LiAlH4 In THF Research Articles

Synthesis of erythrodiol C-ring derivatives and their activity against Chlamydia trachomatis

To develop new potential agents against Chlamydia trachomatis among oleanane type triterpenoids the synthesis, spectral and X-ray analysis as well as antimicrobial screening of C-12 oxygen and nitrogen derivatives of erythrodiol is presented. The reduction of methyl 3β-acetoxy-12-oxo-oleanoate with LiAlH4 led to isomeric erythrodiol 12β- and 12α-hydroxy-derivatives, their stereochemistry with respect to the position of hydroxyl-group at C-12 was determined based on the multiplets splitting patterns, the magnitude of the spin–spin interaction, and NOESY interactions. Methyl 3β-acetoxy-12-oxo-oleanoate was transformed to 12E-hydroxyimino- and 12E-methoxyimino-derivatives by the interaction with NH2OH∙HCl or CH3ONH2∙HCl, respectively. By Beckmann rearrangement with SOCl2 in dioxane 12E-oxime was converted to C-lactame and its following reduction with LiAlH4 in THF or dioxane led to erythrodiol C-azepanone or C-azepane derivatives. The structure 3-O,12-N-bis-acetyl-derivative of C-azepane-erythrodiol was confirmed by the single crystal X-ray analysis. Erythrodiol 12β-hydroxy- and C-azepane derivatives were found to be lead compounds with significant activity against C. trachomatis with MIC 1.56 and 3.125 μg/mL. Molecular docking was employed to suggest potential binding interaction, the tested compounds are likely to act as Cdu1 protein inhibitors while 12β-hydroxy-erythrodiol exhibited the highest affinity towards this respective target protein. These results indicated that C-ring oxygen and nitrogen erythrodiol derivatives might be considered for further research in the design of antibacterial agents against Chlamydia trachomatis.

Simple Synthesis of Complex Amines from the Diels–Alder Adducts of (–)-Cytisine

AbstractThe Diels–Alder reaction of N-benzylcytisine with N-methyl- and N-benzylmaleimides is 100% endo-selective and gives the corresponding syn- and anti-diastereomers in 11–42% isolated yields. The studies of the reaction progress with LCMS and NMR along with detailed quantum chemical calculations revealed that some Diels–Alder adducts are kinetically and their isomers are thermodynamically controlled products. The Pd/C-catalyzed hydrogenation of benzyl-protected cytisine amine derivatives resulted in the removal of the benzyl group and the addition of hydrogen to the C=C double bond to give the corresponding secondary amines in 45–84% yield. The complete reduction of carbonyl groups in a cytisine derivative with LiAlH4 in THF under reflux afforded the respective tricyclic triamine. Quantum mechanical calculations for the mechanism of the Diels–Alder reaction between the simplest model compounds are presented.

Synthesis and Structural Characteristics of Discrete Organoboron and Organoaluminum Hydrides Incorporating Bulky Eind Groups

The bulky Eind-based aryllithium, (Eind)Li (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl), reacted with BF3·OEt2 in Et2O to form the corresponding aryldifluoroborane (Eind)BF2 (1), along with a trace amount of the sterically congested diarylborane, (Eind)2BH (2). The reaction of 1 with LiAlH4 in THF led to the isolation of the corresponding lithium trihydroborate [Li(thf)]2[(Eind)BH3]2 (3), which can be transformed into the diborane(6), (Eind)HB(μ-H)2BH(Eind) (4), with treatment with Me3SiCl. The Eind-based lithium trihydroaluminate [Li(OEt2)]2[(Eind)AlH3]2 (5) has been synthesized by the reaction of (Eind)Li with LiAlH4 in Et2O. The subsequent addition of Me3SiCl to a solution of 5 in toluene produced the dialumane(6), (Eind)HAl(μ-H)2AlH(Eind) (6), the heavier congener of 4. The dialumane(6) 6 reacted with lithium metal in a mixed solvent of Et2O and toluene to give the diarylalumane, (Eind)2AlH (7), via a disproportionation reaction along with the cleavage and recombination of the Al–C bond. The discrete monomeric structures of 1, 2, and 7 and dimeric structures of 3, 4, 5, and 6 have been determined by X-ray crystallography.

Binuclear aluminum complexes with amine–imine type ligands derived from 1,3-benzenedialdehyde: synthesis, structures and their catalytic properties in ring-opening polymerization

Reaction of 1,3-bis(imino)benzenes with a stoichiometric amount of LiAlH4 in THF yields iminoaminobenzenes L1 and L2. Further reaction of iminoaminobenzenes L1 and L2 with an equivalent of AlR3 in toluene affords macrocyclic binuclear aluminum complexes 1a, 1b, and 2a. These macrocyclic aluminum complexes were characterized by 1H NMR, 13C NMR, and IR spectroscopy. The molecular structures of 1a, 1b, and 2a were further confirmed by X-ray crystallography. X-ray diffraction analysis revealed that 1a, 1b, and 2a adopted a distorted tetrahedral geometry around aluminum. These complexes have efficient activities toward ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol.

Preparation and reactivity of germyl complexes of ruthenium and osmium stabilised by cyclopentadienyl, indenyl and tris(pyrazolyl)borate fragments

Half-sandwich trichlorogermyl complexes Ru(GeCl3)(η5-C5H5)(PPh3)L (1) and Ru(GeCl3)(η5-C9H7)(PPh3)L (2) [L = P(OMe)3 (a), P(OEt)3 (b) and PPh(OEt)2 (c)] were prepared by allowing chloro compounds RuCl(η5-C5H5)(PPh3)L and RuCl(η5-C9H7)(PPh3)L to react with an excess of GeCl2·dioxane in ethanol. Treatment of trichlorogermyl complexes 1 and 2 with LiAlH4 in THF yielded trihydridogermyl derivatives Ru(GeH3)(η5-C5H5)(PPh3)L (3) and Ru(GeH3)(η5-C9H7)(PPh3)L (4). Instead, reaction of trichlorogermyl complexes 1 and 2 with NaBH4 in ethanol afforded triethoxygermyl complexes Ru[Ge(OEt)3](η5-C5H5)(PPh3)L (5) and Ru[Ge(OEt)3](η5-C9H7)(PPh3)L (6). Trichlorogermyl complexes with the tris(pyrazolyl)borate ligand M(GeCl3)(Tp)(PPh3)L [M = Ru (7), Os (10)] were prepared by reacting chloro compounds MCl(Tp)(PPh3)L with an excess of GeCl2·dioxane. Depending on metal centre, nature of phosphite and experimental conditions, the reaction of trichlorogermyl complexes 7 and 10 with LiAlH4 or NaBH4 afforded trihydridogermyl M(GeH3)(Tp)(PPh3)L (8, 12) and triethoxygermyl derivatives M[Ge(OEt)3](Tp)(PPh3)L (9, 11). The complexes were characterised by IR and multinuclear NMR spectroscopy and by X-ray crystal structure determination of 3a.

Preparation and reactivity of stannyl and germyl complexes of cobalt

Trichlorostannyl complex Co(SnCl3)(CO)2(PPh3)2 (1) was prepared by allowing the chloro compound CoCl(CO)2(PPh3)2 to react with SnCl2·2H2O. Instead, treatment of the iodo complex CoI(CO)2[PPh(OEt)2]2 with SnCl2·2H2O afforded a mixture of Co(SnCl2I)(CO)2[PPh(OEt)2]2 (2a) and Co(SnCl3)(CO)2[PPh(OEt)2]2 (2b) derivatives. Trichlorogermyl complexes Co(GeCl3)(CO)2L2 (3, 4) [L = PPh3, PPh(OEt)2] were prepared by allowing halo compounds CoX(CO)2L2 (X = Cl, I) to react with GeCl2·dioxane. Treatment of trihalostannyl complexes Co(SnCl2X)(CO)2L2 (1, 2) (X = Cl, I) with NaBH4 in ethanol yielded tin trihydrido derivatives Co(SnH3)(CO)2L2 (5, 6). Instead, reaction of Co(SnCl2X)(CO)2[PPh(OEt)2]2 (2) with LiAlH4 in THF yielded the hydrido CoH(CO)2[PPh(OEt)2]2 (7). Trimethylstannyl Co(SnMe3)(CO)2L2 (8, 9) and trialkynylstannyl derivatives Co[Sn(CCPh)3](CO)2L2 (10, 11) were prepared by allowing trihalostannyl compounds Co(SnCl2X)(CO)2L2 (1, 2) to react with MgBrMe and with Li+(PhCC)−, respectively, in THF. The complexes were characterised by spectroscopy (IR and 1H, 31P, 13C, 119Sn NMR) and by X-ray crystal structure determination of Co(SnCl2X)(CO)2[PPh(OEt)2]2 (2) and Co(GeCl3)(CO)2[PPh(OEt)2]2 (4).

A short and efficient route from tetrahydrothiophene to thieno[2,3-d][1,3,2]dithiazolium salts

A synthesis of thieno[2,3-d][1,3,2]dithiazolium salts from commercial tetrahydrothiophene has been developed. The reaction of thieno[2,3-f][1,2,3,4,5]pentathiepin with LiAlH4 in THF at −15°C, after treatment with acetyl chloride, led to 2,3-(bisacetylthio)thiophene in high yield. Bis(acetylthio)thiophene reacted with sulfuryl chloride and then trimethylsilyl azide was added to afford a 1,3,2-dithiazolium chloride which was converted into a soluble tetrafluoroborate. Electrolytic reduction under controlled potential yielded a thieno[2,3-d][1,3,2]dithiazolyl radical which was characterized by EPR in frozen methylene dichloride.

ChemInform Abstract: The Novel Synthesis of Fluorinated Unsaturated Phosphonates.

Phosphonic acids are very important compounds in biological system by virtue of their similarity to phosphates. The replacement of oxygen in phosphate esters by a fluoromethylene (CHF) or difluoromethylene (CF2) unit has been received much attention due to the enhancement of biological properties as compared to non-fluorinated analogs. It has been well known that α-fluorinated phosphonates mimic phosphates in their isosteric and isopolar properties. Theoretical calculations have proposed that monofluorophosphonate analogues show more similarity in isosteric and isopolar concept than difluorophosphonate ones. Although a variety of biologically interesting compounds that contain the saturated α-monofluoroalkylphosphonate or α,α-difluoroalkylphosphonate-based mimics has been discovered in recent work via various methods, the synthetic methods for the unsaturated α-monofluorophosphonates or α,α-difluorophosphonates have been quite limited. Especially, the unsaturated α-monofluorophosphonates have been prepared by more limited methods. A recent report has suggested that α-fluorovinylphosphonates are good precursors to αmonofluoroalkylphosphonates via reduction of double bond and also may have interesting biological properties. The previous methods for the preparation of α-fluorovinylphosphonates include Wadsworth-Emmons reaction of lithium fluoromethylenebisphosphonate with aldehydes and ketones, Peterson-olefination of lithium fluorotrimethylsilylphosphonate with aldehydes and ketones, and reaction of lithium fluoromethylenediphosphonate with aldehydes. However, β-phenylthio or β-phenylsulfonyl substituted α-fluorovinylphosphonates which can be transformed to another functionality via phenylthio or phenylsulfonyl group can not be prepared by previous methods. In this paper, we wish to describe a new synthetic method for the preparation of βphenylthio or β-phenylsulfonyl substituted α-fluorovinylphosphonates via addition-elimination of corresponding β-phenylthio or β-phenylsulfonyl substituted α,α-difluoroolefins with triethylphosphite or sodium diethylphosphonate. β-Phenylthio substituted α,α-difluoroolefins 2a-e as starting materials can be prepared in 75-90% yields from the reaction of trifluoromethylated dithioketals 1a-e with a mixture of TiCl4 and LiAlH4 in THF at reflux temperature for 3 h. Further oxidation of 2a-e with MCPBA in CH2Cl2 at room temperature for 3 h afforded the corresponding β-phenylsulfonyl substituted α,α-difluoroolefins 3a-e in 77-88% yields. 1,1-Difluoro-3-phenylsulfonyl-2-phenylthio-1-propene (2f) as an another starting material was prepared in 82% yield from the reaction of 3-bromo-3,3-difluoro-2-phenylthio-1-propene (4) with sodium benzenesulfinate in DMF. The further oxidation of 2f with MCPBA provided the corresponding disulfone in solution, but isolation of this disulfone compound was always failed probably due to the unstability of disulfone compound.

Palladium/Lipase-Catalyzed Asymmetric Reductive Acylation of Ketoximes

The one-pot asymmetric synthesis of optically active amides 3a-h from ketoximes 1a-h with aluminum hydroxide supported palladium catalyst [Pd/AlO(OH)] and lipase (Novozym-435) is described. Thus, the reaction of ketoximes 1a-h (0.30 mmol) with 2 was carried out in the presence of Pd/AlO(OH), Novozym-435 (9 mg), and 4 A MS (100 mg) in toluene under H2 to give the corresponding amides 3a-h with high enan­tioselectivity (83-92% yield, 93-98% ee). Amide 3a (0.26 mmol, 98% ee) was reduced by LiAlH4 in THF to afford the secondary amine 4 in 97% yield with 98% ee.

Synthesis and Characterization of the Monomeric Vicinal Dianion Li2(THF)3[ArNC(SiMe3)2] and the Aluminum and Lithium Derivatives of the Amido Ligand [ArNCH(SiMe3)2]−

Reaction of the imine ArNC(SiMe3)2 (1; Ar = 2,6-iPr2C6H3) with LiAlH4 in THF resulted in the formation of the dimeric hydroaluminate [(THF)2LiH3AlL]2 (2; L = [ArNCH(SiMe3)2]−). 2 reacted with CH3I to give the monomeric aluminum dihydride LAlH2(THF) (3), which can be converted to the diiodide LAlI2(THF) (4) upon treatment with 2 equiv of Me3SiI. The quasi two-coordinate lithium amide Li(OEt2)L (8) with an intramolecular CH−Li interaction was obtained by the deprotonation of the corresponding amine LH (5) generated from hydrolysis of 2. Reduction of 1 with lithium in THF resulted in the first structurally characterized monomeric C−N vicinal dianion, Li2(THF)3[ArNC(SiMe3)2] (6), and the monomeric lithium amide Li(THF)2L (7).

First example of ionic hydrogenation in the bicyclo[1.1.0]butane series

Bicyclo[1.1.0]butanes having an electron-withdrawing sulfonyl group at the bridgehead position (“activated bicyclobutanes”) are known [1] to undergo reduction to cyclobutyl sulfones by the action of LiAlH4 as hydride ion carrier in a way similar to the reduction of activated alkenes (α,β-unsaturated sulfones) to alkyl sulfones with the same reducing agent [2]. Taking into account the olefin-like character of the central bicyclobutane C–C bond [3], it might be expected that bicyclobutanes having an electron-donor group at the bridgehead position, like nucleophilic alkenes (e.g., 2-methylpropene or styrene), will undergo ionic hydrogenation [4, 5] by the action of strong acids in the presence of a hydride ion source (Et3SiH, NaBH4, etc.). However, we have found no published data on such version of hydrogenation of bicyclobutane derivatives. In the present communication we report on the first example of successful ionic hydrogenation in the bicyclobutane series. As initial compound we selected a bridged bicyclobutane derivative, 1-phenyl-7-phenylsulfonyltricyclo[4.1.0.0]heptane (I) [6]. Treatment of I with trifluoroacetic acid and NaBH4 at –10°C under dry argon (i.e., under the conditions of ionic hydrogenation reported in [5]) gave norpinane II in 41% yield. Despite moderate yield, the product can be readily isolated from the reaction mixture by crystallization. Its structure and steric configuration were reliably determined on the basis of the H and C NMR data. As expected, compound I was also reduced with LiAlH4 in THF at 0°C, but the product was compound III (yield 91%) which is epimeric to norpinane II at C. By special experiment we showed that sterically hindered norpinane II is converted almost completely into more stable diastereoisomer III in 5 h on heating with potassium tert-butoxide in boiling THF. We also found that even trace amounts of norpinane III were not formed in the ionic hydrogenation of tricycloheptane I with LiAlH4. 6-exo-Phenyl-7-anti-phenylsulfonylbicyclo[3.1.1]heptane (II). mp 134–135°C (from hexane–ethyl acetate). H NMR spectrum, δ, ppm: 1.80–2.04 m (2H, 3-H); 2.05–2.22 m and 2.23–2.40 m (2H each, 2-H, 4-H); 3.06 d (1H, 6-H, J = 3.1 Hz); 3.23 d (1H, 7-H, J = 3.1 Hz); 3.30 br.s (2H, 1-H, 5-H); 7.22–7.32 m (3H), 7.32–7.43 m (2H), 7.44–7.53 m (2H), 7.56– 7.66 m (1H), and 7.71 d (2H, J = 7.6 Hz) (Harom). C NMR spectrum, δC, ppm: 14.8 (C); 33.0 (C, C); 40.0 (C, C); 47.5 (C); 70.2 (C); 125.7, 126.9 (3C), 127.7 (2C), 127.9 (2C), 128.9 (2C), 133.0, 140.5 (Carom). Found, %: C 72.87; H 6.37. C19H20SO2. Calculated, %: C 73.04; H 6.45.

Synthesis of Methyl Metallocenecarboxylates [{η4‐Ph4–n(SiMe3)nC4}Co{η5‐MeOC(O)C5H4}] (n = 1, 2) and Their Desilylation Reactions: Structural Studies and Conversion to Metallocenecarboxylic Acids and Their Alcohol Derivatives

AbstractThe reaction of (2‐phenylethynyl)trimethylsilane (Me3SiC≡CPh) with [{η5‐MeOC(O)C5H4}Co(PPh3)2] generated in situ results in the exclusive formation of two isomers of methyl metallocenecarboxylates, namely [{trans‐η4‐Ph2(Me3Si)2C4}Co{η5‐MeOC(O)C5H4}] (1) and [{cis‐η4‐Ph2(Me3Si)2C4}Co{η5‐MeOC(O)C5H4}] (2). The reaction of [{η5‐MeOC(O)C5H4}Co(PPh3)(Me3SiC≡CPh)] with PhC≡CPh yields the methyl metallocenecarboxylate [{η4‐Ph3(Me3Si)C4}Co{η5‐MeOC(O)C5H4}] (3) along with [{η4‐Ph4C4}Co{η5‐MeOC(O)C5H4}] (4). The reactions of 1, 2 and 3 with Bu4NF in dmso results in the desilylated complexes [(trans‐η4‐Ph2H2C4)Co{η5‐MeOC(O)C5H4}] (5), [(cis‐η4‐Ph2H2C4)Co{η5‐MeOC(O)C5H4}] (6) and [(η4‐Ph3HC4)Co{η5‐MeOC(O)C5H4}] (7), respectively. Compounds 5, 6 and 7 yield the carboxylic acids [(trans‐η4‐Ph2H2C4)Co{η5‐HOC(O)C5H4}] (8), [(cis‐η4‐Ph2H2C4)Co{η5‐HOC(O)C5H4}] (9) and [(η4‐Ph3HC4)Co{η5‐HOC(O)C5H4}] (10) upon treatment with KOtBu in dmso. Reduction of 5 and 7 with LiAlH4 in thf gives the alcohol complexes [(trans‐η4‐Ph2H2C4)Co(η5‐HOCH2C5H4)] (11) and [(η4‐Ph3HC4)Co(η5‐HOCH2C5H4)] (12) in good yields. Compounds 1–7 and 11 were characterized structurally. These structural studies show interesting variations in the orientations of the cyclobutadiene‐bound phenyl groups when the silyl groups are systematically removed from the cyclobutadiene moiety. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Enantiopure Ruthenocenes Cp*Ru(1,2‐C5H3R1R2) with a Planar Chiral Cyclopentadienyl Ligand and a Pentamethylcyclopentadienyl Spectator Ligand

AbstractKreutzberger’s synthesis was used to produce 6‐(morpholino)fulvene (7a) from 1,3,5‐triazine, cyclopentadiene and morpholine (94 %). Likewise with (S)‐2‐(methoxymethyl)pyrrolidine (HSMP) the 6‐[(S)‐2‐(methoxymethyl)pyrrolidino] analogue 7b was obtained (62 %). Hydride addition from NaBHEt3 in toluene afforded the cyclopentadienides Na[C5H4CH2–N(C2H4)2O] (8a) (83 %) and Na(C5H4CH2–SMP) (8b) (90 %). Cp*Ru(C5H4CH2–SMP) (5) was synthesized from [Cp*RuCl]4 and 8b (84 % yield). The related methyleneiminium salt [Cp*Ru(C5H4CH=SMP)]PF6 (9) was made from [Cp*Ru(MeCN)3]PF6 and 7b and could be transformed into 5 by hydride addition from LiAlH4 in THF. Diastereoselective lithiation of 5 with LisBu in Et2O/cyclohexane and subsequent quenching with electrophiles E–X gave enantiomerically pure (de > 98 %), 1,2‐disubstituted complexes Cp*Ru(E–C5H3CH2–SMP) 10a–i with E = F, Cl, Br, I, Me, CD3, SiMe3, PPh2, Au(PPh3) as oils. The chiral auxiliary was removed from 10a, b, and f by quaternization with MeI and subsequent reductive cleavage with LiAlH4 in THF to afford the exclusively planar chiral complexes Cp*Ru(1‐E‐2‐MeC5H3) 14a (E = F), 14b (E = Cl), and 14f (E = CD3). The complexes 14a,b,f no longer possess central chirality. The crystal structure of 12, a LiI adduct of 10f, gave the absolute configuration via internal reference to the (S)‐stereochemistry of the SMP group. The absolute configuration of the planar chiral complex 14b was determined from the anomalous X‐ray dispersion of the crystals of 14b.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis of 2,4-disubstituted thiophenols and solid state structures of thiocarbamate precursors

A series of thiophenols with different ortho-substituents, 2,4-dimethylthiophenol, 2-tert-butyl-4-methylthiophenol, and 2-(1-adamantyl)-4-methylthiophenol, which display varying degrees of steric hindrance on the 2-position, was prepared from the corresponding phenols. Initial deprotonation of the phenols was achieved with NaH in dimethoxyethane, followed by treatment with N,N-dimethylthiocarbamoyl chloride, to obtain the O-arylthiocarbamates. Thermolysis of the latter compounds resulted in rearrangement, which yields the desired S-arylthiocarbamates. Finally, reduction of the S-arylthiocarbamates with LiAlH4 in THF, followed by acidic workup, allowed the isolation of the thiophenols. All products were characterized by spectroscopic techniques, and in the case of some of the thiocarbamates the solid state structures were determined by single-crystal X-ray diffraction.

C-Substituierte Cyclame aus Cyclotetrapeptiden [1]/ C-Substituted Cyclams from Cyclotetrapeptides [1

The reduction of cyclotetrapeptides cyclo(X-β -Ala-X-β -Ala) (X = Gly, (S)-Ala, (S)-Leu, (S)-Val, (S)-Phe) 1a - 1e with LiAlH4 in THF gives the C-substituted cyclams 2a - 2e.

Hydride Reduction of a Lactate Ester: Optimisation and Scale-Up

The two-step synthesis of (2S)-2-(tetrahydropyran-2-yloxy)propane-1-ol was selected for fine chemical scale-up. The first step, an acid-catalyzed protection of ethyl (S)(−)-lactate with 3,4-dihydro-2H-pyran, could be performed without solvent. The reaction enthalpy was determined to be −48 kJ/mol ethyl (S)(−)-lactate, ensuring safe scale-up. The crude reaction mixture was used in the second step, the hydride reduction. For the reduction of the protected ester a clear solution of 1 M LiAlH4 in THF was used. The reaction enthalpy was determined to be −313 kJ/mol ethyl (2S)-2-(tetrahydropyran-2-yloxy)propionate, and the work-up was optimised with experimental design techniques. Combination of all experimental and theoretical results resulted in a master recipe for a 10-dm3 scale synthesis of (2S)-2-(tetrahydropyran-2-yloxy)propane-1-ol.

An unsolvated lithium trihydroaluminate and the correponding trialkynylaluminates supported by an anionic triazacyclononane ligand

Reaction of the anionic tacn ligand ((tacn)H = 1,4-diisopropyl-1,4,7-triazacyclononane) with LiAlH4 in THF afforded a dimeric, unsolvated lithium trihydroaluminate, which upon treatment with terminal acetylenes HCCR (R = Ph, SiMe3) yielded the corresponding monomeric trialkynylaluminates in which one acetylide ligand bridges the Li and Al atom at the Cα atom while the two terminal acetylide ligands are coordinated to the Al atom.

Synthesis, Characterization, and Interconversion of the Rhenium Polyhydrides [ReH3(η4-NP3)] and [ReH4(η4-NP3)]+ {NP3 = tris[2-(diphenylphosphanyl)ethyl]amine}

The rhenium(III) dichloride complex [ReCl2(η4-NP3)]Cl (1) was prepared from [ReCl3(CH3CN)(PPh3)2] by treatment with the tripodal tetradentate ligand N(CH2CH2PPh2)3 (NP3) in ethanol. The reaction of 1 with LiAlH4 in THF gave the rhenium(III) trihydride [ReH3(η4-NP3)] (2), which was converted into the rhenium(V) tetrahydride [ReH4(η4-NP3)]BPh4 (3) by protonation in CH2Cl2 with HBF4·OMe2, followed by a metathetical reaction with NaBPh4. The classical polyhydride nature of 2 and 3, as well as the overall molecular structures in solution, were determined by NMR spectroscopy, 1H NMR relaxation, and IR spectroscopy. The polyhydride complexes 2 and 3 are stereochemically nonrigid in solution, and the thermodynamic parameters associated with the fluxional processes were determined by variable-temperature NMR studies. A single-crystal X-ray analysis of 3 has shown the complex cation [ReH4(η4-NP3)]+ to be eight-coordinated by the four donor atoms of NP3 and by four terminal hydride ligands in a distorted dodecahedral geometry. An in situ IR study in CH2Cl2 has shown that the protonation of 3 occurs regioselectively at the metal center with no formation of a dihydrogen complex. Kinetic hydrogen bond products of the formula [(η4-NP3)H3Re···HOR] (ROH = C2H5OH, CFH2CH2OH, CF3CH2OH) were intercepted by IR spectroscopy at low temperature. The thermodynamic parameters associated with the formation of the hydrogen bond adducts were determined by either IR spectroscopy applying the Iogansen equation or van’t Hoff plots of the formation constant vs. temperature.

Synthesis, Characterization, and Interconversion of the Rhenium Polyhydrides [ReH3(η4-NP3)] and [ReH4(η4-NP3)]+ {NP3 = tris[2-(diphenylphosphanyl)ethyl]amine}

The rhenium(III) dichloride complex [ReCl2(η4-NP3)]Cl (1) was prepared from [ReCl3(CH3CN)(PPh3)2] by treatment with the tripodal tetradentate ligand N(CH2CH2PPh2)3 (NP3) in ethanol. The reaction of 1 with LiAIH4 in THF gave the rhenium(III) trihydride [ReH3(η4-NP3)] (2), which was converted into the rhenium(V) tetrahydride [ReH4(η4-NP3)]BPha4 (3) by protonation in CH2Cl2 with HBF4·OMe2, followed by a metathetical reaction with NaBPh4. The classical polyhydride nature of 2 and 3, as well as the overall molecular structures in solution, were determined by NMR spectroscopy, 1H NMR relaxation, and IR spectroscopy. The polyhydride complexes 2 and 3 are stereochemically nonrigid in solution, and the thermodynamic parameters associated with the fluxional processes were determined by variable-temperature NMR studies. A single-crystal X-ray analysis of 3 has shown the complex cation [ReH4 (qη4-NP3)]+ to be eight- coordinated by the four donor atoms of NP3 and by four terminal hydride ligands in a distorted dodecahedral geometry. An in situ IR study in CH2Cl2 has shown that the protonation of 3 occurs regioselectively at the metal center with no formation of a dihydrogen complex. Kinetic hydrogen bond products of the formula [(qη4NP3)H3Re··· HOR] (ROH = C2H5OH, CFH2CH2OH, CF3CH2OH) were intercepted by IR spectroscopy at low temperature. The thermodynamic parameters associated with the formation of the hydrogen bond adducts were determined by either IR spectroscopy applying the logansen equation or van't Hoff plots of the formation constant vs. temperature.

Synthesis and Characterization of Derivatives of a Chelating Aluminum Dichloride Complex Containing a 3,5-Di-tert-butylpyrazolato Unit

The chelating aluminum complex [{3,5-N-tBu2pz-N′−CH=C(SiMe3)}AlR1R2] [R1 = R2 = Me (2); R1 = R2 = H (3); R1 = R2 = I (4)] was prepared in modest yield from an organoaluminum dichloride precursor [{3,5-N-tBu2pz-N′−CH=C(SiMe3)}AlCl2] (1). Compounds 2 and 3 were obtained from the reaction of 1 with MeLi in Et2O or with LiAlH4 in THF, respectively. Reaction of 2 or 3 with I2 in toluene gave 4. In addition, the reaction of 1 with two equivalents of water yielded the hydrolyzed product H[3,5-N-tBu2pz-N′−CH=C(SiMe3)] (5). All compounds were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. The X-ray structure analysis shows that complex 2 exhibits one fused five-membered AlC2N2 ring and one pyrazolato ring system. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)