ‐η⁵,η¹‐C₅H₄)Bi–ReCp₂], in the presence of water [{(Cp₂Re)₂Bi}₂O] ( 1 ) is formed selectively. Also [FpH] [Fp = (η⁵‐C₅H₅)(CO)₂Fe] can be employed as a precursor to form heterometallic bismuth compounds. Synthesis of [FpBi{OCH(CF₃)₂}₂]₂ ( 5 ) can be achieved by reaction of [FpH] with [Bi{OCH(CF₃)₂}₃(thf)]₂ and carboxylates [FpBi(O₂CR)₂]₂ are generated upon treatment of [FpH] with [Bi(O₂CR)₃] (R = CH₃, tBu). While the compounds [Fp‐Bi(O₂CR)₂]₂ can also be obtained from reactions with Fp‐Fp, they are formed far more readily using [FpH] as the precursor. They typically crystallize as dimers, like the alkoxide 5 . A monomeric compound of the type [Fp‐BiX₂] ( 6 ) could be isolated for X = thd (tetramethylheptanedionate), that is, after the reaction of [FpH] with [Bi(thd)₃]. Altogether, the results demonstrate the potential of [FpH] as a precursor for [Fp‐BiX₂] compounds, which are formed in reactions with bismuth alkoxides, carboxylates and diketonates.     

Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene

The reactivity of the reduced anthracene complex of scandium [Li(thf)₃][Sc{N(tBu)Xy}₂(anth)] ( 2-anth-Li ) (Xy=3,5-Me₂C₆H₃; anth=C₁₄H₁₀²⁻, thf=tetrahydrofuran) toward Brønsted acid [NEt₃H][BPh₄] and azobenzene is reported. While a stepwise protonation of 2-anth-Li with two equivalents of [NEt₃H][BPh₄] afforded the scandium cation [Sc{N(tBu)Xy}₂(thf)₂][BPh₄] ( 3 ), reduction of azobenzene gave a thermolabile, anionic scandium reduced azobenzene complex [Li(thf)][Sc{N(tBu)Xy}₂(η²-PhNNPh)] ( 4 ), which slowly lost one of the anilide ligands to form the neutral scandium azobenzene complex dimer [Sc{N(tBu)Xy}(μ-η²:η²-Ph₂N₂)]₂ ( 5 ). Exposure of 3 to CO₂ produced the scandium carbamate complex [Sc{κ²-O₂CN(tBu)(Xy)}₂][BPh₄] ( 6 ) as a result of CO₂ insertion into the Sc−N bonds. In an attempt to prepare scandium hydrides, the reaction of 3 with the hydride sources LiAlH₄ and Na[BEt₃H] led to the terminal aluminum hydride [AlH{N(tBu)Xy}₂(thf)] ( 7 ) and the scandium n-butoxide [Sc{N(tBu)(Xy)}₂(μ-OnBu)] ( 8 ) after Sc/Al transmetalation and nucleophilic ring-opening of THF, respectively. All reported compounds isolated in moderate to good yields were fully characterized.     

Synthesis and X‐ray Structures of the Polycyclic Dimers {[PhB(μ‐NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ‐NtBu)2AsN(tBu)Li]2

The metathesis of [PhB(μ‐NtBu)₂]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ‐NtBu)₂AsN(tBu)H] ( 1 ) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ‐NtBu)₂AsN(tBu)Li] ( 2a ). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U‐shaped, centrosymmetric dimer in which the monomeric [PhB(μ‐NtBu)₂AsN(tBu)]^?Li⁺ units are linked by Li‐N interactions to give a six‐rung ladder. Oxidation of 2a with one‐half equivalent of I₂ in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ‐NtBu)₂AsN(tBu)H]LiI}₂ ( 1 ·LiI) with a central Li₂I₂ ring.     

Chiral Fluorinated α‐Sulfonyl Carbanions: Enantioselective Synthesis and Electrophilic Capture,Racemization Dynamics,and Structure

Enantiomerically pure triflones R¹CH(R²)SO₂CF₃ have been synthesized starting from the corresponding chiral alcohols via thiols and trifluoromethylsulfanes. Key steps of the syntheses of the sulfanes are the photochemical trifluoromethylation of the thiols with CF₃Hal (Hal=halide) or substitution of alkoxyphosphinediamines with CF₃SSCF₃. The deprotonation of RCH(Me)SO₂CF₃ (R=CH₂Ph, iHex) with nBuLi with the formation of salts [RC(Me)? SO₂CF₃]Li and their electrophilic capture both occurred with high enantioselectivities. Displacement of the SO₂CF₃ group of (S)‐MeOCH₂C(Me)(CH₂Ph)SO₂CF₃ (95 % ee) by an ethyl group through the reaction with AlEt₃ gave alkane MeOCH₂C(Me)(CH₂Ph)Et of 96 % ee. Racemization of salts [R¹C(R²)SO₂CF₃]Li follows first‐order kinetics and is mainly an enthalpic process with small negative activation entropy as revealed by polarimetry and dynamic NMR (DNMR) spectroscopy. This is in accordance with a C_α? S bond rotation as the rate‐determining step. Lithium α‐(S)‐trifluoromethyl‐ and α‐(S)‐nonafluorobutylsulfonyl carbanion salts have a much higher racemization barrier than the corresponding α‐(S)‐tert‐butylsulfonyl carbanion salts. Whereas [PhCH₂C(Me)SO₂tBu]Li/DMPU (DMPU = dimethylpropylurea) has a half‐life of racemization at ?105 °C of 2.4 h, that of [PhCH₂C(Me)SO₂CF₃]Li at ?78 °C is 30 d. DNMR spectroscopy of amides (PhCH₂)₂NSO₂CF₃ and (PhCH₂)N(Ph)SO₂CF₃ gave N? S rotational barriers that seem to be distinctly higher than those of nonfluorinated sulfonamides. NMR spectroscopy of [PhCH₂C(Ph)SO₂R]M (M=Li, K, NBu₄; R=CF₃, tBu) shows for both salts a confinement of the negative charge mainly to the C_α atom and a significant benzylic stabilization that is weaker in the trifluoromethylsulfonyl carbanion. According to crystal structure analyses, the carbanions of salts {[PhCH₂C(Ph)SO₂CF₃]Li? L }₂ ( L =2 THF, tetramethylethylenediamine (TMEDA)) and [PhCH₂C(Ph)SO₂CF₃]NBu₄ have the typical chiral C_α? S conformation of α‐sulfonyl carbanions, planar C_α atoms, and short C_α? S bonds. Ab initio calculations of [MeC(Ph)SO₂tBu]^? and [MeC(Ph)SO₂CF₃]^? showed for the fluorinated carbanion stronger n_C→σ* and n_O→σ* interactions and a weaker benzylic stabilization. According to natural bond orbital (NBO) calculations of [R¹C(R²)SO₂R]^? (R=tBu, CF₃) the n_C→σ*_{S? R} interaction is much stronger for R=CF₃. Ab initio calculations gave for [MeC(Ph)SO₂tBu]Li ? 2 Me₂O an O,Li,C_α contact ion pair (CIP) and for [MeC(Ph)SO₂CF₃]Li ? 2 Me₂O an O,Li,O CIP. According to cryoscopy, [PhCH₂C(Ph)SO₂CF₃]Li, [iHexC(Me)SO₂CF₃]Li, and [PhCH₂C(Ph)SO₂CF₃]NBu₄ predominantly form monomers in tetrahydrofuran (THF) at ?108 °C. The NMR spectroscopic data of salts [R¹(R²)SO₂R³]Li (R³=tBu, CF₃) indicate that the dominating monomeric CIPs are devoid of C_α? Li bonds.     

The Nature of the UC Double Bond: Pushing the Stability of High‐Oxidation‐State Uranium Carbenes to the Limit

Treatment of [K(BIPM^MesH)] (BIPM^Mes={C(PPh₂NMes)₂}^2?; Mes=C₆H₂‐2,4,6‐Me₃) with [UCl₄(thf)₃] (1 equiv) afforded [U(BIPM^MesH)(Cl)₃(thf)] ( 1 ), which generated [U(BIPM^Mes)(Cl)₂(thf)₂] ( 2 ), following treatment with benzyl potassium. Attempts to oxidise 2 resulted in intractable mixtures, ligand scrambling to give [U(BIPM^Mes)₂] or the formation of [U(BIPM^MesH)(O)₂(Cl)(thf)] ( 3 ). The complex [U(BIPM^Dipp)(μ‐Cl)₄(Li)₂(OEt₂)(tmeda)] ( 4 ) (BIPM^Dipp={C(PPh₂NDipp)₂}^2?; Dipp=C₆H₃‐2,6‐iPr₂; tmeda=N,N,N′,N′‐tetramethylethylenediamine) was prepared from [Li₂(BIPM^Dipp)(tmeda)] and [UCl₄(thf)₃] and, following reflux in toluene, could be isolated as [U(BIPM^Dipp)(Cl)₂(thf)₂] ( 5 ). Treatment of 4 with iodine (0.5 equiv) afforded [U(BIPM^Dipp)(Cl)₂(μ‐Cl)₂(Li)(thf)₂] ( 6 ). Complex 6 resists oxidation, and treating 4 or 5 with N‐oxides gives [{U(BIPM^DippH)(O)₂‐ (μ‐Cl)₂Li(tmeda)] ( 7 ) and [{U(BIPM^DippH)(O)₂(μ‐Cl)}₂] ( 8 ). Treatment of 4 with tBuOLi (3 equiv) and I₂ (1 equiv) gives [U(BIPM^Dipp)(OtBu)₃(I)] ( 9 ), which represents an exceptionally rare example of a crystallographically authenticated uranium(VI)–carbon σ bond. Although 9 appears sterically saturated, it decomposes over time to give [U(BIPM^Dipp)(OtBu)₃]. Complex 4 reacts with PhCOtBu and Ph₂CO to form [U(BIPM^Dipp)(μ‐Cl)₄(Li)₂(tmeda)(OCPhtBu)] ( 10 ) and [U(BIPM^Dipp)(Cl)(μ‐Cl)₂(Li)(tmeda)(OCPh₂)] ( 11 ). In contrast, complex 5 does not react with PhCOtBu and Ph₂CO, which we attribute to steric blocking. However, complexes 5 and 6 react with PhCHO to afford (DippNPPh₂)₂C?C(H)Ph ( 12 ). Complex 9 does not react with PhCOtBu, Ph₂CO or PhCHO; this is attributed to steric blocking. Theoretical calculations have enabled a qualitative bracketing of the extent of covalency in early‐metal carbenes as a function of metal, oxidation state and the number of phosphanyl substituents, revealing modest covalent contributions to U?C double bonds.