Aluminum hydrides with radical-anionic and dianionic acenaphthene-1,2-diimine ligands

The reaction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) with LiAlH₄ affords two products regardless of the solvent used (tetrahydrofuran or diethyl ether). These products were isolated as green and colorless crystals. Green crystals of the complex [(dpp-bian)Al(H)₂Li(THF)₃] (1) were obtained from tetrahydrofuran; colorless crystals of the complex [{dpp-bian(H₂)}Al(H)₂Li(Et₂O)₂] (2), from diethyl ether. The reactions of compound 1 with 2,6-di-tert-butyl-4-methylphenol and benzophenone gave monohydrides [(dpp-bian)Al(H)(OC₆H₂-2,6-Bu₂ ^t-4-Me)][Li(THF)₄] (3) and [(dpp-bian)Al(H)(OCHPh₂)- Li(THF)₂] (4), respectively. The diamagnetic aluminum hydride [(dpp-bian)AlH(THF)] (5) was synthesized by the reaction of dichloroalane HAlCl₂ (in situ) with the disodium salt of dpp-bian in THF; the paramagnetic hydride [(dpp-bian)AlH(Cl)] (6) containing the dpp-bian radical anion was synthesized by the reaction of the monosodium salt (dpp-bian)Na with monochloroalane H₂AlCl (in situ) in diethyl ether. The reaction of compound 6 with tert-butyllithium gives the complex [(dpp-bian)AlBu^t(Et₂O)] (7). Diamagnetic derivatives 1—5 and 7 were characterized by ¹Н NMR spectroscopy; paramagnetic compound 6, by ESR spectroscopy. The molecular structures of compounds 1—7 were determined by single-crystal X-ray diffraction.     

Études calorimétriques en milieu solvant organique: III. Enthalpie de dilution de l'alanate de lithium LiAlH4 dans le tétrahydrofuranneen présence d'halogénure de lithium

Heats of dilution of lithium aluminum hydride in THF, in THFLiBr and in THFLiCl have been established. At a constant concentration of LiBr in THF, dilution of LiAlH₄ is exothermal, and consequently it is shown that lithium aluminum hydride is dissociated in THF.     

Reduction of the groups C=O and C=N with neodymium and dysprosium diiodide hydrides

Neodymium diiodide hydride under mild conditions adds at the carbonyl group of benzophenone to give (diphenylmethoxy)(diiodo)neodymium(iii) of the formula I₂Nd(OCHPh₂)(THF)₄. In reactions of NdI₂H and DyI₂H with N-(2,6-diisopropylphenyl)-9,10-phenanthrenequinonimine, the system of conjugated C=N and C=O groups of the quinone is reduced. The resulting o-aminophenanthrolate complexes are structurally characterized by X-ray diffraction.     

Anionic bipyridyl complexes of lanthanides. Structure of [Yb(bipy)3][Li(THF)4]

Reactions of Sm^II, Tb^III, Tm^II, Yb^II, and Lu^III iodides with 2,2′-bipyridyllithium in THF afford [Li(THF)₄][Ln(bipy) _n ] complexes (n=3 or 4) containing trivalent lanthanides. X-ray structural analysis demonstrated that in the crystalline state, the Yb derivative has the ionic structure, [Li(THF)₄]⁺[Yb(bipy)₃]^?. In THF solutions, the reversible ligand exchange between metal atoms occurs to yield neutral compounds [Ln(bipy) _n?1(THF) _x ] and [Li(bipy)(THF) _y ]. A decrease in the temperature shifts the equilibrium to ionic pairs.     

Comparative reductive desymmetrization of 2,2-disubstituted-cycloalkane-1,3-diones

Reductive desymmetrization of 2-methyl-2-substituted-cycloalkane-1,3-diones can be effected using either NaBH₄ in DME or lithium tri-tert-butoxyaluminum hydride (LTBA) in THF at −60 °C. The former is a new approach that offers slightly greater diastereoselectivity in the reduction of 2,2-disubstituted-cyclopentane-1,3-diones while LTBA is superior with 2,2-disubstituted-cyclohexane-1,3-diones. Both conditions minimize subsequent reduction to diols thereby furnishing high yields of 1,3-ketols. Particularly rapid monoreductions are observed with 2-methyl-2-nitroethylcyclopentane-1,3-dione and 2-cyanoethyl-2-methylcyclopentane-1,3-dione when treated with NaBH₄ in DME at −60 °C. As expected, diastereoselectivity varies considerably with the substitution at C-2.     

Calcium Hydride Catalyzed Highly 1,2‐Selective Pyridine Hydrosilylation

Reaction of the calcium hydride complex (DIPPnacnac‐CaH?THF)₂ with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6‐iPr₂C₆H₃)NC(Me)]₂CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2‐position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac‐Ca(1,2‐dihydropyridide)?(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well‐defined homoleptic products which could be characterized by X‐ray diffraction: Ca(1,2‐dihydroisoquinolide)₂?(isoquinoline)₄ and Ca₃(1,2‐dihydroisoquinolide)₆?(isoquinoline)₆. The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH₃ yields exclusively 1,2‐dihydropyridine and 1,2‐dihydroquinoline silanes with 80–90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe₃)₂]₂?(THF)₂. These calcium complexes represent the first catalysts for the 1,2‐selective hydrosilylation of pyridines.     

A Cationic Zinc Hydride Cluster Stabilized by an N‐Heterocyclic Carbene: Synthesis,Reactivity, and Hydrosilylation Catalysis

The trinuclear cationic zinc hydride cluster [(IMes)₃Zn₃H₄(THF)](BPh₄)₂ ( 1 ) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH₂]₂ with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)]²⁺. A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhS? SPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)₃SiH, giving silylformate as the main product.     

Synthesis and reactivity of bis(heptamethylindenyl) yttrium (Ind*2Y) complexes containing alkyl and hydride ligands: crystal structure of Ind*2YCl(THF)

The syntheses and reactivities of yttrium alkyl and hydride complexes containing a sterically demanding, bis(heptamethylindenyl) ligand set are reported. The chloride complex Ind*₂YCl(THF) (2, Ind* = heptamethylindenyl) was prepared by the reaction of Ind*Na (1, 2 equiv) with YCl₃ in THF. Compound 2 was structurally characterized. Complex reaction mixtures were obtained when compound 2 was treated with KSi(SiMe₃)₃ or (THF)₃LiSi(SiMe₃)₃, although 2 reacted readily with MeLi to yield the methyl complex Ind*₂YMe(THF) (3). Treatment of 3 with H₂ or PhSiH₃ gave the base-stabilized hydride complex Ind*₂YH(THF) (4). The base-free chloride complex Ind*₂YCl (5) was synthesized by the reaction of 1 (2 equiv) with YCl₃ in toluene. Treatment of 2 with LiCH(SiMe₃)₂ yielded the base-free alkyl complex Ind*₂YCH(SiMe₃)₂ (6). No reaction was observed between 6 and CH₄, and complex reaction mixtures were obtained when 6 was treated with H₂ or PhSiH₃. However, when 6 was treated with H₂ in the presence of THF, the transient hydride Ind*₂YH was trapped as complex 4. The increased steric bulk of 6 leads to a slower reaction with PhSiH₃ as compared to Cp*₂YCH(SiMe₃)₂ (7).     

Chemical reactions of cycloalkanespirohydantoins. Part 2. Synthesis of new 4-hydroxyimidazolidinone N3-substituted from cycloalkanespirohydantoins

N₃-Substituted hydantoins have been to undergo lithium aluminum hydride reduction (THF, room temperature, 5 hours) to give 4-hydroxy-2-imidazolidinones in good yields.     

Palladium catalyzed reductive decarboxylation of allyl α-alkenyl-β-ketoesters. A new synthesis of (E)-3-alkenones

The reductive decarboxylation of α-alkenyl derivatives of allyl-β-ketoesters was achieved by use of palladium(0) catalyst generated in situ from Pd(OAc)₂ and PPh₃, with triethylammonium formate as the hydride source, in THF. The reaction proceeds smoothly and cleanly, with linear alkenyl derivatives of allyl-β-ketoesters, to afford (E)-3-alkenones in good to excellent yields (73-92%) and high stereoselectivity (>98%).     

An improved synthesis and some reactions of diethyl 4-oxo-4H-pyran-2,5-dicarboxylate

The reaction of ethyl 2-(dimethylamino)methylene-3-oxobutanoate with diethyl oxalate in the presence of sodium hydride in THF gave diethyl 4-oxo-4H-pyran-2,5-dicarboxylate, from which 4-oxo-4H-pyran-2,5-dicarboxylic and 4-oxo-1-phenyl-1,4-dihydropyridine-2,5-dicarboxylic acids and their derivatives were obtained in good yields.     

Influence of MgCl2 on Grignard reagent composition in tetrahydrofuran. III

Reaction of [MgCl₂(THF)₂] with [NBu₄][BF₄] yields the compounds [NBu₄][MgCl₄] (IV) and [Mg(THF)₆][BF₄]₂ (V). After addition of dioxane the reaction equilibrium shifts in the opposite direction. The formation of [MgCl₂(C₄H₈O₂)₂] in solution does not require the presence of MgCl₂. This compound may be formed in the reaction of dioxane with the ionic or molecular species formed by the magnesium atom in solution. The [NBu₄][BF₄] salt also reacts with the Grignard reagent to produce compound IV which confirms that there is a new equilibrium between [Mg(R)X(THF)_n] and [MgR₂(THF)₂], [MgCl₄]²⁻ and [Mg(THF)₆]²⁺. Bis(tetrahydrofuran)magnesium dichloride, because of its reactivity is only stable in Grignard reagent. For that reason the composition of the Grignard reagent in solution is best described as an equilibrium between [Mg(R)X(THF)_n] and [(THF)₄Mg(μ-Cl)₂MgR₂] and [RMg₂(μ-Cl)₃(THF)₅] rather than as a Schlenk equilibrium.     

Polymerization by alkaline earth metal compounds—II Polymerization of 2- and 4-vinylpyridine,styrene and butadiene by triphenylmethyl derivatives of calcium,strontium and barium

Investigations are reported on polymerizations of 2- and 4- vinylpyridine, styrene and butadiene by a series of related alkaline earth metal initiators, Ph₃CMX(THF)_n (M = Ca, Ba, X = Cl, n = 2; M = Ca, X = Br, n = 4; M = Sr, X = Cl, n = 4; M = Sr, X = Br, n = 5) in tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME) at various temperatures and in the absence of solvent. The polymers have been examined by GPC and aspects of their microstructures determined by ¹³C and/or ¹H NMR spectroscopy and, for polybutadiene, i.r. spectroscopy. Poly-2-vinylpyridine produced by Ph₃CMX(THF)_n is rich in isotactic content; the isotacticity is higher for polymer formed in THF than DME solution, falls with change of initiator in the order M = Ca > Sr > Ba and, in DME, is greater when X = Br. The tacticities of poly-4-vinylpyridine and polystyrene are similar to those obtained from related organometallic initiators. The 1,4-content of polybutadiene decreases with initiator Ph₃CMX(THF)_n in the order M = Ba > Sr > Ca; the trans-1,4 structure generally predominates except when M = Ba from which cis-1,4 links are formed in comparable amounts.     

Iridium Cluster Chemistry: The Synthesis and the Solid State Structures of [HIr5(CO)12]2− and [HIr4(CO)10PPh3]−

The cluster [HIr₅(CO)₁₂]^2- (1) was prepared by condensation of [HIr₄(CO)₁₁]^- and [Ir(CO)₄]^- (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh₃CH₂Ph]₂[HIr₅(CO)₁₂]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr₄(CO)₁₀PPh₃]^- (2) was synthetized by CO displacement on [HIr₄(CO)₁₁]^-, in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir–H distance of 1.57(9) Å. On the contrary, two isomers are present in THF solution, and they interconvert rapidly at room temperature, as shown by¹H and ³¹P NMR spectra.     

High temperature synthesis of some strontium and barium 2,6-dibenzylphenolates

Direct treatment of HOdbp (= 2,6-dibenzylphenol) with strontium or barium metal in the absence of solvent at high temperature provides the corresponding phenolates Sr(Odbp)₂ and Ba(Odbp)₂. Recrystallisation of Ba(Odbp)₂ from THF gave a good yield of the crystalline dimer [Ba(Odbp)₂(THF)]₂ · 2THF. Attempted recrystallisation of Sr(Odbp)₂ from THF mostly yielded microcrystalline material characterized as [Sr(Odbp)₂]_n but on one occasion gave a small crop of crystalline [Sr₉(Odbp)₈(O₂SiMe₂)₄(OH)₂(THF)₆(OH₂)₂] · 6THF derived from the adventitious reaction of Sr(Odbp)₂ with dimethylsilicone grease ({OSiMe₂}_∞). In the solid-state [Ba(Odbp)₂(THF)]₂ · 2THF displays significant intramolecular Ba?π-arene interactions with the pendant benzyl substituents. [Sr₉(Odbp)₈(O₂SiMe₂)₄(OH)₂(THF)₆(OH₂)₂] · 6THF features a square prismatic [Sr(O₂SiMe₂)₄]⁶⁻ core capped by two inverse crown-like square [Sr₄(Odbp)₄(OH)(L)₄]³⁺ units, where L = OH₂ or THF, that are staggered with respect to the cuboidal core.     

Activation of CH bonds in acetylene and terminal alkynes by rhodium(I) species. Crystal structure of cis-(ethynyl)hydride [(NP3)Rh(H)(CCH)]BPh4·1.5C4H8O (NP3 = N(CH2CH2PPh2)3)

The 16-electron fragment (NP₃)Rh⁺ inserts in a highly stereospecific manner across CH bonds from acetylene and 1-alkynes to give the octahedral cis-(alkynyl)hydrides [(NP₃)Rh(H)(CCR)]BPh₄ (R = H, Ph, COOEt). The structure of the cis-(ethynyl)hydride [(NP₃)Rh(H)(CCH)]BPh₄ · 1.5 THF has been established by X-ray diffraction. The trigonal bipyramidal rhodium(I) complex [(NP₃)RhH], reacts with terminal alkynes to give H₂ and the neutral σ-acetylides [(NP₃)Rh(CCR)] (R = Ph, COOEt). These undergo metathesis between terminal alkynes and the σ-acetylide ligand through a mechanism involving consecutive breaking and making of CH bonds.     

Synthesis of a new bidentate NHC-Ag(I) complex and its unanticipated reaction with the Hoveyda-Grubbs first generation catalyst

A new sterically demanding bidentate imidazolium bromide has been prepared and used as ligand precursor for the synthesis of the corresponding NHC-silver(I) complex. The X-ray analysis of the silver(I) complex revealed a rare Ag₄O₄ core cubane cluster. The silver(I) complex reacts readily with the Grubbs first generation catalyst providing a labile alkylidene complex. When the transmetallation was attempted with Hoveyda-Grubbs first generation catalyst in the presence of THF as solvent, two very stable phosphine free bis-bidentate N-heterocyclic carbene complexes, one green and one orange, were formed. Notably, one of these complexes is the first observation of a metal alkylidene group substituted by a NHC ligand, a surprising result since the new complex is formally derived from a nucleophile substitution of a hydride by a NHC ligand on the alkylidene carbon. A proposal for the reaction mechanism is elaborated.     

Ion-solvent interactions: Conductance behavior of NaAlBu4 and Bu4NAlBu4 in benzene and tetrahydrofuran

Conductance measurements are reported for NaAlBu ₄ and Bu ₄ NAlBu ₄ in benzene and in tetrahydrofuran (THF) from a concentration of approximately 5×10^?3 M to the fused state for each salt. This is the first reported study where a comparison of a salt with a small cation is made with one having a large cation in a noncomplexing solvent (benzene) and a complexing solvent (THF). The similarity in conductance behavior in THF and the differences in benzene are considered in terms of ion-ion and ion-solvent interactions.     

Reaction between magnesium chloride and iron(III) chloride in tetrahydrofuran. The crystal structure of Di-μ-chlorodichloroiron(II) tetrakis(tetrahydrofuran)magnesium(II)

The direct reaction between magnesium chloride and iron(III) chloride in tetrahydrofuran (THF) yields the [MgCl(THF)₅][FeCl₄] complex (I). It is unstable and in reacting with THF undergoes reduction to produce the complex FeCl₂(μ-Cl)₂Mg(THF)₄ (II). Crystals of (II) are orthorhombic, space group Pbcn, with a = 9.18(1) b = 16.30(2) c = 15.85(1)Å. The structure was solved by the heavy atom method and refined by least squares to R = 0.053 for 1194 observed diffractometer data. The molecule is heterobimetallic with an Fe…Mg distance 3.455(3)ǎ and the Fe and Mg atoms are bridged by two Cl atoms.     

An exceptionally stable cis-(hydride)(η2-dihydrogen) complex of iron

The cis-(H)(H₂ complex [(PP₃)Fe(H)(H₂)]BPh₄ (PP₃  P(CH₂CH₂PPh₂)₃) has been made by reaction of the chloride [(PP₃)FECl]BPh₄ in THF with NaBH₄ under 1 atm of H₂. In the solid state and in solution at low temperature the complex is octahedral, and the hydride and dihydrogen ligands occupy mutually cis positions. At ambient temperature in solution the complex is trigonal-bipyramidal, and an “H₃” unit occupies an axial position trans to the bridgehead phosphorus atom of PP₃; this results in exceptional thermal and chemical stability of the complex.