Preparation,characterization and catalytic oxidation properties of bis‐quaternary ammonium peroxotungstates and peroxomolybdates complexes

Several novel kinds of bis‐quaternary ammonium peroxotungstates and peroxomolybdates, such as PhCH₂N(CH₂CH₂)₃NCH₂Ph[W₂O₃(O₂)₄], PhCH₂N(CH₂CH₂)₃NCH₂Ph [Mo₂O₃(O₂)₄], [PhCH₂(CH₃)₂NCH₂]₂[W₂O₃(O₂)₄] and [PhCH₂(CH₃)₂NCH₂]₂[Mo₂O₃(O₂)₄], have been synthesized and characterized by elemental analysis, IR and Raman spectroscopy. Their catalytic properties in mild oxidation of benzyl alcohol and ring‐substituted benzyl alcohols were investigated with aqueous 30% H₂O₂ under halide‐ and organic solvent‐free conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical study of PhCH2O4CH2Ph: intermediate in the PhCH2O2 self-reaction

As a possible important intermediate during the oxidation of toluene in gas phase, the PhCH₂O₄CH₂Ph molecule has been invested on the structural parameters at CAM-B3LYP/6-311+g(df,pd) level, the vibrational frequencies at B3LYP-D3(BJ)/6-311+g(df,pd) level, and the potential energy surface of isomerization between main isomers at CCSD(T)-F12/cc-pVDZ-F12 level of theory. Ten PhCH₂O₄CH₂Ph isomers were located, in which the structural parameters of C-O₄-C skeleton are close to those in HO₄H and C₂H₅O₄C₂H₅. However, due to larger steric hindrance of aromatic groups, PhCH₂O₄CH₂Ph has a more open geometry with larger bond angles and dihedral angles in individual isomers. Meanwhile, it seems that the hyperconjugation appears to be stronger between the O-O bonds and aromatic groups, since the O-O bond lengths are slightly shorter than those found in HO₄H and C₂H₅O₄C₂H₅. Harmonic vibrational frequencies of PhCH₂O₄CH₂Ph isomers were first reported here and we found that the frequencies of O₄ torsion and O-O/C-O stretches in PhCH₂O₄CH₂Ph are consistent with those of CH₃O₄CH₃ and C₂H₅O₄C₂H₅. In the progress of isomerization, three transition states were located and a thermodynamic equilibrium between three main isomers may achieve at ambient temperature concerning the characters of energy barrier.

     

Hypercoordinated diorganoantimony(III) compounds of types [2-(Me2NCH2)C6H4]2SbL and [PhCH2N(CH2C6H4)2]SbL (L = Cl,ONO2, OSO2CF3). Synthesis,structure and catalytic behaviour in the Henry reaction

The compounds [2-(Me₂NCH₂)C₆H₄]₂SbL (L = ONO₂ ( 2 ), OSO₂CF₃ ( 3 )) and [PhCH₂N(CH₂C₆H₄)₂]SbL (L = ONO₂ ( 5 ), OSO₂CF₃ ( 6 )) were prepared by reacting [2-(Me₂NCH₂)C₆H₄]₂SbCl ( 1 ) and [PhCH₂N(CH₂C₆H₄)₂]SbCl ( 4 ), respectively, with the appropriate silver(I) salt in a 1:1 molar ratio. The new species 2 – 6 were structurally characterized in solution using multinuclear NMR and in the solid state using infrared spectroscopy. The solid-state structures for compounds 2 , 4 and 6, as well as for the hydrolysis ionic product [{2-(Me₂N⁺HCH₂)C₆H₄}{2-(Me₂NCH₂)C₆H₄}SbOH][CF₃SO₃]⁻ ( 3h ) were determined using single-crystal X-ray diffraction. Medium to strong intramolecular N→ Sb interactions were observed in all these four compounds, thus resulting in hypercoordinated organoantimony(III) species 14-Sb-6 in 2 and 10-Sb-4 in the cation of 3h and in 4 and 6 . Compounds 1 – 6 and the starting amines PhCH₂NMe₂ and PhCH₂N(CH₂C₆H₄Br-2)₂ were investigated as catalysts in the Henry (nitroaldol) addition of nitromethane to benzaldehyde. The activity of compounds 1 – 6 resulted as an effect of the cooperation of the positively charged antimony with the negatively charged nitrogen.     

The Very low-pressure pyrolysis of 2-phenylethylamine. The enthalpy of formation of the aminomethyl radical

The thermal unimolecular decomposition of 2-phenylethylamine (PhCH₂CH₂NH₂) into benzyl and aminomethyl radicals has been studied under very-low-pressure conditions, and the enthalpy of formation of the aminomethyl radicals, ΔH°_{f, 298K} (H₂NCH₂·) = 37.0 ± 2.0 kcal/mol, has been derived from the kinetic data. This result leads to a value for the C—H bond dissociation energy in methylamine, BDE(H₂NCH₂—H) = 94.6 ± 2.0 kcal/mol, which is about 3.4 kcal/mol lower than in C₂H₆ (98 kcal/mol), indicating a sizable stabilization in α-aminoalkyl radicals.     

Mechanism of Thermal Toluene Autoxidation

Aerobic oxidation of toluene (PhCH₃) is investigated by complementary experimental and theoretical methodologies. Whereas the reaction of the chain‐carrying benzylperoxyl radicals with the substrate produces predominantly benzyl hydroperoxide, benzyl alcohol and benzaldehyde originate mainly from subsequent propagation of the hydroperoxide product. Nevertheless, a significant fraction of benzaldehyde is also produced in primary PhCH₃ propagation, presumably via proton rather than hydrogen transfer. An equimolar amount of benzyl alcohol, together with benzoic acid, is additionally produced in the tertiary propagation of PhCHO with benzylperoxyl radicals. The “hot” oxy radicals generated in this step can also abstract aromatic hydrogen atoms from PhCH₃, and this results in production of cresols, known inhibitors of radical‐chain reactions. The very fast benzyl peroxyl‐initiated co‐oxidation of benzyl alcohol generates HO₂^. radicals, along with benzaldehyde. This reaction also causes a decrease in the overall oxidation rate, due to the fast chain‐terminating reaction of HO₂^. with the benzylperoxyl radicals, which causes a loss of chain carriers. Moreover, due to the fast equilibrium PhCH₂OOH+HO₂^.?PhCH₂OO^.+H₂O₂, and the much lower reactivity of H₂O₂ compared to PhCH₂OOH, the fast co‐oxidation of the alcohol means that HO₂^. gradually takes over the role of benzylperoxyl as principal chain carrier. This drastically changes the autoxidation mechanism and, among other things, causes a sharp decrease in the hydroperoxide yield.     

Steric Influence on Reactions of Benzyl Potassium Species with CO

Reactions of benzyl potassium species with CO are shown to proceed via transient carbene-like intermediates that can undergo either dimerization or further CO propagation. In a sterically unhindered case, formal dimerization of the carbene is the dominant reaction pathway, as evidenced by the isolation of ((Ph₃SiO)(PhCH₂)C)₂ 2 and PhCH₂C(O)CH(OH)CH₂Ph 3 . Reactions with increasingly sterically encumbered reagents show competitive reaction pathways involving intermolecular dimerization leading to species analogous to 2 and 3 and those containing newly-formed five-membered rings tBu₂C₆H₂(C(OSiR₃)C(OSiR₃)CH₂) (R=Me 6 , Ph 7 ). Even further encumbered reagents proceed to either dimerize or react with additional CO to give a ketene-like intermediates, thus affording a 7-membered tropolone derivative 14 or the dione (3,5-tBu₂C₆H₃)₃C₆H₂CH₂C(O))₂ 15 .     

Darstellung und stabilität von n,n-disubstituierten β-aminoethyl-magnesiumbromiden; die ersten β-heteroatomsubstituierten grignardverbindungen des typs R2NCH2CH2MgX

R₂NCH₂,CH₂BR (R₂ = Ph₂; Ph, Me; (C₆H₁₁)₂)reacts with highly activated magnesium between ?75 and ?100°c in THF and ether to give the Grignard compounds R₂NCH₂CH₂MgBr, which already decompose between ?90 and?20°c by elimination of ethylene. The thermal stability increases in the sequence R₂ = Ph, Me < Ph₂ < (C₆H₁₁).     

Effect of the Structure of Phase-Transfer Catalyst on the Rate of Alkaline Hydrolysis of N-Benzyloxycarbonylglycine 4-Nitrophenyl Ester in the System Chloroform-Borate Buffer

Onium salts QZ (Z = Cl, Br) having a lipophilic (Q = R₃NR', where R' = C₁₆H₃₃) or readily extractable (into organic phase) cation (Q = Ph₄P) exhibit a high catalytic activity in phase-transfer alkaline hydrolysis of N-benzyloxycarbonylglycine 4-nitrophenyl ester in the two-phase system chloroform-borate buffer (pH 10). No catalytic effect is observed in the presence of hydrophilic ammonium salts [Et₄NCl, Et₃PhCH₂NCl, Me₂(NH₂)+NCH₂CH₂+N(NH₂)Me₂·2Br^-] and those insoluble in organic solvents [(Me)₃+NNH(CH₂)₂COO^-·2H₂O, Me₂(NH₂)+NCH₂CO^-, Me₂(NH₂)+N(CH₂)₃SO₃ ^-]. These data suggest extraction mechanism of the process. The activity of lipophilic cation Q is determined mainly by two factors: its extractibility, on the one hand, and the ability to form micelles, on the other.     

Hypervalent selenium compounds containing N → Se intramolecular interactions: synthesis,characterization and X‐ray structures of [2‐(Me2NCH2)C6H4]SeS(S)PR2 (R = Ph,OiPr)

[2‐(Me₂NCH₂)C₆H₄]Se? S(S)PR₂ [R = Ph (1), OⁱPr (2)] were prepared by reacting [2‐(Me₂NCH₂)C₆H₄]₂Se₂ with the appropriate disulfanes, [R₂P(S)S]₂. The compounds were characterized by multinuclear magnetic resonance (¹H, ¹³C, ³¹P). The molecular structures of 1 and 2 were determined by single‐crystal X‐ray diffraction. Both compounds are monomeric and the nitrogen atom of the pendent CH₂NMe₂ arm is strongly coordinated to the selenium atom. The organophosphorus ligands are monodentate, thus resulting in a T‐shaped coordination geometry around selenium. Copyright © 2002 John Wiley & Sons, Ltd.     

Mechanism of the Nickel-Catalyzed Electrosynthesis of Ketones by Heterocoupling of Acyl and Benzyl Halides

Summary.  The mechanism of the nickel-catalyzed electrosynthesis of ketones by heterocoupling of phenacyl chloride and benzyl bromide has been investigated by fast scan rate cyclic voltammetry with [Ni(bpy)²⁺ ₃](BF₄ ⁻)₂ as the catalytic precursor (bpy = 2,2{−}{ bipyridine}). The key step is an oxidative addition of Ni⁰(bpy) (electrogenerated by reduction of the Ni(II) precursor) to PhCH₂Br whose rate constant is found to be 10 times higher than that of PhCH₂COCl. The complex PhCH₂Ni^IIBr(bpy) formed in the oxidative addition is reduced at the potential of the Ni^II/Ni⁰ reduction by a two-electron process which affords an anionic complex PhCH₂Ni⁰(bpy)⁻ able to react with PhCH₂COCl to generate eventually the homocoupling product PhCH₂COCH₂Ph. The formation of the homocoupling product PhCH₂COCOCH₂Ph is prevented because of the too slow oxidative addition of Ni⁰(bpy) to PhCH₂COCl compared to PhCH₂Br. The formation of the homocoupling product PhCH₂CH₂Ph is also prevented because PhCH₂Ni⁰(bpy)⁻ does not react with PhCH₂Br. This explains why the electrosynthesis of the ketone can be performed selectively in a one-pot procedure, starting from an equal mixture of PhCH₂COCl and PhCH₂Br and a nickel catalyst ligated by the bpy ligand. Received June 27, 2000. Accepted July 11, 2000     

Cyclopalladation of mono-, di- and tribenzylamine by palladium(II) acetate: Influence of bulkiness around the nitrogen atom of benzylamine upon internal metallation

Cyclopalladation of mono-, di- and tribenzylamine has been investigated by reacting the corresponding amines with an equimolar amount of palladium(II) acetate (reaction i), or by heating the corresponding bis-amine complexes [Pd(O₂CMe)₂{(PhCH₂)_nNH_3−n}₂] (n=1, 2) (reaction ii). By the reaction i, all the three amines undergo cyclopalladation. However, in the case of the reaction ii, only the dibenzylamine complex [Pd(O₂CMe)₂{(PhCH₂)₂NH}₂] has been converted into a cyclopalladated complex. The reactivity of the three benzylamines towards cyclopalladation has been discussed in terms of the co-ordinating ability influenced by the bulkiness around the nitrogen atom. Temperature-dependent ¹H-NMR spectra are observed for mononuclear cyclopalladated complexes [Pd(O₂CMe){C₆H₄CH₂N(CH₂Ph)₂–C¹, N}L] (L=PPh₃, AsPh₃) and are attributed to the dissociation of the nitrogen atom in the cyclopalladated chelate ring. A heteroleptic bis-cyclopalladated complex [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] has also been prepared. X-ray crystallographic studies on [{Pd(O₂CMe)[C₆H₄CH₂N(CH₂Ph)₂–C¹, N]}₂] and [Pd[C₆H₄CH₂N(CH₂Ph)₂–C¹, N](C₆H₄CH₂NMe₂–C¹, N)] have been reported.     

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex as an efficient catalyst for oxidation of alcohols with tert-butyl hydroperoxide

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex [PS–(QBIM)₂Cu(II)] was synthesized by functionalization of chloromethylated polystyrene cross-linked with 6.5 % divinyl benzene with 2-(2′-quinolyl)benzimidazole and subsequent treatment with Cu(OAc)₂ in methanol. The complex was characterized by physical, analytical and spectroscopic techniques. Electronic and ESR spectra, together with magnetic susceptibility measurements, indicated that the complex was paramagnetic with distorted octahedral geometry around the copper. The complex was found to be active toward oxidation of various alcohols including phenol, benzyl alcohol and cyclohexanol using 70 % aqueous tert-butyl hydroperoxide under mild conditions. Under the optimized reaction conditions, cyclohexanol gave 100 % conversion to cyclohexanone, benzyl alcohol gave 98 % yield of benzaldehyde and phenol gave 89 % yield of catechol and 4 % of hydroquinone. The complex was recycled five times without much loss in catalytic activity.     

Inactivity of iridium–triphenylphosphine complexes for catalytic imine hydrogenation: formation of neutral, dihydrido-ortho-metallated species

Reactions of cis,trans,cis-[Ir(H)₂(PPh₃)₂(MeOH)₂]PF₆ in MeOH with the imines Ph(R′)C=NR under 1 atm H₂ precipitate the neutral, Ir(III)-dihydrido complexes [Ir(H)₂{RN=C(R′)(o-C ₆H₄)}(PPh₃)₂], where R = alkyl or benzyl, and R′ = Ph, H, or Me; the dihydrides are well characterized through elemental analysis, NMR and IR data and, in one case, with the imine Ph₂C=NCH₂Ph, an X-ray structure. These products are formed via intermediate ortho-metallated species, exemplified by [Ir(H){PhCH₂N=CPh(o-C ₆H₄)}(PPh₃)₂(MeOH)]PF₆ in the case of the Ph₂C=NCH₂Ph reaction; the intermediate then reacts with H₂ (via net heterolytic cleavage: H₂ → H⁻ + H⁺) to give the neutral dihydride and HPF₆ as co-product. The ‘unique’ imine PhCH=NPh, under the same conditions, does not form a dihydride and instead is readily catalytically hydrogenated to PhCH₂N(H)Ph; remarkably, we have shown previously that this imine is ‘unique’ within the corresponding Rh system in that no catalytic hydrogenation occurs because the amine product ‘poisons’ the Rh centre by coordination through the N-phenyl ring.     

Kinetics of Oxidation of Diphenylmethane and Derivatives with Ce(IV) in Aqueous Acidic Acetonitrile

In aqueous acidic acetonitrilc solution cerium(IV) oxidizes diphenylmethane (Ph₂CH₂) to produce diphenylmethanol (Ph₂CHOH) first and then benzophenone (Ph₂CO). With the organic reductant in great excess, both the Ce(IV)-Ph₂CH₂ and Ce(IV)-Ph₂CHOH rcactions follow second-order kinetics. The rates of both reactions increase nonlinearly with increasing [H⁺] or with decreasing [H₂O]. Both kinetic and spectrophotometrc results indicate that replacement of water molecules by complex formation through the phenyl or hydroxyl group plays an important role in activating the reaction. Under similar conditions, the order of relative reactivities toward Ce(IV) oxidation is PhCH₂OH > CH₃CH₂OH > Ph2CHOH > Ph₂CH₂ > PhCH₃> (Ph₂CO, C₆H₆). Mechanistic interpretations of the kinetic results are presented.     

Aspects of transmetallation reactions of 2-Me2NCH2C6H4- and 2,6-(Me2NCH2)C6H3-Metal (Pd,Pt, Hg,Tl) complexes with metal carboxylates and low-valent metal (Pd,Pt) complexes

A study has been made of reactions involving organometallic compounds containing ortho-Me₂NCH₂ substituted aryl ligands. The single step syntheses of the new compounds [(2-Me₂NCH₂C₆H₄)₂TlCl], [ [{(S)-2-Me₂NCH(Me)C₆H₄}₂TlCl], [{(S)-2-Me₂NCH(Me)C₆H₄}TlCl₂], [{2,6-(Me₂NCH₂)₂C₆H₃}TlClBr] and [{2,6-(Me₂NCH₂)₂C₆H₃}HgCl] are described. Stable internal NTl coordination at low temperatures has been established for the C-chiral thallium compounds. Reactions of the other Tl and Hg compounds and of [(2-Me₂NCH₂C₆H₄)₂Hg] with Pd(O₂CMe)₂, and also of the reverse reaction of cis-[(2-Me₂NCH₂C₆H₄)₂Pd] with Hg(O₂CR)₂ or Tl(O₂CR)₃, gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis-[(₂-Me₂NCH₂C₆H₄)₂Pd] with Pd(O₂CR)₂ gave the dimeric compound [{(2-Me₂NCH₂C₆H₄)Pd(O₂CR)}₂]. cis-[(2-Me₂NCH₂C₆H₄)₂Pt] did not react with Pd(O₂CMe)₂, while reaction of trans-[(2-Me₂NCH₂C₆H₄)₂Pt] or cis-[(2-Me₂NC₆H₄CH₂)₂Pt] with Pd(O₂CMe)₂ resulted in decomposition. Upon heating, trans-[(2-Me₂NCH₂C₆H₄)₂Pt] was isomerized to cis-isomer. A redox reaction between [(2-Me₂NCH₂C₆H₄)₂Hg] and [Pt(COD)₂] (COD  1,5-cyclo-octadiene) and [Pd₂(DBA)₃] (DBA  dibenzylideneacetone) gave the cis-isomers of [(2-Me₂NCH₂C₆H₄)₂M] (M  Pd, Pt).The results are discussed in terms of influence of internal coordination of the CH₂NMe₂ group. It is concluded that although internal coordination of the CH₂NMe₂ ligand can stabilize metal—carbon bonds it cannot prevent cleavage of such bonds by electrophiles. In this respect, there is no difference in the behaviour of Hg(O₂CR)₂ and Tl(O₂CR)₃. The reactions are influenced by the metal—nitrogen bond strength, which follows the order PtN > PdN > HgN, TlN. The reactivity of Pt compounds is greatly influenced by their structure and type of ligand. It is proposed that cleavege of PdC bonds occurs mainly by a mechanism involving direct electrophilic attack at the carbon centre.     

Synthesis and Characterization of Metal Complexes (M = Al,Ti, W,Zn) Containing Pyrrole‐imine Ligands

A series of metal compounds (M = Al, Ti, W, and Zn) containing pyrrole‐imine ligands have been prepared and structurally characterized. The reactions of AlMe₃ with one and three equivs of pyrrole‐imine ligand [C₄H₃NH‐(2‐CH=N? CH₂Ph)] ( 1 ) generated aluminum compounds Al[C₄H₃N‐(2‐CH=N? CH₂Ph)]Me₂ ( 2 ) and Al[C₄H₃N‐(2‐CH=NCH₂Ph)]₃ ( 3 ), respectively, in relatively high yield. Reacting two equivs of 1 with Ti(OⁱPr)₄, W(NH^tBu)₂(=N^tBu)₂, or ZnMe₂ afforded Ti[C₄H₃N‐(2‐CH=NCH₂Ph)]₂(OⁱPr)₂ ( 4 ), W[C₄H₃N‐(2‐CH=NCH₂Ph)]₂(=N^tBu)₂ ( 5 ), and Zn[C₄H₃N‐(2‐CH=NCH₂Ph)]₂ ( 6 ), respectively. All the compounds have been characterized by ¹H and ¹³C NMR spectroscopy. Compounds 3 – 6 have also been characterized by single‐crystal X‐ray structural analysis. The biting angles of pyrrole‐imine ligand with metals decrease and their related M? N_pyrrole and M? N_imine bond lengths increase in the order of 6 , 3 , 4 , and 5 .     

Chemical transformations of benzyl derivatives of zirconium

Conclusions Exchange of the -benzyl ligands in the complexes [Cp₂ZrCH₂Ph]₂O, Cp₂Zr(CH₂Ph)₂, and (PhCH₂)₄,Zr was effected by treatment with various reagents, containing a labile H atom. When [Cp₂ZrCH₂C₆H₅]₂O is reacted with phenol the benzyl ligand exchanges for the phenoxy group without destroying the Zr-O-Zr bond, and also the mixed complex Cp₂Zr(OC₆H₅)(CH₂C₆H₅) is formed, with retention of the -benzyl ligand.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 705–707, March, 1984.     

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.     

Rhodium phosphine complexes as homogeneous catalysts: 14. Asymmetric hydrogenation of a Schiff base of acetophenone — effect of phosphine and catalyst structure on enantioselectivity

Using catalysts prepared in situ from [Rh(NBD)Cl]₂ and chiral diphosphines of the type Ph₂PCHRCH₂PPh₂ (R = Ph, i-Pr, PhCH₂) optical yields above 60% were achieved in the hydrogenation of PhMeCNCH₂Ph. Although reproducibility of the results was poor, it can be concluded that the chiral diphosphines DIOP and diPAMP are much less effective, and that the halide ligand is necessary for good enantioselectivity.     

Bildung und Charakterisierung von Oberflächenverbindungen in den Systemen (C6H5CH2)4M/γ-Al2O3 (M = Ti,Zr)

Formation and Characterization of Surface Compounds in the Systems (C₆H₅CH₂)₄M/γ-Al₂O₅ (M = Ti, Zr) By O-bridges anchored surface-compounds are formed by protolytic splitting off of benzyl groups if tetrabenzyltitanium and -zirconium are added to γ-alumina. These compounds contain the metal in different oxidation states in dependence on the carrier/substrate ratio and the density of OH groups on the alumina surface. The different kinds of surface compounds are discussed. Furthermore, the products formed by thermal decomposition and hydrogenolysis of the surface compounds were analysed. With regard to catalytic conversion reactions of hydrocarbons systems of the type (C₆H₅CH₂)₄M/Pt/γ-Al₂O₃were involved in the investigations.