Volume 50, Issue 3

1,2-Di(9-anthryl)ethane (1,2-DAE) was used as a model for coal to study the C -C bond cleavage of the ethano linkage in the radiolysis of solutions containing NaAlH 2 (OCH 2 CH 2 OCH 3 ) 2 [NaAlH 2 (OR) 2 ]. Transient species were investigated by pulse radiolysis of solutions of 1,2-DAE in THF, DME and toluene in the absence and the presence of NaAlH 2 (OR) 2 . In the presence of NaAlH 2 (OR) 2 stabilized, long-lived radical anion/sodium cation pairs of 1,2-DAE were generated even in the non-polar solvent toluene. The reaction mechanisms differ substantially for solutions in the ether solvents (THF or DME) and for solutions in toluene. Steady-state radiolysis ( 60 Co γ-rays) of solutions of 1,2-DAE in toluene containing NaAlH 2 (OR) 2 resulted in the C -C bond cleavage of the ethano linkage. This is attributed to the unstable dianion (1,2-DAE 2- , 2Na + ) formed in two successive radiation- induced reductions via (1,2-DAE ∙- , Na + ). The resulting (9-anthryl)methyl carbanionic fragments C 14 H 9 CH 2 - , Na + react with AlH(OR) 2 generated in the process, to form the aluminate salts [C 14 H 9 CH 2 AlH(OR) 2 - , Na + ]. From the aluminate salts, 9-methylanthracene (9- MA) was obtained by hydrolysis in yields up to 65 wt.%.

N-(2-bromoallyl)-N-methylaniline 1 is easily converted into the propargylamine-zirconocene complex 3 via loss of methane from 2-[zirconocene(methyl)]allyl amine 2. Regioselective insertion reactions with alkenes and benzophenone afford, after iodinolysis, products 4 -10.

Homoleptic tris(1-oxa-1,3-diene)molybdenum and tungsten complexes are formed as yellow, crystalline compounds in 54-80% isolated yield on treatment of the corresponding β-unsubstituted a,β-unsaturated ketones with W(CO) 3 (CH 3 CH 2 CN) 3 or (η 6 -C 6 H 6 )Mo(CO) 3 in refluxing hexane. Reaction of these oxadienes with (η 6 -C 6 H 5 CH 3 ) 2 Mo in tetrahydrofuran or n-hexane provides a new high yield route to homoleptic molybdenum complexes that are otherwise difficult to prepare. X-ray crystal structure analyses of two air-stable, isomeric tungsten complexes reveal a significant contribution of a σ 2 ,η 2 -bonding mode in the coordinated oxadiene moieties. Under reaction conditions that allow the platinum catalyzed hydrogenation of phenyl substituents in these ligands, the coordinated oxadiene fragments are inert, thus demonstrating an unprecedented chemoselectivity in the hydrogenation of arylsubstituted enones. On the other hand, the complexes are labile enough to catalyze the cyclotrimerization of alkynes such as methyl propiolate.

Low-valent titanium prepared by the reduction of TiCl 3 with zinc dust oxidatively adds to α-ketoamides or α-ketoesters with the formation of the corresponding titanium enediolates. These 1,2-difunctional nucleophiles, which have hardly been used in organic synthesis so far, undergo regioselective intramolecular aldol condensation reactions with various electrophiles such as aldehydes, ketones, nitriles, esters and amides. This methodology allows the synthesis of differently substituted coumarin and 2-quinolone derivatives.

Bimetallic Pt/Rh colloids protected by NR 4 + - or PR 4 + groups are accessible by the coreduction of PtCl 2 and RhCl 3 using hydrotriorganoborates in organic media. According to TEM the particle size ranges from 1.9 to 2.5 nm. EDX point analysis of several samples has shown that both metals are present in the particles. The metallic character of the Pt/Rh core confirmed by XANES, and EXAFS data clearly indicate the formation of nanometallic alloys. Colloidal Pt/Rh alloys prepared in this way are very soluble and highly stable in organic phases and serve as sources for heterogeneous hydrogenation catalysts.

Conceptually novel access to chiral arsinites is provided by reacting phenyl-O,O-dimenthylarsonite (1) with bulky nucleophiles e. g. tert-butyl-lithium or iso-propyl-lithium to yield the arsinites 3 and 4. The asymmetric induction determined by GC and NMR is 50% and 30% d.e. A small nucleophile effects double substitution.

Titanium(II) bis(tetrahydrofuran) 1, generated by the treatm ent of TiCl 4 in THF with two equivalents of n-butyllithium at -78 °C, has been found to form carbon-carbon bonds with a variety of organic substrates by reductive coupling. Diphenylacetylene is dimerized to exclusively (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene; benzyl bromide and 9-bromofluorene give their coupled products, bibenzyl and 9,9'-bifluorenyl, as do benzal chloride and benzotrichloride yield the 1,2-dichloro-1,2-diphenylethanes and 1,1,2,2-tetrachloro-1,2-diphenylethane, respectively. Styrene oxide and and cis-stilbene oxide undergo deoxygenation to styrene and fra/«-stilbene, while benzyl alcohol and benzopinacol are coupled to bibenzyl and to a mixture of tetraphenylethylene and 1,1,2,2-tetraphenylethane. Both aliphatic and aromatic ketones are smoothly reductively coupled to a mixture of pinacols and/or olefins in varying proportions. By a choice of experimental conditions either the pinacol or the olefin could be made the predom inant product in certain cases. The reaction has been carried out with heptanal, cyclohexanone, benzonitrile, benzaldehyde, furfural, acetophenone, benzophenone and 9-fluorenone. In a remarkable, multiple reductive coupling, benzoyl chloride is converted into 2,3,4,5-tetraphenylfuran in almost 50% yield. The stereochemical course of two such couplings, that of diphenylacetylene to yield exclusively (E,E)-1,2,3,4-tetraphenyl-l,3-butadiene and that of acetophenone to produce only racemic-2,3-diphenyl-2,3-butanediol, is interpreted to conclude that the couplings proceed via two electron transfer pathways (TET) involving titanium (IV) cyclic intermediates of the titanirene and the oxatitanacyclopropane type, respectively.

This work contributes to the systematic investigation of phosphines. In an attempt to determine the nature, shape, volume and direction of the lone pairs at the phosphorus atoms in phosphines, high resolution X-ray structure analyses of triphenylphosphine, tris(p-methoxyphenyl) phosphine, bis(2,4,6-triisopropylphenyl)phosphine, 1,1 -bis(diphenylphosphino)ethene and 4,5,6-triphenyl-4-phosphaspiro[2.4]hept-5-en have been carried out. New valence force field param eters (TRIPOS force field) are presented which were developed on the basis of the molecular structures of the free phosphines. The results of crystal growing experiments using zone melting techniques are summarized.

The synthesis of low-valent tungsten (0 and II) complexes bearing chiral bidentate phosphino- oxazoline or bisoxazoline ligands is described. The structures of four of the complexes have been determined by single crystal X-ray analyses. Tungsten(II)-allyl complexes of the type [W(CO) 2 (PN)(C 3 H 5 )Cl] (PN = phosphino-oxazoline) are fluxional in solution, but can be crystallized as single diastereoisomers. The complex [W(CO) 3 (PN)(CH 3 CN)], which also crystallizes as a single diastereoisomer, is readily oxidized in solution and solid state, in stark contrast to analogous compounds bearing four carbonyl ligands [W(CO) 4 (PN)] or [W(CO) 4 (NN)] (NN = bisoxazoline) which were found to be stable. [W(CO) 3 (PN)(CH 3 CN)] functions as a highly enantioselective catalyst in allylic substitution reactions with dimethyl sodiomalonate, whereas complexes of the type [W (CO) 2 (PN )(Z -C 3 H 4 )X)] (Z = H, Ph; X = Cl, Br) failed to yield allylic alkylation products.

It has been shown that disubstituted butadiynes react with L 2 Ni(C 2 H 4 ) to yield mononuclear complexes L 2 Ni(η 2 (1:2 )-RC≡C -C ≡CR) (L = o-Tol-O) 3 P, R = SiMe 3 (1), t Bu (2), Ph (3)). For the first time, the crystal structure of a nickel(O) alkyne complex carrying phosphite ligands (2) has been determined. The reaction of (dipy)Ni(cod) (L 2 = dipy) with butadiynes R'C ≡ C -C ≡ CR is strongly influenced by the substituents of the butadiyne. With R' = R = SiMe 3 (4), t Bu (5) and Ph (6) or R' = Ph, R = SiMe 3 (7) and R ' = t Bu, R = SiMe 3 (8) mononuclear complexes (dipy)Ni(η 2 (1:2 )-R'C ≡ C-C ≡ CR ) have been observed. Depending on the stoichiometry with R = R' = Ph (9) and t Bu (10) dinuclear complexes {(dipy)Ni} 2 (μ-η 2 (1:2),η 2 (3 :4 )-R'C ≡ C -C ≡ CR ) having two Ni atoms coordinated to two C ≡ C triple bonds were obtained. By contrast, with R' = R = SiMe 3 (11), R' = t Bu, R = SiMe 3 (12) and R' = Ph, R = SiMe 3 (13) the two Ni-centers were found to coordinate to the same C≡C triple bond to yield another type of a dinuclear complex {(dipy)Ni} 2 (μ-η 2 (1:2),η 2 (1:2 )-R'C ≡ C -C ≡C R). Compound 5 has been characterized by Xray crystal structure analysis. The structures of 2 and 5 are compared to that of the wellknown complex (Ph 3 P) 2 Ni(η 2 (1:2 )- t BuC ≡ C-C ≡C t Bu) [1] to study the influence of different ligands L on the structural details. In comparison to the alkyne complexes L 2 Ni(η 2 -RC≡CR) in butadiyne complexes of the L 2 Ni(η 2 (1:2 )-R'C ≡ C-C ≡ CR ) type there is only a slight effect of the different ligands. The uncomplexed C ≡ C triple bond as a part of the second substituent in conjugation to the complexed C ≡ C triple bond appears to level out the influence of ligands and substituents.

It has been shown that disubstituted butadiynes react with (Ph 3 P) 2 Ni(C 2 H 4 ) [1] or (cod) 2 Ni [2] in the presence of Ph 3 P to yield mononuclear complexes (Ph 3 P) 2 Ni(η 2 (1 :2 ) - R'C ≡ C - C ≡CR) (R' = R = SiMe 3 (1), t Bu (2) Ph (3) and R' = t Bu, R = SiMe 3 (4) or R' = Ph, R = SiMe 3 (5)) or dinuclear complexes {(Ph 3 P) 2 Ni} 2 (μ-η 2 (1 :2),η 2 (3 :4) - R'C ≡C - C ≡CR ) (R' = R = SiMe 3 (6), Ph (7)) depending on the stoichiometry applied. For R' = R = t Bu or R' = t Bu, R = SiMe 3 the dinuclear complexes could not be obtained. Some of the mononuclear complexes with symmetrical (R' = R = SiMe 3 , t Bu, Ph) and unsymmetrical disubstituted (R' = t Bu, R = SiMe 3 ) butadiynes have been characterized by X-ray crystal structure analysis to study the influence of different substituents on the structural details of the bonding. As compared to the alkyne complexes (Ph 3 P) 2 Ni(η 2 -RC ≡CR ) the influence of the different substituents in mononuclear butadiyne-complexes (Ph 3 P) 2 Ni(η 2 (1:2) - R'C ≡C - C ≡CR ) is strongly diminished by the conjugated uncomplexed C ≡C triple bond.

NiCl 2 (PPh 3 ) 2 -catalyzed alkylative olefinations of trithioorthoesters and tetrathioorthocarbonates give the corresponding substituted alkenes. Aliphatic C - S bonds in these substrates can be activated in the nickel-catalyzed cross coupling reaction leading to carbon - carbon bond formation. This reaction can be considered as using trithioorthoesters and tetrathioorthocarbonate as R 3 C 3+ and C 4+ synthons.

The new room temperature stable halfsandw ich complex Cp*Fe(tmeda)Cl (2) has been synthesized by the 1:1 reaction of FeCl 2 (thf) 1.5 with LiCp* in a mixture of THF and TMEDA at - 30 °C. 2 is an ideal starting material for the synthesis of a wide range of new iron complexes. Treatment of 2 with lithium sand in THF in the presence of COD or ethene followed by the addition of TMEDA yields the ferrates [Li(tmeda)][Cp*Fe(cod)] (3) or [Li(tmeda)][Cp*Fe(C 2 H 4 ) 2 ] (4). By delithiation with dichloroethane, 3 and 4 can be transformed into the novel 17 e iron complexes Cp*Fe(cod) (5) and Cp*Fe(C 2 H 4 ) 2 (6). 6 is extremely labile. Since the ethene ligands can be easily displaced, the title compound is a synthetically valuable source of the Cp*Fe fragment. Whereas the photochemically generated 17e dicarbonyl species CpFe(CO) 2 rapidly recombines to give the dimer [CpFe(CO) 2 ] 2 , the isoelectronic 6 is stable in ethene saturated pentane for several days at 0 °C. Without the stabilizing effect of ethene (in pure pentane or under vacuum ), 6 loses ethene to give the dinuclear complex (Cp*Fe) 2 (C 2 H 4 ) 2 (8) irreversibly. The structure of 8 has been characterized by X -ray analysis.

Dimethyl-L-tartrate 1 is converted into 2,3-O-n-heptylidene-decylidene dimethyl-L-tartrates 2 which are reduced with ethyldiboranes alone and then in the presence of 9-methylsulfonyloxy- 9-borabicyclo[3.3.1]nonane (MSBBN ) to yield 2-O -alkyl-L -threitols 4, after deprotection. The amphiphilic compounds 4 are thermotropic mesogens which display the smectic A liquid crystalline phase on melting.

The title complex (1) has been prepared by reaction of ZrCl 4 with 1,2,3,4-(tetraphenyl)- cyclopenta-1,3-dienyl lithium (2). The phenyl substituents on the metallocene ligands exert both steric and electronic effects on the active site obtained by activation of 1 with MAO. Thus this catalytic system shows lower polymerization activity than in case of unsubstituted or methyl-substituted ligands and leads to the formation of ethylene oligomers.

Reaction of the CH-acidic compounds 2-nitropropane, cyclopentadiene and 9-ethylfluorene with HON (nBu) 4 affords the corresponding tetrabutylammonium salts in crystalline form, which have been characterized by X -ray structure analysis. The nitrostabilized salt is not a “naked ” anion (real carbanion). Rather, the α-methylene entities of the N + (nBu) 4 cations form relatively strong hydrogen bonds with the O -atom s of the nitronateanion, forming dimers in a three-dimensional network. In solution dimers in the form of supramolecular ion pairs exist. In contrast, the cyclopentadienyl anion appears to be a real carbanion, since anion and cation do not interact with one another via H -bonding. The structure of the N + (nBu) 4 salt of the 9-ethylfluorenyl anion is a special case in that closer contacts between cation and anion occur, which may be indicative of unusual [CH ··· C] - bonding. All three salts function as initiators in the metal-free anionic polymerization of acrylates and methacrylates at room temperature. In the case of tetrabutylammoniumcyclopentadienide, star polymers are formed.

Ethene was copolymerized with 1-hexene and 1-octadecene at different temperatures to study the influence of the temperature. The stereorigid catalyst [2,4-cyclopentadien-1-yliden- (iso-propyliden)fluoren-9-yliden]zirconium dichloride iPr(CpFlu )ZrCl 2 1 in combination with methylalumoxane MAO was used. The polymerization rate of ethene depends in a wide range on the temperature and the com onom er content in solution. In each case a large rate enhancem ent at low ratios [com onom er]/[ethene] was observed. A t 25 °C the polymerization rate of ethene increases continuously with increasing [1-hexene]/[ethene]-ratio. At 40 °C the consumption of ethene is nearly independent of the 1-hexene content in solution. Finally, at 60 °C, similar to the ethene/1-octadecene-copolymerisation at different temperatures, the polymerization rate of ethene decreases with increasing [1-hexene]/[ethene]-ratio. It is suggested that this behavior is caused by the mobility of the side chains in the copolym er near the active center, probably for sterical reasons. W ith increasing temperatures, the side chain becomes more and more flexible and thus the sterical hindrance is increased. This effect is even stronger with long chain α-olefins. The microstructure of the copolymer was investigated with respect to Marcovian statistic 1. and 2. order. The experimental triad distribution is described satisfactorily only with the second order statistic. Independent of the temperature the r 22 parameter is considerably greater than the r 12 parameter, the insertion of an α-olefin thus being more favored for he sequence {R -(α-olefine)-(α-olefine)-Kat.} than for {R -(ethene)-(α-olefine)-Kat.}. It therefore appears that both last inserted monomers influence the insertion of the subsequent monomer, especially at high comonomer contents. Furthermore, the parameters for the α-olefin insertions r 22 and r 12 are nearly independent of the temperature of polymerization, whereas the r 11 and r 21 parameters increase with increasing temperature.

Cationic palladium catalysts have been used to cooligomerize ethylene and carbon monoxide. At high ethylene/CO ratios (m /m = 10:1) in methylene chloride as a solvent, unsaturated alternating cooligomers of the general structure R[C(O)CH 2 CH 2 ] m H ( m ≥ 1 ; R ≡CH 2 =CH-, CH 2 =CHCH 2 CH2- and CH 3 CH = CHCH 2 -) were obtained for the first time. Single component catalyst precursors [(allyl)Pd(P^X )] + Y - (P^X = Ph 2 P(CH 2 ) n C(= O )OR, Ph 2 P(CH 2 ) 2 P(=O)Ph 2 , Ph 2 P(CH 2 ) n Ph 2 P(CH 2 ) 2 S (=O )Ph, n = 1 - 3 , R = Me, Et; Y - = BF 4 - , SbF 6 - ) with bidentate P,O - and P,S-ligands as well as in situ catalysts with unfunctionalized phosphine ligands were used. With P"Bu 3 as a ligand, selectivities for ethylvinylketone of 40% based on the CO converted were obtained. The hemilabile phosphino-ester and phosphinothiophene ligands behave like monodentate phosphines under catalytic conditions.

The exhaustive hydroboration of the (C ≡ C )-groups in Me 2 Si(C ≡ CMe) 2 (A ) by adding ethyldiboranes(6) at room temperature is presumed to lead initially to the formation of a mixture of the threo- and erythro-3,3,5,6-tetrakis(diethylboryl)-4,4-dimethyl-4-silaheptanes (1a , b). The threo-1a reacts further by borane catalysed intermolecular condensation to the substituted disilatetraboratricyclo[6.2.1.1 6.9 ]dodecane 2 with the formula , whose crystal structure [space group C2/c, a = 19.696(2), b = 10.371(1), c = 16.580(2) Å; β = 125.90(1)°; at 122 K] has been established by X -ray diffraction. In contrast, the erythro-1b undergoes intramolecular, thermal elimination of Et 3 B to give the 1,2-diethyl-2,4-bis(diethylboryl)- 3,3,5-trim ethyl-3-silaborolane (4). If A is added to an excess of undiluted B (“hydridebath”), then the two substituted diastereomers of the 1-carba-arachno-pentaboranes(10) (endo/exo-Et,SiH Me 2 ) (3a, b), are formed preferentially as the result of an initial Si-C ≡-c le a v e d hydroboration.