Showing papers in "Chemische Berichte in 1992"

Enantioselective Synthesis of Optically Active Pyridine Derivatives and C2-Symmetric 2,2′-Bipyridines

Abstract: Optically active pyridine derivatives 2, 15, 18, 19, 21, 26, and 27 are obtained by enantioselective reduction of the corresponding ketones 5, 7, 11–13, 24, and 25 using the chiral borane reagent chlorodiisopinocampheylborane [(Ipc)2BCl]. Nickel(0)-mediated coupling of bromopyridines 2, 15, and 31 gives C2-symmetric 2,2′-bipyridines (R,R)-32, (R,R′)-33, and (S,S)-38, respectively, which form metal complexes with CoII, PdII, CuI, and AgI. Aryl-substituted pyridines 26, and 39–41 are synthesized by palladium(0)-catalyzed cross couplings of 2 and 15 with boronic acids 42–44.

Asymmetrische Katalysen, 77[1] Neue optisch aktive Pyrazolderivate für die enantioselektive Katalyse

Abstract: Asymmetric Catalysis, 77[1]. – New Optically Active Pyrazole Derivatives for Enantioselective Catalysis Starting from the amines 3–6 and the dipyrazolopyrazinedione 2, the optically active (pyrazolylmethyl)amines 11–14 have been synthesized. Furthermore, the preparation of the (+)-camphor-derived optically active pyrazole 17 is described. Pyrazoles 11–13 and 17 are introduced as chiral building blocks into the 2-(1-pyrazolyl)pyridines 30–33. The optically active compounds 23–25 are formed from 2-[3(5)-pyrazolyl]pyridine and 2,6-bis[3(5-)pyrazolyl]pyridine, respectively, and (+)-3-(bromomethyl)pinane. The pyrazole derivatives 27–29 contain (+)-(1-phenylethyl)hydrazine as the optically active component.

Catalyzed Enantioselective Alkylation of Aldehydes

Abstract: Enantioselective alkylation of a variety of aldehydes with diethylzinc was achieved by using catalytic amounts of optically active pyridines and C2-symmetric 2,2′-bipyridines. The products were obtained in good yields with high enantioselectivities. Steric factors of the catalyst structure which govern the stereoselectivity were revealed, and important reaction intermediates were identified by spectroscopic means and singlecrystal X-ray diffraction. The effect of additives on the optical purity of the product was studied. A strong asymmetric amplification was found with catalysts of low ee′s.

Catalytic Enantioselective Conjugate Addition of Dialkylzinc Compounds to Chalcones

Abstract: Conjugate addition of diethylzinc to enones is catalyzed by a complex derived from Ni(acac)2 and C2-symmetric 2,2′-bipyridine 3 or chiral pyridines 5–12. The products are obtained with optical purities up to 89% ee. A strong positive nonlinear relationship between the enantiomeric excess of the ligand and the ee of the product has been observed. The factors which govern catalyst activity and enantioselectivity have been investigated.

Michael Adducts of (Alkynylcarbene)pentacarbonylchromium Complexes: Formation, Stereochemistry, and Thermal Rearrangement

Abstract: β-Donor-substituted α,β-unsaturated chromium carbene complexes (CO)5CrC(OEt)C = CR(XR′n) (X = N, O, S; 3, 9, 11–16, 22–25) have been synthesized by Michael addition of amines, alcohols, and thiols to alkynylcarbene complexes (CO)5CrC-(OEt)CCR (1) The configurations of the newly formed C–C double bonds have been determined by NOE/NOESY measurements and X-ray crystal structure analysis These vinylcarbene complexes lose one carbonyl ligand in refluxing tetrahydrofuran to give tetracarbonyl complexes (CO)4CrC(OEt)C = CR(XR′n) (X = N, O, S; 26–28)

Sterische Cyclopentadienyl-Äquivalente in der Chemie der f-Elemente: Monomere, homoleptische Lanthanid(III)-tris[N,N′-bis(trimethylsilyl)-benzamidinate]

Abstract: Steric Cyclopentadienyl Equivalents in f-Element Chemistry: Monomeric, Homoleptic Lanthanide(III) Tris[N,N′-bis(trimethylsilyl)benzamidinates] Anhydrous lanthanide trichlorides react with N-silylated sodium benzamidinates, Na[4-RC6H4C(NSiMe3)2], (1a–d), to give the monomeric, homoleptic lanthanide(III) benzamidinates [4-RC6H4C(NSiMe3)2]3Ln (2–23, R = H, MeO, CF3, Ph). The molecular structure of [4-MeOC6H4C(NSiMe3)2]3Pr (11) has been determined by X-ray diffraction. Absorption and emission measurements reveal that the three benzamidinate ligands produce an unusually large crystal field which is comparable with that of cyclopentadienyl.

Chiral Organometallic Reagents, V[1] A Test on the Configurational Stability of Chiral Organolithium Compounds Based on Kinetic Resolution; Scope and Limitations

Abstract: The test on the configurational stability of chiral organolithium compounds is based on the kinetic resolution of the racemic organolithium compound on reaction with an enantiomerically pure electrophile. The limits of this test have been evaluated by model calculations. The factors that have been considered are: Optimum values for the kinetic resolution; effects of < 100% enantiomeric purity of the chiral electrophile; parallel side reactions of the organolithium compounds with the electrophile.

α-Oxygen-Substituted Organolithium Compounds and Their Carbenoid Nature: Calculations of the Configurational Stability and of LiCH2OH Model Structures, Crystal Structure of Diphenyl(trimethylsilyloxy)methyllithium · 3 THF, and the Stereochemistry of the (Reverse) Brook Rearrangement

Abstract: The comparatively high configurational stability of α-oxygen-substituted organolithium compounds is confirmed by ab initio calculations [MP2/6–311 + + G(d,p)]. Model calculations of the LiCH2OH structures 21A–D (MP2/6–31G(d)//3–21G and MP2/6–311 + + G(d,p)//MP2/6–311 + + G(d,p)) are in agreement with recently determined crystal structures of α-oxygen-sub-stituted organolithium compounds. They also suggested the preparation of a new structural type (21C) which has been verified by means of diphenyl(trimethylsilyloxy)methyllithium · 3 THF (24 · 3 THF) as shown by X-ray crystallography. The lengthening of the CO bonds in all four α-oxygen-sub-stituted organolithium compounds known to date contrasts strongly with the wealth of structural data from organolithium compounds α-substituted with “typical” acceptor substituents: on lithiation the carbon-acceptor bond length in these compounds is always shortened. This difference is in agreement with a carbenoid character of α-oxygen-substituted organolithium species. Finally, the crystal structure of 24 · 3 THF serves as a model for the surprising stereochemistry of the (reverse) Brook rearrangement.

Room-temperature C-F bond activation of hexafluorobenzene by a tailor-made Pt(0) intermediate, [(dtbpm)Pt(0)]

Abstract: Reductive elimination of neopentane from cis-hydridoneopentyl[η2-bis(di-tert-butylphosphanyl)methane]platinum (II), (dtbpm)Pt(Np)(H) (1), allows to generate the 14-electron fragment [(dtbpm)Pt(0)] (2) at ambient temperature. This highly reactive intermediate is capable of activating C–F bonds of hexafluorobenzene, yielding exclusively the C–F insertion product (dtbpm)Pt(C6F5)F (3).

Unsymmetrical phthalocyanines with a single macrocyclic substituent

Abstract: Unsymmetrical phthalocanines (5–7) with a single macrocyclic substituent are synthesized by the reaction of the boron complex of phthalonitrile (1) with the iminoisoindoline derivatives 2–4 of macrocyclic compounds, i.e. 15-crown-5, monoaza-15-crown-5, and tetraazacyclotetradecane. The monomacrocycle-substituted phthalocyanines are less soluble than the tetra-substituted one.

Darstellung neuartiger monomerer, oligomerer und polymerer Silyltriflate

Abstract: Preparation of New Monomeric, Oligomeric, and Polymeric Silyl Triflates The highly reactive silyl triflates R3SiOSO2CF3 are valuable reagents in organosilicon chemistry. New triflate derivatives of mono- and oligosilanes have been prepared by substitution of phenyl groups or hydrogen atoms for the trifluoromethanesulfonyl group. The presence of the electron-withdrawing triflate group leads to a strong deactivation of the other substituents at the silicon atom, and the displacement of a second phenyl group at the same silicon atom is much slower than the first step. For this reason in the case of phenylated oligosilanes stepwise monosubstitution of the silicon atoms has been found. Other new oligomeric silyl triflates are obtained by reaction of silanediyl(triyl) bis(tris)(trifluoromethanesulfonates) with lithium derivatives of organosilicon compounds. Finally, the cleavage of silicon–phenyl bonds of poly[methyl(phenyl)silanes] by CF3SO3H leads to triflate derivatives of polysilanes.

Metallcarbonyl-Synthesen, XXI. Einfache Synthese eines präparativ nützlichen Alkoxy(carbonyl)metallats

Abstract: Metal Carbonyl Syntheses, XXI – Straightforward Synthesis of a Synthetically Useful Alkoxy(carbonyl)metallate Anionic methoxy complexes are formed upon carbonylation of ammonium perrhenate in methanol at 230–240°C Thus, the dinuclear ionic complex [N(CH3)4][Re2(CO)6(μ-OCH3)3] (2) results in 80% yield at CO pressures of ca 100 bar, while the trinuclear derivative [N(CH3)4][Re3(CO)9(μ3-OCH3)3(μ3-OCH3)] (3) is due to lower pressure conditions (ca 50 bar); 2 yields the bis(carbene) complex 4 of formula fac-Re(CO)3L2I upon treatment with a bis(imidazolium) iodide, thus demonstrating that carbonylrhenium chemistry not necessarily depends on the availability of Re2(CO)10

Verbindungen des Germaniums und Zinns, 10[1] Thermolyse eines Cyclotristannans: Stannylen‐ versus Distannen‐Reaktionen

Abstract: Compounds of Germanium and Tin, 10[1]. — Thermolysis of a Cyclotristannane: Stannylene versus Distannene Reactions Hexakis(2,4,6-triisopropylphenyl)cyclotristannane (1), first described by Masamune and Sita, is easily accessible by treatment of tin(II) chloride with 2,4,6-triisopropylphenylmagnesium bromide. The equilibrium between 1 and its cleavage products bis(2,4,6-triisopropylphenyl)stannylene (2) and tetrakis(2,4,6-triisopropylphenyl)distannene (3) in toluene has been followed by 119Sn-NMR spectroscopy at elevated temperatures. Stannylene 2 can be trapped by open-chain or cyclic diketones as well as by 1,3-dienes. Reaction of 3 with phenylacetylene proceeds in a [2 + 2] fashion to provide the 1,2-distannacyclobutene derivative 5 whose structure was confirmed by X-ray crystallography.

Benzoanellated centropolyquinanes, 11. Synthesis of tribenzotriquinacene and some centro-substituted derivatives

Abstract: The syntheses of tribenzotriquinacene (1a) and five centro-substituted derivatives, 1b-1e and 1g, as well as of the related diindan 13 are reported. The three-step synthetic sequences include the reduction of suitably substituted 2-benz-hydryl-1,3-indandiones 3 to the corresponding 1,3-indandiols 4 and the twofold cyclodehydration of the latter to close two additional five-membered rings at a time. Although the yields of the cyclodehydration step 4 · 1 are only low to moderate (10-33%), the overall approach allows the preparation of 5-50-gram amounts of the centropolyindans in most cases by starting from simple 1,3-indandiones 2a-2c. This includes the new synthesis of the parent tribenzotriquinacene (1a). The related Cs-symmetrical diindan, 4b,9,9a,10-tetrahydroindeno[1,2-a]indene (13), has been prepared in high yield by using the same cyclodehydration technique. Scope and limitations of the double cyclodehydration strategy are described concerning the synthesis of 1,3-indandiones with bulky substituents at C-2 and the cyclization of 1,3-indandiols with an aptitude to undergo heterolytic cleavage of an exocyclic C-2-C- bond, in particular 4f. The course of the reduction of the 2,2-disubstituted 1,3-indandiones with lithium aluminum hydride is discussed on the basis of the stereochemistry of the product 1,3-indandiols.

Organotin cations stabilized by π coordination – synthesis and NMR studies in solution and in the solid state

Abstract: The organoboration of tetraalkynyltin compounds [Sn-(CCR1)4 (1): R1 = Me (a), Et (b), Pr (c), iPr (d), tBu (e)] with triethylborane (2) proceeds stepwise. Intermediates with a cationic triorganotin (3, 5) and a dicationic diorganotin fragment (4), stabilized by intramolecular coordination of one and two alkynyl moieties, respectively, were isolated (3e, 4a) and/or identified by multinuclear NMR in solution (1H, 11B, 13C, 119Sn) and in the solid state (13C and 119Sn CP/MAS) (3e, 4a). The magnitude of 1J(13C13C) in 4a (101.0 Hz) is significantly smaller than that for sodium triethyl-1-propynylborate (7) (119.2 Hz), proving the weak coordination of the CC bond to the dicationic tin fragment. The final products of the organoboration, 1,4,6,9-tetraalkyl-2,7-bis(diethylboryl)-3,8-diethyl-5-stannaspiro[4.4]nona-1,3,6,8-tetraenes (6b–6e) were obtained in high yield.

Organometall-Imide – höhervalente Derivate der d-Metall-Säuren, 3. Synthese und Reaktionen von (Pentamethylcyclopentadienyl)(imido)-Komplexen des Molybdäns und Wolframs und eine effiziente Strategie zur Synthese der Organometallate NBu4[Cp*MO3] (M = Mo, W)

Abstract: Organometallic Imido Complexes – Highervalent Derivatives of the d-Metal Acids, 3[4b]. – Synthesis and Reactions of Pentamethylcyclopentadienyl Imido Complexes of Molybdenum and Tungsten and an Efficient Strategy for the Synthesis of the Organometallates NBu4[Cp*MO3] (M = Mo, W) A convenient and new entry into the chemistry of highvalent pentamethylcyclopentadienyl halfsandwich complexes of molybdenum and tungsten is described. The reaction of Mo-(NtBu)2Cl2 or W(NtBu)2Cl2(py)2 with Cp*Li (Cp* = η5-C5Me5) provides a high-yield route to new complexes Cp*Mo-(NtBu)2Cl (1a) and Cp*W(NtBu)2Cl (1b) which are converted into a variety of diimido, monoimido, and oxo derivatives. Treatment of 1a,b with MeLi yields the highly volatile methyl derivatives Cp*Mo(NtBu)2Me (2a) and Cp*W(NtBu)2Me (2b), while protolysis of 1a,b with an excess of HCl gas leads to selective cleavage of only one imido function with formation of Cp*Mo(NtBu)Cl3 (3a) and Cp*W(NtBu)Cl3 (3b). In contrast, protolysis of 1a,b with aqueous HCl provides a high-yield route to the well-known organometallic oxides [Cp*MoO2]-(μ-O) (4a) and [Cp*WO2](μ-O) (4b). These two key compounds are easily converted into the organomolybdate and organotungstate salts NBu4[Cp*MoO3] (5a) and NBu4[Cp*WO3] (5b) by cleavage of the M–O–M bridge with NBu4[OH]. The X-ray structure of 3a is reported.

Lanthanoiden‐Komplexe, I Solvensfreie Alkoxid‐Komplexe des Neodyms und Dysprosiums. Kristall‐ und Molekülstruktur von trans‐Bis(acetonitril)tris(tri‐tert‐butylmethoxy)neodym

Abstract: Complexes of the Lanthanides, I. – Solvent-Free Alkoxide Complexes of Neodymium and Dysprosium. Crystal and Molecular Structure of trans-Bis(acetonitrile)tris(tri-tert-butylmethoxy)neodymium The first lanthanide complex 3a is obtained from the sterically demanding silanol (tC4H9)3SiOH (, „silox”, 1a) and Nd-[N{Si(CH3)3}2]3 (2a). Similarly, the bulky alcohols, „tritox-H”, tri-tert-butylmethanol (1b), and, „ditox-H”, di-tert-butylmethanol (1c), react with 2a to give the corresponding alkoxide complexes Nd(tritox)3 (3b) and [Nd(ditox)3]2 (3c), respectively. Under the same conditions Dy[N{Si(CH3)3}2]3 (2b) yields the homoleptic ditox derivative 6. The new complexes are all very soluble in aliphatic hydrocarbons. They show a very different thermal stability as, for example, expressed in their sublimation behaviour.

Phosphorus derivatives of anthracene and their dimers

Abstract: The syntheses of the (9-anthracenyl)phosphanes 2 to 7 and of the metal carbonyl complexes 8 and 9 are described. Both 1 and 4 undergo [4 + 4] cycloaddition when irradiated, forming the dimers 10 and 11. Only one of the six possible rotamers for 10 is formed. For 11 one additional rotational isomer is observed. The relationship between the [4 + 4] dimerization and steric effects of the PR2 group is discussed. The compounds 6, 8 and 11 were characterized by X-ray diffraction. The structure of 6 was rendered imprecise by the presence of disordered toluene, but the influence of the bulky anthracenyl groups was clear, with wide CPC angles of 110.4°. The molecule displays imposed threefold symmetry. The two independent molecules of complex 8, which crystallizes as a dichloromethane hemisolvate, are closely similar to each other; the WP bond lengths are 254.3 and 253.4 pm. The WC bonds trans to phosphorus are 4 pm shorter than those cis. The phosphane dimer 11 crystallizes with imposed centrosymmetry. The H atom positions, which could be tentatively identified from difference syntheses, indicate a different rotamer than was formed for the analogous fluorophosphane dimer 10.

Preparation and Structure of Hexakis[(trialkylphosphane)aurio(I)]methanium(2+) Salts [(LAu)6C]2+(X-)2 with LEt3P, iPr3P and XBF4-, B3O3F4-

Abstract: Hexaaurated carbon complexes of the type [(R3PAu)6C](BF4)2, REt (2a), iPr (2b) have been prepared by the reaction of the appropriate (phosphane)gold(I) chlorides R3PAuCl (1a and 1b) with tetrakis(dimethoxyboryl)methane, 13C–enriched at the central carbon atom, in the presence of excess of CsF in HMPT at room temperature. The products 2a and 2b are characterized by standard spectroscopic methods including direct detection of the interstitial C atoms by 13C–NMR spectroscopy. The crystal structure of the compound [(iPr3PAu)6C](B3O3F4)2 · 3 CH2Cl2 (3), obtained from partial (anion) hydrolysis has been determined. It contains dications with a central carbon atom surrounded by six (phosphane)gold(I) units. The edges of the CAu6 octahedron represent short Au–Au contacts (aprox. 3.0 A), which strongly contribute to the formation and stability of these hypercoordinated species. Attempts to prepare a corresponding hexaauriomethanium dication starting from tBu3PAuCl (1c) failed owing to the bulkiness of the (tri-tert-butylphosphane)gold(I) unit. The X–ray structure analysis for 1c verifies an extremely crowded environment of the gold atom with small Au—P—C angles of only 107° leading to efficient shielding of the metal atom by methyl groups.

Transition–Metal–Diene Complexes in Organic Synthesis, 12. Regio‐ and Stereoselectivity of Electrophilic Substitutions of Arylamines by Tricarbonyliron–Complexed Cyclohexadienylium Cations and Oxidative Cyclizations to Carbazoles

Abstract: Electrophilic substitutions of donor–substituted arylamines using tricarbonyliron–complexed cyclohexadienylium cations lead regio- and stereoselectively to the corresponding tricarbonylcyclohexadieneiron complexes The C–C bond formations occur regioselectively in the ortho position with respect to the amino group with arylamines containing a substituent in the para position The initially formed N-alkylated arylamine (kinetic product) is shown to rearrange in an intermolecular process to the C-alkylated arylamine (thermodynamic product) The reported oxidative cyclization to 3–methylcarbazole yields large amounts of the demetalated ligand However, oxidative cyclization to 3–methoxycarbazole is possible under mild reaction conditions (room temperature) by using especially activated manganese dioxides

Investigation of the Enantiomerization Barrier of Homofuran by Computer Simulation of Interconversion Profiles Obtained by Complexation Gas Chromatography

Abstract: By computer simulation of experimental interconversion profiles, obtained by complexation gas chromatography, rate constants of enantiomerization have been determined for homofuran between 95 and 130°C. Since enantiomerization proceeds at similar rates in the mobile and stationary phase, the rate constants obtained by an Arrhenius plot are in excellent agreement with values determined independently by polarimetry between 60 and 90°C. We thus demonstrate that dynamic chromatography can be an easy means for the rapid determination of enantiomerization (or isomerization) barriers of ca. 70–120 kJ mol-1 requiring only minute amounts of racemic sample.

Synthese und Strukturen von (Monoorganyl)amiden und ‐imiden des Zirkoniums und Hafniums

Abstract: Synthesis and Structures of (Monoorganyl)amides and -imides of Zirconium and Hafnium The tetrahalides MCl4 (M = Zr 1 a, Hf 1 b) react with LiNHtBu with elimination of LiCl to yield [(tBuNH)2MNtBu]2 (3) (M = Zr 3a, Hf 3b). Compounds 3 are thermally instable and oli-gomerise above 100 °C with elimination of H2NtBu. The reactions of (η5-C5Me5)MCl3 (M = Zr 1 c, Hf 1 d) with LiNHR (R = tBu 2 a,2,4,6-Me3C6H22 b, 2, 6-iPr2C6H32 c) lead to (η5-C5Me5)M(NHR)3 (4) (R = tBu, M = Zr 4 a, Hf 4 b; R = 2, 4,6-Me3C6H2, M = Zr 4 c, Hf 4 d; R = 2,6-iPr2C6H3, M = Zr 4 e, Hf 4 f). Compounds 4 are thermally very stable and melt without decomposition. When 1 c and 1 d react with LiNHPh (2 d), dimers of composition [(η5-C5Me5)M(NHPh)NPh]2 (M = Zr 5 a, Hf 5 b) are obtained. The complexes (η5-C5Me5)2MCl2 (M = Zr 1 e, Hf 1 f) react with 2 b to form (η5-C5Me5)2M(NHR)2 (6) (M = Zr 6 a, Hf 6 b). Pyridine reacts with 4 e at 85 °C and replaces one molecule of 2,6-iPr2C6H3NH2 to give (η5-C5Me5)Zr-(NHR)NR · Py (7). The single crystal X-ray structures of 4 a, 4 f, 5 b and 7 are described.

Tantaloxide durch Gasphasenhydrolyse, Druckhydrolyse und Transportreaktion aus 2H‐TaS2: Synthesen von TT‐Ta2O5 und T‐Ta2O5 und Kristallstruktur von T‐Ta2O5

Abstract: Tantalum Oxides by Gasphase Hydrolysis, Pressure Digestion, and Chemical Transport of 2H-TaS2: Synthesis of TT-Ta2O5, T-Ta2O5 and X-ray Structure Determination of T-Ta2O5 TT-Ta2O5 is obtained by pressure digestion in water using 2H-TaS2 as starting material at a temperature of 200°C followed by a dehydratization procedure of initially formed amorphous HTaO3. The X-ray powder diagram of TT-Ta2O5 revealed a hexagonal unit cell with space group P6/mmm and lattice constants a = 3.639, c = 3.901 A. This material undergoes a phase transition during heating from 20 to 900°C. The resulting product is crystallizing orthorhombic with space group Pmm2 and lattice constants a = 43.997(8), b = 3.894(1), c = 6.209(3) A and Z = 12. Single crystals of this phase (T-Ta2O5) have been prepared by chemical transport reaction using TT-Ta2O5 as starting material and NH4Cl as transport agent. The structure of T-Ta2O5 consists of pentagonal-bipyramidal coordinated tantalum atoms connected with distorted TaO6 octahedra. The Ta–O distances vary between 1.84 and 3.09 A and the mean Ta–O distance is 1.99 A.

Conversion of ferriosilanes to ferriosilanols by selective oxidation of the sih function by dimethyldioxirane

Abstract: The reaction of ferriohydridosilanes Cp(CO)(L)Fe–SiR2H (R = Me, t-Bu, Ph, o-Tolyl; L = CO, Ph3P) 1a–e with dimethyldioxirane (as an acetone solution) leads directly to the corresponding ferriosilanols Cp(CO)(L)Fe–SiR2OH 2a–e in moderate to excellent yields.

Medium‐Sized Cyclophanes, 20. Synthesis and Conformational Studies of syn‐ and anti‐Dihydroxy[n.2]metacyclophanes

Abstract: syn- and anti-Dimethoxy[n.2]metacyclophanes 9 are obtained by pyrolysis of the corresponding anti-sulfones 8, which are prepared by the reaction of 1,n-bis[3-(chloromethyl)-2-methoxyphenyl]alkanes 6 with Na2S in ethanol under the high dilution conditions, followed by the oxidation of the obtained thiametacyclophanes 7 with m-chloroperbenzoic acid. Demethylation of anti-dimethoxy[n.2]metacyclophanes anti-9 with BBr3 in dichloromethane affords the corresponding anti-dihydroxy[n.2]metacyclophanes anti-10. On the other hand, demethylation of syn-dimethoxy[3.2]-syn- 9b and -[4.2]meta-cyclophane syn-9c gives syn-dihydroxy[n.2]metacyclophanes syn-10b, c, but syn-dimethoxy[5.2]-syn-9d and -[6.2]metacyclophane syn-9e are converted into the corresponding anti-dihydroxy[n.2]metacyclophanes anti-10d, e. AlCl3 · CH3NO2-catalyzed de-tert-butylation of tert-butyl-syn- and -anti-dihydroxy[3.2]- and -[4.2]metacyclophanes syn/anti-10b, c has been carried out in benzene to give the desired metacyclophanes anti-11a–c and syn-11c except syn-dihydroxy-[3.2]metacyclophane syn-11b which is converted into 8,17-epoxy[3.2]metacyclophane 13. The assignment of syn and anti conformations has been confirmed by 1H-NMR analyses and X-ray diffraction studies. The dynamics of the ring inversion and UV spectra are also discussed.

Synthese und Struktur eines neuen Bis[(trimethylphosphan)titanocen]‐Komplexes mit einer verbrückenden C2‐Einheit

Abstract: Bis(trimethylphosphane)titanocene (1) reacts with 2-methylene-1,1-diphenylcyclopropane (2) to give red crystalline (η2-2-methylene-1,1-diphenylcyclopropane)(trimethylphosphane)titanocene (3). In solution complex 3 degrades smoothly to form the new Cp2Ti(PMe3) – C2 – Ti(PMe3)Cp2 complex 4, the crystal structure of which has been elucidated by an X-ray analysis.

Spektroskopischer Nachweis eines Bis(amino)silylens

Abstract: Spectroscopic Identification of a Bis(amino)silylene The photolysis of the silicon diazide 3a in benzene solution and in an Ar matrix is described. Both irradiations cause the elimination of 3 equivalents of N2. Loss of N2 from 3a in benzene leads to the formation of the analytically investigated product or products 4 of uncertain structure. However, the matrix photolysis of 3a results in a compound which is stable up to 77 K and has been identified as the bis(amino)silylene 2d by comparison of its IR spectra with those of the homologous Sn and Ge compond.

Synthesis and X-ray structure of binaphthyl-based macrocyclic diphosphanes and their Ni(II) and Pd(II) complexes

Abstract: 16- and 18-membered diphospha macrocycles (8, 12, and 15) have been synthesized from the corresponding 1,1′-binaphthyl precursors (6, 11, and 14, resp.) and o-phenylenebis(phenylphosphane) by means of high-dilution conditions in 55, 49, and 87% yield. X-ray structure analyses of 8a, 8b, 12b, and 12b · NiCl2 reveal their distinctly different conformations and conformational changes caused by complexation. These structural features are reflected in the pronounced different tendency of the compounds concerned to form Ni(II) and Pd(II) complexes.

Synthesis, Structure, and Reactivity of Chiral Rhenium Amido Complexes of the Formula (η5‐C5H5)Re(NO)(PPh3)(NRR')

Abstract: Reactions of primary and secondary amine complexes [(η5-C5H5)Re(NO)(PPh3)(NHRR')]+ TfO− [2; R/R' = H/H (a), H/CH3 (b), H/C6H5 (d), CH3/CH3 (f), CH2CH2CH2CH2 (h)] with nBuLi give amido complexes (η5-C5H5)Re(NO)(PPh3)(NRR') (1) in quantitative NMR yields. Although 1 d can be isolated in pure form, 1 f is converted upon workup into a dimeric bridging bis(amido) complex, cis-[(η5-C5H5)Re(NO){μ-N(CH3)2}]2. The crystal structure of 1 d exhibits a pyramidal amido nitrogen atom. The diastereotopic methyl groups in 1 f readily exchange, as assayed by variable-temperature NMR. Complexes 1 a, f react with TfOH to regenerate 2a, f, and with TfOR” to give the corresponding alkylated amine complexes. The basicities and nucleophilicities of the amido nitrogen atoms are shown to be greater than those of organic amines.

Alkoxygermanate(II), -stannate(II) und -plumbate(II) zweiwertiger Metall-Ionen, II. Verbindungen des Formeltyps M2El2(OtBu)8

Abstract: Alkoxygermanates(II), -stannates(II), and -plumbates(II) of Divalent Metal Ions, II[1]. – Compounds of the Formula M2El2(OtBu)8 By simple salt-exchange processes the starting materials Na2El2(OtBu)6 (El = Ge, Sn, Pb) can be transformed to germanates, stannates and plumbates of divalent magnesium and divalent transition metals. Two types of compounds are formed in these reactions: MEl2(OtBu)6 [El = Ge, M = Mg (1A), Cr (1B), Mn (1C), Zn (1F); El = Pb, M = Mn (3C), M = Zn (3F)] and M2El2(OtBu)8 [El = Ge, M = Co (1d), Ni (1e); El = Sn, M = Mg (2a), Cr (2b), Mn (2c), Co (2d), Ni (2e); El = Pb, M = Co (3d)]. Single-crystal X-ray diffraction studies have been performed on 1C, 1d, 2a, 2b, 2c, 2d, and 2e, and the structures have been solved. In 1C the Mn atom occupies the center of an elongated O6 octahedron, the germanium(II) atoms displaying pyramidal coordination by three oxygen atoms. The central molecular cage can be described as two MnO3Ge trigonal bipyramids sharing the common central Mn atom and being wrapped by tert-butyl groups linked to the oxygen atoms. The other compounds of the MEl2(OtBu)6 formula seem to be isostructural with the exception of 3F, which displays a 1H-NMR spectrum which is not compatible with this structure. All X-ray structures of the compounds M2El2(OtBu)8 show the same feature: to a central M2(OtBu)2 four-membered ring are spirocyclically connected two M(OtBu)2El rings through the common metal atoms M. The structure is completed by the coordination of an exocyclic tert-butoxy group to the terminal El atoms. The metal atoms M are therefore quasi tetrahedrally coordinated while the Ge and Sn atoms are in pyramidal threefold oxygen atom environments. All molecules display an El M M El one-dimensional arrangement. From susceptibility measurements it is apparent, that in the compounds MEl2(OtBu)6 and M2El2(OtBu)8 the transition metal atoms are in high-spin configurations, which is also supported by the UV spectra. Analysis of the structural data of the series 2a–2e reveal important contributions of the electronic environments of the transition metal atoms to the M M and M Sn distances. A qualitative MO description is used to explain these features. Again it has been shown that the, „geometrical softness” of Ge(OtBu)3 and Pb(OtBu)3 is greater than of Sn(OtBu)3, as the former two can accomodate Cr2+ and Mn2+ in a sixfold coordination site by two units, while Sn(OtBu)3 coordinates Cr2+ and Mn2+ with only two alkoxy groups. When 1C and 2d are allowed to react with nonacarbonyldiiron Mn-Ge2(OtBu)6 · 2 Fe(CO)4 (4) and Co2Sn2(OtBu)8 · 2 Fe(CO)4 (5), respectively, are formed. Compound 4 displays presumably five metal atoms in a linear arrangement while 5 has six metallic elements arranged in one dimension. The latter fact has been unambigously proved by an X-ray structure determination.